Linear Percoll gradient centrifugation of rat anterior pituitary cells. A simple method for prolactin cell enrichment

Pituitary Remodeling Throughout Life: Are Resident Stem Cells Involved?

The pituitary gland has the primordial ability to dynamically adapt its cell composition to changing hormonal needs of the organism throughout life. During the first weeks after birth, an impressive growth and maturation phase is occurring in the gland during which the distinct hormonal cell populations expand. During pubertal growth and development, growth hormone (GH) levels need to peak which requires an adaptive enterprise in the GH-producing somatotrope population. At aging, pituitary function wanes which is associated with organismal decay including the somatopause in which GH levels drop. In addition to these key time points of life, the pituitary's endocrine cell landscape plastically adapts during specific (patho-)physiological conditions such as lactation (need for PRL) and stress (engagement of ACTH). Particular resilience is witnessed after physical injury in the (murine) gland, culminating in regeneration of destroyed cell populations. In many other tissues, adaptive and regenerative processes involve the local stem cells. Over the last 15 years, evidence has accumulated that the pituitary gland houses a resident stem cell compartment. Recent studies propose their involvement in at least some of the cell remodeling processes that occur in the postnatal pituitary but support is still fragmentary and not unequivocal. Many questions remain unsolved such as whether the stem cells are key players in the vivid neonatal growth phase and whether the decline in pituitary function at old age is associated with decreased stem cell fitness. Furthermore, the underlying molecular mechanisms of pituitary plasticity, in particular the stem cell-linked ones, are still largely unknown. Pituitary research heavily relies on transgenic in vivo mouse models. While having proven their value, answers to pituitary stem cell-focused questions may more diligently come from a novel powerful in vitro research model, termed organoids, which grow from pituitary stem cells and recapitulate stem cell phenotype and activation status. In this review, we describe pituitary plasticity conditions and summarize what is known on the involvement and phenotype of pituitary stem cells during these pituitary remodeling events.

Pituitary cell lines and their endocrine applications

The pituitary gland is an important component of the endocrine system, and together with the hypothalamus, exerts considerable influence over the functions of other endocrine glands. The hypothalamus either positively or negatively regulates hormonal productions in the pituitary through its release of various trophic hormones which act on specific cell types in the pituitary to secrete a variety of pituitary hormones that are important for growth and development, metabolism, reproductive and nervous system functions. The pituitary is divided into three sections-the anterior lobe which constitute the majority of the pituitary mass and is composed primarily of five hormone-producing cell types (thyrotropes, lactotropes, corticotropes, somatotropes and gonadotropes) each secreting thyrotropin, prolactin, ACTH, growth hormone and gonadotropins (FSH and LH) respectively. There is also a sixth cell type in the anterior lobe-the non-endocrine, agranular, folliculostellate cells. The intermediate lobe produces melanocyte-stimulating hormone and endorphins, whereas the posterior lobe secretes anti-diuretic hormone (vasopressin) and oxytocin. Representative cell lines of all the six cell types of the anterior pituitary have been established and have provided valuable information on genealogy of the various cell lineages, endocrine feedback control of hormone synthesis and secretions, intrapituitary interactions between the various cell types, as well as the role of specific transcription factors that determine each differentiated cell phenotype. In this review, we will discuss the morphology and function of the cell types that make up the anterior pituitary, and the characteristics of the various functional anterior pituitary cell systems that have been established to be representative of each anterior pituitary cell lineage.

Heterogeneous response of porcine gonadotrope subpopulations to gonadotropin releasing hormone (GnRH) during postnatal development

