Abstract 1074: Potassium Inward Rectifier Expression Is Regulated By TGFβ And BMP In Human Cardiomyocyte Progenitor Cells.
Background: For cell replacement therapy to be considered as an alternative treatment for heart regeneration, stable integration of transplanted cells is required. However, spontaneous contractions of stem/progenitor cell-derived cardiomyocytes may lead to arrhythmias after cell transplantation. A key component in preventing adult ventricular cardiomyocytes from spontaneous beating is the potassium inward rectifier (Kir) channel. Kir channels mediate IK1 currents and are required during phase 3 repolarization and stabilization of the resting membrane potential (RMP) of cardiomyocytes. Increasing the IK1 current in cardiomyocytes results in quiescent and less arrhythmogenic cells. Therefore we analyzed the regulation of Kir2.1 and 2.2 expression in cardiomyocyte progenitor cells (CMPCs) by TGFβ and BMP stimulation.
Methods & Results: CMPCs were isolated from human fetal hearts and differentiated into spontaneous beating cardiomyocytes with a fetal ventricular-like electro-physiological phenotype. RT-PCR demonstrated no or low levels of both Kir2.1 and 2.2 expression in differentiated CMPCs. Stimulation with TGFβ, early during differentiation, improved differentiation efficiency and increased Kir2.1/2.2 expression and IK1 currents. Also, undifferentiated CMPCs hyperpolarized after BMP stimulation. Together this supports functional Kir channel conductance in response to TGFβ and BMP signaling. To determine whether TGFβ and BMP directly regulate Kir 2.1 expression, we performed a Kir 2.1 luciferase reporter assay in COS cells in vitro. Kir 2.1 promoter activity was enhanced upon TGFβ or BMP stimulation. In addition, undifferentiated CMPCs increased their Kir 2.1 expression within several hours after TGFβ or BMP stimulation, as determined by qRT-PCR.
Conclusion: Our data show that expression of Kir 2.1 and 2.2 is enhanced during CMPC differentiation, when stimulated with TGFβ. Increased IK1 currents, in combination with a more negative RMP after stimulation with BMP, could indicate regulation of Kir channels. Concordantly, Kir 2.1 and 2.2 expression is enhanced by TGFβ and BMP. This shows that TGFβ and BMP stimulate hyperpolarization of CMPCs, which may help to prevent arrhythmogenesis after cell transplantation.