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

Abstract

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.

Fig. 1. CD38 expression and ADP-ribosylcyclase activity in the kidneys from CD38^+/+ and CD38^−/− mice

A: Confirmation of CD38^−/− mice by genotyping. CD38 gene-specific PCR product (417 bp) was amplified from WT mice (lane 1, 2, 3), but not from CD38^−/− mice (lane 4, 5, 6). B: CD38 protein expression in the homogenate, cytosol and microsome of the kidneys from CD38^+/+ and CD38^−/− mice by Western blot. C: ADP ribosylcyclase activity in the homogenate, cytosol and microsome of the kidneys from CD38^+/+ and CD38^−/− mice by HPLC. Summarized data showed the conversation rate of β-NAD⁺ into cGDPR, which indicates the activity of ADP-ribosylcyclase. D: Basal values of cADPR in the kidney homogenate from CD38^+/+ and CD38^−/− mice by cycling assay. E: The expression of CD38 in JG apparatus and afferent arterioles around glomerulus was detected by colocalization of CD38 and renin by immunofluorescent confocal microscopy. *P<0.05 vs. CD38^+/+ mice; ^#P<0.05 vs. microsomes in CD38^+/+ mice (n=8).

Fig. 2. Detection of renin production and release from CD38^+/+ and CD38^−/− mice

A: Renin mRNA expression in the kidneys from CD38^+/+ and CD38^−/− mice. B: Immunoblot gel document of renin in kidney homogenate from CD38^+/+ and CD38^−/− mice. C: Plasma renin activity in CD38^+/+ and CD38^−/− mice. *P<0.05 vs. CD38^+/+ mice (n=8).

Fig. 3. Effects of different salt intakes on renin secretion in CD38^+/+ and CD38^−/− mice

Plasma renin activity in CD38^+/+ and CD38^−/− mice. ND: Normal diet, LS: low salt diet, HS: High salt diet. * p<0.05 vs. CD38^+/+ mice; ^# p<0.05 vs. normal diet fed mice (n=8).

Fig. 4. Effects of isoprenaline on renal perfusion pressure, renal blood flow, and plasma renin concentration in CD38^+/+ and CD38^−/− mice

A: Changes in renal perfusion pressure. B: Changes in renal blood flow. C: Changes in plasma renin activity. Ctrl: Control, Iso: Isoprenaline. * p<0.05 vs. CD38^+/+ mice, ^# p<0.05 vs. control mice (n=8).

Fig. 5. Effects of low renal perfusion pressure on renal perfusion pressure, renal blood flow and plasma renin concentration in CD38^+/+ and CD38^−/− mice

A: Changes in renal perfusion pressure. B: Changes in renal blood flow. C: Changes in plasma renin activity. Ctrl: Control, RPP: Renal perfusion pressure. * p<0.05 vs. CD38^+/+ mice, ^# p<0.05 vs. control mice (n=8).