Restoration of SERCA ATPase prevents oxidative stress-related muscle atrophy and weakness

Circulating Biomarkers of Accelerated Sarcopenia in Respiratory Diseases

Skeletal muscle dysfunction is a critical finding in many respiratory diseases. However, a definitive biomarker to assess muscle decline in respiratory diseases is not known. We analyzed the association of plasma levels of glycoprotein Dickkopf-3 (Dkk-3), c-terminal agrin fragment-22 (CAF22) and microRNAs miR-21, miR-134a, miR-133 and miR-206 with hand-grip strength (HGS) and appendicular skeletal mass index (ASMI) in male, 54-73-year-old patients with chronic obstructive pulmonary diseases (COPD), asthma or pulmonary TB (n = 83-101/group). Patients with respiratory diseases showed a reduction in HGS and gait speed, while a reduction in ASMI was only found in patients with pulmonary TB. Among the sarcopenia indexes, HGS showed the strongest correlation with plasma CAF22, miR-21 and miR-206 levels while ASMI showed the strongest correlation with Dkk-3 and miR-133 in respiratory diseases. We found a modest-to-significant increase in the plasma markers of inflammation, oxidative stress and muscle damage, which had varying degrees of correlations with Dkk-3, CAF22 and selected micro RNAs (miRs) in respiratory diseases. Taken together, our data show that plasma levels of Dkk-3, CAF22 and selected miRs can be useful tools to assess accelerated sarcopenia phenotype in the elderly with respiratory diseases.

Interrelation between ROS and Ca2+ in aging and age-related diseases

Calcium (Ca2+) and reactive oxygen species (ROS) are versatile signaling molecules coordinating physiological and pathophysiological processes. While channels and pumps shuttle Ca2+ ions between extracellular space, cytosol and cellular compartments, short-lived and highly reactive ROS are constantly generated by various production sites within the cell. Ca2+ controls membrane potential, modulates mitochondrial adenosine triphosphate (ATP) production and affects proteins like calcineurin (CaN) or calmodulin (CaM), which, in turn, have a wide area of action. Overwhelming Ca2+ levels within mitochondria efficiently induce and trigger cell death. In contrast, ROS comprise a diverse group of relatively unstable molecules with an odd number of electrons that abstract electrons from other molecules to gain stability. Depending on the type and produced amount, ROS act either as signaling molecules by affecting target proteins or as harmful oxidative stressors by damaging cellular components. Due to their wide range of actions, it is little wonder that Ca2+ and ROS signaling pathways overlap and impact one another. Growing evidence suggests a crucial implication of this mutual interplay on the development and enhancement of age-related disorders, including cardiovascular and neurodegenerative diseases as well as cancer.

Mammalian STE20-Like Kinase 2 Promotes Lipopolysaccharides-Mediated Cardiomyocyte Inflammation and Apoptosis by Enhancing Mitochondrial Fission

In this study, we analyzed the role of mammalian STE20-like protein kinase 2 (Mst2), a serine-threonine protein kinase, in Lipopolysaccharides (LPS)-mediated inflammation and apoptosis in the H9C2 cardiomyocytes. Mst2 mRNA and protein levels were significantly upregulated in the LPS-treated H9C2 cardiomyocytes. LPS treatment induced expression of IL-2, IL-8, and MMP9 mRNA and proteins in the H9C2 cardiomyocytes, and this was accompanied by increased caspase-3/9 mediating H9C2 cardiomyocyte apoptosis. LPS treatment also increased mitochondrial reactive oxygen species (ROS) and the levels of antioxidant enzymes, such as GSH, SOD, and GPX, in the H9C2 cardiomyocytes. The LPS-treated H9C2 cardiomyocytes showed lower cellular ATP levels and mitochondrial state-3/4 respiration but increased mitochondrial fragmentation, including upregulation of the mitochondrial fission genes Drp1, Mff, and Fis1. LPS-induced inflammation, mitochondrial ROS, mitochondrial fission, and apoptosis were all significantly suppressed by pre-treating the H9C2 cardiomyocytes with the Mst2 inhibitor, XMU-MP1. However, the beneficial effects of Mst2 inhibition by XMU-MP1 were abolished by carbonyl cyanide-4-(trifluoromethoxy) phenylhydrazone (FCCP), a potent activator of mitochondrial fission. These findings demonstrate that Mst2 mediates LPS-induced cardiomyocyte inflammation and apoptosis by increasing mitochondrial fission.

