Recombinant Human Potassium channel subfamily K member 3 (KCNK3)

What is KCNK3 and what are its alternative nomenclatures in scientific literature?

KCNK3 (Potassium Channel Subfamily K Member 3) is a pH-sensitive potassium channel that belongs to the two-pore domain potassium channel family. In scientific literature, it is also referred to as TWIK-related acid-sensitive potassium channel 1 (TASK-1) or two-pore-domain K+ (K2P) channel 3.1 (K2P3.1). The gene is designated as KCNK3 while the protein is referred to as KCNK3 . This channel was first described in yeast in 1995 and is characterized by the presence of four transmembrane domains and two pore domains per subunit . Understanding the various nomenclatures is essential when conducting literature searches to ensure comprehensive coverage of relevant research.

What is the structural composition of KCNK3 and how does it affect its function?

KCNK3 has a distinctive structure characterized by four transmembrane domains and two pore domains per subunit . The channel is sensitive to variations in extracellular pH, with amino acid residue H98 serving as the primary binding site for extracellular protons (H+). At physiological pH, KCNK3 is approximately 50% active; it becomes fully inhibited at pH 6.4 and 100% activated at pH 8.0 . The channel functions through dimerization, either with other KCNK3 subunits or with closely related acid-sensitive potassium channels . This structural arrangement allows KCNK3 to contribute to the resting membrane potential in various cell types, particularly human pulmonary artery smooth muscle cells. For experimental studies, it's crucial to consider that manipulating the pH of your experimental environment will directly affect channel activity.

In which tissues is KCNK3 predominantly expressed and what are the implications for tissue-specific research?

KCNK3 exhibits widespread expression throughout the body, with significant presence in multiple tissues. Research has identified expression in:

• Pulmonary artery smooth muscle cells and endothelium

• Right ventricle and both right and left atria

• Adrenal gland (associated with primary aldosteronism)

• Adipose tissue (regulates thermogenesis)

• Brain (associated with the blood-brain barrier)

• T cells (where loss affects effector function)

• Pancreas (associated with insulin secretion)

• Carotid bodies (involved in oxygen and metabolism sensing)

This diverse tissue distribution necessitates careful experimental design when studying KCNK3, particularly when selecting appropriate cell culture models or animal systems. Researchers should consider tissue-specific regulatory mechanisms and potential compensatory pathways when designing knockout or knockdown experiments. For immunohistochemistry studies, proper controls are essential as expression levels vary considerably between tissues.

How do KCNK3 mutations contribute to pulmonary arterial hypertension (PAH), and what are the experimental models to study this relationship?

Loss-of-function mutations in KCNK3 have been identified as drivers of hereditary pulmonary arterial hypertension (PAH) . These mutations affect multiple pathological processes associated with PAH development. The comprehensive experimental approach to studying this relationship includes:

• Patient-derived cell models: Mesenchymal cells differentiated from induced pluripotent stem cells (iPSCs) from PAH patients with KCNK3 mutations provide valuable insights into altered gene expression patterns .

• Animal models: Total knockout KCNK3 mice subjected to different stressors (hypoxic, metabolic, and inflammatory) help determine the mechanisms by which KCNK3 mutation predisposes to PAH .

• Mass cytometry analysis: This technique identifies candidate immune cell types involved in inflammation-mediated PAH in subjects with KCNK3 mutations .

Research findings demonstrate that Kcnk3^fl/fl mice exhibit increased numbers of muscularized vessels and significant increases in CD45+ (pan-circulating) and CD3ε+ (T cell) inflammatory cells . Additionally, cytokine analysis reveals two-fold or greater increases in 14 of 30 cytokines or chemokines, with particularly dramatic increases (~10-fold) in CXCL9 and CXCL10 . These findings suggest that altered immune function plays a crucial role in KCNK3-associated PAH.

What is the relationship between KCNK3 and sleep apnea, and how can researchers effectively model this connection?

Recent research has identified a previously unknown developmental disorder with associated sleep apnea (DDSA) caused by rare de novo gain-of-function mutations in KCNK3 . Unlike the loss-of-function mutations associated with PAH, these gain-of-function mutations cluster near the recently identified lower X-gate of the TASK-1 channel. Affected individuals exhibit global developmental delay, hypotonia, various structural malformations, and sleep apnea .

