A better understanding of the pathways that regulate regeneration of the coronary vasculature is of fundamental importance for the advancement of strategies to treat patients with heart disease. Here, we aimed to investigate the origin and clonal dynamics of endothelial cells (ECs) associated with neovascularization in the adult mouse heart following myocardial infarction (MI). Furthermore, we sought to define murine cardiac endothelial heterogeneity and to characterize the transcriptional profiles of pro-angiogenic resident ECs in the adult mouse heart, at single-cell resolution.
The pathogenesis of chronic obstructive pulmonary disease is not fully understood. The objective of this study was to compare circulating endothelial progenitor cells in patients with chronic obstructive pulmonary disease to age, sex, and cigarette smoking matched healthy controls. Patients with chronic obstructive pulmonary disease (n = 37) and healthy controls (n = 19) were matched by age, sex, and smoking status. Circulating hematopoietic progenitor cells (CD34(+) or CD133(+) mononuclear cells) and endothelial progenitor cells (CD34(+)KDR(+) or CD34(+)CD133(+)KDR(+) mononuclear cells) were quantified by flow cytometry. Endothelial cell-colony forming units from peripheral blood mononuclear cells were quantified in vitro and phenotypic analysis carried out using immunocytochemistry. Patients with chronic obstructive pulmonary disease had more circulating mononuclear cells compared with controls (8.4 ± 0.6 vs. 5.9 ± 0.4 × 10(9) cells/l; P = 0.02). CD34(+) hematopoietic progenitor cells were reduced as a proportion of mononuclear cells in patients compared with controls (0.99 ± 0.12 vs. 1.9 ± 0.12%; P = 0.02); however, there were no differences in the absolute number of CD34(+), CD34(+)KDR(+), or CD34(+)CD133(+)KDR(+) cells (P > 0.05 for all). Endothelial cell-colony forming units were increased in patients with chronic obstructive pulmonary disease compared with controls (13.7 ± 5.2 vs. 2.7 ± 0.9 colonies; P = 0.048). In contrast to previous studies, the number of circulating progenitor cells was not reduced in patients with chronic obstructive pulmonary disease compared with carefully matched controls. It seems unlikely that circulating endothelial progenitor cells or failure of angiogenesis plays a central role in the development of emphysema.
Cardiovascular disease (CVD) is the leading cause of mortality worldwide claiming almost 17.9 million deaths annually. A primary cause is atherosclerosis within the coronary arteries, which restricts blood flow to the heart muscle resulting in myocardial infarction (MI) and cardiac cell death. Despite substantial progress in the management of coronary heart disease (CHD), there is still a significant number of patients developing chronic heart failure post-MI. Recent research has been focused on promoting neovascularisation post-MI with the ultimate goal being to reduce the extent of injury and improve function in the failing myocardium. Cardiac cell transplantation studies in pre-clinical models have shown improvement in cardiac function; nonetheless, poor retention of the cells has indicated a paracrine mechanism for the observed improvement. Cell communication in a paracrine manner is controlled by various mechanisms, including extracellular vesicles (EVs). EVs have emerged as novel regulators of intercellular communication, by transferring molecules able to influence molecular pathways in the recipient cell. Several studies have demonstrated the ability of EVs to stimulate angiogenesis by transferring microRNA (miRNA, miR) molecules to endothelial cells (ECs). In this review, we describe the process of neovascularisation and current developments in modulating neovascularisation in the heart using miRNAs and EV-bound miRNAs. Furthermore, we critically evaluate methods used in cell culture, EV isolation and administration.
Myofibroblasts are ubiquitous cells with features of both fibroblasts and smooth muscle cells. We suggest that the bone marrow can contribute to myofibroblast populations in a variety of tissues and that this is exacerbated by injury. To assess this, female mice were transplanted with male bone marrow and the male cells were tracked throughout the body and identified as myofibroblasts. Skin wounding and paracetamol administration were used to assess whether myofibroblast engraftment was modulated by damage. Following radiation injury, a proportion of myofibroblasts in the lung, stomach, esophagus, skin, kidney, and adrenal capsule were bone-marrow derived. In the lung, there was significantly greater engraftment following paracetamol administration (17% versus 41% p < 0.005). Bone-marrow-derived fibroblasts were also found. We suggest that bone marrow contributes to a circulating population of cells and, in the context of injury, these cells are recruited and contribute to tissue repair.
