Comparative transcriptome analysis of skeletal muscle in ADSSL1 myopathy

Two Brothers With ADSS1 Myopathy: A Report of Clinical, Radiological, and Autopsy Findings

ADSS1 myopathy, previously known as adenylosuccinate synthetase-like 1 (ADSSL1) myopathy, is an autosomal recessive muscle disease caused by variants in ADSS1 (adenylosuccinate synthase 1). ADSS1 myopathy is complicated by respiratory muscle weakness or cardiomyopathy as well as limb muscle weakness. We analyzed two siblings with ADSS1 myopathy, both harboring compound heterozygous pathogenic variants (c.781G>A/c.919delA) in ADSS1 and provided details of their phenotypes together with muscle imaging and autopsy findings. Although it was reported that ADSS1 myopathy usually began with lower limb muscle weakness, our cases showed early involvement of the cervical paraspinal muscle, triceps brachii muscle, flexor digitorum superficialis and profundus muscles, rectus abdominis muscle, gluteus maximus and medius muscles, and cardiomyopathy. While a previous study reported that the trunk and hip muscles were relatively spared, atrophy of paraspinal muscles, gluteus medius and maximus muscles, and adductor muscles were observed. Our two siblings allowed for long-term follow-up and will be useful reference cases. We evaluated the frequency of fibers with nemaline bodies in various autopsied muscles and found that the ratio of fibers with nemaline bodies was lower compared to other nemaline myopathies. Postmortem examination revealed, for the first time, nemaline bodies in the diaphragm and myocardium, associated with respiratory failure and cardiomyopathy.

Current insights in ultra-rare adenylosuccinate synthetase 1 myopathy - meeting report on the First Clinical and Scientific Conference. 3 June 2024, National Centre for Advancing Translational Science, Rockville, Maryland, the United States of America

The inaugural Clinical and Scientific Conference on Adenylosuccinate Synthetase 1 (ADSS1) myopathy was held on June 3, 2024, at the National Institutes of Health (NIH) National Center for Advancing Translational Sciences (NCATS) in Rockville, Maryland, USA.

ADSS1 myopathy is an ultra-rare, inherited neuromuscular disease.

Features of geographical patient clusters in South Korea, Japan, India and the United States of America were characterised and discussed.

Pre-clinical animal and cell-based models were discussed, providing unique insight into disease pathogenesis.

The biochemical pathogenesis was discussed, and potential therapeutic targets identified.

Potential clinical and pre-clinical biomarkers were discussed.

An ADSS1 myopathy consortium was established and a roadmap for therapeutic development created.

The de novo purine synthesis enzyme Adssl1 promotes cardiomyocyte proliferation and cardiac regeneration

There is a short window during which the neonatal heart has the proliferative capacity to completely repair damage, an ability that is lost in adulthood. Inducing proliferation in adult cardiomyocytes by reactivating cell cycle reentry after myocardial infarction (MI) improves cardiac function. De novo purine synthesis is a critical source of nucleotides for cell proliferation. Here, using loss- and gain-of-function genetic approaches, we explored the role of the muscle-specific de novo purine synthesis enzyme Adssl1 in cardiac regeneration. Deletion of Adssl1 in mouse neonatal hearts reduced cardiomyocyte proliferation and attenuated heart regeneration after apical resection. Conversely, cardiomyocyte-specific Adssl1 overexpression extended the postnatal regenerative window and induced robust cell cycle reentry after MI, which decreased fibrotic scar size and improved cardiac function. RNA sequencing analysis suggested that Adssl1 overexpression induced strong dedifferentiation and cell cycle entry. Moreover, LC-MS/MS analysis showed that Adssl1 overexpression was associated with increased amounts of purine metabolites, including inosine, which is in clinical use. Administration of exogenous inosine promoted cardiac repair after MI in adult mice. At a molecular level, the increase in purine metabolite production mediated by Adssl1 enhanced the activity of the proliferation-promoting mTORC1 pathway. Our study identifies a role for Adssl1 in supporting cardiomyocyte proliferation and cardiac regeneration.

