Up-regulation of Human myo-Inositol Oxygenase by Hyperosmotic Stress in Renal Proximal Tubular Epithelial Cells

Study on the osmotic response and function of myo-inositol oxygenase in euryhaline fish nile tilapia (Oreochromis niloticus)

To understand the role of myo-inositol oxygenase (miox) in the osmotic regulation of Nile tilapia, its expression was analyzed in various tissues. The results showed that the expression of miox gene was highest in the kidney, followed by the liver, and was significantly upregulated in the kidney and liver under 1 h hyperosmotic stress. The relative luminescence efficiency of the miox gene transcription starting site (-4,617 to +312 bp) under hyperosmotic stress was measured. Two fragments (-1,640/-1,619 and -620/-599) could induce the luminescence activity. Moreover, the -1,640/-1,619 and -620/-599 responded to hyperosmotic stress and high-glucose stimulation by base mutation, suggesting that osmotic and carbohydrate response elements may exist in this region. Finally, the salinity tolerance of Nile tilapia was significantly reduced after the knocking down of miox gene. The accumulation of myo-inositol was affected, and the expression of enzymes in glucose metabolism was significantly reduced after the miox gene was knocked down. Furthermore, hyperosmotic stress can cause oxidative stress, and MIOX may help maintain the cell redox balance under hyperosmotic stress. In summary, MIOX is essential in osmotic regulation to enhance the salinity tolerance of Nile tilapia by affecting myo-inositol accumulation, glucose metabolism, and antioxidant performance.NEW & NOTEWORTHY Myo-inositol oxygenase (MIOX) is the rate-limiting enzyme that catalyzes the first step of MI metabolism and determines MI content in aquatic animals. To understand the role of miox in the osmotic regulation of Nile tilapia, we analyzed its expression in different tissues and its function under hyperosmotic stress. This study showed that miox is essential in osmotic regulation to enhance the salinity tolerance of Nile tilapia by affecting myo-inositol accumulation, glucose metabolism, and antioxidant performance.

Knock-out of dipeptidase CN2 in human proximal tubular cells disrupts dipeptide and amino acid homeostasis and para- and transcellular solute transport

AIM

Although of potential biomedical relevance, dipeptide metabolism has hardly been studied. We found the dipeptidase carnosinase-2 (CN2) to be abundant in human proximal tubules, which regulate water and solute homeostasis. We therefore hypothesized, that CN2 has a key metabolic role, impacting proximal tubular transport function.

METHODS

A knockout of the CN2 gene (CNDP2-KO) was generated in human proximal tubule cells and characterized by metabolomics, RNA-seq analysis, paracellular permeability analysis and ion transport.

RESULTS

CNDP2-KO in human proximal tubule cells resulted in the accumulation of cellular dipeptides, reduction of amino acids and imbalance of related metabolic pathways, and of energy supply. RNA-seq analyses indicated altered protein metabolism and ion transport. Detailed functional studies demonstrated lower CNDP2-KO cell viability and proliferation, and altered ion and macromolecule transport via trans- and paracellular pathways. Regulatory and transport protein abundance was disturbed, either as a consequence of the metabolic imbalance or the resulting functional disequilibrium.

CONCLUSION

CN2 function has a major impact on intracellular amino acid and dipeptide metabolism and is essential for key metabolic and regulatory functions of proximal tubular cells. These findings deserve in vivo analysis of the relevance of CN2 for nephron function and regulation of body homeostasis.

Inositols in treating polycystic ovary syndrome and non-insulin dependent diabetes mellitus: now and the future

INTRODUCTION

This Expert Opinion covers recent updates in the use of Inositol in polycystic ovary syndrome (PCOS) and type II diabetes and gives support to researchers and clinicians.

AREAS COVERED

This article discusses the role of Myo-Inositol (MI) and D-Chiro-Inositol (DCI) in physiological function, the use of MI in PCOS, the risks of using DCI in reproductive conditions, the 40:1 combination of MI/DCI in PCOS. Furthermore, we discuss the issues of insulin resistance and how α-lactalbumin may increase the intestinal bioavailability of MI. The paper then transitions to talk about the use of inositols in diabetes, including type II diabetes, Gestational Diabetes Mellitus (GDM), and double diabetes. Literature searches were performed with the use of PubMed, Google Scholar, and Web of Science between July and October 2023.

EXPERT OPINION

Inositol therapy has grown in the clinical field of PCOS, with it demonstrating an efficacy like that of metformin. The use of α-lactalbumin has further supported the use of MI, as issues with intestinal bioavailability have been largely overcome. In contrast, the effect of inositol treatment on the different PCOS phenotypes remains an outstanding question. The use of inositols in type II diabetes requires further study despite promising analogous data from GDM.

Regulations of myo-inositol homeostasis: Mechanisms, implications, and perspectives

Phosphorylation is the most common module of cellular signalling pathways. The dynamic nature of phosphorylation, which is conferred by the balancing acts of kinases and phosphatases, allows this modification to finely control crucial cellular events such as growth, differentiation, and cell cycle progression. Although most research to date has focussed on protein phosphorylation, non-protein phosphorylation substrates also play vital roles in signal transduction. The most well-established substrate of non-protein phosphorylation is inositol, whose phosphorylation generates many important signalling molecules such as the second messenger IP₃, a key factor in calcium signalling. A fundamental question to our understanding of inositol phosphorylation is how the levels of cellular inositol are controlled. While the availability of protein phosphorylation substrates is known to be readily controlled at the levels of transcription, translation, and/or protein degradation, the regulatory mechanisms that control the uptake, synthesis, and removal of inositol are underexplored. Potentially, such mechanisms serve as an important layer of regulation of cellular signal transduction pathways. There are two ways in which mammalian cells acquire inositol. The historic use of radioactive ³H-myo-inositol revealed that inositol is promptly imported from the extracellular environment by three specific symporters SMIT1/2, and HMIT, coupling sodium or proton entry, respectively. Inositol can also be synthesized de novo from glucose-6P, thanks to the enzymatic activity of ISYNA1. Intriguingly, emerging evidence suggests that in mammalian cells, de novo myo-inositol synthesis occurs irrespective of inositol availability in the environment, prompting the question of whether the two sources of inositol go through independent metabolic pathways, thus serving distinct functions. Furthermore, the metabolic stability of myo-inositol, coupled with the uptake and endogenous synthesis, determines that there must be exit pathways to remove this extraordinary sugar from the cells to maintain its homeostasis. This essay aims to review our current knowledge of myo-inositol homeostatic metabolism, since they are critical to the signalling events played by its phosphorylated forms.

A Contemporary Insight of Metabolomics Approach for Type 1 Diabetes: Potential for Novel Diagnostic Targets

High-throughput omics has been widely applied in metabolic disease, type 1 diabetes (T1D) was one of the most typical diseases. Effective prevention and early diagnosis are very important because of infancy and persistent characteristics of T1D. The occurrence and development of T1D is a chronic and continuous process, in which the production of autoantibodies (ie serum transformation) occupies the central position. Metabolomics can evaluate the metabolic characteristics of serum before seroconversion, the changes with age and T1D complications. And the addition of natural drug metabolomics is more conducive to the systematic and comprehensive diagnosis and treatment of T1D. This paper reviewed the metabolic changes and main pathogenesis from pre-diagnosis to treatment in T1D. The metabolic spectrum of significant abnormal energy and glucose-related metabolic pathway, down-regulation of lipid metabolism and up-regulation of some antioxidant pathways has appeared before seroconversion, indicating that the body has been in the dual state of disease progression and disease resistance before T1D onset. Some metabolites (such as methionine) are closely related to age, and the types of autoantibodies produced are age-specific. Some metabolites may jointly predict DN with eGFR, and metabolomics can further contribute to the pathogenesis based on the correlation between DN and DR. Many natural drug components have been proved to act on abnormal metabolic pathways of T1D and have a positive impact on some metabolic levels, which is very important for further finding therapeutic targets and developing new drugs with small side effects. Metabolomics can provide auxiliary value for the diagnosis of T1D and provide a new direction to reveal the pathogenesis of T1D and find new therapeutic targets. The development of T1D metabolomics shows that high-throughput research methods are expected to be introduced into clinical practice.

