Background: We previously demonstrated that chronic hypoxia has pivotal roles in the progression of tubulointerstitial injury from the early stage of the uninephrectomized Thy1 nephritis model. We have also shown that pretreatment of cobalt confers renoprotection in the ischemia/reperfusion (I/R) injury, in association with the up-regulation of hypoxia-inducible factor (HIF)-regulated genes. Here, we tested the hypothesis that cobalt administration not only attenuates acute ischemic insult, but also ameliorates tubulointerstitial injury secondary to chronic hypoxia.
Methods: We applied sustained cobalt treatment to the uninephrectomized Thy1 nephritis model at 3 to 5 weeks, when tubular hypoxia appeared. Histologic evaluation, including glomerular and peritubular capillary networks, was made at 8 weeks. HIF activation was confirmed by real-time polymerase chain reaction (PCR) analyses for HIF-regulated genes, such as erythropoietin (EPO), vascular endothelial growth factor (VEGF), and heme oxygenase 1 (HO-1). Up-regulation of HIF-1alpha and HIF-regulated genes was also verified by Western blotting analysis. To elucidate responsible mechanisms of cobalt in the amelioration of tubuloniterstitial injury, terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate (dUTP) nick end labeling (TUNEL) staining was conducted at 5 weeks. A combination therapy with angiotensin receptor blocker (ARB), olmesartan, was also challenged.
Results: Although the intervention did not change glomerular structural damage or urinary protein excretion rate, tubulointerstitial injury was improved in cobalt-treated animals when compared with the vehicle-treated group. The amelioration was associated with the parallel up-regulation of renoprotective, HIF-regulated gene expression. TUNEL staining revealed that the number of apoptotic cells was reduced in the cortex by cobalt administration, suggesting that renoprotection was achieved partly through its antiapoptotic properties. Furthermore, it was demonstrated that cobalt treatment exerts additional renoprotective effects with the ARB treatment in this model.
Conclusion: Maneuvers to activate HIF in the ischemic tubulointerstitium will be a new direction to future therapeutic strategies.