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Saturated Fatty Acids Induce Ceramide-associated Macrophage Cell Death
Published on: October 31, 2017
How macrophages deal with death
1Molecular Neurobiology Laboratory, Immunobiology and Microbial Pathogenesis Laboratory, The Salk Institute for Biological Studies, La Jolla, CA, USA. lemke@salk.edu.
Abstract:
Tissue macrophages rapidly recognize and engulf apoptotic cells. These events require the display of so-called eat-me signals on the apoptotic cell surface, the most fundamental of which is phosphatidylserine (PtdSer). Externalization of this phospholipid is catalysed by scramblase enzymes, several of which are activated by caspase cleavage. PtdSer is detected both by macrophage receptors that bind to this phospholipid directly and by receptors that bind to a soluble bridging protein that is independently bound to PtdSer. Prominent among the latter receptors are the MER and AXL receptor tyrosine kinases. Eat-me signals also trigger macrophages to engulf virus-infected or metabolically traumatized, but still living, cells, and this 'murder by phagocytosis' may be a common phenomenon. Finally, the localized presentation of PtdSer and other eat-me signals on delimited cell surface domains may enable the phagocytic pruning of these 'locally dead' domains by macrophages, most notably by microglia of the central nervous system.
Insights
Tissue macrophages engulf dying cells using "eat-me" signals like phosphatidylserine (PtdSer). This process, crucial for cellular health, involves specific receptors and scramblase enzymes.
Area of Science:
- Cell biology
- Immunology
- Molecular biology
Background:
- Macrophages are key immune cells that clear apoptotic cells.
- Phosphatidylserine (PtdSer) externalization acts as a primary
- eat-me
- signal on apoptotic cells.
- Scramblase enzymes, often activated by caspases, mediate PtdSer externalization.
Purpose of the Study:
- To elucidate the mechanisms by which macrophages recognize and engulf apoptotic cells.
- To highlight the role of phosphatidylserine (PtdSer) as a critical eat-me signal.
- To explore the broader implications of eat-me signals in cellular homeostasis and disease.
Main Methods:
- Review of existing literature on phagocytosis and cell signaling.
- Analysis of molecular pathways involved in PtdSer externalization and recognition.
- Examination of receptor-ligand interactions, including MER and AXL tyrosine kinases.
Main Results:
- Phosphatidylserine (PtdSer) externalization, catalyzed by scramblases, is essential for apoptotic cell recognition.
- Macrophage receptors directly bind PtdSer or recognize it via bridging proteins.
- Eat-me signals also mediate the engulfment of stressed, living cells ('murder by phagocytosis') and localized cell domain pruning.
Conclusions:
- Phosphatidylserine (PtdSer) is a fundamental eat-me signal for efficient efferocytosis.
- The MER and AXL receptor tyrosine kinases play significant roles in PtdSer recognition.
- Eat-me signals contribute to tissue homeostasis, immune surveillance, and potentially neuroprotection by microglia.
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