Marta E. Couce

Leptin and leptin receptor expression in rat and mouse pituitary cells.

Leptin is a circulating hormone secreted mainly by adipose tissue. Recent studies have shown leptin production by other tissues, including the placenta, stomach, and mammary tissues. Various reports have suggested that the anterior pituitary may have a role in the regulatory effects of leptin. We recently localized leptin in the human anterior pituitary, but analysis of leptin in rodent pituitary has not been previously reported. In this study we examined rat and mouse pituitary tissues and various cell lines for leptin by RT-PCR, immunohistochemistry, and Western blotting. Leptin receptor messenger RNA was also examined in these tissues by RT-PCR. Leptin was present in a small percentage of rat (4.8 ± 0.7%) and mouse (7 ± 2%) pituitary cells. Colocalization studies with leptin and pituitary hormones showed leptin expression mainly in TSH cells (24 ± 2% of TSH cells in the rat pituitary and 31 ± 1% of TSH cells in the mouse pituitary). A folliculo-stellate (FS) cell line, TtT/GF, also expressed leptin. Th...

Localization of leptin receptor in the human brain.

Leptin (OB protein), the product of the adipose-specific ob gene, exerts important effects in the regulation of food intake and energy expenditure. Based upon results from animal studies, several groups have suggested that this action may be exerted in the brain, specifically in the hypothalamic region. However, to date, the localization of the OB-R in the human brain has not been described. One aim of this study was to contribute to a better understanding of the role that the central nervous system plays in the pathogenesis of obesity in humans. A first stage was to determine the OB-R expression in the human brain by means of immunohistochemistry and Western blotting. Several brain regions from 17 lean, 14 obese, and 4 diabetic (NIDDM) subjects, obtained from archival autopsy material, were sampled. Brain samples from neocortex, hypothalamus, medualla, limbic system, pineal and cerebellum were routinely processed in paraffin and analyzed with the avidin-biotin immunoperoxidase and diaminobenzidine detection method. Western blotting (WB) analysis was done on fresh brain tissue from an obese patient. Specific OB-R immunoreactivity was localized in the choroid plexus epithelium, ependymal lining, and neurons of the hypothalamic nuclei (arcuate, suprachiasmatic, mamillary, paraventricular, dorsomedial, supraoptic and posterior), nucleus basalis of Meynert, inferior olivary nuclei and cerebellar Purkinje cells. No differences in OB-R immunoreactivity were found among the three groups examined. WB analysis yielded 97- and 125-kD bands in the hypothalamus and cerebellum. In summary, this paper presents the first evidence to indicate the specific localization of the OB-R in the brain of lean, obese and NIDDM subjects.

The Long Form of the Leptin Receptor (OB-Rb) Is Widely Expressed in the Human Brain

Leptin exerts important effects on the regulation of food intake and energy expenditure by acting in the brain. Leptin action is mediated by the interaction with a receptor that is alternatively spliced, resulting in at least five different isoforms. The long form (OB-Rb) has a long intracellular domain that is essential for intracellular signal transduction. The specific aim of this study was to further investigate the role that the brain may play in the pathogenesis of obesity in humans. We studied the expression of OB-R mRNA (both short or common and long isoforms) in the brains of obese, lean and diabetic subjects, by in situ hybridization, semiquantitative RT-PCR and Northern blots analysis. We used two alternative probes: one that recognizes all known splice variants (OB-Ra) and a second that recognizes only the long form, OB-Rb. Several brain regions, including hypothalamus, cerebellum, neocortex, entorrhinal cortex, amygdala, and rostral medulla, were evaluated. In situ hybridization studies revealed that both OB-Ra and OB-Rb mRNAs are widely distributed in the human brain. The specific hybridization signal with both probes was detected exclusively in the cytoplasm of the cell body, dendrites and proximal axons of neurons. Hypothalamic nuclei, Purkinje cells and dentate nuclei of the cerebellum, inferior olivary and cranial nerves nuclei in the medulla, amygdala and neurons from both neocortex and entorrhinal cortex demonstrated positive signals. The hybridization signal obtained in ependyma was lower than that in neurons and no specific hybridization was detected in glial cells. No significant differences were identified among the regions or among the three groups studied. These results match those previously obtained by us [Couce et al.: Neuroendocrinology 1997;66:145] in which the distribution of the OB-R protein in the human brain was first described. RT-PCR indicated that the OB-Rb was highly expressed in the hypothalamus and cerebellum. No significant differences of OB-Ra or OB-Rb mRNA expression were identified in lean or obese individuals in these two cerebral regions. The levels of OB-Rb were significantly higher in cerebellum compared to hypothalamus in lean and obese individuals. The original hypothesis that OB-Rb is present only in the hypothalamus needs to be reconsidered. This OB-Rb isoform seems to be widely expressed in the human brain with highest levels in the cerebellum. Obesity and hyperleptinemia appears not to be associated with down-regulation of the OB-Rb in the human brain.

