The role of p53 tumor suppressor gene and bcl-2 protooncogene in rat corpus luteum death

Possible Mechanisms for Maintenance and Regression of Corpus Luteum Through the Ubiquitin-Proteasome and Autophagy System Regulated by Transcriptional Factors

The corpus luteum (CL) is an important tissue of the female reproductive process which is established through ovulation of the mature follicle. Pulsatile release of prostaglandin F_2α from the uterus leads to the regression of luteal cells and restarts the estrous cycle in most non-primate species. The rapid functional regression of the CL, which coincides with decrease of progesterone production, is followed by its structural regression. Although we now have a better understanding of how the CL is triggered to undergo programmed cell death, the precise mechanisms governing CL protein degradation in a very short period of luteolysis remains unknown. In this context, activation of ubiquitin-proteasome pathway (UPP), unfolded protein response (UPR) and autophagy are potential subcellular mechanisms involved. The ubiquitin-proteasome pathway (UPP) maintains tissue homeostasis in the face of both internal and external stressors. The UPP also controls physiological processes in many gonadal cells. Emerging evidence suggests that UPP dysfunction is involved in male and female reproductive tract dysfunction. Autophagy is activated when cells are exposed to different types of stressors such as hypoxia, starvation, and oxidative stress. While emerging evidence points to an important role for the UPP and autophagy in the CL, the key underlying transcriptional mechanisms have not been well-documented. In this review, we propose how CL regression may be governed by the ubiquitin-proteasome and autophagy pathways. We will further consider potential transcription factors which may regulate these events in the CL.

The involvement of proliferation and apoptosis in the early human gonad development

Distributions of the Ki-67, TP53, caspase-3 and AIFM1 markers were histologically investigated in the 5th to 9th week developing gonads of 12 human conceptuses using immunohistochemical and immunofluorescence methods. Between the 5th and 8th developmental week, proliferation gradually increased in the surface gonad epithelium (26-52 %) and stroma (19-42 %), but then slightly decreased in the surface epithelium (35 %) during the early foetal period. In medulla, low proliferation activity decreased from 15 to 12 % between the 7th and 9th week. At earliest stages of gonadal development, primordial germ cells (PGC) were only rarely TP53 positive. In the 7th and 8th week, almost all PGC-s displayed TP53 positivity, while their number decreased in early fetal period. During the investigated period, caspase-3 reactivity gradually decreased in surface epithelium, while it increased in PGC and medulla of developing gonad AIFM1-positivity first appeared in surface gonad epithelium and then predominantly in PCG-s while caspase-3 characterized different cell populations within the developing gonad. AIFM1 and caspase-3 co-localized only during the migration of PCG-s. The number and distribution of Ki-67, TP53, caspase-3 and AIFM1 reacting cells changed coincidently with development end regression of the sex cords in indifferent and early fetal gonad. Our results indicate that the number of PGC might be controlled by balance of TP53 and AIFM1, leading to caspase-3 independent cell death. Other cell populations are probably eliminated by caspase-3-dependent cell death. Both pathways of cell death seem to operate during early human gonad development, while their intensity varies depending on the cell type and developmental period analysed.

Expression of luteal estrogen receptor, interleukin-1, and apoptosis-associated genes after PGF2alpha administration in rabbits at different stages of pseudopregnancy

