Stem cell conversion to the cardiac lineage requires nucleotide signalling from apoptosing cells

Abstract

Pluripotent stem cells can be driven by manipulation of Wnt signaling through a series of states similar to those that occur during early embryonic development, transitioning from an epithelial phenotype into the cardiogenic mesoderm lineage and ultimately into functional cardiomyocytes. Strikingly, we observed that initiation of differentiation in induced pluripotent stem cells (iPSCs) and embryonic stem cells (ESCs) triggers widespread apoptosis, followed by a synchronous epithelial-mesenchymal transition (EMT). Apoptosis is caused by absence of bFGF from the differentiation medium. EMT requires induction of transcription factors SNAI1/SNAI2 downstream of MESP1 expression, and double knock-out of SNAI1/2 , or loss of MESP1 in iPSCs blocks EMT and prevents cardiac differentiation. Remarkably, blockade of early apoptosis chemically or by ablation of pro-apoptotic genes also completely prevents the EMT, suppressing even the earliest events in mesoderm conversion, including BRA/T, TBX6 , and MESP1 induction. Conditioned medium from WNT-activated WT iPSCs overcomes the block to EMT by cells incapable of apoptosis (Apop-), suggesting involvement of soluble factors from apoptotic cells in mesoderm conversion. Knockout of the PANX1 channel blocked EMT, while treatment with a purinergic P2 receptor inhibitor or addition of apyrase demonstrated a requirement for nucleotide triphosphate signaling. ATP and/or UTP was sufficient to induce a partial EMT in Apop- cells treated with WNT activator. Notably, knockout of the ATP/UTP-specific P2Y2 receptor blocked EMT and mesoderm induction. We conclude that nucleotides, in addition to acting as chemo-attractants for clearance of apoptotic cells can function as essential paracrine signals that, with WNT signaling, create a logical AND gate for mesoderm specification.

Inhibition of nucleotide biosynthesis disrupts lipid accumulation and adipogenesis

“…Recent studies reveal that although nucleotide biosynthesis inhibition limits proliferation, it stimulates cell migration and the epithelial–mesenchymal transition transcriptional program characterized by N-cadherin and vimentin upregulation ( 39 ). Furthermore, perturbing nucleotide abundance regulates differentiation in various cell systems; depletion of nucleotides stimulates acute myeloid leukemia differentiation, but elevation in nucleotides may also promote cardiac mesoderm lineage through paracrine signaling ( 40 , 41 ). Now our study adds a new role of nucleotide biosynthesis in the regulation of adipogenesis.…”

Heart generation via blastocyst complementation in Mesp1/2-deficient mice

“…By exploiting the developmental organ niche, blastocyst complementation can be used to generate organs from PSCs. Mesp1 is a key regulator of cardiovascular differentiation that is expressed transiently in the cardiac mesoderm 16,19,20 . We analyzed Mesp1-Cre/R26-tdTomato mice to determine the cell lineages formed from Mesp1 + cells.…”

“…Mesp1 and Mesp2 double-knockout (Mesp1/2-DKO) mice die at embryonic day (E) nine because of defects in mesoderm formation and its derivatives, including hearts 17–19 . MESP1 deficiency in human PSCs inhibits epithelial-mesenchymal transition and hinders cardiac differentiation, highlighting the importance and conserved functions of Mesp1 and 2 in cardiogenesis 20 . Using mouse and rat PSCs, we investigated whether blastocyst complementation could be used to generate hearts in Mesp1/2-DKO mice.…”

Circular RNAs regulate parental gene expression: A new direction for molecular oncology research

“…In addition, circ-VANGL1 knockdown was also found to prevent tumor cell cycle progression, resulting in more cells blocked at the G0/G1 stage ( 23 ). Metastatic ability was a key hallmark of cancer progression, and this characteristic could be achieved through epithelial-mesenchymal transition, circTFRC could inhibit miR-107 expression to facilitate downstream host gene expression and thus promote epithelial-mesenchymal transition in bladder cancer metastatic progression ( 24 , 63 ). Moreover, this ability was also found in circ-TFF1, which could induce epithelial-mesenchymal transition and therefore promote breast cancer tumor cells metastasis through the ceRNA mechanism ( 25 ).…”