Transcriptome Profiles Reveal a 12-Signature Metabolic Prediction Model and a Novel Role of Myo-Inositol Oxygenase in the Progression of Prostate Cancer

Prostate adenocarcinoma (PRAD) is an extremely common type of cancer in the urinary system. Here, we aimed to establish a metabolic signature to identify novel targets in a predictive model of PRAD patients. A total of 133 metabolic differentially expressed genes (MDEGs) were identified with significant prognostic value. Least absolute shrinkage and selection operator (LASSO) regression analysis was used to construct a 12-mRNA signature model, a metabolic prediction model (MPM), in 491 PRAD patients. The risk score of the MPM significantly predicted the progression of PRAD patients (p < 0.001, area under the curve (AUC) = 0.745). Furthermore, myo-inositol oxygenase (MIOX), the most prominently upregulated metabolic enzyme and hub gene in the protein-protein interaction network of the MPM, showed significant prognostic implications. Next, MIOX expression in normal prostate tissues was lower than in PRAD tissues, and high MIOX expression was significantly associated with disease progression (p = 0.005, HR = 2.274) in 81 PRAD patients undergoing first-line androgen receptor signaling inhibitor treatment from the Renji cohort. Additionally, MIOX was significantly involved in the abnormal immune infiltration of the tumor microenvironment and associated with the DNA damage repair process of PRAD. In conclusion, this study provides the first opportunity to comprehensively elucidate the landscape of prognostic MDEGs, establish novel prognostic modeling of MPM using large-scale PRAD transcriptomic data, and identify MIOX as a potential prognostic target in PRAD patients from multiple cohorts. These findings help manage risk assessment and provide valuable insights into treatment strategies for PRAD.

Modulation of gentamicin-induced acute kidney injury by myo-inositol oxygenase via the ROS/ALOX-12/12-HETE/GPR31 signaling pathway

In this investigation, a potentially novel signaling pathway in gentamicin-induced acute kidney injury-worsened by overexpression of proximal tubular enzyme, myo-inositol oxygenase (MIOX)-was elucidated. WT, MIOX-transgenic (MIOX-Tg), and MIOX-KO mice were used. Gentamicin was administered to induce tubular injury. MIOX-Tg mice had severe tubular lesions associated with increased serum creatinine and proteinuria. Lesions were relatively mild, with no rise in serum creatinine and no albuminuria in MIOX-KO mice. Transfection of HK-2 cells with MIOX-pcDNA led to increased gentamicin-induced reactive oxygen species (ROS). Marked increase of ROS-mediated lipid hydroperoxidation was noted in MIOX-Tg mice, as assessed by 4-HNE staining. This was associated with increased expression of arachidonate 12-lipoxygenase (ALOX-12) and generation of 12-hydroxyeicosatetraenoic acid (12-HETE). In addition, notable monocyte/macrophage influx, upregulation of NF-κB and inflammatory cytokines, and apoptosis was observed in MIOX-Tg mice. Treatment of cells with ALOX-12 siRNA abolished gentamicin-mediated induction of cytokines and 12-HETE generation. HETE-12 treatment promoted this effect, along with upregulation of various signaling kinases and activation of GPCR31. Similarly, treatment of cells or mice with the ALOX-12 inhibitor ML355 attenuated inflammatory response, kinase signaling cascade, and albuminuria. Collectively, these studies highlight a potentially novel mechanism (i.e., the ROS/ALOX-12/12-HETE/GPR31 signaling axis) relevant to gentamicin-induced nephrotoxicity modulated by MIOX.

Myo-inositol oxygenase overexpression exacerbates cadmium-induced kidney injury via oxidant stress and necroptosis

Conceivably, like other forms of acute kidney injury, cadmium-induced renal injury may also be associated with oxidative stress and various forms of cell death, including necroptosis, a form of regulated necrosis-associated cell death. Myo-inositol oxygenase (MIOX), an enzyme localized in renal proximal tubules, regulates oxidative stress and programmed cell death in various forms of renal injuries. Herein, the role and potential mechanism(s) by which MIOX potentiates cadmium-induced renal tubular damage were investigated. Overexpression of MIOX exacerbated cadmium-induced cell death and proximal tubular injury in mice, whereas MIOX gene disruption attenuated cellular damage in vitro and in vivo. Furthermore, necroptosis was observed in the renal tubular compartment, and, more importantly, it was corroborated by inhibitor experiments with necrostatin-1 (Nec-1). Coadministration of Nec-1 dampened including receptor-interacting protein kinase (RIP)1/RIP3/mixed-lineage kinase domain-like signaling, which is relevant to the process of necroptosis. Interestingly, the necroptosis induced by cadmium in tubules was modulated by MIOX expression profile. Also, the increased reactive oxygen species generation and NADPH consumption were accelerated by MIOX overexpression, and they were mitigated by Nec-1 administration. These findings suggest that MIOX-potentiated redox injury and necroptosis are intricately involved in the pathogenesis of cadmium-induced nephropathy, and this may yield novel potential therapeutic targets for amelioration of cadmium-induced kidney injury.NEW & NOTEWORTHY This is a seminal article documenting the role of myo-inositol oxygenase (MIOX), a renal proximal tubule-specific enzyme, in the exacerbation of cadmium-induced acute kidney injury by perturbing redox balance and inducing necroptosis. MIOX gene disruption or administration of necrostatin-1 (a necroptosis inhibitor) diminished cadmium-induced renal damage, in both in vitro and in vivo systems, suggesting a therapeutic potential of MIOX to attenuate necroptosis and relevant signaling pathways in cadmium-induced renal injury.

Regulated cell death in cisplatin-induced AKI: relevance of myo-inositol metabolism

Regulated cell death (RCD), distinct from accidental cell death, refers to a process of well-controlled programmed cell death with well-defined pathological mechanisms. In the past few decades, various terms for RCDs were coined, and some of them have been implicated in the pathogenesis of various types of acute kidney injury (AKI). Cisplatin is widely used as a chemotherapeutic drug for a broad spectrum of cancers, but its usage was hampered because of being highly nephrotoxic. Cisplatin-induced AKI is commonly seen clinically, and it also serves as a well-established prototypic model for laboratory investigations relevant to acute nephropathy affecting especially the tubular compartment. Literature reports over a period of three decades have indicated that there are multiple types of RCDs, including apoptosis, necroptosis, pyroptosis, ferroptosis, and mitochondrial permeability transition-mediated necrosis, and some of them are pertinent to the pathogenesis of cisplatin-induced AKI. Interestingly, myo-inositol metabolism, a vital biological process that is largely restricted to the kidney, seems to be relevant to the pathogenesis of certain forms of RCDs. A comprehensive understanding of RCDs in cisplatin-induced AKI and their relevance to myo-inositol homeostasis may yield novel therapeutic targets for the amelioration of cisplatin-related nephropathy.

