Mitochondrial NDUFS3 regulates the ROS-mediated onset of metabolic switch in transformed cells

Aerobic glycolysis in transformed cells is an unique metabolic phenotype characterized by a hyperactivated glycolytic pathway even in the presence of oxygen. It is not clear if the onset of aerobic glycolysis is regulated by mitochondrial dysfunction and, if so, what the metabolic windows of opportunity available to control this metabolic switch (mitochondrial to glycolytic) landscape are in transformed cells. Here we report a genetically-defined model system based on the gene-silencing of a mitochondrial complex I subunit, NDUFS3, where we demonstrate the onset of metabolic switch in isogenic human embryonic kidney cells by differential expression of NDUFS3. By means of extensive metabolic characterization, we demonstrate that NDUFS3 gene silencing systematically introduces mitochondrial dysfunction thereby leading to the onset of aerobic glycolysis in a manner dependent on NDUFS3 protein levels. Furthermore, we show that the sustained imbalance in free radical dynamics is a necessary condition to sustain the observed metabolic switch in cell lines with the most severe NDUFS3 suppression. Together, our data reveal a novel role for mitochondrial complex I subunit NDUFS3 in regulating the degree of mitochondrial dysfunction in living cells, thereby setting a “metabolic threshold” for the observation of aerobic glycolysis phenotype within the confines of mitochondrial dysfunction.

Myopathy reversion in mice after restauration of mitochondrial complex I

Myopathies are common manifestations of mitochondrial diseases. To investigate whether gene replacement can be used as an effective strategy to treat or cure mitochondrial myopathies, we have generated a complex I conditional knockout mouse model lacking NDUFS3 subunit in skeletal muscle. NDUFS3 protein levels were undetectable in muscle of 15‐day‐old smKO mice, and myopathy symptoms could be detected by 2 months of age, worsening over time. rAAV9‐Ndufs3 delivered systemically into 15‐ to 18‐day‐old mice effectively restored NDUFS3 levels in skeletal muscle, precluding the development of the myopathy. To test the ability of rAAV9‐mediated gene replacement to revert muscle function after disease onset, we also treated post‐symptomatic, 2‐month‐old mice. The injected mice showed a remarkable improvement of the mitochondrial myopathy and biochemical parameters, which remained for the duration of the study. Our results showed that muscle pathology could be reversed after restoring complex I, which was absent for more than 2 months. These findings have far‐reaching implications for the ability of muscle to tolerate a mitochondrial defect and for the treatment of mitochondrial myopathies.

NDUFS3 depletion permits complex I maturation and reveals TMEM126A/OPA7 as an assembly factor binding the ND4-module intermediate

Complex I (CI) is the largest enzyme of the mitochondrial respiratory chain, and its defects are the main cause of mitochondrial disease. To understand the mechanisms regulating the extremely intricate biogenesis of this fundamental bioenergetic machine, we analyze the structural and functional consequences of the ablation of NDUFS3, a non-catalytic core subunit. We show that, in diverse mammalian cell types, a small amount of functional CI can still be detected in the complete absence of NDUFS3. In addition, we determine the dynamics of CI disassembly when the amount of NDUFS3 is gradually decreased. The process of degradation of the complex occurs in a hierarchical and modular fashion in which the ND4 module remains stable and bound to TMEM126A. We, thus, uncover the function of TMEM126A, the product of a disease gene causing recessive optic atrophy as a factor necessary for the correct assembly and function of CI.

Human mitochondrial NDUFS3 protein bearing Leigh syndrome mutation is more prone to aggregation than its wild-type

