Abstract 4139898: A Non-invasive <i>In Vivo</i> Experimental Model of Heart Failure Using Optogenetic Tachypacing in Larval Zebrafish

Background: Tachycardia can drive heart failure (HF). Traditionally, this is experimentally modeled using an implantable pacemaker, an invasive, technically demanding, and low-throughput methodology. Genetically-expressed light-activated ion channels (‘optogenetics’) provide an alternative approach for in vivo cardiac stimulation, which if applied in transparent zebrafish embryos, may be used for non-invasive, cost-effective, high-throughput HF and drug screening studies. Objective: Establish a non-invasive in vivo experimental model of HF using optogenetic tachypacing in larval zebrafish. Methods: Larval zebrafish expressing cation-nonspecific channelrhodopsin-2 (ChR2), chloride-specific anion channelrhodopsin-1 (ACR1), or green fluorescent protein (GFP, as a light-exposed, non-paced control) in cardiomyocytes were exposed to intermittent tachypacing (15s on, 15s off) by programmed light pulses from 2-7 days post fertilization (dpf). At 7 dpf: (i) in vivo atrial and ventricular mechanical function was assessed by end-diastolic area (EDA), end-systolic area (ESA), and ejection fraction (EF) with video microscopy; (ii) cardiac structure was measured by atrial and ventricular area in fixed larvae with fluorescent imaging; and (iii) gene expression of cardiac-specific HF biomarkers (atrial and brain natriuretic peptide [ anp , bnp ], atrial- and ventricular-specific myosin heavy chain-a and -b [ myh6 , myh7 ], and a-smooth muscle actin [ acta2 ]) was quantified by qPCR. Values across groups were compared by one-way ANOVA, with Šídák post hoc tests. Results: In vivo , atrial and ventricular EDA were greater in ChR2 (+191%, p &lt;0.0001; +66%, p &lt;0.0001) and ACR1 (+58%, p =0.005; +40%, p =0.0004) hearts compared to control, as was ESA (ChR2: +245%, p &lt;0.0001; +67%, p &lt;0.0001 and ACR1: +89%, p &lt;0.0001; +53%, p &lt;0.0001). Atrial EF was lower in ChR2 (-26%, p =0.0006) and ACR1 (-26%, p =0.0032) hearts, while ventricular EF was unchanged. Atrial and ventricular area were also greater in fixed ChR2 hearts (+191%, p &lt;0.0001; +35%, p =0.0005), while only atrial area was greater in ACR1 hearts (+55%, p =0.0236). Expression of anp , bnp , and myh6 were greater in both ChR2 (11x, 22x , 58x; p &lt;0.05 for each) and ACR1 (6x, 4x, 15x; p &lt;0.05 for each) hearts. Conclusion: Intermittent optogenetic-tachypacing with either ChR2 or ACR1 induces HF in larval zebrafish, which may represent novel experimental models for insight into HF mechanisms and as pre-clinical tools for the development of new HF therapies.