Impact of aging and oxidative stress on specific components of excitation contraction coupling in regulating force generation

Neuroprotective treatment with the nitrone compound OKN-007 mitigates age-related muscle weakness in aging mice

Despite the universal impact of sarcopenia on compromised health and quality of life in the elderly, promising pharmaceutical approaches that can effectively mitigate loss of muscle and function during aging have been limited. Our group and others have reported impairments in peripheral motor neurons and loss of muscle innervation as initiating factors in sarcopenia, contributing to mitochondrial dysfunction and elevated oxidative stress in muscle. We recently reported a reduction in α motor neuron loss in aging mice in response to the compound OKN-007, a proposed antioxidant and anti-inflammatory agent. In the current study, we asked whether OKN-007 treatment in wildtype male mice for 8-9 months beginning at 16 months of age can also protect muscle mass and function. At 25 months of age, we observed a reduction in the loss of whole-body lean mass, a reduced loss of innervation at the neuromuscular junction and well-preserved neuromuscular junction morphology in OKN-007 treated mice versus age matched wildtype untreated mice. The loss in muscle force generation in aging mice (~ 25%) is significantly improved with OKN-007 treatment. In contrast, OKN-007 treatment provided no protection in loss of muscle mass in aging mice. Mitochondrial function was improved by OKN-007 treatment, consistent with its potential antioxidative properties. Together, these exciting findings are the first to demonstrate that interventions through neuroprotection can be an effective therapy to counter aging-related muscle dysfunction.

Changes in muscle strength and risk of cardiovascular disease among middle-aged and older adults in China: Evidence from a prospective cohort study

BACKGROUND

Evidence indicates that low muscle strength is associated with an increased cardiovascular diseases (CVDs) risk. However, the association between muscle strength changes based on repeated measurements and CVD incidence remains unclear.

METHODS

The study used data from the China Health and Retirement Longitudinal Study in 2011 (Wave 1), 2013 (Wave 2), 2015 (Wave 3), and 2018 (Wave 4). Low muscle strength was defined as handgrip strength <28 kg for men or <18 kg for women, or chair-rising time ≥12 s. Based on changes in muscle strength from Waves 1 to 2, participants were categorized into four groups of Normal-Normal, Low-Normal, Normal-Low, and Low-Low. CVD events, including heart disease and stroke, were recorded using a self-reported questionnaire during Waves 3 and 4 visits. Cox proportional hazards models were used to investigate the association between muscle strength changes and CVD incidence after multivariable adjustments. Hazard ratios (HRs) and 95% confidence intervals (95% CIs) were estimated with the Normal-Normal group as the reference.

RESULTS

A total of 1164 CVD cases were identified among 6608 participants. Compared to participants with sustained normal muscle strength, the CVD risks increased progressively across groups of the Low-Normal (HR = 1.20, 95% CI: 1.01-1.43), the Normal-Low (HR = 1.35, 95% CI: 1.14-1.60), and the Low-Low (HR = 1.76, 95% CI: 1.49-2.07). Similar patterns were observed for the significant associations between muscle strength status and the incidence risks of heart disease and stroke. Subgroup analyses showed that the significant associations between CVD and muscle strength changes were consistent across age, sex, and body mass index (BMI) categories.

CONCLUSIONS

The study found that muscle strength changes were associated with CVD risk. This suggests that continuous tracking of muscle status may be helpful in screening cardiovascular risk.

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.

Proteomic reference map for sarcopenia research: mass spectrometric identification of key muscle proteins of organelles, cellular signaling, bioenergetic metabolism and molecular chaperoning

During the natural aging process, frailty is often associated with abnormal muscular performance. Although inter-individual differences exit, in most elderly the tissue mass and physiological functionality of voluntary muscles drastically decreases. In order to study age-related contractile decline, animal model research is of central importance in the field of biogerontology. Here we have analyzed wild type mouse muscle to establish a proteomic map of crude tissue extracts. Proteomics is an advanced and large-scale biochemical method that attempts to identify all accessible proteins in a given biological sample. It is a technology-driven approach that uses mass spectrometry for the characterization of individual protein species. Total protein extracts were used in this study in order to minimize the potential introduction of artefacts due to excess subcellular fractionation procedures. In this report, the proteomic survey of aged muscles has focused on organellar marker proteins, as well as proteins that are involved in cellular signaling, the regulation of ion homeostasis, bioenergetic metabolism and molecular chaperoning. Hence, this study has establish a proteomic reference map of a highly suitable model system for future aging research.

