Homeobox B9 facilitates hypertrophic scar formation via activating the mitogen-activated protein kinase signaling pathway

The functions and underlying mechanisms of homeobox B9 (HOXB9) in scar formation remain unclear; therefore, the present study aimed to investigate whether HOXB9 is highly expressed in hypertrophic scar formation. Immunohistochemistry was performed to examine the expression levels of laminin, fibronectin (FN), collagen type I (Col1) and HOXB9 in hypertrophic scar and healthy skin tissues, and in lentivirus-constructed HOXB9-overexpressed or -silenced fibroblasts (FBs). Reverse transcription-quantitative polymerase chain reaction and western blotting were performed to evaluate the mRNA and protein expression levels of HOXB9, laminin, FN, Col1, extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), p38, p-c-Jun N-terminal kinase (JNK), p-ERK and p-p38. A gel contraction assay was used to evaluate the effect of HOXB9 on FB contraction. Co-immunoprecipitation assays were performed to verify the reciprocal interactions between HOXB9 and ERK, JNK and p38. It was demonstrated that HOXB9, laminin, FN and Col1 were upregulated in hypertrophic scar tissues, and HOXB9 upregulated laminin, FN, Col1, p-ERK, p-JNK and p38, potentially by interacting directly with p38. Furthermore, FBs overexpressing HOXB9 exhibited enhanced contractile capacity. In conclusion, the present study demonstrated that HOXB9 may facilitate hypertrophic scar formation via activating the mitogen-activated protein kinase signaling pathway.