Epidermal growth factor enhances expression of connexin 43 protein in cultured porcine preantral follicles

Connexin 43 (Cx43) and gap junctional coupling appear to play a critical role in early follicular development because absence of Cx43 disrupts progression of follicles beyond primary stages in transgenic mouse ovaries. Two experimental culture systems were used to determine whether epidermal growth factor (EGF) stimulates expression of Cx43 in early porcine follicular development. Ovarian explants were collected from 32- to 40-day-old gilts and cultured for 6 days on membrane inserts in Waymouth MB 752/1 medium supplemented with 0, 50, or 500 ng/ml mouse EGF. Western blot analysis demonstrated significant increases (P < 0.05) in relative amounts of Cx43 protein (both phosphorylated and nonphosphorylated) with 50 and 500 ng/ml of EGF as compared with control cultures. Preantral follicles were enzymatically isolated from 70- to 86-day-old gilts and cultured for 8 days in collagen matrices. Medium and EGF treatments were the same as previously described. Western blot analysis demonstrated a significant increase (P < 0.05) in relative amounts of Cx43 protein with 50 and 500 ng/ml of EGF as compared with control cultures. EGF increased expression of Cx43 protein in secondary preantral follicles in a dose-dependent manner, which suggests that EGF or similar growth factor molecules may modulate early folliculogenesis by stimulating expression of Cx43 gap junctions.     

pGhrelin对离体猪脂肪细胞Caspase-3活性及基因表达的影响

研究新近发现的猪Ghrelin (porcine ghrelin,pGhrelin)对猪前体脂肪细胞Caspase-3活性及其基因表达的影响．采用细胞培养技术,以仔猪背部皮下前体脂肪细胞为靶细胞,经0、1、10和100 nmol/L pGhrelin处理细胞48 h后,于倒置生物显微镜下进行脂肪细胞形态学观察．利用MTT法测定pGhrelin对细胞增殖的影响．采用分光光度法检测Caspase-3活性．以实时荧光定量RT-PCR方法测定Caspase-3的基因表达．结果显示,10 nmol/L pGhrelin可以显著降低脂肪细胞Caspase-3的活性与mRNA的表达水平(P < 0.05),100 nmol/L pGhrelin对猪脂肪前体细胞增殖有极显著促进作用(P < 0.01)．上述结果表明,pGhrelin可以下调Caspase-3的活性与基因表达,促进脂肪细胞增殖,抑制脂肪细胞凋亡,其机制可能与Caspase-3依赖性凋亡调节信号通路有关．     

Zearalenone induces apoptosis and necrosis in porcine granulosa cells via a caspase-3- and caspase-9-dependent mitochondrial signaling pathway

Zearalenone is a mycotoxin produced mainly by Fusarium. There are numerous incidences of mycotoxicosis in laboratory and domestic animals, especially in pigs. However, little is known about molecular mechanisms of zearalenone toxicity. Granulosa cells are the maximal cell population in follicles, and they play an essential role in the development and maturation of follicles. The objective of this study was to explore the effect of zearalenone at high concentrations on proliferation and apoptosis of porcine granulosa cells and uncover signaling pathway underlying the cytotoxicity of zearalenone. We found that zearalenone reduced the proliferation of porcine granulosa cells in a dose-dependent manner as shown by the MTT assay and zearalenone resulted in an obvious apoptosis and necrosis in porcine granulosa cells as determined by the TUNEL analysis and flow cytometry. In addition, TUNEL assay with caspase inhibitors showed that zearalenone triggered a caspase-3- and caspase-9-dependent apoptotic process in porcine granulosa cells. Fluorescence spectrophotometer displayed that zearalenone led to a loss of mitochondrial transmembrane potential of porcine granulosa cells but enhanced reactive oxygen species (ROS) levels of the cells. Notably, Western blots revealed that caspase-3 and caspase-9 were activated by zearalenone in porcine granulosa cells. Collectively, our results suggest that zearalenone induces apoptosis and necrosis of porcine granulosa cells in a dose-dependent manner via a caspase-3- and caspase-9-dependent mitochondrial pathway. This study thus offers a novel insight into molecular mechanisms by which zearalenone has adverse cytotoxicity on reproduction.     

