TY - JOUR T1 - Paradoxical Effects on Force Generation after Efficient <em>β</em><sub>1</sub>-Adrenoceptor Knockdown in Reconstituted Heart Tissue JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 39 LP - 46 DO - 10.1124/jpet.113.210898 VL - 349 IS - 1 AU - Christiane Neuber AU - Oliver J. Müller AU - Felix C. Hansen AU - Alexandra Eder AU - Anika Witten AU - Frank Rühle AU - Monika Stoll AU - Hugo A. Katus AU - Thomas Eschenhagen AU - Ali El-Armouche Y1 - 2014/04/01 UR - http://jpet.aspetjournals.org/content/349/1/39.abstract N2 - Stimulation of myocardial β1-adrenoceptors (AR) is a major mechanism that increases cardiac function. We investigated the functional consequences of genetic β1-AR knockdown in three-dimensional engineered heart tissue (EHT). For β1-AR knockdown, short interfering RNA (siRNA) sequences targeting specifically the β1-AR (shB1) and a scrambled control (shCTR) were subcloned into a recombinant adeno-associated virus (AAV)–short hairpin RNA (shRNA) expression system. Transduction efficiency was ∼100%, and radioligand binding revealed 70% lower β1-AR density in AAV6-shB1–transduced EHTs. Force measurements, performed over the culture period of 14 days, showed paradoxically higher force generation in AAV6-shB1 compared with shCTR under basal (0.19 ± 0.01 versus 0.13 ± 0.01 mN) and after β-AR-stimulated conditions with isoprenaline (Δfractional shortening: 72 ± 5% versus 34 ± 4%). Large scale gene expression analysis revealed that AAV6-shCTR compared with nontransduced EHTs showed only few differentially regulated genes (&lt;20), whereas AAV6-shB1 induced marked changes in gene expression (&gt;250 genes), indicating that β1-AR knockdown itself determines the outcome. None of the regulated genes pointed to obvious off-target effects to explain higher force generation. Moreover, compensational regulation of β2-AR signaling or changes in prominent β1-AR downstream targets could be ruled out. In summary, we show paradoxically higher force generation and isoprenaline responses after efficient β1-AR knockdown in EHTs. Our findings 1) reveal an unexpected layer of complexity in gene regulation after specific β1-AR knockdown rather than unspecific dysregulations through transcriptional interference, 2) challenge classic assumptions on the role of cardiac β1-AR, and 3) may open up new avenues for β-AR loss-of-function research in vivo. ER -