Transcriptome Analysis Reveals Altered Inflammatory Pathway in an Inducible Glial Cell Model of Myotonic Dystrophy Type 1

Individual transcriptomic response to strength training for patients with myotonic dystrophy type 1

Myotonic dystrophy type 1 (DM1), the most common form of adult-onset muscular dystrophy, is caused by a CTG expansion resulting in significant transcriptomic dysregulation that leads to muscle weakness and wasting. While strength training is clinically beneficial in DM1, molecular effects had not been studied. To determine whether training rescued transcriptomic defects, RNA-Seq was performed on vastus lateralis samples from 9 male patients with DM1 before and after a 12-week strength-training program and 6 male controls who did not undergo training. Differential gene expression and alternative splicing analysis were correlated with the one-repetition maximum strength evaluation method (leg extension, leg press, hip abduction, and squat). While training program-induced improvements in splicing were similar among most individuals, rescued splicing events varied considerably between individuals. Gene expression improvements were highly varied between individuals, and the percentage of differentially expressed genes rescued after training were strongly correlated with strength improvements. Evaluating transcriptome changes individually revealed responses to the training not evident from grouped analysis, likely due to disease heterogeneity and individual exercise response differences. Our analyses indicate that transcriptomic changes are associated with clinical outcomes in patients with DM1 undergoing training and that these changes are often specific to the individual and should be analyzed accordingly.

The Bi-directional Relationship Between Sleep and Inflammation in Muscular Dystrophies: A Narrative Review

Muscular dystrophies vary in presentation and severity, but are associated with profound disability in many people. Although characterised by muscle weakness and wasting, there is also a very high prevalence of sleep problems and disorders which have significant impacts on quality of life in these individuals. There are no curative therapies for muscular dystrophies, with the only options for patients being supportive therapies to aid with symptoms. Therefore, there is an urgent need for new therapeutic targets and a greater understanding of pathogenesis. Inflammation and altered immunity are factors which have prominent roles in some muscular dystrophies and emerging roles in others such as type 1 myotonic dystrophy, signifying a link to pathogenesis. Interestingly, there is also a strong link between inflammation/immunity and sleep. In this review, we will explore this link in the context of muscular dystrophies and how it may influence potential therapeutic targets and interventions.

RNA Foci Formation in a Retinal Glial Model for Spinocerebellar Ataxia Type 7

Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disorder characterized by cerebellar ataxia and retinopathy. SCA7 is caused by a CAG expansion in the ATXN7 gene, which results in an extended polyglutamine (polyQ) tract in the encoded protein, the ataxin-7. PolyQ expanded ataxin-7 elicits neurodegeneration in cerebellar Purkinje cells, however, its impact on the SCA7-associated retinopathy remains to be addressed. Since Müller glial cells play an essential role in retinal homeostasis, we generate an inducible model for SCA7, based on the glial Müller MIO-M1 cell line. The SCA7 pathogenesis has been explained by a protein gain-of-function mechanism, however, the contribution of the mutant RNA to the disease cannot be excluded. In this direction, we found nuclear and cytoplasmic foci containing mutant RNA accompanied by subtle alternative splicing defects in MIO-M1 cells. RNA foci were also observed in cells from different lineages, including peripheral mononuclear leukocytes derived from SCA7 patient, suggesting that this molecular mark could be used as a blood biomarker for SCA7. Collectively, our data showed that our glial cell model exhibits the molecular features of SCA7, which makes it a suitable model to study the RNA toxicity mechanisms, as well as to explore therapeutic strategies aiming to alleviate glial dysfunction.

Myotonic dystrophy RNA toxicity alters morphology, adhesion and migration of mouse and human astrocytes

Brain dysfunction in myotonic dystrophy type 1 (DM1), the prototype of toxic RNA disorders, has been mainly attributed to neuronal RNA misprocessing, while little attention has been given to non-neuronal brain cells. Here, using a transgenic mouse model of DM1 that expresses mutant RNA in various brain cell types (neurons, astroglia, and oligodendroglia), we demonstrate that astrocytes exhibit impaired ramification and polarization in vivo and defects in adhesion, spreading, and migration. RNA-dependent toxicity and phenotypes are also found in human transfected glial cells. In line with the cell phenotypes, molecular analyses reveal extensive expression and accumulation of toxic RNA in astrocytes, which result in RNA spliceopathy that is more severe than in neurons. Astrocyte missplicing affects primarily transcripts that regulate cell adhesion, cytoskeleton, and morphogenesis, and it is confirmed in human brain tissue. Our findings demonstrate that DM1 impacts astrocyte cell biology, possibly compromising their support and regulation of synaptic function.

