Nickerson, Cheryl

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder associated with chronic abdominal pain along with recurrent diarrhea, constipation, or both that afflicts millions of people worldwide. Currently, the etiological foundation of the disorder remains enigmatic. However, there is mounting evidence suggesting that serotonin may play a critical role in the pathophysiology of IBS. DNA microarrays analyzing the transcriptomes of 11 IBS patients versus 13 asymptomatic control patients have identified a series of 858 differentially‐expressed genes that may characterize the IBS pathological state. Gene ontology (GO) analysis of this subset of genes revealed that nodes featuring serotonin‐related pathways displayed the highest number of functions relative to other GO groups. Quantitative real‐time polymerase chain reaction (qRT‐PCR) analysis of IBS patient‐derived RNA displayed reduced expression of the rate‐limiting enzyme of the serotonin biosynthetic pathway, tryptophan hydroxylase 1 (TPH1), relative to a pool of RNA comprised of eight control patients. Further, this analysis revealed potential compensatory regulation of several other genes integral to the maintenance of serotonin metabolism. In addition, concentrations of serum 25‐hydroxyvitamin D in both the IBS and control sampled populations indicated a trend towards decreased vitamin D levels within the IBS cohort, regardless of IBS subtype. Finally, vitamin D was shown to be effective in regulating the expression of several key serotonin metabolism genes, alluding to a potential link between vitamin D and serotonin pathways modulating IBS. These findings suggest that the pathogenesis of IBS may be associated with abnormal serotonin metabolism and/or vitamin D deficiency, and provide novel insight into possible treatment regimes. Support or Funding Information Wisconsin Network for Health Research

Abstract Infection of certain strains of mice with Theiler’s murine encephalomyelitis virus results in persistence of virus and an immune-mediated primary demyelination in the central nervous system that resembles multiple sclerosis. Because susceptibility/resistance to demyelination in B10 congeneic mice maps strongly to class I MHC genes (D region) we tested whether expression of a human class I MHC gene (HLA-B27) would alter susceptibility to Theiler’s murine encephalomyelitis virus-induced demyelination. Transgenic HLA-B27 mice were found to co-express human and endogenous mouse class I MHC genes by flow microfluorimetry analysis of PBL. In the absence of the human transgene, H-2stf, or v mice but not H-2b mice had chronic demyelination and persistence of virus at 45 days after infection. No difference in degree of demyelination, meningeal inflammation, or virus persistence was seen between transgenic HLA-B27 and nontransgenic littermate mice of H-2f or H-2v haplotype. In contrast, H-2s (HLA-B27+) mice showed a dramatic decrease in extent of demyelination and number of virus-Ag+ cells in the spinal cord compared with H-2s (HLA-B27-) littermate mice. In addition, none of the eight H-2s mice homozygous for HLA-B27 gene had spinal cord lesions even though infectious virus was isolated chronically from their central nervous system. Expression of HLA-B27 transgene did not interfere with the resistance to demyelination normally observed in B10 (H-2b) mice. These experiments demonstrate that expression of a human class I MHC gene can modulate a virus-induced demyelinating disease process in the mouse.

HLA-B27 transgenic mice in the context of various H-2 haplotypes were produced. A high expression of the HLA-B27 antigen was observed in mice homozygous for H-2b, H-2f, H-2s, H-2p, H-2r, and H-2k haplotypes. Mice of the H-2v haplotype expressed HLA-B27 at an intermediate level. Expression of HLA-B27 was minimal in mice of the H-2q and H-2d haplotypes. This was observed both on the B10 background and in DBA/2 or BALB/c mice. Only minimal expression of HLA-B27 could be detected in B10.PL (KuDd) or B10.RKDB (KkSkDdLb) mice, indicating that the low level of HLA-B27 expression maps to the H-2D gene or a very closely linked gene. Integration and transcription of the HLA-B27 gene does not appear to be different between high-expressing haplotypes and low-expressing haplotypes as determined by Southern and Northern blot analysis. However, expression of HLA-B27 on the cell surface correlated with the amount of HLA-B27 and beta 2M that could be immunoprecipitated with an anti-B27 antibody. Therefore, the association of the B27 heavy chain with endogenous beta 2M and subsequent expression on the cell surface are disrupted in mice with some class I H-2D genes. Possible mechanisms that might contribute to this defect in assembly, transport, and expression of class I molecules are discussed.