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Antigen presentation by major histocompatibility complex class I (MHC-I) and class II (MHC-II) molecules is a prerequisite for T cell engagement during the activation as well as the effector phase. The central nervous system (CNS) is unique in that cells resident in the parenchyma, glia and neurons, do not constitutively (or very sparsely at best) express MHC molecules (Aloisi et al., 2000; Sedgwick and Hickey, 1997; Xiao and Link, 1998), making them invisible to T cells. Additional restrictions on T cell surveillance are imposed by the absence of classical lymphatic drainage, the blood—brain barrier (BBB), and the unique anatomy of the brain microvasculature (Bechmann et al., 2007; Galea et al., 2007; Hickey, 2001; Xiao and Link, 1998; Lowenstein, 2002). Infiltrating cells not only have to cross the vascular wall to penetrate into the perivascular space, but more importantly overcome the barrier formed by the glia limitans to access the CNS parenchyma. While the first step is generally not associated with pathology, penetration from the perivascular space of postcapillary venules into the parenchyma is more restricted and once overcome, associated with clinical consequences (Bechmann et al., 2007). In the resting state, perivascular macrophages are maintained by replacement with circulating monocytes. However the glial limitans is not breached, and thus, these cells are considered to be located outside the confines of the BBB. While diffusion of soluble factors and antibodies is restricted by the BBB, especially by the tight, continuous, unfenestrated capillary epithelium, leukocyte infiltration preferentially occurs at distal sites in postcapillary venules (Bechmann et al., 2007). BBB permeability and leukocyte infiltration are thus not necessarily functionally nor physically linked. The barriers separating CNS parenchyma from the circulation explains the rare presence of T cells in the normal CNS parenchyma, despite the ability of peripherally activated and memory T cells to traffic to non lymphoid tissues independent of antigen presentation (Masopust et al., 2004). Nevertheless, T cells activated during an infection or auto-immune response, are able to enter into, and migrate within the brain parenchyma, even in the presence of an intact, non-inflamed BBB (Cabarrocas et al., 2003; Chen et al., 2005; Evans et al., 1996; Hickey, 2001). However, although entry of activated T cells into the CNS is independent of their antigen specificity, only those T cells that recognize antigen are retained. Thus, barriers limiting T cell surveillance of the brain are rapidly overcome following CNS infections and other inflammatory conditions (Griffin, 2003; Ransohoff et al., 2003). Under such conditions, it is also likely that a number of non-activated, bystander T cells, as well as other leukocytes, including B cells are able to penetrate into the brain parenchyma. Mechanisms propagating protective versus pathogenic potential of T cells in varying disease models are complex and require more in depth exploration. This chapter highlights recent advances relating to antigen presentation functions by resident CNS cells and effects exerted by CD8 T cells in vivo with an emphasis on anti-viral functions. [ABSTRACT FROM AUTHOR]

Multiple sclerosis (MS) is a multi-factorial disease associated with chronic autoimmune inflammation of the central nervous system (CNS). In MS, and the relevant animals models experimental autoimmune encephalomyelitis (EAE), and Theiler's murine encephalitis virus-induced demyelinating disease (TMEV-IDD), myelin destruction is mediated by neuroantigen-specific CD4+ T cells (Gonatas et al., 1986; Miller et al., 1997; Wekerle, 1991). MS and EAE share clinical and histopathological similarities. Mononuclear cells (MNCs) accumulate in demyelinated lesions in the white and grey matter of the brain and spinal cord. Infiltrates are composed of CD4+ and CD8+ T cells, B cells, macrophages and dendritic cells (DCs). CD4+ T cells and DCs are critical for the initiation and progression of EAE as CD4+ T cell depletion renders mice resistant to EAE (Jameson et al., 1994; McDevitt et al., 1987; Sedgwick and Mason, 1986; Waldor et al., 1985), and DCs from the CNS uniquely activate naïve myelin-specific T cells by acquiring and processing endogenous myelin peptides (Bailey et al., 2007). The initiating events in MS are unknown, but studies in the EAE and TMEV-IDD animal models indicate that CNS damage is caused by direct and indirect effects of inflammatory cytokines and chemokines (e.g. TNF, IFN-γ, IL-17, CCL2, etc.) (Begolka et al., 1998; Chen et al., 2006; Karpus et al., 1995; Powell et al., 1990), that induce the activation and recruitment of monocyte/macrophages and resident microglia, that cause axon damage and demyelination by bystander mechanisms (Cammer et al., 1978; Rivers and Schwentker, 1935). [ABSTRACT FROM AUTHOR]

For many years, the central nervous system (CNS) was considered an "immunologically privileged site" — a perspective based on limited immune surveillance when compared to peripheral tissue, muted expression of MHC molecules in the context of an apparent lack of professional antigen presenting cells, and the absence of a classical lymphatic drainage system. Together, these observations supported the notion that the CNS was unable to mount and/or support an immune response. However, over time this view evolved and it is now clear that CNS tissue is neither immunologically inert nor privileged, rather, its immune response is exquisitely sensitive to antigenic challenge. Indeed, overwhelming evidence now indicates that upon microbial infection of the CNS there is often a dynamic and orchestrated localized immune response that culminates with infiltration of antigen-specific lymphocytes, usually resulting in control and elimination of the invading pathogen. It is important to note that not all effective immune responses originating in the CNS are completely beneficial to the host; alternatively, there are instances where immune cell infiltration following infection is associated with severe neuropathology resulting in death or chronic neurodegenerative disease. [ABSTRACT FROM AUTHOR]

The immune system plays a critical role in CNS disorders and spinal cord injury (SCI). Primary trauma to the adult mammalian spinal cord is immediately followed by secondary degeneration in which the inflammatory response is thought to be detrimental. This inflammatory response is mediated by small, chemotropic cytokines, called chemokines, which are secreted by a variety of cell types in the CNS including neurons, glia, and vascular cells. Here, we review studies which provide insight into the functional role of chemokines in neuroinflammation and disease, with an emphasis on SCI. More specifically, this review emphasizes studies which indicate that ablation of the T cell chemotactic CXC chemokine ligand 10 (CXCL10) results in diminished neuropathology associated with decreased immune cell infiltration into the CNS. Importantly, these findings reveal that targeting chemokines such as CXCL10 may offer a powerful therapeutic approach for the treatment of neuroinflammatory diseases. [ABSTRACT FROM AUTHOR]

