Expression of apoptosis-related proteins in involuting mammary gland of sow

The expression of apoptosis-related proteins: TGF-beta1 (local inductor), T GF-beta -receptor, Bar (promoter), Bcl-2 (inhibitor) and CPP-32 (executor o f apoptosis); the subcellular distribution of Bar; as well as the number an d morphology of apoptotic cells in low-, moderate-, and high-involuted mamm ary glands of sow (four to six days after weaning) were investigated. The i mmunohistochemical study demonstrated a statistically significant increase in the integrated optical density (IOD) of lobuloalveolar mammary tissue la belling with anti-Bax antibody from low- through moderate-, to high-involut ed glands. The immunoelectron microscopy revealed that Bar was localised in the cytosol, on the membranes of mitochondrium and rough endoplasmic retic ulum, in nuclear envelope pores, and over heterochromatin of mammary epithe lial cells. The increase in Bax/Bcl-2 ratio (2.3, 2.6 and 5.6 for low-, mod erate-, and high-involuted glands, respectively) indicated the increasing s usceptibility of mammary epithelial cells to apoptosis in the course of inv olution. The highest Bax/Bcl-2 ratio in high-involuted glands coincided wit h the highest expression of CPP-32 (caspase 3), TGF-beta1 and TGF-beta1 rec eptor. The number of apoptotic cells (simultaneous TUNEL and Hoechst 33342 staining) was 2.7, 3.4 and 3.8% for low-, moderate-, and high-involuted gla nds, respectively. The ultrastructural evaluation showed characteristic mor phological features of apoptosis such as: margination and condensation of c hromatin; pyknosis and fragmentation of the nucleus; and formation of apopt otic bodies. Phagocytosis of apoptotic cells by macrophages was also docume nted. The results of the present study suggest the involvement of Bax/Bcl-2 check-point in the regulation, CPP-32 in the execution, but TGF-beta1 in t he induction of apoptosis of mammary epithelial cells in the involuting mam mary gland of sow. (C) 2001 Elsevier Science Inc. Ah rights reserved.