The mast cell stabiliser ketotifen decreases visceral hypersensitivity and improves intestinal symptoms in patients with irritable bowel syndrome

Background Mast cell activation is thought to be involved in visceral hypersensitivity, one of the main characteristics of the irritable bowel syndrome (IBS). A study was therefore undertaken to investigate the effect of the mast cell stabiliser ketotifen on rectal sensitivity and symptoms in patients with IBS. Methods 60 patients with IBS underwent a barostat study to assess rectal sensitivity before and after 8 weeks of treatment. After the initial barostat, patients were randomised to receive ketotifen or placebo. IBS symptoms and health-related quality of life were scored. In addition, mast cells were quantified and spontaneous release of tryptase and histamine was determined in rectal biopsies and compared with biopsies from 22 age- and gender-matched healthy volunteers. Results Ketotifen but not placebo increased the threshold for discomfort in patients with IBS with visceral hypersensitivity. This effect was not observed in normosensitive patients with IBS. Ketotifen significantly decreased abdominal pain and other IBS symptoms and improved quality of life. The number of mast cells in rectal biopsies and spontaneous release of tryptase were lower in patients with IBS than in healthy volunteers. Spontaneous release of histamine was mostly undetectable but was slightly increased in patients with IBS compared with healthy volunteers. Histamine and tryptase release were not altered by ketotifen. Conclusions This study shows that ketotifen increases the threshold for discomfort in patients with IBS with visceral hypersensitivity, reduces IBS symptoms and improves health-related quality of life. Whether this effect is secondary to the mast cell stabilising properties of ketotifen or H-1 receptor antagonism remains to be further investigate

Viperin mRNA is a novel target for the human RNase MRP/RNase P endoribonuclease

RNase MRP is a conserved endoribonuclease, in humans consisting of a 267-nucleotide RNA associated with 7–10 proteins. Mutations in its RNA component lead to several autosomal recessive skeletal dysplasias, including cartilage-hair hypoplasia (CHH). Because the known substrates of mammalian RNase MRP, pre-ribosomal RNA, and RNA involved in mitochondrial DNA replication are not likely involved in CHH, we analyzed the effects of RNase MRP (and the structurally related RNase P) depletion on mRNAs using DNA microarrays. We confirmed the upregulation of the interferon-inducible viperin mRNA by RNAi experiments and this appeared to be independent of the interferon response. We detected two cleavage sites for RNase MRP/RNase P in the coding sequence of viperin mRNA. This is the first study providing direct evidence for the cleavage of a mRNA by RNase MRP/RNase P in human cells. Implications for the involvement in the pathophysiology of CHH are discussed

Whole-exome re-sequencing in a family quartet identifies POP1 mutations as the cause of a novel skeletal dysplasia

Recent advances in DNA sequencing have enabled mapping of genes for monogenic traits in families with small pedigrees and even in unrelated cases. We report the identification of disease-causing mutations in a rare, severe, skeletal dysplasia, studying a family of two healthy unrelated parents and two affected children using whole-exome sequencing. The two affected daughters have clinical and radiographic features suggestive of anauxetic dysplasia (OMIM 607095), a rare form of dwarfism caused by mutations of RMRP. However, mutations of RMRP were excluded in this family by direct sequencing. Our studies identified two novel compound heterozygous loss-of-function mutations in POP1, which encodes a core component of the RNase mitochondrial RNA processing (RNase MRP) complex that directly interacts with the RMRP RNA domains that are affected in anauxetic dysplasia. We demonstrate that these mutations impair the integrity and activity of this complex and that they impair cell proliferation, providing likely molecular and cellular mechanisms by which POP1 mutations cause this severe skeletal dysplasia

GAMETOPHYTE DEFECTIVE 1, a Putative Subunit of RNases P/MRP, Is Essential for Female Gametogenesis and Male Competence in Arabidopsis

RNA biogenesis, including biosynthesis and maturation of rRNA, tRNA and mRNA, is a fundamental process that is critical for cell growth, division and differentiation. Previous studies showed that mutations in components involved in RNA biogenesis resulted in abnormalities in gametophyte and leaf development in Arabidopsis. In eukaryotes, RNases P/MRP (RNase mitochondrial RNA processing) are important ribonucleases that are responsible for processing of tRNA, and transcription of small non-coding RNAs. Here we report that Gametophyte Defective 1 (GAF1), a gene encoding a predicted protein subunit of RNases P/MRP, AtRPP30, plays a role in female gametophyte development and male competence. Embryo sacs were arrested at stages ranging from FG1 to FG7 in gaf1 mutant, suggesting that the progression of the gametophytic division during female gametogenesis was impaired in gaf1 mutant. In contrast, pollen development was not affected in gaf1. However, the fitness of the mutant pollen tube was weaker than that of the wild-type, leading to reduced transmission through the male gametes. GAF1 is featured as a typical RPP30 domain protein and interacts physically with AtPOP5, a homologue of RNases P/MRP subunit POP5 of yeast. Together, our data suggest that components of the RNases P/MRP family, such as RPP30, play important roles in gametophyte development and function in plants

