Rationale:
Activated cardiac fibroblasts (CF) are crucial players in the cardiac damage response; excess fibrosis, however, may result in myocardial stiffening and heart failure development. Inhibition of activated CF has been suggested as a therapeutic strategy in cardiac disease, but whether this truly improves cardiac function is unclear.
Objective:
To study the effect of CF ablation on cardiac remodeling.
Methods and Results:
We characterized subgroups of murine CF by single-cell expression analysis and identified periostin as the marker showing the highest correlation to an activated CF phenotype. We generated bacterial artificial chromosome–transgenic mice allowing tamoxifen-inducible Cre expression in periostin-positive cells as well as their diphtheria toxin-mediated ablation. In the healthy heart, periostin expression was restricted to valvular fibroblasts; ablation of this population did not affect cardiac function. After chronic angiotensin II exposure, ablation of activated CF resulted in significantly reduced cardiac fibrosis and improved cardiac function. After myocardial infarction, ablation of periostin-expressing CF resulted in reduced fibrosis without compromising scar stability, and cardiac function was significantly improved. Single-cell transcriptional analysis revealed reduced CF activation but increased expression of prohypertrophic factors in cardiac macrophages and cardiomyocytes, resulting in localized cardiomyocyte hypertrophy.
Conclusions:
Modulation of the activated CF population is a promising approach to prevent adverse cardiac remodeling in response to angiotensin II and after myocardial infarction.
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.
Higher severity of CHF is associated with reduced levels of LXs. Plasma LXA4 appears to be a valuable marker for risk stratification in CHF. Furthermore, the ASA-related increase in urinary 15-epi-LXA4 suggests enhanced renal synthesis of this eicosanoid and may represent a disregarded benefit of ASA.
Background:
G protein–coupled receptors are important regulators of contractility and differentiation in vascular smooth muscle cells (SMCs), but the specific function of SMC-expressed orphan G protein–coupled receptor class C group 5 member B (GPRC5B) is unclear.
Methods:
We studied the role of GPRC5B in the regulation of contractility and dedifferentiation in human and murine SMCs in vitro and in iSM-
Gprc5b
-KO (tamoxifen-inducible, SMC-specific knockout) mice under conditions of arterial hypertension and atherosclerosis in vivo.
Results:
Mesenteric arteries from SMC-specific
Gprc5b
-KOs showed ex vivo significantly enhanced prostacyclin receptor (IP)–dependent relaxation, whereas responses to other relaxant or contractile factors were normal. In vitro, knockdown of GPRC5B in human aortic SMCs resulted in increased IP-dependent cAMP production and consecutive facilitation of SMC relaxation. In line with this facilitation of IP-mediated relaxation, iSM-
Gprc5b
-KO mice were protected from arterial hypertension, and this protective effect was abrogated by IP antagonists. Mechanistically, we show that knockdown of GPRC5B increased the membrane localization of IP both in vitro and in vivo and that GPRC5B, but not other G protein–coupled receptors, physically interacts with IP. Last, we show that enhanced IP signaling in GPRC5B-deficient SMCs not only facilitates relaxation but also prevents dedifferentiation during atherosclerosis development, resulting in reduced plaque load and increased differentiation of SMCs in the fibrous cap.
Conclusions:
Taken together, our data show that GPRC5B regulates vascular SMC tone and differentiation by negatively regulating IP signaling.
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