Recombinant Mouse NADH dehydrogenase [ubiquinone] 1 subunit C2 (Ndufc2)

What is Ndufc2 and what is its role in mitochondrial function?

Ndufc2 is a membrane protein subunit of mitochondrial respiratory chain complex I (NADH:ubiquinone oxidoreductase), specifically assigned to the ND2 module within the proton-pumping membrane arm of complex I. The protein localizes to the intermembrane space and makes contact with at least 12 other subunits including components of the ND1 module (NDUFA8), ND2 module (NDUFA10, NDUFA11, NDUFS5, NDUFC1, and ND2), and ND4 module (NDUFB1, NDUFB5, NDUFB10, NDUFB11, and ND4) . These extensive protein interactions highlight Ndufc2's importance in complex I assembly and stability. Complexome profiling data indicates that Ndufc2 plays a critical scaffolding role in the assembly of the membrane arm of complex I, particularly involving the ND2 module and possibly the ND1 module .

How is Ndufc2 expression measured in research settings?

Researchers typically quantify Ndufc2 expression using reverse-transcription polymerase chain reaction (RT-PCR) techniques. The established protocol involves:

• RNA extraction from tissue or cellular samples

• cDNA synthesis using random examer primers (typically using Superscript III First-Strand)

• Quantitative PCR with Ndufc2-specific primers:

  • Forward: 5′-GGCTTGTCTACATCGGCTTC-3′

  • Reverse: 5′-TGATGGTCCCTCACAGCATA-3′

  • Reference gene (β-actin): Forward 5′-AGATGACCCAGATCATGTTTGAGA-3′; Reverse 5′-ATAGGGACATGCGGAGACCG-3′

PCR conditions typically include an initial denaturation at 94°C for 10 minutes followed by 40 cycles of 94°C for 15 seconds and 60°C for 15 seconds . Expression levels are calculated from standard curves and normalized to β-actin mRNA levels to account for variations in starting material .

What model systems are available for studying Ndufc2?

Several experimental models have been developed to study Ndufc2 function:

Cellular Models:

• A10 vascular smooth muscle cell line (derived from rat embryonic thoracic aorta) with siRNA-mediated Ndufc2 silencing

• HEK293T NDUFC2-knockout cell lines for studying complex I assembly

• Patient-derived fibroblasts from individuals with NDUFC2 mutations

Animal Models:

• SHR-Ndufc2 mutant rat strains (SHR-Ndufc2em1Mcwi and SHR-Ndufc2em2Mcwi) generated using zinc finger nuclease (ZFN) technology

• Stroke-prone spontaneously hypertensive rat (SHRSP), which exhibits reduced Ndufc2 expression upon Japanese-style stroke-permissive diet (JD)

What is Ndufc2's role in complex I assembly and how can this be studied?

Ndufc2 serves as a critical scaffold for proper assembly of the membrane arm of complex I. Complexome profiling of patient fibroblasts with NDUFC2 mutations has revealed that loss of NDUFC2 causes:

• Accumulation of specific complex I assembly intermediates, particularly the Q module

• Stalling of complex I assembly at the Q module formation stage

• Defective incorporation of the ND1 subunit into the inner mitochondrial membrane

• Loss of stable ND1 and ND2 modules, indicating these proximal P-modules cannot preassemble independently without NDUFC2

Methodological approach to study complex I assembly:

• Blue native polyacrylamide gel electrophoresis (BN-PAGE) to separate native protein complexes

• Mass spectrometry-based complexome profiling to identify and quantify protein components

• Detection of assembly intermediates using antibodies against specific complex I subunits

• Validation through lentiviral rescue experiments (transducing wild-type NDUFC2 cDNA)

Experimental evidence shows that in patient fibroblasts, assembly of the Q module (containing NDUFA5, NDUFS2, NDUFS3, NDUFS7, and NDUFS8) appears unaffected, but there is characteristic accumulation of a ~300 kDa assembly intermediate comprising the Q module along with the assembly factor TIMMDC1 and the NDUFA13 subunit .

What are the biochemical consequences of Ndufc2 deficiency?

Ndufc2 deficiency results in severe mitochondrial dysfunction characterized by:

Complex I deficiency:

• Decreased complex I enzyme activity

• Reduced steady-state levels of complex I subunits

• Diminished formation of complex I-containing supercomplexes

Bioenergetic abnormalities:

• Reduced mitochondrial membrane potential

• Decreased ATP production

• Increased reactive oxygen species (ROS) production

Molecular consequences:

• Inflammation (increased inflammatory markers)

• Oxidative stress

• Impaired cellular function and viability

Importantly, these biochemical abnormalities can be partially rescued by reintroduction of wild-type NDUFC2. In rescue experiments with patient fibroblasts, lentiviral transduction of wild-type NDUFC2 cDNA led to increased complex I assembly and elevated steady-state levels of other complex I subunits, confirming the pathogenicity of NDUFC2 variants .

