Differentiation of Murine Bone Marrow-Derived Smooth Muscle Progenitor Cells Is Regulated by PDGF-BB and Collagen

HDACs regulate the differentiation of endothelial cells from human iPSCs

Human induced pluripotent stem cells (hiPSCs) possess the potential to differentiate toward vascular cells including endothelial cells (ECs), pericytes, and smooth muscle cells. Epigenetic mechanisms including DNA methylation and histone modification play a crucial role in regulating lineage differentiation and specification. Herein, we utilized a three-stage protocol to induce differentiation of mesoderm, vascular progenitors, and ECs from hiPSCs and investigated the regulatory effects of histone acetylation on the differentiation processes. We found that the expression of several histone deacetylases (HDACs), including HDAC1, HDAC5, and HDAC7, were greatly upregulated at the second stage and downregulated at the third stage. Interestingly, although HDAC1 remained in the nucleus during the EC differentiation, HDAC5 and HDAC7 displayed cytosol/nuclear translocation during the differentiation process. Inhibition of HDACs with sodium butyrate (NaBt) or BML210 could hinder the differentiation of vascular progenitors at the second stage and facilitate EC induction at the third stage. Further investigation revealed that HDAC may modulate the stepwise EC differentiation via regulating the expression of endothelial transcription factors ERG, ETS1, and MEF2C. Opposite to the expression of EC markers, the smooth muscle/pericyte marker ACTA2 was upregulated at the second stage and downregulated at the third stage by NaBt. The stage-specific regulation of ACTA2 by HDAC inhibition was likely through regulating the expression of TGFβ2 and PDGFB. This study suggests that HDACs play different roles at different stages of EC induction by promoting the commitment of vascular progenitors and impeding the later stage differentiation of ECs.

Modified method for effective primary vascular smooth muscle progenitor cell culture from peripheral blood

In previous studies, vascular smooth muscle progenitor cells (vSMPCs) isolated from peripheral blood mononuclear cells (PBMCs) were cultured using medium containing platelet-derived growth factor-BB (PDGF-BB) for 4 weeks. However, this method requires long culture periods of up to 4 weeks and yields low cell counts. Therefore, we proposed the modified method to improve the cell yield and purity and to reduce the cell culture period. PBMCs were isolated from human peripheral blood and cultured by the conventional method using medium containing PDGF-BB alone or the modified method using medium containing PDGF-BB, basic fibroblast growth factor (bFGF), and insulin-transferrin-selenium ITS for 4 weeks. The purity of vSMPCs was analyzed for the expression of a- smooth muscle actin (SMA) by flow cytometry and significantly higher in the modified method than conventional methods at the 1st and 2nd weeks. Also, mRNA expression of a-SMA by real-time PCR was significantly higher in the modified method than conventional method at the 2 weeks. The yield of vSMPCs by trypan blue exclusion assay was significantly higher in the modified method than conventional method at the 1st, 2nd and 3rd weeks. The primary culture using the modified method with PDGF-BB, bFGF, and ITS not only improved cell purity and yield, but also shortened the culture period, compared to the conventional culture method for vSMPCs. The modified method will be a time-saving and useful tool in various studies related to vascular pathology.

Do Induced Pluripotent Stem Cell Characteristics Correlate with Efficient In Vitro Smooth Muscle Cell Differentiation? A Comparison of Three Patient-Derived Induced Pluripotent Stem Cell Lines

