Abstract P111: Deletion Of Na + /H + Exchanger 3 Selectively In The Proximal Tubules Doesn’T Prevent The Development Of Doca-salt Hypertension In Pt- Nhe3 -/- Mice

We have previously shown that genetic deletion of Na + /H + exchanger 3 (NHE3) selectively in the proximal tubules lowered basal blood pressure and attenuated the development of angiotensin II (Ang II)-induced hypertension by promoting the pressure-natriuresis response. However, it is not known whether deletion of the NHE3 gene selectively in the proximal tubules attenuates salt-sensitive hypertension induced by DOCA-Salt. In the present study, we tested the hypothesis that the development of DOCA-Salt hypertension is attenuated by genetic deletion of NHE3 selectively in the proximal tubules of the kidney. To test the hypothesis, mice with proximal tubule-specific deletion of NHE3, i.e., PT- Nhe3 -/- , were generated using the iL- Sglt2-Cre / Nhe3 flox approach. Adult male PT- Nhe3 -/- mice were treated with or without DOCA (10 mg/10 g body wt., subcutaneously), supplemented with 2% high salt diet, for 4 weeks. Basal and weekly systolic (SBP), diastolic (DBP), and mean arterial pressure (MAP) were determined using the indirect tail-cuff method, whereas 24 hr. urinary sodium, potassium, and chloride excretion were determined using a metabolic cage. Compared with the time-control group (n=12), treatment with DOCA-salt moderately but significantly increased systolic SBP from 96 ± 3 mmHg to 126 ± 5 mmHg in PT- Nhe3 -/- mice (n=8; P <0.01). DBP and MAP increased to similar extents in response to DOCA-salt treatment ( P <0.05). As expected, DOCA-salt hypertension significantly increased the pressure-natriuresis response, i.e., 24 hr. urinary sodium excretion by 55% (Control: 152 ± 19 vs. DOCA-Salt: 236 ± 2 μmol/24 hr; P <0.01), potassium excretion by 52% (Control: 147 ± 16 vs. DOCA-Salt: 224 ± 18 μmol/24 hr; P <0.01), and chloride excretion by 71% (Control: 181 ± 27 vs. DOCA-Salt: 310 ± 31 μmol/24 hr; P <0.01), respectively. Taken together, these data do not support our hypothesis and suggest that deletion of NHE3 selectively in the proximal tubules doesn’t prevent the development of DOCA-Salt hypertension in PT- Nhe3 -/- mice.

Intratubular, Intracellular, and Mitochondrial Angiotensin II/AT1 (AT1a) Receptor/NHE3 Signaling Plays a Critical Role in Angiotensin II-Induced Hypertension and Kidney Injury

Hypertension is well recognized to be the most important risk factor for cardiovascular diseases, stroke, and end-stage kidney failure. A quarter of the world’s adult populations and 46% of the US adults develop hypertension and currently require antihypertensive treatments. Only 50% of hypertensive patients are responsive to current antihypertensive drugs, whereas remaining patients may continue to develop cardiovascular, stroke, and kidney diseases. The mechanisms underlying the poorly controlled hypertension remain incompletely understood. Recently, we have focused our efforts to uncover additional renal mechanisms, pathways, and therapeutic targets of poorly controlled hypertension and target organ injury using novel animal models or innovative experimental approaches. Specifically, we studied and elucidated the important roles of intratubular, intracellular, and mitochondrial angiotensin II (Ang II) system in the development of Ang II-dependent hypertension. The objectives of this invited article are to review and discuss our recent findings that (a) circulating and intratubular Ang II is taken up by the proximal tubules via the (AT₁) AT_1a receptor-dependent mechanism, (b) intracellular administration of Ang II in proximal tubule cells or adenovirus-mediated overexpression of an intracellular Ang II fusion protein selectively in the mitochonria of the proximal tubules induces blood pressure responses, and (c) genetic deletion of AT₁ (AT_1a) receptors or the Na⁺/H⁺ exchanger 3 selectively in the proximal tubules decreases basal blood pressure and attenuates Ang II-induced hypertension. These studies provide a new perspective into the important roles of the intratubular, intracellular, and mitochondrial angiotensin II/AT₁ (AT_1a) receptor signaling in Ang II-dependent hypertensive kidney diseases.