A pilot investigation of muscle integrity in patients with ADSSL1 myopathy using electrical impedance myography

INTRODUCTION/AIMS

ADSSL1 myopathy (OMIM 617030) is a recently discovered, congenital myopathic disease caused by a pathogenic variant in ADSSL1. ADSSL1 is an enzyme involved in the purine nucleotide process and facilitates the conversion of inosine monophosphate to adenosine monophosphate within myocytes. Electrical impedance myography (EIM) is a portable, non-invasive, and cost-effective method for characterizing muscle integrity. Three ADSSL1 patients are presented in whom characterization of muscle integrity using EIM was performed.

METHODS

A 15-y-old male, 20-y-old female, and 63-y-old male each with a pathogenic variant in ADSSL1 [c.901G > A] as well as three, age-gender matched healthy controls (HCs) were enrolled. Study participants were phenotyped using a virtual EIM procedure.

RESULTS

ADSSL1 myopathy patients presented with variable onset of physical disability, disease progression, and severity of muscle weakness. Across multiple proximal and distal muscles groups and relative to HCs, ADSSL1 myopathy patients demonstrated lower phase and reactance values, while resistance was higher, which together indicated diseased muscle.

DISCUSSION

EIM can provide a novel, non-invasive and objective biomarker to evaluate muscle integrity in patients with ADSSL1 myopathy. Combining EIM with musculoskeletal imaging and histologic assessments in follow-up studies may further inform on the pathophysiology of ADSSL1 myopathy.

Transcriptome profiling of skeletal muscles from Korean patients with Bethlem myopathy

Bethlem myopathy is one of the collagens VI-related muscular dystrophies caused by mutations in the collagen VI genes. The study was designed to analyze the gene expression profiles in the skeletal muscle of patients with Bethlem myopathy. Six skeletal muscle samples from 3 patients with Bethlem myopathy and 3 control subjects were analyzed by RNA-sequencing. 187 transcripts were significantly differentially expressed, with 157 upregulated and 30 downregulated transcripts in the Bethlem group. Particularly, 1 (microRNA-133b) was considerably upregulated, and 4 long intergenic non-protein coding RNAs, LINC01854, MBNL1-AS1, LINC02609, and LOC728975, were significantly downregulated. We categorized differentially expressed gene using Gene Ontology and showed that Bethlem myopathy is strongly associated with the organization of extracellular matrix (ECM). Kyoto Encyclopedia of Genes and Genomes pathway enrichment reflected themes with significant enrichment of the ECM-receptor interaction (hsa04512), complement and coagulation cascades (hsa04610), and focal adhesion (hsa04510). We confirmed that Bethlem myopathy is strongly associated with the organization of ECM and the wound healing process. Our results demonstrate transcriptome profiling of Bethlem myopathy, and provide new insights into the path mechanism of Bethlem myopathy associated with non-protein coding RNAs.

An autopsied case of ADSSL1 myopathy

ADSSL1 myopathy is an inherited myopathy with limb weakness, respiratory muscle paralysis, dysphagia, and myocardial symptoms. We present an autopsy case of a 66-year-old male carrying compound heterozygous variants c.781G>A (p.D261N) and c.919delA (p.I307fs) in ADSSL1. He had not run fast since school with no family history. He showed a gradual progression of limb weakness and developed dyspnoea, dysphagia, and Brugada syndrome at the age of 56. The magnetic resonance imaging (MRI) revealed bright tongue sign. Muscle biopsy showed only chronic myopathic changes. He died of respiratory muscle weakness at the age of 66. Autopsy revealed that there were many fibres with vacuoles and nemaline rods in the biceps brachii, tongue, diaphragm, and iliopsoas. Many lipopigments and nuclear clumps were also detected. The myocardium and central nervous system had only nonspecific age-related changes. This is the first autopsied case to clarify the terminal state of ADSSL1 myopathy.

