Immunohistochemical and ultrastructural visualization of different routes of oocyte elimination in adult rats

Autophagy favors survival of corpora lutea during the long-lasting pregnancy of the South American plains vizcacha, Lagostomus maximus (Rodentia, Caviomorpha)

The corpus luteum (CL) is a transient endocrine gland that plays a crucial role in establishing and maintaining pregnancy. Although autophagy and apoptosis have been suggested as cooperative mechanisms, their interaction within the CL of pregnant mammals has not been thoroughly investigated. To understand the collaborative function of autophagy and apoptosis in the CL, we analyzed both mechanisms during pregnancy in the South American plains vizcacha, Lagostomus maximus. This rodent undergoes a decline in progesterone levels during mid-gestation, a reactivation of the hypothalamus-hypophysis-gonadal axis, and the incorporation of new functional secondary CL. Our analysis of autophagy markers BECLIN 1 (BECN1), SEQUESTOSOME1 (SQSTM1), Microtubule-associated protein light chain 3 (LC3B), and lysosomal-associated membrane protein 1 (LAMP1) and anti- and pro-apoptotic markers BCL2 and ACTIVE CASPASE 3 (A-C3) revealed interactive behaviors between both processes. Healthy primary and secondary CL exhibited positive expression of BECN1, SQSTM1, LC3B, and LAMP1, while regressed CL displayed enhanced expression of these autophagy markers along with nuclear A-C3. Transmission electron microscopy revealed a significant formation of autophagic vesicles in regressed CL during full-term pregnancy, whereas healthy CL exhibited a low number of autophagy vesicles. The co-localization between LC3B and SQSTM1 and LC3B with LAMP1 was observed in both healthy and regressed CL during pregnancy, while co-localization of BECN1 and BCL2 was only detected in healthy CL. LC3B and ACTIVE CASPASE 3 co-localization were detected in a subset of luteal cells within the regressing CL. We propose that autophagy could act as a survival mechanism in the CL, allowing the pregnancy to progress until full-term, while also serving as a mechanism to eliminate remnants of regressed CL, thereby providing the necessary space for subsequent follicular maturation.

Activation of interleukin 33-NFκB axis in granulosa cells during atresia and its role in disposal of atretic follicles†

It has been previously shown that the cytokine interleukin 33 is required for two processes, i.e., autophagic digestion of granulosa cells and recruitment of macrophages into atretic follicles, for full disposal of atretic follicles. Now, this study shows that activation of interleukin 33-suppression of tumorigenicity 2-Nuclear Factor ĸB (NFκB) axis in granulosa in early atretic follicles may regulate those two events. Injection of human chorionic gonadotropin has been shown to induce a transient peak of interleukin 33 expression with synchronized atresia. In this model, interleukin 33-independent expression of suppression of tumorigenicity 2 in granulosa cells was detected in early atretic follicles before macrophage invasion. The activation of NFκB pathway in ovaries was further demonstrated in vivo in Tg mice with luciferase-reporter for NFκB activation; the activation was microscopically localized to granulosa cells in early atretic follicles. Importantly, antibody blockage of interleukin 33 or interleukin 33 Knock-out (KO) (Il33-/-) not only inhibited NFκB activity in ovaries, but it also altered expression of two key genes, i.e., reduction in proinflammatory interleukin6 (IL6) expression, and a surge of potential autophagy-inhibitory mammalian target of rapamycin (mTOR) expression in atretic follicles. By contrast, apoptosis and other genes, such as interleukin1β (IL1β) were not affected. In conclusion, in parallel to apoptosis, atresia signals also trigger activation of the interleukin 33-suppression of tumorigenicity 2-NFκB pathway in granulosa, which leads to (1) down-regulated expression of mTOR that is a negative regulator of autophagy and (2) up-regulated expression of proinflammatory IL6.

