Mammary gland involution is a physiological process in which the entire organ is remodeled through the process of apoptosis. Apoptosis of secretory alveolar cells is initiated at the time of weaning, followed by the collapse and disappearance of the entire lobuloalveolar compartment. While apoptotic figures were rare in mammary epithelium of lactating mice, their number increased after weaning and reached a maximum on day 3 of involution. Active cell death continued until day 5 after weaning and only little parenchyma remained on day 8, when remodeling of the gland was completed. Bax mRNA levels increased during the first day of involution independent of the presence or absence of p53. Bax protein was detected in an increasing number of cells after weaning, peaking at day 3 and decreasing thereafter. Low levels of bcl-x mRNA and protein were present during lactation, followed by a sharp increase during the first 2 days of involution. The bcl-xS splice variant of bcl-x can promote cell death, and bcl-xL has a protective function in cell culture. The ratio of bcl-xS versus bcl-xL remained stable in the virgin, pregnant and lactating gland. However, during the first 2 days of involution, bcl-xS expression increased six-fold more than bcl-xL. To further evaluate the role of Bcl-xS which was less abundant in the mammary cells than Bcl-xL, cotransfection studies were performed in cell culture. They confirmed that Bcl-xS protein can facilitate apoptosis even when Bcl-xL is present in excess. These findings point to a significant role for Bax and Bcl-xS in the regulation of apoptosis of secretory alveolar cells during involution.

Atherogenic lipoproteins stimulate O2- formation and induction of apoptosis in HUVECs and RA, and may thereby influence the pathogenesis of atherosclerosis.

1 The physiological role of the angiotensin II AT2 receptor subtype is not fully characterized. We studied whether AT2 receptor could antagonize AT1 mediated superoxide formation in endothelial cells. 2 In quiescent human umbilical vein endothelial cells (HUVEC) superoxide formation was measured after long-term incubation (6 h) with angiotensin II in the presence or absence of its receptor blocker candesartan (AT1) or PD123319 (AT2) using the cytochrome c assay. In separate experiments, the e ects of AT2 mediated e ects on activities of cellular phosphates including the src homology 2 domain containing phosphatases (SHP-1) was studied. 3 The basal superoxide formation (0.19+0.03 nmol superoxide mg protein 71 min 71 ) in HUVEC was increased by 37.1% after exposure to angiotensin II (100 nM,) which was due to an activation of a NAD(P)H oxidase. This was abolished by candesartan (1 mM) as well as the tyrosine kinase inhibitor genistein. In contrast, blockade of AT2 receptors by PD123319 enhanced the superoxide formation by 73.7% in intact cells. Stimulation of AT2 went along with an increased activity of tyrosine phosphatases in total cell lysates (29.8%) and, in particular, a marked stimulation of src homology 2 domain containing phosphatases (SHP-1, by 293.4%). The tyrosine phosphatase inhibitor vanadate, in turn, prevented the AT2 mediated e ects on superoxide formation. The expression of both angiotensin II receptor subtypes AT1 and AT2 was con®rmed by RT ± PCR analysis. 4 It is concluded that AT2 functionally antagonizes the AT1 induced endothelial superoxide formation by a pathway involving tyrosine phosphatases.

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