Cellular responses to oxygen are increasingly recognized as critical in normal development and physiology, and are implicated in pathological processes. Many of these responses are mediated by the transcription factors HIF-1 and HIF-2. Their regulation occurs through oxygen-dependent proteolysis of the alpha subunits HIF-1alpha and HIF-2alpha, respectively. Both are stabilized in cell lines exposed to hypoxia, and recently HIF-1alpha was reported to be widely expressed in vivo. In contrast, regulation and sites of HIF-2alpha expression in vivo are unknown, although a specific role in endothelium was suggested. We therefore analyzed HIF-2alpha expression in control and hypoxic rats. Although HIF-2alpha was not detectable under baseline conditions, marked hypoxic induction occurred in all organs investigated, including brain, heart, lung, kidney, liver, pancreas, and intestine. Time course and amplitude of induction varied between organs. Immunohistochemistry revealed nuclear accumulation in distinct cell populations of each tissue, which were exclusively non-parenchymal in some organs (kidney, pancreas, and brain), predominantly parenchymal in others (liver and intestine) or equally distributed (myocardium). These data indicate that HIF-2 plays an important role in the transcriptional response to hypoxia in vivo, which is not confined to the vasculature and is complementary to rather than redundant with HIF-1.

Abstract. Oxygen tensions in the kidney are heterogeneous, and their changes presumably play an important role in renal physiologic and pathophysiologic processes. A family of hypoxia-inducible transcription factors (HIF) have been identified as mediators of transcriptional responses to hypoxia, which include the regulation of erythropoietin, metabolic adaptation, vascular tone, and neoangiogenesis. In vitro, the oxygen-regulated subunits HIF-1␣ and -2␣ are expressed in inverse relationship to oxygen tensions in every cell line investigated to date. The characteristics and functional significance of the HIF response in vivo are largely unknown. Highamplification immunohistochemical analyses were used to study the expression of HIF-1␣ and -2␣ in kidneys of rats exposed to systemic hypoxia bleeding anemia, functional anemia (0.1% carbon monoxide), renal ischemia, or cobaltous chloride (which is known to mimic hypoxia). These treatments led to marked nuclear accumulation of HIF-1␣ and -2␣ in different renal cell populations. HIF-1␣ was mainly induced in tubular cells, including proximal segments with exposure to anemia/carbon monoxide, in distal segments with cobaltous chloride treatment, and in connecting tubules and collecting ducts with all stimuli. Staining for HIF-1␣ colocalized with inducible expression of the target genes heme oxygenase-1 and glucose transporter-1. HIF-2␣ was not expressed in tubular cells but was expressed in endothelial cells of a small subset of glomeruli and in peritubular endothelial cells and fibroblasts. The kidney demonstrates a marked potential for upregulation of HIF, but accumulation of HIF-1␣ and HIF-2␣ is selective with respect to cell type, kidney zone, and experimental conditions, with the expression patterns partly matching known oxygen profiles. The expression of HIF-2␣ in peritubular fibroblasts suggests a role in erythropoietin regulation.Sufficient oxygenation is a prerequisite for organ function. However, oxygen delivery to organs and tissue oxygen tensions within organs vary considerably. The kidney is characterized by an interesting paradox with respect to its oxygen supply. Although blood flow is high in relation to organ weight and the arteriovenous oxygen difference is small, shunt diffusion of oxygen and heterogeneous utilization lead to marked oxygen gradients (1,2). Oxygen supply to the renal medulla barely exceeds demand, and medullary oxygen tensions are approximately 10 mmHg (3-6). Cortical oxygen tensions are more heterogeneous but are also frequently less than the venous oxygen tensions (4,6 -8).The effects of oxygen on cellular functions of the kidney are poorly understood. High rates of oxygen consumption in the proximal tubule and thick ascending limb, together with limited oxygen supply, are thought to be responsible for the high sensitivity to ischemic injury (2,9,10). A physiologic function directly related to renal oxygen tensions is the production of erythropoietin (EPO) by peritubular cortical fibroblasts (11-13). Regulation of EPO occurs at the mRN...

Hypoxia-inducible factor (HIF)-1alpha and -2alpha are key regulators of the transcriptional response to hypoxia and pivotal in mediating the consequences of many disease states. In the present work, we define their temporo-spatial accumulation after myocardial infarction and systemic hypoxia. Rats were exposed to hypoxia or underwent coronary artery ligation. Immunohistochemistry was used for detection of HIF-1alpha and -2alpha proteins and target genes, and mRNA levels were determined by RNase protection. Marked nuclear accumulation of HIF-1alpha and -2alpha occurred after both systemic hypoxia and coronary ligation in cardiomyocytes as well as interstitial and endothelial cells (EC) without pronounced changes in HIF mRNA levels. While systemic hypoxia led to widespread induction of HIF, expression after coronary occlusion occurred primarily at the border of infarcted tissue. This expression persisted for 4 wk, included infiltrating macrophages, and colocalized with target gene expression. Subsets of cells simultaneously expressed both HIF-alpha subunits, but EC more frequently induced HIF-2alpha. A progressive increase of HIF-2alpha but not HIF-1alpha occurred in areas remote from the infarct, including the interventricular septum. Cardiomyocytes and cardiac stromal cells exhibit a marked potential for a prolonged transcriptional response to ischemia mediated by HIF. The induction of HIF-1alpha and -2alpha appears to be complementary rather than solely redundant.

Allocation of kidneys from donors older than 64 years to recipients older than 64 years was started in 1999 to improve use of older donor kidneys. Kidneys are allocated locally without HLA-matching to keep cold ischemia short.We compared survival and rejection rates in elderly patients allocated in the old-for-old program (ESP) to patients aged 60 years and older based on HLA-matching, expected ischemia and waiting time (ETKAS).The 69 ESP patients were older (67.9 ± ± 2.5 vs. 63.9 ± ± 2.9 years), had older donors (71.2 ± ± 3.9 vs. 44.6 ± ± 14.5 years) and more HLA-mismatches (4.2 ± ± 1.2 vs. 1.6 ± ± 1.7) than the 71 ETKAS patients, while ischemia was shorter (7.8 ± ± 3.4 vs. 14.2 ± ± 5.5 h). ESP and ETKAS had similar graft (1-year: 83.6% vs. 86.9%) and patient survival (85.2% vs. 89.5%). With the introduction of ESP, use of older recipients and donors rose from less than 2% to 16% and 11%, respectively. Incidence of acute rejections was significantly higher in the ESP group (1 year: 43.2% vs. 27.4%) and significantly correlated with the degree of HLA-matching.Introduction of old-for-old allocation allows successful expansion of the donor and recipient pool without affecting patient and graft survival. HLA-matching should not be ignored, as the risk of acute rejection in elderly patients is substantial.

Urinary concentrations of tenascin and TIMP-1 are elevated in association with renal disease and may reflect specific aspects of renal fibrosis.