Reactive oxygen species signalling in the deterioration of quality of mammalian oocytes cultured in vitro: Protective effect of antioxidants

The in vitro fertilization (IVF) is the first choice of infertile couples worldwide to plan for conception. Besides having a significant advancement in IVF procedure, the success rate is still poor. Although several approaches have been tested to improve IVF protocol, minor changes in culture conditions, physical factors and/or drug treatment generate reactive oxygen species (ROS) in oocytes. Due to large size and huge number of mitochondria, oocyte is more susceptible towards ROS-mediated signalling under in vitro culture conditions. Elevation of ROS levels destabilize maturation promoting factor (MPF) that results in meiotic exit from diplotene as well as metaphase-II (M-II) arrest in vitro. Once meiotic exit occurs, these oocytes get further arrested at metaphase-I (M-I) stage or metaphase-III (M-III)-like stage under in vitro culture conditions. The M-I as well as M-III arrested oocytes are not fit for fertilization and limits IVF outcome. Further, the generation of excess levels of ROS cause oxidative stress (OS) that initiate downstream signalling to initiate various death pathways such as apoptosis, autophagy, necroptosis and deteriorates oocyte quality under in vitro culture conditions. The increase of cellular enzymatic antioxidants and/or supplementation of exogenous antioxidants in culture medium protect ROS-induced deterioration of oocyte quality in vitro. Although a growing body of evidence suggests the ROS and OS-mediated deterioration of oocyte quality in vitro, their downstream signalling and related mechanisms remain poorly understood. Hence, this review article summarizes the existing evidences concerning ROS and OS-mediated downstream signalling during deterioration of oocyte quality in vitro. The use of various antioxidants against ROS and OS-mediated impairment of oocyte quality in vitro has also been explored in order to increase the success rate of IVF during assisted reproductive health management.

A matter of new life and cell death: programmed cell death in the mammalian ovary

BACKGROUND

The mammalian ovary is a unique organ that displays a distinctive feature of cyclic changes throughout the entire reproductive period. The estrous/menstrual cycles are associated with drastic functional and morphological rearrangements of ovarian tissue, including follicular development and degeneration, and the formation and subsequent atrophy of the corpus luteum. The flawless execution of these reiterative processes is impossible without the involvement of programmed cell death (PCD).

MAIN TEXT

PCD is crucial for efficient and careful clearance of excessive, depleted, or obsolete ovarian structures for ovarian cycling. Moreover, PCD facilitates selection of high-quality oocytes and formation of the ovarian reserve during embryonic and juvenile development. Disruption of PCD regulation can heavily impact the ovarian functions and is associated with various pathologies, from a moderate decrease in fertility to severe hormonal disturbance, complete loss of reproductive function, and tumorigenesis. This comprehensive review aims to provide updated information on the role of PCD in various processes occurring in normal and pathologic ovaries. Three major events of PCD in the ovary-progenitor germ cell depletion, follicular atresia, and corpus luteum degradation-are described, alongside the detailed information on molecular regulation of these processes, highlighting the contribution of apoptosis, autophagy, necroptosis, and ferroptosis. Ultimately, the current knowledge of PCD aberrations associated with pathologies, such as polycystic ovarian syndrome, premature ovarian insufficiency, and tumors of ovarian origin, is outlined.

CONCLUSION

PCD is an essential element in ovarian development, functions and pathologies. A thorough understanding of molecular mechanisms regulating PCD events is required for future advances in the diagnosis and management of various disorders of the ovary and the female reproductive system in general.

Mouse oocytes sequester aggregated proteins in degradative super-organelles

Oocytes are among the longest-lived cells in the body and need to preserve their cytoplasm to support proper embryonic development. Protein aggregation is a major threat for intracellular homeostasis in long-lived cells. How oocytes cope with protein aggregation during their extended life is unknown. Here, we find that mouse oocytes accumulate protein aggregates in specialized compartments that we named endolysosomal vesicular assemblies (ELVAs). Combining live-cell imaging, electron microscopy, and proteomics, we found that ELVAs are non-membrane-bound compartments composed of endolysosomes, autophagosomes, and proteasomes held together by a protein matrix formed by RUFY1. Functional assays revealed that in immature oocytes, ELVAs sequester aggregated proteins, including TDP-43, and degrade them upon oocyte maturation. Inhibiting degradative activity in ELVAs leads to the accumulation of protein aggregates in the embryo and is detrimental for embryo survival. Thus, ELVAs represent a strategy to safeguard protein homeostasis in long-lived cells.