Glucose-6-phosphate dehydrogenase deficiency contributes to metabolic abnormality and pulmonary hypertension

We have previously reported that several patients with idiopathic pulmonary hypertension (PH) had different types of G6PD deficiency. However, the role of G6PD in PH is multifactorial because G6PD is involved in controlling oxidative stress, metabolic switch, and red blood cell fragility. To delineate the contribution of G6PD to PH pathogenesis, we utilized a mouse line with decreased expression of G6PD (10% from wild-type level). We confirmed that mice with G6PD deficiency develop spontaneous pulmonary hypertension with pulmonary artery and right heart remodeling. G6PD deficiency resulted in increased free hemoglobin and activation of the p38 pathway, which we recently reported induces the development of PH in the sugen/hypoxia model via endothelial barrier dysfunction. Metabolomics analysis of G6PD deficient mice indicates the switch to alternative metabolic fluxes that feed into the pentose phosphate pathway (PPP), resulting in the upregulation of oxidative stress, fatty acid pathway, and reduction in pyruvate production. Thus, G6PD deficiency did not reduce PPP flux that is important for proliferation but activated collateral pathways at the cost of increased oxidative stress. Indeed, we found the upregulation of myo-inositol oxidase, reduction in GSH/GSSG ratio, and increased nitration in the lungs of G6PD-deficient mice. Increased oxidative stress also results in the activation of PI3K, ERK1/2, and AMPK that contribute to the proliferation of pulmonary vasculature. Therefore, G6PD deficiency has a multimodal effect, including hemolysis, metabolic reprogramming, and oxidative stress leading to the PH phenotype in mice.

Myo-inositol oxygenase expression profile modulates pathogenic ferroptosis in the renal proximal tubule

Overexpression of myo-inositol oxygenase (MIOX), a proximal tubular enzyme, exacerbates cellular redox injury in acute kidney injury (AKI). Ferroptosis, a newly coined term associated with lipid hydroperoxidation, plays a critical role in the pathogenesis of AKI. Whether or not MIOX exacerbates tubular damage by accelerating ferroptosis in cisplatin-induced AKI remains elusive. Cisplatin-treated HK-2 cells exhibited notable cell death, which was reduced by ferroptosis inhibitors. Also, alterations in various ferroptosis metabolic sensors, including lipid hydroperoxidation, glutathione peroxidase 4 (GPX4) activity, NADPH and reduced glutathione (GSH) levels, and ferritinophagy, were observed. These perturbations were accentuated by MIOX overexpression, while ameliorated by MIOX knockdown. Likewise, cisplatin-treated CD1 mice exhibited tubular damage and derangement of renal physiological parameters, which were alleviated by ferrostatin-1, a ferroptosis inhibitor. To investigate the relevance of MIOX to ferroptosis, WT mice, MIOX-overexpressing transgenic (MIOX-Tg) mice, and MIOX-KO mice were subjected to cisplatin treatment. In comparison with cisplatin-treated WT mice, cisplatin-treated MIOX-Tg mice had more severe renal pathological changes and perturbations in ferroptosis metabolic sensors, which were minimal in cisplatin-treated MIOX-KO mice. In conclusion, these findings indicate that ferroptosis, an integral process in the pathogenesis of cisplatin-induced AKI, is modulated by the expression profile of MIOX.

Myo-inositol Oxygenase (MIOX) Overexpression Drives the Progression of Renal Tubulointerstitial Injury in Diabetes

Conceivably, upregulation of myo-inositol oxygenase (MIOX) is associated with altered cellular redox. Its promoter includes oxidant-response elements, and we also discovered binding sites for XBP1, a transcription factor of endoplasmic reticulum (ER) stress response. Previous studies indicate that MIOX's upregulation in acute tubular injury is mediated by oxidant and ER stress. Here, we investigated whether hyperglycemia leads to accentuation of oxidant and ER stress while these boost each other's activities, thereby augmenting tubulointerstitial injury/fibrosis. We generated MIOX-overexpressing transgenic (MIOX-TG) and MIOX knockout (MIOX-KO) mice. A diabetic state was induced by streptozotocin administration. Also, MIOX-KO were crossbred with Ins2 ^Akita to generate Ins2 ^Akita/KO mice. MIOX-TG mice had worsening renal functions with kidneys having increased oxidant/ER stress, as reflected by DCF/dihydroethidium staining, perturbed NAD-to-NADH and glutathione-to-glutathione disulfide ratios, increased NOX4 expression, apoptosis and its executionary molecules, accentuation of TGF-β signaling, Smads and XBP1 nuclear translocation, expression of GRP78 and XBP1 (ER stress markers), and accelerated tubulointerstitial fibrosis. These changes were not seen in MIOX-KO mice. Interestingly, such changes were remarkably reduced in Ins2 ^Akita/KO mice and, likewise, in vitro experiments with XBP1 siRNA. These findings suggest that MIOX expression accentuates, while its deficiency shields kidneys from, tubulointerstitial injury by dampening oxidant and ER stress, which mutually enhance each other's activity.

The Protective Effect of Basic Fibroblast Growth Factor on Diabetic Nephropathy Through Remodeling Metabolic Phenotype and Suppressing Oxidative Stress in Mice

Diabetic nephropathy is a common complication in diabetes, but still lack of effective therapeutic strategies. This study aimed to investigate the therapeutic effect of basic fibroblast growth factor (bFGF) in db/db mice with diabetic nephropathy and explore its possible metabolic mechanisms using a nuclear magnetic resonance-based metabolomic approach. We found that bFGF treatment significantly alleviate urinary albumin to creatinine ratio and renal fibrosis in db/db mice, suggesting a potential renal protective effect. Metabolomics results reveal that bFGF remodeled metabolic phenotypes of the kidney and urine in db/db mice, mainly involving energy metabolism, methylamine metabolism, osmoregulation, and oxidative stress. Furthermore, the results show that bFGF-induced reductions of oxidative stress and apoptosis in db/db mice might be mediated by NOX-ROS-Nrf2 signaling. Therefore, our study suggests that the protective effect of bFGF on diabetic nephropathy could be mediated by remodeling metabolic phenotype and suppressing oxidative stress.

Does myo-inositol oxygenase, the only enzyme to catalyze myo-inositol in vivo, play a role in the etiology of polycystic ovarian syndrome?

In polycystic ovary syndrome (PCOS), myo-inositol (MI) supplements have shown many beneficial effects. In this study, therefore, we aimed to investigate the serum level of myo-inositol oxygenase (MIOX), which is the only enzyme catalyzing MI in vivo, in patients with PCOS. Serum MIOX enzyme levels and other laboratory parameters were compared between sixty patients, who were diagnosed with PCOS for the first time, and sixty healthy individuals at similar age and sex. MIOX serum levels were not different between two groups (p = 0.7428). MIOX median and 95% CI were 19.4 and 10.6-39.1 in the control group and 16.4 and 7.6-46.2 in the patient group respectively. Demographic data, biochemical and hematological parameters, hormone parameters were not different except from the lymphocyte count between the two groups. Lymphocyte count was higher in the patient group. Although the ratio of LH/FSH was higher in the patient group, it was not statistically significant. Our results suggest that serum MIOX levels do not change in PCOS. It was, therefore, concluded that MI deficiency observed in PCOS was not related to the level of MIOX enzyme which cleaves MI.

Myo-inositol Oxygenase as a Novel Marker in the Diagnosis of Acute Kidney Injury

Background

Due to the lack of diagnostic efficiency of serum creatinine in acute kidney injury (AKI), there is a pressing need to develop novel diagnostic markers. Therefore, in this study, we evaluated myo–inositol oxygenase (MIOX), neutrophil gelatinase-associated lipocalin (NGAL) and cystatin C in terms of their applicability in the diagnosis of AKI.

Methods

We enrolled a total of 39 AKI patients and 38 healthy controls in the study. We compared the levels of serum MIOX, NGAL and cystatin C between the two groups.

