AG490 promotes HIF-1α accumulation by inhibiting its hydroxylation

Regulation of FGF23: Beyond Bone

PURPOSE OF REVIEW

Fibroblast growth factor 23 (FGF23) is a bone- and bone marrow-derived hormone that is critical to maintain phosphate homeostasis. The principal actions of FGF23 are to reduce serum phosphate levels by decreasing kidney phosphate reabsorption and 1,25-dihydroxyvitamin D synthesis. FGF23 deficiency causes hyperphosphatemia and ectopic calcifications, while FGF23 excess causes hypophosphatemia and skeletal defects. Excess FGF23 also correlates with kidney disease, where it is associated with increased morbidity and mortality. Accordingly, FGF23 levels are tightly regulated, but the mechanisms remain incompletely understood.

RECENT FINDINGS

In addition to bone mineral factors, additional factors including iron, erythropoietin, inflammation, energy, and metabolism regulate FGF23. All these factors affect Fgf23 expression, while some also regulate FGF23 protein cleavage. Conversely, FGF23 may have a functional role in regulating these biologic processes. Understanding the bi-directional relationship between FGF23 and non-bone mineral factors is providing new insights into FGF23 regulation and function.

LPS-induced inflammation desensitizes hepatocytes to Fas-induced apoptosis through Stat3 activation-The effect can be reversed by ruxolitinib

Recent studies have established a concept of tumour necrosis factor‐α (TNF‐α)/Fas signalling crosstalk, highlighting TNF‐α as a critical cytokine in sensitizing hepatocytes to death induced by Fas activation. However, in the exact inflammatory response, besides TNF‐α, many other mediators, that might modulate apoptotic response differentially, are released. To resolve the issue, we studied the effects of lipopolysaccharide (LPS), one of the crucial inductors of inflammation in the liver, on apoptotic outcome. We show that LPS‐induced inflammation diminishes the sensitivity of hepatocytes to Fas stimulus in vivo at caspase‐8 level. Analysis of molecular mechanisms revealed an increased expression of various pro‐inflammatory cytokines in non‐parenchymal liver cells and hepatocyte‐specific increase in Bcl‐xL, associated with signal transducer and activator of transcription 3 (Stat3) phosphorylation. Pre‐treatment with ruxolitinib, a selective Janus kinase (JAK) 1/2 inhibitor, prevented the LPS‐induced Stat3 phosphorylation and restored the sensitivity of hepatocytes to Fas‐mediated apoptosis. Furthermore, ruxolitinib pre‐treatment diminished the LPS‐induced Bcl‐xL up‐regulation without an inhibitory effect on LPS‐induced expression of pro‐inflammatory cytokines. In summary, although the reports are showing that the effects of isolated pro‐inflammatory mediators, such as TNF‐α or neutrophils, are pro‐apoptotic, the overall effect of inflammatory milieu on hepatocytes in vivo is Stat3‐dependent desensitization to Fas‐mediated apoptosis.

pVHL-mediated regulation of the anti-angiogenic protein thrombospondin-1 decreases migration of Clear Cell Renal Carcinoma Cell Lines

Thrombospondin-1 (TSP-1) is a multifunctional matrix protein with antitumor activities due in part to its ability to inhibit angiogenesis, which in turn contributes to determine the fate of many tumours. Previous studies have shown that TSP-1 expression supports normal kidney angiostasis, and decreased TSP-1 levels contribute to the angiogenic phenotype of renal cell carcinomas (RCC). The loss of the von Hippel-Lindau tumour suppressor gene (VHL) in these tumours favours stabilization of the Hypoxia Inducible Factors (HIF), which in turn contribute to adapt tumour cells to hostile environments promoting tumour progression. However, HIF-independent regulation of certain genes might also be involved. We have previously shown that TSP-1 is regulated in hypoxia in clear cell RCC (ccRCC) in a HIF-independent manner; however, the effect of VHL protein (pVHL) on TSP-1 expression has not been evaluated. Our results proved that pVHL loss or mutation in its alpha or beta domain significantly decreased TSP-1 levels in ccRCC in a HIF-independent manner. Furthermore, this regulation proved to be important for ccRCC cells behaviour showing that decreased TSP-1 levels rendered ccRCC cells more migratory. This data substantiates a unique regulation pattern for TSP-1 in a pVHL-dependent manner, which may be relevant in the aggressiveness of ccRCC.

