The hypoxia-inducible factor-α prolyl hydroxylase inhibitor FG4592 ameliorates renal fibrosis by inducing the H3K9 demethylase JMJD1A.

The transcription factors hypoxia-inducible factor-1α and -2α (HIF-1α/2α) are the major regulators of the cellular response to hypoxia and play a key role in renal fibrosis associated with acute and chronic kidney disease. Jumonji domain-containing 1a (JMJD1A), a histone H3 lysine 9 (H3K9) demethylase, is reported to be an important target gene of HIF-α. However, whether JMJD1A and H3K9 methylation status play a role in renal fibrosis is unclear. Here, we investigated the involvement of HIF-α, JMJD1A, and monomethylated/dimethylated H3K9 (H3K9me1/H3K9me2) levels in unilateral ureteral obstruction (UUO)-induced renal fibrosis in mice. Intraperitoneal administration of FG4592, an inhibitor of HIF-α prolyl hydroxylase, which controls HIF-α protein stability, significantly attenuated renal fibrosis on days 3 and 7 following UUO. FG4592 concomitantly increased JMJD1A expression, decreased H3K9me1/me2 levels, reduced profibrotic gene expression, and increased erythropoietin expression in renal tissues of UUO mice. The beneficial effects of FG4592 on renal fibrosis were inhibited by the administration of JMJD1A-specific siRNA to mice immediately following UUO. Incubation of normal rat kidney-49F and/or -52E cells with transforming growth factor-ß1 (TGF-ß1) in vitro resulted in upregulated expression of α-smooth muscle actin and H3K9me1/me2, and these effects were inhibited by cotreatment with FG4592. In contrast, FG4592 treatment further enhanced the TGF-ß1-stimulated upregulation of JMJD1A but had no effect on TGF-ß1-stimulated expression of the H3K9 methyltransferase euchromatic histone-lysine N-methyltransferase 2. Collectively, these findings establish a crucial role for the HIF-α1/2-JMJD1A-H3K9me1/me2 regulatory axis in the therapeutic effect of FG4592 in renal fibrosis.NEW & NOTEWORTHY Using a mouse model of renal fibrosis and transforming growth factor-ß1-stimulated rat cell lines, we show that treatment with FG4592, an inhibitor of hypoxia-inducible factor-1α and -2α (HIF-1α/2α) prolyl hydroxylase decreases renal fibrosis and concomitantly reduces methylated lysine 9 of histone H3 (H3K9) levels via upregulation of Jumonji domain-containing 1a (JMJD1A). The results identify a novel role for the HIF-1α/2α-JMJD1A-H3K9 regulatory axis in suppressing renal fibrosis.

Upregulation of Mineralocorticoid Receptor Contributes to Development of Salt-Sensitive Hypertension after Ischemia-Reperfusion Injury in Rats.

The ischemia-reperfusion injury (IRI) of rat kidneys is used as a model of acute kidney injury. Salt-sensitive hypertension occurs in rats after IRI, and the distal nephrons play important roles in the development of this condition. We investigated the role of the mineralocorticoid receptor (MR) in the progression of IRI-induced salt-sensitive hypertension in rats. Fourteen days after right-side nephrectomy, IRI was induced by clamping the left renal artery, with sham surgery performed as a control. IRI rats were provided with normal water or water with 1.0% NaCl (IRI/NaCl), or they were implanted with an osmotic mini-pump to infuse vehicle or aldosterone (IRI/Aldo). Esaxerenone, a non-steroidal MR blocker (MRB), was administered to IRI/NaCl and IRI/Aldo rats for 6 weeks. MR expression increased by day 7 post-IRI. Blood pressure and urinary protein excretion increased in IRI/NaCl and IRI/Aldo rats over the 6-week period, but these effects were negated by MRB administration. The MRB attenuated the expression of the gamma-epithelial sodium channel (ENaC) and renal damage. The ENaC inhibitor, amiloride, ameliorated hypertension and renal damage in IRI/NaCl and IRI/Aldo rats. Our findings thus showed that MR upregulation may play a pivotal role in ENaC-mediated sodium uptake in rats after IRI, resulting in the development of salt-sensitive hypertension in response to salt overload or the activation of the renin-angiotensin-aldosterone system.

