Defective insulin clearance plays a primary role in the pathogenesis of chronic kidney disease in mice with null deletion of Ceacam2 gene
Endogenous insulin clearance occurs primarily in hepatocytes and to a lower extent in kidneys proximal tubule cells (KPTCs). CEACAM1 promotes receptor-mediated insulin uptake to be degraded in hepatocytes in a phosphorylation-dependent manner. Its deletion/inactivation causes hyperinsulinemia-driven insulin resistance, steatohepatitis and liver fibrosis. CEACAM2, the dominant CEACAM protein in murine KPTCs, shares a high homology with CEACAM1. Thus, we examined whether it regulates renal insulin disposal to maintain renal homeostasis. KPTCs derived from Ceacam2 null mice (Cc2-/-) exhibited lower receptor-mediated insulin uptake. Combined with the gradual decline in CEACAM1-dependent hepatic insulin clearance, impaired renal insulin clearance contributed to chronic hyperinsulinemia and insulin resistance starting at 10 months of age in Cc2-/-males. This was followed by proteinuria and reduced glomerular filtration rate in association with glomerulosclerosis and tubulointerstitial damage. Increased collagen deposition in Cc2-/- kidneys could be mediated in part, by hyperinsulinemia-driven activation of the 5{beta}1 integrin-focal adhesion kinase (FAK) signaling pathways. Together, the data demonstrated that loss of CEACAM2 impaired renal insulin clearance that contributed to hyperinsulinemia and resultant insulin resistance, followed by kidney dysfunction and renal fibrosis. This study provided an in vivo demonstration of the regulation of kidney function by insulin clearance along the liver-kidney axis.