Adiponectin, Disease, and Exercise: A Narrative Review

Introduction Adiponectin, the most abundant circulating peptide secreted by adipocytes, regulates metabolism through blood glucose control and fatty acid oxidation. In contrast to the initial dogma that adipose tissue is the only source of adiponectin secretion, it has recently been demonstrated that skeletal muscle can also produce and secrete it. Hence, the identification of skeletal muscle as a source of adiponectin expression has attracted the interest of many researchers to explore its role as a circulating adipokine, as well as a myokine, with autocrine/paracrine properties. Numerous animal studies have described adiponectin as a salutary cytokine because of insulin-sensitizing, anti-inflammatory, anti-atherogenic, and anti-cancer properties. Paradoxically, other evidence suggests that elevated adiponectin levels can be associated with the induction or existence of some pathologies. However, underlying mechanisms involved in this paradox are not well-understood. On the other hand, many studies have shown the beneficial effects of long-term exercise on increased adiponectin levels, regardless of exercise protocol and status of participants. However, even approximately 25 years after the discovery of adiponectin, its properties and related mechanisms responsible for its high circulating levels, as well as how it affects various tissues and organs, remain unclear. Therefore, this study aimed to summarize and discuss the literature available to date regarding the introduction of adiponectin, its receptors, and signaling pathways in adipose tissue and skeletal muscle, along with its changes in disease and exercise conditions.