Zuhier Awan1, Geneviève Dubuc2, May Faraj3, Robert Dufour2, Nabil G Seidah4, Jean Davignon2, Rémi Rabasa-Lhoret5, Alexis Baass6. 1. Laboratory of Biochemical Neuroendocrinology, Clinical Research Institute of Montreal (IRCM), QC, Canada. Electronic address: zuhier.awan@ircm.qc.ca. 2. Hyperlipidemia and Atherosclerosis Research Group, Clinical Research Institute of Montreal (IRCM), QC, Canada. 3. Platform for Research in Obesity, Metabolism and Diabetes (PROMD), Metabolic Unit Laboratory, Clinical Research Institute of Montreal (IRCM), QC, Canada; Department of Nutrition, Faculty of Medicine, University of Montreal, QC, Canada. 4. Laboratory of Biochemical Neuroendocrinology, Clinical Research Institute of Montreal (IRCM), QC, Canada. 5. Platform for Research in Obesity, Metabolism and Diabetes (PROMD), Metabolic Unit Laboratory, Clinical Research Institute of Montreal (IRCM), QC, Canada; Department of Nutrition, Faculty of Medicine, University of Montreal, QC, Canada; Montreal Diabetes Research Center (MDRC) and Endocrinology Division of Montreal University Hospital (CHUM), QC, Canada. 6. Hyperlipidemia and Atherosclerosis Research Group, Clinical Research Institute of Montreal (IRCM), QC, Canada; Platform for Research in Obesity, Metabolism and Diabetes (PROMD), Metabolic Unit Laboratory, Clinical Research Institute of Montreal (IRCM), QC, Canada; Department of Medicine, Faculty of Medicine, McGill University, QC, Canada.
Abstract
BACKGROUND: PCSK9 (proprotein convertase subtilisin/kexin type 9) promotes the degradation of the LDLR (LDL receptor) in hepatocytes, leading to an increase in plasma LDL-C (LDL cholesterol). Previous animal studies have shown that insulin stimulates PCSK9 transcription and observational human studies showed a positive correlation between plasma PCSK9 concentration and fasting insulinemia. OBJECTIVE: The purpose of this study was to investigate the effects of chronic and acute hyperinsulinemia on PCSK9 in a large cohort of human subjects as well as at a cellular level. METHODS: The in vivo effect of hyperinsulinemia on plasma PCSK9 concentration was studied using euglycemic-hyperinsulinemic clamps in 82 non-diabetic post-menopausal obese patients. We studied the in vitro effects of insulin stimulation on PCSK9 mRNA as well as on protein expression and secretion in HepG2 and Huh7 cells. RESULTS: Analysis of the pre and post-clamp data revealed a 15.4% (p<0.001) lowering of plasma PCSK9 concentration after acute insulin induction. In vitro studies post-insulin stimulation showed that mRNA levels of PCSK9 reduced by 25% in HepG2 cells (p<0.027) and by 59% in Huh7 cells (p<0.01). Intracellular concentration of PCSK9 were 10% lower in HepG2 cells (p<0.05) and 35% lower in Huh7 cells (p<0.05). CONCLUSIONS: Our results show an inhibitory effect of acute hyperinsulinemia on PCSK9 in humans both in vitro and in vivo. This data may assist in evaluating PCSK9 levels in individuals on insulin therapy.
BACKGROUND:PCSK9 (proprotein convertase subtilisin/kexin type 9) promotes the degradation of the LDLR (LDL receptor) in hepatocytes, leading to an increase in plasma LDL-C (LDL cholesterol). Previous animal studies have shown that insulin stimulates PCSK9 transcription and observational human studies showed a positive correlation between plasma PCSK9 concentration and fasting insulinemia. OBJECTIVE: The purpose of this study was to investigate the effects of chronic and acute hyperinsulinemia on PCSK9 in a large cohort of human subjects as well as at a cellular level. METHODS: The in vivo effect of hyperinsulinemia on plasma PCSK9 concentration was studied using euglycemic-hyperinsulinemic clamps in 82 non-diabetic post-menopausal obesepatients. We studied the in vitro effects of insulin stimulation on PCSK9 mRNA as well as on protein expression and secretion in HepG2 and Huh7 cells. RESULTS: Analysis of the pre and post-clamp data revealed a 15.4% (p<0.001) lowering of plasma PCSK9 concentration after acute insulin induction. In vitro studies post-insulin stimulation showed that mRNA levels of PCSK9 reduced by 25% in HepG2 cells (p<0.027) and by 59% in Huh7 cells (p<0.01). Intracellular concentration of PCSK9 were 10% lower in HepG2 cells (p<0.05) and 35% lower in Huh7 cells (p<0.05). CONCLUSIONS: Our results show an inhibitory effect of acute hyperinsulinemia on PCSK9 in humans both in vitro and in vivo. This data may assist in evaluating PCSK9 levels in individuals on insulin therapy.