Changes in fine structure of pericytes and novel desmin-immunopositive perivascular cells during postnatal development in rat anterior pituitary gland

Alteration of Extracellular Matrix Components in the Anterior Pituitary Gland of Neonatal Rats Induced by a Maternal Bisphenol A Diet during Pregnancy

The extracellular matrix (ECM) plays crucial roles in the anterior pituitary gland via the mechanism of cell-ECM interaction. Since bisphenol A (BPA), a well-known endocrine disruptor, can cross through the placenta from mother to fetus and bind with estrogen receptors, cell populations in the neonatal anterior pituitary gland could be the target cells affected by this chemical. The present study treated maternal rats with 5000 µg/kg body weight of BPA daily throughout the pregnancy period and then investigated the changes in ECM-producing cells, i.e., pericytes and folliculostellate (FS) cells, including their ECM production in the neonatal anterior pituitary at Day 1. We found that pericytes and their collagen synthesis reduced, consistent with the increase in the number of FS cells that expressed several ECM regulators-matrix metalloproteinase (MMP) 9 and the tissue inhibitors of metalloproteinase (TIMP) family. The relative MMP9/TIMP1 ratio was extremely high, indicating that the control of ECM homeostasis was unbalanced. Moreover, transmission electron microscopy showed the unorganized cell cluster in the BPA-treated group. This study revealed that although the mother received BPA at the "no observed adverse effect" level, alterations in ECM-producing cells as well as collagen and the related ECM balancing genes occurred in the neonatal anterior pituitary gland.

Insight into the Characteristics of Novel Desmin-Immunopositive Perivascular Cells of the Anterior Pituitary Gland Using Transmission and Focused Ion Beam Scanning Electron Microscopy

Recently, another new cell type was found in the perivascular space called a novel desmin-immunopositive perivascular (DIP) cell. However, the differences between this novel cell type and other nonhormone-producing cells have not been clarified. Therefore, we introduced several microscopic techniques to gain insight into the morphological characteristics of this novel DIP cell. We succeeded in identifying novel DIP cells under light microscopy using desmin immunocryosection, combining resin embedding blocks and immunoelectron microscopy. In conventional transmission electron microscopy, folliculostellate cells, capsular fibroblasts, macrophages, and pericytes presented a flat cisternae of rough endoplasmic reticulum, whereas those of novel DIP cells had a dilated pattern. The number of novel DIP cells was greatest in the intact rats, though nearly disappeared under prolactinoma conditions. Additionally, focused ion beam scanning electron microscopy showed that these novel DIP cells had multidirectional processes and some processes reached the capillary, but these processes did not tightly wrap the vessel, as is the case with pericytes. Interestingly, we found that the rough endoplasmic reticulum was globular and dispersed throughout the cytoplasmic processes after three-dimensional reconstruction. This study clearly confirms that novel DIP cells are a new cell type in the rat anterior pituitary gland, with unique characteristics.

Characteristics of pericytes in diethylstilbestrol (DES)-induced pituitary prolactinoma in rats

Prolactinomas are the most common tumor of the human pituitary. They result in excessive prolactin secretion and important changes in the vasculature. Pericytes are perivascular cells associated with capillaries and have crucial roles in physiological and pathological neovascularization. We previously reported that pericytes produce type I and III collagens in the anterior pituitary of adult rats. In addition, pituitary pericytes contained well-developed cell organelles and actively synthesized collagens during early postnatal development. However, the characteristics of pericytes in pituitary tumors are unclear. In this study, we used diethylstilbestrol (DES)-treated rats as an animal model of prolactinoma. Using five common pericyte markers, more pericytes were observed in rats treated with DES for 3 months (prolactinoma) compared to the control. Transmission electron microscopy revealed that attached and semidetached pericytes exhibited active cell organelles. Moreover, we identified pericyte migration between capillaries. Although the fine structure of pituitary pericytes was active in prolactinoma, expressions of type I and III collagen mRNAs were greatly diminished. In sum, the characteristics and functions of pericytes were altered in pituitary tumors. This study is the first to clarify fine structural changes of pericytes in rat prolactinomas and improves our understanding of the function of pericytes under pathological conditions.

