br Author disclosure statement br Acknowledgements Authors w
Author disclosure statement
Acknowledgements Authors would like to thank Dr. T. Ramakrishna Murti for his valuable comments and linguistic corrections in the manuscript. Authors would also like to thank D.I Biotech (Seoul, Korea) for support to analyze neurite outgrowth. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MEST) (NRF-2014R1A2A2A01006556 and NRF-2013R1A1A2062711), and CSIR network project BSC 0115 (mIND) INDIA (BSC-0115).
Introduction Smooth muscle cells (SMCs) form the walls of blood vessels, providing the healthy vessel with its structure and contributing to the formation and progression of atherosclerotic plaques. Alterations in the normal structure or function of the differentiated VSMCs play a major role in a number of diseases, including atherosclerosis, cancer, and hypertension (Owens et al., 2004). A better understanding of the mechanisms and molecular regulation of VSMC differentiation is needed for both prevention and treatment of these diseases. Stem cells are long-lived cells with a remarkable capability of both self-renewal and differentiation into multiple specialized cell types (Weissman, 2000). ESCs are pluripotent stem cells derived from the inner cell mass of a Phos-tag (Thomson et al., 1998). Several in vitro models have been well established to understand the regulation of VSMC differentiation, but the underlying molecular mechanisms have not been fully clarified (Xie et al., 2011). MicroRNAs (miRs) are small non-coding RNAs (~22 nucleotides) that bind to complementary sites of their target mRNAs and inhibit their translation (Hutvagner et al., 2001; Rossi, 2005). They are diverse in sequence and expression patterns (Ambros, 2001). In recent studies, miRs have been suggested to play a major role in regulating gene expression in most organisms and have been implicated in regulating the self-renewal and differentiation program of stem cells (Ivey et al., 2008; Martinez and Gregory, 2010). Emerging evidence clearly suggests that miRs play a broad role in multiple aspects of endothelial biology, and have been proven to be critical in mediating endothelial cell (EC) differentiation (Zhou et al., 2014). Previous studies have shown that miRs can affect VSMC biology, including phenotypic switching, proliferation, and migration. Especially, miR-143/miR-145, miR-21, and miR-133 have been reported to play a role in VSMC differentiation (Robinson and Baker, 2012). MicroRNA-29a (miR-29a) has been extensively investigated in different fields. Roberta et al. reported that miR-29a is significantly associated with hypertrophy and fibrosis, suggesting that miR-29a can be a potential biomarker for hypertrophic cardiomyopathy (Roncarati et al., 2014). MiR-29a also functions as a negative regulator of collagen gene expression. Maintaining miR-29a expression would have beneficial effects in fibrotic diseases (van Rooij et al., 2008). As an important regulator of the inflammatory response, miR-29a regulates scavenger receptor expression by targeting lipoprotein lipase (Chen et al., 2011). In addition, miR-29a has been implicated in malignancies (Pekarsky and Croce, 2010) and found to be highly expressed in the endothelium (Poliseno et al., 2006). However, little is known about the functional involvement of miR-29a in VSMC biology. In the current study, we aimed to investigate the biologic activity of miR-29a in VSMC differentiation from ESCs and have uncovered a novel mechanism that miR-29a regulates VSMC differentiation via suppression of a transcription factor, YY1.
Materials and methods
Discussion Alteration in the normal structure or function of differentiated VSMCs plays a major role in a number of diseases, including atherosclerosis, hypertension, and cancer. The underlying molecular mechanisms of VSMC differentiation remain to be elucidated. Accumulating evidence has demonstrated that the gene regulatory program of VSMC differentiation from pluripotent stem cells is orchestrated by a coordinated molecular network with various signaling pathways and molecules involved, such as mechanical forces, contractile agonists, extracellular matrix components (laminin and type I and IV collagen), Matrix Metalloproteinases (Chen et al., 2013), neuronal factors, reactive oxygen species (Zhou et al., 2013), endothelial SMC interactions, thrombin, TGF family, notch family (Tang et al., 2010), and miRs. Although all of these factors have been shown to promote expression of at least some VSMC marker genes in cultured cell systems (Owens et al., 2004; Xie et al., 2011), our understanding of the molecular mechanisms underlying VSMC differentiation from ESCs is still far from complete. In this study, we revealed an important role of miR-29a in regulating VSMC specific gene expression and VSMC differentiation from ESCs in vitro and in vivo. We presented the first evidence to support a functional role of YY1 in VSMC differentiation and VSMC specific gene regulation. We also provided the evidence to support that the identified target gene of miR-29a, YY1, functions as an important VSMC differentiation gene repressor during VSMC differentiation from stem cells.