Biology subjects

Bauer, R. C.

Publications and source records attributed to Bauer, R. C..

8 recordsLinked to original sources

bioRxiv2025

Depot-Specific Roles for C/EBPα in White Adipose Tissue Development and Metabolism

Rates of obesity and its associated metabolic comorbidities continue to rise in the developed world. It is well established that in obesity, the distribution and not just amount of excess white adipose tissue (WAT) correlates with a persons risk for comorbidities such as coronary artery disease and type 2 diabetes. Thus, understanding the specific mechanisms that drive WAT development in specific adipose depots could elucidate novel mechanisms of metabolic disease. SNPs near the gene CEBPA have been associated with multiple cardiometabolic traits by human genome-wide association studies, including waist-to-hip ratio, suggesting that CEBPA regulates WAT distribution. CEBPA encodes a well characterized transcription factor (C/EBP) that is long recognized as a master regulator of adipocyte differentiation, yet depot-specific roles for C/EBP have not been previously described. To further investigate this genetic link, we generated mice with adipocyte-specific Cebpa knockout (Cebpa_ASKO) and found that these mice are almost entirely lacking gonadal WAT (gWAT) despite the inguinal WAT (iWAT) being present in near normal amounts. Despite developing, Cebpa_ASKO iWAT contains fewer and larger adipocytes, and fails to expand when challenged with high fat diet. RNA-seq and functional studies demonstrate evidence of altered lipid metabolism and adipocyte function in Cebpa_ASKO iWAT. Finally, Cebpa_ASKO mice have multiple other metabolic phenotypes, including lipid-laden BAT, increased hepatic triglycerides, and increased plasma cholesterol, all of which worsen with prolonged high fat diet feeding. Taken together, these data highlight depot-specific roles for C/EBP in adipose tissue development, as well as the importance of adipocyte C/EBP in maintaining metabolic homeostasis.

physiology↗

bioRxiv2025

Comprehensive Multimodal Profiling of Atherosclerosis Reveals Bhlhe40 as a Potential Regulator of Vascular Smooth Muscle Cell Phenotypic Modulation

BackgroundVascular smooth muscle cells (VSMCs) play a central role in atherosclerosis by undergoing phenotypic modulation from a quiescent, contractile state to a range of synthetic phenotypes, including fibroblast-like, macrophage-like, and lipid-laden foam cell-like states. However, a comprehensive multimodal characterization and understanding of the transcriptional programs driving these transitions remain incomplete. MethodsTo comprehensively define the phenotypic diversity of VSMCs during atherosclerosis progression, we performed in-depth profiling using cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq) and bulk RNA sequencing in a VSMC lineage-tracing atherosclerotic mouse model. Insights from these datasets guided the design of targeted in vitro experiments to investigate candidate regulatory mechanisms. ResultsSingle-cell multi-omics revealed extensive cellular heterogeneity within atherosclerotic plaques, including a rare population of VSMC-derived macrophage-like cells, whose presence was confirmed by histological analysis. These studies also identified a substantial population of VSMC-derived foam cells, comprising approximately 70% of all foam cells in the lesions. These cells exhibited activation of gene programs associated with lipid metabolism, proliferation, and tumor-like features. The transcription factor Bhlhe40 emerged as a key regulator of this phenotypic transition, with elevated expression in VSMC-derived foam cells during disease progression. Functional knockdown of Bhlhe40 suppressed VSMC phenotypic switching and foam cell characteristics, underscoring its potential role as a driver of VSMC modulation. ConclusionsThese findings advance our understanding of VSMC phenotypic modulation in atherosclerosis and highlight Bhlhe40 as a key regulator of this process. Elucidating the mechanisms governing VSMC plasticity may offer new therapeutic opportunities to reduce cardiovascular risk by targeting disease-driving cellular transitions.

molecular biology↗

bioRxiv2024

Single-Cell RNA-Seq Reveals Adventitial Fibroblast Alterations during Mouse Atherosclerosis

