Microglia activation is essential for BMP7-mediated retinal reactive gliosis

Subramanian Dharmarajan,Nader Sheibani,Teri L Belecky-Adams,Christine M Sorenson,Debra L Fisk

doi:10.1186/s12974-017-0855-0

Abstract

BackgroundOur previous studies have shown that BMP7 is able to trigger activation of retinal macroglia. However, these studies showed the responsiveness of Müller glial cells and retinal astrocytes in vitro was attenuated in comparison to those in vivo, indicating other retinal cell types may be mediating the response of the macroglial cells to BMP7. In this study, we test the hypothesis that BMP7-mediated gliosis is the result of inflammatory signaling from retinal microglia.MethodsAdult mice were injected intravitreally with BMP7 and eyes harvested 1, 3, or 7 days postinjection. Some mice were treated with PLX5622 (PLX) to ablate microglia and were subsequently injected with control or BMP7. Processed tissue was analyzed via immunofluorescence, RT-qPCR, or ELISA. In addition, cultures of retinal microglia were treated with vehicle, lipopolysaccharide, or BMP7 to determine the effects of BMP7-isolated cells.ResultsMice injected with BMP7 showed regulation of various inflammatory markers at the RNA level, as well as changes in microglial morphology. Isolated retinal microglia also showed an upregulation of BMP-signaling components following treatment. In vitro treatment of retinal astrocytes with conditioned media from activated microglia upregulated RNA levels of gliosis markers. In the absence of microglia, the mouse retina showed a subdued gliosis and inflammatory response when exposed to BMP7.ConclusionsGliosis resulting from BMP7 is mediated through an inflammatory response from retinal microglia.

Highlights

Our previous studies have shown that bone morphogenetic protein 7 (BMP7) is able to trigger activation of retinal macroglia
Bone morphogenetic protein (BMP) signaling in retinal microglia Previous studies have shown that BMP7 triggers reactive gliosis of the retinal macroglia
To determine if any of these pathways were activated in the microglia of controlor BMP7-treated retina, double-label immunohistochemistry was performed using antibodies to phospho SMAD 1/5/9, phospho TAK1, and PU.1 on adult retinas following intravitreal injection of vehicle or BMP7

Summary

Introduction

Our previous studies have shown that BMP7 is able to trigger activation of retinal macroglia. These studies showed the responsiveness of Müller glial cells and retinal astrocytes in vitro was attenuated in comparison to those in vivo, indicating other retinal cell types may be mediating the response of the macroglial cells to BMP7. We test the hypothesis that BMP7-mediated gliosis is the result of inflammatory signaling from retinal microglia. The mammalian retina consists of at least two distinct glial populations: the macroglia, which includes Müller glia and retinal astrocytes, and the microglia. Any injury or disease leading to retinal damage or disruption of the homeostasis triggers the glial cells to become active, a response termed reactive gliosis.

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