Characteristics of Skeletal Muscle Fibers of SOD1 Knockout Mice

Senolytic treatment does not mitigate oxidative stress-induced muscle atrophy but improves muscle force generation in CuZn superoxide dismutase knockout mice

Oxidative stress is associated with tissue dysfunctions that can lead to reduced health. Prior work has shown that oxidative stress contributes to both muscle atrophy and cellular senescence, which is a hallmark of aging that may drive in muscle atrophy and muscle contractile dysfunction. The purpose of the study was to test the hypothesis that cellular senescence contributes to muscle atrophy or weakness. To increase potential senescence in skeletal muscle, we used a model of oxidative stress-induced muscle frailty, the CuZn superoxide dismutase knockout (Sod1KO) mouse. We treated 6-month-old wildtype (WT) and Sod1KO mice with either vehicle or a senolytic treatment of combined dasatinib (5 mg/kg) + quercetin (50 mg/kg) (D + Q) for 3 consecutive days every 15 days. We continued treatment for 7 months and sacrificed the mice at 13 months of age. Treatment with D + Q did not preserve muscle mass, reduce NMJ fragmentation, or alter muscle protein synthesis in Sod1KO mice when compared to the vehicle-treated group. However, we observed an improvement in muscle-specific force generation in Sod1KO mice treated with D + Q when compared to Sod1KO-vehicle mice. Overall, these data suggest that reducing cellular senescence via D + Q is not sufficient to mitigate loss of muscle mass in a mouse model of oxidative stress-induced muscle frailty but may mitigate some aspects of oxidative stress-induced muscle dysfunction.

Sea buckthorn oil regulates primary myoblasts proliferation and differentiation in vitro

Skeletal muscle is the main edible part of meat products, and its development directly affects the yield and palatability of meat. Sea buckthorn oil (SBO) contains plenty of bioactive substances and has been recognized as a potential functional food product. The study aimed to explore the effects and possible mechanisms of SBO on sheep primary myoblast proliferation and myogenic differentiation. The results implied that SBO exhibited a pro-proliferative effect on primary myoblasts, along with up-regulated proliferating cell nuclear antigen (PCNA) and Cyclin D1/cyclin-dependent kinase 4 (CDK4) abundances. And, SBO promoted myotube formation by increasing the expression of myogenin. Meanwhile, we found that SBO inhibited the expression of miRNA-292a. Moreover, the regulatory effect of SBO on myogenic differentiation of myoblasts was attenuated by miRNA-292a mimics. Of note, SBO activated protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway and augmented glucose uptake and glucose transporter 4 (GLUT4) content, which might be attributed to AMP-activated protein kinase (AMPK) activation. Additionally, the results were shown that SBO increased the abundance of antioxidative enzymes, including glutathione peroxidase 4 (Gpx4) and catalase. In summary, these data suggested that SBO regulated the proliferation and myogenic differentiation of sheep primary myoblasts in vitro, which might potentiate the application of SBO in muscle growth.

Targeting neuromuscular junction to treat neuromuscular disorders

The integrity and preservation of the neuromuscular junction (NMJ), the interface between the motor neuron and skeletal muscle, is critical for maintaining a healthy skeletal muscle. The structural and/or functional defects in the three cellular components of NMJ, namely the pre-synaptic terminal, synaptic cleft, and post-synaptic region, negatively affect skeletal muscle mass and/or strength. Therefore, NMJ repair appears to be an appropriate therapy for muscle disorders. Mouse models provide a detailed molecular characterization of various cellular components of NMJ with relevance to human diseases. This review discusses different molecular targets on the three cellular components of NMJ for treating muscle diseases. The potential effects of these therapies on NMJ morphology and motor performance, their therapeutic efficacy, and clinical relevance are discussed. Collectively, the available data supports targeting NMJ alone or as an adjunct therapy in treating muscle disorders. However, the potential impact of such interventions on human patients with muscle disorders requires further investigation.

Revised Airlie House consensus guidelines for design and implementation of ALS clinical trials

OBJECTIVE

To revise the 1999 Airlie House consensus guidelines for the design and implementation of preclinical therapeutic studies and clinical trials in amyotrophic lateral sclerosis (ALS).

METHODS

A consensus committee comprising 140 key members of the international ALS community (ALS researchers, clinicians, patient representatives, research funding representatives, industry, and regulatory agencies) addressed 9 areas of need within ALS research: (1) preclinical studies; (2) biological and phenotypic heterogeneity; (3) outcome measures; (4) disease-modifying and symptomatic interventions; (5) recruitment and retention; (6) biomarkers; (7) clinical trial phases; (8) beyond traditional trial designs; and (9) statistical considerations. Assigned to 1 of 8 sections, committee members generated a draft set of guidelines based on a "background" of developing a (pre)clinical question and a "rationale" outlining the evidence and expert opinion. Following a 2-day, face-to-face workshop at the Airlie House Conference Center, a modified Delphi process was used to develop draft consensus research guidelines, which were subsequently reviewed and modified based on comments from the public. Statistical experts drafted a separate document of statistical considerations (section 9).

