Glucosamine suppresses oxidative stress and induces protective autophagy in osteoblasts by blocking the ROS/Akt/mTOR signaling pathway

Abstract

Oxidative stress is the crucial pathogenic factor in osteoporosis. Cell autophagy, a major form of self-digestion, plays critical functions in different forms of stress by devouring harmful cytosolic proteins or organelles for the renewal of organelles and to maintain cellular homeostasis. Glucosamine (GlcN) has been widely utilized in treatments for patients with osteoarthritis-related joint pain. It has potential antioxidant effects and its pharmacological effect in osteoblasts remains unclear.The present study aimed to investigate whether autophagy participates in the protective effects of GlcN in osteoblasts under oxidative stress and the possible mechanism. First of all, MC3T3-E1 cells were treated with hydrogen peroxide (H 2 O 2 ) to induce oxidative stress, as assessed by viability assays, apoptosis, the intracellular reactive oxygen species production. GlcN was capable of inducing autophagy and protected osteoblasts from those cytotoxic effects. Moreover, it significantly attenuated H 2 O 2 -induced oxidative stress as measured by malondialdehyde, glutathione, nitrite, and superoxide dismutase levels. Importantly, the autophagy level increased in osteoblasts treated with GlcN as represented by an increase in both Beclin1 expression and the LC3 II/I ratio. Immunofluorescence analysis of autophagosomes also confirmed the above results. In addition, GlcN decreased the mammalian target of rapamycin (mTOR) and protein kinase B (Akt). However, the Akt activator (SC79) suppressed the autophagy level induced by GlcN in osteoblasts.Consequently, the antioxidant effects of GlcN were mediated, at least in part, by enhancing autophagy through the Akt/mTOR pathway. These results suggested that GlcN might be a promising candidate for osteoporosis treatment.

Oxidative Stress and Inflammation in Osteoporosis: Molecular Mechanisms Involved and the Relationship with microRNAs

“…Excessive ROS production not only induces the defective formation of osteoblasts, but also negatively affects their activity, viability, proliferation, and apoptosis. This leads to a reduction in osteoblastic number and functionality with consequent beginning and evolution of osteoporotic processes [ 27 , 71 , 72 , 73 , 74 ]. The increase in the intracellular activity of ALP and RANKL, and the decrease in IL-6 production due to oxidative stress alter the mineralization processes in H 2 O 2 -treated MC3T3-E1 cells [ 62 , 75 , 76 ].…”

“…Oxidative stress-activated mTOR signaling pathways can also be involved in osteoporosis by increasing the apoptosis of osteoblasts [ 79 ]. In fact, blocking the Akt/mTOR signaling pathway inhibits the oxidative stress-induced apoptosis in osteoblasts [ 73 ], and the inhibition of mTOR/NF-kB phosphorylation reduces oxidative stress and apoptosis in osteoblasts treated with high levels of glucose [ 79 ]. Hyperglycemia is able to reduce bone quality, and diabetic bone disease is a complication of diabetes mellitus in humans [ 80 , 81 ].…”

“…In these cells, the high levels of glucose increase ROS production and apoptosis through the downregulation of the AMP-activated protein kinase (AMPK)/FOXO3a signaling pathway [ 96 ]. GCs increase osteocyte apoptosis via the upregulation of NADPH-oxidase, subsequently inducing oxidative stress, as demonstrated in the osteocytes of patients affected by steroid-induced avascular necrosis of the femoral head [ 73 ] and in MLO-Y4 cells [ 97 ].…”

Associations of healthy eating index-2015 with osteoporosis and low bone mass density in postmenopausal women: a population-based study from NHANES 2007–2018

“…Apart from the direct positive effect of estrogen deficiency on postmenopausal osteoporosis, oxidative stress, inflammation and immune cell alterations have been acknowledged to contribute to the pathogenesis of postmenopausal osteoporosis, in which healthy diet may play an important role in attenuating the development. Excessive reactive oxygen species production due to estrogen insufficiency not only disrupts the formation and functionality of osteoblasts, but also negatively affects their activity, viability, proliferation, and apoptosis (56)(57)(58)(59)(60). This leads to a reduction in osteoblastic number and functionality with consequent beginning and development of osteoporotic processes, resulting in the altered bone architecture and bone loss that characterize osteoporosis.…”