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  • Coronary artery disease is characterized by a dysfunction of the endothelial cells that form the innermost lining of all blood vessels.
  • A new study has identified five biological pathways regulated by a few genes that could potentially play a prominent role in coronary artery disease through their involvement in endothelial cell function.
  • Notably, these pathways included genes whose role in coronary artery disease has not been previously demonstrated.
  • One of the genes in these pathways, TLNRD1, plays an essential role in endothelial function, cardiovascular health, and potentially coronary artery disease, according to the study.
  • These findings could lead to the development of novel therapies targeting endothelial cell dysfunction in coronary artery disease.

Coronary artery disease is the leading cause of death in the United States. Therapies such as statins, which target high cholesterol levels, can reduce the risk of mortality due to coronary artery disease.

These effects of statins are mediated, in part, by improving blood vessel health. However, there is a lack of therapies for coronary artery disease that directly target the endothelial cells that form the inner lining of blood vessels and influence blood flow.

Identifying genetic risk factors associated with endothelial cell function could help develop therapeutics that target blood vessels.

Research has shown that specific genetic variants are associated with an increased risk of coronary artery disease. These genetic variants regulate the expression of several genes that work together in a small number of major biological pathways.

However, methodological limitations have impeded the identification of major pathways associated with coronary artery disease variants.

A new study using a combination of high-throughput molecular biology techniques and computational methods has identified major biological pathways and novel genes involved in endothelial cell function that could contribute to the risk of coronary artery disease.

The paper reporting the study findings appears in Nature.

Study author Dr. Jesse Engreitz, assistant professor at Stanford University, CA, explained the findings to Medical News Today:

“We found that genetic risk factors for coronary artery disease converge onto a particular pathway in endothelial cells. One of the known roles of this pathway is to tune endothelial cell responses to blood flow, and includes genes that could prove to be good targets for therapies that directly target blood vessels.”

“We also found a new understudied gene, TLNRD1, that plays a key role in this pathway in humans and zebrafish but has previously eluded notice. The list of genes we identified might also prove helpful in identifying individuals who are genetically predisposed to having poor vascular health and, therefore, may respond better to existing medications,” added Dr. Engreitz.

Advances in genome sequencing technologies have facilitated the discovery of genetic variants associated with several diseases. These genome-wide association studies involve examining genomes from a large number of individuals to identify genetic variants associated with a particular disease.

Several of these genetic variants associated with a disease likely regulate a small number of biological pathways, with each pathway consisting of several genes that work together.

Although genetic variants have been identified for several diseases, linking genetic variants to a few converging biological pathways has been challenging.

A majority of these genetic variants identified by genome-wide association studies do not code for proteins. Instead, these noncoding variants regulate the expression of multiple genes nearby that are involved in biological pathways associated with the disease.

However, identifying the specific genes regulated by each variant and playing a role in disease-associated pathways remains challenging.

Moreover, multiple cells contribute to the development and progression of a disease. Different biological pathways operate in each cell type and contribute to the disease. The specific biological pathways in a particular cell type impacted by disease-associated variants have not been fully characterized.

In other words, how genetic variants identified using genome-wide association studies affect biological function is not well understood. In the present study, the researchers investigated the biological pathways associated with genetic variants that are involved in coronary artery disease.

Dr . Engreitz said: “Human genetics has been immensely successful over the last decades in identifying variants that influence risk for disease — there are now 100,000s of associations between genetic loci and particular human diseases and traits. This vast trove of insights could reveal genes that mediate disease and guide therapeutic development.”

“But, it has proven extremely difficult to find the genes, cell types, and pathways underlying each of these associations. Sometimes, it can take a decade to solve this “variant-to-function” problem for even one association,” he added.

More than 300 genetic variants have been identified for coronary artery disease using genome-wide association studies. These coronary artery disease-associated variants are known to impact cells associated with blood vessels and hepatocytes in the liver.

In the present study, the authors specifically examined the variants impacting the function of endothelial cells that are present in the walls of blood vessels.

