Dataset Information

Hepatic Glucagon Signaling Regulates PCSK9 and Low-Density Lipoprotein Cholesterol.

ABSTRACT: RATIONALE:Glucagon is a key hormone that regulates the adaptive metabolic responses to fasting. In addition to maintaining glucose homeostasis, glucagon participates in the regulation of cholesterol metabolism; however, the molecular pathways underlying this effect are incompletely understood. OBJECTIVE:We sought to determine the role of hepatic Gcgr (glucagon receptor) signaling in plasma cholesterol regulation and identify its underlying molecular mechanisms. METHODS AND RESULTS:We show that Gcgr signaling plays an essential role in LDL-C (low-density lipoprotein cholesterol) homeostasis through regulating the PCSK9 (proprotein convertase subtilisin/kexin type 9) levels. Silencing of hepatic Gcgr or inhibition of glucagon action increased hepatic and plasma PCSK9 and resulted in lower LDLR (LDL receptor) protein and increased plasma LDL-C. Conversely, treatment of wild-type (WT) mice with glucagon lowered LDL-C levels, whereas this response was abrogated in Pcsk9-/- and Ldlr-/- mice. Our gain- and loss-of-function studies identified Epac2 (exchange protein activated by cAMP-2) and Rap1 (Ras-related protein-1) as the downstream mediators of glucagon's action on PCSK9 homeostasis. Moreover, mechanistic studies revealed that glucagon affected the half-life of PCSK9 protein without changing the level of its mRNA, indicating that Gcgr signaling regulates PCSK9 degradation. CONCLUSIONS:These findings provide novel insights into the molecular interplay between hepatic glucagon signaling and lipid metabolism and describe a new posttranscriptional mechanism of PCSK9 regulation.

SUBMITTER: Spolitu S

PROVIDER: S-EPMC6457439 | biostudies-literature | 2019 Jan

REPOSITORIES: biostudies-literature

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Hepatic Glucagon Signaling Regulates PCSK9 and Low-Density Lipoprotein Cholesterol.

Spolitu Stefano S Okamoto Haruka H Dai Wen W Zadroga John A JA Wittchen Erika S ES Gromada Jesper J Ozcan Lale L

Circulation research 20190101 1

<h4>Rationale</h4>Glucagon is a key hormone that regulates the adaptive metabolic responses to fasting. In addition to maintaining glucose homeostasis, glucagon participates in the regulation of cholesterol metabolism; however, the molecular pathways underlying this effect are incompletely understood.<h4>Objective</h4>We sought to determine the role of hepatic Gcgr (glucagon receptor) signaling in plasma cholesterol regulation and identify its underlying molecular mechanisms.<h4>Methods and resu ...[more]

