Calpain-10 gene and protein expression in human skeletal muscle: effect of acute lipid-induced insulin resistance and type 2 diabetes

Abstract

Objective: Our objective was to investigate the effect of lipid-induced insulin resistance and type 2 diabetes on skeletal muscle calpain-10 mRNA and protein levels.

Research design and methods: In the first part of this study, 10 healthy subjects underwent hyperinsulinemic euglycemic (4.5 mmol/liter) clamps for 6 h with iv infusion of either saline or a 20% Intralipid emulsion (Fresenius Kabi AG, Bad Homburg, Germany). Skeletal muscle biopsies were taken before and after 3- and 6-h insulin infusion and analyzed for calpain-10 mRNA and protein expression. In the second part of the study, muscle samples obtained after an overnight fast in 10 long-standing, sedentary type 2 diabetes patients, 10 sedentary, weight-matched, normoglycemic controls, and 10 age-matched, endurance-trained cyclists were analyzed for calpain-10 mRNA and protein content.

Results: Intralipid infusion in healthy subjects reduced whole body glucose disposal by approximately 50% (P<0.001). Calpain-10 mRNA (P=0.01) but not protein content was reduced after 6-h insulin infusion in both the saline and Intralipid emulsion trials. Skeletal muscle calpain-10 mRNA and protein content did not differ between the type 2 diabetes patients and normoglycemic controls, but there was a strong trend for total calpain-10 protein to be greater in the endurance-trained athletes (P=0.06).

Conclusions: These data indicate that skeletal muscle calpain-10 expression is not modified by insulin resistance per se and suggest that hyperinsulinemia and exercise training may modulate human skeletal muscle calpain-10 expression.

Figure 1

Glucose disposal during the insulin clamp with (LIPID) or without (CON) the simultaneous infusion of Intralipid. Values are means ± sem (n = 10). *, P < 0.05, **, P < 0.01 from CON values.

Figure 2

The effect of insulin infusion with (LIPID) or without (CON) Intralipid infusion on skeletal muscle calpain-10 mRNA (A) and putative calpain-10 protein isoforms/fragments (B). Values are means ± sem (n = 10). B, All observed bands were quantified and expressed as mean total calpain-10 protein. A representative blot from a single subject shows the observed calpain-10 immunoreactive bands in addition to the control protein (actin, 45 kDa). Calpain-10 and α-actin were analyzed on the same Western blot. *, P < 0.05 from preclamp.

Figure 3

Calpain-10 mRNA (A) and protein expression (B) in type 2 diabetic patients, sedentary normoglycemic controls, and endurance-trained subjects. Values are means ± sem (n = 10 per group). A representative blot from six subjects is shown (two subjects from each group). B, This blot shows the detection of multiple immunoreactive bands for calpain-10, some of which appear to be differentially expressed (arrows). All of these bands were quantified and expressed as mean total calpain-10 protein per group (B). †, P = 0.06 vs. diabetes group.