Energy transfer between the nicotinamide nucleotide transhydrogenase and ATP synthase of Escherichia coli

Membrane bound nicotinamide nucleotide transhydrogenase (TH) catalyses the hydride transfer from NADH to NADP+. Under physiological conditions, this reaction is endergonic and must be energized by the pmf, coupled to transmembrane proton transport. Recent structures of transhydrogenase holoenzymes suggest new mechanistic details, how the long-distance coupling between hydride transfer in the peripheral nucleotide binding sites and the membrane-localized proton transfer occurs that now must be tested experimentally. Here, we provide protocols for the efficient expression and purification of the Escherichia coli transhydrogenase and its reconstitution into liposomes, alone or together with the Escherichia coli F1F0 ATP synthase. We show that E. coli transhydrogenase is a reversible enzyme that can also work as a NADPH-driven proton pump. In liposomes containing both enzymes, NADPH driven H+-transport by TH is sufficient to instantly fuel ATP synthesis, which adds TH to the pool of pmf generating enzymes. If the same liposomes are energized with ATP, NADPH production by TH is stimulated > sixfold both by a pH gradient or a membrane potential. The presented protocols and results reinforce the tight coupling between hydride transfer in the peripheral nucleotide binding sites and transmembrane proton transport and provide powerful tools to investigate their coupling mechanism.

An inconvenient association between granzyme A and Nicotinamide Nucleotide Transhydrogenase

Granzyme A (GzmA) is a serine protease secreted by cytotoxic lymphocytes, with GzmA-/- mouse studies informing our understanding of GzmAs physiological function. We show herein that GzmA-/- mice have a mixed C57BL/6J and C57BL/6N background and retain the full length Nicotinamide Nucleotide Transhydrogenase (Nnt) gene, whereas Nnt is truncated in C57BL/6J mice. Chikungunya viral arthritis was substantially ameliorated in GzmA-/- mice; however, the presence of Nnt, rather than loss of GzmA, was responsible for this phenotype by constraining lymphocyte infiltration. A new CRISPR active site mutant C57BL/6J GzmAS211A mouse provided the first insights into GzmAs bioactivity free of background issues, with circulating proteolytically active GzmA promoting immune-stimulating and pro-inflammatory signatures. Remarkably, k-mer mining of the Sequence Read Archive illustrated that ~27% of Run Accessions and ~38% of Bioprojects listing C57BL/6J as the mouse strain, had Nnt sequencing reads inconsistent with a C57BL/6J background. The Nnt issue has clearly complicated our understanding of GzmA and may similarly have influenced studies across a broad range of fields.

Upregulated expression of LncRNA nicotinamide nucleotide transhydrogenase antisense RNA 1 is correlated with unfavorable clinical outcomes in cancers

Background The nicotinamide nucleotide transhydrogenase antisense RNA 1 (NNT-AS1) is a long non-coding RNA aberrantly expressed in human malignancies. We aimed to analyze available data to evaluate the correlation between NNT-AS1 expression and cancer prognosis. Methods Literature retrieval was performed by systematic searching related databases from inception to April 2, 2020. Studies regarding correlation between NNT-AS1 expression, survival outcomes and clinical characteristics of cancer patients were collected and pooled to calculate the the hazard ratios (HRs) or odds ratios (ORs) with 95% confidence intervals (95% CIs). Results Ten studies comprising 699 patients were included, all of which were conducted in China according to literature selection criteria. Overexpression of NNT-AS1 had a significant association with unfavorable overall survival (OS) (HR = 2.08, 95% CI: 1.84–2.36, P < 0.001). Stratified analysis showed that tumor type, sample size, follow-up months, and survival analysis approach did not change the predictive value of NNT-AS1 on OS. Furthermore, elevated NNT-AS1 level had significant association with distant metastasis (DM) (OR = 2.45, 95% CI: 1.39–4.30), lymph node metastasis (LNM) (OR = 3.92, 95% CI: 1.35–11.41), TNM stage (OR = 4.25, 95% CI: 1.71–10.56), and vascular invasion (OR = 3.98, 95% CI: 2.06–7.71), but was not associated with age and gender. The TCGA dataset further consistently showed that the NNT-AS1 expression was associated with poor OS and disease-free survival. Conclusions High expression of NNT-AS1 is associated with unfavorable survival outcomes and poor clinicopathologic characteristics. However, large-cohort data and geographical studies are still needed to further validate the prognostic value of NNT-AS1 in cancers.

Upregulated Expression of LncRNA Nicotinamide Nucleotide Transhydrogenase Antisense RNA 1 is Correlated with Unfavorable Clinical Outcomes in Cancers

Background: The nicotinamide nucleotide transhydrogenase antisense RNA 1 (NNT-AS1) is a long non-coding RNA aberrantly expressed in human malignancies. We aimed to analyze available data to evaluate the correlation between NNT-AS1 expression and cancer prognosis. Methods: Literature retrieval was performed by systematic searching related databases from inception to April 2, 2020. Studies regarding correlation between NNT-AS1 expression, survival outcomes and clinical characteristics of cancer patients were collected and pooled to calculate the the hazard ratios (HRs) or odds ratios (ORs) with 95% confidence intervals (95% CIs). Results: Ten studies comprising 699 patients were included, all of which were conducted in China according to literature selection criteria. Overexpression of NNT-AS1 had a significant association with unfavorable overall survival (OS) (HR=2.08, 95% CI: 1.84-2.36, P<0.001). Stratified analysis showed that tumor type, sample size, follow-up months, and survival analysis approach did not change the predictive value of NNT-AS1 on OS. Furthermore, elevated NNT-AS1 level had significant association with distant metastasis (DM) (OR=2.45, 95% CI: 1.39-4.30), lymph node metastasis (LNM) (OR=3.92, 95% CI: 1.35-11.41), TNM stage (OR=4.25, 95% CI: 1.71-10.56), and vascular invasion (OR=3.98, 95% CI: 2.06-7.71), but was not associated with age and gender. The TCGA dataset further consistently showed that the NNT-AS1 expression was associated with poor OS and disease-free survival. Conclusions: High expression of NNT-AS1 is associated with unfavorable survival outcomes and poor clinicopathologic characteristics. However, large-cohort data and geographical studies are still needed to further validate the prognostic value of NNT-AS1 in cancers.

