in vivo imaging and data analysis of thyroid hormone action indicator (thai) mice to characterize endocrine disrupting chemical interaction

Imaging of Thyroid Hormone Action Indicator Mice to Assess Endocrine Disruption

Thyroid hormone (TH) signaling is a fundamental regulator of cellular metabolism, essential for normal development and optimal tissue function in adulthood1. Within tissues, TH action is finely controlled by a complex molecular machinery, allowing for tissue-specific maintenance of local TH levels. This autonomy of different tissues from circulating TH levels is of great importance2,3,4.
Numerous chemicals have the potential to disrupt endocrine functions and are found in the environment as pollutants. It is a growing concern that these molecules can enter the food chain through wastewater and agricultural production, thereby impacting the health of livestock and humans5,6,7.
One of the significant challenges in addressing this issue is the sheer number of compounds involved, including both authorized and already banned, but still persistently present, molecules. In recent years, substantial efforts have been made to develop test systems for screening and identifying the disruptive potential of various chemicals8,9,10,11. While these methods excel in high-throughput screening of thousands of compounds and identifying potential threats, a detailed analysis of specific in vivo effects of these molecules is essential to establish the hazards of human exposure. Thus, a multifaceted approach is necessary when studying and characterizing endocrine-disrupting chemicals (EDCs).
In the context of TH regulation, understanding the tissue-specific consequences of EDC exposure requires quantifying local TH action. Although several in vivo models have been developed for this purpose, most rely on endogenous markers as their output measure. Despite being physiological, these markers are subject to numerous regulatory mechanisms, both direct and indirect, making their interpretation more challenging. Therefore, characterizing EDC effects on TH regulation at the tissue level remains a significant challenge12,13.
To address the challenges of measuring tissue-specific TH signaling, the Thyroid Hormone Action Indicator (THAI) mouse model was recently developed. This model allows for specific quantification of changes in local TH action under endogenous conditions. A luciferase transgene was introduced into the mouse genome, which is highly sensitive to regulation by TH action14. This model has demonstrated effectiveness in answering various research questions that require quantifying changes in local tissue TH signaling14,15,16,17,18.
Recognition of one potential use of the THAI model is characterizing tissue-specific effects of EDCs on TH signaling. The model has recently been employed successfully to investigate the tissue-specific effects of tetrabromobisphenol A and diclazuril on TH signaling15. Here, baseline protocols are presented for utilizing in vivo imaging techniques on the THAI model as a test system for characterizing EDCs that disrupt TH function. This method leverages the bioluminescent nature of the luciferin-luciferase reaction. Essentially, the transgenically expressed luciferase enzyme catalyzes the oxidation of administered luciferin, generating luminescent light proportional to the amount of luciferase in the tissue (Figure 1). Consequently, the biological response measured is luciferase activity, which has been validated as a suitable measure of local TH action14. While the THAI model is applicable for quantifying TH action in virtually all tissues, in vivo imaging primarily focuses on TH action in the small intestine (ventral imaging) and the interscapular brown adipose tissue (BAT, dorsal imaging)14.
A significant advantage of the in vivo imaging technique is that it eliminates the need to sacrifice animals for measurements. This allows investigators to design longitudinal and follow-up experiments as self-controlled studies, reducing between-subjects bias and the number of animals used. This aspect is particularly crucial in EDC characterization, and the method&#39;s strength and versatility for this purpose have been previously demonstrated14,15.

Author Spotlight: In Vivo Assessment of Thyroid Hormone Disruption Using the THAI Mouse Model

In vivo Characterization of Endocrine Disrupting Chemical Effects via Thyroid Hormone Action Indicator Mouse

Endocrine disruptors are increasingly present pollutants and they can greatly interfere with thyroid hormone economy. This is a major concern since thyroid hormones are important regulators of biological function. One of our major aims is to measure whether specific molecules and their metabolites are able to disrupt thyroid hormone economy in vivo in mammals.While there are screening methods for such compounds, little is known on how they act in vivo on tissues. This is due to the lack of proper test systems aiming to characterize their tissue specific effects. Additionally, this would require the quantitative measurement of local thyroid hormone action that is also challenging.We developed the thyroid hormone action indicator, or THAI mouse model, in order to characterize thyroid hormone action in the tissues. We realized this would be adequate to measure the thyroid related effects of endocrine disruptors in a tissue specific manner. Notably, the THAI model would allow us to do so in a living mammalian organism.The THAI model enables the in vivo detection of endogenous changes in local thyroid hormone action through bioluminescent imaging. This enables the use of crossover designs, follow up studies, self-control studies, and continuous disruptor exposure. Notably, the THAI model enables us to lower the required number of animals used in the study.