Historically the central nervous system (CNS) has been viewed as a relatively immune sheltered tissue. Under physiological conditions the CNS is devoid of leukocytes, including professional antigen presenting cells (APC), is deficient in key immune accessory molecules such as major histocompatibility molecules (MHC) and is protected by an effective blood brain barrier. Significantly, however, in numerous pathological states including infectious diseases and autoimmune disorders (e.g. multiple sclerosis) immune cells are effectively recruited to and infiltrate in the CNS. This immune response can be a two-edged sword required on the one hand to control infection and facilitate tissue repair and regeneration but on the other causing tissue injury that can result in life threatening complications. Therefore, understanding the mechanisms that control the trafficking of leukocytes to the CNS and the subsequent interactions between these cells that contribute to tissue injury has significant implications. [ABSTRACT FROM AUTHOR]

Autoimmune attack on the nervous system is considered the basis for multiple sclerosis (MS) (Compston and Coles, 2002), and is also implicated in peripheral neuropathies such as Guillain—Barré Syndrome (GBS) (Kiefer et al., 2002). Myelin is probably the major target of autoimmune attack in both diseases, although non-myelin antigens are also recognized by infiltrating T cells and antibodies. Destruction of myelin (demyelination) is a central feature of MS and GBS, with accompanying inflammation viz. infiltrates of T cells and macrophages, neutrophils (depending on the subtype of disease), and B cells, again depending on disease subpathology. A working definition of inflammation is the presence of leukocytes where they don't belong, and it is instructive to consider how leukocytes in demyelinating diseases get to be ‘where they don't belong'. This chapter will attempt to review the role of chemokines in this inflammatory process and how they contribute to the autoimmune pathology in demyelinating diseases. We will focus primarily on central nervous system (CNS) demyelinating disease. [ABSTRACT FROM AUTHOR]

The immune system has evolved numerous mechanisms to protect the host against perceived danger, as well as regulatory mechanisms for the resolution of inflammation and/or repair of the host. While the adaptive immune responses that include specific antibody and T cells are critical in eliminating many pathogenic organisms, the first immune responses are provided by the innate immune system. This immediate response is critical in assessing the level of "danger" or injury and consequently directing the subsequent recruitment of other immune system components. These responses are rapid, and include both cellular elements (phagocytic cells, natural killer cells) and protein elements (the complement system, defensins). Some components of the host response to danger if insufficiently regulated can result excessive inflammation and tissue damage including neurotoxicity in the central nervous system (CNS). Thus, a balance between generating a toxic environment for pathogens while providing reparative functions to the tissues must be maintained, and thus requires monitoring systems and appropriate modulation of immune response mediators. This is certainly the case for the generally proinflammatory complement cascade, a powerful effective mechanism of the immune system. [ABSTRACT FROM AUTHOR]

Pattern recognition receptors (PRRs) are germline encoded receptors utilized by cells of the innate immune system for pathogen recognition. PRRs are classically activated by pathogen-associated molecular patterns (PAMPs) present in whole classes of pathogens, but not in mammalian cells, termed the "infectious nonself model" (Medzhitov and Janeway, 2002). It has also been recent appreciated that there are self-derived products released upon tissue injury or necrotic cell death that can activate PRRs (Morgan et al., 2005). PRR activation leads to opsonization, activation of complement and coagulation cascades, phagocytosis, activation of proinflammatory signaling pathways, and the induction of apoptosis (Janeway and Medzhitov, 2002; Matzinger, 2002). Additionally, activation of the innate immune system is crucial for the induction of adaptive immune responses and the eventual clearance of pathogens (Janeway and Medzhitov, 2002). [ABSTRACT FROM AUTHOR]

Arachidonic acid (AA) is liberated from membrane phospholipids by the action of phospholipases upon stimulation by a variety of extracellular stimuli including neurotransmitters, growth factors, and cytokines (Farooqui et al., 2006). As illustrated in Fig. 6.1, three enzyme systems act on AA to generate prostaglandin H2 via the cyclooxygenase enzymes (COX-1 and COX-2), leukotrienes via the LOX pathways, and epoxyeicosatrienoic acids via the epoxygenase cytochrome P450 pathway. These lipid products are signaling messengers and regulate a wide variety of physiologic functions including cerebral blood flow and synaptic function under basal conditions. Increases in expression and activity of enzymes in each of these three pathways have been documented in a wide spectrum of neurological diseases, including acute insults such as cerebral ischemia and trauma as well as chronic neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. Of the three enzymatic pathways, the cyclooxygenase (COX) pathway has been most studied, and a significant body of evidence links activity of this pathway and downstream prostanoid products to a broad range of neurological diseases. [ABSTRACT FROM AUTHOR]

A growing number of increasingly sophisticated studies over the past two decades have implicated key immune regulatory factors in CNS function and disease. Chief among those factors are cytokines, which were originally described to regulate communication between immune cells. The purpose of this chapter is to review what is known regarding normal expression of key cytokines and their receptors in the CNS as well as their roles in development and disease. We will focus in particular on tumor necrosis factor α (TNF), transforming growth factor β (TGF-β), interleukin 1 (IL-1), IL-6, IL-10 and IL-12. We will discuss how these cytokines modulate not only normal CNS function but how abnormal cytokine signaling may contribute to major acute and chronic CNS diseases. We will rely heavily on studies in experimental mouse models that overproduce or ablate these cytokines and discuss the potential therapeutic benefits from ‘proof-of-concept' targeting studies of specific cytokines in the treatment of CNS diseases. [ABSTRACT FROM AUTHOR]

The development of in vivo imaging technology in mice has been a powerful tool to study mechanisms of physiology and pathology in both the nervous and the immune systems. Recent studies have revolutionized our understanding on how glial cells, T cells and neurons interact with each other and respond to damage in the nervous system. This chapter aims to summarize the advances of in vivo imaging as they relate to microglial activation and present the challenges of utilizing this technology directly in animal models of neuroimmunologic disease. [ABSTRACT FROM AUTHOR]

