Recombinant Pongo pygmaeus NADH dehydrogenase [ubiquinone] 1 subunit C2 (NDUFC2)

What is the structure and localization of NDUFC2 within mitochondrial Complex I?

NDUFC2 (NADH dehydrogenase [ubiquinone] 1 subunit C2) is a membrane protein assigned to the ND2 module within the proton pumping modules of mitochondrial Complex I. The protein localizes to the intermembrane space and makes contact with 12 other subunits, including NDUFA8 within the ND1 module, ND2 module subunits (NDUFA10, NDUFA11, NDUFS5, NDUFC1, and ND2), and ND4 module constituents (NDUFB1, NDUFB5, NDUFB10, NDUFB11, and ND4) . These extensive contacts suggest NDUFC2 plays a crucial scaffolding role in maintaining Complex I structural integrity. The protein consists of 119 amino acids with a predicted molecular weight of approximately 14 kDa .

What is the primary function of NDUFC2 in mitochondrial respiration?

NDUFC2 functions as an accessory subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I). Although not directly involved in catalysis, NDUFC2 is required for complex assembly . Complexome profiling studies have demonstrated that NDUFC2 plays an essential role in the assembly of the membrane arm of Complex I, serving as a potential scaffold for ND1 module formation . Loss of NDUFC2 results in concurrent loss of its associating subunits—particularly those of the ND1 and ND2 modules—leading to failed incorporation of the ND1 subunit into the inner mitochondrial membrane . This structural role is critical for maintaining electron transfer from NADH to ubiquinone in the respiratory chain.

How does NDUFC2 contribute to Complex I assembly?

NDUFC2 is critical for the proper assembly of Complex I, particularly the assembly of the membrane arm. Complexome analysis of cells with NDUFC2 pathogenic variants revealed an accumulation of specific aberrant Complex I assembly intermediates, consistent with stalling of Complex I assembly, particularly the assembly of the ND2 module . Assembly of the Q module appears unaffected by NDUFC2 deficiency, but an accumulation of an assembly intermediate comprising the Q module along with assembly factors occurs, indicating incomplete membrane association . These findings suggest that NDUFC2 plays a crucial role in facilitating the transition from early to middle and late stages of Complex I assembly.

What methods are most effective for assessing NDUFC2 expression levels?

For quantitative assessment of NDUFC2 expression, real-time quantitative polymerase chain reaction (RT-PCR) is highly effective. In previous studies, researchers have successfully used the following primer sets for human NDUFC2: forward 5′-CCTGTATGCTGTGAGGGACC-3′ and reverse 5′-CGACGTTCAGCTCCACAACA-3′, with β-actin (forward 5′-GCAAGAGATGGCCACGGCTG-3′ and reverse 5′-CCACAGGACTCCATGCCCAG-3′) as a reference gene . For rat Ndufc2, primers used include: forward 5′-AGATGACCCAGATCATGTTTGAGA-3′ and reverse 5′-ATAGGGACATGCGGAGACCG-3′ . Expression analysis should include standardization using serially diluted standard curves analyzed simultaneously with unknown samples and corrected for reference gene mRNA levels. Western blotting with anti-NDUFC2 antibodies (e.g., ab192265) can also effectively assess protein levels, with an expected band size of 14 kDa .

How can researchers effectively study NDUFC2 function through loss-of-function approaches?

Several complementary approaches have proven effective for studying NDUFC2 function through loss-of-function:

• RNA interference (siRNA/shRNA): Ndufc2 silencing has been successfully performed in both H9c2 and rat primary cardiomyocytes to explore hypertrophy development and underlying signaling pathways . This approach allows for targeted gene knockdown in cell culture systems.

• CRISPR/Cas9 knockout: NDUFC2-knockout cell lines (such as HEK293T cells) have been used to study the specific effects on complex I assembly and stability .

• Heterozygous knockout animal models: A heterozygous Ndufc2 knockout rat model derived from stroke-resistant spontaneously hypertensive rat (SHRSR) has been developed to study the phenotypic effects of Ndufc2 deficiency in vivo .

