MicroRNA-23a has minimal effect on endurance exercise-induced adaptation of mouse skeletal muscle

Exercise performance in well-trained male mice is promoted by intermittent hyperoxia via improving metabolic properties and capillary profiles

Although training under intermittent hyperoxia has been shown to improve exercise performance, its effect on well-trained mice remains undetermined. Voluntary run for 7 weeks increased maximal work values by 7.4-fold (Bayes factor, BF ≥ 30). Subsequently, mice underwent 4 weeks of treadmill training with (INT) or without (ET) intermittent hyperoxia (30% O2). INT training significantly increased maximal exercise capacity compared to ET (BF ≥ 30). INT group exhibited significantly higher levels of cytochrome-c-oxidase (COX) in soleus muscle (SOL, BF ≥ 3.0). Additionally, INT enhanced 3-hydroxyacyl-CoA-dehydrogenase (HAD) levels in white gastrocnemius (Gw) and plantaris (PL) muscles compared to ET (BF ≥ 3.0). Pyruvate dehydrogenase complex (PDHc) levels were significantly higher in the INT group compared to the ET group in red gastrocnemius and left ventricle (BF ≥ 30). Capillary-to-fiber ratio (C/F) was significantly higher in the INT group than in the ET group in SOL and PL muscles (BF ≥ 3.0). COX, PDHc, capillary density (CD), and catalase protein values in SOL, HAD, and C/F levels in Gw and PL, as well as CD values in Gw showed a significant positive correlation with maximal work values using data from ET and INT groups (p < 0.05). These findings suggest that training under intermittent hyperoxia promotes endurance performance probably by improving metabolic enzyme levels and capillary profiles in well-trained mice.

Circulating microRNAs and physical activity: Impact in diabetes

The term "ci-miRNAs," or "circulating microRNAs," refers to extracellular microRNAs (miRNAs) that exist outside of cells and can be detected in various bodily fluids, including blood, saliva, urine, and breast milk. These ci-miRNAs play a role in regulating gene expression and are mainly recognized for their functions beyond the cell, serving as signaling molecules in the blood. Researchers have thoroughly investigated the roles of these circulating miRNAs in various diseases. The capacity to detect and quantify ci-miRNAs in bodily fluids suggests their potential as biomarkers for monitoring several health conditions, including cancer, heart disease, brain disorders, and metabolic disorders, where fluctuations in miRNA levels may correlate with different physiological and pathological states. Current methods enable researchers to identify and measure miRNAs in these fluids, facilitating the exploration of their roles in health maintenance and disease resistance. Although research on ci-miRNAs is ongoing, recent studies focus on uncovering their significance, assessing their viability as biomarkers, and clarifying their functions. However, our understanding of how various types, intensities, and durations of exercise influence the levels of these miRNAs in the bloodstream is still limited. This section seeks to provide an overview of the changes in ci-miRNAs in response to exercise.

Physical exercise and the functions of microRNAs

MicroRNAs (miRNAs) control RNA translation and are a class of small, tissue-specific, non-protein-coding RNAs that maintain cellular homeostasis through negative gene regulation. Maintenance of the physiological environment depends on the proper control of miRNA expression, as these molecules influence almost all genetic pathways, from the cell cycle checkpoint to cell proliferation and apoptosis, with a wide range of target genes. Dysregulation of the expression of miRNAs is correlated with several types of diseases, acting as regulators of cardiovascular functions, myogenesis, adipogenesis, osteogenesis, hepatic lipogenesis, and important brain functions. miRNAs can be modulated by environmental factors or external stimuli, such as physical exercise, and can eventually induce specific and adjusted changes in the transcriptional response. Physical exercise is used as a preventive and non-pharmacological treatment for many diseases. It is well established that physical exercise promotes various benefits in the human body such as muscle hypertrophy, mental health improvement, cellular apoptosis, weight loss, and inhibition of cell proliferation. This review highlights the current knowledge on the main miRNAs altered by exercise in the skeletal muscle, cardiac muscle, bone, adipose tissue, liver, brain, and body fluids. In addition, knowing the modifications induced by miRNAs and relating them to the results of prescribed physical exercise with different protocols and intensities can serve as markers of physical adaptation to training and responses to the effects of physical exercise for some types of chronic diseases. This narrative review consists of randomized exercise training experiments with humans and/or animals, combined with analyses of miRNA modulation.

miR-23a suppression accelerates functional decline in the rNLS8 mouse model of TDP-43 proteinopathy

