In vitro and in vivo pharmacological role of TLQP-21, a VGF-derived peptide, in the regulation of rat gastric motor functions

BACKGROUND AND PURPOSE

Vgf gene expression has been detected in various endocrine and neuronal cells in the gastrointestinal tract. In this study we investigated the pharmacological activity of different VGF-derived peptides. Among these, TLQP-21, corresponding to the 556-576 fragment of the protein was the unique active peptide, and its pharmacological profile was further studied.

EXPERIMENTAL APPROACH

The effects of TLQP-21 were examined in vitro by smooth muscle contraction in isolated preparations from the rat gastrointestinal tract and, in vivo, by assessing gastric emptying in rats. Rat stomach tissues were also processed for immunohistochemical and biochemical characterization.

KEY RESULTS

In rat longitudinal forestomach strips, TLQP-21 (100 nmol x L(-1)-10 micromol x L(-1)) concentration-dependently induced muscle contraction (in female rats, EC(50) = 0.47 micromol.L(-1), E(max): 85.7 +/- 7.9 and in male rats, 0.87 micromol x L(-1), E(max): 33.4 +/- 5.3; n = 8), by release of prostaglandin (PG)E(2) and PGF(2a) from the mucosal layer. This effect was significantly antagonized by indomethacin and selective inhibitors of either cyclooxygenase-1 (S560) or cyclooxygenase-2 (NS398). Immunostaining and biochemical studies confirmed the presence of VGF in the gastric neuronal cells. TLQP-21, injected i.c.v. (2-32 nmol per rat), significantly decreased gastric emptying by about 40%. This effect was significantly (P < 0.05) blocked by i.c.v. injection of indomethacin, suggesting that, also in vivo, this peptide acts in the brain stimulating PG release.

CONCLUSIONS AND IMPLICATIONS

The present results demonstrate that this VGF-derived peptide plays a central and local role in the regulation of rat gastric motor functions.

Nuclear-mitochondrial interaction

The biogenesis of mitochondria depends on the coordinated expression of nuclear and mitochondrial genomes. Consequently, the control of mitochondrial biogenesis and function depends on extremely complex processes requiring a variety of well orchestrated regulatory mechanisms. It is clear that the interplay of transcription factors and coactivators contributes to the expression of both nuclear and mitochondrial respiratory genes. In addition, the regulation of mitochondria biogenesis depends on proteins that, interacting with messenger RNAs for mitochondrial proteins, influence their metabolism and expression. Moreover, a tight regulation of the import and final assembly of mitochondrial protein is essential to endow mitochondria with functional complexes. These studies represent the basis for understanding the mechanisms involved in the nucleus-mitochondrion communication, a cross-talk essential for the cell.

Reduced GABAB receptor subunit expression and paired-pulse depression in a genetic model of absence seizures

Neocortical networks play a major role in the genesis of generalized spike-and-wave (SW) discharges associated with absence seizures in humans and in animal models, including genetically predisposed WAG/Rij rats. Here, we tested the hypothesis that alterations in GABA(B) receptors contribute to neocortical hyperexcitability in these animals. By using Real-Time PCR we found that mRNA levels for most GABA(B(1)) subunits are diminished in epileptic WAG/Rij neocortex as compared with age-matched non-epileptic controls (NEC), whereas GABA(B(2)) mRNA is unchanged. Next, we investigated the cellular distribution of GABA(B(1)) and GABA(B(2)) subunits by confocal microscopy and discovered that GABA(B(1)) subunits fail to localize in the distal dendrites of WAG/Rij neocortical pyramidal cells. Intracellular recordings from neocortical cells in an in vitro slice preparation demonstrated reduced paired-pulse depression of pharmacologically isolated excitatory and inhibitory responses in epileptic WAG/Rij rats as compared with NECs; moreover, paired-pulse depression in NEC slices was diminished by a GABA(B) receptor antagonist to a greater extent than in WAG/Rij rats further suggesting GABA(B) receptor dysfunction. In conclusion, our data identify changes in GABA(B) receptor subunit expression and distribution along with decreased paired-pulse depression in epileptic WAG/Rij rat neocortex. We propose that these alterations may contribute to neocortical hyperexcitability and thus to SW generation in absence epilepsy.