Chordoid Meningioma: A Clinicopathologic Study of 42 Cases

The term chordoid meningiomas was first used by Kepes et al. in 1987 to describe a meningeal tumor in young patients associated with microcytic anemia and/of dysgammaglobulinemia. Such tumors were composed of spindle or epithelioid cells disposed in chordoma-like clusters and cords in a myxoid matrix and often featured a prominent lymphoplasmacellular infiltrate. Our study includes 42 chordoid meningiomas that represented 0.5% of all meningiomas operated at Mayo Clinic during the interval 1975 to 1997. The male to female ratio was 1:1 and the age range was 12 to 77 years (mean, 47.4 yrs). Only two (5.2%) occurred in children. The majority (88%) were large and supratentorial. No manifestation of systemic disease was noted. Chordoid elements comprised 10% to 100% of the tumors: 34 (81%) were more than 50% chordoid. Thirty-seven tumors (88%) were classified as typical and five as atypical. Lymphoplasmacytic infiltrates varied, being moderate in 10 cases (23.8%), mild in 15 (35.7%), and absent in 17 (40.5%). In 14 (42%) of the 33 cases with available follow up, one or more recurrences were noted. All but one recurrent tumor had been subtotally resected. In 86% of recurrent tumors, the primary lesion was more than 50% chordoid in pattern and contained little or no inflammatory infiltrate. In our experience, chordoid meningiomas are primarily tumors of adults, lack sex predilection, are unassociated with systemic manifestations, and uniformly recur when subtotally excised.

Treatment With Growth Hormone and Dexamethasone in Mice Transgenic for Human Islet Amyloid Polypeptide Causes Islet Amyloidosis and β-Cell Dysfunction

Islet amyloid derived from islet amyloid polypeptide (IAPP) is a well-recognized feature of type II diabetes. However, the mechanism of islet amyloidogenesis is unknown. In vitro studies suggest that amino acid residues 20–29 in human, but not mouse, IAPP confer amyloidogenicity consistent with the absence of spontaneous islet amyloidosis in mice. Several clinical and in vitro studies suggest that increased synthetic rates of IAPP predispose to IAPP-amyloidosis. In the present study, we sought to test the hypothesis that pharmacological induction of insulin resistance in a mouse transgenic (TG) for human IAPP would induce islet amyloid and β-cell dysfunction. TG and non-transgenic (N-TG) control mice were treated with both rat growth hormone (12 μg/day) and dexamethasone (0.24 mg/day) (dex/GH) or received no treatment for 4 weeks, after which animals were killed to examine islet morphology. Treatment with dex/GH caused hyperglycemia (7.3 ± 0.4 vs. 5.2 ± 0.1 mmol/l, TG vs. N-TG, P < 0.001) associated with a decreased plasma insulin concentration (595 ± 51 vs. 996 ± 100 pmol/1, TG vs. N-TG, P < 0.05) in TG versus control mice. Islet amyloid was induced in treated TG mice but not in control mice. Islet amyloid was identified in both intra- and extracellular deposits, the former being associated with evidence of β-cell degeneration. We conclude that dex/GH treatment in mice TG for human IAPP induces IAPP-derived islet amyloid, hyperglycemia, and islet dysfunction. The present model recapitulates the islet morphology and phenotype of type II diabetes.

Is Ghrelin the Culprit for Weight Loss after Gastric Bypass Surgery? A Negative Answer

Background: Ghrelin is a potent appetite stimulator, mainly synthesized in the stomach. Paradoxically, obese subjects have lower plasma ghrelin than lean subjects and increase their weight in spite of low ghrelin levels. The role of ghrelin in weight regulation after bariatric surgery is still controversial. The aim of this study was to evaluate whether rapid weight loss after laparoscopic Roux-en-Y gastric bypass surgery (LRYGBP), was associated with changes in plasma ghrelin levels. In addition, we determined the acute impact of LRYGBP on insulin resistance and adiponectin levels. Methods: 49 morbidly obese subjects who underwent LRYGBP were studied. 19 subjects who underwent other laparoscopic gastrointestinal surgeries acted as the control group. Fasting plasma levels of ghrelin, insulin and adiponectin were determined preoperatively and 2 hours, 10 days and 6 months postoperatively. Results: At 2 hours after LRYGBP, there was a significant reduction in ghrelin and adiponectin levels, which coincided with elevated plasma glucose and insulin levels. Interestingly, once glucose and insulin levels normalized at 6 months after surgery, ghrelin also normalized. Adiponectin reached pre-surgical levels at 10 days after LRYGBP and continued to significantly rise until 6 months postoperatively. Conclusion: Weight loss after LRYGBP occurs in spite of the absence of significant changes in plasma ghrelin levels. Improvement of insulin resistance occurred within 10 days after surgery, and could be related to the normalization of adiponectin levels. This data questions the role of peripheral ghrelin as a cause of weight loss in obese humans after LRYGBP.

