Skewed X-inactivation is common in the general female population

X-inactivation is a well-established dosage compensation mechanism ensuring that X-chromosomal genes are expressed at comparable levels in males and females. Skewed X-inactivation is often explained by negative selection of one of the alleles. We demonstrate that imbalanced expression of the paternal and maternal X-chromosomes is common in the general population and that the random nature of the X-inactivation mechanism can be sufficient to explain the imbalance. To this end, we analyzed blood-derived RNA and whole-genome sequencing data from 79 female children and their parents from the Genome of the Netherlands project. We calculated the median ratio of the paternal over total counts at all X-chromosomal heterozygous single-nucleotide variants with coverage ≥10. We identified two individuals where the same X-chromosome was inactivated in all cells. Imbalanced expression of the two X-chromosomes (ratios ≤0.35 or ≥0.65) was observed in nearly 50% of the population. The empirically observed skewing is explained by a theoretical model where X-inactivation takes place in an embryonic stage in which eight cells give rise to the hematopoietic compartment. Genes escaping X-inactivation are expressed from both alleles and therefore demonstrate less skewing than inactivated genes. Using this characteristic, we identified three novel escapee genes (SSR4, REPS2, and SEPT6), but did not find support for many previously reported escapee genes in blood. Our collective data suggest that skewed X-inactivation is common in the general population. This may contribute to manifestation of symptoms in carriers of recessive X-linked disorders. We recommend that X-inactivation results should not be used lightly in the interpretation of X-linked variants

Functional Screening Identifies MicroRNAs as Multi-Cellular Regulators of Heart Failure

Heart failure (HF) is the leading cause of death in the Western world. Pathophysiological processes underlying HF development, including cardiac hypertrophy, fibrosis and inflammation, are controlled by specific microRNAs (miRNAs). Whereas most studies investigate miRNA function in one particular cardiac cell type, their multicellular function is poorly investigated. The present study probed 194 miRNAs -differentially expressed in cardiac inflammatory disease - for regulating cardiomyocyte size, cardiac fibroblasts collagen content, and macrophage polarization. Of the tested miRNAs, 13%, 26%, and 41% modulated cardiomyocyte size, fibroblast collagen production, and macrophage polarization, respectively. Seventeen miRNAs affected all three cellular processes, including miRNAs with established (miR-210) and unknown roles in cardiac pathophysiology (miR-145-3p). These miRNAs with a multi-cellular function commonly target various genes. In-depth analysis in vitro of previously unstudied miRNAs revealed that the observed phenotypical alterations concurred with changes in transcript and protein levels of hypertrophy-, fibrosis- and inflammation-related genes. MiR-145-3p and miR-891a-3p were identified to regulate the fibrotic response, whereas miR-223-3p, miR-486-3p, and miR-488-5p modulated macrophage activation and polarisation. In conclusion, miRNAs are multi-cellular regulators of different cellular processes underlying cardiac disease. We identified previously undescribed roles of miRNAs in hypertrophy, fibrosis, and inflammation, and attribute new cellular effects to various well-known miRNAs.status: publishe

Macrophage MicroRNA-155 Promotes Cardiac Hypertrophy and Failure

BACKGROUND: Cardiac hypertrophy and subsequent heart failure triggered by chronic hypertension represent major challenges for cardiovascular research. Beyond neurohormonal and myocyte signaling pathways, growing evidence suggests inflammatory signaling pathways as therapeutically targetable contributors to this process. We recently reported that microRNA-155 is a key mediator of cardiac inflammation and injury in infectious myocarditis. Here, we investigated the impact of microRNA-155 manipulation in hypertensive heart disease. METHODS AND RESULTS: Genetic loss or pharmacological inhibition of the leukocyte-expressed microRNA-155 in mice markedly reduced cardiac inflammation, hypertrophy, and dysfunction on pressure overload. These alterations were macrophage dependent because in vivo cardiomyocyte-specific microRNA-155 manipulation did not affect cardiac hypertrophy or dysfunction, whereas bone marrow transplantation from wild-type mice into microRNA-155 knockout animals rescued the hypertrophic response of the cardiomyocytes and vice versa. In vitro, media from microRNA-155 knockout macrophages blocked the hypertrophic growth of stimulated cardiomyocytes, confirming that macrophages influence myocyte growth in a microRNA-155-dependent paracrine manner. These effects were at least partly mediated by the direct microRNA-155 target suppressor of cytokine signaling 1 (Socs1) because Socs1 knockdown in microRNA-155 knockout macrophages largely restored their hypertrophy-stimulating potency. CONCLUSIONS: Our findings reveal that microRNA-155 expression in macrophages promotes cardiac inflammation, hypertrophy, and failure in response to pressure overload. These data support the causative significance of inflammatory signaling in hypertrophic heart disease and demonstrate the feasibility of therapeutic microRNA targeting of inflammation in heart failure.status: publishe