Protein kinase D (PKD) has been linked to inflammatory responses in various pathologic conditions; however, its role in
inflammation-induced dermal
fibrosis has not been evaluated. In this study, we aimed to investigate the roles and mechanisms of
protein kinase D2 (PKD2) in
inflammation-induced dermal
fibrosis and evaluate the therapeutic potential of PKD inhibitors in this disease. Using homozygous
kinase-dead PKD2 knock-in (KI) mice, we examined whether genetic ablation or pharmacologic inhibition of PKD2 activity affected dermal
inflammation and
fibrosis in a
bleomycin (BLM)-induced skin
fibrosis model. Our data showed that dermal thickness and
collagen fibers were significantly reduced in BLM-treated PKD2 KI mice compared with that in wild-type mice, and so was the expression of α-smooth muscle actin and
collagens and the
mRNA levels of transforming growth factor-β1 and
interleukin-6 in the KI mice. Corroboratively, pharmacologic inhibition of PKD by
CRT0066101 also significantly blocked BLM-induced dermal
fibrosis and reduced α-smooth muscle actin,
collagen, and
interleukin-6 expression. Further analyses indicated that loss of PKD2 activity significantly blocked BLM-induced infiltration of monocytes/macrophages and neutrophils in the dermis. Moreover, using bone marrow-derived macrophages, we demonstrated that PKD activity was required for
cytokine production and migration of macrophages. We have further identified Akt as a major downstream target of PKD2 in the early inflammatory phase of the fibrotic process. Taken together, our findings indicate that PKD2 promotes dermal
fibrosis via regulating immune cell infiltration,
cytokine production, and downstream activation of Akt in lesional skin, and targeted inhibition of PKD2 may benefit the treatment of this condition.