Hypertension is characterized by increased sodium reabsorption along the aldosterone-sensitive distal nephron (ASDN) and systemic inflammation. Interleukin-6 (IL-6) is a possible mediator, signaling via the transmembrane IL-6 receptor alpha (IL-6Rα); however, whether IL-6Rα is present in the distal convoluted tubule (DCT) is unknown. Increased sodium reabsorption is not always correlated with increased aldosterone (Aldo). Thus, understanding how Aldo-independent sodium reabsorption occurs is critical. We hypothesize that IL-6 can transactivate the MR via IL-6 Rα, increasing sodium reabsorption via reactive oxygen species (ROS) generation and activation of the sodium-chloride cotransporter (NCC).Design and Method:
Immunofluorescence studies in murine kidney slices (IL-6Rα and NCC) were performed. Murine distal convoluted tubule (mDCT15) cells were transfected with either MR-EGFP or MRE-luciferase constructs- confocal and luciferase assays were performed. Using mDCT15 monolayers, thiazide-sensitive 22Na+-uptake studies were performed.Results:
IF staining revealed a cytosolic expression within the DCT, while apical staining was observed in other nephron segments (Figure 1) demonstrating a differential localization of IL-6Rα. MR-eGFP expression was observed in the cytosol in the vehicle treated cells, yet following IL-6 treatment (30 min), nuclear translocation occurred. To confirm downstream transcriptional activation, transfected mDCT15 cells were treated with vehicle, Aldo or IL-6. Luciferase activity was increased (≅1.5 fold) following IL-6 over MRE-only transfected cells. Since excessive MR stimulation produces ROS generation, we determined if ROS generation stimulates increased NCC-mediated sodium uptake. Increased 22Na+ uptake was observed after ROS generation (pyrogallol, 50 μM) compared to vehicle (1834 ± 19 vs. 1506 ± 18nmol/mg, p < 0.0001, n = 6), which was reduced with superoxide dismutase mimetic (pyrogallol + tempol, 250 μM) (1618 ± 27nmol/mg vs. pyrogallol, p < 0.0001, n = 6).Conclusions:
These data suggest: IL-6Rα is differentially expressed within the cortex, IL-6 can transactivate the MR leading to nuclear translocation and subsequent MRE activation, and ROS generation increases sodium reabsorption via NCC providing evidence for alternate mechanisms of ASDN sodium uptake during conditions where Aldo-mediated MR stimulation may not occur.