Hypoxia-inducible factor prolyl-hydroxylase 2 senses high-salt intake to increase hypoxia inducible factor 1alpha levels in the renal medulla

HIF-1α knockdown attenuates phenotypic transformation and oxidative stress induced by high salt in human aortic vascular smooth muscle cells

Increased dietary salt intake is a well-established risk factor for hypertension and related cardiovascular diseases, involving complex vascular remodeling processes. However, the specific role of hypoxia-inducible factor-1α (HIF-1α) in vascular pathophysiology under high-salt conditions remains poorly understood. This study investigates the role of HIF-1α in high-salt-induced vascular remodeling using human aortic vascular smooth muscle cells (HA-VSMCs) cultured in vitro. HA-VSMCs were divided into three groups: high-salt with HIF-1α knockdown (shHIF-1α + HS), negative control (shcontrol), and high-salt (HS). Cell viability, migration, gene expression, and protein levels were evaluated. High-salt conditions significantly increased mRNA expression of α-smooth muscle actin (α-SMA), smooth muscle protein 22 (SM22), angiotensin II type 1 receptor (AT1R), collagen I, and collagen III (p < 0.0001). HIF-1α knockdown partially attenuated these increases, particularly for α-SMA, SM22, and AT1R (p < 0.01). At the protein level, high-salt exposure markedly elevated expression of collagen III, HIF-1α, osteopontin (OPN), and angiotensin II (Ang II) (p < 0.0001). HIF-1α knockdown significantly reduced the high-salt-induced increases in collagen III and HIF-1α protein levels (p < 0.001) but had a limited effect on OPN and Ang II upregulation. Interestingly, SM22 protein expression was significantly decreased under high-salt conditions (p < 0.0001), an effect partially reversed by HIF-1α knockdown (p < 0.0001). These findings demonstrate that high-salt conditions induce complex changes in gene and protein expression in HA-VSMCs, with HIF-1α playing a crucial role in mediating many of these alterations. The study highlights the differential effects of HIF-1α on various markers of vascular remodeling and suggests that HIF-1α may be a potential therapeutic target for mitigating salt-induced vascular pathology. Further research is warranted to elucidate the mechanisms underlying the HIF-1α-dependent and -independent effects observed in this study.

Renal Medullary Overexpression of Sphingosine-1-Phosphate Receptor 1 Transgene Attenuates Deoxycorticosterone Acetate (DOCA)-Salt Hypertension

BACKGROUND

Our previous studies showed that renal medullary sphingosine-1-phosphate receptor 1 (S1PR1) mediated sodium excretion, high salt intake increased S1PR1 level, deoxycorticosterone acetate (DOCA) blocked high salt-induced S1PR1 in the renal medulla, and that conditional knockout of S1PR1 in the collecting duct aggravated DOCA-salt hypertension. The present study tested the hypothesis that overexpression of S1PR1 transgene in the renal medulla attenuates the sodium retention and hypertension in DOCA-salt mouse model.

METHODS

Male C57BL/6J mice received renal medullary transfection of control or S1PR1-expressing plasmids and then DOCA-salt treatment. Renal sodium excretion and arterial pressure were compared between control and S1PR1-overexpressed mice in response to high salt loading or pressure natriuresis.

RESULTS

S1PR1-transfected mice showed significantly enhanced urinary sodium excretion in response to acute sodium loading (0.93 ± 0.27 in control vs. 4.72 ± 1.12 µmol/min/gKW in S1PR1-overexpressed mice, P < 0.05) and the pressure natriuresis (3.58 ± 1.77 vs. 9.52 ± 1.38, P < 0.05), less positive sodium balance in response to chronic high-salt intake (3.05 ± 0.39 vs. 1.65 ± 0.39 mmol/72 hr, P < 0.05), and consequently, the attenuation of DOCA-salt hypertension (134.2 ± 6.79 vs. 109.8 ± 3.54 mm Hg, P < 0.05). The αENaC protein amount in the renal medulla was not changed, however, the βENaC was significantly decreased and the γENaC was significantly increased in S1PR1-overexpressed mice. The immunostaining showed apical membrane translocation of γENaC, while no change of αENaC and βENaC in control mice, and that the apical membrane translocation of γENaC was blocked in S1PR1-treasffected mice.

CONCLUSIONS

These results suggested that activation of S1PR1 in the renal medulla attenuates DOCA-induced sodium retention and salt-sensitive hypertension associated with inhibition of ENaC.

No benefit of HIF prolyl hydroxylase inhibition for hypertensive renal damage in renovascular hypertensive rats

Introduction: We previously reported that malignant hypertension is associated with impaired capillary density of target organs. Here, we tested the hypothesis that stabilization of hypoxia-inducible factor (HIF) in a modified "preconditioning" approach prevents the development of malignant hypertension. To stabilize HIF, we employed pharmacological inhibition of HIF prolyl hydroxylases (PHD), that profoundly affect HIF metabolism. Methods: Two-kidney, one-clip renovascular hypertension (2K1C) was induced in rats; controls were sham operated. 2K1C rats received either intermittent injections of the PHD inhibitor ICA (2-(1-chloro-4-hydroxyisoquinoline-3-carboxamido) acetate) or placebo. Thirty-five days after clipping, the frequency of malignant hypertension was assessed (based on weight loss and the occurrence of characteristic vascular lesions). In addition, kidney injury was compared between all ICA treated versus all placebo treated 2K1C, regardless of the occurrence of malignant hypertension. HIF stabilization was evaluated by immunohistochemistry, and HIF target gene expression by RT-PCR. Results: Blood pressure was elevated to the same degree in ICA- and placebo-treated 2K1C compared to control rats. ICA treatment did not affect the frequency of malignant hypertension or the extent of kidney tissue fibrosis, inflammation, or capillary density. There was a trend towards higher mortality and worse kidney function in ICA-treated 2K1C rats. ICA increased the number of HIF-1α-positive renal tubular cell nuclei and induced several HIF-1 target genes. In contrast, expression of HIF-2α protein as well as HIF-2 target genes were markedly enhanced by 2K1C hypertension, irrespective of ICA treatment. Discussion: We conclude that intermittent PHD inhibition did not ameliorate severe renovascular hypertension in rats. We speculate that the unexpected strong renal accumulation of HIF-2α in renovascular hypertension, which could not be further augmented by ICA, may contribute to the lack of a benefit from PHD inhibition.

Therapeutic Effects and Molecular Mechanism of Chlorogenic Acid on Polycystic Ovarian Syndrome: Role of HIF-1alpha

Chlorogenic acid (CGA) is a powerful antioxidant polyphenol molecule found in many diets and liquid beverages, playing a preventive and therapeutic role in various diseases caused by oxidative stress and inflammation. Recent research has found that CGA can not only improve clinical symptoms in PCOS patients but also improve follicular development, hormone status, and oxidative stress in PCOS rats, indicating the therapeutic effect of CGA on PCOS. Notably, our previous series of studies has demonstrated the expression changes and regulatory mechanisms of HIF-1alpha signaling in PCOS ovaries. Considering the regulatory effect of CGA on the HIF-1alpha pathway, the present article systematically elucidates the therapeutic role and molecular mechanisms of HIF-1alpha signaling during the treatment of PCOS by CGA, including follicular development, steroid synthesis, inflammatory response, oxidative stress, and insulin resistance, in order to further understand the mechanisms of CGA effects in different types of diseases and to provide a theoretical basis for further promoting CGA-rich diets and beverages simultaneously.

Hypoxia-inducible factors and essential hypertension: narrative review of experimental and clinical data

Hypoxia-inducible factor (HIFs) is a new class of drug developed for the management of anemia in chronic kidney disease (CKD) patients. HIFs increase the production of erythropoietin in the kidney and liver, enhance the absorption and utilization of iron, and stimulate the maturation and proliferation of erythroid progenitor cells. Besides, HIFs regulate many physiologic processes by orchestrating the transcription of hundreds of genes. Essential hypertension (HT) is an epidemic worldwide. HIFs play a role in many biological processes involved in the regulation of blood pressure (BP). In the current review, we summarize pre-clinical and clinical studies investigating the relationship between HIFs and BP regulation in patients with CKD, conflicting issues, and discuss future potential strategies.