To effectively model this connection, researchers should consider:

• Exome sequencing: Parent-offspring exome sequencing has been successful in identifying de novo variants. Six specific de novo missense variants have been identified: L122V, L122P, G129D, N133S, L239P, and L241F .

• Structural analysis: The mutations cluster in two regions of the protein: the second transmembrane helix (M2) and the fourth transmembrane helix (M4) .

• Genotype-phenotype correlation studies: The severity of the gain-of-function effect appears to correlate with the clinical severity of the disorder, suggesting a dose-dependent relationship that can be experimentally validated .

This research direction has significant implications for both understanding the fundamental role of KCNK3 in development and potentially developing targeted treatments for individuals with sleep apnea.

How does KCNK3 expression influence cancer progression, particularly in lung adenocarcinoma?

KCNK3 has emerged as a significant factor in lung adenocarcinoma (LUAD) development and progression. Research has demonstrated that KCNK3 is significantly downregulated in LUAD tissues compared to adjacent normal tissues, and this decreased expression correlates with poor patient prognosis .

To investigate the role of KCNK3 in cancer:

• Expression analysis: RNA sequencing, quantitative real-time PCR, western blot, and immunohistochemistry can be used to quantify KCNK3 levels in tumor versus normal tissues .

• Functional assays: Gain-of-function and loss-of-function experiments reveal that KCNK3 regulates both proliferation and glucose metabolism in LUAD cells. Overexpression of KCNK3 suppresses oncogenesis and glycometabolism both in vitro and in vivo .

• Metabolomics analysis: Targeted metabolomics analysis of LUAD cells can identify energy metabolites affected by KCNK3 expression. Research shows that KCNK3-mediated differential metabolites are primarily enriched in the AMPK signaling pathway .

• Mechanistic studies: Western blot and immunofluorescence analyses demonstrate that KCNK3 suppresses proliferation and glucose metabolism by activating the AMPK-TXNIP pathway in LUAD cells .

These findings suggest that KCNK3 may serve as both a prognostic biomarker and a potential therapeutic target in LUAD, highlighting the importance of investigating potassium channels in cancer research.

What mechanisms regulate KCNK3 channel activity, and how can researchers experimentally manipulate these pathways?

KCNK3 activity is regulated through multiple mechanisms that researchers can experimentally manipulate:

• pH modulation: KCNK3 is highly sensitive to extracellular pH, being 50% active at physiological pH, fully inhibited at pH 6.4, and 100% activated at pH 8.0 . Experimental pH adjustment provides a direct method to control channel activity.

• PKC-mediated regulation: Protein kinase C (PKC) downregulates KCNK3 activity through endocytic trafficking . Researchers can use:

  • Phorbol esters to activate PKC

  • Group I metabotropic glutamate receptor (mGluR) activators

  • PKC inhibitors to prevent channel internalization

• 14-3-3β-dependent trafficking: PKC-mediated KCNK3 internalization requires both 14-3-3β and a novel potassium channel endocytic motif . Experimental approaches include:

  • siRNA-mediated depletion of 14-3-3β

  • Mutation of the endocytic motif

  • Protein-protein interaction assays to study KCNK3/14-3-3β binding

• Hypoxia: KCNK3 activity is modulated by oxygen levels, making hypoxia chambers useful tools for studying oxygen-dependent regulation .

• Volatile anesthetics: As the primary target for volatile anesthetics, KCNK3 can be experimentally modulated using these compounds .

Understanding these regulatory mechanisms allows researchers to design precise experimental interventions to manipulate KCNK3 activity in various cellular contexts.

How do intracellular signaling pathways interact with KCNK3, and what techniques can resolve these complex relationships?

KCNK3 interacts with multiple intracellular signaling pathways that influence its function and expression. Key techniques to resolve these interactions include:

• Phosphorylation studies: KCNK3 activity is regulated by phosphorylation events mediated by PKC . Researchers can use:

  • Phospho-specific antibodies

  • Mass spectrometry to identify phosphorylation sites

  • Phosphomimetic and phospho-dead mutants to study functional effects

• Protein-protein interaction analysis:

  • Co-immunoprecipitation to identify binding partners

  • Proximity ligation assays to visualize protein interactions in situ

  • FRET/BRET to study dynamic interactions in living cells

• AMPK signaling pathway analysis: In lung adenocarcinoma, KCNK3 activates the AMPK-TXNIP pathway to suppress proliferation and glucose metabolism . Techniques include:

