Crypt stem cell survival in the mouse intestinal epithelium is regulated by prostaglandins synthesized through cyclooxygenase-1.

Prostaglandins (PGs) are important mediators of epithelial integrity and function in the gastrointestinal tract. Relatively little is known, however, about the mechanism by which PGs affect stem cells in the intestine during normal epithelial turnover, or during wound repair. PGs are synthesized from arachidonate by either of two cyclooxygenases, cyclooxygenase-1 (Cox-1) or cyclooxygenase-2 (Cox-2), which are present in a wide variety of mamalian cells. Cox-1 is thought to be a constitutively expressed enzyme, and the expression of Cox-2 is inducible by cytokines or other stimuli in a variety of cell types. We investigated the role of PGs in mouse intestinal stem cell survival and proliferation following radiation injury. The number of surviving crypt stem cells was determined 3.5 d after irradiation by the microcolony assay. Radiation injury induced a dose-dependent decrease in the number of surviving crypts. Indomethacin, an inhibitor of Cox-1 and Cox-2, further reduced the number of surviving crypts in irradiated mice. The indomethacin dose response for inhibition of PGE2 production and reduction of crypt survival were similar. DimethylPGE2 reversed the indomethacin-induced decrease in crypt survival. Selective Cox-2 inhibitors had no effect on crypt survival. PGE2, Cox-1 mRNA, and Cox-1 protein levels all increase in the 3 d after irradiation. Immunohistochemistry for Cox-1 demonstrated localization in epithelial cells of the crypt in the unirradiated mouse, and in the regenerating crypt epithelium in the irradiated mouse. We conclude that radiation injury results in increased Cox-1 levels in crypt stem cells and their progeny, and that PGE2 produced through Cox-1 promotes crypt stem cell survival and proliferation.

First Report of Blueberry scorch virus on Highbush Blueberry in Connecticut and Massachusetts.

During June and July 2001, the Marucci Center received 33 foliage samples from healthy- and unhealthy-looking highbush blueberry (Vaccinium corymbosum L.) bushes from growers in Connecticut and Massachusetts, via local extension agents. Unhealthy bushes were reported to exhibit symptoms including leaf chlorosis and necrosis, blossom blight, tip dieback, or a general decline in vigor. Marginal leaf chlorosis, reddening, or necrosis characterized foliage samples from these bushes. Five-leaf samples from each bush were tested for Blueberry scorch virus (BlScV) (3) with Agri-Check detection kits (Hydros, Inc., Falmouth, MA). These kits use an indirect enzyme-linked immunosorbent assay (ELISA) protocol and antibodies developed at Rutgers University that are specific to the two eastern strains of BlScV (NJ1 and NJ2) (1). The ELISA extraction buffer was based on that used by Martin and Bristow (3) with 1% (wt/vol) nonfat dry milk powder added as a blocking agent. Fourteen samples from cvs. Blueray and Berkeley in both states and cvs. Elliott, Bluecrop, and Coville in Massachusetts tested positive for BlScV. These results were confirmed by a second test. Six of seven samples from symptomatic bushes and 8 of 26 samples from asymptomatic bushes harbored BlScV. Virus preparations extracted from five infected plants (two from Connecticut and three from Massachusetts) were examined using reverse transcription-polymerase chain reaction (RT-PCR) with oligonucleotide primers (5'-TGTGTCAAACAATATGGC-3' and 5'-GCATTTCGATGA-TTGCGG-3') designed to amplify a portion of the coat protein gene from any of the three known virus strains (1,2). Sequence analysis of fragments amplified from their coat protein genes revealed that two of the isolates from Massachusetts (GenBank Accession Nos. AY530957 and AY530958) and the two isolates from Connecticut (GenBank Accession Nos. AY530955 and AY530956) were similar but not identical to one another, and these four were most similar to strain NJ2. One isolate from Massachusetts (GenBank Accession No. AY530958) was most similar to strain NJ1. To our knowledge, this is the first report of BlScV on the east coast outside of New Jersey, where it was first reported in 1983 (4). These results indicate that the disease is now present in other blueberry-growing areas in the northeast and is likely to be spreading locally within those areas. Because blueberry scorch is symptomless in propagation material and may take several years to express symptoms in the field, the initial spread of the disease was probably due to the shipping of latently infected plants to BlScV-free areas before reliable testing was available. References: (1) T. D. Cavileer et al. J. Gen. Virol. 75:711, 1994. (2) B. T. Halpern and B. I. Hillman. Plant Dis. 80:219, 1996. (3) R. R. Martin and P. R. Bristow. Phytopathology 78:1636, 1988. (4) A. W. Stretch. (Abstr.) Phytopathology 73:375, 1983.

