Imaging Studies Using Reporter-Gene Transgenic Rats

Introduction to Reporter Gene Imaging

Imaging reporter genes play a leading role in molecular gene imaging and can be used to visualize the expression levels of specific exogenous and endogenous genes and some intracellular biological phenomena, including specific signal transduction pathways, nuclear receptor activities, and protein interactions. Molecular imaging can visualize, qualitatively, and quantify biological processes at the cellular and subcellular levels of living subjects and can detect events that occur in the initial stages of neurological disease progression, including neurotumors.

In transgenic rats, non-invasive techniques that can be repeated are needed to determine the transgene expression in living animals. By evaluating the new reporter protein in cells that mutate with the imaging reporter gene to induce the accumulation of specific imaging signals, the location, duration, and size of transgene expression can be visualized, and the measurement of specific imaging signals provides indirect information that reflects the target gene expression level.

Reporter Gene Imaging Modes

• Optical imaging

Reporter gene: firefly phosphorous (Fluc) gene, green fluorescent protein (GFP) gene

Advantages: convenient operation, short acquisition time, and synchronous measurement capability

• Magnetic resonance imaging (MRI)

Reporter gene: β-caratosiase gene, casein and ferritin genes

Advantages: high spatial resolution (micrometers) and the ability to extract physiological and anatomical information at the same time

• Nuclear medicine imaging

Reporter gene: HSV1-tk protein gene, dopamine 2 receptor (D₂R) gene, estrogen receptor gene

Advantages: very sensitive and highly quantitative, suitable for human subjects

Applications of Reporter Gene Imaging

• Assess neuro-oncology immunotherapy response

Molecular imaging through advanced MRI, positron emission tomography (PET), or single photon emission computed tomography (SPECT) is used to determine the extent and progression of the disease and monitor the response to treatment.

• Neural Stem Cell (NSC) Tracking

NSC is used as a new treatment for brain trauma, stroke, and some neurological diseases (such as Parkinson's disease) in preclinical experiments and clinical settings. To ensure the effectiveness and success of cell therapy, it is essential to track the survival, migration, and differentiation of transplanted cells, and to track their ability to rebuild brain function and their biological effects. Due to its non-invasiveness and good tissue contrast, MRI technology plays an important role in the process of transferring cell therapy from animal experiments to the clinical environment.

Fig.1 The principle of stem cell labeling is used in different imaging methods. (Zheng, 2017)

• Monitoring of gene therapy in the central nervous system

The strategy of reporting genes by PET scanning is used to achieve central nervous system (CNS) monitoring or imaging gene therapy. Fig.2 showed the expression of the PET reporter gene system using the PKM2 reporter gene and its related radiation tracker.

Fig.2 PET imaging tracing rat brain sagittal section of in vitro autoradiography and immunofluorescence staining of PKM2 protein. (Haywood, 2019)

The application of reporter gene molecular imaging in transgenic rats has gradually developed into an important tool for drug discovery and development. In addition, the improvement of equipment, the identification of new targets and genes, and the development of imaging probes make reporter gene imaging play an increasingly important role in the diagnosis and treatment of degenerative diseases and neurotumors.

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References

1. Zheng, Y.; et al. Stem cell tracking technologies for neurological regenerative medicine purposes. Stem cells international. 2017, 2017: 2934149.
2. Haywood, T.; et al. Positron emission tomography reporter gene strategy for use in the central nervous system. Proceedings of the National Academy of Sciences. 2019, 116(23): 11402-11407.