Boys with Duchenne muscular dystrophy (DMD) experience a progressive loss of functional muscle mass, with fibrosis and lipid accumulation. Accurate evaluation of whole‐body functional muscle mass (MM) in DMD patients has not previously been possible and the rate of synthesis of muscle proteins remains unexplored. We used non‐invasive, stable isotope‐based methods from plasma and urine to measure the fractional rate of muscle protein synthesis (FSR) functional muscle mass (MM), and fat free mass (FFM) in 10 DMD (6–17 years) and 9 age‐matched healthy subjects. An oral dose of D3creatine in 70% 2H2O was administered to determine MM and FFM followed by daily 70% 2H2O to measure protein FSR. Functional MM was profoundly reduced in DMD subjects compared to controls (17% vs. 41% of body weight, P < 0.0001), particularly in older, non‐ambulant patients in whom functional MM was extraordinarily low (<13% body weight). We explored the urine proteome to measure FSR of skeletal muscle‐derived proteins. Titin, myosin light chain and gelsolin FSRs were substantially lower in DMD subjects compared to controls (27%, 11% and 40% of control, respectively, P < 0.0001) and were strongly correlated. There were no differences in muscle‐derived sarcoplasmic proteins FSRs (creatine kinase M‐type and carbonic anhydrase‐3) measured in plasma. These data demonstrate that both functional MM, body composition and muscle protein synthesis rates can be quantified non‐invasively and are markedly different between DMD and control subjects and suggest that the rate of contractile but not sarcoplasmic protein synthesis is affected by a lack of dystrophin. Key points Duchenne muscular dystrophy (DMD) results in a progressive loss of functional skeletal muscle but total body functional muscle mass or rates of muscle protein synthesis have not previously been assessed in these patients. D3‐creatine dilution was used to measure total functional muscle mass and oral 2H2O was used to examine the rates of muscle protein synthesis non‐invasively in boys with DMD and healthy controls using urine samples. Muscle mass was profoundly lower in DMD compared to control subjects, particularly in older, non‐ambulant patients. The rates of contractile protein synthesis but not sarcoplasmic proteins were substantially lower in DMD. These results may provide non‐invasive biomarkers for disease progression and therapeutic efficacy in DMD and other neuromuscular diseases.
Objectives Short-term energy deficit reduces acute measures of mixed muscle protein synthesis (MPS) and suppresses the hypothalamic-pituitary axis and endogenous testosterone synthesis. We hypothesized that testosterone supplementation could mitigate the effects of energy deficit on MPS. We conducted a randomized, double-blind, placebo-controlled trial to determine the effects of 28 days of tightly-controlled severe energy deficit (deficit 55% of total energy requirements) on measures of mixed-MPS and proteome-wide protein dynamics in non-obese men either given 200 mg testosterone enanthate (Testosterone, n = 24) or placebo (Placebo, n = 26) injections per week. Methods Participants received daily aliquots of deuterated water (2H2O) for 42 consecutive days (14-d weight maintenance period followed by 28-d energy deficit). Muscle biopsies were collected at rest in a fasted state at the end of the weight maintenance phase (PRE) and at the middle (MID) and end (POST) of the 28-d energy deficit. Mixed-MPS and proteome-wide protein fractional synthesis rates (FSR) were quantified. Changes over time and differences between Testosterone and Placebo were determined for mixed-MPS, and cross-sectional comparisons between Testosterone and Placebo were performed at MID and POST for proteome dynamics. Results In both Testosterone and Placebo, mixed-MPS were 40% and 33% lower (P < 0.0005) at MID and POST energy deficit, respectively, compared to PRE, with no differences between groups or between MID and POST. Proteome-wide FSR of individual muscle proteins did not differ between Testosterone and Placebo at any time point. However, at POST, the number of individual proteins with higher FSR in Testosterone than Placebo was significant by 2-tailed binomial test (P < 0.05), with values ranging from 20–32% higher FSR for myofibrillar, mitochondrial and cytosolic proteins. Conclusions Findings confirm the pronounced effect of short-term severe energy deficit on mixed-MPS and suggest the anabolic suppression occurs largely independent of testosterone. However, proteome-wide protein dynamics may reveal a novel time sensitive signal by which supplemental testosterone triggers a delayed increase in MPS, providing a synthetic mechanism for muscle mass preservation or accrual. Funding Sources Supported by DHP JPC-5/MOMRP; authors’ views not official U.S. Army or DoD policy.
Desminopathy the most common intermediate filament disease in humans. Desmin is an essential part of the filamentous network that aligns myofibrils, anchors nuclei and mitochondria, and connects the z-discs and the sarcolemma. We created a rat model with a mutation in R349P DES, analog to the most frequent R350P DES missense mutation in humans. To examine the effects of a chronic, physiological exercise stimulus on desminopathic muscle, we subjected R349P DES rats and their wildtype (WT) and heterozygous littermates to a treadmill running regime. We saw significantly lower running capacity in DES rats that worsened over the course of the study. We found indicators of increased autophagic and proteasome activity with running in DES compared to WT. Stable isotope labeling and LC-MS analysis displayed distinct adaptations of the proteomes of WT and DES animals at baseline as well as with exercise: While key proteins of glycolysis, mitochondria and thick filaments increased their synthetic activity with running in WT, these proteins were higher at baseline in DES and did not change with running. The results suggest an impairment in adaption to chronic exercise in DES muscle and a subsequent exacerbation in the functional and histopathological phenotype.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.