Making a good egg: human oocyte health, aging, and in vitro development

Mammalian eggs (oocytes) are formed during fetal life and establish associations with somatic cells to form primordial follicles that create a store of germ cells (the primordial pool). The size of this pool is influenced by key events during the formation of germ cells and by factors that influence the subsequent activation of follicle growth. These regulatory pathways must ensure that the reserve of oocytes within primordial follicles in humans lasts for up to 50 years, yet only approximately 0.1% will ever be ovulated with the rest undergoing degeneration. This review outlines the mechanisms and regulatory pathways that govern the processes of oocyte and follicle formation and later growth, within the ovarian stroma, through to ovulation with particular reference to human oocytes/follicles. In addition, the effects of aging on female reproductive capacity through changes in oocyte number and quality are emphasized, with both the cellular mechanisms and clinical implications discussed. Finally, the details of current developments in culture systems that support all stages of follicle growth to generate mature oocytes in vitro and emerging prospects for making new oocytes from stem cells are outlined.

Dissection of the autophagic route in oocytes from atretic follicles

BACKGROUND INFORMATION

Autophagy is a conserved process that functions as a cytoprotective mechanism; it may function as a cell death process called programmed cell death type II. There is considerable evidence for the presence of autophagic cell death during oocyte elimination in prepubertal rats. However, the mechanisms involved in this process have not been deciphered.

RESULTS

Our observations revealed autophagic cell death in oocytes with increased labeling of the autophagic proteins Beclin 1, light chain 3 A (LC3 A), and lysosomal-associated membrane protein 1 (Lamp1). Furthermore, mTOR and phosphorylated (p)-mTOR (S2448) proteins were significantly decreased in oocytes with increased levels of autophagic proteins, indicating autophagic activation. Moreover, phosphorylated protein kinase B (p-AKT) was not expressed by oocytes, but mitogen-activated protein kinase/extracellular signalregulated kinase (MAPK/ERK) signaling was observed. Additionally, selective and elevated mitochondrial degradation was identified in altered oocytes.

CONCLUSIONS

All these results suggest that mTOR downregulation, which promotes autophagy, could be mediated by low energy levels and sustained starvation involving the phosphoinositide 3-kinase (PI3K)/AKT/mTOR and MAPK/ERK pathways.

SIGNIFICANCE

In this work, we analyzed the manner in which autophagy is carried out in oocytes undergoing autophagic cell death by studying the behavior of proteins involved in different steps of the autophagic pathway.

Advanced Maternal Age Deteriorates the Developmental Competence of Vitrified Oocytes in Mice

Advanced maternal age (AMA) is known to be related to the decrease in the quality and quantity of oocytes. Oocyte vitrification is now considered an established assisted reproductive technology for fertility preservation. However, it remains unclear whether the oocytes in older women are more sensitive to various insults during vitrification. Thus, we evaluated whether AMA affects cellular and molecular features and developmental outcomes of oocytes after vitrification in mice. The oocytes were grouped as young fresh (YF), young vitrified/warmed (YV), aged fresh (AF), and aged vitrified/warmed (AV). The survival rate of AV oocytes was significantly lower than that of YV oocytes. The rates of fertilization, cleavage, and blastocyst formation of AV oocytes were significantly lower than those of other groups. AV oocytes were represented as aberrations in mitochondria distribution, microvacuole size, and autophagosome formation, leading to delayed embryo development in mice. This delay was associated with a reduced number of total cells and trophectoderm in the blastocyst developed from AV oocytes. Collectively, AMA exaggerates the vulnerability of oocytes to cryo-damage that occurs during vitrification in mice, suggesting that the current vitrification protocols optimized for oocytes from young females should be modified for oocytes from aged women.

17β-estradiol improves the developmental ability, inhibits reactive oxygen species levels and apoptosis of porcine oocytes by regulating autophagy events

OBJECTIVES

Estrogen plays a critical role in the development and apoptosis of oocytes. Autophagy is an evolutionarily conserved and exquisitely regulated self-eating cellular process with important biological functions including the regulation of reproduction. This study aimed to determine the effect of autophagy regulated by the biologically active form of estrogen (17β-estradiol) in porcine oocyte maturation in vitro.

MATERIALS AND METHODS

We measured the effects of oocyte developmental competencies and autophagic activity in the porcine oocyte regulated by 17β-estradiol using autophagic inhibitor (Autophinib). In addition, we studied the role of autophagy in reactive oxygen species (ROS) levels, mitochondrial distribution, Ca²⁺ production, mitochondrial membrane potential (ΔΨm), and early apoptosis by caspase-3, -8 activity in the mature oocytes.