Skeletal muscle dysfunction may contribute to the progression and severity of amyotrophic lateral sclerosis (ALS). In the present study, we characterized the skeletal muscle pathophysiology in an inducible transgenic mouse model (rNLS8) that develops a TAR-DNA binding protein (TDP-43) proteinopathy and ALS-like neuropathology and disease progression; representative of >90% of all familial and sporadic ALS cases. As we previously observed elevated levels of miR-23a in skeletal muscle of patients with familial and sporadic ALS, we also investigated the effect of miR-23a suppression on skeletal muscle pathophysiology and disease severity in rNLS8 mice. Five weeks after disease onset TDP-43 protein accumulation was observed in tibialis anterior (TA), quadriceps (QUAD) and diaphragm muscle lysates and associated with skeletal muscle atrophy. In the TA muscle TDP-43 was detected in muscle fibres that appeared atrophied and angular in appearance and that also contained β-amyloid aggregates. These fibres were also positive for neural cell adhesion molecule (NCAM), but not embryonic myosin heavy chain (eMHC), indicating TDP-43/ β-amyloid localization in denervated muscle fibres. There was an upregulation of genes associated with myogenesis and NMJ degeneration and a decrease in the MURF1 atrophy-related protein in skeletal muscle. Suppression of miR-23a impaired rotarod performance and grip strength and accelerated body weight loss during early stages of disease progression. This was associated with increased AchRα mRNA expression and decreased protein levels of PGC-1α. The TDP-43 proteinopathy-induced impairment of whole body and skeletal muscle functional performance is associated with muscle wasting and elevated myogenic and NMJ stress markers. Suppressing miR-23a in the rNLS8 mouse model of ALS contributes to an early acceleration of disease progression as measured by decline in motor function.

Effect of immune modulation on the skeletal muscle mitochondrial exercise response: An exploratory study in mice with cancer

Cancer causes mitochondrial alterations in skeletal muscle, which may progress to muscle wasting and, ultimately, to cancer cachexia. Understanding how exercise adaptations are altered by cancer and cancer treatment is important for the effective design of exercise interventions aimed at improving cancer outcomes. We conducted an exploratory study to investigate how tumor burden and cancer immunotherapy treatment (anti-PD-1) modify the skeletal muscle mitochondrial response to exercise training in mice with transplantable tumors (B16-F10 melanoma and EO771 breast cancer). Mice remained sedentary or were provided with running wheels for ~19 days immediately following tumor implant while receiving no treatment (Untreated), isotype control antibody (IgG2a) or anti-PD-1. Exercise and anti-PD-1 did not alter the growth rate of either tumor type, either alone or in combination therapy. Untreated mice with B16-F10 tumors showed increases in most measured markers of skeletal muscle mitochondrial content following exercise training, as did anti-PD-1-treated mice, suggesting increased mitochondrial content following exercise training in these groups. However, mice with B16-F10 tumors receiving the isotype control antibody did not exhibit increased skeletal muscle mitochondrial content following exercise. In untreated mice with EO771 tumors, only citrate synthase activity and complex IV activity were increased following exercise. In contrast, IgG2a and anti-PD-1-treated groups both showed robust increases in most measured markers following exercise. These results indicate that in mice with B16-F10 tumors, IgG2a administration prevents exercise adaptation of skeletal muscle mitochondria, but adaptation remains intact in mice receiving anti-PD-1. In mice with EO771 tumors, both IgG2a and anti-PD-1-treated mice show robust skeletal muscle mitochondrial exercise responses, while untreated mice do not. Taken together, we postulate that immune modulation may enhance skeletal muscle mitochondrial response to exercise in tumor-bearing mice, and suggest this as an exciting new avenue for future research in exercise oncology.

The secret messages between mitochondria and nucleus in muscle cell biology

Over two thousand proteins are found in the mitochondrial compartment but the mitochondrial genome codes for only 13 proteins. The majority of mitochondrial proteins are products of nuclear genes and are synthesized in the cytosol, then translocated into the mitochondria. Most of the subunits of the five respiratory chain complexes in the inner mitochondrial membrane, which generate a proton gradient across the membrane and produce ATP, are encoded by nuclear genes. Therefore, it is quite clear that import of nuclear-encoded proteins into the mitochondria is essential for mitochondrial function. Nuclear to mitochondrial communication is well studied. However, there is another arm to this communication, mitochondria to nucleus retrograde signaling. This plays an important role in the maintenance of cellular homeostasis, and is less well studied. Several transcription factors, including Sp1, SIRT3 and GSP2, are activated by altered mitochondrial function. These activated transcription factors then translocate to the nucleus. Based on the mitochondrially generated molecular signal, nuclear genes are targeted, which alters transcription of nuclear genes that code for mitochondrial proteins. This review article will mainly focus on this interactive and bi-directional communication between mitochondria and nucleus, and how this communication plays a significant role in muscle cell biology.

