Nicotinamide Nucleotide Transhydrogenase Gene Research Articles

Lack of NAD(P)+ transhydrogenase activity in patients with primary adrenal insufficiency due to NNT variants.

Pathogenic variants in the nicotinamide nucleotide transhydrogenase gene (NNT) are a rare cause of primary adrenal insufficiency (PAI), as well as functional impairment of the gonads. Despite the description of different homozygous and compound heterozygous NNT variants in PAI patients, the extent to which the function and expression of the mature protein are compromised remains to be clarified. The activity and expression of mitochondrial NAD(P)+ transhydrogenase (NNT) were analyzed in blood samples obtained from patients diagnosed with PAI due to genetically confirmed variants of the NNT gene (n = 5), heterozygous carriers as their parents (n = 8), and healthy controls (n = 26). NNT activity was assessed by a reverse reaction assay standardized for digitonin-permeabilized peripheral blood mononuclear cells (PBMCs). The enzymatic assay was validated in PBMC samples from a mouse model of NNT absence. Additionally, the PBMC samples were evaluated for NNT expression by western blotting and reverse transcription quantitative polymerase chain reaction and for mitochondrial oxygen consumption. NNT activity was undetectable (<4% of that of healthy controls) in PBMC samples from patients, independent of the pathogenic genetic variant. In patients' parents, NNT activity was approximately half that of the healthy controls. Mature NNT protein expression was lower in patients than in the control groups, while mRNA levels varied widely among genotypes. Moreover, pathogenic NNT variants did not impair mitochondrial bioenergetic function in PBMCs. The manifestation of PAI in NNT-mutated patients is associated with a complete lack of NNT activity. Evaluation of NNT activity can be useful to characterize disease-causing NNT variants.

Testicular impairment in Primary Adrenal Insufficiency caused by Nicotinamide Nucleotide Transhydrogenase (NNT) deficiency - a case report: implication of oxidative stress and importance of fertility preservation

IntroductionNicotinamide nucleotide transhydrogenase (NNT) gene deficiency has recently been shown to be involved in Primary Adrenal Insufficiency (PAI). NNT encodes an inner mitochondrial membrane protein that produces large amounts of NADPH. NADPH is used in several biosynthesis pathways and the oxidoreduction of free radicals by the glutathione and thioredoxin systems in mitochondria. Patients with PAI due to NNT deficiency may also exhibit extra-adrenal manifestations, usually including gonadal impairment.Case reportWe present the case of a 35-year-old patient referred to our center for primary infertility with non-obstructive azoospermia, in a context of PAI and obesity. PAI genetic exploration carried out at the age of thirty revealed NNT deficiency due to the presence of two deleterious mutations (one on each allele) in the NNT gene. Scrotal ultrasound revealed a right Testicular Adrenal Rest Tumor (TART). Intensification of glucocorticoid therapy over the course of 8 months failed to reduce the TART volume or improve sperm production and endocrine function. No spermatozoa were found after surgical exploration of both testes, and subsequent histopathological analysis revealed bilateral Sertoli cell-only syndrome. A retrospective review of the hypothalamic-pituitary-gonadic axis hormonal assessment over 20 years showed progressive impairment of testicular function, accelerated during adulthood, leading to hypergonadotropic hypogonadism and non-obstructive azoospermia when the patient reached his thirties, while the PAI remained controlled over the same period.ConclusionThis case report provides, for the first time, direct evidence of complete germ line loss in an azoospermic man with NNT deficiency. Additional data further support the hypothesis of a determinant role of oxidative cellular damage due to reactive oxygen species (ROS) imbalance in the severe gonadal impairment observed in this NNT-deficient patient. Early and regular evaluation of gonadal function should be performed in patients with PAI, especially with NNT deficiency, as soon as the patients reach puberty. Fertility preservation options should then be provided in early adulthood for these patients.

Nicotinamide Nucleotide Transhydrogenase Is Essential for Adrenal Steroidogenesis: Clinical and In Vitro Lessons.

