Comprehensive ECG reference intervals in C57BL/6N substrains provide a generalizable guide for cardiac electrophysiology studies in mice.

Reference ranges provide a powerful tool for diagnostic decision-making in clinical medicine and are enormously valuable for understanding normality in pre-clinical scientific research that uses in vivo models. As yet, there are no published reference ranges for electrocardiography (ECG) in the laboratory mouse. The first mouse-specific reference ranges for the assessment of electrical conduction are reported herein generated from an ECG dataset of unprecedented scale. International Mouse Phenotyping Consortium data from over 26,000 conscious or anesthetized C57BL/6N wildtype control mice were stratified by sex and age to develop robust ECG reference ranges. Interesting findings include that heart rate and key elements from the ECG waveform (RR-, PR-, ST-, QT-interval, QT corrected, and QRS complex) demonstrate minimal sexual dimorphism. As expected, anesthesia induces a decrease in heart rate and was shown for both inhalation (isoflurane) and injectable (tribromoethanol) anesthesia. In the absence of pharmacological, environmental, or genetic challenges, we did not observe major age-related ECG changes in C57BL/6N-inbred mice as the differences in the reference ranges of 12-week-old compared to 62-week-old mice were negligible. The generalizability of the C57BL/6N substrain reference ranges was demonstrated by comparison with ECG data from a wide range of non-IMPC studies. The close overlap in data from a wide range of mouse strains suggests that the C57BL/6N-based reference ranges can be used as a robust and comprehensive indicator of normality. We report a unique ECG reference resource of fundamental importance for any experimental study of cardiac function in mice.

Physiological Expression of AMPKγ2RG Mutation Causes Wolff-Parkinson-White Syndrome and Induces Kidney Injury in Mice.

Mutations of the AMP-activated kinase gamma 2 subunit (AMPKγ2), N488I (AMPKγ2NI) and R531G (AMPKγ2RG), are associated with Wolff-Parkinson-White (WPW) syndrome, a cardiac disorder characterized by ventricular pre-excitation in humans. Cardiac-specific transgenic overexpression of human AMPKγ2NI or AMPKγ2RG leads to constitutive AMPK activation and the WPW phenotype in mice. However, overexpression of these mutant proteins also caused profound, non-physiological increase in cardiac glycogen, which might abnormally alter the true phenotype. To investigate whether physiological levels of AMPKγ2NI or AMPKγ2RG mutation cause WPW syndrome and metabolic changes in other organs, we generated two knock-in mouse lines on the C57BL/6N background harboring mutations of human AMPKγ2NI and AMPKγ2RG, respectively. Similar to the reported phenotypes of mice overexpressing AMPKγ2NI or AMPKγ2RG in the heart, both lines developed WPW syndrome and cardiac hypertrophy; however, these effects were independent of cardiac glycogen accumulation. Compared with AMPKγ2WT mice, AMPKγ2NI and AMPKγ2RG mice exhibited reduced body weight, fat mass, and liver steatosis when fed with a high fat diet (HFD). Surprisingly, AMPKγ2RG but not AMPKγ2NI mice fed with an HFD exhibited severe kidney injury characterized by glycogen accumulation, inflammation, apoptosis, cyst formation, and impaired renal function. These results demonstrate that expression of AMPKγ2NI and AMPKγ2RG mutations at physiological levels can induce beneficial metabolic effects but that this is accompanied by WPW syndrome. Our data also reveal an unexpected effect of AMPKγ2RG in the kidney, linking lifelong constitutive activation of AMPK to a potential risk for kidney dysfunction in the context of an HFD.

HRAS germline mutations impair LKB1/AMPK signaling and mitochondrial homeostasis in Costello syndrome models.

Germline mutations that activate genes in the canonical RAS/MAPK signaling pathway are responsible for rare human developmental disorders known as RASopathies. Here, we analyzed the molecular determinants of Costello syndrome (CS) using a mouse model expressing HRAS p.G12S, patient skin fibroblasts, hiPSC-derived human cardiomyocytes, a HRAS p.G12V zebrafish model, and human fibroblasts expressing lentiviral constructs carrying HRAS p.G12S or HRAS p.G12A mutations. The findings revealed alteration of mitochondrial proteostasis and defective oxidative phosphorylation in the heart and skeletal muscle of CS mice that were also found in the cell models of the disease. The underpinning mechanisms involved the inhibition of the AMPK signaling pathway by mutant forms of HRAS, leading to alteration of mitochondrial proteostasis and bioenergetics. Pharmacological activation of mitochondrial bioenergetics and quality control restored organelle function in HRAS p.G12A and p.G12S cell models, reduced left ventricle hypertrophy in CS mice, and diminished the occurrence of developmental defects in the CS zebrafish model. Collectively, these findings highlight the importance of mitochondrial proteostasis and bioenergetics in the pathophysiology of RASopathies and suggest that patients with CS may benefit from treatment with mitochondrial modulators.

