Acute Microbial Protease Supplementation Increases Net Postprandial Plasma Amino Acid Concentrations After Pea Protein Ingestion in Healthy Adults: A Randomized, Double-Blind, Placebo-Controlled Trial.

BACKGROUND: Digestibility is a primary factor in determining the quality of dietary protein. Microbial protease supplementation may be a strategy for improving protein digestion and subsequent postprandial plasma amino acid availability. OBJECTIVES: To assess the effect of co-ingesting a microbial protease mixture with pea protein on postprandial plasma amino acid concentrations. DESIGN: A mixture of 3 microbial protease preparations (P3) was tested for proteolytic efficacy in an in vitro static simulation of gastrointestinal digestion. Subsequently, in a randomized, double-blind, placebo-controlled crossover trial, 24 healthy adults (27 ± 4 y; 12 females, 12 males) ingested 25 g pea protein isolate (20 g protein, 2.2 g fat) with either P3 or maltodextrin placebo (PLA). Blood samples were collected at baseline and throughout a 0‒5 h postprandial period and both the early (0-2 h) iAUC and total (0-5 h) iAUC were examined. RESULTS: Plasma glucose concentrations decreased in both conditions (P < 0.001), with higher concentrations after P3 ingestion compared with PLA (P < 0.001). Plasma insulin concentrations increased for both conditions (P < 0.001) with no difference between conditions (P = 0.331). Plasma total amino acid (TAA) concentrations increased over time (P < 0.001) with higher concentrations observed for P3 compared with PLA (P = 0.010) during the 0‒5 h period. There was a trend for elevated essential amino acid (EAA) concentrations for P3 compared with PLA (P = 0.099) during the 0‒5 h postprandial period but not for leucine (P = 0.282) or branched-chain amino acids (BCAA, P = 0.410). The early net exposure (0‒2 h iAUC) to amino acids (leucine, BCAA, EAA, and TAA) was higher for P3 compared with PLA (all, P < 0.05). CONCLUSIONS: Microbial protease co-ingestion increases plasma TAA concentrations (0-5 h) and leucine, BCAA, EAA, and TAA availability in the early postprandial period (0‒2 h) compared with ingesting pea protein with placebo in healthy adults.

Dietary fish oil supplement induces age-specific contractile and proteomic responses in muscles of male rats.

BACKGROUND: Dietary fish oil (DFO) has been identified as a micronutrient supplement with the potential to improve musculoskeletal health in old age. Few data are available for effects of DFO on muscle contractility, despite the significant negative impact of muscle weakness on age-related health outcomes. Accordingly, the effects of a DFO intervention on the contractile function and proteomic profile of adult and aged in an animal model of aging were investigated. METHODS: This preliminary study evaluated 14 adult (8 months) and 12 aged (22 months) male, Sprague-Dawley rats consuming a DFO-supplemented diet or a control diet for 8 weeks (7 adult and 6 aged/dietary group). Animal weight, food intake and grip strength were assessed at the start and end of the FO intervention. In situ force and contractile properties were measured in the medial gastrocnemius muscle following the intervention and muscles were processed for 2-D gel electrophoresis and proteomic analysis via liquid chromatography with tandem mass spectrometry, confirmed by immunoblotting. Effects of age, diet and age x diet interaction were evaluated by 2-way ANOVA. RESULTS: A significant (P = 0.022) main effect for DFO to increase (~ 15%) muscle contractile force was observed, without changes in muscle mass. Proteomic analysis revealed a small number of proteins that differed across age and dietary groups at least 2-fold, most of which related to metabolism and oxidative stress. In seven of these proteins (creatine kinase, triosephosphate isomerase, pyruvate kinase, parvalbumin, beta-enolase, NADH dehydrogenase and Parkin7/DJ1), immunoblotting corroborated these findings. Parvalbumin showed only an effect of diet (increased with DFO) (P = 0.003). Significant age x diet interactions were observed in the other proteins, generally demonstrating increased expression in adult and decreased expression aged rats consuming DFO (all P > 0.011). However, correlational analyses revealed no significant associations between contractile parameters and protein abundances. CONCLUSIONS: Results of this preliminary study support the hypothesis that DFO can enhance musculoskeletal health in adult and aged muscles, given the observed improvement in contractile function. The fish oil supplement also alters protein expression in an age-specific manner, but the relationship between proteomic and contractile responses remains unclear. Further investigation to better understand the magnitude and mechanisms muscular effects of DFO in aged populations is warranted.

