Time-keepers (zeitgebers) in peripheral organs are feeding, light, hormones, and their tissue specific downstream signaling cascades. The cAMP signaling by cAMP Responsive Element Modulator CREM and its splice variant Inducible cAMP Early Repressor ICER is linked to SCN and the circadian regulation of the pineal melatonin synthesis but little is known regarding its influence in other organs. With our experiment we tested which core clock genes are controlled in liver and adrenal by CREM / ICER, in the absence of light and with no feeding time cues. In vivo, Crem loss-of-function results in fine-tuning of all measured adrenal clock genes (Per 1,2,3, Cry 1,2, Bmal1, Rev-erbtwo-way ANOVA), while only Per1 and Cry1 were affected in the liver. Icer is circadian in the adrenal with maximum gene expression at ZT 12 and highest protein levels around ZT 20. Icer and Per1 both respond to cAMP stimuli in an immediate early fashion. In immortal cells forskolin up-regulates Per1 after 2 hours and de novo synthesized protein leads to Per1 attenuation. We show that this protein is ICER: Per1 is up-regulated in cells with overexpressed Icer antisense transcript and mobility-shift experiments identify ICER binding to CRE elements of Per1 promoter. We propose that ICER acts as a noise filter for different signals that could affect adrenal transcription. Since ICER is an immediate early repressor, the circadian nature of adrenal Icer could serve as a time dependent gating mechanism.
COBISS.SI-ID: 30528473
Cholesterol is linked to many multifactorial disorders including different forms of liver disease where development and severity depend on the sex. We performed a detailed analysis of cholesterol and bile acid synthesis pathways at the level of genes and metabolites combined with expression studies of hepatic cholesterol uptake and transport in female and male mice fed with high-fat diet with or without cholesterol. Lack of dietary cholesterol led to stronger response of the sterol sensing mechanism in females, resulting in higher expression of cholesterogenic genes compared to males. With cholesterol in the diet, genes were down-regulated in both sexes; however, males maintained a more efficient hepatic metabolic flux through the pathway. Females had higher content of hepatic cholesterol but this was likely not due to diminished excretion but rather due to increased synthesis and absorption. Dietary cholesterol and sex were not important for the gallbladder bile acids composition. Both sexes also did not up-regulate Cyp7a1 upon cholesterol load and there was no compensatory up-regulation of Abcg5 or Abcg8 transporters. On the other hand, females had higher expression of the Ldlr and Cd36 genes. These findings explain sexual dimorphism of cholesterol metabolism in response to dietary cholesterol in a high-fat diet, which contributes importantly to understanding the sex-basis of cholesterol-associated liver diseases.
COBISS.SI-ID: 3268744
We investigated the housekeeping cytochrome P450 CYP51A1 encoding lanosterol 14-demethylase from cholesterol synthesis that was so far not directly linked to human disorders. By direct sequencing of CYP51A1 in 188 women with spontaneous preterm delivery and 188 unrelated preterm infants (gestational age (37 weeks) we identified 22 variants where 10 are novel and rare. In infants there were two novel CYP51A1 variants where damaging effects of p.Tyr145Asp from the substrate recognition region, but not p.Asn193Asp, were predicted by PolyPhen2 and SIFT. This was confirmed by molecular modeling showing that Tyr145Asp substitution results in changed electrostatic potential of the CYP51 protein surface and lengthened distance to the heme which prevents hydrogen bonding. The CYP51 Tyr145Asp mutation is rare and thus very interesting for further structure/function relationship studies. From the 12 identified known variants rs6465348 was chosen for family based association studies due to its high minor allele frequency. Interestingly, this CYP51A1 common variant associates with small for gestational age weight in newborns (p = 0.028) and lower blood total cholesterol and low density lipoprotein cholesterol levels in mothers in 2nd trimester of pregnancy (p = 0.042 and p = 0.046 respectively). Our results indicate a new link between a cholesterol synthesis gene CYP51A1 and pregnancy pathologies.
COBISS.SI-ID: 31046873