Avaliação morfológica e molecular de lesões colônicas em modelo de colite experimental induzida por dextran sulfato de sódio / Morphological and molecular evaluation of colonic lesions in a mouse model of experimental colitis induced by Dextran Sulfate Sodium (DSS)

RESUMO

A retocolite ulcerativa (RU) é uma doença inflamatória crônica que caracteristicamente afeta o reto e o intestino grosso e cuja etiologia ainda é desconhecida. Os pacientes portadores de RU apresentam um alto risco para o desenvolvimento de câncer colorretal (CCR). O desenvolvimento e a progressão do câncer associado à RU envolvem vários eventos genéticos que parecem ser diferentes dos observados nos cânceres esporádicos... O modelo animal de colite através do uso de DSS desenvolve displasia e câncer muito similares aos observados em humanos. O estudo da carcinogênese do cólon nestes animais pode ser de grande valia para o melhor entendimento das alterações que ocorrem em humanos e pode proporcionar o descobrimento de novos marcadores ou mesmo regimes quimiopreventivos para o câncer relacionado à RU. O objetivo deste estudo é elucidar os eventos moleculares das neoplasias relacionadas à RU no modelo experimental animal de colite induzida por DSS, traçando um paralelo com os estudos moleculares realizados em humanos. Para isto, foram utilizadas duas abordagens. A primeira, relacionada com a pesquisa de alterações moleculares nas neoplasias originadas no modelo de colite pelo uso de DSS e Azoxymethane (AOM) em animais sadios, onde foram avaliados os genes Trp53, k-ras, Apc e ß-catenina. A segunda, relacionada com o uso de DSS em animais alterados geneticamente para o gene Trp53, considerado o evento inicial nos tumores associados à RU... Nos animais geneticamente alterados para o gene Trp53 a pesquisa de mutação no gene k-ras foi negativa. Estes animais demonstraram a presença de displasia e câncer, também muito similares aos humanos, sendo que os animais homozigotos (p53-/-) apresentaram uma maior incidência de lesões quando comparados aos animais heterozigotos (p53+/-) e controles p53 (+/+)...

ABSTRACT

Ulcerative Colitis (UC) is a diffuse inflammatory disease of the colorectum, which etiology is unknown. UC patients are at increased risk of developing colorectal cancer (CRC). Development and progression of UC-associated to CRC involves multiple genetic alterations that appear to be different from those of sporadic cancer. Alterations of APC gene and k-ras gene are less frequent than in sporadic colorectal neoplasia. Although, alterations of TP53 gene is a frequently observed in both UC associated tumors and sporadic tumors, this alteration is an early event in UC related tumors but it is occurs late in sporadic tumors. Dextran Sulfate Sodium (DSS) mouse colitis model develop dysplasia and cancer similar to UC in human. Studies of colon carcinogenesis in this model can be very useful to elucidate mechanisms and provide development of markers or hemoprevention approaches in the human situation. The aim of this study is to establish the molecular events in a DSS mouse colitis model associated neoplasia in parallel with the molecular alterations seen in humans. Two different approaches had been used to achieve this goal. First, investigate molecular events in neoplastic lesions developed in a mouse model of colitis using DSS in combination with Azoxymethane (AOM) in healthy animals. In this approach, it was investigate genes, such as Trp53, k-ras, ß-catenin and Apc. Second, evaluate genetic events in mice deficient in the Trp53 gene, considered an early event in RUassociated tumors. Besides k-ras evaluation, it was also evaluated the histological aspects of the colonic lesions in this model. ß-catenin mutation (codons 32 and 34) and translocation ß-catenin were observed in healthy animals using DSS/AOM. No mutation of k-ras and Apc were observed and Apc LOH was not informative. DSS induced colitis in p53 deficient mice developed dysplasia and cancer. p53-/- (homozygous) showed a higher incidence of tumors when compared with p53+/- (heterozygous) and p53+/+ (wild-type) animals. No mutation of k-ras gene was observed. Besides dysplasia and cancer, p53-/- and p53+/- animals developed colite cystica profunda and hyperplastic lesions, both observed in patients with UC. The further accumulation of data originated in studies with mouse models of colitis related-neoplasia chemically-induced should provide information for better understand UC- related colorectal neoplasia in humans (AU)