Loss of microRNA-23-27-24 clusters in skeletal muscle is not influential in skeletal muscle development and exercise-induced muscle adaptation

MicroRNAs are small regulatory noncoding RNAs that repress gene expression at the posttranscriptional level. Previous studies have reported that the expression of miR-23, miR-27, and miR-24, driven from two miR-23–27–24 clusters, is altered by various pathophysiological conditions. However, their functions in skeletal muscle have not been clarified. To define the roles of the miR-23–27–24 clusters in skeletal muscle, we generated double-knockout (dKO) mice muscle-specifically lacking the miR-23–27–24 clusters. The dKO mice were viable and showed normal growth. The contractile and metabolic features of the muscles, represented by the expression of the myosin heavy chain and the oxidative markers PGC1-α and COX IV, were not altered in the dKO mice compared with wild-type mice. The dKO mice showed increased cross-sectional areas of the oxidative fibers. However, this dKO did not induce functional changes in the muscles. The dKO mice also showed normal adaptation to voluntary wheel running for 4 weeks, including the glycolytic-to-oxidative fiber type switch, and increases in mitochondrial markers, succinate dehydrogenase activity, and angiogenesis. In conclusion, our data demonstrate that the miR-23–27–24 clusters have subtle effects on skeletal muscle development and endurance-exercise-induced muscle adaptation.

Fibromyalgia: Genetics and epigenetics insights may provide the basis for the development of diagnostic biomarkers

Fibromyalgia is a disease characterized by chronic widespread pain with additional symptoms, such as joint stiffness, fatigue, sleep disturbance, cognitive dysfunction, and depression. Currently, fibromyalgia diagnosis is based exclusively on a comprehensive clinical assessment, according to 2016 ACR criteria, but validated biological biomarkers associated with fibromyalgia have not yet been identified. Genome-wide association studies investigated genes potentially involved in fibromyalgia pathogenesis highlighting that genetic factors are possibly responsible for up to 50% of the disease susceptibility. Potential candidate genes found associated to fibromyalgia are SLC64A4, TRPV2, MYT1L, and NRXN3. Furthermore, a gene-environmental interaction has been proposed as triggering mechanism, through epigenetic alterations: In particular, fibromyalgia appears to be characterized by a hypomethylated DNA pattern, in genes implicated in stress response, DNA repair, autonomic system response, and subcortical neuronal abnormalities. Differences in the genome-wide expression profile of microRNAs were found among multiple tissues, indicating the involvement of distinct processes in fibromyalgia pathogenesis. Further studies should be dedicated to strength these preliminary findings, in larger multicenter cohorts, to identify reliable directions for biomarker research and clinical practice.

Exercise-induced mitochondrial biogenesis coincides with the expression of mitochondrial translation factors in murine skeletal muscle

The process of mitochondrial translation, in which mitochondrial (mt)DNA-encoded genes are translated into proteins, is crucial for mitochondrial function and biogenesis. In each phase, a series of mitochondrial translation factors is required for the synthesis of mtDNA-encoded mitochondrial proteins. Two mitochondrial initiation factors (mtIF2 and mtIF3), three mitochondrial elongation factors (mtEFTu, mtEFTs, and mtEFG1), one mitochondrial release factor (mtRF1L), and two mitochondrial recycling factors (mtRRF1 and mtRRF2) are mitochondrial translation factors that coordinate each translational phase. Exercise increases both nuclear DNA- and mtDNA-encoded mitochondrial proteins, resulting in mitochondrial biogenesis in skeletal muscles. Therefore, mitochondrial translation factors are likely regulated by exercise; however, it is unclear whether exercise affects mitochondrial translation factors in the skeletal muscles. We investigated whether exercise training comprehensively increases this series of mitochondrial translation factors, as well as mtDNA-encoded proteins, in the skeletal muscle. Mice were randomly assigned to either the sedentary or exercise group and housed in standard cages with or without a running wheel for 1 and 8 weeks. The expression levels of mitochondrial translation factors in the plantaris and soleus muscles were then measured. Exercise training concomitantly upregulated mitochondrial translation factors and mitochondrial proteins in the plantaris muscle. However, in the soleus muscle, these comprehensive upregulations were not detected. These results indicate that exercise-induced mitochondrial biogenesis coincides with the upregulation of mitochondrial translation factors.

miRNA-23a/27a attenuates muscle atrophy and renal fibrosis through muscle-kidney crosstalk

BACKGROUND

The treatment of muscle wasting is accompanied by benefits in other organs, possibly resulting from muscle-organ crosstalk. However, how the muscle communicates with these organs is less understood. Two microRNAs (miRs), miR-23a and miR-27a, are located together in a gene cluster and regulate proteins that are involved in the atrophy process. MiR-23a/27a has been shown to reduce muscle wasting and act as an anti-fibrotic agent. We hypothesized that intramuscular injection of miR-23a/27a would counteract both muscle wasting and renal fibrosis lesions in a streptozotocin-induced diabetic model.