Analysis of cytochrome C oxidase subunits III and IV expression in developing rat brain

Cytochrome c oxidase (COX) complex is built up with both nucleus- and mitochondrion-encoded subunits. Biogenesis and assembly of the complex thus requires fine cross-talk between the two compartments. In order to shed light on the regulation of nuclear-mitochondrial interactions, we studied the expression of COXIII (mitochondrion-encoded) and COXIV (nucleus-encoded) in adult rat tissues and rat developing brain. We found that the levels of COXIV protein and mRNA are not linearly related, thus suggesting a post-transcriptional mode of regulation. In agreement with this observation, we report the presence of a protein that specifically binds to the 3'-untranslated region of COXIV mRNA. This factor, that forms with RNA a complex of about 60 kDa, is present both in the cytoplasm and mitochondria, where its concentration decreases throughout development with inverse correlation with COXIV accumulation. Interestingly, using an antibody raised in our laboratory, we found that, in developing rat brain, COXIII does not localize exclusively to mitochondria, but is also present in the cytosol, where it could exert a yet unknown regulatory role.

[Prevention of hypoglycemia in patients with type 1 diabetes]

Hypoglycaemia is the most common metabolic disorder in type 1 diabetic patients. It is rarely dangerous, but significantly alters the quality of life and hinders the achievement of "normoglycaemia". Even if hypoglycaemia is impossible to be avoided, both its frequency and severity may be reduced if patients follow several practical recommendations. After having defined hypoglycaemia, we shall briefly describe its pathophysiology and its main causes in type 1 diabetic patients. Afterwards, the different approaches of prevention of hypoglycaemia will be discussed. We will particularly stress the need to revise the glycaemic target in high-risk patients, the role of optimising insulin therapy, the valuable help of blood glucose monitoring, the critical support of diet adjustments, and the appropriate management in case of physical activity. There is no doubt that patient's education plays a crucial role in such a strategy that aims at preventing severe hypoglycaemia in type 1 diabetic individuals.

Isolation and characterization of VGF peptides in rat brain. Role of PC1/3 and PC2 in the maturation of VGF precursor

The neurotrophin responsive gene vgf is widely expressed in central and peripheral neurones, and in certain neuroendocrine cell populations. Its encoded VGF precursor protein (proVGF1: 617 amino acids in rat, 615 in man, > 85% homology) gives rise to several low molecular weight species. We studied a range of neuroendocrine and neuronal cells, in which VGF-processing products were prominent with an apparent molecular weight of 20 and 10 kDa (VGF20 and VGF10, respectively). Such peptides were recognized by antibodies specific for the C-terminal rat VGF nonapeptide, thus indicating that they included the C-terminus of proVGF. Ectopic expression of the neuroendocrine-specific prohormone convertases PC1/3 or PC2 in GH3 cells showed that both could generate VGF20, while VGF10 was preferentially produced by PC1/3. Site-directed mutagenesis was used to identify the KRKRKK(488) motif as the target within VGF sequence which leads to the production of VGF20. Molecular characterization of rat VGF10, on the other hand, revealed that this peptide is produced by cleavage at the RPR(555) site. By the combined use of high-resolution separation techniques, matrix-assisted laser desorption/ionization time of flight (MALDI-ToF) mass spectrometry and manual Edman degradation we identified in rat brain a VGF fragment analogous to bovine peptide V and two novel peptides also derived from the C-terminal region of proVGF.

