Activation of hypoxia-inducible factors prevents diabetic nephropathy.

Hyperglycemia results in increased oxygen consumption and decreased oxygen tension in the kidney. We tested the hypothesis that activation of hypoxia-inducible factors (HIFs) protects against diabetes-induced alterations in oxygen metabolism and kidney function. Experimental groups consisted of control and streptozotocin-induced diabetic rats treated with or without chronic cobalt chloride to activate HIFs. We elucidated the involvement of oxidative stress by studying the effects of acute administration of the superoxide dismutase mimetic tempol. Compared with controls, diabetic rats displayed tissue hypoxia throughout the kidney, glomerular hyperfiltration, increased oxygen consumption, increased total mitochondrial leak respiration, and decreased tubular sodium transport efficiency. Diabetic kidneys showed proteinuria and tubulointerstitial damage. Cobalt chloride activated HIFs, prevented the diabetes-induced alterations in oxygen metabolism, mitochondrial leak respiration, and kidney function, and reduced proteinuria and tubulointerstitial damage. The beneficial effects of tempol were less pronounced after activation of HIFs, indicating improved oxidative stress status. In conclusion, activation of HIFs prevents diabetes-induced alteration in kidney oxygen metabolism by normalizing glomerular filtration, which reduces tubular electrolyte load, preventing mitochondrial leak respiration and improving tubular transport efficiency. These improvements could be related to reduced oxidative stress and account for the reduced proteinuria and tubulointerstitial damage. Thus, pharmacologic activation of the HIF system may prevent development of diabetic nephropathy.

Hypoxia and fibrosis in chronic kidney disease: crossing at pericytes.

Chronic kidney disease (CKD) is placing an increasing burden on patients and societies because no decisive therapy has been established. Tubulointerstitial lesions accompanied by fibrosis, inflammatory cells, and capillary rarefaction not only characterize, but also aggravate renal dysfunction in CKD. In this setting, renal cells, particularly tubular cells, suffer from hypoxia caused by the imbalance of blood perfusion and oxygen demand despite their adaptive responses represented by upregulation of hypoxia-inducible factors (HIFs). Fibrosis is a pathological state characterized by excess extracellular matrix (ECM) deposition, which is also a hallmark and causative factor of many chronic diseases including CKD. Recent studies have suggested that the dominant origin of ECM-producing myofibroblasts (MFs) may be pericytes, which are indispensable cells for maintaining proper capillary functions, as they wrap capillaries and stabilize them through a fine-tuned interplay with endothelial cells. During fibrosis, pericytes are activated and detach from capillaries before conversion into MFs, which compromises capillaries and worsens hypoxia. We also discuss how hypoxia and HIFs affect fibrogenesis. Given that hypoxia is caused by insufficient angiogenesis and that fibrosis results from pericyte loss, restoration of pericytes should be an intriguing target for overcoming both hypoxia and fibrosis. We propose the deactivation of MFs to recover lost pericytes as a promising therapy for CKD.

Role of hypoxia in progressive chronic kidney disease and implications for therapy.

PURPOSE OF REVIEW: Chronic hypoxia in the tubulointerstitium has been recognized as a final common pathway that leads to the development of end-stage renal disease. Hypoxia-inducible factor (HIF), a master regulator of the adaptive response against hypoxia, is involved in the pathogenesis of chronic kidney disease (CKD). This review focuses on HIF and novel therapeutic strategies targeting HIF. RECENT FINDINGS: Although HIF upregulation is beneficial against hypoxic kidney injury, it may be harmful under certain pathological conditions. Recent advances in epigenetic changes provide an additional layer of complexity to our understanding of gene regulation in response to hypoxia, which is most likely involved in the progression of CKD. On the basis of this novel knowledge, the pharmacological activation and modulation of HIF is emerging as a novel therapeutic target. SUMMARY: HIF plays a crucial role in the pathophysiology of CKD. The underlying molecular mechanisms, including epigenetics, have been thoroughly investigated. On the basis of the experimental data available to date, the pharmacological activation of HIF is likely a novel promising therapy for CKD.

A multicenter cross-sectional study of circulating soluble urokinase receptor in Japanese patients with glomerular disease.