Blood pressure and the kidney cortex transcriptome response to high-sodium diet challenge in female nonhuman primates

Blood pressure (BP) is influenced by genetic variation and sodium intake with sex-specific differences; however, studies to identify renal molecular mechanisms underlying the influence of sodium intake on BP in nonhuman primates (NHP) have focused on males. To address the gap in our understanding of molecular mechanisms regulating BP in female primates, we studied sodium-naïve female baboons (n = 7) fed a high-sodium (HS) diet for 6 wk. We hypothesized that in female baboons variation in renal transcriptional networks correlates with variation in BP response to a high-sodium diet. BP was continuously measured for 64-h periods throughout the study by implantable telemetry devices. Sodium intake, blood samples for clinical chemistries, and ultrasound-guided kidney biopsies were collected before and after the HS diet for RNA-Seq and bioinformatic analyses. We found that on the LS diet but not the HS diet, sodium intake and serum 17 β-estradiol concentration correlated with BP. Furthermore, kidney transcriptomes differed by diet-unbiased weighted gene coexpression network analysis revealed modules of genes correlated with BP on the HS diet but not the LS diet. Our results showed variation in BP on the HS diet correlated with variation in novel kidney gene networks regulated by ESR1 and MYC; i.e., these regulators have not been associated with BP regulation in male humans or rodents. Validation of the mechanisms underlying regulation of BP-associated gene networks in female NHP will inform better therapies toward greater precision medicine for women.

The hypoxia-inducible factor prolyl hydroxylase inhibitor FG4592 promotes natriuresis through upregulation of COX2 in the renal medulla

The renal medulla is a key site for the regulation of renal sodium excretion. However, the molecular mechanism remains unclear. Cyclooxygenase 2 (COX2) is specifically expressed in the renal medulla and contributes to the maintenance of the electrolyte/water balance in the body. Hypoxia-inducible factors (HIFs) have also been found to be expressed in the renal medulla, probably owing to the hypoxic conditions in the renal medulla. This study was designed to test the effects of HIF activation on renal sodium handling and renal medullary COX2 expression. Our data showed that HIF activation by the prolyl hydroxylase inhibitor (PHI) FG4592 enhanced natriuresis in mice challenged with a high-salt diet. In addition, FG4592 upregulated the expression of COX2 in the renal medulla. An in vitro study further supported the finding that HIF can induce the expression of COX2 and that this induction is mediated through direct binding to the promoter region of the Cox2 gene, facilitating its transcription. In addition, the COX2 inhibitor celecoxib diminished the natriuretic effect of FG4592. Together, these results suggest that HIF activation promotes sodium excretion through upregulation of COX2 in the renal medulla and therefore maintains sodium homeostasis in the body.

Contribution of Oxidative Stress to HIF-1-Mediated Profibrotic Changes during the Kidney Damage

Hypoxia and oxidative stress are the common causes of various types of kidney injury. During recent years, the studies on hypoxia inducible factor- (HIF-) 1 attract more and more attention, which can not only mediate hypoxia adaptation but also contribute to profibrotic changes. Through analyzing related literatures, we found that oxidative stress can regulate the expression and activity of HIF-1α through some signaling molecules, such as prolyl hydroxylase domain-containing protein (PHD), PI-3K, and microRNA. And oxidative stress can take part in inflammation, epithelial-mesenchymal transition, and extracellular matrix deposition mediated by HIF-1 via interacting with classical NF-κB and TGF-β signaling pathways. Therefore, based on previous literatures, this review summarizes the contribution of oxidative stress to HIF-1-mediated profibrotic changes during the kidney damage, in order to further understand the role of oxidative stress in renal fibrosis.

Overexpression of MicroRNA-429 Transgene Into the Renal Medulla Attenuated Salt-Sensitive Hypertension in Dahl S Rats

BACKGROUND

We have previously shown that high salt stimulates the expression of miR-429 in the renal medulla, which induces mRNA decay of HIF prolyl-hydroxylase 2 (PHD2), an enzyme to promote the degradation of hypoxia-inducible factor (HIF)-1α, and increases the HIF-1α-mediated activation of antihypertensive genes in the renal medulla, consequently promoting extra sodium excretion. Our preliminary results showed that high salt-induced increase of miR-429 was not observed in Dahl S rats. This present study determined whether correction of this impairment in miR-429 would reduce PHD2 levels, increase antihypertensive gene expression in the renal medulla and attenuate salt-sensitive hypertension in Dahl S rats.

METHODS

Lentiviruses encoding rat miR-429 were transfected into the renal medulla in uninephrectomized Dahl S rats. Sodium excretion and blood pressure were then measured.

RESULTS

Transduction of lentiviruses expressing miR-429 into the renal medulla increased miR-429 levels, decreased PHD2 levels, and upregulated HIF-1α target gene NOS-2, which restored the adaptive mechanism to increase the antihypertensive gene after high-salt intake in Dahl S rats. Functionally, overexpression of miR-429 transgene in the renal medulla significantly improved pressure natriuretic response, enhanced urinary sodium excretion, and reduced sodium retention upon extra sodium loading, and consequently, attenuated the salt-sensitive hypertension in Dahl S rats.

CONCLUSIONS

Our results suggest that the impaired miR-429-mediated PHD2 inhibition in response to high salt in the renal medulla may represent a novel mechanism for salt-sensitive hypertension in Dahl S rats and that correction of this impairment in miR-429 pathway could be a therapeutic approach for salt-sensitive hypertension.

Collecting duct-specific knockout of sphingosine-1-phosphate receptor 1 aggravates DOCA-salt hypertension in mice

OBJECTIVE

We have previously reported that renal medullary sphingosine-1-phosphate (S1P) regulates sodium excretion via the S1P type-1 receptor (S1PR1). As S1PR1 is predominantly expressed in collecting ducts (CD), the present study tested the hypothesis that the CD-S1PR1 pathway plays a critical role in sodium excretion and contributes to salt-sensitive hypertension.

METHODS

CD-specific S1PR1 knockout mice were generated by crossing aquaporin-2-Cre mice with S1PR1-floxed mice. Renal sodium excretion and arterial pressure were compared between wild type and KO mice in response to high-salt challenges and treatment of deoxycorticosterone acetate (DOCA) salt.

RESULTS

Protein levels of renal medullary S1PR1 were increased by 100% after high-salt intake, whereas DOCA treatment with high-salt intake blocked the increase of S1PR1 levels. Urinary sodium excretions in knockout mice were decreased by 60% compared with wild type mice after acute intravenous sodium loading (0.84 ± 0.16 vs. 2.22 ± 0.62 μmole/min per g kwt). The pressure natriuresis was impaired in knockout mice compared with wild type mice (4.32 ± 1.04 vs. 8.73 ± 0.19 μmole/min per g kwt). The chronic high-salt intake-induced positive sodium balance was enhanced in knockout mice compared with wild type mice (5.27 ± 0.39 vs. 2.38 ± 1.04 mmol/100 g BW per 24 h). After 10-day DOCA-salt treatment, knockout mice developed more severe hypertension than wild type mice (SBP 142 ± 8 vs. 115 ± 4 mmHg).

CONCLUSION

The deletion of CD-S1PR1 reduced sodium excretion, promoted sodium retention, and accelerated DOCA-salt-induced salt-sensitive hypertension, suggesting that the CD-S1PR1 signaling is an important antihypertensive pathway by promoting sodium excretion and that impairment of renal medullary S1PR1 may represent a novel mechanism for salt-sensitive hypertension.