Lipopolysaccharide is radioprotective in the mouse intestine through a prostaglandin-mediated mechanism.

BACKGROUND & AIMS: The bone marrow and the intestine are the major sites of radiation-induced injury. The cellular response to radiation injury in the intestine or bone marrow can be modulated by agents given before irradiation. Lipopolysaccharide is known to be radioprotective in the bone marrow, but its effect on the intestine is not known. We sought to determine if lipopolysaccharide is radioprotective in the intestine and, if so, to determine the mechanism of its radioprotective effects. METHODS: Mice were treated with parenteral lipopolysaccharide or vehicle and then irradiated (14 Gy total body irradiation in a cesium irradiator). The number of surviving intestinal crypts was assessed 3.5 days after irradiation using a clonogenic assay. RESULTS: Parenteral administration of lipopolysaccharide 2-24 hours before irradiation resulted in a 2-fold increase in the number of surviving crypts 3.5 days after irradiation. The radioprotective effects of lipopolysaccharide could be eliminated by coadministration of a selective inhibitor of cyclooxygenase 2. Lipopolysaccharide was radioprotective in wild-type mice but not in mice with a disrupted cyclooxygenase 2. Parenteral administration of lipopolysaccharide resulted in increased production of prostaglandins in the intestine and in the induction of cyclooxygenase 2 expression in subepithelial fibroblasts and in villous, but not crypt, epithelial cells. CONCLUSIONS: Lipopolysaccharide is radioprotective in the mouse intestine through a prostaglandin-dependent pathway.

Prostaglandins prevent decreased epithelial cell proliferation associated with dextran sodium sulfate injury in mice.

BACKGROUND & AIMS: Although dextran sodium sulfate (DSS)-induced colitis is a commonly used model of colonic injury, the mechanism of this model is not understood. The aim of this study was to determine the contribution of prostaglandins to the mechanism of DSS-induced epithelial injury. METHODS: Mice were treated with 3% DSS in the drinking water for 5 days followed by water only (recovery). Tissue prostaglandin E2 (PGE2) levels were measured, proliferating cells per cecal crypt were determined by bromodeoxyuridine labeling, and the cellular localization of cyclooxygenase (COX)-1 and COX-2 was determined by immunohistochemistry. RESULTS: DSS decreased the number of proliferating epithelial cells per crypt by approximately 90% and decreased the height of cecal crypts by 40%. Administration of dimethyl PGE2 with DSS reversed the effect of DSS on proliferation but not its effect on crypt shortening. COX-1 was expressed in the crypt epithelium and lamina propria mononuclear cells; DSS treatment down-regulated COX-1 expression only in the epithelium. Dimethyl PGE2 reversed the effect of DSS on COX-1 expression. Recovery was associated with a return to normal COX-1 expression in the epithelium. COX-2 was expressed in lamina propria mononuclear cells. CONCLUSIONS: Epithelial cell proliferation in the presence of DSS contains a PGE2-sensitive component.

Bovine IgG1, but not IgG2, binds to human B cells and inhibits antibody secretion.

