NM ROGERS1,2, B SANGANERIA1, M EL-RASHID1
1Westmead Institute for Medical Research, Sydney, NSW; 2University of Pittsburgh, Pittsburgh, PA, USA
Aim: To investigate mechanisms underlying cellular damage in acute kidney injury.
Background: Acute kidney injury (AKI) initiates a complex pathophysiological cascade leading to epithelial cell death. Recent studies identify autophagy, the mechanism of intracellular recycling of cytoplasmic constituents, as important in protection against AKI. We have reported that the protein thrombospondin-1 (TSP1), and its receptor CD47, are induced in AKI. However their role in regulating injury is unknown.
Methods: Age and gender-matched wild-type (WT) and CD47-/- mice were challenged with renal ischemia-reperfusion injury (IRI), a standard model of AKI. All animals underwent analysis of renal function and biomolecular phenotyping. Human and murine WT and CD47-/- renal tubular epithelial cells (rTEC) were studied in vitro.
Results: CD47-/- mice were resistant to renal IRI, with decreased serum urea and creatinine, and ameliorated histological changes compared to WT animals. CD47-/- mice demonstrated robust upregulation of key autophagy genes, including Atg5, Atg7, Beclin-1, and LC3 at baseline and post-IRI. WT mice demonstrated negligible autophagy expression at all time points. rTEC from CD47-/- mice displayed basal upregulation of autophagy that was preserved under exogenous stress (hypoxia, treatment with the CD47 ligand TSP1), and correlated with enhanced viability compared to WT cells. Treatment of WT rTEC with a CD47 antagonist antibody or oligonucleotide to block TSP1-CD47 signalling increased autophagy. Finally, in a syngeneic mouse kidney transplantation model, treatment with a CD47 blocking antibody improved renal function and decreased histologic damage compared to control mice, and this was associated with increased autophagy.
Conclusions: These data suggest that activated CD47 is a proximate promoter of AKI through inhibition of autophagy, and point to CD47 as a target to restore renal function following injury.