Polyprenol-Based Lipofecting Agents for In Vivo Delivery of Therapeutic DNA to Treat Hypertensive Rats

Development of efficient vectors for transfection is one of the major challenges in genetic engineering. Previous research demonstrated that cationic derivatives of polyisoprenoids (PTAI) may serve as carriers of nucleic acids. In the present study, the effectiveness of two PTAI-based formulations (PTAI-6–8 and 10–14) was investigated and compared to the commercial reagents. The purpose of applied gene therapy was to enhance the expression of vascular endothelial growth factor (VEGF-A) in the renal medulla of spontaneously hypertensive rats (SHR) and to test its potential as a novel antihypertensive intervention. In the first part of the study (in vitro), we confirmed that PTAI-based lipoplexes efficiently transfect XC rat sarcoma cells and are stable in 37 °C for 7 days. In the in vivo experiments, we administered selected lipoplexes directly to the kidneys of conscious SHR (via osmotic pumps). There were no blood pressure changes and VEGF-A level in renal medulla was significantly higher only for PTAI-10–14-based formulation. In conclusion, despite the promising results, we were not able to achieve VEGF-A expression level high enough to verify VEGF-A gene therapy usefulness in SHR. However, results of our study give important indications for the future development of PTAI-based DNA carriers and kidney-targeted gene delivery.

Effects of empagliflozin on nondiabetic salt-sensitive hypertension in uninephrectomized rats

Impaired pressure natriuresis (PN) underlies salt-sensitive hypertension, and renal inflammation and hypoxia-inducible factor-1 (HIF-1) have been implicated in the modulation of systemic hypertension. Although sodium-glucose cotransporter-2 (SGLT2) inhibitors were reported to lower blood pressure (BP) in type 2 diabetes mellitus, whether they have a role in nondiabetic hypertensive kidney diseases is unclear. The present study was undertaken to investigate whether nondiabetic salt-sensitive hypertension and accompanying renal inflammation are ameliorated by SGLT2 inhibition. Male Sprague-Dawley rats were randomly divided into three groups: sham controls (SCs), uninephrectomized controls (UCs), and empagliflozin-treated rats (ETs). All rats were fed a rodent diet with 8% NaCl throughout the study period. Empagliflozin was orally administered for 3 weeks after uninephrectomy. Systolic blood pressure was recorded weekly, and kidneys were harvested for immunoblotting, immunohistochemistry, and quantitative PCR analysis at the end of the animal experiment. Systolic BP was significantly decreased in ETs that were orally given empagliflozin for 3 weeks after uninephrectomy. Although ETs did not show any increase in weekly measured urine sodium, the right-shifted PN relationship in UCs was improved by empagliflozin treatment. The expression of HIF-1α was increased in the renal outer medulla of ETs. Consistent with this, HIF prolyl-hydroxylase-2 protein and mRNA were decreased in ETs. The abundance of CD3 and ED-1 immunostaining in UCs was reduced by empagliflozin treatment. The increased IL-1ß, gp91phox, and NOX4 mRNA levels in UCs were also reversed. Empagliflozin restored impaired PN in nondiabetic hypertensive kidney disease in association with increased renal medullary expression of HIF-1α and amelioration of renal inflammation.

Cellular cholesterol modifies flow-mediated gene expression

Downregulation of heme oxygenase-1 (HO-1), cyclooxygenase-2 (COX2), and nitric oxide synthase-2 (NOS2) in the kidneys of Dahl rodents causes salt sensitivity, while restoring their expression aids in Na⁺ excretion and blood pressure reduction. Loading cholesterol into collecting duct (CD) cells represses fluid shear stress (FSS)-mediated COX2 activity. Thus, we hypothesized that cholesterol represses flow-responsive genes necessary to effectuate Na⁺ excretion. To this end, CD cells were used to test whether FSS induces these genes and if cholesterol loading represses them. Mice fed either 0% or 1% cholesterol diet were injected with saline, urine volume and electrolytes were measured, and renal gene expression determined. FSS-exposed CD cells demonstrated increases in HO-1 mRNA by 350-fold, COX2 by 25-fold, and NOS2 by 8-fold in sheared cells compared with static cells (P < 0.01). Immunoblot analysis of sheared cells showed increases in HO-1, COX2, and NOS2 protein, whereas conditioned media contained more HO-1 and PGE₂ than static cells. Cholesterol loading repressed the sheared mediated protein abundance of HO-1 and NOS2 as well as HO-1 and PGE₂ concentrations in media. In cholesterol-fed mice, urine volume was less at 6 h after injection of isotonic saline (P < 0.05). Urinary Na⁺ concentration, urinary K⁺ concentration, and osmolality were greater, whereas Na⁺ excretion was less, at the 6-h urine collection time point in cholesterol-fed versus control mice (P < 0.05). Renal cortical and medullary HO-1 (P < 0.05) and NOS2 (P < 0.05) mRNA were repressed in cholesterol-fed compared with control mice. Cholesterol acts to repress flow induced natriuretic gene expression, and this effect, in vivo, may contribute to renal Na⁺ avidity.

HIF Activation Against CVD in CKD: Novel Treatment Opportunities

Cardiovascular disease is a common and serious complication in patients with chronic kidney disease (CKD). One of the fundamental functions of the cardiovascular system is oxygen delivery, therefore cardiovascular disease inherently is linked to insufficient tissue oxygenation. Advances in our knowledge of cellular oxygen sensing by a family of prolyl hydroxylases (PHDs) and their role in regulating hypoxia-inducible factors (HIFs) have led to the discovery of PHD inhibitors as HIF stabilizers. Several small-molecule PHD inhibitors are currently in clinical trials for the treatment of anemia in CKD. An additional advantage of PHD inhibition may be found in the potential impact on cardiovascular consequences associated with CKD. Several preclinical studies have suggested a potential benefit of HIF activation in myocardial infarction, cardiac remodeling, atherosclerosis, and peripheral artery disease. Ameliorating glucose and lipid metabolism and lowering blood pressure may also contribute to cardiovascular protection. On the other hand, the broad spectrum of HIF-dependent functions also may include unwanted side effects. Clinical application of PHD inhibitors therefore necessitates careful evaluation of the net systemic effect of HIF activation.

Activation of NF-κB signaling pathway during HCG-induced VEGF expression in luteal cells

Vascular endothelial growth factor (VEGF) plays an essential role in luteal angiogenesis, the present study therefore utilized luteal cells cultured in vitro to further investigate the activation and contribution of nuclear factor (NF)-κB to VEGF expression induced by human chorionic gonadotrophin (HCG). The present results showed HCG induced VEGF expression as well as hypoxia-inducible factor (HIF)-1α mRNA and protein expressions, which was blocked by NF-κB inhibitor pyrrolidine dithiocarbamate (PDTC). Further analysis found that these increases of VEGF and HIF-1α mRNA induced by HCG were also blocked by NF-κB siRNA transfection, which was consistent with PDTC treatment. However, HIF-1α siRNA treatment significantly decreased HCG induced-VEGF expression with no effect on NF-κB mRNA expression. Furthermore, combination of HIF-1α siRNA and PDTC treatment did not further decrease VEGF mRNA expression, and the result of chromatin immunoprecipitation indicated NF-κB may regulate HIF-1α transcription through binding with its promoter. Taken together, the present results clearly demonstrated that NF-κB was activated to regulate VEGF expression by increasing HIF-1α transcription in luteal cells treated with HCG. Therefore, the present study provided a new and important mechanism of luteal angiogenesis during the formation of corpus luteum in mammals.

Skin Sodium and Hypertension: a Paradigm Shift?

Purpose of Review

Dietary sodium is an important trigger for hypertension and humans show a heterogeneous blood pressure response to salt intake. The precise mechanisms for this have not been fully explained although renal sodium handling has traditionally been considered to play a central role.

Recent Findings

Animal studies have shown that dietary salt loading results in non-osmotic sodium accumulation via glycosaminoglycans and lymphangiogenesis in skin mediated by vascular endothelial growth factor-C, both processes attenuating the rise in BP. Studies in humans have shown that skin could be a buffer for sodium and that skin sodium could be a marker of hypertension and salt sensitivity.

Summary

Skin sodium storage could represent an additional system influencing the response to salt load and blood pressure in humans.

Regulation of hypoxia inducible factor/prolyl hydroxylase binding domain proteins 1 by PPARα and high salt diet

BACKGROUND

Hypoxia inducible factor (HIF)/prolyl hydroxylase domain (PHD)-containing proteins are involved in renal adaptive response to high salt (HS). Peroxisome proliferator activated receptor alpha (PPARα), a transcription factor involved in fatty acid oxidation is implicated in the regulation of renal function. As both HIF-1α/PHD and PPARα contribute to the adaptive changes to altered oxygen tension, this study tested the hypothesis that PHD-induced renal adaptive response to HS is PPARα-dependent.

