Essential role of endothelial T-cadherin in the transcytosis of circulating high-molecular-weight adiponectin to sub-vascular tissues

BACKGROUND: Adiponectin, an adipocyte-derived protein, has diverse organ-protective effects, which are associated with its accumulation in vascular endothelial cells (VECs) as well as in various extravascular cell types, including skeletal muscle cells and cardiomyocytes. T-cadherin, a high-affinity binding partner for multimeric adiponectin, facilitates this accumulation; however, the mechanism by which high-molecular-weight (HMW) adiponectin transverses the endothelium remains unclear. METHOD AND RESULTS: We showed that tamoxifen-induced T-cadherin deficiency in VECs alone significantly increased plasma adiponectin levels, similar to inducible systemic T-cadherin deletion. The intravenous administration of adiponectin to adiponectin-deficient VEC-specific T-cadherin knockout mice markedly impaired the clearance of intravenously injected adiponectin, resulting in significant reductions in the accumulation of hexameric and HMW adiponectin, particularly the octadecameric (18-mer) form, not only in VECs, to note, but also in skeletal muscle and heart tissues. Furthermore, endothelial T-cadherin deficiency led to activation of innate immune signaling and cardiac remodeling, even under physiological conditions. In vitro experiments using MDCK II cells demonstrated that T-cadherin mediated the apical-to-basolateral transport of 18-mer adiponectin, largely preserving its HMW form. Additionally, intracellular adiponectin colocalized with the recycling endosome marker RAB11, and Rab11 deficiency significantly impaired its transcytosis. Similarly, in human VECs, T-cadherin knockdown significantly reduced basolateral adiponectin transport. CONCLUSIONS: These findings identify vascular endothelial T-cadherin as a key mediator of HMW adiponectin transcytosis via the recycling endosome pathway, enabling its traversal from the circulation to sub-vascular tissues/cells and offering a mechanistic basis for the systemic organ-protective effects of adiponectin.