Abstract
The role of the estrogen receptor beta (ERbeta) in the colon has received considerable interest, yet in vivo models are needed to better define its protective actions. In the present study, wild-type (WT), ERalpha, and ERbeta knockout (alphaERKO and betaERKO) mice were injected with azoxymethane, a colon chemical carcinogen. Fourteen weeks after azoxymethane exposure, the incidence of aberrant crypt foci (ACF) was assessed by methylene blue staining. betaERKO mice showed significantly higher incidence (P < 0.001) of ACF (15.0 +/- 2.5) compared with alphaERKO (3.4 +/- 1.0) and WT (4.6 +/- 1.0) mice. The colons in several betaERKO mice had increased thickness and loss of normal morphology. It has been reported that ERbeta plays a role in the maintenance of the colonic crypt architecture; this may explain the loss of crypt organization in the colonic epithelium of betaERKO mice. The presence of mucin-depleted foci (MDF) has been shown, both in humans and in rodents, as an early event in colon cancer. Therefore, to surpass the limitations with ACF scoring, we performed Alcian blue-neutral red staining to assess the presence of MDF. This assay allowed the assessment of precancerous lesions on all the betaERKO mice colons (38.3 +/- 4.0; P < 0.001), comparing to WT and alphaERKO mice (6.6 +/- 1.5 and 10.0 +/- 1.9, respectively), and served to confirm the ACF results. Together, these data support the use of MDF staining as a biomarker for precancerous lesions and the protective role of ERbeta in colon carcinogenesis.