Responses to short‐term acid loading in proximal‐tubule‐select insulin/insulin‐like growth factor receptor dual knockout mice

Abstract

Acidosis has been associated with increased renal gluconeogenesis, which in the absence of liver compensation, can lead to hyperglycemia. Acidosis leads to glutamine uptake in the proximal tubule (PT) to liberate bicarbonate and neutralize acids. The remaining carbon skeleton can be used for glucose production at this site. Whether insulin or the related hormone, insulin‐like‐growth‐factor, type 1 (IGF1), modulate these responses to acidosis is unclear. To address this, we bred mice with dual knockout (KO) of the insulin (Insr) and the Igf1r receptors from PT by Cre‐lox recombination using a γ‐glutamyl transferase promoter. KO mice had on average 40% lower expression of both Igf1r and Insr in cortex homogenates. To address the effects of acidosis, male (M) and female (F) wild‐type (WT, Cre negative) and KO (Cre positive) mice were provided ad libitum access to normal drinking water or a water‐based solution containing 1.5% NH4Cl for 7 days (n = 6/treatment/genotype/sex). Fasting (18‐hr) blood glucose was determined in a subset of mice after one week of control then acid treatment. MKO mice showed the greatest mean rise in fasting blood glucose with acid (mg/dl, delta acid‐control): −1.67 (MWT); +15.75 (MKO); −6.40 (FWT); +4.08 (FKO). Urine (24 hr) was collected in metabolic cages on days 5–6. Acid water led to a 30–64% reduction in urine volume in all groups except MWT (ml, delta acid‐control): +0.49 (MWT); −0.54 (MKO); −0.90 (FWT); −1.50 (FKO). Blood chemistry revealed greater sensitivity to acid loading in the male KO. Mean deltas (acid‐control) for blood bicarbonate, base excess, and anion gap, respectively were (mM): −5.73, −7.8, +1.24 (MWT); −8.86, −11.30, +4.67 (MKO); −7.35, −10.36, +4.74 (FWT); −1.67, −1.92, −0.6 (FKO). Western blotting for 3 rate‐limiting enzymes in gluconeogenesis conducted on the cortex from male mice revealed a significant rise in glucose‐6‐phosphatase (G6P), phosphoenolpyruvate carboxykinase (PEPCK), and fructose bisphosphatase (FBP1) in the acid drinking WT males (16–34%). In contrast, MKO mice had a significant reduction in G6P (22%) with acid water; however, FBP1 was increased by acid drinking to a greater extent (60%) in the KO, (as compared to WT, significant interaction). Overall our studies reveal a role for PT‐associated Insr and/or Igf1r signaling in regulating PT responses to an acid load and glucose homeostasis.Support or Funding InformationGeorgetown University Medical CenterGeorgetown/Howard CTSA awardThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.