On the regulatory importance of 27-hydroxycholesterol in mouse liver.

27-Hydroxycholesterol (27OH) is a strong suppressor of cholesterol synthesis and a weak activator of LXR in vitro. The regulatory importance of 27OH in vivo is controversial. Here we utilized male mice with increased levels of 27OH either due to increased production (CYP27A1 transgenic mice) or reduced metabolism (Cyp7b1-/- mice). We also used mice lacking 27OH due to a knockout of Cyp27a1. The latter mice were treated with cholic acid to compensate for reduced bile acid synthesis. The effects of the different levels of 27OH on Srebp- and other LXR-regulated genes in the liver were investigated. In the liver of CYP27tg mice we found a modest increase of the mRNA levels corresponding to the LXR target genes Cyp7b1 and Abca1. A number of other LXR-regulated genes were not affected. The effect on Abca1 mRNA was not seen in the liver of Cyp7b1-/- mice. There were little or no effects on cholesterol synthesis. In the liver of the Cyp27-/- mice treated with 0.025% cholic acid there was no significant effect of the knockout on the LXR target genes. In a previous work triple-knockout mice deficient in the biosynthesis of 24S-hydroxycholesterol, 25-hydroxycholesterol and 27OH were shown to have impaired response to dietary cholesterol, suggesting side-chain oxidized oxysterols to be mediators in cholesterol-induced effects on LXR target genes at a transcriptional level (Chen W. et al., Cell Metab. 5 (2007) 73-79). The hydroxylated oxysterol responsible for the effect was not defined. We show here that treatment of wildtype mice with dietary cholesterol under the same conditions as in the above study induced the LXR target genes Lpl, Abcg8 and Srebp1c in wild type mice but failed to activate the same genes in mice lacking 27-hydroxycholesterol due to a knockout of Cyp27. We failed to demonstrate the above effects at the protein level (Abcg8) or at the activity level (Lpl). The results suggest that 27OH is not an important regulator of Srebp- or LXR regulated genes under basal conditions in mouse liver. On the other hand 27OH appears to mediate cholesterol-induced effects on some LXR target genes at a transcriptional level under some in vivo conditions.

Estrogen receptor subtypes and afferent signaling in the bladder.

PURPOSE: The influence of estrogen on bladder function has been the subject of several experimental and clinical studies. In addition to the well-known estrogen receptor (ER)alpha, recently the ER subtype ERbeta was discovered. We investigated potential changes in bladder function in mice lacking either 1 or both receptor subtypes compared with WT mice. MATERIALS AND METHODS: Female mice lacking genes for ERalpha (ERKO), ERbeta (BERKO) or both and their WT littermates were used for the study. Continuous cystometry in awake animals was performed before and after intravesical administration of capsaicin. In addition, in vitro responses to electrical field stimulation before and after incubation with scopolamine and alpha,beta-methylene adenosine triphosphate, and to carbachol were investigated. RESULTS: Control cystometry revealed no significant difference in urodynamic parameters among all strains. After capsaicin instillation the micturition interval and volume decreased, and micturition pressure increased in WT, ERbeta and 2 gene mice, while no changes were seen in ERKO mice. In vitro contractility was similar in all groups. Incubation with scopolamine and alpha,beta-methylene adenosine triphosphate led to significant decreases in the response to electrical field stimulation. There was no difference in the response to carbachol among the groups. CONCLUSIONS: The lack of ERalpha and/or ERbeta had little effect on in vitro contractility or on continuous cystometry in awake animals. The lack of response to capsaicin instillation in ERKO suggests that ER subtypes are important for vanilloid receptor function and mechano-afferent signaling.