The anterior pituitary gland comprises 5 types of hormone-producing cells and non-endocrine cells, such as folliculostellate (FS) cells. The cells form a lobular structure surrounded by extracellular matrix (ECM) but are not randomly distributed in each lobule; hormone-producing cells have affinities for specific cell types (topographic affinity), and FS cells form a homotypic meshwork. To determine whether this cell and ECM organization can be reproduced in vitro, we developed a 3-dimensional (3D) model that utilizes hanging drop cell culture. We found that the topographic affinities of hormone-producing cells were indeed maintained (ie, GH to ACTH cells, GH to TSH cells, PRL to LH/FSH cells). Fine structures in hormone-producing cells retained their normal appearance. In addition, FS cells displayed well-developed cytoplasmic protrusions, which interconnected with adjacent FS cells to form a 3D meshwork. In addition, reassembly of gap junctions and pseudofollicles among FS cells was observed in cell aggregates. Major ECM components—collagens and laminin—were deposited and distributed around the cells. In sum, the dissociated anterior pituitary cells largely maintained their in vivo anterior pituitary architectures. This culture system appears to be a powerful experimental tool for detailed analysis of anterior pituitary cell organization.

Laminin is a key component of the basement membrane and is involved in the structural scaffold and in cell proliferation and differentiation. Research has identified 19 laminin isoforms, which are assemblies of α, β, and γ chains (eg, the α1, β1, and γ1 chains form the laminin 111 isoform). Although laminin is known to be present in the anterior pituitary, the specific laminin isoforms have not been identified. This study used molecular biological and histochemical techniques—namely, RT-PCR, immunohistochemistry, and in situ hybridization—to identify the laminin isoforms and laminin-producing cells in rat anterior pituitary. RT-PCR showed that laminin α1, α3, and α4 genes were expressed in anterior pituitary. Immunohistochemistry revealed laminin α1 in gonadotrophs and laminin α4 in almost all vascular endothelial cells. Laminin α3 was seen in a subset of vascular endothelial cells. We then performed in situ hybridization to localize β and γ chains in these cells and found that laminin β1, β2, and γ1 were expressed in gonadotrophs and that laminin β1 and γ1 were expressed in endothelial cells. In conclusion, we identified gonadotroph-type (laminin 111 and 121) and vascular-type (laminin 411 and 311) laminin isoforms in rat anterior pituitary.

Cell–matrix interaction is required for tissue development. Laminin, a major constituent of the basement membrane, is important for structural support and as a ligand in tissue development. Laminin has 19 isoforms, which are determined by combinational assembly of five , three , and three chains (eg, laminin 121 is 1, 2, and 1). However, no report has identified the laminin isoforms expressed during pituitary development. We used in situ hybridization to investigate all laminin chains expressed during rat anterior pituitary development. The 5 chain was expressed during early pituitary development (embryonic day 12.5–15.5). Expression of 1 and 4 chains was noted in vasculature cells at embryonic day 19.5, but later diminished. The 1 chain was re-expressed in parenchymal cells of anterior lobe from postnatal day 10 (P10), while the 4 chain was present in vasculature cells from P30. The 2 and 3 chains were transiently expressed in vasculature cells and anterior lobe, respectively, only at P30. Widespread distribution of and chains was also observed during development. These findings suggest that numerous laminin isoforms are involved in anterior pituitary gland development and that alteration of the expression pattern is required for proper development of the gland.

Proteoglycans are components of the extracellular matrix and comprise a specific core protein substituted with covalently linked glycosaminoglycan chains. Small leucine-rich proteoglycans (SLRPs) are a major family of proteoglycans and have key roles as potent effectors in cellular signaling pathways. Research during the last two decades has shown that SLRPs regulate biological functions in many tissues such as skin, tendon, kidney, liver, and heart. However, little is known of the expression of SLRPs, or the characteristics of the cells that produce them, in the anterior pituitary gland. Therefore, we have determined whether SLRPs are present in rat anterior pituitary gland. We have used real-time reverse transcription with the polymerase chain reaction to analyze the expression of SLRP genes and have identified the cells that produce SLRPs by using in situ hybridization with a digoxigenin-labeled cRNA probe. We have clearly detected the mRNA expression of SLRP genes, and cells expressing decorin, biglycan, fibromodulin, lumican, proline/arginine-rich end leucine-rich repeat protein (PRELP), and osteoglycin are located in the anterior pituitary gland. We have also investigated the possible double-staining of SLRP mRNA and pituitary hormones, S100 protein (a marker of folliculostellate cells), desmin (a marker of capillary pericytes), and isolectin B4 (a marker of endothelial cells). Decorin, biglycan, fibromodulin, lumican, PRELP, and osteoglycin mRNA have been identified in S100-protein-positive and desmin-positive cells. Thus, we conclude that folliculostellate cells and pericytes produce SLRPs in rat anterior pituitary gland.

The anterior pituitary gland is organized tissue comprising hormone-producing cells and folliculostellate (FS) cells. FS cells interconnect to form a meshwork, and their cytoplasmic processes are anchored by a basement membrane containing laminin. Recently, we developed a three-dimensional (3D) cell culture that reproduces this FS cell architecture. In this study of the novel function of FS cells, we used transgenic rats that express green fluorescent protein in FS cells for the 3D culture. Anterior pituitary cells were cultured with different proportions of FS cells (0%, 5%, 10%, and 20%). Anterior pituitary cells containing 5–20% FS cells formed round/oval cell aggregates, whereas amorphous cell aggregates were formed in the absence of FS cells. Interestingly, immunohistochemistry showed laminin-immunopositive cells instead of extracellular laminin deposition in FS cell-deficient cell aggregates. Double-immunostaining revealed that these laminin-immunopositive cells were gonadotrophs. Laminin mRNA expression did not differ in relation to the presence or absence of FS cells. When anterior pituitary cells with no FS cells were cultured with FS cell-conditioned medium, the proportion of laminin-immunopositive cells was lower than in control. These results suggest that a humoral factor from FS cells is required for laminin release from gonadotrophs.