Stimulation of the Kidney Toll-Like Receptor Pathway during Salt-Sensitive Hypertension is Mediated by Overactivation of the ET_AReceptor Only in Males

The potent vasoactive peptide endothelin-1 (ET-1) is critically implicated in the development and progression of hypertension-induced kidney injury and inflammation. Dysfunction of the ET B receptor and the consequent overactivation of the ET-1/ET A receptor axis results in exaggerated kidney damage and T cell inflammation under high salt conditions, but no changes in macrophage infiltration. However, if overactivation of the ET-1 system induces other innate immunity pathways in the kidney during salt-sensitive hypertension remains unclear. The toll-like receptor (TLR) pathway is part of the innate immune system and upon stimulation via pathogen-associated-molecular patterns (PAMPs) and damage associated molecular patterns (DAMPs) leads to the production of inflammatory cytokines. We hypothesized that overactivation of the ET A receptor results in exaggerated upregulation and activation of the TLR pathway in the kidney during salt-sensitive hypertension. Male and female transgenic (TG) control and ET B deficient (ET B def) rats (n=6-8/group) were placed on a normal salt (1% NaCl, NSD) or high salt (4% NaCl, HSD) diet for 3 wks. At the end of the studies, kidneys were separated in cortex and outer medulla, and expression of genes involved in the TLR pathway was assessed with RT-PCR ( Rplp1 was used as housekeeping gene). In response to HSD, and compared to TG control rats, male ET B def rats showed a marked upregulation of Tlr2 ( TG vs. ET B def: 24.8±6.4 vs. 78.9±4.6, p<0.0001), Tlr4 (6.9±2.0 vs. 17.5±4.0, p=0.003) and Tlr7 (3.3±1.1 vs. 10.7±1.8, p<0.0001) in the kidney cortex. HSD also led to TLR pathway activation in the male ET B def cortex, as demonstrated by the prominent expression of the adaptor protein MyD88 (2.0±0.5 vs. 9.3±1.3, p<0.0001), master regulator of inflammation Nfκβ (2.7±0.8 vs. 7.9±1.4, p=0.0003) and pro-inflammatory cytokine Il1β (1.0±0.3 vs. 2.9±0.8, p=0.002) in this region of the kidney. In contrast, the TLR response to HSD was attenuated and the genotype difference was absent in female kidneys ( Tlr2 (TG vs. ET B def:3.5±0.8 vs. 4.4±1.6, p>0.05), Tlr4 (10.5±3.5 vs. 9.6±3.2, p>0.05), Tlr7 (10.6±3.5 vs. 7.5±2.5, p>0.05), MyD88 (6.2±2.0 vs. 5.3±1.7, p>0.05) and Nfκβ (5.8±2.2 vs. 4.3±1.4, p>0.05)). Of note, salt-sensitive hypertension did not induce changes in the TLR pathway within the outer medulla in either sex or genotype. Our results demonstrate that overactivation of the ET A receptor during salt-sensitive hypertension results in upregulation and activation of the kidney TLR pathway in males but not females, and that this response is specific to the kidney cortex. Thus, pharmacological blockade of the ET A receptor may be more effective in protecting male, but not female, hypertensive patients against kidney damage and inflammation. UAB Summer Research Academy funds to TS, P30 DK079337 and KURE R25 DK115353 to BSM, KUH PRIME U2C DK133422 & TL1 DK139566 to AJB, and NIH K01HL145324 and UAB DOM URiM funds to CDM. This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.