Characterization of Cytokine Responses to Retinal Detachment in Rats

Abstract

Abstract: : Purpose: To characterize the molecular and cellular responses that occur after retinal detachment (RD), the expression of growth factors, cytokines, and chemokines were examined in a rat model of experimental RD. Methods: RD was induced in adult rats by subretinal injection of sodium hyaluronate. Retinal tissues were collected at various time points after the induction of detachment. Expression of gene transcripts of 19 cytokines and growth factors was quantified by real time polymerase chain reaction (QPCR). To identify the cellular sources of the expressed genes, cell samples from various layers of the retina were obtained using laser capture microdissection (LCM) technique, and their mRNAs were isolated. Expression of proteins was determined by immunohistochemistry and Enzyme Linked–Immuno–Sorbent Assay (ELISA). Photoreceptor cell death was assessed using a TdT–dUTP terminal nick–end labeling (TUNEL) assay. Results: Within 72 hours after RD, a significant increase in mRNA level for tumor necrosis factor alpha (TNFa), interleukin–1 beta (IL–1b), monocyte chemotactic protein–1 (MCP–1), and basic fibroblast growth factor (bFGF) were detected in the neural retina. LCM revealed increased expression of mRNA for bFGF and MCP–1 in all retinal layers, though bFGF was especially evident in the outer nuclear layer (ONL) and MCP–1 in the inner nuclear layer (INL). TNF–a was increased in the ONL and INL, and IL–1b was increased in the GCL. Time course experiments showed that TNFa, IL–1b and MCP–1 increased within 1 hour after RD, while bFGF was increased by 24 hours. Increased protein expressions for TNFa, IL–1b and MCP–1 were demonstrated by ELISA at 6 hours after detachment. Immunohistochemistry indicated TNFa and bFGF expression in the whole retina, with IL–1b specifically expressed in astrocytes and MCP–1 in Müller cells. Subretinal administration of exogenous MCP–1 protein increased TUNEL positive cells in ONL 24 hours after RD. Conclusions: Retinal glial cells, including astrocytes and Müller cells, are a major source of cytokine induction after RD, and the increased expression of MCP–1 is an important cause of photoreceptor degeneration associated with RD. This study provides a new avenue for developing therapeutic strategies that protect retinal cell degeneration and prevent vision loss after RD.

Keywords: gene/expression • retinal development • cell death/apoptosis