Signaling in cAMP-stimulated ecdysteroidogenesis in prothoracic glands of the silkworm, Bombyx mori

In the present study, we investigated downstream pathways of cyclic adenosine monophosphate (cAMP) signaling (which is related to prothoracicotropic hormone (PTTH)-stimulated ecdysteroidogenesis) in Bombyx mori prothoracic glands (PGs). Results showed that treatment with either dibutyryl cAMP (dbcAMP) or 1-methyl-3-isobutylxanthine (MIX) inhibited phosphorylation of adenosine 5'-monophosphate-activated protein kinase (AMPK) and activated phosphorylation of the translational repressor, 4E-binding protein (4E-BP), a marker of target of rapamycin (TOR) signaling. A chemical activator of AMPK (5-aminoimidazole-4-carboxamide-1-β-d-ribofuranoside, AICAR) increased dbcAMP-inhibited AMPK phosphorylation and blocked dbcAMP-stimulated phosphorylation of 4E-BP, indicating that inhibition of AMPK phosphorylation lies upstream of dbcAMP-stimulated TOR signaling. Treatment of PGs with dbcAMP and MIX also stimulated phosphorylation of a 37-kDa protein, as recognized by a protein kinase C (PKC) substrate antibody, indicating that cAMP activates PKC signaling. Treatment with either LY294002 or AICAR did not affect dbcAMP-stimulated phosphorylation of the PKC-dependent 37-kDa protein, indicating that cAMP-stimulated PKC signaling is not related to phosphoinositide 3-kinase (PI3K) or AMPK. In addition, dbcAMP-stimulated ecdysteroidogenesis in PGs was partially inhibited by pretreatment with either LY294002, AICAR, or calphostin C. From these results, we concluded that AMPK/TOR/4E-BP and PKC pathways are involved in ecdysteroidogenesis of PGs stimulated by cAMP signaling in B. mori.

Dibutyryl-cAMP and roscovitine differently affect premature meiotic resumption and embryo development of vitrified immature porcine oocytes

Vitrification and warming can trigger premature meiosis in immature porcine oocytes. Our aim was to compare the efficacies of two meiotic inhibitors, dibutyryl-cAMP and roscovitine for the meiosis synchronization during in vitro maturation (IVM) of porcine oocytes vitrified at the germinal vesicle (GV) stage. We first compared the efficacy of 1 mM dibutyryl-cAMP and 25 μM roscovitine on meiotic arrest during the first 22 h of IVM. Dibutyryl-cAMP could maintain the GV stage in 83.5% of oocytes; however, roscovitine was even more effective (96.6%), whereas only 17.4% of the oocytes remained at the GV stage without these additives. Temporal meiotic arrest for 22 h by roscovitine did not reduce the percentage of oocytes reaching the Metaphase II stage during subsequent IVM. However, after parthenogenetic stimulation or in vitro fertilization, subsequent embryo development to the blastocyst stage was compromised after roscovitine treatment, whereas dibutyryl-cAMP improved the percentage of blastocyst development. In conclusion, dibutyryl-cAMP could derogate but not completely prevent premature meiosis in vitrified oocytes, whereas roscovitine could more efficiently prevent it. However, for embryo production, the use of roscovitine was disadvantageous, whereas the use of dibutyryl-cAMP was beneficial.

Response of the porcine MYH4-promoter and MYH4-expressing myotubes to known anabolic and catabolic agents in vitro

Myosin heavy chain-IIB (MyHC-IIB; encoded by MYH4 or Myh4) expression is often associated with muscle hypertrophic growth. Unlike other large mammals, domestic pig breeds express MyHC-IIB at both the mRNA and protein level.

Aim

To utilise a fluorescence-based promoter-reporter system to test the influence of anabolic and catabolic agents on increasing porcine MYH4-promoter activity and determine whether cell hypertrophy was subsequently induced.

Methods

C2C12 myoblasts were co-transfected with porcine MYH4-promoter-driven ZsGreen and CMV-driven DsRed expression plasmids. At the onset of differentiation, treatments (dibutyryl cyclic-AMP (dbcAMP), Des(1–3) Insulin-Like Growth Factor-1 (IGF-I), triiodo-l-thyronine (T3) and dexamethasone (Dex)) or appropriate vehicle controls were added and cells maintained for up to four days. At day 4 of differentiation, measurements were collected for total fluorescence and average myotube diameter, as indicators of MYH4-promoter activity and cell hypertrophy respectively.

