C1QTNF9 Human

What is the molecular structure and composition of human C1QTNF9?

Human C1QTNF9 (also known as CTRP9) is an approximately 40 kDa glycoprotein that belongs to the C1q and TNF-related protein family. Like all members of this protein family, CTRP9 consists of four distinct domains:

• An N-terminal signal peptide

• A domain with one or more conserved Cys residues

• A collagenous domain containing variable Gly-X-Y repeats that can be hydroxylated

• A C-terminal globular C1q domain

The protein circulates in the bloodstream as homotrimers and higher-order multimers. Additionally, it can form heterotrimers with adiponectin, which may contribute to its diverse physiological functions . The human CTRP9 protein spans from Asn16 to Pro333 in its mature form, with 85% amino acid sequence identity shared with its mouse and rat orthologs .

The collagenous region of CTRP9 contains multiple hydroxylated proline residues, which are important for the protein's structural stability and function . This post-translational modification is characteristic of collagen-like domains and affects protein folding and intermolecular interactions.

What is the tissue expression pattern of human C1QTNF9?

In mouse models, CTRP9 has been detected in multiple tissues beyond adipose tissue, including:

• Heart

• Lung

• Muscle

• Kidney

• Testis

• Lymph node

• Smooth muscle

• Prostate

• Thymus

• Uterus

Interestingly, LacZ staining in myocardial sections of CTRP9 knockout mice (with a lacZ cassette replacing exons 1-3) showed exclusive expression in capillary and venous endothelial cells within the heart . This suggests cell-specific expression patterns within cardiac tissue.

The Human Protein Atlas provides a comprehensive overview of C1QTNF9 expression across 44 different human tissues, though the specific expression levels in each tissue are not detailed in the search results .

How can researchers detect and quantify C1QTNF9 in experimental settings?

Several methodological approaches can be employed for detecting and quantifying C1QTNF9 in research contexts:

• Western Blot Analysis: Using specific antibodies such as Sheep Anti-Human CTRP9/C1qTNF9 Antigen Affinity-purified Polyclonal Antibody. Under reducing conditions, CTRP9 appears as a band of approximately 42 kDa on immunoblots. PVDF membranes are recommended, along with appropriate secondary antibodies (e.g., HRP-conjugated Anti-Sheep IgG) .

• Quantitative Real-Time PCR (qRT-PCR): For analyzing CTRP9 mRNA expression levels in tissues. This technique has been used to demonstrate that CTRP9 is significantly upregulated in hypertrophied mouse hearts (after aortic constriction) and in hypertrophied human hearts (24±4-fold versus healthy human myocardium) .

• LacZ Staining: In transgenic models with reporter genes, LacZ staining can be used to visualize the cellular localization of CTRP9 expression, as demonstrated in C1qtnf9 knockout mice .

• Recombinant Protein Standards: Commercially available recombinant human CTRP9 protein can be used as standards for quantification assays. These are typically available with or without carrier proteins such as BSA .

• ELISA: Though not explicitly mentioned in the search results, enzyme-linked immunosorbent assays would be appropriate for quantifying CTRP9 in serum or tissue samples.

When working with CTRP9 protein samples, it's crucial to avoid repeated freeze-thaw cycles, and proper storage conditions (-20 to -70°C) should be maintained to preserve protein integrity .

What signaling pathways are activated by C1QTNF9 in cardiac and metabolic tissues?

CTRP9 activates several crucial signaling pathways that mediate its cardioprotective and metabolic effects:

• AMPK Pathway: CTRP9 stimulates the phosphorylation of adenosine monophosphate (AMP)-dependent kinase (AMPK) in mouse models. This activation appears to be essential for its cardioprotective effects following acute myocardial infarction .

• Akt Signaling: CTRP9 activates protein kinase B (Akt), which plays a role in cell survival and metabolism. This pathway is particularly important in preventing cardiomyocyte death during ischemia/reperfusion injury .

