Study on a mechanical signal during efferocytosis

Abstract

Phagocytosis of apoptotic cells, called efferocytosis, is an indispensable cellular process for tissue homeostasis. This process is accompanied by tremendous cytoskeletal rearrangement and plasma membrane transformation to ingest apoptotic cells as large as phagocytes. However, whether these dynamics generate a mechanical signal that regulates signaling during efferocytosis remains elusive. In part I, I report that tension between phosphatidylserine (PS) and its receptors at the phagocytic synapse functions as a checkpoint validating apoptotic cells being phagocytosed. Mechanistically, increased membrane tension of phagocytes via Rac1-dependent actin polymerization induced tension of PS-PSR, leading to phosphoinositide 3-kinase recruitment to PSRs, which resulted in Rac1 inactivation and myosin II phosphorylation required for phagocytic cup closure. In part II, I explored the effect of tension between CD47-SIRPα on phagocytosis, but found that phagocytes engulfed the beads regardless of tension between CD47-SIRPα. In part III, I report that Tim-4 acts as a scavenger receptor required to engulf exogenous particles such as E. coli and S. aureus as well as apoptotic cells. In part IV, in a different context from the previous parts, I report the development of a new biosensor detecting two analytes simultaneously. Two types of probes (a hybridization probe and an aptamer probe) using oligonucleotide-chemosensor conjugate as a backbone were synthesized and tested whether they could detect mRNA&Zn2+ or ATP&Zn2+, respectively. Although mRNA was not detected using the hybridization probe, the aptamer probe exhibited four different characteristics of fluorescence in the presence or absence of ATP or Zn2+ without spectral crosstalk or fluorescence interference. Therefore, the oligonucleotide-chemosensor conjugate can be used as a novel scaffold that can simultaneously detect various biomarkers for the diagnosis of various diseases.