Circulation research最新文献

Background: FHF (fibroblast growth factor homologous factor) variants associate with arrhythmias. Although FHFs are best characterized as regulators of voltage-gated sodium channel (VGSC) gating, recent studies suggest broader, non-VGSC-related functions, including regulation of Cx43 (connexin 43) gap junctions and hemichannels, mechanisms that have generally been understudied or disregarded.

Methods: We assessed cardiac conduction and cardiomyocyte action potentials in mice with constitutive cardiac-specific Fgf13 ablation (cFgf13^KO) while targeting Cx43 gap junctions and hemichannels pharmacologically. We characterized FGF13 regulation of Cx43 abundance and subcellular distribution. With proximity labeling proteomics, we investigated novel candidate mechanisms underlying FGF13 regulation of Cx43.

Results: FGF13 ablation prolonged the QRS and QT intervals. Carbenoxolone, a Cx43 gap junction uncoupler, markedly prolonged the QRS duration, leading to conduction system block in cFgf13^KO but not in wild-type mice. Optical mapping revealed markedly decreased conduction velocity during ventricular pacing. Microscopy revealed perturbed trafficking of Cx43, reduced localization in the intercalated disc, and suggested decreased membrane Cx43 but increased Cx43 hemichannels in cardiomyocytes from cFgf13^KO mice. Resting membrane potential was depolarized, and action potential duration at 50% repolarization was prolonged in cFgf13^KO cardiomyocytes. Both were restored toward wild-type values with Gap19 (a Cx43 hemichannel inhibitor), expression of FGF13, or expression of a mutant FGF13 incapable of binding to VGSCs, emphasizing VGSC-independent regulation by FGF13. To assess the functional impact of resting membrane potential depolarization, hearts were subjected to hypokalemia, which had no effect in wild-type hearts but fully rescued conduction velocity in cFgf13^KO hearts. Proteomic analyses revealed candidate roles for FGF13 in the regulation of vesicular-mediated transport. FGF13 ablation destabilized microtubules and reduced the expression of tubulins and MAP4, the major cardiac microtubule regulator.

Conclusions: FGF13 regulates microtubule-dependent trafficking and targeting of Cx43 and impacts cardiac impulse propagation via VGSC-independent mechanisms.

Background: Separation of the pulmonic and systemic circulation is essential for terrestrial life, and mammals have evolved distinct cardiac chambers with specialized structures and functions. Transcriptomics profiling revealed cellular heterogeneity between heart chambers. However, the mechanisms underlying chamber-specific transcriptomic and metabolic differences-and their functional significance-remain poorly understood. The Hippo/YAP (yes-associated protein) pathway is a conserved signaling network that regulates diverse cellular processes. The Hippo kinases inhibit YAP in cardiac fibroblasts (CF) to restrict fibrosis and inflammation. Nonetheless, how YAP regulates the metabolic microenvironment during homeostasis and fibroinflammation remains unclear.

Methods: We investigated YAP and glycolysis activity in the 4 cardiac chambers by scoring the expression of YAP target genes and glycolysis genes in human single-nucleus RNA sequencing data. To compare glucose uptake between the left and right atria, we measured isotope-labeled glucose uptake in isolated mouse atria. To study the role of YAP in CFs, we inactivated the Hippo kinases, Lats1 and Lats2, in mouse CFs and performed metabolic studies, snRNA-seq, single-nucleus assay for transposase-accessible chromatin with sequencing, and spatial transcriptomics.

Results: Metabolic and sequencing approaches revealed that Hippo-deficient CFs activated glycolysis to promote fibroinflammation. Inhibition of glycolysis or lactate production suppressed Hippo-deficient CF-induced fibrosis. Elevated YAP activity disrupted fibroblast lineage fidelity by inducing an osteochondroprogenitor cell state. Blocking macrophage expansion pharmacologically reduced Hippo-deficient CF proliferation and fibrosis. Sequencing and functional studies showed that macrophages secreted IGF1 (insulin-like growth factor 1) to activate IGF1 signaling in Hippo-deficient CFs to increase cell proliferation and fibrosis.

Conclusions: We discovered that right atrial CFs are more glycolytic and have higher YAP activity than CFs in other heart chambers. YAP activation in CFs induces glycolysis to drive fibrosis. YAP disrupts fibroblast lineage fidelity, driving them to a SOX9 (SRY-box transcription factor 9)-expressing osteochondroprogenitor cell state. Mechanistically, YAP activates the secretion of CSF1 (colony-stimulating factor 1) to promote macrophage expansion. Blocking macrophage expansion reduces Hippo-deficient CF proliferation, osteochondroprogenitor differentiation, and fibrosis, revealing that macrophages signal reciprocally to regulate CF cell states. Genomic and functional studies revealed that the upregulated IGF1 receptor in Hippo-deficient CFs enables them to receive macrophage-secreted IGF1, thereby further enhancing CF proliferation and fibrosis.

Background: Peripheral artery disease is a severe ischemic vascular pathology without effective pharmacological approaches and improving angiogenesis to recover blood perfusion is a promising therapeutic strategy. Endothelial cells are the primary cell type contributing to angiogenesis in response to ischemia. However, the molecular mechanisms regulating ischemia-induced angiogenesis remain elusive.

Methods: We used a discovery-driven approach to identify elevated SRSF1 (serine/arginine splicing factor 1) expression in endothelial cells after ischemia. We used loss- and gain-of-function approaches to explore the role of SRSF1 in angiogenesis both in vivo and in vitro. A mouse model of hindlimb ischemia was used to evaluate ischemia-induced angiogenesis. We also investigated the mechanisms through transcriptome, enhanced crosslinking and immunoprecipitation sequencing, RNA pull-down, and chromatin immunoprecipitation-quantitative polymerase chain reaction analysis.

Results: Proteomic analyses identified endogenous SRSF1 accumulated in endothelial cells of the ischemic muscle and responded to hypoxia. Mice deficient in endothelial SRSF1 exhibited impaired blood flow recovery and impaired vasculature formation after hindlimb ischemia. Importantly, overexpression of SRSF1 enhanced blood flow recovery and angiogenesis after hindlimb ischemia. SRSF1 overexpression enhanced the angiogenic functions of human endothelial cells, promoting tube formation, sprouting capability, and cell migration, while SRSF1 knockdown suppressed these functions. Mechanistically, SRSF1 modulated the alternative splicing of ATF3 (activating transcription factor 3) by directly binding to ATF3 pre-mRNA (precursor messenger RNA), and SRSF1 overexpression elevated full-length ATF3 transcript at the expense of truncated ATF3Δzip2 transcript. ATF3 then bound directly to the KLF2 (Krüppel-like factor 2) promoter, suppressed KLF2 expression and downstream S1PR1 (sphingosine-1-phosphate receptor 1) signaling. Through upregulation of full-length ATF3 and downregulating KLF2-S1PR1 signaling, SRSF1 promoted endothelial tube formation and angiogenesis. In addition, alprostadil, the prostaglandin E1 analog, could activate the SRSF1 signaling to improve endothelial angiogenesis in vitro and in vivo.

Conclusions: Our findings identified SRSF1 as a novel regulator of ischemia-induced angiogenesis that enhances endothelial angiogenic functions by regulating the ATF3-KLF2-S1PR1 pathway. These results suggest that modulation of endothelial SRSF1 may represent a promising therapeutic approach for treating ischemic vascular diseases.