Substance P Increases STAT6-Mediated Transcription Activation of Lymphocyte Cytosolic Protein 2 to Sustain M2 Macrophage Predominance in Pediatric Asthma

Substance P (SP) is a neuropeptide released by neurons and participates in various biological processes, including inflammation. M2 macrophages are major immune cells associated with type 2 inflammation in asthma. This study investigates the effect of SP on macrophage phenotype in pediatric asthma and the underpinning factors. Asthmatic children exhibited an increased level of SP, along with a higher proportion of M2 macrophages in their bronchoalveolar lavage fluid. Flow cytometry revealed that SP treatment enhanced the M2 polarization of 12-O-tetradecanoylphorbol 13-acetate-treated THP-1 cells (macrophages) in vitro. By contrast, the administration of a neutralizing antibody of SP reduced the M2 macrophage population, mitigated inflammatory cell infiltration in mouse lung tissues, and decreased the population of immune cells in the mouse bronchoalveolar lavage fluid. SP up-regulated the expression of STAT6, which, in turn, activated the transcription of lymphocyte cytosolic protein 2 (LCP2). The population of macrophages and allergic inflammatory responses in mice were reduced by STAT6 inhibition but restored by LCP2 overexpression. Collectively, the present study demonstrates that SP sustains M2 macrophage predominance and allergic inflammation in pediatric asthma by enhancing STAT6-dependent transcription activation of LCP2.