  • Western blotting for AMPK, p-AMPK, and TXNIP

  • AMPK activity assays

  • Pharmacological AMPK activators/inhibitors in rescue experiments

• Metabolic pathway analysis:

  • Targeted metabolomics to identify altered metabolites

  • Seahorse analysis to measure oxygen consumption and extracellular acidification

  • Glucose uptake and lactate production assays

• Surface expression dynamics:

  • Biotinylation assays to quantify surface vs. internalized channels

  • Live-cell imaging with pH-sensitive GFP tags to track channel trafficking

These techniques provide complementary approaches to dissect the complex regulatory networks controlling KCNK3 function in different cellular contexts.

What are the optimal cellular and animal models for studying KCNK3 function in different physiological contexts?

Selecting appropriate models is crucial for KCNK3 research across different physiological contexts:

Cellular Models:

• Patient-derived iPSCs: Particularly valuable for studying hereditary conditions like PAH. iPSCs can be differentiated into various cell types including:

  • Mesenchymal cells for studying gene expression patterns

  • Pulmonary artery smooth muscle cells to investigate vascular function

  • Cardiomyocytes to study cardiac effects

• Primary cell cultures:

  • Pulmonary artery smooth muscle cells for vascular studies

  • Cerebellar granule neurons for neuronal KCNK3 function

  • T cells for immunological research

• Cancer cell lines: For oncological research, particularly lung adenocarcinoma cell lines with varying KCNK3 expression levels

Animal Models:

• KCNK3 knockout mice: Total knockout models subjected to different stressors (hypoxic, metabolic, inflammatory) help determine how KCNK3 mutation predisposes to diseases like PAH

• Conditional knockout models: Tissue-specific Cre-loxP systems enable targeting KCNK3 deletion to specific tissues of interest

• Knock-in models: For studying specific mutations identified in human patients with gain or loss-of-function variants

• Stress models: Exposing animals to:

  • Hypoxia chambers to model pulmonary hypertension

  • Lipopolysaccharide (LPS) to induce inflammatory responses

  • Metabolic stressors to examine glucose metabolism effects

The choice of model should be guided by the specific aspect of KCNK3 biology under investigation, with consideration for tissue-specific expression patterns and regulatory mechanisms.

What technical challenges exist in the recombinant expression and purification of KCNK3, and how can researchers overcome them?

Recombinant expression and purification of KCNK3 present several technical challenges that researchers must address:

Expression Challenges:

• Membrane protein expression: As a transmembrane protein, KCNK3 can be difficult to express in heterologous systems. Strategies include:

  • Testing multiple expression systems (bacterial, yeast, insect, mammalian)

  • Using specialized strains optimized for membrane protein expression

  • Employing fusion tags that enhance folding and membrane insertion

• Functional assembly: Ensuring proper dimerization and functional assembly requires:

  • Co-expression of partner subunits when studying heterodimers

  • Verification of proper folding using conformation-specific antibodies

  • Electrophysiological validation of expressed channels

Purification Challenges:

• Detergent selection: Critical for maintaining protein stability and function:

  • Mild detergents like DDM, LMNG, or digitonin preserve structure

  • Detergent screening to identify optimal conditions

  • Consideration of lipid-detergent mixed micelles

• Purity assessment: Methods include:

  • SDS-PAGE and Western blotting

  • Size-exclusion chromatography

  • Mass spectrometry for definitive identification

• Functional validation: Crucial to ensure purified protein retains native properties:

  • Reconstitution into liposomes or nanodiscs for functional studies

  • Electrophysiological recordings to confirm channel properties

  • pH sensitivity assays to verify characteristic responses

Structural Analysis Considerations:

• Cryo-EM preparation: For structural studies, considerations include:

  • Grid preparation optimization for membrane proteins

  • Detergent selection compatible with cryo-EM

  • Antibody fragment co-complexation to increase particle size

• Crystallization: If pursuing X-ray crystallography:

  • Lipidic cubic phase methods often succeed for membrane proteins

  • Construct optimization to remove disordered regions

  • Crystal optimization screening

Successful recombinant expression requires methodical optimization of each step in the process, with continual functional validation to ensure the expressed protein accurately represents native KCNK3.