Results

We found that the concentrations of serum creatinine, blood-urea nitrogen, MIOX and cystatin C were higher in the AKI group. According to the receiver operating characteristic analysis, the area under the curve (AUC) values were 0.694 (95% CI 0.579-0.794) for MIOX and 0.976 (95% CI; 0.912-0.997) for cystatin C. For MIOX, when the cut-off concentration was set to 77.3 pg/mL, the diagnostic sensitivity and specificity were found to be 53.8% (95% CI; 37.2-69.9) and 81.5 (95% CI; 65.7-92.3), respectively. For cystatin C, at the cut-off value of 14 mg/L, the diagnostic sensitivity and specificity were 94.8% (95% CI; 82.7-99.4) and 94.7 % (95% CI 82.3-99.4), respectively.

Conclusion

The measurement of serum MIOX and cystatin C levels is valuable for the diagnosis of AKI. Further research is needed for the evaluation of the potential use of MIOX as a kidney-specific enzyme in the early diagnosis of AKI.

Nutritional and Acquired Deficiencies in Inositol Bioavailability. Correlations with Metabolic Disorders

Communities eating a western-like diet, rich in fat, sugar and significantly deprived of fibers, share a relevant increased risk of both metabolic and cancerous diseases. Even more remarkable is that a low-fiber diet lacks some key components-as phytates and inositols-for which a mechanistic link has been clearly established in the pathogenesis of both cancer and metabolic illness. Reduced bioavailability of inositol in living organisms could arise from reduced food supply or from metabolism deregulation. Inositol deregulation has been found in a number of conditions mechanistically and epidemiologically associated to high-glucose diets or altered glucose metabolism. Indeed, high glucose levels hinder inositol availability by increasing its degradation and by inhibiting both myo-Ins biosynthesis and absorption. These underappreciated mechanisms may likely account for acquired, metabolic deficiency in inositol bioavailability.

Beneficial Effects of Myo-Inositol Oxygenase Deficiency in Cisplatin-Induced AKI

Overexpression of the proximal tubular enzyme myo-inositol oxygenase (MIOX) induces oxidant stress in vitro However, the relevance of MIOX to tubular pathobiology remains enigmatic. To investigate the role of MIOX in cisplatin-induced tubular AKI, we generated conditional MIOX-overexpressing transgenic (MIOX-TG) mice and MIOX-knockout (MIOX-/-) mice with tubule-specific MIOX overexpression or knockout, respectively. Compared with cisplatin-treated wild-type (WT) mice, cisplatin-treated MIOX-TG mice had even greater increases in urea, creatinine, and KIM-1 levels and more tubular injury and apoptosis, but these effects were attenuated in cisplatin-treated MIOX-/- mice. Similarly, MIOX-TG mice had the highest and MIOX-/- mice had the lowest renal levels of Bax, cleaved caspase-3, and NADPH oxidase-4 expression and reactive oxygen species (ROS) generation after cisplatin treatment. In vitro, cisplatin dose-dependently increased ROS generation in LLC-PK1 cells. Furthermore, MIOX overexpression in these cells accentuated cisplatin-induced ROS generation and perturbations in the ratio of GSH to oxidized GSH, whereas MIOX-siRNA or N-acetyl cysteine treatment attenuated these effects. Additionally, the cisplatin-induced enhancement of p53 activation, NF-κB binding to DNA, and NF-κB nuclear translocation in WT mice was exacerbated in MIOX-TG mice but absent in MIOX-/- mice. In vitro, MIOX-siRNA or NAC treatment reduced the dose-dependent increase in p53 expression induced by cisplatin. We also observed a remarkable influx of inflammatory cells and upregulation of cytokines in kidneys of cisplatin-treated MIOX-TG mice. Finally, analysis of genomic DNA in WT mice revealed cisplatin-induced hypomethylation of the MIOX promoter. These data suggest that MIOX overexpression exacerbates, whereas MIOX gene disruption protects against, cisplatin-induced AKI.

High Glucose-Induced Hypomethylation Promotes Binding of Sp-1 to Myo-Inositol Oxygenase: Implication in the Pathobiology of Diabetic Tubulopathy

The catabolic enzyme myo-inositol oxygenase (MIOX) is expressed in proximal tubules and up-regulated in the diabetic state. Previously, we reported its transcriptional and translation regulation by high glucose (HG), osmolytes, and fatty acids. However, its epigenetic regulation is unknown. Bisulfite sequencing revealed that both human and mouse MIOX promoters, enriched with CpG sites, are hypomethylated and unmethylated under HG ambience and hyperglycemic states associated with increased MIOX expression. Eletrophoretic mobility shift assays revealed increased binding of unmethylated oligos with nucleoproteins of cells maintained under HG. In addition, a strong binding of specificity protein (Sp)-1 transcription factor with MIOX promoter was observed under HG, especially with unmethylated Sp-1 oligo. Specificity of binding was established by supershift assays and treatment with the Sp-1 inhibitor mithramycin. Promoter analysis revealed an increase in luciferase activity under HG, which was reduced after mutation of the Sp-1-binding site. Sp1 siRNA treatment reduced mRNA and protein expression of Sp-1 and MIOX and generation of reactive oxygen species derived from NADPH oxidase (NOX)-4 and mitochondrial sources. In addition, there was reduced expression of hypoxia-inducible factor-1α relevant in the pathogenesis of diabetic nephropathy. Sp1 siRNA treatment reduced fibronectin expression, an extracellular matrix protein that is increased in diabetic nephropathy and tubulopathy. HG-induced MIOX expression was also reduced with the treatment of apelin-13, which deacetylates histones. Overall, these findings highlight the epigenetic regulation of MIOX in the pathogenesis of diabetic tubulopathy.

myo-Inositol Oxygenase Overexpression Accentuates Generation of Reactive Oxygen Species and Exacerbates Cellular Injury following High Glucose Ambience: A NEW MECHANISM RELEVANT TO THE PATHOGENESIS OF DIABETIC NEPHROPATHY

Diabetic nephropathy (DN) is characterized by perturbations in metabolic/cellular signaling pathways with generation of reactive oxygen species (ROS). The ROS are regarded as a common denominator of various pathways, and they inflict injury on renal glomerular cells. Recent studies indicate that tubular pathobiology also plays a role in the progression of DN. However, the mechanism(s) for how high (25 mm) glucose (HG) ambience induces tubular damage remains enigmatic. myo-Inositol oxygenase (MIOX) is a tubular enzyme that catabolizes myo-inositol to d-glucuronate via the glucuronate-xylulose (G-X) pathway. In this study, we demonstrated that G-X pathway enzymes are expressed in the kidney, and MIOX expression/bioactivity was up-regulated under HG ambience in LLC-PK1 cells, a tubular cell line. We further investigated whether MIOX overexpression leads to accentuation of tubulo-interstitial injury, as gauged by some of the parameters relevant to the progression of DN. Under HG ambience, MIOX overexpression accentuated redox imbalance, perturbed NAD(+)/NADH ratios, increased ROS generation, depleted reduced glutathione, reduced GSH/GSSG ratio, and enhanced adaptive changes in the profile of the antioxidant defense system. These changes were also accompanied by mitochondrial dysfunctions, DNA damage and induction of apoptosis, accentuated activity of profibrogenic cytokine, and expression of fibronectin, the latter two being the major hallmarks of DN. These perturbations were largely blocked by various ROS inhibitors (Mito Q, diphenyleneiodonium chloride, and N-acetylcysteine) and MIOX/NOX4 siRNA. In conclusion, this study highlights a novel mechanism where MIOX under HG ambience exacerbates renal injury during the progression of diabetic nephropathy following the generation of excessive ROS via an unexplored G-X pathway.

