Activated CD47 regulates multiple vascular and stress responses: implications for acute kidney injury and its management

Abstract

Ischemia-reperfusion injury (IRI) remains a significant source of early and delayed renal transplant failure. Therapeutic interventions have yet to resolve this ongoing clinical challenge although the reasons for this remain unclear. The cell surface receptor CD47 is widely expressed on vascular cells and in tissues. It has one known soluble ligand, the stress-released matricellular protein thrombospondin-1 (TSP1). The TSP1-CD47 ligand receptor axis controls a number of important cellular processes, inhibiting survival factors such as nitric oxide, cGMP, cAMP, and VEGF, while activating injurious pathways such as production of reactive oxygen species. A role of CD47 in renal IRI was recently revealed by the finding that the TSP1-CD47 axis is induced in renal tubular epithelial cells (RTEC) under hypoxia and following IRI. The absence of CD47 in knockout mice increases survival, mitigates RTEC damage, and prevents subsequent kidney failure. Conversely, therapeutic blockade of TSP1-CD47 signaling provides these same advantages to wild-type animals. Together, these findings suggest an important role for CD47 in renal IRI as a proximate promoter of injury and as a novel therapeutic target.

Fig. 1.

Activated CD47 is a proximate regulator of multiple cell survival and cell death pathways. CD47 is a potent and redundant inhibitor of the canonical nitric oxide (NO) pathway, limiting endothelial NO synthase (eNOS) activation (5), soluble guanylyl cyclase (sGC) stimulation (48), and the downstream cGMP target PKG (51). Thrombospondin-1 (TSP1) activation of CD47 decreases VEGF signaling by altering CD47 and VEGF receptor (VEGFR2) coassociation (54), to limit both NO-dependent and -independent effects of VEGF. TSP1, presumably via CD47, inhibits adenylyl cyclase to limit cAMP production (100). CD47 also limits mitochondrial energetics and promotes reactive oxygen species (ROS) and programmed cell death (26).

Fig. 2.

Absence of CD47 activation provides significant survival advantage and renal cytoprotection following ischemia-reperfusion injury (IRI) in null mice. A: wild-type (WT) C57BL/6 male mice invariably died within 50 h following renal IRI. In contrast, similarly challenged CD47^−/− mice all survived as highlighted by Kaplan-Meyer analysis. B: WT mice subjected to 24-h reperfusion following bilateral renal ischemia demonstrated marked corticomedullary damage, characterized by widespread tubular epithelial cell necrosis (arrows) and cast formation (arrowheads). CD47^−/− mice had minimal alterations in cytoarchitecture on histological examination. Representative images of kidneys from both mice are shown (periodic acid-Schiff-stained; original magnification ×200, with insets at ×400).

Fig. 3.

Antibody blockade of CD47 activation preserves renal cytoarchitecture following IRI through targeting multiple survival and injury pathways. A: WT C57BL/6 male mice received a single ip injection of a CD47-blocking antibody (clone 301) 90 min before renal IRI. In contrast to untreated animals and animals receiving a matched isotype control antibody, all mice treated with the CD47 monoclonal antibody demonstrated preservation of near normal cytoarchitecture. Representative images of kidneys from animals treated with a CD47-blocking antibody show decreased tubular necrosis, tubular dilatation, and cast formation compared with kidney tissue sections from isotype control antibody-treated and untreated animals (original magnification ×200, insets at ×400). B: in addition to inhibiting multiple survival and growth factor pathways, in renal IRI activated CD47 can stimulate pathological ROS production including superoxide production (O₂^·−) though upregulation of inducible NOS (iNOS) (86) to promote programmed cell death (64, 68, 86). Therapeutic blockade of the TSP1-CD47 axis with monoclonal antibodies enhances prosurvival pathways while inhibiting cell death pathways.