Effects of β-hydroxy-β-methylbutyrate on skeletal muscle mitochondrial content and dynamics, and lipids after 10 days of bed rest in older adults

Loss of muscle mass during periods of disuse likely has negative health consequences for older adults. We have previously shown that β-hydroxy-β-methylbutyrate (HMB) supplementation during 10 days of strict bed rest (BR) attenuates the loss of lean mass in older adults. To elucidate potential molecular mechanisms of HMB effects on muscle during BR and resistance training rehabilitation (RT), we examined mediators of skeletal muscle mitochondrial dynamics, autophagy and atrophy, and intramyocellular lipids. Nineteen older adults (60–76 yr) completed 10 days BR followed by 8-wk RT rehabilitation. Subjects were randomized to either HMB (3 g/day HMB; n = 11) or control (CON; n = 8) groups. Skeletal muscle cross-sectional area (CSA) was determined by histology from percutaneous vastus lateralis biopsies. We measured protein markers of mitochondrial content [oxidative phosphorylation (OXPHOS)], fusion and fission (MFN2, OPA1, FIS1, and DRP1), autophagy (Beclin1, LC3B, and BNIP3), and atrophy [poly-ubiquinated proteins (poly-ub)] by Western blot. Fatty acid composition of several lipid classes in skeletal muscle was measured by infusion-MS analysis. Poly-ub proteins and OXPHOS complex I increased in both groups following BR ( P < 0.05, main effect for time), and muscle triglyceride content tended to increase following BR in the HMB group ( P = 0.055). RT rehabilitation increased OXPHOS complex II protein ( P < 0.05), and total OXPHOS content tended ( P = 0.0504) to be higher in HMB group. In addition, higher levels of DRP1 and MFN2 were maintained in the HMB group after RT ( P < 0.05). BNIP3 and poly-ub proteins were significantly reduced following rehabilitation in both groups ( P < 0.05). Collectively, these data suggest that HMB influences mitochondrial dynamics and lipid metabolism during disuse atrophy and rehabilitation. NEW & NOTEWORTHY Mitochondrial content and dynamics remained unchanged over 10 days of BR in older adults. HMB stimulated intramuscular lipid storage as triacylglycerol following 10 days of bed rest (BR) and maintained higher mitochondrial OXPHOS content and dynamics during the 8-wk resistance exercise rehabilitation program.

Download Full-text

The mTORC1 signaling repressors REDD1/2 are rapidly induced and activation of p70S6K1 by leucine is defective in skeletal muscle of an immobilized rat hindlimb

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.00409.2012 ◽

2013 ◽

Vol 304 (2) ◽

pp. E229-E236 ◽

Cited By ~ 60

Author(s):

Andrew R. Kelleher ◽

Scot R. Kimball ◽

Michael D. Dennis ◽

Rudolf J. Schilder ◽

Leonard S. Jefferson

Keyword(s):

Skeletal Muscle ◽

Protein Synthesis ◽

Molecular Mechanisms ◽

Bed Rest ◽

Disuse Atrophy ◽

Sprague Dawley ◽

Ribosomal Protein S6 ◽

Sprague Dawley Rats ◽

Mtorc1 Signaling ◽

Limb Immobilization

Limb immobilization, limb suspension, and bed rest cause substantial loss of skeletal muscle mass, a phenomenon termed disuse atrophy. To acquire new knowledge that will assist in the development of therapeutic strategies for minimizing disuse atrophy, the present study was undertaken with the aim of identifying molecular mechanisms that mediate control of protein synthesis and mechanistic target of rapamycin complex 1 (mTORC1) signaling. Male Sprague-Dawley rats were subjected to unilateral hindlimb immobilization for 1, 2, 3, or 7 days or served as nonimmobilized controls. Following an overnight fast, rats received either saline or l-leucine by oral gavage as a nutrient stimulus. Hindlimb skeletal muscles were extracted 30 min postgavage and analyzed for the rate of protein synthesis, mRNA expression, phosphorylation state of key proteins in the mTORC1 signaling pathway, and mTORC1 signaling repressors. In the basal state, mTORC1 signaling and protein synthesis were repressed within 24 h in the soleus of an immobilized compared with a nonimmobilized hindlimb. These responses were accompanied by a concomitant induction in expression of the mTORC1 repressors regulated in development and DNA damage responses (REDD) 1/2. The nutrient stimulus produced an elevation of similar magnitude in mTORC1 signaling in both the immobilized and nonimmobilized muscle. In contrast, phosphorylation of 70-kDa ribosomal protein S6 kinase 1 (p70S6K1) on Thr229 and Thr389 in response to the nutrient stimulus was severely blunted. Phosphorylation of Thr229 by PDK1 is a prerequisite for phosphorylation of Thr389 by mTORC1, suggesting that signaling through PDK1 is impaired in response to immobilization. In conclusion, the results show an immobilization-induced attenuation of mTORC1 signaling mediated by induction of REDD1/2 and defective p70S6K1 phosphorylation.

