Inhibition of Canonical Transient Receptor Potential 5 Channels Polarizes Macrophages to an M1 Phenotype

Transient receptor potential (TRP) channels are widely expressed in the mammals. However, the functions of canonical TRP (TRPC) in inflammatory responses are largely unknown. The present study was focused on the effect of canonical TRP5 (TRPC5) channel on the polarization of macrophage to an M1 phenotype.Polarization of macrophages was studied in TRPC5 knockout (TRPC5-/-) mice and in Raw264.7, a mouse macrophage cell line. Indicators of M1 type polarized macrophage were measured in the aorta of mice. Inhibition of TRPC5 in macrophages was achieved by the administration of ML204 (a non-selective TRPC5 antagonist) or the silencing of the TRPC5 gene with short hairpin RNA. Lipopolysaccharide (LPS) was used to stimulate Raw264.7 cells to an M1 type polarization. Proinflammatory cytokines tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 were measured in mice or cells, and protein expressions of Akt, phosphorylated (p)-Akt, IκBα, p-IκBα, and NF-κB were analyzed in Raw264.7 cells.In TRPC5-/- mice the number of M1 type polarization of macrophages infiltrating into the aortic walls were significantly increased. The serum levels of inflammatory cytokines, TNF-α and IL-6 were also increased. Furthermore, after treated with ML204 or silenced the gene of TRPC5, the releases of TNF-α, IL-1β and IL-6 from lipopolysaccharide-stimulated RAW264.7 cells were significantly increased. Meanwhile, phosphorylations of Akt and IκBα were upregulated, and the shift of NF-κB from the cytoplasm to nucleus was markedly enhanced.The activation of TRPC5 may inhibit the polarization of macrophage to an M1 phenotype by regulating Akt/IκB/NF-κB signaling pathways.