Enhanced renin release and content in juxtaglomerular (JG) cells from VAMP8 knockout mice

Abstract

Renin is essential for angiotensin II production and blood pressure control. Renin is stored in granules in juxtaglomerular (JG) cells. We showed that vesicle associated membrane protein 2 (VAMP2), a member of SNARE family, mediates stimulated renin exocytosis in JG cells. However, the VAMP isoform required for constitutive renin release is unknown. In other cells VAMP8 mediates granule maturation and constitutive exocytosis. We hypothesized that VAMP8 mediates constitutive renin release in JG cells. We used primary cultures of JG cells from wild type (WT) and VAMP8 knockout (V8‐KO) mice and measured VAMP8 localization and renin released to the medium during 1 hr. In wild type, VAMP8 was expressed in JG cell granules. Baseline renin release was 5‐fold higher in V8‐KO than WT (WT=0.06±0.01; KO=0.3±0.05 μgAngI/hr/mg prot.; p<0.05). Total renin content was 5‐fold higher in V8‐KO than WT (WT=2.9±0.2; KO=16.7±0.6 μgAngI/hr/mg prot.; p<0.05). The fraction of total renin released to the media was similar in V8‐KO and WT JG cells (WT: 1.6±0.3; KO: 1.7±0.5% of total renin) indicating higher number of granules in V8‐KO, or higher renin content/granule. Immunolabeling of renin and confocal imaging showed enlarged granules and vacuoles in JG cells from V8‐KO. We concluded that: 1) VAMP8 does not mediate constitutive renin exocytosis; and 2) VAMP8 may play an inhibitory role in transcription, translation or processing of renin. 5F32HL096346