Cell death by apoptosis during involution of the lactating breast in mice and rats

Truncation of the beta-catenin binding domain of E-cadherin precedes epithelial apoptosis during prostate and mammary involution

A potential target of hormone action during prostate and mammary involution is the intercellular junction of adjacent secretory epithelium. This is supported by the long-standing observation that one of the first visible stages of prostate and mammary involution is the disruption of interepithelial adhesion prior to the onset of apoptosis. In a previous study addressing this aspect of involution, we acquired compelling evidence indicating that the disruption of E-cadherin-dependent adhesion initiates apoptotic programs during prostate and mammary involution. In cultured prostate and mammary epithelial cells, inhibition of E-cadherin-dependent aggregation resulted in cell death following apoptotic stimuli. Loss of cell-cell adhesion in the nonaggregated population appeared to result from the rapid truncation within the cytosolic domain of the mature, 120-kDa species of E-cadherin (E-cad(120)). Immunoprecipitations from cell culture and involuting mammary gland demonstrated that this truncation removed the beta-catenin binding domain from the cytoplasmic tail of E-cadherin, resulting in a non-beta-catenin binding, membrane-bound 97-kDa species (E-cad(97)) and a free cytoplasmic 35-kDa form (E-cad(35)) that is bound to beta-catenin. Examination of E-cadherin expression and cellular distribution during prostate and mammary involution revealed a dramatic reduction in junctional membrane staining that correlated with a similar reduction in E-cad(120) and accumulation of E-cad(97) and E-cad(35). The observation that E-cadherin was truncated during involution suggested that hormone depletion activated the same apoptotic pathway in vivo as observed in vitro. Based on these findings, we hypothesize that truncation of E-cadherin results in the loss of beta-catenin binding and cellular dissociation that may signal epithelial apoptosis during prostate and mammary involution. Thus, E-cadherin may be central to homeostatic regulation in these tissues by coordinating adhesion-dependent survival and dissociation-induced apoptosis.

Apoptosis in vascular endothelial cells caused by serum deprivation, oxidative stress and transforming growth factor-beta

Vascular endothelial cell apoptosis has previously been shown to play a role in the pathogenesis of hypertension-induced vessel deletion and damage. In the present in vitro study we analyse several possible relevant causative factors of vascular endothelial cell apoptosis, namely, serum deprivation and nutrient depletion, oxidative stress in the forms of hypoxia, hyperoxia or free radical damage, and altered levels of transforming growth factor-beta1 (TGF-beta1) protein. An established cell line, bovine aortic endothelial cells (BAEC), was maintained in complete growth medium (RPMI-1640 plus 15% fetal calf serum and antibiotics, abbreviated as RPMI) in 25cm2 flasks or in 12-well plates on glass coverslips. Confluent but actively-growing cultures were treated with either hypoxia (PO2 of RPMI = 50mmHg), serum-free media (SFM), SFM plus hypoxia, hyperoxia (PO2 of RPMI = 450mmHg), hydrogen peroxide (H2O2, 1mM) in SFM, or TGF-beta1 protein (10ng/mL) in SFM. Appropriate control cultures were used. BAEC were collected 48h or 72h after all treatments except for TGF-beta1 and H2O2 treatments that were collected at 16-18h. Cell death was assessed using morphological characteristics or in situ end labeling (ISEL), cell proliferation assessed using proliferating cell nuclear antigen (PCNA), and TGF-beta1 expression assessed using transcript levels or immunohistochemistry. All treatments significantly increased levels of apoptosis over control cultures (P<0.05), and decreased levels of cell proliferation. Treatment with TGF-beta1 protein or SFM plus hypoxia induced greatest levels of apoptosis. TGF-beta1 protein and transcript levels were decreased in treated cultures, results suggesting that a paracrine source of TGF-beta1 protein would be needed as a cause of endothelial cell apoptosis in viva. Future therapies against inappropriate vessel deletion in disease states may use the known gene-driven nature of apoptosis to modify this sort of cell death in endothelial cells.

Influence of microenvironment on mammary epithelial cell survival in primary culture

Mammary epithelial cells cultured on Engelbreth-Holm-Swarm (EHS) matrix form multicellular structures termed mammospheres, in which cells and matrix become arranged around a central luminal space. In the presence of lactogenic hormones, cells within mammospheres become polarized, form tight intercellular junctions, and secrete milk proteins vectorially into the luminal space. This study examined the mechanism of lumen formation. Histological examination of developing mammospheres showed that cavitation was associated spatially and temporally with the appearance of fragmented nuclear material in apoptotic bodies, and with the presence of cells positively labeled by terminal deoxynucleotide transferase-mediated deoxyuridine nick end-labeling (TUNEL). Analysis of [(32)P]-deoxynucleotide end-labeled genomic DNA by electrophoresis and autoradiography showed DNA laddering indicative of apoptosis. A transient increase in laddering coincided with both lumen formation and the presence of TUNEL-positive cells. Lumen formation, DNA laddering, and detection of TUNEL-positive cells were all accelerated when matrix composition was altered. They were also impaired coordinately when caspase inhibitor was present during the first two days of culture. Therefore, lumen formation in mammosphere cultures is due to selective apoptosis of centrally located cells. Mammosphere cavitation was accompanied by redistribution of matrix constituents to the mammosphere periphery. Western blotting and Western ligand blotting of culture medium showed that lumen formation was also associated with a transient increase in insulin-like growth factor binding protein-5 (IGFBP5), a factor implicated in mammary apoptosis in vivo. We propose that epithelial cell survival during mammosphere development is induced selectively through stabilization by basement membrane constituents, which may act directly on the epithelial cell or confer protection against autocrine apoptotic factors.

Suppression of epithelial apoptosis and delayed mammary gland involution in mice with a conditional knockout of Stat3

Mammary gland involution is characterized by extensive apoptosis of the epithelial cells. At the onset of involution, Stat3 is specifically activated. To address the function of this signaling molecule in mammary epithelial apoptosis, we have generated a conditional knockout of Stat3 using the Cre-lox recombination system. Following weaning, a decrease in apoptosis and a dramatic delay of involution occurred in Stat3 null mammary tissue. Involution is normally associated with a significant increase in IGFBP-5 levels. This was observed in control glands, but not in the absence of Stat3. IGFBP-5 has been suggested to induce apoptosis by sequestering IGF-1 to casein micelles, thereby inhibiting its survival function. Our findings suggest that IGFBP-5 is a direct or indirect target for Stat3 and its upregulation is essential to normal involution. No marked differences were seen in the regulation of Stat5, Bcl-x(L), or Bax in the absence of Stat3. Precocious activation of Stat1 and increases in levels of p53 and p21 occurred and may act as compensatory mechanisms for the eventual initiation of involution observed in Stat3 null mammary glands. This is the first demonstration of the importance of a Stat factor in signaling the initiation of physiological apoptosis in vivo.