Metabolomic profiling reveals severe skeletal muscle group-specific perturbations of metabolism in aged FBN rats.

Mammalian skeletal muscles exhibit age-related adaptive and pathological remodeling. Several muscles in particular undergo progressive atrophy and degeneration beyond median lifespan. To better understand myocellular responses to aging, we used semi-quantitative global metabolomic profiling to characterize trends in metabolic changes between 15-month-old adult and 32-month-old aged Fischer 344 × Brown Norway (FBN) male rats. The FBN rat gastrocnemius muscle exhibits age-dependent atrophy, whereas the soleus muscle, up until 32 months, exhibits markedly fewer signs of atrophy. Both gastrocnemius and soleus muscles were analyzed, as well as plasma and urine. Compared to adult gastrocnemius, aged gastrocnemius showed evidence of reduced glycolytic metabolism, including accumulation of glycolytic, glycogenolytic, and pentose phosphate pathway intermediates. Pyruvate was elevated with age, yet levels of citrate and nicotinamide adenine dinucleotide were reduced, consistent with mitochondrial abnormalities. Indicative of muscle atrophy, 3-methylhistidine and free amino acids were elevated in aged gastrocnemius. The monounsaturated fatty acids oleate, cis-vaccenate, and palmitoleate also increased in aged gastrocnemius, suggesting altered lipid metabolism. Compared to gastrocnemius, aged soleus exhibited far fewer changes in carbohydrate metabolism, but did show reductions in several glycolytic intermediates, fumarate, malate, and flavin adenine dinucleotide. Plasma biochemicals showing the largest age-related increases included glycocholate, heme, 1,5-anhydroglucitol, 1-palmitoleoyl-glycerophosphocholine, palmitoleate, and creatine. These changes suggest reduced insulin sensitivity in aged FBN rats. Altogether, these data highlight skeletal muscle group-specific perturbations of glucose and lipid metabolism consistent with mitochondrial dysfunction in aged FBN rats.

Genetic and Phenotypic Characterization of Bacillus velezensis Strain BV379 for Human Probiotic Applications.

Bacterial spore-forming Bacillaceae species, including Bacillus subtilis and Heyndrickxia coagulans, are increasingly utilized for probiotic dietary supplementation. Bacillus velezensis is a Bacillus species that is frequently used as a direct-fed microbial in animal feed but less so as a probiotic for humans. The objective of this study was to characterize the suitability of the Bacillus velezensis strain BV379 for probiotic applications by (1) in silico screening for both adverse genetic elements and putatively beneficial traits, (2) in vitro evaluation of interactions with human intestinal epithelial cells, and (3) in vitro characterization of BV379 spore viability at various temperatures, pH, and in the presence of bile salt. In silico screening of the BV379 genome revealed few genes encoding Bacillaceae-associated toxins, virulence factors, and enzymes involved in the production of toxins. While BV379 encodes five antimicrobial resistance genes, minimum inhibitory concentration assays determined that BV379 is susceptible to all eight clinically relevant antibiotics tested. Preliminary cell culture experiments showed that BV379 lysates did not adversely impact human intestinal epithelial cell viability and monolayer permeability. It was also determined that BV379 spores can easily tolerate the harsh pH, bile salt, and microaerobic conditions typical of the GI tract. Altogether, the results presented herein support the safety and potential of Bacillus velezensis strain BV379 for use as an oral probiotic.

Deficiency of α-actinin-3 is associated with increased susceptibility to contraction-induced damage and skeletal muscle remodeling.

