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Loss of strength in human and animal models of aging can be partially attributed to a well-recognized decrease in muscle mass; however, starting at middle-age, the normalized force (force/muscle cross-sectional area) in the knee extensors and single muscle fibers declines in a curvilinear manner. Strength is lost faster than muscle mass and is a more consistent risk factor for disability and death. Reduced expression of the voltage sensor Ca2+ channel α1 subunit (Cav1.1) with aging leads to excitation-contraction uncoupling, which accounts for a significant fraction of the decrease in skeletal muscle function. We recently reported that in addition to its classical cytoplasmic location, fast skeletal muscle troponin T3 (TnT3) is fragmented in aging mice, and both full-length TnT3 (FL-TnT3) and its carboxyl-terminal (CT-TnT3) fragment shuttle to the nucleus. Here, we demonstrate that it regulates transcription of Cacna1s, the gene encoding Cav1.1. Knocking down TnT3 in vivo downregulated Cav1.1. TnT3 downregulation or overexpression decreased or increased, respectively, Cacna1s promoter activity , and the effect was ablated by truncating the TnT3 nuclear localization sequence. Further, we mapped the Cacna1s promoter region and established the consensus sequence for TnT3 binding to Cacna1s promoter. Systemic administration of BDA-410, a specific calpain inhibitor, prevented TnT3 fragmentation, and Cacna1s and Cav1.1 downregulation and improved muscle force generation in sedentary old mice. [ABSTRACT FROM AUTHOR]

The voltage-gated calcium channel (Ca v ) β 1a subunit (Ca v β 1a ) plays an important role in excitation–contraction coupling (ECC), a process in the myoplasm that leads to muscle-force generation. Recently, we discovered that the Ca v β 1a subunit travels to the nucleus of skeletal muscle cells where it helps to regulate gene transcription. To determine how it travels to the nucleus, we performed a yeast two-hybrid screening of the mouse fast skeletal muscle cDNA library and identified an interaction with troponin T3 (TnT3), which we subsequently confirmed by co-immunoprecipitation and co-localization assays in mouse skeletal muscle in vivo and in cultured C2C12 muscle cells. Interacting domains were mapped to the leucine zipper domain in TnT3 COOH-terminus (160–244 aa) and Ca v β 1a NH 2 -terminus (1–99 aa), respectively. The double fluorescence assay in C2C12 cells co-expressing TnT3/DsRed and Ca v β 1a /YFP shows that TnT3 facilitates Ca v β 1a nuclear recruitment, suggesting that the two proteins play a heretofore unknown role during early muscle differentiation in addition to their classical role in ECC regulation. [ABSTRACT FROM AUTHOR]

Regular exercise, particularly resistance training (RT), is the only therapy known to consistently improve muscle strength and quality (force per unit of mass) in older persons, but there is considerable variability in responsiveness to training. Identifying sensitive diagnostic biomarkers of responsiveness to RT may inform the design of a more efficient exercise regimen to improve muscle strength in older adults. MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression. We quantified six muscle specific miRNAs (miR-1, -133a, -133b, -206, -208b and -499) in both muscle tissue and blood plasma, and their relationship with knee extensor strength in seven older (age = 70.5 ± 2.5 years) adults before and after 5 months of RT. MiRNAs differentially responded to RT; muscle miR-133b decreased, while all plasma miRNAs tended to increase. Percent changes in knee extensor strength with RT showed strong positive correlations with percent changes in muscle miR-133a, -133b, and -206 and with percent changes in plasma and plasma/muscle miR-499 ratio. Baseline level of plasma or plasma/muscle miR-499 ratio further predicts muscle response to RT, while changes in muscle miR-133a, -133b, and -206 may correlate with muscle TNNT1 gene alternative splicing in response to RT. Our results indicate that RT alters muscle specific miRNAs in muscle and plasma, and that these changes account for some of the variation in strength responses to RT in older adults. [ABSTRACT FROM AUTHOR]

Slow skeletal muscle troponin T (TNNT1) pre-messenger RNA alternative splicing (AS) provides transcript diversity and increases the variety of proteins the gene encodes. Here, we identified three major TNNT1 splicing patterns (AS1–3), quantified their expression in the vastus lateralis muscle of older adults, and demonstrated that resistance training modifies their relative abundance; specifically, upregulating AS1 and downregulating AS2 and AS3. In addition, abundance of TNNT1 AS2 correlated negatively with single muscle fiber–specific force after resistance training, while abundance of AS1 correlated negatively with Vmax. We propose that TNNT1 AS1, AS2 and the AS1/AS2 ratio are potential quantitative biomarkers of skeletal muscle adaptation to resistance training in older adults, and that their profile reflects enhanced single fiber muscle force in the absence of significant increases in fiber cross-sectional area. [ABSTRACT FROM PUBLISHER]

Objective. Posttransplantation diabetes mellitus (PTDM) is a known complication of transplantation that affects the prognosis. Tacrolimus (Tac or FK506) is a widely used immunosuppressant that has been reported to be a risk factor for PTDM and to further induce complications in heart and skeletal muscles, but the mechanism is still largely unknown. In our preliminary experiments, we found that after Tac treatment, blood glucose increased, and the weight of skeletal muscle declined. Here, we hypothesize that tacrolimus can induce PTDM and influence the atrophy of skeletal muscle. Methods. We designed preliminary experiments to establish a tacrolimus-induced PTDM model. Gene expression profiles in quadriceps muscle from this rat model were characterized by oligonucleotide microarrays. Then, differences in gene expression profiles in muscle from PTDM rats that received tacrolimus and control subjects were analyzed by using GeneSpring GX 11.0 software (Agilent). Functional annotation and enrichment analysis of differentially expressed genes (DEGs) helped us identify clues for the side effects of tacrolimus. Results. Our experiments found that the quadriceps in tacrolimus-induced PTDM group were smaller than those in the control group. The study identified 275 DEGs that may be responsible for insulin resistance and the progression of PTDM, including 86 upregulated genes and 199 downregulated genes. GO and KEGG functional analysis of the DEGs showed a significant correlation between PTDM and muscle development. PPI network analysis screened eight hub genes and found that they were related to troponin and tropomyosin. Conclusions. This study explored the molecular mechanism of muscle atrophy in a tacrolimus-induced PTDM model by bioinformatics analyses. We identified 275 DEGs and identified significant biomarkers for predicting the development and progression of tacrolimus-induced PTDM. [ABSTRACT FROM AUTHOR]

