Adiponectin, also known as Acrp30, AdipoQ, GBP-28, and apM1, is a 244-amino acid protein primarily secreted by adipose tissue. It was identified almost simultaneously by four different research groups using various approaches . Adiponectin is the most abundant peptide secreted by adipocytes and plays a crucial role in regulating metabolic processes, including glucose regulation and fatty acid oxidation .
Adiponectin circulates in the blood in three isoforms: high-molecular weight (HMW), middle-molecular weight (MMW), and low-molecular weight (LMW) complexes . These isoforms are produced through multimerization, a process involving several endoplasmic reticulum-associated proteins such as ER oxidoreductase 1-α (Ero1-α), ER resident protein 44 (ERp44), disulfide-bond A oxidoreductase-like protein (DsbA-L), and glucose-regulated protein 94 (GPR94) . The HMW complexes are particularly significant as they have predominant actions in metabolic tissues .
Adiponectin has several important biological functions:
Adiponectin exerts its effects through two main receptors, AdipoR1 and AdipoR2 . These receptors are expressed in various tissues, including the liver, skeletal muscle, and vascular endothelial cells. Upon binding to its receptors, adiponectin activates several signaling pathways that lead to increased glucose uptake and fatty acid oxidation .
Given its beneficial effects on metabolism, adiponectin has been studied as a potential therapeutic target for treating obesity, insulin resistance, type 2 diabetes, and cardiovascular diseases . Studies have shown that adiponectin administration in humans and rodents can have insulin-sensitizing, anti-atherogenic, and anti-inflammatory effects . In certain settings, it has also been observed to decrease body weight .