Sarcomeric α-actinins (α-actinin-2 and -3) are a major component of the Z-disk in skeletal muscle, where they crosslink actin and other structural proteins to maintain an ordered myofibrillar array. Homozygosity for the common null polymorphism (R577X) in ACTN3 results in the absence of fast fiber-specific α-actinin-3 in ∼20% of the general population. α-Actinin-3 deficiency is associated with decreased force generation and is detrimental to sprint and power performance in elite athletes, suggesting that α-actinin-3 is necessary for optimal forceful repetitive muscle contractions. Since Z-disks are the structures most vulnerable to eccentric damage, we sought to examine the effects of α-actinin-3 deficiency on sarcomeric integrity. Actn3 knockout mouse muscle showed significantly increased force deficits following eccentric contraction at 30% stretch, suggesting that α-actinin-3 deficiency results in an increased susceptibility to muscle damage at the extremes of muscle performance. Microarray analyses demonstrated an increase in muscle remodeling genes, which we confirmed at the protein level. The loss of α-actinin-3 and up-regulation of α-actinin-2 resulted in no significant changes to the total pool of sarcomeric α-actinins, suggesting that alterations in fast fiber Z-disk properties may be related to differences in functional protein interactions between α-actinin-2 and α-actinin-3. In support of this, we demonstrated that the Z-disk proteins, ZASP, titin and vinculin preferentially bind to α-actinin-2. Thus, the loss of α-actinin-3 changes the overall protein composition of fast fiber Z-disks and alters their elastic properties, providing a mechanistic explanation for the loss of force generation and increased susceptibility to eccentric damage in α-actinin-3-deficient individuals.

Slack length reduces the contractile phenotype of the Swine carotid artery.

Contraction is the primary function of adult arterial smooth muscle. However, in response to vessel injury or inflammation, arterial smooth muscle is able to phenotypically modulate from the contractile state to several 'synthetic' states characterized by proliferation, migration and/or increased cytokine secretion. We examined the effect of tissue length (L) on the phenotype of intact, isometrically held, initially contractile swine carotid artery tissues. Tissues were studied (1) without prolonged incubation at the optimal length for force generation (1.0 Lo, control), (2) with prolonged incubation for 17 h at 1.0 Lo, or (3) with prolonged incubation at slack length (0.6 Lo) for 16 h and then restoration to 1.0 Lo for 1 h. Prolonged incubation at 1.0 Lo minimally reduced the contractile force without substantially altering the mediators of contraction (crossbridge phosphorylation, shortening velocity or stimulated actin polymerization). Prolonged incubation of tissues at slack length (0.6 Lo), despite return of length to 1.0 Lo, substantially reduced contractile force, reduced crossbridge phosphorylation, nearly abolished crossbridge cycling (shortening velocity) and abolished stimulated actin polymerization. These data suggest that (1) slack length treatment significantly alters the contractile phenotype of arterial tissue, and (2) slack length treatment is a model to study acute phenotypic modulation of intact arterial smooth muscle.

Microbial inulinase promotes fructan hydrolysis under simulated gastric conditions.

Fermentable oligo-, di-, monosaccharides and polyols (FODMAPs) have emerged as key contributors to digestive discomfort and intolerance to certain vegetables, fruits, and plant-based foods. Although strategies exist to minimize FODMAP consumption and exposure, exogenous enzyme supplementation targeting the fructan-type FODMAPs has been underexploited. The objective of this study was to test the hydrolytic efficacy of a food-grade, non-genetically engineered microbial inulinase preparation toward inulin-type fructans in the INFOGEST in vitro static simulation of gastrointestinal (GI) digestion. Purified inulin was shown to undergo acid-mediated hydrolysis at high gastric acidity as well as predominantly inulinase-mediated hydrolysis at lower gastric acidity. Inulinase dose-response simulations of inulin, garlic, and high-fructan meal digestion in the gastric phase suggest that as little as 50 inulinase units (INU) and up to 800 INU per serving promote fructan hydrolysis better than the control simulations without inulinase. Liquid chromatography-mass spectrometry (LC-MS) profiling of fructo-oligosaccharides (FOS) in the gastric digestas following inulinase treatment confirms the fructolytic activity of inulinase under simulated digestive conditions. Altogether, these in vitro digestion data support the use of microbial inulinase as an exogenous enzyme supplement for reducing dietary fructan-type FODMAP exposure.

The Probiotic Bacillus subtilis MB40 Improves Immunity in a Porcine Model of Listeriosis.

