Abstract 131: Gata4 Ablation In Smooth Muscle Cells Reduces Aortic Root Dilation In A Murine Model Of Loeys-Dietz Syndrome

Loeys-Dietz syndrome (LDS) is a connective tissue disorder characterized by predisposition to aneurysm. Although dilation can develop in all segments of the arterial tree, the aortic root is especially prone to disease. This aortic region is primarily composed of vascular smooth muscle cells (VSMCs) derived from secondary heart field (SHF) progenitors, while VSMCs derived from the cardiac neural crest (CNC) predominate in the more distal ascending aorta. Although intrinsic differences have been found between these two types of VSMCs, it remains unclear how these may contribute to localized risk. To identify transcripts associated with the vulnerability of the aortic root in LDS, we performed single cell transcriptomic analysis on proximal aortas from 16-week-old control and Tgfbr1 M318R/+ LDS mice, which carry a kinase-inactivating mutation in TGF-β Receptor 1. We identified four major VSMC clusters regardless of genotype, with two clusters being defined by CNC-enriched transcripts and two clusters by SHF-enriched transcripts. The latter were defined by expression of Gata4 , which codes for a transcription factor required for development of SHF-derived vascular structures, as well as by higher expression of transcripts previously involved in aneurysm pathogenesis such as Thbs1 , Tgfb1, and Tgfb3. In situ RNA hybridization confirmed that Gata4 -expressing VSMCs were enriched in the aortic root and proximal ascending aorta, with almost no expression in the more distal ascending aorta, suggesting that this transcript defined the aortic region most susceptible to the effects of the Tgfbr1 M318R/+ mutation. GATA4 protein levels were also upregulated in the aortic root of LDS mice. To test if excessive GATA4 expression or activity in VSMCs contributed to aortic root dilation in LDS, we generated LDS mice in which Gata4 was specifically deleted in VSMCs by tamoxifen administration at 6 weeks of age. We found that this intervention significantly reduced aortic root growth from 8 to 20 weeks of age. Although the mechanisms remain under investigation, these data suggest that expression of Gata4 might sensitize specific subsets of aortic VSMCs to the effects of an LDS mutation, rendering the aortic root more susceptible to disease.