Voluntary Exercise Modulates Neuroimmune Response in Colonic Inflammation Induced by Endometriosis

Abstract

Endometriosis is a complex gynecological disease characterized by the growth of endometrial tissue outside of the uterine cavity. Some symptoms that are prevalent in women with endometriosis are dysmenorrhea, infertility, pelvic pain, and gastrointestinal symptoms (GI). Among the GI symptoms, women with endometriosis experience painful bowel movements, diarrhea, constipation, and bloating similar to irritable bowel syndrome (IBS). Enteric glial cells (EGC), when reactive, are known to play a role in the inflammation of IBS. Reactive EGC are also involved in the polarization of macrophages to a proinflammatory phenotype; while exercise is known to promote activation of PPARγ, a nuclear receptor known for its anti-inflammatory activity, which is expressed in anti-inflammatory macrophages. We hypothesize that exercise can reduce endometriosis-induced expression of the glial fibrillary acidic protein (GFAP) and S100B, markers of reactive enteric gliosis; and promote expression of PPARγ in colonic macrophages. Methods Three groups of female Sprague Dawley rats were used: Sham Control (n=4), Endo Control (n=5), and Endo Exercise (n=5). Endometriosis was induced by suturing 4 pieces of autologous uterine tissue from the right uterine horn on the intestinal mesentery, while the Sham group only received the sutures without implants. After surgery Endo Exercise group was exposed to voluntary wheel running for 60 days, while control groups were individually housed in standard cages. On Day 60 we sacrificed the animals, examined them for endometriosis development, assessed colonic macroscopic score, and collected a piece of distal colon. We performed double immunofluorescence staining using GFAP/S100B and CD68/PPARγ antibodies, respectively, on slides containing formalin-fixed paraffin-embedded colonic tissue. Results After normalizing the mean fluorescent intensity (MFI) to DAPI, we found that the Endo Control group has a significant increase in GFAP MFI (0.57±0.06; p<0.01) compared to Sham Control (0.32±0.03), which was reduced significantly by exercise (0.38±0.01; p<0.05). Similarly, exercise significantly decreased S100B MFI (0.67±0.06; p<0.05) compared to Endo Control (1.34±0.16), although Endo Control was not significantly higher than Sham Control (0.94±0.20). For CD68/PPARγ, we found that Endo Exercise increased significantly the percentage of macrophages expressing PPARγ (88.43±3.45%; p<0.05) compared to Endo Control (51.14±10.44%). Endo Control had significantly higher macroscopic colonic damage (2.04±0.41; p<0.01) compared to Sham Control (0.26±0.14) and Endo Exercise (0.38±0.12). Conclusions These results show that endometriosis induces colonic inflammation and enteric reactive gliosis, while exercise intervention restores gut homeostasis, possibly through the increase of anti-inflammatory macrophages expressing PPARγ. Altogether, these results suggest exercise may prove beneficial to improve endometriosis-induced GI symptoms.