Activation of inositol phospholipid breakdown by prostaglandin F2 alpha without any stimulation of proliferation in quiescent NIH-3T3 fibroblasts

Differentially expressed circular RNAs in orbital adipose/connective tissue from patients with thyroid-associated ophthalmopathy

Our study aimed to investigate the differentially expressed circRNAs and their potential roles in orbital adipose/connective tissue from patients with thyroid-associated ophthalmopathy (TAO). The orbital adipose/connective tissue samples from three TAO patients and three control individuals were collected for RNA sequencing after depletion of ribosomal RNA. Differentially expressed mRNAs and up-regulated circRNAs were used for co-expression analysis. Functional and pathway enrichment analysis were conducted for the up- and down-regulated mRNAs in the circRNA-mRNA co-expression network. Meanwhile, circRNA-miRNA interaction network was established by miRanda software. The expression levels of mRNAs and circRNAs in control and TAO samples were determined by qRT-PCR. Among all the 16,329 circRNAs predicted from RNA sequencing data, 163 circRNAs (95 down-regulated and 68 up-regulated) were differentially expressed in TAO samples. Besides, 607 differentially expressed mRNAs were identified. The co-expression analysis showed circRNA_14940 was correlated with CCND1 and TNXB, while circRNA_10135 was correlated with PTGFR, and circRNA_14936 was correlated with TNFRSF19. The up-regulated CCND1 participated in Wnt signaling pathway. The down-regulated TNXB was involved in the ECM-receptor interaction, focal adhesion, and PI3K-Akt signaling pathway. PTGFR participated in neuroactive ligand-receptor interaction and calcium signaling pathway. TNFRSF19 was involved in cytokine-cytokine receptor interaction. In the interaction network, circRNA_14936 could interact with hsa-miR-10392-3p, and circRNA_12367 could interact with hsa-miR-1228-3p. Moreover, the expression changes of MMP2, TNXB, PTGFR, CCND1, and TNFRSF19, as well as circRNA_14936, circRNA_14940, and circRNA_12367 were validated by qRT-PCR. In conclusion, the differentially expressed circRNAs might participate in pathogenesis of TAO, and we speculated that circRNA_14940-CCND1-Wnt signaling pathway might be an important regulatory axis.

Effects of prostaglandin F(2α) on adipocyte biology relevant to graves' orbitopathy

BACKGROUND

In Graves' orbitopathy (GO), increased proliferation, excess adipogenesis, and hyaluronan overproduction produce GO exophthalmos. Enophthalmos occurs in some glaucoma patients treated with Bimatoprost (prostaglandin F2α, PGF2α) eye drops. We hypothesized that enophthalmos is secondary to reductions in orbital tissue proliferation, adipogenesis, and/or increased lipolysis. We aimed to determine which of these is affected by PGF2α by using the 3T3-L1 murine preadipocyte cell line and primary human orbital fibroblasts (OFs) from GO patients (n=5) and non-GO (n=5).

METHODS

3T3-L1 cells and orbital OFs were cultured alone or with PGF2α (all experiments used 10(-8) to 10(-6) M) and counted on days 1/2/3 or 5, respectively; cell cycle analysis (flow cytometry) was applied. Adipogenesis (in the presence/absence of PGF2α) was evaluated (day 7 or 15 for 3T3-L1 and primary cells, respectively) morphologically by Oil Red O staining and quantitative polymerase chain reaction measurement of adipogenesis markers (glycerol-3-phosphate dehydrogenase and lipoprotein lipase, respectively). For lipolysis, in vitro-differentiated 3T3-L1 or mature orbital adipocytes were incubated with norepinephrine and PGF2α and free glycerol was assayed. Appropriate statistical tests were applied.