Changing myoepithelial cell distribution during regeneration of rat parotid glands

The distribution of the myoepithelial cells during regeneration of the rat parotid gland after atrophy induced by one week of parotid duct ligation was investigated by immunohistochemistry for actin and transmission electron microscopy (TEM). Immunohistochemically, residual ducts were surrounded by actin-positive cells when clips were removed from the duct. Three days later, most of the newly formed acini originating from the residual ducts were also embraced by actin-positive cells. After 10 days, actin-positivity tended to be seen as dots around acini that decreased in number day by day. On day 21 actin-positive cells mainly surrounded intercalated ducts with only a few positive reactions identified at the acinar periphery. Electron microscopically, residual ducts and newly formed acini were peripherally embraced by myoepithelial cells before day 5. After day 7, shift of myoepithelial cells from the periphery of acini to the duct-acinar junctional region was identified. Then few myoepithelial cells were identified at the periphery of acini. These observations indicate that myoepithelial cells migrate from the acinar periphery to the duct-acinar junctional region during rat parotid regeneration, and that such behaviour is closely related to that seen during rat parotid development.

Effects of secretion removal on bovine mammary gland function following an extended milk stasis

The objective of this study was to determine whether lactation function could be reinitiated after a period of extended milk stasis. Involution was induced by milk stasis in lactating Holstein cows for a period of 11 d. On d 11, one side of the mammary gland was milked twice daily for 3 d. The contralateral side remained unmilked for the 14-d experimental period. Cows were slaughtered, and mammary tissue was collected from both udder halves for further analysis. Mammary secretion volume was partially restored in the milked udder half, but reestablished milk yields were variable among cows. A partial recovery of lactation function was further indicated by elevated levels of lactose and protein profiles resembling milk in mammary secretions from the milked glands. Lactose and protein profiles from the unmilked glands were similar to those of glands undergoing involution. Lactoferrin levels were elevated in secretions from the milked and unmilked udder halves. Casein and lactoferrin synthesis by mammary explants and beta-casein and lactoferrin mRNA abundance in mammary tissues corresponded to protein profiles from milked and unmilked mammary secretions. alpha-Lactalbumin mRNA was variable but was more abundant in the milked glands compared with the unmilked glands. Lectin fluorescence microscopy for soybean agglutinin preferentially stained the apical surface of the mammary epithelial cells from the milked glands. Staining was absent in the unmilked glands and suggested resumption of lactation function in all such milked glands. These results suggest that mammary involution can be partially reversible after 11 d of milk stasis.

Structural elements common to mitosis and apoptosis

Both mitotic and apoptotic cells display hypercondensation of the chromatin and loss of the nuclear envelope (Lazebnik et al., 1993). Herein, we describe a third similarity between the two processes. We have observed, initially in apoptotic cells of the PC-12 lineage clusters of 40-60 (approximately 50) nm vesicles adjoined by a minor contingent of tubule vesicular elements of 100-200 nm which are indistinguishable from their vesicular counterparts in mitotic PC-12 cells. The clusters of approximately 50 nm vesicles were subsequently observed in all studied rat tissue cells in apoptosis (plasma cells and macrophages, secretory epithelial cells from pancreatic acini, ventral lobe of prostate and mammary gland). Clusters of approximately 50 nm vesicles comparable to those of the PC-12 cells were found in HeLa cells treated with human alfa TNF, in WEHI-3 cells exposed to VM 26 (a teneposide) (Sesso et al., 1997) and in HL-60 cells treated with thapsigargin. PC-12 and HeLa cells affixed to coverslips were double labelled and examined with the fluorescence microscope to reveal simultaneously the disposition of the chromatin with Hoechst stain and the distribution of the fluorescence of Golgi or of Golgi-associated proteins. A common pattern of fluorescence was observed in a minor proportion of apoptotic cells using three different antibodies used. The label frequently appeared as finely dispersed granules in the cytoplasm. In some apoptotic cells, relatively coarse granules were observed. This pattern of label distribution is compatible with the disposition of vesicular clusters we have encountered in apoptotic PC-12 cells sectioned serially or semi serially. In such sections of both mitotic and apoptotic PC-12 cells, we noticed that the conglomerates of 50 nm vesicles were frequently associated with cisternae of the rough ER. Vesicles of similar size were also noted pinching off from the extremities of Golgi cisternae reduced in size. These cisternae diminish in length and width when they are in the process of disassembling at the very beginning of mitosis and in apoptosis.

Regulation of osteoblast levels during bone healing

OBJECTIVE

To confirm the occurrence of programmed cell death of osteoblasts during bone healing and to evaluate the role of interleukin-1beta (IL-1beta) in regulating osteoblast concentration.

STUDY DESIGN

Electron microscopic study of the response of rats to a controlled bone injury, and a randomized controlled study of the effect of IL-1beta administered continuously for three days.

METHODS

A standardized defect (1.1 millimeter in diameter, 0.5 millimeter deep) was created unilaterally on the anteromedial surface of the tibia. In some animals, the injury site was recovered five days after operation and processed for ultrastructural evaluation of osteoblasts in the callus. In another group, IL-1beta was delivered to the bone defect using micro-osmotic pumps (0.5 nanograms/hour); control rats received vehicle only. The bones were recovered one to fourteen days after injury, and concentrations of proliferating cells, osteoblasts, and apoptotic bodies were determined. The amount of callus that formed in the defect was measured.

RESULTS

Osteoblasts in the callus exhibited ultrastructural changes characteristic of cells undergoing apoptosis, including condensation of chromatin, membrane blebbing, formation of apoptotic bodies, and phagocytosis by nearby osteoblasts. Addition of IL-1beta significantly increased the number of osteoblasts at the injury site and significantly decreased the number of apoptotic bodies in relation to the number of osteoblasts. The amount of callus in the bone defect was not affected by IL-1beta treatment.

CONCLUSION

The role of programmed cell death of osteoblasts as a normal concomitant of bone healing was confirmed. Evidence was found suggesting that IL-1beta mediated the appearance and disappearance of osteoblasts, possibly by affecting the rates of differentiation and apoptosis, respectively. Understanding these mechanisms conceivably could lead to the ability to control osteoblast levels at an injury site.

