Insights into muscle degeneration from heritable inclusion body myopathies

Anti-Valosin-Containing Protein (VCP/p97) Autoantibodies in Inclusion Body Myositis and Other Inflammatory Myopathies

OBJECTIVE

The rationale for this study was based on reports that valosin-containing protein (VCP) mutations are found in hereditary inclusion body myositis (IBM) and VCP was detected in rimmed vacuoles of sporadic IBM (sIBM) muscle biopsies. Autoantibodies to VCP have not been reported in sIBM or other inflammatory myopathies (IIMs). The aim of this study was to determine the frequency and clinical significance of anti-VCP antibodies in sIBM and other IIMs.

METHODS

Sera were collected from 73 patients with sIBM and 383 comparators or controls, including patients with IIM (n = 69), those with juvenile dermatomyositis (JDM) (n = 67), those with juvenile idiopathic arthritis (JIA) (n = 47), those with primary biliary cholangitis (PBC) (n = 105), controls that were age matched to patients with sIBM (similarly aged controls [SACs]) (n = 63), and healthy controls (HCs) (n = 32). Immunoglobulin G antibodies to VCP were detected by addressable laser bead immunoassay using a full-length recombinant human protein.

RESULTS

Among patients with sIBM, 26.0% (19/73) were positive for anti-VCP. The frequency in disease controls was 15.0% (48/320). Among SACs, the frequency was 1.6% (1/63), and in HCs 0% (0/32). Frequencies were 17.5% (11/63) for IIM, 25.7% (27/105) for PBC, 3.0% (2/67) for JDM, and 17.0% (8/47) for JIA. The sensitivity, specificity, positive predictive value, and negative predictive value of anti-VCP for sIBM were 26.0%, 87.2%, 28.4%, and 85.9%, respectively. Of patients with sIBM, 15.1% (11/73) were positive for both anti-VCP and anti-cytosolic 5'-nucleotidase 1A (NT5c1A). Eleven percent of patients (8/73) were positive for anti-VCP, but negative for anti-NT5c1A.

CONCLUSION

Anti-VCP has low sensitivity and moderate specificity for sIBM but may help fill the seronegative gap in sIBM. Further studies are needed to determine whether anti-VCP is a biomarker for a clinical phenotype that may have clinical value.

Effect of GNE Mutations on Cytoskeletal Network Proteins: Potential Gateway to Understand Pathomechanism of GNEM

GNE myopathy is an inherited neuromuscular disorder caused by mutations in GNE (UDP-N-acetylglucosamine 2-epimerase/N-acetyl mannosamine kinase) gene catalyzing the sialic acid biosynthesis pathway. The characteristic features include muscle weakness in upper and lower extremities, skeletal muscle wasting, and rimmed vacuole formation. More than 200 GNE mutations in either epimerase or kinase domain have been reported worldwide. In Indian subcontinent, several GNE mutations have been recently identified with unknown functional correlation. Alternate role of GNE in various cellular processes such as cell adhesion, migration, apoptosis, protein aggregation, and cytoskeletal organization have been proposed in recent studies. We aim to understand and compare the effect of various GNE mutations from Indian origin on regulation of the cytoskeletal network. In particular, F-actin dynamics was determined quantitatively by determining F/G-actin ratios in immunoblots for specific proteins. The extent of F-actin polymerization was visualized by immunostaining with Phalloidin using confocal microscopy. The proteins regulating F-actin dynamics such as RhoA, cofilin, Arp2, and alpha-actinin were studied in various GNE mutants. The altered level of cytoskeletal organization network proteins affected cell migration of GNE mutant proteins as measured by wound healing assay. The functional comparison of GNE mutations will help in better understanding of the genotypic severity of the disease in the Indian population. Our study offers a potential for identification of therapeutic molecules regulating actin dynamics in GNE specific mutations.

Circulating factors associated with sarcopenia during ageing and after intensive lifestyle intervention

BACKGROUND

Ageing, chronic diseases, prolonged inactivity, and inadequate nutrition pose a severe threat to skeletal muscle health and function. To date, experimental evidence suggests that ageing-related subclinical inflammation could be an important causative factor in sarcopenia. Although inflammatory signalling has been implicated in the pathogenesis of experimental animal models of sarcopenia, few studies have surveyed the clinical association between circulating factors and muscle mass in patients before and after lifestyle interventions. In this study, we evaluated whether proinflammatory cytokines are associated with the onset of sarcopenia, which circulating factors are associated with the severity of sarcopenia, and how these factors change after lifestyle interventions in sarcopenic elderly persons.

