Apoptosis, or programed cell death, is a common occurrence during development, pathogenesis and tissue homeostasis. The efficient removal of apoptotic cell corpses is crucial for preventing inflammation and a potentially damaging immune response. For this reason, enhancing apoptotic corpse clearance may be an effective strategy to resolve damaging inflammation following infection or aggressive cancer therapies that overwhelm the endogenous system for removing apoptotic cells. Developing these therapies requires a deeper understanding for how apoptotic corpse clearance pathways are activated. Dying cells recruit phagocytes through `eat me' signals, the most widespread of which is phosphatidylserine (PS). Several PS-recognizing receptors have been implicated in apoptotic corpse clearance but many aspects of their function are still unclear: does each receptor regulate distinct aspects of the corpse clearance pathway or do they additively converge on the same downstream targets? How are the PS receptors activated and how is this activation translated into F-actin reorganization and engulfment? In particular, the phosphatidylserine receptor (PSR) plays a highly conserved role in promoting clearance of apoptotic corpses, but the mechanism by which PSR promotes corpse clearance is not known. I will examine the collaboration between two conserved PS- recognizing receptors, the PS receptor (PSR) and CED-1/Draper, using a combination of in vivo imaging in C. elegans and reconstituting engulfment pathways in Drosophila S2 cells. In the C. elegans germline, I will use a dual inverted selective plane microscope (diSPIM) to examine phagocytic cup formation, F-actin dynamics and efficiency of corpse clearance. This will determine which steps in the apoptotic corpse clearance program are regulated by PSR-1, CED-1 or both receptors. To rapidly dissect the mechanism for PSR function, I will reconstitute the apoptotic corpse clearance pathway in Drosophila S2 cells. My preliminary data shows that ectopically expressing dPSR transforms S2 cells from poor phagocytes into efficient engulfers of PS-coated glass microspheres. I will determine if PSR partitions with Draper or F-actin into microdomains of active signaling in the plasma membrane, whether nuclear or only membrane-bound PSR signaling is required to promote engulfment, and if PSR is activated by oligomerization. Together, these studies will give insight into the function of PSR, a highly conserved yet poorly understood PS receptor, and elucidate how multiple PS receptors collaborate to promote clearance of apoptotic cell corpses.

Public Health Relevance

Apoptotic corpse clearance is an immunologically quiescent process that mediates the removal of dead or dying cells. Enhancing apoptotic corpse clearance may be an effective strategy to limit inflammation following aggressive cancer therapies or reduce chronic inflammation. This project aims to elucidate mechanisms for triggering clearance of apoptotic cells, focusing on understanding receptors that recognize dead or dying cells.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Postdoctoral Individual National Research Service Award (F32)
Project #
1F32GM120990-01
Application #
9192004
Study Section
Special Emphasis Panel (ZRG1)
Program Officer
Maas, Stefan
Project Start
2016-12-01
Project End
2019-11-30
Budget Start
2016-12-01
Budget End
2017-11-30
Support Year
1
Fiscal Year
2016
Total Cost
Indirect Cost
Name
University of California San Francisco
Department
Pharmacology
Type
Schools of Medicine
DUNS #
094878337
City
San Francisco
State
CA
Country
United States
Zip Code
94118
Morrissey, Meghan A; Williamson, Adam P; Steinbach, Adriana M et al. (2018) Chimeric antigen receptors that trigger phagocytosis. Elife 7: