Profile of IGF-binding proteins secreted by intestinal epithelial cells changes with differentiation

Growth and Puberty in Children with Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBD) are gastrointestinal tract pathologies of unknown etiology; they have an alternating trend, with active and silent phases. IBD are classified in two main forms: ulcerative colitis (UC) and Crohn’s disease (CD). Both have chronic and recurrent course, gastrointestinal symptoms, and extraintestinal manifestations. The altered immune response role seems to be important both in UC and CD. In the majority of cases, CD begins with abdominal pain, diarrhea, decrease in appetite, and weight loss; there can be also perianal fistulas, rhagades, and perianal recurrent abscesses. In addition, retarded growth and delayed puberty can precede the development of the disease or can even be predominant at onset. Growth retardation is found in 40% of IBD patients, but the underlying mechanism of this and other extra-intestinal manifestations are partially known: the main hypotheses are represented by malnutrition and inflammatory response during the active phase of the disease. The increased level of pro-inflammatory cytokines can influence growth, but also the onset of puberty and its progression. In addition, it could be essential to clarify the role and the possible effects of all the currently used treatments concerning growth failure and delayed puberty.

Dietary modulation of GALT

Changes in diet greatly affect the mucosal immune system, particularly in diseases such as Crohn's disease and necrotizing enterocolitis. This article examines the hypothesis that alterations in the luminal environment of the intestine regulate the expression of genes in the enterocyte responsible for signaling to immune cells. Genes expressed by the epithelium orchestrate leukocytes in the lamina propria. For example, chemokine expression in the mouse intestinal epithelium, through transgenic means, induced the recruitment of neutrophils and lymphocytes into intestinal tissues. Diet alters the expression of the genes responsible for signaling by a variety of pathways. The introduction of a normal diet to a weanling mouse up-regulates MHC class II expression through a particular isoform of the class II transactivator, a protein that acts in the nucleus. SCFA concentrations in the intestinal lumen vary markedly with diet. SCFAs increase IL-8 and insulin-like growth factor binding protein-2 expression by inhibiting histone deacetylase activity in the enterocyte. Down-regulation of gene expression by butyrate can act through acetylation of the inhibitory transcription factor Sp3. The review therefore describes a number of molecular pathways, explaining how changes in diet may alter leukocyte recruitment by regulating enterocyte gene expression. Myofibroblasts enhance enterocyte chemotactic activity by cleaving inactive precursors; and myofibroblast genes also are regulated by SCFA. It is likely that other similar regulatory mechanisms remain to be discovered.

Intestinotrophic effects of exogenous IGF-I are not diminished in IGF binding protein-5 knockout mice

IGF binding protein-5 (IGFBP-5) modulates the availability of IGF-I to its receptor and potentiates the intestinotrophic action of IGF-I. Our aim was to test the hypothesis that stimulation of intestinal growth due to coinfusion of IGF-I with total parenteral nutrition (TPN) solution is dependent on increased expression of IGFBP-5 through conducting our studies in IGFBP-5 knockout (KO) mice. IGFBP-5 KO, heterozygote (HT) and wild type (WT) male and female mice were maintained with TPN or TPN plus coinfusion of IGF-I [recombinant human (rh)IGF-I; 2.5 mg x kg(-1) x day(-1)] for 5 days. The concentration of IGF-I in serum was 73% greater (P < 0.0001) in mice given TPN + IGF-I infusion compared with TPN alone. IGF-I attenuated the 2-3 g loss of body weight associated with TPN in WT mice, whereas KO and HT mice did not show improvement in body weight with IGF-I treatment. KO and HT mice had significantly greater levels of circulating IGF-I binding proteins (IGFBPs) compared with WT mice. Intestinal growth due to IGF-I was observed in all groups treated with IGF-I based on greater concentrations of protein and DNA in small intestine and colon and significantly greater crypt depth and muscularis thickness in jejunum. Jejunal expression of IGFBP-5 mRNA was greater in WT mice, whereas IGFBP-3 mRNA was greater in KO mice treated with IGF-I. In summary, the absence of the IGFBP-5 gene did not block the ability of IGF-I to stimulate intestinal growth, possibly because greater jejunal expression of IGFBP-3 compensates for the absence of IGFBP-5.

Identification of a novel SP3 binding site in the promoter of human IGFBP4 gene: role of SP3 and AP-1 in regulating promoter activity in CaCo2 cells

