Melatonin reduces endoplasmic reticulum stress and corneal dystrophy‐associated TGFBI TGFBI p through activation of endoplasmic reticulum‐associated protein degradation

摘要

Abstract Endoplasmic reticulum ( ER ) stress?is emerging as a factor for?the?pathogenesis?of granular corneal dystrophy type 2 ( GCD 2). This study was designed to investigate the molecular mechanisms underlying the protective effects of melatonin on ER stress in GCD 2. Our results showed that GCD 2 corneal fibroblasts were more susceptible to ER stress‐induced death than were wild‐type cells. Melatonin significantly inhibited GCD 2 corneal cell death, caspase‐3 activation, and poly ( ADP ‐ribose) polymerase 1 cleavage caused by the ER stress inducer, tunicamycin. Under ER stress, melatonin significantly suppressed the induction of immunoglobulin heavy‐chain‐binding protein (BiP) and activation of inositol‐requiring enzyme 1α ( IRE 1α), and their downstream target, alternative splicing of X‐box binding protein 1(XBP1). Notably, the reduction in BiP and IRE 1α by melatonin was suppressed by the ubiquitin‐proteasome inhibitor, MG 132, but not by the autophagy inhibitor, bafilomycin A1, indicating involvement of the ER ‐associated protein degradation ( ERAD ) system. Melatonin treatment reduced the levels of transforming growth factor‐β‐induced protein ( TGFBI p) significantly, and this reduction was suppressed by MG 132. We also found reduced mRNA expression of the? ERAD ?system components HRD 1 and SEL 1L , and a reduced level of SEL 1L protein in GCD 2 cells. Interestingly, melatonin treatments enhanced SEL 1L levels and suppressed the inhibition of SEL 1L N ‐glycosylation caused by tunicamycin. In conclusion, this study provides new insights into the mechanisms by which melatonin confers its protective actions during ER stress. The results also indicate that melatonin might have potential as a therapeutic agent for ER stress‐related diseases including GCD 2.