METHODS

PPARα wild type (WT) and knock out (KO) mice were fed a low salt (LS) (0.03% NaCl) or a HS (8% NaCl) diet for 8 days and treated with hydralazine. PPARα and heme oxygenase (HO)-1 expression were evaluated in the kidney cortex and medulla. A 24-h urinary volume (UV), sodium excretion (UNaV), and nitrite excretion (UNOx V) were also determined.

RESULTS

PHD1 expression was greater in the medulla as compared to the cortex of PPARα WT mice (p<0.05) fed with a LS (0.03% NaCl) diet. The HS diet (8% NaCl) downregulated PHD1 expression in the medulla (p<0.05) but not the cortex of WT mice whereas expression was downregulated in the cortex (p<0.05) and medulla (p<0.05) of KO mice. These changes were accompanied by HS-induced diuresis (p<0.05) and natriuresis (p<0.05) that were greater in WT mice (p<0.05). Similarly, UNOx V, index of renal nitric oxide synthase (NOS) activity or availability and heme oxygenase (HO)-1 expression was greater in WT (p<0.05) but unchanged in KO mice on HS diet. Hydralazine, a PHD inhibitor, did not affect diuresis or natriuresis in LS diet-fed WT or KO mice but both were increased (p<0.05) in HS diet-fed WT mice. Hydralazine also increased UNOx V (p<0.05) with no change in diuresis, natriuresis, or HO-1 expression in KO mice on HS diet.

CONCLUSIONS

These data suggest that HS-induced PPARα-mediated downregulation of PHD1 is a novel pathway for PHD/HIF-1α transcriptional regulation for adaptive responses to promote renal function via downstream signaling involving NOS and HO.

Inhibition of microRNA-429 in the renal medulla increased salt sensitivity of blood pressure in Sprague Dawley rats

BACKGROUND

We have previously shown that high salt intake suppresses the expression of prolyl hydroxylase domain-containing protein 2 (PHD2), an enzyme promoting the degradation of hypoxia-inducible factor (HIF)-1α, and increases HIF-1α along with its target genes in the renal medulla, which promotes sodium excretion and regulates salt sensitivity of blood pressure. However, it remains unknown how high salt inhibits the expression of PHD2.

METHOD AND RESULTS

The current study first revealed that high-salt-induced PHD2 inhibition was due to the enhanced decay of mRNA. We then found that high salt significantly increased the expression of miR-429, which was subsequently proven to target the 3'-untranslated region of PHD2 and reduce PHD2 levels, in the renal medulla. To define the functional role of renal medullary miR-429 in the regulation of PHD2/HIF-1α-mediated renal adaptation to high salt intake and salt sensitivity of blood pressure, we locally inhibited miR-429 in the renal medulla by locked nucleic acid anti-miR-429 in uninephrectomized rats. Our results demonstrated that inhibition of miR-429 remarkably increased the levels of PHD2, which disrupted PHD2-associated adaptive activation of HIF-1α-mediated gene expression in response to high salt in the renal medulla and consequently inhibited urinary sodium excretion, enhanced sodium retention in response to chronic sodium overloading, and as a result, produced a salt-sensitive hypertension.

CONCLUSION

It is concluded that miR-429 is an important upstream mediator in PHD2/HIF-1α-associated renal adaptation to high salt intake and that deficiency in miR-429-mediated PHD2 inhibition in response to high salt in the renal medulla may represent a pathogenic mechanism for salt-sensitive hypertension.

Novel Mechanism for Buffering Dietary Salt in Humans: Effects of Salt Loading on Skin Sodium, Vascular Endothelial Growth Factor C, and Blood Pressure

High dietary sodium intake triggers increased blood pressure (BP). Animal studies show that dietary salt loading results in dermal Na⁺ accumulation and lymphangiogenesis mediated by VEGF-C (vascular endothelial growth factor C), both attenuating the rise in BP. Our objective was to determine whether these mechanisms function in humans. We assessed skin electrolytes, BP, and plasma VEGF-C in 48 healthy participants randomized to placebo (70 mmol sodium/d) and slow sodium (200 mmol/d) for 7 days. Skin Na⁺ and K⁺ concentrations were measured in mg/g of wet tissue and expressed as the ratio Na⁺:K⁺ to correct for variability in sample hydration. Skin Na⁺:K⁺ increased between placebo and slow sodium phases (2.91±0.08 versus 3.12±0.09; P=0.01). In post hoc analysis, there was a suggestion of a sex-specific effect, with a significant increase in skin Na⁺:K⁺ in men (2.59±0.09 versus 2.88±0.12; P=0.008) but not women (3.23±0.10 versus 3.36±0.12; P=0.31). Women showed a significant increase in 24-hour mean BP with salt loading (93±1 versus 91±1 mm Hg; P<0.001) while men did not (96±2 versus 96±2 mm Hg; P=0.91). Skin Na⁺:K⁺ correlated with BP, stroke volume, and peripheral vascular resistance in men but not in women. No change was noted in plasma VEGF-C. These findings suggest that the skin may buffer dietary Na⁺, reducing the hemodynamic consequences of increased salt, and this may be influenced by sex.

Effects of dimethyl carbonate-induced autophagic activation on follicular development in the mouse ovary

Dimethyl carbonate (DMC) is a widely used industrial chemical, which may be increasingly used in the future. However, its toxicity profile remains largely unknown. The present study was designed to investigate the effects of DMC exposure on the ovaries and the effect of autophagy activation on follicular development. Rats were randomly divided into a control group and low, medium and high dose DMC groups (all n=10). Histological analyses identified no marked differences in the rate of apoptosis between the control and low dose groups; however, marked apoptosis occurred in the medium and high dose groups. The expression of cleaved caspase-3 was significantly increased in the medium and high dose groups, which was consistent with changes observed in the expression of Bcl-2 and Bax. These results indicated that DMC exposure induces toxicity on ovarian function via the induction of apoptosis. The increased expression of the autophagy-related proteins light chain 3II, beclin-1 and p62 following exposure to DMC further indicated that autophagy was activated primarily in the granulosa cells of ovarian follicles in a dose-dependent manner. In addition, the changes in the expression of hypoxia inducible factor 1 α subunit (HIF-1α) and its target protein BCL2 interacting protein 3 (BNIP3) indicated that they may serve a role in the follicular development process induced by DMC. The results of the current study demonstrated that DMC exposure activated autophagy in the ovarian tissue. Furthermore, exposure to low doses of DMC may protect follicular development by activating the HIF-1α/BNIP3 signaling pathway. Taken together, these results indicate that exposure to medium and high doses of DMC induced follicular atresia by activating the apoptotic signaling pathway. This may be an important mechanism of regulating follicular development and ovarian function in mammals.

Intrarenal signaling mediated by CCK plays a role in salt intake-induced natriuresis

The natriuretic hormone CCK exhibits its gene transcripts in total kidney extracts. To test the possibility of CCK acting as an intrarenal mediator of sodium excretion, we examined mouse kidneys by 1) an in situ hybridization technique for CCK mRNA in animals fed a normal- or a high-sodium diet; 2) immuno-electron microscopy for the CCK peptide, 3) an in situ hybridization method and immunohistochemistry for the CCK-specific receptor CCKAR; 4) confocal image analysis of receptor-mediated Ca2+ responses in isolated renal tubules; and 5) metabolic cage experiments for the measurement of urinary sodium excretion in high-salt-fed mice either treated or untreated with the CCKAR antagonist lorglumide. Results showed the CCK gene to be expressed intensely in the inner medulla and moderately in the inner stripe of the outer medulla, with the expression in the latter being enhanced by high sodium intake. Immunoreactivity for the CCK peptide was localized to the rough endoplasmic reticulum of the medullary interstitial cells in corresponding renal regions, confirming it to be a secretory protein. Gene transcripts, protein products, and the functional activity for CCKAR were consistently localized to the late proximal tubule segments (S2 and S3) in the medullary rays, and the outer stripe of the outer medulla. Lorglumide significantly diminished natriuretic responses of mice to a dietary sodium load without altering the glomerular filtration rate. These findings suggest that the medullary interstitial cells respond to body fluid expansion by CCK release for feedback regulation of the late proximal tubular reabsorption.

