Folliculostellate cells of the pituitary

Follicular cells in pituitary neuroendocrine tumors

Follicular cells (FCs) are thought to be agranular, non-hormone-producing stellate cells distributed throughout the adenohypophysis, occasionally arranged around colloid-filled follicles, and thought to be more prominent in the vicinity of necrosis and apoptotic cells. A distinct but similar cell type, the folliculostellate cell (FSC), is a sustentacular cell that is negative for keratins and stains for S100, GFAP, and SOX10. While several studies have examined FSCs in pituitary neuroendocrine tumors (PitNETs), the distribution and derivation of FCs in these lesions is unclear. We examined the presence and distribution of FCs in 104 PitNETs obtained by trans-sphenoidal surgery, using immunohistochemistry for keratins as well as the full complement of immunohistochemical stains for tumor characterization. The tumors included 9 somatotroph, 5 mammosomatotroph, 7 lactotroph, 7 immature PIT1-lineage, 2 acidophil stem cell, 17 corticotroph, 53 gonadotroph, 2 null cell, and 2 unusual plurihormonal tumors. CK-positive FCs were only identified in gonadotroph PitNETs and were found in 12 (23%) of those tumors; all other tumor types were negative for FCs. FCs express keratins identified by CAM5.2, AE1/AE3, CK18, and CK19 antibodies. FCs were identified scattered singly among hormone-producing neuroendocrine cells, in small clusters of 3-5 cells and surrounding colloid-filled follicles, as well as linearly along intratumoral blood vessels. Sequential stains showed that FCs express nuclear SF1 and GATA3, transcription factors of gonadotrophs, and multiplex immunohistochemistry confirmed colocalization of SF1 in the nucleus of keratin-positive FCs. In this series, FCs were exclusively found in gonadotroph PitNETs and occurred in 23% of those tumors. Co-expression of gonadotroph transcription factors in FCs supports the concept of cellular plasticity and transformation of neoplastic hormone-producing neuroendocrine cells to FCs. Further studies are required to determine if and why gonadotrophs alone undergo this transformation, the function of these cells and whether they have prognostic value.

Seasonal plasticity of the pituitary pars intermedia of the one-humped camel (Camelus dromedarius)

The pituitary pars intermedia of Camelus dromedarius is well developed and completely surrounds the pars nervosa. Two major groups of cells are present: endocrine (ec) and glial-like cells (glc). The ec group is composed of three morphologically distinct cell types. Type I, or polyhedral light cells (LC-I) and type II, or polyhedral dark cells (DC-II), have secretory granules of heterogeneous electron density whose size ranges from 170 to 300nm. Type III cells are elongated with homogeneous electron-dense secretory granules of 80-200nm. The glc make up an organized network, form follicles in the centrolobular zones and are positive for vimentin and S-100β immunolabelling. The nerve fibres penetrating the lobe are numerous, and can be classified into two types according to the membrane bound vesicles found in their endings (ne). Ultrastructural quantitative analysis revealed significant variations in PI elements between winter and summer seasons (F=8.014, p=0.006). DC-II cells characterized by developed biosynthetic machinery and a large pool of secretory granules storage are increased with the ne in winter. However, LC-I cells showing frequent cytoplasmic degranulation are predominant with glc in summer. Thus, important cellular remodelling occurs in the dromedary PI that may depend upon, or perhaps anticipate, external living conditions.

Immunohistochemical and morphometric study of pituitary pars distalis folliculostellate cells of nonpregnant and pregnant viscachas

Pituitary folliculostellate cells (FSC) have several functions. Morphological, immunohistochemical and physiological characteristics of these cells have been reported for many mammalian species. There is little information, however, about the effect of pregnancy on FSC, particularly in wild animals. We conducted an immunohistochemical and morphometric study of the effect of pregnancy on FSC in viscacha, a seasonal breeder with a long gestation period. Immunohistochemistry and image analysis were used to measure the percentages of S-100-positive total, cellular, and colloidal areas and the number of FSC. In all groups studied, FSC were either isolated or arranged in small groups. These cells exhibited irregular nuclei, stellate shape, and cytoplasmic processes that delimited the follicles or contacted blood vessels. They expressed S-100 protein, which was localized both intracellularly (FSC) and extracellularly (follicular colloid). Some FSC were immunostained by anti-GFAP or anti-vimentin in the cytoplasm surrounding the nucleus and in the cytoplasmic processes, respectively. Morphometric parameters showed variation between nonpregnant and pregnant females. These variations were greatest during mid-pregnancy. We demonstrated that distribution of the FSC in pituitary pars distalis and expression of S-100 protein differ in nonpregnant and pregnant viscachas. Our findings suggest that FSC are involved in intrapituitary regulation of the hormone-secreting cells during pregnancy, probably by a paracrine mechanism.

