Abstract
MicroRNAs (miRNAs) are key players in many biological processes and are considered as an emerging class of pharmacology drugs for diagnosis and therapy. However to fully exploit the therapeutic potential of miRNAs, it is becoming crucial to monitor their expression pattern using medical imaging modalities. Recently, we developed a method called RILES, for RNAi-Inducible Luciferase Expression System that relies on an engineered regulatable expression system to switch-ON the expression of the luciferase gene when a miRNA of interest is expressed in cells. Here we investigated whether replacing the luciferase reporter gene with the human sodium iodide symporter (hNIS) reporter gene will be also suited to monitor the expression of miRNAs in a clinical setting context. We provide evidence that radionuclide imaging of miRNA expression using hNIS is feasible although it is not as robust as when the luciferase reporter gene is used. However, under appropriate conditions, we monitored the expression of several miRNAs in cells, in the liver and in the tibialis anterior muscle of mice undergoing muscular atrophy. We demonstrated that radiotracer accumulation in transfected cells correlated with the induction of hNIS and with the expression of miRNAs detected by real time PCR. We established the kinetic of miRNA-23a expression in mice and demonstrated that this miRNA follows a biphasic expression pattern characterized by a loss of expression at a late time point of muscular atrophy. At autopsy, we found an opposite expression pattern between miRNA-23a and one of the main transcriptional target of this miRNA, APAF-1, and as downstream target, Caspase 9. Our results report the first positive monitoring of endogenously expressed miRNAs in a nuclear medicine imaging context and support the development of additional work to establish the potential therapeutic value of miRNA-23 to prevent the damaging effects of muscular atrophy.
Highlights
MicroRNAs are a class of small non-coding RNAs that regulate gene expression at the post-transcriptional level by binding mainly to the 3’-end of mRNA transcripts to induce translational repression and/or mRNA degradation [1]
The addition of a gamma emitting radiotracer such as 99mTcO4- results in the intracellular accumulation of radiotracers in the RINES expressing cells that can be monitored using a 2D planar gamma counter for in vitro studies and a SPECT camera for in vivo analysis
We have demonstrated that positive monitoring of miRNA expression is feasible in a clinical setting using the RILES system coupled with human NIS (hNIS) as reporter gene, 99mTc04- as radiotracer and a SPECT/computed tomography (CT) camera
Summary
MicroRNAs (miRNAs) are a class of small non-coding RNAs that regulate gene expression at the post-transcriptional level by binding mainly to the 3’-end of mRNA transcripts to induce translational repression and/or mRNA degradation [1]. Some miRNA imaging probes have been successfully developed in preclinical animal models They can be subtyped in two categories: probes using reporter genes (biological probes) and probes using fluorescent oligonucleotides (synthetic probes) [4, 5]. NIS has been used for over 70 years to diagnose and treat human thyroid diseases [7] It is a 13 membrane spanning glycoprotein expressed on the basolateral surface of thyroid follicular cells where it is responsible for the active transport of iodide from blood to the thyroid gland for the synthesis of T3 and T4 hormones. It was demonstrated that the human NIS (hNIS) is a relevant nuclear medicine reporter gene for monitoring the kinetic and location of hNIS gene transfer in animal models, providing biosafety information before the administration of therapeutic doses of radioisotopes [8, 9]. The clinical imaging potential of hNIS was validated in cancer patients administrated with oncolytic virus encoding hNIS to monitor the spread of the virus
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