Osteoporosis regulation by salubrinal through eIF2α mediated differentiation of osteoclast and osteoblast

Abstract

Nuclear factor-κB (NF-κB) ligand (RANKL) was shown to induce osteoclast differentiation by increasing the expression of c-Fos, NFATc1 and TRAP. Salubrinal treatment to bone marrow macrophage (BMM) cells, however, significantly blocked NFATc1 expression and osteoclast differentiation by RANKL. Overexpression of NFATc1 further confirmed that NFATc1 is a key factor affected by salubrinal in osteoclast differentiation by RANKL. Unexpectedly, NFATc1 and c-Fos mRNA expressions were not affected by salubrinal, implicating that NFATc1 expression is regulated at a translational stage. In support of this, salubrinal increased the phosphorylation of a translation factor eIF2α, decreasing the global protein synthesis including NFATc1. In contrast, a phosphorylation mutant plasmid pLenti-eIF2α-S51A restored RANKL-induced NFATc1 expression and osteoclast differentiation even in the presence of salubrinal. Furthermore, knockdown of ATF4 significantly reduced salubrinal-induced osteoblast differentiation as evidenced by decreased calcium accumulation and lowered expressions of the osteoblast differentiation markers, alkaline phosphatase and RANKL in MC3T3-E1 osteoblast cells. Salubrinal treatment to co-cultured BMM and MC3T3-E1 cells also showed reduction of osteoclast differentiation. Finally, salubrinal efficiently blocked osteoporosis in mice model treated with RANKL as evidenced by elevated bone mineral density (BMD) and other osteoporosis factors. Collectively, our data indicate that salubrinal could affect the differentiation of both osteoblast and osteoclast, and be developed as an excellent anti-osteoporosis drug. In addition, modulation of ATF4 and NFATc1 expressions through eIF2α phosphorylation could be a valuable target for the treatment of osteoporosis.

17β-Estradiol inhibits ER stress-induced apoptosis through promotion of TFII-I-dependent Grp78 induction in osteoblasts

“…ER stress-induced apoptosis acts as a causative agent of osteoporosis. [22][23][24][25][26] Our observations indicated that 17b-E 2 may contribute to protective effects on ER stress-induced apoptosis in osteoblasts. Osteoporosis is a highly prevalent disease and results in massive costs both to the individual and to the society through associated fragility fractures.…”

“…[17][18][19][20][21] ER stressinduced apoptosis of osteoblasts has also been implicated in the pathogenesis of osteoporosis. [22][23][24][25][26] Our study found that the MC3T3-E1 cells, the mouse calvaria osteoblasts, were led into the decrease of cellular viability in response to ER stress. However, pretreatment with 17b-E 2 can increase the viability of osteoblasts in ER stress in a dose-dependent manner between 0.1 nM and 100 nM and the effects plateaued at 10 nM.…”

“…[1][2][3][4][5] ER stress has been implicated as a crucial mechanism of apoptosis in various cell death processes, including osteoblast apoptosis during the development of osteoporosis. [22][23][24][25][26] Protective effects of estrogen on apoptosis of various cells have been indicated. [32][33][34] However, it is not entirely clear if estrogen can protect osteoblasts against ER stress-induced apoptosis.…”

“…ER stress has been reported to be involved in apoptosis induction that occurs during various pathophysiological progresses, including osteoporosis. [22][23][24][25][26] The ER stress is generally activated in response to various stressful conditions, such as hypoxia, the accumulation of unfolded or misfolded proteins, the alterations of calcium homeostasis, low glucose levels and others. [8][9][10] Recent reports have shown that ER stress occurs during osteogenic differentiation.…”

“…22 ER stress-associated osteoblast apoptosis is one of the most predominant pathogenesis of osteoporosis. [23][24][25][26] Thus, an intriguing question in osteoblasts is an outcome of survival in ER stress. The balance between cell death responses and cell survival responses may decide the occurrence and development of osteoporosis.…”