Mitochondrial targeted catalase improves muscle strength following arteriovenous fistula creation in mice with chronic kidney disease

Hand dysfunction is a common observation after arteriovenous fistula (AVF) creation for hemodialysis access and has a variable clinical phenotype; however, the underlying mechanism responsible is unclear. Grip strength changes are a common metric used to assess AVF-associated hand disability but has previously been found to poorly correlate with the hemodynamic perturbations post-AVF placement implicating other tissue-level factors as drivers of hand outcomes. In this study, we sought to test if expression of a mitochondrial targeted catalase (mCAT) in skeletal muscle could reduce AVF-related limb dysfunction in mice with chronic kidney disease (CKD). Male and female C57BL/6J mice were fed an adenine-supplemented diet to induce CKD prior to placement of an AVF in the iliac vascular bundle. Adeno-associated virus was used to drive expression of either a green fluorescent protein (control) or mCAT using the muscle-specific human skeletal actin (HSA) gene promoter prior to AVF creation. As expected, the muscle-specific AAV-HSA-mCAT treatment did not impact blood urea nitrogen levels (P = 0.72), body weight (P = 0.84), or central hemodynamics including infrarenal aorta and inferior vena cava diameters (P > 0.18) or velocities (P > 0.38). Hindlimb perfusion recovery and muscle capillary densities were also unaffected by AAV-HSA-mCAT treatment. In contrast to muscle mass and myofiber size which were not different between groups, both absolute and specific muscle contractile forces measured via a nerve-mediated in-situ preparation were significantly greater in AAV-HSA-mCAT treated mice (P = 0.0012 and P = 0.0002). Morphological analysis of the post-synaptic neuromuscular junction uncovered greater acetylcholine receptor cluster areas (P = 0.0094) and lower fragmentation (P = 0.0010) in AAV-HSA-mCAT treated mice. Muscle mitochondrial oxidative phosphorylation was not different between groups, but AAV-HSA-mCAT treated mice had lower succinate-fueled mitochondrial hydrogen peroxide emission compared to AAV-HSA-GFP mice (P < 0.001). In summary, muscle-specific scavenging of mitochondrial hydrogen peroxide significantly improves neuromotor function in mice with CKD following AVF creation.

SEPN1-related myopathy depends on the oxidoreductase ERO1A and is druggable with the chemical chaperone TUDCA

Selenoprotein N (SEPN1) is a protein of the endoplasmic reticulum (ER) whose inherited defects originate SEPN1-related myopathy (SEPN1-RM). Here, we identify an interaction between SEPN1 and the ER-stress-induced oxidoreductase ERO1A. SEPN1 and ERO1A, both enriched in mitochondria-associated membranes (MAMs), are involved in the redox regulation of proteins. ERO1A depletion in SEPN1 knockout cells restores ER redox, re-equilibrates short-range MAMs, and rescues mitochondrial bioenergetics. ERO1A knockout in a mouse background of SEPN1 loss blunts ER stress and improves multiple MAM functions, including Ca2+ levels and bioenergetics, thus reversing diaphragmatic weakness. The treatment of SEPN1 knockout mice with the ER stress inhibitor tauroursodeoxycholic acid (TUDCA) mirrors the results of ERO1A loss. Importantly, muscle biopsies from patients with SEPN1-RM exhibit ERO1A overexpression, and TUDCA-treated SEPN1-RM patient-derived primary myoblasts show improvement in bioenergetics. These findings point to ERO1A as a biomarker and a viable target for intervention and to TUDCA as a pharmacological treatment for SEPN1-RM.

Modulation of sarcopenia phenotypes by glutathione peroxidase 4 overexpression in mice