Desmin expression profile in reactive astrocytes in the 3-nitropropionic acid-lesioned striatum of rat: Characterization and comparison with glial fibrillary acidic protein and nestin

Desmin, a muscle-specific, type-III intermediate-filament protein, is reportedly expressed in astrocytes in the central nervous system. These cells become reactive astrocytes in response to brain injuries. To elucidate whether desmin is involved in this process, we examined the spatiotemporal expression profiles of desmin and their relationship with two astroglial intermediate filaments, glial fibrillary acidic protein (GFAP) and nestin, in the striatum of rats treated with the mitochondrial toxin 3-nitropropionic acid (3-NP). Weak, constitutive immunoreactivity for desmin was observed in astrocytes generally, and in reactive astrocytes in the peri-lesional area, its expression increased in parallel with that of GFAP over 3 d post-lesion and was maintained until at least day 28. Desmin, GFAP, and nestin showed characteristic time-dependent expression patterns in reactive astrocytes forming the astroglial scar; delayed and long-lasting induction of desmin and GFAP, and rapid but transient induction of nestin. In the lesion core, desmin was expressed in two categories of perivascular cells: nestin-negative and nestin-positive. These findings show that desmin, together with GFAP and nestin, is a dynamic component of intermediate filaments in activated astroglia, which may account for the dynamic structural changes seen in these cells in response to brain injuries.

Folliculostellate cell interacts with pericyte via TGFβ2 in rat anterior pituitary

The anterior pituitary gland comprises five types of endocrine cells plus non-endocrine cells including folliculostellate cells, endothelial cells, and capillary mural cells (pericytes). In addition to being controlled by the hypothalamic-pituitary-target organ axis, the functions of these cells are likely regulated by local cell and extracellular matrix (ECM) interactions. However, these complex interactions are not fully understood. We investigated folliculostellate cell-mediated cell-to-cell interaction. Using S100β-GFP transgenic rats, which express GFP in folliculostellate cells, we designed a three-dimensional cell culture to examine the effects of folliculostellate cells. Interestingly, removal of folliculostellate cells reduced collagen synthesis (Col1a1 and Col3a1). Because pericytes are important collagen-producing cells in the gland, we stained for desmin (a pericyte marker). Removal of folliculostellate cells resulted in fewer desmin-positive pericytes and less desmin mRNA. We then attempted to identify the factor mediating folliculostellate cell-pericyte interaction. RT-PCR and in situ hybridization revealed that the important profibrotic factor transforming growth factor beta-2 (TGFβ2) was specifically expressed in folliculostellate cells and that TGFβ receptor II was expressed in pericytes, endothelial cells, and parenchymal cells. Immunocytochemistry showed that TGFβ2 induced SMAD2 nuclear translocation in pericytes. TGFβ2 increased collagen synthesis in a dose-dependent manner. This action was completely blocked by TGFβ receptor I inhibitor (SB431542). Diminished collagen synthesis in folliculostellate cell-deficient cell aggregates was partially recovered by TGFβ2. TGFβ2-mediated folliculostellate cell-pericyte interaction appears to be essential for collagen synthesis in rat anterior pituitary. This finding sheds new light on local cell-ECM interactions in the gland.

Maintenance of the Extracellular Matrix in Rat Anterior Pituitary Gland: Identification of Cells Expressing Tissue Inhibitors of Metalloproteinases

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.

Histochemical Analysis of Laminin α Chains in Diethylstilbestrol-Induced Prolactinoma in Rats

Laminin, a major basement membrane component, is important in structural support and cell proliferation and differentiation. Its 19 isoforms are assemblies of α, β, and γ chains, and the α chains (α1-5) determine the isoform characteristics. Although our previous studies showed alterations in α chain expressions during anterior pituitary development, their expressions in pituitary tumors yet to be determined. The present study used a rat model of diethylstilbestrol (DES)-induced prolactinoma to examine α chain expressions during prolactinoma tumorigenesis (0–12 weeks of DES treatment) by in situ hybridization and immunohistochemistry. mRNA of α1, α3, and α4 chains was detected in control and after 4 weeks of DES treatment. These expressions were undetectable after 8 weeks of DES treatment and in prolactinoma (12 weeks of DES treatment). Immunohistochemistry showed that the α1 chain was localized in some anterior pituitary cells in control and after 4 weeks of treatment and in endothelial cells after 8 weeks of treatment. The α3 and α4 chains were expressed in endothelial cells, and immunoreactivity and the number of immunopositive cells decreased during DES treatment. These findings suggest that alteration of laminin α chains is related to abnormal cell proliferation and neovascularization during development of DES-induced prolactinoma.

Changes in laminin chain expression in pre- and postnatal rat pituitary gland

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 α, three β, and three γ chains (eg, laminin 121 is α1, β2, and γ1). 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 α5 chain was expressed during early pituitary development (embryonic day 12.5–15.5). Expression of α1 and α4 chains was noted in vasculature cells at embryonic day 19.5, but later diminished. The α1 chain was re-expressed in parenchymal cells of anterior lobe from postnatal day 10 (P10), while the α4 chain was present in vasculature cells from P30. The α2 and α3 chains were transiently expressed in vasculature cells and anterior lobe, respectively, only at P30. Widespread distribution of β and γ 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.