Results

Porcine MYH4-promoter activity increased during C2C12 myogenic differentiation, with a marked increase between days 3 and 4. MYH4-promoter activity was further increased following four days of dbcAMP treatment and average myotube diameter was significantly increased by dbcAMP. Porcine MYH4-promoter activity also tended to be increased by T3 treatment, but there were no effects of Des(1–3) IGF-I or Dex treatment, whereas average myotube diameter was increased by Des(1–3) IGF-I, but not T3 or Dex.

Conclusion

Porcine MYH4-promoter activity responded to dbcAMP, Des(1–3) IGF-I and T3 treatment in vitro as observed previously in reported in vivo studies. However, we report that increased MYH4-promoter activity was not always associated with muscle cell hypertrophy. The fluorescence-based reporter system offers a useful tool to study muscle cell hypertrophic growth.

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In vitro porcine MYH4-promoter-reporter system to test anabolic & catabolic agents.

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Changes in porcine MYH4-promoter activity & myotube diameter measured in tandem.

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MYH4-promoter activity responded to dbcAMP, Des(1–3) IGF-I and T3 as seen in vivo.

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Increased MYH4-promoter activity was not always associated with cell hypertrophy.

Changes in expression of serine biosynthesis and integrated stress response genes during myogenic differentiation of C2C12 cells

Skeletal muscle is a highly metabolic and dynamic tissue that is formed through the complex and well-organised process of myogenesis. Although there is a good understanding about the role of the Muscle Regulatory Factors during myogenesis, little is known about the potential interplay of other metabolic proteins. The aim of this study was to determine the endogenous mRNA expression profile for a novel group of genes, recently associated with β2-adrenergic agonist (BA) induced muscle hypertrophy in pigs [1], during myogenic differentiation in C2C12 cells and their response to dibutyryl cyclic-AMP (dbcAMP). These genes included mitochondrial phosphoenolpyruvate carboxykinase (PCK2/PEPCK-M), genes involved in serine biosynthesis (Phosphoglycerate dehydrogenase, PHGDH; Phosphoserine aminotransferase-1, PSAT1; Phosphoserine phosphatase, PSPH) and those involved in an integrated stress response (Asparagine synthetase, ASNS; Sestrin-2, SESN2; and Activating transcription factor-5, ATF5). A coordinated peak in endogenous PCK2, PHGDH, PSAT1, PSPH, ASNS, ATF5 and SESN2 mRNA expression was observed at day 2 of differentiation (P < 0.001) in C2C12 cells, which coincided with the peak in myogenin mRNA. Myotube hypertrophy was induced with dbcAMP (1 mM) treatment from day 0, thereby mimicking the in vivo BA response. Although dbcAMP treatment from day 0 induced larger myotubes and increased both myosin heavy chain-IIB (MyHC-IIB) and pyruvate carboxylase (PC) mRNA, the expression of PCK2, PHGDH, PSAT1 and ASNS mRNA were all unaffected. Treatment with dbcAMP from day 4 increased MyHC-IIB mRNA, however this was less dramatic compared to the response observed following treatment from day 0, but there was no effect on PC mRNA. There was also no effect of dbcAMP treatment from day 4 on PCK2, PHGDH, PSAT1 and ASNS mRNA. To conclude, the coordinated day 2 peak in endogenous expression of PCK2, PHGDH, PSAT1, PSPH, ASNS, ATF5 and SESN2 mRNA may relate to a shift in biosynthetic demand required to initiate myogenic differentiation. However, dbcAMP had no effect on the expression of these genes in vitro suggesting that the effects observed in BA-treated pigs might be via other signalling pathways from the activation of the β2-adrenergic receptor, but independent of cAMP, or that there are species differences in the response.

Effects of cyclic AMP on the differentiation and bioenergetics of rat C6 glioma cells

INTRODUCTION

Elevation in the level of intracellular cAMP is known to induce astrocytic differentiation of C6 glioma cells by unknown mechanisms.

METHODS

Therefore, cytoskeletal protein genes (phalloidin) fluorescents to investigate morphological changes, cell proliferation assay, MTT assay, flow cytometry, western blotting, in-cell western, immune-cytochemical (protein expression and localization), and oxygen electrodes (oxygen consumption rate) after a treatment with 0.25 mM dbcAMP were conducted.

