Biology subjects

Mayr, M.

Publications and source records attributed to Mayr, M..

11 recordsLinked to original sources

bioRxiv2026

Dietary depletion of glutamine is atheroprotective

Heart attacks and strokes are late-stage complications of rupture of unstable atherosclerotic plaques. Stable plaques contain stabilizing matrix-producing fibrotic cells, largely smooth muscle cell (SMC)-derived. The molecular drivers of SMC phenotypic transitions to beneficial fibrotic or destabilizing inflammatory and calcifying phenotypes are unclear. Since atherosclerosis develops over decades, there is extensive interest in identifying dietary alterations that enhance plaque stability. We demonstrate that SMC acquire a fibrotic phenotype dependent on glutamine-derived metabolites supporting both catabolism and collagen synthesis. Moreover, dietary glutamine restriction decreases mortality of mice susceptible to atherosclerotic plaque rupture. Lesions from glutamine-restricted mice are smaller and have increased SMC investment. This study identifies dietary glutamine as a driver of cardiovascular mortality, suggesting a new strategy for reducing late-stage complications of atherosclerosis.

physiology↗

bioRxiv2025

Female-biased vascular smooth muscle cell gene regulatory networks predict MYH9 as a key regulator of fibrous plaque phenotype

Atherosclerosis, a chronic inflammatory condition driving coronary artery disease (CAD), manifests in two primary plaque types: unstable atheromatous plaques and stable fibrous plaques. While significant research has focused on atheromatous plaques, recent studies emphasize the growing importance of fibrous plaques, particularly in females under 50 years of age, where erosion on fibrous plaques significantly contributes to coronary thrombosis. The molecular mechanisms underlying sex differences in atherosclerotic plaque characteristics, including vascular smooth muscle cell (VSMC) contributions, remain understudied. Therefore, we utilized sex-specific gene regulatory networks (GRNs) derived from VSMC gene expression data from 119 male and 32 female heart transplant donors to identify molecular drivers of fibrous plaques. GRN analysis revealed two female-biased networks in VSMC, GRNfloralwhite and GRNyellowgreen, enriched for inflammatory signaling and actin remodeling pathways, respectively. Single-cell RNA sequencing of carotid plaques from female and male patients confirmed the sex specificity of these networks in VSMCs. Further sub cellular phenotyping of the single-cell RNA sequencing revealed a sex-specific gene expression signature within GRNyellowgreen for VSMCs enriched for contractile and vasculature development pathways. Bayesian network modeling of the GRNyellowgreen identified MYH9 as a key driver gene. Indeed, elevated MYH9 protein expression in atherosclerotic plaques was associated with higher smooth muscle cell content and lower lipid content in female plaques, suggesting its involvement in fibrous plaque formation. Further proteomic analysis confirmed MYH9s upregulation in female fibrous plaques only and its correlation with stable plaque features. These findings provide novel insights into sex-specific molecular mechanisms regulating fibrous plaque formation.

genomics↗

bioRxiv2025

Diversity and single-cell activity of endolithic microbes in sediment-hosted carbonate nodules within and below the sulfate-methane transition zone

