Combined mineralocorticoid and glucocorticoid deficiency is caused by a novel founder nicotinamide nucleotide transhydrogenase mutation that alters mitochondrial morphology and increases oxidative stress

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

BACKGROUND

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.

OBJECTIVE

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.

DESIGN

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).

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

A novel mutation in the NNT gene causing familial glucocorticoid deficiency, with a literature review

Familial glucocorticoid deficiency (FGD) is an autosomal recessive disorder characterized by low cortisol levels despite elevated adrenocorticotropin (ACTH). Mineralocorticoid secretion is classically normal. Clinical manifestations are secondary to low cortisol levels (recurrent hypoglycemia, chronic asthenia, failure to thrive, seizures) and high levels of ACTH (cutaneous-mucosal hyperpigmentation). FGD is often caused by mutations in the ACTH melanocortin 2 receptor gene (MC2R, 18p11.21, FGD type 1) or melanocortin receptor 2 accessory protein gene (MRAP, 21q22.11, FGD type 2). But mutations have also been described in other genes: the steroidogenic acute regulatory protein (STAR, 8q11.2q13.2, FGD type 3), nicotinamide nucleotide transhydrogenase (NNT, 5p12, FGD type 4) and thioredoxin reductase 2 genes (TXNRD2, 22q11.21, FGD type 5). We report the case of a 3-year-old boy recently diagnosed with FGD type 4 due to a novel mutation in NNT gene. A homozygous variant in exon 18 of the NNT gene, NM_012343.3:c.2764C>T, p.(Arg922*), determines a stop codon and, consequently, a non-functional truncated protein or absence of protein due to the nonsense-mediated decay (NMD) mechanism. We review the recent literature on NNT mutations and clinical presentations, which are broader than suspected. This disorder can result in significant morbidity and is potentially fatal if untreated. Precise diagnosis allows correct treatment and follow-up.

Harnessing the power of nutritional antioxidants against adrenal hormone imbalance-associated oxidative stress

Oxidative stress, resulting from dysregulation in the secretion of adrenal hormones, represents a major concern in human health. The present review comprehensively examines various categories of endocrine dysregulation within the adrenal glands, encompassing glucocorticoids, mineralocorticoids, and androgens. Additionally, a comprehensive account of adrenal hormone disorders, including adrenal insufficiency, Cushing's syndrome, and adrenal tumors, is presented, with particular emphasis on their intricate association with oxidative stress. The review also delves into an examination of various nutritional antioxidants, namely vitamin C, vitamin E, carotenoids, selenium, zinc, polyphenols, coenzyme Q10, and probiotics, and elucidates their role in mitigating the adverse effects of oxidative stress arising from imbalances in adrenal hormone levels. In conclusion, harnessing the power of nutritional antioxidants has the potential to help with oxidative stress caused by an imbalance in adrenal hormones. This could lead to new research and therapeutic interventions.

Loss of Nicotinamide nucleotide transhydrogenase sensitizes embryos to ethanol-induced neural crest and neural apoptosis via generation of reactive oxygen species

Fetal alcohol spectrum disorders (FASD) are a continuum of birth defects caused by prenatal alcohol exposure. FASD are the most common environmentally induced birth defect and are highly variable. The genetics of an individual influence the severity of their FASD phenotype. However, the genes that sensitize an individual to ethanol-induced birth defects are largely unknown. The ethanol-sensitive mouse substrain, C57/B6J, carries several known mutations including one in Nicotinamide nucleotide transhydrogenase (Nnt). Nnt is a mitochondrial transhydrogenase thought to have an important role in detoxifying reactive oxygen species (ROS) and ROS has been implicated in ethanol teratogenesis. To directly test the role of Nnt in ethanol teratogenesis, we generated zebrafish nnt mutants via CRISPR/Cas9. Zebrafish embryos were dosed with varying concentrations of ethanol across different timepoints and assessed for craniofacial malformations. We utilized a ROS assay to determine if this could be a contributing factor of these malformations. We found that exposed and unexposed mutants had higher levels of ROS compared to their wildtype counterparts. When treated with ethanol, nnt mutants experienced elevated apoptosis in the brain and neural crest, a defect that was rescued by administration of the antioxidant, N-acetyl cysteine (NAC). NAC treatment also rescued most craniofacial malformations. Altogether this research demonstrates that ethanol-induced oxidative stress leads to craniofacial and neural defects due to apoptosis in nnt mutants. This research further supports the growing body of evidence implicating oxidative stress in ethanol teratogenesis. These findings suggest that antioxidants can be used as a potential therapeutic in the treatment of FASD.