• Patient-derived fibroblasts: Fibroblasts from patients with pathogenic NDUFC2 variants provide a valuable resource for studying the consequences of NDUFC2 dysfunction .

For each approach, assessment of mitochondrial function should include measurements of Complex I assembly (blue native PAGE), activity (spectrophotometric assays), mitochondrial membrane potential, ATP levels, and reactive oxygen species production .

What methodologies are recommended for studying the functional consequences of NDUFC2 variants?

A comprehensive approach to studying NDUFC2 variants should include:

• Expression analysis: RT-PCR and western blot to determine the effect of variants on gene and protein expression levels. The TT genotype at NDUFC2/rs11237379 has been shown to associate with significantly reduced gene expression .

• Complexome profiling: This powerful technique allows visualization of assembly intermediates and can reveal specific defects in Complex I assembly associated with NDUFC2 variants .

• Functional complementation: Introduction of wild-type NDUFC2 into cells with NDUFC2 variants (via lentiviral transduction) can confirm pathogenicity by rescuing Complex I defects .

• Mitochondrial function assessment: Measurement of oxygen consumption rate, mitochondrial membrane potential, ATP production, and ROS generation to determine the impact on mitochondrial bioenergetics .

• Pathway analysis: Investigation of downstream signaling pathways affected by NDUFC2 deficiency, such as SIRT3-AMPK-AKT-MnSOD in cardiomyocytes .

How are NDUFC2 variants associated with cardiovascular pathologies?

NDUFC2 variants have been significantly associated with several cardiovascular conditions:

• Left Ventricular Hypertrophy (LVH): Patients carrying the TT genotype at NDUFC2/rs11237379 showed significant differences in cardiac parameters, including increased septal thickness (p=0.07), posterior wall thickness (p=0.008), relative wall thickness (p=0.021), and LV mass/BSA (p=0.03), compared to subjects with CC or CT genotypes . Similarly, the A allele at NDUFC2/rs641836 was associated with increased septal thickness (p=0.017), posterior wall thickness (p=0.011), LV mass (p=0.003), and LV mass/BSA (p=0.002) .

• Acute Coronary Syndrome (ACS): NDUFC2 mRNA levels were significantly downregulated in peripheral blood mononuclear cells from patients experiencing ACS, along with evidence of greater mitochondrial structural damage and dysfunction .

• Ischemic Stroke: The T allele variant at NDUFC2/rs11237379 was associated with increased occurrence of early-onset ischemic stroke by a recessive mode of transmission (odds ratio [OR]=1.39; CI, 1.07–1.80; p=0.012). Subjects carrying both TT/rs11237379 and the A allele variant at NDUFC2/rs641836 had further increased risk of stroke (OR=1.56; CI, 1.14–2.13; p=0.006) .

The mechanistic link between these associations involves NDUFC2 deficiency-dependent mitochondrial dysfunction, leading to increased oxidative stress, inflammation, and cellular damage in cardiovascular tissues .

What cellular mechanisms link NDUFC2 deficiency to pathological outcomes?

NDUFC2 deficiency leads to several interrelated cellular mechanisms that contribute to pathological outcomes:

• Impaired Complex I Assembly: Loss of NDUFC2 function disrupts the assembly of Complex I, particularly affecting the ND1 and ND2 modules, leading to reduced electron transport chain function .

• Mitochondrial Dysfunction: NDUFC2 deficiency reduces mitochondrial membrane potential and ATP production, compromising cellular energy metabolism .

• Increased Oxidative Stress: Defective Complex I assembly results in increased production of reactive oxygen species (ROS), leading to oxidative damage to cellular components .

• Inflammation: In vitro studies have shown that NDUFC2 silencing promotes the expression of inflammatory markers, including tumor necrosis factor α (TNFα), intercellular adhesion molecule 1 (ICAM), vascular cell adhesion molecule 1 (VCAM), matrix metallopeptidase 9 (MMP9), and CD40 ligand (CD40L) .