Probiotics for humans and direct-fed microbials for livestock are increasingly popular dietary ingredients for supporting immunity. The aim of this study was to determine the effects of dietary supplementation of Bacillus subtilis MB40 (MB40) on immunity in piglets challenged with the foodborne pathogen Listeria monocytogenes (LM). Three-week-old piglets (n = 32) were randomly assigned to four groups: (1) basal diet, (2) basal diet with LM challenge, (3) MB40-supplemented diet, and (4) MB40-supplemented diet with LM challenge. Experimental diets were provided throughout a 14-day (d) period. On d8, piglets in groups 2 and 4 were intraperitoneally inoculated with LM at 108 CFU/mL per piglet. Blood samples were collected at d1, d8, and d15 for biochemical and immune response profiling. Animals were euthanized and necropsied at d15 for liver and spleen bacterial counts and intestinal morphological analysis. At d15, LM challenge was associated with increased spleen weight (p = 0.017), greater circulating populations of neutrophils (p = 0.001) and monocytes (p = 0.008), and reduced ileal villus height to crypt depth ratio (p = 0.009), compared to non-challenged controls. MB40 supplementation reduced LM bacterial counts in the liver and spleen by 67% (p < 0.001) and 49% (p < 0.001), respectively, following the LM challenge, compared to the basal diet. MB40 supplementation was also associated with decreased circulating concentrations of monocytes (p = 0.007). Altogether, these data suggest that MB40 supplementation is a safe and well-tolerated approach to enhance immunity during systemic Listeria infection.

Integrative genomics identifies DSCR1 (RCAN1) as a novel NFAT-dependent mediator of phenotypic modulation in vascular smooth muscle cells.

Vascular smooth muscle cells (SMCs) display remarkable phenotypic plasticity in response to environmental cues. The nuclear factor of activated T-cells (NFAT) family of transcription factors plays a critical role in vascular pathology. However, known functional NFAT gene targets in vascular SMCs are currently limited. Publicly available whole-genome expression array data sets were analyzed to identify differentially expressed genes in human, mouse and rat SMCs. Comparison between vehicle and phenotypic modulatory stimuli identified 63 species-conserved, upregulated genes. Integration of the 63 upregulated genes with an in silico NFAT-ome (a species-conserved list of gene promoters containing at least one NFAT binding site) identified 18 putative NFAT-dependent genes. Further intersection of these 18 potential NFAT target genes with a mouse in vivo vascular injury microarray identified four putative NFAT-dependent, injury-responsive genes. In vitro validations substantiated the NFAT-dependent role of Cyclooxygenase 2 (COX2/PTGS2) in SMC phenotypic modulation and uncovered Down Syndrome Candidate Region 1 (DSCR1/RCAN1) as a novel NFAT target gene in SMCs. We show that induction of DSCR1 inhibits calcineurin/NFAT signaling through a negative feedback mechanism; DSCR1 overexpression attenuates NFAT transcriptional activity and COX2 protein expression, whereas knockdown of endogenous DSCR1 enhances NFAT transcriptional activity. Our integrative genomics approach illustrates how the combination of publicly available gene expression arrays, computational databases and empirical research methods can answer specific questions in any cell type for a transcriptional network of interest. Herein, we report DSCR1 as a novel NFAT-dependent, injury-inducible, early gene that may serve to negatively regulate SMC phenotypic switching.

Autosomal-dominant distal myopathy associated with a recurrent missense mutation in the gene encoding the nuclear matrix protein, matrin 3.

Distal myopathies represent a heterogeneous group of inherited skeletal muscle disorders. One type of adult-onset, progressive autosomal-dominant distal myopathy, frequently associated with dysphagia and dysphonia (vocal cord and pharyngeal weakness with distal myopathy [VCPDM]), has been mapped to chromosome 5q31 in a North American pedigree. Here, we report the identification of a second large VCPDM family of Bulgarian descent and fine mapping of the critical interval. Sequencing of positional candidate genes revealed precisely the same nonconservative S85C missense mutation affecting an interspecies conserved residue in the MATR3 gene in both families. MATR3 is expressed in skeletal muscle and encodes matrin 3, a component of the nuclear matrix, which is a proteinaceous network that extends throughout the nucleus. Different disease related haplotype signatures in the two families provided evidence that two independent mutational events at the same position in MATR3 cause VCPDM. Our data establish proof of principle that the nuclear matrix is crucial for normal skeletal muscle structure and function and put VCPDM on the growing list of monogenic disorders associated with the nuclear proteome.

Genome-wide microarray analyses identify the protein C receptor as a novel calcineurin/nuclear factor of activated T cells-dependent gene in vascular smooth muscle cell phenotypic modulation.

