Ubiquitin‐specific protease 11‐mediated CD36 deubiquitination acts on C1q/TNF‐related protein 9 against atherosclerosis

AIMS: Atherosclerosis is a huge threaten to the human health, C1q/TNF‐related protein 9 (CTRP9) has been previously reported possessing vascular protective functions. Our study is aimed to reveal the mechanism of the regulative effects of CTRP9 on the foam cell formation. METHODS AND RESULTS: Primary human macrophages were isolated from human monocytes donated by healthy volunteers. CCK‐8 assay was performed for determining the cell viability. Oil Red O staining was employed for measuring the lipid accumulation. Cholesterol ester and cholesterol concentration were detected by commercial kits for evaluating the intracellular cholesterol. Ubiquitination assay was performed to reveal the ubiquitination level of CD36, cycloheximide assay was applied for determining the half‐life of CD36 protein. Quantitative real‐time PCR and western blot assays were performed for detecting the mRNA and protein expression. Pre‐treatment with CTRP9 in primary human macrophages markedly suppressed the cholesterol accumulation concentration after oxidized low‐density lipoprotein treatment. CD36 was significantly increased after oxidized low‐density lipoprotein exposure while was reduced by CTRP9 treatment. Up‐regulation of CD36 significantly reversed the CTRP9‐mediated protective effects in foam cells. The differential expression levels of several deubiquitinating enzymes preliminarily indicated that USP11 was obviously decreased after CTRP9 treatment. USP11 knockdown decreased the CD36 protein expression and pre‐treatment with 10 μg/mL MG132 significantly maintained the CD36 level from USP11 knock down. Up‐regulation of CD36 reversed the alterations on the cholesterol metabolism caused by CTRP9 or USP11 knockdown. CONCLUSIONS: CTRP9 regulates the USP11/CD36 axis to protect the macrophages form transforming into foam cells by suppressing intracellular lipid and cholesterol accumulation, which is a potential therapeutic agent for atherosclerosis.