Nicotinamide nucleotide transhydrogenase (NNT) acts as an antioxidant defense mechanism. NNT mutations cause familial glucocorticoid deficiency (FGD). How impaired oxidative stress disrupts adrenal steroidogenesis remains poorly understood. To ascertain the role played by NNT in adrenal steroidogenesis. The genotype-phenotype association of a novel pathogenic NNT variant was evaluated in a boy with FGD. Under basal and oxidative stress (OS) induced conditions, transient cell cultures of the patient's and controls' wild-type (WT) mononuclear blood cells were used to evaluate antioxidant mechanisms and mitochondrial parameters (reactive oxygen species [ROS] production, reduced glutathione [GSH], and mitochondrial mass). Using CRISPR/Cas9, a stable NNT gene knockdown model was built in H295R adrenocortical carcinoma cells to determine the role played by NNT in mitochondrial parameters and steroidogenesis. NNT immunohistochemistry was assessed in fetal and postnatal human adrenals. The homozygous NNT p.G866D variant segregated with the FGD phenotype. Under basal and OS conditions, p.G866D homozygous mononuclear blood cells exhibited increased ROS production, and decreased GSH levels and mitochondrial mass than WT NNT cells. In line H295R, NNT knocked down cells presented impaired NNT protein expression, increased ROS production, decreased the mitochondrial mass, as well as the size and the density of cholesterol lipid droplets. NNT knockdown affected steroidogenic enzyme expression, impairing cortisol and aldosterone secretion. In human adrenals, NNT is abundantly expressed in the transition fetal zone and in zona fasciculata. Together, these studies demonstrate the essential role of NNT in adrenal redox homeostasis and steroidogenesis.

ODP055 The methylation pattern of a unique Bilateral para-overian Adrenal Rest Tumor in a girl with Nicotinamide Nucleotide Transhydrogenase mutation

Abstract Background Patients with NNT (Nicotinamide Nucleotide Transhydrogenase) gene mutations, a rare cause of glucocorticoid and mineralocorticoid deficiency require hormone replacement therapy. Adrenal Rest Tumor (ART) in females, reported so far only in noncompliant patients with congenital adrenal hyperplasia and elevated ACTH levels, is very rare (&amp;lt;20 cases world-wide). This study characterizes the pathophysiology, the molecular ontogeny and methylation analysis of a unique ART in a female with adrenal failure due to the G200S mutation in NNT Clinical presentation and Method: A 15-year-old girl, with homozygous G200S NNT-mutation followed for adrenal insufficiency reappeared to follow-up with severe virilization and elevated serum testosterone (28.3 nmol/l) and ACTH (&amp;gt; 1500 pmol/l). Pelvic MRI and Ultrasound demonstrated one sided paraovarian round tumor with pathological vascularization. Laparoscopic exploration revealed bilateral para ovarian mesosalpinx masses involving the serosa of the Fallopian tube, (3 and 1 cm in diameter). The testosterone level normalized within one day after surgical removal of those masses (0.2 nmol/l). Results Histopathology demonstrated a pattern of adrenal rest tissue with strong intracellular positive staining for adrenal markers such as SF-1, calretinin, MART1, inhibin and the pituitary marker ACTH. The staining for ovarian characteristic markers such as PAX 8 was negative. Studying mRNA extracted from the tissue by RT-PCR revealed the positive Gene expression of Cyp17a1, Cyp21a2 and Mc2r cDNA but not Pomc suggesting adrenal but not pituitary origin of the tissue. We further profiled the epigenomic profile of several adrenal rest tumors from both ovarian and testes origins using the Infinium Methylation EPIC array. We characterized the adrenal-specific features by comparing the tumors from the two different originating sites to published methylation array data on healthy adrenal tissue. We further investigated cancer-specific methylation changes to identify activated cancer pathways, and used the methylation arrays to identify somatic copy number alterations. Finally, we analyzed the likely developmental origin of these tumors by comparing to published methylation array data of developmental and adult reproductive tissues. Conclusion This study exemplifies severe virilization that resulted from a unique and rare type of ART in ovarian related tissue that was caused by incompliance to treatment in a patient with NNT gene mutation. The laparoscopic surgical findings indicate that imaging techniques may be insufficient in identification of such rest tumors and call for laparoscopy when clinical findings are suggestive. An early detection of this tumor could preserve fertility. Using histopathology markers cDNA studies and epigenomic profiling by methylation studies, our study shows for the first time that female ART originates from adrenal cells. The growth of a functional androgen producing "tumor" indicates that functional NNT protein is NOT required for androgen synthesis in contrast to glucocorticoids and that a zona reticularis similar tissue in ART is responsive to ACTH stimulation. Presentation: No date and time listed