Effect of the photoperiod and administration of melatonin on folliculostellate cells of the pituitary pars distalis of adult male viscacha (Lagostomus maximus maximus)

Numerous reports have shown the effect of photoperiod and melatonin administration on the different hormone secreting cell types in the pituitary pars distalis. The viscacha (Lagostomus maximus maximus) is a rodent with photoperiod-dependent seasonal reproduction. The aim of this study was to examine the effect of photoperiod seasonal variations and melatonin administration on the folliculostellate cells in pituitary pars distalis of viscacha. Immunohistochemistry and image analysis were used to measure the percentage of S-100-positive area (total, cellular and colloidal) and the number of folliculostellate cells. The S-100 protein was immunolocalized at intracellular (folliculostellate cells) and extracellular (follicular colloid) levels. The morphometric parameters analyzed exhibited seasonal variations with highest values in the summer (long photoperiod) and lowest values in the winter (short photoperiod). The administration of melatonin caused a significant decrease of immunostaining. Results suggest that the natural photoperiod might be the most important environmental signal causing the decrease in folliculostellate cells immunostaining observed in the winter. These findings agree with seasonal changes previously reported in endocrine cells and suggest that folliculostellate cells may be involved in the paracrine regulation of the secretory activity of pituitary pars distalis through S-100 protein production.

Percoll Density Gradient-Enriched Populations of Rat Pituitary Cells: Interleukin 6 Secretion, Proliferative Activity, and Nitric Oxide Synthase Expression

We used a discontinuous Percoll density gradient centrifugation to prepare enriched populations of prolactin (PRL), growth hormone (GH), and folliculo-stellate (FS) cells from rat anterior pituitaries in order to characterize these various cell populations. After cell dissociation and centrifugation, enriched PRL cells (55% of total cells as determined by immunocytochemistry [ICC] were present in Fraction 1 (Fr1) (density ([d]) = 1.059). Fr2 (d=1.071) had enriched S100-positive FS cells (31% of total cells), but enriched GH cell (60% of total cells) were present in Fr3 (d=1.094). Interleukin 6 (IL-6) was secreted mainly by enriched PRL cells in Fr1 (350 pg/mL/106 cells) and Fr2 (194 pg/mL/106 cells), and much less by the enriched GH cells inFr3 (16 pg/mL/106). Proliferation studies with combined 3H-thymidine and ICC for pituitary hormones showed that only the PRL cell had significant prolifereative activity. Immunostaining showed that immediately after separation, all three isoforms of nitric oxide synthase (NOS) were expressed anterior pituitary cells. After 3 d of culture, there was a marked increase in nuclear staining for neuronal NOS (nNOS) in all three fractions, whereas inducible NOS (iNOS) and endothelial NOS (eNOS) rexpression did not change significantly. These results indicate that: 1. Enriched populations of PRL, FS, and GH pituitary cells can be readily obtained with a rapid discontinuous percoll density separation procedure. 2. PRL cells from different fractions of the gradient show differenet proliferation rates and IL-6 secretion varied in different enriched cell populations. 3. Although all three isoforms of NOS were expressed in rat pituitary cells, nNOS is the prindipal isoform in anterior pituitary cells, and its expression was icreased after 3 d of culture of anterior pitutuitary cells.

Investigation of the Presence of Apotipoprotein E, G lycosaminoglycans, Basement Membrane Proteins, and Protease inhibitors in Senile interstitial Amyloid of the Pituitary

