Thrombospondin-1, endothelium and systemic vascular tone

Roles of TSP1-CD47 signaling pathway in senescence of endothelial cells: cell cycle, inflammation and metabolism

Endothelial cells (ECs) serve as a barrier with forming a monolayer lining in the surface of vascular system. Many mature cell types are post-mitotic like neurons, but ECs have the ability to grow during angiogenesis. Vascular endothelial growth factor (VEGF) stimulates growth of vascular ECs derived from arteries, veins, and lymphatics and induces angiogenesis. Senescence of ECs is regarded as a key contributor in aging-induced vascular dysfunction via evoking increase of ECs permeability, impairment of angiogenesis and vascular repair. Several genomics and proteomics studies on ECs senescence reported changes in gene and protein expression that directly correlate with vascular systemic disorder. CD47 functions as a signaling receptor for secreted matricellular protein thrombospondin-1 (TSP1) and plays an important role in several fundamental cellular functions, including proliferation, apoptosis, inflammation, and atherosclerotic response. TSP1-CD47 signaling is upregulated with age in ECs, concurrent with suppression of key self-renewal genes. Recent studies indicate that CD47 is involved in regulation of senescence, self-renewal and inflammation. In this review, we highlight the functions of CD47 in senescent ECs, including modulation of cell cycle, mediation of inflammation and metabolism by the experimental studies, which may provide CD47 as a potential therapeutic target for aging-associated vascular dysfunction.

Shear stress-mediated upregulation of GTP cyclohydrolase/tetrahydrobiopterin pathway ameliorates hypertension-related decline in reendothelialization capacity of endothelial progenitor cells

OBJECTIVES

Guanosine triphosphate cyclohydrolase/tetrahydrobiopterin (GTPCH)/(BH4) pathway has been proved to regulate the function of endothelial progenitor cells (EPCs) in deoxycorticosterone acetate-salt hypertensive mice, indicating that GTPCH/BH4 pathway may be an important repair target for hypertension-related endothelial injury. Shear stress is an important nonpharmacologic strategy to modulate the function of EPCs. Here, we investigated the effects of laminar shear stress on the GTPCH/BH4 pathway and endothelial repair capacity of circulating EPCs in hypertension.

METHOD

Laminar shear stress was loaded on the human EPCs from hypertensive patients and normotensive patients. The in-vitro function, in-vivo reendothelialization capacity and GTPCH/BH4 pathway of human EPCs were evaluated.

RESULTS

Both in-vitro function and reendothelialization capacity of EPCs were lower in hypertensive patients than that in normotensive patients. The GTPCH/BH4 pathway of EPCs was downregulated in hypertensive patients. Shear stress increased in-vitro function and reendothelialization capacity of EPCs from hypertensive patients and normotensive patients. Furthermore, shear stress upregulated the expression of GTPCH I and levels of BH4, nitric oxide, and cGMP of EPCs, and reduced thrombospondin-1 expression. With treatment of GTPCH knockdown or nitroarginine methyl ester inhibition, shear stress-induced increased levels of BH4, nitric oxide and cGMP of EPCs was suppressed. When GTPCH/BH4 pathway of EPCs was blocked, the effects of shear stress on in-vitro function and reendothelialization capacity of EPCs were inhibited.

CONCLUSION

The study demonstrates for the first time that shear stress-induced upregulation of the GTPCH/BH4 pathway ameliorates hypertension-related decline in endothelial repair capacity of EPCs. These findings provide novel nonpharmacologic therapeutic approach for hypertension-related endothelial repair.