Molecular changes in transcription and metabolic pathways underlying muscle atrophy in the CuZnSOD null mouse model of sarcopenia

Mice lacking the superoxide anion scavenger CuZn superoxide dismutase (Sod1^-/- mice) develop a number of age-related phenotypes, including an early progression of muscle atrophy and weakness (sarcopenia) associated with loss of innervation. The purpose of this study was to delineate the early development of sarcopenia in the Sod1^-/- mice and to measure changes in the muscle transcriptome, proteome, and eicosanoid profile at the stage when sarcopenia is markedly induced in this model (7-9 months of age). We found a strong correlation between muscle atrophy and mitochondrial state 1 hydroperoxide production, which was 40% higher in isolated mitochondria from Sod1^-/- mouse gastrocnemius muscle by 2 months of age. The primary pathways showing altered gene expression in Sod1^-/- mice identified by RNA-seq transcriptomic analysis are protein ubiquitination, synaptic long-term potentiation, calcium signaling, phospholipase C signaling, AMPK, and TWEAK signaling. Targeted proteomics shows elevated expression of mitochondrial proteins, fatty acid metabolism enzymes, tricarboxylic acid (TCA) cycle enzymes, and antioxidants, while enzymes involved in carbohydrate metabolism are downregulated in Sod1^-/- mice. LC-MS analysis of lipids in gastrocnemius muscle detected 78 eicosanoids, of which 31 are significantly elevated in muscle from Sod1^-/- mice. These data suggest that mitochondrial hydroperoxide generation is elevated prior to muscle atrophy and may be a potential driving factor of changes in the transcriptome, proteome, and eicosanoid profile of the Sod1^-/- mice. Together, these analyses revealed important molecular events that occur during muscle atrophy, which will pave the way for future studies using new approaches to treat sarcopenia.

Muscle unloading: A comparison between spaceflight and ground-based models

Prolonged unloading of skeletal muscle, a common outcome of events such as spaceflight, bed rest and hindlimb unloading, can result in extensive metabolic, structural and functional changes in muscle fibres. With advancement in investigations of cellular and molecular mechanisms, understanding of disuse muscle atrophy has significantly increased. However, substantial gaps exist in our understanding of the processes dictating muscle plasticity during unloading, which prevent us from developing effective interventions to combat muscle loss. This review aims to update the status of knowledge and underlying mechanisms leading to cellular and molecular changes in skeletal muscle during unloading. We have also discussed advances in the understanding of contractile dysfunction during spaceflights and in ground-based models of muscle unloading. Additionally, we have elaborated on potential therapeutic interventions that show promising results in boosting muscle mass and strength during mechanical unloading. Finally, we have identified key gaps in our knowledge as well as possible research direction for the future.

Cerebral ischemia-reperfusion is modulated by macrophage-stimulating 1 through the MAPK-ERK signaling pathway

Cerebral ischemia-reperfusion (IR) injury is associated with mitochondrial damage. Macrophage-stimulating 1 (MST1) reportedly stimulates mitochondrial apoptosis by suppressing BCL-2. We investigated whether MST1 promotes the progression of cerebral IR injury by inducing mitochondrial dysfunction in vivo and in vitro. Western blot analysis, quantitative polymerase chain reaction, immunofluorescence, and mitochondrial function assays were conducted in cells from wild-type and Mst1-knockout mice subjected to cerebral IR injury. MST1 expression in wild-type glial cells increased following cerebral IR injury. Cerebral IR injury reduced the mitochondrial membrane potential and mitochondrial metabolism in glial cells, while it enhanced mitochondrial reactive oxygen species generation and mitochondrial calcium levels in these cells. The deletion of Mst1 attenuated cerebral IR injury by improving mitochondrial function and reducing mitochondrial damage. The mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway was suppressed in wild-type glial cell upon cerebral IR injury but was reactivated in Mst1-knockout glial cell. Accordingly, blocking the MAPK/ERK pathway abolished the beneficial effects of Mst1 deletion during cerebral IR injury by inducing mitochondrial damage in glial cells. Our results suggest that cerebral IR injury is associated with MST1 upregulation in the brain, while the genetic ablation of Mst1 can attenuate mitochondrial damage and sustain brain function following cerebral IR injury.

