Adiponectin (also known as AdipoQ or ACRP30) is a 244 amino acid monomer adipokine with a molecular weight of approximately 26 kDa. Adiponectin is the most abundant peptide hormone secreted by white adipocytes. Since discovering adiponectin in the 1990s, it has become a widely accepted biomarker for obesity-related diseases such as metabolic syndrome, Type 2 Diabetes mellitus, and atherosclerotic cardiovascular disease (ASCVD).
Adiponectin is present at high concentrations in plasma (3–30 μg/ml), which accounts for up to 0.05% of total serum protein. Adiponectin forms a wide range of multimeric species, including low molecular weight (LMW) trimers, medium molecular weight (MMW) hexamers, and high-molecular-weight (HMW) multimers. The HMW is considered to be the most biologically active form of adiponectin. Adiponectin contains two distinct domains; the N-terminal domain is a collagen-like sequence, and the C-terminal globular domain is homologous to the globular complement factor C1q. The C-terminal globular domain of adiponectin is highly similar to the structure of tumor necrosis factor-α (TNF-alpha).
Adiponectin plays a major role in cellular processes such as energy metabolism, insulin sensitivity, and inflammation. Adiponectin elicits biological activities through interaction with the cell surface receptors AdipoR1 and AdipoR2. T-cadherin (also known as cadherin 13 and H-cadherin) is considered a non-signaling receptor for adiponectin. AdipoRs are expressed in most tissues, including immune cells such as monocytes, B cells, and NK cells. However, AdipoR1 is mainly expressed in skeletal muscle, while AdipoR2 is mostly expressed in the liver. T-cadherin is highly expressed in injured vascular endothelial and smooth muscle cells.
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