Biology subjects

Rohrer, L.

Publications and source records attributed to Rohrer, L..

4 recordsLinked to original sources

bioRxiv2026

The COPI coatomer influences LDL receptor activity, hepatic lipid storage, and apoB secretion

BackgroundDecreased hepatic removal of low density lipoproteins (LDL) and increased apolipoprotein B (apoB) production cause hypercholesterolemia, a major causal risk factor of atherosclerotic cardiovascular disease (ASCVD). By a genome-wide siRNA screen, we previously identified subunits of the Coat protein I (COPI) complex to limit LDL uptake into Huh-7 hepatocarcinoma cells. MethodsThese findings were validated by targeted in vitro experiments as well as genetic association studies in humans and three mouse models with mutated or disrupted COPI genes. ResultsSilencing of COPA, COPB1, COPB2, ARCN1, COPG1, and COPZ1 in Huh-7 cells resulted in decreased uptake of LDL and aberrant glycosylation and altered cell surface abundance of the LDL receptor (LDLR) as well as increased apoB secretion and cellular lipid storage. Single nucleotide polymorphisms of ARCN1 were associated with lower ARCN1 expression and higher levels of LDL-cholesterol (LDL-C). Rare variants of COPA and COPG1 were enriched among patients with LDL-C > 5 mmol/L. Patients and mice carrying other rare immunopathogenic missense variants of COPA and COPG1 did not present with elevated plasma levels of LDL-C, while hepatic knockdown of murine Copg1 increased the concentrations of non-HDL-cholesterol in plasma and triglycerides in the liver. ConclusionsThe COPI coatomer regulates LDLR activity and apoB secretion as well as lipid content of liver cells. Loss of function of some variants of COPI genes are associated with higher LDL-C levels.

cell biology↗

bioRxiv2023

Mapping the dynamic cell surface interactome of high-density lipoprotein reveals Aminopeptidase N as modulator of its endothelial uptake

Heterogeneous high-density lipoprotein (HDL) particles, which can contain hundreds of proteins, affect human health and disease through dynamic molecular interactions with cell surface proteins. How HDL mediates its long-range signaling functions and interactions with various cell types is largely unknown. Due to the complexity of HDL, we hypothesize that multiple receptors engage with HDL particles resulting in condition-dependent receptor-HDL interaction clusters at the cell surface. Here we used the mass spectrometry-based and light-controlled proximity labeling strategy LUX-MS in a discovery-driven manner to decode HDL-receptor interactions. Surfaceome nanoscale organization analysis of hepatocytes and endothelial cells using LUX-MS revealed that the previously known HDL-binding protein scavenger receptor SCRB1 is embedded in a cell surface protein community, which we term HDL synapse. Modulating the endothelial HDL synapse, composed of 60 proteins, by silencing individual members showed that the HDL synapse can be assembled in the absence of SCRB1 and that the members are interlinked. The aminopeptidase AMPN (also known as CD13) was identified as an HDL synapse member that directly influences HDL uptake into the primary human aortic endothelial cells (HAECs). Our data indicate that preformed cell surface residing protein complexes modulate HDL function and suggest new theragnostic opportunities.

