Potentiation of Psoriasis-Like Inflammation by PCSK9

Abstract

Psoriasis is a systemic inflammatory disease, associated with metabolic disorders, including high level of low-density lipoprotein. PCSK9, which promotes the degradation of low-density lipoprotein receptors and, therefore, the increased concentration of circulating low-density lipoprotein, is also involved in inflammation. This study aims to examine the role of PCSK9 in psoriasis and to investigate the potential of topically applying small interfering RNA targeting Pcsk9 as a psoriasis treatment. We investigated the expression of PCSK9 in lesions of psoriasis patients and imiquimod-induced psoriatic reactions in Pcsk9-knockout and Pcsk9 small interfering RNA-treated mice, and we also used cultured human keratinocytes to investigate the role of PCSK9 in regulating cell proliferation and apoptosis. We found that PCSK9 is overexpressed in psoriatic lesions and that suppressing Pcsk9 can decrease the inflammatory reaction induced by imiquimod treatment and inhibit hyperproliferation of keratinocytes. We also found that suppressing PCSK9 can significantly alter the cell cycle and induce apoptosis of human keratinocytes. Taken together, our findings indicate that PCSK9 plays an important role in psoriasis and may be a therapeutic target.

Figure 1.. Overexpression of PCSK9 in lesions of psoriasis patients.

(a, b) Quantification of PCSK9 mRNA and protein in PP and NN. *P < 0.05, t test. (c) Western blot image. (d) Immunohistochemistry image of PP. Scale bar = 100 μm. (e) Immunohistochemistry image of NN. Scale bar = 100 μm. NN, normal healthy skin; PP, psoriatic plaque.

Figure 2.. IMQ induces the expression of Pcsk9 in mouse skin.

(a) Quantification of Pcsk9 mRNA expression in the IMQ-treated skin and the controls. *P < 0.05, t test. (b) Immunohistochemistry staining of normal skin and IMQ-treated skin by Pcsk9 antibody. Scale bars = 100 μm. IMQ, imiquimod.

Figure 3.. The depletion of Pcsk9 suppresses IMQ-induced psoriasis-like reactions in vivo.

(a) Scores of erythema, scaling, thickness, and cumulative scores of WT mice and Pcsk9^−/− mice during IMQ treatment. *P < 0.05, t test. (b) Representative photos of dorsal skin in WT and Pcsk9^−/− mice with IMQ and vehicle treatments. (c) Hematoxylin and eosin staining of dorsal skin in WT and Pcsk9^−/− mice with and without IMQ treatment. Scale bars = 100 μm. (d) Thickness of epidermis of normal skin and IMQ-induced skin in WT and Pcsk9^−/− mice. *P < 0.05 comparing IMQ-treated skin between WT and Pcsk9^−/− mice, **P < 0.05 comparing control skin and IMQ-treated skin in WT and Pcsk9^−/− mice. Con, control; IMQ, imiquimod; KO, knockout; WT, wild type.

Figure 4.. The depletion of Pcsk9 suppresses keratinocyte proliferation and inflammation induced by IMQ.

Immunohistochemistry staining of normal and IMQ-treated skin by Ki67, NF-κB (p65), and phosphorylated NF-κB (p-p65) antibodies. Scale bars = 100 μm. IMQ, imiquimod; WT, wild type.

Figure 5.. Topical application of siRNA suppresses Pcsk9 and reduces IMQ-induced psoriasis-like reactions.

(a, b) Quantification of Pcsk9 mRNA and protein expression in the si-Pcsk9 transfected skin (48 hours after the treatment) and the controls. *P < 0.05, t test. (c) Western blot image. (d) Representative photos of dorsal skin in si-Con and si-Pcsk9 mice after 5 days of IMQ treatment. (e) Scores of erythema, scaling, thickness, and total scores of si-Con and si-Pcsk9 mice during IMQ treatment. *P < 0.05, t test. Con, control; IMQ, imiquimod; siRNA, small interfering.

Figure 6.. The suppression of PCSK9 inhibits proliferation and induces apoptosis of human keratinocytes in vitro.

(a) Quantification of PCSK9 mRNA expression in cultured human keratinocytes transfected by si-Con and si-PCSK9. (b) MTT assay shows the viability of si-Con and si-PCSK9 transfected keratinocytes. (c–e) Percentages of G0/G1, S, and G2/M phase of keratinocytes transfected by si-Con and si-PCSK9 (24, 48, and 72 hours). (f) Percentage of apoptotic cells in keratinocytes transfected by si-Con and si-PCSK9 (24, 48, and 72 hours). (g) Percentage of apoptotic cells in si-Con– and si-PCSK9– transfected keratinocytes after exposure to narrow band–UVB in a concentration range from 0 to 150 mJ/cm². *P < 0.05, t test. Con, control; h, hour; MTT, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; si, small interfering.