Endothelin‐1 Receptor B (ETB) Deficient Rats Fed High Salt Diet Display Differential Mitochondria‐Related Gene Expression in the Kidney Cortex and Outer Medulla

Abstract

Levels of the vasoactive peptide endothelin‐1 (ET‐1) are persistently elevated in patients and animal models of salt‐sensitive hypertension. Our group recently reported that loss of ETB receptor function and the consequent overactivation of the ET‐1/ETA receptor axis are associated with exaggerated kidney damage, T cell inflammation and apoptosis under high salt conditions. Importantly, the molecular mechanisms by which ET‐1 leads to high salt‐induced renal damage remain unclear. These studies aimed to determine if the overactivation of the ET‐1/ETA axis alters the kidney expression of genes involved in mitochondrial biogenesis and function during high salt consumption. Male ETB deficient (ETB def) and transgenic (TG) control rats were placed on a high salt diet (HSD, 4.0% NaCl) for 3 weeks. At the end of this HSD period, 24h urine was collected and kidneys were separated in cortex and outer medulla. Urinary protein excretion was measured as a marker of kidney damage and the kidney expression of 84 mitochondria‐related genes was assessed by qRT‐PCR arrays. Compared to TG controls, high salt‐fed ETB def rats presented with greater kidney damage as indicated by elevated protein excretion (TG control vs. ETB def, 73.9±8.0 vs. 121.4±10.0 mg/day; n=5/group; p=0.01). In addition, ETB def rats fed HSD displayed cortical overexpression of 13 genes involved in energy metabolism, apoptosis, mitochondrial biogenesis, and regulation of the production of reactive oxygen species (selected examples of ETB def vs. TG control genetic expression (n=3/group): Ucp1, 19‐fold increase (p=0.03); Bnip3 (p=0.003) and Scl25a21 (p=0.004), 6‐fold; Mfn1,5‐fold (p=0.03); and Dnm1l, 4‐fold (p=0.004)). On the other hand, when the same comparisons were made in the kidney outer medullary region, we found that deficiency of the ETB receptor resulted in a 50% reduction in the expression of 29 genes (among them, genes involved in mitochondrial membrane polarization, transport and dynamics; p<0.05). These results demonstrate a differential effect of ETAoveractivation on mitochondrial homeostasis in the kidney cortical and outer medullary regions during high salt consumption, with overactivation of the ET‐1/ETA axis leading to exaggerated mitochondrial function in the cortex and downregulation of this function in the outer medulla.