Cell shape determines gene expression: cardiomyocyte morphotypic transcriptomes.

Cardiomyocytes undergo considerable changes in cell shape. These can be due to hemodynamic constraints, including changes in preload and afterload conditions, or to mutations in genes important for cardiac function. These changes instigate significant changes in cellular architecture and lead to the addition of sarcomeres, at the same time or at a later stage. However, it is currently unknown whether changes in cell shape on their own affect gene expression and the aim of this study was to fill that gap in our knowledge. We developed a single-cell morphotyping strategy, followed by single-cell RNA sequencing, to determine the effects of altered cell shape in gene expression. This enabled us to profile the transcriptomes of individual cardiomyocytes of defined geometrical morphotypes and characterize them as either normal or pathological conditions. We observed that deviations from normal cell shapes were associated with significant downregulation of gene expression and deactivation of specific pathways, like oxidative phosphorylation, protein kinase A, and cardiac beta-adrenergic signaling pathways. In addition, we observed that genes involved in apoptosis of cardiomyocytes and necrosis were upregulated in square-like pathological shapes. Mechano-sensory pathways, including integrin and Src kinase mediated signaling, appear to be involved in the regulation of shape-dependent gene expression. Our study demonstrates that cell shape per se affects the regulation of the transcriptome in cardiac myocytes, an effect with possible implications for cardiovascular disease.

Network analysis reveals a causal role of mitochondrial gene activity in atherosclerotic lesion formation.

BACKGROUND AND AIMS: Mitochondrial damage and augmented production of reactive oxygen species (ROS) may represent an intermediate step by which hypercholesterolemia exacerbates atherosclerotic lesion formation. METHODS: To test this hypothesis, in mice with severe but genetically reversible hypercholesterolemia (i.e. the so called Reversa mouse model), we performed time-resolved analyses of mitochondrial transcriptome in the aortic arch employing a systems-level network approach. RESULTS: During hypercholesterolemia, we observed a massive down-regulation (>28%) of mitochondrial genes, specifically at the time of rapid atherosclerotic lesion expansion and foam cell formation, i.e. between 30 and 40 weeks of age. Both phenomena - down-regulation of mitochondrial genes and lesion expansion - were largely reversible by genetically lowering plasma cholesterol (by >80%, from 427 to 54 ± 31 mg/L) at 30 weeks. Co-expression network analysis revealed that both mitochondrial signature genes were highly connected in two modules, negatively correlating with lesion size and supported as causal for coronary artery disease (CAD) in humans, as expression-associated single nucleotide polymorphisms (eSNPs) representing their genes overlapped markedly with established disease risk loci. Within these modules, we identified the transcription factor estrogen related receptor (ERR)-α and its co-factors PGC1-α and -ß, i.e. two members of the peroxisome proliferator-activated receptor γ co-activator 1 family of transcription regulators, as key regulatory genes. Together, these factors are known as major orchestrators of mitochondrial biogenesis and antioxidant responses. CONCLUSIONS: Using a network approach, we demonstrate how hypercholesterolemia could hamper mitochondrial activity during atherosclerosis progression and pinpoint potential therapeutic targets to counteract these processes.

Poliovirus Receptor-Related 2: A Cholesterol-Responsive Gene Affecting Atherosclerosis Development by Modulating Leukocyte Migration.

OBJECTIVE: Recently, poliovirus receptor-related 2 (Pvrl2) emerged as a top gene in a global gene expression study aiming to detect plasma cholesterol-responsive genes causally related to atherosclerosis regression in hypercholesterolemic mice. PVRL2 is an adherens junction protein implied to play a role in transendothelial migration of leukocytes, a key feature in atherosclerosis development. In this study, we investigated the effect of Pvrl2 deficiency on atherosclerosis development and transendothelial migration of leukocytes activity. APPROACH AND RESULTS: Pvrl2-deficient mice bred onto an atherosclerosis-prone background (Pvrl2-/-Ldlr-/-Apob100/100) had less atherosclerotic lesions and more stable plaques compared with littermate controls (Pvrl2+/+Ldlr-/-Apob100/100). Pvrl2-/-Ldlr-/-Apob100/100 mice also showed a 49% decrease in transendothelial migration of leukocytes activity observed using the in vivo air pouch model. In accordance, augmented arterial wall expression of Pvrl2 during atherosclerosis progression coincided with an increased gene expression of migrating leukocytes into the vessel wall. Both in human and mice, gene and protein expression of PVRL2 was predominantly observed in the vascular endothelium according to the immunohistochemical and gene expression data. In addition, the cholesterol responsiveness of PVRL2 was also observed in humans. CONCLUSIONS: PVRL2 is a plasma cholesterol-responsive gene acting at endothelial sites of vascular inflammation that could potentially be a new therapeutic target for atherosclerosis prevention through its suggested transendothelial migration of leukocytes modulating activity.