Colonic Lesions,Cytokine Profiles,and Gut Microbiota in Plasminogen-Deficient Mice

Plasminogen-deficient (FVB/NPan-plg^tm1Jld, plg^tm1Jld) mice, which are widely used as a wound-healing model, are prone to spontaneous rectal prolapses. The aims of this study were 1) to evaluate the fecal microbiome of plg^tm1Jld mice for features that might contribute to the development of rectal prolapses and colonic inflammation and 2) to assess the relevance of the inflammatory phenotype to the variability in wound healing in this model. The plg^tm1Jld mice exhibited delayed wound healing, and they could be divided into 3 distinct groups that differed according to the time until wound closure. Colonic lesions in plg^tm1Jld mice, which were characterized by necrotizing ulcerations and cystically dilated glands, were restricted to the intermediate and distal parts of the colon. The cytokine profile was indicative of chronic tissue damage, but the genetic modification did not change the composition of the gut microbiota, and none of the clinical or biochemical parameters correlated with the gut microbiota composition.Several studies using plasminogen-deficient (plg^tmJld) mice have demonstrated that plasminogen, the proenzyme of plasmin, can degrade fibrin and other extracellular matrix proteins.⁴⁴ Plasminogen is essential for wound healing in skin,⁴⁰ which begins with inflammation, followed by epithelial proliferation, and thereafter tissue remodeling. Because the migrating keratinocytes of plg^tm1Jld mice have a decreased ability to dissect the platelet-rich fibrin matrix, they exhibit severely impaired wound healing.^15,40 In addition, plasmin mediates various pathologic processes, such as tumor growth and cancer metastasis,⁸ and therapeutic intervention related to plasminogen has shown encouraging results in experimental tumors.³¹ Therefore, one important application of these mice is the induction of wound healing to study basic mechanistic functions of plasmin, such as the clearance of the extracellular matrix and activation of tumor growth factors.³¹Spontaneous rectal prolapse and colonic ulceration in plg^tm1Jld mice compromise studies using these mice by leading to loss of body weight (wasting disease)⁶ and wellbeing-related, early study termination.⁶ Like other inflammatory conditions, rectal prolapse and chronic colonic inflammation might affect wound healing and contribute to the wide interindividual variation in the wound-healing processes of plg^tm1Jld mice.^28,40The development of rectal prolapses and colonic ulcerations in plg^tm1Jld mice reportedly is due to vascular occlusion.⁶ This pathologic condition is alleviated by superimposing fibrinogen deficiency on plasminogen deficiency, suggesting that fibrin is the primary substrate for plasmin.^7,15 The wide variation in effective tissue remodeling during the wound healing of plasminogen-deficient mice remains unexplained.Wound healing depends to a large extent on cells and factors of the immune system.^3,53 We previously have shown that disease development in mouse models for various inflammatory conditions, including type 1 diabetes,^17-19,35 type 2 diabetes,^4,13,42 atopic dermatitis³⁰ and inflammatory bowel disease,²⁰ is influenced by the composition of gut microbiota. Therefore, gut inflammation can be presumed to interfere with wound healing and thus may increase the uncontrolled interindividual variation in these models. In addition, gut inflammatory conditions in humans, such as inflammatory bowel disease⁴³ and irritable bowel syndrome,²³ are linked to dysbiosis in the intestine. In mice deficient in IL10 or IL2 and in rats carrying HLA-B27,⁵² inflammatory bowel disease can be alleviated by germ-free status^10,49,52 or ampicillin.²⁰ However, the possible role of the gut microbiome in rectal prolapse, colonic lesions, and wound healing in plasminogen-deficient mice has not previously been assessed.The aims of the current study were 1) to evaluate the fecal microbiome of plg^tm1Jld mice and their unaffected WT littermates for features that might contribute to their rectal prolapse and colonic inflammation phenotypes and 2) to assess the relevance of the inflammatory phenotype to the variability in wound healing in this model.