Human induced pluripotent stem cells (iPSCs) have the potential to repair/regenerate smooth muscle cells (SMCs) in different organs. However, there are many challenges in their translation to clinical therapies. In this study, we describe our observations of in vitro SMC differentiation in three iPSC lines derived from human fibroblasts using retroviral, episomal, and mRNA/miRNA reprogramming methods. We sought to elucidate correlations between differentiation characteristics and efficiencies that can facilitate large-scale production of differentiated cells for clinical applications, and to report differences in pluripotency marker expression in differentiated cells from different iPSC lines. A standardized SMC differentiation protocol was used to induce the CD31⁺/CD34⁺ vascular progenitor cell phenotype. These were sorted by magnetic-activated (MACS) and fluorescence-activated cell sorting (FACS), and then treated with PDGF-BB and smooth muscle growth medium for further differentiation into smooth muscle progenitor cells (pSMCs). The expression of SMC and pluripotency markers in early- and late-passage (P1 and P4) pSMCs was analyzed. A total of 36 differentiation runs was performed on the three patient iPSC lines. All pSMC populations expressed SMC markers and Ki67 consistent with the progenitor phenotype. Initial iPSC density correlated positively with the sorted cell FACS efficiency, and this correlation could be fit to a quadratic equation. We also observed that a specific "honeycomb" pattern of the starting cultured iPSCs cultured correlated with higher efficiency in all three iPSC lines. Pluripotency marker expression decreased significantly to nearly undetectable levels in all three lines. There was no significant change in SMC and pluripotent marker expression between passage 1 and 4. In summary, our observations suggest that the method of iPSC reprogramming does not affect iPSC differentiation into pSMCs. Protocol efficiency can be modeled mathematically and coupled with the initial "honeycomb" cell pattern to optimize production of large cell numbers for clinical therapies.

MicroRNA-20b-5p inhibits platelet-derived growth factor-induced proliferation of human fetal airway smooth muscle cells by targeting signal transducer and activator of transcription 3

Pediatric asthma is still a health threat to the pediatric population in recent years. The airway remodeling induced by abnormal airway smooth muscle (ASM) cell proliferation is an important cause of asthma. MicroRNAs (miRNAs) are important regulators of ASM cell proliferation. Numerous studies have reported that miR-20b-5p is a critical regulator for cell proliferation. However, whether miR-20b-5p is involved in regulating ASM cell proliferation remains unknown. In this study, we aimed to investigate the potential role of miR-20b-5p in regulating the proliferation of fetal ASM cell induced by platelet-derived growth factor (PDGF). Here, we showed that miR-20b-5p was significantly decreased in fetal ASM cells treated with PDGF. Biological experiments showed that the overexpression of miR-20b-5p inhibited the proliferation while miR-20b-5p inhibition markedly promoted the proliferation of fetal ASM cells. Bioinformatics analysis and luciferase reporter assay showed that miR-20b-5p directly targeted the 3'-UTR of signal transducer and activator of transcription 3 (STAT3). Further data showed that miR-20b-5p negatively regulated the expression of STAT3 in fetal ASM cells. Moreover, miR-20b-5p regulates the transcriptional activity of STAT3 in fetal ASM cells. Overexpression of STAT3 reversed the inhibitory effect of miR-20b-5p overexpression on fetal ASM cell proliferation while the knockdown of STAT3 abrogated the promoted effect of miR-20b-5p inhibition on fetal ASM cell proliferation. Overall, our results show that miR-20b-5p impedes PDGF-induced proliferation of fetal ASM cells through targeting STAT3. Our study suggests that miR-20b-5p may play an important role in airway remodeling during asthma and suggests that miR-20b-5p may serve as a potential therapeutic target for pediatric asthma.

Vascular precursor cells in tissue injury repair

Vascular precursor cells include stem cells and progenitor cells giving rise to all mature cell types in the wall of blood vessels. When tissue injury occurs, local hypoxia and inflammation result in the generation of vasculogenic mediators which orchestrate migration of vascular precursor cells from their niche environment to the site of tissue injury. The intricate crosstalk among signaling pathways coordinates vascular precursor cell proliferation and differentiation during neovascularization. Establishment of normal blood perfusion plays an essential role in the effective repair of the injured tissue. In recent years, studies on molecular mechanisms underlying the regulation of vascular precursor cell function have achieved substantial progress, which promotes exploration of vascular precursor cell-based approaches to treat chronic wounds and ischemic diseases in vital organ systems. Verification of safety and establishment of specific guidelines for the clinical application of vascular precursor cell-based therapy remain major challenges in the field.