Structural analysis suggests that renin is released by compound exocytosis.

The mode of renin release from renal juxtaglomerular cells into circulation is still unsolved in several aspects. Here we studied the intracellular organization of renin-storage vesicles and their changes during controlled stimulation of renin release. This was accomplished using isolated perfused mouse kidneys with 3-dimensional electron microscopic analyses of renin-producing cells. Renin was found to be stored in a network of single granules and cavern-like structures, and dependent on the synthesis of glycosylated prorenin. Acute stimulation of renin release led to increased exocytosis in combination with intracellular fusion of vesicles to larger caverns and their subsequent emptying. Renin release from the kidneys of SCID-beige mice, which contain few but gigantic renin-storage vesicles, was no different from that of kidneys from wild-type mice. Thus, our findings suggest that renin is released by mechanisms similar to compound exocytosis.

Prostaglandin E2 inhibits migration of colonic lamina propria fibroblasts.

BACKGROUND: Migration of colonic lamina propria fibroblasts (CLPF) is an important mechanism during wound healing in inflammatory bowel disease (IBD). The concentration of prostaglandin E2 (PGE2) is increased in the intestinal mucosa of IBD patients. We therefore investigated the role of PGE2 in CLPF migration. METHODS: Primary cultures of CLPF were isolated from healthy controls and Crohn's disease patients. Migration assays were performed in the Boyden chamber and scratch assays. EP receptors, PGE2, intracellular cyclic adenosine monophosphate (cAMP), expression and distribution of F-actin, alpha-smooth muscle actin (SMA), and myosin light chain (MLC) were determined by immunoblotting, immunocytochemistry, and enzyme-linked immunosorbent assay (ELISA). RESULTS: All four EP receptor subtypes were present on CLPF. PGE2 and agonists to the EP2 and EP4 receptor reduced the migration of CLPF. Blockade of the EP2 and the EP4 receptor inhibited the effect of PGE2 on CLPF migration. An increase in intracellular cAMP reduced CLPF migration. PGE2 increased the concentrations of cAMP in CLPF, with abrogation after addition of EP2 and EP4 receptor antagonists. PGE2 and forskolin decreased the expression of alpha-SMA and F-actin and reduced cell polarization and lamellipodium formation in a scratch assay. In addition, forskolin reduced the phosphorylation of MLC (pMLC) and led to lack of accumulation of pMLC in the leading edge of CLPF. CONCLUSIONS: PGE2 reduced the migration of CLPF via elevation of intracellular cAMP. Potential mechanisms are changes in expression of cytoskeletal proteins, failure of CLPF to polarize, and a decreased amount of pMLC. This might be a possible reason for the impairment of intestinal wound healing in IBD.