OBJECTIVE One of the suggested mechanisms of obesity-induced insulin resistance is mitochondrial dysfunction in target tissues such as skeletal muscle. In our study, we examined whether resistin, an adipokine associated with obesity-mediated insulin resistance, induced metabolic disorders by impairing mitochondrial homeostasis.

METHODS The morphology and function of mitochondria of skeletal muscle were examined in resistin-knockout and humanized resistin mice that were subjected to high-fat diet for 3 months. Morphology was examined by transmission electron microscopy. Mitochondria bioenergetics of skeletal muscle were evaluated using a Seahorse XF96 analyzer. Human skeletal myoblasts were used for in vitro studies on signaling mechanisms in responses to resistin.

RESULTS A high-fat diet in humanized resistin mice increased fragmented and shorter mitochondria in the skeletal muscle, whereas resistin-knockout mice had healthy normal mitochondria. In vitro studies showed that human resistin treatment impaired mitochondrial homeostasis by inducing mitochondrial fission, leading to a decrease in ATP production and mitochondrial dysfunction. Induction of mitochondrial fission by resistin was accompanied by increased formation of mitochondria-associated ER membranes (MAM). At the same time, resistin induced up-regulation of the protein kinase A (PKA) pathway. This activation of PKA induced phosphorylation of Drp1 at serine 616, leading to Drp1 activation and subsequent induction of mitochondrial fission. The key molecule that mediated human resistin-induced mitochondrial fission was adenylyl cyclase-associated protein 1 (CAP1), which was reported as a bona fide receptor for human resistin. Moreover, our newly developed biomimetic selective blocking peptide could repress human resistin-mediated mitochondrial dysfunction. High-fat diet-fed mice showed lower exercise capacity and higher insulin resistance, which was prevented by a novel peptide to block the binding of resistin to CAP1 or in the CAP1-knockdown mice.

CONCLUSIONS Our study demonstrated that human resistin induces mitochondrial dysfunction by inducing abnormal mitochondrial fission. This result suggests that the resistin-CAP1 complex could be a potential therapeutic target for the treatment of obesity-related metabolic diseases such as diabetes and cardiometabolic diseases.