Download Full-text

MEF2 as upstream regulator of the transcriptome signature in human skeletal muscle during unloading

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00452.2017 ◽

2018 ◽

Vol 315 (4) ◽

pp. R799-R809 ◽

Cited By ~ 3

Author(s):

Eric Rullman ◽

Rodrigo Fernandez-Gonzalo ◽

Igor B. Mekjavić ◽

Thomas Gustafsson ◽

Ola Eiken

Keyword(s):

Skeletal Muscle ◽

Molecular Mechanisms ◽

Vastus Lateralis ◽

Bed Rest ◽

Peroxisome Proliferator ◽

Peroxisome Proliferator Activated Receptor ◽

Muscle Gene Expression ◽

Transcriptional Signature ◽

Upstream Regulator ◽

Transcriptome Signature

Our understanding of skeletal muscle structural and functional alterations during unloading has increased in recent decades, yet the molecular mechanisms underpinning these changes have only started to be unraveled. The purpose of the current investigation was to assess changes in skeletal muscle gene expression after 21 days of bed rest, with a particular focus on predicting upstream regulators of muscle disuse. Additionally, the association between differential microRNA expression and the transcriptome signature of bed rest were investigated. mRNAs from musculus vastus lateralis biopsies obtained from 12 men before and after the bed rest were analyzed using a microarray. There were 54 significantly upregulated probesets after bed rest, whereas 103 probesets were downregulated (false discovery rate 10%; fold-change cutoff ≥1.5). Among the upregulated genes, transcripts related to denervation-induced alterations in skeletal muscle were identified, e.g., acetylcholine receptor subunit delta and perinatal myosin. The most downregulated transcripts were functionally enriched for mitochondrial genes and genes involved in mitochondrial biogenesis, followed by a large number of contractile fiber components. Upstream regulator analysis identified a robust inhibition of the myocyte enhancer factor-2 (MEF2) family, in particular MEF2C, which was suggested to act upstream of several key downregulated genes, most notably peroxisome proliferator-activated receptor γ coactivator 1-α (PGC-1α)/peroxisome proliferator-activated receptors (PPARs) and CRSP3. Only a few microRNAs were identified as playing a role in the overall transcriptome picture induced by sustained bed rest. Our results suggest that the MEF2 family is a key regulator underlying the transcriptional signature of bed rest and, hence, ultimately also skeletal muscle alterations induced by systemic unloading in humans.

Download Full-text

Chronic disuse and skeletal muscle structure in older adults: sex-specific differences and relationships to contractile function

AJP Cell Physiology ◽

10.1152/ajpcell.00014.2015 ◽

2015 ◽

Vol 308 (11) ◽

pp. C932-C943 ◽

Cited By ~ 14

Author(s):

Damien M. Callahan ◽

Timothy W. Tourville ◽

Mark S. Miller ◽

Sarah B. Hackett ◽

Himani Sharma ◽

...