Effects of gonadotropins on oocyte maturation and progesterone production by porcine ovarian follicles cultured in vitro

Effects of gonadotropins on the maturation of isolated oocytes and production of progesterone by porcine ovarian follicles from gonadotropin treated gilts have been studied in vitro. The addition of gonadotropins (2 I. U./ml, PMSG, HGC or 2 mg/ml FSH) to the culture medium resulted in increasing the number (84 - 90 %) of isolated oocytes which reached metaphase II. Expansion of the whole cumulus mass was observed only in media containing PMSG, whereas FSH or HCG alone did not cause these marked changes in the cumulus cells. Denudation of the eggs prior to culture gave no significant differences in the maturation rates between oocytes cultured in media with or without gonadotropins. In vitro maturation of follicle-enclosed oocytes took place only in HCG treated animals. Removing the ovary at 15 or 60 minutes after intravenous HCG administration induced oocyte maturation only in 22% and 17% respectively. A sharp increase in the number of oocytes which resume meiosis during follicle culture was observed 4 hours after HCG injection (84 %) and all of the oocytes of the gilts ovariectomized at 8 hours after HCG injection matured during the culture period. The progesterone production of isolated follicles from control gilts (only PMSG injected) increased slowly during a 96-hour culture period (from 48 to 240 ng progesterone/follicle), whereas the secretion of progesterone was drastically increased after a 15 minute interval between HCG injection and ovariectomy (from 42 to 950 ng progesterone/follicle). Follicles removed 24 hours after HCG injection showed a further increase in steroid production (2000 ng progesterone/follicle) and consistently secreted large amounts of progesterone during the culture period.     

The impact of antiandrogen 2-hydroxyflutamide on the expression of steroidogenic enzymes in cultured porcine ovarian follicles

We used our model system for agonism and antagonism of the androgen receptor (AR), in which the porcine ovarian follicles were exposed on the excessive concentration of an AR agonist- testosterone (T) or an AR antagonist- 2-hydroxyflutamide (2-Hf) to: (1) analyze the spatiotemporal expression of ovarian 3β-hydroxysteroid dehydrogenase (3β-HSD), cytochrome P450 17α-hydroxylase/c17,20-lyase (P450c17) and cytochrome P450 aromatase (P450arom); (2) to determine the contribution of AR-mediated action during steroidogenesis and (3) to establish some correlations between the onset and expression pattern of the investigated proteins. Whole follicles (6–8 mm in diameter) isolated from mature porcine ovaries have been incubated (for 24 h) in an organ culture system in the presence of T (10^?7 M), 2-Hf (1.7 × 10^?4 M) or both T and 2-hydroxyflutamide (T+2-Hf, at the same concentrations as when added separately). Thereafter, sections obtained from cultured follicles were processed for main steroidogenic enzymes detection by immunohistochemistry. Moreover, expression of their mRNA and protein was determined by real-time PCR and Western blot analysis. Progesterone, androgens and estradiol concentrations in the culture media were measured by radioimmunoassays (RIA). Our results demonstrated that 2-Hf can influence the steroidogenic activity of porcine follicles in vitro through the blockade of AR. It was shown that follicular 2-Hf treatment brought about dramatic decline in the production of the investigated steroids. What is more the addition of 2-Hf separately caused a negative effect on 3β-HSD and P450c17 mRNA and protein expression by ovarian follicles, while it was without effect on P450arom mRNA level. Quite opposite effect was observed in case of the simultaneous addition of 2-Hf and T. It caused high increase, in both P450arom mRNA and its protein. What was interesting, addition T+2-Hf evoked 3β-HSD and P450c17 increase on mRNA level, but decreased their protein expression. This was against our expectations but the reason for that finding remains undiscovered, intriguing and worth reporting. These results suggest that alike, steroidogenic enzymes activity and their expression is associated with the presence of androgens and AR in the porcine ovary.     