OBJECTIVE: Calcineurin (Cn) and the nuclear factor of activated T cells (NFAT) family of transcription factors are critical in vascular smooth muscle cell (SMC) development and pathology. Here, we used a genomics approach to identify and validate NFAT gene targets activated during platelet-derived growth factor-BB (PDGF-BB)-induced SMC phenotypic modulation. METHODS AND RESULTS: Genome-wide expression arrays were used to identify genes both (1) differentially activated in response to PDGF-BB and (2) whose differential expression was reduced by both the Cn inhibitor cyclosporin A and the NFAT inhibitor A-285222. The 20 most pharmacologically sensitive genes were validated by quantitative reverse transcription-polymerase chain reaction analysis of PDGF-BB-stimulated SMCs in the presence of Cn/NFAT inhibitors, including the VIVIT peptide. In all experiments, protein C receptor (PROCR) gene activation was reduced. We showed that PROCR expression was virtually absent in untreated, quiescent SMCs. PDGF-BB stimulation, however, induced significant PROCR promoter activation and downstream protein expression in a Cn/NFAT-dependent manner. Mutation of a species-conserved, NFAT binding motif significantly attenuated PDGF-BB-induced PROCR promoter activity, thereby distinguishing NFAT as the first PROCR transcriptional activator to date. Moreover, SMC PROCR expression was upregulated in the neointima as early as 7 days following acute vascular injury in rat carotid arteries. CONCLUSION: We hereby report PROCR as a novel, NFAT-dependent gene that may be implicated in vascular restenosis and consequent inward remodeling.

Preclinical Safety Assessment of Bacillus subtilis BS50 for Probiotic and Food Applications.

Despite the commercial rise of probiotics containing Bacillaceae spp., it remains important to assess the safety of each strain before clinical testing. Herein, we performed preclinical analyses to address the safety of Bacillus subtilis BS50. Using in silico analyses, we screened the 4.15 Mbp BS50 genome for genes encoding known Bacillus toxins, secondary metabolites, virulence factors, and antibiotic resistance. We also assessed the effects of BS50 lysates on the viability and permeability of cultured human intestinal epithelial cells (Caco-2). We found that the BS50 genome does not encode any known Bacillus toxins. The BS50 genome contains several gene clusters involved in the biosynthesis of secondary metabolites, but many of these antimicrobial metabolites (e.g., fengycin) are common to Bacillus spp. and may even confer health benefits related to gut microbiota health. BS50 was susceptible to seven of eight commonly prescribed antibiotics, and no antibiotic resistance genes were flanked by the complete mobile genetic elements that could enable a horizontal transfer. In cell culture, BS50 cell lysates did not diminish either Caco-2 viability or monolayer permeability. Altogether, BS50 exhibits a robust preclinical safety profile commensurate with commercial probiotic strains and likely poses no significant health risk to humans.

Fungal digestive enzymes promote macronutrient hydrolysis in the INFOGEST static in vitro simulation of digestion.

The objective of this study was to test the hydrolytic efficacy of 6 fungal enzymes in the INFOGEST static in vitro simulation of gastrointestinal (GI) digestion. First, the INFOGEST protocol was adapted for testing of exogenous enzymes. Second, a dose-response study of 3 individual fungal proteases, a lipase, and an amylase with glucoamylase demonstrated improved dietary protein, lipid, and carbohydrate hydrolysis, respectively, from an oral nutritional supplement (ONS) under simulated gastric or GI conditions, compared to pepsin and pancreatin-based control conditions. Third, a combination of the 6 enzymes (BC-006) improved macronutrient digestion, including enhanced release of individual amino acids from ONS and mixed meal substrates. Finally, we validated digestive models of aging and proton pump inhibitor (PPI) use, and showed that BC-006 improved gastric digestion under these compromised digestive conditions. The INFOGEST static simulation is a feasible tool to rapidly screen and profile exogenous enzymes for digestive efficacy in vitro.

