Novel insights into the mechanistic gene regulation of STAT3 in bone cells
Many cells are involved in the orchestra that is bone homeostasis--particularly osteoclasts and osteoblasts, which mediate remodeling of bones. This creates a balance that must be kept in check, otherwise pathologies arise. The JAK-STAT signaling pathway is crucial to maintaining this balance. It has long been known that the transcription factor STAT3 has more profound effects on bone homeostasis than other members of the STAT family of proteins. Recently, a genetic condition called Job’s Syndrome has been specifically linked to point mutations in the Stat3 gene. These patients present with severe bone abnormalities, including prominent foreheads, broad nasal bridges, and abnormal eye spacing. For this reason, our lab has extensively studied conditional knockouts of Stat3 in all three types of bones cells in mice and observed severe deficiencies in numerous parameters of normal bone phenotypes. STAT3 seems to play a principal role in the signaling that takes place upon mechanical loading of bone tissues and calling cells into action where they are needed. Furthermore, STAT3 has been found to be up-regulated in the early-response gene cluster following mechanical loading. Our current approach to studying STAT3’s effects on bone includes both in vivo and in vitro comparisons of WT and KO STAT3 models. The conditional knockout of STAT3 in 8-week old mice revealed significant phenotypic variations as compared to the WT controls, while no significant differences were observed in cKO newborn pups. We also looked at immortalized WT and STAT3 KO cell lines. The STAT3 KO cells had diminished proliferation rates and decreased differentiation capabilities. Furthermore, STAT3 KO cells showed significantly reduced mRNA levels of both Wnt3a and Wnt5a when exposed to fluid shear stress. By employing available ChIP-seq data, we were able to elucidate the genome-wide binding patterns of STAT3. From the peak distribution, we can begin to uncover novel downstream effectors of STAT3 signaling that are responsible for the observed phenotypes in our conditional knockout mouse model. A preliminary look at the ChIP-seq data reveals Wnt and Nrf2 signaling to be under the putative control of STAT3. In our further research, we endeavor to experimentally confirm the ChIP-seq data for STAT3 with RNA-seq experiments in the hopes of finding potential therapeutic targets for bone pathologies.
Li, Purdue University.
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