Thyroid dysfunction is classified into hyperthyroidism and congenital hypothyroidism (CH). Both hyperthyroidism and CH can cause heart lesions; however, the mechanisms involved remain unclear. The left ventricle was collected from eu-, hyper-, and hypothyroid rat. RNA was extracted and reverse-transcripted to cDNA. Real-time fluorescence quantitation-PCR was used to quantify the differential expression of thyroid hormone receptor (TR) subtype mRNA among eu-, hyper-, and hypothyroid rat myocardium. Here, we show that compared with the normal myocardium, TRα1 mRNA expression was upregulated by 51% (P<0.01), TRα2 mRNA expression was downregulated by 58% (P<0.01), and TRβ1 mRNA expression remained unchanged in hyperthyroid rat myocardium (P>0.05). TRα1, TRα2, and TRβ1 were expressed in normal and hypothyroid rat myocardium throughout the developmental process. In hypothyroid rats, myocardial TRα1 mRNA expression was generally downregulated and the expression peak appeared late. Myocardial TRα2 mRNA expression was generally upregulated and the expression peak appeared late. Myocardial TRβ1 mRNA expression was generally downregulated and changed similarly with the control group. In addition, the hypogenetic myocardium can be seen in the hypothyroid rat by pathology study. Taken together, the abnormal expression of TR subtype mRNA may have a close relationship with the pathogenesis of CH and hyperthyroidism heart disease.
C R Liu, L Y Li, F Shi, X Y Zang, Y M Liu, Y Sun and B H Kan
SJ Zhu, Y Li, H Li, YL Wang, ZJ Xiao, P Vihko and YS Piao
The biosynthesis of 17beta-estradiol (E(2)) in human placenta involves the actions of aromatase and 17beta-hydroxysteroid dehydrogenase type 1 (17HSD1). Aromatase, an enzyme complex comprised of P450aromatase (P450arom) and NADH-cytochrome P450 reductase, converts androgens to estrogens, whereas 17HSD1 catalyzes the reduction of estrone to E(2). In the present study, the effects of retinoic acids (RAs) on P450arom and 17HSD1 expression in placental cells were investigated. Treatment with all-trans-RA (at-RA) or 9cis-RA increased E(2) production in JEG-3 choriocarcinoma cells and cytotrophoblast (CTB) cells isolated from normal early placentas. Meanwhile, the activity of aromatase and expression of P450arom mRNA were induced by at-RA in JEG-3 cells. Northern blot analysis showed that the effect on P450arom mRNA expression occurs in a dose- and time-dependent fashion. Similar to at-RA and 9cis-RA, Ro40-6055, the retinoic acid receptor alpha (RARalpha)-selective activator, increased the expression of P450arom and 17HSD1 mRNA in JEG-3 cells. On the other hand, Ro41-5253 (Ro41), the RARalpha-selective antagonist, blocked the stimulatory effect of RAs on P450arom expression. Surprisingly, Ro41 induced the activity and mRNA expression of 17HSD1 in JEG-3 cells, which is in contrast to the expected inhibitory effect and, moreover, remarkably potentiated the induction by at-RA and 9cis-RA. However, reporter gene analysis revealed that the influence of Ro41 on the transcription of the HSD17B1 gene, which encodes 17HSD1, is considerably milder in JEG-3 cells, and it only additively enhanced the effect of at-RA. Finally, it was found that at-RA and 9cis-RA increased the expression of P450arom and 17HSD1 mRNA in CTB cells, but to a lesser extent. The data suggest that RAs may play a role in promoting the biosynthesis of E(2 )in the placenta. In addition, Ro41 has divergent effects on gene expression in JEG-3 cells.
Yuxin Xie, Lianhe Chu, Yun Liu, Kathy W Y Sham, Jianzhen Li and Christopher H K Cheng
Gonadotropin signaling plays a pivotal role in the spermatogenesis of vertebrates, but exactly how gonadotropins regulate the process in non-mammalian species remains elusive. Using a gene knockout approach in zebrafish, we have previously demonstrated the non-canonical action of gonadotropin signaling on spermatogenesis by analyzing four single mutant lines (lhb, lhr, fshb and fshr) and three double mutant lines (lhb;fshb, lhr;fshr and fshb;lhr). In this study, we further investigated the actions of gonadotropins on the testis by establishing three other double-mutant zebrafish lines (lhb;lhr, fshb;fshr and lhb;fshr). All lhb;lhr and fshb;fshr mutant males were fertile. Analysis on the gonadosomatic index and testicular histology in these lhb;lhr and fshb;fshr mutants demonstrated that Lh signaling and Fsh signaling could functionally compensate each other in the testis. Intriguingly, it was found that the lhb;fshr mutant male fish were also morphologically and histologically normal and functionally fertile, a phenomenon which could be explained by the cross-activation of Lhr by Fsh. We have demonstrated this cross-reactivity for the first time in zebrafish. Fsh was shown to activate Lhr using three different assay systems, in which Lh-Fshr activation was also confirmed. Taken together, we conclude that the action of Lh signaling and Fsh signaling is redundant in that either alone can support zebrafish spermatogenesis based on two observations. First, that either Lh signaling or Fsh signaling alone is sufficient to support male fertility. Second, that the two gonadotropin ligands could promiscuously activate both receptors. Apart from revealing the complexity of gonadotropin signaling in controlling male reproduction in zebrafish, this study also shed light toward a better understanding on the evolution of gonadotropin signaling in vertebrates from fish to mammals.