The probiotic Bacillus subtilis BS50 decreases gastrointestinal symptoms in healthy adults: a randomized, double-blind, placebo-controlled trial

Abstract: Durable spore-forming probiotics are increasingly formulated into foods, beverages, and dietary supplements. To help meet this demand, the safety and efficacy of daily supplementation of Bacillus subtilis BS50 for 6 weeks was investigated in a randomized, double-blind, placebo-controlled, parallel clinical trial of 76 healthy adults. Before and during supplementation, gastrointestinal symptoms were recorded daily using a multi-symptom questionnaire. Clinical chemistry, hematology, plasma lipids, and intestinal permeability and inflammation markers were measured at baseline and end of study. Compared to placebo, 2 × 109 colony-forming units (CFU) BS50 per day increased the proportion of participants showing improvement from baseline to week 6 in the composite score for bloating, burping, and flatulence (47.4% vs. 22.2%), whereby the odds of detecting an improvement were higher with BS50 (OR [95% CI]: 3.2 [1.1, 8.7], p = .024). Analyses of individual gastrointestinal symptoms indicate that BS50 increased the proportion of participants showing an improvement at week 6 compared to placebo for burping (44.7% vs. 22.2%, p = .041) and bloating (31.6% vs. 13.9%, p = .071), without affecting other symptoms. There were no clinically meaningful changes in clinical chemistry, hematology, plasma lipids and intestinal permeability and other inflammation markers. In conclusion, the results suggest that dietary supplementation of 2 × 109 CFU Bacillus subtilis BS50 per day is a well-tolerated and safe strategy to alleviate gas-related gastrointestinal symptoms in healthy adults. ABBREVIATIONS: AE adverse event; BHD bowel habits diary; BMI body mass index; BSS Bristol Stool Scale; CFU colony-forming unit; CRP C-reactive protein; FGID functional gastrointestinal disorder; GI gastrointestinal; GITQ Gastrointestinal Tolerance Questionnaire; GLP-1 glucagon-like peptide 1; GSRS Gastrointestinal Symptom Rating Scale; HDL-C high-density lipoprotein-cholesterol; IBS irritable bowel syndrome; IL-10 interleukin-10; ITT intent-to-treat; LBP lipopolysaccharide binding protein; LDL-C low-density lipoprotein-cholesterol; PP per protocol; PYY peptide YY; TG triglyceride; total-C total cholesterol.

Cyclosporine up-regulates Krüppel-like factor-4 (KLF4) in vascular smooth muscle cells and drives phenotypic modulation in vivo.

Cyclosporine A (CSA, calcineurin inhibitor) has been shown to block both vascular smooth muscle cell (VSMC) proliferation in cell culture and vessel neointimal formation following injury in vivo. The purpose of this study was to determine molecular and pathological effects of CSA on VSMCs. Using real-time reverse transcription-polymerase chain reaction, Western blot analysis, and immunofluorescence microscopy, we show that CSA up-regulated the expression of Krüppel-like factor-4 (KLF4) in VSMCs. KLF4 plays a key role in regulating VSMC phenotypic modulation. KLF4 antagonizes proliferation, facilitates migration, and down-regulates VSMC differentiation marker gene expression. We show that the VSMC differentiation marker genes smooth muscle alpha-actin (ACTA2), transgelin (TAGLN), smoothelin (SMTN), and myocardin (MYOCD) are all down-regulated by CSA in VSMC monoculture, whereas cyclin-dependent kinase inhibitor-1A (CDKN1A) and matrix metalloproteinase-3 (MMP3) are up-regulated. CSA did not affect the abundance of the VSMC microRNA (MIR) markers MIR143 and MIR145. Administration of CSA to rat carotid artery in vivo resulted in acute and transient suppression of ACTA2, TAGLN, SMTN, MYOCD, and smooth muscle myosin heavy chain (MYH11) mRNA levels. The tumor suppressor genes KLF4, p53, and CDKN1A, however, were up-regulated, as well as MMP3, MMP9, and collagen-VIII. CSA-treated arteries showed remarkable remodeling, including breakdown of the internal elastic lamina and reorientation of VSMCs, as well as increased KLF4 immunostaining in VSMCs and endothelial cells. Altogether, these data show that cyclosporin up-regulates KLF4 expression and promotes phenotypic modulation of VSMCs.

The deacetylase HDAC4 controls myocyte enhancing factor-2-dependent structural gene expression in response to neural activity.

