Melatonin Inhibits Glucose-Induced Apoptosis in Osteoblastic Cell Line Through PERK-eIF2α-ATF4 Pathway

Abstract

Osteoporosis is a common disease resulting in deteriorated microarchitecture and decreased bone mass. In type 2 diabetes patients, the incidence of osteoporosis is significantly higher accompanied by increased apoptosis of osteoblasts. In this study, using the osteoblastic cell line MC3T3-E1, we show that high glucose reduces cell viability and induces apoptosis. Also, high glucose leads to endoplasmic reticulum (ER) stress (ERS) via an increase in calcium flux and upregulation of the ER chaperone binding immunoglobulin protein (BiP). Moreover, it induces post-translational activation of eukaryotic initiation factor 2 alpha (eIF2α) which functions downstream of PKR-like ER kinase (PERK). This subsequently leads to post-translational activation of the transcription factor 4 (ATF4) and upregulation of C/EBP-homologous protein (CHOP) which is an ER stress-induced regulator of apoptosis, as well as downstream effectors DNAJC3, HYOU1, and CALR. Interestingly, melatonin treatment significantly alleviates the high-glucose induced changes in cell growth, apoptosis, and calcium influx by inhibiting the PERK-eIF2α-ATF4-CHOP signaling pathway. Additionally, the MC3T3-E1 cells engineered to express a phosphodead eIF2α mutant did not show high glucose induced ER stress, confirming that melatonin protects osteoblasts against high-glucose induced changes by decreasing ER-stress induced apoptosis by impacting the PERK-eIF2α-ATF4-CHOP signaling pathway. The protective of melatonin against high glucose-induced ER stress and apoptosis was attenuated when the cells were pre-treated with a melatonin receptor antagonist, indicating that the effect of melatonin was mediated via the melatonin receptors in this context. These findings lay the provide mechanistic insights of melatonin’s protective action on osteoblasts and will be potentially be useful in ongoing pre-clinical and clinical studies to evaluate melatonin as a therapeutic option for diabetic osteoporosis.

Pharmacological Disruption of Phosphorylated Eukaryotic Initiation Factor-2α/Activating Transcription Factor 4/Indian Hedgehog Protects Intervertebral Disc Degeneration via Reducing the Reactive Oxygen Species and Apoptosis of Nucleus Pulposus Cells

“…As an upstream of ATF4, the phosphorylation of eukaryotic initiation factor-2α (eIF2α) preferentially facilitates the ATF4 activation, which transduces signals to the cytoplasm and nucleus to cause the imbalance of cellular homeostasis ( Harding et al, 2003 ; Liu and Zhang, 2020 ). Inhibiting the phosphorylated eIF2α (p-eIF2α) leads to a decrease in the post-translational activation of ATF4 ( Zhao et al, 2020a ; Zhou et al, 2020 ). The current literature of ATF4 on the process of apoptosis mainly mentions its positive regulation.…”

New insights into the role of melatonin in diabetic cardiomyopathy

“…Melatonin reduces the expression of P-PERK, P-eIF2α, and P-ATF4, then affects the expression of CHOP and attenuates apoptosis of osteoblastic cells. 180 Taken together, it is evident that melatonin inhibits ER stress, thereby protecting cells from apoptosis. It is noteworthy, however, that melatonin does not significantly reduce the increased expression of IRE1α caused by diabetes.…”

Roles of Inflammasome in Cigarette Smoke-Related Diseases and Physiopathological Disorders: Mechanisms and Therapeutic Opportunities

“…Besides NAC, other therapies antagonizing ROS were also explored to modulate inflammasome activation in cigarette smoke-induced diseases. Melatonin (N-acetyl-5-methoxytryptamine) is a neuroendocrine hormone synthesized by tryptophan and serotonin metabolism, and secreted from the pineal gland ( 62 , 63 ). Melatonin was found to play an important role in relieving oxidative stress injury ( 64 , 65 ).…”