Leptin and leptin receptor in anterior pituitary function.

Leptin is a 16 kDa protein that exerts important effects on the regulation of food intake and energy expenditure by interacting with the leptin receptor in the brain and in many other tissues. Although leptin is produced mainly by white adipose tissue, several laboratories have shown low levels of leptin production by a growing number of tissues including the anterior pituitary gland.Many studies have implicated leptin in anterior pituitary function including the observation that homozygous mutations of the leptin receptor gene led to morbid obesity, lack of pubertal development and decreased GH and TSH secretion. In addition, leptin functions as a neuroendocrine hormone and regulates many metabolic activities. Leptin also interacts with and regulates the hypothalamic-pituitary-adrenal, the hypothalamic-pituitary-thyroid and the hypothalamic-pituitary-gonadal axes.All of the anterior pituitary cell types express the leptin receptor. However, leptin has been localized in specific subtypes of anterior pituitary cells indicating cell type-specific production of leptin in the anterior pituitary. Subcellular localization of leptin indicates co-storage with secretory granules and implicates hypothalamic releasing hormones in leptin secretion from anterior pituitary hormone cells. Leptin signal transduction in the anterior pituitary has been shown to involve the janus protein-tyrosine kinase (JAK)/signal transducer and activation of transcription (STAT) as well as suppressor of cytokine signalling (SOCS). These proteins are activated by tyrosine-phosphorylation in anterior pituitary cells. The various steps in pituitary leptin signal transduction remain to be elucidated.

Gliosarcoma with epithelial differentiation: immunohistochemical and molecular characterization. A case report and review of the literature

Few reported cases of gliosarcomas or glioblastomas with epithelial-like areas exist. Most cases were originally diagnosed as metastatic carcinoma. Focal expression of glial fibrillary acidic protein has helped characterize these tumors as having a glial origin. We report a case of gliosarcoma with multifocal, extensive areas of well-differentiated carcinoma; demonstrating squamous and glandular differentiation. The expression of glial fibrillary acidic protein and epithelial phenotype were mutually exclusive. We performed extensive immunohistochemical analyses and comparative genotypic analysis using microdissection to secure representative glial and epithelial components. Loss of heterozygosity was analyzed with a panel of 12 polymorphic microsatellite markers designed to indicate allelic loss and situated in proximity to known tumor suppressor genes located on chromosomes 1p, 9p, 10q, 17p and 19q. We found comparable patterns of acquired allelic loss between the glial and carcinomatous components, strongly supporting the monoclonal origin of this neoplasm. This case represents an extreme form of phenotypic divergence in a malignant glioma, and constitutes a difficult diagnostic challenge. This heterogeneity reflects the potential for a range of phenotypic expression in malignant gliomas that needs to be recognized. We suggest microdissection genotyping as a molecular technique to better characterize these tumors.

Leptin access into the brain: A saturated transport mechanism in obesity

In spite of extensive research in the last few years, we still do not have a clear understanding of how does leptin access its targets in the brain, and whether there is postreceptor defect in the brain of obese individuals. Recent data have shown that leptin is produced in the pituitary, where its receptor is also present. A better understanding of how leptin reaches the brain and how it modulates the release of hypothalamic neuropeptides and pituitary hormones is needed. This information is crucial in order to better understand the role that leptin may play in the pathophysiology of diseases, such as obesity, delayed puberty, or growth defects.

Potential role of hypothalamic ghrelin in the pathogenesis of human obesity.

Ghrelin is a potent appetite stimulator, mainly synthesized in the stomach but also made in the brain. Paradoxically, obese subjects have lower plasma ghrelin than lean subjects and increase their weight in spite of low ghrelin levels. We hypothesize that central, and not peripheral ghrelin, is primarily responsible for overeating in humans. The aim of this study was to determine hypothalamic ghrelin levels in lean vs obese subjects. We collected anterior hypothalamus from lean and obese patients at the time of autopsy, and Western blots and semiquantitative RT-PCR for ghrelin and neuropeptide Y (NPY) were carried out. Our results showed that ghrelin expression was significantly higher in the hypothalamus of obese subjects compared to lean ones. This finding correlates with similar increases in NPY in the obese group. Ghrelin and NPY mRNA levels followed the same trend and were significantly higher in the hypothalamus in obese compared to lean subjects, suggesting a central origin for the increased protein content in the obese subjects. In conclusion, obesity in humans is associated with elevated central ghrelin. This data questions the significance of the role of peripheral ghrelin in the regulation of appetite in humans and suggests an important role for central ghrelin in the pathogenesis of obesity in humans.