Nicotinamide Nucleotide Transhydrogenase (NNT) is essential for adrenal steroidogenesis: clinical and in vitro lessons

BACKGROUND

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.

OBJECTIVE

To ascertain the role played by NNT in adrenal steroidogenesis.

METHODS

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 post-natal human adrenals.

RESULTS

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 when compared to 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.

CONCLUSION

Together, these studies demonstrate the essential role of NNT in adrenal redox homeostasis and steroidogenesis.

Mitochondrial NAD(P)+ Transhydrogenase: From Molecular Features to Physiology and Disease

Significance: Proton-translocating NAD(P)⁺ transhydrogenase, also known as nicotinamide nucleotide transhydrogenase (NNT), catalyzes a reversible reaction coupling the protonmotive force across the inner mitochondrial membrane and hydride (H^-, a proton plus two electrons) transfer between the mitochondrial pools of NAD(H) and NADP(H). The forward NNT reaction is a source of NADPH in the mitochondrial matrix, fueling antioxidant and biosynthetic pathways with reductive potential. Despite the greater emphasis given to the net forward reaction, the reverse NNT reaction that oxidizes NADPH also occurs in physiological and pathological conditions. Recent Advances: NNT (dys)function has been linked to various metabolic pathways and disease phenotypes. Most of these findings have been based on spontaneous loss-of-function Nnt mutations found in the C57BL/6J mouse strain (Nnt^C57BL/6J mutation) and disease-causing Nnt mutations in humans. The present review focuses on recent advances based on the mouse Nnt^C57BL/6J mutation. Critical Issues: Most studies associating NNT function with disease phenotypes have been based on comparisons between different strains of inbred mice (with or without the Nnt^C57BL/6J mutation), which creates uncertainties over the actual contribution of NNT in the context of other potential genetic modifiers. Future Directions: Future research might contribute to understanding the role of NNT in pathological conditions and elucidate how NNT regulates physiological signaling through its forward and reverse reactions. The importance of NNT in redox balance and tumor cell proliferation makes it a potential target of new therapeutic strategies for oxidative-stress-mediated diseases and cancer. Antioxid. Redox Signal. 36, 864-884.

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.

Nicotinamide nucleotide transhydrogenase mutation analysis in Chinese patients with thyroid dysgenesis

Thyroid dysgenesis (TD) accounts for 80% cases of congenital hypothyroidism, which is the most common neonatal disorder. Until now, the gene mutations have been reported associated with TD can only account for 5% cases, suggesting the genetic heterogeneity of the pathology. Nicotinamide nucleotide transhydrogenase (NNT) plays a crucial role in regulating redox homeostasis, patients carrying NNT mutations have been described with a clinical phenotype of hypothyroidism. As TD risk is increased in the context of several syndromes and redox homeostasis is vital for thyroid development and function, NNT might be a candidate gene involved in syndromic TD. Therefore, we performed target sequencing (TS) in 289 TD patients for causative mutations in NNT and conducted functional analysis of the gene mutations. TS and Sanger sequence were used to screen the novel mutations. For functional analysis, we performed western blot, measurement of NADPH/NADP_total and H₂ O₂ generation, cell proliferation, and wounding healing assay. As a result, three presumably pathogenic mutations (c.811G > A, p.Ala271Ser; c.2078G > A, p.Arg693His; and c.2581G > A, p.Val861Met) in NNT had been identified. Our results showed the damaging effect of NNT mutations on stability and catalytic activity of proteins and redox balance of cells. In conclusion, our findings provided novel insights into the role of the NNT isotype in thyroid physiopathology and broaden the spectrum of pathogenic genes associated with TD. However, the pathogenic mechanism of NNT in TD is still need to be investigated in further study.

