Growth factors and the gut

The effect of ileal interposition surgery on enteroendocrine cell numbers in the UC Davis type 2 diabetes mellitus rat

AIM

To investigate the short-term effect of ileal interposition (IT) surgery on gut morphology and enteroendocrine cell numbers in the pre-diabetic UC Davis type 2 diabetes mellitus (UCD-T2DM) rat.

STUDY DESIGN

Two-month old male UCD-T2DM rats underwent either sham (n=5) or IT (n=5) surgery. Intestines were collected 1.5months after surgery. The jejunum, ileum and colon regions were processed for histochemical and immunohistochemical labeling and stereological analyses of changes in gut morphometry and number of enteroendocrine cells.

RESULTS

Stereological analysis showed that intestinal volume, luminal surface area and the number of all chromogranin A-positive enteroendocrine cells were markedly increased in the IT rats compared with sham-operated animals. Subanalyses of the glucagon-like peptide 2, cholecystokinin, serotonin cells and the neurotensin immunoreactive sub-pool of enteroendocrine cells in the IT region revealed an increase in numbers across phenotypes. However, the density of the different cell types varied.

CONCLUSION

IT surgery in the UCD-T2DM rat leads to rapid alterations in gut morphometry and an increase in the number of enteroendocrine cells. This effect may potentially explain why IT surgery delays the onset of type 2 diabetes in the UCD-T2DM rat.

The role of disulfide bonds in the structure and function of murine epidermal growth factor (mEGF)

A systematic study using solid phase peptide synthesis has been undertaken to examine the role of the disulfide bonds in the structure and function of mEGF. A combination of one, two and three native disulfide pair analogues of an active truncated (4-48) form of mEGF have been synthesised by replacing specific cysteine residues with isosteric a-amino-n-butyric acid (Abu). Oxidation of the peptides was performed using either conventional aerobic oxidation at basic pH, in DMSO under acidic conditions or via selective disulfide formation using orthogonal protection of the cysteine pairs. The contribution of individual, or pairs of, disulfide bonds to EGF structure was evaluated by CD and (1)H-NMR spectroscopy. The mitogenic activity of each analogue was determined using Balb/c 3T3 mouse fibroblastsAs we have reported previously (Barnham et al. 1998), the disulfide bond between residues 6 and 20 can be removed with significant retention of biological activity (EC50 20-50 nM). The overall structure of this analogue was similar to that of native mEGF, indicating that the loss of the 6-20 disulfide bridge did not affect the global fold of the molecule. We now show that removal of any other disulfide bond, either singly or in pairs, results in a major disruption of the tertiary structure, and a large loss of activity (EC50>900 nM). Remarkably, the linear analogue appears to have greater activity (EC50 580 nM) than most one and two disulfide bond analogues although it does not have a definable tertiary structure.

Vesicle-associated protein-A is differentially expressed during intestinal smooth muscle cell differentiation

Gastrointestinal (GI) smooth muscle diseases represent a major health concern affecting in excess of 2 million people each year. Little is currently known regarding the molecular mechanisms controlling either normal or pathogenic GI smooth muscle development. In an effort to identify the specific gene products responsible for modulating GI smooth muscle cell (SMC) differentiation, we performed differential display on distinct intestinal SMC (ISMC) phenotypes. This analysis identified over 40 unique transcripts that appeared to be differentially expressed in distinct SMC phenotypes. One such transcript that appeared to be preferentially expressed in immature smooth muscle myocytes was identified as vesicle-associated membrane protein, associated protein A (VAP-A). Northern blot analysis confirmed that VAP-A was expressed threefold higher in immature smooth muscle myocytes when compared with both smooth muscle myoblasts and mature smooth muscle myocytes. VAP-A mRNA was differentially expressed during normal rat development and showed peak levels of expression in the intestine during late embryogenesis and early neonatal development. These observations provide the first evidence that VAP-A-mediated membrane trafficking may play an important role in modulating ISMC differentiation.

A Neu differentiation factor (NDF) domain essential for proliferation and alterations in morphology of colonic epithelial cells in vitro

The Neu Differentiation Factors (NDFs, also termed "heregulins") are a family of proteins that were first isolated as ligands for the HER2 (ergB2, or p185neu) receptor protein tyrosine kinase. Here we show that NDF acts to stimulate the proliferation and alter the cellular morphology of colonic epithelial cells in culture. Dramatic NDF-induced changes in cellular morphology were noted in the colonic epithelial cell line, LIM 1215. In addition, the expression of specific cell proteins, such as carcinoembryonic antigen and integrin beta 4, was induced in LIM 1215 cells by NDF. These effects were more pronounced with the beta isoform than with the alpha isoform of NDF. The EGF-homology domain of NDF beta was sufficient to stimulate the proliferation and alteration in cell morphology. The use of chemically synthesized chimeric NDF alpha and NDF beta proteins enabled use to identify a region of seven amino acids in the EGF-homology domain of NDF beta that is required for both activities. These in vitro experiments suggest that NDF may act as a regulator of growth and differentiation of colonic epithelial cells in vivo.

Molecular marker for development of interstitial cystitis in rat model: isoactin gene expression

PURPOSE

To determine whether the differential expression of bladder smooth muscle isoactin can be used as a molecular marker for the development of interstitial cystitis (IC).