• SIRT3-AMPK-AKT-MnSOD Signaling: In cardiomyocytes, NDUFC2 deficiency affects this key signaling pathway, contributing to hypertrophic responses .

These mechanisms form a cascade of cellular dysfunction that ultimately leads to tissue damage and disease manifestations in affected organ systems.

What animal models are available for studying NDUFC2-related pathologies?

Several animal models have been developed for studying NDUFC2-related pathologies:

• Heterozygous Ndufc2 Knockout Rat: Derived from the stroke-resistant spontaneously hypertensive rat strain (SHRSR), this model develops renal damage and stroke when fed with a high-salt/low potassium Japanese style diet, resembling the phenotype of the stroke-prone SHR (SHRSP) . This model has been valuable for studying the role of NDUFC2 in cerebrovascular and renal pathologies.

• Ndufc2-silenced Cardiomyocytes: Both H9c2 cells and rat primary cardiomyocytes with Ndufc2 silencing have been used to study hypertrophy development and the underlying signaling pathways . These cellular models have helped elucidate the SIRT3-AMPK-AKT-MnSOD pathway as a major mechanism in NDUFC2 deficiency-related cardiac hypertrophy.

• NDUFC2 Knockout Cell Lines: HEK293T cells with NDUFC2 knockout have been used to investigate the specific effects on Complex I assembly and stability .

These models provide complementary approaches for understanding the tissue-specific effects of NDUFC2 deficiency and testing potential therapeutic interventions.

How does NDUFC2 interact with other mitochondrial proteins in Complex I assembly?

NDUFC2 forms extensive interactions with other Complex I subunits, playing a crucial role in assembly and stability. Structural studies have revealed that NDUFC2 makes contact with 12 other subunits across different modules of Complex I . These interactions appear critical for proper module integration during Complex I assembly.

Complexome profiling of cells with NDUFC2 deficiency has revealed that loss of NDUFC2 causes concurrent loss of its associating subunits—particularly those of the ND1 and ND2 modules . While the Q module can form independently, the absence of NDUFC2 prevents its proper incorporation into the membrane. The ND4 module can still form in the absence of NDUFC2, but fails to integrate into the holoenzyme .

These findings suggest NDUFC2 functions as a molecular scaffold, facilitating interactions between multiple Complex I subunits during the assembly process. Without NDUFC2, the proper spatial arrangement of these subunits is compromised, leading to stalled assembly and accumulation of incomplete intermediates.

What genetic and epigenetic factors regulate NDUFC2 expression?

While the specific regulatory mechanisms controlling NDUFC2 expression are not fully elucidated in the provided search results, several genetic factors have been identified:

• Polymorphic Variants: The T allele at NDUFC2/rs11237379 has been shown to associate with significantly reduced gene expression . The functional significance of this variant was documented by its direct relationship with gene expression level, with TT genotype carriers showing significantly lower NDUFC2 expression compared to CC or CT genotypes .

• Disease States: NDUFC2 expression is altered in various pathological conditions. For example, NDUFC2 mRNA levels were significantly downregulated in peripheral blood mononuclear cells from patients experiencing acute coronary syndrome compared to stable angina patients . NDUFC2 also appears down-regulated in skeletal muscle cells of subjects affected by insulin resistance and is associated with insulin secretion in vivo .

Further research is needed to identify specific transcription factors, enhancers, repressors, and epigenetic modifications that regulate NDUFC2 expression under both physiological and pathological conditions. Understanding these regulatory mechanisms could provide new opportunities for therapeutic interventions aimed at modulating NDUFC2 expression.

How can NDUFC2 research contribute to therapeutic approaches for mitochondrial diseases?

NDUFC2 research offers several promising avenues for therapeutic development in mitochondrial diseases:

• Gene Therapy Approaches: Research has demonstrated that introduction of wild-type NDUFC2 into fibroblasts from patients with NDUFC2 pathogenic variants via lentiviral transduction can ameliorate Complex I defects, increasing steady-state levels of Complex I subunits and levels of fully assembled complex . This proof-of-concept supports the potential of gene therapy approaches for NDUFC2-related disorders.