Loss of Nnt Increases Expression of Oxidative Phosphorylation Complexes in C57BL/6J Hearts

Nicotinamide nucleotide transhydrogenase (NNT) is a proton pump in the inner mitochondrial membrane that generates reducing equivalents in the form of NAPDH, which can be used for anabolic pathways or to remove reactive oxygen species (ROS). A number of studies have linked NNT dysfunction to cardiomyopathies and increased risk of atherosclerosis; however, biallelic mutations in humans commonly cause a phenotype of adrenal insufficiency, with rare occurrences of cardiac dysfunction and testicular tumours. Here, we compare the transcriptomes of the hearts, adrenals and testes from three mouse models: the C57BL/6N, which expresses NNT; the C57BL/6J, which lacks NNT; and a third mouse, expressing the wild-type NNT sequence on the C57BL/6J background. We saw enrichment of oxidative phosphorylation genes in the C57BL/B6J in the heart and adrenal, possibly indicative of an evolved response in this substrain to loss of Nnt. However, differential gene expression was mainly driven by mouse background with some changes seen in all three tissues, perhaps reflecting underlying genetic differences between the C57BL/B6J and -6N substrains.

Role of Oxidative DNA Damage and Repair in Atrial Fibrillation and Ischemic Heart Disease

Atrial fibrillation (AF) and ischemic heart disease (IHD) represent the two most common clinical cardiac diseases, characterized by angina, arrhythmia, myocardial damage, and cardiac dysfunction, significantly contributing to cardiovascular morbidity and mortality and posing a heavy socio-economic burden on society worldwide. Current treatments of these two diseases are mainly symptomatic and lack efficacy. There is thus an urgent need to develop novel therapies based on the underlying pathophysiological mechanisms. Emerging evidence indicates that oxidative DNA damage might be a major underlying mechanism that promotes a variety of cardiac diseases, including AF and IHD. Antioxidants, nicotinamide adenine dinucleotide (NAD⁺) boosters, and enzymes involved in oxidative DNA repair processes have been shown to attenuate oxidative damage to DNA, making them potential therapeutic targets for AF and IHD. In this review, we first summarize the main molecular mechanisms responsible for oxidative DNA damage and repair both in nuclei and mitochondria, then describe the effects of oxidative DNA damage on the development of AF and IHD, and finally discuss potential targets for oxidative DNA repair-based therapeutic approaches for these two cardiac diseases.

Mitochondrial NAD(P)+ Transhydrogenase is Unevenly Distributed in Different Brain Regions, and its Loss Causes Depressive-like Behavior and Motor Dysfunction in Mice

NAD(P)⁺ transhydrogenase (NNT) links redox states of the mitochondrial NAD(H) and NADP(H) via a reaction coupled to proton-motive force across the inner mitochondrial membrane. NNT is believed to be ubiquitously present in mammalian cells, but its expression may vary substantially in different tissues. The present study investigated the tissue distribution and possible roles of NNT in the mouse brain. The pons exhibited high NNT expression/activity, and immunohistochemistry revealed intense NNT labeling in neurons from brainstem nuclei. In some of these regions, neuronal NNT labeling was strongly colocalized with enzymes involved in the biosynthesis of 5-hydroxytryptamine (5-HT) and nitric oxide (NO), which directly or indirectly require NADPH. Behavioral tests were performed in mice lacking NNT activity (Nnt^-/-, mice carrying the mutated Nnt^C57BL/6J allele from the C57BL/6J strain) and the Nnt^+/+ controls. Our data demonstrated that aged Nnt^-/- mice (18-20 months old), but not adult mice (3-4 months old), showed an increased immobility time in the tail suspension test that was reversed by fluoxetine treatment, providing evidence of depressive-like behavior in these mice. Aged Nnt^-/- mice also exhibited behavioral changes and impaired locomotor activity in the open field and rotarod tests. Despite the colocalization between NNT and NO synthase, the S-nitrosation and cGMP levels were independent of the Nnt genotype. Taken together, our results indicated that NNT is unevenly distributed throughout the brain and associated with 5-THergic and NOergic neurons. The lack of NNT led to alterations in brain functions related to mood and motor behavior/performance in aged mice.

Effect of glucose deprivation on the expression of genes encoding glucocorticoid receptor and some related factors in ERN1-knockdown U87 glioma cells

OBJECTIVE

The aim of the present study was to examine the effect of glucose deprivation on the expression of genes encoded glucocorticoid receptor (NR3C1) and some related proteins (NR3C2, AHR, NRIP1, NNT, ARHGAP35, SGK1, and SGK3) in U87 glioma cells in response to inhibition of endoplasmic reticulum stress signaling mediated by ERN1/IRE1 (endoplasmic reticulum to nucleus signaling 1/inositol requiring enzyme 1) for evaluation of their possible significance in the control of glioma growth through endoplasmic reticulum stress signaling mediated by IRE1 and glucose deprivation.