RESULTS

The population doubling time of 3T3-L1 was 27.3±1.4 hours-significantly increased by dimethyl sulfoxide 0.02% to 44.6±4.8 hours (p=0.007) and further significantly increased (p=0.049 compared with dimethyl sulfoxide) by 10(-8) M PGF2α to 93.6±19.0 hours, indicating reduced proliferation, which was caused by prolongation of G2/M. GO OFs proliferated significantly more rapidly than non-GO (population doubling time 5.36±0.34 or 6.63±0.35 days, respectively, p=0.035), but the proliferation of both was significantly reduced (dose dependent from 10(-8) M) by PGF2α, again with prolongation of G2/M. Adipogenesis in 3T3-L1 cells was minimally affected by PGF2α when assessed morphologically, but the drug significantly reduced transcripts of the glycerol-3-phosphate dehydrogenase differentiation marker. GO OFs displayed significantly higher adipogenic potential than non-GO, but in both populations, adipogenesis, evaluated by all 3 methods, was significantly reduced (dose dependent from 10(-8) M) by PGF2α. There was no effect of PGF2α on basal or norepinephrine-induced lipolysis, in 3T3-L1 or human OFs, either GO or non-GO.

CONCLUSIONS

The results demonstrate that PGF2α significantly reduces proliferation and adipogenesis and that human OFs are more sensitive to its effects than 3T3-L1. Consequently, PGF2α could be effective in the treatment of GO.

A study of histopathological features of latanoprost-treated irides with or without darkening compared with non-latanoprost-treated irides

OBJECTIVES

To study the histopathological features of latanoprost-treated irides with or without darkening, compared with non-latanoprost-treated irides.

METHODS

Iridectomy specimens and patient history forms were independently examined by 3 ophthalmic pathologists in a masked fashion. Specimens were evaluated for premalignant changes and for differences in level of pigmentation and degrees of cellularity, inflammation, and vascular abnormalities.

RESULTS

The specimens consisted of 22 latanoprost-treated darkened irides, 35 latanoprost-treated irides without darkening, and 35 non-latanoprost-treated irides. There was a statistically significant decrease in the number of nuclear invaginations and prominent nucleoli in latanoprost-treated darkened irides compared with the other 2 groups (P = .004 and P = .005, respectively). The average thickness and pigmentation of the anterior border layer was greater in the latanoprost-treated darkened irides than in the other 2 groups (P = .03 and P = .02, respectively). The latanoprost-treated darkened irides had increased pigmentation of the stroma (P < .001), stromal fibroblasts (P < .001), melanocytes (P = .005), vascular endothelium (P = .02), and adventitia (P < .001) relative to the other 2 groups.

CONCLUSIONS

There is no histopathological evidence of premalignant changes in latanoprost-treated darkened irides. The latanoprost-induced iris color changes are due to a thickening of the anterior border layer and an increased amount of melanin in the anterior border layer and within the stromal melanocytes.

Positive and negative regulation of cell proliferation through prostaglandin receptors in NIH-3T3 cells

Among major eicosanoids and their analogs, prostaglandin (PG) F2 alpha > PGD2 > PGE1 > or = PGE2 > iloprost, a stable agonist of PGI2, dose-dependently stimulated DNA synthesis in quiescent NIH-3T3 cells. PGF2 alpha, PGD2, and PGE2, in that order, formed inositol phosphates and elevated intracellular Ca2+ ([Ca2+]i) but did not form cAMP nor inhibit forskolin-induced cAMP formation. Iloprost, PGI2, and PGE1 induced cAMP formation dose dependently with an ED50 of around 10(-7) M, and PGE2 at more than 10(-6) M did it. [3H]PGF2 alpha and [3H]PGD2 bindings membranes from NIH-3T3 cells were displaced in the order of PGF2 alpha > PGD2 > or = PGE2, while [3H]PGE2 binding was displaced by PGE2 > PGD2 > or = PGF2 alpha. Expression of mRNA encoding EP1 and EP4 (EP2) subtypes could be detected by reverse transcription- polymerase chain reaction using primers specific for EP1 and EP4 (EP2) cDNAs, but not that of EP3 subtype mRNA. The dose dependence of cAMP formation on iloprost and PGI2 and that of [Ca2+]i elevation on PGF2 alpha, D2, and E2 were similar to that of [3H]thymidine incorporation on the corresponding agonists. Fluprostenol (1 microM), a PGF2 alpha receptor agonist > 17-phenyl-trinor-PGE2 (1 microM), an EP1 receptor agonist stimulated [3H]thymidine incorporation, but an EP3 receptor agonist, ONO-AP-324 nor an EP4 (EP2) receptor agonist, 11-deoxy-PGE1 (1 microM) did not. Iloprost, dibutyryl cAMP, forskolin, or cholera toxin, when applied alone, enhanced [3H]thymidine incorporation, while they inhibited [3H]thymidine incorporation induced by submaximal concentrations of PGF2 alpha or epidermal growth factor (EGF), when applied within 12 hr after agonist stimulation. These results suggest that the proliferation of NIH-3T3 cells is stimulated by PGs via the PGF2 alpha receptor, EP1 subtype of PGE receptor, and the PGI2/PGE1 receptor through [Ca2+]i- and cAMP-dependent pathways, and that cAMP pathway negatively cross-talks with [Ca2+]i-or receptor tyrosine kinase-mediated DNA synthesis in a cell cycle-dependent manner.