Klotho overexpression protects against renal aging along with suppression of transforming growth factor-ß1 signaling pathways.

Klotho is an antiaging protein reported to suppress transforming growth factor-ß1 (TGF-ß1) signaling. Aging kidneys are characterized by interstitial fibrosis, accumulation of cell cycle-arrested cells, and increased levels of oxidative stress. TGF-ß1 signaling is involved in these processes. In this study, we investigated whether klotho overexpression improves these features in the kidneys of aging mice and examined the inhibitory effect of klotho on signaling molecules related to transforming growth of TGF-ß1. Klotho transgenic (KLTG) and wild-type (WT) mice were used, and 8-wk-old and 24-mo-old mice were defined as young and aging, respectively. We found that klotho expression was decreased in aging WT mice, but it was maintained in aging KLTG mice. Klotho overexpression improved the survival of 24-mo-old mice. Although the serum Ca2+ level was significantly lower in aging KLTG mice than in aging WT mice, the serum phosphate level did not differ between these mice. Klotho overexpression attenuated the increases in blood pressure, serum blood urea nitrogen level, and serum creatinine level in aging mice. Interstitial fibrosis, accumulation of cell cycle-arrested cells, and oxidative stress did not differ between young KLTG and WT mice, but they were significantly suppressed in aging KLTG mice compared with aging WT mice. Furthermore, the expression of TGF-ß1-related signaling molecules was increased in aging WT mice, whereas it was inhibited in aging KLTG mice. These data suggest that klotho overexpression protects against kidney aging along with suppression of TGF-ß1 signaling pathways.NEW & NOTEWORTHY Klotho is considered as an antiaging protein, and its overexpression may be a candidate therapy for protection against kidney damage with advanced aging. Although multiple factors are involved in the aging process, we showed that klotho overexpression inhibited interstitial fibrosis, accumulation of cell cycle-arrested cells, and increased levels of oxidative stress in the kidneys of aging mice, suppressing transforming growth factor-ß1-related signaling pathways. The present data showed that klotho overexpression protects against age-associated kidney damage.

Klotho protects chromosomal DNA from radiation-induced damage.

Klotho is an anti-aging, single-pass transmembrane protein found mainly in the kidney. Although aging is likely to be associated with DNA damage, the involvement of Klotho in protecting cells from DNA damage is still unclear. In this study, we examined DNA damage in human kidney cells and mouse kidney tissue after ionizing radiation (IR). The depletion and overexpression of Klotho in human kidney cells reduced and increased the cell survival rates after IR, respectively. The formation of γ-H2AX foci, representing DNA damage, was significantly elevated immediately after IR in cells with Klotho depletion and decreased in cells overexpressing Klotho. These results were confirmed in mouse renal tissues after IR. Quantification of DNA damage by a comet assay revealed that the Klotho knockdown significantly increased the amount of DNA damage immediately after IR, suggesting that Klotho protects chromosomal DNA from the induction of damage, rather than facilitating DNA repair. Consistent with this notion, Klotho was detected in both the nucleus and cytoplasm. In the nucleus, Klotho may serve to protect chromosomal DNA from damage, leading to its anti-aging effects.

A Combination of Iohexol Treatment and Ionizing Radiation Exposure Enhances Kidney Injury in Contrast-Induced Nephropathy by Increasing DNA Damage.

Contrast media has been shown to induce nephropathy (i.e., contrast-induced nephropathy) after various types of radiological examinations. The molecular mechanism of contrast-induced nephropathy has been unclear. In this study, we investigated the mechanism of contrast-induced nephropathy by examining the effects of combined treatment of contrast medium and ionizing radiation on kidney cells in vitro and kidney tissue in vivo. In human renal tubular epithelium cells, immunofluorescence analysis revealed that iohexol increased the numbers of radiation-induced γH2AX nuclear foci. The numbers of γH2AX nuclear foci remained high at 24 h, suggesting that some radiation-induced double-strand breaks remain unrepaired in the presence of iohexol. We established a mouse model of contrast-induced nephropathy, then showed that iohexol and ionizing radiation synergistically reduced renal function and induced double-strand breaks. Importantly, iohexol induced significant macrophage accumulation and oxidative DNA damage in the kidneys of contrast-induced nephropathy model mice in the absence of ionizing radiation; these effects were amplified by ionizing radiation. The results suggest that underlying inflammation and oxidative DNA damage caused by iohexol contribute to the enhancement of radiation-induced double-strand breaks, leading to contrast-induced nephropathy.