Pericytes were first described by Rouget in 1873 and since then much has been speculated on their nature and role(s). They are located between the inner and outer vascular basement membrane of arterioles, capillaries, and venules, and are thus part of the vascular wall. In standard hematoxylin-eosin or Nissl-stained sections, pericytes are difficult to recognize, but they can be identified under the electron microscope and in semithin sections, where the vascular basement membranes are visible. Moreover several antibodies demark their unique morphology and therefore, allow clear-cut identification at the light microscopic level. [ABSTRACT FROM AUTHOR]

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease (Selkoe, 2005). Histologically, it is characterized by the deposition of extracellular senile plaques composed primarily of beta amyloid (Aβ) peptides and intracellular inclusions, termed neurofibrillary tangles, made up of primarily hyperphosphorylated tau protein (Braak and Braak, 1997a, b; Grundke-Iqbal et al., 1986; Selkoe, 2001). In addition, AD brains demonstrate significant neuron loss and abundant gliosis (McGeer et al., 1986). The mechanisms by which these pathology occur, however, is debatable. It has been hypothesized that inflammatory events contribute to both the histological and behavioral progression of disease (Akiyama et al., 2000). The histological data demonstrating gliotic changes in AD brains as compared to agematched controls certainly supports the notion that microglia, in particular, may mediate the changes that are observed. Reactive microglia with swollen bodies and shortened, thickened processes are histologically identified in close association with the fibrillar or congophilic plaques in the AD brain (Itagaki et al., 1989; Miyazono et al., 1991). Although the percentage of microglia associated with fibrillar plaques is greater, they are also localized, in a more ramified phenotype, with the diffuse plaques (Itagaki et al., 1989; Mattiace et al., 1990; Sasaki et al., 1997). These data suggest that microglia develop a specific reactive phenotype in association with plaques as Aβ undergoes a transition from a nonfibrillar to fibrillar, congophilic conformation (Sheng et al., 1997). In fact, some studies suggest that microglia are involved in the earliest stages of plaque deposition perhaps even dictating where plaques are depositing in the brain (Griffin et al., 1995; Sheng et al., 1995, 1998). Moreover, AD brains have increased protein levels of several proinflammatory mediators commonly associated with reactive microgliosis, including cytokines: interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α, activated complement components, and cyclooxygenase (COX)-2 when compared to controls (Akiyama et al., 2000; Dickson et al., 1993; Eikelenboom et al., 1989; Luterman et al., 2000; Mrak and Griffin, 2000; O'Banion et al., 1997; Strauss et al., 1992; Xiang et al., 2006;). Strikingly similar observations have been made while examining transgenic mouse models of disease over the last decade. The majority of the mouse models that have been created over-express human mutant forms of the amyloid precursor protein (APP) and/or mutant forms of the proteins responsible for gamma secretase cleavage of APP, presenilin (PS) 1 and PS2. These animal models have consistently demonstrated that reactive microgliosis occurs in association with fibrillar plaque formation as detected histologically with multiple immuno-markers (Morgan et al., 2005). Collectively, a voluminous body of data strengthens the proposition that APP and its proteolytic fragments are involved in not just plaque deposition but also the reactive microgliosis observed in AD brains. [ABSTRACT FROM AUTHOR]

Mobility of pastoralists in arid and semi-arid zones renders access to primary social services difficult. The experiences, local concepts and propositions of nomadic communities of Chad were essential to fill the information gaps on how to provide adapted health services to mobile communities. In Chad, we have taken an iterative, corkscrew-like research and action strategy: a better understanding of the determinants of health and communities' health priorities - obtained by interdisciplinary collaborations between medicine, anthropology, epidemiology, social geography and microbiology - were integrated in the participatory identification of intervention options out of a range of possible responses by the health and veterinary services. Recommendations from national stakeholder workshops paved the way for implementing and testing new interventions. All stakeholders reviewed outcomes of interventions periodically. The programme provided opportunities for participatory processes and actions that were defined in an open way at the beginning. An appropriate North-South research partnership framework and the long-term commitment of all partners have been crucial in the process of building stakeholders' ownership. University curricula rarely enable scientists to communicate with other disciplines, and researchers first needed to acquire skills in crossing the boundaries between human and natural sciences and between sectors. We describe here in a chronologic way the elements that led to innovative health and veterinary services for nomadic pastoralists of Chad; such as joint vaccination services of the public health and the livestock sectors and subsequent initiatives that were initiated by the nomadic communities once they began to trust the programme. [ABSTRACT FROM AUTHOR]

Many of the neuromuscular (e.g., muscular dystrophy) and neurometabolic (e.g., mitochondrial cytopathies) disorders share similar final common pathways of cellular dysfunction that may be favorably influenced by creatine monohydrate (CrM) supplementation. Studies using the mdx model of Duchenne muscular dystrophy have found evidence of enhanced mitochondrial function, reduced intra-cellular calcium and improved performance with CrM supplementation. Clinical trials in patients with Duchenne and Becker's muscular dystrophy have shown improved function, fat-free mass, and some evidence of improved bone health with CrM supplementation. In contrast, the improvements in function in myotonic dystrophy and inherited neuropathies (e.g., Charcot-Marie-Tooth) have not been significant. Some studies in patients with mitochondrial cytopathies have shown improved muscle endurance and body composition, yet other studies did not find significant improvements in patients with mitochondrial cytopathy. Lower-dose CrM supplementation in patients with McArdle's disease (myophosphorylase deficiency) improved exercise capacity, yet higher doses actually showed some indication of worsened function. Based upon known cellular pathologies, there are potential benefits from CrM supplementation in patients with steroid myopathy, inflammatory myopathy, myoadenylate deaminase deficiency, and fatty acid oxidation defects. Larger randomized control trials (RCT) using homogeneous patient groups and objective and clinically relevant outcome variables are needed to determine whether creatine supplementation will be of therapeutic benefit to patients with neuromuscular or neurometabolic disorders. Given the relatively low prevalence of some of the neuromuscular and neurometabolic disorders, it will be necessary to use surrogate markers of potential clinical efficacy including markers of oxidative stress, cellular energy charge, and gene expression patterns [ABSTRACT FROM AUTHOR]

