Ageing is associated with diminished apoptotic cell clearance in vivo

AbstractApoptotic cell clearance by phagocytes is a fundamental process during development, homeostasis and the resolution of inflammation. However, the demands placed on phagocytic cells such as macrophages by this process, and the limitations these interactions impose on subsequent cellular behaviours are not yet clear. Here we seek to understand how apoptotic cells affect macrophage function in the context of a genetically-tractable Drosophila model in which macrophages encounter excessive amounts of apoptotic cells. We show that loss of the glial transcription factor repo, and corresponding removal of the contribution these cells make to apoptotic cell clearance, causes macrophages in the developing embryo to be challenged with large numbers of apoptotic cells. As a consequence, macrophages become highly vacuolated with cleared apoptotic cells and their developmental dispersal and migration is perturbed. We also show that the requirement to deal with excess apoptosis caused by a loss of repo function leads to impaired inflammatory responses to injury. However, in contrast to migratory phenotypes, defects in wound responses cannot be rescued by preventing apoptosis from occurring within a repo mutant background. In investigating the underlying cause of these impaired inflammatory responses, we demonstrate that wound-induced calcium waves propagate into surrounding tissues, including neurons and glia of the ventral nerve cord, which exhibit striking calcium waves on wounding, revealing a previously unanticipated contribution of these cells during responses to injury. Taken together these results demonstrate important insights into macrophage biology and how repo mutants can be used to study macrophage-apoptotic cell interactions in the fly embryo.Furthermore, this work shows how these multipurpose cells can be ‘overtasked’ to the detriment of their other functions, alongside providing new insights into which cells govern macrophage responses to injury in vivo.

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Persistence of apoptotic cells without autoimmune disease or inflammation in CD14−/− mice

The Journal of Cell Biology ◽

10.1083/jcb.200410057 ◽

2004 ◽

Vol 167 (6) ◽

pp. 1161-1170 ◽

Cited By ~ 96

Author(s):

Andrew Devitt ◽

Kate G. Parker ◽

Carol Anne Ogden ◽

Ceri Oldreive ◽

Michael F. Clay ◽

...

Keyword(s):

Autoimmune Disease ◽

Apoptotic Cell ◽

Apoptotic Cells ◽

Autoantibody Production ◽

Apoptotic Cell Clearance ◽

Cell Clearance ◽

Surface Receptor ◽

Anti Inflammatory

Interaction of macrophages with apoptotic cells involves multiple steps including recognition, tethering, phagocytosis, and anti-inflammatory macrophage responses. Defective apoptotic cell clearance is associated with pathogenesis of autoimmune disease. CD14 is a surface receptor that functions in vitro in the removal of apoptotic cells by human and murine macrophages, but its mechanism of action has not been defined. Here, we demonstrate that CD14 functions as a macrophage tethering receptor for apoptotic cells. Significantly, CD14−/− macrophages in vivo are defective in clearing apoptotic cells in multiple tissues, suggesting a broad role for CD14 in the clearance process. However, the resultant persistence of apoptotic cells does not lead to inflammation or increased autoantibody production, most likely because, as we show, CD14−/− macrophages retain the ability to generate anti-inflammatory signals in response to apoptotic cells. We conclude that CD14 plays a broad tethering role in apoptotic cell clearance in vivo and that apoptotic cells can persist in the absence of proinflammatory consequences.

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Faculty Opinions recommendation of Boosting apoptotic cell clearance by colonic epithelial cells attenuates inflammation in vivo.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.726260385.793519401 ◽

2016 ◽

Author(s):

Philippe Saas ◽

Sylvain Perruche ◽

Etienne Daguindau

Keyword(s):

Epithelial Cells ◽

Apoptotic Cell ◽

Colonic Epithelial Cells ◽

Apoptotic Cell Clearance ◽

Cell Clearance

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Microglia in the developing retina couple phagocytosis with the progression of apoptosis via P2RY12 signaling