METHODS

The expression of NR3C1, NR3C2, AHR, NRIP1, NNT, ARHGAP35, SGK1, and SGK3 genes in U87 glioma cells transfected by empty vector pcDNA3.1 (control cells) and cells without ERN1 signaling enzyme function (transfected by dnERN1) under glucose deprivation was studied by real time quantitative polymerase chain reaction.

RESULTS

It was shown that the expression level of NR3C2, AHR, SGK1, SGK3, and NNT genes was up-regulated in control U87 glioma cells under glucose deprivation condition in comparison with the control cells growing with glucose. At the same time, the expression of NRIP1 gene is down-regulated in these glioma cells under glucose deprivation, but NR3C1 and ARHGAP35 genes was resistant to this experimental condition. We also showed that inhibition of ERN1 signaling enzyme function significantly modified the response of most studied gene expressions to glucose deprivation condition. Thus, effect of glucose deprivation on the expression level of NR3C2, AHR, and SGK1 genes was significantly stronger in ERN1 knockdown U87 glioma cells since the expression of NNT gene was resistant to glucose deprivation condition. Moreover, the inhibition of ERN1 enzymatic activities in U87 glioma cells led to up-regulation of ARHGAP35 gene expression and significant down-regulation of the expression of SGK3 gene in response to glucose deprivation condition.

CONCLUSIONS

Results of this study demonstrated that glucose deprivation did not change the expression level of NR3C1 gene but it significantly affected the expression of NR3C2, AHR, NRIP, SGK1, SGK3, and NNT genes in vector-transfected U87 glioma cells in gene specific manner and possibly contributed to the control of glioma growth since the expression of most studied genes in glucose deprivation condition was significantly dependent on the functional activity of IRE1 signaling enzyme.

Hormones and oxidative stress: an overview

In aerobes, oxygen is essential for maintenance of life. However, incomplete reduction of oxygen leads to generation of reactive oxygen species. These oxidants oxidise biological macromolecules present in their vicinity and thereby impair cellular functions causing oxidative stress (OS). Aerobes have evolved both enzymatic and nonenzymatic antioxidant defences to protect themselves from OS. Although hormones as means of biological coordination involve in regulation of physiological activities of tissues by regulating metabolism, any change in their normal titre leads to pathophysiological states. While, hormones such as melatonin, insulin, oestrogen, progesterone display antioxidant features, thyroid hormone, corticosteroids and catecholamines elicit free radical generation and OS, and the role of testosterone in inducing OS is debateable. This review is an attempt to understand the impact of free radical generation and cross talk between the hormones modulating antioxidant defence system under various pathophysiological conditions.

Nicotinamide nucleotide transhydrogenase is required for brain mitochondrial redox balance under hampered energy substrate metabolism and high-fat diet

Among mitochondrial NADP-reducing enzymes, nicotinamide nucleotide transhydrogenase (NNT) establishes an elevated matrix NADPH/NADP⁺ by catalyzing the reduction of NADP⁺ at the expense of NADH oxidation coupled to inward proton translocation across the inner mitochondrial membrane. Here, we characterize NNT activity and mitochondrial redox balance in the brain using a congenic mouse model carrying the mutated Nnt gene from the C57BL/6J strain. The absence of NNT activity resulted in lower total NADPH sources activity in the brain mitochondria of young mice, an effect that was partially compensated in aged mice. Nonsynaptic mitochondria showed higher NNT activity than synaptic mitochondria. In the absence of NNT, an increased release of H₂ O₂ from mitochondria was observed when the metabolism of respiratory substrates occurred with restricted flux through relevant mitochondrial NADPH sources or when respiratory complex I was inhibited. In accordance, mitochondria from Nnt^-/- brains were unable to sustain NADP in its reduced state when energized in the absence of carbon substrates, an effect aggravated after H₂ O₂ bolus metabolism. These data indicate that the lack of NNT in brain mitochondria impairs peroxide detoxification, but peroxide detoxification can be partially counterbalanced by concurrent NADPH sources depending on substrate availability. Notably, only brain mitochondria from Nnt^-/- mice chronically fed a high-fat diet exhibited lower activity of the redox-sensitive aconitase, suggesting that brain mitochondrial redox balance requires NNT under the metabolic stress of a high-fat diet. Overall, the role of NNT in the brain mitochondria redox balance especially comes into play under mitochondrial respiratory defects or high-fat diet.