METHODS

We generated an adeno-associated virus (AAV) that overexpresses the miR-23a∼27a∼24-2 precursor RNA and injected it into the tibialis anterior muscle of streptozotocin-induced diabetic mice. Muscle cross-section area (immunohistology plus software measurement) and muscle function (grip strength) were used to evaluate muscle atrophy. Fibrosis-related proteins were measured by western blot to monitor renal damage. In some cases, AAV-GFP was used to mimic the miR movement in vivo, allowing us to track organ redistribution by using the Xtreme Imaging System.

RESULTS

The injection of AAV-miR-23a/27a increased the levels of miR-23a and miR-27a as well as increased phosphorylated Akt, attenuated the levels of FoxO1 and PTEN proteins, and reduced the abundance of TRIM63/MuRF1 and FBXO32/atrogin-1 in skeletal muscles. It also decreased myostatin mRNA and protein levels as well as the levels of phosphorylated pSMAD2/3. Provision of miR-23a/27a attenuates the diabetes-induced reduction of muscle cross-sectional area and muscle function. Curiously, the serum BUN of diabetic animals was reduced in mice undergoing the miR-23a/27a intervention. Renal fibrosis, evaluated by Masson trichromatic staining, was also decreased as were kidney levels of phosphorylated SMAD2/3, alpha smooth muscle actin, fibronectin, and collagen. In diabetic mice injected intramuscularly with AAV-GFP, GFP fluorescence levels in the kidneys showed linear correlation with the levels in injected muscle when examined by linear regression. Following intramuscular injection of AAV-miR-23a∼27a∼24-2, the levels of miR-23a and miR-27a in serum exosomes and kidney were significantly increased compared with samples from control virus-injected mice; however, no viral DNA was detected in the kidney.

CONCLUSIONS

We conclude that overexpression of miR-23a/27a in muscle prevents diabetes-induced muscle cachexia and attenuates renal fibrosis lesions via muscle-kidney crosstalk. Further, this crosstalk involves movement of miR potentially through muscle originated exosomes and serum distribution without movement of AAV. These results could provide new approaches for developing therapeutic strategies for diabetic nephropathy with muscle wasting.

Voluntary exercise slows breast tumor establishment and reduces tumor hypoxia in ApoE-/- mice

Exercise reduces the risk of breast cancer development and improves survival in breast cancer patients. However, the underlying mechanisms of this protective effect remain to be fully elucidated, and it is unclear whether exercise can attenuate the protumor effects of obesity and related hyperlipidemia on breast cancer growth and development. We hypothesized that exercise attenuates the negative effect of hyperlipidemia through normalization of the tumor microenvironment and improved T cell infiltrate. Hyperlipidemic ApoE^-/- mice with orthotopic EO771 breast tumors were randomly assigned to one of two voluntary running groups or sedentary controls, and muscular cytochrome c oxidase subunit IV (COX-IV) expression was used as a biomarker for the level of exercise. Tumors from mice with high muscular COX-IV expression took significantly longer to reach 100 mm³ ( P = 0.008), but showed no difference in growth rate once the tumor was established. Wheel running appeared to reduce internal metastases, but did not affect T cell infiltrate or the proportion of regulatory and cytotoxic T cells within the tumor. Serum levels of monocyte chemoattractant protein-1 (MCP-1) were significantly increased by tumor burden ( P = 0.02) and correlated with spleen weight ( P < 0.0001, R = 0.65). Furthermore, tumor hypoxia was significantly decreased in mice with high muscular COX-IV expression ( P = 0.01). Taken together, these results indicate that wheel running can slow the establishment of primary and secondary EO771 breast tumors and induce beneficial changes in the breast tumor microenvironment in ApoE^-/- mice. NEW & NOTEWORTHY In this first study to investigate the effect of exercise on tumor behavior in a hyperlipidemic model, we hypothesized that wheel running would counteract the protumorigenic environment generated by hyperlipidemia. Wheel running slowed establishment of primary and secondary tumors and reduced tumor hypoxia but did not affect exponential tumor growth in ApoE^-/- mice. Overall, voluntary wheel running induced favorable microenvironmental changes in breast tumors.

