Recombinant Human Claudin-10 (CLDN10)

What is Claudin-10 (CLDN10) and what are its primary functions?

CLDN10 is a member of the claudin family of tight junction proteins, with a full-length sequence of 228 amino acids in humans. It primarily functions by forming paracellular channels that polymerize in tight junction strands with both cation- and anion-selective properties. These channels convey epithelial permeability in a process known as paracellular tight junction permeability . The protein plays essential roles in controlling ion selectivity in epithelial barriers, particularly in renal tubules and sweat glands. CLDN10 is crucial for proper sweat production and renal function, contributing significantly to ion homeostasis across epithelial barriers .

What are the primary isoforms of CLDN10 and how do they differ functionally?

CLDN10 exists in two major isoforms with distinct functional properties:

The differential expression of these isoforms creates segment-specific permeability properties throughout the nephron. Quantitative PCR analysis has confirmed that CLDN10a transcripts are abundant in the proximal convoluted tubule (PCT), whereas CLDN10b predominates in the thick ascending limb (TAL) .

What experimental techniques are most effective for studying Recombinant Human CLDN10?

Recombinant Human CLDN10 protein can be effectively studied using several methodological approaches:

• Protein Expression and Purification: Recombinant Human CLDN10 can be expressed in Wheat germ expression systems, yielding the full-length protein (1-228 aa) .

• Immunological Techniques: The protein is suitable for ELISA and Western Blot (WB) applications . When developing antibodies, monoclonal approaches may offer greater specificity, as demonstrated in recent studies .

• Genetic Manipulation: Targeted deletion using homologous recombination and Cre-loxP systems allows for tissue-specific claudin-10 knockout models, such as the TAL-specific deletion model .

• Electrophysiological Measurements: Isolated tubule preparations can be used for measuring transepithelial voltage (Vte), resistance (Rte), and paracellular ion permeability through dilution potential and bi-ionic diffusion potential measurements .

• Immunolocalization: Immunofluorescence microscopy with co-staining for other tight junction proteins (e.g., ZO-1) or segment-specific markers (e.g., NKCC2 for TAL) helps determine the subcellular localization and tissue distribution of CLDN10 .

How does CLDN10 deletion affect paracellular ion selectivity in renal tubules?

Deletion of CLDN10 in the thick ascending limb (TAL) of Henle's loop dramatically alters paracellular permeability for monovalent and divalent cations. Experimental evidence from isolated tubule studies reveals several key findings:

• Altered Transepithelial Properties: CLDN10 deletion results in a 1.6-fold increase in transepithelial voltage (Vte) and a 1.3-fold increase in transepithelial resistance (Rte), with no significant difference in short-circuit currents (I'sc) .

• Changed Dilution Potentials: NaCl dilution potential is dramatically diminished in CLDN10-deficient mice (-4.2 ± 1.7 mV) compared to controls (-23.2 ± 1.3 mV) .

• Reversed Bi-ionic Diffusion Potentials: The bi-ionic diffusion potentials (luminal Na+ against basolateral Mg2+ or Ca2+) change polarity in CLDN10-knockout tubules compared with controls:

  • For Mg2+: 4.9 ± 1.0 mV in knockout mice vs. -7.4 ± 1.1 mV in controls

  • For Ca2+: 11 ± 1.5 mV in knockout mice vs. -0.7 ± 1.2 mV in controls

• Shifted Permeability Ratios: The calculated relative permeabilities show a decrease in PNa/PCl accompanied by strong increases in PMg/PNa and PCa/PNa, suggesting that the absence of CLDN10 alters the permeability sequence from favoring monovalent cations to favoring divalent cations .

These functional changes explain the phenotypic observations of hypermagnesemia and nephrocalcinosis in CLDN10-deficient mice.

What are the physiological consequences of CLDN10 deletion in the kidney?

The deletion of CLDN10 in the thick ascending limb leads to significant alterations in renal function and systemic ion homeostasis. The following table summarizes key physiological parameters altered in CLDN10-deficient mice compared to controls:

*P < 0.05; **P < 0.01; ***P < 0.001

The most striking consequences include:

• Hypermagnesemia: Almost twofold higher serum Mg2+ concentration with correspondingly reduced fractional excretion (FE) of Mg2+ (52% of control values) .

