Renal inflammation and elevated blood pressure in a mouse model of reduced {beta}-ENaC

Abstract

Previous studies suggest β-epithelial Na(+) channel protein (β-ENaC) may mediate myogenic constriction, a mechanism of blood flow autoregulation. A recent study demonstrated that mice with reduced levels of β-ENaC (β-ENaC m/m) have delayed correction of whole kidney blood flow responses, suggesting defective myogenic autoregulatory capacity. Reduced renal autoregulatory capacity is linked to renal inflammation, injury, and hypertension. However, it is unknown whether β-ENaC m/m mice have any complications associated with reductions in autoregulatory capacity such as renal inflammation, injury, or hypertension. To determine whether the previously observed altered autoregulatory control was associated with indicators of renal injury, we evaluated β-ENaC m/m mice for signs of renal inflammation and tissue remodeling using marker expression. We found that inflammatory and remodeling markers, such as IL-1β, IL-6, TNF-α, collagen III and transforming growth factor-β, were significantly upregulated in β-ENaC m/m mice. To determine whether renal changes were associated with changes in long-term control of blood pressure, we used radiotelemetry and found that 5-day mean arterial blood pressure (MAP) was significantly elevated in β-ENaC m/m (120 ± 3 vs. 105 ± 2 mmHg, P = 0.016). Our findings suggest loss of β-ENaC is associated with early signs of renal injury and increased MAP.

Fig. 1.

Indications of renal inflammation and signs of subtle renal injury in a mouse model of reduced β-epithelial Na channel (ENaC). A, left: representative images of renal cortical sections stained with the F4/80 antibody to identify macrophage infiltration (arrows). The sections were counterstained with hematoxylin-and-eosin. Right: group data showing that kidneys from mutant mice (m/m, n = 6) contain 2-fold more F4/80-positive cells than wild-type (+/+, n = 8). Shown is Western blotting detection of leukocyte marker target of an antiproliferative antibody (TAPA-1; B) and inflammatory cytokines TNF-α (C), IL-6 (D), IL-1β (E), as well as transforming growth factor (TGF)-β₁ (F), a growth factor associated with proliferation and expansion of matrix, and collagen III (G), a marker of extracellular matrix. Protein samples were obtained from whole kidney lysates in wild-type (+/+, n = 3) and mutant mice (m/m, n = 3). β-Actin loading control is shown below the corresponding blot. Quantitative data are shown on the right. Values are means ± SE. P values for analysis with t-test are provided. *Significantly different from control, P < 0.05.

Fig. 2.

Blood pressure and heart rate (HR) in normal salt (0.4% Na⁺)-fed animals. Mean arterial pressure (MAP), diastolic arterial pressure (DAP), systolic arterial pressure (SAP), and heart rate (HR) are shown in panels A, B, C, and D, respectively, in wild-type (+/+, filled bars, n = 7) and homozygous β-ENaC mutant mice (m/m, open bars, n = 8). Pressures for 12-h light (L) and dark (D) cycles for each of 5 days are shown (left). Values are means ± SE. *Significantly different from wild-type (+/+) control animals, P < 0.05.

Fig. 3.

Locomotor activity during light and dark cycles. A: mean locomotor activity for 12-h L and D cycles for each of 5 days. B: mean locomotor activity for L and D cycles over 5-day period. Values are means ± SE. *Significantly different from wild-type (+/+) control animals, P < 0.05.

Fig. 4.

Blood pressure and HR variability. Pressure and HR variability during the last 24 h of telemetry recording are shown for MAP (A), HR (B), DAP (C), and SAP (D). *Significantly different from wild-type (+/+) control animals, P < 0.05.