1 Diet-induced hepatic steatosis abrogates cell-surface LDLR by inducing de novo PCSK9 expression in mice Paul F. Lebeau 1* , Jae Hyun Byun 1* , Khrystyna Platko 1 , Melissa E. MacDonald 1 , Samantha V. Poon 1 , Mahi Faiyaz 1 , Nabil G. Seidah 2 and Richard C. Austin 1† From the 1 Department of Medicine, McMaster University, St. Joseph’s Healthcare Hamilton, Hamilton, Ontario, L8N 4A6, Canada, and the 2 Laboratory of Biochemical Neuroendocrinology, Montreal Clinical Research Institute, affiliated to the University of Montreal, Montreal, Quebec H2W 1R7, Canada. Running title: NAFLD affects the PCSK9-LDLR axis Footnotes: *Both authors contributed to this work equally; † To whom correspondence should be addressed: 50 Charlton Ave. East, Room T-3313, Hamilton, Ontario L8N 4A6, Canada. Tel.: 905-522- 1155 (ext. 35175); Fax: 905-540-6589; E-mail: austinr@taari.ca. Key words: Cardiometabolic disease, CVD, ER stress, HFD, LDL, Liver, NAFLD, SREBP2 ABSTRACT The worldwide prevalence of non- alcoholic fatty liver disease (NAFLD) is increasing rapidly. Although this condition is generally benign, accumulating evidence now suggests that patients with NAFLD are also at increased risk of cardiovascular disease (CVD); the leading cause of death in developed nations. Despite the well-established role of the liver as a central regulator of circulating low-density lipoprotein (LDL) cholesterol levels, a known driver of CVD, the mechanism(s) by which hepatic steatosis contributes to CVD remains elusive. Interestingly, a recent study has shown that circulating proprotein convertase subtilisin/kexin type 9 (PCSK9) levels correlate positively with liver steatosis grade. Given that PCSK9 degrades the LDL receptor (LDLR) and prevents the removal of LDL from the blood into the liver, in the present study we examined the effect of hepatic steatosis on LDLR expression and circulating LDL cholesterol levels. We now report that in a manner consistent with findings in human patients, diet- induced steatosis increases circulating PCSK9 levels as a result of de novo expression in mice. We also report the novel finding that steatosis abrogates hepatic LDLR expression and increases circulating LDL levels in a PCSK9- dependent manner. These findings provide important mechanistic insights as to how hepatic steatosis modulates lipid regulatory genes like PCSK9 and the LDLR, and also highlights a novel mechanism by which liver disease may contribute to CVD. INTRODUCTION Liver fat accumulation due to reasons other than excessive alcohol consumption, or more often referred to as NAFLD, currently has an estimated occurrence of 30-46% in developed nations (1). Given the current trends in global consumption of unhealthy dietary fats and sugars, it is no surprise that NAFLD is increasing in prevalence as these factors play a central role in its development (2). Although NAFLD is characterized by liver fat accumulation with no sign of liver injury, this initial stage often progresses to non-alcoholic steatohepatitis (NASH); a state characterized histologically by necroinflammation and hepatocyte damage (3). NAFLD and its complications are estimated to be the primary cause of liver-related mortality and liver transplantation within the next 20 years (4). Evidence that patients with NAFLD are at higher risk of developing CVD, which is among the leading causes of death worldwide (5), is now accumulating (6-9). Given that both http://www.jbc.org/cgi/doi/10.1074/jbc.RA119.008094 The latest version is at JBC Papers in Press. Published on April 19, 2019 as Manuscript RA119.008094 by guest on March 24, 2020 http://www.jbc.org/ Downloaded from