Dissecting the JGA: new functions for JG cells?

8-Br-cADPR, a TRPM2 ion channel antagonist, inhibits renal ischemia-reperfusion injury

The transient receptor potential melastatin-2 (TRPM2) channel belongs to the transient receptor potential channel superfamily and is a cation channel permeable to Na⁺ and Ca ²⁺ . The TRPM2 ion channel is expressed in the kidney and can be activated by various molecules such as hydrogen peroxide, calcium, and cyclic adenosine diphosphate (ADP)-ribose (cADPR) that are produced during acute kidney injury. In this study, we investigated the role of 8-bromo-cyclic ADP-ribose (8-Br-cADPR; a cADPR antagonist) in renal ischemia-reperfusion injury using biochemical and histopathological parameters. CD38, cADPR, tumor necrosis factor-α, interleukin-1β, and myeloperoxidase (inflammatory markers), urea and creatinine, hydrogen peroxide (oxidant), and catalase (antioxidant enzyme) levels that increase with ischemia-reperfusion injury decreased in the groups treated with 8-Br-cADPR. In addition, renin levels were elevated in the groups treated with 8-Br-cADPR. Histopathological examination revealed that 8-Br-cADPR reduced renal damage and the expression of caspase-3 and TRPM2. Our results suggest that the inhibition of TRPM2 ion channel may be a new treatment modality for ischemic acute kidney injury.

Regulation of renin release via cyclic ADP-ribose-mediated signaling: evidence from mice lacking CD38 gene

BACKGROUND/AIMS

Despite extensive studies, the intracellular regulatory mechanism of renin production and release is still poorly understood. The present study was designed to test whether CD38-ADP-ribosylcyclase signaling pathway contributes to the regulation of renin production and release, and to examine whether CD38 gene knockout (CD38(-/-)) can change this important renal endocrinal function.

METHODS

ADP-ribosylcyclase activity was estimated utilizing HPLC, cADPR levels from western blot, plasma renin activity from RIA kit, urinary sodium and potassium excretion from fame photometry.

RESULTS

The expression of CD38 and the activity of ADP-ribosylcyclase to produce cyclic ADP-ribose (cADPR) were nearly abolished in the kidney from CD38(-/-) mice, indicating that CD38 gene is a major enzyme responsible for the generation of cADPR in vivo. Mice lacking CD38 gene showed increased plasma renin activity (PRA) in either conscious or anesthetized status (P<0.05). Low salt intake significantly increased, but high salt intake significantly decreased renin release in both CD38(+/+) and CD38(-/-) mice. In acute experiments, it was demonstrated that plasma renin activity (PRA) significantly increased upon isoprenaline infusion in CD38(-/-) mice compared to CD38(+/+) mice. Accompanied with such increase in PRA, glomerular filtration rate (GFR), renal blood flow (RBF), urine volume (UV) and sodium excretion (UNaV) more significantly decreased in CD38(-/-) than CD38(+/+) mice. Similarly, more increases in PRA but more decreases in GFR, RBF, UV and UNaV were observed in CD38(-/-) than CD38(+/+) mice when they had a low renal perfusion pressure (RPP).

CONCLUSION

CD38-cADPR-mediated signaling may importantly contribute to the maintenance of low PRA and participate in the regulation of renal hemodynamics and excretory function in mice.