• Nephrocalcinosis: Extensive medullary calcium deposits in the outer stripe of the outer medulla and at the transition to the inner medulla, as revealed by von Kossa and alizarin red S staining .

• Polyuria and Polydipsia: Increased urine volume with decreased urine osmolality, accompanied by increased water intake .

• Urinary Acidification: More acidic urine in knockout mice (pH 5.5 vs. 6.3 in controls) .

These findings demonstrate that CLDN10 is a key determinant of cation selectivity in the TAL, and its absence leads to a shift from paracellular sodium transport to hyperabsorption of calcium and magnesium.

What is the role of CLDN10 in cancer progression, particularly in renal cell carcinoma?

CLDN10 exhibits significant oncogenic potential in clear cell renal cell carcinoma (ccRCC), extending beyond its conventional tight junction functions. Research has demonstrated that:

• Prognostic Value: High CLDN10 expression predicts poor outcome in ccRCC patients and represents an independent prognostic marker for cancer-specific survival .

• Promotion of Malignant Phenotypes: Cell surface CLDN10 promotes multiple cancer hallmarks including:

  • Enhanced cell viability

  • Increased proliferation

  • Accelerated cell migration

  • Augmented tumor growth

• Signaling Pathway Activation: CLDN10 activates the mTOR signaling pathway and the expression of downstream targets, including MYC target genes .

• Protein-Protein Interactions: CLDN10 forms a complex with the amino acid transporter LAT1, and this CLDN10-LAT1 signaling axis facilitates malignant phenotypes in ccRCC cells .

• Structural Interactions: Structural prediction and immunoprecipitation analyses strongly suggest an interaction between the first transmembrane domain of CLDN10 (CLDN10-TM1) and LAT1 .

These findings highlight CLDN10 as a potential therapeutic target in ccRCC and suggest that disrupting the CLDN10-LAT1 interaction might represent a novel approach for treating this aggressive cancer type.

How can researchers effectively investigate CLDN10 function using genetic knockout models?

Researchers can employ the following methodological approach to investigate CLDN10 function using genetic knockout models:

• Conditional Knockout Strategy:

  • Generate mice with loxP sites flanking critical exons (e.g., exons 2 and 3) of the CLDN10 gene using homologous recombination in embryonic stem cells .

  • The targeted deletion should affect all splice variants (e.g., CLDN10a and CLDN10b) and result in a premature stop codon in all encoded isoforms .

• Tissue-Specific Deletion:

  • Cross floxed CLDN10 mice with animals expressing Cre recombinase under a tissue-specific promoter (e.g., kidney-specific cadherin-16 promoter for TAL-specific deletion) .

  • This approach allows for studies of CLDN10 function in specific nephron segments while avoiding potential embryonic lethality of global knockouts.

• Validation of Knockout Efficiency:

  • Confirm deletion at the protein level using Western blot analysis of tissue membrane extracts .

  • Verify segment-specific deletion using quantitative PCR (qPCR) with cDNA generated from isolated nephron segments .

  • Perform immunofluorescence microscopy with co-staining for segment-specific markers to visually confirm the absence of the protein in targeted segments .

• Phenotypic Characterization:

  • Conduct histological examination using appropriate stains (e.g., von Kossa and alizarin red S for calcium deposits) .

  • Analyze serum and urine parameters, including electrolytes, acid-base status, and osmolality .

  • Calculate fractional excretion rates for various ions to assess specific tubular functions .

• Functional Studies:

  • Perform ex vivo tubule perfusion studies to measure transepithelial voltage and resistance .

  • Conduct dilution potential and bi-ionic diffusion potential measurements to determine paracellular permeability properties .

  • Calculate relative ion permeabilities to assess changes in ion selectivity .

This comprehensive approach allows for detailed characterization of CLDN10's physiological roles and the consequences of its disruption in specific tissues or cell types.

What are the optimal expression systems for recombinant human CLDN10 production?

When producing recombinant human CLDN10 for research purposes, the choice of expression system is critical for obtaining functional protein. The available search results indicate that Wheat germ expression systems have been successfully used to produce full-length human CLDN10 protein (1-228 amino acids) . This system is particularly useful for producing membrane proteins like claudins, as it can facilitate proper folding and post-translational modifications.

