Scientific Abstract

Proposal No.   IBD-0066
Principal Investigator:  Judith Bond, Ph.D. (replacement PI);  Jacqueline Crisman, Ph.D. (original PI)
Applicant Organization:  The Pennsylvania State University College of Medicine (Hershey, U.S.A.)
Project Title: Intestinal leukocyte infiltration is mediated by meprin beta
Period of Award:  June 1, 2003 - July 31, 2004

Intestinal leukocyte deposition and activity is critical to the pathogenesis of inflammatory bowel diseases (IBD).  In fact, blockade of macrophage and T cell infiltration and activity is an extremely efficacious means of mitigating IBD.

Strong evidence supports the hypothesis that meprin β metalloprotease is an important mediator of leukocyte dissemination in the intestine.  Meprins are large oligomeric proteases comprised of α and/or β subunits.  Only the β subunit contains a transmembrane domain, thus any form of meprin that contains β is membrane-bound, while meprins that contain solely a subunits are secreted.  The expression of meprins appears to be highly restricted to two tissues, the kidney and intestine, with specific localization to the apical surface of the intestinal and renal proximal tubule epithelium.  However, leukocytes in samples from human IBD also express meprins.  Furthermore, the expression of meprins by leukocytes seems to be restricted to the intestinal immune system, as leukocytes in other tissues (including blood, spleen and kidney) do not express meprins, regardless of the inflammatory status of the tissue.  Since circulating leukocytes do not express meprins normally, it is likely that attachment of leukocytes to circulatory vessels in the intestine is a proximal event leading to the induction of meprins.  In fact, meprin β(+) leukocytes can attach to the intima of blood vessels in the mouse mesenteric lymph node.

We have access to a unique strain of mice genetically deficient for the meprin β gene (meprin β null mice).  When compared to wild-type leukocytes, meprin β null leukocytes migrate equally well in response to a chemoattractant.  However, deletion of the meprin β gene decreased 8-fold the number of leukocytes able to migrate through matrigel when compared to wild-type leukocytes.
 
We propose that meprin β is pivotal to the dissemination of leukocytes (in particular macrophages) to normal or inflamed intestine and mesenteric lymph node.  Fluorescently labeled leukocytes from meprin β null or wild-type mice will be administered to meprin β null and wild-type recipients, with (aim #2) and without (aim #1) sodium dextran sulfate (DSS)-mediated intestinal inflammation.  The deposition of these leukocytes in the intestinal immune system will be assessed by flow cytometry and immunofluorescence.  The aims are: #1-To assess the role of meprin β in the dissemination leukocytes to normal intestine and mesenteric lymph node, #2-To assess the role of meprin β in the dissemination leukocytes to the intestine and mesenteric lymph node, after induction of DSS-mediated experimental IBD.  Furthermore, these studies will also begin to examine the role of meprin β in T cell and B cell dissemination to the intestinal immune system.