Spatial distribution of “Tissue-Specific” antigens in the developing human heart and skeletal muscle. II. An immunohistochemical analysis of myosin heavy chain isoform expression patterns in the embryonic heart

Previous studies have reported the existence of skeletal muscle fibers that coexpress multiple myosin heavy chain isoforms. These surveys have usually been limited to studying the polymorphic profiles of skeletal muscle fibers from a limited number of muscles (i.e., usually <4). Additionally, few studies have considered the functional implications of polymorphism. Hence, the primary objective of this study was to survey a relatively large number of rat skeletal muscle/muscle regions and muscle fibers ( n≈ 5,000) to test the hypothesis that polymorphic fibers represent a larger fraction of the total pool of fibers than do so-called monomorphic fibers, which express only one myosin heavy chain isoform. Additionally, we used Hill's statistical model of the force-velocity relationship to differentiate the functional consequences of single-fiber myosin heavy chain isoform distributions found in these muscles. The results demonstrate that most muscles and regions of rodent skeletal muscles contain large proportions of polymorphic fibers, with the exception of muscles such as the slow soleus muscle and white regions of fast muscles. Several muscles were also found to have polymorphic profiles that are not consistent with the I↔IIA↔IIX↔IIB scheme of muscle plasticity. For instance, it was found that the diaphragm muscle normally contains I/IIX fibers. Functionally, the high degree of polymorphism may 1) represent a strategy for producing a spectrum of contractile properties that far exceeds that simply defined by the presence of four myosin heavy chain isoforms and 2) result in relatively small differences in function as defined by the force-velocity relationship.

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Clustering of GLUT4, TUG, and RUVBL2 protein levels correlate with myosin heavy chain isoform pattern in skeletal muscles, but AS160 and TBC1D1 levels do not

Journal of Applied Physiology ◽

10.1152/japplphysiol.00631.2011 ◽

2011 ◽

Vol 111 (4) ◽

pp. 1106-1117 ◽

Cited By ~ 36

Author(s):

Carlos M. Castorena ◽

James G. MacKrell ◽

Jonathan S. Bogan ◽

Makoto Kanzaki ◽

Gregory D. Cartee

Keyword(s):

Skeletal Muscle ◽

Myosin Heavy Chain ◽

Heavy Chain ◽

Skeletal Muscles ◽

Vastus Lateralis ◽

Mhc I ◽

Myosin Heavy Chain Isoform ◽

Protein Levels ◽

Positive Correlations ◽

Tensor Fasciae Latae

Skeletal muscle is a heterogeneous tissue. To further elucidate this heterogeneity, we probed relationships between myosin heavy chain (MHC) isoform composition and abundance of GLUT4 and four other proteins that are established or putative GLUT4 regulators [Akt substrate of 160 kDa (AS160), Tre-2/Bub2/Cdc 16-domain member 1 (TBC1D1), Tethering protein containing an UBX-domain for GLUT4 (TUG), and RuvB-like protein two (RUVBL2)] in 12 skeletal muscles or muscle regions from Wistar rats [adductor longus, extensor digitorum longus, epitrochlearis, gastrocnemius (mixed, red, and white), plantaris, soleus, tibialis anterior (red and white), tensor fasciae latae, and white vastus lateralis]. Key results were 1) significant differences found among the muscles (range of muscle expression values) for GLUT4 (2.5-fold), TUG (1.7-fold), RUVBL2 (2.0-fold), and TBC1D1 (2.7-fold), but not AS160; 2) significant positive correlations for pairs of proteins: GLUT4 vs. TUG ( R = 0.699), GLUT4 vs. RUVBL2 ( R = 0.613), TUG vs. RUVBL2 ( R = 0.564), AS160 vs. TBC1D1 ( R = 0.293), and AS160 vs. TUG ( R = 0.246); 3) significant positive correlations for %MHC-I: GLUT4 ( R = 0.460), TUG ( R = 0.538), and RUVBL2 ( R = 0.511); 4) significant positive correlations for %MHC-IIa: GLUT4 ( R = 0.293) and RUVBL2 ( R = 0.204); 5) significant negative correlations for %MHC-IIb vs. GLUT4 ( R = −0.642), TUG ( R = −0.626), and RUVBL2 ( R = −0.692); and 6) neither AS160 nor TBC1D1 significantly correlated with MHC isoforms. In 12 rat muscles, GLUT4 abundance tracked with TUG and RUVBL2 and correlated with MHC isoform expression, but was unrelated to AS160 or TBC1D1. Our working hypothesis is that some of the mechanisms that regulate GLUT4 abundance in rat skeletal muscle also influence TUG and RUVBL2 abundance.

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