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Peroxisome proliferator-activated receptors (PPARs) may play an important role in the pathomechanism/pathogenesis of Alzheimer’s disease (AD) and several other neurological/neuropsychiatric disorders. AD leads to progressive alterations in the redox state, ion homeostasis, lipids, and protein metabolism. Significant alterations in molecular processes and the functioning of several signaling pathways result in the degeneration and death of synapses and neuronal cells, leading to the most severe dementia. Peroxisome proliferator-activated receptor alpha (PPAR-α) is among the processes affected by AD; it regulates the transcription of genes related to the metabolism of cholesterol, fatty acids, other lipids and neurotransmission, mitochondria biogenesis, and function. PPAR-α is involved in the cholesterol transport to mitochondria, the substrate for neurosteroid biosynthesis. PPAR-α-coding enzymes, such as sulfotransferases, which are responsible for neurosteroid sulfation. The relation between PPAR-α and cholesterol/neurosteroids may have a significant impact on the course and progression of neurodegeneration/neuroprotection processes. Unfortunately, despite many years of intensive studies, the pathogenesis of AD is unknown and therapy for AD and other neurodegenerative diseases is symptomatic, presenting a significant goal and challenge today. This review presents recent achievements in therapeutic approaches for AD, which are targeting PPAR-α and its relation to cholesterol and neurosteroids in AD and neuropsychiatric disorders.

Peroxisome proliferator-activated receptors α (PPARα) are members of the nuclear receptors family and a very potent transcription factor engaged in the regulation of lipid and energy metabolism. Recent data suggest that PPARα could play an important role in the pathomechanism of Alzheimer’s disease (AD) and other neuropsychiatric disorders. This study focused on the effect of a synthetic ligand of PPARα, GW7647 on the transcription of genes encoding proteins of mitochondria biogenesis and dynamics in the brain of AD mice. The experiments were carried out using 12-month-old female FVB-Tg mice with the V717I mutation of amyloid precursor protein (APP + ) and mice without the transgene (APP – ). Moreover, APP + and APP – mice were treated for 14 days with GW7647 administered subcutaneously with a dose 5 mg/kg b.w. Brain cortex was used and qRT-PCR was performed. Our data indicated that GW7647 upregulated the expression of genes encoding proteins of mitochondria biogenesis in ADTg mice. GW7647 enhanced the level of mRNA of Ppargc1, Nrf2 and Tfam in APP + as compared to APP – mice treated with GW7647. Moreover, our studies demonstrated that GW7647 had no effect on genes that regulate mitochondria fission and fusion of ADTg mice as correlated to mice without the transgene. Our results indicate that the ligand of PPARα, GW7647 may exert a promising neuroprotective effect through the regulation of transcription of genes coding proteins of mitochondria biogenesis. These data suggest that activation of PPARα at an early stage of AD could be a helpful strategy for slowing the progression of neurodegeneration.

In the current study, we analyzed the effects of the systemic inflammatory response (SIR) and amyloid β (Aβ) peptide on the expression of genes encoding cyclins and cyclin-dependent kinase (Cdk) in: (i) PC12 cells overexpressing human beta amyloid precursor protein (βAPP), wild-type (APPwt-PC12), or carrying the Swedish mutantion (APPsw-PC12); (ii) the murine hippocampus during SIR; and (iii) Alzheimer’s disease (AD) brain. In APPwt-PC12 expression of cyclin D2 (cD2) was exclusively reduced, and in APPsw-PC12 cyclins cD2 and also cA1 were down-regulated, but cA2, cB1, cB2, and cE1 were up-regulated. In the SIR cD2, cB2, cE1 were found to be significantly down-regulated and cD3, Cdk5, and Cdk7 were significantly up-regulated. Cyclin cD2 was also found to be down-regulated in AD neocortex and hippocampus. Our novel data indicate that Aβ peptide and inflammation both significantly decreased the expression of cD2, suggesting that Aβ peptides may also contribute to downregulation of cD2 in AD brain.