Authigenic carbonate concretions ( nodules) precipitate in marine seep sediments as a result of anaerobic oxidation of methane (AOM). These rocks host active endolithic microbial communities and persist as important methane sinks. Still, how these communities and their activity differ from those in adjacent seep sediments, particularly as a function of proximity to the sulfate-methane transition zone (SMTZ), remains understudied. Here, we sampled sediments and nodules within and below the SMTZ (0-57 cm deep) at four active deep-sea seep areas in Santa Monica Basin, CA. Measurements of high nodule porosities (43-51%) coupled to strong similarities between sediment and nodule 16S rRNA-based community profiles, including below the SMTZ, suggest continued perfusion and exchange between buried nodules and surrounding sediment. Shared, depth-dependent transitions in methanotrophic taxa (ANME-1, ANME-2, ANME-3) and methanogenic taxa (Methanofastidiosales) below the SMTZ were also consistent with trends in porewater methane and sulfate concentrations, porewater DIC, and nodule {delta}13C values -- underscoring the impact of different geochemical conditions on community structure and suggestive of under-characterized physiological plasticity in ANME-1. Laboratory-based BONCAT incubations of nodules within the SMTZ over [~]14-weeks revealed active sulfide production and translationally active endolithic microorganisms. However, cells from parallel nodule incubations recovered below the SMTZ showed weak-to-negligible BONCAT-based activity despite similar cell abundances -- suggestive of low activity on shorter timescales or dormancy. Together, these data challenge the interpretation of passively recorded microbiological signatures in seep sediment-hosted carbonate nodules and expand our understanding of how these endolithic communities may be actively shaped by past and present conditions. ImportanceThis study advances earlier investigations of microbial communities in buried seep carbonate nodules by integrating microbiological profiles of nodules and sediments, sediment geochemistry, single-cell activity measurements, and nodule mineral, geochemical, and physical characteristics within and below the sulfate-methane transition zone in deep-sea methane seeps. This approach allows us to view how nodule-hosted, endolithic microbial communities change relative to their surrounding sediments across multiple geochemical contexts and better understand how formation history and environmental conditions might affect community identity and metabolic function. Results indicate that the seep nodule and surrounding sediment communities are closely linked across diverse geochemical conditions. This connectivity between sediments and carbonate nodules is distinct from that observed in exhumed seep carbonates, with implications regarding how microbial community composition within these nodules are interpreted, suggesting that instead of a passive recorder of the communities at the time of formation, these nodules appear to retain diverse, metabolically viable communities.

microbiology↗

bioRxiv2023

LncRNA Bigheart trans-activates gene expression in a feed forward mechanism that facilitates calcineurin-NFAT signaling in myocardial hypertrophy

Terminally differentiated cardiomyocytes exhibit hypertrophy as a default response to injury by translating biomechanical stress into a complex network of intracellular signaling events. The molecular intricacies how calcium-dependent signaling engage molecular circuits and epigenetic modifications to activate deleterious gene programs remain enigmatic. Here we report on the re-activation of the evolutionarily conserved lncRNA "Bigheart", which is repressed in the postnatal myocardium and quickly re-activated in a calcineurin-NFAT-dependent fashion in the diseased myocardium in man and mouse. In line, AAV9-mediated overexpression of lncRNA Bigheart in otherwise healthy primary cardiomyocytes or mouse hearts suffices to drive maladapative hypertrophy. Conversely, mice receiving a "Gapmer" antisense oligonucleotide designed to specifically silence endogenous lncRNA Bigheart display resistance to biomechanical stress-induced myocardial remodeling, indicating its requirement in left ventricular hypertrophy. Mechanistically, lncRNA Bigheart recruits the RNA binding proteins hnRNP-F1 and HMGB1 to modulate the local chromatin environment and trans-activate Bigheart target genes including Rcan1 to stimulate calcineurin-NFAT coupling. Our observations confirm that human heart failure arises from specific susceptibilities in gene regulatory circuits that are amenable for therapeutic intervention using RNA-based therapeutics.

molecular biology↗

bioRxiv2023

ARF6 as a novel activator of HIF-2alpha in pulmonary arterial hypertension

ADP-ribosylation factor 6 (ARF6), a GTPase associated with cancer metastasis, is activated in the lung endothelium in pulmonary arterial hypertension (PAH). To identify ARF6-regulated pathways relevant to PAH, we performed a state-of-the-art proteomic analysis of human pulmonary artery endothelial cells (HPAECs) overexpressing the wildtype, constitutively active, fast-cycling and dominant negative mutants of ARF6. The analysis revealed a novel link of ARF6 with hypoxia-inducible factor (HIF), in addition to endocytotic vesicle trafficking, cell proliferation, angiogenesis, oxidative stress and lipid metabolism. Active ARF6 markedly increased expression and activity of HIF-2, critical in PAH, with HIF-1 relatively unaffected. Hypoxic ARF6 activation was a prerequisite for HIF-2 activation and HIF-dependent gene expression in HPAECs, PAH blood-derived late outgrowth endothelial colony forming cells (ECFCs) and hypoxic mouse lungs in vivo. A novel ARF6 inhibitor, chlortetracycline (CTC), reduced hypoxia-induced HIF-2 activation, proliferation and angiogenesis in HPAECs and reduced HIF-2 expression in lung and heart tissues of hypoxic mice. PAH ECFCs showed elevated expression and activity of ARF6 and HIF2, which was attenuated by CTC. Oral CTC attenuated development of PH in chronically hypoxic mice. In conclusion, we are first to demonstrate a key role of ARF6 in the regulation of HIF-2 activation in vitro and in vivo and show that HIF-2, a master-regulator of vascular remodelling in PAH, can be targeted by a clinically approved antibiotic chlortetracycline.

