3rd Annual BMRP Investigator Meeting - Abstract

Immunomodulatory Effects of Growth Hormone in Experimental Colitis

Xiaonan Han, Danuta Sosnowksa, Erin Bonkowski and Lee Denson^a

Cincinnati Children’s Hospital Medical Center (Cincinnati, Ohio, U.S.A.)

Background:  Crypt epithelial cell (CEC) apoptosis is a prominent feature of the mucosal injury in inflammatory bowel disease (IBD).  GH administration reduces inflammation and promotes healing in experimental colitis, although the molecular mechanisms are poorly understood.  Anti-apoptotic effects of GH in epithelial cells have been linked to activation of STAT5 and an increase in the cellular bcl-2/bax ratio, while activation of STAT5 in T cells may promote a regulatory phenotype.  Conversely, NFκB and STAT3 activation and upregulation of iNOS and fasL have been implicated in chronic inflammation and CEC apoptosis in colitis.  We hypothesized that GH would reduce inflammation and CEC apoptosis in colitis in association with alterations in STAT3/5 and NFκB activation and bcl-2/bax, fasL, and iNOS expression.

Methods:  Colitic interleukin-10 null (IL-10) mice and wild-type (WT) controls received GH (3 mcg/gm SQ twice daily) or PBS for three weeks.  IL-10 null mice also received anti-TNF or isotype control antibody (1 mg IP), as a single dose or weekly for three weeks.  T84 human colon carcinoma cells and Jurkat human T cell leukemia cells were treated with IL-6 ± GH. NFκB and STAT3/5 activation were determined by Western blot (WB) and EMSA.  GH receptor (GHR), Bax, bcl-2, fas, fasL and iNOS expression and localization were determined by WB, real-time PCR, and immunohistochemistry.  Cellular apoptosis was assessed by TUNEL and activated caspase 3 staining.

Results:  The GHR was expressed in CEC and LPMC.  GH reduced mucosal inflammation and CEC apoptosis in colitis.  This was associated with activation of STAT5, upregulation of bcl-2, and downregulation of bax in CEC.  NFκB and STAT3 were activated and iNOS and fasL expression were upregulated in colitis; these were reduced by GH administration to a degree comparable to that observed after TNFα neutralization.  GH also activated STAT5 and reduced IL-6 dependent activation of STAT3 in T84 and Jurkat cells in culture.

Conclusion:  GH exerts both anti-inflammatory and anti-apoptotic effects in experimental colitis in association with CEC STAT5 activation and downregulation of STAT3/NFκB activation.  These combined effects contribute to the observed improvement in both inflammation and mucosal healing.

^aPrincipal Investigator