Toxicogenomic analysis of pharmacological active coumarins isolated from Calophyllum brasiliense

Calophyllum brasiliense (Calophyllaceae) is a tropical rain forest tree, mainly distributed in South and Central America. It is an important source of bioactive natural products like, for instance soulatrolide, and mammea type coumarins. Soulatrolide is a tetracyclic dipyranocoumarins and a potent inhibitor of HIV-1 reverse transcriptase and Mycobacterium tuberculosis. Mammea A/BA and A/BB coumarins, pure or as a mixture, are highly active against several leukemia cell lines, Trypanosoma cruzi and Leishmania amazonensis. In the present work, a toxicogenomic analysis of Soulatrolide and Mammea A/BA + A/BB (3:1) mixture was performed in order to validate the toxicological potential of this type of compounds. Soulatrolide or mixture of mammea A/BA + A/BB (3:1) was administered orally to male mice (CD-1) at dose of 100 mg/kg/daily, for 1 week. After this time, mice were sacrificed, and RNA extracted from the liver of treated animals. Transcriptomic analysis was performed using Affymetrix Mouse Gene 1.0 ST Array. Robust microarray analysis (RMA) and two way ANOVA test revealed for mammea mixture treatment 46 genes upregulated and 72 downregulated genes; meanwhile, for soulatrolide 665 were upregulated and 1077 downregulated genes. Enrichment analysis for such genes revealed that in both type of treatments genetic expression were mainly involved in drug metabolism. Overall results indicate a safety profile. The microarray data complies with MIAME guidelines and are deposited in GEO under accession number GSE72755.

Identification and characterization of two novel (neuro)endocrine long coiled-coil proteins

We have identified a novel vertebrate-specific gene by applying a Differential Display method on two distinct subtypes of pituitary melanotropes showing divergent secretory phenotypes of hypo- and hypersecretion. A paralogue of this gene was also identified. The existence of a long coiled-coil domain and a C-terminal transmembrane domain in the sequences, together with the Golgi distribution of the proteins in transfected cells, suggest that they can be considered as new members of the golgin family of proteins. Both genes were primarily expressed in (neuro)endocrine tissues in vertebrates thus supporting a role for these proteins in the regulated secretory pathway.

Differential expression and processing of chromogranin A and secretogranin II in relation to the secretory status of endocrine cells

Chromogranin A (CgA) and secretogranin II (SgII) are neuroendocrine secretory proteins that participate in regulation of the secretory pathway and also serve as precursors of biologically active peptides. To investigate whether there is a relationship between the expression, distribution, and processing of CgA and SgII and the degree of secretory activity, we employed two melanotrope subpopulations of the pituitary intermediate lobe that exhibit opposite secretory phenotypes. Thus, although one of the melanotrope subtypes shows high secretory activity, the other exhibits characteristics of a hormone storage phenotype. Our data show that SgII expression levels were higher in secretory melanotropes, whereas CgA expression showed similar rates in both cell subsets. The use of various antibodies revealed the presence of the unprocessed proteins as well as three CgA-derived peptides (67, 45, and 30 kDa) and six SgII-derived peptides (81, 66, 55, 37, 32, and 30 kDa) in both subpopulations. However, the smallest molecular forms of both granins predominated in secretory melanotropes, whereas the largest SgII- and CgA-immunoreactive peptides were more abundant in storage melanotropes, which is suggestive of a more extensive processing of granins in the secretory subset. Confocal microscopy studies showed that CgA immunoreactivity was higher in storage cells, but SgII immunoreactivity was higher in secretory melanotropes. Taken together, our results indicate that SgII and CgA are differentially regulated in melanotrope subpopulations. Thus, SgII expression is strongly related to the secretory activity of melanotrope cells, whereas CgA expression may not be related to secretory rate, but, rather, to hormone storage in this endocrine cell type.

