Prostatic intraepithelial neoplasia in genetically engineered mice

Abstract

Several mouse models of human prostate cancer were studied to identify and characterize potential precursor lesions containing foci of atypical epithelial cells. These lesions exhibit a sequence of changes suggesting progressive evolution toward malignancy. Based on these observations, a grading system is proposed to classify prostatic intraepithelial neoplasia (PIN) in genetically engineered mice (GEM). Four grades of GEM PIN are proposed based on their architecture, differentiation pattern, and degree of cytological atypia. PIN I lesions have one or two layers of atypical cells. PIN II has two or more layers of atypical cells. PIN III has large, pleomorphic nuclei with prominent nucleoli and the cells tend to involve the entire lumen with expansion of the duct outlines. PIN IV lesions contain atypical cells that fill the lumen and bulge focally into, and frequently compromise, the fibromuscular sheath. Within the same cohorts, the lower grade PINs first appear earlier than the higher grades. Morphometric and immunohistochemical analyses confirm progressive change. Although the malignant potential of PIN IV in mice has not been proven, GEM PIN is similar to human PIN. This PIN classification system is a first step toward a systematic evaluation of the biological potential of these lesions in GEM.

Figure 1.

Whole mounts showing examples of dissected, unfixed, and unstained coagulating glands from a normal prostate from a 23-week-old GEM Nkx3.1+/− × PTEN+/− male (A) and a 23-week-old GEM Nkx3.1−/− × PTEN+/− male with nodular foci of PIN (B). Note the dark masses in B (arrows) that show the areas of cellular proliferation. The bulging profiles of the foci are consistent with GEM PIN III or IV. This type of visualization provides information about the number and volume of the lesions.

Figure 2.

A panel of H&E-stained slides from a Nkx3.1−/− × PTEN+/− mouse with low-magnification images (A, C, E, and G) and higher magnification images (B, D, F, and H) illustrating the histological and cytological patterns of PIN I (A and B), PIN II (C and D), PIN III (E and F), and PIN IV (G and H). These images show the details of the criteria for each grade described in the text. Scale bars document the magnification (G and H).

Figure 3.

A panel of images from Nkx3.1−/− × PTEN+/− mice illustrating the immunohistochemical distribution of SMA (A), laminin (B), CK8 (C), CK14 (D), E-cadherin (E), and androgen receptors (F) in normal and PIN. The SMA (A) and laminin (B) are discontinuous or missing (A, arrows) around PIN IV lesions. The CK8 (C) is highly expressed in PIN III and PIN IV (C) with a displacement of the stain from the basolateral membranes in normal cell to a diffuse cytoplasmic stain in PIN III and IV. E-cadherin is also up-regulated in the higher grade PIN (E). The basal cells are identified by anti-CK14 (D). Note that they are increased in PIN lesions. Androgen receptors are also prominent in PIN (F).

Figure 4.

Graphs representing the results of the morphometric analysis of DNA content (A) and nuclear size (B). The DNA content is normalized for relative area using Bins formula. Note that normal, PIN I, and PIN II have relatively similar nuclear size and DNA content. Also note that the relative DNA increases with the grade of PIN (A). The nuclear size also increases with the PIN grade (B). This analysis confirms the visual impressions and suggests that the grading system is consistent with the changes in the nuclear size and DNA content.

Figure 5.

Histograms representing the relative proportions of diffuse atypical hyperplasia (AH) and PIN I to PIN IV in a single cohort of 43 Nkx3.1−/− × PTEN+/− males sacrificed at different ages. Note the relative increases in the higher grade PIN with age.