RESULTS

Undifferentiated cells (media without dbcAMP) showed a flat polygonal appearance, whereas those cultured in the presence of 0.25 mM dbcAMP exhibited a more differentiated astrocytic morphology. They had more numerous neurite-like thin processes. The cell proliferation of differentiated c6 glioma reduced at day 2 and then started to increase at day 3 till day 5 compared to undifferentiated c6 glioma cells. In terms of flow-cytometry data, dbcAMP had no apoptotic effect on the C6 glioma cells. There was an increase in the protein expression GFAP (specific marker for astrocytes). There was no significant effect between undifferentiated and 5-day differentiation regarding their response to glucose 10 mM. In addition, there were no significant effects of glucose on the basal of 5-day differentiation of C6 glioma cells. However, there was a significant correlation between the concentration of glucose and inhibition of the basal oxygen consumption. Finally, glucose 10 mM did not stimulate NAD (P)H levels of C6 glioma cells.

CONCLUSION

The above results showed that cAMP induce C6 glioma cells differentiation without affecting its bioenergetics. Therefore cAMP is considered to be the best differentiating agent.

Differential regulation of the expression of aquaporins 3 and 9 by Auphen and dbcAMP in the SMMC-7721 hepatocellular carcinoma cell line

Aquaglycero-aquaporins (agAQPs) are the structural foundation of rapid water transport and they appear to participate in cancer proliferation and malignancy. AQP3 expression is increased and AQP9 expression is decreased in hepatocellular carcinoma (HCC) compared to normal liver, which suggests their possible use as targets for cancer treatment. AQP-based modifiers, such as Auphen and dibutyryladenosine 3', 5'-cyclic monophosphate (dbcAMP), might be used to treat several diseases and as chemical tools for assessing the functions of AQPs in biological systems. We investigated the effects of both Auphen on AQP3 and dbcAMP on AQP9 in SMMC-7721 cells. We used western blotting, real-time quantitative polymerase chain reaction (qPCR) and immunohistochemistry to evaluate changes in AQP3 and AQP9 expression in SMMC-7721 cells after culturing with Auphen and dbcAMP, respectively. We also determined the proliferation of SMMC-7721 cells. We found that compared to HL-7702 (L02) liver cells, Auphen increased AQP3 expression in tumor cells, whereas dbcAMP decreased expression of AQP9 in these cells. Also, high concentrations of Auphen and dbcAMP inhibited proliferation of SMMC-7721 cells in vitro. Auphen and dbcAMP may inhibit HCC development and could be considered targets for HCC diagnosis and therapy.

Slow sulfide donor GYY4137 differentiates NG108-15 neuronal cells through different intracellular transporters than dbcAMP

Cellular differentiation is the process, by which a cell changes from one cell type to another, preferentially to the more specialized one. Calcium fluxes play an important role in this action. Differentiated NG108-15 or PC12 cells serve as models for studying neuronal pathways. NG108-15 cell line is a reliable model of cholinergic neuronal cells. These cells differentiate to a neuronal phenotype due to the dibutyryl cAMP (dbcAMP) treatment. We have shown that a slow sulfide donor - GYY4137 - can also act as a differentiating factor in NG108-15 cell line. Calcium is an unavoidable ion required in NG108-15 cell differentiation by both, dbcAMP and GYY4137, since cultivation in EGTA completely prevented differentiation of these cells. In this work we focused primarily on the role of reticular calcium in the process of NG108-15 cell differentiation. We have found that dbcAMP and also GYY4137 decreased reticular calcium concentration by different mechanisms. GYY4137 caused a rapid decrease in type 2 sarco/endoplasmic calcium ATPase (SERCA2) mRNA and protein, which results in lower calcium levels in the endoplasmic reticulum compared to the control, untreated group. The dbcAMP revealed rapid increase in expression of the type 3 IP3 receptor, which participates in a calcium clearance from the endoplasmic reticulum. These results point to the important role of reticular calcium in a NG108-15 cell differentiation.

Artificial control maturation of porcine oocyte by dibutyryl cyclicAMP

In this study, we investigated the effects of various durations of dibutyryl cyclic AMP (dbcAMP) treatment on the in vitro maturation (IVM) and subsequent development of parthenogenetically activated embryos. Immature porcine oocytes were cultured with or without 1 mM dbcAMP during the first 20, 28, or 36 h of culture, and then incubated for an additional 24 h without dbcAMP. The expression of Wee1B, Myt, and Cdc25B and the level of maturation promoting factor (MPF) in metaphase II oocytes were analyzed by real-time PCR (qRT-PCR) and enzyme linked immunosorbent assay (ELISA), respectively. The distribution of actin microfilaments in oocytes was also assessed. Subsequently, apoptotic cells in blastocysts from each group were visualized by transferase-mediated dUTP nick-end labeling staining. Results showed that oocytes extruded the first polar body between 12 and 18 h after being released from dbcAMP. MPF activity in oocytes at 28 + 24 h and 36 + 24 h after dbcAMP treatment was higher than that in the control group. Significantly more blastocysts were present among embryos in 28 + 24 h (54.28% vs. 39.11%, P < 0.05) and 36 + 24 h (47.24% vs. 32.94%, P < 0.05) groups than among embryos cultured in the absence of dbcAMP. However, the number of total and apoptotic cells was not significantly different between groups. The distribution of actin microfilaments was abnormal in oocytes cultured for 60 h without dbcAMP. In addition, the expression of Wee1B, Myt, and Cdc25B was higher in the control group at 44 h than in the dbcAMP group, but there were no differences in expression at the other time points. In conclusion, dbcAMP treatment delays oocyte maturation and maintains oocyte quality.