Apoptosis, proliferation, and sex hormone receptors in superficial parts of human endometrium at the end of the secretory phase

Apoptosis with one regulator, Bcl-2, and proliferation with the marker Ki-67 were studied in 75 endometrial biopsies representing superficial parts of endometrium from 35 regularly menstruating women premenstrually and menstrually. Hormonal withdrawal was studied in serum samples and potentiated in epithelium by the decreasing 17beta-estradiol and progesterone receptor scores 4 days premenstrually. The apoptotic index increased 2 days before the onset of menstruation and peaked on the second menstrual day. The high apoptotic index together with low proliferation in endometrial epithelium at the end of the menstrual cycle are similar to the involution process seen in other hormone-dependent organs. In stroma, the apoptotic index increased later, at the onset of menstruation, and the increase was lower than that in epithelium. The Ki-67 index increased during the last 3 days of the secretory phase, parallel with an increasing progesterone receptor score and decreasing Bcl-2 staining, and peaked at the onset of menstruation. The findings in stroma concur with high proliferation at the end of the menstrual cycle and high cell turnover during menstruation, suggesting the participation of stroma in the renewal process of endometrium.

Mammary involution in dairy animals

Lifetime milk production is maximized when dairy cows are pregnant during approximately 70% of each lactation. Between lactations, a nonlactating period is necessary for optimal milk production in the succeeding lactation. With cessation of milking, alveolar structure is largely maintained and little or no loss of cells occurs. However, increased apoptosis and cell proliferation, relative to that in lactating glands during the same stage of gestation, suggest that a nonlactating period serves to promote cell turnover prior to the next lactation. Even in the absence of pregnancy, mammary involution in dairy animals occurs at a slower rate than in rodents; alveolar structure is maintained for several weeks and lactation can be reinitiated after four weeks or more of involution. Although apoptosis appears to be initiated within a similar time frame to that in rodents, the maximum proportion of apoptotic epithelial cells appears to be lower than in rodents, and apoptosis may be accompanied by an initial increase in cell proliferation. The ability to manipulate apoptosis and cell proliferation during the nonlactating period and during lactation is expected to provide enormous benefits to the dairy industry.

Regulation of p53 and its targets during involution of the mammary gland

Post-lactational involution of the mammary gland provides a system in which to study the expression and function of genes that regulate apoptosis in the context of a normal tissue. The functions of the p53 tumor suppressor gene have been extensively studied as a mediator of apoptosis in response to DNA damage, but its regulation in normal physiologic processes has been poorly characterized. Expression of p53 mRNA was shown to be among the first genes to be induced in mammary tissue following weaning of neonates. Although involution proceeds in the absence of a functional p53 gene, it is delayed compared to normal individuals. Therefore, involution can be viewed as biphasic with initial responses being sensitive to p53, whereas secondary responses being p53-independent. These observations can be exploited to determine the subset of genes that are p53-responsive and that mediate the effects of p53 in normal mammary tissue.

Transcription factor activities and gene expression during mouse mammary gland involution

Maintenance of mammary epithelial differentiation and milk production during lactation is a consequence of milk removal and the presence of lactogenic hormones, particularly glucocorticoids, insulin and prolactin. After weaning the fall in lactogenic hormones and milk stasis lead to involution, a process that is mainly characterized by three events: (i) downregulation of milk protein gene expression, (ii) loss of epithelial cells by apoptosis and, (iii) tissue remodeling and preparation of the gland for a new pregnancy. Each of these processes is likely to depend on the activity of specific sets of transcription factors in the mammary epithelium and stroma that ensure the timely and spatially coordinated expression of critical gene products such as mediators of apoptosis (e.g., caspase-1 and regulators of tissue remodeling events (e.g., matrix metalloproteinases). Here we describe signal transduction events such as activation of protein kinase A and JNK and changes in the activity of several transcription factors including Stat5, Stat3, NF1, Oct-1, and AP-1 during the early and late phases of mammary gland involution. We discuss their possible role in regulating and coordinating involution with emphasis on the apoptotic process of involution.

Clearance: the last and often forgotten stage of apoptosis

Engulfment by a phagocyte is the final common event in the life of most apoptotic cells. Phagocytosis of apoptotic bodies prior to their lysis prevents the release of potentially toxic or immunogenic intracellular contents and activates an anti-inflammatory response, at least in macrophages. We are beginning to understand the mechanisms by which macrophages and other phagocytes recognize apoptotic cells in vitro, but we are a long way from determining their relative importance in vivo. The involuting mammary gland undergoes massive cell loss by apoptosis. The dying alveolar epithelial cells can be shed into the lumen or can be phagocytosed by macrophages and viable epithelial cells. Yet we know virtually nothing about the mechanisms mediating recognition and uptake in the mammary gland. It is likely that clearance of apoptotic cells is critical to normal remodeling of the gland in preparation for the next wave of lactation. The mammary gland, therefore, provides an ideal organ in which to study the mechanisms and consequences of apoptotic cell clearance in vivo.

Control of milk secretion and apoptosis during mammary involution

Lactation depends on regular suckling or milking of the mammary gland. Without this stimulus, milk secretion stops and mammary involution is induced. Involution caused by abrupt cessation of milk removal is characterized by de-differentiation and apoptosis of mammary epithelial cells, the extent and time course of the latter varying between species. Apoptosis is inhibited and milk secretion is restored by re-suckling, if milk stasis is of short duration. Mammary involution and apoptosis also occur during weaning, even in concurrently-pregnant animals when the interval between lactations is restricted, suggesting that tissue remodeling is essential for subsequent lactation. Declining milk production in ruminants after peak lactation is also associated with, and probably results from, net cell loss by apoptosis. Involution and apoptosis are controlled by changes in systemic galactopoietic hormone levels, and by intra-mammary mechanisms responsive to milk removal. Milk stasis precipitated by litter removal or cessation of milking may involve intra-mammary control related to physical distension of the epithelium. Local control of apoptosis in rodents during weaning, and after peak lactation in dairy animals, may be due to the actions of milk-borne survival factors or their inhibitors, and can be manipulated by frequency of milk removal.

Adhesion-mediated signaling in the regulation of mammary epithelial cell survival

Tissue architecture in multicellular organisms is maintained through adhesive interactions between cells and their neighbors, and between cells and the underlying extracellular matrix. These interactions are important in the dynamic regulation of tissue organization as well as the control of cell proliferation, differentiation and apoptosis. The ultimate goal of this regulation is to promote cell growth and differentiation only when the cell is in the correct location, and to delete cells that have become displaced from their proper environment. It therefore plays an important role in development and tissue remodeling. In this review we consider the molecular mechanisms by which cell-matrix interactions contribute to cell survival, and discuss their role in mammary gland development and function.