10.1101/2020.01.30.925859 ◽

2020 ◽

Author(s):

Zachary I. Blume ◽

Jared M. Lambert ◽

Anna G. Lovel ◽

Diana M. Mitchell

Keyword(s):

Real Time ◽

Apoptotic Cell ◽

List Type ◽

Apoptotic Cells ◽

Real Time Imaging ◽

Microglial Phagocytosis ◽

Apoptotic Cell Clearance ◽

Cell Clearance ◽

Dying Cells

AbstractBackgroundMicroglia colonize the developing vertebrate central nervous system coincident with detection of developmental apoptosis. Our understanding of apoptosis in intact tissue in relation to microglial clearance of dying cells is largely based on fixed samples, which is limiting given that microglia are highly motile and mobile phagocytes. Here, we used a system of microglial depletion and in vivo real-time imaging in zebrafish to directly address microglial phagocytosis of apoptotic cells during normal retinal development, the relative timing of phagocytosis in relation to apoptotic progression, and the contribution of P2RY12 signaling to this process.ResultsDepletion of microglia resulted in accumulation of numerous apoptotic cells in the retina. Real-time imaging revealed precise timing of microglial engulfment with the progression of apoptosis, and dynamic movement and displacement of engulfed apoptotic cells. Inhibition of P2RY12 signaling delayed microglial clearance of apoptotic cells.ConclusionsMicroglial engulfment of dying cells is coincident with apoptotic progression and requires P2RY12 signaling, indicating that microglial P2RY12 signaling is shared between development and injury response. Our work provides important in vivo insight into the dynamics of apoptotic cell clearance in the developing vertebrate retina and provides a basis to understand microglial phagocytic behavior in health and disease.Bullet PointsLevels and location of developmental apoptosis in the zebrafish retina are elusive due to rapid and efficient clearance by microgliaMicroglial clearance of apoptotic cells is timed with the progression of apoptosis of the engulfed cell so that many cells are cleared in relatively early apoptotic stagesP2RY12 signaling is involved in microglial sensing and clearance of cells undergoing normal developmental apoptosis, indicating shared signals in microglial responses to cell death in both healthy and injured tissueGrant SponsorsNIH NIGMS Grant No. P20 GM103408

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A Hierarchical Role for Classical Pathway Complement Proteins in the Clearance of Apoptotic Cells in Vivo

Journal of Experimental Medicine ◽

10.1084/jem.192.3.359 ◽

2000 ◽

Vol 192 (3) ◽

pp. 359-366 ◽

Cited By ~ 510

Author(s):

Philip R. Taylor ◽

Anna Carugati ◽

Valerie A. Fadok ◽

H. Terence Cook ◽

Mark Andrews ◽

...

Keyword(s):

Lupus Erythematosus ◽

Apoptotic Cell ◽

Classical Pathway ◽

Apoptotic Cells ◽

In Vivo Models ◽

Complement Proteins ◽

Apoptotic Cell Clearance ◽

Cell Clearance ◽

C1q Deficiency

The strongest susceptibility genes for the development of systemic lupus erythematosus (SLE) in humans are null mutants of classical pathway complement proteins. There is a hierarchy of disease susceptibility and severity according to the position of the missing protein in the activation pathway, with the severest disease associated with C1q deficiency. Here we demonstrate, using novel in vivo models of apoptotic cell clearance during sterile peritonitis, a similar hierarchical role for classical pathway complement proteins in vivo in the clearance of apoptotic cells by macrophages. Our results constitute the first demonstration of an impairment in the phagocytosis of apoptotic cells by macrophages in vivo in a mammalian system. Apoptotic cells are thought to be a major source of the autoantigens of SLE, and impairment of their removal by complement may explain the link between hereditary complement deficiency and the development of SLE.