Mechanical factors tune the sensitivity of mdx muscle to eccentric strength loss and its protection by antioxidant and calcium modulators

Background

Dystrophin deficiency sensitizes skeletal muscle of mice to eccentric contraction (ECC)-induced strength loss. ECC protocols distinguish dystrophin-deficient from healthy, wild type muscle, and test the efficacy of therapeutics for Duchenne muscular dystrophy (DMD). However, given the large lab-to-lab variability in ECC-induced strength loss of dystrophin-deficient mouse skeletal muscle (10–95%), mechanical factors of the contraction likely impact the degree of loss. Therefore, the purpose of this study was to evaluate the extent to which mechanical variables impact sensitivity of dystrophin-deficient mouse skeletal muscle to ECC.

Methods

We completed ex vivo and in vivo muscle preparations of the dystrophin-deficient mdx mouse and designed ECC protocols within physiological ranges of contractile parameters (length change, velocity, contraction duration, and stimulation frequencies). To determine whether these contractile parameters affected known factors associated with ECC-induced strength loss, we measured sarcolemmal damage after ECC as well as strength loss in the presence of the antioxidant N-acetylcysteine (NAC) and small molecule calcium modulators that increase SERCA activity (DS-11966966 and CDN1163) or lower calcium leak from the ryanodine receptor (Chloroxine and Myricetin).

Results

The magnitude of length change, work, and stimulation duration ex vivo and in vivo of an ECC were the most important determinants of strength loss in mdx muscle. Passive lengthening and submaximal stimulations did not induce strength loss. We further showed that sarcolemmal permeability was associated with muscle length change, but it only accounted for a minimal fraction (21%) of the total strength loss (70%). The magnitude of length change also significantly influenced the degree to which NAC and small molecule calcium modulators protected against ECC-induced strength loss.

Conclusions

These results indicate that ECC-induced strength loss of mdx skeletal muscle is dependent on the mechanical properties of the contraction and that mdx muscle is insensitive to ECC at submaximal stimulation frequencies. Rigorous design of ECC protocols is critical for effective use of strength loss as a readout in evaluating potential therapeutics for muscular dystrophy.

Sphingosine kinase 1 promotes cerebral ischemia-reperfusion injury through inducing ER stress and activating the NF-κB signaling pathway

Endoplasm reticulum stress and inflammation response have been found to be linked to cerebral ischemia-reperfusion (IR) injury. Sphingosine kinase 1 (SPHK1) has been reported to be a novel endoplasm reticulum regulator. The aim of our study is to figure out the role of SPHK1 in cerebral IR injury and verify whether it has an ability to regulate inflammation and endoplasm reticulum stress. Hydrogen peroxide was used to induce cerebral IR injury. Enzyme-linked immunosorbent assay, quantitative polymerase chain reaction, western blots, and immunofluorescence were used to measure the alterations of cell viability, inflammation response, and endoplasm reticulum stress. The results demonstrated that after exposure to hydrogen peroxide, cell viability was reduced whereas SPHK1 expression was significantly elevated. Knockdown of SPHK1 attenuated hydrogen peroxide-mediated cell death and reversed cell viability. Our data also demonstrated that SPHK1 deletion reduced endoplasm reticulum stress and alleviated inflammation response in hydrogen peroxide-treated cells. In addition, we also found that SHPK1 modulated endoplasm reticulum stress and inflammation response to through the NF-κB signaling pathway. Inhibition of NF-κB signaling pathway has similar results when compared with the cells with SPHK1 deletion. Altogether, our results demonstrated that SPHK1 upregulation, induced by hydrogen peroxide, is responsible for cerebral IR injury through inducing endoplasm reticulum stress and inflammation response in a manner working through the NF-κB signaling pathway. This finding provides new insight into the molecular mechanism to explain the neuron death induced by cerebral IR injury.