How can researchers effectively conduct KCNK3 mutation analysis in clinical samples, and what are the key considerations for data interpretation?

Conducting KCNK3 mutation analysis in clinical samples requires a systematic approach:

Sample Collection and Processing:

• Sample types:

  • Blood samples for germline mutations

  • Tissue biopsies for somatic mutations in diseases like cancer

  • Preservation methods critical for maintaining DNA/RNA quality

• Nucleic acid extraction:

  • Optimization for high-quality DNA/RNA from limited clinical material

  • Quantification and quality assessment before sequencing

Sequencing Approaches:

• Targeted sequencing: For focused analysis of KCNK3 and related genes

  • Custom panels including commonly mutated regions

  • Deep sequencing coverage (>500×) to detect low-frequency variants

• Whole exome sequencing: Particularly valuable for identifying novel variants

  • Parent-offspring trios essential for identifying de novo mutations

  • Coverage of 100× or greater recommended

• RNA sequencing: To detect expression changes and splicing variants

  • Paired with DNA sequencing to correlate genotype with expression

Data Analysis and Interpretation:

• Variant calling pipelines:

  • Use multiple algorithms to increase detection confidence

  • Filtering strategies to prioritize pathogenic variants

• Pathogenicity prediction:

  • In silico tools (SIFT, PolyPhen, CADD) to predict functional impact

  • Structural modeling to understand mutation effects on protein function

• Variant classification:

  • ACMG guidelines for systematic classification

  • Consideration of variant location (e.g., clustering in transmembrane domains)

  • Comparison with known pathogenic variants

Functional Validation:

• Electrophysiological studies: To determine channel function alterations

  • Patch-clamp recording to measure current changes

  • pH sensitivity assessment for acid-sensitive function

• Cell-based assays:

  • Proliferation, migration, metabolism effects in disease-relevant cells

  • Rescue experiments to confirm causality

Key considerations for data interpretation include distinguishing pathogenic from benign variants, correlating mutation location with functional effects, and considering the heterozygous versus homozygous state of mutations in the context of disease mechanisms.

What techniques are most effective for studying KCNK3's role in immune function, and how should researchers design experiments to investigate this relationship?

KCNK3 has emerging roles in immune function that require specialized techniques for investigation:

Immune Cell Phenotyping:

• Mass cytometry (CyTOF): Provides high-dimensional analysis of immune cell populations

  • Enables identification of specific immune cell subsets affected by KCNK3 mutations

  • Appropriate panel design should include markers for major immune lineages and activation states

• Flow cytometry: For quantification and isolation of immune populations

  • Multicolor panels to identify specific populations (CD45+, CD3ε+)

  • Sorting capabilities for downstream functional assays

Functional Immune Assays:

• T cell function assessment:

  • Proliferation assays following stimulation

  • Cytokine production measurement via ELISA or intracellular staining

  • Cytotoxicity assays for effector function evaluation

• Inflammatory response characterization:

  • Cytokine/chemokine profiling via multiplex assays or "dot blot" arrays

  • Quantification of multiple inflammatory mediators simultaneously

In Vivo Inflammation Models:

• LPS challenge model: Particularly relevant as research shows KCNK3^fl/fl mice have enhanced sensitivity to LPS

  • Low-dose LPS administration (appropriate dosing critical)

  • Monitoring of inflammatory response parameters

  • Tissue collection for histology and molecular analysis

• Tissue analysis:

  • Immunofluorescence for inflammatory cell infiltration (CD45+, CD3ε+)

  • Histological assessment of tissue damage

  • RNA-seq for global transcriptional responses

Experimental Design Considerations:

• Controls: Include both:

  • Vehicle-treated wild-type and KCNK3-deficient animals

  • LPS-treated wild-type animals for comparison

• Time course: Capture both acute and resolution phases of inflammation

• Dose-response: Determine threshold for inflammatory responses

• Sex considerations: Include both male and female animals to assess sex-specific differences

• Data analysis: Use appropriate statistical methods for cytokine arrays with multiple comparisons

This research approach will help elucidate the mechanisms by which KCNK3 regulates immune function, potentially leading to therapeutic strategies for KCNK3-associated inflammatory conditions.

What approaches show promise for therapeutic targeting of KCNK3 in diseases like PAH and cancer, and what preclinical validation strategies are recommended?

