Effects of Adiponectin on DSS-induced Acute Ulcerative Colitis in Mice

Abstract

Inflammatory Bowel Disease (IBD) comprising of Ulcerative colitis (UC) and Crohn's disease (CD) is marked by chronic and repetitive inflammation and immune response. Acute UC has been characterized by severe inflammation of colonic epithelia and the underlying layers. As the epithelial tissue lining of the gut gets abraded, an anatomical feature of gut inflammation, the colonic epithelial crypts start losing their normal structure. Consequently, cellular components of the immune system begin to infiltrate the mucosal layers of the colon. Acute inflammation also affects the numbers and function of epithelial and goblet cells residing inside the crypts, resulting in altered ratios between them and an abnormal mucus production from the goblet cells. Adiponectin (APN), an adipocytokine, secreted by adipocytes, has been shown to possess both pro- as well as anti-inflammatory effects on the gut. In case of acute inflammation, it has been shown to act as a pro-inflammatory molecule such that, its absence has a protective role against inflammation. In the present study we have tried to show the protective role of APN absence against acute ulcerative colitis in a murine model. WT (C57Bl/6) and APNKO mice (n = 5) were housed in the animal facility at University of South Carolina. The mice were given 2.5% DSS ad libitum in drinking water for 5 days, followed by normal drinking water for next 5 days to induce acute inflammation. Mice were injected with 1.5 mg/kg of recombinant Adiponectin intraperitoneally every alternative day for a period of 10 days and sacrificed by cervical dislocation on day 11. The clinical score parameters including weight loss, diarrhea and blood in stools were measured on a scale of 12. Food and water consumption was also recorded. Histological staining procedures including Hematoxylin and Eosin, BrdU, Alcian blue and TUNEL assay were used to study the relative numbers of epithelial and goblet cells, and the extent of proliferation and immune cell infiltration and cell death. Expression levels of proand anti-inflammatory proteins and cytokines were also studied using several genomic and proteomic techniques. The intraperitoneal injections of APN worsened the symptoms of acute ulcerative colitis in the experimental mice. The proteomic and genomic studies showed an increase in the expression of pro-inflammatory proteins. A higher expression of pro-inflammatory cytokines such as IL-6 and TNF-α was observed. The external administration of APN to DSS-treated APNKO mice exhibited the highest clinical score and lowest goblet cell numbers, indicating the reduced secretion of mucus in the colon tissue, which indicate a reduce protection from DSS induced insult of the colon tissue. There was no significant difference between DSS-treated WT mice and the DSS-treated APNKO mice which were administered APN externally. However WT mice treated with DSS showed highest degree of inflammation and immune cell infiltration. It can be concluded that the absence of APN serves a protective role against DSS-induced acute ulcerative colitis by increasing the density of the goblet cells and epithelial cell proliferation.