What mediates the effects of thrombospondin-1 in pulmonary hypertension? New evidence for a dual-pronged role of CD47

Hypertensive Patients Exhibit Enhanced Thrombospondin-1 Levels at High-Altitude

Thrombospondin-1 (THBS1) levels elevate under hypoxia and have relevance in several cardiovascular disorders. The association of THBS1 with endothelial dysfunction implies its important role in hypertension. To establish the hypothesis, we screened patients with hypertension and their respective controls from the two different environmental regions. Cohort 1 was composed of Ladakhis, residing at 3500 m above sea level (ASL), whereas Cohort 2 was composed of north-Indians residing at ~200 m ASL. Clinical parameters and circulating THBS1 levels were correlated in the case–control groups of the two populations. THBS1 levels were significantly elevated in hypertension patients of both cohorts; however, the levels were distinctly enhanced in the hypertensive patients of HA as compared to normoxia (p < 0.002). The observation was supported by the receiver operating curve analysis with an area under curve of 0.7007 (0.627–0.774) demonstrating the discriminatory effect of hypobaric hypoxia on the levels as compared to normoxia (p < 0.011). Significant correlation of THBS1 and mean arterial pressure was observed with upraised positive correlations in the hypertensive highlanders as compared to the hypertensive patients from sea-level. The prevalence of differential distribution of THBS1 and CD47 genes variants, their interactions, and association with the THBS1 levels were also determined. Genotype-interactions between THBS1 rs2228263 and CD47 rs9879947 were relevant and the regression analysis highlighted the association of risk genotype-interactions with increased THBS1 levels in hypertension. Genetic studies of additional thrombospondin pathway-related genes suggest the complex role of THBS1 in the presence of its family members and the related receptor molecules at HA.

Is CD47 a potentially promising therapeutic target in cardiovascular diseases? - Role of CD47 in cardiovascular diseases

CD47 (cluster of differentiation 47) is a ubiquitously expressed transmembrane protein that belongs to the immunoglobulin superfamily. CD47 is both a receptor for the matricellular protein thrombospondin-1 (TSP-1) and a ligand for signal-regulatory protein alpha (SIRPα). Suppression of CD47 activity enhances angiogenesis and blood flow, restores phagocytosis by macrophages, improves ischemic tissue survival, attenuates ischemia reperfusion injury, and reverses atherosclerotic plaque formation. In conclusion, these observations suggest a pathogenic role of CD47 in the development of cardiovascular diseases (CVDs) and indicate that CD47 might be a potentially promising molecular target for treating CVDs. Herein, we highlight the role of CD47 in the CVD pathogenesis and discuss the potential clinical application by targeting CD47 for treating CVDs.

Thrombospondin-1 Serum Levels In Hypertensive Patients With Endothelial Dysfunction After One Year Of Treatment With Perindopril

Background

Thrombospondin-1 (TSP-1) is a matricellular functional protein of the extracellular matrix. As it is not constitutively present extracellularly, its secretion is enhanced in several situations, namely injury, chronic pathology, tissue remodeling, angiogenesis, and aging. Over the last decade, TSP-1 has been reported to be involved in complex and opposing biological effects on vasculature in the context of NO signaling. Several studies have reported high patient TSP-1 plasma levels, indicating that the protein can potentially serve as a prognostic marker for pulmonary arterial hypertension.

Materials and methods

Here, we aimed to quantify TSP-1 serum levels in hypertensive patients with endothelial dysfunction before and after one year of treatment with Perindopril (an antihypertensive drug with vasoprotective properties).

Results

After one year of treatment, TSP-1 levels increased in hypertensive patients compared to baseline (T0: 8061.9 ± 3684.80 vs T1: 15380±5887 ng/mL, p<0.001) and compared to non-hypertensive controls (9221.03 ± 6510.21 ng/mL). In contrast, pentraxin-3 plasma levels were decreased after one year of Perindopril treatment in both hypertensive (T0: 0.91 ± 0.51 vs T1: 0.50 ± 0.24 ng/mL, p<0.001) and control group (1.36 ±1.5 ng/mL) patients, although flow-mediated vasodilation and intima-media thickness assessment parameters were not significantly changed. Systolic and diastolic blood pressure values as well as levels of fibrinogen, high-sensitivity C-reactive protein, triglycerides, and alanine aminotransferase were found to be significantly lower after one year of treatment with Perindopril. High levels of TSP-1 strongly correlated with platelet count (positive), lymphocytes (positive), red cell distribution width-CV (positive), systolic blood pressure (negative), and mean corpuscular hemoglobin (negative) after one year of treatment. Blood urea nitrogen was found to be a protective factor for TSP-1, while glucose and heart rate were found to be risk factors prior to and after treatment.

Regulation of Cellular Redox Signaling by Matricellular Proteins in Vascular Biology, Immunology, and Cancer

SIGNIFICANCE

In contrast to structural elements of the extracellular matrix, matricellular proteins appear transiently during development and injury responses, but their sustained expression can contribute to chronic disease. Through interactions with other matrix components and specific cell surface receptors, matricellular proteins regulate multiple signaling pathways, including those mediated by reactive oxygen and nitrogen species and H2S. Dysregulation of matricellular proteins contributes to the pathogenesis of vascular diseases and cancer. Defining the molecular mechanisms and receptors involved is revealing new therapeutic opportunities. Recent Advances: Thrombospondin-1 (TSP1) regulates NO, H2S, and superoxide production and signaling in several cell types. The TSP1 receptor CD47 plays a central role in inhibition of NO signaling, but other TSP1 receptors also modulate redox signaling. The matricellular protein CCN1 engages some of the same receptors to regulate redox signaling, and ADAMTS1 regulates NO signaling in Marfan syndrome. In addition to mediating matricellular protein signaling, redox signaling is emerging as an important pathway that controls the expression of several matricellular proteins.

CRITICAL ISSUES

Redox signaling remains unexplored for many matricellular proteins. Their interactions with multiple cellular receptors remains an obstacle to defining signaling mechanisms, but improved transgenic models could overcome this barrier.

FUTURE DIRECTIONS

Therapeutics targeting the TSP1 receptor CD47 may have beneficial effects for treating cardiovascular disease and cancer and have recently entered clinical trials. Biomarkers are needed to assess their effects on redox signaling in patients and to evaluate how these contribute to their therapeutic efficacy and potential side effects. Antioxid. Redox Signal. 27, 874-911.