Regulation and function of renal medullary cyclooxygenase-2 during high salt loading

Prostaglandins (PGs) are important autocrine/paracrine regulators that contribute to sodium balance and blood pressure control. Along the nephron, the highest amount of PGE₂ is found in the distal nephron, an important site for fine-tuning of urinary sodium and water excretion. Cylooxygenase-2 (COX-2) is abundantly expressed in the renal medulla and its expression along with urinary PGE₂ excretion is highly induced by chronic salt loading. Factors involved in high salt-induced COX-2 expression in the renal medulla include the hypertonicity, fluid shear stress (FSS), and hypoxia-inducible factor-1 alpha (HIF-1 alpha). Site-specific inhibition of COX-2 in the renal medulla of Sprague-Dawley rats causes sodium retention and salt-sensitive hypertension. Together, these results support the concept that renal medullary COX-2 functions an important natriuretic mediator that is activated by salt loading and its products promote sodium excretion and contribute to maintenance of sodium balance and blood pressure.

Hsp90β is involved in the development of high salt-diet-induced nephropathy via interaction with various signalling proteins

A high-salt diet often leads to a local intrarenal increase in renal hypoxia and oxidative stress, which are responsible for an excess production of pathogenic substances. Here, Wistar Kyoto/spontaneous hypertensive (WKY/SHR) rats fed a high-salt diet developed severe proteinuria, resulting from pronounced renal inflammation, fibrosis and tubular epithelial cell apoptosis. All these were mainly non-pressure-related effects. Hsp90β, TGF-β, HIF-1α, TNF-α, IL-6 and MCP-1 were shown to be highly expressed in response to salt loading. Next, we found that Hsp90β might play the key role in non-pressure-related effects of salt loading through a series of cellular signalling events, including the NF-κB, p38 activation and Bcl-2 inactivation. Hsp90β was previously proven to regulate the upstream mediators in multiple cellular signalling cascades through stabilizing and maintaining their activities. In our study, 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG) or Hsp90β knockdown dramatically alleviated the high-salt-diet-induced proteinuria and renal damage without altering blood pressure significantly, when it reversed activations of NF-κB, mTOR and p38 signalling cascades. Meanwhile, Co-IP results demonstrated that Hsp90β could interact with and stabilize TAK1, AMPKα, IKKα/β, HIF-1α and Raptor, whereas Hsp90β inhibition disrupted this process. In addition, Hsp90β inhibition-mediated renal improvements also accompanied the reduction of renal oxidative stress. In conclusion, salt loading indeed exhibited non-pressure-related impacts on proteinuria and renal dysfunction in WKY/SHR rats. Hsp90β inhibition caused the destabilization of upstream mediators in various pathogenic signalling events, thereby effectively ameliorating this nephropathy owing to renal hypoxia and oxidative stress.

Mesenchymal stem cell transplantation inhibited high salt-induced activation of the NLRP3 inflammasome in the renal medulla in Dahl S rats

Inflammasomes activate caspase-1 to produce interleukin (IL)-1β. Activation of the NLRP3 inflammasome is involved in various renal pathological conditions. It remains unknown whether the NLRP3 inflammasome activation participates in the abnormal renal response to high-salt (HS) diet in Dahl salt-sensitive (S) rats. In addition, our lab recently showed that transplantation of mesenchymal stem cells (MSCs) attenuated HS-induced inflammation in the renal medulla in Dahl S rat. However, it is unclear whether the anti-inflammatory action of MSCs is associated with inhibition of the NLRP3 inflammasome. The present study determined the response of the NLRP3 inflammasome to HS intake and the effect of MSC transplantation on the NLRP3 inflammasome in the renal medulla in Dahl S rats. Immunostaining showed that the inflammasome components NLRP3, ASC, and caspase-1 were mainly present in distal tubules and collecting ducts. Interestingly, the renal medullary levels of these inflammasome components were remarkably increased after a HS diet in Dahl S rats, while remaining unchanged in normal rats. This HS-induced activation of the NLRP3 inflammasome was significantly blocked by MSC transplantation into the renal medulla in Dahl S rats. Furthermore, infusion of a caspase-1 inhibitor into the renal medulla significantly attenuated HS-induced hypertension in Dahl S rats. These data suggest that HS-induced activation of the NLRP3 inflammasome may contribute to renal medullary dysfunction in Dahl S rats and that inhibition of inflammasome activation may be one of the mechanisms for the anti-inflammatory and anti-hypertensive effects of stem cells in the renal medulla in Dahl S rats.

Expression and contribution of the HIF-1α/VEGF signaling pathway to luteal development and function in pregnant rats

Vascular endothelial growth factor (VEGF) is vital in normal and abnormal angiogenesis in the ovary, particularly during the early development of the corpus luteum in the ovary. However, the molecular regulation of the expression VEGF during luteal development in vivo remains to be fully elucidated. As the expression of VEGF is mediated by hypoxia‑inducible factor (HIF)‑1α in luteal cells cultured in vitro, determined in our previous study, the present study was performed to confirm the hypothesis that HIF‑1α is induced and then regulates the expression of VEGF and VEGF‑dependent luteal development/function in vivo. This was investigated using a pregnant rat model treated with a small‑molecule inhibitor of HIF‑1α, echinomycin (Ech). The development of the corpus luteum in the pregnant rat ovary was identified via performing assays of the serum progesterone, testosterone and estradiol concentrations by radioimmunoassay, accompanied with determination of the changes in the expression levels of HIF‑1α and VEGF by reverse transcription‑quantitative polymerase chain reaction at different days of the developmental process. On day 5, serum progesterone levels were markedly increased, whereas serum levels of testosterone and estradiol did not change significantly. On day 17, the highest level of serum progesterone was observed, however, this was not the case for testosterone and estradiol. Further analysis of the expression levels of HIF‑1α and VEGF revealed that their changes were consistent with the changes in serum levels of progesterone, which occurred in the development of the corpus luteum in the ovaries of pregnant rats. Further investigation demonstrated that Ech inhibited luteal development through inhibiting the expression of VEGF, mediated by HIF‑1α, and subsequent luteal function, which was determined by detecting changes in serum progesterone on days 8 and 14. Taken together, these results demonstrated that HIF‑1α‑mediated expression of VEGF may be one of the important mechanisms regulating ovarian luteal development in mammals in vivo, which may provide novel strategies in treatment for fertility control and for certain types of ovarian dysfunction, including polycystic ovarian syndrome, ovarian hyperstimulation syndrome and ovarian neoplasia.

Interactions between HIF-1α and AMPK in the regulation of cellular hypoxia adaptation in chronic kidney disease

Renal hypoxia contributes to chronic kidney disease (CKD) progression, as validated in experimental and human CKD. In the early stages, increased oxygen consumption causes oxygen demand/supply mismatch, leading to hypoxia. Hence, early targeting of the determinants and regulators of oxygen consumption in CKD may alter the disease course before permanent damage ensues. Here, we focus on hypoxia inducible factor-1α (HIF-1α) and AMP-activated protein kinase (AMPK) and on the mechanisms by which they may facilitate cellular hypoxia adaptation. We found that HIF-1α activation in the subtotal nephrectomy (STN) model of CKD limits protein synthesis, inhibits apoptosis, and activates autophagy, presumably for improved cell survival. AMPK activation was diminished in the STN kidney and was remarkably restored by HIF-1α activation, demonstrating a novel role for HIF-1α in the regulation of AMPK activity. We also investigated the independent and combined effects of HIF-1α and AMPK on cell survival and death pathways by utilizing pharmacological and knockdown approaches in cell culture models. We found that the effect of HIF-1α activation on autophagy is independent of AMPK, but on apoptosis it is partially AMPK dependent. The effects of HIF-1α and AMPK activation on inhibiting protein synthesis via the mTOR pathway appear to be additive. These various effects were also observed under hypoxic conditions. In conclusion, HIF-1α and AMPK appear to be linked at a molecular level and may act as components of a concerted cellular response to hypoxic stress in the pathophysiology of CKD.