Preadipocyte differentiation blocked by prostaglandin stimulation of prostanoid FP2 receptor in murine 3T3-L1 cells

Treatment of 3T3-L1 preadipocytes with arachidonic acid resulted in a dose-dependent inhibition of adipocyte differentiation. The cells failed to accumulate fat droplets and did not express stearoyl-CoA desaturase 1 mRNA, a marker for late-stage differentiation. The inhibition of differentiation was reversed by the addition of cyclooxygenase inhibitors ibuprofen or indomethacin. Inhibitors of the lipoxygenase and cytochrome P-450 epoxygenase pathways were unable to reverse the effect of arachidonic acid. Dexamethasone, one of the adipogenic agents normally used to induce differentiation, could be replaced with cyclooxygenase inhibitors in the differentiation cocktail. This implicated dexamethasone as a modulator of prostaglandin synthesis in culture. Prostaglandins F2 alpha (ED50 = 0.4 nM), E2, and D2 prevented differentiation, each with a specific, dose-dependent affinity. Prostaglandin F2 alpha was the most potent inhibitor of differentiation, suggesting that a prostanoid FP2 receptor (FP receptor) mediates the prostaglandin action. Fluprostenol (ED50 = 0.3 nM), a selective FP receptor agonist, prevented differentiation, confirming the involvement of an FP receptor in the inhibition of 3T3-L1 preadipocyte differentiation. Stimulation of the FP receptor for 1 h during the first day of differentiation was sufficient to cause substantial inhibition. Endogenous PGF2 alpha production was lower in differentiating cells compared to unstimulated preadipocytes. These data suggest that PGF2 alpha production by preadipocytes plays a role in maintaining the undifferentiated state.

Role of Ca2+ in the early stages of murine adipocyte differentiation as evidenced by calcium mobilizing agents

We have investigated the effect of the endoplasmic reticulum Ca(2+)-ATPase inhibitor thapsigargin and the calcium ionophore A23187 on the differentiation of 3T3-L1 preadipocytes. Treatment of 3T3-L1 preadipocytes with either agent resulted in a dose-dependent inhibition of adipocyte differentiation. The cells accumulated neither fat droplets nor the adipocyte-specific mRNAs encoding stearoyl-CoA desaturase 1 (SCD1) and adipocyte-P2 (aP2). These late markers of differentiation were specifically affected, because thapsigargin and A23187 did not inhibit the expression of beta-tubulin mRNA. No inhibition of differentiation or the expression of the mRNAs occurred when the drugs were added either prior to or 2 days after the initiation of differentiation. Thapsigargin and A23187 were also shown to dramatically block cell proliferation and DNA replication, which occur early in differentiation. Furthermore, during the first 48 h, thapsigargin and A23187 mediated an elevated and prolonged expression of the immediate-early gene corresponding to c-myc, and altered intracellular levels of calcium. Our results suggests that changes in intracellular calcium levels elicited by thapsigargin and A23187 prevent differentiation of 3T3-L1 preadipocytes into adipocytes by blocking the postconfluent mitotic phase of the differentiation process and also by mediating c-myc gene expression.