Serum ethanolamine plasmalogens improve detection of cognitive impairment among elderly with high excretion levels of urinary myo-inositol: A cross-sectional study

BACKGROUND

Several reports have implicated myo-inositol (MI) in myelin formation. We hypothesized that MI is involved in this process through facilitating the biosynthesis of ethanolamine plasmalogens (PlsEtns), which are the major component of myelin membranes, and essential for myelin formation and function. Excessive MI urinary excretion possibly causes PlsEtn deficiency, leading to demyelinating diseases including dementia.

METHODS

We examined the association between cognitive impairment, serum levels of PlsEtn, and baseline levels of urinary MI excretion, in the enrollment of 55 memory clinic outpatients and 107 cognitively normal elderly.

RESULTS

Serum PlsEtns were independently associated with cognitive impairment, and significantly reduced in memory clinic outpatients, especially in those with high urinary MI, as compared to normal elderly. On the other hand, there was no direct association between urinary MI and cognitive impairment, but urinary MI was significantly associated with serum hemoglobin A1c and amyloid β 1-40. The interaction between PlsEtn and urinary MI for cognitive impairment was statistically confirmed, and their combined usage improved diagnosis of cognitive impairment.

CONCLUSIONS

We proposed the involvement of MI and PlsEtn in cognitive impairment pathology. In conclusion, serum PlsEtn may be useful in detecting cognitive decline among elderly with hyperglycemia.

Transcriptional and Translational Modulation of myo-Inositol Oxygenase (Miox) by Fatty Acids: IMPLICATIONS IN RENAL TUBULAR INJURY INDUCED IN OBESITY AND DIABETES

The kidney is one of the target organs for various metabolic diseases, including diabetes, metabolic syndrome, and obesity. Most of the metabolic studies underscore glomerular pathobiology, although the tubulo-interstitial compartment has been underemphasized. This study highlights mechanisms concerning the pathobiology of tubular injury in the context of myo-inositol oxygenase (Miox), a tubular enzyme. The kidneys of mice fed a high fat diet (HFD) had increased Miox expression and activity, and the latter was related to phosphorylation of serine/threonine residues. Also, expression of sterol regulatory element-binding protein1 (Srebp1) and markers of cellular/nuclear damage was increased along with accentuated apoptosis and loss of tubular brush border. Similar results were observed in cells treated with palmitate/BSA. Multiple sterol-response elements and E-box motifs were found in the miox promoter, and its activity was modulated by palmitate/BSA. Electrophoretic mobility and ChIP assays confirmed binding of Srebp to consensus sequences of the miox promoter. Exposure of palmitate/BSA-treated cells to rapamycin normalized Miox expression and prevented Srebp1 nuclear translocation. In addition, rapamycin treatment reduced p53 expression and apoptosis. Like rapamycin, srebp siRNA reduced Miox expression. Increased expression of Miox was associated with the generation of reactive oxygen species (ROS) in kidney tubules of mice fed an HFD and cell exposed to palmitate/BSA. Both miox and srebp1 siRNAs reduced generation of ROS. Collectively, these findings suggest that HFD or fatty acids modulate transcriptional, translational, and post-translational regulation of Miox expression/activity and underscore Miox being a novel target of the transcription factor Srebp1. Conceivably, activation of the mTORC1/Srebp1/Miox pathway leads to the generation of ROS culminating into tubulo-interstitial injury in states of obesity.

Renal depletion of myo-inositol is associated with its increased degradation in animal models of metabolic disease

Renal depletion of myo-inositol (MI) is associated with the pathogenesis of diabetic nephropathy in animal models, but the underlying mechanisms involved are unclear. We hypothesized that MI depletion was due to changes in inositol metabolism and therefore examined the expression of genes regulating de novo biosynthesis, reabsorption, and catabolism of MI. We also extended the analyses from diabetes mellitus to animal models of dietary-induced obesity and hypertension. We found that renal MI depletion was pervasive across these three distinct disease states in the relative order: hypertension (−51%) > diabetes mellitus (−35%) > dietary-induced obesity (−19%). In 4-wk diabetic kidneys and in kidneys derived from insulin-resistant and hypertensive rats, MI depletion was correlated with activity of the MI-degrading enzyme myo-inositol oxygenase (MIOX). By contrast, there was decreased MIOX expression in 8-wk diabetic kidneys. Immunohistochemistry localized the MI-degrading pathway comprising MIOX and the glucuronate-xylulose (GX) pathway to the proximal tubules within the renal cortex. These findings indicate that MI depletion could reflect increased catabolism through MIOX and the GX pathway and implicate a common pathological mechanism contributing to renal oxidative stress in metabolic disease.

Metabonomic analysis of potential biomarkers and drug targets involved in diabetic nephropathy mice

Diabetic nephropathy (DN) is one of the lethal manifestations of diabetic systemic microvascular disease. Elucidation of characteristic metabolic alterations during diabetic progression is critical to understand its pathogenesis and identify potential biomarkers and drug targets involved in the disease. In this study, (1)H nuclear magnetic resonance ((1)H NMR)-based metabonomics with correlative analysis was performed to study the characteristic metabolites, as well as the related pathways in urine and kidney samples of db/db diabetic mice, compared with age-matched wildtype mice. The time trajectory plot of db/db mice revealed alterations, in an age-dependent manner, in urinary metabolic profiles along with progression of renal damage and dysfunction. Age-dependent and correlated metabolite analysis identified that cis-aconitate and allantoin could serve as biomarkers for the diagnosis of DN. Further correlative analysis revealed that the enzymes dimethylarginine dimethylaminohydrolase (DDAH), guanosine triphosphate cyclohydrolase I (GTPCH I), and 3-hydroxy-3-methylglutaryl-CoA lyase (HMG-CoA lyase) were involved in dimethylamine metabolism, ketogenesis and GTP metabolism pathways, respectively, and could be potential therapeutic targets for DN. Our results highlight that metabonomic analysis can be used as a tool to identify potential biomarkers and novel therapeutic targets to gain a better understanding of the mechanisms underlying the initiation and progression of diseases.

Alteration of the kidney membrane proteome of Mizuhopecten yessoensis induced by low-level methyl parathion exposure

Methyl parathion (MP) is a widely used organophosphorus pesticide that causes severe health and environmental effects. We investigated the alteration of the proteomic profile in the membrane enriched fraction of the kidneys of the scallop Mizuhopecten yessoensis exposed to low-level MP. Gas chromatography analysis showed that MP residues were significantly accumulated in the kidneys and the digestive glands of the scallops. According to two-dimensional electrophoresis, 17 proteins were differentially modulated under MP exposure. The mRNA expressions of 12 differential proteins were analyzed using quantitative PCR, and 10 showed consistent alteration of mRNA level with that of protein expression level. Altered expressions of two proteins (mitochondrial processing peptidase and α-tubulin) were also examined using Western blotting, showing that the mitochondrial processing peptidase was down-regulated but α-tubulin remained unchanged in response to MP exposure. Subcellular locations of all the identified proteins that were predicted using bioinformatics tools indicate that few of them are permanently located in the membrane. The differentially expressed proteins are involved in several critical biological processes, and their relevance to human health has been illuminated. These data taken together have provided some novel insights into the chronic toxicity mechanism of MP and have suggested mitochondrial processing peptidase as a potential biomarker for human health and environmental monitoring.

