María Carmen Iglesias-Osma

Ras-GRF1 signaling is required for normal β-cell development and glucose homeostasis

Development of diabetes generally reflects an inadequate mass of insulin‐producing β‐cells. β‐cell proliferation and differentiation are regulated by a variety of growth factors and hormones, including insulin‐like growth factor I (IGF‐I). GRF1 is a Ras‐guanine nucleotide exchange factor known previously for its restricted expression in brain and its role in learning and memory. Here we demonstrate that GRF1 is also expressed in pancreatic islets. Interest ingly, our GRF1‐deficient mice exhibit reduced body weight, hypoinsulinemia and glucose intolerance owing to a reduction of β‐cells. Whereas insulin resistance is not detected in peripheral tissues, GRF1 knockout mice are leaner due to increased lipid catabolism. The reduction in circulating insulin does not reflect defective glucose sensing or insulin production but results from impaired β‐cell proliferation and reduced neogenesis. IGF‐I treatment of isolated islets from GRF1 knockouts fails to activate critical downstream signals such as Akt and Erk. The observed phenotype is similar to manifestations of preclinical type 2 diabetes. Thus, our observations demonstrate a novel and specific role for Ras‐GRF1 pathways in the development and maintenance of normal β‐cell number and function.

Role of μ-opioid receptors in insulin release in the presence of inhibitory and excitatory secretagogues

In mouse pancreatic islets incubated under static conditions, the inhibitory effects on glucose-evoked insulin release induced by adrenaline (1 microM), clonidine (2 microM) and UK 14,304 (brimonidine, 0.001-1 microM) were abolished by naloxone (30 nM). Only CTOP (D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Phe-Thr-NH(2), 0.1 microM), a very selective mu-opioid receptor antagonist, blocked the response to UK 14,304. Glucose-induced insulin secretion was attenuated by both beta-endorphin (0.01 microM) and endomorphin-1 (0.1 microM). Naloxone and CTOP prevented these inhibitory responses. The stimulatory effect of glibenclamide (1 microM) was also reduced by endomorphin-1. However, when islets were incubated in the presence of K(+) (30 mM), carbachol (100 microM) or forskolin (0.1 microM), neither the inhibitory effect induced by UK 14,304 was reversed by naloxone, nor endomorphin-1 altered the responses promoted by the excitatory agents. Thus, alpha(2)-adrenoceptor stimulation might inhibit glucose-induced insulin secretion by releasing endogenous opioids. Mu-Opioid receptor activation and opening of K(ATP) channels could be involved in the response.

Differential sensitivity to adrenergic stimulation underlies the sexual dimorphism in the development of diabetes caused by Irs-2 deficiency

The diabetic phenotype caused by the deletion of insulin receptor substrate-2 (Irs-2) in mice displays a sexual dimorphism. Whereas the majority of male Irs-2(-/-) mice are overtly diabetic by 12 weeks of age, female Irs-2(-/-) animals develop mild obesity and progress less rapidly to diabetes. Here we investigated β-cell function and lipolysis as potential explanations for the gender-related differences in this model. Glucose-stimulated insulin secretion was enhanced in islets from male null mice as compared to male WT whereas this response in female Irs-2(-/-) islets was identical to that of female controls. The ability of α(2)-adrenoceptor (α(2)-AR) agonists to inhibit insulin secretion was attenuated in male Irs2 null mice. Consistent with this, the expression of the α(2A)-AR was reduced in male Irs-2(-/-) islets. The response of male Irs-2(-/-) islets to forskolin was enhanced, owing to increased production of cAMP. Basal lipolysis was increased in male Irs-2(-/-) but decreased in female Irs-2(-/-) mice, concordant with the observation that adipose tissue is sparse in males whereas female Irs2 null mice are mildly obese. Adipocytes from both male and female Irs-2(-/-) were resistant to the anti-lipolytic effects of insulin but female Irs-2(-/-) fat cells were additionally resistant to the catabolic effects of beta-adrenergic agonists. This catecholamine resistance was associated with impaired generation of cAMP. Consequently, targets of cAMP-dependent protein kinase (PKA) which mediate lipolysis were not phosphorylated in adipose tissue of female Irs-2(-/-) mice. Our findings suggest that IRS-2 deficiency in mice alters the expression and/or sensitivity of components of adrenergic signaling.