We previously observed that milk-derived bovine IgG, but not serum-derived bovine IgG, strongly inhibits antibody secretion by pokeweed mitogen (PWM)-stimulated human peripheral blood mononuclear cells (PBMC). Bovine milk contains a greater percentage of IgG1 (90%) than does bovine serum (53%). To determine whether bovine IgG subclasses have different functional capabilities, we have examined the effects of bovine IgG1 and IgG2 subclasses upon not only antibody secretion but also mitogenesis by human PBMC. Both bovine IgG subclasses markedly inhibited PWM-stimulated mitogenesis. However, only bovine IgG1, and not IgG2, inhibited antibody secretion during a 14-day in vitro culture period. Also, antibody secretion was inhibited following a 24-hr preincubation of human PBMC with bovine IgG1, but not with IgG2. To determine whether these differences corresponded to specificities of human Fc gamma receptors on subsets of mononuclear cells, fluorescence-activated cell sorter (FACS) analyses were performed. Both bovine IgG subclasses bound to human monocytes. However, only bovine IgG1 bound to human B cells, and bovine IgG1 bound more avidly to human B cells than did human IgG. One model to explain these findings is that inhibition of mitogenesis may be due to the binding of both bovine IgG1 and IgG2 subclasses to monocytes; whereas subclass-specific inhibition of antibody secretion may result from the selective binding of bovine IgG1, but not bovine IgG2, to B cells. The observation that bovine IgG1 has a greater avidity for human B lymphocyte Fc receptors than human IgG may have important implications for future studies of Fc gamma receptors on human leucocytes.

Inhibition of antibody secretion by 5-aminosalicylic acid.

We have examined the effects of sulfasalazine and its metabolites sulfapyridine and 5-aminosalicylic acid on antibody secretion by normal peripheral blood and intestinal mononuclear cells. Sulfasalazine and 5-aminosalicylic acid both inhibited pokeweed mitogen-stimulated secretion of immunoglobulins (Igs) A, G, and M by peripheral blood mononuclear cells in a dose-dependent manner, whereas sulfapyridine had little effect. Sulfasalazine and 5-aminosalicylic acid also inhibited spontaneous secretion of IgA by intestinal mononuclear cells, but sulfapyridine did not. Sulfasalazine inhibited pokeweed mitogen-stimulated lymphocyte proliferation, while 5-aminosalicylic acid and sulfapyridine exhibited minimal inhibition. Sulfasalazine was toxic for peripheral blood mononuclear cells, whereas 5-aminosalicylic acid and sulfapyridine were not toxic. Thus, the inhibition of antibody secretion by sulfasalazine was due to direct toxicity. On the other hand, 5-aminosalicylic acid, the therapeutically active component of sulfasalazine, was neither toxic nor antiproliferative, and appeared to exert its effects on metabolic pathways directly related to antibody synthesis. The calculated ID50 values of 5-aminosalicylic acid for antibody secretion were 1.35 mM for IgA and 1.05 mM for IgG, concentrations that are achieved in the colons of treated individuals. Indomethacin did not inhibit antibody secretion at pharmacologically relevant concentrations. 5-Aminosalicylic acid mediated inhibition of antibody secretion may play a role in inflammatory bowel disease by stopping antibody-mediated memory events involved in the induction or perpetuation of the disease process.

Cyclooxygenase 2 is induced in colonic epithelial cells in inflammatory bowel disease.

BACKGROUND & AIMS: Prostaglandins are synthesized by cyclooxygenases (COX)-1 and -2. The expression and cellular localization of COX-1 and COX-2 in normal human colon and inflammatory bowel disease (IBD) surgical resections were studied. METHODS: COX-1 and COX-2 protein expression and cellular localization were assessed by Western blotting and immunohistochemistry. RESULTS: COX-1 protein was expressed at equal levels in normal, Crohn's disease, and ulcerative colitis colonic epithelial cells. COX-2 protein was not detected in normal epithelial cells but was detected in Crohn's disease and ulcerative colitis epithelial cells. Immunohistochemistry of normal, Crohn's colitis, and ulcerative colitis tissue showed equivalent COX-1 expression in epithelial cells in the lower half of the colonic crypts. COX-2 expression was absent from normal colon, whereas in Crohn's colitis and ulcerative colitis, COX-2 was observed in apical epithelial cells and in lamina propria mononuclear cells. In Crohn's ileitis, COX-2 was present in the villus epithelial cells. In ulcerative colitis, colonic epithelial cells expressing COX-2 also expressed inducible nitric oxide synthase. CONCLUSIONS: COX-1 was localized in the crypt epithelium of the normal ileum and colon, and its expression was unchanged in IBD. COX-2 was undetectable in normal ileum or colon, but it was induced in apical epithelial cells of inflamed foci in IBD.