The RPE-derived NF-κB/HO-1/MCP-1 pathway mediated Microglia Recruitment Involved in the Outer Blood-Retinal Barrier Breakdown in Experimental Diabetic Retinopathy

To investigate the mechanisms underlying the microglia recruitment and its causal role in the breakdown of the outer blood-retinal barrier (oBRB) in diabetic retinopathy (DR).

The Sprague-Dawley rats were adopted to establish diabetic model by intraperitoneal injection of streptozotocin. Twelve weeks later, the retinal pigment epithelium (RPE)-choroid complexes and retinal paraffin sections were examined with immunofluorescence. RNA-sequencing was performed on glyoxal-treated ARPE-19 cells, followed by bioinformatic analysis to identify significant genes and pathways. Transwell assays were employed to establish the co-culture system and investigate the interactions between ARPE-19 and BV2 microglial cells. The results were further validated by the inhibitor or siRNAs targeting NF-κB, HO-1, and MCP-1.

In 12-week diabetic rat retinas, microglia were observed to accumulate in the vicinity of the RPE cells, accompanied by the disruption of ZO-1. The expressions of ZO-1 and occludin remained largely unchanged in ARPE-19 cells when treated with glyoxal alone. However, when co-cultured with BV2 microglial cells, the expression levels of ZO-1 and occludin in glyoxal-treated ARPE-19 cells were significantly decreased, which were effectively prevented by siMCP-1. Mechanistically, RNA-sequencing analysis revealed that the activation of the NF-κB/HO-1/MCP-1 pathway in glyoxal-treated ARPE-19 cells significantly contributed to the recruitment of microglia. The above effects were reversed by BAY 11–7082, siHO-1 or siMCP-1.

Under diabetic conditions, microglia are recruited by RPE cells via the NF-κB/HO-1/MCP-1 pathway, which subsequently results in the oBRB breakdown. This study provides a novel mechanistic insight for the interaction between microglia and RPE cells, and implies a potential therapeutic strategy for the treatment of DR.