Adiponektiini

Adiponektiini, or adiponectin, is a protein hormone secreted mainly by adipocytes. It circulates in plasma as several multimeric forms—low-, middle-, and high-molecular-weight complexes—and as a globular fragment produced by proteolytic cleavage. The ADIPOQ gene encodes adiponectin in humans, with most expression in adipose tissue.

Adiponektiini acts through receptors ADIPOR1 and ADIPOR2 (and, in some tissues, T-cadherin). Receptor signaling activates AMPK and PPAR-α pathways, promoting fatty acid oxidation in liver and muscle and reducing hepatic glucose production, thereby improving insulin sensitivity. It also exerts anti-inflammatory effects and supports endothelial function.

Clinically, lower adiponektiini levels are associated with obesity, insulin resistance, type 2 diabetes, and metabolic syndrome, while levels are higher in lean individuals. Levels increase with weight loss and exercise and correlate with reduced cardiovascular risk. Because of these associations, adiponectin is studied as a biomarker and potential therapeutic target.

Isoforms differ in multimeric state and activity: full-length adiponectin forms include trimers, hexamers, and high-molecular-weight multimers, while globular adiponectin has distinct receptor interactions. Regulation is influenced by nutrition, inflammation, and hormonal signals, and post-translational modifications affect its secretion and activity.