Aortic carboxypeptidase-like protein regulates vascular adventitial progenitor and fibroblast differentiation through myocardin related transcription factor A

Early Injury Landscape in Vein Harvest by Single-Cell and Spatial Transcriptomics

BACKGROUND

Vein graft failure following cardiovascular bypass surgery results in significant patient morbidity and cost to the healthcare system. Vein graft injury can occur during autogenous vein harvest and preparation, as well as after implantation into the arterial system, leading to the development of intimal hyperplasia, vein graft stenosis, and, ultimately, bypass graft failure. Although previous studies have identified maladaptive pathways that occur shortly after implantation, the specific signaling pathways that occur during vein graft preparation are not well defined and may result in a cumulative impact on vein graft failure. We, therefore, aimed to elucidate the response of the vein conduit wall during harvest and following implantation, probing the key maladaptive pathways driving graft failure with the overarching goal of identifying therapeutic targets for biologic intervention to minimize these natural responses to surgical vein graft injury.

METHODS

Employing a novel approach to investigating vascular pathologies, we harnessed both single-nuclei RNA-sequencing and spatial transcriptomics analyses to profile the genomic effects of vein grafts after harvest and distension, then compared these findings to vein grafts obtained 24 hours after carotid-carotid vein bypass implantation in a canine model (n=4).

RESULTS

Spatial transcriptomic analysis of canine cephalic vein after initial conduit harvest and distention revealed significant enrichment of pathways (P<0.05) involved in the activation of endothelial cells (ECs), fibroblasts, and vascular smooth muscle cells, namely pathways responsible for cellular proliferation and migration and platelet activation across the intimal and medial layers, cytokine signaling within the adventitial layer, and ECM (extracellular matrix) remodeling throughout the vein wall. Subsequent single-nuclei RNA-sequencing analysis supported these findings and further unveiled distinct EC and fibroblast subpopulations with significant upregulation (P<0.05) of markers related to endothelial injury response and cellular activation of ECs, fibroblasts, and vascular smooth muscle cells. Similarly, in vein grafts obtained 24 hours after arterial bypass, there was an increase in myeloid cell, protomyofibroblast, injury response EC, and mesenchymal-transitioning EC subpopulations with a concomitant decrease in homeostatic ECs and fibroblasts. Among these markers were genes previously implicated in vein graft injury, including VCAN, FBN1, and VEGFC, in addition to novel genes of interest, such as GLIS3 and EPHA3. These genes were further noted to be driving the expression of genes implicated in vascular remodeling and graft failure, such as IL-6, TGFBR1, SMAD4, and ADAMTS9. By integrating the spatial transcriptomics and single-nuclei RNA-sequencing data sets, we highlighted the spatial architecture of the vein graft following distension, wherein activated and mesenchymal-transitioning ECs, myeloid cells, and fibroblasts were notably enriched in the intima and media of distended veins. Finally, intercellular communication network analysis unveiled the critical roles of activated ECs, mesenchymal-transitioning ECs, protomyofibroblasts, and vascular smooth muscle cells in upregulating signaling pathways associated with cellular proliferation (MDK [midkine], PDGF [platelet-derived growth factor], VEGF [vascular endothelial growth factor]), transdifferentiation (Notch), migration (ephrin, semaphorin), ECM remodeling (collagen, laminin, fibronectin), and inflammation (thrombospondin), following distension.

CONCLUSIONS

Vein conduit harvest and distension elicit a prompt genomic response facilitated by distinct cellular subpopulations heterogeneously distributed throughout the vein wall. This response was found to be further exacerbated following vein graft implantation, resulting in a cascade of maladaptive gene regulatory networks. Together, these results suggest that distension initiates the upregulation of pathological pathways that may ultimately contribute to bypass graft failure and presents potential early targets warranting investigation for targeted therapies. This work highlights the first applications of single-nuclei and spatial transcriptomic analyses to investigate venous pathologies, underscoring the utility of these methodologies and providing a foundation for future investigations.

