Engineering a bio-artificial human intestine and wiring it up with nerves..!!
Remember the last time you did scuba diving or sea walking? What’s the first thing you noticed? Oh yes, the weightless feeling and then being mesmerised by the beauty of the corals. These corals have tentacles that ensnare planktons and as they absorb the nutrients, a huge wave rolls over mixing the water and the nutrients. This dynamic nutrient-fluid exchange is similar to our digestive system. The one-way peristaltic movement of the gut acts like an ocean current, pushing in food with finger-like folds called villi that are the tentacles which promote absorption of the nutrients.
Brain in the gut!
This internal motility and fluid exchange is possible because of the seamless integration of enteric nervous system with the walls of the intestine. These nerves are what makes the fluids to move and the tumbling motion and grumbling noises we feel so conscious about. When these nerves fail to function, causing enteric neuropathy, it leads to a spectrum of digestive diseases such as inflammatory bowel disease, and secondarily diabetes mellitus, Parkinson’s disease. The lack of a human model for enteric nervous system, prompted researchers at Cincinnati Children’s Hospital, to develop an intestine organoid system with a functional nervous system.
A previous study in 2010 by the same group documented the successful generation of a human intestine organoid, albeit without enteric nerves. Hence this organoid did not exhibit the characteristic motility and contractile movements. Pluripotent stem cells were generated using the skin cells from a patient. On culturing these stem cells along with the required nutrients and growth factors in a proteinaceous matrix (called Matrigel ,to support three-dimensional growth) they self-organized and form a basic intestinal tissue. In a separate dish, they generated embryonic-stage nerve cells called neural crest cells, which are the precursors for the enteric nerves.
“One day this technology will allow us to grow a section of healthy intestine for transplant into a patient, but the ability to use it now to test and ask countless new questions will help human health to the greatest extent,” said Michael Helmrath, MD, co-lead study investigator and surgical director of the Intestinal Rehabilitation Program at Cincinnati Children’s.
In the right place at the right time!
Putting together the neural crest cells and the intestinal tissue at the exact time, was the bottleneck in this study. After a few different approaches based on the expertise of the study’s co-author, Samantha Brugmann, a developmental biologist, the appropriate mix grown for 28 days allowed the organoid to grow into a complex functional system, resembling a fetal intestine.
“Many oral medications give you diarrhoea, cramps and impair intestinal motility. A fairly immediate goal for this technology that would help the largest number of people as a first-pass screen for new drugs to look for off-target toxicities and prevent side effects in the intestine,” explained Jim Wells, PhD, co-lead investigator and director of the Pluripotent Stem Cell Facility at Cincinnati Children’s.
What if these mini-guts move out of their comfort zone?
To assess the success of the engineering,the organoids were transplanted into mice with suppressed immune systems to test formation of mature nerves. After 6-10 weeks of growth, blood vessels penetrated into what was now a mature intestinal tissue and immune cells trickled from the mice’s body itself. A single electric impulse triggered a prolonged wave of contractions in the organoids that had a nervous system, but did not do so in structures lacking nerves.
Using this model, the group identified molecular pathways involved in Hirschsprung’s disease, a congenital condition which causes poor muscular movement and thus problems with passing stool. One form of the disease caused by a mutation in the gene PHOX2B, was modelled in the intestinal organoids and the system proved to be well-suited for such mechanistic studies.
“My collaborator, and co-corresponding author Dr Helmrath, a paediatric surgeon, is developing transplant models using these more functional human intestinal tissues to study how they function when transplanted into the luminal stream of animals,” says Wells.