cell biology↗

bioRxiv2022

Integrative single-cell meta-analysis reveals disease-relevant vascular cell states and markers in human atherosclerosis

Coronary artery disease (CAD) and atherosclerosis are characterized by plaque formation in the arteries wall. CAD progression involves complex interactions and phenotypic plasticity within and between distinct vascular and immune cell lineages. Single-cell RNA-seq (scRNA-seq) studies have highlighted lineage-specific transcriptomic signatures, but the reported cell phenotypes in humans remain controversial. Here, we meta-analyzed four scRNA-seq datasets, creating the first map of human cell diversity in atherosclerosis. We generated an atlas of 118,578 high-quality cells, characterized cell-type diversity and provided insights into smooth muscle cell (SMC) phenotypic modulation, transcription factor activity and cell-cell communication. We integrated genome-wide association study (GWAS) data and uncovered a critical role for modulated SMC phenotypes in CAD and coronary calcification. Finally, we identified candidate markers of fibromyocyte and fibrochondrogenic human SMCs (LTBP1 and CRTAC1) that may serve as proxies of atherosclerosis progression. Altogether, we created a unified cellular map of atherosclerosis informing cell state-specific mechanistic and translational studies of cardiovascular diseases.

genomics↗

bioRxiv2022

Human blood vessel organoids reveal a critical role for CTGF in maintaining microvascular integrity

The microvasculature plays a key role in tissue perfusion, transport of mediators, and exchange of gases and metabolites to and from tissues. Microvascular dysfunction has emerged as an important contributor to cardiovascular diseases. In this study we used human blood vessel organoids (BVOs) as a model of the microvasculature to delineate the mechanisms of microvascular dysfunction caused by metabolic rewiring. BVOs fully recapitulated key features of the normal human microvasculature, including reliance of mature endothelial cells (ECs) on glycolytic metabolism, as concluded from metabolic flux assays using 13C-glucose labelling and mass spectrometry-based metabolomics. Treatment of BVOs with PFK15, a pharmacological inhibitor of glycolysis, resulted in rapid tissue restructuring, vessel regression with reduced pericyte coverage and alterations in tight junction morphology. Proteomic analysis of the BVO secretome revealed remodelling of the extracellular matrix and differential expression of paracrine mediators such as CTGF. Treatment with recombinant CTGF recovered tight junction formation and increased pericyte coverage in microvessels. Our metabolic and proteomics findings demonstrate that BVOs rapidly undergo restructuring in response to metabolic changes and identify CTGF as a critical paracrine regulator of microvascular integrity.

cell biology↗

bioRxiv2021

Temporal in vivo platelet labelling in mice reveals age-dependent receptor expression and conservation of specific mRNAs

The proportion of young platelets, also known as newly formed or reticulated, within the overall platelet population has been clinically correlated with adverse cardiovascular outcomes. Our understanding of this is incomplete, however, because of limitations in the technical approaches available to study platelets of different ages. In this study we have developed and validated an in vivo temporal labelling approach using injectable fluorescent anti-platelet antibodies to sub-divide platelets by age and assess differences in functional and molecular characteristics. With this approach we found that young platelets (<24h old) in comparison to older platelets respond to stimuli with greater calcium flux and degranulation, and contribute more to the formation of thrombi in vitro and in vivo. Sequential sampling confirmed this altered functionality to be independent of platelet size with no size differences or changes relative to the global population seen at any age. The age associated decrease in thrombotic function was accompanied by significant decreases in the surface expression of GPVI and CD31 (PECAM-1) and an increase in CD9. Platelet mRNA content also decreased with age but at different rates for individual mRNAs indicating apparent conservation of those encoding granule proteins. Our pulse-chase type approach to define circulating platelet age has allowed timely re-examination of commonly held beliefs regarding size and reactivity of young platelets whilst providing novel insights into the temporal regulation of receptor and protein expression. Overall, future application of this validated tool will inform on age-based platelet heterogeneity in physiology and disease.

