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Amyloid-β (Aβ) is thought to be neuronally derived in Alzheimer's disease (AD). However, transcripts of amyloid precursor protein (APP) and amyloidogenic enzymes are equally abundant in oligodendrocytes (OLs). By cell-type-specific deletion of Bace1 in a humanized knock-in AD model, APP NLGF , we demonstrate that OLs and neurons contribute to Aβ plaque burden. For rapid plaque seeding, excitatory projection neurons must provide a threshold level of Aβ. Ultimately, our findings are relevant for AD prevention and therapeutic strategies., (© 2024. The Author(s).)

The incidence of Alzheimer's disease (AD), the leading cause of dementia, increases rapidly with age, but why age constitutes the main risk factor is still poorly understood. Brain ageing affects oligodendrocytes and the structural integrity of myelin sheaths 1 , the latter of which is associated with secondary neuroinflammation 2,3 . As oligodendrocytes support axonal energy metabolism and neuronal health 4-7 , we hypothesized that loss of myelin integrity could be an upstream risk factor for neuronal amyloid-β (Aβ) deposition, the central neuropathological hallmark of AD. Here we identify genetic pathways of myelin dysfunction and demyelinating injuries as potent drivers of amyloid deposition in mouse models of AD. Mechanistically, myelin dysfunction causes the accumulation of the Aβ-producing machinery within axonal swellings and increases the cleavage of cortical amyloid precursor protein. Suprisingly, AD mice with dysfunctional myelin lack plaque-corralling microglia despite an overall increase in their numbers. Bulk and single-cell transcriptomics of AD mouse models with myelin defects show that there is a concomitant induction of highly similar but distinct disease-associated microglia signatures specific to myelin damage and amyloid plaques, respectively. Despite successful induction, amyloid disease-associated microglia (DAM) that usually clear amyloid plaques are apparently distracted to nearby myelin damage. Our data suggest a working model whereby age-dependent structural defects of myelin promote Aβ plaque formation directly and indirectly and are therefore an upstream AD risk factor. Improving oligodendrocyte health and myelin integrity could be a promising target to delay development and slow progression of AD., (© 2023. The Author(s).)

A key feature of advanced brain aging includes structural defects of intracortical myelin that are associated with secondary neuroinflammation. A similar pathology is seen in specific myelin mutant mice that model 'advanced brain aging' and exhibit a range of behavioral abnormalities. However, the cognitive assessment of these mutants is problematic because myelin-dependent motor-sensory functions are required for quantitative behavioral readouts. To better understand the role of cortical myelin integrity for higher brain functions, we generated mice lacking Plp1 , encoding the major integral myelin membrane protein, selectively in ventricular zone stem cells of the mouse forebrain. In contrast to conventional Plp1 null mutants, subtle myelin defects were restricted to the cortex, hippocampus, and underlying callosal tracts. Moreover, forebrain-specific Plp1 mutants exhibited no defects of basic motor-sensory performance at any age tested. Surprisingly, several behavioral alterations reported for conventional Plp1 null mice (Gould et al., 2018) were absent and even social interactions appeared normal. However, with novel behavioral paradigms, we determined catatonia-like symptoms and isolated executive dysfunction in both genders. This suggests that loss of myelin integrity has an impact on cortical connectivity and underlies specific defects of executive function. These observations are likewise relevant for human neuropsychiatric conditions and other myelin-related diseases., Competing Interests: SA, CD, SS, AS, ME, AR, KH, KL, HW, HE No competing interests declared, KN Reviewing editor, eLife, (© 2023, Arinrad, Depp et al.)

Astrocyte-derived cholesterol supports brain cells under physiological conditions. However, in demyelinating lesions, astrocytes downregulate cholesterol synthesis, and the cholesterol that is essential for remyelination has to originate from other cellular sources. Here, we show that repair following acute versus chronic demyelination involves distinct processes. In particular, in chronic myelin disease, when recycling of lipids is often defective, de novo neuronal cholesterol synthesis is critical for regeneration. By gene expression profiling, genetic loss-of-function experiments, and comprehensive phenotyping, we provide evidence that neurons increase cholesterol synthesis in chronic myelin disease models and in patients with multiple sclerosis (MS). In mouse models, neuronal cholesterol facilitates remyelination specifically by triggering oligodendrocyte precursor cell proliferation. Our data contribute to the understanding of disease progression and have implications for therapeutic strategies in patients with MS., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2021 The Author(s). Published by Elsevier Inc. All rights reserved.)