What pathological conditions are associated with Ndufc2 dysfunction?

Leigh Syndrome:
Bi-allelic pathogenic variants in NDUFC2 have been documented as causing early-onset Leigh syndrome, a progressive neurodegenerative disorder representing the first confirmed cases of mitochondrial disease due to NDUFC2 mutations . Clinical features include:

• Developmental regression

• Elevated lactate levels

• Characteristic neuroimaging abnormalities (basal ganglia, thalami, and substantia nigra lesions)

Stroke Susceptibility:
Evidence from both animal models and human genetic studies suggests NDUFC2 contributes to stroke risk:

• Animal models:

  • In stroke-prone spontaneously hypertensive rats (SHRSP), Ndufc2 is significantly downregulated under Japanese-style stroke-permissive diet

  • SHRSR (stroke-resistant) rats carrying heterozygous Ndufc2 deletion developed renal abnormalities and stroke occurrence similar to SHRSP

• Human genetic studies:

  • T allele variant at NDUFC2/rs11237379 is associated with reduced gene expression

  • This variant shows increased occurrence of early-onset ischemic stroke with recessive mode of transmission (odds ratio=1.39; CI, 1.07–1.80; P=0.012)

  • Individuals carrying both TT/rs11237379 and A allele variant at NDUFC2/rs641836 had further increased stroke risk (OR=1.56; CI, 1.14–2.13; P=0.006)

What techniques are used for Ndufc2 gene manipulation in experimental models?

siRNA-Mediated Silencing:
For transient knockdown in cell culture:

• Cell preparation: Culture cells (e.g., A10 vascular smooth muscle cells) in appropriate medium

• Transfection mixture: Combine Ndufc2-specific siRNA (33 nmol/L final concentration) with Lipofectamine 2000 in OPTI-MEM

• Transfection: Incubate cells with transfection mixture for 5 hours, then replace with complete medium

• Analysis: Perform experiments 72 hours post-transfection

CRISPR/Cas9 or Zinc Finger Nuclease (ZFN) for Animal Models:
For generating Ndufc2-deficient rat models:

• Design ZFN constructs specific for rat Ndufc2 exon 1 sequence

• Inject in vitro-transcribed ZFN mRNA into rat embryos

• Transfer to pseudopregnant females

• Screen offspring for mutations using Surveyor Nuclease assay with primers flanking the target sequence:

  • Ndufc2_F: 5′-CGCATCAATATGATGAACGG-3′

  • Ndufc2_R: 5′-CGCTGAAAACTCTAGACGGG-3′

• Confirm mutations by Sanger sequencing

This approach has successfully generated rat models with 9-bp deletion (del-9 ACGGGCCTG; Ndufc2-m1) and 107-bp deletion in Ndufc2 .

How can Ndufc2 function be rescued in experimental systems?

Lentiviral transduction with wild-type NDUFC2 has been successfully used to rescue Ndufc2 function in patient fibroblasts:

• The procedure involves transduction of subject fibroblasts with lentiviral particles containing wild-type NDUFC2 cDNA

• Doxycycline induction (72 hours) allows for expression of the introduced wild-type NDUFC2

• This approach leads to:

  • Increased NDUFC2 protein levels

  • Elevated steady-state levels of other complex I subunits

  • Increased levels of fully assembled complex I

  • Improved mitochondrial function

It's worth noting that the rescue may be partial, with protein levels not always reaching control levels. This could be due to the continued presence of mutant NDUFC2 or aberrant subassembly species affecting the assembly process .

NDUFC2 Mutations Associated with Leigh Syndrome

Biochemical Consequences of NDUFC2 Deficiency in Patient Fibroblasts

NDUFC2 Variants Associated with Stroke Risk in Humans

What are the emerging questions in Ndufc2 research?

Future research on Ndufc2 could focus on several promising areas:

• Detailed structural analysis of Ndufc2's interactions within complex I using cryo-electron microscopy

• Development of therapeutic approaches targeting Ndufc2 dysfunction, including gene therapy approaches

• Investigation of tissue-specific effects of Ndufc2 deficiency

• Further exploration of the link between Ndufc2 variants and stroke risk in diverse populations

• Examination of potential interactions between Ndufc2 and environmental factors in disease pathogenesis

These research directions could significantly advance our understanding of mitochondrial biology and provide new therapeutic targets for mitochondrial diseases and stroke prevention.