Martin Wohlwend

Deciphering the regulatory consequences of sequence divergence across human evolution is essential to understanding the molecular basis of human-specific traits and disease. Although millions of derived alleles distinguish humans from great apes, only a small fraction are likely to influence human-specific traits. Previous studies have focused on regions of elevated sequence divergence, assuming that rapid evolution reflects functional adaptation, yet individual high-impact regulatory mutations evade such scans. Here, we apply sequence-to-function deep learning to predict chromatin accessibility across modern human, archaic hominin, and great ape personalized genomes, identifying lineage-specific cis-regulatory elements (linCREs) across diverse cellular contexts. Compared to conserved elements, linCREs are shorter, less pleiotropic, less conserved, and enriched in neurodevelopmental pathways. Many linCREs occur in regions with limited sequence divergence that acceleration-based approaches would overlook. We validate lineage-specific enhancer activity through luciferase reporter assays and demonstrate that a single motif-generating derived allele nominated by model interpretability tools drives a hominin-specific neurodevelopmental enhancer.

Fast twitch muscle fibers are prone to degradation in skeletal muscle pathologies, such as sarcopenia and muscular dystrophies. We previously showed that the exercise‐induced long noncoding RNA CYTOR promotes fast‐twitch myogenesis. Here, we identify an independent functional element within human CYTOR, and optimize its RNA delivery. In human primary myoblasts exogenous CYTOR exon 2 recapitulates the effect of full‐length CYTOR by boosting fast‐twitch myogenic differentiation. Furthermore, chemically modified CYTOR exon 2 RNA ^ΨU (N1‐me‐PseudoU, 7‐methyl guanosine 5′Cap, polyA) enhances RNA stability and reduces immunogenicity to CYTOR ^exon2 RNA. Viral‐ or chemically optimized RNA‐mediated CYTOR ^exon2 administration drives commitment toward myogenic maturation in Duchenne muscular dystrophy‐derived primary myoblasts, myogenic progenitor cells, and mouse embryonic stem cells. Furthermore, CYTOR ^{exon2, m1ΨU} improves key disease characteristics in dystrophic myotubes, including calcium handling and mitochondrial bioenergetics. In summary, we identify CYTOR exon 2 as the functional domain of CYTOR that can be delivered in a disease context using chemical modifications. This is of particular importance given the susceptibility of fast muscle fibers in different muscle pathologies such as aging and dystrophies, and the oncogenic effect of CYTOR exon 1. This study, therefore, highlights the potential of identifying functional domains in noncoding RNAs. Delivery, or targeting of RNA domains might constitute next‐generation RNA therapeutics.

Fast twitch, type II muscle fibers are particularly prone to degradation in skeletal muscle pathologies, such as sarcopenia and muscular dystrophies. We previously showed that endogenous activation of the exercise-induced long noncoding RNA CYTOR promotes fast-twitch myogenesis. In the present study, we identify an independent pro-myogenic element within human CYTOR and optimize its RNA delivery. In human primary myoblasts exogenous, vector-based CYTOR ^{exon 2} recapitulates the effect of full-length CYTOR by enhancing fast-twitch myogenic differentiation. Furthermore, chemically modified CYTOR ^{exon 2} RNA ^ΨU (N1-me-PseudoU, 7-methyl guanosine 5’Cap, polyA tail) enhanced RNA stability and reduced the immunogenic response to CYTOR ^{exon 2} RNA. We demonstrate that viral- or chemically optimized RNA-mediated CYTOR ^{exon 2} administration enhances the commitment towards myogenic maturation in Duchenne muscular dystrophy-derived primary myoblasts, induced myogenic progenitor cells and mouse embryonic stem cells. Furthermore, chemically optimized CYTOR ^{exon 2} improves key disease characteristics in dystrophic myotubes, including calcium handling and mitochondrial bioenergetics. In summary, our findings identify CYTOR exon 2 as the pro-myogenic domain of CYTOR that can be delivered in a disease context using chemical modifications. This is of particular importance given the susceptibility of type II muscle fibers in different muscle pathologies such as aging and dystrophies, and the reported oncogenic effect of CYTOR exon 1. Our study, therefore, highlights the potential of identifying functional domains in noncoding RNAs. Delivery, or targeting of such RNA domains could constitute next-generation RNA therapeutics.

One of the analyses in the final paper comprises C. elegans skeletal muscle morphology experiments upon Cers1 inhibition (Figure 4E). This experiment was conducted by Amélia Lalou at École Polytechnique Fédérale de Lausanne (EPFL). During the review process, Amélia Lalou was accidentally removed from the author list. We are therefore formally correcting the eLife paper to include Amélia Lalou in the author list. She has reviewed the manuscript, supports the conclusion and agrees to be responsible for all the parts of the paper in its published form. All authors have agreed to the change.

