Gastric GDF15 levels are regulated by age, sex, and nutritional status in rodents and humans

AIM

Growth differentiation factor 15 (GDF15) is a stress response cytokine that has been proposed as a relevant metabolic hormone. Descriptive studies have shown that plasma GDF15 levels are regulated by short term changes in nutritional status, such as fasting, or in obesity. However, few data exist regarding how GDF15 levels are regulated in peripheral tissues. The aim of the present work was to study the variations on gastric levels of GDF15 and its precursor under different physiological conditions, such as short-term changes in nutritional status or overfeeding achieved by HFD. Moreover, we also address the sex- and age-dependent alterations in GDF15 physiology.

METHODS

The levels of gastric and plasma GDF15 and its precursor were measured in lean and obese mice, rats and humans by western blot, RT-PCR, ELISA, immunohistochemistry and by an in vitro organ culture system.

RESULTS

Our results show a robust regulation of gastric GDF15 production by fasting in rodents. In obesity an increase in GDF15 secretion from the stomach is reflected with an increase in circulating levels of GDF15 in rats and humans. Moreover, gastric GDF15 levels increase with age in both rats and humans. Finally, gastric GDF15 levels display sexual dimorphism, which could explain the difference in circulating GFD15 levels between males and females, observed in both humans and rodents.

CONCLUSIONS

Our results provide clear evidence that gastric GDF15 is a critical contributor of circulating GDF15 levels and can explain some of the metabolic effects induced by GDF15.

Progesterone pre-treatment potentiates EGF pathway signaling in the breast cancer cell line ZR-75

Progesterone in hormone replacement therapy (HRT) preparations increases, while hysterectomy greatly reduces, the incidence of breast cancer. Cross-talk between the progesterone and growth factor signaling pathways occurs at multiple levels and this maybe a key factor in breast cancer survival and progression. To test this hypothesis, we characterized the effect of progesterone pre-treatment on the sensitization of the epidermal growth factor (EGF) signaling pathway to EGF in the breast cancer cell line ZR-75. For the first time in ZR-75 cells and in agreement with previous work using synthetic progestins, we demonstrate that pre-treatment with the natural ligand progesterone increases EGF receptor (EGFR) levels and subsequent ligand-dependent phosphorylation. Downstream we demonstrate that progesterone alone increases erk-1 + 2 phosphorylation, potentiates EGF-phosphorylated erk-1 + 2 and maintains these levels elevated for 24 h; over 20 h longer than in vehicle treated cells. Additionally, progesterone increased the levels of STAT5, another component of the EGF signaling cascade. Progesterone increased EGF mediated transcription of a c-fos promoter reporter and the nuclear localization of the native c-fos protein. Furthermore, progesterone and EGF both alone and in combination, significantly increase cell proliferation. Several results presented herein demonstrate the conformity between the action of the natural ligand progesterone with that of synthetic progestins such as MPA and R5020 and allows the postulation that the progestin/progesterone-dependent increase of EGF signaling provides a survival advantage to burgeoning cancer cells and may contribute to the breast cancer risk associated with endogenous progesterone and with progestin-containing HRT.

Effect of nitric oxide synthase inhibitors on ovum transport and oviductal smooth muscle activity in the rat oviduct

The effect of the inhibition of nitric oxide synthase (NOS) on ovum transport and oviductal motility in rats was investigated. Three different NOS inhibitors were injected into the ovarian bursa at oestrus or day 3 of pregnancy. Oviducts and uteri were flushed 24 h later and the presence of ova was recorded. In oestrous and pregnant rats, treatment resulted in accelerated egg transport, as shown by a decrease in the number of ova present in the oviducts. In cyclic rats, intrabursal injection of 1 mg kg-1 of either N-monomethyl-L-arginine (L-NMMA) or N omega nitro-L-arginine methyl ester (L-NAME) elicited a 30% reduction in the number of ova present in the oviducts, whereas in pregnant animals, the same dose of L-NMMA produced a reduction of 40%. Simultaneous administration of the NO donor spermine NONOate (5 mg kg-1) completely reversed the effect of L-NMMA. Tubal motility was assessed by microsphere displacement analysis within the oviduct. Surrogate ova were transferred to the oviductal lumen at oestrus and 24 h later the effect of intraoviductal injection of 1 microgram L-NMMA or vehicle was assessed. The microspheres in the isthmus showed an oscillating motion, and periods in which movement was not detectable. However, L-NMMA treatment produced a 3.6-fold increase in the maximum instant velocities and a significant reduction in the resting periods of the microspheres compared with the control group (P < 0.001). These results provide evidence that NO inhibition increases tubal motility that results in accelerated ovum transport, and indicate that NO could act as a paracrine signal between different layers of the oviductal wall, providing a role for endogenous NO in regulation of tubal function.