Glucocorticoid deficiency causes transcriptional and post-transcriptional reprogramming of glutamine metabolism

Background

Deficient glucocorticoid biosynthesis leading to adrenal insufficiency is life-threatening and is associated with significant co-morbidities. The affected pathways underlying the pathophysiology of co-morbidities due to glucocorticoid deficiency remain poorly understood and require further investigation.

Methods

To explore the pathophysiological processes related to glucocorticoid deficiency, we have performed global transcriptional, post-transcriptional and metabolic profiling of a cortisol-deficient zebrafish mutant with a disrupted ferredoxin (fdx1b) system.

Findings

fdx1b^−/− mutants show pervasive reprogramming of metabolism, in particular of glutamine-dependent pathways such as glutathione metabolism, and exhibit changes of oxidative stress markers. The glucocorticoid-dependent post-transcriptional regulation of key enzymes involved in de novo purine synthesis was also affected in this mutant. Moreover, fdx1b^−/− mutants exhibit crucial features of primary adrenal insufficiency, and mirror metabolic changes detected in primary adrenal insufficiency patients.

Interpretation

Our study provides a detailed map of metabolic changes induced by glucocorticoid deficiency as a consequence of a disrupted ferredoxin system in an animal model of adrenal insufficiency. This improved pathophysiological understanding of global glucocorticoid deficiency informs on more targeted translational studies in humans suffering from conditions associated with glucocorticoid deficiency.

Fund

Marie Curie Intra-European Fellowships for Career Development, HGF-programme BIFTM, Deutsche Forschungsgemeinschaft, BBSRC.

Nicotinamide phosphoribosyltransferase and the hypothalamic-pituitary-adrenal axis of the rat

Nicotinamide phosphoribosyltransferase (Nampt), also termed visfatin, catalyses the rate‑limiting step in the nicotinamide adenine dinucleotide (NAD) salvage pathway. In addition to its intracellular function (iNampt), extracellular Nampt (eNampt) also affects numerous intracellular signalling pathways. The current study investigated the role of Nampt in the regulation of the hypothalamic‑pituitary‑adrenal (HPA) axis in rats. At 1 h after intraperitoneal administration of eNampt (4 µg/100 g) in adult male rats, serum adrenocorticotropic hormone(ACTH) and aldosterone levels remained unchanged, while corticosterone levels were notably elevated compared with the control group, as determined by ELISA. The results of reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) demonstrated that, in the hypothalami of eNampt‑treated rats, the mRNA expression levels of Fos proto‑oncogene, which is also termed c‑Fos, were not significantly different compared with the control group; however, the mRNA expression levels of proopiomelanocortin (POMC) were markedly increased in the pituitary gland of eNampt‑treated rats compared with the control group. Furthermore, in hypothalamic explants, ELISA results demonstrated that the addition of the eNampt protein exhibited no effect on corticotropin‑releasing hormone (CRH) release into the incubation medium and prevented potassium ion‑induced CRH release. Additionally, the eNampt‑induced increase in ACTH output by pituitary gland explants was not statistically significant, compared with the control group. However, RT‑qPCR indicated that exposure of pituitary gland explants to eNampt and CRH increased the levels of POMC mRNA expression; the effect of eNampt, but not CRH, was inhibited by FK866, which is a specific Nampt inhibitor. In primary rat adrenocortical cell cultures, eNampt exhibited no effect on basal aldosterone or corticosterone secretion, while increases in aldosterone and corticosterone levels in response to ACTH were retained. To assess the potential role of iNampt in the regulation of adrenal steroidogenesis, experiments involving a specific Nampt inhibitor, FK866, were performed. Exposure of cultured cells to FK866 notably lowered basal aldosterone and corticosterone output compared with the control group, and completely eliminated the response of cultured cells to ACTH. The results of the present study indicated that the injected eNampt may have increased the corticosterone serum levels by acting at the pituitary level. In addition, iNampt may exert a tonic stimulating effect on the secretion of aldosterone and corticosterone from rat adrenocortical cells, as normal iNampt levels were required to retain the response of cultured rat adrenocortical cells to ACTH. Thus, these data suggest an important physiological role of both iNampt and eNampt in the regulation of the HPA axis activity in the rat.

