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

Abstract

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.

Keywords: anterior pituitary; diethylstilbestrol; laminin; prolactinoma; rat.

Fig. 1.

Expression and localization of α chains in rat anterior pituitary during diethylstilbestrol (DES) treatment (normal: a, e, i, m, q, u; 4-week DES: b, f, j, n, r, v; 8-week DES: c, g, k, o, s, w; 12-week DES: d, h, l, p, t, x). The top panels show hematoxylin and eosin staining (H&E) in control and after 4, 8, and 12 weeks of DES treatment (a–d): (a: control) A sagittal section of the lateral wing of the gland shows capillaries lined by flat endothelial cells with spindle nuclei; (b: 4-week DES) Capillaries are tortuous, and the lumens are larger than in control; (c: 8-week DES) Capillaries are tortuous, and the lumens are larger than in 4-week DES; (d: 12-week DES) Capillaries are branched, and there is an extensive area of hemorrhage and hemosiderin deposition. In situ hybridization of the α1, α2, α3, α4, and α5 chains is shown in (e–h), (i–l), (m–p), (q–t), and (u–x), respectively. Positive signals for α chains are seen in cell cytoplasm (purple). Asterisk: capillary. Bars=100 μm (a–d) and 10 μm (e–x).

Fig. 2.

Immunohistochemistry of α chains in rat anterior pituitary during diethylstilbestrol (DES) treatment (normal: a, e, i; 4-week DES: b, f, j; 8-week DES: c, g, k; 12-week DES: d, h, l). Laminin immunofluorescence using anti-α1 chain (a–d), anti-α3 chain (e–h), and anti-α4 chain (i–l) antibodies is shown in green. Isolectin B4 was used as an endothelial cell marker (red) and DAPI was used a nuclear marker (blue). Arrowhead: α1 chain-immunopositive endothelial cells. Bar=10 μm.