Growth factors, apoptosis, and survival of mammary epithelial cells

Programmed cell death (apoptosis) occurs regularly during normal growth and development of the mammary gland. One of the most dramatic examples of apoptosis is evident during the remodeling of the breast that accompanies postlactational involution. Transgenic mouse models have demonstrated that overexpression of polypeptides such as transforming growth factor alpha (TGFalpha) and insulin like growth factor I (IGF-I) can block this remodeling, suggesting that these growth factors may be acting as survival factors for the mammary epithelium. In contrast, transgenic mice that overexpress the growth inhibitor transforming growth factor beta (TGF-beta) show increased apoptosis in the mammary epithelium throughout mammary development, suggestive of a mechanism working to counterbalance the survival factors. Experiments with mammary epithelial cell lines cultured in vitro have confirmed that these growth factors can indeed regulate apoptosis and survival in mammary epithelial cells; EGF, IGF-I, and basic fibroblast growth factor (bFGF) act as survival factors for mammary epithelial cells, while TGF-beta induces their death. In breast cancer, cytotoxic drugs and hormone ablation increase the expression of TGF-beta, which may function to induce cell death by either paracrine or autocrine mechanisms. Lastly, although it has very limited expression in the breast, TNFalpha has been shown to be effective in the rapid, direct induction of cell death in breast cancer cell lines. Together, these studies describe a complex dynamic pattern of cell death-inducing and survival factors that promote the development of the mature mammary gland and that rapidly remodel the tissue after lactation.

Inhibition of microvascular endothelial apoptosis in tissue explants by serum albumin

Plasma factors appear to inhibit endothelial cell (EC) apoptosis in vivo so that flow influences microvascular form. The identity of these factors has not, however, been established. Earlier, we reported that apoptosis in isolated, serum-deprived human EC is inhibited by albumin (Alb). Here, we demonstrate likely biological relevance of this to vascular remodelling in experiments with tissue explants. Rat skin explants were incubated in medium M199 with or without serum, bovine Alb, or human Alb. EC in paraffin sections of explants were labelled by lectin histochemistry and the relative proportion of apoptotic was EC determined. Apoptosis was confirmed by transmission electron microscopy and terminal deoxynucleotidyl transferase labelling. Serum-free culture induced EC apoptosis (P < 0.02) and this was strongly inhibited by Alb at physiological concentrations (P < 0.01). This was not a nonspecific protein effect, as mercaptoethanol denaturation destroyed the activity and ovalbumin was not protective. Also, protection was not due to serum contaminants, as recombinant human Alb had activity identical to that of native material. The dose response was identical for all Alb preparations tested, with maximal activity at physiological concentrations. Protection was not limited to rat tissue as similar results were obtained with human gingival explants. These data support a role for Alb as a plasma antiapoptotic factor for EC in tissues.

Comparative effect of chlormadinone acetate and diethylstilbestrol as promoters in mammary tumorigenesis of rats irradiated with gamma-rays during lactation

The purpose of this study was to determine the promotional role of estrogen and progestin in the development of radiation-induced mammary tumors. To eliminate the effects of endogenous ovarian hormones on tumor promotion, all rats were ovariectomized immediately after the initiation by irradiation with 2.6 Gy gamma-rays at day 21 of lactation, and were divided into 3 groups. For the control experiment, rats were implanted with a cholesterol pellet 1 month after the irradiation. Only one rat developed a fibroadenoma (4.3% mammary tumor incidence) during the 1 year period of the implantation. In the other two groups, chlormadinone acetate (CMA) to increase progestin level or diethylstilbestrol (DES) to increase estrogenic activity were administered, respectively, as tumor promoters for 1 year. Treatment with CMA did not significantly increase the incidence of mammary tumors as compared with the controls. However, administration of DES resulted in a significantly higher mammary tumor incidence (79.3%) than control treatment. Compared with cholesterol administration, DES treatment caused an increase in prolactin concentration in serum (5-fold), and reduction of estradiol-17beta concentration (22% of control). These results suggest that DES ia a potent effective promoter for tumorigenesis of radiation-initiated mammary cells, but CMA is not. DES may act directly on the irradiated mammary cells by binding to ER, and indirectly by stimulating prolactin secretion from the pituitary glands.

Vascular endothelial growth factor regulates endothelial cell survival through the phosphatidylinositol 3'-kinase/Akt signal transduction pathway. Requirement for Flk-1/KDR activation

Vascular endothelial growth factor (VEGF) has been found to have various functions on endothelial cells, the most prominent of which is the induction of proliferation and differentiation. In this report we demonstrate that VEGF or a mutant, selectively binding to the Flk-1/KDR receptor, displayed high levels of survival activity, whereas Flt-1-specific ligands failed to promote survival of serum-starved primary human endothelial cells. This activity was blocked by the phosphatidylinositol 3'-kinase (PI3-kinase)-specific inhibitors wortmannin and LY294002. Endothelial cells cultured in the presence of VEGF and the Flk-1/KDR-selective VEGF mutant induced phosphorylation of the serine-threonine kinase Akt in a PI3-kinase-dependent manner. Akt activation was not detected in response to stimulation with placenta growth factor or an Flt-1-selective VEGF mutant. Furthermore, a constitutively active Akt was sufficient to promote survival of serum-starved endothelial cells in transient transfection experiments. In contrast, overexpression of a dominant-negative form of Akt blocked the survival effect of VEGF. These findings identify the Flk-1/KDR receptor and the PI3-kinase/Akt signal transduction pathway as crucial elements in the processes leading to endothelial cell survival induced by VEGF. Inhibition of apoptosis may represent a major aspect of the regulatory activity of VEGF on the vascular endothelium.

Fibrinolytic proteins in apoptotic human umbilical vein endothelial cells

Endothelial cells express fibrinolytic proteins including: urokinase (u-PA) and tissue type (t-PA) plasminogen activators, type-1 (PAI-1) and 2 (PAI-2) plasminogen activator inhibitors, and u-PA receptor (u-PAR). Apoptotic endothelial cells detach, potentially forming both local and circulating microthrombi in vivo. In this article, apoptotic human umbilical vein endothelium was obtained by serum starvation and compared with nonapoptotic cells rescued from death with fresh medium containing serum. Antigen levels for t-PA, PAI-1, PAI-2, and u-PAR were reduced greatly in apoptosis (p< 0.05). In contrast, u-PA levels were similar in apoptotic as compared with rescued cells (p<0.05). Radioactive amino acids were used to determine absolute levels of protein synthesis and degradation in these cells. Reduced antigen levels likely were due to proteolysis as there was 98% total protein degradation and very little protein synthesis in apoptotic endothelial cells. Also, u-PA levels in apoptotic endothelial cells were not affected by the protein synthesis inhibitor cycloheximide. Endothelial cells in inflammatory sites are exposed to cytokines, which increase both apoptosis and u-PA levels. Data from this article support the idea that maintained u-PA levels in apoptotic endothelium may protect from micro-thrombosis in inflammatory sites as well as in the circulation.

