In this study, generation of a Winnie x Ccr6-/- mouse model and identification of homozygous genotype of the same was achieved. An appropriate genotyping technique for each mouse strain was optimised and utilised. The respective genotypes were confirmed by performing an SNP assay for Winnie mice and PCR followed by agarose gel electrophoresis for Ccr6-/-mice. Generation of Winnie x Ccr6-/- mice was achieved; further assessments of its phenotype and its effects on inflammation in the absence of
Ccr6 would be a valuable asset in understanding the role of CCR6 in the disease process of IBD.
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Chapter 4
Clinical assessment and histopathological examination of
Winnie x Ccr6
-/-mice
4.1 Introduction
An important focus of our study was the assessment of the novel model Winnie x Ccr6-/-
phenotype. In this chapter, phenotype assessments of Winnie x Ccr6-/- mice pertaining to clinical parameters and changes in the histopathology of this strain are outlined. The Winnie mice phenotype has been extensively studied based on clinical, histological, molecular and immunological aspects, and it is a well-established spontaneous chronic colitis model [43,145,175]. It is imperative to validate the phenotype of any experimental mouse strain as it ascertains the utility of that animal in the field of biomedical research. A systematic approach for the assessment of phenotype of experimental mice which may have been genetically altered was outlined by Wood et al. [176]. Primary-level and secondary-level assessments were suggested as a guideline to assist in the phenotype assessment process of experimental animals, precisely mice or rats. The primary-level assessments are basically to identify abnormalities, whilst the secondary-level assessments are for quantification and evaluation of abnormalities. Both primary and secondary phenotype assessments are vital in studying the current mouse models used for investigating diseases in biomedical research [176].
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The phenotype and colitis assessments in Winniex Ccr6-/- mice were performed based on previously established protocols [131]. The specific parameters included the evaluation of colon weight, colon length, and colon weight by body weight ratio. Colon weight is regarded as a significant indicator of colitis, and the histopathology of colon tissue sections and small intestine stained with H&E were examined and graded using a blinded grading system developed for intestinal inflammation based on the standard protocol of histological scoring for colitis [131,177]. In the present study, the phenotype evaluation process noted other general aspects with regard to the experimental animal’s general well- being as part of the assessment process.
Ccr6-/- mice were developed to study various diseases such as RA, psoriasis and EAE [91,109]. Ccr6-/-mouse models are also considered a very important tool in understanding lung and gut diseases. Ccr6 is implicated as a susceptibility locus in CD and the role of CCR6-mediated colitis has been advanced by the development of Ccr6-/- mouse models in order to study the disease process of IBD in vivo. Due to the absence of Ccr6, the development of disease and the alteration of immune responses can be studied by using
Ccr6-/- mice. Defective leukocyte homeostasis and changes in the cytokine milieu in the intestinal mucosa are attributed to the absence of Ccr6 [98]. Winnie, a spontaneous chronic colitis mouse model develops mild distal colitis by 6 weeks of age [145].
Colonic inflammation displayed by the Winnie strain is due to the homozygous missense point mutation in the mucin 2 gene (Muc2). The resulting endoplasmic reticulum stress leads to the development of colonic inflammation similar to that of ulcerative colitis seen in humans [43].The SNP is the nominal Winnie mutation, and the substitution of cysteine with tyrosine in the D3 domain at the N terminus of Muc2 was identified in Winnie mice [43]. The goblet cell dysfunction occurs due to the mutation in Winnie mice and, unlike
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other contrived models, colitis spontaneously occurs in this phenotype as a result. There is a significant knowledge gap that exists regarding our understanding of the exact disease processes contributing to both UC and CD in IBD. The Winnie mouse model, which exhibits colonic inflammation due to a primary epithelial cell defect, ascertains the need for the secretion of mucin in order to maintain the integrity of the secretory cell, thereby preventing the occurrence of colonic inflammation.
The crosstalk between the colonic epithelial cells and luminal microbes, followed by the mucosal immune responses that occur during the colonic inflammation, needs to be addressed in order to understand the disease pathogenesis and progression. The reciprocal paracrine interaction of epithelial cells and immune cells in the intestine needs to be understood in order to relate or mimic IBD in vivo. The involvement of both the adaptive and innate immune system is well showcased in Winnie mice colitis. Hence serves as a potential mouse model for spontaneously occurring colitis to explore the role of the Ccr6
gene in this colitic context.