Our knowledge of coding RNAs, such as the function of mRNAs, has contributed immensely to our understanding of fundamental cellular processes such as regulation of gene expression and cell differentiation. Recently, transcripts in intergenic regions or within introns of vascular-specific genes are emerging as a new class of RNA molecules that may play a role in the intricate regulation of angiogenesis, the growth of new blood vessels from existing vasculature. These RNAs are referred to as non-coding RNAs (ncRNAs), and are classified as long (>200 bp) (lncRNAs) or short (<200 bp) (sncRNAs) depending on their sizes. Recent evidence suggests that a majority of lncRNAs in the genome do not code for proteins. They are located in the sense (S) or antisense (AS) orientation and, to date, the functional significance of these ncRNAs is poorly understood. Our long-term goal is to understand the underlying mechanisms utilized by ncRNAs during embryonic vascular development in order to effectively block them in disease states affected by deregulated vessel growth such as tumor angiogenesis and Vascular Anomalies (VAs). To pursue this long-term goal, the objective of this application is to study lncRNAs identified by our group for vascular gene delta like 4 (Dll4) that is located in AS direction to the Dll4 gene, and hereafter referred t as Dll4AS. We have identified multiple lncRNAs (Dll4AS1-3) for the vascular gene Dll4 in mice, and each Dll4AS RNA is expressed to varying levels in murine endothelial cell line (MS1) and primary human endothelial cells (ECs). Our central hypothesis is that, Transcriptional regulation of Dll4 occurs via a chromatin-mediated mechanism whereby regions in the Dll4 genomic locus are responsible for Dll4AS and Dll4 expression. This regulation is critical for normal angiogenesis (tip vs. stalk cell specification), and is deregulated in abnormal angiogenesis (artery-vein malformation), events associated with Notch signaling. This hypothesis is formulated based on preliminary data from our group that changes in both Dll4 and Dll4AS mRNA is observed under various experimental modulations such as cellular confluence, Notch inhibition, growth factor, and drug treatments. Further, we have identified a specific genomic region in the Dll4 locus that regulates the expression of both Dll4AS and Dll4 sense RNA, and knocking down the Dll4AS RNAs by silencing RNA-based approach in vitro in mouse ECs showed lower Dll4 expression in mouse ECs, and increases proliferation. Also, levels of both Dll4 and Dll4AS vary in different VAs sub-types. The proposed hypothesis will be tested by pursuing three specific aims: 1) Define the factors and mechanism involved in the regulation of Dll4 gene and Dll4AS; 2) Determine the role of dll4AS-dll4mRNA regulation in embryonic angiogenesis; and 3) Determine the extent of DLL4AS-DLL4 mRNA regulation in VAs. In each of these aims, we will employ a variety of cell biology, molecular, and developmental biology approaches to unravel the mechanistic basis for regulation of Dll4AS and Dll4 sense RNA in the developing vasculature, and its implications in VAs. The approach is innovative because exploiting the sensitivity of this regulation would benefit strategies where modulating the cognate transcript (DLL4) up or down using lncRNAs would be beneficial therapeutically for clinical conditions where more (peripheral artery disease) or less (tumor growth) angiogenesis is recommended. The proposed research is significant because identifying lncRNA signatures in select VA patient samples may serve as a diagnostic tool to distinguish between the sub-sets of these anomalies, and thus help in the accurate prognosis and treatment options in the clinic for these patients. DLL4AS RNA in itself could be a target for VAs, which would facilitate RNA-based therapeutic approaches such as Aptamers that have been successful in the clinic setting.
The proposed research is relevant to public health because vascular anomalies (VAs) represent an important clinical problem that has few therapeutic options. The successful development of RNA-based therapeutics for VAs will provide much needed options for treatment. This proposal and its mechanistic focus on regulation of Dll4AS RNA will provide the rationale for developing RNA-based therapeutics targeting Dll4. Thus, the proposed research is directly relevant to NIH's mission of reducing the burden of debilitating health conditions from diseases affected by deregulated vasculature.
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