Functional role of Interleukin-6 and Interleukin-10 in the reproductive processes of a teleost fish, Anabas testudineus

Abstract

In mammals, interleukin-6 (IL-6) and interleukin-10 (IL-10) has an important function during the reproductive processes, however, the functions of IL-6 and IL-10 in fish have not been elucidated. In the present study, there was quantification of de novo synthesis of ovarian IL-6, IL-10 and tumor necrosis factor-alpha (TNFα) in control and hCG treated fish and results were compared with those from an in vitro study where there was evaluation of the regulatory functions of gonadotropins and TNFα of IL-6 and Il-10 secretions. Relatively greater concentrations of ovarian IL-6 at the post-GVBD (post-germinal vesicle breakdown) stage and higher concentration of ovarian IL-10 in post vitellogenic (PV) and post-GVBD stages indicates IL-6 and IL-10 can modulates reproductive processes. The hCG-induced increase in relative abundance of IL-6 and IL-10 (in vitro) mRNA transcript and secretion from the ovary were attenuated when there was administration of the inhibitor of TNF-α secreting enzyme, TAPI-I, which indicates TNF-α modulates IL-6 secretion and facilitate the production of IL-10. Treatments with IL-6 induced a marked increase in ovulation rate but there was no direct involvement of IL-10 during the time of maturation and ovulation. In vitro established that Il-6 induced ovulation by activating matrix metalloproteinase (MMP). Furthermore, treatment with IL-6 resulted in production of prostaglandin as indicated by the IL-6 induced increase in the abundance of ptgs2 mRNA transcript in the ovary of Anabas testudineus. IL-10 during this process mostly play the regulatory role of the cytokine environment in the oocyte the inhibition of IL-6 when treated with IL-10 in PV follicle establish the fact. Furthermore, results indicate the source of IL-6 and IL-10 in the ovary, is the granulosa cells for IL-6 and both theca and granulosa cells for IL-10 with secretion of IL-6 and IL-10 being induced by the additions of hCG and TNFα in the medium. There was also an IL-6-induced increase in abundance of receptors (IL-6 Rα and gp130) to which it binds indicating IL-6 autoregulates this population of receptors. There was also marked increase in IL-10 receptor IL-10R1 and IL-10R2 suggesting their involvement during the reproductive processes. Stat-3 activation ensured the involvement of IL-6 during the time of ovulation. Results from this study, for the first time, elucidate the reproductive functions of IL-6 in a teleost fish.