Transcriptional and post-translational modulation of myo-inositol oxygenase by high glucose and related pathobiological stresses

Renal-specific oxidoreductase/myo-inositol oxygenase (RSOR/MIOX) catabolizes myo-inositol and is implicated in the pathogenesis of diabetic nephropathy. How high glucose (HG) ambience up-regulates its expression and enzyme activity was investigated. MIOX up-regulation was associated with an increase in enzyme activity, which was reduced to basal levels with phosphatase treatment. Using phosphothreonine, protein kinase A (PKA), and PKC substrate antibodies, analyses of kidney lysates of diabetic animals and LLC-PK1/HK-2 cells subjected to HG ambience indicated MIOX to be a phosphoprotein. Kinase phosphorylated recombinant RSOR/MIOX proteins had increased activity confined to exons 2-5. Mutants with substituted phosphorylation sites had a minimal increase in activity. Treatment of cells with PKC, PKA, and PDK1 kinase activators increased activity, whereas inhibitors reduced it. Inhibitors also reduced the phosphorylation and activity of MIOX induced by HG. Besides HG, exposure of cells to oxidants H(2)O(2) and methylglyoxal up-regulated MIOX expression and its phosphorylation and activity, whereas antioxidants N-acetylcysteine, β-naphthoflavone, and tertiary butyl hydroquinone reduced MIOX expression. Treatment with HG or oxidants or overexpression of MIOX induced nuclear translocation of redox-sensitive transcription factor Nrf2, which binds to antioxidant response elements of various promoters. Promoter analyses revealed an increase in luciferase activity with HG and oxidants. Analyses of antioxidant response elements and carbohydrate response elements revealed an accentuation of DNA-protein interactions with oxidants and under HG ambience. ChIP-PCR and immunofluorescence studies revealed nuclear translocation of carbohydrate response element-binding protein. These findings suggest that phosphorylation of RSOR/MIOX enhances its activity, which is augmented by HG via transcriptional/translational events that are also modulated by diabetes-related pathobiological stresses.

Inhibition of TLR4-induced IκB kinase activity by the RON receptor tyrosine kinase and its ligand, macrophage-stimulating protein

The RON receptor tyrosine kinase regulates the balance between classical (M1) and alternative (M2) macrophage activation. In primary macrophages, the ligand for Ron, macrophage-stimulating protein (MSP), inhibits the expression of inducible NO synthase, a marker of classically activated macrophages, whereas promoting the expression of arginase I, a marker of alternative activation. Ron(-/-) mice express increased levels of IL-12, a product of classically activated macrophages, after endotoxin administration, resulting in increased serum IFN-γ levels and enhanced susceptibility to septic shock. In this study, we demonstrate that MSP inhibits LPS-induced IL-12p40 expression, and this inhibition is dependent on the docking site tyrosines in Ron. To further define this inhibition, we examined the effect of Ron on signaling pathways downstream of Ron. We found that MSP does not inhibit the MyD88-independent activation of IFN regulatory factor 3 and production of IFN-β in response to LPS, nor does it inhibit MyD88-dependent TGF-β-activated kinase phosphorylation or MAPK activation in primary macrophages. However, the induction of IκB kinase activity, IκB degradation, and DNA binding of NF-κB after LPS stimulation is delayed in the presence of MSP. In addition, Ron inhibits serine phosphorylation of p65 and NF-κB transcriptional activity induced by LPS stimulation of TLR4. Finally, MSP inhibits the NF-κB-dependent upregulation of the nuclear IκB family member, IκBζ, a positive regulator of secondary response genes including IL-12p40. LPS also induces expression of Ron and an N-terminally truncated form of Ron, Sf-Ron, in primary macrophages, suggesting that the upregulation of Ron by LPS could provide classical feedback regulation of TLR signaling.

Polymorphisms of myo-inositol oxygenase gene are associated with Type 1 diabetes mellitus

Myo-inositol oxygenase (MIOX) is the first and rate-limiting enzyme in myo-inositol (MI) metabolism pathway. The increase in MIOX enzyme activity is in proportion to serum glucose concentrations and may be responsible for the MI depletion found in the diabetic complications. The aim was to investigate whether single nucleotide polymorphisms (SNPs) in the MIOX gene are associated with Type 1 diabetes mellitus (T1D) and its complications. Four hundred thirty Caucasian patients with T1D were recruited: 172 patients had diabetic nephropathy, 140 had diabetic retinopathy/neuropathy, 118 patients had diabetes for ≥20 years without microvascular complications and 224 were normal controls. Three SNPs, rs761745 (C/T), and rs2232873 (A/G) in the promoter and rs1055271 (C/G) in the 3'-untranslated were genotyped commercially. The frequencies of the CC genotype (0.36 vs. 0.44; P=.034) and C allele (0.60 vs. 0.68; P=.011) of rs761745 were significantly lower in patients with T1D compared with normal controls. Patients with T1D had a decreased frequency of the combination genotypes of CC (rs761745), GG (rs2232873) and GC (rs1055271) compared with the normal controls (0.13 vs. 0.22, P=.0027, Pc=0.014). The haplotypes with C/G/G and C/G/C were less common in patients with T1D compared to normal controls (0.59 vs. 0.70, P=.021) and the haplotypes with T/G/C and T/G/G ware more common in patients with T1D compared to normal controls (0.37 vs. 0.26; P=.021). In summary, our results demonstrated that the polymorphism (rs761745) in the promoter region of MIOX gene may be associated with the development of T1D in our studied population.

Pathobiology of renal-specific oxidoreductase/myo-inositol oxygenase in diabetic nephropathy: its implications in tubulointerstitial fibrosis

Renal-specific oxido-reductase/myoinositol oxygenase (RSOR/MIOX) is expressed in renal tubules. It catabolizes myo-inositol and its expression is increased in diabetic mice and in LLC-PK(1) cells under high-glucose ambience. Aldose reductase (AR) is another aldo-keto reductase that is expressed in renal tubules. It regulates the polyol pathway and plays an important role in glucose metabolism, osmolyte regulation, and ECM pathobiology via the generation of advanced glycation end products, reactive oxygen species, and activation of transforming growth factor (TGF)-beta. In view of the similarities between AR and RSOR/MIOX, the pathobiology of RSOR/MIOX and some of the cellular pathways affected by its overexpression were investigated. An increased expression of fibronectin was noted by transfection of LLC-PK(1) cells with pcDNA3.1-RSOR/MIOX. Similar changes were observed in LLC-PK(1) cells under high-glucose ambience, and they were notably lessened by RSOR/MIOX-small interfering (si) RNA treatment. The changes in tubulointerstitial fibronectin expression were also observed in the kidneys of db/db mice having high levels of RSOR. The pcDNA3.1-RSOR/MIOX transfectants had an increased NADH/NAD(+) ratio, PKC and TGF-beta activity, Raf1:Ras association, and p-ERK phosphorylation. These changes were significantly reduced by the inhibitors of PKC, aldose reductase, Ras farnesylation, and MEK1. Similar increases in various the above-noted parameters were observed under high-glucose ambience. Such changes were partially reversed with RSOR-siRNA treatment. Expression of E-cadherin and vimentin paralleled in cells overexpressing RSOR/MIOX or subjected to high-glucose ambience. These studies suggest that RSOR/MIOX modulates various downstream pathways affected by high-glucose ambience, and conceivably it plays a role in the pathobiology of tubulointerstitium in diabetic nephropathy.

Insights into the (superoxo)Fe(III)Fe(III) intermediate and reaction mechanism of myo-inositol oxygenase: DFT and ONIOM(DFT:MM) study

The (superoxo)Fe(III)Fe(III) reactive species and the catalytic reaction mechanism of a diiron enzyme, myo-inositol oxygenase (MIOX), were theoretically investigated by means of density functional theory (DFT) and ONIOM quantum mechanical/molecular mechanical (QM/MM) approaches. The ground state of the (superoxo)Fe(III)Fe(III) intermediate was shown to have a side-on coordination geometry and an S = 1/2 spin state, wherein the two iron sites are antiferromagnetically coupled while the superoxide site and the nearest iron are ferromagnetically coupled. A full reaction pathway leading to a D-glucuronate product from myo-inositol was proposed based on ONIOM computational results. Two major roles of the enzyme surrounding during the catalytic reaction were identified. One is to facilitate the initial H-abstraction step, and the other is to restrict the movement of the substrate via H-bonding interactions in order to avoid unwanted side reactions. In our proposed mechanism, O-O bond cleavage has the highest barrier, thus constituting the rate-limiting step of the reaction. The unique role of the bridging hydroxide ligand as a catalytic base was also identified.