Overexpression of hypoxia-inducible factor prolyl hydoxylase-2 attenuates hypoxia-induced vascular endothelial growth factor expression in luteal cells

Vascular endothelial growth factor (VEGF)-dependent angiogenesis has a crucial role in the corpus luteum formation and their functional maintenances in mammalian ovaries. A previous study by our group reported that activation of hypoxia‑inducible factor (HIF)‑1α signaling contributes to the regulation of VEGF expression in the luteal cells (LCs) in response to hypoxia and human chorionic gonadotropin. The present study was designed to test the hypothesis that HIF prolyl‑hydroxylases (PHDs) are expressed in LCs and overexpression of PHD2 attenuates the expression of VEGF induced by hypoxia in LCs. PHD2-overexpressing plasmid was transfected into LC2 cells, and successful plasmid transfection and expression was confirmed by reverse transcription quantitative polymerase chain reaction and western blot analysis. In addition, the present study investigated changes of HIF‑1α and VEGF expression after incubation under hypoxic conditions and PHD2 transfection. PHD2 expression was significantly higher expressed than the other two PHD isoforms, indicating its major role in LCs. Moreover, a significant increase of VEGF mRNA expression was identified after incubation under hypoxic conditions, which was, however, attenuated by PHD2 overexpression in LCs. Further analysis also indicated that this hypoxia‑induced increase in the mRNA expression of VEGF was consistent with increases in the protein levels of HIF‑1α, which is regulated by PHD-mediated degradation. In conclusion, the results of the present study indicated that PHD2 is the main PHD expressed in LCs and hypoxia‑induced VEGF expression can be attenuated by PHD2 overexpression through HIF‑1α‑mediated mechanisms in LCs. This PHD2-mediated transcriptional activation may be one of the mechanisms regulating VEGF expression in LCs during mammalian corpus luteum development.

Stem cell conditioned culture media attenuated albumin-induced epithelial-mesenchymal transition in renal tubular cells

Background

Proteinuria-induced epithelial-mesenchymal transition (EMT) plays an important role in progressive renal tubulointerstitial fibrosis in chronic renal disease. Stem cell therapy has been used for different diseases. Stem cell conditioned culture media (SCM) exhibits similar beneficial effects as stem cell therapy. The present study tested the hypothesis that SCM inhibits albumin-induced EMT in cultured renal tubular cells.

Methods

Rat renal tubular cells were treated with/without albumin (20 μmg/ml) plus SCM or control cell media (CCM). EMT markers and inflammatory factors were measured by Western blot and fluorescent images.

Results

Albumin induced EMT as shown by significant decreases in levels of epithelial marker E-cadherin, increases in mesenchymal markers fibroblast-specific protein 1 and α-smooth muscle actin, and elevations in collagen I. SCM inhibited all these changes. Meanwhile, albumin induced NF-κB translocation from cytosol into nucleus and that SCM blocked the nuclear translocation of NF-κB. Albumin also increased the levels of pro-inflammatory factor monocyte chemoattractant protein-1 (MCP)-1 by nearly 30 fold compared with control. SCM almost abolished albumin-induced increase of MCP-1.

Conclusion

These results suggest that SCM attenuated albumin-induced EMT in renal tubular cells via inhibiting activation of inflammatory factors, which may serve as a new therapeutic approach for chronic kidney diseases.

Expression and clinical significance of the HIF-1a/ET-2 signaling pathway during the development and treatment of polycystic ovary syndrome

Polycystic ovary syndrome (PCOS) is a major health problem in reproductive-aged women worldwide, but the precise pathogenesis of PCOS remains unclear. Our previous study revealed that hypoxia-inducible factor (HIF)-1a mediated endothelin (ET)-2 signaling plays an important role in ovulation in rats. Therefore, the present study used a PCOS rat model to test the hypotheses that HIF-1a signaling is expressed and inhibited in ovaries during PCOS formation and that the HIF-1a/ET-2 signaling pathway is a target of dimethyldiguanide (DMBG) in the clinical treatment of PCOS. First, the development of a PCOS model and the effect of DMBG treatment were examined through ovarian histology and serum hormone levels, which were consistent with previous reports. Second, HIF-1a and ET-2 expression were detected by immunohistochemistry and western blot. The results showed decreased HIF-1a/ET-2 expression in the ovaries of PCOS rats, whereas DMBG treatment reversed the protein decreases and improved the PCOS symptoms. Third, to understand the molecular mechanism, HIF-1a/ET-2 mRNA expression was also examined. Interestingly, HIF-1a mRNA increased in the ovaries of PCOS rats, while ET-2 mRNA decreased, indicating that HIF-1a protein degradation may be involved in POCS development and treatment. Finally, HIF prolyl hydroxylase (PHD) activity was examined to further clarify the contribution of HIF-1a signaling to the development and treatment of PCOS. The results suggested that the inhibition of HIF-1a/ET-2 signaling may be caused by increased PHD activity in PCOS. DMBG-treated PCOS may further activate HIF-1a signaling at least partly through inhibiting PHD activity. Taken together, these results indicate that HIF-1a signaling is inhibited in a PCOS rat model through increasing PHD activity. DMBG treatment improved PCOS by rescuing this pathway, suggesting that HIF-1a signaling plays an important role in the development and treatment of PCOS. This HIF-1a-mediated ET-2 signaling pathway may be an important mechanism regulating PCOS formation and treatment in mammalian ovaries in vivo and should be a new clinical target for PCOS prevention and treatment in the future.

Transplantation of mesenchymal stem cells into the renal medulla attenuated salt-sensitive hypertension in Dahl S rat

Adult stem cell deficiency has been implicated in the pathogenic mechanism for various diseases. Renal medullary dysfunction is one of the major mechanisms for the development of hypertension in Dahl salt-sensitive (S) rats. The present study first detected a stem cell deficiency in the renal medulla in Dahl S rats and then tested the hypothesis that transplantation of mesenchymal stem cells (MSCs) into the renal medulla improves salt-sensitive hypertension in Dahl S rats. Immunohistochemistry and flowcytometry analyses showed a significantly reduced number of stem cell marker CD133+ cells in the renal medulla from Dahl S rats compared with controls, suggesting a stem cell deficiency. Rat MSCs or control cells were transplanted into the renal medulla in uninephrectomized Dahl S rats, which were then treated with a low- or high-salt diet for 20 days. High-salt-induced sodium retention and hypertension was significantly attenuated in MSC-treated rats compared with control cell-treated rats. Meanwhile, high-salt-induced increases of proinflammatory factors, monocyte chemoattractant protein-1, and interleukin-1β, in the renal medulla were blocked by MSC treatment. Furthermore, immunostaining showed that high-salt-induced immune cell infiltration into the renal medulla was substantially inhibited by MSC treatment. These results suggested that stem cell defect in the renal medulla may contribute to the hypertension in Dahl S rats and that correction of this stem cell defect by MSCs attenuated hypertension in Dahl S rats through anti-inflammation.

KEY MESSAGE

Stem cell defect in the renal medulla may contribute to salt-sensitive hypertension Stem cell therapy is a potential therapeutic strategy for salt-sensitive hypertension Normal stem cell inhibits the inflammatory response to high salt in the renal medulla.

Silencing of hypoxia-inducible factor-1α gene attenuates chronic ischemic renal injury in two-kidney, one-clip rats

Overactivation of hypoxia-inducible factor (HIF)-1α is implicated as a pathogenic factor in chronic kidney diseases (CKD). However, controversy exists regarding the roles of HIF-1α in CKD. Additionally, although hypoxia and HIF-1α activation are observed in various CKD and HIF-1α has been shown to stimulate fibrogenic factors, there is no direct evidence whether HIF-1α is an injurious or protective factor in chronic renal hypoxic injury. The present study determined whether knocking down the HIF-1α gene can attenuate or exaggerate kidney damage using a chronic renal ischemic model. Chronic renal ischemia was induced by unilaterally clamping the left renal artery for 3 wk in Sprague-Dawley rats. HIF-1α short hairpin (sh) RNA or control vectors were transfected into the left kidneys. Experimental groups were sham+control vector, clip+control vector, and clip+HIF-1α shRNA. Enalapril was used to normalize blood pressure 1 wk after clamping the renal artery. HIF-1α protein levels were remarkably increased in clipped kidneys, and this increase was blocked by shRNA. Morphological examination showed that HIF-1α shRNA significantly attenuated injury in clipped kidneys: glomerular injury indices were 0.71 ± 0.04, 2.50 ± 0.12, and 1.34 ± 0.11, and the percentage of globally damaged glomeruli was 0.02, 34.3 ± 5.0, and 6.3 ± 1.6 in sham, clip, and clip+shRNA groups, respectively. The protein levels of collagen and α-smooth muscle actin also dramatically increased in clipped kidneys, but this effect was blocked by HIF-1α shRNA. In conclusion, long-term overactivation of HIF-1α is a pathogenic factor in chronic renal injury associated with ischemia/hypoxia.