Many links are reported or suspected between the functioning of creatine, phosphocreatine, the creatine kinase isoenzymes or the creatine biosynthesis enzymes on one hand, and health or disease on the other hand. The aim of the present book was to outline our current understanding on many of these links. In this chapter, we summarize the main messages and conclusions presented in this book. In addition, we refer to a number of recent publications that highlight the pleiotropy in physiological functions of creatine and creatine kinase, and which suggest that numerous discoveries on new functions of this system are still ahead of us. Finally, we present our views on the most promising future avenues of research to deepen our knowledge on creatine and creatine kinase. In particular, we elaborate on how state-of-the-art high-throughput analytical ("omics") technologies and systems biology approaches may be used successfully to unravel the complex network of interdependent physiological functions related to creatine and creatine kinase [ABSTRACT FROM AUTHOR]

Creatine, a small molecule present in muscular tissue of many vertebrates, evolves to one of the most widely used and successful dietary supplements of recent decades (Graham and Hatton, 1999). Importantly, in the industrial manufacturing process, a high quality standard must be maintained. Validated analytical methods capable of providing reliable and consistent analysis of the main substance, side products and potentially harmful impurities must be employed. The principles of those determinations and the nature of possible by-products will be elucidated in this chapter. In addition, the pure creatine produced may be unstable under certain conditions, e.g. within special formulations or galenical forms. Some hints how to deal with this fact and how to avoid instability will also be discussed. Thus, this chapter will serve as a survey of the paths of chemical synthesis of creatine, its chemistry, properties, stability, analytical determination methods and legal status [ABSTRACT FROM AUTHOR]

The literature on creatine supplementation supporting its efficacy has grown rapidly and has included studies in both healthy volunteers and patient populations. However, the first rule in the development of therapeutic agents is safety. Creatine is well-tolerated in most individuals in short-term studies. However, isolated reports suggest creatine may be associated with various side effects affecting several organ systems including skeletal muscle, the kidney and the gastrointestinal tract. The majority of clinical studies fail to find an increased incidence of side effects with creatine supplementation. To date, studies have not found clinically significant deviations from normal values in renal, hepatic, cardiac or muscle function. Few data are available on the long-term consequences of creatine supplementation [ABSTRACT FROM AUTHOR]

Research has demonstrated that creatine supplementation has some therapeutic benefit with respect to muscle function and more recently neurological function. Despite the growing body of literature on the pharmacologic effect of creatine, very little is known about the disposition of creatine after supraphysiologic doses. The movement of creatine throughout the body is governed by transport processes which impact the absorption of creatine from the intestine, clearance of creatine from the kidney, and access of creatine to target tissues. With repeated doses of creatine, it appears that the clearance of creatine decreases mainly due to the saturation of skeletal muscle stores. Insulin and insulin-stimulating foods appear to enhance muscle uptake of creatine but at the same time, high carbohydrate meals may slow the absorption of creatine from the intestine. Little is known about creatine disposition in special populations including the elderly and patients with neuromuscular disease. Knowledge of creatine disposition in these clinically relevant populations can help remove some of the guess work of dose selection during clinical trials [ABSTRACT FROM AUTHOR]

Significant progress has been made in identifying neuroprotective agents and their translation to patients with neurological disorders. While the direct causative pathways of neurodegeneration remain unclear, they are under great clinical and experimental investigation. There are a number of interrelated pathogenic mechanisms triggering molecular events that lead to neuronal death. One putative mechanism reported to play a prominent role in the pathogenesis of neurological diseases is impaired energy metabolism. If reduced energy stores play a role in neuronal loss, then therapeutic strategies that buffer intracellular energy levels may prevent or impede the neurodegenerative process. Recent studies suggest that impaired energy production promotes neurological disease onset and progression. Sustained ATP levels are critical to cellular homeostasis and may have both direct and indirect influence on pathogenic mechanisms associated with neurological disorders. Creatine is a critical component in maintaining cellular energy homeostasis, and its administration has been reported to be neuroprotective in a wide number of both acute and chronic experimental models of neurological disease. In the context of this chapter, we will review the experimental evidence for creatine supplementation as a neurotherapeutic strategy in patients with neurological disorders, including Huntington's disease, Parkinson's disease, amyotrophic lateral sclerosis, and Alzheimer's disease, as well as in ischemic stroke, brain and spinal cord trauma, and epilepsy [ABSTRACT FROM AUTHOR]

The daily oral ingestion of supplementary creatine monohydrate can substantially elevate the creatine content of human skeletal muscle. This chapter aims to summarize the current knowledge regarding the impact muscle creatine loading can have on exercise performance and rehabilitation. The major part of the elevation of muscle creatine content is already obtained after one week of supplementation, and the response can be further enhanced by a concomitant exercise or insulin stimulus. The elevated muscle creatine content moderately improves contractile performance in sports with repeated high-intensity exercise bouts. More chronic ergogenic effects of creatine are to be expected when combined with several weeks of training. A more pronounced muscle hypertrophy and a faster recovery from atrophy have been demonstrated in humans involved in resistance training. The mechanism behind this anabolic effect of creatine may relate to satellite cell proliferation, myogenic transcription factors and insulin-like growth factor-1 signalling. An additional effect of creatine supplementation, mostly when combined with training, is enhanced muscle glycogen accumulation and glucose transporter (GLUT4) expression. Thus, creatine may also be beneficial in sport competition and training characterized by daily glycogen depletion, as well as provide therapeutic value in the insulin-resistant state [ABSTRACT FROM AUTHOR]

