Reversal of diet-induced insulin resistance with a single bout of exercise in the rat: the role of PTP1B and IRS-1 serine phosphorylation

Abstract

Lifestyle interventions including exercise programmes are cornerstones in the prevention of obesity-related diabetes. In this study, we demonstrate that a single bout of exercise inhibits high-fat diet-induced insulin resistance. Diet-induced obesity (DIO) increased the expression and activity of the protein tyrosine phosphatase 1B (PTP1B) and attenuated insulin signalling in gastrocnemius muscle of rats, a phenomenon which was reversed by a single session of exercise. In addition, DIO was observed to lead to serine phosphorylation of insulin receptor substrate 1 (IRS-1), which was also reversed by exercise in muscle in parallel with a reduction in c-Jun N-terminal kinase (JNK) activity. Thus, acute exercise increased the insulin sensitivity during high-fat feeding in obese rats. Overall, these results provide new insights into the mechanism by which exercise restores insulin sensitivity.

Figure 1. Effects of acute exercise on glucose uptake and glycogen content in control, DIO and DIO + EXE rats

A, steady-state glucose infusion rates obtained from averaged rates of 90–120 min of 10% unlabelled glucose infusion during hyperinsulinaemic–euglycaemic clamp procedures in the control, DIO and DIO rats submitted to acute exercise. B, glucose transport in gastrocnemius muscle was evaluated by 2-deoxy-d-glucose uptake during the last 45 min of the hyperinsulinaemic–euglycaemic clamp studies. C, muscular glycogen content is expressed as mg (100 g tissue)⁻¹. Bars represent means ±s.e.m. of n = 5 rats. *P < 0.05, versus DIO rats.

Figure 2. Insulin signalling in muscle of controls, DIO and DIO + EXE rats

Muscle extracts from rats injected with saline or insulin were prepared as described in the Methods. A, tissue extracts were immunoprecipitated (IP) with anti-IRβ antibody and immunoblotting (IB) with anti-PY antibody (upper panel) or anti-IRβ antibody (lower panel). B and C, tissue extracts were also IP with anti-IRS-1 and anti-IRS-2 antibodies and IB with anti-PY antibody (upper panels), anti-PI3K antibodies (middle panels) or anti-IRS-1, anti-IRS-2 antibody (lower panel). D, muscle extracts were IB with anti-phospho Akt and anti-Akt antibody (upper and lower panel, respectively). The results of scanning densitometry were expressed as arbitrary units. Bars represent means ±s.e.m. of n = 6–8 rats. *P < 0.05, versus DIO rats.

Figure 3. Effect of acute exercise on PTP1B protein levels, activity and PTP1B association with IRβand IRS-1

A, PTP1B protein level in DIO and DIO + EXE rats were compared with control group. B, PTP1B assay was performed as described in the Methods. C, tissue extracts were immunoprecipitated (IP) with anti-IRβ followed by immunoblotting (IB) with anti-PTP1B antibody or anti-IRβ antibody (upper and lower panels). D, insulin-stimulated IRβ phosphorylation (•) and the IRβ–PTP1B association (□) were determined using IP with anti-IRβ and IB with anti-PY antibody and IP with anti-IRβ followed by IB with anti-PTP1B antibody. E, IP with anti-IRS-1 followed by IB with anti-PTP1B antibody to evaluated the IRS-1–PTP1B association (upper panel). Muscle extracts were also IP with anti-IRS-1 and IB with anti-IRS-1 antibody (lower panels). The results of scanning densitometry were expressed as arbitrary units. Bars represent means ±s.e.m. of n = 6–8 rats. *P < 0.05, versus control and #P < 0.05, DIO + EXE versus DIO.

Figure 4. Effect of acute exercise on IRS-1 serine phosphorylation, JNK activity, IκBα degradation and IRS-1 and JNK protein levels in muscle of controls, DIO and DIO + EXE rats

Tissue extracts were immunoblotted (IB) with anti-IRS-1307 phosphoserine antibody (A upper panel), anti IRS-1 antibody (A lower panel), anti-phospho JNK antibody (B upper panel), anti-JNK antibody (B lower panel), antiphospho-c-Jun antibody (C), anti-IκBα antibody (D) and anti-SOCS3 (E) in control, DIO and DIO + EXE rats. The results of scanning densitometry were expressed as arbitrary units. Bars represent means ±s.e.m. of n = 6–8 rats. *P < 0.05, versus control and #P < 0.05, DIO + EXE versus DIO.