Proton-Translocating Nicotinamide Nucleotide Transhydrogenase: A Structural Perspective

Nicotinamide nucleotide transhydrogenase (TH) is an enzyme complex in animal mitochondria and bacteria that utilizes the electrochemical proton gradient across membranes to drive the production of NADPH. The enzyme plays an important role in maintaining the redox balance of cells with implications in aging and a number of human diseases. TH exists as a homodimer with each protomer containing a proton-translocating transmembrane domain and two soluble nucleotide binding domains that mediate hydride transfer between NAD(H) and NADP(H). The three-domain architecture of TH is conserved across species but polypeptide composition differs substantially. The complex domain coupling mechanism of TH is not fully understood despite extensive biochemical and structural characterizations. Herein the progress is reviewed, focusing mainly on structural findings from 3D crystallization of isolated soluble domains and more recently of the transmembrane domain and the holo-enzyme from Thermus thermophilus. A structural perspective and impeding challenges in further elucidating the mechanism of TH are discussed.

Genetic defects in pediatric-onset adrenal insufficiency in Japan

CONTEXT

Most patients with pediatric-onset primary adrenal insufficiency (PAI), such as 21-hydroxylase deficiency, can be diagnosed by measuring the urine or serum levels of steroid metabolites. However, the etiology is often difficult to determine in a subset of patients lacking characteristic biochemical findings.

OBJECTIVE

To assess the frequency of genetic defects in Japanese children with biochemically uncharacterized PAI and characterize the phenotypes of mutation-carrying patients.

METHODS

We enrolled 63 Japanese children (59 families) with biochemically uncharacterized PAI, and sequenced 12 PAI-associated genes. The pathogenicities of rare variants were assessed based on in silico analyses and structural modeling. We calculated the proportion of mutation-carrying patients according to demographic characteristics.

RESULTS

We identified genetic defects in 50 (85%) families: STAR in 19, NR0B1 in 18, SAMD9 in seven, AAAS in two, NNT in two, MC2R in one and CDKN1C in one. NR0B1 defects were identified in 78% of the male patients that received both glucocorticoid and mineralocorticoid replacement therapy and had normal male external genitalia. STAR defects were identified in 67% of female and 9% of male patients. Seven of the 19 patients with STAR defects developed PAI at age two or older, out of whom, five did not have mineralocorticoid deficiency.

CONCLUSIONS

Molecular testing elucidated the etiologies of most biochemically uncharacterized PAI patients. Genetic defects such as NR0B1 defects are presumed based on phenotypes, while others with broad phenotypic variability, such as STAR defects, are difficult to diagnose. Molecular testing is a rational approach to diagnosis in biochemically uncharacterized PAI patients.

Three-Dimensional Model of Human Nicotinamide Nucleotide Transhydrogenase (NNT) and Sequence-Structure Analysis of its Disease-Causing Variations

Defective mitochondrial proteins are emerging as major contributors to human disease. Nicotinamide nucleotide transhydrogenase (NNT), a widely expressed mitochondrial protein, has a crucial role in the defence against oxidative stress. NNT variations have recently been reported in patients with familial glucocorticoid deficiency (FGD) and in patients with heart failure. Moreover, knockout animal models suggest that NNT has a major role in diabetes mellitus and obesity. In this study, we used experimental structures of bacterial transhydrogenases to generate a structural model of human NNT (H‐NNT). Structure‐based analysis allowed the identification of H‐NNT residues forming the NAD binding site, the proton canal and the large interaction site on the H‐NNT dimer. In addition, we were able to identify key motifs that allow conformational changes adopted by domain III in relation to its functional status, such as the flexible linker between domains II and III and the salt bridge formed by H‐NNT Arg882 and Asp830. Moreover, integration of sequence and structure data allowed us to study the structural and functional effect of deleterious amino acid substitutions causing FGD and left ventricular non‐compaction cardiomyopathy. In conclusion, interpretation of the function–structure relationship of H‐NNT contributes to our understanding of mitochondrial disorders.

