UQCRC1 Human

How is UQCRC1 expression regulated in different tissues?

UQCRC1 expression varies significantly across tissues, with highest expression observed in metabolically active organs. In neural tissues, UQCRC1 is abundant in the substantia nigra and striatum, regions predominantly affected in Parkinson's disease . In pathological contexts, UQCRC1 expression patterns can become dysregulated. For instance, in pancreatic ductal adenocarcinoma (PDAC), UQCRC1 expression shows a gradual increase during progression from pancreatic intraepithelial neoplasias (PanIN) to full PDAC, with elevated expression observed in 72.3% of PDAC cases . This tissue-specific expression pattern likely reflects the varying energetic demands across different cell types.

What UQCRC1 mutations have been identified in Parkinson's disease patients?

Several pathogenic UQCRC1 variants have been identified in families with autosomal dominant parkinsonism:

These variants were absent in control subjects and healthy participants from the Taiwan Biobank exome database, suggesting they are rare pathogenic mutations rather than common polymorphisms .

How do UQCRC1 mutations affect mitochondrial function in neurons?

UQCRC1 mutations disrupt mitochondrial function through several mechanisms:

• Complex III-specific dysfunction: UQCRC1 mutations (particularly p.Tyr314Ser) significantly reduce complex III oxygen consumption while not affecting complexes I, II, or IV .

• Bioenergetic deficits: Mutant UQCRC1 expression leads to decreased maximal respiration and ATP production in neurons .

• Oxidative stress: Neurons expressing mutant UQCRC1 show increased reactive oxygen species production, especially under stress conditions .

• Mitochondrial morphology alterations: Electron microscopy revealed that UQCRC1 p.Tyr314Ser knock-in mice develop abnormal mitochondrial ultrastructure, with irregularly shaped, elongated, and vacuolated mitochondria in nigral neurons. Specifically, 35% of neuronal mitochondria in these mutants were abnormally elongated (p=0.007) with irregular shapes and more turns in the outer membrane compared to wild-type mice (p=0.021) .

These mitochondrial defects ultimately contribute to neurite retraction, dopaminergic neuronal loss, and the development of parkinsonian symptoms .

What animal models have been developed to study UQCRC1 function?

Researchers have developed several complementary animal models to investigate UQCRC1 function:

• Drosophila models:

  • CRISPR/Cas9-based fly UQCRC1 null mutants with a 4-bp deletion causing frameshift and early termination at amino acid 111

  • Flies with neuronal knockdown of uqcrc1 that exhibit age-dependent parkinsonism-resembling defects

  • Heterozygous UQCRC1 p.Tyr314Ser knock-in flies expressing human wild-type or mutant UQCRC1 in a heterozygous null background

• Mouse models:

  • UQCRC1 p.Tyr314Ser knock-in mice that exhibit age-dependent motor dysfunction, dopaminergic neuronal loss, peripheral neuropathy, and impaired complex III activity

  • These mouse models respond to levodopa treatment, which significantly improves their motor dysfunction

These complementary models allow for comprehensive investigation of UQCRC1 function across different species and experimental contexts.

How can CRISPR/Cas9 be utilized to generate UQCRC1 mutant cell lines?

CRISPR/Cas9 has been effectively employed to generate various UQCRC1 mutant models:

Methodology for SH-SY5Y cell lines:

• Design guide RNAs targeting specific regions of the UQCRC1 gene

• Transfect cells with Cas9 and guide RNA expression constructs

• Select and isolate cell clones

• Perform sequence confirmation to verify introduced mutations

• For splicing variants, conduct RT-PCR to examine cDNA expression patterns

For Drosophila models:

• Inject Drosophila UQCRC1-targeted single guide RNA into vas-Cas9(X) embryos

• Identify candidate mutants through screening

• Confirm mutations through sequencing (e.g., 4-bp deletion causing frameshift)

After establishing these models, researchers assessed neuronal morphology, mitochondrial function, and complex III activity to characterize the functional consequences of UQCRC1 mutations .

How does UQCRC1 interact with cytochrome c in apoptotic pathways?

UQCRC1 plays a critical role in regulating cytochrome c-mediated apoptosis through direct interaction:

• Under normal conditions, UQCRC1 associates with cytochrome c, helping maintain its localization within the mitochondria .

• In UQCRC1-deficient conditions, cytochrome c levels increase in the cytoplasmic fraction, triggering activation of the caspase cascade and apoptotic cell death .

• Mechanistic studies demonstrated that depleting cytochrome c or expressing the anti-apoptotic protein p35 effectively ameliorates uqcrc1-mediated neurodegeneration in Drosophila models .