Effects of verapamil and elgodipine on isoprenaline-induced metabolic responses in rabbits

Verapamil (0.17 microg kg(-1) min(-1) intravenous, i.v.) but not elgodipine (35 ng kg(-1) min(-1)) modestly enhanced the weak blood glucose increase induced by the i.v. infusion of isoprenaline (0.3 microg kg(-1) min(-1)) in conscious rabbits. However, elgodipine but not verapamil suppressed the increase in circulating insulin evoked by the agonist. Both drugs enhanced the rise in plasma lactate mediated by isoprenaline but only elgodipine potentiated the lipolytic effect of the agonist. In isolated islets elgodipine (10(-6) M) blocked forskolin (10(-6) M)-induced insulin release. However, in rabbit adipocytes elgodipine potentiated both glycerol release and cAMP accumulation induced by isoprenaline (10(-8)-10(-6) M). Excess K(+) (40-60 mM) did not alter basal lipolysis or the response to isoprenaline in either rabbit or mouse adipocytes. Therefore, Ca2+ influx through L-type Ca2+ channels does not seem to play a significant role in the lipolytic effect of isoprenaline. Metabolic alterations found with Ca2+ channel antagonists were of minor intensity and probably devoid of pathological implications.

Relevance of pituitary aromatase and estradiol on the maintenance of the population of prolactin-positive cells in male mice

In previous studies we demonstrated the expression of aromatase in pituitary cells. This expression is gender related, and is also associated with the presence of prolactinomas. To ascertain the relevance of aromatase in modulating the populations of prolactin-positive pituitary cells an immunocytochemical and morphometric study of prolactin-positive pituitary cells was carried out using the pituitary glands of adult male and female aromatase-knockout (ArKO) mice. Additionally has been determined if pituitary aromatase is involved in a gender-linked differentiated regulation of the prolactin-producing pituitary cells. Compared to wild-type mice, the knockout animals of both genders showed a significant decrease (p<0.01) in the cellular and nuclear areas of their prolactin cells, as well as in the percentages of the prolactin-positive cells and the proliferating prolactin cells. Our results suggest that estradiol is responsible for the maintenance of the population of prolactin cell in males and, so as not to disturb the endocrine reproductive environment, estradiol is synthesized inside the pituitary by circulating testosterone via means of aromatase P450, which acts in paracrine way. This new role for pituitary aromatase may well explain the previous findings establishing that the pituitary expression of aromatase is higher in males than in females, and the association between the development of prolactinomas and the increased expression of aromatase in tumours.

Adipocitocinas: implicaciones en el pronóstico y tratamiento farmacológico de patología cardiovascular

Las adipocitocinas, factores derivados del tejido graso con propiedades reguladoras, estan implicadas en la fisiopatologia de procesos ateromatosos y metabolicos tales como: cardiopatia isquemica, resistencia a la insulina, obesidad, dislipidemia y diabetes mellitus. El aumento de los depositos de tejido adiposo visceral determina una peor evolucion para esas afecciones. Farmacos como los inhibidores de la enzima convertidora de la angiotensina (IECA), las tiazolidindionas (glitazonas) o los antagonistas del receptor de angiotensina-II, generalmente asociados con la adecuada medicacion hipolipidemiante (estatinas, fibratos) o antiobesidad (orlistat, sibutramina, rimonabant), incrementarian las adipocitocinas con propiedades anti-inflamatorias e insulino-sensibilizadoras (es decir, adiponectina o visfatina), mientras que reducirian aquellas pro-inflamatorias y trombogenicas (como leptina, factor de necrosis tumoral [TNF]-a, inhibidor del activador del plasminogeno tipo 1 [PAI-1]). Por tanto, estas medidas terapeuticas farmacologicas podrian tener un efecto beneficioso al disminuir la morbimortalidad y mejorar el pronostico de los pacientes que padecen dichas enfermedades, todas ellas relacionadas con un elevado riesgo cardiovascular.

Endothelial immunocytochemical expression of pituitary IL-1β and its relation to ACTH-positive cells is regulated by corticosterone in the male rat

HighlightsWe analyzed the relationship among the pituitary cells expressing IL‐1&bgr; and ACTH.Immunocytochemical expression of both polypeptides was studied in stress situations.IL‐1&bgr; was located in pituitary endothelial cells at the hypophyseal portal vessels.Pituitary endothelial expression of IL‐1&bgr; was independent of the treatment.Endothelial pituitary IL‐1&bgr; could regulate ACTH in a paracrine fashion. Abstract Interleukin‐1 beta (IL‐1&bgr;) is a cytokine linking the neuroendocrine system and metabolic homeostasis. We have previously demonstrated the relevance of IL‐1&bgr; for maintaining the pituitary ACTH‐producing cells by immuno‐blocking its effects in pituitary cultures. However, the morphological characteristics and the intimate relationship of the pituitary cells expressing IL‐1&bgr; and ACTH remain unknown. For determining pituitary variations of immunoreactivity for IL‐1&bgr; and its relation with ACTH‐positive cells under stress situations, we performed an immunohistochemical analysis of the expression of IL‐1&bgr; and ACTH in the pituitary gland of adult rats, in the absence or presence of corticosterone, by establishing different groups: untreated, sham‐operated, and bilaterally adrenalectomized animals. In the rats subjected to surgery, the glucocorticoid was administered on the same day of the intervention and on the third day post‐surgery. Interestingly, it was observed that IL‐1&bgr; was located in the pituitary endothelial cells at the hypophyseal portal vessels, regardless of the treatment schedule. When comparing the pituitary immunoreactive surface to IL‐1&bgr; expression without corticosterone, adrenalectomized animals displayed a significantly greater area than the sham‐operated animals. Corticosterone significantly inhibited the effect of adrenalectomy depending on the time interval it was administered. By in situ hybridization, IL‐1&bgr; mRNA expression was also correlated with immnunocytochemical expression of pituitary IL‐1&bgr;. Our results demonstrate that IL‐1&bgr; is a constitutive element in endothelial portal pituitary vessels and under stress experimental conditions IL‐1&bgr; increases its expression and its relation with ACTH‐positive cells, suggesting that IL‐1&bgr; could participate in an autocrine‐paracrine fashion thereby modulating the pituitary population of ACTH‐positive cells.