ODP646 Deficient NNT Reduces Mitochondrial Mass and Cholesterol Trafficking in the Adrenal Cortex, Accumulating ROS and Impairing Steroids Production

Abstract Background The mitochondrial enzyme nicotinamide nucleotide transhydrogenase (NNT) is essential in the antioxidant defense mechanisms. In addition, adrenal cortex cells appear to require NNT for normal steroidogenesis. However, to date, the mechanisms involved in NNT regulation of steroidogenesis are not fully understood. Aim To assess how NNT regulates steroidogenesis by characterizing how a loss-of-function NNT mutation impairs antioxidants mechanisms in adrenal cells resulting in FGD. Methods Genomic DNA of a boy with FGD was evaluated by whole-exome sequencing (WES). Candidate variants were analyzed in silico and confirmed by Sanger sequencing. Genotype-phenotype association of a new homozygous loss-of-function NNT variant with FGD was assessed in vitro. We built a stable knockdown model of the NNT gene in the H295R adrenal cell line using CRISPR Cas9 technology. We evaluated the effect of alterations in NNT on Cholesterol Trafficking (NBD-Cholesterol) and mitochondrial parameters (DCFDA and Mitotracker) as well as on adrenal steroidogenesis by cortisol (RIA) and aldosterone (ELISA) production. In this NNT stable knockdown model, we inserted the commercial plasmid NNT HaloTag human ORF in pFN21A (FHC01572) containing the wild type (WT) sequence of the NNT gene and the direct site mutagenesis. Results WES revealed the NNT p. G866D pathogenic variant in the affected patient. The familial pedigree analysis confirmed the segregation of this variant with FGD in homozygosis. The clone selected after NNT modification by the CRISPR- Cas9 system showed a 75% reduction in NNT protein expression. The NNT-deficient cell clone increased reactive oxygen species (ROS) production (p&amp;lt;0. 0001), decreased mitochondrial mass (p&amp;lt;0. 0001), and decreased density (p=0. 03) of cholesterol lipid droplets as well as cortisol (p&amp;lt;0,0001) and aldosterone (p=0. 006) secretion. Reexpression of NNT in an NNT-deficient cell clone restored the ROS levels (p&amp;lt;0. 0001). Compared to wild-type (WT), both under basal and oxidative stress conditions after stimulation of 10uM forskolin, homozygous p. G866D NNT exhibited increased ROS production (p=0. 0002; p&amp;lt;0. 0001, respectively). Conclusions Deficient NNT decreases mitochondrial mass and impairs cholesterol trafficking by reducing cholesterol droplets mass, leading to the loss of antioxidants mechanisms and accumulation of ROS. NNT impairment in adrenal cells decreases cortisol and aldosterone secretion. Altogether, these data enlighten the mechanisms by which NNT mutations result in primary adrenal insufficiency. Presentation: No date and time listed

Long-Term Follow-Up of Three Family Members with a Novel NNT Pathogenic Variant Causing Primary Adrenal Insufficiency.

Nicotinamide nucleotide transhydrogenase (NNT) deficiency causes primary adrenal insufficiency (PAI) and possibly some extra-adrenal manifestations. A limited number of these patients were previously described. We present the clinical and genetic characteristics of three family members with a biallelic novel pathogenic variant in the NNT gene. The patients were followed until the ages of 21.6, 20.2, and 4.2 years. PAI was diagnosed in the eldest two brothers after an Addisonian crisis and the third was diagnosed at the age of 4.5 months in the asymptomatic stage due to the genetic screening of family members. Whole exome sequencing with a targeted interpretation of variants in genes related to PAI was performed in all the patients. The urinary steroid metabolome was determined by gas chromatography–mass spectrometry in the asymptomatic patient. The three patients, who were homozygous for c.1575dup in the NNT gene, developed isolated glucocorticoid deficiency. The urinary steroid metabolome showed normal excretion of cortisol metabolites. The adolescent patients had slow pubertal progression with low–normal testicular volume, while testicular endocrine function was normal. Bone mineral density was in the range for osteopenia in both grown-up siblings. Echocardiography revealed no structural or functional heart abnormalities. This article is among the first with a comprehensive and chronologically-detailed description of patients with NNT deficiency.

