Bespoke blood vessels

There is a saying that goes, “A man is as old as his arteries.” Indeed, many health conditions originate from one’s blood vessels, which is why understanding how blood vessels age is the impetus for our research. With the goal of preventive medicine in mind, we are finding ways to restore blood vessel health before adverse outcomes happen. One major limitation in biomedical research is the lack of tools to reliably study human biology. Hence, we pioneered novel methods of converting human stem cells into blood vessel cells, including those found in the heart and brain.

These methods have contributed significantly to the development of personalised blood vessel models, enabling us and the wider scientific community to investigate how underlying physiology is perturbed in individual patients.

Studying those prone to vascular diseases

What makes blood vessels in our brain differ from those in our heart? Blood vessels develop to meet the metabolic demands of different organs, resulting in a great diversity of shapes and sizes depending on the organ they serve.

To understand how this heterogeneity comes about, we invented methods to derive organ-specific blood vessel cell types (such as smooth muscle cells and endothelial cells) using human pluripotent stem cells that self-renew. These vascular cell populations greatly facilitate research studies such as gene editing and rigorous hypothesis testing (Figure 1).

Figure 1: (A) Vascular smooth muscle cells and (B) endothelial cells created from human stem cells express relevant vascular and functional markers. The endothelial cells form tubular structures, resembling a vascular network.

One of the key applications of our work is in understanding what makes certain people genetically predisposed to vascular diseases. Advances in genome sequencing have revealed genetic variations that are associated with cardiovascular diseases and stroke. However, the translation of these findings into the intended benefit of therapy and diagnostics has been impeded by limitations in animal models or commercially available human primary cells.

To capture the diverse and complex genotypes found in humans, we convert patients’ stem cells into their own vascular cells, from which we can extract molecular information and study how cellular functions are altered due to the presence of genetic risk variants.

Testing drugs for safety and efficacy

The high attrition rates of drug candidates, as well as drug withdrawal due to previously unidentified side effects, have created a shift from the use of pre-clinical research animals towards human cellular models that provide more predictive human responses.

In a recent effort, we generated vascular cell populations from human pluripotent stem cells, arranged them into 3D co-cultures within supportive gel matrices, and directed their self-assembly into microtissues resembling microvasculature (Figure 2A).

The 3D vascular constructs were then used to screen a library of environmental and chemical compounds for immunological and toxicological responses. We found that chlorothalonil and heptadecafluorooctanesulfonic acid in particular affected endothelial cell survival. In dose-response studies, endothelial cells demonstrated lower tolerance for both chemicals as compared to smooth muscle cells (Figure 2B).

Figure 2: (Top) A 3D vascular construct made up of smooth muscle cells (green) and endothelial cells (red). (Bottom) Dose-response curves of chemicals to identify toxicity to vascular cells (red: endothelial cells; blue: smooth muscle cells; purple: co-cultures). Reprinted from Stem Cells and Development (2019), DOI: 10.1089/scd.2018.0246, published by Mary Ann Liebert, Inc., New Rochelle, NY, with permission.

Our blood vessel models recapitulate bona fide aspects of human biology and physiology. They enable early pre-clinical and toxicological testing, thereby providing more accurate safety assessment of therapeutic candidates in comparison to animal models.

In addition, the ability to create blood vessels from specific individuals opens the door to evaluating drug responders versus non-responders. Taken together, we hope that our research will inform personalised strategies for managing diseases through restoring blood vessel health.

Author: Christine Cheung

Nanyang Asst Prof Christine Cheung, NTU Provost’s Chair in Medicine, leads the Laboratory of Molecular and Vascular Medicine at NTU’s Lee Kong Chian School of Medicine. She has won prestigious accolades in recent years, including being named one of the world’s best scientists under the age of 40 by the World Economic Forum in 2019, and receiving the L’Oréal Singapore For Women in Science National Fellowship and Junior Chamber International Ten Outstanding Young Persons Singapore Award for her achievements in medical innovation. Last year, she also won the Human Frontier Science Programme Young Investigator Grant, which provides funding of US$250,000 per year for three years for her studies on how the human brain is assembled during the embryonic stage and the role that blood vessels play in that process.

Parts of the research presented here have been published in Stem Cells and Development (2019), DOI: 10.1089/scd.2018.0246; Stem Cells Translational Medicine (2017), DOI: 10.5966/sctm.2016-0129; Cell Reports (2014), DOI: 10.1016/j.celrep. 2014.08.065; and Nature Biotechnology (2012), DOI: 10.1038/nbt.2107.

The article appeared first in NTU’s research & innovation magazine Pushing Frontiers (issue #16, February 2020).