Therapeutic targeting of KCNK3 shows considerable promise for treating conditions including PAH and cancer:

Therapeutic Approaches:

• Channel activators for loss-of-function conditions (PAH):

  • Development of small molecules that enhance KCNK3 activity

  • Screening of compound libraries against recombinant KCNK3

  • Structure-based drug design targeting known regulatory sites

• Channel inhibitors for gain-of-function conditions:

  • Potential application in developmental disorders with sleep apnea

  • Targeting of the specific conformational changes caused by gain-of-function mutations

• Gene therapy approaches:

  • Viral vector delivery of functional KCNK3 to affected tissues

  • CRISPR-based correction of pathogenic mutations

  • RNA therapeutics to modulate expression levels

• Targeting downstream pathways:

  • AMPK pathway modulators for cancer applications

  • Anti-inflammatory agents for immune-mediated effects in PAH

Preclinical Validation Strategies:

Research indicates that KCNK3's role in multiple pathways—including inflammatory responses in PAH and the AMPK-TXNIP pathway in cancer —provides diverse targeting opportunities. The development of isoform-specific modulators with optimal tissue distribution profiles represents a key challenge in advancing these therapeutic approaches to clinical application.

How can researchers effectively correlate KCNK3 expression or mutation status with clinical outcomes, and what biomarker development strategies should be considered?

Correlating KCNK3 status with clinical outcomes requires rigorous methodological approaches and comprehensive biomarker development:

Clinical Correlation Approaches:

• Patient cohort studies:

  • Prospective collection of samples with comprehensive clinical data

  • Longitudinal follow-up to capture disease progression and outcomes

  • Statistical power calculations to ensure adequate sample size

• Expression analysis methodologies:

  • RNA-seq or qPCR for mRNA quantification

  • Immunohistochemistry with validated antibodies for protein detection

  • Digital pathology with automated scoring for objective quantification

• Mutation analysis platforms:

  • Targeted sequencing panels for known pathogenic regions

  • Whole exome sequencing for novel variant discovery

  • Functional classification of variants using in silico and in vitro methods

Biomarker Development Strategy:

• Discovery phase:

  • Comprehensive omics approach (genomics, transcriptomics, proteomics)

  • Identification of KCNK3-associated signature in accessible samples (blood, urine)

  • Machine learning algorithms to identify predictive patterns

• Validation phase:

  • Independent cohort testing with predetermined endpoints

  • Assessment of sensitivity, specificity, PPV, and NPV

  • Comparison with existing clinical biomarkers

• Clinical assay development:

  • Standardization of protocols for clinical laboratory implementation

  • Determination of reference ranges and cutoff values

  • Quality control measures for reproducibility

Clinical Outcome Measures:

For PAH:

• Hemodynamic parameters (pulmonary vascular resistance, mean pulmonary arterial pressure)

• Functional capacity (6-minute walk distance, WHO functional class)

• Right ventricular function (imaging parameters)

• Survival and time to clinical worsening

For cancer (particularly LUAD):

Integration with Clinical Decision Making:

• Development of algorithms incorporating KCNK3 biomarker status with other clinical parameters

• Risk stratification models to guide treatment selection

• Predictive biomarkers for response to specific therapies

Research has already demonstrated significant correlations between KCNK3 downregulation and poor prognosis in lung adenocarcinoma , suggesting its potential utility as a prognostic biomarker. For PAH, the identification of specific KCNK3 mutations in patients provides opportunity for genetic testing and risk stratification . Continued refinement of these approaches will enhance the clinical utility of KCNK3 as both a diagnostic and prognostic biomarker across multiple disease contexts.

What emerging technologies and approaches might advance our understanding of KCNK3 biology in the next decade?

Several cutting-edge technologies and approaches are poised to transform KCNK3 research:

• Single-cell technologies:

  • Single-cell RNA sequencing to resolve cell-specific KCNK3 expression patterns

  • Single-cell proteomics to understand protein-level regulation

  • Spatial transcriptomics to map KCNK3 expression in tissue context
    These approaches will reveal heterogeneity in KCNK3 expression and function across cell populations that is masked in bulk tissue analyses.

• Advanced structural biology:

  • Cryo-EM for high-resolution structures of KCNK3 in different conformational states

  • Molecular dynamics simulations to understand channel gating mechanisms

  • In situ structural studies to visualize channels in native membranes
    These methods will provide unprecedented insights into how mutations affect channel structure and function.

