Cell Fusion Stage in Osteoclast Formation

Wednesday, September 24, 2014 — Poster Session IV
10:00 a.m. –12:00 p.m.	FAES Academic Center	NICHD	CELLBIO-14

* FARE Award Winner

Authors

• S.K. Verma
• E. Leikina
• K. Melikov
• L.V. Chernomordik

Abstract

Little is known about cell fusion process generating osteoclasts, cells that resorb our bones in their continuous remodeling. Here we isolated fusion stage from preceding stages of osteoclast formation and for the first time identified proteins involved in different fusion steps. To trigger osteoclastogenesis, we applied RANKL to RAW macrophage-like cells or M-CSF and then RANKL to human monocytes. We blocked fusion by applying a reversible hemifusion inhibitor lysophosphatidylcholine (LPC), accumulated the ready-to-fuse macrophages for 16h and then removed LPC. This fusion-synchronization approach has allowed us to accumulate the ready-to-fuse macrophages and concentrate cell fusion events that would normally develop within 16h to develop within 90 min. We report that fusion-committed macrophages expose at their surface phosphatidylserine (PS), lipid that is normally found only in the inner leaflet of the plasma membrane and this non-apoptotic PS externalization is important for macrophage fusion. We also established that early stages in fusion process involve extracellular PS-binding proteins — annexins and subsequent syncytium formation involve dynamin. Both annexins and dynamin play important role in myoblast fusion. Thus, our results suggest a striking conservation of cell-cell fusion mechanisms in development and regeneration of bones and muscles.

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