Circulating adiponectin and adiponectin receptor expression in skeletal muscle: effects of exercise

Abstract

Excess visceral fat can regulate insulin sensitivity and energy metabolism by releasing adipokines into the circulation which then bind with their cognate receptors in various tissues and alter glucose and lipid metabolism. Circulating levels of adiponectin, which promotes glucose uptake into skeletal muscle and increases fat oxidation rates, are decreased in obesity. Strategies to enhance the insulin-like and insulin-sensitizing actions of adiponectin have been shown to be effective in improving metabolic abnormalities associated with obesity and diabetes. Interestingly, the insulin-sensitizing effects of exercise have similar metabolic effects as adiponectin in that exercise also promotes glucose uptake into muscle and increases rates of fatty acid oxidation. Recent studies have begun to examine the potential role of adiponectin in mediating the insulin-sensitizing action of exercise by investigating changes in plasma adiponectin levels and tissue-specific adiponectin receptor (AdipoR) expression. In this review, we have summarized the key findings to date which suggest that changes in expression of AdipoR isoforms in skeletal muscle, rather than circulating total adiponectin levels, may be of physiological importance.

Adiponectin Receptors Form Homomers and Heteromers Exhibiting Distinct Ligand Binding and Intracellular Signaling Properties

“…These data indicate that the various forms of adiponectin operate differently on AdipoR complexes, which could in turn affect the endocytic trafficking and signaling of the receptor complex. In this regard it is important to stress that the different forms of adiponectin mediate distinct and often tissue-specific effects (14,51). Together, these and our findings support the notion that activation of distinct signal transduction pathways by the different adiponectin isoforms is due at least in part to the presence of AdipoR complexes.…”

Physical exercise-induced hippocampal neurogenesis and antidepressant effects are mediated by the adipocyte hormone adiponectin

“…Interestingly, we observed an increase in hippocampal adiponectin without a concomitant increase in the serum of WT runners. This could reflect that the 2-wk training is insufficient to produce a substantial elevation of adiponectin in the circulation (12) or that exercise potentially facilitates the transport of adiponectin from the circulation into the brain. It is also possible that this increase was produced by adipose or nervous tissues inside the brain (33).…”

“…Additionally, both receptors have been found in several brain regions, including cortex, hypothalamus, pituitary gland, and hippocampus (11). One of the unique features of adiponectin is that, like exercise, it promotes glucose uptake in skeletal muscle and suppresses glucose production in liver (12). Furthermore, both adiponectin and exercise exhibit antidiabetic, antiinflammatory, antiatherogenic and cardio-protective properties (13).…”

Obesity, inflammation, and insulin resistance

“…Adiponectin plays an important role in lipid and glucose homeostasis, both directly and as a modulator of insulin sensitivity (Vu, Riddell, Sweeney, 2007). In addition, it has anti-inflammatory, antiapoptotic, and proangiogenic activity, but mechanisms for these are not well known (Krentz, Von Mühlen, Barrett-Connor, 2009;Landskroner-Eiger et al, 2009).…”