Non-invasive in vivo imaging of UCP1 expression in live mice via near-infrared fluorescent protein iRFP720

Use of CIDEA Reporter Mouse Model for Screening Thermogenic Fat-Activating Drugs

Excessive fat accumulation is a risk factor for metabolic diseases. Activating non-shivering thermogenesis in adipose tissue increases energy expenditure and potentially reverses obesity-related metabolic dysfunctions. While brown/beige adipocytes specialize in non-shivering thermogenesis and catabolic lipid metabolism, thermogenic stimuli and pharmacological intervention can induce the recruitment and metabolic activation of these cell types in adipose tissue. Thus, these adipocytes are attractive therapeutic targets to combat obesity, and there is an increasing need for efficient screening strategies for thermogenic drugs. Cell death-inducing DNA fragmentation factor-like effector A (CIDEA) is a well-known marker of the thermogenic capacity of brown and beige adipocytes. We recently developed a CIDEA reporter mouse model that expresses multicistronic mRNAs encoding CIDEA, luciferase 2, and tdTomato proteins under endogenous Cidea promoter control. Here, we introduce the CIDEA reporter model system as a tool for in vitro and in vivo screening of drug candidate molecules with thermogenic effects and provide a detailed protocol to monitor CIDEA reporter expression.

Transgenic mice encoding modern imaging probes: Properties and applications

Modern biology is increasingly reliant on optical technologies, including visualization and longitudinal monitoring of cellular processes. The major limitation here is the availability of animal models to track the molecules and cells in their natural environment in vivo. Owing to the integrity of the studied tissue and the high stability of transgene expression throughout life, transgenic mice encoding fluorescent proteins and biosensors represent unique tools for in vivo studies in norm and pathology. We review the strategies for targeting probe expression in specific tissues, cell subtypes, or cellular compartments. We describe the application of transgenic mice expressing fluorescent proteins for tracking protein expression patterns, apoptotic events, tissue differentiation and regeneration, neurogenesis, tumorigenesis, and cell fate mapping. We overview the possibilities of functional imaging of secondary messengers, neurotransmitters, and ion fluxes. Finally, we provide the rationale and perspectives for the use of transgenic imaging probes in translational research and drug discovery.

Optogenetic manipulation and photoacoustic imaging using a near-infrared transgenic mouse model

Optogenetic manipulation and optical imaging in the near-infrared range allow non-invasive light-control and readout of cellular and organismal processes in deep tissues in vivo. Here, we exploit the advantages of Rhodopseudomonas palustris BphP1 bacterial phytochrome, which incorporates biliverdin chromophore and reversibly photoswitches between the ground (740-800 nm) and activated (620-680 nm) states, to generate a loxP-BphP1 transgenic mouse model. The mouse enables Cre-dependent temporal and spatial targeting of BphP1 expression in vivo. We validate the optogenetic performance of endogenous BphP1, which in the activated state binds its engineered protein partner QPAS1, to trigger gene transcription in primary cells and living mice. We demonstrate photoacoustic tomography of BphP1 expression in different organs, developing embryos, virus-infected tissues and regenerating livers, with the centimeter penetration depth. The transgenic mouse model provides opportunities for both near-infrared optogenetics and photoacoustic imaging in vivo and serves as a source of primary cells and tissues with genomically encoded BphP1.

Development of CIDEA reporter mouse model and its application for screening thermogenic drugs