Effects of testosterone and 2-hydroxyflutamide on progesterone receptor expression in porcine ovarian follicles in vitro

The purpose of the study was to test the possible role of the androgen receptor (AR) agonist (testosterone; T), an AR antagonist (2-hydroxyflutamide; 2-Hf) or combination of both (T + 2-Hf) on progesterone receptor (PGR) expression in cultured porcine granulosa cells (GCs) or whole follicles. GCs isolated from mature pig follicles (6–8 mm in diameter) were cultured for 48 h. Experimental cultures were carried out with the addition of T (10^?7 M), 2-Hf (1.7 × 10^?4 M) or both T and 2-Hf for the last 24 h of culture. To better imitate in vivo conditions, isolated whole porcine follicles (6–8 mm in diameter) were cultured for 24 h in an organ culture system, with the addition of the same factors. The cells or sections obtained from cultured follicles were processed for PGR immunocytochemical or immuno-histochemical staining. In addition, expression of PGR protein was determined by Western blot and progesterone (P₄) concentrations in the culture media were measured by a radioimmunoassay. We found that isoform A of PGR is expressed in both granulosal and follicular cultures. The 2-Hf in the presence of T increased PGR protein expression in porcine GCs and whole follicles. In both granulosal and follicular cultures, 2-Hf or T alone inhibited P₄ secretion, but simultaneous addition of 2-Hf and T increased P₄ secretion. Our results indicate that androgens may be involved in the control of PGR expression in porcine GCs in vitro. Moreover, we suggest a potential auto/paracrine regulation of the follicular function by androgen-dependent signaling pathway.     

Hamster Bcl-2 protein is cleaved in vitro and in cells by caspase-9 and caspase-3

Full-length cDNA of hamster bcl-2 (771 nt) was cloned by RT-PCR and inserted into pGEX-4T-1 to produce the recombinant hamster Bcl-2 protein. The purified recombinant Bcl-2 protein (26.4 kDa) was used as a substrate for the active human caspase-3 and caspase-9 in vitro. It is shown here that Bcl-2 is efficiently cleaved by caspase-3 to a 23 kDa fragment. Although not possessing a putative caspase-9 cleavage site in its sequence, hamster Bcl-2 was also cleaved by caspase-9 into exactly the same 23 kDa cleavage product, indicating that cleavage occurred at the same site. Caspase-3- and caspase-9-mediated cleavage of Bcl-2 was efficiently blocked by caspase-3 (zDEVD) and caspase-9 (zLEHD) inhibitor, respectively. We also show that caspase-9/-3-mediated cleavage of Bcl-2 occurs in vivo during apoptosis in CHO-HSV-TK cells after exposure to the antiviral drug ganciclovir.     

Localization of bradykinin B(2) receptor in the follicles of porcine ovary and increased expression of matrix metalloproteinase-3 and -20 in cultured granulosa cells by bradykinin treatment.

We have recently shown that not only bradykinin, but also all components for the production of bradykinin, can be detected within the follicle of porcine ovaries. To elucidate the relevance of the intrafollicular bradykinin-producing system to its physiological role, we investigated the distribution of bradykinin receptor (B(2)R) mRNA and the protein in porcine ovaries. A cDNA encoding porcine B(2)R was first cloned from a porcine uterus cDNA library. The receptor mRNA was scarcely detected in the ovary by Northern blot analysis. Polymerase chain reaction analysis with total RNAs isolated from the ovary and from granulosa cells of small and large follicles demonstrated the ovarian expression of B(2)R mRNA. The B(2)R protein was detected by Western blot analysis in extracts of isolated granulosa cells. In situ hybridization of B(2)R mRNA and immunohistochemical analysis of the protein revealed that the receptor is expressed in the theca and granulosa cells of all growing follicles. The effect of bradykinin on the expression of some matrix metalloproteinase (MMP) genes was examined using isolated granulosa cells. Bradykinin treatment induced MMP-3 and MMP-20 gene expression to an extreme degree. The expression of MT1-MMP was also affected by bradykinin treatment. These results suggest that MMPs play a role in follicle rupture during ovulation. The present study provides new information regarding the mechanisms of bradykinin-induced ovulation in porcine ovaries.     