H Y Li, Y X Liu, L Harvey, S Shafaeizadeh, E M van der Beek and W Han
The prevalence of gestational diabetes mellitus (GDM) is estimated at 14% globally, and in some countries, such as Singapore, exceeds 20%. Both women and children exposed to GDM have an increased risk of later metabolic diseases, cardiovascular disease and other health issues. Beyond lifestyle changes and pharmaceutical intervention using existing type 2 diabetes medications for expecting women, there are limited treatment options for women with GDM; targeting better outcomes of potentially affected infants is unexplored. Numerous animal models have been generated for understanding of pathological processes of GDM development and for development of treatment strategies. These models, however, suffer from limited windows of opportunity to examine risk factors and potential intervention options. By combining short-term high-fat diet (HFD) feeding and low-dose streptozotocin (STZ) treatments before pregnancy, we have established a mouse model with marked transient gestation-specific hyperglycemia, which allows testing of nutritional and pharmacological interventions before, during and beyond pregnancy.
Y Yang, J Cao, W Xiong, J Zhang, Q Zhou, H Wei, C Liang, J Deng, T Li, S Yang, L Xu and L Xu
It has been documented that stress or glucocorticoids have conflicting effects on memory under different conditions. However, it is not fully understood why stress can either impair or enhance memory. Here, we have examined the performance of six age groups of Wistar rats in a water maze spatial task to evaluate the effects of stress under different conditions. We found that the impairment or enhancement effect of an 'elevated platform' (EP) stress on memory was dependent on previous stress experience and on age. EP stress impaired memory retrieval in water maze naive animals, but enhanced rather than impaired memory retrieval in young water maze stress-experienced animals. Furthermore, exogenously applied corticosterone or foot shock stress before water maze training prevented the impairment of memory retrieval that should be induced by treatment with corticosterone or foot shock before the 'probe trial'. Again, memory retrieval was enhanced in young animals under these conditions, and this enhancement can be prevented by the glucocorticoid receptor antagonist RU 38486. Thus, glucocorticoid receptor activation not only induced impairment of memory but also increased the capacity of young animals to overcome a later stress. The present findings suggest that the effect of stress on memory can be switched from impairment to enhancement dependent on both stress experience and age.
Michelle W M Li, Weiliang Xia, Dolores D Mruk, Claire Q F Wang, Helen H N Yan, Michelle K Y Siu, Wing-yee Lui, Will M Lee and C Yan Cheng
The timely restructuring of the blood–testis barrier (BTB) that facilitates the migration of preleptotene and leptotene spermatocytes from the basal to the adluminal compartment in the seminiferous epithelium of adult rat testes, which occurs at late stage VII through early stage VIII of the epithelial cycle, is a crucial cellular event of spermatogenesis. However, the regulation of BTB dynamics at the biochemical level remains elusive. In this study, tumor necrosis factor α (TNFα), a secretory product of Sertoli and germ cells in rat testes, was shown to affect junction dynamics in vivo. Following an acute administration of recombinant TNFα directly to adult rat testes in vivo at 0.5 and 2 μg/testis (with a body weight ~300 g), this treatment significantly and transiently disrupted the BTB. It also transiently inhibited the steady-state protein levels of occludin, zonula occludens-1, and N-cadherin, but not junction adhesion molecule-A, α-, and β-catenin in testes at the BTB site as illustrated by immunoblottings, immunohistochemistry, electron microscopy, and fluorescent microscopy. This transient disruption of the BTB integrity induced by TNFα treatment was further demonstrated by a functional test to assess the passage of a fluorescent dye (e.g. fluorescein-5-isothiocyanate) from the systemic circulation to the adluminal compartment. Additionally, both the phosphorylated-Ser/Thr protein kinase activated by MAP kinase kinase (p-p38) and phosphorylated-externally regulated kinase (p-ERK) mitogen -activated protein kinase-signaling pathways were transiently activated. Collectively, these data coupled with the recently published in vitro studies have illustrated that the BTB is likely utilizing a novel mechanism in which localized production of TNFα by Sertoli and germ cells into the microenvironment at the basal compartment facilitates the timely restructuring (‘opening’?) of the BTB during spermatogenesis to facilitate germ cell migration.