Interleukin-6 Modulates Action Potential Generation in Freshly Isolated Rat Dorsal Root Ganglia Neurons And its Stimulating Effect Is Exacerbated in Polycystic Kidney Disease

Abstract

Our laboratory has demonstrated a central role for increased afferent nerve renal activity (ARNA) in the progression of cystogenesis in the PCK rat model of polycystic kidney disease (PKD). The underlying cause for the pathological increase in ARNA is unknown. Inflammatory cell infiltration and increased proinflammatory cytokine content, such as interleukin 6 (IL-6), have been reported in PKD. We hypothesized inflammatory cytokines directly increase sensory nerve activity, and this response is exacerbated in PKD. We measured action potential generation (AP) in freshly isolated dorsal root ganglion (DRG) neurons in PCK rats and non-cystic controls, and their response to IL-6. DRGs (T10-L1) were isolated from Sprague-Dawley (SD) or PCK rat (Age: 10-26 weeks) spinal cords, enzymatically digested and mechanically dissociated. Neurons were plated on coverslips, and AP were recorded within 24-hours (whole-cell patch-clamp). We tested the effects of IL-6 (0.04 μg/ml) and bradykinin (BK; 40μg/ml) on AP under 100, 200 pA, and 300 pA current clamp steps. IL-6 elicited either an excitatory response or inhibitory response in AP. In excitatory cells (EC), AP was normalized to BK peak response at +300 pA. In inhibited cells (IC), AP was normalized to baseline at +300 pA. PCK and IL-6 effects were assessed by two-way ANOVA (Bonferroni post hoc test;*p<.05); data as mean ± SEM. Proportion of ECs and ICs did not differ between SD and PCK rats. IL-6 increased AP at 300 pA from 0.48±0.28 (baseline) to 0.95±0.05 (p<.05) in SD ECs cells. BK further increased AP, showing no cell fatigue by IL-6 exposure. In PCK ECs, IL-6 increased AP at 100 pA (0.07±0.05 vs. 0.52±0.25), at 200 pA (0.47±0.27 vs. 1.39±0.81), and 300 pA (0.54±0.25 vs. 1.11±0.47). BK further increased AP at 100 pA to 0.70± 0.28 but decreased AP at 200 pA to 1.21±0.40 and at +300 pA to 1.00±0.00, indicating that neurons activity was likely plateaued by IL-6 at +200 and +300 pA. In both SD and PCK ICs, there was a main effect of IL-6 and BK treatment across all current steps (p<0.05). In SD ICs, IL-6 decreased AP at 200 pA (1.03±0.67 vs. 0.28±0.24) and 300 pA (1.00±0.00 vs. 0.28±0.24). BK had no effect at +200 pA and partially reversed the effect of IL-6 at +300 pA (AP increase to 0.53±0.27). In PCK ICs, IL-6 decreased AP at +200 pA (0.21±0.08 vs. 0.11±0.09) and +300 pA (1.00±0.00 vs. 0.42±0.24). BK increased AP at +200 pA (0.67±0.37) and +300 pA (0.71±0.33). These data partially support our hypothesis that IL-6 increases sensory nerve discharge. This effect was not observed uniformly across cells, as there were inhibitory and excitatory responses in both PCK and SD rats. We conclude that pro-inflammatory cytokine IL-6 can increase a subset of DRG neuron activity and responsiveness, an effect potentiated in PKD. This neuro-immune interaction might contribute to the underlying increase in ARNA and cystogenesis in PKD. Further experimentation is underway to test neuronal sensitivity to IL-6 and other inflammatory cytokines, as well as the posited potentiated effects in PKD. Supported in part by the PKD Foundation Research Award 1022534 (CB); NIDDK/PKD RRC Pilot and Feasibility Award U24DK126110 (CB). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.