Mouse macrophages show different requirements for phosphatidylserine receptor Tim4 in efferocytosis

Y Yanagihashi, K Segawa, R Maeda… - Proceedings of the …, 2017 - National Acad Sciences
Y Yanagihashi, K Segawa, R Maeda, Y Nabeshima, S Nagata
Proceedings of the National Academy of Sciences, 2017National Acad Sciences
Protein S (ProS) and growth arrest-specific 6 (Gas6) bind to phosphatidylserine (PtdSer) and
induce efferocytosis upon binding TAM-family receptors (Tyro3, Axl, and Mer). Here, we
produced mouse ProS, Gas6, and TAM-receptor extracellular region fused to IgG fragment
crystallizable region in HEK293T cells. ProS and Gas6 bound Ca2+ dependently to PtdSer
(K d 20–40 nM), Mer, and Tyro3 (K d 15–50 nM). Gas6 bound Axl strongly (K d< 1.0 nM), but
ProS did not bind Axl. Using NIH 3T3-based cell lines expressing a single TAM receptor, we …
Protein S (ProS) and growth arrest-specific 6 (Gas6) bind to phosphatidylserine (PtdSer) and induce efferocytosis upon binding TAM-family receptors (Tyro3, Axl, and Mer). Here, we produced mouse ProS, Gas6, and TAM-receptor extracellular region fused to IgG fragment crystallizable region in HEK293T cells. ProS and Gas6 bound Ca2+ dependently to PtdSer (Kd 20–40 nM), Mer, and Tyro3 (Kd 15–50 nM). Gas6 bound Axl strongly (Kd < 1.0 nM), but ProS did not bind Axl. Using NIH 3T3-based cell lines expressing a single TAM receptor, we showed that TAM-mediated efferocytosis was determined by the receptor-binding ability of ProS and Gas6. Tim4 is a membrane protein that strongly binds PtdSer. Tim4 alone did not support efferocytosis, but enhanced TAM-dependent efferocytosis. Resident peritoneal macrophages, Kupffer cells, and CD169+ skin macrophages required Tim4 for TAM-stimulated efferocytosis, whereas efferocytosis by thioglycollate-elicited peritoneal macrophages or primary cultured microglia was TAM dependent, but not Tim4 dependent. These results indicate that TAM and Tim4 collaborate for efficient efferocytosis in certain macrophage populations.
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