Keyword(s):

Older Adults ◽

Skeletal Muscle ◽

Myosin Heavy Chain ◽

Heavy Chain ◽

Cross Sectional Area ◽

Sectional Area ◽

Mitochondrial Content ◽

Cross Sectional ◽

Muscle Structure ◽

Muscle Disuse

In older adults, we examined the effect of chronic muscle disuse on skeletal muscle structure at the tissue, cellular, organellar, and molecular levels and its relationship to muscle function. Volunteers with advanced-stage knee osteoarthritis (OA, n = 16) were recruited to reflect the effects of chronic lower extremity muscle disuse and compared with recreationally active controls ( n = 15) without knee OA but similar in age, sex, and health status. In the OA group, quadriceps muscle and single-fiber cross-sectional area were reduced, with the largest reduction in myosin heavy chain IIA fibers. Myosin heavy chain IIAX fibers were more prevalent in the OA group, and their atrophy was sex-specific: men showed a reduction in cross-sectional area, and women showed no differences. Myofibrillar ultrastructure, myonuclear content, and mitochondrial content and morphology generally did not differ between groups, with the exception of sex-specific adaptations in subsarcolemmal (SS) mitochondria, which were driven by lower values in OA women. SS mitochondrial content was also differently related to cellular and molecular functional parameters by sex: greater SS mitochondrial content was associated with improved contractility in women but reduced function in men. Collectively, these results demonstrate sex-specific structural phenotypes at the cellular and organellar levels with chronic disuse in older adults, with novel associations between energetic and contractile systems.

Download Full-text

Impact of resistance exercise during bed rest on skeletal muscle sarcopenia and myosin isoform distribution

Journal of Applied Physiology ◽

10.1152/jappl.1998.84.1.157 ◽

1998 ◽

Vol 84 (1) ◽

pp. 157-163 ◽

Cited By ~ 163

Author(s):

Marcas M. Bamman ◽

Mark S. F. Clarke ◽

Daniel L. Feeback ◽

Robert J. Talmadge ◽

Bruce R. Stevens ◽

...

Keyword(s):

Skeletal Muscle ◽

Resistance Exercise ◽

Vastus Lateralis ◽

Bed Rest ◽

Vastus Lateralis Muscle ◽

Neural Activation ◽

Type I ◽

Cross Sectional ◽

Maximum Voluntary Isometric Contraction ◽

Leg Press

Bamman, Marcas M., Mark S. F. Clarke, Daniel L. Feeback, Robert J. Talmadge, Bruce R. Stevens, Steven A. Lieberman, and Michael C. Greenisen. Impact of resistance exercise during bed rest on skeletal muscle sarcopenia and myosin isoform distribution. J. Appl. Physiol. 84(1): 157–163, 1998.—Because resistance exercise (REx) and bed-rest unloading (BRU) are associated with opposing adaptations, our purpose was to test the efficacy of REx against the effects of 14 days of BRU on the knee-extensor muscle group. Sixteen healthy men were randomly assigned to no exercise (NoEx; n = 8) or REx ( n = 8). REx performed five sets of leg press exercise with 80–85% of one repetition maximum (1 RM) every other day during BRU. Muscle samples were removed from the vastus lateralis muscle by percutaneous needle biopsy. Myofiber distribution was determined immunohistochemically with three monoclonal antibodies against myosin heavy chain (MHC) isoforms (I, IIa, IIx). MHC distribution was further assessed by quantitative gel electrophoresis. Dynamic 1-RM leg press and unilateral maximum voluntary isometric contraction (MVC) were determined. Maximal neural activation (root mean squared electromyogram) and rate of torque development (RTD) were measured during MVC. Reductions ( P < 0.05) in type I (15%) and type II (17%) myofiber cross-sectional areas were found in NoEx but not in REx. Electrophoresis revealed no changes in MHC isoform distribution. The percentage of type IIx myofibers decreased ( P < 0.05) in REx from 9 to 2% and did not change in NoEx. 1 RM was reduced ( P < 0.05) by 9% in NoEx but was unchanged in REx. MVC fell by 15 and 13% in NoEx and REx, respectively. The agonist-to-antagonist root mean squared electromyogram ratio decreased ( P < 0.05) 19% in REx. RTD slowed ( P < 0.05) by 54% in NoEx only. Results indicate that REx prevented BRU-induced myofiber atrophy and also maintained training-specific strength. Unlike spaceflight, BRU did not induce shifts in myosin phenotype. The reported benefits of REx may prove useful in prescribing exercise for astronauts in microgravity.