Cumulative Dialytic Glucose Exposure is a Risk Factor for Peritoneal Fibrosis and Angiogenesis in Pediatric Patients Undergoing Peritoneal Dialysis Using Neutral-pH Fluids.

Introduction: Neutral-pH dialysate has been reported to be beneficial to prevent the peritoneal pathological changes in adult peritoneal dialysis (PD) patients, but its use is controversial in pediatric PD patients. In addition, the impact of cumulative dialytic glucose exposure has not been examined. Methods: Pediatric PD patients using conventional fluids (conventional group, n = 31) or those using neutral-pH fluids (neutral-pH group, n = 33) were compared. Clinical risk factors for peritoneal pathological changes in the neutral-pH group were analyzed using generalized linear modeling. Furthermore, the mechanisms of peritoneal pathological changes were explored using immunohistochemical studies and cultured cells. Results: The median (interquartile range) duration of dialysis was 3.2 (1.7-5.3) years in overall patients. After propensity score matching, the conventional group showed increased thickening of the submesothelial compact (SMC) zone and lower luminal-to-vessel diameter (L/V) ratio than the neutral-pH group. In the neutral-pH group, the cumulative dialytic glucose exposure was an independent risk factor for greater thickness of the SMC zone (odds ratio [OR], 1.54; 95% confidence interval [CI], 1.16-2.05) and higher submesothelial microvessel density (OR, 1.29; 95% CI, 1.01-1.64). Immunohistochemical study showed that cumulative dialytic glucose exposure correlated with the proportion of the tissue expressing hypoxia inducible factor -1α (HIF-1α) and vascular endothelial growth factor-α (VEGF-α). In human peritoneal mesothelial cells, high glucose significantly increased HIF-1α and VEGF-α expressions. Conclusion: Cumulative dialytic glucose exposure is an independent risk factor for peritoneal fibrosis and angiogenesis in pediatric patients undergoing PD using neutral-pH fluids, which might be associated with greater VEGF-α production by myofibroblasts implying a hypoxic response.

Klotho deficiency intensifies hypoxia-induced expression of IFN-α/ß through upregulation of RIG-I in kidneys.

Hypoxia is a common pathway to the progression of end-stage kidney disease. Retinoic acid-inducible gene I (RIG-I) encodes an RNA helicase that recognizes viruses including SARS-CoV2, which is responsible for the production of interferon (IFN)-α/ß to prevent the spread of viral infection. Recently, RIG-I activation was found under hypoxic conditions, and klotho deficiency was shown to intensify the activation of RIG-I in mouse brains. However, the roles of these functions in renal inflammation remain elusive. Here, for in vitro study, the expression of RIG-I and IFN-α/ß was examined in normal rat kidney (NRK)-52E cells incubated under hypoxic conditions (1% O2). Next, siRNA targeting RIG-I or scramble siRNA was transfected into NRK52E cells to examine the expression of RIG-I and IFN-α/ß under hypoxic conditions. We also investigated the expression levels of RIG-I and IFN-α/ß in 33 human kidney biopsy samples diagnosed with IgA nephropathy. For in vivo study, we induced renal hypoxia by clamping the renal artery for 10 min in wild-type mice (WT mice) and Klotho-knockout mice (Kl-/- mice). Incubation under hypoxic conditions increased the expression of RIG-I and IFN-α/ß in NRK52E cells. Their upregulation was inhibited in NRK52E cells transfected with siRNA targeting RIG-I. In patients with IgA nephropathy, immunohistochemical staining of renal biopsy samples revealed that the expression of RIG-I was correlated with that of IFN-α/ß (r = 0.57, P<0.001, and r = 0.81, P<0.001, respectively). The expression levels of RIG-I and IFN-α/ß were upregulated in kidneys of hypoxic WT mice and further upregulation was observed in hypoxic Kl-/- mice. These findings suggest that hypoxia induces the expression of IFN-α/ß through the upregulation of RIG-I, and that klotho deficiency intensifies this hypoxia-induced expression in kidneys.

