NDUFS2 Human

What is the structural role of NDUFS2 in mitochondrial complex I?

NDUFS2 is a core subunit of mitochondrial respiratory chain complex I that contributes to the ubiquinone/rotenone binding site and is necessary for the assembly and catalytic activity of the complex . It plays a critical structural role by forming interfaces with other subunits. For example, in healthy individuals, the glutamic acid residue at position 57 (Glu57) makes a possible ion pair with Arg382 of NDUFS1, and also makes nonbonding contacts with Gly661, Ala662, Asn663, Tyr664, Leu381, Arg382, and Ser383 . These interactions are crucial for the structural integrity of complex I. When studying NDUFS2 function, researchers should consider these protein-protein interactions as potential mechanisms through which mutations may disrupt complex I assembly and function.

How does NDUFS2 contribute to mitochondrial energy production?

NDUFS2 is essential for the catalytic activity of complex I in the electron transport chain. Methodologically, researchers can assess NDUFS2's contribution to energy production by measuring:

• NADH oxidation rates in isolated mitochondria

• Mitochondrial membrane potential using fluorescent probes like JC-1

• ATP production in cells with normal versus altered NDUFS2 expression

Research demonstrates that overexpression of NDUFS2 significantly increases mitochondrial membrane potential in pancreatic cancer cell lines (Panc05.04), thereby modulating mitochondrial function . Conversely, knockdown of NDUFS2 markedly decreases mitochondrial membrane potential, accompanied by aggravated mitochondrial cell death . These findings indicate NDUFS2's critical role in maintaining mitochondrial function and cellular energy homeostasis.

What patterns of inheritance are observed with pathogenic NDUFS2 mutations?

Pathogenic NDUFS2 mutations typically follow an autosomal recessive inheritance pattern. Research shows that affected individuals generally carry compound heterozygous mutations, with each parent contributing one mutant allele. For instance, in a cohort study of patients with complex I deficiency, four unrelated white Caucasian patients were found to carry a heterozygous NDUFS2 mutation (c.875T>C, p.M292T) in conjunction with secondary unique heterozygous mutations in the same gene .

In each case, parental testing confirmed that each parent was heterozygous for only one of the two substitutions identified in the respective patients . This pattern of compound heterozygosity is consistent with autosomal recessive inheritance and important for genetic counseling and family studies. When designing genetic studies of NDUFS2, researchers should include parental samples whenever possible to confirm inheritance patterns.

How do specific NDUFS2 mutations correlate with clinical phenotypes?

Different NDUFS2 mutations produce distinct clinical phenotypes, with varying disease severity and tissue involvement. The following mutations have been characterized:

Researchers investigating genotype-phenotype correlations should consider both the specific position of mutations and their biochemical consequences. Mutations affecting the interface with other complex I subunits typically cause severe phenotypes due to structural disruption of the complex .

What are the optimal methods for measuring complex I activity in NDUFS2 research?

When investigating NDUFS2 function or the impact of mutations, measuring complex I activity is crucial. Methodologically, researchers should:

• Use multiple complementary approaches to assess complex I function

• Normalize complex I activity to another mitochondrial enzyme (typically citrate synthase)

• Include appropriate controls and biological replicates

Standard laboratory methods include:

• Spectrophotometric assays measuring NADH oxidation rates (expressed as nanomoles NADH oxidized/min/unit citrate synthase)

• Ratio measurements of complex I to complex II activities to control for mitochondrial content

• Analysis in multiple tissues when possible (muscle homogenates most commonly used)

In clinical studies, control ranges for complex I activity in muscle homogenates typically fall around 0.104 ± 0.036 nanomoles NADH oxidized/min/unit citrate synthase . NDUFS2 mutations generally reduce activity to 13-27% of control values .

What genetic models are most effective for studying NDUFS2 function in development?

Conditional knockout models using tissue-specific Cre-lox systems have proven valuable for studying NDUFS2 function during development. For neural development studies, the hGFAP-Cre/Ndufs2-flox mouse model has been particularly informative .

This approach involves:

• Generating mice with floxed Ndufs2 alleles

• Crossing with transgenic lines expressing Cre recombinase under tissue-specific promoters

• Analyzing phenotypes at different developmental stages

For example, using the human glial fibrillary acidic protein (hGFAP) promoter to drive Cre expression targets radial glial cells (RGCs) and adult neural stem cells . This model revealed that NDUFS2 deficiency and resulting mitochondrial complex I dysfunction severely impairs brain development, with animals showing decreased cortical thickness, hippocampal abnormalities, and early postnatal death between P7 and P9 .

When designing similar studies, researchers should carefully select Cre driver lines based on the specific cell populations of interest and validate recombination efficiency.

How does NDUFS2 function differ in neural stem cells compared to differentiated neurons?

NDUFS2 and functional mitochondrial complex I are particularly critical for neural stem cell (NSC) viability, proliferation, and differentiation. Research methodologies to investigate this include:

• Isolating neural stem and progenitor cells (NSPCs) from control and NDUFS2-deficient animals

• Culturing neurospheres under proliferation and differentiation conditions

• Analyzing lineage markers for neurons, astrocytes, and oligodendrocytes

Studies using hGFAP-NDUFS2 mice have demonstrated that:

These findings suggest differential metabolic requirements among neural lineages, with neurons and oligodendrocytes being more dependent on oxidative phosphorylation than astrocytes.

What is the role of NDUFS2 in cancer cell metabolism and tumor progression?

