Human enteric nervous system progenitor dynamics during development and disease

The proper function of our gut is controlled, in an involuntary fashion, by a complex network of nerves, the enteric nervous system (ENS), also known as the 'second brain'. The ENS is produced in utero by specialised cell populations known as ENS progenitors and Schwann cell precursors (SCPs). Mistakes in the generation of the ENS by these progenitors, often due to defects in our DNA (mutations), lead to birth conditions called enteric neuropathies that are marked by lack of nerves in the gut. The most common enteric neuropathy is Hirschsprung disease, which is a life-threatening intestinal disorder affecting approximately 1 in 5,000 newborn children. The lack of enteric nerves in Hirschsprung disease is usually caused by mutations in a gene called RET, which is important for the proper function of ENS progenitors. Strikingly, RET mutations do not seem to affect SCPs, the other complementary source of ENS cells. To better understand the causes of HSCR, it is therefore important to examine how ENS progenitors/SCPs produce enteric nerves and how RET mutations affect this process. To address this issue, we propose to use human stem cells to generate healthy and RET-mutant ENS progenitors and SCPs, and kept in culture in a petri dish. We will then study in detail the behaviour of the RET-mutant cell populations after their injection in gut tissue isolated from human patients and mice, and grown in the petri dish. Comparison of mutant and healthy cells will help us understand what goes wrong in Hirschsprung disease and will ultimately assist the development of therapies against this devastating childhood disease.

The enteric nervous system (ENS) is a complex and highly interconnected network of neurons and glia that is critical for proper gut function. It is mainly derived by an embryonic multipotent cell population, the vagal neural crest (NC), which gives rise to ENS progenitors that colonize the developing gut in a rostro-caudal direction and generate enteric neurons and glia. Intestinal innervation also includes an extrinsic axis (based on projections from the central nervous system to the gut) that mediates gut crosstalk with the brain and facilitates the invasion of a second distinct progenitor population contributing to ENS development, Schwann cell precursors (SCPs), a multipotent cell population, which is mainly derived from the trunk NC and contributes to enteric neurogenesis in the colon. Defects in the generation of the ENS during embryonic development result in a range of life-threatening disorders known as enteric neuropathies. Hirschsprung disease (HSCR) is the most representative of these conditions, affecting 1 in 5,000 live births. It is caused by various mutations, predominantly perturbing RET signalling levels, which in turn disrupt ENS progenitor dynamics leading to absence of enteric neurons in the distal bowel. Thus, defining how ENS progenitors/SCPs drive human ENS development and how RET mutations influence this process is crucial for gaining a better understanding of HSCR. We recently described the efficient in vitro generation of human ENS progenitors and SCPs from human pluripotent stem cells (hPSCs). Here, we propose to employ these in vitro-derived cell populations together with human and mouse gut explant models to elucidate how impaired RET signalling influences human ENS progenitor/SCP dynamics.