Insulin-like growth factor binding protein 4 (IGFBP4/BP4) gene expression plays an important role in the transition from proliferation to differentiation of a human colon cancer cell line, CaCo2. We recently cloned and identified multiple cis elements (including putative binding sites for activator protein 1 (AP-1) and specificity proteins (Sps) ) in the promoter of human BP4 gene, and measured a significant upregulation of the promoter activity in response to c-Jun. We therefore examined the role of the single AP-1 site (-869/-863) and other cis elements, in regulating the expression of hBP4 gene, in the current studies. Deletion of a 25 bp sequence from -872 to -848, which contains the AP-1 site, significantly reduced BP4 promoter activity by approximately 50%. Surprisingly, mutation of the AP-1 site did not produce significant alteration in the activity of the BP4 promoter. However, mutation of 7 bp (5'-TGCTGCA) at the 3' end of the AP-1 site resulted in significantly decreasing the promoter activity by >50%. Proteins bound to the 25 bp probe (-872/-848) could be supershifted by antibodies specific for JunD and Sp3 in an EMSA. JunD binding was abolished on mutation of the AP-1 site and Sp3 binding was abolished on mutation of the 7 bp at -861/-855; binding of the purified Sp3 protein to the 25 bp probe was similarly abolished on mutation of the newly discovered Sp3 binding site (TGCTGCA). BP4 promoter activity was upregulated in insect cells in response to Sp3 expression, confirming a functional importance of the novel Sp3 binding site. These studies suggest that the Sp3 binding site, rather than the AP-1 site, may be playing a significant role in regulating the expression of IGFBP4 gene in CaCo2 cells.

Mesenchymal IGF-I overexpression: paracrine effects in the intestine, distinct from endocrine actions

Local IGF-I expression is frequently increased in intestinal mesenchyme during adaptive growth of intestinal epithelium, but paracrine growth effects of IGF-I in vivo are not defined. We tested whether overexpression of IGF-I in intestinal mesenchyme increases epithelial growth and if effects are distinct from known effects of circulating IGF-I. SMP8-IGF-I-transgenic (TG) mice overexpress IGF-I driven by an alpha-smooth muscle actin promoter. Mucosal and muscularis growth were assessed in the jejunum, ileum, and colon of SMP8-IGF-I-TG mice and wild-type littermates. Abundance of the SMP8-IGF-I transgene and IGF binding protein (IGFBP)-3 and -5 mRNAs was determined. Mucosal growth was increased in SMP8-IGF-I-TG ileum but not jejunum or colon; muscularis growth was increased throughout the bowel. IGFBP-5 mRNA was increased in SMP8-IGF-I-TG jejunum and ileum and was specifically upregulated in ileal lamina propria. Overexpression of IGF-I in intestinal mesenchymal cells has preferential paracrine effects on the ileal mucosal epithelium and autocrine effects on the muscularis throughout the bowel. Locally expressed IGF-I has distinct actions on IGFBP expression compared with circulating IGF-I.

Peptide growth factors regulate insulin-like growth factor binding protein production by fetal rat lung fibroblasts

Insulin-like growth factor (IGF) binding proteins (IGFBPs) are expressed in fetal lung and may provide important post-translational regulation of IGF-induced mitogenesis during lung organogenesis. Because of the observation that growth factors can control cell growth through regulation of IGFBPs, we examined IGFBP production by fetal lung fibroblasts following stimulation by peptide growth factors important for fetal lung growth and development. Fetal lung fibroblasts were cultured in serum-free medium supplemented with various growth factors for up to 48 h, and IGFBPs in conditioned medium (CM) were analyzed by ligand blot and immunoblot techniques. Accumulation of CM IGFBP-3 was increased and IGFBP-2 decreased by incubation with either keratinocyte growth factor (KGF) or epidermal growth factor (EGF). The effect of these factors on IGFBP-3 accumulation increased with time but the effects of KGF on CM IGFBP-2 decreased over 48 h of incubation. CM IGFBP-4 was increased by 24 and 48 h incubation with basic fibroblast growth factor (bFGF; 2.1- and 2.7-fold increases at 24 and 48 h, respectively) and platelet-derived growth factor-BB (PDGF-BB; 4.2- and 14.9-fold increases at 24 and 48 h, respectively), and 48 h incubation with EGF (6.3-fold increase). In 48-h coincubation experiments, EGF in combination with PDGF-BB or with bFGF, and bFGF in combination with PDGF-BB, resulted in IGFBP-4 accumulations twice that expected from a summation of the effects of either growth factor alone (IGFBP-4 increased 9.8-, 4.0-, and 1.8-fold by PDGF-BB, EGF, and bFGF, respectively; and 27.1-, 37.3-, and 13.0-fold by PDGF-BB plus EGF, PDGF-BB plus bFGF, and EGF plus bFGF, respectively). These results suggest synergistic effects of these growth factors on IGFBP-4 accumulation in fetal lung fibroblast CM. Because IGFBPs are known to regulate DNA synthesis, we speculate that peptide growth factors may alter cell proliferation in fetal lung, in part through their effect on IGFBPs.