Myotonic dystrophy type 1 (DM1) is characterized by debilitating neurological symptoms. Dinca et al. demonstrate the pronounced impact of DM1 on the morphology and RNA metabolism of astrocytes. Their findings suggest astroglial pathology in DM1 brain dysfunction.

Blood Transcriptome Profiling Links Immunity to Disease Severity in Myotonic Dystrophy Type 1 (DM1)

The blood transcriptome was examined in relation to disease severity in type I myotonic dystrophy (DM1) patients who participated in the Observational Prolonged Trial In DM1 to Improve QoL- Standards (OPTIMISTIC) study. This sought to (a) ascertain if transcriptome changes were associated with increasing disease severity, as measured by the muscle impairment rating scale (MIRS), and (b) establish if these changes in mRNA expression and associated biological pathways were also observed in the Dystrophia Myotonica Biomarker Discovery Initiative (DMBDI) microarray dataset in blood (with equivalent MIRS/DMPK repeat length). The changes in gene expression were compared using a number of complementary pathways, gene ontology and upstream regulator analyses, which suggested that symptom severity in DM1 was linked to transcriptomic alterations in innate and adaptive immunity associated with muscle-wasting. Future studies should explore the role of immunity in DM1 in more detail to assess its relevance to DM1.

Cellular Senescence and Aging in Myotonic Dystrophy

Myotonic dystrophy (DM) is a dominantly inherited multisystemic disorder affecting various organs, such as skeletal muscle, heart, the nervous system, and the eye. Myotonic dystrophy type 1 (DM1) and type 2 (DM2) are caused by expanded CTG and CCTG repeats, respectively. In both forms, the mutant transcripts containing expanded repeats aggregate as nuclear foci and sequester several RNA-binding proteins, resulting in alternative splicing dysregulation. Although certain alternative splicing events are linked to the clinical DM phenotypes, the molecular mechanisms underlying multiple DM symptoms remain unclear. Interestingly, multi-systemic DM manifestations, including muscle weakness, cognitive impairment, cataract, and frontal baldness, resemble premature aging. Furthermore, cellular senescence, a critical contributor to aging, is suggested to play a key role in DM cellular pathophysiology. In particular, several senescence inducers including telomere shortening, mitochondrial dysfunction, and oxidative stress and senescence biomarkers such as cell cycle inhibitors, senescence-associated secretory phenotype, chromatin reorganization, and microRNA have been implicated in DM pathogenesis. In this review, we focus on the clinical similarities between DM and aging, and summarize the involvement of cellular senescence in DM and the potential application of anti-aging DM therapies.

Influence of age and sex on microRNA response and recovery in the hippocampus following sepsis

Sepsis, defined as a dysregulated host immune response to infection, is a common and dangerous clinical syndrome. The excessive host inflammatory response can induce immediate and persistent cognitive decline, which can be worse in older individuals. Sex-specific differences in the outcome of infectious diseases and sepsis appear to favor females. We employed a murine model to examine the influence of age and sex on the brain's microRNA (miR) response following sepsis. Young and old mice of both sexes underwent cecal ligation and puncture (CLP) with daily restraint stress. Expression of hippocampal miR was examined in age- and sex-matched controls at 1 and 4 days post-CLP. Few miR were modified in a similar manner across age or sex and these few miR were generally associated with neuroprotection against inflammation. Similar to previous work examining transcription, young females exhibited a better recovery of the miR profile from day 1 to day 4, relative to young males and old females. For young males and all female groups, the initial response mainly involved a decrease in miR expression. In contrast, old males exhibited only upregulated miR on day 1 and day 4 and many of the miR upregulated on day 1 and day 4 were linked to neurodegeneration, increased neuroinflammation, and cognitive impairment. The results emphasize age and sex differences in epigenetic mechanisms that likely contribute to susceptibility or resilience to cognitive impairment due to sepsis.