Extensive identification of genes involved in congenital and structural heart disorders and cardiomyopathy.

Clinical presentation of congenital heart disease is heterogeneous, making identification of the disease-causing genes and their genetic pathways and mechanisms of action challenging. By using in vivo electrocardiography, transthoracic echocardiography and microcomputed tomography imaging to screen 3,894 single-gene-null mouse lines for structural and functional cardiac abnormalities, here we identify 705 lines with cardiac arrhythmia, myocardial hypertrophy and/or ventricular dilation. Among these 705 genes, 486 have not been previously associated with cardiac dysfunction in humans, and some of them represent variants of unknown relevance (VUR). Mice with mutations in Casz1, Dnajc18, Pde4dip, Rnf38 or Tmem161b genes show developmental cardiac structural abnormalities, with their human orthologs being categorized as VUR. Using UK Biobank data, we validate the importance of the DNAJC18 gene for cardiac homeostasis by showing that its loss of function is associated with altered left ventricular systolic function. Our results identify hundreds of previously unappreciated genes with potential function in congenital heart disease and suggest causal function of five VUR in congenital heart disease.

Ultrasound-Guided Approaches to Improve Orthotopic Mouse Xenograft Models for Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) is the second leading cause of cancer death worldwide. While curative approaches for early stage HCC exist, effective treatment options for advanced HCC are lacking. Furthermore, there are no efficient chemopreventive strategies to limit HCC development once cirrhosis is established. One challenge for drug development is unsatisfactory animal models. In this article, we describe an orthotopic xenograft mouse model of human liver cancer cell lines through image-guided injection into the liver. This technique provides a less invasive yet highly efficient approach to engraft human HCC into mouse liver. Similarly, image-guided injections are used to deliver chemotherapeutics locally, enabling reduction in potential systemic adverse effects, while reducing the required dose for a therapeutic effect. In summary, this image-guided strategy provides a novel and convenient approach to improve current HCC mouse models. © 2019 The Authors. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Non-invasive quantitative imaging of hepatocellular carcinoma growth in mice by micro-CT using liver-targeted iodinated nano-emulsions.

Hepatocellular carcinoma (HCC) is the only cancer for which non-invasive diagnosis is recognized by international guidelines. Contrast agent free ultrasound imaging, computed tomography (CT) and/or magnetic resonance imaging are techniques used for early detection and confirmation. Clinical evidence depicts that CT is 30% less precise as compared to MRI for detection of small tumors. In our work, we have reported some novel tools that can enhance the sensitivity and precision of CT applied to preclinical research (micro-CT). Our system, containing non-toxic nano-droplets loaded with iodine has high contrasting properties, liver and hepatocyte specificity and strong liver persistence. Micro-CT was performed on HCC model implanted in nude mice by intrahepatic injection. Contrast agent was administrated intravenously. This method allows an unprecedented high precision of detection, quantitative measurement of tumor volume and quantitative follow-up of the tumor development.

Multimodal imaging of a humanized orthotopic model of hepatocellular carcinoma in immunodeficient mice.

The development of multimodal strategies for the treatment of hepatocellular carcinoma requires tractable animal models allowing for advanced in vivo imaging. Here, we characterize an orthotopic hepatocellular carcinoma model based on the injection of luciferase-expressing human hepatoma Huh-7 (Huh-7-Luc) cells in immunodeficient mice. Luciferase allows for an easy repeated monitoring of tumor growth by in vivo bioluminescence. The intrahepatic injection was more efficient than intrasplenic or intraportal injection in terms of survival, rate of orthotopic engraftment, and easiness. A positive correlation between luciferase activity and tumor size, evaluated by Magnetic Resonance Imaging, allowed to define the endpoint value for animal experimentation with this model. Response to standard of care, sorafenib or doxorubicin, were similar to those previously reported in the literature, with however a strong toxicity of doxorubicin. Tumor vascularization was visible by histology seven days after Huh-7-Luc transplantation and robustly developed at day 14 and day 21. The model was used to explore different imaging modalities, including microtomography, probe-based confocal laser endomicroscopy, full-field optical coherence tomography, and ultrasound imaging. Tumor engraftment was similar after echo-guided intrahepatic injection as after laparotomy. Collectively, this orthotopic hepatocellular carcinoma model enables the in vivo evaluation of chemotherapeutic and surgical approaches using multimodal imaging.