This regulatory function represents a novel mechanism by which UQCRC1 deficiency contributes to neurodegeneration beyond its established role in oxidative phosphorylation. The molecular interface between UQCRC1 and cytochrome c may represent a potential therapeutic target for neuroprotection .

What cellular phenotypes result from UQCRC1 dysfunction?

UQCRC1 dysfunction leads to diverse cellular phenotypes across different model systems:

• Neuronal morphology defects:

  • SH-SY5Y cells expressing mutant UQCRC1 (p.Tyr314Ser, p.Ile311Leu, or the splicing variant) exhibit significantly shortened neurites compared to wild-type cells

  • Quantitative analysis showed wild-type control neurites averaged 82.6±10.8 μm in length, while UQCRC1 p.Tyr314Ser neurites measured only 42.6±7.3 μm (p=0.008)

• Mitochondrial functional deficits:

  • Decreased complex III activity

  • Reduced ATP production

  • Increased reactive oxygen species generation

• Apoptotic activation:

  • Increased cytoplasmic cytochrome c

  • Activated caspase cascade

• In vivo consequences:

  • Dopaminergic neuronal loss

  • Peripheral neuropathy

  • Age-dependent locomotor defects

These phenotypes establish a clear mechanistic link between UQCRC1 mutations and neurodegeneration.

What role does UQCRC1 play in cancer progression?

Contrary to its protective role in neurons, UQCRC1 appears to have pro-tumorigenic functions in certain cancers:

• Expression pattern in PDAC:

  • UQCRC1 expression gradually increases during progression from PanIN stages to PDAC in mouse models

  • Elevated expression observed in 72.3% of PDAC cases

  • High expression correlates with poor prognosis

• Functional impact on cancer cells:

  • UQCRC1 promotes PDAC cell growth in both in vitro experiments and in vivo mouse models

  • Enhances colony formation capacity

  • Increases tumor growth in subcutaneous and orthotopic models

• Metabolic mechanism:

  • UQCRC1 overexpression increases mitochondrial oxidative phosphorylation and ATP production

  • The excess ATP is released extracellularly via pannexin 1 channels

  • Extracellular ATP acts as an autocrine/paracrine signal to promote cell proliferation through the ATP/P2Y2-RTK/AKT axis

• Therapeutic implications:

  • UQCRC1 knockdown or ATP release blockage effectively inhibits PDAC growth

  • May represent a potential therapeutic target

These findings highlight the context-dependent roles of UQCRC1 in different diseases and tissues.

Which techniques are most effective for measuring UQCRC1-associated mitochondrial function?

Several complementary techniques have been successfully employed to assess UQCRC1-associated mitochondrial function:

• Seahorse extracellular flux analysis:

  • Measures oxygen consumption rates (OCRs) in real-time

  • Allows assessment of basal respiration, ATP production, maximal respiration, and spare respiratory capacity

  • Can be combined with specific inhibitors to isolate individual complex activities

• Complex-specific activity assays:

  • Selective inhibition of individual respiratory chain complexes allows isolation of complex III-specific effects

  • This approach demonstrated that UQCRC1 mutations specifically impair complex III without affecting complexes I, II, or IV

• Reactive oxygen species measurement:

  • Fluorescent probes to detect ROS production under basal conditions and after stress

• Transmission electron microscopy:

  • Visualizes mitochondrial ultrastructure and morphological abnormalities

  • Quantifies parameters such as number, shape, elongation, and membrane irregularities

  • Revealed significant morphological alterations in UQCRC1 mutant mitochondria

The combination of these techniques provides comprehensive assessment of mitochondrial function from biochemical, metabolic, and structural perspectives.

How can neurite morphology be quantitatively assessed in UQCRC1 mutant models?

Neurite morphology can be quantitatively assessed using these methodological approaches:

• Cell differentiation protocol:

  • Differentiate SH-SY5Y cells with retinoic acid to induce neurite outgrowth

  • Ensure comparable UQCRC1 protein expression levels across cell lines through western blot

• Imaging techniques:

  • Confocal microscopy to visualize neurite structures

  • Immunostaining for neuronal markers and cytoskeletal proteins

• Quantitative analysis:

  • Measure neurite length from cell body to furthest terminal

  • Compare average lengths between wild-type and mutant cells

  • Statistical analysis to determine significance of differences

Using this approach, researchers demonstrated that SH-SY5Y cells expressing mutant UQCRC1 variants had significantly shortened neurites compared to wild-type controls (wild-type: 82.6±10.8 μm; p.Tyr314Ser: 42.6±7.3 μm; p.Ile311Leu: 55.1±9.5 μm; aberrant splicing variant: 54.1±10.2 μm) .