BackgroundAtherosclerotic cardiovascular disease (ASCVD) remains the leading cause of mortality in the western world despite the success of lipid lowering therapies, highlighting the need for novel lipid-independent therapeutic strategies. Genome-wide association studies (GWAS) have identified numerous genes associated with ASCVD that function in the vessel wall, suggesting that vascular cells mediate ASCVD, and that the genes and pathways essential for this vascular cell function may be novel therapeutic targets for the treatment of ASCVD. Furthermore, some of these implicated genes appear to function in the adventitial layer of the vasculature, suggesting these cells are able to potentiate ASCVD. MethodsTo investigate the role of adventitial cells in atherosclerosis, we conducted single-cell RNA sequencing (scRNA-seq) of the aortic adventitia during atherogenesis in male Ldlr-/- mice via pools of three mice, two samples per condition. We cross-referenced the scRNA-seq data with human ASCVD GWAS to identify regulators of adventitial responses in ASCVD. These regulators were then validated in vitro in human adventitial fibroblasts. ResultsWe identified four adventitial fibroblast populations, all of which displayed shifts in population size and gene expression over the course of atherogenesis. SERPINH1, an ASCVD-linked GWAS gene, was differentially expressed in adventitial fibroblasts during atherogenesis. Knockdown of SERPINH1 in vitro reduced fibroblast migration and altered subcluster marker gene expression. ConclusionsThese findings reveal dynamic changes in adventitial fibroblasts during atherosclerosis and suggest that reduced SERPINH1 expression disrupts adventitial fibroblast function, contributing to ASCVD progression.

genomics↗

bioRxiv2024

ADAMTS7 Promotes Smooth Muscle Cell Foam Cell Expansion in Atherosclerosis

Human genetic studies have repeatedly associated ADAMTS7 with atherosclerotic cardiovascular disease. Subsequent investigations in mice demonstrated that ADAMTS7 is proatherogenic and induced in response to vascular injury. However, the cell-specific mechanisms governing ADAMTS7 proatherogenicity remain unclear. To determine which vascular cell types express ADAMTS7, we interrogated single-cell RNA sequencing of human carotid atherosclerosis and found ADAMTS7 expression in smooth muscle cells (SMCs), endothelial cells (ECs), and fibroblasts. We subsequently created SMC- and EC-specific Adamts7 conditional knockout and transgenic mice. Conditional knockout of Adamts7 in either cell type does not reduce atherosclerosis, whereas transgenic induction in either cell type increases atherosclerosis. In SMC transgenic mice, this increase coincides with an expansion of lipid-laden SMC foam cells and a decrease in fibrous cap formation. RNA-sequencing in Adamts7 overexpressing SMCs revealed an upregulation of lipid genes typically assigned to macrophages. Mechanistically, ADAMTS7 increases SMC oxLDL uptake through CD36, whose expression is upregulated by PU.1. ATAC-seq and motif analysis revealed increased chromatin accessibility at AP-1 enriched regions, consistent with AP-1 dependent remodeling of PU.1-regulated lipid-handling loci. In summary, ADAMTS7 promotes atherosclerosis by driving SMC foam cell formation through an AP-1/PU.1/CD36 regulatory axis.

pathology↗

bioRxiv2023

Single-cell multimodal profiling of atherosclerosis identifies CD200 as a lineage marker of vascular smooth muscle cells and their derived cells

Vascular smooth muscle cells (VSMCs) play a central role in the development of atherosclerosis due in part to their capability to phenotypically transition into either a protective or harmful state. However, the ability to identify and trace VSMCs and their progeny in vivo is limited due to the lack of well-defined VSMC cell surface markers. Therefore, investigations into VSMC fate must utilize lineage-tracing mouse models, which are time-consuming and challenging to generate and not feasible in humans. Here, we employed CITE-seq to characterize the phenotypic expression of 119 cell surface proteins in mouse atherosclerosis. We found that CD200 is a highly expressed and specific marker of VSMCs, which persists even with phenotypic modulation. We validated our findings using a combination of flow cytometry, qPCR, and immunohistochemistry, all confirming that CD200 can identify and mark VSMCs and their derived cells in early to advanced mouse atherosclerotic lesions. Additionally, we describe a similar expression pattern of CD200 in human coronary and carotid atherosclerosis. Thus, our data support the use of CD200 as a lineage marker for VSMCs and VSMC-derived cells in mouse and human atherosclerosis.