Our laboratory previously showed lipid hydroperoxides and oxylipin levels are elevated in response to loss of skeletal muscle innervation and are associated with muscle pathologies. To elucidate the pathological impact of lipid hydroperoxides, we overexpressed glutathione peroxidase 4 (GPx4), an enzyme that targets reduction of lipid hydroperoxides in membranes, in adult CuZn superoxide dismutase knockout (Sod1KO) mice that show accelerated muscle atrophy associated with loss of innervation. The gastrocnemius muscle from Sod1KO mice shows reduced mitochondrial respiration and elevated oxidative stress (F2 -isoprostanes and hydroperoxides) compared to wild-type (WT) mice. Overexpression of GPx4 improved mitochondrial respiration and reduced hydroperoxide generation in Sod1KO mice, but did not attenuate the muscle loss that occurs in Sod1KO mice. In contrast, contractile force generation is reduced in EDL muscle in Sod1KO mice relative to WT mice, and overexpression of GPx4 restored force generation to WT levels in Sod1KO mice. GPx4 overexpression also prevented loss of muscle contractility at the single fibre level in fast-twitch fibres from Sod1KO mice. Muscle fibres from Sod1KO mice were less sensitive to both depolarization and calcium at the single fibre level and exhibited a reduced activation by S-glutathionylation. GPx4 overexpression in Sod1KO mice rescued the deficits in both membrane excitability and calcium sensitivity of fast-twitch muscle fibres. Overexpression of GPx4 also restored the sarco/endoplasmic reticulum Ca2+ -ATPase activity in Sod1KO gastrocnemius muscles. These data suggest that GPx4 plays an important role in preserving excitation-contraction coupling function and Ca2+ homeostasis, and in maintaining muscle and mitochondrial function in oxidative stress-induced sarcopenia. KEY POINTS: Knockout of CuZn superoxide dismutase (Sod1KO) induces elevated oxidative stress with accelerated muscle atrophy and weakness. Glutathione peroxidase 4 (GPx4) plays a fundamental role in the reduction of lipid hydroperoxides in membranes, and overexpression of GPx4 improves mitochondrial respiration and reduces hydroperoxide generation in Sod1KO mice. Muscle contractile function deficits in Sod1KO mice are alleviated by the overexpression of GPx4. GPx4 overexpression in Sod1KO mice rescues the impaired muscle membrane excitability of fast-twitch muscle fibres and improves their calcium sensitivity. Sarco/endoplasmic reticulum Ca2+ -ATPase activity in Sod1KO muscles is decreased, and it is restored by the overexpression of GPx4. Our results confirm that GPx4 plays an important role in preserving excitation-contraction coupling function and Ca2+ homeostasis, and maintaining muscle and mitochondrial function in oxidative stress-induced sarcopenia.

L-Carnitine improves mechanical responses of cardiomyocytes and restores Ca2+ homeostasis during aging

L-Carnitine (β-hydroxy-γ-trimethylaminobutyric acid, LC) is a crucial molecule for the mitochondrial oxidation of fatty acids. It facilitates the transport of long-chain fatty acids into the mitochondrial matrix. The reduction in LC levels during the aging process has been linked to numerous cardiovascular disorders, including contractility dysfunction, and disrupted intracellular Ca2+ homeostasis. The aim of this study was to examine the effects of long-term (7 months) LC administration on cardiomyocyte contraction and intracellular Ca2+ transients ([Ca2+]i) in aging rats. Male albino Wistar rats were randomly assigned to either the control or LC-treated groups. LC (50 mg/kg body weight/day) was dissolved in distilled water and orally administered for a period of 7 months. The control group received distilled water alone. Subsequently, ventricular single cardiomyocytes were isolated, and the contractility and Ca2+ transients were recorded in aging (18 months) rats. This study demonstrates, for the first time, a novel inotropic effect of long-term LC treatment on rat ventricular cardiomyocyte contraction. LC increased cardiomyocyte cell shortening and resting sarcomere length. Furthermore, LC supplementation led to a reduction in resting [Ca2+]i level and an increase in the amplitude of [Ca2+]i transients, indicative of enhanced contraction. Consistent with these results, decay time of Ca2+ transients also decreased significantly in the LC-treated group. The long-term administration of LC may help restore the Ca2+ homeostasis altered during aging and could be used as a cardioprotective medication in cases where myocyte contractility is diminished.

Calcium channelopathies in neurodegenerative disorder: an untold story of RyR and SERCA

INTRODUCTION

Recent neuroscience breakthroughs have shed light on the sophisticated relationship between calcium channelopathies and movement disorders, exposing a previously undiscovered tale focusing on the Ryanodine Receptor (RyR) and the Sarco/Endoplasmic Reticulum Calcium ATPase (SERCA). Calcium signaling mainly orchestrates neural communication, which regulates synaptic transmission and total network activity. It has been determined that RyR play a significant role in managing neuronal functions, most notably in releasing intracellular calcium from the endoplasmic reticulum.

AREAS COVERED

It highlights the involvement of calcium channels such as RyR and SERCA in physiological and pathophysiological conditions.

EXPERT OPINION

Links between RyR and SERCA activity dysregulation, aberrant calcium levels, motor and cognitive dysfunction have brought attention to the importance of RyR and SERCA modulation in neurodegenerative disorders. Understanding the obscure function of these proteins will open up new therapeutic possibilities to address the underlying causes of neurodegenerative diseases. The unreported RyR and SERCA narrative broadens the understanding of calcium channelopathies in movement disorders and calls for more research into cutting-edge therapeutic approaches.