NNT mutations: a cause of primary adrenal insufficiency, oxidative stress and extra-adrenal defects

OBJECTIVE

Nicotinamide nucleotide transhydrogenase (NNT), one of the several genes recently discovered in familial glucocorticoid deficiencies (FGD), is involved in reactive oxygen species detoxification, suggesting that extra-adrenal manifestations may occur, due to the sensitivity to oxidative stress of other organs rich in mitochondria. Here, we sought to identify NNT mutations in a large cohort of patients with primary congenital adrenal insufficiency without molecular etiology and evaluate the degree of adrenal insufficiency and onset of extra-adrenal damages.

METHODS

Sanger or massive parallel sequencing of NNT and patient monitoring.

RESULTS

Homozygous or compound heterozygous NNT mutations occurred frequently (26%, 13 unrelated families, 18 patients) in our cohort. Seven new mutations were identified: p.Met337Val, p.Ala863Glu, c.3G>A (p.Met1?), p.Arg129*, p.Arg379*, p.Val665Profs*29 and p.Ala704Serfs*19. The most frequent mutation, p.Arg129*, was found recurrently in patients from Algeria. Most patients were diagnosed belatedly (8-18 months) after presenting severe hypoglycemia; others experiencing stress conditions were diagnosed earlier. Five patients also had mineralocorticoid deficiency at onset. One patient had congenital hypothyroidism and two cryptorchidism. In follow-up, we noticed gonadotropic and genitalia impairments (precocious puberty, testicular inclusions, interstitial Leydig cell adenoma, azoospermia), hypothyroidism and hypertrophic cardiomyopathy. Intrafamilial phenotype heterogeneity was also observed.

CONCLUSIONS

NNT should be sequenced, not only in FGD, but also in all primary adrenal insufficiencies for which the most frequent etiologies have been ruled out. As NNT is involved in oxidative stress, careful follow-up is needed to evaluate mineralocorticoid biosynthesis extent, and gonadal, heart and thyroid function.

Adipogenic placenta-derived mesenchymal stem cells are not lineage restricted by withdrawing extrinsic factors: developing a novel visual angle in stem cell biology

Current evidence implies that differentiated bone marrow mesenchymal stem cells (BMMSCs) can act as progenitor cells and transdifferentiate across lineage boundaries. However, whether this unrestricted lineage has specificities depending on the stem cell type is unknown. Placental-derived mesenchymal stem cells (PDMSCs), an easily accessible and less invasive source, are extremely useful materials in current stem cell therapies. No studies have comprehensively analyzed the transition in morphology, surface antigens, metabolism and multilineage potency of differentiated PDMSCs after their dedifferentiation. In this study, we showed that after withdrawing extrinsic factors, adipogenic PDMSCs reverted to a primitive cell population and retained stem cell characteristics. The mitochondrial network during differentiation and dedifferentiation may serve as a marker of absent or acquired pluripotency in various stem cell models. The new population proliferated faster than unmanipulated PDMSCs and could be differentiated into adipocytes, osteocytes and hepatocytes. The cell adhesion molecules (CAMs) signaling pathway and extracellular matrix (ECM) components modulate cell behavior and enable the cells to proliferate or differentiate during the differentiation, dedifferentiation and redifferentiation processes in our study. These observations indicate that the dedifferentiated PDMSCs are distinguishable from the original PDMSCs and may serve as a novel source in stem cell biology and cell-based therapeutic strategies. Furthermore, whether PDMSCs differentiated into other lineages can be dedifferentiated to a primitive cell population needs to be investigated.

Attention to Background Strain Is Essential for Metabolic Research: C57BL/6 and the International Knockout Mouse Consortium

The International Knockout Mouse Consortium (IKMC) introduces its targeted constructs into C57BL/6N embryonic stem cells. However, breeding with a Cre-recombinase and/or Flp-recombinase mouse is required for the generation of a null allele with the IKMC cassette. Many recombinase strains are in the C57BL/6J background, resulting in knockout animals on a mixed strain background. This can lead to variability in metabolic data and the use of improper control groups. While C57BL/6N and C57BL/6J are derived from the same parental C57BL/6 strain, there are key genotypic and phenotypic differences between these substrains. Many researchers may not even be aware of these differences, as the shorthand C57BL/6 is often used to describe both substrains. We found that 58% of articles involving genetically modified mouse models did not completely address background strain. This review will describe these two substrains and highlight the importance of separate consideration in mouse model development. Our aim is to increase awareness of this issue in the diabetes research community and to provide practical strategies to enable researchers to avoid mixed strain animals when using IKMC knockout mice.