Cerebral creatine deficiency syndromes (CCDSs) are a group of inborn errors of creatine metabolism comprising two autosomal recessive disorders that affect the biosynthesis of creatine - i.e. arginine:glycine amidinotransferase deficiency (AGAT; MIM 602360) and guanidinoacetate methyltransferase deficiency (GAMT; MIM 601240) - and an X-linked defect that affects the creatine transporter, SLC6A8 deficiency (SLC6A8; MIM 300036). The biochemical hallmarks of these disorders include cerebral creatine deficiency as detected in vivo by 1H magnetic resonance spectroscopy (MRS) of the brain, and specific disturbances in metabolites of creatine metabolism in body fluids. In urine and plasma, abnormal guanidinoacetic acid (GAA) levels are found in AGAT deficiency (reduced GAA) and in GAMT deficiency (increased GAA). In urine of males with SLC6A8 deficiency, an increased creatine/creatinine ratio is detected. The common clinical presentation in CCDS includes mental retardation, expressive speech and language delay, autistic like behaviour and epilepsy. Treatment of the creatine biosynthesis defects has yielded clinical improvement, while for creatine transporter deficiency, successful treatment strategies still need to be discovered. CCDSs may be responsible for a considerable fraction of children and adults affected with mental retardation of unknown etiology. Thus, screening for this group of disorders should be included in the differential diagnosis of this population. In this review, also the importance of CCDSs for the unravelling of the (patho)physiology of cerebral creatine metabolism is discussed [ABSTRACT FROM AUTHOR]

Recent observations in two patients, one with AGAT deficiency (AGAT-D) and one with GAMT deficiency (GAMT-D), both diagnosed already at birth, provide first evidence for important therapeutic effects of pre-symptomatic treatment with creatine (Cr) supplementation in AGAT-D and Cr supplementation plus guanidinoacetate lowering strategies in GAMT-D. Although long-term data are lacking, the results suggest that complete prevention of neurological sequelae in early treated patients could be feasible (Battini et al., 2006; Schulze et al., 2006) [ABSTRACT FROM AUTHOR]

Creatine and phosphocreatine provide an intracellular, high-energy phosphate buffering system, essential to maintain ATP levels in tissues with high energy demands. A specific plasma membrane creatine transporter (CRT) is required for the cellular uptake of creatine. This transporter is related to the \UPgamma -aminobutyric acid (GAT) and norepinephrine (NET) transporters and is part of a large gene family of Na+- and Cl--dependent neurotransmitter transporters, now known as solute carrier family 6 (SLC6). CRT is essential for normal brain function as mutations in the CRT gene (SLC6A8) result in X-linked mental retardation, associated with the almost complete lack of creatine in the brain, severe speech and language delay, epilepsy, and autistic behaviour. Insight into the structure and function of the CRT has come from studies of creatine transport by tissues and cells, in vitro studies of CRT mutations, identification of mutations associated with CRT deficiency, and from the recent high resolution structure of a prokaryotic homologue of the SLC6 transporters. CRT antibodies have been developed enabling the localization of creatine uptake sites in the brain, retina, muscle and other tissues. These tools in conjunction with the use of appropriate cell models should allow further progress in our knowledge on the regulation and cellular trafficking of the CRT. Development of suitable mouse models may allow improved understanding of the importance of the CRT for normal brain function and how the transporter is regulated in vivo [ABSTRACT FROM AUTHOR]

Mice with an under- or over-expression of enzymes catalyzing phosphoryl transfer in high-energy supplying reactions are particulary attractive for in vivo magnetic resonance spectroscopy (MRS) studies as substrates of these enzymes are visible in MR spectra. This chapter reviews results of in vivo MRS studies on transgenic mice with alterations in the expression of the enzymes creatine kinase and guanidinoacetate methyltransferase. The particular metabolic consequences of these enzyme deficiencies in skeletal muscle, brain, heart and liver are addressed. An overview is given of metabolite levels determined by in vivo MRS in skeletal muscle and brain of wild-type and transgenic mice. MRS studies on mice lacking guanidinoacetate methyltransferase have demonstrated metabolic changes comparable to those found in the deficiency of this enzyme in humans, which are (partly) reversible upon creatine feeding. Apart from being a model for a creatine deficiency syndrome, these mice are also of interest to study fundamental aspects of the biological role of creatine. MRS studies on transgenic mice lacking creatine kinase isoenzymes have contributed significantly to the view that the creatine kinase reaction together with other enzymatic steps involved in high-energy phosphate transfer builds a large metabolic energy network, which is highly versatile and can dynamically adapt to genotoxic or physiological challenges [ABSTRACT FROM AUTHOR]

In this review, we summarize the main structural and functional data on the role of the phosphocreatine (PCr) -- creatine kinase (CK) pathway for compartmentalized energy transfer in cardiac cells. Mitochondrial creatine kinase, MtCK, fixed by cardiolipin molecules in the vicinity of the adenine nucleotide translocator, is a key enzyme in this pathway. Direct transfer of ATP and ADP between these proteins has been revealed both in experimental studies on the kinetics of the regulation of mitochondrial respiration and by mathematical modelling as a main mechanism of functional coupling of PCr production to oxidative phosphorylation. In cells in vivo or in permeabilized cells in situ, this coupling is reinforced by limited permeability of the outer membrane of the mitochondria for adenine nucleotides due to the contacts with cytoskeletal proteins. Due to these mechanisms, at least 80% of total energy is exported from mitochondria by PCr molecules. Mathematical modelling of intracellular diffusion and energy transfer shows that the main function of the PCr -- CK pathway is to connect different pools (compartments) of ATP and, by this way, to overcome the local restrictions and diffusion limitation of adenine nucleotides due to the high degree of structural organization of cardiac cells [ABSTRACT FROM AUTHOR]

Evidence is increasing that the creatine/phosphocreatine shuttle system plays an essential role in energy homeostasis in the brain and retina to ensure proper development and function. Thus, our understanding of the mechanism of creatine supply and creatine usage in the brain and retina and of creatine supplementation in patients with creatine deficiency syndromes is an important step towards improved therapeutic strategies for brain and retinal disorders. Our recent research provides novel molecular-anatomical evidence that,(i) at the blood-brain barrier and the inner blood-retinal barrier, the creatine transporter (CRT/SLC6A8) functions as a major pathway for supplying creatine to the brain and retina, and that (ii) local creatine is preferentially synthesized in the glial cells, e.g., oligodendrocytes, astrocytes, and Müller cells, in the brain and retina. Thus, the blood-brain barrier and inner blood-retinal barrier play important roles not only in supplying energy sources (glucose and lactate), but also in supplying an energy ‘buffer' (creatine). These findings lead to the novel insight that the creatine/phosphocreatine shuttle system is based on an intricate relationship between the blood-brain barrier, inner blood-retinal barrier, glia, and neurons (photoreceptor cells) to maintain and ensure energy homeostasis in the brain and retina [ABSTRACT FROM AUTHOR]

