Hu'po Anshen decoction promotes fracture healing in mice with traumatic brain injury through BMP2‐COX2‐ATF4 signaling pathway

Hu'po Anshen decoction (HPASD), a traditional Chinese medicine used to treat concussion and fracture, could regulate the expression of bone morphogenetic protein 2 (BMP2). However, whether HPASD affects the fracture healing of traumatic brain injury (TBI) combined with a fracture through BMP2 and its downstream signals remains obscure. The chondrocyte‐specific BMP2 conditional knockout mice and chondrocyte‐specific cyclooxygenase‐2 (COX2) overexpression mice were generated. BMP2 conditional knockout mice were treated with fracture surgery, fracture combined with TBI, or fracture combined with TBI followed by different doses of HPASD (2.4, 4.8, and 9.6 g/kg), respectively. TBI was induced by Feeney's weight‐drop technique. The fracture callus formation and fracture sites were determined by X‐ray, micro‐CT, and histological analyses. The expressions of chondrocyte‐, osteoblast‐, and BMP2/COX2 signal‐related targets were determined by quantitative reverse transcription‐polymerase chain reaction (qRT‐PCR) and western blot assays. The specific absence of BMP2 in chondrocytes led to the prolonged formation of cartilage callus, a delay in the osteogenesis initiation and the downregulation of RUNX2, Smad1/5/9, EP4, ERK1/2, RSK2, ATF4. Overexpression of COX2 partially reverses the effects of chondrocyte‐specific BMP2 knockout mice. HPASD promoted cartilage callus formation and osteogenesis initiation, as accompanied by upregulated expression levels of RUNX2, Smad1/5/9, EP4, ERK1/2, RSK2, and ATF4 in a time‐dependent and concentration‐dependent manner in chondrocyte‐specific BMP2 knockout mice. Overall, our findings demonstrated that HPASD induced COX2 transcription through the BMP2‐Smad1/5/9‐RUNX2 axis, and then affected fracture healing through the COX2‐mediated EP4‐ERK1/2‐RSK2‐ATF4 axis. Schematics to illustrate growth effects, fracture, or fracture combination with traumatic brain injury models of chondrocyte‐specific BMP2 conditional knockout mice with Hu'po Anshen decoction (HPASD) treatment and pCOL2A1 promoter drives COX2 overexpression transgenic mice that are reported in this study. Taken together, this present study provided ample evidence that BMP2, Cox2, and HPASD have the promise to become therapeutic strategies in treating a fracture in combination with traumatic brain injury.