Intracellular calcium release is required for caspase-3 and -9 activation

Increase in intracellular Ca2+ [Ca2+]i regulates many biological functions including apoptosis, but the protein(s) linking [Ca2+]i and apoptosis are not completely understood. We have previously shown that IP3R-deficient cells are resistant to T-cell receptor (TCR)-induced apoptosis due to lack of Ca2+ release from endoplasmic reticulum (ER) and calcineurin activation. Here we show that caspase-9 and -3 are not activated in IP3R-deficient cells after TCR stimulation, consistent with the resistance of these cells to apoptosis. However, we also demonstrate that Bcl-2 expression in IP3R-deficient cells is comparable to control cells. Taken together, these results strongly suggest that IP3R-mediated Ca2+ release plays a critical role in regulating the activity of caspases-3 and -9 independent of Bcl-2.     

Mitomycin C induces apoptosis and caspase-8 and -9 processing through a caspase-3 and Fas-independent pathway

Caspase-3 activity has been described to be essential for drug-induced apoptosis. Recent results suggest that in addition to its downstream executor function, caspase-3 is also involved in the processing of upstream caspase-8 and -9. To test the absolute requirement for caspase-3, we examined mitomycin C (MMC)-induced apoptosis in the caspase-3 deficient human breast cancer cell line MCF-7. MMC was used as anticancer drug since this agent was preferentially active compared to chemotherapeutic compounds with differing mechanisms of action such as cisplatin, docetaxel, or lovastatin. MMC treatment led to pronounced caspase-8, -9, and -7 processing and early morphological features of apoptosis within 48 h. This could be inhibited by the broad-spectrum caspase inhibitor z-VAD.fmk and to a lesser extent by z-IETD.fmk and z-LEHD.fmk, which have a certain preference for inhibiting caspase-8 and -9, respectively. MMC induced apoptosis in MCF-7 cells was not mediated by the death receptor pathway as demonstrated by experiments using the inhibiting anti-Fas antibody ZB4 and transfections with CrmA, a viral serpin inhibitor of caspase-8, and the dominant negative Fas-associated death domain (FADD-DN). Stable expression with Bcl-2 significantly prevented the processing of caspase-9 but also of caspase-8 and blocked the induction of apoptosis. Thus, we provide evidence that caspase-3 activity is dispensable for MMC-induced apoptosis and for caspase-8 and -9 processing in MCF-7 cells.     

Release of an endothelial cell growth factor from cultured porcine thyroid follicles

It has been proposed from in vivo studies that thyroid angiogenesis during thyroid enlargement may be due to paracrine mitogenic factors released by epithelial thyroid cells. To study this paracrine growth regulating communication between thyroid cells and endothelial cells in vitro, culture medium from isolated porcine thyroid follicles was investigated for a growth promoting effect on porcine aortal endothelial cells. Serum-free conditioned medium (CM) from thyroid follicles in suspension culture contains a dose-related mitogenic activity which stimulates endothelial cell growth up to 197%. Stimulation of the thyroid follicles with TSH (1 mU/ml) significantly reduced the mitogenic activity for endothelial cells in CM to 131%. Thyroid hormones had no influence on mitogenic activity in CM. When follicles were treated with iodide (20 microM) during CM production, no proliferation of endothelial cells was observed by this CM. In contrast, CM from epidermal growth factor-treated thyroid follicles significantly enhanced the mitogenic activity for endothelial cells up to 235%. The mitogenic activity was precipitable by saturated ammonium sulfate, showed high affinity to heparin by chromatography on heparin-sepharose, and was abolished after treatment of CM with trypsin. On gel electrophoresis the heparin-binding fraction showed a double band with a mol wt of 15 and 15.5 k. These data show a paracrine mitogenic activity on endothelial cells released by thyroid follicles which is regulated by TSH, epidermal growth factor, and iodide in parallel with the direct effect of these substances on thyroid cell growth. The data suggest that the mitogenic factor is a polypeptide, which belongs to the heparin-binding growth factors.     

