Abstract
Purpose :
Our earlier studies have established the mechanism of ER stress-mediated junction protein alterations in activated endothelial cells as observed in diabetic retinopathy (DR). We further tested the efficacy of Tauroursodeoxycholic acid (TUDCA), an ER stress inhibitor as a promising therapeutic agent for the treatment of DR. The mechanism of action of this drug is still unclear. The goal of the current study is to identify the potential receptor through which TUDCA mediates its protective effects.
Methods :
Mouse retinal tissues from DR and control mice were assessed for G protein-coupled bile acid receptor 1/Takeda G protein-coupled receptor 5 (GPBAR1/TGR5). Human retinal endothelial cells (HRECs) silenced for TGR5 receptor, were stimulated with TNFα (TNF, 20ng/mL) and high glucose (HG, 30mM) and assessed for ER stress with and without 20mM TUDCA. Endothelial permeability, transendothelial migration of activated leukocytes and release of cAMP were assessed in TGR5 silenced cells with TGR5 agonist and antagonists serving as additional controls.
Results :
Retinal expression of TGR5 showed a 2-fold increase in DR mice correlated with >2-fold increase in TGR5 expression in HRECs exposed to TNF+HG. HRECs exposed to TNF+HG demonstrated a 2-fold increase in GRP78, a 30% increase in cAMP, a 3-fold increase in transendothelial migration of activated leukocytes with a concomitant increase in permeability as assessed by a decrease in resistance in the ECIS assay. Interestingly, TUDCA via acting through TGR5 reversed these effects significantly. On the other hand, HRECs silenced for TGR5 and challenged with TUDCA failed to reverse the TNF+HG induced ER stress and other effects.
Conclusions :
Our data suggest that TGR5 is the cognate receptor on retinal endothelial cells. Perturbation of TGR5 receptor in the retina might play a role in linking retinal ER stress to neurovascular dysfunction in DR. Additionally, TUDCA and other GPBAR1/TGR5 antagonists need to be further investigated, to determine their potential in attenuating vascular permeability in vivo.
This is a 2020 ARVO Annual Meeting abstract.