• eNOS Activation: In mice, CTRP9 has been shown to stimulate phosphorylation of endothelial nitric oxide synthase (eNOS), which may contribute to vascular function .

• Protein Kinase A Signaling: Some studies suggest that CTRP9 may also mediate its protective effects through protein kinase A activation .

• mTOR Signaling Inhibition: Mechanistically, CTRP9 has been found to inhibit prohypertrophic mTOR signaling in cardiac myocytes, which explains its anti-hypertrophic effects. siRNA-mediated downregulation of mTOR in neonatal rat cardiomyocytes abolished the anti-hypertrophic effect of CTRP9 .

• Receptor Interaction: CTRP9 likely exerts its effects by binding to the adiponectin receptor 1 (AdipoR1). siRNA-mediated downregulation of AdipoR1 in cardiomyocytes abolished the anti-hypertrophic effect of CTRP9, confirming the importance of this receptor in CTRP9 signaling .

Understanding these signaling pathways is crucial for researchers seeking to exploit CTRP9's therapeutic potential in cardiac and metabolic diseases.

What role does C1QTNF9 play in diabetic cardiomyopathy pathophysiology?

CTRP9 exerts significant protective effects against diabetic cardiomyopathy through multiple mechanisms:

• Prevention of Diastolic Dysfunction: CTRP9 knockout mice exhibit left ventricular diastolic dysfunction after 12 weeks of high-fat diet (HFD) feeding. Conversely, overexpression of CTRP9 in the heart rescues HFD-induced diastolic dysfunction, demonstrating its protective role .

• Regulation of Cardiac Metabolism: Through dynamic 18F-fluoro-deoxyglucose (FDG) positron-emission tomography (PET) imaging, researchers have shown that CTRP9 is necessary to prevent cardiac insulin resistance and to mediate myocardial glucose uptake .

• Anti-inflammatory Effects: RNA sequencing reveals an upregulation of genes related to immune response activation in CTRP9 knockout mice, accompanied by increased leukocyte count in the heart. Cardiac CTRP9 overexpression counteracts inflammation, which may contribute to ameliorating diabetic cardiomyopathy .

• Protection from Cardiomyocyte Death: Administration of globular recombinant CTRP9 (lacking large parts of the N-terminal region) prevents cardiomyocyte death during ischemia/reperfusion injury in both normal and diabetic mice .

• Beneficial Effects in Post-MI Remodeling: CTRP9 has been shown to provide protection in remodeling after myocardial infarction, which is particularly relevant for diabetic patients who have a higher incidence of heart failure after MI .

These findings suggest that therapeutic strategies aimed at increasing CTRP9 expression or activity could be beneficial for preventing or treating diabetic cardiomyopathy.

What experimental models are most appropriate for studying C1QTNF9 function?

Several experimental models have been successfully employed to study CTRP9 function:

• Transgenic Mouse Models:

  • CTRP9 knockout mice (KO): Created by replacing exons 1-3 of the gene with a lacZ cassette. These mice exhibit enhanced hypertrophic response after two weeks of transverse aortic constriction (TAC) and develop left ventricular diastolic dysfunction after 12 weeks of HFD feeding .

  • Heterozygous knockout mice (HETs): Useful for dose-dependent studies of CTRP9 function .

  • Systemic CTRP9 overexpression mice: These mice are resistant to high-fat diet-induced obesity, demonstrating CTRP9's metabolic effects .

• Diet-Induced Models:

  • High-fat diet feeding (60 kcal-% fat) for 12 weeks in C57BL/6J mice serves as a model for metabolic dysfunction and diabetic cardiomyopathy .

• Cardiac Pressure Overload Models:

  • Transverse aortic constriction (TAC) for 2 weeks induces cardiac hypertrophy, with CTRP9 expression significantly upregulated in these hypertrophied hearts .