Regulatory role of Sirt1 on the gene expression of fatty acid‐binding protein 3 in cultured porcine adipocytes

To investigate whether Sirt1 could modulate fatty acid‐binding protein 3 (FABP3), we treated porcine adipocytes either with the Sirt1 inhibitor nicotinamide (NAM), with the Sirt1 activator resveratrol (RES), or by knockdown of Sirt1 by Sirt1‐siRNA. NAM or knockdown with Sirt1‐siRNA significantly inhibited Sirt1 mRNA expression, while increasing FABP3 mRNA levels. RES or RES + Sirt1‐siRNA treatments further proved that Sirt1 negatively regulated FABP3 gene expression in adipocytes. We also found a similar Sirt1 regulation pattern for PPARγ to that of FABP3 in adipocytes. Furthermore, NAM/RES + PPARγ‐siRNA treatments showed that Sirt1 may regulate the FABP3 gene expression partly through the PPARγ‐mediated signals. In summary, Sirt1 regulates the expression of FABP3 gene in adipocytes, and PPARγ apparently plays an important role in this process. J. Cell. Biochem. 107: 984–991, 2009. © 2009 Wiley‐Liss, Inc.     

Effects of inorganic iodide, epidermal growth factor and phorbol ester on hormone synthesis by porcine thyroid follicles cultured in suspension.

Porcine thyroid follicles cultured in suspension for 96 h synthesized and secreted thyroid hormones in the presence of thyrotropin (TSH). The secretion of newly synthesized hormones was assessed by determining the contents of thyroxine (T4) and triiodothyronine (T3) in the media and by paperchromatographic analysis of 125I-labelled hormones in the media where the follicles were cultured in the presence and absence of inhibitors of hormone synthesis. The hormone synthesis and secretion was modified by exogenously added NaI (0.1-100 microM). The maximal response was obtained at 1 microM. Thyroid peroxidase (TPO) activity in the cultured follicles with TSH for 96 h was dose-dependently inhibited by NaI. One hundred microM of NaI completely inhibited TSH-induced TPO activity. Moreover, both epidermal growth factor (EGF: 10(-9) and 10(-8) M) and phorbol 12-myristate 13-acetate (PMA: 10(-8) and 10(-7) M) inhibited de novo hormone synthesis. An induction of TPO activity by TSH was also inhibited by either agent. These data provide direct evidences that thyroid hormone synthesis is regulated by NaI as well as TSH at least in part via regulation of TPO activity and also that both EGF and PMA are inhibitory on thyroid hormone formation.     

Analysis of caspase-3, caspase-8 and caspase-9 enzymatic activities in mouse oocytes and zygotes

The current consensus in the literature is that ovulated oocytes that are not fertilized die by apoptosis, but the details of the proteins involved in the apoptotic pathways have not been elucidated. In this paper we confirm that caspase-3, the executioner of apoptosis, is expressed in mouse oocytes, and show that two initiators of apoptosis, caspase-8 and caspase-9, are expressed in mouse oocytes. Comparisons were made of caspase-3, -8, and -9 activities in superovulated oocytes that were freshly collected or allowed to age in vivo or in vitro. We found that caspase-3 activity significantly increased in aged oocytes compared with young oocytes (p < 0.001), and that both caspase-8 activity and caspase-9 activity decreased in aged oocytes compared with young oocytes (p < 0.001 for caspase-8 and p < 0.05 for caspase-9 activity). A comparison of superovulated with naturally ovulated oocytes showed the same amount of caspase-8 activity in each, but a significant (p < 0.001) decrease in caspase-9 activity in naturally ovulated compared with superovulated oocytes. There was no difference in caspase-3, -8, or -9 activity in oocytes compared with zygotes. Finally, we showed that culture of oocytes in staurosporine increased the activity of caspase-8 and caspase-9. In conclusion, the finding of both caspase-8 and caspase-9 activity in oocytes shows that unfertilized oocytes have the machinery to undergo apoptosis by using either the extrinsic (caspase-8 dependent) or intrinsic (caspase-9 dependent) pathways.     