Download Full-text

Artificial gravity as a countermeasure to microgravity: a pilot study examining the effects on knee extensor and plantar flexor muscle groups

Journal of Applied Physiology ◽

10.1152/japplphysiol.91130.2008 ◽

2009 ◽

Vol 107 (1) ◽

pp. 39-46 ◽

Cited By ~ 40

Author(s):

V. J. Caiozzo ◽

F. Haddad ◽

S. Lee ◽

M. Baker ◽

William Paloski ◽

...

Keyword(s):

Skeletal Muscle ◽

Muscle Biopsy ◽

Vastus Lateralis ◽

Knee Extensor ◽

Bed Rest ◽

Artificial Gravity ◽

Knee Extensors ◽

Plantar Flexors ◽

Flexor Muscle ◽

Cross Sectional

The goal of this project was to examine the effects of artificial gravity (AG) on skeletal muscle strength and key anabolic/catabolic markers known to regulate muscle mass. Two groups of subjects were selected for study: 1) a 21 day-bed rest (BR) group ( n = 7) and 2) an AG group ( n = 8), which was subjected to 21 days of 6° head-down tilt bed rest plus daily 1-h exposures to AG (2.5 G at the feet). Centrifugation was produced using a short-arm centrifuge with the foot plate ∼220 cm from the center of rotation. The torque-velocity relationships of the knee extensors and plantar flexors of the ankle were determined pre- and posttreatment. Muscle biopsy samples obtained from the vastus lateralis and soleus muscles were used for a series of gene expression analyses (mRNA abundance) of key factors implicated in the anabolic vs. catabolic state of the muscle. Post/pre torque-velocity determinations revealed greater decrements in knee extensor performance in the BR vs. AG group ( P < 0.04). The plantar flexors of the AG subjects actually demonstrated a net gain in the torque-velocity relationship, whereas in the BR group, the responses declined (AG vs. BR, P < 0.001). Muscle fiber cross-sectional area decreased by ∼20% in the BR group, whereas no losses were evident in the AG group. RT-PCR analyses of muscle biopsy specimens demonstrated that markers of growth and cytoskeletal integrity were higher in the AG group, whereas catabolic markers were elevated in the BR group. Importantly, these patterns were seen in both muscles. We conclude that paradigms of AG have the potential to maintain the functional, biochemical, and structural homeostasis of skeletal muscle in the face of chronic unloading.

Download Full-text

Skeletal Muscle Energetics and Mitochondrial Function Are Impaired Following 10 Days of Bed Rest in Older Adults

The Journals of Gerontology Series A ◽

10.1093/gerona/glaa001 ◽

2020 ◽

Vol 75 (9) ◽

pp. 1744-1753 ◽

Cited By ~ 6

Author(s):

Robert A Standley ◽

Giovanna Distefano ◽

Michelle B Trevino ◽

Emily Chen ◽

Niven R Narain ◽

...

Keyword(s):

Older Adults ◽

Skeletal Muscle ◽

Mitochondrial Respiration ◽

Vastus Lateralis ◽

Mitochondrial Gene ◽

Bed Rest ◽

Primary Objective ◽

Significant Deterioration ◽

Muscle Energetics ◽

Gene Transcripts

Abstract Background Older adults exposed to periods of inactivity during hospitalization, illness, or injury lose muscle mass and strength. This, in turn, predisposes poor recovery of physical function upon reambulation and represents a significant health risk for older adults. Bed rest (BR) results in altered skeletal muscle fuel metabolism and loss of oxidative capacity that have recently been linked to the muscle atrophy program. Our primary objective was to explore the effects of BR on mitochondrial energetics in muscle from older adults. A secondary objective was to examine the effect of β-hydroxy-β-methylbuturate (HMB) supplementation on mitochondrial energetics. Methods We studied 20 older adults before and after a 10-day BR intervention, who consumed a complete oral nutritional supplement (ONS) with HMB (3.0 g/d HMB, n = 11) or without HMB (CON, n = 9). Percutaneous biopsies of the vastus lateralis were obtained to determine mitochondrial respiration and H2O2 emission in permeabilized muscle fibers along with markers of content. RNA sequencing and lipidomics analyses were also conducted. Results We found a significant up-regulation of collagen synthesis and down-regulation of ribosome, oxidative metabolism and mitochondrial gene transcripts following BR in the CON group. Alterations to these gene transcripts were significantly blunted in the HMB group. Mitochondrial respiration and markers of content were both reduced and H2O2 emission was elevated in both groups following BR. Conclusions In summary, 10 days of BR in older adults causes a significant deterioration in mitochondrial energetics, while transcriptomic profiling revealed that some of these negative effects may be attenuated by an ONS containing HMB.

