Bradykinin regulates osteoblast differentiation by Akt/ERK/NFκB signaling axis.

Bradykinin (BK), a well known mediator of pain and inflammation, is also known to be involved in the process of bone resorption. The present study therefore evaluated the role of BK in osteoblast lineage commitment. Our data showed that BK inhibits the migration of bone marrow mesenchymal stem cells, but does not affect their viability. Moreover, BK also inhibits osteoblastic differentiation by significantly downregulating the levels of mRNAs for osteopontin, runX2, col24, osterix, osteocalcin genes and bone mineralization (P < 0.05). Further, BK was found to elicit the BK receptors (BDKR1 and BDKR2) mediated activation of ERK1/2 and Akt pathways, which finally led to the activation of NFκB. BK also promoted the osteoclast differentiation of bone marrow derived preosteoclast cells by upregulating the expression of c-fos, NFATC1, TRAP, clcn7, cathK, and OSCAR genes and increasing TRAP activity through NFκB pathway. In conclusion, our data suggest that BK decreases the differentiation of osteoblasts with concomitant increase in osteoclast formation and thus provides new insight into the mechanism of action of BK in modulating bone resorption.