Thrombospondin-1 Activation of Signal-Regulatory Protein-α Stimulates Reactive Oxygen Species Production and Promotes Renal Ischemia Reperfusion Injury
2014
Ischemia reperfusion injury (IRI) causes tissue and organ injury, in part, through alterations in tissue blood flow and the production of reactive oxygen species. The cell surface receptor signal-regulatory protein-α (SIRP-α) is expressed on inflammatory cells and suppresses phagocytosis, but the function of SIRP-α in IRI has not been determined. We reported previously that the
matricellular protein
thrombospondin-1is upregulated in IRI. Here, we report a novel interaction between
thrombospondin-1and SIRP-α on nonphagocytic cells. In cell-free experiments,
thrombospondin-1bound SIRP-α. In vascular smooth muscle cells and renal tubular epithelial cells, treatment with
thrombospondin-1led to phosphorylation of SIRP-α and downstream activation of
Src homology domain2–containing phosphatase-1.
Thrombospondin-1also stimulated phosphorylation of p47phox (an organizer subunit for
nicotinamide adenine dinucleotide phosphate(
NADPH)
oxidase1/2) and increased production of superoxide, both of which were abrogated by knockdown or antibody blockade of SIRP-α. In rodent
aortic rings, treatment with
thrombospondin-1increased the production of superoxide and inhibited nitric oxide–mediated vasodilation in a SIRP-α–dependent manner. Renal IRI upregulated the
thrombospondin-1–SIRP-α signaling axis and was associated with increased superoxide production and cell death. A SIRP-α antibody that blocks
thrombospondin-1activation of SIRP-α mitigated the effects of renal IRI, increasing blood flow, suppressing production of reactive oxygen species, and preserving
cellular architecture. A role for
CD47in SIRP-α activation in these pathways is also described. Overall, these results suggest that
thrombospondin-1binding to SIRP-α on nonphagocytic cells activates
NADPH oxidase, limits vasodilation, and promotes renal IRI.
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