Pulsatile exocytosis is functionally associated with GnRH gene expression in immortalized GnRH-expressing cells

Pulsatile release of GnRH is essential for proper reproductive function, but little information is available on the molecular processes underlying this intermittent activity. Recently, GnRH gene expression (GnRH-GE) episodes and exocytotic pulses have been identified separately in individual GnRH-expressing cells, raising the exciting possibility that both activities are linked functionally and are fundamental to the pulsatile process. To explore this, we monitored GnRH-GE (using a GnRH promoter-driven luciferase reporter) and exocytosis (by FM1-43 fluorescence) in the same, living GT1-7 cells. Our results revealed a strong temporal association between exocytotic pulses and GnRH-GE episodes. To determine whether a functional link existed, we blocked one process and evaluated the other. Transcriptional inhibition with actinomycin D had only a modest influence on exocytosis, suggesting that exocytotic pulse activity was not dictated acutely by episodes of gene expression. In contrast, blockage of exocytosis with anti-SNAP-25 (which obstructs secretory granule fusion) abolished GnRH-GE pulse activity, indicating that part of the exocytotic process is responsible for triggering episodes of GnRH-GE. When taken together, our findings suggest that a careful balance is maintained between release and biosynthesis in GT1-7 cells. Such a property may be important in the hypothalamus to ensure that GnRH neurons are in a constant state of readiness to respond to changes in reproductive function.

Melanotrope cell plasticity: a key mechanism for the physiological adaptation to background color changes

The intermediate lobe of the pituitary secretes the melanotropic hormone alpha-MSH, which in amphibians plays a crucial role in skin color adaptation. It has been previously demonstrated that, in the frog Rana ridibunda, the intermediate lobe is composed of two distinct subpopulations of melanotrope cells that can be separated in vitro by using Percoll density gradients. These two melanotrope cell subsets, referred to as high-density (HD) and low-density (LD) cells, differ in their ultrastructural characteristics as well as in their biosynthetic and secretory activity. However, the specific, physiological role of the heterogeneity displayed by melanotrope cells remains elusive. In the present study, we investigated the effects of background color adaptation on melanotrope cell subpopulations. We found that adaptation of frogs to dark or white environment did not modify either the overall number of cells per intermediate lobe or the apoptotic and proliferation rates of melanotrope cells. On the other hand, adaptation of the animals to a white background significantly increased the proportion of hormone-storage HD cells and caused a concomitant decrease in that of LD cells (which exhibit higher levels of alpha-MSH release and POMC messenger RNA than HD cells). Conversely, after black-background adaptation the proportion of LD cells was markedly increased, suggesting that interconversion of HD cells to LD cells occurs during physiological activation of the intermediate lobe. In addition, black-background adaptation also enhanced alpha-MSH release by both cell subpopulations and increased inositol phosphate production in LD cells. These data indicate that, in frog, the proportions of the two melanotrope cell subsets undergo marked modifications during skin color adaptation, likely reflecting the occurrence of a secretory cell cycle whose dynamics are highly correlated to the hormonal demand imposed by the environment.

Synchronized exocytotic bursts from gonadotropin-releasing hormone-expressing cells: dual control by intrinsic cellular pulsatility and gap junctional communication

Periodic secretion of GnRH from the hypothalamus is the driving force for the release of gonadotropic hormones from the pituitary, but the roles of individual neurons in the context of this pulse generator are not known. In this study we used FM1-43 to monitor the membrane turnover associated with exocytosis in single GT1-7 neurons and found an intrinsic secretory pulsatility (frequency, 1.4 +/- 0.1/h; pulse duration, 17.3 +/- 0.6 min) that, during time in culture, became progressively synchronized among neighboring cells. Voltage-gated calcium channels and gap junctional communication each played a major role in synchronized pulsatility. An L-type calcium channel inhibitor, nimodipine, abolished synchronized pulsatility. In addition, functional gap junction communication among adjacent cells was detected, but only under conditions where pulsatile synchronization was also observed, and the gap junction inhibitor octanol abolished both without affecting pulse frequency or duration. Our results, therefore, provide strong evidence that the GnRH pulse generator in GT1-7 cells arises from a single cell oscillator mechanism that is synchronized through network signaling involving voltage-gated calcium channels and gap junctions.