Fiber type-selective exercise effects on AS160 phosphorylation

Abstract

Earlier research using muscle tissue demonstrated that postexercise elevation in insulin-stimulated glucose uptake (ISGU) occurs concomitant with greater insulin-stimulated Akt substrate of 160 kDa (AS160) phosphorylation (pAS160) on sites that regulate ISGU. Because skeletal muscle is a heterogeneous tissue, we previously isolated myofibers from rat epitrochlearis to assess fiber type-selective ISGU. Exercise induced greater ISGU in type I, IIA, IIB, and IIBX but not IIX fibers. This study tested if exercise effects on pAS160 correspond with previously published fiber type-selective exercise effects on ISGU. Rats were studied immediately postexercise (IPEX) or 3.5 h postexercise (3.5hPEX) with time-matched sedentary controls. Myofibers dissected from the IPEX experiment were analyzed for fiber type (myosin heavy chain isoform expression) and key phosphoproteins. Isolated muscles from the 3.5hPEX experiment were incubated with or without insulin. Myofibers (3.5hPEX) were analyzed for fiber type, key phosphoproteins, and GLUT4 protein abundance. We hypothesized that insulin-stimulated pAS160 at 3.5hPEX would exceed sedentary controls only in fiber types characterized by greater ISGU postexercise. Values for phosphorylation of AMP-activated kinase substrates (acetyl CoA carboxylaseSer79 and AS160Ser704) from IPEX muscles exceeded sedentary values in each fiber type, suggesting exercise recruitment of all fiber types. Values for pAS160Thr642 and pAS160Ser704 from insulin-stimulated muscles 3.5hPEX exceeded sedentary values for type I, IIA, IIB, and IIBX but not IIX fibers. GLUT4 abundance was unaltered 3.5hPEX in any fiber type. These results advanced understanding of exercise-induced insulin sensitization by providing compelling support for the hypothesis that enhanced insulin-stimulated phosphorylation of AS160 is linked to elevated ISGU postexercise at a fiber type-specific level independent of altered GLUT4 expression.

In vivo glucoregulation and tissue-specific glucose uptake in female Akt substrate 160 kDa knockout rats

“…A method was recently described using rat skeletal muscle that enables the measurement of glucose uptake and fiber type based on myosin heavy chain isoform expression in a single muscle fiber [11,12], but it is unlikely these analyses would be feasible using single fibers from mouse skeletal muscle. Rats have also proven to be extremely valuable for detecting a potential role for AS160 in the processes responsible for improved insulin sensitivity in skeletal muscle [13][14][15][16], so information about both male and female AS160-KO rats will be useful for future mechanistic studies.…”

Fiber type-specific effects of acute exercise on insulin-stimulated AS160 phosphorylation in insulin-resistant rat skeletal muscle

“…Recent research has indicated that the effect of acute exercise on insulin-stimulated glucose uptake is fiber type-specific in skeletal muscle from healthy rats (9). A subsequent study evaluated fiber type-selective AS160 phosphorylation in insulin-stimulated muscles from healthy rats and reported that those fiber types with exercise-induced improvement in insulin-stimulated glucose uptake were also characterized by greater AS160 phosphorylation (61). These findings provided evidence at the fiber type-specific and cellular levels consistent with the idea that AS160 plays a role in the increased insulin sensitivity after exercise in insulin-sensitive muscle.…”

“…Earlier research indicated that acute exercise can increase AS160 phosphorylation in muscles from insulin-resistant rats and humans (11,44), but the effects of exercise on fiber type-specific AS160 phosphorylation have not been reported. The evidence that exercise effects on AS160 phosphorylation are fiber type-specific in muscles from healthy rats (61) and that exercise effects on insulin-stimulated glucose uptake is fiber type-specific in muscles from insulin-resistant rats (43), provides a clear rationale for evaluating fiber-type-specific signaling processes in insulin-resistant muscle after exercise. Therefore, our first aim was to evaluate fiber-type-specific effects of exercise (both immediately postexercise and 3-h postexercise with and without insulin) on the phosphorylation of key signaling proteins (AMPK, Akt, and AS160) that have been implicated in the regulation of exercise effects on skeletal muscle glucose uptake.…”

No matter the type, when it comes to recovery all fibres are similar

“…For instance, Wang et al . (2019) reported increased TBC1D4 Ser704 phosphorylation in type I and type II fibres, but not type IIx (a subset of type II fibres) 3.5 h after exercise under insulin‐stimulated conditions. However, studies examining the underlying molecular signalling that may potentially distinguish type I and type II fibres from each other during recovery from exercise in human subjects are sparse.…”