Autophagy protects osteoblasts from advanced glycation end products-induced apoptosis through intracellular reactive oxygen species

Abstract

Patients with type II diabetes are susceptible to fracture; however, these patients typically have normal bone mineral density. Thus, such fractures cannot be entirely explained by advanced glycation end products (AGEs)-induced osteoblast apoptosis. Autophagy is a molecular process allowing cells to degrade unnecessary or dysfunctional cellular organelles, and closely interacts with apoptosis. The aim of this study was to determine whether autophagy participated in the pathology of AGEs-treated osteoblasts, and the possible mechanism of such an involvement. Osteoblastic MC3T3-E1 cells were used. Autophagy was evaluated by detecting the level of LC3 via western blotting and immunofluorescence. p62/SQSTM1 expression was also assessed by western blotting. The autophagy inducer rapamycin (RA) and the autophagy inhibitor 3-methyladenine were used to determine whether autophagy has effect on AGEs-induced apoptosis. N-Acetylcysteine (NAC), reactive oxygen species (ROS) inhibitor, was used to determine whether ROS and mitochondrial damage were involved in autophagy regulation. The results showed that the autophagy level was increased in MC3T3-E1 cells treated with AGEs, as represented by an increase in both the total LC3 level and the LC3II/LC3I ratio, as well as a decrease in p62/SQSTMI expression. Further inducing autophagy by RA attenuated AGEs-induced apoptosis. The antioxidant NAC suppresses AGEs-induced autophagy in osteoblastic MC3T3-E1 cells. These results demonstrate that autophagy participates in the pathology of AGEs-treated osteoblasts, and may play a protective role in AGEs-induced apoptosis in osteoblastic MC3T3-E1 cells. ROS and mitochondrial damage are essential in upregulating AGEs-induced autophagy.

Involvement of autophagy in tantalum nanoparticle-induced osteoblast proliferation

“…45 In the present study, treatment with rapamycin or 3-MA alone had no significant influence on cell viability, which was consistent with previous studies revealing that pretreatment with rapamycin (no more than 2 μM) or 3-MA (no more than 10 mM) had no significant influence on cell viability, differentiation, mineralization, apoptosis of osteoblasts, or the expression of autophagy and osteogenesis-related factors. 23,37,46,47 The cell viability further increased when the cells were pretreated with rapamycin but obviously decreased when they were pretreated with 3-MA, revealing that autophagy was involved in the Ta-NP-induced cell proliferation and had a promoting effect. This statement is consistent with the finding that nano-TiO 2 -induced autophagy played a protective role against oxidative stress and promoted cell proliferation.…”

“…Autophagy is a complicated catabolic pathway that regulates the lysosomal degradation of unnecessary organelles and foreign bodies to maintain cell homeostasis, thus playing a cytoprotective role in cell growth, survival, proliferation, and differentiation. [35][36][37] Any extracellular factors can be recognized as foreign and can be taken up by cells through a number of membrane-mediated mechanisms in which the foreign bodies are internalized in lysosomes, endosomes, or autophagosomes. 38,39 In the initial stage of autophagy, a small vesicular sac called an isolation membrane elongates and subsequently encloses a portion of the cytoplasm and then forms a double-membraned structure called an autophagosome.…”

“…49 However, once the autophagy threshold is exceeded, which means that the protection from autophagy has reached its limit, cell death is inevitable if harmful factors persist. 37 In MC3T3-E1 osteoblasts, basal autophagy occurs at a low level to ensure physiological homeostasis. When treated with Ta-NPs at a relatively low concentration of 10 μg/mL, the MC3T3-E1 osteoblasts could remain in a compensatory stage, with a 20% increase in cell viability, while autophagy remained below the threshold.…”

Advanced Glycation End Products, Diabetes, and Bone Strength

“…Hyperglycemia and AGEs suppress osteoblastic differentiation and mineralization, accompanied by enhanced RAGE expression [61–63]. A reactive oxygen species (ROS) inhibitor and autophagy inducer prevent AGE-induced osteoblast apoptosis, indicating that the elevation of oxidative stress and inhibition of autophagy are involved in this event [64]. Recently, a rat model with an autograft implant containing AGEs showed that the mineral apposition rate (MAR), mineralized surface per bone surface (MS/BS), and bone formation rate (BFR) were significantly reduced, suggesting that the AGEs that accumulated in the matrix are also involved in the reduced bone formation in vivo [65].…”

Overactivated autophagy contributes to steroid-induced avascular necrosis of the femoral head

“…For examples, Liu et al observed that the natural flavonoid isoliquiritigenin decreased microtubule-associated protein 1 light chain 3 (LC3) and Beclin 1 accumulation, suppressed autophagy and exerted anti-osteoclastogenic effects (10). Yang et al also identified that autophagy protected osteoblasts from apoptosis induced by advanced glycation end products through the intracellular reactive oxygen species pathway (11). However, the degree of autophagy activity in SANFH remains unclear.…”