MKL1 Mediates Epigenetic Regulation In Cardiovascular Disease

Pulmonary hypertension contributes to the morbidity and mortality of adult and pediatric patients with various lung and heart diseases.Importantly, many of these diseases or conditions are associated with persistent or intermittent hypoxia.Chronic hypoxic exposure induces changes in the structure of pulmonary arteries, as well as in the biochemical and functional phenotypes of each of the vascular cell types. Hypoxia induces changes in the endothelial cell, for example, hypoxia can increase expression of cell adhesion molecule(CAM) on endothelial cells, leading to proinflammatory interactions with circulating cells that collectively participate in the pulmonary hypertensive response. The molecular switch that hypoxia induces CAM transactivation is not clearly defined.Megakaryocytic leukemia 1(MKL1), also known as MRTF-A(myocardin-related transcription factor A) or MAL (myeloid acute leukemia). As a transcriptional regulator, MKL1 potentiates SRF-dependent transactivation of genes specific to cells of the muscle lineage thereby playing a key role in the phenotypic modulation of smooth muscle cells. Our previous study reported that oxLDL promoted the nuclear accumulation of MKL1. Then, MKL1 is recruited to the ICAM-1 promoter by interacting with NF-κB/p65, and contributes to the proatherogenic agenda initiated by oxLDL. In addition, one important feature of MKL1 is that it can tie the epigenetic machinery to regulate genes expression. Our previous research indicated that MKL1 can interact with ASH2, a component of the histone H3K4 methyltransferase complex and regulate the transcription of pro-inflammatory cytokines in macrophages.Here we report that MKL1 deficiency ameliorates HPH in mice paralleling a decrease in CAM expression in the lungs with a concomitant reduction of leukocyte adhesion. In cultured human vascular endothelial cells(HVECs), over-expression of MKL1 enhanced, while depletion of MKL1 dampened, hypoxia induced CAM transactivation. In response to hypoxia, MKL1 formed a complex with NF-B on the CAM promoters. Of intrigue, MKL1 was responsible for recruiting a histone H3K4 methyltransferase complex to ICAM-1 promoter. Finally, endothelial specific silencing of ASH2 and WDR5, two key components of the H3K4 methyltransferase complex, ameliorated HPH in mice. Therefore, our data portray MKL1 as a determining factor of HPH, and suggest that MKL1 may be one of the effective target in clinical treatment of hypoxic pulmonary hypertension.The vascular endothelium plays a fundamental role in the maintenance of rhythmic vascular tone, by regular relaxation and contraction. Increased synthesis of endothelin-1 (ET-1) by HVECs in response to hypoxia underscores persistent vasoconstriction observed in patients with pulmonary hypertension. The molecular mechanism whereby hypoxia stimulates ET-1 gene transcription is not well understood. Here we report that MKL1 potentiated hypoxia-induced ET-1 transactivation in HVECs. Disruption of MKL1 activity by either a dominant negative mutant or small interfering RNA mediated knockdown dampened ET-1 synthesis. MKL1 was recruited to the proximal ET-1 promoter region in HVECs challenged with hypoxic stress by the sequence-specific transcription factor serum response factor (SRF). Chromatin immunoprecipitation analysis of the ET-1 promoter revealed that MKL1 loss-of-function erased histone modifications consistent with transcriptional activation. In addition, MKL1 was indispensable for the occupancy of Brgl and Brm, key components of the chromatin remodeling complex, on the ET-1 promoter. Brg1 and Brm modulated ET-1 transactivation by impacting histone modifications. In conclusion, our data have delineated a MKL1-centered complex that links epigenetic maneuverings to ET-1 transactivation in HVECs under hypoxic conditions.ET-1 was initially identified as a potent vasoconstrictor contributing to the maintenance of vascular rhythm. Later studies have implicated ET-1, when aberrantly up-regulated within the vasculature, in a range of human pathologies with a role in the disruption of vascular homeostasis. ET-1 has been shown to invoke strong pro-inflammatory response in vascular smooth muscle cells (VSMCs); the underlying mechanism, however, remains elusive. Here we report that the transcriptional modulator MKL1 mediates the activation of pro-inflammatory mediators by ET-1 in VSMCs. MKL1 silencing attenuated ET-1 induced synthesis and release of pro-inflammatory mediators including IL-6, MCP-1 and IL-1β. In addition, MKL1 was indispensible for the accumulation of active histone modifications on the gene promoters. Of intrigue, MKL1 interacted with and recruited ASH2 to transactivate pro-inflammatory genes in response to ET-1 treatment. The chromatin remodeling protein BRG1 and BRM were also required for ET-1 dependent induction of pro-inflammatory mediators by communicating with ASH2, a process dependent on MKL1. In conclusion, our data have identified a novel epigenetic complex responsible for vascular inflammation inflicted by ET-1.Endothelial dysfunction and vascular inflammation causes vascular injury and promote a series of cardiovascular diseases, including atherosclerosis, myocardial hypertrophy and pulmonary arterial pressure. Our studies mainly focused on the molecular mechanism of hypoxic pulmonary hypertention.We reported that MKL1 can crosstalk with chromatin remodeling protein and histone H3K4 methyltransferase complex, induced CAM and ET-1 transactivation. And then promote the inflammatory response to vascular injury.As such, targeted inhibition of MKL1 is expected to become the effective intervention of cardiovascular disease.