In mammals, creatine is taken up from the diet and can be synthesized endogenously by a two-step mechanism involving the enzymes arginine:glycine amidinotransferase (AGAT) and guanidinoacetate methyltransferase (GAMT). Creatine (Cr) is taken up by cells through a specific transporter, CT1. While the major part of endogenous synthesis of Cr is thought to occur in kidney, pancreas and liver, the brain widely expresses AGAT, GAMT and CT1, both during development and in adulthood. The adult central nervous system (CNS) has a limited capacity to take up Cr from periphery, and seems to rely more on its endogenous Cr synthesis. In contrast, the embryonic CNS might be more dependent on Cr supply from periphery than on endogenous synthesis. This review will focus on the expression and function of AGAT, GAMT and CT1 in the mammalian CNS, both during development and in adulthood. Emphasis will also be placed on their specific roles in the different cell types of the brain, to analyze which brain cells are responsible for the CNS capacity of (i) endogenous Cr synthesis and (ii) Cr uptake from the periphery, and which brain cells are the main Cr consumers. The potential role of CT1 as guanidinoacetate transporter between "AGAT-only" and "GAMT-only" expressing cells will also be explored [ABSTRACT FROM AUTHOR]

The creatine kinase (CK)/phosphocreatine (PCr) energy buffering system is widespread in animal groups. Recent genomic sequencing and experimental results support the view that the capacity for creatine biosynthesis and membrane transport may have evolved quite early, perhaps coincident with CK. Conventional wisdom would suggest that CK evolved from an ancestral protein most similar to the CK homologue, arginine kinase. This early CK gene subsequently diverged into the cytoplasmic, mitochondrial and flagellar CK gene families. It is now clear that both the mitochondrial and cytoplasmic-flagellar genes were present prior to the divergence of sponges from the multi-cellular animal (metazoan) lineage, possibly as long as a billion years ago. Sponges constitute the most ancient, extant metazoan group. It is likely that the primary function of the CK-PCr system in these primitive animals was to mitigate reaction-diffusion constraints in highly polarized cells such as spermatozoa and choanocytes, the water current generating cells in sponges [ABSTRACT FROM AUTHOR]

Altered gene expression resulting from changes in the post-translational modification patterns of the histones and DNA is collectively termed epigenetics. Such changes are inherited albeit there are no alterations in the DNA sequence. Epigenetic regulation of gene expression is implemented by a wide repertoire of histone and DNA modifying enzymes including the acetyltransferases and deacetylases, the methyltransferases and kinases among others. Therefore, a regulation of these enzyme activities affords a tighter regulation of gene expression. Conversely, aberrant enzymatic activities lead to unregulated gene expression, resulting in several diseases such as RTS (loss of CBP HAT activity) and Spinal and Bulbar muscular atrophy (HATs and HMTases), apart from several forms of cancers, particularly myeloid leukemia (RAR-PML or RAR-PLZF fusion proteins resulting in the mistargeting of HDACs). Thus these enzymes have emerged as novel targets for the design of therapeutics. In this direction, several small molecule modulators (activators and inhibitors) of HATs, HDACs and HMTases are being reported in literature. This chapter introduces the different histone modifying enzymes involved in gene regulation, their connection to disease manifestation and focuses on the role of small molecule modulators in understanding enzyme function and also the design and the evolution of chromatin therapeutics [ABSTRACT FROM AUTHOR]

Human Immunodeficiency Virus type 1 (HIV-1) infection can now be treated effectively in many patients in the developed world, using combinations of antiretroviral therapeutics, called Highly Active Anti-Retroviral Therapy (HAART). However, despite prolonged treatment with HAART, the persistence of latently HIV-1-infected cellular reservoirs harboring transcriptionally silent but replication-competent proviruses represents the major hurdle to virus eradication. These latently infected cells are a permanent source for virus reactivation and lead to a rebound of the viral load after interruption of HAART. Therefore, a greater understanding of the molecular mechanisms regulating proviral latency and reactivation should lead to rational strategies aimed at purging these cellular reservoirs of HIV-1. This review summarizes our current knowledge and understanding of the elements involved in HIV-1 transcriptional reactivation: (1) the site of integration; (2) the transcription factor NF-κB, which is induced by proinflammatory cytokines (such as TNFα) and binds to two κB sites in the HIV-1 promoter region; (3) the specific remodeling of a single nucleosome (called nuc-1 and located immediately downstream of the HIV-1 transcription start site under latency conditions) upon activation of the HIV-1 promoter; (4) post-translational acetylation of histones and of non-histone proteins (following treatment with deacetylases inhibitors, which induce viral transcription and nuc-1 remodeling); and (5) the viral trans-activator Tat, which promotes transcription by mediating the recruitment to the HIV-1 promoter of histone-modifying enzymes and ATP-dependent chromatin remodeling complexes required for nucleosome disruption and transcriptional processivity. Finally, this review highlights experimental therapies aimed at administrating HIV-1 gene expression activators (such as HDAC inhibitors) combined with an effective HAART in order to reactivate and decrease/eliminate the pool of latently HIV-1-infected cellular reservoirs [ABSTRACT FROM AUTHOR]

Post-synthetic modification of histone proteins in chromatin architecture plays a central role in the epigenetic regulation of transcription. Histone acetylation and methylation are the two major modifications that function as a specific transcription regulator in response to various cellular signals. Albeit the mechanism of action of these modifications in transcription is not well understood, recent discovery of histone acetyltransferase (HAT) and methyltransferase (HMT) activities within transcriptional regulators has an important implication for histone modification to be a key player for the precise regulation of transcription processes. Here, we discuss recent advances made on histone acetylation and methylation as a fundamental process to modulate gene transcription, with a particular emphasis on their combinatorial effects in transcriptional control [ABSTRACT FROM AUTHOR]

