Zebrafish models for ARVC8 analysis and drug discovery

INTRODUCTION: Desmoplakin is one the most abundant desmosomal proteins in cardiac and epithelial tissues. In humans, dominat mutations in the desmoplakin gene (DSP) cause Arrhythmogenic Right Ventricular Cardio​myopathy 8 (ARVC8), a dominant cardiomyopathy, frequently involved in juvenile sudden death. Current ARVC models are based on cell lines and transgenic mice. In this context, it has been shown that suppression of DSP expression leads to a reduction in canonical Wnt signaling, suggesting that this pathway could be a molecular target for ARVC therapeutic intervention. In order to address this issue, the present study aims to evaluate the pathogenic mechanisms of DSP mutations in vivo, using zebrafish (Danio rerio) as an innovative model for this disease. In zebrafish, the desmoplakin gene is present with two isoforms, dspa and dspb, both orthologous to the single DSP in humans. PURPOSE: The purpose of this study is the generation and the phenotypic characterization of transient ARVC8 zebrafish models using a morpholino-mediated knock-down strategy. In addition, by taking advantage of zebrafish pathway reporter lines, we aim to verify if Wnt signaling and/or other molecular cascades might be involved in ARVC8 pathogenesis. The final goal is the assessment of our ARVC8 model as a suitable tool for molecularly-targeted drug discovery. METHODS: To evaluate the expression of dspa and dspb during zebrafish embryonic development and adulthood, we used whole-mount in situ hybridization (WISH) and semi quantitative RT_PCR. Knockdown of zebrafish dspa and dspb genes was obtained by a morpholino (MO)-based antisense strategy. Specifically, we injected anti-dspa and anti-dspb MO oligos in both wild types and pathway-specific lines reporting the activity of Wnt, Bmp, TGFbeta, FGF, Shh, Notch, CREB, Hippo and Hypoxia signaling. RESULTS: We found that both dspa and dspb are expressed during zebrafish embryonic development, while the molecular analysis of cDNAs from different adult tissues demonstrates that both dspa and dspb are highly expressed in heart and skin, with dspa more strongly detectable compared to dspb. MO-mediated knock-down of both dspa and dspb leads to delayed development, microcephaly, pericardial edema and, particularly in dspb knock-down embryos, decreased heart rate. TEM analysis of cardiac and skin tissues under dspa+dspb simultaneous knock-down shows reduced and disorganized desmososmes. As far as concerns the analysis of previously mentioned signaling pathways, we observed a specific reduction of Wnt signaling responsiveness in the cardiac region of both dspa and dspb knock- down embryos (Fig. 1). CONCLUSION: Our results show that transient knock-down of zebrafish desmoplakin genes is able to phenocopy some ARVC8 features, such as cardiac and cutaneous desmosomal defects, heart rate alteration and Wnt signaling reduction, pointing to zebrafish as a suitable ARVC8 model for in vivo screening of molecularly-targeted drugs