Abstract 3257: Injection of Wild Type Embryonic Stem Cells Into Mst1 Transgenic Blastocysts Prevents Adult-Onset Cardiomyopathy
Embryonic stem cells (ESCs) have the capacity to differentiate into a wide range of cell types. This unique feature places ESCs at the center of the regenerative arena. Our laboratory utilizes ESCs to study the molecular mechanisms by which congenital diseases can be corrected. We previously described that blastocyst injection of WT ESCs into various knockout mouse models of human disease prevents disease with just 20 –30% chimerism. Is it possible to also correct disease in a mouse model of dilated cardiomyopathy, which is triggered by overexpression (rather than absence) of a key molecule? We injected 15 LacZ-marked WT ESCs into human mammalian sterile 20 like-kinase 1 (Mst1) transgenic blastocysts that are predisposed to cardiac-specifically overexpress Mst1, a pro-apoptotic factor, and to develop an adult dilated cardiomyopathy. The degree of ESC incorporation was determined by X-gal staining of tail biopsies, and later confirmed at sacrifice by Mst1 immunofluorescence on heart sections. Clearly defined patches of Mst1 positive (derived from the Mst1 transgenic blastocyst) and Mst1 negative (derived from the ES-derived cells) areas were observed in the chimeric hearts. Detection of transgenic Mst1 was confirmed by western blot analysis with heart extracts. Five month-old chimeric mice containing greater than 40% of ESCs (chim>40) have normal hearts at histological (H&E) and functional (echocardiography) levels. Chim>40 mice displayed normal heart/body ratio and the lungs were not congested. The hearts had normal size and an ejection fraction above 60%, similar to those of WT mice. However, chimeric mice containing fewer than 20% of ESCs (chim<20) developed severe dilated cardiomyopathy. Chim<20 mice displayed an increased heart/body ratio, the lungs were congested and the hearts were enlarged with and ejection fraction below 40%, similar to those of non-chimeric, Mst1 transgenic mice. The experiments suggest that an adult-onset cardiac myopathy induced by overexpression of Mst1 can be neutralized by developmental incorporation of at least 40% WT ESCs. However, since overexpression of the Mst1 transgene is not abolished in the rescued chimeras, the Mst1 non-overexpressing ES-derived cells may be targeting pathways that lie downstream of Mst1.