A multidisciplinary approach to studying crypt-villus homeostasis and regeneration in the intestinal epithelium

We aim to study the mechanisms regulating the continuous renewal of the intestinal epithelium in physiological conditions and its recovery following injury. This understanding will contribute to the identification of strategies for maintaining the health and preventing diseases of the gastrointestinal (GI) tract.

The intestinal epithelium forms the first barrier between the gut lumen and the body. The epithelial cell monolayer lining the small intestine has a complex architecture, with invaginations into the intestinal wall called crypts located between finger-like projections into the lumen called villi. Several crypts surround a villus forming a crypt-villus unit; each crypt is involved in more than one unit, providing cells to more than one villus. Intestinal stem cells located at the base of each crypt proliferate and give rise to epithelial cells, which migrate to the tip of the neighbouring villi, from where they are shed into the gut lumen. In the healthy intestine, the dimensions and cell number on this crypt-villus unit remain remarkably constant during adult life. This implies that the rate of cell shedding from the villus tip is balanced by the rate at which new cells produced within the supporting crypts migrate from these crypts onto the villus.

Therefore, the maintenance of the functional integrity of the intestinal barrier requires a tight coordination of the numbers of crypts and villi, cell production in the crypts, cell migration along the crypt-villus axis, and cell shedding from the villus. Failure of regulation of these processes may result in cells escaping normal growth controls and tumour formation. Inflammatory processes are characterized by enhanced cell shedding that may fail to be compensated by the increase of cell proliferation within the crypts leading to the loss of the integrity of the intestinal barrier. In addition, the intestinal lesions in coeliac disease reflect a severe alteration of the balance between cell apoptosis on the villi and cell proliferation within the crypts. The subject of this proposal is gaining insight into the mechanisms underlying the maintenance of the equilibrium between crypts and villi in the intestinal epithelium and how this balance is regained after injury. This is essential to maintain the health of the GI tract and to develop novel preventive strategies for intestinal pathologies such as tumourigenesis, ulcerative inflammatory processes and coeliac disease.

However, such questions cannot currently be resolved by experimentation alone, since it is not possible to collect in vivo time course imaging of entire crypt/villus units over prolonged periods. To this end, mathematical and/or computational modelling represents an alternative framework within which to conduct in-silico experiments that complement the in-vitro experimental approaches. We plan to integrate computational models with experimental data to elucidate the biophysical mechanisms that may coordinate cell proliferation within the crypt, cell migration along the crypt-villus axis and cell shedding from the villus in order to preserve the numbers and size of crypts and villi within the small intestine. Computational simulations of the validated models will then be performed to predict the dynamics of epithelial recovery after injury. We will also identify potential early markers of altered epithelium.

Using a combination of computational modelling and experimental measurements, we aim to understand the tight coordination between villi and crypts during the continuous renewal of the small intestinal epithelium and how the equilibrium is recovered after perturbations.

Experimental measurements will be gathered from healthy, altered and injured intestine. Counts and morphometric measurements of crypts and villi, cell proliferation, migration and shedding rates, cell size and cell density will be experimentally determined along the much studied murine small intestine in control conditions as well as after blocking cell proliferation by cytosine arabinoside, enhancing cell proliferation by glucagon-like peptide-2 and injuring the epithelium by bacterial lipopolysaccharide.

The spatio-temporal modelling of cell dynamics in the crypt-villus unit will be modelled by building on the individual cell models (IBMs) for the crypt already developed by the applicants. While it is feasible to simulate an IBM of one crypt-villus unit in a reasonable time, simulations comprising large populations of villi and crypts are likely to become computationally intractable. We will therefore investigate the relationship between populations of crypts and villi at the macroscopic level using 'mean-field' models. We will use the existing resources of Chaste, a software library for modelling soft tissues, to implement models and as a simulation suite.

Importantly, theory and experiments will be intertwined through the "predict-test-refine-predict" cycle to develop and test hypotheses regarding the regulation of cellular proliferation and migration along the crypt-villus axis, the mechanism of intestinal cell shedding and apoptosis and the relationship between these cellular phenomena and the maintenance of crypts and villi. Model simulations will be used to generate predictions on epithelium recovery after injury that will be tested experimentally, leading to refinement of the mode.

This project proposal is targeting gut health to improve health and well-being across the life span by a multidisciplinary approach that integrates theoretical and experimental approaches. This is specifically targeted by the "Systems approaches to the bioscience" theme of the BBSRC research strategy priority "Exploiting new ways of working". Our project, specifically responds to the cross-council priority "Lifelong health and well-being" and the theme "Ageing research: lifelong health and well-being" of the priority "Basic bioscience underpinning health". BBSRC strategic priorities are devised to increase the impact of the BBSRC science on worldwide (and specifically on the UK) society and economy.

Our research focuses on understanding the basic mechanisms of regulation between intestinal villi and crypts and how their balance is recovered after injury and damage. As a result, we expect to gain continued and greater understanding of the fundamental aspects of this biological system. Our beneficiaries in the short term will be mainly those in the academic community while there is number of potential applications with economic and societal impacts in the long term.

Impact on Society

The public will be the first long term beneficiary of our research through enhanced gut health, gut tolerance to perturbations and recovery after injury, and the early detection of risk factors for GI-tract disease, leading to improved lifelong wellbeing and quality of life.
NHS and specialist services (e.g. gastroenterologists) will benefit from science-based advice and evidence to support improved strategies for a healthier gut. The output of our research may lead to develop novel prevention practices for intestinal tumourigenesis, chronic or inflammatory processes, intestinal ulcers and coeliac disease.

Enhancing the professional skills base. The staff working on the project and the participants in the workshops will be trained in a highly interdisciplinary area of knowledge. Knowledge in developing computing and modelling tools for Medicine and Biology is increasingly relevant to the public and private employment sector.

Inspiring young people. The integration of theoretical and experimental approaches that we propose, provides excellent opportunities for school and undergraduate science students to understand how biological systems work as a whole and to grasp the importance of multi disciplinary approaches to address unanswered scientific questions, contributing to the BBSRC public engagement priority by addressing young people in mathematics for biology.

Public opinion and policy makers. The generation of robust computing tools for in silico simulation of gut behaviour may provide an alternative platform to minimise the use of animals in research. Potentially, this will help policy makers address some public opinion concerns about animal testing.

Impact on Economy

A decreased UK Public spend might be envisaged from the reduced pressure on Health and Social care systems resulting from an improved gut health and wellbeing.

Industry, such as Biomedical industries and Biopharmaceutical companies, may benefit from strong evidence-based advice that may lead to the development of novel therapies and early markers for intestinal tumourigenesis, chronic inflammatory processes and coeliac disease. The output of this research on the kinetics of the intestinal epithelium renewal and regeneration might provide information to develop strategies to reduce the intestinal side effects of drugs treatments such as the highly used non-steroidal anti-inflammatory drugs. The small and large intestine account for 20-40% of all drug side effects [Best Pract Res Cl Ga 2010 24:133-141]. Thus, there is great potential to translate new ideas and results into exploitable outcomes and further strategic developmental proposals (EC, Human Frontiers programme) as well as attracting R&D investment from Global business into the UK economy.