Abstract
Purpose:
Diabetic retinopathy (DR) is a leading cause of blindness in working-age population. Increasing evidence suggests that ER stress and inflammation contributes to the pathogenesis of DR. Müller glia cells constitute the major glial component of the retina. The purpose of the present study is to examine the role of X-box binding protein 1 (XBP1), a central regulator of ER stress response, in Müller cell-derived retinal inflammation and vascular leakage in diabetes.
Methods:
Müller cell-specific conditional Xbp1 knockout (Xbp1Müller-/-) mice were generated by crossing inducible Müller-Cre mice with Xbp1 flox/flox mice. Diabetes was induced by streptozotocin in Xbp1Müller-/- mice and their littermate controls (Xbp1Müller+/+). Expression of retinal ER stress markers and inflammatory cytokines was examined by real-time qPCR, Western blotting and immunostaining. Retinal vascular permeability was measured by FITC-conjugated dextran method after 2 months of diabetes.
Results:
Successful reduction (>90%) in Xbp1 gene expression was confirmed in retinal Müller cells of Xbp1Müller-/- mice. After 2 months of diabetes, mRNA and protein levels of major inflammatory cytokines (VEGF and TNF-α) were increased in retinas of Xbp1Müller-/- mice compared to the control. In addition, XBP1 deficiency resulted in greater ER stress in diabetic retinas, as evidenced by enhanced expression of GRP78, p-eIF2α, ATF4, CHOP, ATF6 and p-JNK. Consistently, retinal vascular permeability was significantly increased in diabetic Xbp1Müller-/- mice. Increased ER stress and inflammatory gene expression was also found in retinal Müller cells isolated from Xbp1Müller-/- mice.
Conclusions:
XBP1 deficiency in Müller cells exacerbates retinal ER stress and inflammation in diabetes. This result indicates that increased ER stress in Müller cell is an important contributing factor in inflammatory cytokine production and inflammation-related vascular damage in DR.