Unique suppression of prostaglandin H synthase-2 expression by inhibition of histone deacetylation, specifically in human amnion but not adjacent choriodecidua

Abstract

The key molecular regulatory mechanisms that govern and coordinate the molecular alterations that underpin the process of human labor remain incompletely understood although enhanced intrauterine prostaglandin production is known to be requisite. Studies from cancer tissues have indicated that at least one key enzyme of prostaglandin biosynthesis can have its activity severely reduced by increased histone deacetylation and enhanced DNA methylation status. We have advanced the hypothesis that similar regulation may occur in intrauterine tissues during pregnancy to prevent inadvertent activation of this powerful initiating signal by dampening responses to premature activation by agents such as cytokines. Our studies have shown that responsiveness of amnion, a key intrauterine tissue, to interleukin-1beta is abrogated by inhibition of histone deacetylation, whereas PGDH amounts were increased basally. The findings do integrate well with others concerning progesterone (inhibitory) actions such that a decrease in the level of histone acetylation in human gestational tissues near term might herald a coordinated series of events that all result in a positive drive for parturition. Hence, a new level of regulatory action and potential therapeutic targets for pathologies such as preterm labor can flow from these findings.

Figure 1.

The effects of altering DNA methylation and histone acetylation status on PGE₂ production by human amnion explants. Alterations in DNA methylation and histone deacetylation resulted in a reduction of IL-1β-induced PGE production by human amnion explants. Basal PGE₂ production was not altered by either treatment (□). In all treatments, there was a statistically significant increase in PGE₂ production upon treatment with IL-1β (13-fold in controls, ▪). IL-1β treatment resulted in fivefold stimulation with ADC treatment, which is a statistically significant reduction from non-ADCtreated control. PGE₂ production increased only 0.8-fold when explants were stimulated with IL-1β after ADC and TSA treatment, which is almost a complete abrogation of the response and again statistically significantly reduced when compared with the 5 μM ADC treatment or control. Data are presented as the production of PGE₂ (pg/mg wet weight/24 h); ^*p < 0.05, n = 5.

Figure 2.

The effects of altering DNA methylation and histone acetylation status on PGHS-1 and PGHS-2 expression by human amnion explants. Altering the DNA methylation or histone deacetylation status in human amnion explants effects the expression of PGHS-1 and PGHS-2. Basal expression (□) of PGHS-1 was significantly reduced when the DNA methylation status was altered. This was also observed when the explants were stimulated with IL-1β (▪). Explants were cultured for 24 h after the addition of IL-1β. Alterations of the histone deacetylation status did not effect basal expression of PGHS-1; however, there was a significant reduction when the human amnion explants were stimulated with IL-1β. There was no observed effect on PGHS-2 expression upon altering the DNA methylation and histone deacetylation status of human amnion explants. Stimulation with IL-1β resulted in a significant increase in PGHS-2 expression. Alteration of DNA methylation had no effect on IL-1β-induced PGHS-2 expression; however, altering the histone deacetylation resulted in a significant reduction of PGHS-2 expression. Data are presented as the expression of PGHS-1 or PGHS-2 divided by the expression of β-actin to account for differences in loading. ^*p < 0.05 compared with untreated control ^#p < 0.05 compared with IL-1β-treated control, n = 3.

Figure 3.

The effects of altering DNA methylation and histone acetylation status on cPLA2 and PGDH expression by human amnion explants. Altering the DNA methylation or histone deacetylation status in human amnion explants had no effect on basal (□) or in the presence of IL-1β (▪) cPLA2 expression in amnion explants. Explants were cultured for 24 h after the addition of IL-1β. Neither altering the DNA methylation or histone deacetylation status of human amnion explants effected cPLA2 expression. Stimulation with IL-1β resulted in a statistically significant increase in PGDH expression by human amnion explants. Basally, altering the DNA methylation and histone deacetylation status also resulted in a statistically significant decrease in PGDH expression. Histone deacetylation resulted in a further reduction in PGDH expression when there was a stimulation with IL-1β. ^*p < 0.05 compared with untreated control; ^#p < 0.05 compared with IL-1β-treated control, n = 3.

Figure 4.

The effects of altering DNA methylation and histone acetylation status on PGE₂ production by human choriodecidual explants. Alterations in DNA methylation and histone deacetylation effected basal PGE₂ production by human choriodecidual explants. Basal production of PGE₂ (□) statistically increased when the DNA methylation and histone deacetylation status of human choriodecidual explants were altered. In all treatments, stimulation with LPS (▪) resulted in a significant increase in PGE₂ production; however, altering the DNA methylation or histone deacetylation did not affect the stimulated levels of PGE₂ produced. Data are presented as the production of PGE₂ as a percentage of control values. ^*p < 0.05, n = 3.

Figure 5.

The effects of altering DNA methylation and histone acetylation status on PGHS-1 and PGHS-2 expression by human amnion explants. Alterations of DNA methylation and histone deacetylation had effects on PGHS-1 expression upon stimulation with LPS (▪), but not basally (□). Explants were cultured for 24 h after the addition of LPS. Altering the DNA methylation or histone deacetylation status of human choriodecidual explants had no effect on the basal expression of PGHS-1. LPS stimulation of human choriodecidual explants had no effect on PGHS-1 expression; however, treatment with ADC or ADC+TSA resulted in a significant decrease in PGHS-1 expression. No treatment examined had any significant effects on PGHS-2 expression. ^#p < 0.05 compared with LPS treated control, n = 3.

Figure 6.

The effects of altering DNA methylation and histone acetylation status on cPLA2 and PGDH expression by human choriodecidual explants. Alterations in histone deacetylation status of human choriodecidual explants effects the basal (□) expression of PGDH. cPLA2 expression was also examined, but there were no detectable levels in human choriodecidual explants. PGDH expression was significantly increased when the histone deacetylation status was altered. On stimulation with LPS (▪), there was a statistically significant increase in PGDH expression, treatment with ADC or ADC+TSA had no effect on the LPS-induced expression levels. Explants were cultured for 24 h after the addition of LPS. ^*p < 0.05 compared with untreated control, n = 3.