Interaction between functional domains of Bacillus thuringiensis insecticidal crystal proteins

Interactions among the three structural domains of Bacillus thuringiensis Cry1 toxins were investigated by functional analysis of chimeric proteins. Hybrid genes were prepared by exchanging the regions coding for either domain I or domain III among Cry1Ab, Cry1Ac, Cry1C, and Cry1E. The activity of the purified trypsin-activated chimeric toxins was evaluated by testing their effects on the viability and plasma membrane permeability of Sf9 cells. Among the parental toxins, only Cry1C was active against these cells and only chimeras possessing domain II from Cry1C were functional. Combination of domain I from Cry1E with domains II and III from Cry1C, however, resulted in an inactive toxin, indicating that domain II from an active toxin is necessary, but not sufficient, for activity. Pores formed by chimeric toxins in which domain I was from Cry1Ab or Cry1Ac were slightly smaller than those formed by toxins in which domain I was from Cry1C. The properties of the pores formed by the chimeras are therefore likely to result from an interaction between domain I and domain II or III. Domain III appears to modulate the activity of the chimeric toxins: combination of domain III from Cry1Ab with domains I and II of Cry1C gave a protein which was more strongly active than Cry1C.

Video imaging analysis of the plasma membrane permeabilizing effects of Bacillus thuringiensis insecticidal toxins in Sf9 cells

The size and ionic selectivity of the pores formed by the insecticidal crystal protein Cry1C from Bacillus thuringiensis in the plasma membrane of Sf9 cells, an established cell line derived from the fall armyworm Spodoptera frugiperda, were analyzed with a video imaging technique. Changes in the permeability of the membrane were estimated from the rate of osmotic swelling of the cells. In the presence of Cry1C, which is toxic to Sf9 cells, the permeability of the cell membrane to KCl and glucose increased in a dose-dependent manner. In contrast, Cry1Aa, Cry1Ab and Cry1Ac, toxins to which Sf9 cells are not susceptible, had no detectable effect. Pores formed by Cry1C allowed the diffusion of sucrose, but were impermeable to the trisaccharide raffinose. On the basis of the hydrodynamic radii of these substances, the diameter of the pores was estimated to be 1.0-1.2 nm. In the presence of salts, the rate of swelling of cells exposed to Cry1C was about equally influenced by the size of the anion as by that of the cation, indicating that the ionic selectivity of the pores is low.

Sperm interaction with human oviductal cells in vitro

In this article we describe the in-vitro interaction between human spermatozoa and oviductal epithelial cell monolayers. Freshly obtained spermatozoa were added to culture dishes containing human oviductal cells (co-culture), culture medium (control) or culture medium which had previously been used for culture of oviductal cells (conditioned medium). At 0, 5, 24, and 48 h of incubation the percentage of motile spermatozoa was determined and their motion characteristics analysed. Aliquots were taken to determine the percentage of acrosome-reacted spermatozoa. The spermatozoa were motile for a longer period in the presence of oviductal cells (54 +/- 9% co-culture versus 18 +/- 3% control, at 48 h) and the kinetics of the acrosome reaction exhibited a different pattern. In the control the percentage of reacted spermatozoa increased progressively throughout incubation. In co-culture, there was an increase only at 5 h; thereafter, the percentage of acrosome reactions did not change. Spermatozoa incubated in conditioned medium exhibited a behaviour halfway between the control and the co-culture. The pattern of sperm movement was not different in any of the experimental conditions. Although there was no binding between spermatozoa and oviductal epithelial cells, the frequency of the ciliary beat increased after spermatozoa were added to the oviductal cell monolayers. These results suggest that incubation with oviductal cells increases sperm survival, stabilizes the acrosome, and modifies the frequency of ciliary beat.