Proliferation and apoptosis of fibroblasts and smooth muscle cells in rat uterine cervix throughout gestation and the effect of the antiprogesterone onapristone

OBJECTIVE

The purpose of this study was to determine the relative percentages of apoptosis and proliferation in fibroblasts and cervical smooth muscles throughout gestation and the effect of an antiprogesterone on these processes.

STUDY DESIGN

Rats were studied at days 5, 15, 18, and 21 and immediately postpartum (day 22). Apoptosis and proliferation as detected by specific immunohistochemistry quantitative morphometric analysis was performed. Onapristone, an antiprogesterone, was used to study effects of hormonal change on these processes in 16- and 19-day timed-pregnant rats.

RESULTS

Proliferation of fibroblasts and smooth muscle cells was highest in early pregnancy and decreased progressively, whereas apoptosis increased progressively in later pregnancy. Onapristone inhibited apoptosis.

CONCLUSION

Changes in cervical cellular turnover are initiated early in gestation and are under hormonal influence. Antiprogesterone inhibits cell death at days 16 and 19 of gestation.

Lactation status influences expression of CCAAT/enhancer binding protein isoform mRNA in the mouse mammary gland

The CCAAT/enhancer binding proteins (C/EBPs) are a highly conserved family of DNA binding proteins implicated in the transcriptional control of genes involved in cell growth and differentiation in a variety of tissues. The expression of C/EBP-alpha, beta, and delta mRNA in the normal mouse mammary gland was investigated during pregnancy, lactation, and involution via Northern blotting and in situ hybridization. Mammary gland C/EBP-alpha mRNA is detectable at low levels during pregnancy and postlactational involution. C/EBP-beta mRNA levels are elevated during pregnancy, decline slightly in midlactation, and are induced within 48 hours of the onset of involution. C/EBP-delta mRNA content is low throughout pregnancy and lactation, but increases dramatically (>100-fold) within 12 hours after the onset of postlactational involution. In situ hybridization demonstrates that mammary epithelial cells are responsible for the expression of C/EBP-delta mRNA during involution. In contrast to mammary gland, C/EBP-alpha is the predominate isoform expressed in liver with relatively low expression of C/EBP-beta and C/EBP-delta mRNA. Liver C/EBP isoform mRNA levels are unaffected by lactation status. These results demonstrate the tissue-specific regulation of C/EBPs. The pronounced sequential induction of C/EBP-delta and C/EBP-beta during postlactational involution is consistent with a role for C/EBPs in the regulation of mammary epithelial cell apoptosis.

Compensatory nutrition-directed mammary cell proliferation and lactation in rats

The proper use of a time-dependent and controlled nutrition regimen during the hormone-sensitive growth phase before first parturition can significantly affect mammary growth and subsequent lactation performance. The objective of the present study was to determine if a compensatory nutrition regimen improves lactation performance by affecting proliferation and apoptosis of mammary epithelial cells. Forty female rats (7 weeks of age, average weight 148 g) were assigned to either (1) control, free access to diet or (2) stair-step compensatory nutrition regimen, an alternating 3-4-week schedule beginning with an energy-restricted diet (31.2% restriction) for 3 weeks, followed by the control diet for 4 weeks. Estimated milk yield was greater (P < 0.05) on day 15 of lactation in the compensatory nutrition group than in the control group. Mammary cell proliferation values were 1.4- and 2.7-fold greater in mammary tissue from the compensatory group during pregnant and early lactating stages respectively, compared with those from the control group. Ornithine decarboxylase (EC 4.1.17) mRNA was 24% higher (P < 0.05) in mammary tissues of rats from the compensatory nutrition group during pregnancy than in those from the control group. These results indicate that the compensatory nutrition regimen imposed during the peripubertal growth phase stimulated mammary epithelial cell proliferation and improved lactation performance.

Biochemical and molecular mechanisms regulating apoptosis

In eukaryotes, the regulation of tissue cell numbers is a critical homeostatic objective that is achieved through tight control of apoptosis, mitosis and differentiation. While much is known about the genetic regulation of cell growth and differentiation, the molecular basis of apoptosis is less well understood. Genes involved in both cell proliferation and apoptosis reflect the role of some stimuli in both of these processes, the cell response depending on the overall cellular milieu. Recent research has given fascinating insights into the complex genetic and molecular mechanisms regulating apoptosis. A picture is emerging of the initiation in certain cells, after an apoptotic trigger, of sequential gene expression and specific signal transduction cascades that guide cells along the cell death pathway. Changes in gene expression precede the better known biochemical and morphological changes of apoptosis. It seems possible that, as a result of increased understanding of the cellular events preceding cell death, apoptosis may become more amenable to manipulation by appropriate drug- and gene-based therapies.

Variation of bcl-2 expression in breast ducts and lobules in relation to plasma progesterone levels: overexpression and absence of variation in fibroadenomas

Some women with benign breast disease eventually develop breast cancer. The mammary gland undergoes tissue remodelling according to hormonal influences, involving a balance between quiescence, proliferation, and mechanisms of cell death. Proliferation and/or apoptotic events could therefore be investigated to help understand the mechanisms of benign lesion formation and identify mastopathies with a poor prognosis. bcl-2 expression was analysed by immunohistochemistry in 75 benign mastopathies. Protein levels were quantitated with an image analyser in various epithelial structures on frozen sections, including adenoses, fibroadenomas, ductal epithelial hyperplasias, cysts, and apparently normal surrounding lobules and ducts. bcl-2 levels were equivalent in apparently normal lobules and ducts, as well as in cysts and ductal hyperplasias. bcl-2 staining was significantly higher in fibroadenomas, known to be of lobular origin [mean = 10.1, quantitative immunochemistry score (QIC) arbitrary units (AU), n = 19], than in normal lobules (mean = 5.1 AU, n = 43, P = 7 x 10(-5). bcl-2 levels in normal lobules and ducts varied according to the menstrual cycle, being higher during the follicular than the luteal phase (P = 1.8 x 10(-2) and P = 1.7 x 10(-2), respectively). This was further supported by a statistical link (P = 5 x 10(-3) between high levels of circulating progesterone and weak bcl-2 staining in lobules and ducts. This progesterone-dependent variation was absent in fibroadenomas. No statistical correlation was found between bcl-2 expression and circulating levels of oestradiol, and follicle-stimulating or luteotrophic hormones. Although these are only preliminary results, they suggest an influence of progesterone on bcl-2 expression which might be lost in fibroadenomas. A hypothesis is proposed concerning the potential involvement of altered regulation of the apoptotic process in the formation of such benign lesions.

