Renal parenchymal hypoxia, hypoxia response and the progression of chronic kidney disease.

Renal parenchymal hypoxia, documented under a variety of clinical conditions, conceivably contributes to the progression chronic kidney disease. In this review, normal physiologic medullary hypoxia and abnormal profiles of renal pO(2) in chronic kidney diseases are presented, and the mechanisms leading to anomalous renal tissue oxygenation are discussed. Direct measurements of pO(2) with oxygen electrodes, immunostaining with pimonidazole (which binds to regions with very low pO(2)), or the detection of hypoxia-inducible factor (HIF)-alpha (which accumulates in hypoxic regions, initiating hypoxia-adaptive responses), all serve to detect the distribution and extent of renal parenchymal hypoxia under experimental settings. The use of BOLD MRI as a noninvasive tool, detecting deoxygenated hemoglobin in hypoxic renal tissues, has evolved from experimental settings to human studies. All these modalities indicate that abnormal renal oxygenation develops under conditions such as chronic glomerular, tubulointerstitial or renovascular disease, in diabetes, hypertension, aging, renal hypertrophy, anemia or obstructive uropathy. Abnormal renal tissue hypoxia modifies the pattern of regional gene expression, evoking a host of adaptive and renoprotective pathways (such as HIF-mediated erythropoietin or heme-oxygenase-1), in parallel with the induction of potentially harmful mediators that participate in the progression of chronic kidney injury. Slowing the progression of chronic kidney disease may be achieved by a better understanding of these parallel processes and the accomplishment of a selective control of such protective and maladaptive responses.