Expression of the transmembrane lysosomal protein SCARB2/Limp-2 in renin secretory granules controls renin release.

Background/aims: Renin processing and storage is believed to occur in lysosome-like structures in the afferent arteriole. SCARB2/Limp-2 is a transmembrane lysosomal protein responsible for the intracellular trafficking of β-glucocerebrosidase. This study aimed to confirm the expression of SCARB2/Limp-2 in renin secretory granules, and explore its role in renin processing and secretion.

Methods: Co-localisation studies of (pro)renin with lysosomal membrane proteins, SCARB2/Limp-2, LAMP-1 and LAMP-2, were performed in mouse and human kidney sections. Intrarenal expression and secretion of (pro)renin in wild-type (WT) and Limp-2(-/-) mice were compared with and without stimulation.

Results: SCARB2/Limp-2, LAMP-1 and LAMP-2 co-localised with (pro)- renin in mouse and human kidney. Plasma renin concentration was increased in Limp-2(-/-) mice when compared to WT littermates. No change in (pro)renin expression, however, was observed in Limp-2(-/-) mouse kidney cortex by immunofluorescence microscopy, Western blotting, quantitative RT-PCR or the ultrastructural appearance of renin secretory granules. Acute stimulation of renin release by isoprenaline or hydralazine was similar in WT and Limp-2(-/-) mice. Following chronic salt restriction, however, immunofluorescence microscopy showed less (pro)renin expressed in Limp-2(-/-) compared with WT mouse kidneys, and there was significantly less prorenin but not renin by Western blotting in Limp-2(-/-) mouse kidney cortex, despite no difference in circulating renin levels.

Conclusion: Renin secretory granules possess integral lysosomal proteins, confirming that they are indeed modified lysosomes. Limp-2 deficiency leads to a minor increase in circulating renin. Limp-2, however, is not required for acute or chronic stimulation of renin release.