NDUFS3 is an integral subunit of the Q module of the mitochondrial respiratory Complex-I. The combined mutation (T145I + R199W) in the subunit is reported to cause optic atrophy and Leigh syndrome accompanied by severe Complex-I deficiency. In the present study, we have cloned and overexpressed the human NDUFS3 subunit and its double mutant in a soluble form in Escherichia coli. The wild-type (w-t) and mutant proteins were purified to homogeneity through a serial two-step chromatographic purification procedure of anion exchange followed by size exclusion chromatography. The integrity and purity of the purified proteins was confirmed by Western blot analysis and MALDI-TOF/TOF. The conformational transitions of the purified subunits were studied through steady state as well as time resolved fluorescence and CD spectroscopy under various denaturing conditions. The mutant protein showed altered polarity around tryptophan residues, changed quenching parameters and also noticeably altered secondary and tertiary structure compared to the w-t protein. Mutant also exhibited a higher tendency than the w-t protein for aggregation which was examined using fluorescent (Thioflavin-T) and spectroscopic (Congo red) dye binding techniques. The pH stability of the w-t and mutant proteins varied at extreme acidic pH and the molten globule like structure of w-t at pH1 was absent in case of the mutant protein. Both the w-t and mutant proteins showed multi-step thermal and Gdn-HCl induced unfolding. Thus, the results provide insight into the alterations of NDUFS3 protein structure caused by the mutations, affecting the overall integrity of the protein and finally leading to disruption of Complex-I assembly.

NDUFB11 and NDUFS3 play a role in atherosclerosis and chronic stress

OBJECTIVE

Atherosclerosis is characterized by the formation of fibrofatty plaques in the intima of arteries, resulting in thickening of the vessel wall and narrowing of the lumen. Chronic stress refers to individuals in a state of long-term chronic stress. However, the relationship between NDUFB11 and NDUFS3 and atherosclerosis and chronic stress is unclear.

METHOD

The atherosclerosis with chronic stress group data file was used. DEGs were screened and WGCNA was performed. Construction and analysis of PPI Network. Functional enrichment analysis, GSEA, gene expression heatmap, immune infiltration analysis and mRNA analysis were performed. CTD was used to find diseases most related to core genes. WB was performed. TargetScan was used to screen miRNAs of DEGs.

RESULTS

1708 DEGs were identified. According to GO analysis, they were mainly enriched in catabolic processes, organic acid metabolism processes, carboxylic acid metabolism processes. KEGG analysis showed that they were mainly enriched in metabolic pathways, fatty acid metabolism, pentose phosphate pathway, glycolysis / gluconeogenesis, fructose and mannose metabolism. Gene expression heatmap showed that the core genes (NDUFB11, NDUFS3) were lowly expressed in samples of those with atherosclerosis accompanied by chronic stress and highly expressed in the normal samples. NDUFB11 and NDUFS3 were associated with necrosis, hyperplasia, inflammation, renal disease, weight loss, memory impairment, and cognitive impairment. WB showed that the expression level of NDUFS3 in atherosclerosis and chronic stress was lower than that in control group.

CONCLUSIONS

NDUFB11 and NDUFS3 are underexpressed in atherosclerosis and chronic stress; the lower NDUFB11 and NDUFS3 levels, the worse the prognosis.

Metabolic imaging in multiple time scales

We report here a novel combination of time-resolved imaging methods for probing mitochondrial metabolism in multiple time scales at the level of single cells. By exploiting a mitochondrial membrane potential reporter fluorescence we demonstrate the single cell metabolic dynamics in time scales ranging from microseconds to seconds to minutes in response to glucose metabolism and mitochondrial perturbations in real time. Our results show that in comparison with normal human mammary epithelial cells, the breast cancer cells display significant alterations in metabolic responses at all measured time scales by single cell kinetics, fluorescence recovery after photobleaching and by scaling analysis of time-series data obtained from mitochondrial fluorescence fluctuations. Furthermore scaling analysis of time-series data in living cells with distinct mitochondrial dysfunction also revealed significant metabolic differences thereby suggesting the broader applicability (e.g. in mitochondrial myopathies and other metabolic disorders) of the proposed strategies beyond the scope of cancer metabolism. We discuss the scope of these findings in the context of developing portable, real-time metabolic measurement systems that can find applications in preclinical and clinical diagnostics.

Mitochondrial Ultrastructural Defects in NDUFS3-Related Disorder

Complex I, the largest multisubunit enzyme complex of the respiratory chain, has a vital role in the energy production of the cell, and the clinical spectrum of complex I deficiency varies from severe lactic acidosis in infants to muscle weakness in adults. Pathogenic variants of NDUFS3 (constitutes the catalytic core of the complex I) have been reported in a small number of patients with variable phenotypes. We describe a girl with a history of infantile-onset nonepileptic myoclonus, who developed myopathy at the age of 2 years. Next-generation sequencing revealed compound heterozygous for two variants in the NDUSF3 gene. The electron-microscopic study of the skeletal muscle showed an increase in the number of mitochondria inside the myofibers; mitochondria were variably enlarged with some irregularity and were aligned perpendicular to the myofibrils in a stacked-up manner. This is the first description of mitochondrial ultrastructural abnormality in an individual with NDUFS3-related disorder.