Deciphering the Complex Molecular Pathogenesis of Myotonic Dystrophy Type 1 through Omics Studies

Omics studies are crucial to improve our understanding of myotonic dystrophy type 1 (DM1), the most common muscular dystrophy in adults. Employing tissue samples and cell lines derived from patients and animal models, omics approaches have revealed the myriad alterations in gene and microRNA expression, alternative splicing, 3′ polyadenylation, CpG methylation, and proteins levels, among others, that contribute to this complex multisystem disease. In addition, omics characterization of drug candidate treatment experiments provides crucial insight into the degree of therapeutic rescue and off-target effects that can be achieved. Finally, several innovative technologies such as single-cell sequencing and artificial intelligence will have a significant impact on future DM1 research.

Brain Pathogenesis and Potential Therapeutic Strategies in Myotonic Dystrophy Type 1

Myotonic dystrophy type 1 (DM1) is the most common muscular dystrophy that affects multiple systems including the muscle and heart. The mutant CTG expansion at the 3′-UTR of the DMPK gene causes the expression of toxic RNA that aggregate as nuclear foci. The foci then interfere with RNA-binding proteins, affecting hundreds of mis-spliced effector genes, leading to aberrant alternative splicing and loss of effector gene product functions, ultimately resulting in systemic disorders. In recent years, increasing clinical, imaging, and pathological evidence have indicated that DM1, though to a lesser extent, could also be recognized as true brain diseases, with more and more researchers dedicating to develop novel therapeutic tools dealing with it. In this review, we summarize the current advances in the pathogenesis and pathology of central nervous system (CNS) deficits in DM1, intervention measures currently being investigated are also highlighted, aiming to promote novel and cutting-edge therapeutic investigations.

Deciphering the mechanisms underlying brain alterations and cognitive impairment in congenital myotonic dystrophy

Myotonic dystrophy type 1 (DM1) is a multisystemic and heterogeneous disorder caused by the expansion of CTG repeats in the 3' UTR of the myotonic dystrophy protein kinase (DMPK) gene. There is a congenital form (CDM1) of the disease characterized by severe hypotonia, respiratory insufficiency as well as developmental delays and intellectual disabilities. CDM1 infants manifest important brain structure abnormalities present from birth while, in contrast, older patients with adult-onset DM1 often present neurodegenerative features and milder progressive cognitive deficits. Promising therapies targeting central molecular mechanisms contributing to the symptoms of adult-onset DM1 are currently in development, but their relevance for treating cognitive impairment in CDM1, which seems to be a partially distinct neurodevelopmental disorder, remain to be elucidated. Here, we provide an update on the clinical presentation of CDM1 and review recent in vitro and in vivo models that have provided meaningful insights on its consequences in development, with a particular focus on the brain. We discuss how enhanced toxic gain-of-function of the mutated DMPK transcripts with larger CUG repeats and the resulting dysregulation of RNA-binding proteins may affect the developing cortex in utero. Because the methylation of CpG islets flanking the trinucleotide repeats has emerged as a strong biomarker of CDM1, we highlight the need to investigate the tissue-specific impacts of these chromatin modifications in the brain. Finally, we outline promising potential therapeutic treatments for CDM1 and propose future in vitro and in vivo models with great potential to shed light on this disease.

How Inflammation Pathways Contribute to Cell Death in Neuro-Muscular Disorders

Neuro-muscular disorders include a variety of diseases induced by genetic mutations resulting in muscle weakness and waste, swallowing and breathing difficulties. However, muscle alterations and nerve depletions involve specific molecular and cellular mechanisms which lead to the loss of motor-nerve or skeletal-muscle function, often due to an excessive cell death. Morphological and molecular studies demonstrated that a high number of these disorders seem characterized by an upregulated apoptosis which significantly contributes to the pathology. Cell death involvement is the consequence of some cellular processes that occur during diseases, including mitochondrial dysfunction, protein aggregation, free radical generation, excitotoxicity and inflammation. The latter represents an important mediator of disease progression, which, in the central nervous system, is known as neuroinflammation, characterized by reactive microglia and astroglia, as well the infiltration of peripheral monocytes and lymphocytes. Some of the mechanisms underlying inflammation have been linked to reactive oxygen species accumulation, which trigger mitochondrial genomic and respiratory chain instability, autophagy impairment and finally neuron or muscle cell death. This review discusses the main inflammatory pathways contributing to cell death in neuro-muscular disorders by highlighting the main mechanisms, the knowledge of which appears essential in developing therapeutic strategies to prevent the consequent neuron loss and muscle wasting.