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Boosting Apoptotic Cell Clearance by Colonic Epithelial Cells Attenuates Inflammation In Vivo

Immunity ◽

10.1016/j.immuni.2016.02.005 ◽

2016 ◽

Vol 44 (4) ◽

pp. 807-820 ◽

Cited By ~ 55

Author(s):

Chang Sup Lee ◽

Kristen K. Penberthy ◽

Karen M. Wheeler ◽

Ignacio J. Juncadella ◽

Peter Vandenabeele ◽

...

Keyword(s):

Epithelial Cells ◽

Apoptotic Cell ◽

Colonic Epithelial Cells ◽

Apoptotic Cell Clearance ◽

Cell Clearance

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Phagocytic clearance of apoptotic, necrotic, necroptotic and pyroptotic cells

Biochemical Society Transactions ◽

10.1042/bst20200696 ◽

2021 ◽

Author(s):

Georgia K. Atkin-Smith

Keyword(s):

Cell Death ◽

Apoptotic Cell ◽

Cell Types ◽

Rapid Expansion ◽

Apoptotic Cell Clearance ◽

Cell Clearance ◽

Functional Consequences ◽

Dying Cells ◽

Cell Engulfment

Although millions of cells in the human body will undergo programmed cell death each day, dying cells are rarely detected under homeostatic settings in vivo. The swift removal of dying cells is due to the rapid recruitment of phagocytes to the site of cell death which then recognise and engulf the dying cell. Apoptotic cell clearance — the engulfment of apoptotic cells by phagocytes — is a well-defined process governed by a series of molecular factors including ‘find-me’, ‘eat-me’, ‘don't eat-me’ and ‘good-bye’ signals. However, in recent years with the rapid expansion of the cell death field, the removal of other necrotic-like cell types has drawn much attention. Depending on the type of death, dying cells employ different mechanisms to facilitate engulfment and elicit varying functional impacts on the phagocyte, from wound healing responses to inflammatory cytokine secretion. Nevertheless, despite the mechanism of death, the clearance of dying cells is a fundamental process required to prevent the uncontrolled release of pro-inflammatory mediators and inflammatory disease. This mini-review summarises the current understandings of: (i) apoptotic, necrotic, necroptotic and pyroptotic cell clearance; (ii) the functional consequences of dying cell engulfment and; (iii) the outstanding questions in the field.

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Chemokines act as phosphatidylserine-bound “find-me” signals in apoptotic cell clearance

PLoS Biology ◽

10.1371/journal.pbio.3001259 ◽

2021 ◽

Vol 19 (5) ◽

pp. e3001259

Author(s):

Sergio M. Pontejo ◽

Philip M. Murphy

Keyword(s):

Chemokine Receptors ◽

Apoptotic Cell ◽

Apoptotic Cells ◽

Anionic Phospholipid ◽

Anionic Phospholipids ◽

Apoptotic Cell Clearance ◽

Cell Clearance ◽

G Protein Coupled ◽

Positively Charged

Removal of apoptotic cells is essential for maintenance of tissue homeostasis. Chemotactic cues termed “find-me” signals attract phagocytes toward apoptotic cells, which selectively expose the anionic phospholipid phosphatidylserine (PS) and other “eat-me” signals to distinguish healthy from apoptotic cells for phagocytosis. Blebs released by apoptotic cells can deliver find-me signals; however, the mechanism is poorly understood. Here, we demonstrate that apoptotic blebs generated in vivo from mouse thymus attract phagocytes using endogenous chemokines bound to the bleb surface. We show that chemokine binding to apoptotic cells is mediated by PS and that high affinity binding of PS and other anionic phospholipids is a general property of many but not all chemokines. Chemokines are positively charged proteins that also bind to anionic glycosaminoglycans (GAGs) on cell surfaces for presentation to leukocyte G protein–coupled receptors (GPCRs). We found that apoptotic cells down-regulate GAGs as they up-regulate PS on the cell surface and that PS-bound chemokines, unlike GAG-bound chemokines, are able to directly activate chemokine receptors. Thus, we conclude that PS-bound chemokines may serve as find-me signals on apoptotic vesicles acting at cognate chemokine receptors on leukocytes.

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