AAV (Serotype 6)

Mammalian cardiomyocytes exit the cell cycle perinatally, and although cardiomyocytes differentiated from human induced pluripotent stem cells (hiPSC-CM) are phenotypically immature, their intrinsic cell cycle activity remains limited. microRNA is a key regulator of cardiomyocyte proliferation, and when adeno-associated virus encoding microRNA-199a (miR-199a) expression was injected directly into infarcted pig hearts, cardiac function and fibrosis markers were significantly improved, but the treatment was also associated with lethal arrhythmia. Here, the researchers transduced the same vector (AAV6-miR-199a) into hiPSC-CMs and then evaluated these cells in a mouse model of myocardial infarction. The findings confirmed that AAV6-mediated overexpression of miR-199a increased the proliferation of cultured and transplanted hiPSC-derived cardiomyocytes (hiPSC-CMs), and that AAV6-miR-199a–transduced hiPSC-CMs significantly improved cardiac function and scar size, with no evidence of sudden death, after transplantation into infarcted mouse hearts.

Here, researchers found that the ratio of Serine-127–phosphorated YAP (p-YAP) to total YAP abundance was significantly lower (Figures 1A, B), while nuclear YAP levels were significantly greater, in AAV6-miR-199a–than in AAV6-Control–transduced hiPSC-CMs (Figures 1C, D). Relative YAP protein levels in AAV6-miR-199a nuclei were quantified by the fluorescence density of YAP-positive nuclei in AAV6-miR-199a and normalized to that in the AAV6-Control group. Therefore, miR-199a overexpression may have reduced ubiquitin-mediated proteasomal YAP degradation and increased nuclear YAP abundance, which may have contributed to the enhanced proliferation and cell-cycle activity observed in AAV6-miR-199a–transduced hiPSC-CMs.

Figure 1. miR-199a overexpression reduced YAP phosphorylation and increased nuclear YAP abundance in hiPSC-CMs. (Bian W, et al., 2021)