First histone lysine methyltransferase (HLMTase) was discovered in 2000. Since then, there are reports of dozens of novel HLMTases in different eukaryotes including plant, fungus, insect, nematode and vertebrate. The enzymes and their specific histone-lysine modifications have enormous impacts on the regulation of chromatin structure and function. Furthermore, various histone methyl-lysine demethylases (HLDMases) have been identified recently. In this chapter, histone H3 lysine 9 specific methyltransferases will be discussed as model enzymes involved in the regulation of chromatin function [ABSTRACT FROM AUTHOR]

In eukaryotic cells, relaxed interphase chromatin undergoes pronounced changes resulting in formation of highly condensed mitotic chromosomes. Moreover, chromatin condensation is particularly evident during mitosis and apoptotic cell death, whereas chromatin relaxation is necessary for replication, repair, recombination and transcription. The post-translational modifications of histone tails such as reversible acetylation, phosphorylation and methylation play a critical role in dynamic condensation/relaxation that occurs during the cell cycle. Histone phosphorylation is believed to play a direct role in mitosis, cell death, repair, replication and recombination. However, definitive roles for this modification in these processes have not yet been elucidated. In this review, we discuss recent progress in studies of histone phosphorylation [ABSTRACT FROM AUTHOR]

The MYST family of histone acetyltransferases is highly conserved in eukaryotes and is responsible for the majority of acetylation events. These enzymes are exclusively found in multisubunit protein complexes, which structure is also very well conserved. Recent studies have shed light on the precise functions of these HAT complexes. They play critical roles in gene-specific transcription regulation, DNA damage response and repair, as well as DNA replication. Such roles in basic nuclear functions suggest that alteration of these MYST HAT complexes could lead to malfunctioning cells, leading to cell death, uncontrolled growth and/or disease. Indeed, many of these enzymes and their associated factors have been implicated in several forms of cancers. This chapter summarizes the current knowledge on MYST HAT complexes, their functions and link to human diseases. [ABSTRACT FROM AUTHOR]

During the development and maintenance of the central nervous system, neurons receive specific instructions to differentiate, survive or die, the correct choice being crucial for the maturation of a functional brain and to face pathological conditions. At the transcriptional level, chromatin remodeling enzymes participates in such processes. In this paper, we will see that disruption of the Histone acetyl transferase (HAT)/Deacetylase (HDAC) balance is often observed in different contexts of neurological disorders and more particularly during neuronal apoptosis. During the last 5 years, it has been evidenced that the chromatin acetylation status was greatly impaired in different neurodegenerative diseases, a common mechanism being the loss of function of a specific HAT: the CREB-binding protein (CBP). We will review the last attempts of the use of small molecules antagonizing HDAC activity (HDAC inhibitors) to restore proper levels of acetylation and enhance neuronal survival, both in in vitro and in vivo models of neurodegenerative diseases such as polyglutamine-related diseases and amyotrophic lateral sclerosis. Although this strategy lacks specificity towards CBP, certain of these molecules display promising therapeutic properties [ABSTRACT FROM AUTHOR]

One of the major mechanisms through which eukaryotic cells respond to developmental and environmental signals is by changing their gene expression patterns. This complex and tightly regulated process is largely regulated at the level of RNA polymerase II-mediated transcription. Within this process an important class of transcriptional regulators are the histone acetyltransferases (HATs), proteins that acetylate histones and non-histone substrates. While hyperacetylation of histones is generally associated with active genes, the effect of acetylation of nonhistone proteins varies between substrates resulting in for example alterations in (sub-nuclear) protein localization or protein stability. Given the central role of HATs in transcriptional regulation and other cellular processes, it may not be surprising that genetic alterations in the genes encoding HATs, resulting in aberrant forms of these regulatory proteins, have been linked with various human diseases, including congenital developmental disorders and various forms of cancer, including leukaemia. Here we will review mutations found in genes encoding human HATs and discuss the (putative) functional consequences on the function of these proteins. So far the lessons learned from naturally occurring mutations in humans have proven to be invaluable and recapitulating such genetic alterations in various experimental systems will extend our knowledge even further. This seems particularly relevant given the wide range of diseases in which acetyltransferases have been implicated and may help to open up new therapeutic avenues [ABSTRACT FROM AUTHOR]

The DNA in eukaryotic genome is compartmentalized into various domains by a series of loops tethered onto the base of nuclear matrix. Scaffold/ Matrix attachment regions (S/MAR) punctuate these attachment sites and govern the nuclear architecture by establishing chromatin boundaries. In this context, specific proteins that interact with and bind to MAR sequences called MAR binding proteins (MARBPs), are of paramount importance, as these sequences spool the proteins that regulate transcription, replication, repair and recombination. Recent evidences also suggest a role for these cis-acting elements in viral integration, replication and transcription, thereby affecting host immune system. Owing to the complex nature of these nucleotide sequences, less is known about the MARBPs that bind to and bring about diverse effects on chromatin architecture and gene function. Several MARBPs have been identified and characterized so far and the list is growing. The fact that most the MARBPs exist in a co-repressor/ co-activator complex and bring about gene regulation makes them quintessential for cellular processes. This participation in gene regulation means that any perturbation in the regulation and levels of MARBPs could lead to disease conditions, particularly those caused by abnormal cell proliferation, like cancer. In the present chapter, we discuss the role of MARs and MARBPs in eukaryotic gene regulation, recombination, transcription and viral integration by altering the local chromatin structure and their dysregulation in disease manifestation [ABSTRACT FROM AUTHOR]

Post-translational modifications of nonhistone proteins play a significant role in regulating the chromatin structure, dynamics and thereby gene regulation. Among the different posttranslational modifications, reversible acetylation of non-histone proteins has profound functional implications on wide range of cellular processes. The acetylation status of these proteins is regulated by several cellular and non-cellular factors like viruses, physiological stresses, DNA damaging agents and ROS. Mutations found in the acetylation sites of these proteins and aberrant acetylation are related to imbalances in different cellular pathways and various diseases. Several factor acetyltransferases and deacetylases are known to regulate the acetylation of the nonhistone proteins. Modulators of these enzymes derived from natural as well as synthetic sources can thus have important therapeutic implications. Designing strategies to specifically target the acetylation of these proteins can be used as a valuable tool for new generation drugs [ABSTRACT FROM AUTHOR]

