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Anaphylactic shock is a severe allergic reaction involving multiple organs including the bronchial and cardiovascular system. Most anaphylactic mediators, like platelet-activating factor (PAF), histamine, and others, act through G protein – coupled receptors, which are linked to the heterotrimeric G proteins Gq /G 11 , G12/G13 , and Gi . The role of downstream signaling pathways activated by anaphylactic mediators in defi ned organs during anaphylactic reactions is largely unknown. Using genetic mouse models that allow for the conditional abrogation of G q /G 11 - and G 12 /G 13 -mediated signaling pathways by inducible Cre/loxP-mediated mutagenesis in endothelial cells (ECs), we show that Gq /G11 -mediated signaling in ECs is required for the opening of the endothelial barrier and the stimulation of nitric oxide formation by various infl ammatory mediators as well as by local anaphylaxis. The systemic effects of anaphylactic mediators like histamine and PAF, but not of bacterial lipopolysaccharide (LPS), are blunted in mice with endothelial G alpha q/G alpha 11 deficiency. Mice with endothelium-specific G alpha q /G alpha 11 deficiency, but not with G alpha 12/G alpha 13 deficiency, are protected against the fatal consequences of passive and active systemic anaphylaxis. This identifies endothelial Gq/G11 -mediated signaling as a critical mediator of fatal systemic anaphylaxis and, hence, as a potential new target to prevent or treat anaphylactic reactions.
Background and aims: Despite the clinical importance of atherosclerosis, the origin of cells within atherosclerotic plaques is not fully understood. Due to the lack of a definitive lineage-tracing strategy, previous studies have provided controversial results about the origin of cells expressing smooth muscle and macrophage markers in atherosclerosis. We here aim to identify the origin of vascular smooth muscle (SM) cells and macrophages within atherosclerosis lesions.
Methods: We combined a genetic fate mapping approach with single cell expression analysis in a murine model of atherosclerosis.
Results: We found that 16% of CD68-positive plaque macrophage-like cells were derived from mature SM cells and not from myeloid sources, whereas 31% of αSMA-positive smooth muscle-like cells in plaques were not SM-derived. Further analysis at the single cell level showed that SM-derived CD68+ cells expressed higher levels of inflammatory markers such as cyclooxygenase 2 (Ptgs2, p = 0.02), and vascular cell adhesion molecule (Vcam1, p = 0.05), as well as increased mRNA levels of genes related to matrix synthesis such as Col1a2 (p = 0.01) and Fn1 (p = 0.04), than non SM-derived CD68+ cells.
Conclusions: These results demonstrate that smooth muscle cells within atherosclerotic lesions can switch to a macrophage-like phenotype characterized by higher expression of inflammatory and synthetic markers genes that may further contribute to plaque progression.
The mouse bitter taste receptors Tas2r143, Tas2r135, and Tas2r126 are encoded by genes that cluster on chromosome 6 and have been suggested to be expressed under common regulatory elements. Previous studies indicated that the Tas2r143/Tas2r135/Tas2r126 cluster is expressed in the heart, but other organs had not been systematically analyzed. In order to investigate the expression of this bitter taste receptor gene cluster in non-gustatory tissues, we generated a BAC (bacterial artificial chromosome) based transgenic mouse line, expressing CreERT2 under the control of the Tas2r143 promoter. After crossing this line with a mouse line expressing EGFP after Cre-mediated recombination, we were able to validate the Tas2r143-CreERT2 transgenic mouse line and monitor the expression of Tas2r143. EGFP-positive cells, indicating expression of members of the cluster, were found in about 47% of taste buds, and could also be found in several other organs. A population of EGFP-positive cells was identified in thymic epithelial cells, in the lamina propria of the intestine and in vascular smooth muscle cells of cardiac blood vessels. EGFP-positive cells were also identified in the epithelium of organs readily exposed to pathogens including lower airways, the gastrointestinal tract, urethra, vagina, and cervix. With respect to the function of cells expressing this bitter taste receptor cluster, RNA-seq analysis in EGFP-positive cells isolated from the epithelium of trachea and stomach showed expression of genes related to innate immunity. These data further support the concept that bitter taste receptors serve functions outside the gustatory system.
G-protein-coupled receptor (GPCR) expression is extensively studied in bulk cDNA, but heterogeneity and functional patterning of GPCR expression in individual vascular cells is poorly understood. Here, we perform a microfluidic-based single-cell GPCR expression analysis in primary smooth muscle cells (SMC) and endothelial cells (EC). GPCR expression is highly heterogeneous in all cell types, which is confirmed in reporter mice, on the protein level and in human cells. Inflammatory activation in murine models of sepsis or atherosclerosis results in characteristic changes in the GPCR repertoire, and we identify functionally relevant subgroups of cells that are characterized by specific GPCR patterns. We further show that dedifferentiating SMC upregulate GPCRs such as Gpr39, Gprc5b, Gprc5c or Gpr124, and that selective targeting of Gprc5b modulates their differentiation state. Taken together, single-cell profiling identifies receptors expressed on pathologically relevant subpopulations and provides a basis for the development of new therapeutic strategies in vascular diseases.
Myogenic vasoconstriction is an autoregulatory function of small arteries. Recently, G-protein-coupled receptors have been involved in myogenic vasoconstriction, but the downstream signalling mechanisms and the in-vivo-function of this myogenic autoregulation are poorly understood. Here, we show that small arteries from mice with smooth muscle-specific loss of G12/G13 or the Rho guanine nucleotide exchange factor ARHGEF12 have lost myogenic vasoconstriction. This defect was accompanied by loss of RhoA activation, while vessels showed normal increases in intracellular [Ca2+]. In the absence of myogenic vasoconstriction, perfusion of peripheral organs was increased, systemic vascular resistance was reduced and cardiac output and left ventricular mass were increased. In addition, animals with defective myogenic vasoconstriction showed aggravated hypotension in response to endotoxin. We conclude that G12/G13- and Rho-mediated signaling plays a key role in myogenic vasoconstriction and that myogenic tone is required to maintain local and systemic vascular resistance under physiological and pathological condition.