Severe Virilization in a Girl With the Homozygous G200SNicotinamide Nucleotide Transhydrogenase Mutation Is Surprisingly Caused by Rare Bilateral Para-Overian Adrenal Rest Tumors

Background: Patients with NNT (Nicotinamide Nucleotide Transhydrogenase) gene mutations, a rare cause of glucocorticoid and mineralocorticoid deficiency require hormone replacement therapy. Adrenal Rest Tumor (ART) in females is very rare (<20 cases world-wide) and was reported only in noncompliant patients with congenital adrenal hyperplasia having extremely elevated ACTH levels. This study characterizes the clinical characteristics, the pathophysiology and the molecular ontogeny of a unique ART in a female with adrenal failure due to the G200S mutation in NNT. Clinical presentation and Method: A 15-year-old girl, with homozygous G200S NNT-mutation that caused adrenal insufficiency reappeared to follow-up after several years with severe virilization and elevated serum testosterone (28.3 nmol/l) and ACTH (> 1500 pmol/l) levels. Pelvic MRI and Ultrasound demonstrated one sided para-ovarian round tumor with pathological vascularization. Laparoscopic exploration revealed bilateral para-ovarian mesosalpinx masses involving the serosa of the Fallopian tube (3 and 1 cm in diameter); the testosterone level normalized within one day after removal of those masses (0.2 nmol/l). Results: Histopathology demonstrated a pattern of adrenal rest tissue with strong intracellular positive staining for adrenal markers such as SF-1, calretinin, MART1, inhibin and the pituitary corticotroph marker-ACTH. The staining for ovarian characteristic markers such as PAX 8 was negative. Studying mRNA extracted from the tissue by RT-PCR revealed the presence of CYP17A1, CYP21A2 and MC2R (ACTH receptor) cDNA confirming typical adrenocortical transcriptional pattern in the tissue. cDNA of POMC was not detected suggesting that in spite of dense ACTH staining the tissue is not classically originated from pituitary corticotrophs. Methylome studies to further characterise the tissue are underway. Conclusion: This study exemplifies severe virilization that resulted from a unique and rare type of ART in ovarian related tissue that was caused by incompliance to treatment in a patient with NNT gene mutation. Given the ubiquitous expression of NNT and its reported pathophysiology as free radicals scavenger in all adrenocortical layers, it is surprising to have high ACTH induced severe virilization in spite of severe NNT dysfunction and adrenal insufficiency. This study may indicate timely testosterone screening in females with NNT mutation and when increased they should probably be laparoscopically surveyed for ART even when not detected by imaging. How NNT mutation damages mineralo and glucocorticoid secreting cells while androgen secreting cells are rescued is a theme for further studies.

Downregulation of nicotinamide nucleotide transhydrogenase and its naturally occurring antisense RNA in gastric cancer.

Nicotinamide Nucleotide Transhydrogenase (NNT) gene encodes a protein, which is an important antioxidative enzyme that converts NADH to NADPH. This enzyme provides a significant proportion of the entire NADPH resourcein the mitochondria. Previous reports have shown possible contribution of this gene in the carcinogenesis process. In the current research, we evaluated expression levels of NNT gene and a naturally occurring antisense RNA (NNT-AS1) in gastric cancer specimens compared to their corresponding adjacent noncancerous tissues (ANCTs). Both NNT1 and NNT-AS1 genes were significantly downregulated in tumor tissues compared to ANCTs (expression ratio=0.369, p=.045 and expression ratio=0.368, p=.043, respectively). Transcript levels of NNT1 and NNT-AS1 were associated with the location of the primary tumor (p=.003 and .002, respectively). Moreover, expressions of both genes were significantly elevated in tumors with lymphatic/vascular invasion compared to tumors without lymphatic/vascular invasion (p=.001 and p=.005). No other remarkable associations were noticed between transcript levels of genes in tumor tissues and patients' information. Based on the area under curve (AUC) values in the receiver operating characteristic (ROC) curves, the diagnostic power of NNT1 and NNT-AS1 were estimated to be 0.62 and 0.63, respectively. Although we demonstrated dysregulation of NNT1 and NNT-AS1 in gastric tumor specimens in association with clinical data of patients, these two genes are not supposed to be appropriate biomarkers for gastric cancer.