Circulating microRNA Profiles as Liquid Biopsies for the Characterization and Diagnosis of Fibromyalgia Syndrome

This work was aimed at investigating the circulating microRNA (miRNA) profiles in serum and saliva of patients affected by fibromyalgia syndrome (FM), correlating their expression values with clinical and clinimetric parameters and to suggest a mathematical model for the diagnosis of FM. A number of 14 FM patients and sex- and age-matched controls were enrolled in our study. The expression of a panel of 179 miRNAs was evaluated by qPCR. Statistical analyses were performed in order to obtain a mathematical linear model, which could be employed as a supporting tool in the diagnosis of FM. Bioinformatics analysis on miRNA targets were performed to obtain the relevant biological processes related to FM syndrome and to characterize in details the disease. Six miRNAs were found downregulated in FM patients compared to controls. Five of these miRNAs have been included in a linear predictive model that reached a very high sensitivity (100 %) and a high specificity (83.3 %). Moreover, miR-320b displayed a significant negative correlation (r = -0.608 and p = 0.036) with ZSDS score. Finally, several biological processes related to brain function/development and muscular functions were found potentially implicated in FM syndrome. Our study suggests that the study of circulating miRNA profiles coupled to statistical and bioinformatics analyses is a useful tool to better characterize the FM syndrome and to propose a preliminary model for its diagnosis.

Skeletal Muscle Satellite Cells, Mitochondria, and MicroRNAs: Their Involvement in the Pathogenesis of ALS

Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND), is a fatal motor neuron disorder. It results in progressive degeneration and death of upper and lower motor neurons, protein aggregation, severe muscle atrophy and respiratory insufficiency. Median survival with ALS is between 2 and 5 years from the onset of symptoms. ALS manifests as either familial ALS (FALS) (~10% of cases) or sporadic ALS (SALS), (~90% of cases). Mutations in the copper/zinc (CuZn) superoxide dismutase (SOD1) gene account for ~20% of FALS cases and the mutant SOD1 mouse model has been used extensively to help understand the ALS pathology. As the precise mechanisms causing ALS are not well understood there is presently no cure. Recent evidence suggests that motor neuron degradation may involve a cell non-autonomous phenomenon involving numerous cell types within various tissues. Skeletal muscle is now considered as an important tissue involved in the pathogenesis of ALS by activating a retrograde signaling cascade that degrades motor neurons. Skeletal muscle heath and function are regulated by numerous factors including satellite cells, mitochondria and microRNAs. Studies demonstrate that in ALS these factors show various levels of dysregulation within the skeletal muscle. This review provides an overview of their dysregulation in various ALS models as well as how they may contribute individually and/or synergistically to the ALS pathogenesis.

Impaired exercise tolerance, mitochondrial biogenesis, and muscle fiber maintenance in miR-133a-deficient mice

Exercise promotes multiple beneficial effects on muscle function, including induction of mitochondrial biogenesis. miR-133a is a muscle-enriched microRNA that regulates muscle development and function. The role of miR-133a in exercise tolerance has not been fully elucidated. In the current study, mice that were deficient in miR-133a demonstrated low maximal exercise capacity and low resting metabolic rate. Transcription of the mitochondrial biogenesis regulators peroxisome proliferator-activated receptor-γ coactivator 1-α, peroxisome proliferator-activated receptor-γ coactivator 1-β, nuclear respiratory factor-1, and transcription factor A, mitochondrial were lower in miR-133a-deficient muscle, which was consistent with lower mitochondrial mass and impaired exercise capacity. Six weeks of endurance exercise training increased the transcriptional level of miR-133a and stimulated mitochondrial biogenesis in wild-type mice, but failed to improve mitochondrial function in miR-133a-deficient mice. Further mechanistic analysis showed an increase in the miR-133a potential target, IGF-1 receptor, along with hyperactivation of Akt signaling, in miR-133a-deficient mice, which was consistent with lower transcription of the mitochondrial biogenesis regulators. These findings indicate an essential role of miR-133a in skeletal muscle mitochondrial biogenesis, exercise tolerance, and response to exercise training.-Nie, Y., Sato, Y., Wang, C., Yue, F., Kuang, S., Gavin, T. P. Impaired exercise tolerance, mitochondrial biogenesis, and muscle fiber maintenance in miR-133a-deficient mice.