An Epigenetic Spin to ALS and FTD

Amyotrophic lateral sclerosis: translating genetic discoveries into therapies

Recent advances in sequencing technologies and collaborative efforts have led to substantial progress in identifying the genetic causes of amyotrophic lateral sclerosis (ALS). This momentum has, in turn, fostered the development of putative molecular therapies. In this Review, we outline the current genetic knowledge, emphasizing recent discoveries and emerging concepts such as the implication of distinct types of mutation, variability in mutated genes in diverse genetic ancestries and gene-environment interactions. We also propose a high-level model to synthesize the interdependent effects of genetics, environmental and lifestyle factors, and ageing into a unified theory of ALS. Furthermore, we summarize the current status of therapies developed on the basis of genetic knowledge established for ALS over the past 30 years, and we discuss how developing treatments for ALS will advance our understanding of targeting other neurological diseases.

Emerging insights into the complex genetics and pathophysiology of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a fatal neurodegenerative disease. The discovery of genes associated with amyotrophic lateral sclerosis, commencing with SOD1 in 1993, started fairly gradually. Recent advances in genetic technology have led to the rapid identification of multiple new genes associated with the disease, and to a new understanding of oligogenic and polygenic disease risk. The overlap of genes associated with amyotrophic lateral sclerosis with those of other neurodegenerative diseases is shedding light on the phenotypic spectrum of neurodegeneration, leading to a better understanding of genotype-phenotype correlations. A deepening knowledge of the genetic architecture is allowing the characterisation of the molecular steps caused by various mutations that converge on recurrent dysregulated pathways. Of crucial relevance, mutations associated with amyotrophic lateral sclerosis are amenable to novel gene-based therapeutic options, an approach in use for other neurological illnesses. Lastly, the exposome-the summation of lifetime environmental exposures-has emerged as an influential component for amyotrophic lateral sclerosis through the gene-time-environment hypothesis. Our improved understanding of all these aspects will lead to long-awaited therapies and the identification of modifiable risks factors.

Histone Methylation Regulation in Neurodegenerative Disorders

Advances achieved with molecular biology and genomics technologies have permitted investigators to discover epigenetic mechanisms, such as DNA methylation and histone posttranslational modifications, which are critical for gene expression in almost all tissues and in brain health and disease. These advances have influenced much interest in understanding the dysregulation of epigenetic mechanisms in neurodegenerative disorders. Although these disorders diverge in their fundamental causes and pathophysiology, several involve the dysregulation of histone methylation-mediated gene expression. Interestingly, epigenetic remodeling via histone methylation in specific brain regions has been suggested to play a critical function in the neurobiology of psychiatric disorders, including that related to neurodegenerative diseases. Prominently, epigenetic dysregulation currently brings considerable interest as an essential player in neurodegenerative disorders, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), Amyotrophic lateral sclerosis (ALS) and drugs of abuse, including alcohol abuse disorder, where it may facilitate connections between genetic and environmental risk factors or directly influence disease-specific pathological factors. We have discussed the current state of histone methylation, therapeutic strategies, and future perspectives for these disorders. While not somatically heritable, the enzymes responsible for histone methylation regulation, such as histone methyltransferases and demethylases in neurons, are dynamic and reversible. They have become promising potential therapeutic targets to treat or prevent several neurodegenerative disorders. These findings, along with clinical data, may provide links between molecular-level changes and behavioral differences and provide novel avenues through which the epigenome may be targeted early on in people at risk for neurodegenerative disorders.

From Multi-Omics Approaches to Precision Medicine in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating and fatal neurodegenerative disorder, caused by the degeneration of upper and lower motor neurons for which there is no truly effective cure. The lack of successful treatments can be well explained by the complex and heterogeneous nature of ALS, with patients displaying widely distinct clinical features and progression patterns, and distinct molecular mechanisms underlying the phenotypic heterogeneity. Thus, stratifying ALS patients into consistent and clinically relevant subgroups can be of great value for the development of new precision diagnostics and targeted therapeutics for ALS patients. In the last years, the use and integration of high-throughput "omics" approaches have dramatically changed our thinking about ALS, improving our understanding of the complex molecular architecture of ALS, distinguishing distinct patient subtypes and providing a rational foundation for the discovery of biomarkers and new individualized treatments. In this review, we discuss the most significant contributions of omics technologies in unraveling the biological heterogeneity of ALS, highlighting how these approaches are revealing diagnostic, prognostic and therapeutic targets for future personalized interventions.

Neuroinflammation and histone H3 citrullination are increased in X-linked Dystonia Parkinsonism post-mortem prefrontal cortex

Neuroinflammation plays a pathogenic role in neurodegenerative diseases and recent findings suggest that it may also be involved in X-linked Dystonia-Parkinsonism (XDP) pathogenesis. Previously, fibroblasts and neuronal stem cells derived from XDP patients demonstrated hypersensitivity to TNF-α, dysregulation in NFκB signaling, and an increase in several pro-inflammatory markers. However, the role of inflammatory processes in XDP patient brain remains unknown. Here we demonstrate that there is a significant increase in astrogliosis and microgliosis in human post-mortem XDP prefrontal cortex (PFC) compared to control. Furthermore, there is a significant increase in histone H3 citrullination (H3R2R8R17cit₃) with a concomitant increase in peptidylarginine deaminase 2 (PAD2) and 4 (PAD4), the enzymes catalyzing citrullination, in XDP post-mortem PFC. While there is a significant increase in myeloperoxidase (MPO) levels in XDP PFC, neutrophil elastase (NE) levels are not altered, suggesting that MPO may be released by activated microglia or reactive astrocytes in the brain. Similarly, there was an increase in H3R2R8R17cit₃, PAD2 and PAD4 levels in XDP-derived fibroblasts. Importantly, treatment of fibroblasts with Cl-amidine, a pan inhibitor of PAD enzymes, reduced histone H3 citrullination and pro-inflammatory chemokine expression, without affecting cell survival. Taken together, our results demonstrate that inflammation is increased in XDP post-mortem brain and fibroblasts and unveil a new epigenetic potential therapeutic target.