Characterization of prostaglandin F2 alpha receptor of mouse 3T3 fibroblasts and its functional expression in Xenopus laevis oocytes

Prostaglandin (PG) F2 alpha increased [3H]thymidine incorporation into quiescent NIH 3T3 cells, stimulated phosphoinositide breakdown, and raised intracellular Ca2+ concentration ([Ca2+]i) in a dose-dependent manner with ED50 values of 2.0 x 10(-8) M, 4.6 x 10(-8) M, and 7.5 x 10(-8) M, respectively. The increase in [3H]thymidine incorporation with PGF2 alpha was additive with that seen with epidermal growth factor (EGF) or insulin. The peak [Ca2+]i increase with PGF2 alpha was still obvious in the absence of extracellular Ca2+ and was insensitive to islet activating protein (IAP) pretreatment. Membranes prepared from NIH 3T3 cells exhibited a specific binding for PGF2 alpha, which was sensitive to GTP gamma S but not sensitive to IAP pretreatment. Xenopus laevis oocytes injected with NIH 3T3 cell mRNA between 18S and 28S rRNA fractionated by sucrose gradient, expressed a PGF2 alpha-specific Cl- current when examined by voltage clamp. This Cl- current was also insensitive to IAP pretreatment and not affected by extracellular Ca2+ concentration ([Ca2+]o). These results indicate 1) that the NIH 3T3 cells expressed a specific PGF2 alpha receptor which is linked to phosphoinositide-specific phospholipase C (PLC) activation and to mobilization of Ca2+ via an IAP-insensitive G-protein(s), 2) that this PGF2 alpha receptor may play an active role in the proliferation of NIH 3T3 cells, and 3) that this PGF2 alpha receptor can be expressed in the oocyte system.

Platelet derived growth factor induces c-fos and c-myc mRNA in rat aortic smooth muscle cells in primary culture without elevation of intracellular Ca2+ concentration

Platelet derived growth factor (PDGF) has been shown to induce c-fos and c-myc proto-oncogenes. In the present study, we investigated the effects of genistein, a tyrosine kinase inhibitor, and NiCl2, a Ca2+ influx blocker, on PDGF-induced Ca2+ transient and on expression of c-fos and c-myc mRNA. In the presence of extracellular Ca2+, PDGF induced elevation of intracellular Ca2+ concentration ([Ca2+]i) and increases in c-fos and c-myc mRNA, as detected by reverse transcription polymerase chain reaction (RT-PCR) and Northern hybridization. PDGF-induced [Ca2+]i elevation was composed of an initial transient increase (first component) followed by steady state elevation (second component). Genistein (10 microM) blocked the 1st, but not the 2nd, component of [Ca2+]i elevation induced by PDGF. NiCl2 (1 mM) and removal of extracellular Ca2+ inhibited the 2nd, but not the 1st, component. In the presence of 10 microM genistein and 1 mM NiCl2, PDGF induced c-fos and c-myc mRNA, although the [Ca2+]i elevation could be completely blocked by these two agents. These results indicate that elevation of [Ca2+]i is not a prerequisite condition for PDGF to induce c-fos and/or c-myc mRNA in rat aortic smooth muscle cells in primary culture.

