BACKGROUND:Mouse osteogenic potential is regulated by the JAK-STAT signaling pathway,and interleukin-9 can regulate multiple cellular functions through the JAK-STAT pathway,which has the potential to be a novel cytokine that regulates osteogenic potential. OBJECTIVE:To investigate the effect of interleukin-9 deficiency on osteogenic potential in mice METHODS:The femurs collected from 2-month-old wild-type and interleukin-9 knockout mice were subjected to Micro-CT scanning to analyze the changes in bone mass.Then,hematoxylin-eosin staining,Masson staining,and immunohistochemical staining of type Ⅰ collagen were performed on the slices of the femurs of mice.Bone marrow cells from 2-month-old wild-type and interleukin-9 knockout mice were extracted for colony-forming assay and detection of osteogenic gene expression in bone marrow mesenchymal stem cells.To further verify whether interleukin-9 worked through the JAK-STAT pathway,the expression of STAT3 protein was detected by western blot. RESULTS AND CONCLUSION:Micro-CT results showed the bone mass of interleukin-9 knockout mice decreased significantly compared with that of wild-type mice.In addition,the bone mineral density,bone volume fraction,trabecular number significantly decreased and trabecular separation markedly escalated in interleukin-9 knockout mice.The findings of hematoxylin-eosin staining were consistent with Micro-CT results.Interleukin-9 knockout mice had lower bone trabecular density.Type I collagen immunohistochemistry staining and Masson staining indicated the number of type Ⅰ collagen positive osteoblasts was significantly reduced and the capacity of collagen formation was damaged in interleukin-9 knockout mice.The results of colony-forming assay indicated that the mineralization capacity of osteoblast in interleukin-9 knockout mice were significantly lower than that in wild-type mice.Western blot results showed that osteogenesis induction activated STAT3 signaling,and the pSTAT3 level in wild-type mice with osteogenic induction was significantly higher than that in interleukin-9 knockout mice with osteogenic induction.These findings suggest that interleukin-9 regulates osteogenesis through the JAK-STAT3 pathway and interleukin-9 deficiency inhibits osteoblast differentiation and function,which may lead to reduced bone mass in interleukin-9 knockout mice.