Chronic stress and impaired glucocorticoid receptor (GR) feedback are important factors for the compromised hypothalamic–pituitary–adrenal (HPA) axis activity. We investigated the effects of chronic 21 day isolation of Wistar rats on the extrinsic negative feedback part of HPA axis: hippocampus (HIPPO) and prefrontal cortex (PFC). In addition to serum corticosterone (CORT), we followed GR subcellular localization, GR phosphorylation at serine 232 and serine 246, expression of GR regulated genes: GR, CRF and brain-derived neurotropic factor (BDNF), and activity of c-Jun N-terminal kinase (JNK) and Cdk5 kinases that phosphorylate GR. These parameters were also determined in animals subjected to acute 30 min immobilization, which was taken as ‘normal’ adaptive response to stress. In isolated animals, we found decreased CORT, whereas in animals exposed to acute immobilization, CORT was markedly increased. Even though the GR was predominantly localized in the nucleus of HIPPO and PFC in acute, but not in chronic stress, the expression of GR, CRF, and BDNF genes was similarly regulated under both acute and chronic stresses. Thus, the transcriptional activity of GR under chronic isolation did not seem to be exclusively dependent on high serum CORT levels nor on the subcellular location of the GR protein. Rather, it resulted from the increased Cdk5 activation and phosphorylation of the nuclear GR at serine 232 and the decreased JNK activity reflected in decreased phosphorylation of the nuclear GR at serine 246. Our study suggests that this nuclear isoform of hippocampal and cortical GR may be related to hypocorticism i.e. HPA axis hypoactivity under chronic isolation stress.
Miroslav Adzic, Jelena Djordjevic, Ana Djordjevic, Ana Niciforovic, Constantinos Demonacos, Marija Radojcic and Marija Krstic-Demonacos
Ljupka Gligorovska, Biljana Bursać, Sanja Kovačević, Nataša Veličković, Gordana Matić and Ana Djordjevic
The macrophage migration inhibitory factor (MIF) is a proinflammatory cytokine involved in inflammation, regulation of energy metabolism and glucocorticoid action. Chronic low-grade inflammation may be caused by fructose intake, contributing to visceral adipose tissue (VAT) dysfunction. Since MIF is a known antagonist of glucocorticoid signaling, and deregulated glucocorticoid signaling can contribute to lipid metabolism disturbances, we hypothesized that altered MIF signaling might underlie fructose-induced adiposity through glucocorticoid action. We analyzed physiological and biochemical parameters, adipose tissue histology, insulin sensitivity and lipid metabolism in WT and MIF−/− C57Bl/6J mice consuming 20% fructose solution for 9 weeks. Glucocorticoid prereceptor metabolism and glucocorticoid receptor (GR) protein level were examined in VAT, together with the expression of glucocorticoid-target genes involved in lipid metabolism. The expression of adipogenic and lipogenic transcriptional regulators peroxisome proliferator-activated receptor gamma (PPARG) and sterol regulatory element-binding protein 1c (SREBP1c) was also assessed. Results showed disturbed insulin sensitivity in all MIF−/− mice, regardless of the diet. Mice on fructose diet had increased energy intake, but increased visceral adiposity and enlarged adipocytes were observed only in fructose-fed MIF−/− mice. Increased VAT corticosterone level and 11 beta-hydroxysteroid dehydrogenase type 1, hexose-6-phosphate dehydrogenase and GR protein levels were observed in the same animals, together with induced expression of examined lipogenic genes and accumulation of PPARG and SREBP1c. In conclusion, the results showed that dietary fructose was associated with increased visceral adiposity through activation of GR-regulated lipogenic genes, but only in the absence of MIF, which set the state of hyperinsulinemia and insulin resistance.