Characterization of a marker for tracheal basal cells

An IgM monoclonal antibody (1D9/B3) is characterized, which specifically recognizes basal cells of the upper airway epithelium. Although morphological features have been used to follow cell lineage and differentiation, an objective assessment of differentiation can be enhanced by characterizing the expression of specific antigens that form the phenotypic profile of specialized cells. Mice were immunized with rabbit tracheal basal cells that had been obtained by pronase digestion and purified into a subpopulation of basal cells by flow cytometry. Six immunization experiments produced five hybridomas specific to epithelial cells. A hybridoma whose supernatant immunocytochemically stained the basal cell subpopulation of rabbit tracheal cells was selected. The antibody reacted with tracheal basal cells in rabbit, rat, sheep, pig, and human tracheal sections, and in cultured monolayers of tracheal epithelial cells of the same species. The antibody did not react with the basal cells of other rabbit tissue, including the skin, or other rabbit epithelia. Confocal microscopy and exposure of tracheal epithelial cells to fluorescent-tagged monoclonal antibody 1D9/B3 prior to loading on to flow cytometry showed that the basal cell antibody recognized an intracellular epitope. The epitope for the 1D9/B3 antibody was characterized by Western blotting. The 1D9/B3 antibody appears to be a distinct and specific marker to the airway epithelial basal cell and will be useful in studies of airway epithelial differentiation, injury, and regeneration.

Characterization of a marker of differentiation for tracheal ciliated cells independent of ciliation

Although morphologic features have been used to follow cell lineage and differentiation, an objective assessment of differentiation can be best established by characterizing the expression of specific proteins that form the phenotypic profile of differentiated cells. Thus, specific markers or probes are required to unequivocally identify the various types of cells resulting from differentiation in a cell lineage. We report characterization of an IgM monoclonal antibody (5B4/H3), which recognized a surface antigen of approximately 130 kD unique to ciliated cells. The antibody reacted with the lumenal surface of the ciliated cells in transmission electron micrographs, in immunohistochemical staining of tracheal sections, and in cultured monolayers of tracheal epithelial cells. Flow cytometry, performed on enzymatically dispersed tracheal epithelial cells tagged with 5B4/H3 and fluorescent-labeled goat anti-mouse IgA/IgG/IgM, produced a population of fluorescent ciliated cells and a mixed nonfluorescent, nonciliated cell population. Ciliated cells were followed in vitro by time-lapse video microscopy for 48 to 72 h. Some of the ciliated cells lost their cilia under these culture conditions, but these cells were still found to react with the 5B4/H3 antibody. The antigen detected by this antibody remained on the surface of the cells after they lost their cilia. These results indicate that 5B4/H3 recognized a cell surface antigen that is specific to the ciliated cells and is independent of cell morphology. This marker will be useful in tissue culture studies of airway epithelial lineage, or differentiation, in which cell morphology is variable and cannot be used as a reliable marker of differentiation.

Enrichment of subpopulations of respiratory epithelial cells using flow cytometry

The application of flow cytometry to enrich airway epithelial cell subpopulations is described. A complementary epithelial cell preparative technique is also outlined. The ability of the airway epithelium to protect the lung from environmental insults results from a complex interaction among the different cells that form its matrix. The separation of the different epithelial cell types is an essential step in the studies of mechanisms of the controlling factors of cell repair, cell differentiation, and neoplastic transformation. Epithelial cells of the New Zealand white rabbit trachea are prepared using enzymatic digestion and microdissection. Small sections of tracheal wall are dissected into pieces approximately 10 mm2. The mucosa is dissected and placed in 0.15% hyaluronidase for 40 min at 22 degrees C. Mucus is removed, and the mucosa is then placed in 0.1% pronase at 37 degrees C for 30 min. With careful dissection, the epithelium can be dissected from the mucosa in 10-mm2 sheets. Sheets of epithelial cells are placed in 6 ml of an enzymatic solution containing collagenase, 0.2% bovine serum albumin, 0.04% soya bean trypsin inhibitor, 0.06 ml of 1 M Hepes buffer for 3 h at 37 degrees C. The cells are gently pipetted during the 3-h period, yielding a suspension of viable cells. Subpopulations of these different cell types are enriched using an Orthocytofluorograph 50111. A krypton ion laser was used for excitation of cells at 488 nm. Forward-angle and 90 degrees scatter were gated on the histogram. The purification of the ciliated, basal, and secretory cells was 90%, 97%, and 94%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of an in vitro model of primate cervical goblet cells

