Interactions of DPP-4 and integrin β1 influences endothelial-to-mesenchymal transition

Integrin beta 1 and dipeptidyl peptidase (DPP)-4 play roles in endothelial cell biology. Vascular endothelial growth factor (VEGF)-A inhibits endothelial-to-mesenchymal transition (EndMT) through VEGF-R2, but through VEGF-R1 promotes EndMT by reducing the bioavallability of VEGF-A. Here we tested whether DPP-4-integrin beta 1 interactions have a role in EndMT in the renal fibrosis of diabetic nephropathy. In streptozotocin-induced fibrotic kidneys in diabetic CD-1 mice, levels of endothelial DPP-4, integrin beta 1, and phospho-integrin beta 1 were all higher and associated with plasma cystatin C elevation. The DPP-4 inhibitor linagliptin ameliorated kidney fibrosis, reduced plasma cystatin C levels, and suppressed endothelial levels of DPP-4, integrin beta 1, and phospho-integrin beta 1. In cultured endothelial cells, DPP-4 and integrin beta 1 physically interacted. Suppression of DPP-4 by siRNA was associated with suppression of integrin beta 1 and vice versa. Knockdown of either integrin beta 1 or DPP-4 resulted in the silencing of TGF-beta 2-induced TGF-beta receptor heterodimer formation, smad3 phosphorylation, and EndMT. DPP-4 negatively regulated endothelial viability signaling by VEGF-R2 suppression and VEGF-R1 induction in endothelial cells. Thus, DPP-4 and integrin beta 1 interactions regulate key endothelial cell signal transduction in both physiological and pathological conditions including EndMT. Hence, inhibiting DPP-4 may be a therapeutic target for treating kidney fibrosis in diabetes.