For researchers designing CLDN10 expression experiments, several considerations are important:

• Protein Sequence: Ensure that the complete amino acid sequence (1-228 aa) is included in the expression construct to maintain full functionality .

• Fusion Tags: Consider the addition of purification tags that will facilitate downstream applications while minimally affecting protein function.

• Membrane Integration: As CLDN10 is a transmembrane protein, expression systems must support proper membrane insertion and topology.

• Isoform Selection: Choose the appropriate isoform (CLDN10a or CLDN10b) based on the specific research question, as they have distinct ion selectivity properties .

• Functionality Testing: Verify the functionality of the recombinant protein using electrophysiological methods or permeability assays to ensure that it retains native channel-forming properties.

The recombinant protein produced should be suitable for various applications, including ELISA and Western blot analyses .

How can researchers effectively differentiate between CLDN10 isoforms in experimental settings?

Distinguishing between CLDN10 isoforms is critical for understanding their distinct functional roles. Researchers can employ the following methodological approaches:

• Isoform-Specific PCR:

  • Design primers that target unique regions of CLDN10a and CLDN10b transcripts for quantitative PCR analysis.

  • This approach has successfully demonstrated that CLDN10a transcripts are abundant in the proximal convoluted tubule (PCT), whereas CLDN10b predominates in the thick ascending limb (TAL) .

• Isoform-Specific Antibodies:

  • Develop antibodies that recognize unique epitopes in different CLDN10 isoforms.

  • The generation of monoclonal antibodies with high specificity can be achieved through careful epitope selection and comprehensive validation .

• Functional Characterization:

  • Utilize the different ion selectivity properties of the isoforms for identification:

    • CLDN10a forms anion-selective paracellular channels

    • CLDN10b forms cation-selective paracellular channels

  • Perform permeability assays and electrophysiological measurements to differentiate between these functional properties.

• Expression Pattern Analysis:

  • Map the tissue distribution of different isoforms using a combination of RT-PCR, Western blotting, and immunohistochemistry.

  • Correlate expression patterns with known functional properties of different nephron segments.

• Isoform-Specific Knockdown/Knockout:

  • Design RNA interference or CRISPR-Cas9 targeting strategies specific to each isoform.

  • Validate the specificity of targeting by measuring remaining expression of each isoform.

These approaches, used in combination, provide robust methods for distinguishing between CLDN10 isoforms in experimental settings.

What are the implications of CLDN10 dysregulation in human diseases?

CLDN10 dysregulation has been implicated in several disease states, with significant clinical implications:

• Renal Disorders:

  • Alterations in CLDN10 function may contribute to disorders of magnesium and calcium homeostasis.

  • The mouse knockout model demonstrates that CLDN10 deficiency leads to hypermagnesemia and nephrocalcinosis, suggesting that human CLDN10 mutations might underlie similar conditions .

  • The observed polyuria and altered urinary acidification in CLDN10-deficient models suggest potential roles in disorders of urinary concentration and acid-base balance .

• Cancer Progression:

  • High CLDN10 expression represents an independent prognostic marker for poor cancer-specific survival in clear cell renal cell carcinoma (ccRCC) .

  • CLDN10 promotes multiple malignant phenotypes in ccRCC cells, including enhanced viability, proliferation, migration, and tumor growth .

  • The CLDN10-LAT1 interaction activates mTOR signaling and downstream targets, suggesting potential therapeutic targeting opportunities .

• Epithelial Barrier Dysfunction:

  • Given CLDN10's role in paracellular ion transport, its dysregulation may contribute to disorders characterized by epithelial barrier dysfunction in various tissues.

  • Altered ion selectivity due to CLDN10 mutations or expression changes could disrupt tissue microenvironments and contribute to pathophysiology.

Understanding these disease associations provides researchers with potential translational directions for CLDN10-focused research.

How might the CLDN10-LAT1 interaction be targeted therapeutically in cancer?

The discovery that CLDN10 forms a complex with the amino acid transporter LAT1 to promote malignant phenotypes in clear cell renal cell carcinoma (ccRCC) suggests several therapeutic targeting strategies:

• Disruption of Protein-Protein Interaction:

  • Structural prediction and immunoprecipitation analyses indicate an interaction between the first transmembrane domain of CLDN10 (CLDN10-TM1) and LAT1 .