The aim of our study was to test whether local- or organ-limited interstitial amyloid of the pituitary is associated with the presence of glycosaminoglycans, basement membrane proteins, protease inhibitors, and apolipoprotein E (apo E), as previously observed in other amyloid syndromes. Serial sections from amyloidotic and nonamyloidotic autopsy pituitaries of patients age 85 yr and over were stained with Congo red, Alcian blue, and, applying immunohistochemistry, with antibodies directed against fibronectin, collagen IV, laminin, apo E, a(1)-antitrypsin and a(1)-antichymotrypsin. Interstitial amyloid was deposited in the immediate vicinity of capillaries and around the acini of the anterior lobe. Glycosaminoglycans were found in capillaries and around the acini of both nonamyloidotic and amyloidotic glands and they were also related spatially to amyloid deposits. Immunostaining of nonamyloidotic and amyloidotic glands demonstrated the presence of fibronectin, collagen IV, and laminin, which was related to basement membranes (fibronectin, collagen IV, and laminin), interstitium, and serum (fibronectin only). In amyloidotic glands, each basement membrane protein presented with an additional spatial relationship to amyloid deposits. Apo E was found in amyloidotic cases only within the amyloid deposits. The results are consistent with the presence of glycosaminoglycans, basement membrane proteins, and apo E in local interstitial amyloid deposits of the pituitary, as previously described in other amyloid syndromes, such as inflammatory related AA-amyloidosis or AB-amyloidosis related to Alzheimer's disease.

The Anterior Pituitary in Hemochromatosis

Pituitary changes in the case of a 69-year-old man with hemochromatosis are reported. The patient died of complications of hepatocellular carcinoma. The pituitary removed at autopsy was studied by histology, histochemistry, immunocytochemistry, electron microscopy, and X-ray diffraction. Preferential localization of iron deposits was demonstrated within gonadotrophs, which, at the ultrastructural level, displayed selective, severe cellular injury. X-ray diffraction revealed the deposition of iron-accumulated lysosomes. Iron storage also was noted in stellate cells. We consider selective injury of pituitary gonadotrophs to be the basis of hypogonadism in iron-overloaded states.

Amyloid Deposits in Pituitaries and Pituitary Adenomas: Immunohistochemistry and In Situ Hybridization

The patterns of deposition and immunoreactivity of interstitial amyloid were studied in 11 pituitary glands obtained at autopsy and 9 surgically resected pituitary adenomas using Congo red staining and a panel of antisera directed against 5 major amyloid fibril proteins and all pituitary hormones. The deposition pattern of amyloid in pituitary glands differed from that in adenomas but all amyloid deposits showed an immunostaining with anti-amyloid X-light chain. The remaining antisera were immunonegative. In situ hybridization using an oligodeoxyribonucleotide-probe complementary to the mRNA coding for the constant region of human X-light chain yielded no hybridization signals in the pituitaries or pituitary adenomas, excluding local synthesis and secretion of immunoglobulins. Since no case studied suffered from generalized AX-amyloidosis and adsorption of immunoglobulins to the unknown amyloid fribril protein of the pituitary seems to be unlikely, crossreaction of the polyclonal antisera with an undefined antigen is probable. The similar immunostaining properties of amyloid deposits in "normal" pituitaries and pituitary adenomas suggest they both originate from the same precursor protein.

S-100 protein immunopositivity in human nontumorous hypophyses and pituitary adenomas

The presence, distribution, and morphological appearance of S-100 protein-immunoreactive cells in the human hypophysis were studied by immunocytochemistry. One hundred and twelve nonadenomatous pituitaries from fetuses to adults and pituitaries affected by several lesions including metastases, acute infarcts, and lymphocytic hypophysitis, as well as 115 pituitary adenomas were examined.S-100 protein immunoreactivity was detected in neurohy-pophyseal pituicytes and stellate cells of the pars distalis from 5 months following birth. In adults, S-100 protein-immunopositive cells displayed a preferential topographical association with growth hormone-, follicle-stimulating hormone-, luteinizing hormone-, and alpha-sub-unit-immunoreactive cells and with capillary walls. Colloid-containing follicles were mainly lined by hormone-containing cells, although scattered S-100 protein-immunoreactive processes or cell bodies were also observed forming their walls.No major changes in S-100 protein-immunoreactive cells were observed in the pituitary parenchyma bordering metastatic, inflammatory, necrotic, or adenomatous tissues. Eighteen of 115 pituitary adenomas contained a variable number of S-100 protein-immunoreactive cells. No preferential association of these cells with any type of pituitary adenoma was found.We propose that S-100 protein expression in the nontumorous adenohypophysis and pituitary adenomas may constitute a dynamic process and that S-100 protein-positive cells may constitute a heterogeneous cell population composed of pure, fully differentiated stellate cells and of transdifferentiated follicular cells.