The researchers used laboratory cultures of genetically modified endothelial cells obtained from the human aorta, the blood vessel that carries oxygenated blood to the rest of the body.

The genome of these endothelial cells was sequenced, and then a computational model was used to map genes whose expression was influenced by the coronary artery disease-associated variant.

With the help of data on coronary artery disease-associated variants identified by previous studies, the researchers identified nearly 2,000 genes close to these variants.

Among these genes, the expression of 254 genes was regulated by the coronary artery disease-associated variants.

The researchers then identified the programs or pathways associated with coronary artery disease. They used CRISPR interference (CRISPRi) to individually inhibit the expression of each gene identified in the vicinity of the coronary artery disease-associated variants.

Subsequently, the researchers examined the changes in the gene expression profile of the endothelial aorta cells upon the inhibition of individual candidate genes.

Using computational methods, genes that showed similar patterns of changes in expression profile were categorized as coregulated genes.

These coregulated genes were classified as a biological program or pathway. The analysis generated 50 such programs, several of which were involved in processes that were not specific to endothelial cells or coronary artery disease.

The researchers then examined programs in which the 254 genes regulated by coronary artery disease-associated variants were overrepresented. They identified five such programs, which encompassed 41 coronary artery disease-associated genes and 43 variants.

While these programs included genes that have been implicated in coronary artery disease, a majority of genes in these pathways have not yet been identified as risk factors for this condition.

In addition, all five programs were regulated by genes associated with the pathway associated with cerebral cavernous malformations (CCM), a condition involving the formation of tiny, abnormal clusters of blood vessels in the brain.

Specifically, the analysis revealed that the CCM2 gene and other genes in the CCM pathway were involved in the regulation of all five coronary artery disease pathways.

Previous studies have shown that the CCM pathway modulates the function of endothelial cells in blood vessels and regulates blood flow.

However, CCM2 and other CCM pathway genes have not been shown to be involved in coronary artery disease. The present study found that inhibiting the expression of CCM pathways modulated the expression of genes that have been shown to be involved in coronary artery disease. These findings indicate the involvement of genes in the CCM pathway in coronary artery disease.

The researchers further examined the role of one of the novel CCM pathway genes, TLNRD1. They focused on TLNRD1 because the gene is one of the strongest regulators of the five coronary artery disease pathways. The role of TLNRD1 in endothelial cell function has not been characterized so far.

The researchers found that TLNRD1 interacts with CCM2 and, consequently, examined whether TLNRD1 performed a function similar to CCM2. The disruption of TLNRD1 in cells cultured in the laboratory altered the barrier function of endothelial cells. Such an impaired barrier function of endothelial cells has been implicated in cardiovascular diseases.

In addition, the disruption of the TLNRD1 expression in zebrafish also adversely impacted heart and blood vessel development in a zebrafish model.

These results support the role of the TLNRD1 gene in sustaining blood flow and could be a risk factor for coronary artery disease development.

Besides aiding the identification of new therapeutic targets for coronary artery disease, the methodological approach used by the study could facilitate the discovery of novel biological pathways associated with other diseases.

Dr. Engrietz said: “In this study, we developed a new methodology to extract lessons from human genetic data. Here, we took a new approach leveraging CRISPR tools, which we use to simultaneously break every candidate gene in different endothelial cells in a dish and measure what happens to these cells. From there, we use computational models to learn which sets of genes are working together in pathways.”

“With this comprehensive and systematic data, we are able to much better interpret genetic associations and here identify likely causal genes for 40 out of [approximately] 300 loci for coronary artery disease in a single pass. We think this tool will be a powerful approach for studying many other heritable diseases in the future,” added Dr. Engrietz.

Dr. Cheng-Han Chen, board-certified interventional cardiologist and medical director of the Structural Heart Program at MemorialCare Saddleback Medical Center in Laguna Hills, CA, not involved in this study, commented that:

“This research has the potential to open an entirely new field of research, as it might be able to identify the molecular connections more efficiently between gene variants and clinical disease. With such a strategy, researchers would then be able to target the biological pathways through therapeutics to improve clinical outcomes.”