Transcription factors in the pathogenesis of diabetic nephropathy

Approximately a third of patients with diabetes develop diabetic kidney disease, and diabetes is the leading cause of end-stage renal disease in most developed countries. Hyperglycaemia is known to activate genes that ultimately lead to extracellular matrix accumulation, the hallmark of diabetic nephropathy. Several transcription factors have been implicated in glucose-mediated expression of genes involved in diabetic nephropathy. This review focuses on the transcription factors upstream stimulatory factors 1 and 2 (USF1 and 2), activator protein 1 (AP-1), nuclear factor (NF)-kappaB, cAMP-response-element-binding protein (CREB), nuclear factor of activated T cells (NFAT), and stimulating protein 1 (Sp1). In response to high glucose, several of these transcription factors regulate the gene encoding the profibrotic cytokine transforming growth factor beta, as well as genes for a range of other proteins implicated in inflammation and extracellular matrix turnover, including thrombospondin 1, the chemokine CCL2, osteopontin, fibronectin, decorin, plasminogen activator inhibitor 1 and aldose reductase. Identifying the molecular mechanisms by which diabetic nephropathy occurs has important clinical implications as therapies can then be tailored to target those at risk. Strategies to specifically target transcription factor activation and function may be employed to halt the progression of diabetic nephropathy.

Strategies for acquiring the phospholipid metabolite inositol in pathogenic bacteria, fungi and protozoa: making it and taking it

myo-Inositol (inositol) is an essential nutrient that is used for building phosphatidylinositol and its derivatives in eukaryotes and even in some eubacteria such as the mycobacteria. As a consequence, fungal, protozoan and mycobacterial pathogens must be able to acquire inositol in order to proliferate and cause infection in their hosts. There are two primary mechanisms for acquiring inositol. One is to synthesize inositol from glucose 6-phosphate using two sequentially acting enzymes: inositol-3-phosphate synthase (Ino1p) converts glucose 6-phosphate to inositol 3-phosphate, and then inositol monophosphatase (IMPase) dephosphorylates inositol 3-phosphate to generate inositol. The other mechanism is to import inositol from the environment via inositol transporters. Inositol is readily abundant in the bloodstream of mammalian hosts, providing a source from which many pathogens could potentially import inositol. However, despite this abundance of inositol in the host, some pathogens such as the bacterium Mycobacterium tuberculosis and the protist parasite Trypanosoma brucei must be able to make inositol de novo in order to cause disease (M. tuberculosis) or even grow (T. brucei). Other pathogens such as the fungus Candida albicans are equally adept at causing disease by importing inositol or by making it de novo. The role of inositol acquisition in the biology and pathogenesis of the parasite Leishmania and the fungus Cryptococcus are being explored as well. The specific strategies used by these pathogens to acquire inositol while in the host are discussed in relation to each pathogen's unique metabolic requirements.

myo-Inositol oxygenase: a radical new pathway for O(2) and C-H activation at a nonheme diiron cluster

The enzyme myo-inositol oxygenase (MIOX) catalyzes conversion of myo-inositol (cyclohexan-1,2,3,5/4,6-hexa-ol or MI) to d-glucuronate (DG), initiating the only known pathway in humans for catabolism of the carbon skeleton of cell-signaling inositol (poly)phosphates and phosphoinositides. Recent kinetic, spectroscopic and crystallographic studies have shown that the enzyme activates its substrates, MI and O(2), at a carboxylate-bridged nonheme diiron(ii/iii) cluster, making it the first of many known nonheme diiron oxygenases to employ the mixed-valent form of its cofactor. Evidence suggests that: (1) the Fe(iii) site coordinates MI via its C1 and C6 hydroxyl groups; (2) the Fe(ii) site reversibly coordinates O(2) to produce a superoxo-diiron(iii/iii) intermediate; and (3) the pendant oxygen atom of the superoxide ligand abstracts hydrogen from C1 to initiate the unique C-C-bond-cleaving, four-electron oxidation reaction. This review recounts the studies leading to the recognition of the novel cofactor requirement and catalytic mechanism of MIOX and forecasts how remaining gaps in our understanding might be filled by additional experiments.

Computational modeling and in silico analysis of differential regulation of myo-inositol catabolic enzymes in Cryptococcus neoformans

Background

Inositol is a key cellular metabolite for many organisms. Cryptococcus neoformans is an opportunistic pathogen which primarily infects the central nervous system, a region of high inositol concentration, of immunocompromised individuals. Through the use of myo-inositol oxygenase C. neoformans can catabolize inositol as a sole carbon source to support growth and viability.

Results

Three myo-inositol oxygenase gene sequences were identified in the C. neoformans genome. Differential regulation was suggested by computational analyses of the three gene sequences. This included examination of the upstream regulatory regions, identifying ORE/TonE and UAS_INO sequences, conserved introns/exons, and in frame termination sequences. Homology modeling of the proteins encoded by these genes revealed key differences in the myo-inositol active site.

Conclusion

The results suggest there are two functional copies of the myo-inositol oxygenase gene in the C. neoformans genome. The functional genes are differentially expressed in response to environmental inositol concentrations. Both the upstream regulatory regions of the genes and the structure of the specific proteins suggest that MIOX1 would function when inositol concentrations are low, whereas MIOX2 would function when inositol concentrations are high.

Cellular Response to Hyperosmotic Stresses

Cells in the renal inner medulla are normally exposed to extraordinarily high levels of NaCl and urea. The osmotic stress causes numerous perturbations because of the hypertonic effect of high NaCl and the direct denaturation of cellular macromolecules by high urea. High NaCl and urea elevate reactive oxygen species, cause cytoskeletal rearrangement, inhibit DNA replication and transcription, inhibit translation, depolarize mitochondria, and damage DNA and proteins. Nevertheless, cells can accommodate by changes that include accumulation of organic osmolytes and increased expression of heat shock proteins. Failure to accommodate results in cell death by apoptosis. Although the adapted cells survive and function, many of the original perturbations persist, and even contribute to signaling the adaptive responses. This review addresses both the perturbing effects of high NaCl and urea and the adaptive responses. We speculate on the sensors of osmolality and document the multiple pathways that signal activation of the transcription factor TonEBP/OREBP, which directs many aspects of adaptation. The facts that numerous cellular functions are altered by hyperosmolality and remain so, even after adaptation, indicate that both the effects of hyperosmolality and adaptation to it involve profound alterations of the state of the cells.