RESULTS

The results showed that the oocyte meiotic progression and early embryonic development were gradually decreased with Autophinib treatment, which was improved by 17β-estradiol. Immunofluorescence experiments revealed that 17β-estradiol primarily could promote the autophagy in the mature oocytes, and block the reduced-autophagic events by Autophinib. Moreover, 17β-estradiol improved the Autophinib induced high ROS levels, abnormal mitochondrial distribution and low Ca²⁺ production in mature oocytes. Analyses of early apoptosis and ΔΨm showed that autophagy inhibition was accompanied by increased cellular apoptosis, and 17β-estradiol reduced apoptosis rates of mature oocytes. Importantly, autophagy was downregulated by treatment with Autophinib, an activation of caspase-8 and cleaved caspase-3 increased. Those effects were abolished by 17β-estradiol, which could upregulate autophagy.

CONCLUSIONS

Our study have showed important implications that 17β-estradiol could promote efficacy of the development of porcine oocytes, enhance the autophagy, reduce ROS levels and apoptosis activity in vitro maturation.

Pathways coordinating oocyte attrition and abundance during mammalian ovarian reserve establishment

The mammalian ovarian reserve is comprised of a finite pool of primordial follicles, representing the lifetime reproductive capacity of females. In most mammals, the reserve is produced during embryonic and early postnatal development with oocyte numbers peaking during mid-to-late gestation, and then experiencing a dramatic decline continuing until shortly after birth. Oocytes remaining after the bulk of this attrition are subsequently surrounded by a layer of somatic pre-granulosa cells with these units then referred to as "primordial follicles." The complex and varied cell death mechanisms intrinsic to this process are not only characteristic of, but also essential for, the proper formation of this pool of follicles, and as a result must be immaculately balanced to ensure long-term fertility and reproductive health. Too few follicles can lead to Primary Ovarian Insufficiency, resulting in fertility loss and other features of aging, such as an overall shorter lifespan. On the other hand, whereas an excess of follicles might extend reproductive lifespan, this might also be the underlying etiology of other ovarian pathologies. The last decade, in particular, has vastly expanded our understanding of oocyte attrition and determinants of ovarian reserve abundance. By continuing to decipher the intricacies underlying the cell death processes and development of the initial primordial follicle pool, we may be in a much better position to understand idiopathic cases of premature follicle depletion and improve ovarian health in reproductive-age women.

A dual death/survival role of autophagy in the adult ovary of Lagostomus maximus (Mammalia- Rodentia)

Follicular atresia is a cell death event that occurs in the great majority of follicles before ovulation in the mature mammalian ovary. Germ cell loss has been mainly associated to apoptosis although autophagy also seems to be at play. Aimed to increase our understanding on the possible cooperating role of autophagy and apoptosis in follicular atresia and/or follicular survival, we analyzed both programmed cell death mechanisms in a rodent model, the South American plains vizcacha, Lagostomus maximus. Female vizcacha shows highly suppressed apoptosis-dependent follicular atresia in the adult ovary, with continuous folliculogenesis and massive polyovulation. This strategy of massive ovulation requires a permanent remodeling of the ovarian architecture to maintain the availability of quiescent primordial follicles throughout the individual's reproductive lifespan. We report here our analysis of autophagy (BECN1, LAMP1 and LC3B-I/II) and apoptosis (BCL2 and ACTIVE CASPASE-3) markers which revealed interactive behaviors between both processes, with autophagy promoting survival or cell death depending on the ovarian structure. Strong BECN1, LC3B-II and LAMP1 staining was observed in atretic follicles and degenerating corpora lutea that also expressed nuclear ACTIVE CASPASE-3. Healthy follicles showed a slight expression of autophagy proteins but a strong expression of BCL2 and no detectable ACTIVE CASPASE-3. Transmission electron microscopy revealed a high formation of autophagosomes, autolysosomes and lysosomes in atretic follicles and degenerating corpora lutea and a low number of autophagic vesicles in normal follicles. The co-expression of LC3B-BECN1, LC3B-LAMP1 and LC3B-ACTIVE CASPASE-3 was only detected in atretic follicles and degenerating corpora lutea, while co-expression of BCL2-BECN1 was only observed in normal follicles. We propose that autophagy could act as a mechanism to eliminate altered follicles and remnant corpora lutea providing the necessary space for maturation of primordial follicles that continuously enter the growing follicular pool to sustain massive ovulation.

