Dr. Heather McCauley describes her work investigating enteroendocrine regulation of nutrient absorption using PSC-derived human intestinal organoids
Improving Knowledge of Childhood Malabsorptive Disease with PSC-Derived Intestinal Organoids
What inspired you to pursue scientific research?
In college, at the University of Southern California, I took a nutrition and metabolism course and the professor mentioned that she had a research lab investigating some of the topics we were discussing in class. After class, she offered to give me a tour of the lab and I volunteered as a research assistant on the spot. We ran a lot of Western blots in the lab, the first day that I was in the dark room I saw something that no one else in the world had ever seen before. I was hooked.
What led you to studies in your current field?
I wanted to use a human model system to investigate the cell biology regulating nutrition and metabolism and I wasn’t satisfied with traditional cell culture models or relying on patient biopsies and blood samples. PSC-derived human intestinal organoids are the perfect tool for this as they are both robust and genetically tractable.
What hobbies do you have outside of the lab?
I enjoy weightlifting and CrossFit. I think it’s important to have a competitive outlet and push yourself to do things outside of your comfort zone (and outside of the lab!). Plus, it’s really fun to throw around a heavy barbell! I coach the 6:00 AM CrossFit class a couple of times per week at my gym and it really sets the tone for my day ahead.
Please describe the focus of your current research.
I am investigating enteroendocrine regulation of nutrient absorption using PSC-derived human intestinal organoids. Some kids are born with mutations in the gene responsible for enteroendocrine cell development (NEUROG3). These patients present with malabsorptive diarrhea and have to receive all their nutrients via an IV. Enteroendocrine cells only make up 2-3% of the intestinal epithelium, but collectively form the largest endocrine system in the body. They are important nutrient sensors, but it remains unclear why the absence of enteroendocrine cells would result in profound malabsorption.
What are your key findings thus far in trying to determine how enteroendocrine cells help regulate nutrient absorption?
We have some evidence that enteroendocrine hormones regulate the electrophysiology of the enterocyte, and that loss of hormones produced by enteroendocrine cells results in abnormal electrical responses to glucose and dipeptides. What’s really fascinating is that in a static environment the intestinal epithelium appears to be essentially normal without enteroendocrine cells. It’s only in a complex physiological environment, with input from enteric neurons, that the defects become apparent. We have also found that simply adding back some exogenous enteroendocrine hormones can rescue some of these defects, which directly translates to potential therapies for patients.
Was there anything specific about traditional cell culture systems as models for human nutritional absorption and metabolism that you found limiting?
Traditionally, human models of nutrition and absorption were limited to cell lines made from cancerous intestinal cells, which grow very well in culture. These cells were invaluable in learning about mechanisms of human intestinal transport but are unable to recapitulate human intestinal development. Similarly, patient biopsies can be grown in culture but are often difficult for researchers to obtain and only portray adult intestinal epithelial function without providing insights into intestinal development. Many metabolic and malabsorptive diseases are developmental in origin, so it seemed important to study intestinal development in the context of genetic variants that cause malabsorptive disorders. With technology that allows us to model intestinal development via the directed differentiation of pluripotent stem cells, we can grow patient-specific, 3D, miniature intestine containing relevant supporting mesenchymal cells and even enteric neurons. This allows us to model developmental disorders of the intestine, including malabsorptive disorders, in a way previously unavailable.
The Wells lab has a history of forging new ground in developing broadly useful model systems. Do you think being in this environment provides you with a unique perspective on the types of tools that may be available for researchers in the future?
First and foremost, in the Wells lab we are developmental biologists. This means that we bring a unique perspective to creating new model systems by most accurately recapitulating the signals and dynamic environment experienced by a developing embryo. I think this forces us to think about tissue-tissue interactions and expand our systems to include diverse cell types and think about how these diverse cell types may be affecting any favorite tissue. We are poised to bridge organ development and tissue engineering. Maybe that’s why I’m so excited about future developments in organ-on-chip technology.
What do you consider to be the most important advance(s) in intestinal research in the last five years?
The last five years have seen an explosion of advanced culture systems for recapitulating intestinal biology in a dish. We are now able to study some unique human biology and disease processes, create patient-specific PSC lines and use CRISPR/Cas9 gene editing for both disease modeling and mutation correction. I believe the most important advance has been the robustness of the tools that have allowed hundreds of labs around the world to use 3D intestinal organoids and enteroids to answer their specific biological questions.
What breakthroughs do you anticipate in the next five years?
The next five years are going to bring advances in microfluidic systems and organs-on-chips that combine multiple different tissue types and allow researchers to model tissue-tissue interactions in a dish. I think it would be really cool to see how specific intestinal mutations affect other metabolic organ systems, such as adipose tissue or skeletal muscle, and vice versa.
Are there any specific fields or applications that, from your perspective, will benefit the most from further development and availability of organon-on-chip systems?
I think it’s becoming increasingly evident that the more we can accurately replicate the in vivo complexity of human tissues in vitro, the more significant our organoid systems will become. For example, we know that flow of fluids through the lumen of the developing intestine is important for its growth and maturation and yet the technology for high-throughout intraluminal flow through 3D organoids is still just around the corner. In addition, luminal flow of chyme, pancreatic enzymes and bile acids might be essential to more accurately modeling nutrient absorption in vitro.
What impact do you see organoids having on the intestinal field? What technical hurdles remain before this can be realised?
Organoids are already being used for patient-specific drug screening and disease modeling, and this realistically allows for personalized medicine to become widespread and routine. The biggest hurdles remaining involve scaling up and reducing batch to batch variability.
Have you tried IntestiCult™ or STEMdiff™ media or would you find it useful to have a commercially available medium to perform your organoid cultures?
Switching to IntestiCult from cobbled-together homemade enteroid media was a game-changer in getting my tissue-derived enteroid cultures healthy and robust. Having the media essentially ready to use saves an enormous amount of time, and my cultures have never looked better.
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Heather McCauley, PhD