Aging-dependent mitochondrial bioenergetic impairment in the skeletal muscle of NNT-deficient mice.

Overall health relies on features of skeletal muscle that generally decline with age, partly due to mechanisms associated with mitochondrial redox imbalance and bioenergetic dysfunction. Previously, aged mice genetically devoid of the mitochondrial NAD(P)+ transhydrogenase (NNT, encoded by the nicotinamide nucleotide transhydrogenase gene), an enzyme involved in mitochondrial NADPH supply, were shown to exhibit deficits in locomotor behavior. Here, by using young, middle-aged, and older NNT-deficient (Nnt-/-) mice and age-matched controls (Nnt+/+), we aimed to investigate how muscle bioenergetic function and motor performance are affected by NNT expression and aging. Mice were subjected to the wire-hang test to assess locomotor performance, while mitochondrial bioenergetics was evaluated in fiber bundles from the soleus, vastus lateralis and plantaris muscles. An age-related decrease in the average wire-hang score was observed in middle-aged and older Nnt-/- mice compared to age-matched controls. Although respiratory rates in the soleus, vastus lateralis and plantaris muscles did not significantly differ between the genotypes in young mice, the rates of oxygen consumption did decrease in the soleus and vastus lateralis muscles of middle-aged and older Nnt-/- mice. Notably, the soleus, which exhibited the highest NNT expression level, was the muscle most affected by aging, and NNT loss. Additionally, histology of the soleus fibers revealed increased numbers of centralized nuclei in older Nnt-/- mice, indicating abnormal morphology. In summary, our findings suggest that NNT expression deficiency causes locomotor impairments and muscle dysfunction during aging in mice.

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.

INTRODUCTION: Nicotinamide 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 REPORT: We 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. CONCLUSION: This 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.

RéSUMé: INTRODUCTION: Le gène Nicotinamide Nucleotide Transhydrogenase (NNT) a été récemment impliqué dans l'Insuffisance Surrénalienne Primaire (ISP). Il code pour une protéine de la membrane mitochondriale interne qui produit de fortes quantités de NADPH. Le NADPH est utilisé par plusieurs voies de biosynthèse et dans l'oxydo-réduction de radicaux libres par les voies de signalisation impliquant le glutathion et la thioredoxine dans la mitochondrie. Les patients avec une ISP, en lien avec un déficit du gène NNT, peuvent également présenter des manifestations extra-surrénaliennes, dont une altération gonadique. CAS CLINIQUE: Nous présentons le cas clinique d'un homme de 35 ans adressé à notre centre d'Assistance Médicale à la Procréation pour infertilité primaire avec azoospermie non obstructive, dans un contexte d'ISP et d'obésité. L'exploration génétique effectuée à l'âge de 30 ans a identifié un déficit complet de la protéine NNT dû à la présence de deux mutations hétérozygotes (une sur chaque allèle), délétères. L'échographie scrotale a montré une tumeur testiculaire d'origine surrénalienne à droite. L'intensification du traitement par glucocorticoides pendant 8 mois n'a pas réduit le volume de la tumeur ni amélioré la production spermatique ou la fonction testiculaire endocrine. Aucun spermatozoïde n'a été retrouvé après exploration chirurgicale testiculaire bilatérale, en lien avec un syndrome de Cellules de Sertoli Seules. L'étude rétrospective de l'axe hypothalamo-hypophysaire-gonadique monte une altération progressive de la fonction testiculaire, accélérée à l'âge adulte, aboutissant à un hypogonadisme hypergonadotrope et une azoospermie non-obstructive à 30 ans, alors que l'ISP était contrôlée pendant cette période. CONCLUSION: Ce cas clinique met en évidence pour la première fois une disparition complète de la lignée germinale chez un patient avec un déficit en NNT. Il avance des arguments en faveur de l'hypothèse d'un rôle déterminant des dommages cellulaires, dus à un excès de radicaux oxygénés dans cette atteinte régulière de la fonction gonadique. Cette dernière devrait être suivie à partir de la puberté chez les patients ISP et plus particulièrement ceux ayant un déficit en NNT. Une préservation de la fertilité pourrait leur être proposée lorsqu'ils deviennent adultes.

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.