Inference of cell type-specific gene regulatory networks on cell lineages from single cell omic datasets

Cell type-specific gene expression patterns are outputs of transcriptional gene regulatory networks (GRNs) that connect transcription factors and signaling proteins to target genes. Single-cell technologies such as single cell RNA-sequencing (scRNA-seq) and single cell Assay for Transposase-Accessible Chromatin using sequencing (scATAC-seq), can examine cell-type specific gene regulation at unprecedented detail. However, current approaches to infer cell type-specific GRNs are limited in their ability to integrate scRNA-seq and scATAC-seq measurements and to model network dynamics on a cell lineage. To address this challenge, we have developed single-cell Multi-Task Network Inference (scMTNI), a multi-task learning framework to infer the GRN for each cell type on a lineage from scRNA-seq and scATAC-seq data. Using simulated and real datasets, we show that scMTNI is a broadly applicable framework for linear and branching lineages that accurately infers GRN dynamics and identifies key regulators of fate transitions for diverse processes such as cellular reprogramming and differentiation.

Aqueous extract of Salvia miltiorrhiza Bunge reduces blood pressure through inhibiting oxidative stress, inflammation and fibrosis of adventitia in primary hypertension

Background: Hypertension is a major risk factor for cardiovascular diseases and the leading cause of mortality worldwide. Despite the availability of antihypertensive drugs, alternative treatments are needed due to the adverse events associated with their use. Previous studies have shown that SABP, a combination of aqueous active metabolites of Salvia Miltiorrhiza Bunge DSS, Sal-A, Sal-B and PAL, has a significant antihypertensive effect. However, the underlying mechanisms remain unknown. Objective: This study aimed to determine the effects of SABP on vascular inflammation, oxidative stress, and vascular remodeling in spontaneously hypertensive rats (SHRs). Additionally, the response of adventitial fibroblasts in SHRs to SABP treatment was also studied, including their proliferation, differentiation, and migration. Methods: SABP or perindopril (positive control) were administered intraperitoneally to SHRs, and systolic blood pressure was measured using a tail-cuff approach. The effects of SABP on oxidative stress, inflammation, and vascular remodeling were investigated by transmission electron microscopy, histochemical staining, and Western blot. Adventitial fibroblasts were isolated and cultured from the adventitia of thoracic aorta in SHR and WKY rats. CCK8 assay, wound healing method and immunostaining were used to observe the effect of SABP on fibroblasts proliferation, migration and transformation into myofibroblasts. Moreover, Western blot analysis was also performed to detect the proteins related to oxidative stress, inflammation and fibrosis in adventitial fibroblasts. Results: SHRs displayed higher blood pressure with significant vascular remodeling compared to WKY rats. The thoracic aorta and adventitial fibroblasts of SHRs exhibited significant oxidative stress, inflammation and fibrosis. SABP treatment repressed oxidative stress, inflammatory reaction and vascular remodeling of thoracic aorta in SHR through the ROS/TLR4/NF-κB signaling pathway, and inhibited fibrosis of thoracic aorta. Additionally, SABP inhibited the proliferation and migration of adventitial fibroblasts and their transformation to myofibroblasts in vitro through the TGFβ/Smad3 signaling pathway. Conclusion: These findings suggest that SABP have potential as an alternative treatment for hypertension by ameliorating oxidative stress, inflammation and fibrosis. Further research is needed to fully understand the mechanisms underlying the effects of SABP.

How vascular smooth muscle cell phenotype switching contributes to vascular disease

Vascular smooth muscle cells (VSMCs) are the most abundant cell in vessels. Earlier experiments have found that VSMCs possess high plasticity. Vascular injury stimulates VSMCs to switch into a dedifferentiated type, also known as synthetic VSMCs, with a high migration and proliferation capacity for repairing vascular injury. In recent years, largely owing to rapid technological advances in single-cell sequencing and cell-lineage tracing techniques, multiple VSMCs phenotypes have been uncovered in vascular aging, atherosclerosis (AS), aortic aneurysm (AA), etc. These VSMCs all down-regulate contractile proteins such as α-SMA and calponin1, and obtain specific markers and similar cellular functions of osteoblast, fibroblast, macrophage, and mesenchymal cells. This highly plastic phenotype transformation is regulated by a complex network consisting of circulating plasma substances, transcription factors, growth factors, inflammatory factors, non-coding RNAs, integrin family, and Notch pathway. This review focuses on phenotypic characteristics, molecular profile and the functional role of VSMCs phenotype landscape; the molecular mechanism regulating VSMCs phenotype switching; and the contribution of VSMCs phenotype switching to vascular aging, AS, and AA. Video Abstract.