Novel Regulators of Serum Lipid Levels and Atherosclerosis

Cardiovascular Disease is the leading cause of mortality in the United States, and its incidence is expected to grow. Both environmental and genetic factors contribute to Cardiovascular Disease. Elevated fasting and postprandial plasma cholesterol and triglyceride levels have been recognized as important risk factors for Cardiovascular Disease. However, despite large-scale human Genome- Wide Association Studies (GWAS), it is predicted that only 25% of the genes that contribute to altered serum lipid levels have been identified. Thus, there is a clear need to identify additional genes and genetic pathways that contribute to Cardiovascular Disease. Experimental organisms, including mice, can help elucidate the genetic basis of this disease. The Zinc fingers and homeoboxes (Zhx) family of proteins is comprised of Zhx1, Zhx2 and Zhx3. Structural features of Zhx proteins and several studies indicate that Zhx proteins are transcription factors involved in gene regulation. Furthermore, Zhx proteins are ubiquitously expressed, suggesting that they could regulate target gene expression in a number of different tissues. These proteins are found only in vertebrate organisms, and little is known about their physiological function. We recently showed that Zhx2 controls serum lipid levels and influences the formation of atherosclerotic plaques. Preliminary evidence suggests that Zhx3 also regulates serum lipid levels. Based on these data, we propose to investigate further the roles of Zhx2 and Zhx3 in controlling serum lipid levels and atherosclerosis. To accomplish this, we will develop and utilize mouse models. We recently developed mice that contain a floxed allele of Zhx2. In aim 1, we will use these mice to delete Zhx2 specifically in liver or adipose tissue. These mice (and control littermates) will be placed on a normal or high fat diet for 8 weeks, followed by analysis of serum lipids and atherosclerotic plaques. These studies will allow us to determine how Zhx2 target genes in the liver and adipose tissue contribute to serum lipid homeostasis and atherosclerotic plaque formation. In the second aim, we will develop mice that contain a floxed allele of Zhx3 by gene targeting in embryonic stem cells. These mice will be used in future studies in which Zhx3 can be deleted in specific tissues. The data generated from these aims will form the basis for future studies that will explore Zhx2 and Zhx3 and other genetic factors that control serum lipid levels and atherosclerotic lesion formation.