Role of Protein Kinase C and Phosphoinositide 3‐Kinase‐Akt in Substance P‐Induced Proinflammatory Pathways in Mouse Macrophages

Abstract

Neuropeptide modulation of immune cell function is an important mechanism of neuro‐immune inter‐system cross‐talk. Substance P (SP) is one such key neuropeptide involved. In this study, we investigated the yet unexplored cellular mechanisms of SP‐mediated inflammatory responses in macrophages using a mouse macrophage‐like cell line RAW 264.7 and isolated peritoneal macrophages. We found that the conventional PKCα and novel PKCδ and εwere selectively activated by SP via its primary neurokinin‐1 receptor (NK‐1R) on the cells. Activation of these PKC isoforms mediated the activation of downstream extracellular signal‐regulated kinase‐1/2 (ERK1/2) and the transcription factor NF‐kappaB (NF‐κB) which drove the transcription of inducible chemokines in macrophages. Additionally, phosphoinositide 3‐kinase (PI3K)‐Akt was also activated by SP/NK‐1R in macrophages. Inhibition of PI3K‐Akt pathway attenuated ERK1/2 and NF‐κB activation suggesting it also played a part in SP‐induced cellular inflammatory response. Kinetic analysis indicated that PKC isoforms induced early ERK1/2 activation while PI3K‐Akt contributed to the pathway at later time points. It was further demonstrated that PKC and PI3K‐Akt were activated independent of each other. Collectively, our results suggest that SP/NK‐1R activates two convergent proinflammatory signaling pathways, PKCs and PI3K‐Akt, resulting in ERK1/2, NF‐κB activation and chemokine production in mouse macrophages.