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Dynamin-related protein 1 inhibition reduces hepatic PCSK9 secretion.

AIMS
Proteostasis maintains protein homeostasis and participates in regulating critical cardiometabolic disease risk factors, including proprotein convertase subtilisin/kexin type 9 (PCSK9). Endoplasmic reticulum (ER) remodeling through release and incorporation of trafficking vesicles mediates protein secretion and degradation. We hypothesized that ER remodeling that drives mitochondrial fission participates in cardiometabolic proteostasis.


METHODS AND RESULTS
We used in vitro and in vivo hepatocyte inhibition of a protein involved in mitochondrial fission, dynamin-related protein 1 (DRP1). Here, we show that DRP1 promotes remodeling of select ER microdomains by tethering vesicles at ER. A DRP1 inhibitor, mitochondrial division inhibitor 1 (mdivi-1) reduced ER localization of a DRP1 receptor, mitochondrial fission factor, suppressing ER remodeling-driven mitochondrial fission, autophagy, and increased mitochondrial calcium buffering and PCSK9 proteasomal degradation. DRP1 inhibition by CRISPR/Cas9 deletion or mdivi-1 alone or in combination with statin incubation in human hepatocytes and hepatocyte-specific Drp1-deficiency in mice reduced PCSK9 secretion (-78.5%). In HepG2 cells, mdivi-1 increased low-density lipoprotein receptor via c-Jun transcription and reduced PCSK9 mRNA levels via suppressed sterol regulatory binding protein-1c. Additionally, mdivi-1 reduced macrophage burden, oxidative stress, and advanced calcified atherosclerotic plaque in aortic roots of diabetic Apoe-deficient mice and inflammatory cytokine production in human macrophages.


CONCLUSIONS
We propose a novel tethering function of DRP1 beyond its established fission function, with DRP1-mediated ER remodeling likely contributing to ER constriction of mitochondria that drives mitochondrial fission. We report DRP1-driven remodeling of select ER microdomains may critically regulate hepatic proteostasis and identify mdivi-1 as a novel small molecule PCSK9 inhibitor.


TRANSLATIONAL PERSPECTIVE
PCSK9 is a critical protein participating in degradation of low-density lipoprotein receptor, a receptor involved in clearance of circulating low-density lipoprotein. Anti-PCSK9 therapies approved for clinical use are currently limited to antibody therapies. PCSK9 siRNA therapy is also showing promise in clinical trials, but small molecule PCSK9 inhibitors have proven difficult to develop. This study identifies a small molecule inhibitor of a mitochondrial fission protein, DRP1 in human hepatocytes and hepatocyte DRP1-deficiency in mice reduces PCSK9 secretion, providing initial proof-of-concept for novel small molecule PCSK9 inhibition.