In previous papers, we showed the porcine gonadotrope population to be composed of three GtH subpopulations that can be separated by density using a continuous Percoll density gradient. We also demonstrated that these subpopulations exhibited different hormonal storage patterns and morphological features during porcine postnatal development at three representative ages: neonates (30 days), prepubers (5-6 months) and matures (16-18 months). In this work, we investigated whether these morphologically heterogeneous subpopulations are also functionally different. Thus, the effect of the hypothalamic gonadotropic hormone-releasing factor (GnRH) on these subpopulations was assessed in order to ascertain whether a mutual relationship between the reported morphological features, hormonal storage patterns and physiological response to the stimulation can be established. For this purpose, gonadotropin secretion was measured by cell immunoblot assay and hormonal content by scanning cytophotometry. Low-density gonadotropes (1.049 g/cm3), present in the three age groups studied, were mainly composed of bihormonal LH/FSH cells in neonates and monohormonal LH cells in prepubers and matures. GnRH stimulation was found to increase both LH and FSH secretion, as well as the intracellular content. These results indicate that GnRH can stimulate both the synthesis and release of both gonadotropins in this subpopulation. Middle-density gonadotropes (1.062 g/cm3), present in prepubers and matures only, were composed of bihormonal cells. GnRH stimulated the secretion of LH and FSH in prepubers and matures, but decreased hormonal contents except that of LH in prepubers. However, GnRH stimulation increased the proportion of immunoreactive gonadotropes (particularly monohormonal cells). Finally, high-density cells (1.087 g/cm3), present in neonates and prepubers only, were mostly composed of bihormonal LH/FSH gonadotropes, and exhibited low (neonates) or no response (prepubers) in terms of LH release and content when treated with GnRH. In conclusion, these results indicate that porcine gonadotrope subpopulations are morphologically and physiologically heterogeneous. The heterogeneity remained through porcine postnatal development, thus suggesting that all the subpopulations are physiologically relevant. However, the different hormonal storage patterns between subsets of the same density suggest age-related differences within each subpopulation due, at least in part, to the different physiological condition of the animals during development.

Application of a Percoll density gradient to separate and enrich porcine pituitary cell types

The application of a Percoll density gradient cell separation procedure to the pituitary gland of neonatal, prepubertal and mature pigs is described. After enzymatic dispersion, cell viability was 90% to 98% as determined by uptake of Trypan Blue. Recovery of dissociated cells after application of the gradient ranged from 80% to 95%. The dissociated cells were separated in several fractions that were characterized immunocytochemically using different antisera. We obtained highly enriched fractions of gonadotrope (gonadotropins), somatotrope (growth hormone) and lactotrope (prolactin) cells for each age. Concentration of the cell types (purity) was higher than 60% in the following fractions: 1) gonadotropin cells, fraction 15 (1.033 g/cc of density) from mature animals; 2) growth hormone cells, fraction 3 (1.121 g/cc of density) from neonatal animals and fraction 9 (1.087 g/cc) from prepubertal animals; and 3) prolactin cells, fraction 7 (1.094 g/cc) and 10 (1.082 g/cc) from neonatal animals and fraction 14 (1.051 g/cc) from mature pigs. In thyrotrope (thyroid-stimulating hormone) and corticotrope (adrenocorticotropin) cells, enriched fractions were also obtained, although the values of purity were lower (20% to 58%). In conclusion, the proposed cell separation and enrichment technique is suitable for the isolation, purification and examination of porcine pituitary cell types and subpopulations, and offers major advantages such as simplicity, rapidity, efficiency and reproducible results.

Cell surface antibodies in type 1 (insulin-dependent) diabetic patients. I. Presence of immunoglobulins M which bind to rat pituitary cells

A standardized method has been developed for the assay of cell surface antibodies in IgM- and IgG-fractions from human serum. Suspensions of adult rat islet B cells, islet non-B cells, and anterior pituitary cells were used as antigen source and a cell sorter as analyser of the immunoglobulin binding to individual cells. Assay conditions were selected wherein no surface antibodies were detected in 33 control subjects younger than 20 years. In 30% of Type 1 (insulin-dependent) diabetic patients, surface antibodies were measured with rat anterior pituitary cells as well as with rat islet B cells. Binding to pituitary cells occurred with IgM- and IgG-fractions and correlated positively with IgG binding to islet B cells. At onset of the disease, the prevalence of IgM-rat anterior pituitary cell surface antibodies was higher than that of IgG-rat anterior pituitary cell surface antibodies. Cell surface antibodies were also detected in first-degree relatives of Type 1 diabetic patients, but corresponded primarily to IgM-rat anterior pituitary cell surface antibodies. It is concluded that the development of Type 1 diabetes in subjects younger than 20 years is associated with the generation of both IgM and IgG cell surface antibodies. The IgM surface antibodies may result from stimulated production of polyreactive natural autoantibodies and could precede the switch to the formation of monoreactive IgG autoantibodies. The assay of IgM cell surface antibodies can be useful in studies on the sequence of immune events in diabetes and other autoimmune disease.