Small molecules for reprogramming and transdifferentiation

Abstract

Pluripotency reprogramming and transdifferentiation induced by transcription factors can generate induced pluripotent stem cells, adult stem cells or specialized cells. However, the induction efficiency and the reintroduction of exogenous genes limit their translation into clinical applications. Small molecules that target signaling pathways, epigenetic modifications, or metabolic processes can regulate cell development, cell fate, and function. In the recent decade, small molecules have been widely used in reprogramming and transdifferentiation fields, which can promote the induction efficiency, replace exogenous genes, or even induce cell fate conversion alone. Small molecules are expected as novel approaches to generate new cells from somatic cells in vitro and in vivo. Here, we will discuss the recent progress, new insights, and future challenges about the use of small molecules in cell fate conversion.

Keywords: Adult cells; Chemical compound; Direct conversion; Regeneration; Tissue repair.

Fig. 1

Representative small molecules and their mechanisms for pluripotency reprogramming. Inhibition TGF-β signaling by its receptors SB431542, Repsox, and A83-01 facilitates the mesenchymal–epithelial transition and early stage reprogramming. Activation of Wnt signaling by a GSK-3β inhibitor (CHIR99021, Kenpaullone) can induce expression of pluripotency-associated genes. Inhibition of MAPK/ERK signaling by MEK inhibitor PD0325901 suppresses the differentiation of pluripotent stem cells and promotes the late-stage reprogramming. Reduction of DNA methylation levels in somatic cells by DNA methyltransferase inhibitors 5-azacytidine (5-aza), RG108, and 3-deazaneplanocin A (DZNep) enhances reprogramming. Increasing the histone acetylation level by histone deacetylase inhibitors valproic acid (VPA), trichostatin A (TSA), sodium butyrate (NaB), and suberanilohydroxamic acid (SAHA) enhances expression of pluripotency-associated genes and reprogramming efficiency. Vitamin C reduces repressive H3K9me2/3, H3K27me3 histone mark and increases active H3K4me3 at promoters of pluripotency-associated genes and reduces active H3K36me2/3 at promoters of cell senescence-associated genes, promoting reprogramming. BIX-01294, an inhibitor of H3K9me3 methyltransferase G9a, reduces repressive H3K9me3 mark and replaces Sox2 during reprogramming. EPZ004777 inhibits H3K79 histone methyltransferase Dot1l and improves the reprogramming rate. Tranylcypromine, an inhibitor of lysine-specific demethylase 1(LSD1), enables Oct4-based reprogramming. Promotion of glycolytic metabolism (PS48, fructose 2, 6-bisphosphate, quercetin) and autophagy metabolism (rapamycin, PP242, SMER28) can enhance reprogramming

Fig. 2

Modulation of signaling pathways promotes the induction of iPSCs, cardiac cells, and neural cells from somatic cells. The Notch, JAK-STAT, TGF-β, Bmp, Wnt, Hedgehog, MAPK/ERK, ROCK, and mTOR signaling pathways and the small molecules (red rectangle) that target them are simply presented in the diagram. The inhibition and activation of these signaling pathways regulate gene expressions and control the cell fate determination of somatic cells. Green arrows indicate the contribution to cell induction and red blunt-headed arrows indicate the inhibition to cell induction. Blue arrows indicate the activation to signaling pathways and blue blunt-headed arrows indicate the inhibition to signaling pathways

Fig. 3

Small molecules promote transcription factor-based transdifferentiation. Fibroblasts can be converted to cardiomyocytes or cardiovascular progenitor cells by transient expression of OSKM (Oct4, Sox2, Klf4, c-Myc) or only Oct4 combined with treatment with small molecules. Alternatively, ectopic expression of cardiac-associated transcription factors GMT (Gata4, Mef2c, Tbx5) or GHMT (Gata4, Hand2, Mef2c, Tbx5) can induce cardiomyocytes. Small molecules (A83-01, an inhibitor of TGF-β receptor inhibitor, and Y-27632, a ROCK inhibitor) can promote GHMT-based cardiac conversion. Fibroblasts can be induced to neurons (ABM, Ascl1, Brn2, Myt1l; ABMN; Ascl1, Brn2, Myt1l, NeuroD1), specific neuronal subtypes (ANL, Ascl1, Nurr1, Lmx1a; AFLBM, Ascl1, Lmx1a, Foxa2, Brn2, and Myt1l; ALFNEP, Ascl1, Lmx1a, Foxa2, Nurr1, En1, and Pitx3; BN, Brn3a, Nrg1 or Ngn2; AFLF, Ascl1, Foxa2, Lmx1b, and FEV; AFSDL, Ascl1, Foxg1, Sox2, Dlx5, Lhx6), neural stem cells (BSF, Brn2, Sox2, FoxG1; SKMB, Sox2, Klf4, c-Myc, Brn4; S, Sox2) by ectopic expression of neural-associated transcription factors. Small molecules combined with transcription factors (BN; Ascl1, Ngn2; N, Ngn2; A, Ascl1) can generate specific neuronal subtypes