Role of the superior ovarian nerve in the regulation of follicular development and steroidogenesis in the morning of diestrus 1

PURPOSE

Little is known about the role of the superior ovarian nerve (SON) in follicular development during the estrus cycle. The aim of the present study was to analyze the role of neural signals arriving through the SON at the ovaries in the regulation of follicular development and ovarian steroid secretion in diestrus 1 of cyclic rats.

METHODS

Cyclic rats were subjected to left, right, or bilateral SON sectioning or to unilateral or bilateral laparotomy at diestrus 1 at 11:00 h. Animals were sacrificed 24 h after surgery.

RESULTS

Compared to laparotomized animals, unilateral SON sectioning decreased the number of preovulatory follicles, while bilateral SON sectioning resulted in a decreased number of atretic preantral follicles. An important observation was the presence of invaginations in the follicular wall of large antral and preovulatory follicles in animals with denervation. Furthermore, left SON sectioning increased progesterone levels but decreased testosterone levels, which are effects that were not observed in animals that were subjected to right denervation.

CONCLUSIONS

At 11:00 h of diestrus 1, the SON was found to stimulate follicle development, possibly via neural signals, such as noradrenaline and/or vasoactive intestinal peptide, and this stimulation induced the formation of follicle-stimulating hormone receptors. The role of the SON in the regulation of ovarian steroid secretion is asymmetric: the left SON inhibits the regulation of progesterone and stimulates testosterone secretion, and the right nerve does not participate in these processes.

Beclin 1 Interacts With Active Caspase-3 and Bax in Oocytes From Atretic Follicles in the Rat Ovary

Oocyte cell death is a normal process in the mammalian ovary during follicular growth. Recent reports have demonstrated the presence of pro-apoptotic and pro-autophagic proteins during oocyte elimination. The goal of this study was to identify the interactions between proteins involved in different types of programmed cell death in the same oocyte during follicular atresia. We evaluated the presence of Beclin 1 and its interaction with the pro-apoptotic proteins active caspase-3, Bax, and Bak by means of histochemical observations, ultrastructural immunodetection, and immunoprecipitation techniques in ovaries from prepubertal (28- and 33-day-old), juvenile (40-day-old), and young adult (90-day-old) rats. In this study, we identified that oocyte elimination occurred with a high quantity of pro-autophagic protein Beclin 1 and increased the presence of the pro-apoptotic proteins active caspase-3, Bax, and Bak. Conversely, the antiapoptotic protein Bcl-2 was reduced in oocytes from atretic follicles. In addition, Beclin 1 was shown to interact with active caspase-3 and Bax. Our results suggest that the increase in Beclin 1 is directly related to the rise of pro-apoptotic proteins, which could promote the apoptotic process during oocyte elimination.

Abundances of autophagy-related protein LC3B in granulosa cells, cumulus cells, and oocytes during atresia of pig antral follicles

In mammals, apoptosis has been accepted as the type of programmed cell death (PCD) that occurs in ovarian follicles undergoing atresia. Results of recent studies, however, indicate autophagy may be an alternative mechanism involved in follicle depletion through independent or tandem actions with apoptosis. Western blotting and immunofluorescence procedures were used in the present study to investigate the abundances of LC3B protein in freshly collected granulosa cells (GCs), cumulus cells (CCs), and oocytes to evaluate whether autophagy is an important process of antral follicle atresia in sexually mature sows. Furthermore, apoptosis was analyzed using annexin V and TUNEL assays in the same cellular cohorts to evaluate the correlation between the two processes. Immunostaining results indicate autophagy was induced in the majority of GCs, CCs, and oocytes from early and advanced stage atretic follicles. The quantitative results of western blot analysis indicate there is a progressive increase (P <  0.05) in abundance of autophagy-related protein (LC3B-II) in these cells compared with cells in non-atretic follicles. Furthermore, there is confirmation that apoptosis occurs in the GCs of atretic follicles, thus indicating that in pigs apoptosis and autophagy are processes in GCs that regulate PCD and as a consequence antral follicle depletion. There was a greater abundance of LC3B-II in CCs and oocytes of atretic follicles, while apoptosis was not detected. It, therefore, is suggested that in these cells the two processes function independently, with autophagy having a cytoprotective rather than PCD mechanism of action.