Peripheral a-helical CRF (9-41) does not reverse stress-induced mast cell dependent visceral hypersensitivity in maternally separated rats

Background Acute stress-induced hypersensitivity to colorectal distention was shown to depend on corticotropin releasing factor (CRF)-induced mast cell degranulation. At present it remains unclear whether CRF also induces chronic poststress activation of these cells. Accordingly, the objective of this study was to compare pre- and poststress CRF-receptor antagonist treatment protocols for their ability to, respectively, prevent and reverse mast cell dependent visceral hypersensitivity in a rat model of neonatal maternal separation. Methods The visceromotor response to colonic distention was assessed in adult maternally separated and non-handled rats before and at different time points after 1 h of water avoidance (WA). Rats were treated with the mast cell stabilizer doxantrazole and the CRF receptor-antagonist a-helical- CRF (9-41). Western blotting was used to assess mucosal protein levels of the mast cell protease RMCP-2 and the tight junction protein occludin. Key Results In maternally separated, but not in nonhandled rats, WA induced chronic hypersensitivity (up to 30 days) to colorectal distention. Visceral hypersensitivity was prevented, but could not be reversed by administration of a-helical-CRF (9-41). In contrast, however, the mast cell stabilizer doxantrazole reversed visceral hypersensitivity. Compared with vehicle-treated rats, pre-WA a-helical-CRF (9-41) treated animals displayed higher mucosal RMCP-2 and occludin levels. Conclusions & Inferences Water avoidance-stress leads to persistent mast cell dependent visceral hypersensitivity in maternally separated rats, which can be prevented, but not reversed by blockade of peripheral CRF-receptors. We conclude that persistent poststress mast cell activation and subsequent visceral hypersensitivity are not targeted by CRF-receptor antagonist

Susceptibility to stress induced visceral hypersensitivity in maternally separated rats is transferred across generations

In irritable bowel syndrome (IBS), familial clustering and transfer across generations may largely depend on environmental factors but this is difficult to establish in the human setting. Therefore, we aimed to set up a relevant animal model. We investigated whether susceptibility to stress induced visceral hypersensitivity in maternally separated (MS) Long Evans rats can be transferred across generations without further separation protocols and, if so, whether this depends on maternal care. At adult age, we evaluated pre- vs post water avoidance (WA) changes in visceromotor response to distension in non-handled second filial generation offspring (NH-F2) of previously separated MS-F1 dams. Furthermore, the role of maternal care was evaluated by cross-fostering F2 offspring of NH-F1 and MS-F1 dams and subsequent sensitivity measurements at adult age. Involvement of mast cells in post stress hypersensitivity of NH-F2 rats was evaluated by mast cell stabilization. In adult NH-F2 offspring of MS-F1 dams, post-WA hypersensitivity to colorectal distension was observed in 80% of rats compared with 19% in offspring of NH-F1 dams. Cross-fostered pups adapted to the phenotype of the foster mother: pups of NH-F1 dams nursed by MS-F1 dams showed post-WA hypersensitivity to distension at adult age and vice versa (100% and 20% respectively). In NH-F2 rats, post-WA hypersensitivity was reversed by mast cell stabilizer doxantrazole. Maternal separated-induced susceptibility to stress-triggered visceral hypersensitivity is transferred across generations and this transfer depends on maternal care. Thus, MS is a suitable model to evaluate environmental triggers relevant to IBS clustering in familie

Neuronal control of experimental colitis occurs via sympathetic intestinal innervation

Vagus nerve stimulation is currently clinically evaluated as a treatment for inflammatory bowel disease. However, the mechanism by which this therapeutic intervention can have an immune-regulatory effect in colitis remains unclear. We determined the effect of intestine-specific vagotomy or intestine-specific sympathectomy of the superior mesenteric nerve (SMN) on dextran sodium sulfate (DSS)-induced colitis in mice. Furthermore, we tested the efficacy of therapeutic SMN stimulation to treat DSS-induced colitis in rats. Vagal and SMN fibers were surgically dissected to achieve intestine-specific vagotomy and sympathectomy. Chronic SMN stimulation was achieved by implantation of a cuff electrode. Stimulation was done twice daily for 5 minutes using a biphasic pulse (10 Hz, 200 μA, 2 ms). Disease activity index (DAI) was used as a clinical parameter for colitis severity. Colonic cytokine expression was measured by quantitative PCR and ELISA. Intestine-specific vagotomy had no effect on DSS-induced colitis in mice. However, SMN sympathectomy caused a significantly higher DAI compared to sham-operated mice. Conversely, SMN stimulation led to a significantly improved DAI compared to sham stimulation, although no other parameters of colitis were affected significantly. Our results indicate that sympathetic innervation regulates the intestinal immune system as SMN denervation augments, and SMN stimulation ameliorates DSS-induced colitis. Surprisingly, intestine-specific vagal nerve denervation had no effect in DSS-induced coliti