SECRETION AND HORMONAL-REGULATION OF INTERLEUKIN-6 PRODUCTION BY MOUSE UTERINE STROMAL AND POLARIZED EPITHELIAL-CELLS CULTURED INVITRO

Uterine stromal (USC) and uterine epithelial (UEC) cells were isolated from immature and mature mice to determine their ability to secrete interleukin-6 (IL-6) in response to ovarian steroids, IL-1-alpha, and soluble products produced by the heterologous cell type. In addition, the effect of IL-6 on embryo attachment and outgrowth in vitro was determined. UEC cultured on nitrocellulose filter inserts in a polarized manner secreted IL-6 with a 2.5- to 5-fold apical vs. basal preference, as determined by a B9 hybridoma cell proliferation assay and enzyme-linked immunosorbent assay. The hormonal status of animals at the time uteri were removed did not influence subsequent secretion of IL-6, as UEC isolated from immature, diestrous, and estrous stage mice exhibited both a similar amount and had a similar apical preference for secretion of IL-6. The addition of 17-beta-estradiol (E) to UEC cultures markedly inhibited total IL-6 secretion, but did not affect vectorial secretion. The inhibitory effect of E on IL-6 secretion by UEC was consistent with an apparent decrease in IL-6 transcript observed by a reverse transcriptase polymerase chain reaction assay. Other transcripts detected by this assay in UEC included IL-1-alpha, but not IL-1-beta or tumor necrosis factor-alpha. Secretion of IL-6 by UEC was not stimulated by IL-1-alpha, conditioned medium from USC, or coculture with USC. USC secreted IL-6, and while this also was inhibited by E, progesterone was more effective in this regard at physiological concentrations. In addition, there was a synergistic effect of E plus progesterone on inhibition of IL-6 secretion by USC. Secretion of IL-6 by USC was stimulated by IL-1-alpha, and coculture studies demonstrated the ability of UEC to stimulate a several-fold increase in IL-6 secretion by USC. The cytokine transcripts detected in USC cultures included IL-6 and IL-1-alpha, but not IL-1-beta. Transcripts for tumor necrosis factor-alpha were present in USC only after culture with IL-1-alpha. IL-6 added to blastocysts on laminin-coated tissue culture wells resulted in a transient inhibition of the rate of blastocyst attachment and, to a greater extent, an inhibition of the rate of embryo outgrowth. In addition, IL-6 inhibited the size of embryo outgrowths at 24 and 48 h of culture. The present studies demonstrate the ability of UEC and USC to secrete IL-6 in a manner that is regulated by steroid hormones and via cell-cell interactions through the release of soluble factors. Secretion of IL-6 by UEC and USC may offer a means of intercellular communication within the uterus which may play a role in regulating implantation.