Multi-Omics Analysis of Key microRNA-mRNA Metabolic Regulatory Networks in Skeletal Muscle of Obese Rabbits

microRNAs (miRNAs), small non-coding RNA with a length of about 22 nucleotides, are involved in the energy metabolism of skeletal muscle cells. However, their molecular mechanism of metabolism in rabbit skeletal muscle is still unclear. In this study, 16 rabbits, 8 in the control group (CON-G) and 8 in the experimental group (HFD-G), were chosen to construct an obese model induced by a high-fat diet fed from 35 to 70 days of age. Subsequently, 54 differentially expressed miRNAs, 248 differentially expressed mRNAs, and 108 differentially expressed proteins related to the metabolism of skeletal muscle were detected and analyzed with three sequencing techniques (small RNA sequencing, transcriptome sequencing, and tandem mass tab (TMT) protein technology). It was found that 12 miRNAs and 12 core genes (e.g., CRYL1, VDAC3 and APIP) were significantly different in skeletal muscle from rabbits in the two groups. The network analysis showed that seven miRNA-mRNA pairs were involved in metabolism. Importantly, two miRNAs (miR-92a-3p and miR-30a/c/d-5p) regulated three transcription factors (MYBL2, STAT1 and IKZF1) that may be essential for lipid metabolism. These results enhance our understanding of molecular mechanisms associated with rabbit skeletal muscle metabolism and provide a basis for future studies in the metabolic diseases of human obesity.

Antimania-Like Effect of Panax ginseng Regulating the Glutamatergic Neurotransmission in REM-Sleep Deprivation Rats

Previous studies have shown the therapeutic properties of ginseng and ginsenosides on hyperactive and impulsive behaviors in several psychiatric diseases. Herein, we investigated the effect of Panax ginseng Meyer (PG) on hyperactive/impulsive behaviors in a manic-like animal model, sleep deprivation (SD) rats. Male rats were sleep-deprived for 48 h, and PG (200 mg/kg) was administered for 4 days, from 2 days prior to the start of SD to the end date of SD. The elevated plus maze (EPM) test showed that PG alleviated the increased frequency of entries into and spent time within open arms by SD. In order to investigate the molecular mechanism on this effect of PG, we assessed differentially expressed genes (DEGs) in the prefrontal cortex of PG-treated SD rats using RNA sequencing (RNA-seq) and performed gene-enrichment analysis for DEGs. The gene-enrichment analysis showed that PG most prominently affected the glutamatergic synapse pathway. Among the glutamatergic synapse pathway genes, particularly, PG enhanced the expressions of glutamate transporter Slc1a3 and Slc1a2 reduced in SD rats. Moreover, we found that PG could inhibit the SD-induced phosphorylation of the NR2A subunit of the NMDA receptor. These results suggested that PG might have a therapeutic effect against the manic-like behaviors, regulating the glutamatergic neurotransmission.

Expanding the disease phenotype of ADSSL1-associated myopathy in non-Korean patients

Adenylosuccinate synthase (ADSSL1) is a muscle specific enzyme involved in the purine nucleotide cycle and responsible for the conversion of inosine monophosphate to adenosine monophosphate. Since 2016, when mutations in the ADSSL1 gene were first described to be associated with an adult onset distal myopathy, nine patients with compound heterozygous variants in the ADSSL1 gene, all of Korean origin, have been identified. Here we report a novel ADSSL1 mutation and describe two sporadic cases of Turkish and Indian origin. Many of the clinical features of both patients and muscle histopathology and muscle MRI findings, were in accordance with previously reported findings in the adult onset distal myopathy individuals. However, one of our patients presented with progressive, proximally pronounced weakness, severe muscle atrophy and early contractures. Thus, mutations in ADSSL1 have to be considered in patients with both distal and proximal muscle weakness and across various ethnicities.