Cobalt promotes angiogenesis via hypoxia-inducible factor and protects tubulointerstitium in the remnant kidney model

Tubulointerstitial hypoxia has been implicated in a number of progressive renal diseases, and several lines of evidence indicate that the administration of angiogenic growth factors ameliorates tubulointerstitial injury. We hypothesized that induction of hypoxia-inducible factors (HIF) mediates renoprotection by their angiogenic properties. At 5 - 9 weeks after subtotal nephrectomy, cobalt was administered to rats to activate HIF. Histological evaluation demonstrated that the tubulointerstitial injury was significantly ameliorated in animals that received cobalt ( score: 2.51 +/- 0.12 ( cobalt) vs 3.21 +/- 0.24 ( vehicle), P<0.05). Furthermore, animals receiving cobalt had fewer vimentin- and TdT-mediated dUTP nick-end labeling ( TUNEL)- positive tubular cells. The renoprotective effect of cobalt was associated with the preservation of peritubular capillary networks ( rarefaction index: 13.7 +/- 0.4 ( cobalt) vs 18.6 +/- 0.9 ( vehicle), P<0.01). This improvement in capillary networks was accompanied by an increased number of proliferating (PCNA-positive) glomerular and peritubular endothelial cells. The angiogenesis produced by this method was not accompanied by an increase in vascular permeability. Furthermore, in vitro experiments clarified that HIF-1 in tubular epithelial cells promotes proliferation of endothelial cells and that HIF-2 overexpressed in renal endothelial cells mediates migration and network formation. Collectively, these findings demonstrate a renoprotective role of HIF through angiogenesis and provide a rationale for therapeutic approaches to target HIF for activation.