Recent research has uncovered an important role for NDUFS2 in cancer, particularly in pancreatic adenocarcinoma (PAAD). Methodological approaches to study NDUFS2 in cancer include:

• Overexpression and knockdown experiments in cancer cell lines

• Assessment of proliferation, migration, and colony formation

• Analysis of mitochondrial function and cell death pathways

• Identification of protein interaction partners

Studies have shown that NDUFS2 is upregulated in pancreatic adenocarcinoma and plays a critical role in the survival, proliferation, and migration of pancreatic cancer cells by inhibiting mitochondrial cell death . Specifically:

• NDUFS2 overexpression promotes cell-cycle progression with elevated S-phase percentage

• NDUFS2-silenced cells show cell cycle impediment at G0/G1 phase

• Colony formation capability is significantly enhanced in NDUFS2-overexpressed cells

• NDUFS2 overexpression increases mitochondrial membrane potential and inhibits mitochondrial cell death

• NDUFS2 silencing results in shorter and fewer mitochondria in cancer cells

Furthermore, proteomic analyses have identified OTUB1, a deubiquitinase, as an interaction partner of NDUFS2. Overexpression of OTUB1 increases NDUFS2 expression at the protein level, suggesting a potential regulatory mechanism for NDUFS2 stability in cancer cells .

What diagnostic criteria should be used when suspecting NDUFS2-related mitochondrial disease?

Diagnosing NDUFS2-related mitochondrial disease requires a multifaceted approach. Researchers and clinicians should consider:

• Clinical presentation: Leigh syndrome, complex I deficiency, cardiomyopathy, encephalopathy

• Biochemical testing: Isolated complex I deficiency in muscle homogenates (<30% of control values)

• Genetic analysis: Sequencing of NDUFS2 and other complex I-related genes

• Family history: Consistent with autosomal recessive inheritance

The diagnostic workflow should include:

• Measurement of complex I activity in muscle homogenates, normalized to citrate synthase or complex II

• Complete sequencing of NDUFS2 and other relevant nuclear-encoded complex I subunits

• Analysis of parental samples to confirm inheritance patterns

• Exclusion of mitochondrial DNA mutations that could cause similar phenotypes

Studies have shown that patients with NDUFS2 mutations typically present with complex I activity reduced to 13-27% of control values . The specific mutations most commonly associated with disease include p.M292T (often found in compound heterozygous state with other mutations) .

How can haplotype analysis inform the study of recurrent NDUFS2 mutations?

Haplotype analysis can provide valuable insights into the origins and spread of recurrent mutations in NDUFS2. For example, the p.M292T mutation has been observed in multiple unrelated patients of white Caucasian ancestry .

Methodological approaches include:

• Genotyping patients and parents for microsatellite markers flanking the NDUFS2 gene

• Analysis of single nucleotide polymorphisms (SNPs) with appropriate minor allele frequencies

• Selection of markers at regular intervals upstream and downstream of the gene

Researchers have used markers such as D1S2635, D1S2707, D1S2771, D1S2705, D1S2675, D1S2844, and D1S1677, as well as SNPs with minor allele frequencies of 0.15-0.48 located at ~100 kb intervals around NDUFS2 .

This approach can help determine whether recurrent mutations represent independent mutational events or are derived from a common ancestor (founder effect), which has implications for population screening and genetic counseling.

What therapeutic approaches show promise for NDUFS2-related mitochondrial disorders?

Current research on therapeutic approaches for NDUFS2-related disorders is still in early stages. Promising research directions include:

• Gene therapy approaches to deliver functional NDUFS2 to affected tissues

• Small molecule compounds that can bypass complex I deficiency

• Mitochondrially-targeted antioxidants to reduce oxidative stress

• Metabolic modifiers that can enhance residual complex I function

Researchers investigating therapeutic approaches should consider tissue-specific requirements for NDUFS2 function, as the search results indicate differential effects of NDUFS2 deficiency across tissues. For example, while brain development is severely affected in hGFAP-NDUFS2 mice, peripheral nervous system structures like superior cervical ganglia, adrenal medulla, and carotid bodies remain relatively normal .

This suggests potential differences in compensatory mechanisms across tissues that could be exploited therapeutically. Future research should focus on identifying these tissue-specific dependencies and developing targeted interventions.

How might targeting the OTUB1/NDUFS2 axis influence cancer treatment strategies?

The recently identified interaction between NDUFS2 and the deubiquitinase OTUB1 presents an intriguing target for cancer therapeutics, particularly in pancreatic cancer. Research approaches to explore this interaction include:

• Development of small molecule inhibitors targeting the OTUB1-NDUFS2 interaction

• Investigation of combination therapies targeting both mitochondrial function and canonical cancer pathways

• Exploration of biomarkers to identify patients most likely to benefit from NDUFS2-targeted therapies

Studies have shown that OTUB1 overexpression increases NDUFS2 protein levels, while OTUB1 knockdown reverses this effect . This suggests that OTUB1 may stabilize NDUFS2 by preventing its ubiquitination and subsequent degradation.

Given NDUFS2's role in maintaining mitochondrial membrane potential and inhibiting mitochondrial cell death in cancer cells , disrupting the OTUB1/NDUFS2 axis could potentially sensitize cancer cells to apoptosis. This represents a novel approach to targeting the altered metabolism of cancer cells, which often rely on mitochondrial function despite the Warburg effect.

Future research in this area should focus on validating this axis as a therapeutic target in diverse cancer types and developing specific inhibitors with minimal effects on normal tissues.