IMMUNE-ENDOCRINE INTERACTIONS IN THE MOUSE TESTIS - CYTOKINE-MEDIATEDINHIBITION OF LEYDIG-CELL STEROIDOGENESIS

Immune activation by intraperitoneal (ip) injection of lipopolysacchar ide (LPS) results in the inhibition of mouse Leydig cell steroidogenes is. Previously, we demonstrated that LPS-injection (200 mu g mouse) ca used a chronic, reversible inhibition of 17 alpha-hydroxylase/C-17,C-2 0 lyase (P450c17) messenger RNA (mRNA) levels in Leydig cells from day -1 to day-5 after injection. A marked increase in interleukin-1 beta(I L-1 beta) mRNA expression in immune-activated testicular interstitial macrophages paralleled the inhibition of P450c17 expression. Recently we have demonstrated that both recombinant murine interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha) inhibited 8-bromo-cAMP (8 -Br-cAMP)-stimulated testosterone production as well as both mRNA and protein levels of P450c17 and cholesterol sidechain cleavage enzyme (P 450scc) in mouse Leydig cells in vitro. In the present study, we inves tigated whether in vivo immune-activation of macrophages by LPS-inject ion can modulate Leydig cell steroidogenic enzyme expression acutely. Testicular interstitial macrophages and Leydig cells were purified, RN A was extracted, and both cytokine and steroidogenic enzyme mRNA level s were measured. In parallel, plasma TNF alpha levels were also determ ined. The inhibitory effects of LPS-injection on P450scc and P450c17 e xpression became significant at 6 h after injection compared to contro l groups, whereas the inhibition of 3 beta-hydroxysteroid dehydrogenas e/Delta(5)-> Delta(4)-isomerase (SP-HSD) was significant within 4 h fo llowing injection. The steroidogenic enzyme affected earliest by LPS-i njection was 3 beta-HSD, but the later effect on P450c17 was the most pronounced. P450c17 was inhibited almost 100% at 24 h after LPS-inject ion. LPS induced a rapid increase in IL-1 beta mRNA in testicular inte rstitial macrophages. IL-1 beta mRNA was significantly increased by 89 .8 +/- 29.8-fold over the control within 2 h after the injection. IL-1 beta mRNA levels declined at 6-8 h, then increased again at 24 h. In addition, LPS also induced detectable TNF alpha mRNA expression in tes ticular interstitial macrophages as soon as 2 h after injection, which peaked at 6-8 h, then declined by 24 h after LPS-injection. Moreover, plasma TNF alpha was rapidly and significantly increased at 2 h (76.9 +/- 0.2 U/ml, vs control), then declined quickly P<0.05 injection. Th e current study demonstrates injection increases plasma TNF alpha leve ls and stimulates testicular interstitial macrophages to express both TNF alpha and IL-1 beta mRNA. This immune activation apparently causes the inhibition of steroidogenic enzyme mRNA expression in Leydig cell s. These results demonstrate that immune-endocrine interactions contri bute to the regulation of Leydig cell steroidogenesis in vivo. This re gulation may be mediated by both paracrine and endocrine mechanisms vi a macrophage- and monocyte-secreted TNF alpha and IL-1 beta.