• Targeted Pharmacological Interventions: Understanding the downstream consequences of NDUFC2 deficiency, such as the SIRT3-AMPK-AKT-MnSOD signaling pathway in cardiomyocytes , provides targets for pharmacological intervention. Compounds that activate these pathways might mitigate the consequences of NDUFC2 deficiency.

• Personalized Medicine Based on Genotype: The identification of specific NDUFC2 variants associated with increased risk of cardiovascular and cerebrovascular conditions (e.g., rs11237379, rs641836) suggests opportunities for personalized risk assessment and preventive interventions .

• Mitochondrial-Targeted Antioxidants: Given the increased oxidative stress associated with NDUFC2 deficiency, mitochondrial-targeted antioxidants might be particularly beneficial for patients with NDUFC2-related mitochondrial dysfunction .

Advancing our understanding of NDUFC2's role in Complex I assembly and function will continue to reveal new therapeutic targets and approaches for treating mitochondrial diseases and related conditions.

What are the key considerations for using recombinant NDUFC2 in experimental systems?

When working with recombinant NDUFC2 proteins, such as Recombinant Pongo pygmaeus NADH dehydrogenase [ubiquinone] 1 subunit C2 (NDUFC2), researchers should consider several technical aspects:

• Storage Conditions: Recombinant NDUFC2 should be stored in Tris-based buffer with 50% glycerol, optimized for this protein. For short-term storage, keep at -20°C, and for extended storage, conserve at -20°C or -80°C. Repeated freezing and thawing should be avoided, and working aliquots should be stored at 4°C for up to one week .

• Sequence Verification: Ensure the recombinant protein contains the complete amino acid sequence required for your experiments. The full-length NDUFC2 protein from Pongo pygmaeus consists of 119 amino acids with the sequence: MIARRNPEPLRFLPDEARSLPPPKLTDPRLLYLGFLGYCSGLIDNLIRRRPIATAGLHRQLLYITAFFFAGYYLVKRENYLYAVRDREMFGYMKLHPEEFPEEEKKTYGEIFEKFHPVH .

• Functional Validation: Before using in complex experiments, validate the functionality of the recombinant protein through appropriate activity assays or binding studies to ensure it maintains native conformational properties.

• Species Considerations: When studying across species, consider the conservation of NDUFC2 structure and function. While there is high homology across mammalian species, subtle differences may affect experimental outcomes when using non-human recombinant proteins in human systems.

What analytical techniques provide the most comprehensive assessment of NDUFC2 function?

A comprehensive assessment of NDUFC2 function requires multiple complementary analytical techniques:

• Complexome Profiling: This powerful technique combines blue native gel electrophoresis with quantitative mass spectrometry to resolve and identify protein complexes and their subunits. It has been instrumental in revealing the role of NDUFC2 in Complex I assembly and identifying specific assembly intermediates that accumulate in its absence .

• Blue Native Polyacrylamide Gel Electrophoresis (BN-PAGE): This technique separates intact protein complexes according to their molecular weight and is crucial for analyzing Complex I assembly and stability in response to NDUFC2 manipulation .

• Spectrophotometric Complex I Activity Assays: These assays measure the NADH:ubiquinone oxidoreductase activity of Complex I and can quantify the functional consequences of NDUFC2 deficiency .

• Mitochondrial Function Assays: Assessment of mitochondrial membrane potential (using fluorescent dyes like JC-1 or TMRM), ATP production, oxygen consumption rate (using platforms like Seahorse XF Analyzer), and ROS production provides a comprehensive view of mitochondrial bioenergetics affected by NDUFC2 .

• Imaging Techniques: Electron microscopy for ultrastructural analysis of mitochondrial morphology and confocal microscopy with appropriate fluorescent probes can reveal changes in mitochondrial network dynamics associated with NDUFC2 dysfunction .

The combination of these techniques provides a more complete understanding of NDUFC2's role in mitochondrial function than any single approach.