Cell death-inducing DNA fragmentation factor-like effector A (CIDEA) is a lipid droplet-associated protein and is a known marker of the thermogenic capacity of brown/beige adipocytes. To monitor the expression of CIDEA in live mice in a non-invasive manner, we generated CIDEA reporter mice expressing multicistronic mRNAs encoding CIDEA, luciferase 2, and tdTomato proteins under the control of the Cidea promoter. The expression level of endogenous CIDEA protein in adipose tissue was not affected by the expression of polycistronic reporters. The two CIDEA reporters, luciferase 2 and tdTomato, correctly reflected CIDEA protein levels. Importantly, luciferase activity was induced by cold exposure and the treatment with β3-adrenergic receptor agonist CL316,243 in interscapular and inguinal adipose tissue, which was detectable by in vivo bioluminescence imaging. We further evaluated the effects of candidate brown adipogenic agents using this CIDEA reporter system and demonstrated a positive correlation between drug-induced luciferase activity and thermogenic gene expression levels both in vitro and in vivo. Collectively, we established a dual CIDEA reporter mouse model in which fluorescence and luminescence signals correctly reflect CIDEA expression, and therefore, suggested that this reporter system can be used to evaluate the thermogenic efficacy of candidate molecules.

UCP1 expression in the mouse adrenal gland is not upregulated by thermogenic conditions

The uncoupling protein 1 (UCP1) gene is known to be highly expressed in brown adipose tissue (BAT) that functions in thermogenesis. It has been shown that UCP1 mRNA is localized to the mouse adrenal gland, but its significance remains elusive. To explore how UCP1 expression in the adrenal gland is regulated, we generated a reporter knock-in mouse in which the GFP gene was inserted into the UCP1 locus using CRISPR-Cas9 system. Firstly, we confirmed by Western blot analysis UCP1-driven GFP protein expression in interscapular BAT of the knock-in mice kept at 4 °C. Immunohistochemistry showed that GFP protein was detected in the adrenal gland of the knock-in mice. More intense GFP expression was observed in the adrenal medulla than in the cortex of the reporter mice irrespectively of cold exposure. Immunohistochemistry using anti-UCP1 antibody, as well as Western blot analysis verified UCP1 protein expression in the wild-type adrenal medulla. These results suggest that the mouse adrenal gland is a novel organ expressing UCP1 protein and its expression is not upregulated by cold exposure.

Environmental DNA preserved in marine sediment for detecting jellyfish blooms after a tsunami

Environmental DNA (eDNA) can be a powerful tool for detecting the distribution and abundance of target species. This study aimed to test the longevity of eDNA in marine sediment through a tank experiment and to use this information to reconstruct past faunal occurrence. In the tank experiment, juvenile jack mackerel (Trachurus japonicus) were kept in flow-through tanks with marine sediment for two weeks. Water and sediment samples from the tanks were collected after the removal of fish. In the field trial, sediment cores were collected in Moune Bay, northeast Japan, where unusual blooms of jellyfish (Aurelia sp.) occurred after a tsunami. The samples were analyzed by layers to detect the eDNA of jellyfish. The tank experiment revealed that after fish were removed, eDNA was not present in the water the next day, or subsequently, whereas eDNA was detectable in the sediment for 12 months. In the sediment core samples, jellyfish eDNA was detected at high concentrations above the layer with the highest content of polycyclic aromatic hydrocarbons, reflecting tsunami-induced oil spills. Thus, marine sediment eDNA preserves a record of target species for at least one year and can be used to reconstruct past faunal occurrence.

iRFP (near-infrared fluorescent protein) imaging of subcutaneous and deep tissue tumours in mice highlights differences between imaging platforms

BACKGROUND

In vivo imaging using fluorescence is used in cancer biology for the detection, measurement and monitoring of tumours. This can be achieved with the expression of fluorescent proteins such as iRFP, which emits light at a wavelength less attenuated in biological tissues compared to light emitted by other fluorescent proteins such as GFP or RFP. Imaging platforms capable of detecting fluorescent tumours in small animals have been developed but studies comparing the performance of these platforms are scarce.

RESULTS

Through access to three platforms from Xenogen, Bruker and Li-Cor, we compared their ability to detect iRFP-expressing subcutaneous tumours as well as tumours localised deeper within the body of female NSG mice. Each platform was paired with proprietary software for image analyse, but the output depends on subjective decisions from the user. To more objectively compare platforms, we developed an 'in house' software-based approach which results in lower measured variability between mice.

