title: Insights on the involvement of (-)-epigallocatechin gallate in ER stress-mediated apoptosis in age-related macular degeneration.
abstract: Endoplasmic reticulum (ER) stress-mediated apoptosis is a well-known factor in the pathogenesis of age-related macular degeneration (AMD). ER stress leads to accumulation of misfolded proteins, which in turn activates unfolded protein response (UPR) of the cell for its survival. The prolonged UPR of ER stress promotes cell death; however, the transition between adaptation and ER stress-induced apoptosis has not been clearly understood. Hence, the present study investigates the regulatory effect of (-)-epigallocatechin gallate (EGCG) on ER stress-induced by hydrogen peroxide (H2O2) and disturbance of calcium homeostasis by thapsigargin (TG) in mouse retinal pigment epithelial (MRPE) cells. The oxidant molecules influenced MRPE cells showed an increased level of intracellular calcium [Ca2+]iin ER and transferred to mitochondria through ER-mitochondrial tether site then increased ROS production. EGCG restores [Ca2+]ihomeostasis by decreasing ROS production through inhibition of prohibitin1 which regulate ER-mitochondrial tether site and inhibit apoptosis. Effect of EGCG on ER stress-mediated apoptosis was elucidated by exploring the UPR signalling pathways. EGCG downregulated GRP78, CHOP, PERK, ERO1α, IRE1α, cleaved PARP, cleaved caspase 3, caspase 12 and upregulated expression of calnexinin MRPE cells. In addition to this, inhibition of apoptosis by EGCG was also confirmed with expression of proteins Akt, PTEN and GSK3β. MRPE cells with EGCG upregulates phosphorylation of Akt at ser473 and phospho ser380 of PTEN, but phosphorylation at ser9 of GSK3β was inhibited. Further, constitutively active (myristoylated) CA-Akt transfected in MRPE cells had an increased Akt activity in EGCG influenced cells. These findings strongly suggest that antioxidant molecules inhibit cell death through the proper balancing of [Ca2+]iand ROS production in order to maintain UPR of ER in MRPE cells. Thus, modulation of UPR signalling may provide a potential target for the therapeutic approaches of AMD.
authors: Department of Biotechnology, Kalasalingam University, Anand Nagar, Krishnankoil, Tamil Nadu, 626 126, India.|Department of Ophthalmic Research, Cole Eye Institute, Cleveland Clinic, Cleveland, OH, 44195, USA.
authors: Bose
authors: B
authors: Karthikeyan
authors: Department of Biotechnology, Kalasalingam University, Anand Nagar, Krishnankoil, Tamil Nadu, 626 126, India.
authors: Lakshminarasimhan
authors: L
authors: Harini
authors: Department of Microbiology, Bharathidasan University, Tiruchirappalli, Tamil Nadu, 620 024, India.
authors: Vaithilingam
authors: V
authors: Krishnakumar
authors: Department of Microbiology, Bharathidasan University, Tiruchirappalli, Tamil Nadu, 620 024, India.
authors: Velu Rajesh
authors: VR
authors: Kannan
authors: Department of Biotechnology, Kalasalingam University, Anand Nagar, Krishnankoil, Tamil Nadu, 626 126, India.|International Research Centre, Kalasalingam University, Krishnankoil, Tamil Nadu, 626 126, India.
authors: Krishnan
authors: K
authors: Sundar
authors: Department of Biotechnology, Kalasalingam University, Anand Nagar, Krishnankoil, Tamil Nadu, 626 126, India. t.kathiresan@klu.ac.in.|International Research Centre, Kalasalingam University, Krishnankoil, Tamil Nadu, 626 126, India. t.kathiresan@klu.ac.in.
authors: Thandavarayan
authors: T
authors: Kathiresan
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects*; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000235:genetics; D002392:Catechin / Q000008:administration & dosage / Q000031:analogs & derivatives*; D000091342:Endoplasmic Reticulum Chaperone BiP; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects* / Q000235:genetics; D006801:Humans; D006861:Hydrogen Peroxide / Q000633:toxicity; D008268:Macular Degeneration / Q000188:drug therapy* / Q000235:genetics; D051379:Mice; D008928:Mitochondria / Q000187:drug effects / Q000235:genetics; D018384:Oxidative Stress / Q000187:drug effects; D017382:Reactive Oxygen Species / Q000378:metabolism; D019284:Thapsigargin / Q000008:administration & dosage; D056811:Unfolded Protein Response / Q000187:drug effects / Q000235:genetics*
chemical_list: D000975:Antioxidants; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; C000717248:Hspa5 protein, mouse; D017382:Reactive Oxygen Species; D019284:Thapsigargin; D002392:Catechin; D006861:Hydrogen Peroxide; C045651:epigallocatechin gallate; D002118:Calcium
keywords: AMD; Akt; Caspase; EGCG; ER-mitochondrial tether site; Intracellular calcium; ROS