Evaluation of the effects of immunization against PCSK9 on selected microRNAs involved in cholesterol homeostasis

Abstract Background MicroRNAs (miRNAs) have been discovered as novel modulators of gene expression. These molecules are involved in regulating lipid metabolism through a complicated interactive mechanism involving gene regulatory networks and can play a role in metabolic diseases. PCSK9 (proprotein convertase subtilisin/Kexin 9) is a critical regulator in cholesterol homeostasis. PCSK9 inhibition is an effective therapeutic strategy for the treatment of dyslipidemia. Accordingly, it is essential to identify the controlling mechanisms of the PCSK9 and the effects of its inhibitors on microRNAs involved in cholesterol homeostasis. Purpose Considering the role that miR-27a, miR-30c, and miR-191 play in regulating genes involved in cholesterol homeostasis, we investigated the effect of immunization against PCSK9 on the mentioned miRNAs. Methods A PCSK9 immunogenic peptide constructed by linking a short PCSK9 mimotope peptide to a tetanus peptide was used for immunization. The PCSK9 immunogenic peptide construct was mixed homogeneously with 0.4% alum adjuvant at a ratio of 1:1 for use as vaccine formulation. Mice in the vaccinated group were inoculated subcutaneously in four terms with bi-weekly intervals. In order to assess the expression of miRNAs in vaccinated mice' livers, sampling was carried out two weeks after the last injection. The levels of miR-27a, miR-30c, and miR-191 expression in the liver of vaccinated mice were evaluated using real-time quantitative PCR, and relative expression levels were presented as fold change normalized to U6 as the internal control. Results Hepatic miR-27a expression was significantly decreased in vaccinated mice compared with the control mice (fold change: 0.731±0.1, p=0.027). There was a borderline nonsignificant reduction in the hepatic expression of miR-30c in the vaccine group compared to the control group (fold change: 0.569±0.1, p=0.078). No significant difference was detected in the hepatic expression of miR-191 between the vaccine and control groups (fold change: 0.852±0.1, p=0.343). Conclusions Immunization against PCSK9 leads to decreased hepatic expression of miR-27a. Since miR-27a is involved in the regulation of targets like angiopoietin-like 3 and glycerol-3-phosphate acyltransferase 1, its reduction may explain part of the lipid-lowering activity of PCSK9 vaccine. Funding Acknowledgement Type of funding sources: None.