Blocking Thrombospondin-1/CD47 Signaling Alleviates Deleterious Effects of Aging on Tissue Responses to Ischemia

Abstract

Objective-Decreased blood flow secondary to peripheral vascular disease underlies a significant number of chronic diseases that account for the majority of morbidity and mortality among the elderly. Blood vessel diameter and blood flow are limited by the matricellular protein thrombospondin-1 (TSP1) through its ability to block responses to the endogenous vasodilator nitric oxide (NO). In this study we investigate the role TSP1 plays in regulating blood flow in the presence of advanced age and atherosclerotic vascular disease. Methods and Results-Mice lacking TSP1 or CD47 show minimal loss of their resistance to ischemic injury with age and increased preservation of tissue perfusion immediately after injury. Treatment of WT and apolipoprotein E-null mice using therapeutic agents that decrease CD47 or enhance NO levels reverses the deleterious effects of age-and diet-induced vasculopathy and results in significantly increased tissue survival in models of ischemia. Conclusion-With increasing age and diet-induced atherosclerotic vascular disease, TSP1 and its receptor CD47 become more limiting for blood flow and tissue survival after ischemic injury. Drugs that limit TSP1/CD47 regulation of blood flow could improve outcomes from surgical interventions in the elderly and ameliorate vascular complications attendant to aging. Key Words: nitric oxide Ⅲ thrombospondin-1 Ⅲ perfusion Ⅲ ischemia Ⅲ wound healing C omplications from peripheral vascular disease, including coronary artery disease and myocardial infarction, stroke, and ischemic vascular disease affect some 80% of people over the age of 65. The elderly have significant alterations in vascular anatomy including a loss of vascular networks 1 and alterations in vascular response to injury. 2 Age is a recognized risk factor for complications after surgery including delayed and incomplete wound healing and tissue loss and accounts for significant morbidity and mortality in this group. [3][4][5][6] Animal studies have confirmed the impact of aging on wound healing. [7][8][9] Tissue perfusion is regulated through the control of blood vessel diameter, which itself is controlled by the contractile state of vascular smooth muscle cells (VSMCs). Nitric oxide (NO) is a primary and ubiquitous dilator of blood vessels. 10 NO is constitutively produced in blood vessels by endothelial nitric oxide synthase (eNOS). NO activates soluble guanylate cyclase (sGC) leading to cGMP production and vasodilation. In aged vascular cells, 11 animals, and people, both eNOS expression and NO production 12 are decreased.We recently reported that thrombospondin-1 (TSP1) blocks NO-driven VSMC relaxation in a CD47-dependent manner. 13-15 NO-driven alterations in blood flow are substantially greater in the absence of TSP1 or CD47. Given the deleterious effects of aging on the cardiovascular system, we wanted to determine whether blocking of TSP1 inhibition of NO signaling would provide significant tissue protection in senescent animals. Aged WT and apolipoprotein E (apoE)-null mice (with diet-driv...

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

“…Mechanistic studies demonstrated that TSP1 blocked the dephosphorylation of myosin light chain-2 induced by treating these cells with NO and thereby promoted F-actin assembly and contraction of the smooth muscle cells. Notably, the elevated tissue cGMP levels found in young male Thbs1 -/-mice persisted as those mice were aged to 12-16 months, but cGMP levels fell significantly with age in male WT mice (86), consistent with the reported elevations in tissue TSP1 and CD47 levels with aging (19,105,207,213). Thus, TSP1 physiologically opposes the activity of NO to regulate vascular tone, but this balance becomes perturbed with increasing age.…”

“…The ability of a CD47 antibody and antisense morpholino suppression of CD47 to restore normal ischemic injury responses to aged WT mice is proof of principle that therapeutics targeting this pathway could have broad clinical applications (86,213).…”

Thrombospondins: from structure to therapeutics

“…Wild type mice aged to between 14 and 18 months demonstrated even greater degrees of tissue necrosis to an ischemic insult than young animals, with some animals experiencing complete flap loss [128]. TSP1-and CD47-null animals subjected to the same ischemic insult showed near complete tissue survival in the face of advanced age.…”

“…In the absence of TSP1, the vascular response to NO remains more dynamic and confers a performance advantage despite advanced age compared to young animals. Even more interesting, in apoE-null mice, which acquire diet induced atherosclerotic vascular disease [129], ischemic tissue survival was significantly enhanced through suppressing CD47 in the tissue unit [128].…”

CD47 deficiency confers cell and tissue radioprotection by activation of autophagy

“…Mice that lack CD47 or its ligand THBS1 are profoundly resistant to a variety of ischemic injuries including soft tissue ischemia and ischemia/reperfusion, 48 liver and renal ischemia/reperfusion injury, 34,49 spinal cord injury, 50 focal cerebral ischemia 51 and radiation. This makes CD47 blockade or agents that downregulate its expression attractive approaches CD47 primes cells by stabilizing mRNA to engage the autophagy machinery in an efficient manner to insure cell survival.…”