Localization of mitochondrial Hsp56 chaperonin during sea urchin development

We have previously demonstrated that Paracentrotus lividus nuclear genome encodes for the heat shock inducible chaperonin homolog Hsp 56 (1) and that the mature protein is localized in the mitochondrial matrix (2). In this paper we report that constitutive Hsp56 is maternally inherited, in fact it is present in the in unfertilized eggs, and that it has a perinuclear specific localization during cleavage. In the later stages both the constitutive and the heat shock inducible chaperonin has a specific territorial distribution. Moreover following heat shock, the Hsp56 appears in the cytoplasm and in the postmitochondrial supernatant beside the mitochondrial fraction.

Expression, processing, and secretion of the neuroendocrine VGF peptides by INS-1 cells

The neurotropin-inducible gene vgf is expressed in neuronal and endocrine tissues. It encodes a secretory protein that is proteolytically processed in neuronal cells to low molecular mass polypeptides. In the present report, we show that vgf is expressed in different insulinoma cell lines and in normal rat pancreatic islets. In the insulinoma-derived beta-cell line INS-1, vgf messenger RNA was transcriptionally up-regulated by increased levels ofintracellular cAMP, but not by the addition of glucose (20 mM) or phorbol 12-myristate 13-acetate (100 nM). Furthermore, nerve growth factor failed to stimulate vgf gene expression. In INS-1 cells, the VGF protein was shown to be processed in a post endoplasmic reticulum compartment to produce a peptide profile similar to that seen in neurons. The release of such VGF peptides occurred at a low rate in the absence of secretory stimuli (<2%/h). A 3-fold increase in the rate of release was seen after the addition of glucose (15 mM), a 4-fold increase was seen after (Bu)2cAMP (1 mM), and a 6-fold increase was seen after phorbol 12-myristate 13-acetate (100 nM). These results indicated that insulin-containing cells produce VGF-derived peptides that are released via a regulated pathway in response to insulin secretagogues.

Tau cleavage and dephosphorylation in cerebellar granule neurons undergoing apoptosis

Cerebellar granule cells undergo apoptosis in culture after deprivation of potassium and serum. During this process we found that tau, a neuronal microtubule-associated protein that plays a key role in the maintenance of neuronal architecture, and the pathology of which correlates with intellectual decline in Alzheimer's disease, is cleaved. The final product of this cleavage is a soluble dephosphorylated tau fragment of 17 kDa that is unable to associate with microtubules and accumulates in the perikarya of dying cells. The appearance of this 17 kDa fragment is inhibited by both caspase and calpain inhibitors, suggesting that tau is an in vivo substrate for both of these proteases during apoptosis. Tau cleavage is correlated with disruption of the microtubule network, and experiments with colchicine and taxol show that this is likely to be a cause and not a consequence of tau cleavage. These data indicate that tau cleavage and change in phosphorylation are important early factors in the failure of the microtubule network that occurs during neuronal apoptosis. Furthermore, this study introduces new insights into the mechanism(s) that generate the truncated forms of tau present in Alzheimer's disease.

Centrifugation does not alter spatial distribution of 'BEP4' mRNA in paracentrotus lividus EGG

Paracentrotus lividus unfertilized eggs were centrifuged in a sucrose gradient, so to split each into two parts: a nucleated light fragment and an anucleated heavy fragment. Northern blot analyses utilizing a bep4 probe as animal marker and H2A histone gene and 12S-mit RNA as controls indicate that the eggs are elongated along the animal-vegetal axis during centrifugation and thereafter split into an animal and a vegetal half. Treatment of the eggs with colchicine before centrifugation abolishes the animal localization of bep4 mRNA.

Sea urchin mitochondrial matrix contains a 56-kDa chaperonine-like protein

Paracentrotus lividus mitochondrial matrix contains a constitutive hsp of 56-KDa which cross reacts with a serum anti-hsp-60 chaperonine from yeast mitochondria. The localization of hsps preexisting or newly synthesized in different subcellular fractions of gastrula embryos is also analyzed by two-dimensional electrophoresis.