Download Full-text

Physiology of a Microgravity Environment Invited Review: Microgravity and skeletal muscle

Journal of Applied Physiology ◽

10.1152/jappl.2000.89.2.823 ◽

2000 ◽

Vol 89 (2) ◽

pp. 823-839 ◽

Cited By ~ 332

Author(s):

Robert H. Fitts ◽

Danny R. Riley ◽

Jeffrey J. Widrick

Keyword(s):

Skeletal Muscle ◽

Muscle Atrophy ◽

Thin Filament ◽

Molecular Mechanisms ◽

Skeletal Muscle Atrophy ◽

Microgravity Environment ◽

Type I ◽

Fiber Types ◽

Maximal Velocity ◽

Cross Sectional

Spaceflight (SF) has been shown to cause skeletal muscle atrophy; a loss in force and power; and, in the first few weeks, a preferential atrophy of extensors over flexors. The atrophy primarily results from a reduced protein synthesis that is likely triggered by the removal of the antigravity load. Contractile proteins are lost out of proportion to other cellular proteins, and the actin thin filament is lost disproportionately to the myosin thick filament. The decline in contractile protein explains the decrease in force per cross-sectional area, whereas the thin-filament loss may explain the observed postflight increase in the maximal velocity of shortening in the type I and IIa fiber types. Importantly, the microgravity-induced decline in peak power is partially offset by the increased fiber velocity. Muscle velocity is further increased by the microgravity-induced expression of fast-type myosin isozymes in slow fibers (hybrid I/II fibers) and by the increased expression of fast type II fiber types. SF increases the susceptibility of skeletal muscle to damage, with the actual damage elicited during postflight reloading. Evidence in rats indicates that SF increases fatigability and reduces the capacity for fat oxidation in skeletal muscles. Future studies will be required to establish the cellular and molecular mechanisms of the SF-induced muscle atrophy and functional loss and to develop effective exercise countermeasures.

Download Full-text

Leucine augments specific skeletal muscle mitochondrial respiratory pathways during recovery following 7 days of physical inactivity in older adults

Journal of Applied Physiology ◽

10.1152/japplphysiol.00810.2020 ◽

2021 ◽

Author(s):

Emily J. Arentson-Lantz ◽

Jasmine Mikovic ◽

Nisha Bhattarai ◽

Christopher S. Fry ◽

Séverine Lamon ◽

...

Keyword(s):

Older Adults ◽

Skeletal Muscle ◽

Body Weight ◽

Insulin Sensitivity ◽

Bed Rest ◽

Metabolic Clearance ◽

Leucine Supplementation ◽

Respiratory Capacity ◽

Antioxidant Defense Systems ◽

Mitochondrial Respiratory

Leucine supplementation attenuates the loss of skeletal muscle mass and function in older adults during bed rest. We sought to determine if leucine could also preserve and/or restore mitochondrial function and muscle oxidative capacity during periods of disuse and rehabilitation. Healthy older adults (69.1 ± 1.1 years) consumed a structured diet with supplemental leucine (LEU: 0.06 g/ kg body weight/ meal; n=8) or alanine (CON: 0.06 g/ kg body weight/meal; n=8) during 7 days of bed rest and 5 days of inpatient rehabilitation. A 75 g oral glucose tolerance test was performed at baseline (PreBR), after bed rest (PostBR) and rehabilitation (PostRehab) and used to calculate an indicator of insulin sensitivity, metabolic clearance rate. (MCR). Tissue samples from the m. vastus lateralis were collected PreBR, PostBR, and PostRehab to assess mitochondrial respiratory capacity and protein markers of the oxidative phosphorylation and a marker of the antioxidant defense systems. During bed rest, leucine tended to preserve insulin sensitivity (Change in MCR, CON vs. LEU: -3.5 ± 0.82 vs LEU: -0.98 ± 0.88, p=0.054), but had no effect on mitochondrial respiratory capacity (Change in State 3+succinate CON vs. LEU -8.7 ± 6.1 vs. 7.3 ± 4.1 pmol O2/sec/mg tissue, p=0.10) Following rehabilitation, leucine increased ATP-linked respiration (CON vs. LEU: -8.9 ± 6.2 vs. 15.5± 4.4 pmol O2/sec/mg tissue, p=0.0042). While the expression of mitochondrial respiratory and antioxidant proteins was not impacted, leucine supplementation preserved specific pathways of mitochondrial respiration, insulin sensitivity and a marker of oxidative stress during bed rest and rehabilitation.