NNT and NNT-AS1 expression levels are not different between bipolar patients and healthy subjects

Nicotinamide nucleotide transhydrogenase (NNT) participates in redox and energy interconnections. Nnt silencing in N27 dopaminergic cells has changed basal, extra, and greatest mitochondrial oxygen absorption rates and made these cell vulnerable to constant upsurges in H2O2. NNT-antisense RNA1 (NNT-AS1) is transcribed from the opposite stand of NNT gene and is possibly involved in regulation of NNT expression. Based on the reports of previous studies regarding dys-regulation of oxidative stress markers in bipolar patients, we designed the current study to assess peripheral expression of NNT and NNT-AS1 in bipolar patients and healthy subjects. Transcript levels of NNT and NNT-AS1 were not significantly different between bipolar patients and controls. No significant correlation was found between relative expression of genes and age of study participants. Moreover, expression of either gene was correlated with age at disease onset or disease duration in cases. However, significant pairwise correlation was found between expressions of these genes in bipolar patients. Our results imply that NNT does not participate in dys-regulation of oxidative stress in bipolar disease.

Raf kinase inhibitor protein mediates myocardial fibrosis under conditions of enhanced myocardial oxidative stress

Fibrosis is a hallmark of maladaptive cardiac remodelling. Here we report that genome-wide quantitative trait locus (QTL) analyses in recombinant inbred mouse lines of C57BL/6 J and DBA2/J strains identified Raf Kinase Inhibitor Protein (RKIP) as genetic marker of fibrosis progression. C57BL/6 N-RKIP−/− mice demonstrated diminished fibrosis induced by transverse aortic constriction (TAC) or CCl4 (carbon tetrachloride) treatment compared with wild-type controls. TAC-induced expression of collagen Iα2 mRNA, Ki67+ fibroblasts and marker of oxidative stress 8-hydroxyguanosine (8-dOHG)+ fibroblasts as well as the number of fibrocytes in the peripheral blood and bone marrow were markedly reduced in C57BL/6 N-RKIP−/− mice. RKIP-deficient cardiac fibroblasts demonstrated decreased migration and fibronectin production. This was accompanied by a two-fold increase of the nuclear accumulation of nuclear factor erythroid 2-related factor 2 (Nrf2), the main transcriptional activator of antioxidative proteins, and reduced expression of its inactivators. To test the importance of oxidative stress for this signaling, C57BL/6 J mice were studied. C57BL/6 J, but not the C57BL/6 N-strain, is protected from TAC-induced oxidative stress due to mutation of the nicotinamide nucleotide transhydrogenase gene (Nnt). After TAC surgery, the hearts of Nnt-deficient C57BL/6 J-RKIP−/− mice revealed diminished oxidative stress, increased left ventricular (LV) fibrosis and collagen Iα2 as well as enhanced basal nuclear expression of Nrf2. In human LV myocardium from both non-failing and failing hearts, RKIP-protein correlated negatively with the nuclear accumulation of Nrf2. In summary, under conditions of Nnt-dependent enhanced myocardial oxidative stress induced by TAC, RKIP plays a maladaptive role for fibrotic myocardial remodeling by suppressing the Nrf2-related beneficial effects.

A novel homozygous insertion and review of published mutations in the NNT gene causing familial glucocorticoid deficiency (FGD)

