Loss of X-box binding protein 1 in Müller cells augments retinal inflammation in a mouse model of diabetes

Abstract

Aims/hypothesis Müller glia (MG) are major sources of retinal cytokines, and their activation is closely linked to retinal inflammation and vascular leakage in diabetic retinopathy. Previously, we demonstrated that X-box binding protein 1 (XBP1), a transcription factor activated by endoplasmic reticulum (ER) stress in diabetic retinopathy, is involved in regulation of inflammation in retinal endothelial cells. Now, we have explored the role of XBP1 and ER stress in the regulation of MGderived proinflammatory factors, and their influence on vascular permeability in diabetic retinopathy. Methods MG-specific conditional Xbp1 knockout (Xbp1 Müller−/− ) mice were generated by crossing Xbp1 flox/flox mice with Müller-Cre transgenic mice. Diabetes was modelled by induction with streptozotocin, and retinal vascular permeability was measured with FITC-conjugated dextran 2 months after induction. Primary Müller cells were isolated from Xbp1 Müller−/− and Xbp1 Müller+/+ mice and exposed to hypoxia and high levels of glucose. Levels of ER-stress and inflammatory factors were examined by real-time PCR, western blotting or immunohistochemistry. Results Xbp1 Müller−/− mice exhibited normal retinal development and retinal function and expressed similar levels of ER-stress and inflammatory genes to Xbp1 Müller+/+ littermates. In diabetes-inducing conditions, compared with Xbp1 Müller+/+ mice, Xbp1 Müller−/− mice had higher mRNA levels of retinal Vegf (also known as Vegfa) and Tnf-α (also known as Tnf) and ERstress marker genes Grp78 (also known as Hspa5), Atf4, Chop (also known as Ddit3) and Atf6 and higher protein levels of vascular endothelial growth factor (VEGF), TNF-α, phospho-c-Jun N-terminal kinase (JNK), 78 kDa glucose-regulated protein (GRP78), phospho-eukaryotic translation initiation factor (eIF)2α and activating transcription factor (ATF)6. Retinal vascular permeability was significantly higher in diabetic Xbp1 Müller−/− mice than in diabetic Xbp1 Müller+/+ mice (p < 0.01). Results obtained in vitro with primary Müller cells isolated from Xbp1 Müller−/− mice confirmed higher expression levels of inflammatory and ER-stress markers (but not GRP78) than in cells from Xbp1 Müller+/+ mice. Moreover, XBP1-deficient Müller cells were more susceptible to high-glucose-or hypoxia-induced ER stress and inflammation than cells from Xbp1 Müller+/+ mice. Inhibition of ER stress with chemical chaperones suppressed hypoxia-induced VEGF and TNF-α production in XBP1-deficient Müller cells.Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00125-018-4776-y) contains peer-reviewed but unedited supplementary material, which is available to authorised users.

Associations of hypertension Diabetes Smoking History and SNPs with Responses to Aflibercept Treatment for tAMD and PCV

“…In the PCV group, the one-year change in CRT indicated significant improvement in non-diabetic as compared to diabetic patients. Another study demonstrated an increase in VEGF production in murine models of retinal inflammation with diabetes as compared to those without diabetes [13].…”

Characterization of Retinal Microvascular Complications and the Effects of Endoplasmic Reticulum Stress in Mouse Models of Diabetic Atherosclerosis

“…17 In healthy cells, the UPR reduces ER stress levels via upregulation of ER chaperones, promotion of ERassociated degradation of misfolded proteins, and increased regulation of protein translation. 17 However, under conditions of prolonged and irremediable ER stress, the apoptotic branch of the UPR is activated, causing death of affected cells. 17,20,21 Although factors such as abnormal glucose and lipid metabolism, oxidative stress, excess cytokine release, and autophagy are likely implicated, [22][23][24] the pathophysiologic mechanism involved in the progression of DR has yet to be fully elucidated.…”

“…17 However, under conditions of prolonged and irremediable ER stress, the apoptotic branch of the UPR is activated, causing death of affected cells. 17,20,21 Although factors such as abnormal glucose and lipid metabolism, oxidative stress, excess cytokine release, and autophagy are likely implicated, [22][23][24] the pathophysiologic mechanism involved in the progression of DR has yet to be fully elucidated. 25 Interestingly, many of these factors are regulated by pathways involved in the UPR.…”

“…4 , 13 Diabetes is known to induce ER dysfunction, resulting in the accumulation of misfolded proteins (ER stress) and retinal inflammation. 17 – 19 In response, cells activate the UPR to enhance protein folding capacity and restore ER homeostasis. 17 In healthy cells, the UPR reduces ER stress levels via upregulation of ER chaperones, promotion of ER-associated degradation of misfolded proteins, and increased regulation of protein translation.…”

“… 17 – 19 In response, cells activate the UPR to enhance protein folding capacity and restore ER homeostasis. 17 In healthy cells, the UPR reduces ER stress levels via upregulation of ER chaperones, promotion of ER-associated degradation of misfolded proteins, and increased regulation of protein translation. 17 However, under conditions of prolonged and irremediable ER stress, the apoptotic branch of the UPR is activated, causing death of affected cells.…”