The physiological balance between excitation and inhibition in the brain is significantly affected in Alzheimer’s disease (AD). Several neuroactive compounds and their signaling pathways through various types of receptors are crucial in brain homeostasis, among them glutamate and γ-aminobutyric acid (GABA). Activation of microglial receptors regulates the immunological response of these cells, which in AD could be neuroprotective or neurotoxic. The novel research approaches revealed the complexity of microglial function, including the interplay with other cells during neuroinflammation and in the AD brain. The purpose of this review is to describe the role of several proteins and multiple receptors on microglia and neurons, and their involvement in a communication network between cells that could lead to different metabolic loops and cell death/survival. Our review is focused on the role of glutamatergic, GABAergic signaling in microglia–neuronal cross-talk in AD and neuroinflammation. Moreover, the significance of AD-related neurotoxic proteins in glutamate/GABA-mediated dialogue between microglia and neurons was analyzed in search of novel targets in neuroprotection, and advanced pharmacological approaches.

Molecular studies have provided increasing evidence that Parkinson’s disease (PD) is a protein conformational disease, where the spread of alpha-synuclein (ASN) pathology along the neuraxis correlates with clinical disease outcome. Pathogenic forms of ASN evoke oxidative stress (OS), neuroinflammation, and protein alterations in neighboring cells, thereby intensifying ASN toxicity, neurodegeneration, and neuronal death. A number of evidence suggest that homeostasis between bioactive sphingolipids with opposing function—e.g., sphingosine-1-phosphate (S1P) and ceramide—is essential in pro-survival signaling and cell defense against OS. In contrast, imbalance of the “sphingolipid biostat” favoring pro-oxidative/pro-apoptotic ceramide-mediated changes have been indicated in PD and other neurodegenerative disorders. Therefore, we focused on the role of sphingolipid alterations in ASN burden, as well as in a vast range of its neurotoxic effects. Sphingolipid homeostasis is principally directed by sphingosine kinases (SphKs), which synthesize S1P—a potent lipid mediator regulating cell fate and inflammatory response—making SphK/S1P signaling an essential pharmacological target. A growing number of studies have shown that S1P receptor modulators, and agonists are promising protectants in several neurological diseases. This review demonstrates the relationship between ASN toxicity and alteration of SphK-dependent S1P signaling in OS, neuroinflammation, and neuronal death. Moreover, we discuss the S1P receptor-mediated pathways as a novel promising therapeutic approach in PD.

Recent data indicate that Alzheimer’s disease (AD) is associated with disturbances of the circadian rhythm in patients. We examined the effect of amyloid-β (Aβ) peptide, the main component of the senile plaques playing a critical role in the deregulation of calcium (Ca 2+ ) homeostasis in AD, on the circadian oscillation of cytosolic calcium (Ca 2+ ) levels in vitro . The experiments we carried out in human primary skin fibroblasts. This cell line was previously shown to exhibit circadian rhythms of clock genes. Moreover, the basic clock properties of these peripheral cells closely mimic those measured physiologically and behaviorally in human and do not change during aging. In this study we showed that i) cytosolic Ca 2+ oscillations depend on the activation of purinergic P2X7 receptors; and ii) these oscillations are abolished in the presence of Aβ. In total, our new findings may help to deepen our understanding of the molecular mechanisms involved in AD-related circadian alterations.

Acute systemic inflammatory response (SIR) triggers an alteration in the transcription of brain genes related to neuroinflammation, oxidative stress and cells death. These changes are also characteristic for Alzheimer’s disease (AD) neuropathology. Our aim was to evaluate gene expression patterns in the mouse hippocampus (MH) by using microarray technology 12 and 96 h after SIR evoked by lipopolysaccharide (LPS). The results were compared with microarray analysis of human postmortem hippocampal AD tissues. It was found that 12 h after LPS administration the expression of 231 genes in MH was significantly altered (FC > 2.0); however, after 96 h only the S100a8 gene encoding calgranulin A was activated (FC = 2.9). Gene ontology enrichment analysis demonstrated the alteration of gene expression related mostly to the immune-response including the gene Lcn2 for Lipocalin 2 (FC = 237.8), involved in glia neurotoxicity. The expression of genes coding proteins involved in epigenetic regulation, histone deacetylases (Hdac4,5,8,9,11) and bromo- and extraterminal domain protein Brd3 were downregulated; however, Brd2 was found to be upregulated. Remarkably, the significant increase in expression of Lcn2, S100a8, S100a9 and also Saa3 and Ch25h, was found in AD brains suggesting that early changes of immune-response genes evoked by mild SIR could be crucial in AD pathogenesis.