CONCLUSIONS

Our comparisons showed that all three platforms allowed for reliable detection and monitoring of subcutaneous iRFP tumour growth. The biggest differences between platforms became apparent when imaging deeper tumours with the Li-Cor platform detecting most tumours and showing the highest dynamic range.

Non-invasive Reporter Gene Imaging of Cell Therapies, including T Cells and Stem Cells

Cell therapies represent a rapidly emerging class of new therapeutics. They are intended and developed for the treatment of some of the most prevalent human diseases, including cancer, diabetes, and for regenerative medicine. Currently, they are largely developed without precise assessment of their in vivo distribution, efficacy, or survival either clinically or preclinically. However, it would be highly beneficial for both preclinical cell therapy development and subsequent clinical use to assess these parameters in situ to enable enhancements in efficacy, applicability, and safety. Molecular imaging can be exploited to track cells non-invasively on the whole-body level and can enable monitoring for prolonged periods in a manner compatible with rapidly expanding cell types. In this review, we explain how in vivo imaging can aid the development and clinical translation of cell-based therapeutics. We describe the underlying principles governing non-invasive in vivo long-term cell tracking in the preclinical and clinical settings, including available imaging technologies, reporter genes, and imaging agents as well as pitfalls related to experimental design. Our emphasis is on adoptively transferred T cell and stem cell therapies.

How Non-invasive in vivo Cell Tracking Supports the Development and Translation of Cancer Immunotherapies

Immunotherapy is a relatively new treatment regimen for cancer, and it is based on the modulation of the immune system to battle cancer. Immunotherapies can be classified as either molecular or cell-based immunotherapies, and both types have demonstrated promising results in a growing number of cancers. Indeed, several immunotherapies representing both classes are already approved for clinical use in oncology. While spectacular treatment successes have been reported, particularly for so-called immune checkpoint inhibitors and certain cell-based immunotherapies, they have also been accompanied by a variety of severe, sometimes life-threatening side effects. Furthermore, not all patients respond to immunotherapy. Hence, there is the need for more research to render these promising therapeutics more efficacious, more widely applicable, and safer to use. Whole-body in vivo imaging technologies that can interrogate cancers and/or immunotherapies are highly beneficial tools for immunotherapy development and translation to the clinic. In this review, we explain how in vivo imaging can aid the development of molecular and cell-based anti-cancer immunotherapies. We describe the principles of imaging host T-cells and adoptively transferred therapeutic T-cells as well as the value of traceable cancer cell models in immunotherapy development. Our emphasis is on in vivo cell tracking methodology, including important aspects and caveats specific to immunotherapies. We discuss a variety of associated experimental design aspects including parameters such as cell type, observation times/intervals, and detection sensitivity. The focus is on non-invasive 3D cell tracking on the whole-body level including aspects relevant for both preclinical experimentation and clinical translatability of the underlying methodologies.

Preclinical in vivo imaging for brown adipose tissue

Brown adipose tissue (BAT) has multiple functions in the human body, including the production of heat and increasing energy consumption. However, BAT is also related to many kinds of diseases, such as obesity and metabolic disorders. The progression of such diseases occurs at the cellular level, and thus, imaging techniques could prove greatly beneficial for determining optimal therapeutic regimens. Currently, positron-emission tomography (PET) is considered to be the gold standard for assessing the function of activated BAT. However, PET also has inherent disadvantages, and, thus, recent efforts have been focused on exploring, and potentially developing, new imaging techniques to better observe BAT and evaluate its metabolic function. Researchers have already achieved promising success with computed tomography, magnetic resonance approaches, ultrasound, new tracers for use in PET, and other imaging techniques through in vivo and in vitro animal experiments. Since, these studies have shown that BAT may serve as an effective therapeutic target for treatment of metabolic dysfunction diseases, the development of an efficient in vivo BAT imaging technique that is applicable to humans will prove to be of great clinical value. In this review, classical PET imaging technique is highlighted as well as the current status of preclinical imaging methods developed for BAT examination.