The dynamic expression for estrogen receptor subtype-1 (ESR1), interleukin-1beta (IL1B), and apoptosis-associated genes, as well as nitric oxide synthase activity, were examined in corpora lutea (CL) of rabbits after prostaglandin F(2alpha) (PGF(2alpha)) administration on either day 4 or day 9 of pseudopregnancy. By reverse transcriptase polymerase chain reaction, the steady-state level of ESR1 transcript was lower (P < 0.01) and that of anti-apoptotic B-cell CLL/lymphoma 2 (BCL2) -like 1 (BCL2L1) was greater in day 4 (P < 0.01) than in day 9 CL. Western blot analysis revealed that BCL2-associated X protein (BAX) abundance was greater in day 4 (P < 0.01) than in day 9 CL, whereas BCL2L1 protein was undetectable at both luteal stages. After PGF(2alpha), ESR1 transcript decreased (P < 0.01) in day 9 CL, whereas IL1B mRNA showed a transitory increase (P < 0.01) at both stages. The pro-apoptotic tumor protein p53 (TP53) gene had diminished (P < 0.01) on day 4 and on day 9 after a transitory increase (P < 0.01), whereas the BAX/BCL2L1 expression ratio increased (P < 0.01) in day 9 CL 24 h after treatment. Following PGF(2alpha), TP53 protein increased (P < 0.01) at both luteal stages, and BAX decreased (P < 0.01) in day 4 CL but increased (P < 0.01) 24 h later in day 9 CL; BCL2L1 became detectable 6 h later in day 4 CL. Nitric oxide synthase activity temporarily increased (P < 0.01) following PGF(2alpha). These findings suggest that PGF(2alpha) regulates luteolysis by ESR1 mRNA down-regulation and modulation of pro- and anti-apoptotic pathways in CL that have acquired a luteolytic capacity.

Response gene to complement 32 expression is induced by the luteinizing hormone (LH) surge and regulated by LH-induced mediators in the rodent ovary

Response gene to complement 32 (Rgc32) has recently been suggested to be expressed in the ovary and regulated by RUNX1, a transcription factor in periovulatory follicles. In the present study, we determined the expression profile of the Rgc32 gene in the rodent ovary throughout the reproductive cycle and the regulatory mechanism(s) involved in Rgc32 expression during the periovulatory period. Northern blot and in situ hybridization analyses revealed the up-regulation of Rgc32 expression in periovulatory follicles. Rgc32 mRNA was also localized to newly forming corpora lutea (CL) and CL from previous estrous cycles. Further studies using hormonally induced luteal and luteolysis models revealed a transient increase in levels of Rgc32 mRNA at the time of functional regression of the CL. Next, the regulation of Rgc32 expression was investigated in vitro using rat preovulatory granulosa cells. The effect of human chorionic gonadotropin on Rgc32 expression was mimicked by forskolin, but not phorbol 12-myristate 13-acetate, and was mediated by the activation of progesterone receptors and the epidermal growth factor-signaling pathway. The mechanism by which RUNX1 regulates Rgc32 expression was investigated using chromatin immunoprecipitation and Rgc32 promoter-luciferase reporter assays. Data from these assays revealed direct binding of RUNX1 in the Rgc32 promoter region in vivo as well as the involvement of RUNX binding sites in the transactivation of the Rgc32 promoter in vitro. In summary, the present study demonstrated the spatial/temporal-specific expression of Rgc32 in the ovary, and provided evidence of LH-initiated and RUNX1-mediated expression of Rgc32 gene in luteinizing granulosa cells.

Physiological and pathological cell deaths in the reproductive organs

Apoptosis of testicular germ cells and oocytes and their supporting cells in the gonads occurs at physiological and normal conditions or after exposure to pathological stimuli. Cell-death regulators, including Bcl-2 family members, caspases, Fas and p53 are thought to be involved in these processes. This article reviews the details of the apoptotic machinery in the reproductive organs by describing briefly the abnormal phenotypes observed in transgenic and gene-ablated mice.

Luteolytic effect of prolactin is dependent on the degree of differentiation of luteal cells in the rat

