Each box that the research group of Dr David Elliott from Monash University sends to international collaborators contains about half a million purified human heart muscle cells. Isolated from other cell types through a remarkable new technique, they are the material through which researchers can study heart function and test therapies for the diseases that attack the engine room of the human body.
One of the keys to ultimate success in finding treatments for heart disease is a deeper understanding of how the cardiac cells within the muscular wall of the heart are both damaged and repaired. For years, scientists and drug companies have been working with unpurified cell lines, unsure of whether the effects they observe, such as cell death, are caused by a reaction of the cardiomyocytes (heart muscle cells) themselves, or by surrounding, supporting cells.
In 2011, an international team led by Dr Elliott, and which also included Monash Professors Andrew Elefanty and Ed Stanley, published a paper in Nature Methods outlining research that would guarantee a potentially inexhaustible supply of heart cells. It was not only the researchers who were glowing from what was lauded as a foundational advance in stem cell science – the cells also glowed.
“Researchers need to study cardiac cells in vitro to understand more about the progression of various forms of the disease,” Dr Elliott says. “They need to be able to screen new drugs safely and establish whether or not they are toxic to heart tissue – but obtaining enough mature, live cardiac cells to do this has proved remarkably difficult.”
Cracking the challenge was a four-year task for the 26 scientists from Monash, the Walter and Eliza Hall Institute, the Baker IDI Heart and Diabetes Institute, the Leiden University Medical Centre and the Netherlands Proteomics Centre.
They had a little help from a jellyfish – Aequorea victoria, an almost crystal-clear medusa jellyfish that haunts the Atlantic waters off North America and Europe. Since the 1990s, stem cell scientists have been using a green fluorescent protein from the jellyfish as an invaluable way to mark cells by making them glow green in ultraviolet light.
“When you grow a culture of embryonic stem cells, you can encourage it to produce specialised cardiac cells using certain growth factors,” Dr Elliott says. “But how do you then identify and separate these from the smooth muscle cells and other types in the culture? That was the first big challenge.”
Through a genetic procedure, the team modified human embryonic stem cell cultures with the fluorescent jellyfish protein so that it would hook up exclusively to a gene called NKX2-5. This gene goes into action in the earliest stages of embryo development, when the tiny heart begins to form, and helps to shape the growing tissue into a mature organ. The researchers could therefore make potential cardiac cells reveal their identity by glowing bright green under ultraviolet light. Better still, the cells did this several days before actually maturing into beating heart cells, which meant the team could identify the fully developed cardiomyocytes as well as heart progenitor cells, which are destined to differentiate into heart cells.
But after identifying these cells, how would the researchers physically isolate them? The team solved this second challenge by identifying a pair of proteins on the surface of the glowing cardiac cells, which they were able to use as biochemical ‘handles’. They grabbed them with specialised antibodies, a cheap and efficient way to separate the cardiomyocytes from other cells.