systems biology↗

bioRxiv2022

Decoding functional high-density lipoprotein particle surfaceome interactions

High-density lipoprotein (HDL) is a mixture of complex particles mediating reverse cholesterol transport in the human body and several cytoprotective activities. Despite its relevance for human health, many aspects of HDL-mediated lipid trafficking and cellular signaling remain elusive at the molecular level. During HDLs journey throughout the body, its function is mediated through interactions with cell surface receptors on different cell types. Using four different cellular model systems HDL is interacting with, we comparatively analyzed their surfaceomes to define the HDL receptome. Surfaceome analysis of EA.hy926, HEPG2, foam cells, and human aortic endothelial cells (HAEC) revealed the main currently known HDL-receptor scavenger receptor B1 (SCRB1), as well as 154 shared cell surface receptors representing potential HDL interaction receptor candidates. Since vascular endothelial growth factor A (VEGF-A) was recently found as a regulatory factor of transendothelial transport of HDL, we next analyzed the VEGF modulated surfaceome of HAEC using auto-CSC technology. VEGF-A treatment led to a remodeling of the surfaceome of HAEC cells including the previously reported higher surfaceome abundance of SCRB1 upon treatment. 165 additional receptors were found on HAEC upon VEGF-A treatment representing SCRB1 co-regulated receptors potentially involved in HDL function. Using HATRIC-based ligand receptor capturing (HATRIC-LRC) technology on human endothelial cells, we specifically aimed for the identification of other bona fide (co-)receptors of HDL beyond SCRB1. HATRIC-LRC enabled, next to SCRB1, the identification of the receptor tyrosine-protein kinase Mer (MERTK), which we show is directly contributing to endothelial HDL binding and uptake. Subsequent proximity ligation assays (PLA) demonstrate furthermore the spatial vicinity of MERTK and SCRB1 on the endothelial cell surface. The data shown provide direct evidence for a complex and dynamic HDL receptome and that receptor nanoscale organization may influence functional HDL binding and uptake. List of human gene and protein names discussed in the paperABCA1: Phospholipid-transporting ATPase ABCA1 (ABCA1) ABCA7: Phospholipid-transporting ATPase ABCA7 (ABCA7) ABCG1: ATB-binding cassette G1 (ABCG1) ACVR2A: Activin receptor type-2A (AVR2A) APOA1: Apolipoprotein A1 (APOA1) APOB: Apolipoprotein B (APOB) APOC3: Apolipoprotein C-III (APOC3) APOH: Beta-2-glycoprotein 1 (APOH) APOM: Apolipoprotein M (APOM) ATP5MF: Ecto-F1-ATPase (ATPK) CD4: T-cell surface glycoprotein CD4 (CD4) CD14: Monocyte differentiation antigen CD14 (CD14) CD36: platelet glycoprotein 4 (CD36) EGFR: Epidermal growth factor receptor (EGFR) ITGAM: Integrin alpha-M (ITAM) ITGAV: Integrin alpha-V (ITAV) KDR: Vascular endothelial growth factor receptor 2 (VGFR2) KIT: Mast/stem cell growth factor receptor Kit (KIT) MEGF8: Multiple epidermal growth factor-like domains protein 8 (MEGF8) MEGF10: Multiple epidermal growth factor-like domains protein 10 (MEGF10) MERTK: tyrosine-protein kinase Mer (MERTK) MRC2: C-type mannose receptor 2 (MRC2) MSR1: Macrophage scavenger receptor types I and II (MSRE) PCDHAC1: Protocadherin alpha-C1 (PCDC1) PLTP: Phospholipid transfer protein (PLTP) S1PR1: sphingosine 1-phosphate receptor 1 (S1PR1) S1PR2: sphingosine 1-phosphate receptor 2 (S1PR2) S1PR3: sphingosine 1-phosphate receptor 3 (S1PR3) SCARA3: Scavenger receptor class A member 3 (SCAR3) SCARB1: Scavenger receptor B1 (SCRB1) SLC8A3: Sodium/calcium exchanger 2 (NAC2) TF: Transferrin (TRFE) TFRC: Transferrin receptor protein 1 (TFR1) VEGFA: vascular endothelial growth factor A (VEGF-A) Significance statementA molecular understanding of the high-density lipoprotein (HDL) receptome would provide the rational basis for modulating reverse cholesterol transport. Here we used cellular model systems mimicking tissues involved in HDL-trafficking and reverse cholesterol transport to define the HDL receptome. The receptor tyrosine-protein kinase Mer (MERTK) was identified as a novel mediator of HDL binding and uptake in human aortic endothelial cells. Endothelial MERTK resides within the surfaceome proximal to SCRB1 representing a potential co-receptor. The molecular nanoscale organization of the cell-specific surfaceome may influence cellular HDL interactions and functionality.

molecular biology↗

bioRxiv2020

Sphingosine-1-phosphate receptors 1 and 3 regulate the expression of SR-B1 in human aortic endothelial cells

Several vasoprotective functions of high-density lipoproteins (HDL) on the endothelium have been shown to depend on the presence of sphingosine-1-phosphate (S1P) receptors (S1PRs) as well as scavenger receptor class B type 1 (SR-B1). Interference with the presence of S1P or the activity of S1PR1 or S1PR3 mimics many effects seen by the interference with SR-B1. This raises the question on interactions between S1P receptors and SR-B1. We investigated the influence of S1PRs on SR-B1 expression in human aortic endothelial cells. Silencing or pharmacological inhibition of S1PR1 or S1PR3 down-regulated SCARB1 mRNA expression as well as SR-B1 protein abundance. RNA interference with S1PR1 or S1PR3 also decreased cellular association of 125I-HDL with HAECs. Further mechanistic studies showed that knockdown of S1PR1 or S1PR3 reduced SR-B1 protein by inducing its degradation through deceasing Akt activity. Moreover, silencing of S1PR1 or S1PR3 suppressed SCARB1 mRNA expression by decreasing cellular cAMP levels. In conclusion, we provide evidence for an as yet unappreciated interaction, namely the regulation of SR-B1 abundance by S1PRs on both transcriptional and post-translational levels, suggesting that interactions of S1PRs and SR-B1 regulate signaling functions of HDL as well as uptake of lipoproteins in endothelial cells.

cell biology↗