Age-related muscle wasting and dysfunction render the elderly population vulnerable and incapacitated, while underlying mechanisms are poorly understood. Here, we implicate the CERS1 enzyme of the de novo sphingolipid synthesis pathway in the pathogenesis of age-related skeletal muscle impairment. In humans, CERS1 abundance declines with aging in skeletal muscle cells and, correlates with biological pathways involved in muscle function and myogenesis. Furthermore, CERS1 is upregulated during myogenic differentiation. Pharmacological or genetic inhibition of CERS1 in aged mice blunts myogenesis and deteriorates aged skeletal muscle mass and function, which is associated with the occurrence of morphological features typical of inflammation and fibrosis. Ablation of the CERS1 orthologue lagr-1 in Caenorhabditis elegans similarly exacerbates the age-associated decline in muscle function and integrity. We discover genetic variants reducing CERS1 expression in human skeletal muscle and Mendelian randomization analysis in the UK biobank cohort shows that these variants reduce muscle grip strength and overall health. In summary, our findings link age-related impairments in muscle function to a reduction in CERS1, thereby underlining the importance of the sphingolipid biosynthesis pathway in age-related muscle homeostasis.

Age-related muscle wasting and dysfunction render the elderly population vulnerable and incapacitated, while underlying mechanisms are poorly understood. Here, we implicate the CERS1 enzyme of the de novo sphingolipid synthesis pathway in the pathogenesis of age-related skeletal muscle impairment. In humans, CERS1 abundance declines with aging in skeletal muscle cells and, correlates with biological pathways involved in muscle function and myogenesis. Furthermore, CERS1 is upregulated during myogenic differentiation. Pharmacological or genetic inhibition of CERS1 in aged mice blunts myogenesis and deteriorates aged skeletal muscle mass and function, which is associated with the occurrence of morphological features typical of inflammation and fibrosis. Ablation of the CERS1 orthologue lagr-1 in C. elegans similarly exacerbates the age-associated decline in muscle function and integrity. We discover genetic variants reducing CERS1 expression in human skeletal muscle and Mendelian randomization analysis in the UK biobank cohort shows that these variants reduce muscle grip strength and overall health. In summary, our findings link age-related impairments in muscle function to a reduction in CERS1, thereby underlining the importance of the sphingolipid biosynthesis pathway in age-related muscle homeostasis.

Age-related muscle wasting and dysfunction render the elderly population vulnerable and incapacitated, while underlying mechanisms are poorly understood. Here, we implicate the CERS1 enzyme of the de novo sphingolipid synthesis pathway in the pathogenesis of age-related skeletal muscle impairment. In humans, CERS1 abundance declines with aging in skeletal muscle cells and, correlates with biological pathways involved in muscle function and myogenesis. Furthermore, CERS1 is upregulated during myogenic differentiation. Pharmacological or genetic inhibition of CERS1 in aged mice blunts myogenesis and deteriorates aged skeletal muscle mass and function, which is associated with the occurrence of morphological features typical of inflammation and fibrosis. Ablation of the CERS1 orthologue lagr-1 in C. elegans similarly exacerbates the age-associated decline in muscle function and integrity. We discover genetic variants reducing CERS1 expression in human skeletal muscle and Mendelian randomization analysis in the UK biobank cohort shows that these variants reduce muscle grip strength and overall health. In summary, our findings link age-related impairments in muscle function to a reduction in CERS1 , thereby underlining the importance of the sphingolipid biosynthesis pathway in age-related muscle homeostasis.

Disruption of mitochondrial function and protein homeostasis plays a central role in aging. However, how these processes interact and what governs their failure in aging remain poorly understood. Here, we showed that ceramide biosynthesis controls the decline in mitochondrial and protein homeostasis during muscle aging. Analysis of transcriptome datasets derived from muscle biopsies obtained from both aged individuals and patients with a diverse range of muscle disorders revealed that changes in ceramide biosynthesis, as well as disturbances in mitochondrial and protein homeostasis pathways, are prevalent features in these conditions. By performing targeted lipidomics analyses, we found that ceramides accumulated in skeletal muscle with increasing age across Caenorhabditis elegans , mice, and humans. Inhibition of serine palmitoyltransferase (SPT), the rate-limiting enzyme of the ceramide de novo synthesis, by gene silencing or by treatment with myriocin restored proteostasis and mitochondrial function in human myoblasts, in C. elegans , and in the skeletal muscles of mice during aging. Restoration of these age-related processes improved health and life span in the nematode and muscle health and fitness in mice. Collectively, our data implicate pharmacological and genetic suppression of ceramide biosynthesis as potential therapeutic approaches to delay muscle aging and to manage related proteinopathies via mitochondrial and proteostasis remodeling.

Duchenne muscular dystrophy (DMD), the most common muscular dystrophy, is a severe muscle disorder, causing muscle weakness, loss of independence, and premature death. Here, we establish the link between sphingolipids and muscular dystrophy. Transcripts of sphingolipid de novo biosynthesis pathway are up-regulated in skeletal muscle of patients with DMD and other muscular dystrophies, which is accompanied by accumulation of metabolites of the sphingolipid pathway in muscle and plasma. Pharmacological inhibition of sphingolipid synthesis by myriocin in the mdx mouse model of DMD ameliorated the loss in muscle function while reducing inflammation, improving Ca ²⁺ homeostasis, preventing fibrosis of the skeletal muscle, heart, and diaphragm, and restoring the balance between M1 and M2 macrophages. Myriocin alleviated the DMD phenotype more than glucocorticoids. Our study identifies inhibition of sphingolipid synthesis, targeting multiple pathogenetic pathways simultaneously, as a strong candidate for treatment of muscular dystrophies.

Exercise activates the lncRNA Cytor , which reestablishes fast-twitch muscle fibers in aged skeletal muscle, improving morphology and function.