Preliminary study on the pathogenesis of anal fistula

BACKGROUNDAnal gland infection is one of the main pathogenic factors of anal fistula. The anal gland is mainly consist of columnar epithelial cells and goblet cells. Goblet cells could secrete mucins which maintain the surface mucous gel layer of intestine to prevent columnar epithelial cells from the direct acting of bacteria. The absence or diminished secretion of goblet cells could lead to the exposure of columnar epithelial cells to bacteria. In recent years, studies have found that most of the microorganisms in perianal abscess and anal fistula are intestinal bacteria. So, it can be considered that the occurrence and development of anal fistula is closely related to gut microbiota. However, the molecular mechanism of gut microbiota acting on the epithelial cells of anal gland leading to the occurrence and development of anal fistula has not been explored. METHODSAnal fistula tissues were collected from 30 patients, and HE staining was employed to observe pathological changes of anal gland. Stool specimens were collected from normal group (14 normal subjects), preoperative group (21 subjects before surgery) and postoperative group (16 subjects after surgery). High-throughput 16S rRNA gene sequencing was performed to explore differences among different groups. RESULTSIt was found by HE staining that normal anal gland is composed of a large number of columnar epithelial cells as well as goblet cells, while the anal gland of patients with anal fistula is seriously lack of goblet cells. In the normal ones, a large number of vacuoles formed by the dye dissolution of mucin particles can be seen at the top of the goblet cells, and a large amount of mucin secretion can be seen in the center of the anal gland. The results of high-throughput 16S rRNA gene sequencing showed that there were significant statistical differences in species richness, species evenness and species composition between the preoperation group and the normal group (P1 =0.00004), and between the preoperative group and the postoperative group (P2 =0.00003). It also showed that PWY-6471 metabolic pathway was the most significant difference between the preoperative group and the postoperative group (P=0.0033). CONCLUSIONSThe occurrence of anal fistula may be related to the abnormal permeability of mucus layer and the change of intestinal flora composition. The absence or diminished secretion of goblet cells may cause exception of the permeability of mucus layer which makes the columnar epithelial cells of anal gland exposed to the direct contact of peptidoglycan. The metabolite of pathogenic microorganisms could activate the signal pathway (i.g. NLR/NF-{kappa}B) which leading to the overexpression of inflammatory factors and cause anal fistula.