Biallelic variants in two complex I genes cause abnormal splicing defects in probands with mild Leigh syndrome

Leigh syndrome is a genetically heterogeneous disorder resulting from deficient oxidative energy biogenesis. The syndrome is characterized by subacute episodic decompensations, transiently elevated lactate, and necrotizing brain lesions most often in the striatum and brainstem. Acute decompensation is often triggered by viral infections. Sequalae from repeated episodes leads to progressive neurological deterioration and death. The severity of Leigh syndrome varies widely, from a rapid demise in childhood to rare adult presentations. Although the causes of Leigh syndrome include genes affecting a variety of different pathways, more than 75 of them are nuclear or mitochondrial encoded genes involved in the assembly and catalytic activity of mitochondrial respiratory complex I. Here we report the detailed clinical and molecular phenotype of two adults with mild presentations of NDUFS3 and NDUFAF6-related Leigh Syndrome. Mitochondrial assays revealed slightly reduced complex I activity in one proband and normal complex I activity in the other. The proband with NDUFS3-related Leigh syndrome was mildly affected and lived into adulthood with novel biallelic variants causing aberrant mRNA splicing (NM_004551.2:c.419G > A; p.Arg140Gln; NM_004551.2:c.381 + 6 T > C). The proband with NDUFAF6-related Leigh syndrome had biallelic variants that cause defects in mRNA splicing (NM_152416.3:c.371 T > C; p.Ile124Thr; NM_152416.3:c.420 + 2_420 + 3insTA). The mild phenotypes of these two individuals may be attributed to some residual production of normal NDUFS3 and NDUFAF6 proteins by NDUFS3 and NDUFAF6 mRNA isoforms alongside mutant transcripts. Taken together, these cases reported herein suggest that splice-regulatory variants to complex I proteins could result in milder phenotypes.

Moringa oleifera leaf extract suppresses TIMM23 and NDUFS3 expression and alleviates oxidative stress induced by Aβ1-42 in neuronal cells via activation of Akt

Background and purpose

Oxidative stress plays an important role in Alzheimer's disease (AD) pathogenesis. Moringa oleifera leaf (MOL) extract has been shown to have antioxidant activities. Here, we studied the antioxidative and anti-apoptotic effects of water-soluble MOL extract in an amyloid beta (Aβ)-induced oxidative stress model of AD.

Experimental approach

The effect of amyloid beta (Aβ)1-42 and MOL extract on differentiated SH-SY5Y cell viability was assessed by MTT assay. Cells were treated with Aβ1-42, MOL extract, or MOL extract followed by Aβ1-42. The mitochondrial membrane potential (ΔΨm) and the reactive oxygen species (ROS) were evaluated by flow cytometry and dihydroethidium (DHE) assay, respectively. Western blotting was used to assess the expression of mitochondrial proteins TIMM23 and NDUFS3, apoptosis-related proteins Bax, Bcl-2, and cleaved caspase-3 along with fluorescence analysis of caspase-3/7, and Akt phosphorylation.

Findings/Results

MOL extract pretreatment at 25, 50, and 100 μg/mL prevented ΔΨm reduction. At 100-μg/mL, MOL extract decreased TIMM23 and NDUFS3 proteins and DHE signals in Aβ1-42-treated cells. MOL extract pretreatment (25, 50, and 100 μg/mL) also alleviated the apoptosis indicators, including Bax, caspase-3/7 intensity, and cleaved caspase-3, and increased Bcl-2 levels in Aβ1-42-treated cells, consistent with a reduction in the number of apoptotic cells. The protective effects of MOL extract were possibly mediated through Akt activation, evidenced by increased Akt phosphorylation.

Conclusion and implications

The neuroprotective effect of MOL extract could be mediated via the activation of Akt, leading to the suppression of oxidative stress and apoptosis in an Aβ1-42 model of AD.