The loss of STAT3 in mature osteoclasts has detrimental effects on bone structure

Abstract

Signal Transducer and Activator of Transcription 3 (STAT3) has recently been shown to be involved in bone development and has been implicated in bone diseases, such as Job's Syndrome. Bone growth and changes have been known for many years to differ between sexes with male bones tending to have higher bone mass than female bones and older females tending to lose bone mass at faster rates than older males. Previous studies using conditional knock mice with Stat3 specifically deleted from the osteoblasts showed both sexes exhibited decreased bone mineral density (BMD) and strength. Using the Cre-Lox system with Cathepsin K promotor driving Cre to target the deletion of the Stat3 gene in mature osteoclasts (STAT3-cKO mice), we observed that 8-week old STAT3-cKO female femurs exhibited significantly lower BMD and bone mineral content (BMC) compared to littermate control (CN) females. There were no differences in BMD and BMC observed between male knockout and male CN femurs. However, micro-computed tomography (μCT) analysis showed that both male and female STAT3-cKO mice had significant decreases in bone volume/tissue volume (BV/TV). Bone histomorphometry analysis of the distal femur, further revealed a decrease in bone formation rate and mineralizing surface/ bone surface (MS/BS) with a significant decrease in osteoclast surface in female, but not male, STAT3-cKO mice. Profiling gene expression in an osteoclastic cell line with a knockdown of STAT3 showed an upregulation of a number of genes that are directly regulated by estrogen receptors. These data collectively suggest that regulation of STAT3 differs in male and female osteoclasts and that inactivation of STAT3 in osteoclasts affects bone turnover more in females than males, demonstrating the complicated nature of STAT3 signaling pathways in osteoclastogenesis. Drugs targeting the STAT3 pathway may be used for treatment of diseases such as Job's Syndrome and osteoporosis.

JAK/STAT pathway and molecular mechanism in bone remodeling

“…Recently, several studies have shown that different factors are involved during the osteoclastogenesis process [ 46 ]. This process leads to maturation and differentiation of osteoclasts from the monocyte/macrophage lineage.…”

“…Moreover, in a very recent study conducted by Davidson et al, it is highlighted that the participation of STAT3, during the regulation of the osteoclastogenic process, occurs in a different way in female than male osteoclastic cells. So, these data suggest that the STAT3 signal may have a key role in bone turnover [ 46 , 84 , 85 ]. Initially, an inactivating STAT3 mutation was found, which leads to a disease called Job syndrome.…”

Brd2/4 and Myc regulate alternative cell lineage programmes during early osteoclast differentiation in vitro

“…While transcriptome analysis of developing OC has been previously reported at >24h post-RANKL exposure ( An et al., 2014 ; Bae et al., 2017 ; Davidson et al., 2020 ; Park-Min et al., 2014 ), the immediate transcriptional responses triggered by RANKL have not been explored yet. Therefore, to capture the first transcriptional waves during RANKL-driven OC lineage commitment, we performed RNA-seq of RAW264.7 cells at 0, 4, 14, and 24h upon RANKL, I-BET151, and RANKL + I-BET151 treatment ( Figure 1 A).…”

STAT3 activation by catalpol promotes osteogenesis-angiogenesis coupling, thus accelerating osteoporotic bone repair

“…This is normally the consequence of increased bone resorption and decreased bone formation. Besides, more evidence suggested that bone-selective STAT3 knockout mice indicated an osteoporotic phenotype [ 48 , 49 ]. With regard to its role in vessel formation, the association between STAT3 and neovascularization has been widely elucidated.…”