No abstract

Extracellular matrix (ECM) is essential in tissue physiology and pathologic conditions such as tumorigenesis. It affects tumor cell behavior, proliferation, and metastasis. Pituitary adenomas differ in their clinical characteristics, including ECM deposition, and we recently reported that the characteristics of collagen-producing cells differed between control human anterior pituitary gland and pituitary adenomas. ECM deposition is not defined solely by production; degradation and maintenance are also important. Tissue inhibitors of metalloproteinases (TIMPs) help maintain ECM by inhibiting degradation caused by matrix metalloproteases. The present study attempted to characterize TIMP-expressing cells in the human anterior pituitary. Specimens of human pituitary adenomas and control pituitary were obtained during surgery, and in situ hybridization for TIMP1, TIMP2, TIMP3, and TIMP4, followed by immunohistochemistry, was used to characterize TIMP-expressing cells. TIMP expression exhibited a distinct pattern in the human anterior pituitary. Azan staining showed that fibrous matrix deposition varied among pituitary adenomas and that the area of fibrosis was associated with the number and number of types of TIMP3-expressing cells. These results suggest that TIMPs are important in the maintenance of ECM in human pituitary and that TIMP expressions are altered in fibrosis associated with pituitary adenoma.

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.

Midkine (MK) belongs to a family of secreted heparin-binding growth factors and is highly expressed in various tissues during development. MK has multiple functions, such as regulation of cell proliferation, migration, survival and differentiation. We recently reported that MK mRNA is strongly expressed in the developing rat pituitary gland. In the adult pituitary, however, expression of MK and its receptor and the characteristics of the cells that produce them, have not been determined. Therefore, in this study, we investigate whether MK and its receptor, protein tyrosine phosphatase receptor-type Z (Ptprz1), are present in the adult rat pituitary. In situ hybridization, real-time reverse transcription-PCR and immunoblotting were performed to assess MK and Ptprz1 expression. We also characterize MK- and Ptprz1-expressing cells by double-staining with in situ hybridization and immunohistochemical techniques for each pituitary hormone or S100 protein [a marker of folliculostellate (FS) cells]. MK-expressing cells were located in the anterior and posterior lobes but not in the intermediate lobe. Double-staining and immunoblotting revealed that MK mRNA and protein were only expressed in FS cells in the anterior pituitary. Regarding Ptprz1 expression, Ptprz1 mRNA was detected in adrenocorticotropic hormone (ACTH) cells and growth hormone (GH) cells but not in prolactin cells, thyroid-stimulating hormone cells, luteinizing hormone cells, or FS cells. These findings suggest that MK produced in FS cells acts locally on ACTH cells and GH cells via Ptprz1 in the adult rat anterior pituitary.

The extracellular matrix (ECM) is important in creating cellular environments in tissues. Recent studies have demonstrated that ECM components are localized in anterior pituitary cells and affect cell activity. Thus, clarifying the mechanism responsible for ECM maintenance would improve understanding of gland function. Tissue inhibitors of metalloproteinases (TIMPs) are endogenous inhibitors of matrix metalloproteinases and participate in ECM degradation. In this study, we investigated whether cells expressing TIMPs are present in rat anterior pituitary gland. Reverse transcription polymerase chain reaction was used to analyze expression of the TIMP family (TIMP1-4), and cells producing TIMPs in the gland were identified by using in situ hybridization. Expression of TIMP1, TIMP2, and TIMP3 mRNAs was detected, and the TIMP-expressing cells were located in the gland. The TIMP-expressing cells were also investigated by means of double-staining with in situ hybridization and immunohistochemical techniques. Double-staining revealed that TIMP1 mRNA was expressed in folliculostellate cells. TIMP2 mRNA was detected in folliculostellate cells, prolactin cells, and thyroid-stimulating hormone cells. TIMP3 mRNA was identified in endothelial cells, pericytes, novel desmin-immunopositive perivascular cells, and folliculostellate cells. These findings indicate that TIMP1-, TIMP2-, and TIMP3-expressing cells are present in rat anterior pituitary gland and that they are involved in maintaining ECM components.