“For multiple reasons, this region has been very hard to study,” says Valentina Lo Sardo, the lead researcher on this project, an assistant professor of Cellular and Regenerative Biology, and a Stem Cell and Regenerative Medicine Center member. “This region is only present in the genome of humans and a few non-human primates, so you cannot make an animal model that faithfully recapitulates the genetics of the human species. What we used instead is something that is very much human specific, which is iPSC. The fact that we can make iPSC from any living donors and from donors that have a specific genotype at this particular region is so important for us. I think it’s an extremely powerful tool.”
Lo Sardo’s lab differentiated the iPSCs into vascular smooth muscle cells and studied how the cells of donors carrying the risk variants at the 9p21.3 locus behaved vs those of donors who carry the protective variants. They discovered that smooth muscle cells carrying the risk version of 9p21.3 behaved differently, shifting in a cell state to resemble the features of cells seen in cartilage and bone.
“This was quite remarkable,” says Lo Sardo. “What we found is that the cells change their transcriptional makeup, and they are in between smooth muscle and these osteochondrogenic [or bone-like] cells. We discovered that these cells are more prone to calcification. And this is very important, because CAD is basically atherosclerosis [a hardening of the arteries] and calcification of the arteries is one of the hallmarks of this type of pathology.” Lo Sardo’s group used genome editing to remove the risk version of 9p21.3 and were able to see that the cells revert to a “healthy” status, showing that “disarming” the risk effect of this genomic region may be valuable to reenabling smooth muscle cells to exert their function.