Transition of Podosomes Into Zipper-Like Structures in Macrophage-Derived Multinucleated Giant Cells

Abstract

Macrophage fusion resulting in the formation of multinucleated giant cells (MGCs) is a multistage process that requires many adhesion-dependent steps and involves the rearrangement of the actin cytoskeleton. The diversity of actin-based structures and their role in macrophage fusion is poorly understood. In this study, we revealed hitherto unrecognized actin-based zipper-like structures (ZLSs) that arise between MGCs formed on the surface of implanted biomaterials. We established an in vitro model for the induction of these structures in mouse macrophages undergoing IL-4mediated fusion. Using this model, we show that over time MGCs develop cell-cell contacts containing ZLSs. Live-cell imaging using macrophages isolated from mRFP-or GFP-Lifeact mice demonstrated that ZLSs are dynamic formations undergoing continuous assembly and disassembly and that podosomes are precursors of these structures. Immunostaining experiments showed that vinculin, talin, integrin αMβ2, and other components of podosomes are present in ZLSs. Macrophages deficient in WASp or Cdc42, two key molecules involved in actin core organization in podosomes, as well as cells treated with the inhibitors of the Arp2/3 complex failed to form ZLSs. Furthermore, E-cadherin and nectin-2 were found between adjoining membranes, suggesting that the transition of podosomes into ZLSs is induced by bridging plasma membranes by junctional proteins.

Heterogeneity and Actin Cytoskeleton in Osteoclast and Macrophage Multinucleation

“…A similar structure is also found in mouse calvarial osteoclasts [ 48 ], OCLs from human blood mononuclear cells [ 136 ], and chicken bone marrow cells primed by 1α, 25(OH) 2 D 3 [ 154 ]. The MGCs on the implanted biomaterials in vivo and the IL-4 induced multinucleated macrophages in vitro also form a zipper-like structure [ 155 ], although it shows different actin dynamics compared to the counterpart in the OCLs. The zipper-like structure and the podosome belt have a distinct arrangement of podosomal proteins [ 145 ].…”