Lack of correlation between the activation of the Ca(2+)-phosphatidylinositol cascade and the regulation of DNA synthesis in the dog thymocyte

Changes in the [Ca2+]i and/or activation of phospholipase C are thought to participate in the control by several growth factors of the mammalian cell proliferation. It has even been claimed that activation of the Ca(2+)-phosphatidylinositol cascade is sufficient to elicit cell proliferation [Jackson et al. (1988) Nature 335, 437-440; Julius et al. (1989) Science 244, 1057-1062]. In this work, we have evaluated the control of DNA synthesis by this cascade in a differentiated epithelial cell model: the dog thyrocyte in primary culture. We first observed that potent activators of the dog thyrocyte (2+)-phosphatidylinositol cascade such as carbachol or bradykinin failed to promote the onset of DNA synthesis in these cells. Moreover, carbachol inhibited the mitogenic effect of thyroid stimulating hormone (TSH) and of epidermal growth factor (EGF). The mitogenic effect of EGF was also reduced by bradykinin. Nevertheless, carbachol enhanced the expression of the protooncogenes c-fos and c-myc mRNAs. The time course of this enhancement was identical to the time course for the induction of c-fos and c-myc mRNAs by phorbol esters or EGF. On the other hand, in most experiments, TSH and EGF were able to trigger the onset of dog thyrocyte DNA synthesis without affecting their intracellular free Ca2+ concentration [Ca2+]i, 45Ca2+ efflux, or inositol phosphate generation. In several experiments, TSH increased the dog thyrocyte 45Ca2+ release and promoted a rise in the [Ca2+]i or the inositol phosphate accumulation but these effects were weak. In contrast to the effect of carbachol, the TSH effects on the [Ca2+]i and the 45Ca2+ efflux appeared slowly, were sustained, and were extremely sensitive to extracellular Ca2+ depletion. They were observed at hormone concentrations higher than the concentration achieving maximal stimulation of DNA synthesis. Similarly, in a few experiments, a slight increase in the [Ca2+]i or in the inositol trisphosphate generation were provoked by EGF. However, these modifications were not associated with an increased mitogenic potency of EGF. Finally, in all experiments, fetal calf serum slightly accelerated the dog thyrocyte 45Ca2+ efflux and increased their inositol phosphate generation.(ABSTRACT TRUNCATED AT 400 WORDS)

Multiple sources of sn-1,2-diacylglycerol in platelet-derived-growth-factor-stimulated Swiss 3T3 fibroblasts. Evidence for activation of phosphoinositidase C and phosphatidylcholine-specific phospholipase D

Platelet-derived growth factor (PDGF) stimulated sn-1,2-diacylglycerol (DAG) mass formation in Swiss 3T3 fibroblasts with a lag time of some 30 s. The response was biphasic, with the second phase being sustained over time. PDGF also stimulated the formation of Ins(1,4,5)P3 with a similar lag time to the DAG response, suggesting that DAG is derived from PtdIns(4,5)P2 hydrolysis at this time point. PDGF-stimulated phosphatidylcholine (PtdCho) hydrolysis in Swiss 3T3 fibroblasts, as measured by the formation of water-soluble choline metabolites and phosphatidylbutanol (PtdBut) accumulation, was by a phospholipase D (PLD)-catalysed pathway which was kinetically downstream of initial PtdIns(4,5)P2 hydrolysis. Accumulation of PtdBut increased up to 15 min, suggesting that PLD activity is not rapidly densitized in response to PDGF. The kinetics of PtdCho hydrolysis closely paralleled the second phase of DAG formation, strongly suggesting that during prolonged stimulation periods PtdCho is a major source of DAG in these cells. However, since PtdIns(4,5)P2 breakdown was also prolonged, PDGF-stimulated DAG may be derived from both phospholipids. Down-regulation of protein kinase C (PKC), by pre-treatment with phorbol 12-myristate 13-acetate, abolished both [3H]choline and [3H]PtdBut formation, suggesting that PLD-catalysed PtdCho hydrolysis may be dependent on PKC activation, supporting its dependence on prior PtdIns(4,5)P2 hydrolysis.

