Acute bout of exercise downregulates thioredoxin-interacting protein expression in rat contracting skeletal muscles.

We previously reported that in rat skeletal muscle, disuse (i.e., decreased muscle contractile activity) rapidly increases thioredoxin-interacting protein (TXNIP), which is implicated in the reduced glucose uptake. Accordingly, we sought herein to (a) determine the effect of exercise (i.e., increased muscle contractile activity) on muscle TXNIP protein expression, and (b) elucidate the mechanisms underlying the changes of TXNIP protein expression in response to exercise. Rat epitrochlearis and soleus muscles were dissected out after an acute bout of 3-hr swimming (without weight loading) or 3-hr treadmill running (15% grade at 9m/min). In a separate protocol, the isolated epitrochlearis and soleus muscles were incubated for 3 hr with AMP-dependent protein kinase activator AICAR. Immediately after the cessation of the 3-hr swimming, the TXNIP protein was decreased in epitrochlearis but not in soleus muscle. Conversely, 3-hr treadmill running decreased the TXNIP protein in soleus but not in epitrochlearis muscle. TXNIP protein was decreased concomitantly with reduced postexercise muscle glycogen, showing that a decrease in TXNIP protein expression occurs in muscles that are recruited during exercise. In addition, 3-hr incubation with AICAR decreased TXNIP protein in both isolated epitrochlearis and soleus muscles. Our results suggest that (a) an acute bout of exercise downregulates TXNIP protein expression in rat contracting skeletal muscles, and (b) the reduction in TXNIP protein expression in contracting muscles is probably mediated by AMPK activation, at least in part.

Immobilization rapidly induces thioredoxin-interacting protein gene expression together with insulin resistance in rat skeletal muscle.

Acute short duration of disuse induces the development of insulin resistance for glucose uptake in rodent skeletal muscle. Because thioredoxin-interacting protein (TXNIP) has been implicated in the downregulation of insulin signaling and glucose uptake, we examined the possibility that muscle disuse rapidly induces insulin resistance via increased TXNIP mRNA and protein expression. Male Wistar rats were subjected to unilateral 6-h hindlimb immobilization by plaster cast. At the end of this period, the soleus muscles from both immobilized and contralateral nonimmobilized hindlimbs were excised and examined. The 6-h immobilization resulted in an increase in TXNIP mRNA and protein expressions together with a decrease in insulin-stimulated 2-deoxyglucose uptake in the rat soleus muscle. Additionally, in the rats euthanized 6 h after the plaster cast removal, TXNIP protein expression and insulin-stimulated glucose uptake in the immobilized muscle had both been restored to a normal level. Various interventions (pretreatment with transcription inhibitor actinomycin D or AMP-dependent protein kinase activator 5-aminoimidazole-4-carboxamide ribonucleotide) also suppressed the increase in TXNIP protein expression in 6-h-immobilized muscle together with partial prevention of insulin resistance for glucose uptake. These results suggested the possibility that increased TXNIP protein expression in immobilized rat soleus muscles was associated with the rapid induction of insulin resistance for glucose uptake in that tissue. NEW & NOTEWORTHY The cellular mechanism by which disuse rapidly induces muscle insulin resistance for glucose uptake remains to be identified. Using a rat hindlimb immobilization model, our findings suggest the possibility that transcriptional upregulation of thioredoxin-interacting protein is associated with the immobilization-induced rapid development of insulin resistance in skeletal muscle.

Immobilization rapidly induces muscle insulin resistance together with the activation of MAPKs (JNK and p38) and impairment of AS160 phosphorylation.

Acute short-duration physical inactivity induces the development of insulin resistance for glucose uptake in skeletal muscle. We examined the possibility that inactivity rapidly induces muscle insulin resistance via the excessive activation of proinflammatory/stress pathways including those of IKK/IκB/NF-κB, JNK, and p38 MAPK We also examined the other possibility that inactivity-induced rapid development of insulin resistance is associated with reduced phosphorylation of AS160, the most distal insulin-signaling protein that have been linked to the regulation of glucose uptake. Male Wistar rats were subjected to unilateral hindlimb immobilization for 6 h. At the end of the immobilization, the soleus muscles from both immobilized and contralateral non-immobilized hindlimbs were dissected out. Immobilization decreased insulin-stimulated 2-deoxyglucose uptake in rat soleus muscle within 6 h. This rapid development of insulin resistance was accompanied by elevated phosphorylation of both JNK and p38 (commonly used indicator of JNK and p38 pathway activity, respectively). In addition, the abundance of SPT2, a rate-limiting enzyme regulating ceramide biosynthesis, was increased in immobilized muscle. Immobilization did not alter the abundance of IκBα (commonly used indicator of IKK/IκB/NF-κB pathway activity). The basal phosphorylation of AS160 at Thr642 and Ser588 was decreased together with the development of insulin resistance. These results suggest the possibility that inactivity-induced rapid development of insulin resistance in immobilized muscle is related to enhanced activation of JNK and/or p38. Elevated ceramide biosynthesis pathway may contribute to this activation. Our results also indicate that decreased basal phosphorylation of AS160 may be involved in inactivity-induced insulin resistance.

Increased postexercise insulin sensitivity is accompanied by increased AS160 phosphorylation in slow-twitch soleus muscle.

A single bout of exercise can enhance insulin-stimulated glucose uptake in both fast-twitch (type II) and slow-twitch (type I) skeletal muscle for several hours postexercise. Akt substrate of 160 kDa (AS160) is most distal insulin signaling proteins that have been proposed to contribute to the postexercise enhancement of insulin action in fast-twitch muscle. In this study, we examined whether the postexercise increase in insulin action of glucose uptake in slow-twitch muscle is accompanied by increased phosphorylation of AS160 and its paralog TBC1D1. Male Wistar rats (~1-month-old) were exercised on a treadmill for 180 min (9 m/min). Insulin (50 µU/mL)-stimulated glucose uptake was increased at 2 h after cessation of exercise in soleus muscle composed of predominantly slow-twitch fibers. This postexercise increase in insulin action of glucose uptake was accompanied by increased phosphorylation of AS160 (detected by phospho-Thr642 and phospho-Ser588 antibody). On the other hand, prior exercise did not increase phosphorylation of TBC1D1 (detected by phospho-Thr590) at 2 h postexercise. These results suggest the possibility that an enhancement in AS160 phosphorylation but not TBC1D1 phosphorylation is involved with increased postexercise insulin action of glucose uptake in slow-twitch muscle.

Elevation of muscle temperature stimulates muscle glucose uptake in vivo and in vitro.

The purpose of this study was to examine whether elevation of muscle temperature per se might be a stimulatory factor to increase muscle glucose uptake. Heat stimulation to rat hindlimbs increased glucose uptake measured in vivo in the extensor digitorum longus (EDL) and soleus muscles with a significant increase in muscle temperature. This thermal effect was observed again when glucose uptake was measured in vitro in both isolated muscles immediately after the heat stimulation in vivo. When heat stimulation was imposed on isolated EDL muscles, glucose uptake was facilitated in proportion to the increase in muscle temperature. The heat stimulation led to a significant amplification in the phosphorylation of AMP-activated protein kinase (AMPK) and Akt, and treatment with compound C, wortmannin, or LY294002 partially blocked the thermal effect on muscle glucose uptake. We provide evidence that elevation of muscle temperature per se can directly stimulate muscle glucose uptake and that this thermal effect is compound C-, wortmannin-, and LY294002-inhibitable.