Renal epithelial sodium channel is critical for blood pressure maintenance and sodium balance in the normal late pregnant rat

Normal pregnancy is a state marked by avid sodium retention and plasma volume expansion. Insufficient plasma volume expansion results in the compromised maternal state of intrauterine growth restriction, which afflicts ∼5% of all human pregnancies. We have recently shown that renal epithelial sodium channel (ENaC) activity in vivo in the late pregnant (LP) rat is increased. To determine the importance of the renal versus extrarenal ENaC in sodium retention and blood pressure regulation during pregnancy, we have chronically blocked the ENaC pharmacologically with daily subcutaneous injections of benzamil and genetically using intrarenal transfection of αENaC short hairpin RNA. Compared with untreated LP control animals, LP rats treated with benzamil retain less sodium and have reduced mean arterial blood pressure. Furthermore, LP rats treated with benzamil had lower maternal body weight gain. Intrarenal transfection of αENaC short hairpin RNA versus scrambled small RNA successfully decreased renal αENaC mRNA expression in LP rats. Intrarenal transfection of αENaC short hairpin RNA reduced maternal sodium retention, body weight gain and pup weight. Redundant physiological systems that protect blood pressure and sodium homeostasis were unable to compensate for the loss of ENaC activity in the pregnant rat. These findings demonstrate that the renal ENaC is necessary for maintaining pregnancy-mediated sodium retention, volume expansion and blood pressure regulation.

Silencing of HIF prolyl-hydroxylase 2 gene in the renal medulla attenuates salt-sensitive hypertension in Dahl S rats

BACKGROUND

In response to high salt intake, transcription factor hypoxia-inducible factor (HIF) 1α activates many antihypertensive genes, such as heme oxygenase 1 (HO-1) 1 and cyclooxygenase 2 (COX-2) in the renal medulla, which is an important molecular adaptation to promote extra sodium excretion. We recently showed that high salt inhibited the expression of HIF prolyl-hydroxylase 2 (PHD2), an enzyme that promotes the degradation of HIF-1α, thereby upregulating HIF-1α, and that high salt-induced inhibition in PHD2 and subsequent activation of HIF-1α in the renal medulla was blunted in Dahl salt-sensitive hypertensive rats. This study tested the hypothesis that silencing the PHD2 gene to increase HIF-1α levels in the renal medulla attenuates salt-sensitive hypertension in Dahl S rats.

METHODS

PHD2 short hairpin RNA (shRNA) plasmids were transfected into the renal medulla in uninephrectomized Dahl S rats. Renal function and blood pressure were then measured.

RESULTS

PHD2 shRNA reduced PHD2 levels by >60% and significantly increased HIF-1α protein levels and the expression of HIF-1α target genes HO-1 and COX-2 by >3-fold in the renal medulla. Functionally, pressure natriuresis was remarkably enhanced, urinary sodium excretion was doubled after acute intravenous sodium loading, and chronic high salt-induced sodium retention was remarkably decreased, and as a result, salt-sensitive hypertension was significantly attenuated in PHD2 shRNA rats compared with control rats.

CONCLUSIONS

Impaired PHD2 response to high salt intake in the renal medulla may represent a novel mechanism for hypertension in Dahl S rats, and inhibition of PHD2 in the renal medulla could be a therapeutic approach for salt-sensitive hypertension.

Effects of echinomycin on endothelin-2 expression and ovulation in immature rats primed with gonadotropins

Echinomycin is a small-molecule inhibitor of hypoxia- inducible factor-1 DNA-binding activity, which plays a crucial role in ovarian ovulation in mammalians. The present study was designed to test the hypothesis that hypoxia-inducible factor (HIF)-1α-mediated endothelin (ET)-2 expressions contributed to ovarian ovulation in response to human chorionic gonadotropin (hCG) during gonadotropin-induced superuvulation. By real-time RT-PCR analysis, ET-2 mRNA level was found to significantly decrease in the ovaries after echinomycin treatment, while HIF-1α mRNA and protein expression was not obviously changed. Further analysis also showed that these changes of ET-2 mRNA were consistent with HIF-1 activity in the ovaires, which is similar with HIF-1α and ET-2 expression in the granulosa cells with gonadotropin and echinomycin treatments. The results of HIF-1α and ET-2 expression in the granulosa cells transfected with cis-element oligodeoxynucleotide (dsODN) under gonadotropin treatment further indicated HIF-1α directly mediated the transcriptional activation of ET-2 during gonadotropin- induced superuvulation. Taken together, these results demonstrated that HIF-1α-mediated ET-2 transcriptional activation is one of the important mechanisms regulating gonadotropin-induced mammalian ovulatory precess in vivo.

Hypoxia-inducible factor prolyl-hydroxylase-2 mediates transforming growth factor beta 1-induced epithelial-mesenchymal transition in renal tubular cells

Transforming growth factor beta 1 (TGF-β1)-induced epithelial-mesenchymal transition (EMT) in kidney epithelial cells plays a key role in renal tubulointerstitial fibrosis in chronic kidney diseases. As hypoxia-inducible factor (HIF)-1α is found to mediate TGF-β1-induced signaling pathway, we tested the hypothesis that HIF-1α and its upstream regulator prolyl hydroxylase domain-containing proteins (PHDs) are involved in TGF-β1-induced EMT using cultured renal tubular cells. Our results showed that TGF-β1 stimulated EMT in renal tubular cells as indicated by the significant decrease in epithelial marker P-cadherin, and the increase in mesenchymal markers α-smooth muscle actin (α-SMA) and fibroblast-specific protein 1 (FSP-1). Meanwhile, we found that TGF-β1 time-dependently increased HIF-1α and that HIF-1α siRNA significantly inhibited TGF-β1-induced EMT, suggesting that HIF-1α mediated TGF-β1 induced-EMT. Real-time PCR showed that PHD1 and PHD2, rather than PHD3, could be detected, with PHD2 as the predominant form of PHDs (PHD1:PHD2=0.21:1.0). Importantly, PHD2 mRNA and protein, but not PHD1, were decreased by TGF-β1. Furthermore, over-expression of PHD2 transgene almost fully prevented TGF-β1-induced HIF-1α accumulation and EMT marker changes, indicating that PHD2 is involved in TGF-β1-induced EMT. Finally, Smad2/3 inhibitor SB431542 prevented TGF-β1-induced PHD2 decrease, suggesting that Smad2/3 may mediate TGF-β1-induced EMT through PHD2/HIF-1α pathway. It is concluded that TGF-β1 decreased PHD2 expression via an Smad-dependent signaling pathway, thereby leading to HIF-1α accumulation and then EMT in renal tubular cells. The present study suggests that PHD2/HIF-1α is a novel signaling pathway mediating the fibrogenic effect of TGF-β1, and may be a new therapeutic target in chronic kidney diseases.