We recently reported that in addition to its classical cytoplasmic location, the fast skeletal muscle Troponin T3 (TnT3) shuttles to the nucleus, where it appears to perform nonclassical transcription regulatory functions. Importantly, changes in the composition of the nucleus-localized pool of TnT3 and its fragments contribute to age-dependent muscle damage and wasting. Here, using ChIP-Seq, we demonstrate that TnT3 associates with DNA consensus sequences including the TGCCT motif, which is required for p53 binding to the promoter area of p53-related genes. Gene set enrichment analysis further demonstrated that the p53 pathway was the most significantly enriched pathway among genes annotated to the TnT3 ChIP-Seq peaks. We further demonstrated a strong correlation ( r  = 0.78, P  = 1 × 10 −4 ) between the expression levels of TNNT3 and TP53-inducible ribonucleotide reductase regulatory subunit M2B (RRM2B) in skeletal muscle tissue of 21 lean non-diabetic human subjects and a significant ( P  < 0.05) reduction in the levels of both gene transcripts in the third age-tertile group [42.3–70 years of age (yoa)] as compared to the second age-tertile (31.3–42.3 yoa). Of note, both TNNT3 and RRM2B expression levels negatively associated with total body fat mass (each with r  = 0.49, P  < 0.05), whereas RRM2B positively correlated with pancreatic β cell function (r RRM2B~HOMA-B  = 0.47, P  = 0.047). This work suggests that reduced TNNT3 gene expression is another mechanism leading to reduced TnT3 and excitation-contraction coupling with aging. Consequently, TnT3 appears to contribute to age-related sarcopenia and possibly other age-related deficiencies such as muscle insulin resistance and β cell dysfunction by interacting with TnT3-binding sequences in the promoter area of p53-related genes, among others, and consequently modulating the transcriptional regulation of these target genes. [ABSTRACT FROM AUTHOR]

Loss of muscle mass and force with age leads to fall risk, mobility impairment, and reduced quality of life. This article shows that BDA-410, a calpain inhibitor, induced loss of body weight and fat but not lean mass or skeletal muscle proteins in a cohort of sedentary 23-month-old mice. Food and water intake and locomotor activity were not modified, whereas BDA-410 treatment decreased intramyocellular lipid and perigonadal fat, increased serum nonesterified fatty acids, and upregulated the genes mediating lipolysis and oxidation, lean phenotype, muscle contraction, muscle transcription regulation, and oxidative stress response. This finding is consistent with our recent report that lipid accumulation in skeletal myofibers is significantly correlated with slower fiber-contraction kinetics and diminished power in obese older adult mice. A proteomic analysis and immunoblot showed downregulation of the phosphatase PPP1R12B, which increases phosphorylated myosin half-life and modulates the calcium sensitivity of the contractile apparatus. This study demonstrates that BDA-410 exerts a beneficial effect on skeletal muscle contractility through new, alternative mechanisms, including enhanced lipolysis, upregulation of "lean phenotype-related genes," downregulation of the PP1R12B phosphatase, and enhanced excitation-contraction coupling. This single compound holds promise for treating age-dependent decline in muscle composition and strength. [ABSTRACT FROM AUTHOR]

Aim: Symptoms of autonomic failure are frequently the presentation of advanced age and neurodegenerative diseases that impair adaptation to common physiologic stressors. The aim of this work was to examine the interaction between the sympathetic and motor nervous system, the involvement of the sympathetic nervous system (SNS) in neuromuscular junction (NMJ) presynaptic motor function, the stability of postsynaptic molecular organization, and the skeletal muscle composition and function. Methods: Since muscle weakness is a symptom of diseases characterized by autonomic dysfunction, we studied the impact of regional sympathetic ablation on muscle motor innervation by using transcriptome analysis, retrograde tracing of the sympathetic outflow to the skeletal muscle, confocal and electron microscopy, NMJ transmission by electrophysiological methods, protein analysis, and state of the art microsurgical techniques, in C57BL6, MuRF1KO and Thy‐1 mice. Results: We found that the SNS regulates motor nerve synaptic vesicle release, skeletal muscle transcriptome, muscle force generated by motor nerve activity, axonal neurofilament phosphorylation, myelin thickness, and myofibre subtype composition and CSA. The SNS also modulates the levels of postsynaptic membrane acetylcholine receptor by regulating the Gαi2‐Hdac4‐Myogenin‐MuRF1pathway, which is prevented by the overexpression of the guanine nucleotide‐binding protein Gαi2 (Q205L), a constitutively active mutant G protein subunit. Conclusion: The SNS regulates NMJ transmission, maintains optimal Gαi2 expression, and prevents any increase in Hdac4, myogenin, MuRF1, and miR‐206. SNS ablation leads to upregulation of MuRF1, muscle atrophy, and downregulation of postsynaptic AChR. Our findings are relevant to clinical conditions characterized by progressive decline of sympathetic innervation, such as neurodegenerative diseases and aging. [ABSTRACT FROM AUTHOR]