Abstract Body: Dietary intake of high fat and sodium has been associated with metabolic syndrome and an increased risk of hypertension, yet the underlying mechanisms remains poorly understood. Few studies have investigated the renal NaCl transport mechanisms that contribute to hypertension in mouse models of diet-induced obesity. We hypothesized that chronic consumption of a high-fat combined with high-salt (HFHS) diet induces salt-sensitive hypertension and impairs renal function, in part through increased NKCC2 expression in the thick ascending limb of Henle’s loop (TAL). To test this, 8-week-old male C57BL/6J mice were divided into four groups to receive: regular chow (NF/NS), high-salt diet (HS; 4% NaCl), high-fat diet (HF; 60% kcal from fat), or combined HFHS diet (60% fat + 4% NaCl). Body weight was recorded at baseline and measured monthly for 16 weeks. Systolic blood pressure (SBP) was measured via tail-cuff plethysmography after a 3-week training period. To assess renal function, glomerular filtration rate (GFR) was measured using FITC-inulin in conscious mice. Protein expression of renal sodium transporters NKCC2 and NCC were quantified via Western Blot.
After 8 weeks, HFHS and HF-fed mice exhibited greater body weight compared to NS or HS groups (Week 16: NS: 33.8±2.0 ; HF: 44.8±0.8 ; HS: 33.3±0.8 ; HFHS: 42.0±2.2 g; n=5; p<0.05 HFHS vs NS). Only the HFHS group showed a sustained increase in SBP from baseline, reaching a 16-week maximum of 145±5 mmHg (Δ +36±5 mmHg from baseline; NS: 119±6, HF 133±12, HS: 132±5 mmHg; p<0.05). At 16 weeks, GFR in the HFHS group declined by 55% (NS: 255±46, HF: 227±19; HS: 241 ± 42, HFHS: 149 ± 30 µl/min; p<0.05 vs NS or HF). Mice were sacrificed after 18 weeks to obtain medullary and cortical tubule suspensions. In medullary TALs, HFHS increased total NKCC2 expression by 280±13%, and phosphorylated Thr96,101 NKCC2 by 400±20% compared to NS. HF alone did not change total or phosphorylated NKCC2. Total and phosphorylated NCC (Thr53) levels in cortical tubule suspensions remained unchanged compared to NS. HF alone did not affect NCC. We conclude that a combined high-fat plus high-salt diet induces salt-sensitive hypertension and impairs renal function. Salt sensitivity may be in part due to enhanced sodium reabsorption via NKCC2 in the TAL. Our data support a role for NKCC2 as a mediator of hypertension in in patients with chronic obesity.