Epithelial apoptosis

Apoptosis is an essential part of the normal cellular phenotype repertoire. In the absence of appropriate survival factors, apoptosis is activated through specific signalling cassettes. Epithelia form distinctive three-dimensional cohesive structures that depend on adhesive interactions in order for these tissues to carry out their specialised roles, such as secretion and reproduction. The cellular programme that triggers apoptosis in epithelial cells has not yet been shown to differ form that in other cell types, yet the unique characteristics of epithelia endow them with specific determinants for survival. In particular, cell-matrix and cell-cell interactions are required to prevent entry of epithelial cells into apoptosis, and soluble factors that have profound effects on epithelia, such as steroid hormones or hepatocyte growth factor, also influence their survival. The regenerative capacity of certain epithelia is controlled by intrinsic expression of survival genes within stem cell populations, and may regulate the susceptibility of different epithelial tissues to undergo carcinogenesis.

Apoptosis is coordinately regulated with osteoblast formation during bone healing

The ultimate fate of the expanded pool of osteoblasts formed following a typical bone injury is unclear. Since necrosis has not been described in the latter stages of bone healing, there must be some other mechanism by which obsolete osteoblasts are cleared from an injury site. We therefore evaluated the possibility that their removal is pre-programmed, by investigating the occurrence of apoptosis in rats that received a standardized bone injury. Histological evidence identical to that found in tissues known to exhibit apoptosis was obtained, thereby showing that programmed cell death was a normal concomitant of fracture healing. The concentration of apoptotic bodies reached its maximum after the differentiative response had peaked, suggesting that the two processes were coordinated. The same result was found in a second group of rats that received the same bone injury plus a simultaneous standardized soft-tissue injury. The combined injuries resulted in more osteoblasts and more apoptotic bodies, but an identical temporal relationship between the peak responses in the two parameters. The results suggested that osteoblasts were removed from the injury site via apoptosis, and that the process was coordinately regulated with differentiation. Since the number of apoptotic bodies per osteoblast varied during healing, it is likely that apoptosis was associated with healing and not merely with osteoblast concentration.

Involution of the sheep mammary gland

Changes in the ovine mammary gland epithelium during initiated involution were studied by light and electron microscopy. Apoptosis of the duct and alveolar epithelial cells was first identified at 2 d after weaning, reached a peak at 4 d and then progressed gradually thereafter. Apoptotic cells were phagocytosed by intraepithelial macrophages and alveolar epithelial cells. Occasional apoptotic epithelial cells were observed in the alveolar and duct lumina. The highly vacuolated cells in the alveolar and duct lumina were confirmed to be macrophages as they were CD45+, MHC class II+. Changes in myoepithelial cells involved shrinkage and extension of cytoplasmic processes into the underlying stroma and no apoptosis was observed. Regression of the blood capillaries was also by apoptosis. The resulting apoptotic bodies were either taken up by adjacent endothelial cells or were shed into the capillary lumen to be phagocytosed later by mural endothelial cells or blood monocytes. The mammary glands were completely involuted by 30 d after weaning. It was concluded that the mammary gland involutes by apoptosis, a process which allows deletion of cells without the loss of the basic architecture and the integrity of the epithelial lining of the gland.

Coordinated expression of matrilysin during TPA-induced apoptosis of LNCaP cells: two parallel processes affected by TPA

Matrix metalloproteinases (MMPs) are upregulated by growth factors and 12-O-tetradecanoyl-phorbol-13-acetate (TPA). TPA (10 nM) induced apoptosis in LNCaP cells grown in serum-free medium at high seeding density, and increased mRNA and secreted protein levels for the MMP matrilysin. While the TPA-augmented increase in matrilysin mRNA was seen at 4 h, secreted matrilysin protein levels at 8 h, TPA-induced DNA ladder formation was seen only at 10 h and the TPA-induced apoptosis was detected at 12 h. The sequence of events suggested a functional role for matrilysin in apoptosis. However, when the MMP inhibitor BB-2516 was used (25 microM, with IC50 of 20 nM for matrilysin), there was no effect of BB-2516 on TPA-induced apoptosis in LNCaP cells (P = 0.2072). This observation indicates that MMPs including matrilysin do not play a primary role in TPA-induced apoptosis in LNCaP cells. We conclude that the TPA-induced apoptosis and the regulation of matrilysin (a TPA-response element (TRE)-containing gene), are independent and parallel processes.

Apoptosis occurs in endothelial cells during hypertension-induced microvascular rarefaction

Disappearance of microvessels (microvascular rarefaction) during hypertension is a process that exacerbates the hypertensive condition. The cellular process by which the vessels disappear is not known. In the present study, we investigate the pathogenic role of cell death, specifically apoptosis, in hypertension-induced microvascular rarefaction. An established rodent one kidney/one clip (1K1C) Goldblatt model of hypertension was used. Histological and ultrastructural characteristics of apoptosis and necrosis were used to define incidence of the two types of cell death. The new method of in situ end-labeling DNA fragmentation known to occur in apoptosis was analyzed, and expression of an apoptosis-related gene, clusterin, identified using Northern blots and in situ hybridization. Microvessels in skeletal muscle were compared in 1K1C animals (n = 3 per time point) and control animals (n = 6) at experimental times after surgery up to established hypertension (1, 2, and 4 days and 1, 2, and 6 weeks). Loss of microvessels in hypertensive animals was verified. Endothelial cell apoptosis, not necrosis, was identified and was more frequent in hypertensive animals than in controls. Apoptosis of endothelial cells was found most often within 1 week after 1K1C surgery. Clusterin mRNA transcripts were increased above control levels in all 1K1C treatments, but expression was not localized specifically above endothelial cells. In this instance, increased expression of clusterin in hypertensive animals may be an epiphenomenon, not directly related to the presence of apoptosis. The results demonstrate a role for apoptosis in the development of microvascular rarefaction in hypertension. The significance of this novel finding is that these results may now be used to direct site-specific anti-apoptosis therapy for treatment of structural rarefaction, at present unaffected by conventional anti-hypertensive therapies.

Apoptosis, cell proliferation and expression of Bcl-2 and Bax in gastric carcinomas: immunohistochemical and clinicopathological study

To clarify the relation between bcl-2 and bax protein (Bcl-2 and Bax) expression with regard to apoptosis and cell proliferation, 82 gastric carcinomas were immunohistochemically investigated. The significance of apoptosis for biological behaviour of the tumours was also examined. The apoptotic indices (AIs) were significantly lower in early-stage than in advanced-stage lesions (P<0.05), being positively correlated with the mitotic indices (MIs) (r=0.447, P<0.001). No association between either AIs or MIs and tumour size (diameter of intramural spreading) was noted. The AIs in the high Bcl-2-immunoreactive score group were significantly smaller than in either the low or the negative categories, whereas they were relatively elevated in the high Bax score group. In addition, an inverse correlation between Bcl-2 and Bax expression was revealed for both AIs and MIs. Although depth of tumour invasion and lymph node status were clearly associated with favourable outcome, no relation between survival rates and average values of either AIs or MIs, or immunoreactive scores for Bcl-2 and Bax was observed. These results indicate that in gastric carcinomas, apoptosis is closely associated with cell proliferation and expression of Bcl-2 and Bax, but appears likely to have no particular biological significance as a prognostic factor.