METHODS

A total of 56 elderly subjects (age ≥ 60 years) with sarcopenia and 56 elderly non-sarcopenic subjects, who met entry criteria and had given informed consent, were selected from the Peking Union Medical College Hospital multicentre prospective longitudinal sarcopenia study for testing relevant circulating factors. Thirty-two elderly subjects from the sarcopenic cohort completed a 12 week intensive lifestyle intervention programme with whey supplements (30 g/day) and a personalized resistance training regimen. The levels of proinflammatory cytokines and metabolic hormones, pre-intensive and post-intensive lifestyle interventions, were measured.

RESULTS

The sarcopenic group was significantly older (72.05 ± 6.54 years; P < 0.001), more likely to be inactive and female (57.1% of all sarcopenic patients), and had a higher prevalence of type 2 diabetes (16% higher risk). Compared with non-sarcopenic subjects, serum interleukin (IL)-6, IL-18, tumour necrosis factor-α (TNF-α), TNF-like weak inducer of apoptosis (TWEAK), and leptin were significantly higher, while insulin growth factor 1, insulin, and adiponectin were significantly lower in sarcopenic patients (all P < 0.05). Logistic regression analyses revealed that high levels of TNF-α (>11.15 pg/mL) and TWEAK (>1276.48 pg/mL) were associated with a 7.6-fold and 14.3-fold increased risk of sarcopenia, respectively. After adjustment for confounding variables, high levels of TWEAK were still associated with a 13.4-fold increased risk of sarcopenia. Intensive lifestyle interventions led to significant improvements in sarcopenic patients' muscle mass and serum profiles of TWEAK, TNF-α, IL-18, insulin, and adiponectin (all P < 0.05).

CONCLUSIONS

High levels of the inflammatory cytokines TWEAK and TNF-α are associated with an increased risk of sarcopenia, while the metabolic hormones insulin growth factor 1, insulin, and adiponectin are associated with a decreased risk of sarcopenia in our Chinese patient cohort. Intensive lifestyle interventions could significantly improve muscle mass, reduce inflammation, and restore metabolic hormone levels in sarcopenic patients. This trial was registered at clinicaltrials.gov as NCT02873676.

Fighting the Cause of Alzheimer's and GNE Myopathy

Age is the common risk factor for both neurodegenerative and neuromuscular diseases. Alzheimer disease (AD), a neurodegenerative disorder, causes dementia with age progression while GNE myopathy (GNEM), a neuromuscular disorder, causes muscle degeneration and loss of muscle motor movement with age. Individuals with mutations in presenilin or amyloid precursor protein (APP) gene develop AD while mutations in GNE (UDP N-acetylglucosamine 2 epimerase/N-acetyl Mannosamine kinase), key sialic acid biosynthesis enzyme, cause GNEM. Although GNEM is characterized with degeneration of muscle cells, it is shown to have similar disease hallmarks like aggregation of Aβ and accumulation of phosphorylated tau and other misfolded proteins in muscle cell similar to AD. Similar impairment in cellular functions have been reported in both disorders such as disruption of cytoskeletal network, changes in glycosylation pattern, mitochondrial dysfunction, oxidative stress, upregulation of chaperones, unfolded protein response in ER, autophagic vacuoles, cell death, and apoptosis. Interestingly, AD and GNEM are the two diseases with similar phenotypic condition affecting neuron and muscle, respectively, resulting in entirely different pathology. This review represents a comparative outlook of AD and GNEM that could lead to target common mechanism to find a plausible therapeutic for both the diseases.

The multifaceted clinical presentation of VCP-proteinopathy in a Greek family

VCP-proteinopathy is a multisystem neurodegenerative disorder caused by mutations in valosin containing protein. Here, we report the first Greek case of VCP-proteinopathy in a 62 year old patient with a slowly progressing muscular weakness since his mid-40s and a severe deterioration during the last year. He also manifested dementia with prominent neuropsychiatric symptoms, including aggression, apathy, palilalia and obsessions. Brain MRI revealed frontal atrophy, while muscle MRI showed diffuse muscle atrophy. Family history was positive and several members of the family had been diagnosed with motor neuron disease, dementia or behavioral symptoms. Sequencing of the VCP gene revealed a pathogenic heterozygous missense mutation p.R159H. Conclusively, the present report highlights the intrafamilial variability and broadens the phenotypic spectrum of VCP-proteinopathy.