Molecular cloning and characterization of the human VGF promoter region

The VGF gene encodes a secretory protein that is expressed in a cell type-restricted pattern in neuroendocrine cells and is up-regulated by nerve growth factor (NGF) in the rat pheochromocytoma PC12 cell line. Here we report the isolation and characterization of the 5'-terminal region of the human VGF gene. In addition to a TATA box and a CCAAT box located at canonical distances from the transcription start site, the human VGF promoter contains several consensus sequences for different transcription factors, including a cyclic AMP response element and an AP-1 element, several GC boxes, and sequences homologous to other neuronal promoters. Transient transfection analysis demonstrates that 2.3 kb of the 5'-flanking sequence acts as a tissue-specific promoter, efficiently used only by neuronal cells that express endogenous VGF. Deletion analysis reveals that a positive regulatory region is located between nucleotides -458 to -204. Negative cis-acting elements that repress promoter activity in cell lines that do not normally express VGF are located between nucleotides -2,305 and -573 and between -458 and -204. The 5'-flanking region of the human VGF gene confers responsiveness to NGF, cyclic AMP, and phorbol ester treatment.

Interplay of the E box, the cyclic AMP response element, and HTF4/HEB in transcriptional regulation of the neurospecific, neurotrophin-inducible vgf gene

vgf is a neurotrophin response-specific, developmentally regulated gene that codes for a neurosecretory polypeptide. Its transcription in neuronal cells is selectively activated by the neurotrophins nerve growth factor (NGF), brain-derived neurotrophic factor, and neurotrophin 3, which induce survival and differentiation, and not by epidermal growth factor. We studied a short region of the rat vgf promoter which is essential for its regulated expression. A cyclic AMP response element (CRE) within this region is necessary for NGF induction of vgf transcription. Two sites upstream of CRE, an E box and a CCAAT sequence, bind nuclear protein complexes and are involved in transcriptional control. The E box has a dual role. It acts as an inhibitor in NIH 3T3 fibroblasts, together with a second E box located downstream, and as a stimulator in the NGF-responsive cell line PC12. By expression screening, we have isolated the cDNA for a basic helix-loop-helix transcription factor, a homolog of the HTF4/HEB E protein, that specifically binds the vgf promoter E box. The E protein was present in various cell lines, including PC12 cells, and was a component of a multiprotein nuclear complex that binds the promoter in vitro. The E box and CRE cooperate in binding to this complex, which may be an important determinant for neural cell-specific expression.

Replication origins and pause sites in sea urchin mitochondrial DNA

We have used a combination of one- and two-dimensional agarose gel electrophoresis, and solution hybridization to strand-specific probes, to map the replication origin of sea urchin mitochondrial DNA and to investigate the structure of replication intermediates. These assays are consistent with replication initiating unidirectionally from the D-loop region by D-loop expansion, as in vertebrates. A prominent site of initiation of lagging-strand synthesis lies at, or near to, the boundary between the genes for ATPase 6 and COIII, which is also close to a pause site for leading-strand synthesis. These findings suggest a role for pause sites in the regulation of mitochondrial transcription and replication, possibly involving template-binding proteins.

AgNOR protein quantity of cervical smears correlates with that of histological sections in cervical intraepithelial neoplasia

The quantitative distribution of AgNOR proteins has been determined by image cytometry in 52 cervical smears obtained from normal cervix (n = 20), grade I CIN (cervical intraepithelial neoplasia) (n = 3), grade II CIN (n = 5) and grade III CIN (n = 24). No significant difference was demonstrated in the mean AgNOR protein area values between normal cervix, CIN I and CIN II, while AgNOR protein scores of CIN III were significantly greater than those of normal cervix (p < 0.05). AgNOR protein quantity was also determined in 17 colposcopic directed biopsies of patients with CIN lesions (3 CIN II and 14 CIN III) already studied by cytological analysis. When AgNOR protein values of histological sections and corresponding cytological smears were compared by linear regression analysis, a significant correlation was found (r = 0.74, p < 0.05). Our results demonstrate that AgNOR protein quantity of cervical smears actually reflects that of the cervical epithelium in situ and may therefore be useful for the cytological diagnosis of cervical lesions.

