Endocrine/paracrine control of pituitary cell proliferation and its involvement in pituitary tumorigenesis

Angiotensin II and Angiotensin Receptors 1 and 2-Multifunctional System in Cells Biology, What Do We Know?

For years, the renin-angiotensin system (RAS) has been perceived as a system whose role is to primarily modulate the functioning of the cardiovascular system. Years of research into the role of RAS have provided the necessary data to confirm that the role of RAS is very complex and not limited to the cardiovascular system. The presence of individual elements of the renin-angiotensin (RA) system allows to control many processes, ranging from the memorization to pro-cancer processes. Maintaining the proportions between the individual axes of the RA system allows for achieving a balance, often called homeostasis. Thus, any disturbance in the expression or activity of individual RAS elements leads to pathophysiological processes.

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.

Locally produced estrogen through aromatization might enhance tissue expression of pituitary tumor transforming gene and fibroblast growth factor 2 in growth hormone-secreting adenomas

Aromatase, a key enzyme in local estrogen synthesis, is expressed in different pituitary tumors including growth hormone (GH)-secreting adenomas. We aimed to evaluate aromatase, estrogen receptor α (ERα), estrogen receptor β (ERβ), pituitary tumor transforming gene (PTTG), and fibroblast growth factor 2 (FGF2) expressions in GH-secreting adenomas, and investigate their correlation with clinical, pathologic, and radiologic parameters. This cross-sectional study was conducted in a tertiary center in Turkey. Protein expressions were determined via immunohistochemical staining in ex vivo tumor samples of 62 patients with acromegaly and ten normal pituitary tissues. Concordantly increased aromatase, PTTG, and FGF2 expressions were detected in the tumor samples as compared with controls (p < 0.001 for all). None of the tumors expressed ERα while ERβ was detected only in mixed somatotroph adenomas. Aromatase, ERβ, PTTG expressions were not significantly different between patients with and without remission (p > 0.05 for all). FGF2 expression was significantly higher in patients without postoperative and late remission (p = 0.002 and p = 0.012, respectively), with sphenoid bone invasion, optic chiasm compression, and somatostatin analog resistance (p = 0.005, p = 0.033, and p = 0.013, respectively). Aromatase, PTTG and FGF2 expressions were positively correlated with each other (r = 0,311, p = 0.008 for aromatase, FGF2; r = 0.380, p = 0.001 for aromatase, PTTG; r = 0.400, p = 0.001 for FGF2, PTTG). PTTG-mediated FGF2 upregulation is associated with more aggressive tumor features in patients with acromegaly. Also, locally produced estrogen through aromatization might have a role in this phenomenon.

Unbiased stereological estimation of the rat fetal pituitary volume and of the total number and volume of TSH cells after maternal dexamethasone application

Glucocorticoids have an inhibitory influence on proliferation activity of the pituitary cells while stimulating apoptosis. Therefore, it was hypothesized that the synthetic glucocorticoid, dexamethasone (DX), has an inhibitory influence on the number of thyroid-stimulating hormone (TSH) cells during fetal development. The effects of maternal administration of DX on stereological parameters of TSH cells, and TSH serum concentration were investigated in 21-day-old rat fetuses. On day 16 of pregnancy, the experimental dams received 1.0 mg DX/kg b.w. subcutaneously, followed by 0.5 mg DX/kg b.w./day on days 17 and 18 of gestation. The control gravid females received the same volume of saline vehicle. TSH cells were stained immunocytochemically by the peroxidase-antiperoxidase (PAP) method. The fetal pituitary volumes were estimated using Cavalieri's principle. A physical disector counting technique in combination with the fractionator sampling method was used for estimation of pituitary TSH cell number. Cell and nuclear volumes were measured with a planar rotator. Maternal DX application was found to cause a significant decrease of pituitary volume and number of TSH cells per pituitary in 21-day-old fetuses in comparison with the control fetuses. TSH cell number expressed per body weight unit declined significantly after maternal DX administration. These results indicate an inhibitory DX influence on proliferative activity of precursors and likely differentiated TSH cells and increased apoptotic prevalence. The histological appearance, volume of TSH cells and TSH serum concentration suggest intensive synthetic activity in TSH cells of DX exposed fetuses.

Mutation in the neural cell adhesion molecule interferes with the differentiation of anterior pituitary secretory cells

The neural cell adhesion molecule (NCAM) and its polysialylated isoform (PSA-NCAM) have been shown to influence the proliferation, differentiation and survival of different cell types. Here, we report the pattern of expression of NCAM and PSA-NCAM in the anterior lobe (AL) of the pituitary gland of the adult mouse. We demonstrate that the majority of cells express NCAM, while PSA-NCAM is retained mostly on corticotropes. Analysis of bromodeoxyuridine (BrdU) incorporation shows that the presence of PSA-NCAM on corticotropes is not related to proliferation but most likely to their functional properties. We subsequently analyzed defects induced by NCAM deficiency in adult NCAM knockout mice. In these mice, all secretory cell types in the AL are present and their distribution within the gland is similar to that in wild-type mice. However, proliferation of AL cells is significantly increased. In particular, more BrdU-positive cells are detected among somatotropes and mammotropes in NCAM-deficient mice. In addition, the percentages of secretory cells are changed: somatotropes are more numerous while the number of corticotropes is reduced. These data demonstrate the involvement of NCAM in the proper generation and/or maintenance of the different cell populations in the AL and suggest the importance of PSA in corticotrope functioning.