Cardiovascular disease is the leading cause of death in the United States and is marked by the development of pathological vascular remodeling which contributes to disease progression. In response to injury or pathological stimuli, resident vascular smooth muscle cells (SMCs) contribute to these remodeling processes by de- differentiating from a quiescent, contractile phenotype towards a proliferative, pro-inflammatory, pro-fibrotic phenotype capable of recruiting immune cells like macrophages and T-cells. The preliminary data supporting this proposal indicates genetic, systemic upregulation of the potent tumor suppressor PTEN maintains SMC differentiation, reduces perivascular immune cell recruitment and blunts remodeling in multiple pre-clinical animal models of cardiovascular disease. This suggests that pharmacologic PTEN upregulation could hold significant therapeutic potential in treating cardiovascular disease by inhibiting vascular remodeling. Currently, the therapeutic potential of PTEN is not fully exploited as there are few compounds known to increase PTEN expression. To fill this knowledge gap, a recently completed high-throughput compound screen (HTS) of over 2,500 compounds using a fluorescence-based PTEN promoter-reporter system was used to identify 11 hit compounds with dose-responsive ability to induce PTEN promoter activity. Recently, JQ1, an inhibitor of the epigenetic reader protein Brd4 that is known to have anti-remodeling effects, was shown to upregulate PTEN. However, preliminary data presented in this proposal suggest that the anti-remodeling effects of JQ1 are blunted in PTEN depleted SMCs both in vitro and in vivo, suggesting that the protective effects of JQ1 are mediated through PTEN upregulation. Little is known about the role of Brd4, the target of JQ1, in regulating PTEN levels in SMCs. However, Brd4 has been shown to interact directly with the histone acetyltransferase p300 and the p65 subunit of the pro-inflammatory transcription factor NFkB, both of which are known to affect PTEN expression. This application presents a novel model of PTEN regulation where competition for limited amounts of p300 drives either PTEN expression through promoter acetylation, or inflammatory gene expression through p300-NFkB interaction mediated by Brd4.
Specific Aim 1 will expand upon the preliminary data and will use in vitro and in vivo PTEN depletion to determine whether the vasculoprotective effects of JQ1 are due to increased PTEN expression mediated by increased p300 activity at the PTEN promoter and inhibition of Brd4-p300-NFkB complex formation.
Specific Aim 2 will extend the results of the completed HTS to test hit compounds in vitro and in vivo for their ability to induce PTEN expression and reduce vascular remodeling, focusing specifically on how PTEN upregulation affects crosstalk between SMCs and recruited macrophages/T-cells. To summarize, these studies will explore a potentially novel mechanism regulating PTEN expression which may play an essential role in mediating the known anti-remodeling effects of JQ1 and will identify novel compounds targeting PTEN that could be developed as new translational therapies for cardiovascular disease.
Vascular remodeling is a key component underlying many of the complications related to cardiovascular disease, which is the leading cause of death in our country. The preliminary results shown in this proposal indicate that increased expression of the tumor suppressor gene PTEN, which has not been studied as a treatment for cardiovascular disease, strongly impairs the processes that drive vascular remodeling. The proposed research will explore a previously unknown mechanism that may cause increased PTEN expression and attempt to identify compounds that elevate PTEN levels to develop new treatments for cardiovascular disease.
