PTEN promoter hypermethylation underlies vascular disease progression

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ABSTRACT Atherosclerosis and restenosis are chronic and acute inflammatory vascular diseases, respectively, characterized by significant vascular remodeling. Phenotypic switching of resident vascular smooth muscle cells (SMCs) plays a unique and critical role in remodeling and is a key event promoting disease progression. While the concept of SMC phenotypic modulation, marked by a shift from a differentiated, contractile phenotype to a dedifferentiated, pro-inflammatory phenotype, is well-accepted, the mechanisms regulating these SMC transitions are complex. Importantly, there are no therapeutics that prevent both the loss of the SMC contractile phenotype and increased inflammation. We previously established that PTEN is critical in the regulation of pathological vascular remodeling. PTEN inactivation promotes a dedifferentiated, inflammatory SMC phenotype. More recently, we defined an entirely unique and essential function for nuclear PTEN as a transcriptional co- factor with SRF, a master transcription factor regulating SMC contractile gene and SMC-specific miR-143/145 expression, and its muscle-specific cofactor, myocardin. PTEN loss prevents SRF-myocardin transcriptional activity. Translationally significant, this activity was confirmed in normal and diseased human coronary arteries as we established that PTEN loss directly correlated with SMC dedifferentiation and atherosclerosis progression and complexity. The mechanism mediating loss of PTEN in this setting was unclear. We recently demonstrated that systemic PTEN elevation blunts angiotensin II (AngII)-mediated vascular remodeling and fibrosis and blocks atherosclerotic lesion progression and injury-mediated neointima formation; these effects are associated with preservation of a contractile SMC phenotype and a reduced inflammatory microenvironment. Thus, our data support that PTEN is an essential driver of the differentiated SMC phenotype through direct transcriptional control of SMC contractile genes and repression of a proinflammatory phenotype and indicate that systemic PTEN upregulation is sufficient to prevent vascular disease progression. A recent unbiased high throughput screen designed to discover novel small molecule activators of PTEN revealed that the DNA methyltransferase 1 (DNMT1) inhibitor, 5-azacytidine (5-aza), robustly upregulates PTEN at the level of transcription, reverses PDGF-mediated SMC dedifferentiation and repression of the DNA methylcytosine deoxygenase, TET2, and blocks pathological vascular remodeling. Importantly, these effects both in vitro and in vivo are mediated via PTEN. We propose that hypermethylation of the PTEN gene is an essential mechanism that reduces PTEN levels and promotes pathological vascular remodeling (Aim One). In addition, we propose that the vascular protective effects mediated by 5-aza are driven through increased PTEN expression, crosstalk between PTEN and TET2, and downstream regulation of miR-143/145 (Aim Two). Finally, we propose that increased PTEN promoter hypermethylation correlates with increased atherosclerosis progression, upregulation of DNMT1, and downregulation of TET2 in diseased human vessels (Aim Three).