Histone deacetylase 4 (HDAC4) binds and inhibits activation of the critical muscle transcription factor myocyte enhancer factor-2 (MEF2). However, the physiological significance of the HDAC4-MEF2 complex in skeletal muscle has not been established. Here we show that in skeletal muscle, HDAC4 is a critical modulator of MEF2-dependent structural and contractile gene expression in response to neural activity. We present evidence that loss of neural input leads to concomitant nuclear accumulation of HDAC4 and transcriptional reduction of MEF2-regulated gene expression. Cell-based assays show that HDAC4 represses structural gene expression via direct binding to AT-rich MEF2 response elements. Notably, using both surgical denervation and the neuromuscular disease amyotrophic lateral sclerosis (ALS) model, we found that elevated levels of HDAC4 are required for efficient repression of MEF2-dependent structural gene expression, indicating a link between the pathological induction of HDAC4 and subsequent MEF2 target gene suppression. Supporting this supposition, we show that ectopic expression of HDAC4 in muscle fibers is sufficient to induce muscle damage in mice. Our study identifies HDAC4 as an activity-dependent regulator of MEF2 function and suggests that activation of HDAC4 in response to chronically reduced neural activity suppresses MEF2-dependent gene expression and contributes to progressive muscle dysfunction observed in neuromuscular diseases.

Effect of acute muscle contusion injury, with and without dietary fish oil, on adult and aged male rats: contractile and biochemical responses.

AIM: Contusion injury in aging muscle has not been studied in detail, but older adults are at risk for such injuries due to increased risk of falls. As falls in older populations are unlikely to be eliminated, interventions to minimize the negative impact of falls, including contusion injury should be pursued. Dietary fish oil (FO) is a common often supplement in older adults, which is associated with factors that might reduce or worsen the negative impact of contusion. METHODS: Here, we investigate whether 8 weeks of FO can blunt the impact of contusion injury in adult (n = 14) and aged (n = 12) rats. We assessed contractility and several biochemical markers in adult and aged gastrocnemius muscles 48 h post-contusion injury, using the uninjured muscles as controls. RESULTS: Injury reduced force production ~40% (P < 0.001), sarcoplasmic reticulum calcium release by ~20% (P = 0.003) and significantly increased several markers of muscle damage (i.e., protein carbonyls, Grp78 abundance (P = 0.022, 0.006, respectively)), and these injury-related changes were not affected by aging. The effects of FO were limited. A main effect (P = 0.018) for FO to increase the myogenic factor Myf5 was observed. In addition FO reduced the injury-associated decline in the mitophagy factor DRP1 (P = 0.027). CONCLUSION: Although age-related differences in certain protein markers differed, aged muscles exhibited no greater acute functional deficits following injury. Similarly, while FO did not reduce functional deficits, it did not worsen them. However, changes in Myf5 and DRP1 with dietary FO suggest the potential to improve recovery from contusion injury, which should be investigated in future studies.

Cellular and Physiological Effects of Dietary Supplementation with ß-Hydroxy-ß-Methylbutyrate (HMB) and ß-Alanine in Late Middle-Aged Mice.

There is growing evidence that severe decline of skeletal muscle mass and function with age may be mitigated by exercise and dietary supplementation with protein and amino acid ingredient technologies. The purposes of this study were to examine the effects of the leucine catabolite, beta-hydroxy-beta-methylbutyrate (HMB), in C2C12 myoblasts and myotubes, and to investigate the effects of dietary supplementation with HMB, the amino acid ß-alanine and the combination thereof, on muscle contractility in a preclinical model of pre-sarcopenia. In C2C12 myotubes, HMB enhanced sarcoplasmic reticulum (SR) calcium release beyond vehicle control in the presence of all SR agonists tested (KCl, P<0.01; caffeine, P = 0.03; ionomycin, P = 0.03). HMB also improved C2C12 myoblast viability (25 µM HMB, P = 0.03) and increased proliferation (25 µM HMB, P = 0.04; 125 µM HMB, P<0.01). Furthermore, an ex vivo muscle contractility study was performed on EDL and soleus muscle from 19 month old, male C57BL/6nTac mice. For 8 weeks, mice were fed control AIN-93M diet, diet with HMB, diet with ß-alanine, or diet with HMB and ß-alanine. In ß-alanine fed mice, EDL muscle showed a 7% increase in maximum absolute force compared to the control diet (202 ± 3vs. 188± 5 mN, P = 0.02). At submaximal frequency of stimulation (20 Hz), EDL from mice fed HMB plus ß-alanine showed an 11% increase in absolute force (88.6 ± 2.2 vs. 79.8 ± 2.4 mN, P = 0.025) and a 13% increase in specific force (12.2 ± 0.4 vs. 10.8 ± 0.4 N/cm2, P = 0.021). Also in EDL muscle, ß-alanine increased the rate of force development at all frequencies tested (P<0.025), while HMB reduced the time to reach peak contractile force (TTP), with a significant effect at 80 Hz (P = 0.0156). In soleus muscle, all experimental diets were associated with a decrease in TTP, compared to control diet. Our findings highlight beneficial effects of HMB and ß-alanine supplementation on skeletal muscle function in aging mice.