Chemotherapy has been a major approach to treat cancer. Both constituents of chromatin, chromosomal DNA and the associated chromosomal histone proteins are the molecular targets of the anticancer drugs. Small DNA binding ligands, which inhibit enzymatic processes with DNA substrate, are well known in cancer chemotherapy. These drugs inhibit the polymerase and topoisomerase activity. With the advent in the knowledge of chromatin chemistry and biology, attempts have shifted from studies of the structural basis of the association of these drugs or small ligands (with the potential of drugs) with DNA to their association with chromatin and nucleosome. These drugs often inhibit the expression of specific genes leading to a series of biochemical events. An overview will be given about the latest understanding of the molecular basis of their action. We shall restrict to those drugs, synthetic or natural, whose prime cellular targets are so far known to be chromosomal DNA [ABSTRACT FROM AUTHOR]

Alteration of nuclear morphology is often used by pathologist as diagnostic marker for malignancies like cancer. In particular, the staining of cells by the silver staining methods (AgNOR) has been proved to be an important tool for predicting the clinical outcome of some cancer diseases. Two major argyrophilic proteins responsible for the strong staining of cells in interphase are the nucleophosmin (B23) and the nucleolin (C23) nucleolar proteins. Interestingly these two proteins have been described as chromatin associated proteins with histone chaperone activities and also as proteins able to regulate chromatin transcription. Nucleolin seems to be over-expressed in highly proliferative cells and is involved in many aspect of gene expression: chromatin remodeling, DNA recombination and replication, RNA transcription by RNA polymerase I and II, rRNA processing, mRNA stabilisation, cytokinesis and apoptosis. Interestingly, nucleolin is also found on the cell surface in a wide range of cancer cells, a property which is being used as a marker for the diagnosis of cancer and for the development of anti-cancer drugs to inhibit proliferation of cancer cells. In addition to its implication in cancer, nucleolin has been described not only as a marker or as a protein being involved in many diseases like viral infections, autoimmune diseases, Alzheimer's disease pathology but also in drug resistance. In this review we will focus on the chromatin associated functions of nucleolin and discuss the functions of nucleolin or its use as diagnostic marker and as a target for therapy [ABSTRACT FROM AUTHOR]

Histone chaperones are the histone interacting factors that stimulate histone transfer reaction without being a part of the final product. They are involved in the histone storage, histone translocation to the nucleus, and histone exchange and histone deposition onto the DNA for replication dependent chromatin assembly. Interestingly, they have also been demonstrated to possess the histone removal activity. While the involvement of the histone chaperones in chromatin transcription is undisputed, the question of their local versus global involvement is under scrutiny. This review enumerates the role played by various histone chaperones in the establishment of chromatin structure and regulation of chromatin transcription. The role of histone chaperones in disease manifestation is not very clear, preliminary results with few histone chaperones suggest that expression and function of these factors dramatically alters in carcinogenesis. This review will also focus on the possible role of histone chaperones in cancer diagnosis and progression [ABSTRACT FROM AUTHOR]

In contrast to canonical histones, which are assembled into nucleosomes during DNA replication, histone variants can be incorporated into specific regions of the genome throughout the cell cycle. Recent findings suggest that histone variants associate with factors mediating their deposition into specialized chromatin domains. The mechanisms of their targeted deposition, their turnover, and their posttranslational modification are not yet fully understood. Emerging evidence indicates that histone variants and associated factors are essential for the epigenetic control of gene expression and other cellular responses. Thus, histone variants and complexes involved in their exchange are likely to play major roles in controlling chromosomal architecture, and their deregulation is expected to be linked to cancers, infertility, mental disorders, ageing, and degenerative diseases [ABSTRACT FROM AUTHOR]

Histone variant are non-allelic forms of the conventional histones. They are expressed at very low levels compared to their conventional counterparts. All the conventional histones, except H4, have histone variants. Together with histone modifications and chromatin remodeling machines, the incorporation of histone variants into the nucleosome is one of the main strategies that the cell uses to regulate transcription, repair, chromosome assembly and segregation. The exact role of the histone variants in these processes is far from clear, but the emerging picture is that the presence of histone variants confers novel structural and functional properties of the nucleosome which affect the chromatin dynamics. In this article we will discuss the functional significance of histone variants on chromatin function and its link to disease manifestation [ABSTRACT FROM AUTHOR]

Poly(ADP-Ribose) Polymerase-1 (PARP-1) is the prototypical and most abundantly expressed member of a family of PARPs that catalyze the polymerization of ADP-ribose (ADPR) units from donor NAD+ molecules on target proteins. PARP-1 plays roles in a variety of genomic processes, including the regulation of chromatin structure and transcription in response to specific cellular signals. PARP-1 also plays important roles in many stress-induced disease states. In this chapter, we review the molecular and cellular aspects of PARP-1's chromatin-modulating activities, as well as the impact that these chromatin-modulating activities have on the regulation of gene expression. In addition, we highlight the potential therapeutic use of drugs that target PARP-1's enzymatic activity for the treatment of human diseases [ABSTRACT FROM AUTHOR]

Alterations of chromatin structure play an important role in gene regulation. One way of doing so involves ATP-dependent chromatin remodelling enzymes that act as molecular machines coupling ATP-hydrolysis to structural changes of the nucleosome. Several recent studies shed important insights into the mechanism of these factors and indicate that they couple DNA translocation within the nucleosome to DNA loop propagation through the nucleosome. This reaction causes the movement of a nucleosome with respect to a given DNA sequence and also drives its disassembly. It is becoming clear that the biology of these factors is very complex considering the plethora of known ATP-dependent nucleosome remodelling factors and their many, in part overlapping functions and varied ways of regulation and targeting. Finally, nucleosome remodelling may only be one aspect of the function of these enzymes, because they may impart or regulate higher order levels of chromatin organization. The importance of these enzymes for normal growth and development is illustrated by disorders and neoplasias linked to mutations of those factors or their misregulation. Given that these enzymes have such profound roles in gene expression and cell proliferation, they may constitute important drug targets for clinical applications in the future [ABSTRACT FROM AUTHOR]