Molecular imaging of transcriptional regulation during inflammation

Abstract

Molecular imaging enables non-invasive visualization of the dynamics of molecular processes within living organisms in vivo. Different imaging modalities as MRI, SPECT, PET and optic imaging are used together with molecular probes specific for the biological process of interest. Molecular imaging of transcription factor activity is done in animal models and mostly in transgenic reporter mice, where the transgene essentially consists of a promoter that regulates a reporter gene. During inflammation, the transcription factor NF-kappaB is widely involved in orchestration and regulation of the immune system and almost all imaging studies in this field has revolved around the role and regulation of NF-kappaB. We here present a brief introduction to experimental use and design of transgenic reporter mice and a more extensive review of the various studies where molecular imaging of transcriptional regulation has been applied during inflammation.

Figure 1

Transgenic reporter mouse. A) Schematic representation of a typical transgene, which is flanked by insulator sequences and including relevant elements for meaningful regulation of reporter gene expression. The core promoter often contains a TATA-box for binding of polymerase II and a transcriptional initiation site. The proximal promoter, which contains regulatory cis-elements, is usually localized upstream to the core promoter; however, enhancer elements can in principal be placed in other parts of the construct. An intron is often included to increase transcription efficiency. The polyA sequence is necessary to stabilize mRNA while the PEST sequence is introduced to exaggerate proteasome degradation and thus decrease the half-life of the protein. This is important to prevent accumulation of the reporter protein and to follow dynamic changes. Finally, the reporter gene needs the necessary elements for successful translation such as Kozak sequence and stop codon. B-D) Imaging of a transgenic reporter mouse after exposure to various inflammatory stimuli. This reporter mouse contains a transgene with NF-κB sites that regulate expression of firefly luciferase generated.