The repair of inflamed, demyelinated lesions as in multiple sclerosis (MS) necessitates the clearance of cholesterol-rich myelin debris by microglia/macrophages and the switch from a pro-inflammatory to an anti-inflammatory lesion environment. Subsequently, oligodendrocytes increase cholesterol levels as a prerequisite for synthesizing new myelin membranes. We hypothesized that lesion resolution is regulated by the fate of cholesterol from damaged myelin and oligodendroglial sterol synthesis. By integrating gene expression profiling, genetics and comprehensive phenotyping, we found that, paradoxically, sterol synthesis in myelin-phagocytosing microglia/macrophages determines the repair of acutely demyelinated lesions. Rather than producing cholesterol, microglia/macrophages synthesized desmosterol, the immediate cholesterol precursor. Desmosterol activated liver X receptor (LXR) signaling to resolve inflammation, creating a permissive environment for oligodendrocyte differentiation. Moreover, LXR target gene products facilitated the efflux of lipid and cholesterol from lipid-laden microglia/macrophages to support remyelination by oligodendrocytes. Consequently, pharmacological stimulation of sterol synthesis boosted the repair of demyelinated lesions, suggesting novel therapeutic strategies for myelin repair in MS.

The gut microbiome was extensively researched for its biological variety and its potential role in propagating diseases outside of the gastrointestinal (GI) tract. Recently, a lot of effort was focused on comprehending the gut-brain axis and the bizarre communication between the GI system and the nervous system. Ample amount of studies being carried out also revealed the involvement of the gut microbiome in enhancing the degree of many neurological disorders, including neurodegenerative diseases. It was widely observed that there were distinct microbiome profiles and dysbiosis within patients suffering from Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and multiple sclerosis. Various approaches to re-establish the balance of the gut microbiome, from antibiotic therapy, fecal microbiota transplant, or ingestion of psychobiotics, are discussed within this review within the specific context of combating neurodegenerative diseases. Present studies and clinical trials indicate that although there is an immense potential of gut microbiome modification to be preventive or therapeutic, there are still many intercalated components of the gut-brain axis at play and thus, more research needs to be carried out to delineate microbiome factors that may potentially alleviate symptoms of neurodegeneration.

Alzheimer's disease (AD) is the most common form of dementia and has affected millions of individuals worldwide. The hallmarks of AD include the amyloid beta plaque deposits, tau neurofibrillary tangles, altered neuronal signaling, alongside decline in memory and cognitive functions. Conventional drug therapies do exist, such as donepezil or aducanumab, but these drugs mostly focus on halting AD progression instead of causing a reversal within the disease. In an effort to ameliorate and ultimately cure AD, researchers have delved into viral-mediated gene therapy to fix this disease from its root molecular causes. To date, adeno-associated virus and lentiviral vectors have remained the most vastly studied among other viral vectors to combat AD. These vectors could be employed alongside various genetic materials based on the types of processes we want to alter to yield a positive effect, such as disruption of amyloidogenic pathway, neuroprotection and lipid metabolism pathways. Recent studies and trials were reviewed in this article, highlighting their clinical significance, differences and limitations between each method. By learning from the different combinations and possibilities of viral-mediated gene transfer, researchers would then get a step closer in ameliorating symptoms and possibly in curing AD.

Background and purpose : Neurological diseases and injuries to the nervous system may cause inadvertent damage to neuronal and synaptic structures. Such phenomenon would lead to the development of neurological and neurodegenerative disorders which might affect memory, cognition and motoric functions. The body has various negative feedback systems which can induce beneficial neuroplastic changes in mediating some neuronal damage; however, such efforts are often not enough to ameliorate the derogatory changes. Materials and methods: Articles discussing studies to induce beneficial neuroplastic changes were retrieved from the databases, National Center for Biotechnology Information (NCBI) and MEDLINE, and reviewed. Results: This review highlights the significance of neuroplasticity in restoring neuronal functions and current advances in research to employ this positive cellular event by inducing synaptogenesis, neurogenesis, clearance of toxic amyloid beta (Aβ) and tau protein aggregates, or by providing neuroprotection. Compounds ranging from natural products (e.g. bilobalides, curcumin) to novel vaccines (e.g. AADvac1, RG7345) have been reported to induce long-lasting neuroplasticity in vitro and in vitro . Activity-dependent neuroplasticity is also inducible by regimens of exercises and therapies with instances in human studies proving major successes. Lastly, mechanical stimulation of brain regions through therapeutic hypothermia or deep brain stimulation has given insight on the larger scale of neuroplasticity within the nervous system. Conclusion: Harnessing neuroplasticity may not only offer an arm in the vast arsenal of approaches being taken to tackle neurological disorders, such as neurodegenerative diseases, but from ample evidence, it also has major implications in neuropsychological disorders.