Upregulated Expression of LncRNA Nicotinamide Nucleotide Transhydrogenase Antisense RNA 1 is Correlated with Unfavorable Clinical Outcomes in Cancers

Background: The nicotinamide nucleotide transhydrogenase antisense RNA 1 (NNT-AS1) is a long non-coding RNA aberrantly expressed in human malignancies. We aimed to analyze available data to evaluate the correlation between NNT-AS1 expression and cancer prognosis. Methods: Literature retrieval was performed by systematic searching related databases from inception to April 2, 2020. Studies regarding correlation between NNT-AS1 expression, survival outcomes and clinical characteristics of cancer patients were collected and pooled to calculate the the hazard ratios (HRs) or odds ratios (ORs) with 95% confidence intervals (95% CIs). Results: Ten studies comprising 699 patients were included, all of which were conducted in China according to literature selection criteria. Overexpression of NNT-AS1 had a significant association with unfavorable overall survival (OS) (HR=2.08, 95% CI: 1.84-2.36, P<0.001). Stratified analysis showed that tumor type, sample size, follow-up months, and survival analysis approach did not change the predictive value of NNT-AS1 on OS. Furthermore, elevated NNT-AS1 level had significant association with distant metastasis (DM) (OR=2.45, 95% CI: 1.39-4.30), lymph node metastasis (LNM) (OR=3.92, 95% CI: 1.35-11.41), TNM stage (OR=4.25, 95% CI: 1.71-10.56), and vascular invasion (OR=3.98, 95% CI: 2.06-7.71), but was not associated with age and gender. The TCGA dataset further consistently showed that the NNT-AS1 expression was associated with poor OS and disease-free survival. Conclusions: High expression of NNT-AS1 is associated with unfavorable survival outcomes and poor clinicopathologic characteristics. However, large-cohort data and geographical studies are still needed to further validate the prognostic value of NNT-AS1 in cancers.

Flux through mitochondrial redox circuits linked to nicotinamide nucleotide transhydrogenase generates counterbalance changes in energy expenditure

Compensatory changes in energy expenditure occur in response to positive and negative energy balance, but the underlying mechanism remains unclear. Under low energy demand, the mitochondrial electron transport system is particularly sensitive to added energy supply (i.e. reductive stress), which exponentially increases the rate of H2O2 (JH2O2) production. H2O2 is reduced to H2O by electrons supplied by NADPH. NADP+ is reduced back to NADPH by activation of mitochondrial membrane potential–dependent nicotinamide nucleotide transhydrogenase (NNT). The coupling of reductive stress-induced JH2O2 production to NNT-linked redox buffering circuits provides a potential means of integrating energy balance with energy expenditure. To test this hypothesis, energy supply was manipulated by varying flux rate through β-oxidation in muscle mitochondria minus/plus pharmacological or genetic inhibition of redox buffering circuits. Here we show during both non-ADP– and low-ADP–stimulated respiration that accelerating flux through β-oxidation generates a corresponding increase in mitochondrial JH2O2 production, that the majority (∼70–80%) of H2O2 produced is reduced to H2O by electrons drawn from redox buffering circuits supplied by NADPH, and that the rate of electron flux through redox buffering circuits is directly linked to changes in oxygen consumption mediated by NNT. These findings provide evidence that redox reactions within β-oxidation and the electron transport system serve as a barometer of substrate flux relative to demand, continuously adjusting JH2O2 production and, in turn, the rate at which energy is expended via NNT-mediated proton conductance. This variable flux through redox circuits provides a potential compensatory mechanism for fine-tuning energy expenditure to energy balance in real time.

Nicotinamide Nucleotide Transhydrogenase (Nnt) is Related to Obesity in Mice

The C57BL/6J (B6J) mouse strain has been widely used as a control strain for the study of metabolic diseases and diet induced obesity (DIO). B6J mice carry a spontaneous deletion mutation in the nicotinamide nucleotide transhydrogenase (Nnt) gene eliminating exons 7–11, resulting in expression of a truncated form of Nnt, an enzyme that pumps protons across the inner mitochondrial membrane. It has been proposed that this mutation in B6J mice is associated with epigonadal fat mass and altered sensitivity to diet induced obesity. To define the role of Nnt in the development of diet induced obesity, we generated first backcross (BC1) hybrids of wild type Nnt C57BL/6NTac and mutated Nnt C57BL/6JRj [(C57BL/6NTac×C57BL/6JRj)F1×C57BL/6NTac]. Body weight gain and specific fat-pad depot mass were measured in BC1 hybrids under high fat diet conditions. Both sexes of BC1 hybrids indicate that mice with Nnt wild type allele are highly sensitive to DIO and exhibit higher relative fat mass. In summary, our data indicate that the Nnt mutation in mice is associated with sensitivity to DIO and fat mass.