METHODS

Three groups of five female Sprague-Dawley rats each underwent urethral catheterization and intravesical instillation of 0.5 ml. of 0.4N HCl. One group was sacrificed one, two and four weeks after the application of HCl, and their bladders harvested for histologic examination and evaluation using Northern blot analysis of bladder smooth muscle isoactins. Five control animals were sacrificed and their bladders harvested to establish isoactin gene expression of bladder smooth muscle in the normal state. The bladders of the rats in each group were excised, immediately frozen in liquid nitrogen, pooled, then stored -70 degrees C until needed for RNA isolation. Isoactin cDNA probes have been developed, therefore isoactin specific cDNA insert fragments were isolated and insert DNA was purified by gel electrophoresis. Total cellular RNA was isolated from 1.0 gm. of bladder smooth muscle from each group. After spectrophotometric quantification, Northern Blot analysis was performed using 2% agarose-formaldehyde gels and Biotrans nylon membranes. Two complete Northern Blot series were run on a single gel and blotted to a single membrane to eliminate gel and blotting discrepancies.

RESULTS

Microscopic histologic analysis revealed detrusor mastocystosis and eosinophilia as has been noted in humans with chronic interstitial cystitis. Two weeks after the intravesical application of hydrochloric acid, the relative expression of gamma-smooth muscle isoactin was noted to increase by 1.7-fold, while alpha-smooth muscle isoactin expression increased by a factor of 9. These effects were seen to stabilize four weeks after acid application.

CONCLUSIONS

The intravesical application of dilute HCl in rats results in a histologic appearance which mimics that seen in humans with interstitial cystitis. The appearance of detrusor mastocytosis and eosinophilia was accompanied by a relative decrease in the expression of gamma- and a relative increase in alpha-smooth muscle isoactin gene expression. This pattern of smooth muscle isoactin expression is consistent with a more immature and possibly synthetic smooth muscle phenotype, which may be responsible for the clinical presentation of those with IC. Northern blot analysis of bladder smooth muscle cells may serve as an effective marker for the development of interstitial cystitis in humans.

Altered expression of TGF alpha and TGF beta 1 in the mucosa of the functioning pelvic ileal pouch

The mucosa of the functioning pelvic ileal pouch undergoes loss of villous height and an increase in crypt cell proliferation as an adaptive response to its new luminal environment. These changes can occur in the absence of inflammation and could be mediated by growth factors such as transforming growth factors alpha and beta 1 (TGF alpha and TGF beta 1). Expression of TGF alpha and TGF beta 1 messenger RNA (mRNA) and protein was determined by in situ hybridization and immunohistochemistry in sections of terminal ileum taken at the time of pouch formation and of subsequent pouch biopsies from 14 patients (total of 90 specimens). Crypt cell proliferation was assessed using the monoclonal antibody MIB-1. As ileal pouch mucosa underwent loss of villous height and crypt hyperplasia, epithelial expression of TGF alpha mRNA and protein decreased. In contrast, TGF beta 1 mRNA and protein were abundant in both normal and flat mucosa. Epithelial expression of TGF beta 1 protein was maximal in flat, inflamed biopsies. These results suggest that although altered expression of TGF alpha and TGF beta 1 mRNA and protein may play some part in the regulation of the adaptive response in ileal pouch mucosa, TGF alpha does not have a direct, positive role in the regulation of crypt cell proliferation.

Inhibitory effects of magnoshinin and magnosalin, compounds from "Shin-i" (Flos magnoliae), on the competence and progression phases in proliferation of subcultured rat aortic endothelial cells

Anti-proliferative effects of magnoshinin and magnosalin derived from "Shin-i" (Flos magnoliae) were investigated using subcultured endothelial cells (EC) of rat aorta. The inhibitory effects of magnoshinin were 2-fold greater at 10 micrograms/ml than that of magnosalin on the increase in cell number when EC were stimulated by 5% fetal bovine serum. In the 3H-thymidine incorporation monitored at 3 hr-intervals, magnoshinin (0.1-3 micrograms/ml) prolonged the starting time of DNA synthesis and reduced the rate of incorporation into EC. Magnosalin (0.3-3 micrograms/ml) reduced only the incorporation rate. These results suggest that magnoshinin inhibits both the competence phase and progression phase, but magnosalin preferentially inhibits the progression phase in EC proliferation.

Cellular and molecular basis of intestinal and pancreatic adaptation

This article reviews the structural and functional changes which develop in the intestine and pancreas in response to a variety of stimuli and which characterise adaptive hyper- or hypo-plasia. It then discusses the principal physiological mechanisms controlling this adaptive growth. In the gut, these include luminal nutrition, endocrine, autocrine and paracrine hormonal influences, growth factors, enterotrophic components of pancreatico-biliary secretions, neural factors, changes in blood flow and mesenchyme-epithelial interactions. The cell biology of adaptive growth involves cell membrane receptors (first messengers) and a cascade of intracellular second messengers, the best studied of which is changes in polyamine metabolism and in related enzymes. The effects of ornithine decarboxylase (ODC) blockade with difluoromethyl ornithine (DFMO) and of diamine oxidase (DAO) blockade with aminoguanidine, are described. In general, DFMO inhibits or prevents adaptive hyperplasia while in the small bowel, aminoguanidine treatment induces 'supranormal' adaptation. However, both the gut and the pancreas transport 'exogenous' (ingested in food and circulating in the blood stream) polyamines across their apical and basolateral membranes. The influence of this exogenous polyamine transport on 'endogenous' (enzyme-regulated) intracellular polyamine concentrations, is largely unknown. Finally, the molecular biology of adaptive growth is described briefly--as illustrated by the use of a growth hormone transgenic model in which mice develop marked intestinal mucosal hyperplasia and increases in the relative abundance of insulin-like growth factor-I (IGF-I) mRNA in the intestine.