Molecular and metabolomic effects of voluntary running wheel activity on skeletal muscle in late middle-aged rats.

We examined the molecular and metabolomic effects of voluntary running wheel activity in late middle-aged male Sprague Dawley rats (16-17 months). Rats were assigned either continuous voluntary running wheel access for 8 weeks (RW+) or cage-matched without running wheel access (RW-). The 9 RW+ rats averaged 83 m/day (range: 8-163 m), yet exhibited both 84% reduced individual body weight gain (4.3 g vs. 26.3 g, P = 0.02) and 6.5% reduced individual average daily food intake (20.6 g vs. 22.0 g, P = 0.09) over the 8 weeks. Hindlimb muscles were harvested following an overnight fast. Muscle weights and myofiber cross-sectional area showed no difference between groups. Western blots of gastrocnemius muscle lysates with a panel of antibodies suggest that running wheel activity improved oxidative metabolism (53% increase in PGC1α, P = 0.03), increased autophagy (36% increase in LC3B-II/-I ratio, P = 0.03), and modulated growth signaling (26% increase in myostatin, P = 0.04). RW+ muscle also showed 43% increased glycogen phosphorylase expression (P = 0.04) and 45% increased glycogen content (P = 0.04). Metabolomic profiling of plantaris and soleus muscles indicated that even low-volume voluntary running wheel activity is associated with decreases in many long-chain fatty acids (e.g., palmitoleate, myristoleate, and eicosatrienoate) relative to RW- rats. Relative increases in acylcarnitines and acyl glycerophospholipids were also observed in RW+ plantaris. These data establish that even modest amounts of physical activity during late middle-age promote extensive metabolic remodeling of skeletal muscle.

Dietary HMB and ß-alanine co-supplementation does not improve in situ muscle function in sedentary, aged male rats.

This study evaluated the effects of dietary ß-hydroxy-ß-methylbutyrate (HMB) combined with ß-alanine (ß-Ala) in sedentary, aged male rats. It has been suggested that dietary HMB or ß-Ala supplementation may mitigate age-related declines in muscle strength and fatigue resistance. A total of 20 aged Sprague-Dawley rats were studied. At age 20 months, 10 rats were administered a control, purified diet and 10 rats were administered a purified diet supplemented with both HMB and ß-Ala (HMB+ß-Ala) for 8 weeks (approximately equivalent to 3 and 2.4 g per day human dose). We measured medial gastrocnemius (MG) size, force, fatigability, and myosin composition. We also evaluated an array of protein markers related to muscle mitochondria, protein synthesis and breakdown, and autophagy. HMB+ß-Ala had no significant effects on body weight, MG mass, force or fatigability, myosin composition, or muscle quality. Compared with control rats, those fed HMB+ß-Ala exhibited a reduced (41%, P = 0.039) expression of muscle RING-finger protein 1 (MURF1), a common marker of protein degradation. Muscle from rats fed HMB+ß-Ala also exhibited a 45% reduction (P = 0.023) in p70s6K phosphorylation following fatiguing stimulation. These data suggest that HMB+ß-Ala at the dose studied may reduce muscle protein breakdown by reducing MURF1 expression, but has minimal effects on muscle function in this model of uncomplicated aging. They do not, however, rule out potential benefits of HMB+ß-Ala co-supplementation at other doses or durations of supplementation in combination with exercise or in situations where extreme muscle protein breakdown and loss of mass occur (e.g., bedrest, cachexia, failure-to-thrive).