Controlled Release of Small Molecules for Cardiac Differentiation of Pluripotent Stem Cells

Induced pluripotent stem cells (iPSCs) have been shown to differentiate to functional cardiomyocytes (CM) with high efficiency through temporally controlled inhibition of the GSK3/Wnt signaling pathways. In this study, we investigated the ability of temporally controlled release of GSK3/Wnt small-molecule inhibitors to drive cardiac differentiation of iPSC without manual intervention. Porous silica particles were loaded with GSK3 inhibitor CHIR99021 or Wnt inhibitor IWP2, and the particles containing IWP2 were coated with 5 wt% poly(lactic-co-glycolic acid) 50:50 to delay release by ∼72 h. iPSCs reprogrammed through mRNA transfection were cultured with these particles up to 30 days. High-performance liquid chromatography suggests a burst release of CHIR99021 within the first 24 h and a delayed release of IWP2 after 72 h. Annexin V/propidium iodide staining did not show a significant effect on apoptosis or necrosis rates. Cultured cells upregulated both early (Nkx 2.5, Isl-1) and late (cTnT, MHC, Cx43) cardiac markers, assayed with a quantitative real-time polymerase chain reaction, and began spontaneous contraction at 3.0 ± 0.6 Hz at 15-21 days after the start of differentiation. CM had clear sarcomeric striations when stained for β-myosin heavy chain, and showed expression and punctate membrane localization of gap junction protein Connexin43. Calcium and voltage-sensitive imaging showed both action potential and calcium transients typical of immature CM. This study showed that the cardiac differentiation of pluripotent stem cells can be directed by porous silica vectors with temporally controlled release of small-molecule inhibitors. These results suggest methods for automating and eliminating variability in manual maintenance of inhibitor concentrations in the differentiation of pluripotent stem cells to CM.