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).