The lysosomal-associated membrane protein LAMP-1 is a novel differentiation marker for HC11 mouse mammary epithelial cells

HC11 cells are a model for mammary epithelial cell differentiation. Following treatment with the lactogenic hormones glucocorticoids, insulin and prolactin the HC11 cells synthesize milk proteins. Stereological analysis at the ultrastructural level suggested that lysosomal biogenesis was activated following lactogenic hormone treatment of HC11 cells. Differentiation was also accompanied by an increase in the cellular content of tri- and tetra-antennary oligosaccharides, which were reactive with isolectin L4 from Phaseolus vulgaris (L-PHA). The lysosomal-associated membrane glycoproteins LAMP-1 and LAMP-2 are the major carriers of this glycosylation pattern. An analysis of LAMP-1 and LAMP-2 expression levels showed that there was a dramatic increase in LAMP-1 following lactogenic hormone treatment of HC11 cells. The control of LAMP-1 expression is mainly post-transcriptional since the level of LAMP-1 RNA is not affected by lactogenic hormones. Stereological analysis also showed an increase in intermediate filament control of differentiated cells. Analysis of the cytokeratins expressed in differentiated cells suggests that HC11 cells have characteristics of a mammary-specific stem cell. Increase in lysosomal vesicles and their contents might play a role in intra- and extra-cellular remodeling, which is characteristic of cell differentiation.

Expression of a 74-kDa nuclear factor 1 (NF1) protein is induced in mouse mammary gland involution. Involution-enhanced occupation of a twin NF1 binding element in the testosterone-repressed prostate message-2/clusterin promoter

Testosterone repressed prostate message-2 (TRPM-2)/clusterin gene expression is rapidly induced in early involution of the mouse mammary gland, after weaning, and in the rat ventral prostate, after castration. A search for involution-enhanced DNaseI footprints in the proximal mouse TRPM-2/clusterin gene promoter led to the identification and characterization (by DNase I footprinting and EMSA) of a twin nuclear factor 1 (NF1) binding element at -356/-309, relative to the proposed transcription start site; nuclear extracts from 2-day involuting mouse mammary gland showed an enhanced footprint over the proximal NF1 element; extracts from involuting prostate showed enhanced occupancy of both NF1 binding elements. Subsequent EMSA and Western analysis led to the detection of a 74-kDa NF1 protein whose expression is triggered in early involution in the mouse mammary gland; such an induced protein is not found in the involuting rat ventral prostate. This protein was not found in lactation where three other NF1 proteins of 114, 68, and 46 kDa were detected. Reiteration of the epithelial cell apoptosis associated with early mammary gland involution, in vitro, in a primary cell culture system, triggered the appearance of the 74-kDa NF1. Overlaying the cells with laminin-rich extracellular matrix suppressed the apoptosis and the expression of the 74-kDa NF1 and, in the presence of lactogenic hormones, initiated milk protein gene expression and the expression of two of the lactation-associated NF1 proteins (68 and 46 kDa). This study, thus, identifies for the first time the occurrence of a switch in expression of different members of the family of NF1 transcription factors as mammary epithelial cells move from the differentiated to the involution/apoptotic state, and it is likely that the involution-specific 74-kDa NF1 accounts for the enhanced NF1 footprint detected on the TRPM-2/clusterin promoter with extracts of mouse mammary gland.

Bcl-2 expression is correlated with a low apoptotic index and associated with progesterone receptor immunoreactivity in endometrial carcinomas

A total of 103 endometrial carcinomas (endometrioid type), as well as 15 samples of normal (atrophic or proliferative phase) and 26 of hyperplastic endometrium, were immunohistochemically investigated for expression of Bcl-2, and oestrogen and progesterone receptors (ER and PR), and the results compared with findings for apoptosis and cell proliferation. Carcinoma cases were subdivided into tubular and solid components on the basis of tumour growth patterns. Immunopositivity for Bcl-2, ER, and PR in tubular components was significantly higher than in the solid category, being negatively associated with histological grading. Immunoreactivity scores revealed that Bcl-2 in the tubular group was positively correlated with PR but not ER, while its expression in normal and hyperplastic endometrium was closely linked with both. Apoptotic and mitotic indices (AI and MI) were both significantly lower in tubular than in solid areas. In the tubular areas, AI, values were significantly lower in the subgroup with a high level of Bcl-2 expression than in either low-level or negative groups. These results indicate that Bcl-2 expression may play a central role in the inhibition of apoptosis in endometrial carcinoma, in particular those cases with tubular components, possibly being associated with PR rather than ER. Changes in the propensity for apoptosis may be related to alterations of tumour growth pattern and of features of differentiation.

Serum albumin is a specific inhibitor of apoptosis in human endothelial cells

Excess blood vessels are removed by apoptosis of endothelial cells, however, the signals responsible for this have not been defined. Apoptosis of cultured human umbilical vein endothelial cells is induced by deprivation of serum or adhesion. In this paper, apoptosis in human umbilical vein and microvascular endothelium was induced by deprivation of serum and or adhesion. Apoptosis was confirmed on the basis of morphology, ultrastructure and internucleosomal cleavage of DNA. Loss of endothelial adhesion was found to be an early event in cultured endothelial cell apoptosis and was exploited to quantitate apoptosis. The effect of: bovine serum albumin; human serum albumin; recombinant human albumin; dithiothreitol reduced human and bovine albumin; CNBr treated human and bovine albumin as well as ovalbumin upon endothelial apoptosis was determined. Native bovine and human albumin as well as recombinant human material inhibited apoptosis at physiological concentrations with identical dose response curves in both umbilical vein and microvascular cells. Dithiothreitol treatment destroyed all protective activity while bovine but not human albumin was partially inactivated by CNBr treatment. The unrelated protein ovalbumin was not protective. Albumin did not inhibit apoptosis if cells were also deprived of adhesion. The data suggest that albumin is a specific inhibitor of human endothelial apoptosis but does not protect cells also deprived of adhesion. Reduced supply of albumin to endothelium in poorly perfused blood vessels may provide a mechanism for the removal of excess blood vessels in remodelling tissues. Also, the failure of albumin to protect endothelial cells deprived of adhesion from apoptosis may reflect the need to remove potentially micro-embolic cells detached due to trauma.