Molecular signatures of age-associated chronic degeneration of shoulder muscles

Chronic muscle diseases are highly prevalent in the elderly causing severe mobility limitations, pain and frailty. The intrinsic molecular mechanisms are poorly understood due to multifactorial causes, slow progression with age and variations between individuals. Understanding the underlying molecular mechanisms could lead to new treatment options which are currently limited. Shoulder complaints are highly common in the elderly, and therefore, muscles of the shoulder's rotator cuff could be considered as a model for chronic age-associated muscle degeneration. Diseased shoulder muscles were characterized by muscle atrophy and fatty infiltration compared with unaffected shoulder muscles. We confirmed fatty infiltration using histochemical analysis. Additionally, fibrosis and loss of contractile myosin expression were found in diseased muscles. Most cellular features, including proliferation rate, apoptosis and cell senescence, remained unchanged and genome-wide molecular signatures were predominantly similar between diseased and intact muscles. However, we found down-regulation of a small subset of muscle function genes, and up-regulation of extracellular region genes. Myogenesis was defected in muscle cell culture from diseased muscles but was restored by elevating MyoD levels. We suggest that impaired muscle functionality in a specific environment of thickened extra-cellular matrix is crucial for the development of chronic age-associated muscle degeneration.

Redox regulation of autophagy in skeletal muscle

Autophagy is a cellular degradative pathway that involves the delivery of cytoplasmic components, including proteins and organelles, to the lysosome for degradation. Autophagy is implicated in the maintenance of skeletal muscle; increased autophagy leads to muscle atrophy while decreased autophagy leads to degeneration and weakness. A growing body of work suggests that reactive oxygen species (ROS) are important cellular signal transducers controlling autophagy. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidases and mitochondria are major sources of ROS generation in skeletal muscle that are likely regulating autophagy through different signaling cascades based on localization of the ROS signals. This review aims to provide insight into the redox control of autophagy in skeletal muscle. Understanding the mechanisms by which ROS regulate autophagy will provide novel therapeutic targets for skeletal muscle diseases.

A Novel Protocol for Directed Differentiation of C9orf72-Associated Human Induced Pluripotent Stem Cells Into Contractile Skeletal Myotubes

In the present study, functional skeletal myotubes were efficiently generated from human induced pluripotent stem cells using a small molecule-based approach. Myotubes derived from patients carrying the C9orf72 repeat expansion show no change in differentiation efficiency and normal TDP-43 localization after as many as 120 days in vitro when compared to unaffected controls. The protocol described in this study for the generation of skeletal myotubes from human induced pluripotent stem cells may serve as a valuable tool in drug discovery and modeling of musculoskeletal and neuromuscular diseases.

Induced pluripotent stem cells (iPSCs) offer an unlimited resource of cells to be used for the study of underlying molecular biology of disease, therapeutic drug screening, and transplant-based regenerative medicine. However, methods for the directed differentiation of skeletal muscle for these purposes remain scarce and incomplete. Here, we present a novel, small molecule-based protocol for the generation of multinucleated skeletal myotubes using eight independent iPSC lines. Through combinatorial inhibition of phosphoinositide 3-kinase (PI3K) and glycogen synthase kinase 3β (GSK3β) with addition of bone morphogenic protein 4 (BMP4) and fibroblast growth factor 2 (FGF2), we report up to 64% conversion of iPSCs into the myogenic program by day 36 as indicated by MYOG⁺ cell populations. These cells began to exhibit spontaneous contractions as early as 34 days in vitro in the presence of a serum-free medium formulation. We used this protocol to obtain iPSC-derived muscle cells from frontotemporal dementia (FTD) patients harboring C9orf72 hexanucleotide repeat expansions (rGGGGCC), sporadic FTD, and unaffected controls. iPSCs derived from rGGGGCC carriers contained RNA foci but did not vary in differentiation efficiency when compared to unaffected controls nor display mislocalized TDP-43 after as many as 120 days in vitro. This study presents a rapid, efficient, and transgene-free method for generating multinucleated skeletal myotubes from iPSCs and a resource for further modeling the role of skeletal muscle in amyotrophic lateral sclerosis and other motor neuron diseases.

Significance

Protocols to produce skeletal myotubes for disease modeling or therapy are scarce and incomplete. The present study efficiently generates functional skeletal myotubes from human induced pluripotent stem cells using a small molecule-based approach. Using this strategy, terminal myogenic induction of up to 64% in 36 days and spontaneously contractile myotubes within 34 days were achieved. Myotubes derived from patients carrying the C9orf72 repeat expansion show no change in differentiation efficiency and normal TDP-43 localization after as many as 120 days in vitro when compared to unaffected controls. This study provides an efficient, novel protocol for the generation of skeletal myotubes from human induced pluripotent stem cells that may serve as a valuable tool in drug discovery and modeling of musculoskeletal and neuromuscular diseases.