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Extracellular Soluble Membranes from Retinal Pigment Epithelial Cells Mediate Apoptosis in Macrophages
Nayan Sanjiv1, Pawarissara Osathanugrah1, Emma Fraser1
1Department of Ophthalmology, Boston University School of Medicine, Boston, MA 02118, USA.
Abstract:
A central characterization of retinal immunobiology is the prevention of proinflammatory activity by macrophages. The retinal pigment epithelial cells (RPEs) are a major source of soluble anti-inflammatory factors. This includes a soluble factor that induces macrophage apoptosis when the activity of the immunomodulating neuropeptide alpha-melanocyte-stimulating hormone (α-MSH) is neutralized. In this manuscript, isolated extracellular soluble membranes (ESMs) from primary RPE were assayed to see if they could be the soluble mediator of apoptosis. Our results demonstrated that RPE ESMs mediated the induction of macrophage apoptosis that was suppressed by α-MSH. In contrast, the RPE line ARPE-19, cultured under conditions that induce similar anti-inflammatory activity to primary RPEs, did not activate apoptosis in the macrophages. Moreover, only the ESMs from primary RPE cultures, and not those from the ARPE-19 cell cultures, expressed mFasL. The results demonstrate that RPE ESMs are a soluble mediator of apoptosis and that this may be a mechanism by which the RPEs select for the survival of α-MSH-induced suppressor cells.
Insights
Retinal pigment epithelial cells (RPEs) release extracellular soluble membranes (ESMs) that trigger macrophage apoptosis, a process inhibited by alpha-melanocyte-stimulating hormone (α-MSH). This mechanism highlights how RPEs regulate immune cell survival.
Area of Science:
- Immunobiology
- Ophthalmology
- Cell Biology
Background:
- Macrophages are key in retinal immunobiology, and their proinflammatory activity must be controlled.
- Retinal pigment epithelial cells (RPEs) secrete anti-inflammatory factors, including a mediator that induces macrophage apoptosis when alpha-melanocyte-stimulating hormone (α-MSH) is neutralized.
Purpose of the Study:
- To investigate if extracellular soluble membranes (ESMs) from primary RPEs act as the soluble mediator of macrophage apoptosis.
- To compare the apoptotic activity of primary RPE ESMs with that of the RPE cell line ARPE-19.
Main Methods:
- Primary RPE cultures and the ARPE-19 cell line were used.
- Extracellular soluble membranes (ESMs) were isolated from primary RPEs and ARPE-19 cells.
- Macrophage apoptosis was assayed in the presence and absence of α-MSH.
- Expression of mFasL in ESMs was analyzed.
Main Results:
- ESMs from primary RPEs induced macrophage apoptosis, which was suppressed by α-MSH.
- ARPE-19 cell line ESMs did not induce macrophage apoptosis, despite exhibiting similar anti-inflammatory activity to primary RPEs.
- Only primary RPE ESMs expressed mFasL, suggesting its role in apoptosis induction.
Conclusions:
- RPE ESMs are identified as a soluble mediator of macrophage apoptosis.
- This mechanism may be crucial for RPEs to selectively eliminate certain immune cells, supporting immune homeostasis in the retina.
- The findings differentiate the function of primary RPE ESMs from the ARPE-19 cell line in immune regulation.
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