Snx10 and PIKfyve are required for lysosome formation in osteoclasts

PICOTTO G; SULTANA F; BATTAGLINO R; MORSE L; ODGREN P; LIU W; PAKRASH J

Mar del Plata

Congreso; LXI Reunión Anual de la SAIC; 2019

Sociedad Argentina de Investigación Clínica

Osteoclast (OC) function require specialized intracellular trafficking for organelle homeostasis. Snx10, a PI3P binding protein, is a member of the sorting nexin family, which plays important roles in cargo sorting in the endosome pathway and localized in early endosomes. It was shown previously that the gene encoding sorting Snx10 is required for osteoclast morphogenesis and function as osteoclasts from humans and mice lacking Snx10 are dysfunctional. The present work aimed to study PIKfyve, another PI3P-binding kinase, which phosphorylates PI3P to PI(3,5)P2 to better understand the role by which Snx10 regulates vesicular transport. PI(3,5)P2 is required for endosome/lysosome maturation. Inhibition of PIKfyve causes endosome enlargement, while overexpression of Snx10 also induces accumulation of early endosomes. This suggests that both Snx10 and PIKfyve may be required for normal endosome/lysosome transition. Apilimod is a small molecule with specific nanomolar inhibitory activity on PIKfyve, but only if OC effector genes CLCN7, OSTM1 and Snx10 are expressed. This observation suggests that Apilimod?s inhibitory effects may be mediated by endosome/lysosome disruption. Here we show that both Snx10 and PIKfyve co-localize to early endosomes in osteoclasts. Furthermore, we observed co-immunoprecipitation and co-localization of Snx10 and PIKfyve in osteoclasts and gastric zymogenic cells. Treatment with 10nM Apilimod or genetic deletion of PIKfyve resulted in accumulation of early endosomes and the inhibition of osteoclast constitution, lysosome formation and secretion of TRAP from differentiated OC. Apilimod-specific inhibition of PIKfyve required Snx10 expression. These findings may provide novel therapeutic approaches to control bone loss by targeting osteoclast trafficking in pathologies that weaken bone structure.