Background and Purpose: The central nervous system (CNS) faces unique difficulties in attaining permanent therapy for neurodegenerative disorder (ND). Genomic level forms of therapy have garnered interest in the recent decade, with the novel CRISPR/Cas9 gene editing tool continuing to be explored due to its efficiency, safety, and adaptability to varying conditions. With the aid of viral vectors as transport vectors, the gene editing tool has produced promising in vitro and in vivo findings in study models. Thus, this review focuses on the recent advancements and update of CRISPR/Cas9 to combat neurodegenerative diseases., Methods: Articles detailing potential applications of CRISPR/Cas9 in neurodegenerative settings were retrieved from PubMed and Google Scholar with the keywords "CRISPR," "gene editing," and "neurodegenerative diseases." Relevant information was collected and critically reviewed., Results: The utility of CRISPR/Cas9 coupled with viral transduction ranges from the disruption of amyloid precursor protein (APP) production at a genomic level in Alzheimer's disease (AD) to the deletion of varying exon portions of the Dmd gene in Duchenne muscular dystrophy (DMD) which would increase dystrophin expression. This usage of CRISPR/Cas9 also extends to experimentally ameliorate the neurodegenerative effects caused by viral infections., Conclusion: The CRISPR/Cas9 gene editing tool is a powerful arsenal in the field of gene therapy and molecular medicine; hence, more research should be called to focus on the ample potential this tool has to offer in the field of neurodegenerative diseases.

Neurodegeneration is typically preceded by neuroinflammation generated by the nervous system to protect itself from tissue damage, however, excess neuroinflammation may inadvertently cause more harm to the surrounding tissues. Attenuating neuroinflammation with non‑steroidal anti‑inflammatory drugs can inhibit neurodegeneration. However, such treatments induce chronic side effects, including stomach ulcers. Madecassoside, a triterpene derived from Centella asiatica, is considered to be an alternative treatment of inflammation. In the present study, the anti‑neuroinflammatory properties of madecassoside were assessed in BV2 microglia cells, which were pre‑treated with madecassoside at a maximum non‑toxic dose (MNTD) of 9.50 µg/ml and a ½ MNTD of 4.75 µg/ml for 3 h and stimulated with 0.1 µg/ml lipopolysaccharide (LPS). The effect of madecassoside was assessed by determining reactive oxygen species (ROS) levels in all groups. Furthermore, the expression of pro‑ and anti‑neuroinflammatory genes and proteins were analyzed using reverse transcription‑quantitative polymerase chain reaction and western blotting, respectively. The results demonstrated that ROS levels in cells treated with the MNTD of madecassoside were significantly reduced compared with cells treated with LPS alone (P<0.05). The expression of pro‑neuroinflammatory genes, including inducible nitric oxide synthase, cyclooxygenase‑2, signal transducer and activator of transcription 1 and nuclear factor‑κB, were significantly downregulated in a dose‑independent manner following treatment with madecassoside. Conversely, the anti‑neuroinflammatory component heme oxygenase 1 was significantly upregulated by 175.22% in the MNTD‑treated group, compared with cells treated with LPS alone (P<0.05). The gene expression profiles of pro‑ and anti‑inflammatory genes were also consistent with the results of western blotting. The results of the present study suggest that madecassoside may be a potent anti‑neuroinflammatory agent. The antioxidative properties of madecassoside, which serve a major role in anti‑neuroinflammation, indicate that this compound may be a functional natural anti‑neuroinflammatory agent, therefore, further in vivo or molecular studies are required.

Glioblastoma multiforme (GBM) is a malignant tumor within the brain. Generally classified as primary and secondary with several different subtypes, ample molecular biomarkers have risen throughout the years which have garnered the attention of researchers. The advancements in genomics and proteomics have allowed researchers to gather prominent molecular biomarkers. All these biomarkers are gathered by means of biopsy or bodily fluid sample collection and are quantitatively analyzed by polymerase chain reaction coupled with other computational technologies. This review highlights the significance, regulation and prevalence of molecular biomarkers such as O 6 -methylguanine-DNA methyltransferase, epidermal growth factor receptor vIII, isocitrate dehydrogenase mutation and several others which expressed differently in different types and molecular subtypes of GBM. The discoveries and roles of GBM-specific microRNAs including miR-21 and miR-10b as biomarkers with promising prognostic values were also delineated. The role and mechanism of biomarkers in GBM tumorigenesis are essential in the development of therapy for patients suffering from the disease itself. Thus, this review also discusses the mechanisms, effects and limitations of therapy such as temozolomide, viral gene transfer, biomarker-based vaccines or even engineered T cells for more specific responses. Biomarkers have displayed a high value and could eventually be utilized as drug targets. It is hoped that by combining different aspects of the disease which present with different biomarkers could lead to the development of a robust, effective and innovative take on GBM therapy., (© 2017 John Wiley & Sons Australia, Ltd.)