We have previously reported the presence of novel subpopulations of pulmonary monocyte-like cells (PMLC) in the human lung; resident PMLC (rPMLC, HLA-DR+CD14++CD16+cells) and inducible PMLC (iPMLC, HLA-DR+CD14++CD16- cells). iPMLC are significantly increased in bronchoalveolar lavage (BAL) fluid following inhalation of lipopolysaccharide (LPS). We have carried out the first functional evaluation of PMLC subpopulations in the inflamed lung, following the isolation of these cells, and other lineages, from BAL fluid using novel and complex protocols. iPMLC, rPMLC, alveolar macrophages (AM), neutrophils, and regulatory T cells were quantified in BAL fluid of healthy subjects at 9 hours post-LPS inhalation (n = 15). Cell surface antigen expression by iPMLC, rPMLC and AM and the ability of each lineage to proliferate and to undergo phagocytosis were investigated using flow cytometry. Basal cytokine production by iPMLC compared to AM following their isolation from BAL fluid and the responsiveness of both cell types following in vitro treatment with the synthetic corticosteroid dexamethasone were assessed. rPMLC have a significantly increased expression of mature macrophage markers and of the proliferation antigen Ki67, compared to iPMLC. Our cytokine data revealed a pro-inflammatory, corticosteroid-resistant phenotype of iPMLC in this model. These data emphasise the presence of functionally distinct subpopulations of the monocyte/macrophage lineage in the human lung in experimental acute lung inflammation.
Cardiac injury leads to the loss of cardiomyocytes which are rapidly replaced by proliferation of surviving cells in zebrafish, but not in mammals. In both the regenerative zebrafish and non-regenerative mammals, cardiac injury induces a sustained macrophage response. Macrophages are required for cardiomyocyte proliferation during zebrafish cardiac regeneration, but the mechanisms whereby macrophages facilitate this crucial process are fundamentally unknown. Using heartbeat-synchronised live imaging, RNA sequencing and macrophage-null genotypes in the larval zebrafish cardiac injury model, we characterise macrophage function and reveal that these cells activate the epicardium, inducing cardiomyocyte proliferation. Mechanistically, macrophages are specifically recruited to the epicardial-myocardial niche triggering the expansion of the epicardium which upregulates vegfaa expression to induce cardiomyocyte proliferation. Our data suggest that epicardial Vegfaa augments a developmental cardiac growth pathway via increased endocardial notch signalling. Identification of this macrophage-dependent mechanism of cardiac regeneration highlights immunomodulation as a potential strategy for enhancing mammalian cardiac repair.
Abstract Ischaemic heart disease is a global healthcare challenge with high morbidity and mortality. Early revascularisation in acute myocardial infarction has improved survival, however, limited regenerative capacity and microvascular dysfunction often lead to impaired function and the development of heart failure. New mechanistic insights are required to identify robust targets for the development of novel strategies to promote regeneration. Single cell RNA sequencing (scRNA-seq) has enabled profiling and analysis of the transcriptomes of individual cells at high resolution. Applications of scRNA-seq have generated single cell atlases for multiple species, revealed distinct cellular compositions for different regions of the heart, and defined multiple mechanisms involved in myocardial injury-induced regeneration. In this review, we summarise findings from studies of healthy and injured hearts in multiple species and spanning different developmental stages. Based on this transformative technology, we propose a multi-species, multi-omics, meta-analysis framework to drive the discovery of new targets to promote cardiovascular regeneration.
Adult bone marrow contains progenitor cells that can extricate themselves from their bone marrow cavity niche, and engraft within foreign tissues, whereupon they produce specific differentiated adult lineages. Bone marrow engraftment is upregulated with increasing regenerative pressure, which has triggered speculation as to the therapeutic potential of bone marrow cells. In this thesis, I describe for the first time, that transplanted adult bone marrow cells engraft within the intestines of mice and humans and give rise to a substantial proportion of the mesenchymal cells in the lamina propria, namely, the intestinal subepithelial myofibroblasts. I show that bone marrow contribution to intestinal myofibroblasts is significantly enhanced in a mouse model of colitis. Furthermore, I show that bone marrow cells form multiple vascular lineages in the mouse colon, with an enhanced propensity in colitis. These results have implications for the use of bone marrow in the treatment of inflammatory bowel disease, either by directly producing mesenchymal and vascular lineages, and/or possibly via the indirect regulation of intestinal epithelial cells. I also report that transplanted bone marrow cells engraft into the skin and contribute to multiple epidermal lineages. These bone marrow-derived cells are commonly located within postulated epidermal stem cell niches, and can express putative epidermal stem cell markers. Bone marrow cell engraftment was significantly enhanced in the wounded epidermis, and bone marrow-derived epidermal cells can proliferate in vivo, and form colonies in vitro. I found no evidence that bone marrow cells fuse with indigenous epidermal cells to form heterokaryons. These results highlight the potential of bone marrow cells in the treatment of diseases of the gastrointestinal tract and skin.
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