Studies of human diseases such as cancer rely on the use of laboratory-grown cell cultures that have often been grown for decades. Now, new research indicates that these cell cultures may not be a reliable copy of real tissue; a finding that casts doubt on the interpretation of many past studies.
The researchers, from the MRC Human Genetics Unit at the University of Edinburgh (Scotland) and Linkoping University (Sweden), have revealed just how quickly cells change their identity when grown in the laboratory. They found that cultured cells undergo significant changes within one week of growth in a laboratory dish.
“We were astonished by the speed and spread of the changes. Many cultured cells used in research have been grown for decades and as a result are likely to have very different properties from the cells they are supposed to model. Our findings suggest that we have to be circumspect about the interpretation of some previous experiments, and our data reinforces a growing realization that cell line models of human diseases, particularly cancer, can be poor surrogates for many aspects of in-vivo biology,” said study author Richard Meehan from the MRC Human Genetics Unit.
For the study (appearing in Genome Biology), the researchers compared the DNA of mouse cells, taken from male and female embryos, with cells that were cultured in plastic dishes. They found a number of indicators that the cultured cells underwent an altered cell state as they became adapted to the cell culture environment, including a decrease in gender differences between male and female cultured cells.
“The mouse cells in culture experienced a rapid reprogramming of their epigenomes – a layer of chemical modifications that mark the genome to control how genes are expressed. This was indicated by a near-complete loss of one epigenetic mark, 5-hydroxymethylcytosine [5hmC], within three days over the whole genome,” explained Meehan.
They also found similar results in an unrelated tissue. Using mouse CD4 T-cells, which have a role in the immune system, they found an almost five-fold reduction in 5hmC levels after three days in culture.
In addition, the researchers saw that there were widespread changes in gene expression for cells in culture, affecting over 7,200 genes. Some of these genes were linked to cell adhesion, possibly reflecting adaptation to growth on a two-dimensional plastic surface, and others were involved in a variety of epigenetic processes.
Interestingly, the researchers found that some of these changes could be prevented by adding Vitamin C to the culture medium. This suggests that by improving culturing techniques, researchers may be able to more accurately match cells grown on a dish to cells that are taken directly from tissues. Such improvements could allow researchers to have more confidence that what they observe in the laboratory accurately reflects what is happening in the body.