Familial glucocorticoid deficiency (FGD) is an autosomal recessive disorder characterized by low levels of cortisol despite high adrenocorticotropin (ACTH) levels, due to the reduced ability of the adrenal cortex to produce cortisol in response to stimulation by ACTH. FGD is a heterogeneous disorder for which causal mutations have been identified in MC2R, MRAP, MCM4 and TXNRD2. Also mutations in STAR and CYP11A1 can sometimes present with a phenotype resembling FGD. Recently, it has been indicated that FGD can also be caused by mutations in NNT (nicotinamide nucleotide transhydrogenase).We identified a 6.67 Mb homozygous region harboring the NNT gene by SNP haplotyping in a 1-year old Dutch boy presenting with FGD, but without mutations in MC2R and MRAP. Exome-sequencing revealed a novel homozygous mutation (NM_012343.3: c.1259dupG) in NNT that was predicted to be disease-causing. The mutation is located in exon 9 and creates a frameshift leading to a premature stop-codon (p.His421Serfs*4) that is known to result in FGD. Both parents were shown to be heterozygous carriers. We reviewed the literature for all the reported NNT mutations and their clinical presentation. The median age of disease onset in 23 reported patients, including the present patient, was 12 months (range 3 days–39 months). There was no difference in age of disease onset between truncating and non-truncating NNT mutations. Based on recent literature, we advise to monitor patients with FGD due to NNT mutations for possible combined mineralocorticoid insufficiency and extra-adrenal manifestations.

Impact of a novel homozygous mutation in nicotinamide nucleotide transhydrogenase on mitochondrial DNA integrity in a case of familial glucocorticoid deficiency

BackgroundFamilial glucocorticoid deficiency (FGD) is a rare autosomal recessive disorder that is characterized by isolated glucocorticoid deficiency. Recently, mutations in the gene encoding for the mitochondrial nicotinamide nucleotide transhydrogenase (NNT) have been identified as a causative gene for FGD; however, no NNT activities have been reported in FGD patients carrying NNT mutations. MethodsClinical, biochemical and molecular analyses of lymphocytes from FDG homozygous and heterozygous carriers for the F215S NNT mutation were performed. ResultsIn this study, we described an FGD-affected Japanese patient carrying a novel NNT homozygous mutation (c.644T>C; F215S) with a significant loss-of-function (NNT activity=31% of healthy controls) in peripheral blood cells' mitochondria. The NNT activities of the parents, heterozygous for the mutation, were 61% of the controls. ConclusionsOur results indicated that (i) mitochondrial biogenesis (citrate synthase activity) and/or mtDNA replication (mtDNA copy number) were affected at ≤60% NNT activity because these parameters were affected in individuals carrying either one or both mutated alleles; and (ii) other outcomes (mtDNA deletions, protein tyrosine nitration, OXPHOS capacity) were affected at ≤30% NNT activity as also observed in murine cerebellar mitochondria from C57BL/6J (NNT−/−) vs. C57BL/6JN (NNT+/+) substrains. General significanceBy studying a family affected with a novel point mutation in the NNT gene, a gene–dose response was found for various mitochondrial outcomes providing for novel insights into the role of NNT in the maintenance of mtDNA integrity beyond that described for preventing oxidative stress.

Adipose tissue metabolism and inflammation are differently affected by weight loss in obese mice due to either a high-fat diet restriction or change to a low-fat diet

Restriction of a high-fat diet (HFD) and a change to a low-fat diet (LFD) are two interventions that were shown to promote weight loss and improve parameters of metabolic health in obesity. Examination of the biochemical and molecular responses of white adipose tissue (WAT) to these interventions has not been performed so far. Here, male C57BL/6JOlaHsd mice, harboring an intact nicotinamide nucleotide transhydrogenase gene, were fed a purified 40 energy% HFD for 14weeks to induce obesity. Afterward, mice were divided into three dietary groups: HFD (maintained on HFD), LFD (changed to LFD with identical ingredients), and HFD-CR (restricted to 70% of the HFD). The effects of the interventions were examined after 5weeks. Beneficial effects were seen for both HFD-CR and LFD (compared to HFD) regarding physiological parameters (body weight and fat mass) and metabolic parameters, including circulating insulin and leptin levels. Macrophage infiltration in WAT was reduced by both interventions, although more effectively by HFD-CR. Strikingly, molecular parameters in WAT differed between HFD-CR and LFD, with increased activation of mitochondrial carbohydrate and fat metabolism in HFD-CR mice. Our results confirm that restriction of the amount of dietary intake and reduction in the dietary energy content are both effective in inducing weight loss. The larger decrease in WAT inflammation and increase in mitochondrial carbohydrate metabolism may be due to a larger degree of energy restriction in HFD-CR, but could also be due to superior effectiveness of dietary restriction in weight loss strategies.