Download Full-text

Cutoff values for appendicular skeletal muscle mass and strength in relation to fear of falling among Brazilian older adults: cross-sectional study

Sao Paulo Medical Journal ◽

10.1590/1516-3180.2017.0049030517 ◽

2017 ◽

Vol 135 (5) ◽

pp. 434-443 ◽

Cited By ~ 5

Author(s):

Ricardo Aurélio Carvalho Sampaio ◽

Priscila Yukari Sewo Sampaio ◽

Luz Albany Arcila Castaño ◽

João Francisco Barbieri ◽

Hélio José Coelho Júnior ◽

...

Keyword(s):

Older Adults ◽

Skeletal Muscle ◽

Muscle Mass ◽

Skeletal Muscle Mass ◽

Fear Of Falling ◽

Cross Sectional Study ◽

Sectional Study ◽

Cross Sectional ◽

Appendicular Skeletal Muscle ◽

Appendicular Skeletal Muscle Mass

Download Full-text

Effects of long-term intradialytic oral nutrition and exercise on muscle protein homeostasis and markers of mitochondrial content in patients on hemodialysis

AJP Renal Physiology ◽

10.1152/ajprenal.00026.2020 ◽

2020 ◽

Vol 319 (5) ◽

pp. F885-F894

Author(s):

Jorge L. Gamboa ◽

Serpil Muge Deger ◽

Bradley W. Perkins ◽

Cindy Mambungu ◽

Feng Sha ◽

...

Keyword(s):

Skeletal Muscle ◽

Resistance Exercise ◽

Muscle Protein ◽

Nutritional Supplementation ◽

Sectional Area ◽

Mitochondrial Content ◽

Protein Energy Wasting ◽

Cross Sectional ◽

Protein Energy

Patients with end-stage kidney disease on maintenance hemodialysis commonly develop protein-energy wasting, a syndrome characterized by nutritional and metabolic abnormalities. Nutritional supplementation and exercise are recommended to prevent protein-energy wasting. In a 6-mo prospective randomized, open-label, clinical trial, we reported that the combination of resistance exercise and nutritional supplementation does not have an additive effect on lean body mass measured by dual-energy X-ray absorptiometry. To provide more mechanistic data, we performed a secondary analysis where we hypothesized that the combination of nutritional supplementation and resistance exercise would have additive effects on muscle protein accretion by stable isotope protein kinetic experiments, muscle mass by MRI, and mitochondrial content markers in muscle. We found that 6 mo of nutritional supplementation during hemodialysis increased muscle protein net balance [baseline: 2.5 (−17.8, 13.0) µg·100 mL−1·min−1 vs. 6 mo: 43.7 (13.0, 98.5) µg·100 mL−1·min−1, median (interquartile range), P = 0.04] and mid-thigh fat area [baseline: 162.3 (104.7, 226.6) cm2 vs. 6 mo: 181.9 (126.3, 279.2) cm2, median (interquartile range), P = 0.04]. Three months of nutritional supplementation also increased markers of mitochondrial content in muscle. Although the study is underpowered to detected differences, the combination of nutritional supplementation and exercise failed to show further benefit in protein accretion or muscle cross-sectional area. We conclude that long-term nutritional supplementation increases the skeletal muscle anabolic effect, the fat cross-sectional area of the thigh, and markers of mitochondrial content in skeletal muscle.

Download Full-text