Relation among Aromatase P450 and Tumoral Growth in Human Prolactinomas

The pituitary gland is part of hypothalamic-pituitary–gonadal axis, which controls development, reproduction, and aging in humans and animals. In addition, the pituitary gland is regulated mainly by hormones and neurotransmitters released from the hypothalamus and by systemic hormones secreted by target glands. Aromatase P450, the enzyme responsible for the catabolization of aromatizable androgens to estrogens, is expressed in different parts of body, including the pituitary gland. Moreover, aromatase P450 is involved in sexual dimorphism where alteration in the level of aromatase can initiate a number of diseases in both genders. On the other hand, the direct actions of estrogens, mainly estradiol, are well known for stimulating prolactin release. Numerous studies have shown that changes in the levels of estrogens, among other factors, have been implicated in the genesis and development of prolactinoma. The pituitary gland can produce estradiol locally in several types of endocrine cells, and it is possible that aromatase could be responsible for the maintenance of the population of lactotroph cells and the modulation of the action of central or peripheral regulators. Aromatase overexpression due to inappropriate gene regulation has clinical effects such as the pathogenesis of prolactinomas. The present study reports on the synthesis of pituitary aromatase, its regulation by gonadal steroids, and the physiological roles of aromatase on pituitary endocrine cells. The involvement of aromatase in the pathogenesis of pituitary tumors, mainly prolactinomas, through the auto-paracrine production of estradiol is reviewed.

Pituitary Aromatase P450 May Be Involved in Maintenance of the Population of Luteinizing Hormone-Positive Pituitary Cells in Mice

As aromatase P450 is located in several pituitary cells, testosterone can be transformed into 17β-estradiol in the gland by the enzyme. The possible role of this transformation in pituitary function remains to be elucidated, but some evidence suggests a physiological and pathophysiological role for pituitary aromatase. To determine its relevance in the modulation of pituitary function, mainly associated with reproduction, luteinizing hormone (LH)-positive cells in the hypophysis of female and male aromatase knockout (ArKO) mice were studied. In all LH-positive cells, significant increases in the cellular (p < 0.01) and nuclear (p < 0.05) areas were found in the ArKO mice compared to the wild-type mice. In the ArKO mice, LH-positive cells were more abundant (p < 0.01); they were characterized by a stronger cytoplasmic reaction and the cells were more polygonal and exhibited more short, thick cytoplasmic prolongations than those in the wild-type mice. Moreover, LH-positive cells showed a greater proliferation rate in the ArKO mice compared to the wild-type mice (p < 0.01). These findings suggest that the local production of estradiol mediated by pituitary aromatase is necessary for the regulation of LH-positive gonadotropic cells, exerting an autoparacrine inhibitory regulation. These results could underlie the higher pituitary aromatase expression observed in male versus female mice. Similar effects were found in ArKO male and female mice, suggesting that in both sexes the effects of estrogens on maintenance of the LH-positive pituitary cell population could be related to the local aromatization of testosterone to estradiol inside the hypophysis. Therefore, aromatase could modulate pituitary LH-positive cells in males through local estradiol synthesis.

Prolactin system in the hippocampus

Among the more than 300 biological actions described for prolactin, its role in the neurogenic capacity of the hippocampus, which increases synaptogenesis and neuronal plasticity, consolidates memory and acts as a neuronal protector against excitotoxicity—effects mediated through its receptors are more recently known. The detection of prolactin in the hippocampus and its receptors, specifically in the Ammon’s horn and dentate gyrus, opened up a new field of study on the possible neuroprotective effect of hormones in a structure involved in learning and memory, as well as in emotional and behavioral processes. It is currently known, although controversial, that prolactin may be related to sex and age and that the hormone could be synthesized in the hippocampus itself. However, the regulatory mechanisms of changes in prolactin or in its hippocampal receptors still remain unknown. This review introduces the reader to general aspects concerning prolactin and its receptors and to what is currently known about the role prolactin plays in the brain and, in particular, in the hippocampus.