Autophagy in hypoxic ovary

Oxygen deprivation affects human health by modulating system as well as cellular physiology. Hypoxia generates reactive oxygen species (ROS), causes oxidative stress and affects female reproductive health by altering ovarian as well as oocyte physiology in mammals. Hypoxic conditions lead to several degenerative changes by inducing various cell death pathways like autophagy, apoptosis and necrosis in the follicle of mammalian ovary. The encircling somatic cell death interrupts supply of nutrients to the oocyte and nutrient deprivation may result in the generation of ROS. Increased level of ROS could induce granulosa cells as well as oocyte autophagy. Although autophagy removes damaged proteins and subcellular organelles to maintain the cell survival, irreparable damages could induce cell death within intra-follicular microenvironment. Hypoxia-induced autophagy is operated through 5' AMP activated protein kinase-mammalian target of rapamycin, endoplasmic reticulum stress/unfolded protein response and protein kinase C delta-c-junN terminal kinase 1 pathways in a wide variety of somatic cell types. Similar to somatic cells, we propose that hypoxia may induce granulosa cell as well as oocyte autophagy and it could be responsible at least in part for germ cell elimination from mammalian ovary. Hypoxia-mediated germ cell depletion may cause several reproductive impairments including early menopause in mammals.

SIRT2 functions in aging, autophagy, and apoptosis in post-maturation bovine oocytes

AIMS

Sirtuins have been implicated in the aging process, however, the functions of SIRT2 in post-maturation aging of oocytes are not fully understood. The purpose of the present investigation was to assess the roles of SIRT2 in aged oocytes and mechanisms involved.

MAIN METHODS

The fresh MII oocytes were aging in vitro, and treated with SIRT2 inhibitor (SirReal2), autophagy activator (Rapamycin), and autophagy inhibitor (3-Ma) for 24 h, respectively. Oocyte activation, cytoplasmic fragmentation, and spindle defects, mitochondrial distribution, ROS levels, ATP production, mitochondrial membrane potential, and early apoptosis were investigated. Western blotting was performed to determine LC3-II accumulation, SQSTM1 degradation, and caspase-3 activity.

KEY FINDINGS

SIRT2 expression gradually decreased in a time-dependent manner during oocyte aging. Treatment with SirReal2 significantly increased the rates of oocyte activation, cytoplasmic fragmentation, and spindle defects. In particular, the high ROS levels, abnormal mitochondrial distribution, low ATP production, and lost ΔΨm were observed in SirReal2-exposed oocytes. Further analysis revealed that LC3-II accumulation and SQSTM1 degradation were induced by SIRT2 inhibition. By performing early apoptosis analysis showed that oocyte aging was accompanied with cellular apoptosis, and SIRT2 inhibition increased apoptosis rates of aged oocytes. Importantly, upregulating autophagy with Rapamycin could mimic the effects of SIRT2 inhibition on apoptosis by increasing caspase-3 activation, whereas downregulating autophagy with 3-MA could abolish those effects by blocking caspase-3 activation.

SIGNIFICANCE

Our results suggest that SIRT2 inactivation is a key mechanism underlying of cellular aging, and SIRT2 inhibition contributes to autophagy-dependent cellular apoptosis in post-maturation oocytes.

Impact of Oxidative Stress on Age-Associated Decline in Oocyte Developmental Competence

Reproductive capacity in women starts to decline beyond their mid-30s and pregnancies in older women result in higher rates of miscarriage with aneuploidy. Age-related decline in fertility is strongly attributed to ovarian aging, diminished ovarian reserves, and decreased developmental competence of oocytes. In this review, we discuss the underlying mechanisms of age-related decline in oocyte quality, focusing on oxidative stress (OS) in oocytes. The primary cause is the accumulation of spontaneous damage to the mitochondria arising from increased reactive oxygen species (ROS) in oocytes, generated by the mitochondria themselves during daily biological metabolism. Mitochondrial dysfunction reduces ATP synthesis and influences the meiotic spindle assembly responsible for chromosomal segregation. Moreover, reproductively aged oocytes produce a decline in the fidelity of the protective mechanisms against ROS, namely the ROS-scavenging metabolism, repair of ROS-damaged DNA, and the proteasome and autophagy system for ROS-damaged proteins. Accordingly, increased ROS and increased vulnerability of oocytes to ROS lead to spindle instability, chromosomal abnormalities, telomere shortening, and reduced developmental competence of aged oocytes.