Sustained delivery of dbcAMP by poly(propylene carbonate) micron fibers promotes axonal regenerative sprouting and functional recovery after spinal cord hemisection

This study describes the use of poly(propylene carbonate) (PPC) electrospun fibers as vehicle for the sustained delivery of dibutyryl cyclic adenosine monophosphate (dbcAMP) to the hemisected spinal cord. The dbcAMP and PPC were uniformly mixed with acetonitrile; then, electrospinning was used to generate micron fibers. The release of dbcAMP was assessed by ELISA in vitro. Our results showed that the encapsulation of dbcAMP in the fibers led to stable and prolonged release in vitro. The PPC micron fibers containing dbcAMP and the PPC micron fibers without dbcAMP were then implanted into the hemisected thoracic spinal cord, followed by testing of the functional recovery and immunohistochemistry. Compared with the control group, sustained delivery of dbcAMP promoted axonal regenerative sprouting and functional recovery and reduced glial scar formation, and the PPC micron fibers without dbcAMP did not have these effects. Our findings demonstrated the feasibility of using PPC electrospun fibers containing dbcAMP for spinal cord injury. The approach described here also will provide a platform for the potential delivery of other axon-growth-promoting or scar-inhibiting agents.

Acetylcholine esterase is a regulator of GFAP expression and a target of dichlorvos in astrocytic differentiation of rat glioma C6 cells. Brain Res. 2013;1537:37-45. [PMID: 24001591 DOI: 10.1016/j.brainres.2013.08.031]

The main target of neurotoxins is neurons because they comprise the main part of neural function, but glial cells may be indirect targets because they support the function of neurons. Among the glial cells, astrocytes in particular act as "nurse cells", regulating neuronal survival and functions. In the present study, to reveal whether a known neurotoxic substance, organophosphate dichlorvos (DDVP), affects the differentiation of astrocytes, we used an astrocyte differentiation model in rat glioma C6 cells. Morphological change and induction of GFAP expression in the differentiating C6 cells were suppressed by DDVP treatment. The known potential targets of DDVP are acetylcholine esterase (AChE), fatty acid amide hydrolase and methyl guanine methyl transferase. Among the specific inhibitors against these enzymes, the AChE inhibitor paraoxon successfully suppressed the cellular morphological changes and the induction of GFAP expression in differentiating C6 cells. These results indicate that DDVP inhibits differentiation in the C6 astrocyte-differentiation model, in which at least AChE inhibition is involved and that AChE is a potent regulator of the differentiation. Furthermore, considering that the main substrate of AChE is ACh, thus, ACh may act as regulators of astrocyte differentiation.

Oxidative stress and phthalate-induced down-regulation of steroidogenesis in MA-10 Leydig cells

Previous studies have shown that phthalate exposure can suppress steroidogenesis. However, the affected components of the steroidogenic pathway, and the mechanisms involved, remain uncertain. We show that incubating MA-10 Leydig cells with mono-(2-ethylhexyl) phthalate (MEHP) resulted in reductions in luteinizing hormone (LH)-stimulated cAMP and progesterone productions. cAMP did not decrease in response to MEHP when the cells were incubated with cholera toxin or forskolin. Incubation of MEHP-treated cells with dibutyryl-cAMP, 22-hydroxycholesterol or pregnenolone inhibited the reductions in progesterone. Increased levels of reactive oxygen species (ROS) occurred in response to MEHP. In cells in which intracellular glutathione was depleted by buthionine sulfoximine pretreatment, the increases in ROS and decreases in progesterone in response to MEHP treatment were exacerbated. These results indicate that MEHP inhibits MA-10 Leydig cell steroidogenesis by targeting LH-stimulated cAMP production and cholesterol transport, and that a likely mechanism by which MEHP acts is through increased oxidative stress.