Tissue-specific processing of the neuroendocrine protein VGF

VGF is a neuroendocrine-specific gene product that is up-regulated by nerve growth factor in the PC12 cell line. In rat neuroendocrine tissues two polypeptides of 90 and 80 kDa were detected by an antiserum to an N-terminal domain of VGF (from residues 4 to 240). In parallel, an antiserum directed against the C-terminal nonapeptide of VGF (from residues 609 to 617) revealed several additional posttranslational products. Peptides of apparent molecular sizes of 20, 18, and 10 kDa were prominent in nerve tissues and the hypophysis but absent in the adrenal medulla, and their relative abundance varied in distinct regions of the CNS. In PC12 cells VGF was proteolytically processed only after nerve growth factor treatment, and primary cultures of rat cerebellar granule cells accumulated the low-molecular-weight forms of VGF during in vitro maturation. In these cells the specific cleavages of VGF occurred in a postendoplasmic reticulum compartment; the processed forms were enriched in the secretory vesicles and were preferentially secreted upon cell membrane depolarization. Distinct differential distribution in the CNS and in vitro release of such posttranslational products indicate that these species may represent biologically relevant forms of VGF that play a role in neuronal communication.

The "VGF" protein in rat adenohypophysis: sex differences and changes during the estrous cycle and after gonadectomy

Gene expression and cell localization of the neuroendocrine protein VGF were studied in the rat anterior pituitary. In females, four antisera against nonoverlapping regions of VGF immunostained a small number of lactotropes and many gonadotropes. In the latter cells, VGF immunoreactivity was localized to a subpopulation of secretory granules. Distinct changes were seen after estrus, with a significant increase in VGF messenger RNA (whole pituitary), whereas VGF immunostaining was strikingly reduced in gonadotropes and somewhat more abundant in lactotropes. In male rats, gene expression was low, and immunoreactivity was restricted to a few lactotropes. After castration or ovariectomy, VGF messenger RNA was high, and VGF immunoreactivity was abundant in gonadotropes. Selective localization and cyclic modulation suggest involvement of the VGF gene product(s) in pituitary gonadotrope and/or lactotrope function.

[The role of prostaglandins in fertility. Experimental research]

Prevention of postoperative adhesion is an issue that continues to elude the abdominal and reproductive surgeon. Adhesions seem to be a result of an inflammatory process and it is well known that prostaglandins play an important role in such an event. In an attempt to improve the results of microsurgery, we have tried in this study to examine the effect of local intraperitoneal application of prostaglandins (PGE2 and PGF2 alpha) on adhesion formation in the rat after traumatizing to the uterine horn. Prostaglandins applied locally were found to increase intraperitoneal adhesion formation at the injured sites, in comparison with controls. Also, we have reported on histological examination an increased accumulation of inflammatory cells in traumatized areas. However, we didn't observe a reduced fertility in rats treated with prostaglandins because these substances induce follicular rupture by activation of proteolytic enzyme located in the follicular wall. We conclude that prostaglandins play an important role in the process of adhesion formation. Using antiprostaglandins agents could improve the outcomes of reproductive surgery.