Involvement of insulin-like growth factor-1 and its binding proteins in proliferation and differentiation of murine bone marrow-derived macrophage precursors

Insulin-like growth factor 1 (IGF-1) and its binding proteins (IGFBPs) are involved in proliferation and differentiation of many cell types. In the present study, the involvement of IGF-1 and IGFBPs in proliferation and differentiation of murine bone marrow-derived macrophages (BMDM) was investigated. L929-conditioned media (LCM) containing abundant macrophage colony-stimulating factor CSF-1 were used to stimulate BMDM development from their bone marrow precursors. The alteration of IGF-1 and IGFBPs during LCM-induced BMDM proliferation and differentiation was first studied. The cells were cultured in RPMI complete media containing 20% LCM for different time periods and then incubated in serum-free media for 24 h. The supernatants were collected for Western ligand blotting and immunoblotting analyses, and the cell pellets for Northern blotting analyses. The mRNA level of IGF-1 increased in a time-dependent manner. An increase of IGFBP-4 accumulation in the conditioned media was also observed during this process. However the mRNA expression of IGFBP-4 remained constant, indicating a posttranscriptional regulation of IGFBP-4 secretion and/or stability. The effects of exogenous recombinant human IGF-1 (rhIGF-1) on BMDM proliferation and differentiation were further studied. Two IGF-1 analogs (long R3 IGF-1 and des [1-3] IGF-1) were also used in parallel with regular IGF-1 to indicate the involvement of IGFBPs in BMDM development. Cells were cultured in complete media containing 20% LCM for different time periods, and then incubated in serum-free media in the presence of rhIGF-1 or its analogs for 24 h. These three forms of IGF-1 all potentiated the proliferation of freshly isolated BMDM precursors (d 0). rhIGF-1 and long R3 IGF-1, but not des (1-3) IGF-1, continued to stimulate the cell proliferation on d 1. The effects of these three forms of IGF-1 on BMDM differentiation were investigated using mannose receptor expression as a marker. Long R3 IGF-1 and des (1-3) IGF-1, but not rhIGF-1, enhanced BMDM differentiation on d 4. The different effects of rhIGF-1 and its analogs on BMDM differentiation suggest that the accumulation of IGFBP-4 in BMDM development might have an inhibitory effect on IGF-1 actions by sequestering free IGF-1.

Macrophage inflammatory protein-2: chromosomal regulation in rat small intestinal epithelial cells

Nonpathogenic, resident bacteria participate in the pathogenesis of inflammation in the small intestine, but the molecular messages produced by such bacteria are unknown. Inflammatory responses involve the recruitment of specific leukocyte subsets. We, therefore, hypothesized that butyrate, a normal bacterial metabolite, may modulate chemokine secretion by epithelial cells, by amplifying their response to proinflammatory signals. We studied the expression of the chemokine, macrophage inflammatory protein-2 (MIP-2) by the rat small intestinal epithelial cell line, IEC-6. Cells were stimulated with lipopolysaccharide or with interleukin 1beta (IL-1beta) and incubated with sodium butyrate. Acetylation of histones was examined in Triton X acetic acid-urea gels by PAGE. Unstimulated IEC-6 cells did not secrete MIP-2. However, lipopolysaccharide and IL-1beta induced MIP-2 expression. Butyrate enhanced MIP-2 secretion both in lipopolysaccharide-stimulated and IL-1beta-stimulated enterocytes; but butyrate alone did not induce MIP-2 expression. Butyrate increased the acetylation of histones extracted from the nuclei of IEC-6 cells. Furthermore, acetylation of histones (induced by trichostatin A, a specific inhibitor of histone deacetylase) enhanced MIP-2 expression by cells stimulated with IL-1beta. In conclusion, trichostatin A reproduced the effects of butyrate on MIP-2 secretion. Butyrate, therefore, increases MIP-2 secretion in stimulated cells by increasing histone acetylation. We speculate that butyrate carries information from bacteria to epithelial cells. Epithelial cells transduce this signal through histone deacetylase, modulating the secretion of chemokines.

Human fetal enterocytes in vitro: modulation of the phenotype by extracellular matrix

The differentiation of small intestinal epithelial cells may require stimulation by microenvironmental factors in vivo. In this study, the effects of mesenchymal and luminal elements in nonmalignant epithelia] cells isolated from the human fetus were studied in vitro. Enterocytes from the human fetus were cultured and microenvironmental factors were added in stages, each stage more closely approximating the microenvironment in vivo. Four stages were examined: epithelial cells derived on plastic from intestinal culture and grown as a cell clone, the same cells grown on connective tissue support, primary epithelial explants grown on fibroblasts with a laminin base, and primary epithelial explants grown on fibroblasts and laminin with n-butyrate added to the incubation medium. The epithelial cell clone dedifferentiated when grown on plastic; however, the cells expressed cytokeratins and villin as evidence of their epithelial cell origin. Human connective tissue matrix from Engelbreth-Holm-Swarm sarcoma cells (Matrigel) modulated their phenotype: alkaline phosphatase activity increased, microvilli developed on their apical surface, and the profile of insulin-like growth factor binding proteins resembled that secreted by differentiated enterocytes. Epithelial cells taken directly from the human fetus as primary cultures and grown as explants on fibroblasts and laminin expressed greater specific enzyme activities in brush border membrane fractions than the cell clone. These activities were enhanced by the luminal molecule sodium butyrate. Thus the sequential addition of connective tissue and luminal molecules to nonmalignant epithelia] cells in vitro induces a spectrum of changes in the epithelial cell phenotype toward full differentiation.