Deletion of the Insulin Receptor in the Proximal Tubule Promotes Hyperglycemia

Abstract

Nearly all renal tubular epithelial cells express insulin receptor. The insulin receptor in the distal tubule appears to modulate BP, but the role of the insulin receptor in the proximal tubule is unknown. Here, we selectively knocked out the insulin receptor from the proximal tubules of mice. Western blotting confirmed a two-to three-fold reduction in renal cortical homogenate insulin receptor-b among knockout mice compared with wild-type littermates. Young knockout mice exhibited a mildly diabetic phenotype, evidenced by higher fasting plasma glucose levels than wild-type mice. Assessments by hyperinsulinemic-euglycemic clamp and a glucose tolerance test revealed no differences in insulin sensitivity or overt pancreatic function, respectively. Renal cortical mRNA expression and enzyme activity of glucose-6-phosphatase, which catalyzes the final step of glucose production, were significantly higher in knockout mice. Taken together, these results support a role for insulin receptor in the proximal tubule in the modulation of systemic glucose levels. Downregulation of the insulin receptor in the proximal tubule, which occurs in insulinresistant states, may promote hyperglycemia through enhanced gluconeogenesis.

Adiponectin, Leptin, and Fatty Acids in the Maintenance of Metabolic Homeostasis through Adipose Tissue Crosstalk

“…An increase in gluconeogenesis, and hence, PEPCK activity, generates additional HCO 3 − exported by the proximal tubule to raise blood pH during metabolic acidosis (Curthoys and Moe, 2014). Deletion of the insulin receptor in tubule epithelium induces systemic hyperglycemia in the mouse (Tiwari et al, 2013). Increased glucose uptake under high glucose and high insulin conditions result in increased glycogen deposition (Gerich et al, 2001) and a reduction in fatty acid oxidation in the cortex (Meyer et al, 1997).…”

Podocytes, Signaling Pathways, and Vascular Factors in Diabetic Kidney Disease

“…Indeed Mima, et al 18 have shown in models of both type 1 and type 2 diabetes that glomerular insulin signaling is lost early in disease progression. Conversely, insulin signaling in the tubular compartment, which controls ion reabsorption from the filtrate, as well as blood pressure and systemic glucose control 19 are not affected. Compelling evidence from human studies shows that systemic insulin resistance is associated with proteinuric kidney disease in non-diabetic patients 20 and that, in the setting of diabetes, insulin resistance predicts those patients who will develop nephropathy in both type 1 21-23 and type 2 diabetes 24 .…”

Greater efficacy of atorvastatin versus a non-statin lipid-lowering agent against renal injury: potential role as a histone deacetylase inhibitor

“…Total RNA (500 ng) from rat Kidney cortex was subjected to RT-qPCR using SYBR-green PCR Master Mix (Applied Biosystems) as described previously7475767778 qPCRs using SYBR green reagent with gene-specific primers and GAPDH gene primers (internal control). The gene specific primers for rat were: E-cadherin- GCCCAGGAAATACACCCCTC (F) and ACTCAGGTCCAAATCAGCCG (R); collagen IVα- GGAGAACAAGGGGTCAGTGG (F) and TCCTGTTGGGGCAAAGTCTC (R); fibronectin- CCTGTGTTCTCCCGTTTCACT (F) and TGTGCTACACCACAGATGTCC (R); TGF-β- TCCCAACTACAGAAAAGCAGTCA (F) and GCAATGCAGACGAAGCAGAC (R); IL6- CCCAACTTCCAATGCTCTCCT (F) and GGATGGTCTTGGTCCTTAGCC (R); IL-18- GAACTGAGCCCCTCCCTACTA (F) and TGTCTTCAATCCATCCCAGAGC (R); MMP-2- AAGGATGGAGGCACGATTGG (F) and GGGAACTTGATGATGGGCGA (R); MMP-9- ATGGTTTCTGCCCCAGTGAG (F) and CCTTTAGTGGTGCAGGCAGA (R); RAGE-GAGGATGAGGGCATCTACAGC (F) and TCACCGGTTTCTGTGACCC (R), and GAPDH gene primers (AGGTCGGTGTGAACGGATTTG(F) and TGTAGACCATGTAGTTGAGGTCA (R).…”

“…Protein levels from rat kidney cortex homogenates and from cell lysates were quantitated using immunoblotting as described by us previously7374757677787980. The antibodies against HDACs (Cell signalling technology, MA USA), E-cadherin, Fibronectin, Collagen, RAGE (Santa Cruz Biotechnology, USA), TGF-beta, Histone H3, acetyl Histone H3 (Abcam MA USA) and anti-acetyl Histone H4 (Millipore) and, anti-β-actin (Cell signalling technology, MA USA) were used and signals were detected using a chemi-luminiscence-based detection system (Amersham).…”