Thrombospondin-1 and CD47 regulation of cardiac, pulmonary and vascular responses in health and disease

Cardiovascular homeostasis and health is maintained through the balanced interactions of cardiac generated blood flow and cross-talk between the cellular components that comprise blood vessels. Central to this cross-talk is endothelial generated nitric oxide (NO) that stimulates relaxation of the contractile vascular smooth muscle (VSMC) layer of blood vessels. In cardiovascular disease this balanced interaction is disrupted and NO signaling is lost. Work over the last several years indicates that regulation of NO is much more complex than previously believed. It is now apparent that the secreted protein thrombospondin-1 (TSP1), that is upregulated in cardiovascular disease and animal models of the same, on activating cell surface receptor CD47, redundantly inhibits NO production and NO signaling. This inhibitory event has implications for baseline and disease-related responses mediated by NO. Further work has identified that TSP1-CD47 signaling stimulates enzymatic reactive oxygen species (ROS) production to further limit blood flow and promote vascular disease. Herein consideration is given to the most recent discoveries in this regard which identify the TSP1-CD47 axis as a major proximate governor of cardiovascular health.

The matricellular protein thrombospondin-1 globally regulates cardiovascular function and responses to stress via CD47

Matricellular proteins play diverse roles in modulating cell behavior by engaging specific cell surface receptors and interacting with extracellular matrix proteins, secreted enzymes, and growth factors. Studies of such interactions involving thrombospondin-1 have revealed several physiological functions and roles in the pathogenesis of injury responses and cancer, but the relatively mild phenotypes of mice lacking thrombospondin-1 suggested that thrombospondin-1 would not be a central player that could be exploited therapeutically. Recent research focusing on signaling through its receptor CD47, however, has uncovered more critical roles for thrombospondin-1 in acute regulation of cardiovascular dynamics, hemostasis, immunity, and mitochondrial homeostasis. Several of these functions are mediated by potent and redundant inhibition of the canonical nitric oxide pathway. Conversely, elevated tissue thrombospondin-1 levels in major chronic diseases of aging may account for the deficient nitric oxide signaling that characterizes these diseases, and experimental therapeutics targeting CD47 show promise for treating such chronic diseases as well as acute stress conditions that are associated with elevated thrombospondin-1 expression.

Gene expression profiling of peripheral blood mononuclear cells in the setting of peripheral arterial disease

BACKGROUND

Peripheral arterial disease (PAD) is a relatively common manifestation of systemic atherosclerosis that leads to progressive narrowing of the lumen of leg arteries. Circulating monocytes are in contact with the arterial wall and can serve as reporters of vascular pathology in the setting of PAD. We performed gene expression analysis of peripheral blood mononuclear cells (PBMC) in patients with PAD and controls without PAD to identify differentially regulated genes.

METHODS

PAD was defined as an ankle brachial index (ABI) ≤0.9 (n = 19) while age and gender matched controls had an ABI > 1.0 (n = 18). Microarray analysis was performed using Affymetrix HG-U133 plus 2.0 gene chips and analyzed using GeneSpring GX 11.0. Gene expression data was normalized using Robust Multichip Analysis (RMA) normalization method, differential expression was defined as a fold change ≥1.5, followed by unpaired Mann-Whitney test (P < 0.05) and correction for multiple testing by Benjamini and Hochberg False Discovery Rate. Meta-analysis of differentially expressed genes was performed using an integrated bioinformatics pipeline with tools for enrichment analysis using Gene Ontology (GO) terms, pathway analysis using Kyoto Encyclopedia of Genes and Genomes (KEGG), molecular event enrichment using Reactome annotations and network analysis using Ingenuity Pathway Analysis suite. Extensive biocuration was also performed to understand the functional context of genes.

RESULTS

We identified 87 genes differentially expressed in the setting of PAD; 40 genes were upregulated and 47 genes were downregulated. We employed an integrated bioinformatics pipeline coupled with literature curation to characterize the functional coherence of differentially regulated genes.

CONCLUSION

Notably, upregulated genes mediate immune response, inflammation, apoptosis, stress response, phosphorylation, hemostasis, platelet activation and platelet aggregation. Downregulated genes included several genes from the zinc finger family that are involved in transcriptional regulation. These results provide insights into molecular mechanisms relevant to the pathophysiology of PAD.