Elevated serum-soluble urokinase receptor (suPAR) levels have been described in patients with focal segmental glomerulosclerosis (FSGS) in several different cohorts. However, it remains unclear whether this is the case for Japanese patients and whether circulating suPAR can be clinically useful as a diagnostic marker. To determine this, we measured serum suPAR levels in 69 Japanese patients with biopsy-proven glomerular diseases in a cross-sectional manner. The serum suPAR levels showed a significant inverse correlation with renal function by univariate (R(2) of 0.242) and multivariate (ß=0.226) analyses. Even after excluding patients with renal dysfunction, no significant difference in the suPAR levels was detected among the groups. Receiver operating characteristic analysis and measures of the diagnostic test performance showed that suPAR was not a useful parameter for differentiating FSGS from the other glomerular diseases (AUC-ROC: 0.621), although a small subgroup analysis showed that patients with FSGS, treated with steroids and/or immunosuppressants, had significantly lower suPAR levels. Patients with ANCA-associated glomerulonephritis had significantly higher levels of suPAR compared with the other disease groups, which may be owing to their lower renal function and systemic inflammation. Thus, suPAR levels are significantly affected by renal function and have little diagnostic value even in patients with normal renal function.

Sperm-associated antigen 4, a novel hypoxia-inducible factor 1 target, regulates cytokinesis, and its expression correlates with the prognosis of renal cell carcinoma.

Hypoxia plays a crucial role in many pathophysiological conditions, including cancer biology, and hypoxia-inducible factor (HIF) regulates transcriptional responses under hypoxia. To elucidate the cellular responses to hypoxia, we performed chromatin immunoprecipitation with deep sequencing in combination with microarray analysis and identified HIF-1 targets. We focused on one of the novel targets, sperm-associated antigen 4 (SPAG4), whose function was unknown. SPAG4, an HIF-1-specific target, is up-regulated in various cultured cells under hypoxia. Examination of SPAG4 expression using a tissue microarray consisting of 190 human renal cell carcinoma (RCC) samples revealed that SPAG4 is an independent prognostic factor of cancer-specific mortality. Live-cell imaging revealed localization of SPAG4 at the intercellular bridge in telophase. We also studied cells in which SPAG4 was knocked down. Hypoxia enhances tetraploidy, which disturbs cell proliferation, and knockdown of SPAG4 increased tetraploid formation and decreased cell proliferation under both normoxic and hypoxic conditions. Studies using deletion mutants of SPAG4 also suggested the involvement of SPAG4 in cytokinesis. Microarray analysis confirmed dysregulation of cytokinesis-related genes by knockdown of SPAG4. In conclusion, SPAG4 is an independent prognostic factor in RCC and plays a crucial role in cytokinesis to defend against hypoxia-induced tetraploid formation. This defensive mechanism may promote survival of cancer cells under hypoxic conditions, thus leading to poor prognosis.

Anthracycline inhibits recruitment of hypoxia-inducible transcription factors and suppresses tumor cell migration and cardiac angiogenic response in the host.

Anthracycline chemotherapeutic agents of the topoisomerase inhibitor family are widely used for the treatment of various tumors. Although targeted tumor tissues are generally situated in a hypoxic environment, the connection between efficacy of anthracycline agents and cellular hypoxia response has not been investigated in depth. Here, we report that doxorubicin (DXR) impairs the transcriptional response of the hypoxia-inducible factor (HIF) by inhibiting the binding of the HIF heterodimer to the consensus -RCGTG- enhancer element. This pleiotropic effect retarded migration of von Hippel-Lindau (VHL)-defective renal cell carcinoma and that of VHL-competent renal cell carcinoma in hypoxia. This effect was accompanied by a coordinated down-regulation of HIF target lysyl oxidase (LOX) family members LOX, LOX-like2 (LOXL2), and LOXL4. Furthermore, DXR suppressed HIF target genes in tumor xenografts, inhibited cardiac induction of HIF targets in rats with acute anemia, and impaired the angiogenic response in the isoproterenol-induced heart failure model, which may account for the clinical fragility of doxorubicin cardiomyopathy. Collectively, these findings highlight the impaired hypoxia response by anthracycline agents affecting both tumors and organs of the cancer host and offer a promising opportunity to develop HIF inhibitors using DXR as a chemical template.