Nicotinamide nucleotide transhydrogenase (NNT) in the central nervous system: morphofuncional characterization in control mice and mice carrying a spontaneous mutation in Nnt gene

Author(s)

Annelise Francisco

• Document type: Doctoral Thesis
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Faculdade de Ciências Médicas
• Defense date: 2020-02-17

Examining board members

Roger Frigério Castilho; Nadja Cristhina de Souza Pinto; Gilberto Eiji Shiguemoto; Alexandre Leite Rodrigues de Oliveira; Marina Rincon Sartori

• Advisor: Roger Frigério Castilho

Abstract

The nicotinamide nucleotide transhydrogenase (NNT) is a transmembrane protein located in the inner mitochondrial membrane that catalyzes the reduction of NADP+ by NADH producing NADPH and NAD+, coupled to the transport of protons from the intermembrane space to the mitochondrial matrix. This protein is expressed in all mammalian and its function is related to the maintenance of mitochondrial and cellular homeostatic mechanisms, such as reactive oxygen species metabolism by glutathione reductase/peroxidase and thioredoxin reductase/peroxiredoxin systems. Pathological changes like familial deficiency of glucocorticoids and mineralocorticoids in humans are linked to NNT deficiency. NNT activity also has relevance in the metabolism and proliferation of tumor cells. There have been advances in research on the role of NNT in cellular metabolism, but details of its influence in physiological and pathological conditions remain to be elucidated. Thus, this study assessed the role of NNT in brain mitochondria redox balance, characterized NNT expression and activity in mouse brains, and finally, investigated a possible functional meaning of the NNT distribution in mouse brain. Comparative studies were conducted by using congenic mice homozygous for the spontaneously mutated NntC57BL/6J allele (C57Unib.B6-Nnt-/-) from the C57BL/6J strain which results in absence of protein expression, and congenic mice with the wild-type alleles that express a functional NNT (C57Unib.B6-Nnt+/+). The absence of NNT in mouse brain mitochondria was related to a redox phenotype identifiable under restricted mitochondrial substrate flux and, especially, when the antioxidant system was challenged by redox imbalance caused by respiratory chain defects or high fat diet. These results indicated NNT as relevant for redox balance in the brain. In addition, NNT was shown to be heterogeneously distributed in the mouse brain, and mainly concentrated in brainstem nuclei. Morphological and behavioral investigations have indicated that NNT is associated with serotonin and ¿NO neurotransmission, possibly by providing NADPH to these neurotransmitters¿ biosynthesis. Nevertheless, the absence of NNT in mice was only able to trigger depressive behavior, anxiety and motor effects in aged mice, suggesting that interactions of other adverse physiological conditions with the NNT mutation is necessary to trigger functional changes. Taken together, our data demonstrate that NNT is relevant to the functions of the central nervous system and emphasize the importance of considering the NNT expression in mice strains employed in nervous system functional assessments, since the interaction between Nnt mutations and genetic modifications, diets and pharmacological treatments may change interpretation of results. (AU)

• FAPESP's process: 15/22063-0 - Antioxidant Role of the Nicotinamide Nucleotide Transhydrogenase (NNT) in the Central Nervous System - Morphofunctional characterization in control mice and spontaneously Nnt gene mutant mice.
• Grantee: Annelise Francisco
• Support Opportunities: Scholarships in Brazil - Doctorate