Final Progress Report

Proposal No.  IBD-0126R2
Principal Investigator:  Helga-Paula Török, M.D. (replacement PI); Christian Folwaczny, M.D. (original PI)
Applicant Organization:  Klinikum der Universität München (Germany)
Project Title:  NOD2/CARD15 mutations and apoptosis in Crohn's disease
Period of Award:  July 1, 2005 – March 31, 2007

Lay Summary of Final Report

Variations in the NOD2 gene, which encodes for an intracellular receptor recognizing specific bacterial products, were associated with Crohn’s disease (CD). The functional link between these gene variants and the development of the disease is not entirely clear. The programmed cell death (apoptosis) of various cell types within the immune system is of paramount importance for the understanding and treatment of immunological-mediated disorders, such as CD. In CD mounting evidence is compatible with a disturbed apoptosis of immunocompetent cells, which is an important factor in the perpetuation of the chronic mucosal inflammation. On the other side, the structure of NOD2 displaying two CARDs (caspase activation and recruitment domains) suggests a role of this protein in the programmed cell death. We proposed here to investigate the role of the NOD2 protein in the apoptosis of immunocompetent cells and to elucidate the effect of Crohn’s disease associated gene variants on these processes.

For this, we first investigated the NOD2-mediated production of pro- and anti-inflammatory factors (cytokines) in cells from CD patients and healthy controls bearing different NOD2 variants. We found that immune cells from individuals with two mutated gene alleles display a disturbed cytokine response after contact with the specific bacterial product recognised by the NOD2 receptor. Among these individuals, the presence of at least one 1007fs mutation, which is the major CD associated NOD2 variant, results in a totally abrogated receptor function. These findings might represent an explanation for the much more severe disease course in these patients. An interesting new finding was that cells from CD patients with two mutated gene alleles display increased basal secretion of IL-12p40, which is part of cytokines with important role in intestinal inflammation. This finding has to be confirmed in further studies and might represent a step toward selectively targeted therapy in these patients.

In a second step we investigated the effect of NOD2-stimulation on the apoptosis of immuncompetent cells. For this we isolated primary cells from peripheral blood and intestinal mucosa from control individuals and CD patients with different NOD2 gene variants. We showed that treatment of primary monocytes with the bacterial product recognised by NOD2 increases programmed cell death rates in these cells. Only primary naïve monocytes showed an increase in apoptosis rates. This effect was mediated through NOD2 and was abrogated in the presence of CD-associated NOD2 mutations. In conclusion, our observation might provide a first link between NOD2 and a disturbed apoptosis of immunocompetent cells in CD. The specific pathways which are involved in NOD2 dependent apoptosis as well as the in vivo situation in the intestinal mucosa have to be further investigated.