Our study focused on the relationship between amyloid β 1-42 (Aβ), sphingosine kinases (SphKs) and mitochondrial sirtuins in regulating cell fate. SphK1 is a key enzyme involved in maintaining sphingolipid rheostat in the brain. Deregulation of the sphingolipid metabolism may play a crucial role in the pathogenesis of Alzheimer's disease (AD). Mitochondrial function and mitochondrial deacetylases, i.e. sirtuins (Sirt3,-4,-5), are also important for cell viability. In this study, we evaluated the interaction between Aβ1-42, SphKs and Sirts in cell survival/death, and we examined several compounds to indicate possible target(s) for a strategy protecting against cytotoxicity of Aβ1-42. PC12 cells were subjected to Aβ1-42 oligomers and SphK inhibitor SKI II for 24-96 h. Our data indicated that Aβ1-42 enhanced SphK1 expression and activity after 24 h, but down-regulated them after 96 h and had no effect on Sphk2. Aβ1-42 and SKI II induced free radical formation, disturbed the balance between pro- and anti-apoptotic proteins and evoked cell death. Simultaneously, up-regulation of anti-oxidative enzymes catalase and superoxide dismutase 2 was observed. Moreover, the total protein level of glycogen synthase kinase-3β was decreased. Aβ1-42 significantly increased the level of mitochondrial proteins: apoptosis-inducing factor AIF and Sirt3, -4, -5. By using several pharmacologically active compounds we showed that p53 protein plays a significant role at very early stages of Aβ1-42 toxicity. However, during prolonged exposure to Aβ1-42, the activation of caspases, MEK/ERK, and alterations in mitochondrial permeability transition pores were additional factors leading to cell death. Moreover, SphK product, sphingosine-1-phosphate (S1P), and Sirt activators and antioxidants, resveratrol and quercetin, significantly enhanced viability of cells subjected to Aβ1-42. Our data indicated that p53 protein and inhibition of SphKs may be early key events responsible for cell death evoked by Aβ1-42. We suggest that activation of S1P-dependent signalling and Sirts may offer a promising cytoprotective strategy.

Sphingosine kinases (Sphk1/2 EC 2.7.1.91) are responsible for synthesis of sphingosine-1-phosphate (S1P) and for regulation of the bioactive sphingolipids homeostasis. Sphingosine-1-phosphate can act as a potent messenger in an autocrine/paracrine manner through five specific G protein-coupled receptors (GPCR) S1P1-5. This sphingolipid is involved in the mechanism of transcription, mitochondrial function, neuronal viability and degeneration. Until now the involvement of Sphk1/2 and sphingolipid alterations in Parkinson's disease (PD) remains unknown. Recent studies have indicated the role of sphingolipids in the regulation of alpha-synuclein (ASN) in the PD brain. Our latest data demonstrated significant inhibition of Sphk1 gene expression and activity in an in vitro PD model, induced by 1-methyl-4-phenylpyridinium (MPP+). The aim of this study was to investigate the role of Sphks inhibition in ASN secretion and in the molecular mechanism of neuronal death in the PD model. Our study was carried out using neuronal dopaminergic SH-SY5Y control cells, transfected with the human gene for ASN or with an empty vector. These cells were treated with MPP+ (1-3 mM), which represents an experimental PD model, or with the Sphks inhibitor (1-5 µM SKI II) for 3-24 h. Our data indicated that MPP+ (3 mM) induced significant alterations of Sphks and S1P lyase (SPL) gene expression. Reduced activity of Sphk1 and Sphk2 in the cytosolic fraction and in the crude nuclear fraction, respectively, was observed. Sphks inhibition evoked enhancement of ASN secretion, suppression of PI3K/Akt phosphorylation and activation of gene expression for the pro-apoptotic Bcl-2 proteins Bax and BH3-only protein Harakiri. Moreover, a lower level of cytochrome c in the mitochondrial fraction and caspase-dependent degradation of DNA-bound enzyme poly(ADP-ribose) polymerase (PARP-1) were observed. The caspase inhibitor (20 µM Z-VAD-FMK) significantly enhanced neuronal cell viability in MPP+ oxidative stress. However, exogenous S1P (1 µM) exerted a more efficient neuroprotective effect as compared to Z-VAD-FMK. In summary, these data indicated that Sphk1 inhibition plays an important role in caspase-dependent apoptotic neuronal death in an experimental PD model.