Calcium Mechanisms in Limb-Girdle Muscular Dystrophy with CAPN3 Mutations

Limb-girdle muscular dystrophy recessive 1 (LGMDR1), previously known as LGMD2A, is a rare disease caused by mutations in the CAPN3 gene. It is characterized by progressive weakness of shoulder, pelvic, and proximal limb muscles that usually appears in children and young adults and results in loss of ambulation within 20 years after disease onset in most patients. The pathophysiological mechanisms involved in LGMDR1 remain mostly unknown, and to date, there is no effective treatment for this disease. Here, we review clinical and experimental evidence suggesting that dysregulation of Ca2+ homeostasis in the skeletal muscle is a significant underlying event in this muscular dystrophy. We also review and discuss specific clinical features of LGMDR1, CAPN3 functions, novel putative targets for therapeutic strategies, and current approaches aiming to treat LGMDR1. These novel approaches may be clinically relevant not only for LGMDR1 but also for other muscular dystrophies with secondary calpainopathy or with abnormal Ca2+ homeostasis, such as LGMD2B/LGMDR2 or sporadic inclusion body myositis.

Cast immobilization of hindlimb upregulates sarcolipin expression in atrophied skeletal muscles and increases thermogenesis in C57BL/6J mice

Mechanical unloading impairs cytosolic calcium (Ca²⁺) homeostasis in skeletal muscles. In this study, we investigated whether sarco(endo)plasmic reticulum Ca²⁺-ATPase (SERCA) itself or one of the regulators of the Ca²⁺ SERCA pump, sarcolipin (SLN), is altered to deregulate Ca²⁺ homeostasis in cast immobilized, atrophied muscles. Hindlimb muscles of 8-wk-old male C57BL/6J mice were subjected to bilateral cast immobilization for 2 wk. Two-week-cast immobilization induced both body weight and skeletal muscle loss. Highly phosphorylated Ca²⁺/calmodulin-dependent protein kinase II in the atrophied muscles suggested that cytosolic Ca²⁺ concentration was elevated. Extremely high expression levels of SLN mRNA and protein were observed in the atrophied muscles. Upregulation of SLN at the transcriptional level was supported by low RCAN1 expression, which is a negative regulator of SLN. We treated C₂C₁₂ cells with dexamethasone to mimic muscle atrophy in vitro and showed a direct relationship between high SLN mRNA expression and low Ca²⁺ uptake by sarcoplasmic reticulum. Since SLN reportedly plays a role in nonshivering thermogenesis, we performed a cold tolerance test of the whole body. As a result, we found that mice with cast immobilization showed high cold tolerance, suggesting that cast immobilization promoted whole body thermogenesis. Although the activity level was decreased during cast immobilization without change in food intake, adipose tissue weights also decreased significantly after cast immobilization. Concomitantly, we conclude that cast immobilization of hindlimb increased thermogenesis in C57Bl/6J mice, probably via high expression of SLN.

HMGB1/autophagy pathway mediates the atrophic effect of TGF-β1 in denervated skeletal muscle

Background

Transforming growth factor beta 1 (TGF-β1) is a classical modulator of skeletal muscle and regulates several processes, such as myogenesis, regeneration and muscle function in skeletal muscle diseases. Skeletal muscle atrophy, characterized by the loss of muscle strength and mass, is one of the pathological conditions regulated by TGF-β1, but the underlying mechanism involved in the atrophic effects of TGF-β1 is not fully understood.

Methods

Mice sciatic nerve transection model was created and gastrocnemius were analysed by western blot, immunofluorescence staining and fibre diameter quantification after 2 weeks. Exogenous TGF-β1 was administrated and high-mobility group box-1 (HMGB1), autophagy were blocked by siRNA and chloroquine (CQ) respectively to explore the mechanism of the atrophic effect of TGF-β1 in denervated muscle. Similar methods were performed in C2C12 cells.

Results

We found that TGF-β1 was induced in denervated muscle and it could promote atrophy of skeletal muscle both in vivo and in vitro, up-regulated HMGB1 and increased autophagy activity were also detected in denervated muscle and were further promoted by exogenous TGF-β1. The atrophic effect of TGF-β1 could be inhibited when HMGB1/autophagy pathway was blocked.

Conclusions

Thus, our data revealed that TGF-β1 is a vital regulatory factor in denervated skeletal muscle in which HMGB1/ autophagy pathway mediates the atrophic effect of TGF-β1. Our findings confirmed a new pathway in denervation-induced skeletal muscle atrophy and it may be a novel therapeutic target for patients with muscle atrophy after peripheral nerve injury.

Electronic supplementary material

The online version of this article (10.1186/s12964-018-0310-6) contains supplementary material, which is available to authorized users.