Deep in the cells of nearly all living things are sequences of DNA known as genes. When genes are activated, they instruct specific proteins to perform specific biological tasks that drive the development or functioning of an organism. In the simplest terms possible, this is the process of gene expression.
It’s no surprise that scientists exploring the frontiers of tissue engineering (the act of growing tissue to study diseases, test drugs, or even transplant organs) are keenly interested in ways to control gene expression.
Gene expression is typically triggered by a cell’s response to its environment, which is always changing and spatially complex. Where things are in relation to one another has a lot to say about what happens next in the chain of events.
That’s why the ability to regulate gene expression is imperative for the field of tissue engineering. Researchers hoping to create disease models or regenerate organs need systems that precisely mimic the degree of complexity found in the natural world.
For years, tissue engineers have used light to cue genes in man-made environments. However, this approach has limitations. Light does not penetrate thick tissue very well. Just try shining a flashlight through your hand. In other cases, drugs have been used to activate genes. But drugs are difficult to aim at a particular gene or cell. Hence the quest for a tool that was both penetrant and precise.
Now, in a breakthrough for tissue engineering, a research team from the Institute for Stem Cell and Regenerative Medicine (ISCRM) has shown that another energy source – heat – can be used to turn on selected genes in three-dimensional tissue models. The findings are detailed in a paper published in Science Advances. Daniel Corbett, a PhD student in the Stevens Lab, is the lead author of the study, which was led by ISCRM faculty member Kelly Stevens, PhD, Assistant Professor of Bioengineering and Laboratory Medicine and Pathology.
In their investigation, Corbett and Stevens developed a cutting-edge system designed to recreate gene expression patterns found in the body’s great multitasker – the liver. “The liver performs a mind boggling number of functions,” says Stevens. “It makes proteins. It metabolizes drugs. It filters blood. And there’s really only one kind of cell doing all these jobs – but what job those cells do depends a great deal on where they are located.”
The compartmentalization of the liver makes it the perfect proving ground to test a tool built to reconstruct the spatial patterns of gene expression. First, the researchers used sophisticated 3D printing equipment, developed with Jordan Miller at Rice University, to print channels similar to the vessels in the liver that carry blood through a series of gradients – a capability shown in a May 2019 paper published in the journal Science. Next, they injected hot water into the channels and engineered liver cells to express a protein that makes fireflies light up – creating a beacon that helped them track how the cells responded.
Stevens and Corbett saw that the application of heat through water induced the cells to activate pathways that are vital for liver functions. The genes they triggered are part of pathways present not just in livers or even in humans, but in living tissue across various stages of development throughout the full spectrum of the animal kingdom.
“The implications are much broader than the liver,” says Stevens. “Ultimately the goal is to improve other disease modeling technologies that are critical for drug testing and to bring us closer to artificial tissues for therapy. Here we demonstrated the viability of a tool that uses genetic engineering, 3D printing, and biomaterials all working together in a system.
Corbett emphasizes the potential of a tool that other researchers can use to explore questions about the downstream effects of gene expression in cells and tissues. “I’m most excited about seeing where this goes and what the reaction of the scientific community will be. It’s one of those “out there” projects that hasn’t really been done before. Hopefully it will create another burst of novel, creative ideas that puts the tool to good use. Just knowing this is feasible opens all kinds of other possibilities about what else we can do.”
This research was funded by NIH NHLBI grant DP2HL137188 (K.R.S.), the NIH NIBIB Cardiovascular Training Grant (D.C.C., T32EB001650), the NIH Environmental Pathology and Toxicology Training (W.B.F., T32ES007032), the NSF Graduate Research Fellowship (B.G., 1450681), the Ford Foundation Predoctoral Fellowship (C.E.O.), the Washington Research Foundation postdoctoral fellowship (M.C.R.), the Robert J. Kleberg, Jr. and Helen C. Kleberg Foundation (J.S.M.), and the Gree Foundation (I.B., K.R.S., and C.A.D.).