[Tubo-ovarian transplantation in the treatment of sterility. Experimental research]

Microsurgical transposition of fallopian tube and ovary has the potential of being an efficient therapeutic treatment in patients with tubal sterility. The Authors present their experience of microsurgical adnexal transplantation in rabbit by two different techniques: the first procedure by microvascular anastomosis of the ovarian vessels, the second one without vascular pedicle. Function is evaluated at various time after grafting by: exploratory laparotomy on day 30 to establish whether circulation to the grafts was still maintained; macroscopic and microscopic examination of ovaries and fallopian tubes. The microvascular techniques prove highly reliable in terms of immediate vascular patency rate but it is disappointing that 50% of the autografts has failed with blocked vessels by day 30. Perhaps this is due to the difficult techniques in anastomosing the ovarian vessels of small caliber. In spite of these outcomes the vascularized autografts were viable and functional after transplantation in contrast with the non-vascularized tubo-ovarian grafts which all failed. This experience encourages to believe that the microsurgical technique could be employed for homograft transplantation in woman with extensive ovarian and tubal damages.

The dynamics of structural modifications of mitochondria at the early stages of sea urchin embryonic development

The organization of the chondriome and the ultrastructure of mitochondria have been studied in eggs and embryos of the sea urchin Paracentrotus lividus. The egg chondriome is characterized by an arrangement in well-delimited clusters. Analysis of mitochondrial clusters on electron micrographs of ultrathin serial sections shows two kinds of mitochondria of different shapes, the rod-shaped and the spherical. The egg mitochondria have a dense matrix and a well-ordered arrangement of cristae which, in rod-shaped variety, are perpendicular to the major axis. Cell division is accompanied by significant changes in intracellular distribution of mitochondria and in their structure. At the stage of 2-4 blastomeres, the clusters break up and numerous mitochondrial rods show signs of fragmentation; most of the observable mitochondria are of spherical shape. At the same time, the matrix becomes less dense, and the orderly arrangement of the cristae disappears. From the blastula to the gastrula stage, the observed modifications are reversed: the number of spherical-shaped mitochondria decreases, while that of the rod-shaped increases; the diameter of the latter is almost equal to the initial diameter of the spherical forms, the matrix becomes dense again and the cristae resume their orderly arrangement.

Studies of the mechanisms of nuclear control over the synthesis of mitochondrial DNA in sea urchin eggs

We have studied the contribution of nuclear genomic activity and of the cytoskeletal integrity in the negative control operated by the nucleus over the mitochondrial genome. We have found that the nuclear control is exerted even in the presence of nuclei that have undergone heavy irradiation such as to block at least DNA replication and in the absence of intact microtubules. Data are presented which suggest some implication of ion (Ca++) movements in this negative control.

The nucleus negatively controls the synthesis of mitochondrial proteins in the sea urchin egg

Enucleation of Paracentrotus lividus eggs, followed by parthenogenetic activation induces a sharp increase in the synthesis of mitochondrial proteins as shown by electrofluorography after in vivo labeling with radioactive amino acids. These results further substantiate the hypothesis that the cell nucleus negatively controls mitochondrial replication in the sea urchin egg.

Biochemical and electron microscopic evidence that cell nucleus negatively controls mitochondrial genomic activity in early sea urchin development

Enucleated halves of sea urchin eggs obtained by centrifugation contain almost all the mitochondrial population of the egg. Removal of the nucleus followed by parthenogenetic activation stimulates the incorporation of [3H]thymidine into the mitochondrial DNA, whereas no such incorportion is observed in activated whole eggs. The block is not the result of a modification in the permeability of the mitochondrial membrane. Electron microscopic observations demonstrated duplication of mitochondrial DNA molecules in activated enucleated halves. No duplication was found in the mitochondrial DNA from activated whole eggs or from nonactivated enucleated halves. We conclude that the cell nucleus exerts a negative control on the activity of the mitochondrial genome through some short-lived nuclear substance(s).

Mitochondrial division in non nucleated sea urchin eggs

An electron microscopic analysis of non nucleated and parthenogenetically activated sea urchin eggs shows figures that can be interpreted as dividing mitochondria. This is in agreement with our previous observations showing that the egg nucleus negatively controls mitochondrial DNA synthesis.