Mucins, are densely packed in secretory granules of goblet cells. Upon exocytosis they undergo massive hydration that results in the formation of the mucus gel. Because the mucin polymer network is held together by tangles and low energy bonds, the rheological properties of this gel are mainly determined by the degree of postexocytotic hydration. Hydration in mucus is governed by a Donnan equilibrium as it is driven by electrostatic interaction among the polyionic charges of the mucins and other fixed polyions. Although, variations of charge density of the mucin polymer could be an efficient physiologic mechanism to control the rate of mucus hydration and rheology, this subject has not been investigated. In here we describe a primary tissue culture system of cervical goblet cells of the monkey uterus. This preparation allows to measure directly the kinetic of hydration of exocytosed mucins. Because the physicochemical parameters of the bathing medium can be effectively controlled, variations in the kinetic of mucins swelling upon exocytosis, can be used as a convenient indicator of fluctuations of charge density in secretory products. Since the cervical mucosa readily respond to endocrine influences, this preparation can provide a useful model to study the effect of hormones or other transmitters on polyionic charge density of secretory product.

Molecular mechanism of mucin secretion: I. The role of intragranular charge shielding

Mucus is an ubiquitous polymer hydrogel that functions as a protective coat on the surface of integument and mucosa of species ranging from simple animals (such as coelenterates) to mammals. The polymer matrix of mucus is made out of long-chain glycoproteins called mucins that are tangled together, forming a randomly woven, highly polyionic network (Lee et al., 1977; Verdugo et al., 1983). Mucin-containing granules, produced by mammalian goblet cells in vitro, undergo massive post-exocytotic swelling. Their swelling kinetics is similar to the swelling of condensed artificial polymer gels (Verdugo, 1984; Tanaka and Fillmore, 1979). We had proposed that mucins must be condensed in the secretory granule and expand by hydration during or after exocytosis (Verdugo, 1984; Tam and Verdugo, 1981). However, the polyionic charges of mucins prevents condensation unless they (the mucins) are appropriately shielded. The present experiments were designed to assert the presence of an intragranular shielding cation and its role in secretion. Giant mucin granules of the slug (Ariolimax columbianus) are released intact from mucus-secreting cells of the slug's skin. They burst spontaneously outside the cell, forming, upon hydration, the typical slug mucus (Deyrup-Olsen et al., 1983). We report here that these granules contain from 2.5 to 3.6 moles calcium/kg dry material, and that calcium is released from the granules immediately before the burst that discharges their secretory product. Therefore, we propose that calcium functions as a shielding cation of polyionic mucins, and that the bursting discharge of mucins from secretory granules must result from the release of calcium from the intragranular compartment.(ABSTRACT TRUNCATED AT 250 WORDS)

The oviductal cilia and Kartagener's syndrome

Women who have Kartagener's syndrome (primary ciliary dyskinesia) may or may not be fertile. The bronchial mucociliary clearance is reduced markedly in most of these women; this has led investigators to the conclusion that the cilia in the respiratory tract are immotile, and that "beating cilia may have no indispensable role in the female reproductive tract." Yet motile cilia are considered by many workers to be essential for normal ovum transport. More recently, bizarre ciliary motion has been described in the respiratory cilia of Kartagener's women. Our hypothesis was that the dyskinetic ciliary activity (or immotility) would be the same in both the respiratory and reproductive tracts and thus explain the fertility (or lack of it) in Kartagener's women. This report shows an identical ultrastructure and absolute immotility of cilia in both the respiratory tract and reproductive tract of a woman with Kartagener's syndrome who has never conceived. From this concordance, we suggest that the fertility of Kartagener's women is explained by the dyskinetic motion of oviductal cilia, and that the ciliated endosalpinx is essential for human reproduction.