  • Small molecule inhibitors or peptide mimetics could be designed to interfere with this specific interaction domain.

  • High-throughput screening approaches could identify compounds that selectively disrupt the CLDN10-LAT1 complex without affecting their individual functions in normal tissues.

• Targeting Downstream Signaling Pathways:

  • CLDN10-LAT1 signaling activates the mTOR pathway and expression of downstream targets, including MYC target genes .

  • Combining CLDN10-LAT1 targeting with mTOR inhibitors might provide synergistic anti-cancer effects.

  • Pathway-specific inhibitors could selectively block the oncogenic signaling without disrupting essential cellular functions.

• Antibody-Based Approaches:

  • Development of monoclonal antibodies that specifically recognize the extracellular domains of CLDN10 involved in LAT1 interaction.

  • These antibodies could potentially block the formation of the CLDN10-LAT1 complex or trigger internalization of CLDN10 from the cell surface.

• Gene Therapy Approaches:

  • CRISPR-Cas9 or siRNA-based strategies could be developed to reduce CLDN10 expression specifically in tumor cells.

  • Viral vectors delivering such gene-modifying payloads could be targeted to ccRCC cells using tumor-specific markers.

These therapeutic strategies represent promising avenues for translating the fundamental understanding of CLDN10-LAT1 interaction into novel cancer treatments.

What are the most promising areas for future CLDN10 research?

Several promising research directions emerge from current understanding of CLDN10 biology:

• Structural Biology:

  • Determining the three-dimensional structure of CLDN10 isoforms at atomic resolution would provide insights into its channel-forming properties.

  • Structural analysis of the CLDN10-LAT1 complex would facilitate rational drug design for cancer therapeutics.

  • Investigation of how CLDN10 interacts with other tight junction proteins to form functional barriers.

• Functional Genomics:

  • Comprehensive analysis of CLDN10 genetic variants in human populations and their association with disease phenotypes.

  • Investigation of epigenetic regulation of CLDN10 expression in different tissues and disease states.

  • Single-cell transcriptomic profiling to understand cell-specific expression patterns of CLDN10 isoforms.

• Systems Biology:

  • Integration of CLDN10 function into comprehensive models of epithelial transport.

  • Network analysis of CLDN10 interactors beyond LAT1 to identify additional signaling mechanisms.

  • Computational modeling of how CLDN10 expression changes affect ion homeostasis at tissue and organ levels.

• Translational Research:

  • Development of selective CLDN10-LAT1 interaction inhibitors as potential cancer therapeutics.

  • Investigation of CLDN10 as a biomarker for renal diseases or cancer progression.

  • Exploration of CLDN10-targeting approaches for modulating epithelial permeability in drug delivery applications.

These research directions hold the potential to significantly advance our understanding of CLDN10 biology and its implications in health and disease.

What methodological advances would facilitate CLDN10 research?

Advancing CLDN10 research would benefit from several methodological innovations:

• Improved Imaging Techniques:

  • Super-resolution microscopy to visualize CLDN10 organization within tight junction strands.

  • Live-cell imaging approaches to monitor CLDN10 dynamics during tight junction assembly and remodeling.

  • Correlative light and electron microscopy to link CLDN10 localization with ultrastructural features.

• Advanced Protein Analysis:

  • Cross-linking mass spectrometry to identify interaction interfaces between CLDN10 and binding partners.

  • Hydrogen-deuterium exchange mass spectrometry to analyze conformational changes during channel formation.

  • Cryo-electron microscopy to determine the structure of CLDN10-containing tight junction complexes.

• Functional Assays:

  • Development of high-throughput assays for measuring CLDN10-mediated paracellular ion transport.

  • Microfluidic systems to analyze epithelial barrier function in physiologically relevant conditions.

  • Organ-on-chip models incorporating CLDN10-expressing epithelia for drug screening and disease modeling.

• Genetic Engineering:

  • CRISPR-Cas9 base editing for introducing specific CLDN10 mutations without disrupting the gene.

  • Inducible, tissue-specific gene modification systems for temporal control of CLDN10 expression.

  • Humanized mouse models expressing human CLDN10 variants for translational research.

These methodological advances would provide researchers with powerful tools to address key questions in CLDN10 biology and accelerate progress toward therapeutic applications.