Interferon-γ enhances the therapeutic effect of mesenchymal stem cells on experimental renal fibrosis.

Mesenchymal stem cells (MSCs) administered for therapeutic purposes can be activated by interferon-γ (IFN-γ) secreted from natural killer cells in injured tissues and exert anti-inflammatory effects. These processes require a substantial period of time, leading to a delayed onset of MSCs' therapeutic effects. In this study, we investigated whether pretreatment with IFN-γ could potentiate the anti-fibrotic ability of MSCs in rats with ischemia-reperfusion injury (IRI) and unilateral ureter obstruction. Administration of MSCs treated with IFN-γ strongly reduced infiltration of inflammatory cells and ameliorated interstitial fibrosis compared with control MSCs without IFN-γ treatment. In addition, conditioned medium obtained from IFN-γ-treated MSCs decreased fibrotic changes in cultured cells induced by transforming growth factor-ß1 more efficiently than that from control MSCs. Most notably, secretion of prostaglandin E2 from MSCs was significantly increased by treatment with IFN-γ. Increased prostaglandin E2 in conditioned medium obtained from IFN-γ-treated MSCs induced polarization of immunosuppressive CD163 and CD206-positive macrophages. In addition, knockdown of prostaglandin E synthase weakened the anti-fibrotic effects of MSCs treated with IFN-γ in IRI rats, suggesting the involvement of prostaglandin E2 in the beneficial effects of IFN-γ. Administration of MSCs treated with IFN-γ might represent a promising therapy to prevent the progression of renal fibrosis.

Hypoxia-preconditioned mesenchymal stem cells prevent renal fibrosis and inflammation in ischemia-reperfusion rats.

BACKGROUND: Mesenchymal stem cells (MSCs) have been reported to promote the regeneration of injured tissue via their paracrine abilities, which are enhanced by hypoxic preconditioning. In this study, we examined the therapeutic efficacy of hypoxia-preconditioned MSCs on renal fibrosis and inflammation in rats with ischemia-reperfusion injury (IRI). METHODS: MSCs derived from rats and humans were incubated in 1% O2 conditions (1%O2 MSCs) for 24 h. After IRI, 1%O2 MSCs or MSCs cultured under normoxic conditions (21%O2 MSCs) were injected through the abdominal aorta. At 7 or 21 days post-injection, the rats were sacrificed and their kidneys were analyzed. In in vitro experiments, we examined whether 1%O2 MSCs enhanced the ability to produce anti-fibrotic humoral factors using transforming growth factor (TGF)-ß1-stimulated HK-2 cells incubated with conditioned medium from MSCs. RESULTS: Administration of rat 1%O2 MSCs (1%O2 rMSCs) attenuated renal fibrosis and inflammation more significantly than rat 21%O2 MSCs. Notably, human 1%O2 MSCs (1%O2 hMSCs) also attenuated renal fibrosis to the same extent as 1%O2 rMSCs. Flow cytometry showed that 1%O2 hMSCs did not change human leukocyte antigen expression. Further in vitro experiments revealed that conditioned medium from 1%O2 MSCs further suppressed TGF-ß1-induced fibrotic changes in HK-2 cells compared with 21%O2 MSCs. Hypoxic preconditioning enhanced vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) secretion. Interestingly, VEGF knockdown in 1%O2 MSCs attenuated HGF secretion and the inhibition of TGF-ß1-induced fibrotic changes in HK-2 cells. In addition, VEGF knockdown in 1%O2 hMSCs reduced the anti-fibrotic effect in IRI rats. CONCLUSIONS: Our results indicate that hypoxia-preconditioned MSCs are useful as an allogeneic transplantation cell therapy to prevent renal fibrosis and inflammation.