Hydrolysis of phosphatidylcholine by phospholipase D is a common response to mitogens which stimulate inositol lipid hydrolysis in Swiss 3T3 fibroblasts

The stimulated hydrolysis of inositol lipids and phosphatidylcholine (PtdCho) by bombesin, [Arg8]vasopressin ([Arg8]Vp) and prostaglandin F2 alpha (PGF2 alpha) was analysed in Swiss 3T3 cells pre-labelled to isotopic equilibrium with either [methyl-3H]choline, myo-[2-3H]inositol or [9,10 (n)-3H]palmitic acid. All three agonists activated the phospholipase D-catalysed hydrolysis of PtdCho as determined by the release of [3H]choline (Cho) and the formation of [3H]phosphatidylbutanol (PtdBut). The release of [3H]choline by each agonist exhibited similar sensitivity to prolonged pre-exposure to the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). The release of [3H]choline exhibited the same dose dependency as the production of total inositol phosphates for each mitogen suggesting that the two responses might be mediated through identical receptors. Acute pre-treatment with TPA allowed the dissociation of inositol lipid hydrolysis from PtdCho breakdown, since it inhibited inositol phosphate accumulation but stimulated choline generation. The loss of mitogen stimulated choline release in cells pre-treated with the phorbol ester for 48 h was not due to loss of stimulated inositol phosphate production which was reproducibly enhanced in these 'down-regulated' cells.

Regulation of bombesin-stimulated inositol 1,4,5-trisphosphate generation in Swiss 3T3 fibroblasts by a guanine-nucleotide-binding protein

The stimulation of inositol phosphate generation by bombesin and GTP analogues was studied in Swiss 3T3 cells permeabilized by electroporation. Bombesin-stimulated inositol phosphate generation is potentiated by guanosine 5'-[gamma-thio]triphosphate (GTP[S]) and inhibited by guanosine 5'-[beta-thio]diphosphate at all peptide concentrations tested, with no change in the EC50 value (concn. giving half-maximal response) for the agonist. Kinetic analysis showed that, although bombesin-stimulated [3H]InsP3 generation in [3H]inositol-labelled cells was rapid (maximal by 5-10 s), the response to GTP[S] alone displayed a distinct lag time of 20-30 s. This lag time was significantly decreased by the addition of bombesin, suggesting that in this system agonist-stimulated GTP/GDP exchange occurs. In addition, bombesin-stimulated generation of Ins(1,4,5)P3 mass at 10 s was enhanced by GTP[S] in the absence of a nucleotide response alone, a result consistent with this proposal. Pretreatment of the cells with phorbol 12-myristate 13-acetate (PMA) resulted in a dose-dependent inhibition of bombesin-, but not GTP[S]-, stimulated inositol phosphate generation. Furthermore, although PMA pretreatment did not affect the lag time for InsP3 formation in response to GTP[S] alone, the degree of synergy between bombesin and the nucleotide was severely decreased at early time points. The results therefore demonstrate that the high-affinity bombesin receptor is coupled via a G-protein to phospholipase C in a manner consistent with a general model for receptor-G-protein interactions and that this coupling is sensitive to phosphorylation by protein kinase C.

Desensitization of prostaglandin F2 alpha-stimulated inositol phosphate generation in NIH-3T3 fibroblasts transformed by overexpression of normal c-Ha-ras-1, c-Ki-ras-2 and c-N-ras genes

The stimulation of inositol phosphate generation in control and ras-gene-transformed NIH-3T3 cells by prostaglandin F2 alpha (PGF2 alpha) was investigated. Compared with the control cells, a desensitization of the response was observed in cells transformed by the overexpression of N-, Ha-, or Ki-ras genes. This desensitization was without effect upon the concentration causing half-maximal effect (EC50), dissociation constant (Kd) or number of PGF2 alpha receptors. Inhibition of PG synthesis was without effect upon desensitization, demonstrating that the effect was not agonist-induced. Desensitization could be induced in NIH-3T3 cells by culturing under conditions where the cells were all in the exponential growth phase, or by a 12 h exposure to a C-kinase-activating phorbol ester. These results suggest that desensitization of certain agonist-induced inositol phospholipid responses in ras-transformed cells is a consequence of increased cell proliferation and associated amplification in C-kinase activity and is an indirect consequence of transformation by ras.