The Role of Hypoxia-Inducible Factor/Prolyl Hydroxylation Pathway in Deoxycorticosterone Acetate/Salt Hypertension in the Rat

KKidney disease could result from hypertension and ischemia/hypoxia. Key mediators of cellular adaptation to hypoxia are oxygen-sensitive hypoxia inducible factor (HIF)s which are regulated by prolyl-4-hydroxylase domain (PHD)-containing dioxygenases. However, HIF activation can be protective as in ischemic death or promote renal fibrosis in chronic conditions. This study tested the hypothesis that increased HIF-1α consequent to reduced PHD expression contributes to the attendant hypertension and target organ damage in deoxycorticosterone acetate (DOCA)/salt hypertension and that PHD inhibition ameliorates this effect. In rats made hypertensive by DOCA/salt treatment (DOCA 50 mg/kg s/c; 1% NaCl orally), PHD inhibition with dimethyl oxallyl glycine (DMOG) markedly attenuated hypertension (P<0.05), proteinuria (P<0.05) and attendant tubular interstitial changes and glomerular damage (P<0.05). Accompanying these changes, DMOG blunted the increased expression of kidney injury molecule (KIM)-1 (P<0.05), a marker of tubular injury and reversed the decreased expression of nephrin (P<0.05), a marker of glomerular injury. DMOG also decreased collagen I staining (P<0.05), increased serum nitrite (P<0.05) and decreased serum 8-isopostane (P<0.05). However, the increased HIF-1α expression (P<0.01) and decreased PHD2 expression (P<0.05) in DOCA/salt hypertensive rats was not affected by DMOG. These data suggest that reduced PHD2 expression with consequent increase in HIF-1α expression probably results from hypoxia induced by DOCA/salt treatment with the continued hypoxia and reduced PHD2 expression evoking hypertensive renal injury and collagen deposition at later stages. Moreover, a PHD inhibitor exerted a protective effect in DOCA/salt hypertension by mechanisms involving increased nitric oxide production and reduced production of reactive oxygen species.

Overexpression of HIF prolyl-hydoxylase-2 transgene in the renal medulla induced a salt sensitive hypertension

Renal medullary hypoxia-inducible factor (HIF)-1α and its target genes, such as haem oxygenase and nitric oxide synthase, have been indicated to play an important role in the regulation of sodium excretion and blood pressure. HIF prolyl hydroxylase domain-containing proteins (PHDs) are major enzymes to promote the degradation of HIF-1α. We recently reported that high salt intake suppressed the renal medullary PHD2 expression and thereby activated HIF-1α-mediated gene regulation in the renal medulla in response to high salt. To further define the functional role of renal medullary PHD2 in the regulation of renal adaptation to high salt intake and the longer term control of blood pressure, we transfected PHD2 expression plasmids into the renal medulla in uninephrectomized rats and determined its effects on pressure natriuresis, sodium excretion after salt overloading and the long-term control of arterial pressure after high salt challenge. It was shown that overexpression of PHD2 transgene increased PHD2 levels and decreased HIF-1α levels in the renal medulla, which blunted pressure natriuresis, attenuated sodium excretion, promoted sodium retention and produced salt sensitive hypertension after high salt challenge compared with rats treated with control plasmids. There was no blood pressure change in PHD2-treated rats that were maintained in low salt diet. These results suggested that renal medullary PHD2 is an important regulator in renal adaptation to high salt intake and a deficiency in PHD2-mediated molecular adaptation in response to high salt intake in the renal medulla may represent a pathogenic mechanism producing salt sensitive hypertension.

Hypoxia inducible factor-1α-mediated gene activation in the regulation of renal medullary function and salt sensitivity of blood pressure

Many enzymes that produce natriuretic factors such as nitric oxide synthase (NOS), hemeoxygenase-1 (HO-1) and cyclooxygenase-2 (COX-2) are highly expressed in the renal medulla. These enzymes in the renal medulla are up-regulated in response to high salt intake. Inhibition of these enzymes within the renal medulla reduces sodium excretion and increases salt sensitivity of arterial blood pressure, indicating that these enzymes play important roles in kidney salt handling and renal adaptation to high salt challenge. However, it remains a question what mechanisms mediate the activation of these enzymes in response to high salt challenge in the renal medulla. Interestingly, these enzymes are oxygen sensitive genes and regulated by transcription factor hypoxia-inducible factor (HIF)-1α. Our recent serial studies have demonstrated that: 1) High salt intake stimulates HIF-1α-mediated gene expression, such as NOS, HO-1 and COX-2, in the renal medulla, which may augment the production of different antihypertensive factors in the renal medulla, mediating renal adaptation to high salt intake and regulating salt sensitivity of arterial blood pressure. 2) HIF prolyl-hydroxylase 2 (PHD2), an enzyme that promotes the degradation of HIF-1α, is highly expressed in renal medulla. High salt intake suppresses the expression of PHD2 in the renal medulla, which increases HIF-1α-mediated gene expressions in the renal medulla, thereby participates in the control of salt sensitivity of blood pressure. 3) The high salt-induced inhibition in PHD2 and the consequent activation of HIF-1α in the renal medulla is not observed in Dahl salt sensitive hypertensive (Dahl/ss) rats. Correction of these defects in PHD2/HIF-1α-associated molecular adaptation in the renal medulla improves sodium excretion, reduces sodium retention and attenuates saltsensitive hypertension in Dahl/ss rats. In conclusion, PHD2 regulation of HIF-1α-mediated gene activation in the renal medulla is an important molecular adaptation to high salt intake; impaired PHD2 regulation of HIF-1α-mediated gene activation in the renal medulla may be responsible for the salt-sensitive hypertension in Dahl/ss rats; correction of these defects may be used to as therapeutic strategies for the treatment of salt-sensitive hypertension.

Overexpression of HIF-1α transgene in the renal medulla attenuated salt sensitive hypertension in Dahl S rats

Hypoxia inducible factor (HIF)-1α-mediated gene activation in the renal medulla in response to high salt intake plays an important role in the control of salt sensitivity of blood pressure. High salt-induced activation of HIF-1α in the renal medulla is blunted in Dahl S rats. The present study determined whether the impairment of the renal medullary HIF-1α pathway was responsible for salt sensitive hypertension in Dahl S rats. Renal medullary HIF-1α levels were induced by either transfection of HIF-1α expression plasmid or chronic infusion of CoCl₂ into the renal medulla, which was accompanied by increased expressions of anti-hypertensive genes, cyclooxygenase-2 and heme oxygenase-1. Overexpression of HIF-1α transgenes in the renal medulla enhanced the pressure natriuresis, promoted the sodium excretion and reduced sodium retention after salt overload. As a result, hypertension induced by 2-week high salt was significantly attenuated in rats treated with HIF-1α plasmid or CoCl₂. These results suggest that an abnormal HIF-1α in the renal medulla may represent a novel mechanism mediating salt-sensitive hypertension in Dahl S rats and that induction of HIF-1α levels in the renal medulla could be a therapeutic approach for the treatment of salt-sensitive hypertension.

Activation of PI3K/mTOR signaling pathway contributes to induction of vascular endothelial growth factor by hCG in bovine developing luteal cells

We recently reported that HIF-1α plays a critical role in the regulation of vascular endothelial growth factor (VEGF) expression in the developing letual cells (LCs) and VEGF-dependent angiogenesis is essential for normal luteal development. Although it is believed that hypoxia is the primary inducer of VEGF, recent reports have also shown that human chorionic gonadotrophin (hCG) up-regulates VEGF expression in developing corpus luteum (CL). Therefore the present study was designed to test the induced effects of hCG on the expression of VEGF and HIF-1α in LCs under normoxic and hypoxic conditions. In addition, we also investigated whether the signaling pathways such as phosphatidylinositol 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) and mitogen-activated protein kinase (MAPK) are involved in hCG-induced VEGF in LCs. A significant increase of VEGF mRNA was found in LCs treated with hCG, which was consistent with the changes of HIF-1α protein, even under hypoxic conditions. However, there was no obvious changes of HIF-1α mRNA in hCG-treated LCs between normoxic and hypoxic conditions, indicating hCG induces VEGF expression by increasing transcription of HIF-1α, while hypoxia mainly increases HIF-1α protein stability. When LCs were pretreated with inhibitors, we found that the PI3K/mTOR signaling pathway is required for HIF-1α and VEGF expression induced by hCG, while the MAPK pathway is not required. Together, these results suggest that activation of IP3K/mTOR signaling pathway contributes to the induction of VEGF and HIF-1α in hCG-treated LCs. To our knowledge this will provide a new insight into the important mechanism of hCG/LH-induced VEGF-dependent angiogenesis in the bovine ovary.