Relative importance of redox buffers GSH and NAD(P)H in age‐related neurodegeneration and Alzheimer disease‐like mouse neurons

Aging, a major risk factor in Alzheimer’s disease (AD), is associated with an oxidative redox shift, decreased redox buffer protection, and increased free radical reactive oxygen species (ROS) generation, probably linked to mitochondrial dysfunction. While NADH is the ultimate electron donor for many redox reactions, including oxidative phosphorylation, glutathione (GSH) is the major ROS detoxifying redox buffer in the cell. Here, we explored the relative importance of NADH and GSH to neurodegeneration in aging and AD neurons from nontransgenic and 3xTg-AD mice by inhibiting their synthesis to determine whether NADH can compensate for the GSH loss to maintain redox balance. Neurons stressed by either depleting NAD(P)H or GSH indicated that NADH redox control is upstream of GSH levels. Further, although depletion of NAD(P)H or GSH correlated linearly with neuron death, compared with GSH depletion, higher neurodegeneration was observed when NAD(P)H was extrapolated to zero, especially in old age, and in the 3xTg-AD neurons. We also observed an age-dependent loss of gene expression of key redox-dependent biosynthetic enzymes, NAMPT (nicotinamide phosphoribosyltransferase), and NNT (nicotinamide nucleotide transhydrogenase). Moreover, age-related correlations between brain NNT or NAMPT gene expression and NADPH levels suggest that these genes contribute to the age-related declines in NAD(P)H. Our data indicate that in aging and more so in AD-like neurons, NAD(P)H redox control is upstream of GSH and an oxidative redox shift that promotes neurodegeneration. Thus, NAD(P)H generation may be a more efficacious therapeutic target upstream of GSH and ROS.

Familial isolated glucocorticoid deficiency: three clinical cases and a brief overview of the current literature

Familial isolated glucocorticoid deficiency (FIGD) is a rare form of primary adrenal insufficiency associated with the resistance of the adrenal cortex to the action of ACTH. This pathology manifests itself in the form of cortisol deficiency despite the normal mineralocorticoid function. Approximately 50% of all FIGD cases are attributable to mutations in two genes (melanocortin 2 receptor gene, MC2R, and melanocortin 2 receptor accessory protein gene, MRAP). In addition, the relationship between FIGD and mutations in nicotinamide nucleotide transhydrogenase gene, NNT, minichromosome maintenance gene, MCM4, and STAR is documented. No genetic defect was found in almost 25% of the cases of isolated deficiency of gucocorticoids. The clinical descriptions of the patients presenting with FIGD including its molecular-genetic diagnostics are of great interest for the understanding of this rare disease.

A spontaneous mutation in the nicotinamide nucleotide transhydrogenase gene of C57BL/6J mice results in mitochondrial redox abnormalities

NADPH is the reducing agent for mitochondrial H2O2 detoxification systems. Nicotinamide nucleotide transhydrogenase (NNT), an integral protein located in the inner mitochondrial membrane, contributes to an elevated mitochondrial NADPH/NADP+ ratio. This enzyme catalyzes the reduction of NADP+ at the expense of NADH oxidation and H+ reentry to the mitochondrial matrix. A spontaneous Nnt mutation in C57BL/6J (B6J-NntMUT) mice arose nearly 3 decades ago but was only discovered in 2005. Here, we characterize the consequences of the Nnt mutation on the mitochondrial redox functions of B6J-NntMUT mice. Liver mitochondria were isolated both from an Nnt wild-type C57BL/6 substrain (B6JUnib-NntW) and from B6J-NntMUT mice. The functional evaluation of respiring mitochondria revealed major redox alterations in B6J-NntMUT mice, including an absence of transhydrogenation between NAD and NADP, higher rates of H2O2 release, the spontaneous oxidation of NADPH, the poor ability to metabolize organic peroxide, and a higher susceptibility to undergo Ca2+-induced mitochondrial permeability transition. In addition, the mitochondria of B6J-NntMUT mice exhibited increased oxidized/reduced glutathione ratios as compared to B6JUnib-NntW mice. Nonetheless, the maximal activity of NADP-dependent isocitrate dehydrogenase, which is a coexisting source of mitochondrial NADPH, was similar between both groups. Altogether, our data suggest that NNT functions as a high-capacity source of mitochondrial NADPH and that its functional loss due to the Nnt mutation results in mitochondrial redox abnormalities, most notably a poor ability to sustain NADP and glutathione in their reduced states. In light of these alterations, the potential drawbacks of using B6J-NntMUT mice in biomedical research should not be overlooked.

