Tauroursodeoxycholic acid blocks endoplasmic reticulum stress mediated visual deficits in diabetic tie2 TNF transgenic mice

Abstract

Purpose : Endoplasmic Reticulum (ER) stress plays a major role in several metabolic disorders including diabetes. Using a pro-inflammatory tie2-TNF mouse model of diabetic retinopathy we have shown age-associated accentuation of ER stress accompanied by endothelial junction protein modifications that affect neurovascular integrity resulting in increased visual deficits. In this study, we have evaluated the efficacy of TUDCA, an ER stress inhibitor as a promising therapeutic target for treatment of diabetic retinopathy.

Methods : Age matched wildtype (WT) and tie2-TNF mice were made diabetic with intraperitoneal injections of Streptozotocin (5 days of 35mg/Kg). Mice were given TUDCA (500mg/kg, subcutaneous) for 4 weeks. The following six groups were assessed for visual function (ERG and OKN) followed by immunohistology and molecular analyses: WT, tie2-TNF, WT-diabetic, tie2-TNF-diabetic, WT-diabetic-TUDCA and tie2-TNF-diabetic-TUDCA.

Results : At 3 months of age, visual acuity in tie2-TNF mice decreased compared to WT mice (0.36±0.01 v/s 0.42±0.001 c/d, p<0.05) with a further decrease (0.32±0.05) in tie2-TNF-diabetic mice. TUDCA treatment ameliorated these effects (0.39±0.005 c/d, p<0.05). Similarly, contrast sensitivity of tie2-TNF mice compared to WT showed an increase in contrast needed (26.1±0.02 v/s 21.7±0.07% at 0.042c/d, p<0.05) with a further increase (35.9±0.07) in tie2-TNF-diabetic mice. TUDCA treatment ameliorated these effects (28.1±0.1%, p<0.05). Similarly, a decrease in b-wave amplitude in tie2-TNF mice was further accentuated in tie2-TNF-diabetic mice (264±34 v/s 212±14 mV, p<0.05) were ameliorated by TUDCA treatment (281±19, p<0.05). A significant 2-13 fold increase in retinal ER stress gene transcript response in tie2-TNF mice was further increased in tie2-TNF-diabetic mice were ameliorated by TUDCA treatment. Immunofluorescence analysis of retina demonstrated increased expression of GFAP in tie2-TNF mice v/s WT (25.8±9.5 v/s 6.4±0.29/100000 µm²; p<0.05). TUDCA treatment ameliorated these effects compared to tie2-TNF-diabetic mice (9±4.0 v/s 31±2.0 /100000 µm²; p<0.05)

Conclusions : Excessive ER stress stimulated by hyperglycemia and ongoing inflammation can account for the vicious cycle of vascular and neural retina destruction in diabetic retinopathy. The safety and efficacy of TUDCA in diabetic retinopathy needs further evaluation.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.