PMID: 30582457

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Project description:Low-density lipoprotein cholesterol (LDL-C) is an important modifiable risk factor for atherosclerotic cardiovascular disease. It is unclear whether the percentage LDL-C lowering with pharmacotherapies differs on the basis of baseline LDL-C levels. To evaluate the association between baseline LDL-C levels and the percentage LDL-C reduction with a statin, ezetimibe, and a PCSK9 inhibitor. This secondary exploratory study analyzed data from 3 randomized placebo-controlled clinical trials (Aggrastat to Zocor-Thrombolysis in Myocardial Infarction 21 [A to Z-TIMI 21], Improved Reduction of Outcomes: Vytorin Efficacy International Trial [IMPROVE-IT], and Further Cardiovascular Outcomes Research With PCSK9 Inhibition in Subjects With Elevated Risk [FOURIER]) of lipid-lowering therapies (statin, ezetimibe, and a PCSK9 inhibitor) and included participants with atherosclerotic cardiovascular disease. Analyses took place form April to October 2020. In A to Z-TIMI 21, 1:1 randomization to simvastatin, 40 mg, daily for 30 days followed by 80 mg daily thereafter vs placebo for 4 months followed by simvastatin, 20 mg, daily thereafter. In IMPROVE-IT, 1:1 randomization to ezetimibe, 10 mg, daily plus simvastatin, 40 mg, daily vs placebo plus simvastatin, 40 mg, daily. In FOURIER, 1:1 randomization to evolocumab, 140 mg, every 2 weeks or 420 mg monthly vs matching placebo. The percentage LDL-C reduction at either 1 month (A to Z-TIMI 21, IMPROVE-IT) or 3 months (FOURIER) as a function of baseline LDL-C level. Data were modeled using a generalized linear regression model. A total of 3187 patients from A to Z-TIMI 21, 10 680 patients from IMPROVE-IT, and 25 847 patients from FOURIER were analyzed. There was a higher percentage reduction in LDL-C levels with evolocumab in patients with lower baseline LDL-C levels, ranging from 59.4% (95% CI, 59.1%-59.8%) in patients with a baseline LDL-C level of 130 mg/dL to 66.1% (95% CI, 65.6%-66.6%) in patients with a baseline LDL-C level of 70 mg/dL (P < .001). In contrast, across the same range of baseline LDL-C level, there was a more modest difference for simvastatin (44.6% [95% CI, 43.9%-45.2%] vs 47.8% [95% CI, 46.4%-49.2%]; P < .001) and minimal difference with ezetimibe (25.0% [95% CI, 23.3%-26.6%] vs 26.2% [95% CI, 24.2%-28.1%]; P = .007). The percentage LDL-C reduction with statins, ezetimibe, and PCSK9 inhibition is not attenuated in patients starting with lower baseline LDL-C levels and is 6.6% greater for PCSK9 inhibition. These data are encouraging for the use of intensive LDL-C-lowering therapy even for patients with lower LDL-C levels.

Project description:CONTEXT:Elevated LDL cholesterol (LDL-C) is an important risk factor for atherosclerosis and cardiovascular disease. Variants in the proprotein convertase subtilisin/kexin type 9 (PCSK9) gene have been associated not only with plasma LDL-C concentration, but also with ischemic heart disease. Little is known about the genetic architecture of PCSK9 and its influence on LDL-C in American Indians. OBJECTIVE:We aimed to investigate the genetic architecture in the 1p32 region encompassing PCSK9 and its influence on LDL-C in American Indians. DESIGN:The Strong Heart Family Study (SHFS) is a family-based genetic study. PARTICIPANTS:Two thousand four hundred fifty eight American Indians from Arizona, Oklahoma, North Dakota, and South Dakota, who were genotyped by Illumina MetaboChip. RESULTS:We genotyped 486 SNPs in a 3.9 Mb region at chromosome 1p32 encompassing PCSK9 in 2458 American Indians. We examined the association between these SNPs and LDL-C. For common variants (MAF ? 1%), meta-analysis across the three geographic regions showed common variants in PCSK9 were significantly associated with higher LDL-C. The most significant SNP rs12067569 (MAF = 1.7 %, ? = 16.9 ± 3.7, P = 5.9 × 10(-6)) was in complete LD (r(2) = 1) with a nearby missense SNP, rs505151 (E670G) (? = 15.0 ± 3.6, P = 3.6 × 10(-5)). For rare variants (MAF < 1%), rs11591147 (R46L, MAF = 0.9%) was associated with lower LDL-C (? = - 31.1 ± 7.1, P = 1.4 × 10(-5)). The mean (SD) of LDL-C was 76.9 (7.8) and 107.4 (1.0) mg/dL for those with and without the R46L mutation, respectively. One person who was homozygous for R46L had LDL-C levels of 11 mg/dL. In one family, 6 out of 8 members carrying the R46L mutation had LDL-C levels below the lower 10% percentile of LDL-C among all study participants. CONCLUSIONS:Both rare and common variants in PCSK9 influence plasma LDL-C levels in American Indians. Follow-up studies may disclose the influence of these mutations on the risk of CVD and responses to cholesterol-lowering medications.

Dataset Information

Hepatic Glucagon Signaling Regulates PCSK9 and Low-Density Lipoprotein Cholesterol.

Publications

Hepatic Glucagon Signaling Regulates PCSK9 and Low-Density Lipoprotein Cholesterol.

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