Deficiency in caspase-9 or caspase-3 induces compensatory caspase activation

Dysregulation of apoptosis contributes to the pathogenesis of many human diseases. As effectors of the apoptotic machinery, caspases are considered potential therapeutic targets. Using an established in vivo model of Fas-mediated apoptosis, we demonstrate here that elimination of certain caspases was compensated in vivo by the activation of other caspases. Hepatocyte apoptosis and mouse death induced by the Fas agonistic antibody Jo2 required proapoptotic Bcl-2 family member Bid and used a Bid-mediated mitochondrial pathway of caspase activation; deficiency in caspases essential for this pathway, caspase-9 or caspase-3, unexpectedly resulted in rapid activation of alternate caspases after injection of Jo2, and therefore failed to protect mice against Jo2 toxicity. Moreover, both ultraviolet and gamma irradiation, two established inducers of the mitochondrial caspase-activation pathway, also elicited compensatory activation of caspases in cultured caspase-3(-/-) hepatocytes, indicating that the compensatory caspase activation was mediated through the mitochondria. Our findings provide direct experimental evidence for compensatory pathways of caspase activation. This issue should therefore be considered in developing caspase inhibitors for therapeutic applications.     

Protein phosphatase inhibitor cantharidin inhibits steroidogenesis and steroidogenic acute regulatory protein expression in cultured rat preovulatory follicles.

The effect of cantharidin, a natural toxicant of blister beetles and a strong inhibitor of protein phosphatases types 1 and 2A, on luteinizing hormone (LH)-induced synthesis of steroidogenic acute regulatory (StAR) protein was studied in a serum-free culture of preovulatory follicles. StAR protein is a steroidogenic tissue-specific, hormone-induced, rapidly synthesized protein previously shown to be involved in the acute regulation of steroidogenesis, probably by promoting the transfer of cholesterol to the inner mitochondrial membrane and the cytochrome P450 side-chain cleavage (P450scc) enzyme. Treatment of preovulatory follicles dissected from ovaries of immature rats primed with pregnant mares' serum gonadotropin (10 IU) with LH for 24 h resulted in a dose-dependent increase in the level of StAR protein that reached a maximum at 100 ng LH/ml. This increase was associated with an increase in progesterone production. Treatment of follicles with increasing concentrations (10 - 1000 ng/ml) of cantharidin suppresssed LH (100 ng/ml)-induced StAR protein levels and progesterone production in a dose-dependent manner. The amount of P450scc protein and the conversion of 22R-hydroxycholesterol to progesterone were not affected by cantharidin. This indicates that cantharidin did not interfere with the activity of P450scc. Cantharidin also decreased StAR protein levels and progesterone production induced by the adenylate cyclase activator forskolin (10(-5) M) or a cAMP analog 8-Br-cAMP (0.5 mM). These results demonstrate that cantharidin inhibits the LH-induced StAR protein levels, and, thus, suggest that phosphoprotein phosphatase activity is required for the cAMP-protein kinase A-stimulated steroidogenic activity of the preovulatory follicle.     

PKC and MEK pathways inhibit caspase-9/-3-mediated cytotoxicity in differentiated cells

Many studies have indicated that differentiated cells inhibit drug-induced cytotoxicity but undifferentiated cells do not, though the mechanisms are unclear. Currently, HL-60 cells are induced to differentiate into macrophage-like cells with Phorbol-12-myristate-13-acetate (TPA) treatment (TPA-differentiated cells). Our study shows that caspase-9/-3-mediated cytotoxicity can be induced in undifferentiated HL-60 cells but not in TPA-differentiated HL-60 cells. However, caspase-9/-3-mediated cytotoxicity can be induced in TPA-differentiated cells if they are pretreated with a protein kinase C (PKC) or a mitogen activated protein kinase (MEK) inhibitor. Taken together, this study demonstrates that TPA-differentiated HL-60 cells inhibit caspases-9/-3-mediated cytotoxicity through the PKC and MEK signaling pathways.