Faculty Collaboration Database

Isoenergetic dietary protein restriction decreases myosin heavy chain IIx fraction and myosin heavy chain production in humans. J Nutr 2004 Feb;134(2):328-34

Date

01/30/2004

Pubmed ID

14747668

DOI

10.1093/jn/134.2.328

Scopus ID

2-s2.0-0942301276 (requires institutional sign-in at Scopus site)   25 Citations

Abstract

The synthesis of muscle protein is restrained during dietary protein restriction. This is widely understood to vary quantitatively with the degree of nutritional deprivation, but there has been little discussion of qualitative changes in muscle protein deriving from dietary protein restriction. We studied 14 healthy subjects in a 2-sample study. Subjects were randomly assigned to a diet providing an ample, American-style protein intake (1.67 g. kg fat-free mass(-1). d(-1)) or a diet approximating the mean minimum adult protein requirement (0.71 g. kg fat-free mass(-1). d(-1)). We found that consumption of an isoenergetic diet at the mean adult minimum protein requirement for 4 wk produced an 81% lower fractional synthesis rate of myosin heavy chain (MHC) proteins in vastus lateralis muscle than did consumption of an ample protein diet (P = 0.05). Protein deprivation altered the skeletal muscle myosin composition such that the proportion of the total myosin content represented by fast-twitch MHC IIx was 51% lower than with ample intake (P = 0.013). The steady state content of MHC IIx messenger RNA (mRNA) did not differ in subjects consuming the minimum requirement of protein, suggesting that the reduced proportion of MHC IIx arises from posttranscriptional events. A 68% lower rate of 3-methylhistidine excretion with protein restriction (P < 0.01) suggests that myofibrillar protein degradation was lower. We conclude that dietary amino acid scarcity produces a change in myosin isoform distribution via posttranscriptional mechanisms. The relative contribution of inhibited myosin synthesis and inhibited degradation to the altered myosin isoform composition remains unknown. This has implications for the mechanisms by which amino acids govern muscle protein composition in vivo, and further exploration is required.

Author List

Brodsky IG, Suzara D, Hornberger TA, Goldspink P, Yarasheski KE, Smith S, Kukowski J, Esser K, Bedno S

MESH terms used to index this publication - Major topics in bold

Adult
Dietary Proteins
Female
Humans
Male
Muscle, Skeletal
Myosin Subfragments
Myosin Type II
Nutritional Physiological Phenomena
Protein Isoforms
RNA, Messenger