Cell death-based approaches in treatment of the urinary tract-associated diseases: a fight for survival in the killing fields

Urinary tract-associated diseases comprise a complex set of disorders with a variety of etiologic agents and therapeutic approaches and a huge global burden of disease, estimated at around 1 million deaths per year. These diseases include cancer (mainly prostate, renal, and bladder), urinary tract infections, and urolithiasis. Cell death plays a key role in the pathogenesis and therapy of these conditions. During urinary tract infections, invading bacteria may either promote or prevent host cell death by interfering with cell death pathways. This has been studied in detail for uropathogenic E. coli (UPEC). Inhibition of host cell death may allow intracellular persistence of live bacteria, while promoting host cell death causes tissue damage and releases the microbes. Both crystals and urinary tract obstruction lead to tubular cell death and kidney injury. Among the pathomechanisms, apoptosis, necroptosis, and autophagy represent key processes. With respect to malignant disorders, traditional therapeutic efforts have focused on directly promoting cancer cell death. This may exploit tumor-specific characteristics, such as targeting Vascular Endothelial Growth Factor (VEGF) signaling and mammalian Target of Rapamycin (mTOR) activity in renal cancer and inducing survival factor deprivation by targeting androgen signaling in prostate cancer. An area of intense research is the use of immune checkpoint inhibitors, aiming at unleashing the full potential of immune cells to kill cancer cells. In the future, this may be combined with additional approaches exploiting intrinsic sensitivities to specific modes of cell death such as necroptosis and ferroptosis. Here, we review the contribution of diverse cell death mechanisms to the pathogenesis of urinary tract-associated diseases as well as the potential for novel therapeutic approaches based on an improved molecular understanding of these mechanisms.

The metabolic bone disease associated with the Hyp mutation is independent of osteoblastic HIF1α expression

Fibroblast growth factor-23 (FGF23) controls key responses to systemic phosphate increases through its phosphaturic actions on the kidney. In addition to stimulation by phosphate, FGF23 positively responds to iron deficiency anemia and hypoxia in rodent models and in humans. The disorder X-linked hypophosphatemia (XLH) is characterized by elevated FGF23 in concert with an intrinsic bone mineralization defect. Indeed, the Hyp mouse XLH model has disturbed osteoblast to osteocyte differentiation with altered expression of a wide variety of genes, including FGF23. The transcription factor Hypoxia inducible factor-1α (HIF1α) has been implicated in regulating FGF23 production and plays a key role in proper bone cell differentiation. Thus the goals of this study were to determine whether HIF1α activation could influence FGF23, and to test osteoblastic HIF1α production on the Hyp endocrine and skeletal phenotypes in vivo. Treatment of primary cultures of osteoblasts/osteocytes and UMR-106 cells with the HIF activator AG490 resulted in rapid HIF1α stabilization and increased Fgf23 mRNA (50–100 fold; p < 0.01–0.001) in a time- and dose-dependent manner. Next, the Phex gene deletion in the Hyp mouse was bred onto mice with a HIF1α/Osteocalcin (OCN)-Cre background. Although HIF1α effects on bone could be detected, FGF23-related phenotypes due to the Hyp mutation were independent of HIF1α in vivo. In summary, FGF23 can be driven by ectopic HIF1α activation under normal iron conditions in vitro, but factors independent of HIF1α activity after mature osteoblast formation are responsible for the disease phenotypes in Hyp mice in vivo.

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In vitro, a HIF activator stabilized HIF1α and increased Fgf23 mRNA expression.

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A novel mouse model was generated by breeding the Hyp mouse onto the HIF1α/Osteocalcin (OCN)-Cre background.

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Factors independent of HIF1α activity are responsible for the disease phenotypes in Hyp mice.

MXRA5 is a TGF-β1-regulated human protein with anti-inflammatory and anti-fibrotic properties

