322 - Early Life Sodium Restriction Programs Cardiometabolic Dysfunction via Angiotensin AT1R in the Hypothalamus

Publication Number: 3311.322

Katie J. McShea, Medical College of Wisconsin, Wauwatosa, WI, United States; Samuel Lawton, Medical College of Wisconsin, Milwaukee, WI, United States; Connie Grobe, Medical College of Wisconsin, Milwaukee, WI, United States; John Reho, Medical College of Wisconsin, Milwaukee, WI, United States; Justin L.. Grobe, Medical College of Wisconsin, Milwaukee, WI, United States; Jeffrey Segar, Medical College of Wisconsin, Milwaukee, WI, United States

Background: Preterm infants are at increased risk adult-onset cardiometabolic disease. These infants are also at risk for sodium (Na) depletion due to renal immaturity. Na deficit is a strong stimulant of the renin-angiotensin system (RAS), and we and others have previously implicated the hypothalamic RAS as a controller of cardiovascular and metabolic functions. Our preclinical studies show Na restriction during critical windows of hypothalamic maturation (e.g., 3-6 wk of age in mice equates to third trimester of gestation in humans), is sufficient to program alterations in cardiometabolic control.

Objective: Test the hypothesis that that early-life Na depletion contributes to programming of cardiometabolic dysfunctions in adulthood via angiotensin II type I receptor (AT1R ) signaling.

Design/Methods: All mice received either a Na restricted (0.04%) or supplemented (0.30%) diet from 3-6 wk of age, and a standard 0.15% Na diet thereafter. A cohort of C57BL/6J (n=8M/group) received the AT1R antagonist losartan (0.3g/L) or vehicle in drink at 9-10 wk of age. A second cohort of mice harboring a conditional allele for the endogenous angiotensin II type 1 receptor (AT1R; Agtr1aFLOX/FLOX) received bilateral injection of an AAV encoding Cre-recombinase (n= 9M+8F) or a GFP control (n=10M+8F) into the hypothalamic arcuate nucleus (ARC). Body composition was assessed by nuclear magnetic resonance, and energy balance evaluated using a Promethion multiplexed phenotyping system at 10 wk of age.

Results: Early-life Na restriction programmed a significant (12%, p< 0.05) increase in resting metabolism at 10 weeks of age that was ameliorated by administration of losartan rate (p < 0.05; Fig 1). Conditional deletion of AT1R from the ARC caused exaggerated body mass (M: 1.1±0.1 vs 2.2±0.1; F: 0.6±0.1 vs 2.2±0.3 g/wk; virus p< 0.01) and adiposity gains associated with failure to increase energy expenditure, while caloric intake was unchanged (Fig 2). Ongoing studies are investigating the impact of these alterations on cardiometabolic function in animals maintained on a standard sodium diet.

Conclusion(s): Early-life Na restriction results in programmed changes in energy expenditure that are maintained into adulthood, even after Na repletion, by a mechanism involving AT1R within the hypothalamic ARC. By extension, these findings identify hypothalamic circuits within the ARC that express AT1R as potential contributors to the life-long increased risk of cardiometabolic disease conferred by preterm birth.

Figure 1. Blockade of AT1R via losartan treatment (0.3g/L in drink) normalizes resting metabolic rate (RMR) after early-life sodium restriction.
PAS abstract Fig 1.pdfRMR (kcal/h) adjusted for fat-free mass (FFM) by General Linear Model (GLM) at 10 weeks of age in C57BL/6J males exposed to vehicle or Losartan between 9–10 weeks of age. *p < 0.05 by Šídák's multiple comparisons test. n=8M for each group.

Figure 2. Conditional genetic deletion of AT₁R from the hypothalamic arcuate nucleus significantly increases weight gain after early-life sodium restriction due to failure to increase energy expenditure.
PAS abstract Fig 2.pdfA, Body mass (g) versus age in Agtr1a^FLOX/FLOX^ mice receiving bilateral injection of AAV-Cre or AAV-GFP into the ARC at 8 weeks of age. *p < 0.05 by Šídák's multiple comparison procedure.B, Average food intake (g/d) at 10 weeks of age, corrected for body mass by GLM.C, 24h average heat production (kcal/h) at 10 weeks of age, corrected for body mass by GLM.For all panels, GFP n=12M+10F vs Cre n=11M+9F.