Inducible Renal Tubule‐specific Insulin Receptor Knockout Mice Have Decreased NCC‐mediated Sodium Reabsorption and Reduced Sensitivity to Mineralocorticoid‐induced Hypertension in Obesity and Insulin Resistance
Authors: Nizar Jonathan M , Walczak Elisabeth M , Dong Wuxing , Bankir Lise , Bhalla Vivek 
Published: November 2023

Increased renal insulin signaling has been hypothesized to increase sodium reabsorption and drive hypertension observed in humans with obesity and insulin resistance. High fat‐fed C57BL/6 mice develop obesity, insulin resistance, increased sodium reabsorption, and a mild sodium‐sensitive increase in blood pressure. To investigate the role of tubular insulin signaling in regulating sodium reabsorption we generated an inducible pan‐tubular insulin receptor KO mouse (iTIRKO) using a Pax8 promoter‐driven tetracycline activator with TetOn‐Cre recombinase. Pax8 promoted genes are expressed throughout the tubule, collecting duct, and partially in the liver. Administration of doxycycline in adult iTIRKO mice, but not wild‐type (WT) littermates, resulted in a dramatic reduction of insulin receptor immunoreactivity in western blots of whole kidney lysates. When fed a high fat diet, these mice develop obesity identical to WT littermates and C57BL/6 mice. In both low and high fat‐fed iTIRKO and WT mice we assayed sodium transporter/channel activity by measuring acute natriuresis in response to selective inhibitors. On a high sodium diet, high fat‐fed WT mice had an enhanced NCC activity that was attenuated in iTIRKO mice as measured by natriuresis after 30mg/kg IP hydrochlorothiazide (HCTZ) (WT 204±19 vs. iTIRKO 117±11 μmol/2hr, p=0.01). NCC activity was similar in low fat‐fed iTIRKO and WT controls (106±24 and 141±23 μmol/2hr, respectively). Natriuresis was similar in all groups after administration of acetazolamide, furosemide, and benzamil. Using radiotelemetry, high fat‐fed iTIRKO mice have a similar blood pressure to WT mice on both 0.1% and 1.5% Na+ diets (mean arterial pressure on 1.5% Na+ diet iTIRKO 111.7±2.1 vs WT 110.4±0.4 mmHg, p=0.22). Chronic 30mg/kg/day HCTZ administration did not reduce blood pressure in high fat‐fed iTIRKO or WT mice (+0.4±0.5 vs. +2.0±0.5 mmHg, respectively, p=0.02). iTIRKO mice demonstrated a significantly attenuated increase in mean arterial pressure with oral administration of 3.6mg/kg fludrocortisone compared to WT mice (iTIRKO 75%±8% compared to WT, p=0.03).

In summary, high fat‐feeding enhances NCC‐mediated sodium reabsorption which is attenuated by deletion of the insulin receptor along the tubule. Tubular IR signaling also contributes to aldosterone‐mediated increased blood pressure. These data provide direct evidence for unaltered insulin sensitivity in the distal convoluted tubule which drives increased sodium reabsorption despite insulin resistance in other tissues. Whether this difference in sodium transport is responsible for the difference in aldosterone‐mediated blood pressure sensitivity is an area of ongoing investigation.

Support or Funding Information

JMN receives support from the Tashia and John Morgridge Endowed Postdoctoral Fellowship and the Child Health Research Institute at Stanford University. EMB received support from the NIH (T32 DK007357). LB and VB receive support from France‐Stanford Center for Interdisciplinary Studies. VB receives support from the NIH (1R01 DK091565).