Current therapy for chronic kidney disease (CKD) is unsatisfactory because of an insufficient understanding of its pathogenesis. Matrix remodelling-associated protein 5 (MXRA5, adlican) is a human protein of unknown function with high kidney tissue expression, not present in rodents. Given the increased expression of MXRA5 in injured tissues, including the kidneys, we have suggested that MXRA5 may modulate kidney injury. MXRA5 immunoreactivity was observed in tubular cells in human renal biopsies and in urine from CKD patients. We then explored factors regulating MXRA5 expression and MXRA5 function in cultured human proximal tubular epithelial cells and explored MXRA5 expression in kidney cancer cells and kidney tissue. The fibrogenic cytokine transforming growth factor-β1 (TGFβ1) up-regulated MXRA5 mRNA and protein expression. TGFβ1-induced MXRA5 up-regulation was prevented by either interference with TGFβ1 activation of the TGFβ receptor 1 (TGFBR1, ALK5) or by the vitamin D receptor agonist paricalcitol. By contrast, the pro-inflammatory cytokine TWEAK did not modulate MXRA5 expression. MXRA5 siRNA-induced down-regulation of constitutive MXRA5 expression resulted in higher TWEAK-induced expression of chemokines. In addition, MXRA5 down-regulation resulted in a magnified expression of genes encoding extracellular matrix proteins in response to TGFβ1. Furthermore, in clear cell renal cancer, von Hippel-Lindau (VHL) regulated MXRA5 expression. In conclusion, MXRA5 is a TGFβ1- and VHL-regulated protein and, for the first time, we identify MXRA5 functions as an anti-inflammatory and anti-fibrotic molecule. This information may yield clues to design novel therapeutic strategies in diseases characterized by inflammation and fibrosis.

Targeting inflammation in diabetic kidney disease: early clinical trials

INTRODUCTION

The age-standardized death rate from diabetic kidney disease increased by 106% from 1990 to 2013, indicating that novel therapeutic approaches are needed, in addition to the renin-angiotensin system (RAS) blockers currently in use. Clinical trial results of anti-fibrotic therapy have been disappointing. However, promising anti-inflammatory drugs are currently on phase 1 and 2 randomized controlled trials.

AREAS COVERED

The authors review the preclinical, phase 1 and 2 clinical trial information of drugs tested for diabetic kidney disease that directly target inflammation as a main or key mode of action. Agents mainly targeting other pathways, such as endothelin receptor or mineralocorticoid receptor blockers and vitamin D receptor activators are not discussed.

EXPERT OPINION

Agents targeting inflammation have shown promising results in the treatment of diabetic kidney disease when added on top of RAS blockade. The success of pentoxifylline in open label trials supports the concept of targeting inflammation. In early clinical trials, the pentoxifylline derivative CTP-499, the CCR2 inhibitor CCX140-B, the CCL2 inhibitor emapticap pegol and the JAK1/JAK2 inhibitor baricitinib were the most promising drugs for diabetic kidney disease. The termination of trials testing the anti-IL-1β antibody gevokizumab in 2015 will postpone the evaluation of therapies targeting inflammatory cytokines.

Pathogenesis of Myeloproliferative Neoplasms: Role and Mechanisms of Chronic Inflammation

Myeloproliferative neoplasms (MPNs) are a heterogeneous group of clonal diseases characterized by the excessive and chronic production of mature cells from one or several of the myeloid lineages. Recent advances in the biology of MPNs have greatly facilitated their molecular diagnosis since most patients present with mutation(s) in the JAK2, MPL, or CALR genes. Yet the roles played by these mutations in the pathogenesis and main complications of the different subtypes of MPNs are not fully elucidated. Importantly, chronic inflammation has long been associated with MPN disease and some of the symptoms and complications can be linked to inflammation. Moreover, the JAK inhibitor clinical trials showed that the reduction of symptoms linked to inflammation was beneficial to patients even in the absence of significant decrease in the JAK2-V617F mutant load. These observations suggested that part of the inflammation observed in patients with JAK2-mutated MPNs may not be the consequence of JAK2 mutation. The aim of this paper is to review the different aspects of inflammation in MPNs, the molecular mechanisms involved, the role of specific genetic defects, and the evidence that increased production of certain cytokines depends or not on MPN-associated mutations, and to discuss possible nongenetic causes of inflammation.

Horizon 2020 in Diabetic Kidney Disease: The Clinical Trial Pipeline for Add-On Therapies on Top of Renin Angiotensin System Blockade

