Background: Glucocorticoids regulate a broad spectrum of physiologic functions essential for life and exert their actions through their ubiquitously expressed glucocorticoid receptor (GR). The GR interacts with several molecules, including the non-coding RNA growth arrest-specific 5 (Gas5), which decreases the transcriptional activity of the GR by preventing its binding to DNA, and reduces tissue sensitivity to glucocorticoids.
Objective and Hypotheses: To create a mouse model of Generalized Glucocorticoid Resistance by inducible overexpression of Gas5 and to investigate its myocardial function.
Methods: Two transgenic lines expressing the reverse transactivator (rtTA) under hnRNP promoter and the Gas5 under Tet responsive P tight promoter were generated and then crossed to create double transgenic mice (Gas5/rtTA), which were then tested for Gas5 inducibility of overexpression by qRT-PCR. The cardiac function was evaluated by echocardiography and 24-hour electrocardiography (ECG).
Results: Genetic constructs of double transgenic mice inducibly overexpressing Gas5 after doxycycline administration (DOX+) were generated. The induction of overexpression of Gas5 in: Gas5/rtTA mice (2 weeks DOX+; 0.78±0.37) compared with i) Gas5/rtTA mice without doxycycline administration (DOX−; 0.14±0.04), ii) single transgenic DOX+ mice where the TetOn system is not functional (0.3*10−4±0.5*10−5), and iii) wild-type (WT) DOX+ mice (0.7*10−5±0.8*10−5) was verified in the myocardium. The cardiac function (% fractional shortening) was significantly decreased in Gas5/rtTA/DOX+ compared with Gas5/rtTA/DOX− mice (44.6±0.8 vs 48.5±0.4; P=0.003) but not compared with WT/DOX+ mice (46.9±0.4, P=0.2). This was mainly due to decreased systolic function in Gas5/rtTA/DOX+ vs Gas5/rtTA/DOX− mice (end-systolic dimension: 1.6±0.1 vs 1.8±0.1 mm; P=0.05). ECG studies did not show differences among the three groups of mice in terms of heart rate, ECG interval measurements and arrhythmias.
Conclusion: We created a mouse model of Generalized Glucocorticoid Resistance and demonstrated impaired cardiac function. Ongoing studies aim to investigate the molecular mechanisms through which glucocorticoid resistance affects myocardial function.
10 Sep 2016 - 12 Sep 2016