Proteomics Analysis of Human Skeletal Muscle Reveals Novel Abnormalities in Obesity and Type 2 Diabetes

Abstract

OBJECTIVEInsulin resistance in skeletal muscle is an early phenomenon in the pathogenesis of type 2 diabetes. Studies of insulin resistance usually are highly focused. However, approaches that give a more global picture of abnormalities in insulin resistance are useful in pointing out new directions for research. In previous studies, gene expression analyses show a coordinated pattern of reduction in nuclear-encoded mitochondrial gene expression in insulin resistance. However, changes in mRNA levels may not predict changes in protein abundance. An approach to identify global protein abundance changes involving the use of proteomics was used here.RESEARCH DESIGN AND METHODSMuscle biopsies were obtained basally from lean, obese, and type 2 diabetic volunteers (n = 8 each); glucose clamps were used to assess insulin sensitivity. Muscle protein was subjected to mass spectrometry–based quantification using normalized spectral abundance factors.RESULTSOf 1,218 proteins assigned, 400 were present in at least half of all subjects. Of these, 92 were altered by a factor of 2 in insulin resistance, and of those, 15 were significantly increased or decreased by ANOVA (P < 0.05). Analysis of protein sets revealed patterns of decreased abundance in mitochondrial proteins and altered abundance of proteins involved with cytoskeletal structure (desmin and alpha actinin-2 both decreased), chaperone function (TCP-1 subunits increased), and proteasome subunits (increased).CONCLUSIONSThe results confirm the reduction in mitochondrial proteins in insulin-resistant muscle and suggest that changes in muscle structure, protein degradation, and folding also characterize insulin resistance.

The proteomic signature of insulin-resistant human skeletal muscle reveals increased glycolytic and decreased mitochondrial enzymes

“…Moreover, significant positive correlations were also observed for summative spot volumes (sum of volumes of all spots with the same identified protein) relating to cytoplasmic malate dehydrogenase (MDH1), an enzyme controlling TCA cycle pool size and providing contractile function [27], and the mitochondrial enzymes ACO2, ATP5A1, ATP5B and GBAS. These results, suggesting reduced TCA cycle and mitochondrial protein content in insulin resistance, are consistent with previous findings of reduced enzyme activities [10,28,29], protein expression [16,17,30], altered phosphorylation [16,31,32], altered transcript levels [10,33,34] or altered flux through mitochondrial ATP synthase [8].…”

“…Thus, these two-dimensional-gel proteomic studies delivered largely consistent findings. Another recent study used one-dimensional SDS-PAGE and label-free MS/MS-based identification and quantification [17]. Of 92 proteins increased more than twofold and of these, the 15 significantly different between OB and/or obese type 2 diabetic and LE participants in that study, only six and one, respectively, were also identified by us.…”

“…Moreover, these earlier attempts involved study groups that were less well matched or rather small. Another more recent study investigated muscle from healthy lean, obese non-diabetic and obese type 2 diabetic individuals using one-dimensional gel separation with SDS-PAGE followed by HPLC-ESI-MS/MS-based identification and quantification [17], and reported significant changes in the abundance of 15 proteins.…”

“…There have been several previous approaches to the study of the human skeletal muscle proteome [13,14] and its alterations in insulin-resistant muscle [15][16][17][18]. Two studies have used the two-dimensional gel approach [15,16].…”

Diet-Induced Obesity Suppresses Expression of Many Proteins at the Blood–Brain Barrier

“…1,2 Proteomic methods have been used to investigate human and mouse obesity, but most reports have focused on changes in adipose tissue. [3][4][5][6] Recent results suggest that the blood-brain barrier (BBB) is activated in obesity; for example, mice with adult-onset obesity show resistance to leptin transport across the BBB, region-specific astrogliosis, and upregulation of astrocytic leptin receptors. 7,8 The BBB is a regulatory interface between the central nervous system (CNS) and the peripheral circulation.…”