In Vivo Imaging and Data Analysis of Thyroid Hormone Action Indicator (THAI) Mice to Characterize Endocrine Disrupting Chemical Interaction

To begin, launch the software compatible with the in vivo imaging system. Log in and wait for the imaging wizard panel to fully load. Click on the Initialize button on the imaging wizard panel to initiate the cooling of the camera.Then set the temperature of the heating pad between 30 to 37 degrees Celsius to keep the animals warm. Next, gently pinch the foot pads of the anesthetized animals to assess their pedal reflex. Intraperitoneally inject 10 microliters per gram body weight of sodium luciferin into the shaved animals.Now align the animal against the camera's center as denoted by the plus symbol in the imaging instrument. Set the imaging time in the image wizard panel to three minutes for luminescence imaging and select the checkboxes for both photo and luminescence. Click on Acquire to take the first measurement.After all measurements have been recorded, convert the image scale to radiance. Now determine the optimal binning and color scale settings for the images and keep it uniform for all images. Then click on ROI tool on the tool palette panel and use the Place ROI option to select the areas of interest on the image.Lastly, click on Measure ROIs and copy the resulting data for exporting into the organizing or statistical software of choice. In vivo imaging of the THAI mice showed that areas that lacked fur, such as foot pads, tail, and nose, had higher basal signals. Luciferase signal was influenced by the thyroid hormone status.Robust signals were observed in the testicular region. The thyroid hormone action was significantly heightened in the brown adipose tissue of cold stressed THAI mice. The treatment did not impact the luciferase signals from the foot pads and tail.Imaging studies also captured the accumulation and clearance of diclazuril, an endocrine-disrupting compound, over a three-week period.

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Research

JoVE Journal

Neuroscience

83 Views.  Institute of Experimental Medicine. To begin, launch the software compatible with the in vivo imaging system. Log in and wait for the imaging wizard panel to fully load. Click on the Initialize button on the imaging wizard panel to initiate the cooling of the camera.Then set the temperature of the heating pad between 30 to 37 degrees Celsius to keep the animals warm. Next, gently pinch the foot pads of the anesthetized animals to assess their pedal reflex. Intraperitoneally inject 10 microliters per gram body weight of s...

Video: In Vivo Imaging and Data Analysis of Thyroid Hormone Action Indicator (THAI) Mice to Characterize Endocrine Disrupting Chemical Interaction

Thyroid hormones (TH) play a critical role in cell metabolism and tissue function. TH economy is susceptible to endocrine disrupting chemicals (EDCs) that can disturb hormone production or action. Many environmental pollutants are EDCs, representing an emerging threat to both human health and agricultural production. This has led to an increased demand for proper test systems to examine the effects of potential EDCs. However, current methodologies face challenges. Most test systems use endogenous markers regulated by multiple, often complex regulatory processes, making it difficult to distinguish direct and indirect effects. Moreover, in vitro test systems lack the physiological complexity of EDC metabolism and pharmacokinetics in mammals. Additionally, exposure to environmental EDCs usually involves a mixture of multiple compounds, including in vivo generated metabolites, so the possibility of interactions cannot be ignored. This complexity makes EDC characterization difficult. The Thyroid Hormone Action Indicator (THAI) mouse is a transgenic model that carries a TH-responsive luciferase reporter system, enabling the assessment of tissue-specific TH action. One can evaluate the tissue-specific effects of chemicals on local TH action by quantifying luciferase reporter expression in tissue samples. Furthermore, with in vivo imaging, the THAI mouse model allows for longitudinal studies on the effects of potential EDCs in live animals. This approach provides a powerful tool for testing long-term exposure, complex treatment structures, or withdrawal, as it enables the assessment of changes in local TH action over time in the same animal. This report describes the process of in vivo imaging measurements on THAI mice. The protocol discussed here focuses on developing and imaging hyper- and hypothyroid mice, which can serve as controls. Researchers can adapt or expand the treatments presented to meet their specific needs, offering a foundational approach for further investigation.

The Thyroid Hormone Action Indicator mouse model was developed to enable tissue-specific quantification of local thyroid hormone action using its endogenous regulatory machinery. Recently, it has been shown that the model is suitable for characterizing endocrine-disrupting chemicals interacting with thyroid hormone economy, both by ex vivo and in vivo methodologies.

Thyroid hormones (TH) play a critical role in cell metabolism and tissue function. TH economy is susceptible to endocrine disrupting chemicals (EDCs) that ...