Eucalyptol ameliorates amyloid-β-induced retinal microvascular permeability and ER stress-mediated apoptosis via inhibition of PERK-elF2α-ATF4-Cas12 pathway in diabetic eyes

Abstract Retinal microvascular endothelial cells are monolayer epithelium form the smooth internal vascular lining for normal blood flow and manage the nutritional requirements and protection of a tissue critical to vision. Prolonged endoplasmic reticulum (ER) stress impairs the protein folding capacity, and the accumulation of unfolded proteins in the ER eventually triggers apoptosis. Here, we investigated whether eucalyptol attenuated amyloid-β-deposited diabetic retinal microvascular permeability and ER stress-mediated apoptosis. Primary human retinal microvascular endothelial cells (HRMVEC) were cultured in media containing 33 mM glucose and 5 µM amyloid-β for 3 days in the presence of 1-20 μM eucalyptol. Eucalyptol at 1-20 μM reversed the reduction of cellular level of phospho-PERK, phospho-elF2α, ATF4, CHOP, Bax and cleaved caspase-12 in 5 µM amyloid-β-loaded retinal endothelial cells. Eucalyptol increased cellular junctional proteins of VE-cadherin and Occludin-1 in Aβ-exposed HRMVEC and diabetic retinas. Furthermore, this compound diminished the enhanced expression of vascular endothelial growth factor (VEGF). In addition, eucalyptol reduced the up-regulation of Ang-2 and elevated the down-regulated Ang-1 and Tie-2 induction which is essential to retinal capillary occlusion and inner BRB permeability. Consistently, oral administration of 10 mg/kg eucalyptol reversed the induction of these proteins in db/db mouse eye tissues. We identified that eucalyptol antagonizes amyloid-β-mediated malfunction of inner blood retinal barrier through blocking ER stress-induced apoptosis in diabetic eyes.