molecular biology↗

bioRxiv2022

Decoding the Variant-to-Function Relationship for LIPA, a Risk Locus for CAD

Translating human genomic discoveries into mechanistic insights requires linking genetic variations to candidate genes and their causal functional phenotypes. Genome-wide association studies have consistently identified LIPA as a risk locus for coronary artery disease (CAD), with previous expression quantitative trait loci (eQTL) analyses prioritizing LIPA as a candidate causal gene. However, functional studies elucidating the causal variants, regulatory mechanisms, target cell types, and their causal impact on atherosclerosis have been lacking. To address this gap, we applied functional genomics and experimental mouse models to establish the variant-to-function relationship at the LIPA locus. Our findings show that CAD risk alleles in the LIPA locus increase LIPA expression and enzyme activity specifically in monocytes/macrophages by enhancing PU.1 binding to an intronic enhancer region that interacts with the LIPA promoter. In myeloid Lipa-overexpressing mice, we observed larger atherosclerotic lesions accompanied by altered macrophage function, including increased macrophage accumulation due to enhanced monocyte recruitment, reduced neutral lipid accumulation, and upregulation of integrin and extracellular matrix pathways. Our work establishes a direct causal link between LIPA risk alleles and increased monocyte/macrophage LIPA that exacerbates atherosclerosis, bridging human functional genomic evidence to the mechanistic understanding of CAD. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=58 SRC="FIGDIR/small/516293v2_ufig1.gif" ALT="Figure 1"> View larger version (20K): org.highwire.dtl.DTLVardef@11ce287org.highwire.dtl.DTLVardef@15c201aorg.highwire.dtl.DTLVardef@13f90c9org.highwire.dtl.DTLVardef@3aa3be_HPS_FORMAT_FIGEXP M_FIG C_FIG

genomics↗

bioRxiv2021

Adipocyte Tribbles1 Regulates Plasma Adiponectin and Plasma Lipids in Mice

Multiple GWAS have identified SNPs in the 8q24 locus near the TRIB1 gene that significantly associate with plasma lipids and coronary artery disease. While subsequent studies have uncovered roles for hepatic and myeloid Trib1 in contributing to either plasma lipids or atherosclerosis, the causal tissue for these GWAS associations remains unclear. The same 8q24 SNPs significantly associate with plasma adiponectin levels in humans as well, suggesting a role for TRIB1 in adipose tissue. Here, we report that adipocyte-specific Trib1 knockout mice (Trib1_ASKO) have increased plasma adiponectin levels and decreased plasma cholesterol and triglycerides. We demonstrate that loss of Trib1 increases adipocyte production and secretion of adiponectin independent of the known TRIB1 function of regulating proteasomal degradation. RNA-seq analysis of adipocytes and livers from Trib1_ASKO mice suggests that alterations in adipocyte function underlie the plasma lipid changes observed in these mice. Secretomics and RNA-seq analysis revealed that Trib1_ASKO mice have increased production of Lpl and decreased production of Angptl4 in adipose tissue, and fluorescent substrate assays confirm an increase in adipose tissue Lpl activity, which likely underlies the observed triglyceride phenotype. In summary, we demonstrate here a novel role for adipocyte Trib1 in regulating plasma adiponectin, total cholesterol, and triglycerides in mice, confirming previous genetic associations observed in humans and providing a novel avenue through which Trib1 regulates plasma lipids and coronary artery disease.

physiology↗

bioRxiv2018

Genetic And Epigenetic Fine Mapping Of Complex Trait Associated Loci In The Human Liver

Deciphering the impact of genetic variation on gene regulation is fundamental to understanding common, complex human diseases. Although histone modifications are important markers of gene regulatory regions of the genome, any specific histone modification has not been assayed in more than a few individuals in the human liver. As a result, the impacts of genetic variation that direct histone modification states in the liver are poorly understood. Here, we generate the most comprehensive genome-wide dataset of two epigenetic marks, H3K4me3 and H3K27ac, and annotate thousands of putative regulatory elements in the human liver. We integrate these findings with genome-wide gene expression data collected from the same human liver tissues and high-resolution promoter-focused chromatin interaction maps collected from human liver-derived HepG2 cells. We demonstrate widespread functional consequences of natural genetic variation on putative regulatory element activity and gene expression levels. Leveraging these extensive datasets, we fine-map a total of 77 GWAS loci that have been associated with at least one complex phenotype. Our results contribute to the repertoire of genes and regulatory mechanisms governing complex disease development and further the basic understanding of genetic and epigenetic regulation of gene expression in the human liver tissue.

genetics↗