The Therapeutical Effect And The Related Mechanisms Of Retinoic Acid In Mouse Epididymitis

Epididymitis is one of the most common urological diseases in males.The presumed mechanism for epididymitis is a bacterial infection ascending from the urinary tract into the male excurrent duct system.It is well known that retinoic acid(RA)elicits anti-inflammatory effects by modulating the humoral and cellular immune responses,maintaining immune homeostasis,and regulating immune cell differentiation.The aim of this study is to investigate the functions and related mechanisms of RA in alleviating the acute inflammation of epididymitis.The mouse model of the epididymitis was induced by injecting Escherichia coli into the cauda epididymis.A histological examination indicated that RA treatment ameliorated the inflammation characterized by a much weaker leukocyte infiltration,and drastic reduction in cytokine secretion including IL-1?,IL-6,TNF?,IFN-?,IL-12p35 and IL-12p40 expressing levels.These results show that RA ameliorates the inflammation in mouse epididymitis.RA treatment significantly increased IL-10 and TGF-?1 expressions,both at gene and protein levels,in the mouse epididymitis.Immunohistochemistry results showed that IL-10 and TGF-?1 were located in the epididymal epithelial cells.Then we treated cultured epididymal epithelial cells with RA.Real-time PCR and western-blot analysis indicated that RA increased expressions of IL-10 and TGF-?1 in both mRNA and protein levels.To further confirm RA could specifically increase the expressions of anti-inflammatory cytokines as IL-10 and TGF-?1 in epididymis,we used lipopolycaccharides(LPS)to stimulate epididymal epithelial cells before RA treatment in vitro.RA could induce much more IL-10 and TGF-?1 expression in LPS activated epididymal epithelial cells,but could not affect the IL-1? and IL-6 expression.The physiological functions of RA are mediated primarily by the RARs,including RARa and RAR? and RARy.The real-time PCR results showed that RAR? and RAR? were highly expressed in both the epididymis and cultured epididymal epithelial cells.We then used a specific RARa antagonist Ro41-5253 and a RAR?antagonist LE135 to block the binding of RA to RARa and RAR?.The results indicate that the effect of RA on TGF-?1 expressions is through its binding to RAR?,whereas the effect of RA on IL-10 expressions is partially dependent on RAR?.RA is synthesized by RALDHs and can be oxidated by CYP26.The real-time PCR results showed that RALDH1 and CYP26C1 were highly expressed in both the epididymis and in cultured epididymal epithelial cells.And epididymal epithelial cells can increase RA level by regulation of the expression of RALDH1 and CYP26C1.In light of these novel results,RA acts as an essential nutrition molecule and is involved in regulating the inflammatory response of epididymis by up-regulating the expression of anti-inflammatory cytokines secreted from the epididymal epithelium.