We studied the morphological and quantitative changes in cyclic corpora lutea (CCL) and in CL of pregnancy (CLP) during structural luteolysis. Elimination of CCL takes several cycles, and cell death occurs as successive apoptotic bursts, from 2100 h in proestrus to 1300 h in estrus. Each apoptotic burst determined a 60% decrease in the CL volume and an 80% decrease in the number of steroidogenic cells (SC). All these changes were inhibited by blocking the preovulatory prolactin (PRL) surge with bromocryptine (CB154). Neither apoptotic cells nor changes in the number of SC were found in regressing CLP from Day 21 of pregnancy to Day 2 postpartum, although there was a 50% decrease in the CLP volume and a 30% decrease in the mean cross-sectional area of SC. Treatment with CB154 on the day of parturition did not modify these regressive changes. On Day 5 postpartum, the volume of the CLP and the number of SC were equivalent in lactating rats (showing high PRL concentrations induced by pup suckling) and nonlactating noncycling rats (in which cyclicity and, therefore PRL surges, were blocked by treatment with LHRH antagonist). However, on Day 10 postpartum, the CLP volume and the number of SC were significantly decreased in lactating rats, and apoptotic cells were frequent. In postpartum cycling rats, the CLP did not show apoptotic cells on the day of the second postpartum estrus (on Day 5 postpartum), whereas on the day of the third postpartum estrus (on Day 9 postpartum), apoptotic cells were abundant. These results indicate that PRL does not induce apoptosis in the CLP before Day 5 postpartum and strongly suggest that the proapoptotic effect of PRL is dependent on the degree of differentiation of luteal cells.

Mechanisms controlling the function and life span of the corpus luteum

The primary function of the corpus luteum is secretion of the hormone progesterone, which is required for maintenance of normal pregnancy in mammals. The corpus luteum develops from residual follicular granulosal and thecal cells after ovulation. Luteinizing hormone (LH) from the anterior pituitary is important for normal development and function of the corpus luteum in most mammals, although growth hormone, prolactin, and estradiol also play a role in several species. The mature corpus luteum is composed of at least two steroidogenic cell types based on morphological and biochemical criteria and on the follicular source of origin. Small luteal cells appear to be of thecal cell origin and respond to LH with increased secretion of progesterone. LH directly stimulates the secretion of progesterone from small luteal cells via activation of the protein kinase A second messenger pathway. Large luteal cells are of granulosal cell origin and contain receptors for PGF(2alpha) and appear to mediate the luteolytic actions of this hormone. If pregnancy does not occur, the corpus luteum must regress to allow follicular growth and ovulation and the reproductive cycle begins again. Luteal regression is initiated by PGF(2alpha) of uterine origin in most subprimate species. The role played by PGF(2alpha) in primates remains controversial. In primates, if PGF(2alpha) plays a role in luteolysis, it appears to be of ovarian origin. The antisteroidogenic effects of PGF(2alpha) appear to be mediated by the protein kinase C second messenger pathway, whereas loss of luteal cells appears to follow an influx of calcium, activation of endonucleases, and an apoptotic form of cell death. If the female becomes pregnant, continued secretion of progesterone from the corpus luteum is required to provide an appropriate uterine environment for maintenance of pregnancy. The mechanisms whereby the pregnant uterus signals the corpus luteum that a conceptus is present varies from secretion of a chorionic gonadotropin (primates and equids), to secretion of an antiluteolytic factor (domestic ruminants), and to a neuroendocrine reflex arc that modifies the secretory patterns of hormones from the anterior pituitary (most rodents).

Immunolocalization and expression of prohibitin, a mitochondrial associated protein within the rat ovaries

This study was designed to determine the cellular distribution and pattern of expression for the mitochondria-associated protein, prohibitin, during the transitional stages of follicular differentiation within the rat ovary. Immunohistochemical staining techniques were used on frozen sections to examine the localization of prohibitin to preantral, antral, preovulatory, and atretic follicles. Prohibitin localization was also determined in corpus luteum from adult rats, in addition to those from infant and juvenile ovaries, before and after gonadotropin stimulation. Western and Northern blotting techniques were used for qualitative and quantitative assessment of prohibitin expression levels within the ovary. Prohibitin was localized within granulosa cells of infant and juvenile ovaries in a relatively heterogeneous staining pattern. The oocyte also exhibited robust prohibitin expression at all stages of follicular development. In addition, strong prohibitin expression was evident in the corpus luteum as well as in follicles undergoing atresia. Additional data derived from studies involving a GnRH-agonist indicate that increases in prohibitin protein expression correlate with the initial events of apoptosis. Collectively, these results support a growth regulatory role for prohibitin within the rat ovary. Therefore, we propose that prohibitin may serve as an important regulator of granulosa cell fate during follicular development.