• Genome editing technologies:

  • Prime editing for precise correction of patient mutations

  • Base editing for targeted nucleotide changes

  • CRISPR activation/interference for endogenous gene modulation

  • Tissue-specific in vivo editing to model disease mutations
    These approaches will enable more precise disease modeling and potential therapeutic development.

• Organoid and microphysiological systems:

  • Patient-derived lung organoids to study KCNK3 in PAH

  • Heart-on-chip models for cardiac electrophysiology

  • Vascular organoids for studying pulmonary vascular remodeling
    These systems provide physiologically relevant models bridging the gap between cell culture and animal studies.

• Multi-omics integration:

  • Combined analysis of genomics, transcriptomics, proteomics, and metabolomics data

  • Network biology approaches to understand KCNK3's position in regulatory networks

  • Systems biology modeling of KCNK3-dependent processes
    These integrative approaches will reveal how KCNK3 functions within complex biological systems.

• Advanced in vivo imaging:

  • Genetically encoded voltage indicators to visualize KCNK3 activity in living tissues

  • Intravital microscopy to observe cellular dynamics in intact organisms

  • PET ligands for non-invasive monitoring of KCNK3 expression
    These technologies will enable real-time visualization of KCNK3 function in physiological contexts.

The integration of these emerging technologies will lead to a more comprehensive understanding of KCNK3 biology, potentially revealing new therapeutic targets and biomarkers for KCNK3-associated diseases.

What key unresolved questions about KCNK3 should researchers prioritize, and what methodological approaches might address these knowledge gaps?

Several critical questions about KCNK3 remain unresolved and warrant prioritization:

• Tissue-specific consequences of KCNK3 mutations

  Key questions:

  • Why do loss-of-function mutations primarily affect the pulmonary vasculature despite widespread expression?

  • How do gain-of-function mutations cause developmental disorders and sleep apnea?

  Methodological approaches:

  • Tissue-specific conditional knockout models

  • Single-cell transcriptomics across multiple tissues from KCNK3 mutant models

  • Comparative physiology studies between vascular beds

  • Patient-derived iPSCs differentiated into multiple lineages

• Mechanistic links between KCNK3 and inflammation

  Key questions:

  • How does KCNK3 regulate inflammatory cell recruitment and activation?

  • What mediates the dramatic increase in cytokines and chemokines in KCNK3-deficient models?

  Methodological approaches:

  • Cell-specific knockout of KCNK3 in immune populations

  • Chimeric mouse models to distinguish intrinsic vs. extrinsic effects

  • High-dimensional immune phenotyping with trajectory analysis

  • Mechanistic studies of KCNK3's role in inflammatory signaling pathways

• KCNK3's role in metabolism

  Key questions:

  • How does KCNK3 regulate the AMPK-TXNIP pathway and glucose metabolism?

  • Is metabolic dysfunction a common mechanism across KCNK3-associated diseases?

  Methodological approaches:

  • Metabolic flux analysis in KCNK3-manipulated cells

  • In vivo metabolic phenotyping of KCNK3 models

  • Mechanistic studies of KCNK3-AMPK interaction

  • Comparative metabolomics across disease models

• Pharmacological modulation strategies

  Key questions:

  • What are the optimal sites for therapeutic targeting of KCNK3?

  • How can tissue-specific modulation be achieved?

  Methodological approaches:

  • Structure-guided drug design based on cryo-EM structures

  • High-throughput screening with electrophysiological readouts

  • Tissue-specific drug delivery systems

  • Allosteric modulator development

• Environmental and epigenetic influences

  Key questions:

  • How do environmental factors modify KCNK3 expression and function?

  • What epigenetic mechanisms regulate KCNK3 in development and disease?

  Methodological approaches:

  • Exposure studies in KCNK3 model systems

  • Epigenetic profiling of the KCNK3 locus across tissues and conditions

  • Chromatin conformation studies to identify regulatory elements

  • DNA methylation and histone modification analysis

Addressing these knowledge gaps will require interdisciplinary approaches combining traditional methods with emerging technologies. The integration of basic science findings with clinical observations will be essential for translating KCNK3 research into therapeutic advances for associated diseases such as PAH, developmental disorders with sleep apnea, and cancer.