Sex differences in angiotensin II-induced hypertension and kidney injury: role of AT1a receptors in the proximal tubule of the kidney

In the present study, we tested the hypothesis that there are significant sex differences in angiotensin II (Ang II)-induced hypertension and kidney injury using male and female wildtype (WT) and proximal tubule-specific AT1a receptor knockout mice (PT-Agtr1a-/-). Twelve groups (n=8-12 per group) of adult male and female WT and PT-Agtr1a-/- mice were infused with a pressor dose of Ang II via osmotic minipump for 2 weeks (1.5 mg/kg/day, i.p.) and simultaneously treated with or without losartan (20 mg/kg/day, p.o.) to determine the respective roles of AT1a receptors in the proximal tubules versus systemic tissues. Basal systolic, diastolic, and mean arterial pressure were approximately 13 ± 3 mmHg lower (P<0.01), while basal 24-h urinary Na+, K+, and Cl- excretion were significantly higher in both male and female PT-Agtr1a-/- mice than WT controls (P<0.01) without significant sex differences between different strains. Both male and female WT and PT-Agtr1a-/- mice developed hypertension (P<0.01), and the magnitudes of the pressor responses to Ang II were similar between male and female WT and PT-Agtr1a-/- mice (n.s.). Likewise, Ang II-induced hypertension was significantly attenuated in both male and female PT-Agtr1a-/- mice (P<0.01). Furthermore, losartan attenuated the hypertensive responses to Ang II to similar extents in both male and female WT and PT-Agtr1a-/- mice. Finally, Ang II-induced kidney injury was attenuated in PT-Agtr1a-/- mice (P<0.01). In conclusion, the present study demonstrates that deletion of AT1a receptors in the proximal tubules of the kidney attenuates Ang II-induced hypertension and kidney injury without revealing significant sex differences.

Resistance exercise training ameliorates chronic kidney disease outcomes in a 5/6 nephrectomy model

Chronic kidney disease (CKD) is defined by decreased glomerular filtration rate (GFR) or increased albumin excretion leading to renal injury. However, exercise training is an important non-pharmacological intervention that ameliorates and protects against Diabetes Mellitus, cardiovascular disease, and CKD.

AIM

Our aim was to evaluate the capability of resistance exercise training (RET) to improve CKD outcomes and the contribution of the renal and muscular Akt/mTOR signaling pathway for RET beneficial effects on a CKD model.

MAIN METHODS

Male Wistar rats were subjected to RET, followed for 10 weeks, and randomly divided into 5 groups: Sham: Sham-operated; sedentary and nephrectomy (5/6Nx) (SNS); exercising post-5/6Nx (SNE); exercising pre-5/6Nx (ENS); exercising pre- and post-5/6Nx (ENE). The systolic blood pressure (BP) was measured. Creatinine, proteinuria, and blood urea nitrogen (BUN) were evaluated. After euthanasia Renal and muscular Akt/mTOR signaling pathways were analyzed.

KEY FINDING

Our study showed that the SNS presented renal injury, hypertension, weight and muscular mass loss and a higher mortality rate. SNS group also decreased renal IL-10 and increased TNF-alfa and TGF-Beta. Renal AKT, mTOR, and rpS6 pathway were increased, PTEN was decreased on SNS. And muscular Akt and mTOR were decreased on SNS.

SIGNIFICANCE

The RET before and after the 5/6Nx ameliorates all these parameters mentioned above, suggesting that RET is a good non-pharmacological approach to diminish complications frequently found in CKD. We also suggest that the AKT-m-TOR pathway can play an important role in these beneficial outcomes of RET on the CKD animal model.

Proximal Tubule-Specific Deletion of Angiotensin II Type 1a Receptors in the Kidney Attenuates Circulating and Intratubular Angiotensin II-Induced Hypertension in PT-Agtr1a-/- Mice

[Figure: see text].