Features of intestinal lesions in the clinical course of inflammatory bowel diseases

Inflammatory bowel diseases (IBD), including ulcerative colitis (UC) and Crohn's disease (CD), are chronic, progressive and relapsing inflammatory disorders of unknown etiology. UC is characterized by inflammation of the large bowel mucosa and submucosa, whereas in CD inflammation is transmural and may involve various sites of the gastrointestinal tract. Superficial mucosal lesions are most prone to heal, whereas deep ulcers or transmural fissures may heal with more difficulty and may be followed by the development of fibrosis and strictures requiring surgery. Inflammation appears to be necessary to trigger the onset of the fibrotic process, but subsequently plays a minor role in its progression. In IBD, anti-inflammatory treatment does not prevent evolution of fibrosis once the process has started. Therefore, the mechanisms that regulate fibrosis appear to be distinct from those regulating inflammation. Intestinal fibrosis is due to an abnormal accumulation of extracellular matrix proteins producted by activated intestinal myofibroblasts. Increased evidence indicate that a number of molecules are involved in the development of the disease and a crosstalk between TGFbeta/Smads pathway and alphavbeta6 integrin, mTOR and PPARgamma could play a crucial role in the development of intestinal fibrosis. Animal models represent a useful tool to investigate the molecular and cellular mechanisms of intestinal inflammation and fibrosis and to test the effectiveness of novel therapeutic strategies for the prevention and treatment of intestinal fibrosis that still remain the major cause of surgical intervention.