• In Vitro Models:

  • Neonatal rat cardiomyocytes stimulated with phenylephrine (PE) to induce hypertrophy, with CTRP9 administration strongly inhibiting this hypertrophic response .

  • siRNA-mediated downregulation of CTRP9, AdipoR1, or mTOR in cardiomyocytes to study molecular mechanisms .

• Viral Vector-Mediated Gene Transfer:

  • Adeno-associated virus (AAV9) vector expressing CTRP9 under the control of the TnT promoter for cardiac-specific overexpression .

  • Adenoviral overexpression of CTRP9 in cell culture systems .

• Administration of Recombinant Protein:

  • Recombinant CTRP9 (particularly the globular form lacking parts of the N-terminal region) has been used to study acute effects in various models .

These diverse experimental approaches provide researchers with multiple options for investigating CTRP9 function in different physiological and pathological contexts.

How does C1QTNF9 interact with obesity and metabolic syndrome?

CTRP9 demonstrates significant interactions with obesity and metabolic syndrome:

• Inverse Correlation with Metabolic Syndrome: In humans, CTRP9 serum levels have been shown to inversely correlate with metabolic syndrome, suggesting its potential role as a biomarker or therapeutic target .

• Protection Against Diet-Induced Obesity: Systemic overexpression of CTRP9 in transgenic mice protects them from weight gain when fed a high-fat diet. This suggests that CTRP9 plays a role in energy homeostasis and metabolism .

• Age-Related Obesity in CTRP9 Deficiency: Recent studies indicate that the absence of CTRP9 in knockout mice triggers obesity in advanced age, further supporting its role in metabolic regulation .

• Protection from Metabolic Dysfunction: Systemic overexpression of CTRP9 appears to protect from not only weight gain but also broader metabolic dysfunction, suggesting effects on multiple metabolic pathways .

• Glucose Homeostasis: CTRP9 plays a role in glucose homeostasis, potentially through its effects on insulin sensitivity. CTRP9 knockout mice exhibited cardiac insulin resistance, while CTRP9 overexpression improved myocardial glucose uptake .

These findings position CTRP9 as a potential therapeutic target for obesity and metabolic syndrome, with possible applications in preventing associated cardiovascular complications.

What methodological approaches are effective for manipulating C1QTNF9 levels in experimental settings?

Researchers have successfully employed several strategies to manipulate CTRP9 levels:

• Genetic Modification:

  • Generation of knockout mice through replacement of exons 1-3 with a lacZ cassette .

  • Creation of transgenic mice with systemic CTRP9 overexpression .

• Viral Vector-Mediated Gene Transfer:

  • Adeno-associated virus (AAV9) expressing CTRP9 under the control of the cardiac-specific TnT promoter for targeted overexpression in the heart. Typical dosage: 1 × 10^12 vg (vector genomes) injected intravenously via tail veins .

  • Adenoviral vectors for in vitro overexpression in cell culture systems .

• RNA Interference:

  • siRNA-mediated downregulation of CTRP9 has been used to study its function in cardiomyocytes, with this approach shown to aggravate cardiomyocyte growth in response to phenylephrine stimulation in vitro .

• Recombinant Protein Administration:

  • Application of globular recombinant CTRP9 (lacking large parts of the N-terminal region) to prevent cardiomyocyte death during ischemia/reperfusion injury and in remodeling after myocardial infarction .

  • Commercially available recombinant human CTRP9 protein (spanning Asn16-Pro333) can be used for experimental studies, available with or without carrier proteins such as BSA .

• Pharmacological Modulation:

  • While not explicitly mentioned in the search results, targeting pathways that regulate CTRP9 expression or its downstream signaling could be an alternative approach.

Each of these approaches has specific advantages and limitations depending on the research question and experimental context. For chronic studies, genetic models or viral vector-mediated expression may be preferable, while acute interventions might benefit from recombinant protein administration or siRNA approaches.