physiology↗

bioRxiv2021

Proteome and functional decline as platelets age in the circulation

Anucleate platelets circulate in the blood of healthy individuals for approximately 7-10 days during which time their protein composition may change. We hypothesized such changes would be linked to altered structure and function. Here, we separated platelets of different ages based on mRNA content and characterised them using proteomics, immunofluorescence and functional assays. Total protein content was 45{+/-}5% (n=4) lower in old platelets compared to young platelets. Predictive proteomic pathway analysis identified associations with 28 biological processes, notably increased haemostasis in young platelets and apoptosis in old platelets. Further studies confirmed platelet ageing was linked to a reduction decrease in cytoskeletal proteins, a reduction in mitochondria number, and lower calcium dynamics and granule secretion. This work delineates physical and functional changes in platelets as they age and serves as a base to examine differences associated with altered mean age of platelet populations in conditions such as immune thrombocytopenia and diabetes.

cell biology↗

bioRxiv2020

Structural Insights on Fusion Mechanisms of Extracellular Vesicles with Model Plasma Membrane

Extracellular vesicles (EVs) represent a potent intercellular communication system. Within a lipid bilayer such small vesicles transport biomolecules between cells and throughout the body, strongly influencing the fate of recipient cells. Due to their specific biological functions they have been proposed as biomarkers for various diseases and as optimal candidates for therapeutic applications. Despite of their extreme biological relevance, the small size (30 to a few hundred nanometers in diameter) of EVs still poses a great challenge for their isolation, quantification and biophysical/biochemical characterization, therefore the complex network of EVs and cells as well as their interaction remains to be further revealed. Here we propose a multiscale platform based on Atomic Force Microscopy, Small Angle X-ray Scattering, Small Angle Neutron Scattering and Neutron Reflectometry to reveal structure-function correlations of purified EVs through the analysis of their interaction with model membrane systems, in form of both supported lipid bilayers and suspended unilamellar vesicles of variably complex composition. The analysis reveals a strong interaction of EVs with the model membranes and preferentially with liquid ordered raft-like lipid domains, and opens the way to understand uptake mechanisms in different vesicle to cell membrane relative compositions.

biophysics↗

bioRxiv2018

Hypoxia-induced epigenetic silencing of polo-like kinase 2 promotes fibrosis in atrial fibrillation

Fibrosis and inflammation promote atrial fibrillation (AF) and worsen its clinical outcome. The underlying molecular mechanisms, that are relevant for effective antifibrotic drug development, are still under debate. This study deciphers a novel mechanistic interplay between polo-like kinase 2 (PLK2) and the pro-inflammatory cytokine osteopontin (OPN) in the pathogenesis of atrial fibrosis. Compared to sinus rhythm (SR) controls, right atrial appendages and isolated right atrial fibroblasts from AF patients showed downregulation of PLK2 mRNA and protein levels, which were accompanied by remarkable hypoxia-sensitive DNA-methylation of the PLK2 promotor. In an experimental setting, both, genetic deletion and pharmacological inhibition of PLK2 induced myofibroblast differentiation and reduced fibroblast proliferation. Notably, proteomics from PLK2-deleted fibroblasts revealed de novo secretion of OPN. Accordingly, we observed higher OPN plasma levels in AF patients with atrial fibrosis compared to non-fibrosis AF patients. Hence, we provide evidence for PLK2 reactivation and/or OPN inhibition as potential novel targets to prevent fibrosis progression in AF.

pharmacology and toxicology↗