Final Progress Report
Proposal No. IBD-0012R
Principal Investigator: Lee A. Denson, M.D.
Current Applicant Organization: Cincinnati Children's Hospital Medical Center (Ohio, U.S.A.)
Original Applicant Organization: Yale University (New Haven, Connecticut, U.S.A.)
Project Title: Mechanisms of growth hormone resistance in experimental colitis
Period of Award: October 1, 2002 - March 31, 2006
Aim 1: Characterize hepatic and colonic GH signaling in murine and human colitis.
We made significant progress towards accomplishing the goals of Aim 1. We hypothesized that 1) liver and colon growth hormone receptor (GHR) abundance is reduced in murine colitis and in children with active Crohn’s disease (CD) relative to controls, and that 2) GH dependent STAT5 activation is reduced murine liver and colon in colitis and in biopsy specimens from affected areas in CD relative to controls. We have determined that the GHR is down regulated in murine liver and colon in experimental colitis, and that this leads to a local reduction in GH dependent STAT5 activation. Systemically, this causes growth failure, while in the colon, this contributes to chronic mucosal inflammation. These results have been presented at national meetings and published in three manuscripts in Gastroenterology and Gut. We have completed enrollment and the majority of the data analysis for a complementary translation study in children with newly diagnosed CD. As expected, growth hormone (GH) secretion was normal, but serum IGF-1 was reduced, in children with newly diagnosed CD relative to healthy controls. This confirmed a state of GH resistance in the children with CD. We have now determined, for the first time, that the GH resistance in CD correlates with a reduction in serum GH binding protein (GHBP), from 693±70 pg/ml in controls to 417±138 pg/ml in children with CD (p=.02). Interestingly, this is more pronounced in buys with CD than girls, correlating with the more severe growth failure in boys. As serum GHBP in humans reflects tissue, primarily liver, GHR abundance, these data suggest that GH resistance in pediatric CD is due to down regulation of the GHR. We have determined that GH resistance, as defined by a reduction in both basal and GH dependent STAT5 activation, is also present in affected colon of subjects with CD relative to controls. Studies have confirmed that STAT5 activation is specifically impaired in colon epithelial cells (CEC) in the CD biopsies; interestingly, a subset of CD samples have exhibited constitutive activation of STAT5 in the lamina propria mononuclear cells (LPMC) and eosinophils. Studies utilizing laser capture microscopy (LCM) have demonstrated that CEC GHR RNA expression is reduced in CD relative to controls. Taken together, these studies have shown that children with newly diagnosed CD exhibit systemic GH resistance, due to down regulation of the GHR, and local GH resistance in the affected colon, also due to down regulation of GHR expression. These leads to reduced GH dependent STAT5 activation in these tissues. Studies in STAT5b deficient mice have now shown that these mice are more susceptible to TNBS colitis, due to a reduction in colon expression of GH:STAT5b target genes including PPARī§ and ZO1-3. A revised manuscript describing these studies is under review at the American Journal of Pathology. Despite this reduction in epithelial GH:STAT5 signaling, we have found that GH signaling in effector T cells is intact in both murine colitis and patients with IBD. GH administration in these settings leads to a novel anti-inflammatory effect involving down regulation of T cell STAT3 activation. We are now testing the effectiveness of growth hormone administration in active pediatric CD in a randomized clinical trial. These initial studies were published in Gastroenterology.
Aim 2: Determine whether anti-TNF restores GH signaling in murine and human colitis.
We have determined that anti-TNF rapidly restores GHR expression and liver and colon GH signaling in mice with experimental colitis. These studies have been published in Gastroenterology and Gut. To date, ten of a planned fifteen children have been enrolled in a prospective patient-based study in this Aim. We hypothesize that Infliximab will 1) increase serum GHBP at 6 weeks and 2) increase age adjusted height velocity z scores at 12 months irrespective of baseline linear growth. Dr. Mark Corkin, a pediatric gastroenterologist at Riley Children’s Hospital in Indianapolis, has agreed to also provide subjects from his institution. Dr. Corkin specializes in the care of children with IBD and has a particular interest in alterations in the GH/IGF-1 axis in this setting. Interim analysis has demonstrated that anti-TNF does up regulate the GH:IGF-1 axis by 6 weeks, and this includes an increase in GHBP abundance. This has then been associated with an increase in height velocity at 12 months. These studies will be completed with support from a new NIDDK R01 grant.
Lay Summary:
Despite the development of newer medications, delayed growth and pubertal development remains a significant problem for most children with Crohn’s Disease (CD), with approximately 20-30% experiencing significant growth failure which persists into adulthood. While this has been felt to be due to combined effects of not eating enough and a direct effect of inflammation associated with CD, the precise cause has not been known. This has limited the development of new therapies to address this problem. Our studies have for the first time identified the basis for systemic problems with growth hormone action in these children, due to down regulation of the cell surface receptor for growth hormone. This then blocks the actions of growth hormone in the body, leading to growth failure. Importantly, we have also identified for the first time a corresponding resistance to growth hormone action in the affected colon which we believe prevents normal healing. Importantly, we have found that blocking the inflammatory protein TNF in experimental colitis will rapidly restore both liver and colon growth hormone action, prior to improvements in weight gain and disease activity. This has indicated that a specific benefit of anti-TNF therapy is restoration of normal growth hormone action, leading to both improved growth and intestinal healing in children. At the same time, we have determined that giving growth hormone can nevertheless exert a previously un-recognized anti-inflammatory effect in experimental colitis which will directly lead to intestinal healing and improved growth. We are now testing growth hormone as a primary therapy in children with active CD. It is quite likely that these studies will lead to the development of novel approaches for optimizing both growth and intestinal healing in children with CD.