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Amino acid starvation-induced LDLR trafficking accelerates lipoprotein endocytosis and LDL clearance.

ABSTRACT: Mammalian cells utilize Akt-dependent signaling to deploy intracellular Glut4 toward cell surface to facilitate glucose uptake. Low-density lipoprotein receptor (LDLR) is the cargo receptor mediating endocytosis of apolipoprotein B-containing lipoproteins. However, signaling-controlled regulation of intracellular LDLR trafficking remains elusive. Here, we describe a unique amino acid stress response, which directs the deployment of intracellular LDLRs, causing enhanced LDL endocytosis, likely via Ca²⁺ and calcium/calmodulin-dependent protein kinase II-mediated signalings. This response is independent of induction of autophagy. Amino acid stress-induced increase in LDL uptake in vitro is comparable to that by pravastatin. In vivo, acute AAS challenge for up to 72 h enhanced the rate of hepatic LDL uptake without changing the total expression level of LDLR. Reducing dietary amino acids by 50% for 2 to 4 weeks ameliorated high fat diet-induced hypercholesterolemia in heterozygous LDLR-deficient mice, with reductions in both LDL and VLDL fractions. We suggest that identification of signaling-controlled regulation of intracellular LDLR trafficking has advanced our understanding of the LDLR biology, and may benefit future development of additional therapeutic strategies for treating hypercholesterolemia.

SUBMITTER: Chen Y

PROVIDER: S-EPMC8892268 | biostudies-literature | 2022 Feb

REPOSITORIES: biostudies-literature

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Amino acid starvation-induced LDLR trafficking accelerates lipoprotein endocytosis and LDL clearance.

Chen Ye Y Wu Xiao X Zhang Jing J Pan Guopin G Wang Xiaoyun X Guo Xiaosun X Wang Jianli J Cui Xiaopei X Gao Haiqing H Cheng Mei M Yang Jingwen J Zhang Cheng C Jiang Fan F

EMBO reports 20220107 3

Mammalian cells utilize Akt-dependent signaling to deploy intracellular Glut4 toward cell surface to facilitate glucose uptake. Low-density lipoprotein receptor (LDLR) is the cargo receptor mediating endocytosis of apolipoprotein B-containing lipoproteins. However, signaling-controlled regulation of intracellular LDLR trafficking remains elusive. Here, we describe a unique amino acid stress response, which directs the deployment of intracellular LDLRs, causing enhanced LDL endocytosis, likely vi ...[more]

PMID: 34994492

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Project description:Background and aimsLeukocytosis, particularly monocytosis, has been shown to promote atherosclerosis in both diabetic and non-diabetic mouse models. We previously showed that hyperglycemia independently promotes monocytosis and impairs the resolution of atherosclerosis. Since patients with chronic diabetes often develop dyslipidemia and also have increased risk for atherosclerosis, we sought to examine how controlling blood glucose affects atherosclerosis development in the presence of severe hyperlipidemia.MethodsDiabetes was induced using streptozotocin (STZ) in low density lipoprotein receptor (Ldlr) knockout (Ldlr-/-) mice after which they were fed a high-cholesterol diet for 4 weeks. Control and diabetic mice were treated with vehicle or sodium glucose cotransporter inhibitor (SGLT2i, Phlorizin or Dapagliflozin) for the duration of the diet.ResultsInduction of diabetes resulted in a dramatic increase in plasma cholesterol (TC) and triglyceride (TG) levels. These mice also exhibited an increased number of circulating monocytes and neutrophils. Monocytosis was driven by increased proliferation of progenitor cells in the bone marrow. Tighter glycemic control by SGLT2i treatment not only reduced monocytosis and atherosclerosis but also improved plasma lipoprotein profile. Interestingly, improved lipoprotein profile was not due to decreased TG synthesis or clearance via low density lipoprotein receptor-related protein (Lrp) 1 or scavenger receptor class B member (Scarb1) pathways, but likely mediated by heparin sulfate proteoglycans (HSPG)-dependent clearance mechanisms in the liver. Further examination of the liver revealed an important role for bile acid transporters (Abcg5, Abcg8) and cytochrome P450 enzymes in the clearance of hepatic cholesterol.ConclusionsThese data suggest that tighter glycemic control in diabetes can improve lipoprotein clearance exclusive of Ldlr, likely via HSPG and bile acid pathways, and has an overall net positive effect on atherosclerosis.

Project description:The target of rapamycin complex 1 (TORC1) pathway is a highly conserved signaling pathway across eukaryotes that integrates nutrient and stress signals to regulate the cellular growth rate and the transition into and maintenance of dormancy. The majority of the pathway's components, including the central TOR kinase, have been lost in the apicomplexan lineage, and it is unknown how these organisms detect and respond to nutrient starvation in its absence. Plasmodium falciparum encodes a putative ortholog of the RNA polymerase (Pol) III repressor Maf1, which has been demonstrated to modulate Pol III transcription in a TOR-dependent manner in a number of organisms. Here, we investigate the role of P. falciparum Maf1 (PfMaf1) in regulating RNA Pol III expression under conditions of nutrient starvation and other stresses. Using a transposon insertion mutant with an altered Maf1 expression profile, we demonstrated that proper Maf1 expression is necessary for survival of the dormancy-like state induced by prolonged amino acid starvation and is needed for full recovery from other stresses that slow or stall the parasite cell cycle. This Maf1 mutant is defective in the downregulation of pre-tRNA synthesis under nutrient-limiting conditions, indicating that the function of Maf1 as a stress-responsive regulator of structural RNA transcription is conserved in P. falciparum Recent work has demonstrated that parasites carrying artemisinin-resistant K13 alleles display an enhanced ability to recover from drug-induced growth retardation. We show that one such artemisinin-resistant line displays greater regulation of pre-tRNA expression and higher survival upon prolonged amino acid starvation, suggesting that overlapping, PfMaf1-associated pathways may regulate growth recovery from both artemisinin treatment and amino acid starvation.IMPORTANCE Eukaryote organisms sense changes in their environment and integrate this information through signaling pathways to activate response programs to ensure survival. The TOR pathway is a well-studied signaling pathway found throughout eukaryotes that is known to integrate a variety of signals to regulate organismal growth in response to starvation and other stresses. The human malaria parasite Plasmodium falciparum appears to have lost the TOR pathway over the course of evolution, and it is unclear how the parasite modulates its growth in response to starvation and drug treatment. Here, we show that Maf1, a protein regulated by TOR in other eukaryotes, plays an important role in maintaining the parasite's viability in the face of starvation and other forms of stress. This suggests that PfMaf1 is a component of a yet-to-be-described nutrient and stress response pathway.

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Amino acid starvation-induced LDLR trafficking accelerates lipoprotein endocytosis and LDL clearance.

Publications

Amino acid starvation-induced LDLR trafficking accelerates lipoprotein endocytosis and LDL clearance.

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