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.