Programmed cell death during mammary tissue involution induced by weaning, litter removal, and milk stasis

Programmed cell death in mammary tissue was studied during natural weaning in lactating mice and after litter removal or milk stasis. All treatments stimulated mammary apoptosis, indicating that this process is an integral part of the tissue's involution after lactation. Induction of apoptosis was slower in natural weaning than after litter removal but occurred earlier when mice were concurrently pregnant during natural weaning. Ipsilateral induction of apoptosis by milk stasis in teat-sealed glands indicates that cell death is under local (i.e., intramammary) as well as endocrine regulation. Apoptosis detected by DNA laddering was associated with changes in expression of p53 and bax, two genes implicated in the regulation of cell death, and was accompanied by structural degeneration characteristic of mammary involution. Reciprocal changes in stromelysin mRNA, and that of its inhibitor TIMP-2, suggested that this structural reorganisation was the result of coordinated changes in gene expression favouring proteolysis of the extracellular matrix.

Morphological detection of cell kinetics and progesterone receptor expression during growth and regression of pregnancy-dependent mammary tumors of GRS/A mice

Cell kinetics (cell proliferation and cell death) and the expression of progesterone receptor (PgR) during growth and regression of pregnancy-dependent mammary tumors (PDMT) of female GRS/A mice were investigated on the histologic level. Cell proliferation was determined using monoclonal anti-proliferating cell nuclear antigen (PCNA) antibody (PC10) and cell death was detected using the TUNEL method. PgR expression was determined using monoclonal anti-PgR antibody (10A9). In growing PDMT (type P tumor) obtained during days 16-20 of pregnancy, numerous PCNA labeling was observed in both the epithelial and mesenchymal cells, whereas PgR was found only in epithelial cells and no TUNEL signal was detected. In regressing PDMT obtained during days 0-5 of lactation, the level of PCNA labeling was low and the PgR-positive cells were preferentially labeled by the TUNEL staining, which led to microcyst formation (cystic degeneration). Pale cell carcinoma was shown to be pregnancy-dependent, since the tumor cells were universally PgR-positive, and TUNEL-positive signal with low PCNA-labeling was detected after the delivery.

Apoptosis: a programmed cell death involved in ovarian and uterine physiology

Apoptosis is a form of programmed cell death which occurs through the activation of a cell-intrinsic suicide machinery. The biochemical machinery responsible for apoptosis is expressed in most, if not all, cells. Contrary to necrosis, an accidental form of cell death, apoptosis does not induce inflammatory reaction noxious for the vicinity. Apoptosis is primarily a physiologic process necessary to remove individual cells that are no longer needed or that function abnormally. Apoptosis plays a major role during development, homeostasis. Many stimuli can trigger apoptotic cell death, but expression of genes can modulate the sensibility of the cell. The aim of this review is to summarise current knowledge of the molecular mechanisms of apoptosis and its roles in human endometrium and ovary physiology.

Feedback control of milk secretion from milk

Extracellular storage allows biologically-active substances in milk to influence mammary function. Among these factors is one which regulates the rate of milk secretion acutely according to frequency or completeness of milk removal in each mammary gland. The active factor in goat's milk has been identified by screening milk constituents for their ability to inhibit milk constituent secretion in tissue and cell culture bioassays, and found to be a novel milk protein. The proteins identified by bioassy in vitro, also inhibited milk secretion in lactating goats in a reversible, concentration-dependent manner. This protein, termed FIL (feedback inhibitor of lactation), acts by reversible blockade of constitutive secretion in the mammary epithelial cell. As the inhibitor is synthesized in the same epithelial cells, feedback inhibition is, therefore, an autocrine mechanism. FIL's unusual mechanism of action also influences other aspects of mammary function. Acute disruption of mammary membrane trafficking is associated with downregulation of prolactin receptors and followed by a decrease in epithelial cell differentiation. Thus, in addition to acutely-regulating milk secretion, FIL may induce the adaptation in mammary cell differentiation which acts in vivo to sustain the secretory response to a sustained change in milk removal. In the long term, matching of milk output to demand is achieved by a change in mammary cell number. This developmental response is also local in nature. Whether it too is due to autocrine modulation by FIL of mechanisms influencing cell proliferation or survival, or elicited by another milk-borne factor, remains to be determined.

In situ detection of apoptosis in regressing corpus luteum of pregnant sow: evidence of an early presence of DNA fragmentation

Luteolysis has been shown to be correlated with apoptosis in rats, sheep, and cows. In pigs, apoptosis has already been demonstrated as regards atretic follicles. The present study has been conducted to evaluate whether apoptosis occurs during corpora lutea regression in the pregnant pig and to investigate the temporal relationship between apoptosis and functional luteolysis. The apoptotic process has been studied through the research of oligonucleosome fragmentation by means of classical electrophoresis methods and by in situ detection on histological luteal sections. The latter method allows the identification of apoptosis and the localization of apoptotic cells. Pregnant sows were cloprostenol (PGF2 alpha analog) treated and ovariectomized 0, 6, 12, 24, 48, and 72 hr after treatment. Corpora lutea were utilized for progesterone and DNA extraction and in situ evaluation of apoptosis. Clear evidence of apoptosis was seen earlier with the in situ technique (6 hr for stromal tissue, 12 hr for luteal cells) than with the classical method (24 hr). Apoptosis was, however, apparent after plasma and tissue progesterone had reached basal levels. In conclusion, these results are consistent with the hypothesis that apoptosis occurs during luteolysis in pigs. Moreover, the data obtained with the in situ technique made it possible to identify signs of structural regression in stromal tissue first than in parenchymal cells. A two-stage activation of apoptosis has been discussed to explain structural changes that occur during luteolysis after cloprostenol treatment in swine corpora lutea.

Overexpression of the death-promoting gene bax-alpha which is downregulated in breast cancer restores sensitivity to different apoptotic stimuli and reduces tumor growth in SCID mice

We have studied the expression of members of the bcl-2 family in human breast cancer. The expression pattern of these genes in breast cancer tissue samples was compared with the expression pattern in normal breast epithelium. No marked difference with regard to bcl-2 and bcl-xL expression was observed between normal breast epithelium and cancer tissue. In contrast, bax-alpha, a splice variant of bax, which promotes apoptosis, is expressed in high amounts in normal breast epithelium, whereas only weak or no expression could be detected in 39 out of 40 cancer tissue samples examined so far. Of interest, downregulation of bax-alpha was found in different histological subtypes. Furthermore, we transfected bax-alpha into breast cancer cell lines under the control of a tetracycline-dependent expression system. We were able to demonstrate for the first time that induction of bax expression in breast cancer cell lines restores sensitivity towards both serum starvation and APO-I/Fas-triggered apoptosis and significantly reduces tumor growth in SCID mice. Therefore, we propose that dysregulation of apoptosis might contribute to the pathogenesis of breast cancer at least in part due to an imbalance between members of the bcl-2 gene family.