Diabetic kidney disease is the most frequent cause of end-stage renal disease. This implies failure of current therapeutic approaches based on renin-angiotensin system (RAS) blockade. Recent phase 3 clinical trials of paricalcitol in early diabetic kidney disease and bardoxolone methyl in advanced diabetic kidney disease failed to meet the primary endpoint or terminated on safety concerns, respectively. However, various novel strategies are undergoing phase 2 and 3 randomized controlled trials targeting inflammation, fibrosis and signaling pathways. Among agents currently undergoing trials that may modify the clinical practice on top of RAS blockade in a 5-year horizon, anti-inflammatory agents currently hold the most promise while anti-fibrotic agents have so far disappointed. Pentoxifylline, an anti-inflammatory agent already in clinical use, was recently reported to delay estimated glomerular filtration rate (eGFR) loss in chronic kidney disease (CKD) stage 3–4 diabetic kidney disease when associated with RAS blockade and promising phase 2 data are available for the pentoxifylline derivative CTP-499. Among agents targeting chemokines or chemokine receptors, the oral small molecule C-C chemokine receptor type 2 (CCR2) inhibitor CCX140 decreased albuminuria and eGFR loss in phase 2 trials. A dose-finding trial of the anti-IL-1β antibody gevokizumab in diabetic kidney disease will start in 2015. However, clinical development is most advanced for the endothelin receptor A blocker atrasentan, which is undergoing a phase 3 trial with a primary outcome of preserving eGFR. The potential for success of these approaches and other pipeline agents is discussed in detail.

Mitochondria-targeted therapies for acute kidney injury

Acute kidney injury (AKI) is a serious clinical condition with no effective treatment. Tubular cells are key targets in AKI. Tubular cells and, specifically, proximal tubular cells are extremely rich in mitochondria and mitochondrial changes had long been known to be a feature of AKI. However, only recent advances in understanding the molecules involved in mitochondria biogenesis and dynamics and the availability of mitochondria-targeted drugs has allowed the exploration of the specific role of mitochondria in AKI. We now review the morphological and functional mitochondrial changes during AKI, as well as changes in the expression of mitochondrial genes and proteins. Finally, we summarise the current status of novel therapeutic strategies specifically targeting mitochondria such as mitochondrial permeability transition pore (MPTP) opening inhibitors (cyclosporine A (CsA)), quinone analogues (MitoQ, SkQ1 and SkQR1), superoxide dismutase (SOD) mimetics (Mito-CP), Szeto-Schiller (SS) peptides (Bendavia) and mitochondrial division inhibitors (mdivi-1). MitoQ, SkQ1, SkQR1, Mito-CP, Bendavia and mdivi-1 have improved the course of diverse experimental models of AKI. Evidence for a beneficial effect of CsA on human cardiac ischaemia-reperfusion injury derives from a clinical trial; however, CsA is nephrotoxic. MitoQ and Bendavia have been shown to be safe for humans. Ongoing clinical trials are testing the efficacy of Bendavia in AKI prevention following renal artery percutaneous transluminal angioplasty.

Therapeutic approaches to diabetic nephropathy--beyond the RAS

Despite improvements in glycaemic and blood pressure control, and the efficacy of renin-angiotensin system (RAS) blockade for proteinuria reduction, diabetic nephropathy is the most frequent cause of end-stage renal disease in developed countries. This finding is consistent with the hypothesis that key pathogenetic mechanisms leading to progression of renal disease are not modified or inactivated by current therapeutic approaches. Although extensive research has elucidated molecular signalling mechanisms that are involved in progression of diabetic kidney disease, a number of high-profile clinical trials of potentially nephroprotective agents have failed, highlighting an insufficient understanding of pathogenic pathways. These include trials of paricalcitol in early diabetic kidney disease and bardoxolone methyl in advanced-stage disease. Various strategies based on encouraging data from preclinical studies that showed renoprotective effects of receptor antagonists, neutralizing antibodies, kinase inhibitors, small compounds and peptide-based technologies are currently been tested in randomized controlled trials. Phase II clinical trials are investigating approaches targeting inflammation, fibrosis and signalling pathways. However, only one trial that aims to provide evidence for marketing approval of a potentially renoprotective drug (atrasentan) is underway-further research into the potential nephroprotective effects of novel glucose-lowering agents is required.

Cross-talk between HIF and p53 as mediators of molecular responses to physiological and genotoxic stresses

Abnormal rates of growth together with metastatic potential and lack of susceptibility to cellular signals leading to apoptosis are widely investigated characteristics of tumors that develop via genetic or epigenetic mechanisms. Moreover, in the growing tumor, cells are exposed to insufficient nutrient supply, low oxygen availability (hypoxia) and/or reactive oxygen species. These physiological stresses force them to switch into more adaptable and aggressive phenotypes. This paper summarizes the role of two key mediators of cellular stress responses, namely p53 and HIF, which significantly affect cancer progression and compromise treatment outcomes. Furthermore, it describes cross-talk between these factors.