RESULTS

In this report, we summarize 112 guidelines and their associated backgrounds and rationales. The full list of guidelines, the statistical considerations, and a glossary of terms can be found in data available from Dryad (appendices e-3-e-5, doi.org/10.5061/dryad.32q9q5d). The authors prioritized 15 guidelines with the greatest potential to improve ALS clinical research.

CONCLUSION

The revised Airlie House ALS Clinical Trials Consensus Guidelines should serve to improve clinical trial design and accelerate the development of effective treatments for patients with ALS.

Preconditioning Contractions Suppress Muscle Pain Markers after Damaging Eccentric Contractions

Inexperienced vigorous exercise, including eccentric contraction (ECC), causes muscle pain and damage. Similar prior light exercise suppresses the development of muscle pain (repeated-bout effect), but the molecular mechanisms behind this are not sufficiently understood. In this study, the influence of a nondamaging preconditioning ECC load (Precon) on muscle pain-related molecules and satellite cell-activating factors was investigated at the mRNA expression level. Nine-week-old male Wistar rats (n=36) were divided into 2 groups: a group receiving only a damaging ECC (100 contractions) load (non-Precon) and a group receiving a nondamaging ECC (10 contractions) load 2 days before receiving the damaging ECC load (Precon). ECC was loaded on the left leg, and the right leg was regarded as the intact control (CTL). The medial head of the gastrocnemius muscle from all rats was excised 2 or 4 days after the damaging ECC loading, and the relative mRNA expression levels of muscle pain- and satellite cell-related molecules were quantitated using real-time RT PCR. Precon suppressed increases in MHC-embryonic and MHC-neonatal mRNA expressions. Enhancement of HGF, Pax7, MyoD, and myogenin mRNA expression was also suppressed, suggesting that Precon decreased the degree of muscle damage and no muscle regeneration or satellite cell activation occurred. Similarly, increases in mRNA expression of muscle pain-related molecules (BKB₂ receptor, COX-2, and mPGEC-1) were also suppressed. This study clearly demonstrated that at the mRNA level, prior light ECC suppressed muscle damage induced by later damaging ECC and promoted recovery from muscle pain.

Double Knockout of Peroxiredoxin 4 (Prdx4) and Superoxide Dismutase 1 (Sod1) in Mice Results in Severe Liver Failure

Mice that are deficient in superoxide dismutase 1 (Sod1), an antioxidative enzyme, are susceptible to developing liver steatosis. Peroxiredoxin 4 (Prdx4) catalyzes disulfide bond formation in proteins via the action of hydrogen peroxide and hence decreases oxidative stress and supports oxidative protein folding for the secretion of lipoproteins. Because elevated reactive oxygen species induce endoplasmic reticulum stress, this negative chain reaction is likely involved in the development of nonalcoholic fatty liver diseases and more advanced steatohepatitis (NASH). In the current study, we generated Prdx4 and Sod1 double knockout (DKO; Prdx4^-/ySod1^-/-) mice and examined whether the combined deletion of Prdx4 and Sod1 aggravated liver pathology compared to single knockout and wild-type mice. The secretion of triglyceride-rich lipoprotein was strikingly impaired in the DKO mice, leading to aggravated liver steatosis. Simultaneously, the activation of caspase-3 in the liver was observed. The hyperoxidation of Prdxs, a hallmark of oxidative stress, occurred in different isoforms that are uniquely associated with Sod1^-/- and Prdx4^-/y mice, and the effect was additive in DKO mouse livers. Because DKO mice spontaneously develop severe liver failure at a relatively young stage, they have the potential for use as a model for hepatic disorders and for testing other potential treatments.

Loss of the antioxidant enzyme CuZnSOD (Sod1) mimics an age-related increase in absolute mitochondrial DNA copy number in the skeletal muscle

Mitochondria contain multiple copies of the circular mitochondrial genome (mtDNA) that encodes ribosomal RNAs and proteins locally translated for oxidative phosphorylation. Loss of mtDNA integrity, both altered copy number and increased mutations, is implicated in cellular dysfunction with aging. Published data on mtDNA copy number and aging is discordant which may be due to methodological limitations for quantifying mtDNA copy number. Existing quantitative PCR (qPCR) mtDNA copy number quantification methods provide only relative abundances and are problematic to normalize to different template input amounts and across tissues/sample types. As well, existing methods cannot quantify mtDNA copy number in subcellular isolates, such as isolated mitochondria and neuronal synaptic terminals, which lack nuclear genomic DNA for normalization. We have developed and validated a novel absolute mtDNA copy number quantitation method that uses chip-based digital polymerase chain reaction (dPCR) to count the number of copies of mtDNA and used this novel method to assess the literature discrepancy in which there is no clear consensus whether mtDNA numbers change with aging in skeletal muscle. Skeletal muscle in old mice was found to have increased absolute mtDNA numbers compared to young controls. Furthermore, young Sod1 ^-/- mice were assessed and show an age-mimicking increase in skeletal muscle mtDNA. These findings reproduce a number of previous studies that demonstrate age-related increases in mtDNA. This simple and cost effective dPCR approach should enable precise and accurate mtDNA copy number quantitation in mitochondrial studies, eliminating contradictory studies of mitochondrial DNA content with aging.