The anti-inflammatory effects of selenium are mediated through 15-deoxy-Delta12,14-prostaglandin J2 in macrophages

Selenium is an essential micronutrient that suppresses the redox-sensitive transcription factor NF-kappaB-dependent pro-inflammatory gene expression. To understand the molecular mechanisms underlying the anti-inflammatory property of selenium, we examined the activity of a key kinase of the NF-kappaB cascade, IkappaB-kinase beta (IKKbeta) subunit, as a function of cellular selenium status in murine primary bone marrow-derived macrophages and RAW264.7 macrophage-like cell line. In vitro kinase assays revealed that selenium supplementation decreased the activity of IKKbeta in lipopolysaccharide (LPS)-treated macrophages. Stimulation by LPS of selenium-supplemented macrophages resulted in a time-dependent increase in 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) formation, an endogenous inhibitor of IKKbeta activity. Further analysis revealed that inhibition of IKKbeta activity in selenium-supplemented cells correlated with the Michael addition product of 15d-PGJ2 with Cys-179 of IKKbeta, while the formation of such an adduct was significantly decreased in the selenium-deficient macrophages. In addition, anti-inflammatory activities of selenium were also mediated by the 15d-PGJ2-dependent activation of the peroxisome proliferator-activated nuclear receptor-gamma in macrophages. Experiments using specific cyclooxygenase (COX) inhibitors and genetic knockdown approaches indicated that COX-1, and not the COX-2 pathway, was responsible for the increased synthesis of 15d-PGJ2 in selenium-supplemented macrophages. Taken together, our results suggest that selenium supplementation increases the production of 15d-PGJ2 as an adaptive response to protect cells against oxidative stress-induced pro-inflammatory gene expression. More specifically, modification of protein thiols by 15d-PGJ2 represents a previously undescribed code for redox regulation of gene expression by selenium.

Crystal structure of a substrate complex of myo-inositol oxygenase, a di-iron oxygenase with a key role in inositol metabolism

Altered metabolism of the inositol sugars myo-inositol (MI) and d-chiro-inositol is implicated in diabetic complications. In animals, catabolism of MI and D-chiro-inositol depends on the enzyme MI oxygenase (MIOX), which catalyzes the first committed step of the glucuronate-xylulose pathway, and is found almost exclusively in the kidneys. The crystal structure of MIOX, in complex with MI, has been determined by multiwavelength anomalous diffraction methods and refined at 2.0-A resolution (R=0.206, Rfree=0.253). The structure reveals a monomeric, single-domain protein with a mostly helical fold that is distantly related to the diverse HD domain superfamily. Five helices form the structural core and provide six ligands (four His and two Asp) for the di-iron center, in which the two iron atoms are bridged by a putative hydroxide ion and one of the Asp ligands, Asp-124. A key loop forms a lid over the MI substrate, which is coordinated in bidentate mode to one iron atom. It is proposed that this mode of iron coordination, and interaction with a key Lys residue, activate MI for bond cleavage. The structure also reveals the basis of substrate specificity and suggests routes for the development of specific MIOX inhibitors.

A coupled dinuclear iron cluster that is perturbed by substrate binding in myo-inositol oxygenase

myo-Inositol oxygenase (MIOX) uses iron as its cofactor and dioxygen as its cosubstrate to effect the unique, ring-cleaving, four-electron oxidation of its cyclohexan-(1,2,3,4,5,6-hexa)-ol substrate to d-glucuronate. The nature of the iron cofactor and its interaction with the substrate, myo-inositol (MI), have been probed by electron paramagnetic resonance (EPR) and Mössbauer spectroscopies. The data demonstrate the formation of an antiferromagnetically coupled, high-spin diiron(III/III) cluster upon treatment of solutions of Fe(II) and MIOX with excess O(2) or H(2)O(2) and the formation of an antiferromagnetically coupled, valence-localized, high-spin diiron(II/III) cluster upon treatment with either limiting O(2) or excess O(2) in the presence of a mild reductant (e.g., ascorbate). Marked changes to the spectra of both redox forms upon addition of MI and analogy to changes induced by binding of phosphate to the diiron(II/III) cluster of the protein phosphatase, uteroferrin, suggest that MI coordinates directly to the diiron cluster, most likely in a bridging mode. The addition of MIOX to the growing family of non-heme diiron oxygenases expands the catalytic range of the family beyond the two-electron oxidation (hydroxylation and dehydrogenation) reactions catalyzed by its more extensively studied members such as methane monooxygenase and stearoyl acyl carrier protein Delta(9)-desaturase.

Oxygen Activation by a Mixed-Valent, Diiron(II/III) Cluster in the Glycol Cleavage Reaction Catalyzed by myo-Inositol Oxygenase

myo-Inositol oxygenase (MIOX) catalyzes the ring-cleaving, four-electron oxidation of its cyclohexan-(1,2,3,4,5,6-hexa)-ol substrate (myo-inositol, MI) to d-glucuronate (DG). The preceding paper [Xing, G., Hoffart, L. M., Diao, Y., Prabhu, K. S., Arner, R. J., Reddy, C. C., Krebs, C., and Bollinger, J. M., Jr. (2006) Biochemistry 45, 5393-5401] demonstrates by Mössbauer and electron paramagnetic resonance (EPR) spectroscopies that MIOX can contain a non-heme dinuclear iron cluster, which, in its mixed-valent (II/III) and fully oxidized (III/III) states, is perturbed by binding of MI in a manner consistent with direct coordination. In the study presented here, the redox form of the enzyme that activates O(2) has been identified. l-Cysteine, which was previously reported to accelerate turnover, reduces the fully oxidized enzyme to the mixed-valent form, and O(2), the cosubstrate, oxidizes the fully reduced form to the mixed-valent form with a stoichiometry of one per O(2). Both observations implicate the mixed-valent, diiron(II/III) form of the enzyme as the active state. Stopped-flow absorption and freeze-quench EPR data from the reaction of the substrate complex of mixed-valent MIOX [MIOX(II/III).MI] with limiting O(2) in the presence of excess, saturating MI reveal the following cycle: (1) MIOX(II/III).MI reacts rapidly with O(2) to generate an intermediate (H) with a rhombic, g < 2 EPR spectrum; (2) a form of the enzyme with the same absorption features as MIOX(II/III) develops as H decays, suggesting that turnover has occurred; and (3) the starting MIOX(II/III).MI complex is then quantitatively regenerated. This cycle is fast enough to account for the catalytic rate. The DG/O(2) stoichiometry in the reaction, 0.8 +/- 0.1, is similar to the theoretical value of 1, whereas significantly less product is formed in the corresponding reaction of the fully reduced enzyme with limiting O(2). The DG/O(2) yield in the latter reaction decreases as the enzyme concentration is increased, consistent with the hypothesis that initial conversion of the reduced enzyme to the MIOX(II/III).MI complex and subsequent turnover by the mixed-valent form is responsible for the product in this case. The use of the mixed-valent, diiron(II/III) cluster by MIOX represents a significant departure from the mechanisms of other known diiron oxygenases, which all involve activation of O(2) from the II/II manifold.

Expression of myo-inositol oxygenase in tissues susceptible to diabetic complications

Alterations of intracellular levels of myo-inositol (MI) have the potential to impact such cellular processes as signaling pathways and osmotic balance. Depletion of MI has been implicated in the etiology of diabetic complications; however, the mechanistic details remain sketchy. myo-Inositol oxygenase (MIOX-EC 1.13.99.1) catalyzes the first committed step of the only pathway of MI catabolism. In the present study, extra-renal tissues and cell types, including those affected by diabetic complications, were examined for MIOX expression. Western blotting results indicated that kidney is the only major organ where MIOX protein is expressed at detectable levels. Immunohistochemical examination of the kidney revealed that the proximal tubular epithelial cells are the only site of MIOX expression in the kidney. Reverse-transcription-polymerase chain reaction (RT-PCR) and Western immunoblot analyses, however, revealed that the cell lines ARPE-19 and HLE-B3, representing human retinal pigmented epithelium and lens epithelium, respectively, also express MIOX. In addition, quantitative real-time RT-PCR analysis of all major tissues in the mouse showed that the sciatic nerve contained MIOX transcript, which was found to be significantly higher than that observed in other non-renal organs. These results indicate that MIOX is found at lower levels in extra-renal tissues where diabetic complications, including nephropathy, neuropathy, retinopathy, and cataract, are frequently observed.