McGurk, F. | bioRxiv Science

bioRxiv2024

CD13 Activation Assembles Signaling Complexes that Promote the Formation of Tunneling Nanotubes in Endothelial Cells

Transmembrane CD13 assembles protein complexes at the plasma membrane to enable diverse cellular processes such as cell-cell adhesion, focal adhesion turnover, endocytosis and recycling of cell surface proteins. In this study, we demonstrate a novel CD13-dependent assembly platform that regulates phosphoinositide (PI) signal transduction during the formation of Tunneling Nanotubes (TNTs). TNTs are actin-based, membrane-delimited bridges that facilitate intercellular communication by connecting distant cells to physically transfer subcellular cargoes. TNTs form between various cell types under stress conditions, but few molecular TNT-inducers exist. Human Kaposis sarcoma-derived endothelial cells (KSECs) readily form stress-induced TNTs capable of transferring Ca2+ and membrane molecules between cells, with clear accumulation of CD13 and actin at the base of the protrusions. Alternatively, CD13-null KSECs form fewer TNTs and Ca2+ transfer is markedly reduced. Mechanistically, CD13-mediated TNT formation requires activation of CD13, Src, FAK and Cdc42 to allow tethering of the IQGAP1 and ARF6 complex at the membrane to activate the phosphatidylinositol-4-phosphate-5-kinase PI5K. This increases local phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) levels to promote the actin-polymerization and membrane protrusion necessary for TNT formation. Therefore, CD13 is a novel molecular PIP regulator and TNT trigger that will facilitate the dissection of downstream pathways and mechanisms regulating TNT formation.

cell biology↗

bioRxiv2023

The Implant-Induced Foreign Body Response is Limited by CD13-Dependent Regulation of Ubiquitination of Fusogenic Proteins

Implanted medical devices from artificial heart valves, arthroscopic joints to implantable sensors often induce a Foreign Body Response (FBR), a form of chronic inflammation resulting from the inflammatory reaction to a persistent foreign stimulus. The FBR is characterized by a subset of multinucleated giant cells (MGCs) formed by macrophage fusion, the Foreign Body Giant cells (FBGCs), accompanied by inflammatory cytokines, matrix deposition and eventually, deleterious fibrotic implant encapsulation. Despite efforts to improve biocompatibility, implant-induced FBR persists, compromising the utility of devices and making efforts to control the FBR imperative for long-term function. Controlling macrophage fusion in FBGC formation presents a logical target to prevent implant failure, but the actual contribution of FBGCs to FBR-induced damage is controversial. CD13 is a molecular scaffold and in vitro induction of CD13KO bone-marrow progenitors generates many more MGCs than WT, suggesting CD13 regulates macrophage fusion. Moreover, in the mesh implant model of FBR, CD13KO mice produced significantly more peri-implant FBGCs with enhanced TGF{beta} expression and increased collagen deposition vs. WT. Pre-fusion, increased protrusion and microprojection formation accompanies hyperfusion in the absence of CD13. Expression of fusogenic proteins driving cell-cell fusion was aberrantly sustained at high levels in CD13KO MGCs, which we show is due to a novel CD13 function, regulating ubiquitin/proteasomal protein degradation. By controlling protein degradation, CD13 becomes a physiologic brake preventing aberrant macrophage fusion and may be a novel therapeutic target to improve success of implanted medical devices. Furthermore, our data directly implicates FBGCs in the detrimental fibrosis that characterizes the FBR.

cell biology↗