Expanding the Phenotypic Spectrum of Nicotinamide Nucleotide Transhydrogenase (NNT) Mutations and using Whole Exome Sequencing to Discover Potential Disease Modifiers

Mutations in the NNT gene (nicotinamide nucleotide transhydrogenase), which is involved in NADPH generation in mitochondria, have recently been described in familial glucocorticoid deficiency. We report two patients, one with isolated glucocorticoid deficiency and the other with a combined glucocorticoid and mineralocorticoid deficiency. Through whole exome sequencing, both cases were found to carry two different NNT mutations, confirming previous results for these patients. Each patient also carries multiple heterozygous protein-altering mutations in other genes involved in steroid hormone biogenesis and regulation. The patient with a combined glucocorticoid and mineralocorticoid deficiency is a compound heterozygote for common missense variants in the ME3 gene (mitochondrial malic enzyme 3), the product of which also generates NADPH in mitochondria. Mutations in NNT are the likely proximal cause of the glucocorticoid deficiency in both patients, but genetic background effects may be important in modulating the specific phenotype of adrenal insufficiency.

A novel homozygous mutation of the nicotinamide nucleotide transhydrogenase gene in a Japanese patient with familial glucocorticoid deficiency

Familial glucocorticoid deficiency (FGD) is a rare autosomal recessive disorder characterized by primary hypocortisolism and normal mineralocorticoid production. Recently, NNT encoding the nicotinamide nucleotide transhydrogenase has been identified as a causative gene for FGD. Thus, we examined NNT in six Japanese FGD patients with no recognizable mutation in the previously known four responsible genes for FGD (MC2R, MRAP, STAR, and MCM4), and identified a novel homozygous substitution (c.644T>C; p.Phe215Ser) in a single 17.5-year-old boy. His parents were heterozygous for this mutation. This substitution was absent from 120 Japanese control subjects and was not registered in public databases including JSNP Database. The phenylalanine residue at the 215th codon was evolutionally conserved, and the p.Phe215Ser was assessed to be a pathologic mutation by in silico protein function analyses. The results, in conjunction with the previous data, imply that NNT mutations account for 5-10% of FGD patients, and that underlying factor(s) still remains to be clarified in a substantial fraction of FGD patients.

Characterization of a nicotinamide nucleotide transhydrogenase gene from the green alga Acetabularia acetabulum and comparison of its structure with those of the corresponding genes in mouse and Caenorhabditis elegans

Proton-pumping nicotinamide nucleotide transhydrogenase (Nnt) is a membrane-bound enzyme that catalyzes the reversible reduction of NADP + by NADH. This reaction is linked to proton translocation across the membrane. Depending on metabolic conditions, the enzyme may be involved in NADPH generation, e.g., for detoxification of peroxides and/or free radicals and protection from ischemic damage. Nnt exists in most prokaryotes and in animal mitochondria. It is composed of 2–3 subunits in bacteria and of a single polypeptide in mitochondria. An open question is whether Nnt exists in any photosynthetic eukaryotes and if so, to which class it belongs. In the present study it is demonstrated that, by cloning and sequencing cDNA and genomic copies of its NNT gene, an ancient alga, Acetabularia acetabulum (Chlorophyta, Dasycladales), contains a nuclear-encoded Nnt. In contrast to photosynthetic bacteria, this algal Nnt is composed of a single polypeptide of the class found in animal mitochondria. Excluding a poly(A) tail, NNT cDNA from A. acetabulum is 3688 bp long, consists of eight exons and spans 17 kb. The NNT gene from mouse was also characterized. Subsequently, the gene organization of the A. acetabulum NNT was compared to those of the homologous mouse (100 kb and 21 exons) and Caenorhabditis elegans (5.1 kb and 18 exons) genes.

Mapping of the rat and mouse nicotinamide nucleotide transhydrogenase gene.

Mapping of the rat and mouse nicotinamide nucleotide transhydrogenase gene.