Substance P induces inflammatory responses involving NF-κB in genetically diabetic mice skin fibroblasts co-cultured with macrophages

Delayed wound healing is an intractable complex of diabetes and substance P (SP) is proved to benefit wound healing, whose functioning mechanism remains elusive. This study aims at revealing whether the influence of SP on diabetic wound healing is dependent on inflammatory responses, particularly NF-κB.

Skin fibroblasts of genetically diabetic mice were co-cultured with bone marrow-derived macrophages, and treated with SP, SP + L703,606 (a neurokinin-1 receptor antagonist), or SP + MG132 (an inhibitor of NF-κB). For macrophages, their migration ability was assessed by Transwell experiments, and their M2 polarization was analyzed by flow cytometry and markers for M2 phenotype. Pro-inflammatory factors in the supernatant were detected by enzyme-linked immunosorbent assay. In fibroblasts, the transcription levels of the four pro-inflammatory factors and the protein levels of NF-κB regulators like inhibitor of NF-κB alpha (IκBα) and IκB kinases (IKKs) were monitored by real-time quantitative PCR and western blot, respectively.

SP could significantly induce migration to fibroblasts (P<0.01), M2 polarization (P<0.001) and pro-inflammatory factor concentration (P<0.01) in the co-culture system. It also promotes the transcription process of pro-inflammatory factors in fibroblasts (P<0.01), and induce activation of IKKα/β and phosphorylation of IκBα, which caused NF-κB activation. All these effects were reversed if NF-κB was inhibited.

The promoting effects of SP on diabetic wound healing was dependent on enhanced inflammatory responses, especially the activation of NF-κB. This study provided evidence for the potential usage of SP in accelerating diabetic wound healing.