Ultrastructural histochemistry in biomedical research: Alive and kicking

The high-resolution images provided by the electron microscopy has constituted a limitless source of information in any research field of life and materials science since the early Thirties of the last century. Browsing the scientific literature, electron microscopy was especially popular from the 1970’s to 80’s, whereas during the 90’s, with the advent of innovative molecular techniques, electron microscopy seemed to be downgraded to a subordinate role, as a merely descriptive technique. Ultra -structural histochemistry was crucial to promote the Renaissance of electron microscopy, when it became evident that a precise localization of molecules in the biological environment was necessary to fully understand their functional role. Nowadays, electron microscopy is still irreplaceable for ultrastructural morphology in basic and applied biomedical research, while the application of correlative light and electron microscopy and of refined ultrastructural histochemical techniques gives electron microscopy a central role in functional cell and tissue biology, as a really unique tool for high-resolution molecular biology in situ.

Necrosis and necroptosis in germ cell depletion from mammalian ovary

The maximum number of germ cells is present during the fetal life in mammals. Follicular atresia results in rapid depletion of germ cells from the cohort of the ovary. At the time of puberty, only a few hundred (<1%) germ cells are either culminated into oocytes or further get eliminated during the reproductive life. Although apoptosis plays a major role, necrosis as well as necroptosis, might also be involved in germ cell elimination from the mammalian ovary. Both necrosis and necroptosis show similar morphological features and are characterized by an increase in cell volume, cell membrane permeabilization, and rupture that lead to cellular demise. Necroptosis is initiated by tumor necrosis factor and operated through receptor interacting protein kinase as well as mixed lineage kinase domain-like protein. The acetylcholinesterase, cytokines, starvation, and oxidative stress play important roles in necroptosis-mediated granulosa cell death. The granulosa cell necroptosis directly or indirectly induces susceptibility toward necroptotic or apoptotic cell death in oocytes. Indeed, prevention of necrosis and necroptosis pathways using their specific inhibitors could enhance growth/differentiation factor-9 expression, improve survivability as well as the meiotic competency of oocytes, and prevent decline of reproductive potential in several mammalian species and early onset of menopause in women. This study updates the information and focuses on the possible involvement of necrosis and necroptosis in germ cell depletion from the mammalian ovary.

Germ cell depletion from mammalian ovary: possible involvement of apoptosis and autophagy

Mammalian ovary contains millions of germ cells during embryonic life but only few of them are culminated into oocytes that achieve meiotic competency just prior to ovulation. The majority of germ cells are depleted from ovary through several pathways. Follicular atresia is one of the major events that eliminate germ cells from ovary by engaging apoptotic as well as non-apoptotic pathways of programmed cell death. Apoptosis is characterized by several morphological changes that include cell shrinkage, nuclear condensation, membrane blebbing and cytoplasmic fragmentation by both mitochondria- as well as death receptor-mediated pathways in encircling granulosa cells and oocyte. Although necroapoptosis have been implicated in germ cell depletion, autophagy seems to play an active role in the life and death decisions of ovarian follicles. Autophagy is morphologically characterized by intracellular reorganization of membranes and increased number of autophagic vesicles that engulf bulk cytoplasm as well as organelles. Autophagy begins with the encapsulation of cytoplasmic constituents in a membrane sac known as autophagosomes. The autophagic vesicles are then destroyed by the lysosomal enzymes such as hydrolases that results in follicular atresia. It seems that apoptosis as well as autophagy could play active roles in germ cells depletion from ovary. Hence, it is important to prevent these two pathways in order to retain the germ cells in ovary of several mammalian species that are either threatened or at the verge of extinction. The involvement of apoptosis and autophagy in germ cell depletion from mammalian ovary is reviewed and possible pathways have been proposed.

Role of autophagy in modulating post-maturation aging of mouse oocytes

Mechanisms for post-maturation oocyte aging (PMOA) are not fully understood, and whether autophagy plays any role in PMOA is unknown. To explore the role of autophagy in PMOA, expression of autophagosomes and effects of the autophagy (macro-autophagy) activity on PMOA were observed in mouse oocytes. Oocyte activation rates and active caspase-3 levels increased continuously from 0 to 18 h of in vitro aging. While levels of microtubule-associated protein light chain 3 (LC3)-II increased up to 12 h and decreased thereafter, contents of p62 decreased from 0 to 12 h and then elevated to basal level by 18 h. However, the LC3-II/I ratio remained unchanged following aging in different media or for different times. During in vitro aging up to 12 h, upregulating autophagy with rapamycin or lithium chloride decreased activation susceptibility, cytoplasmic calcium, p62 contents, oxidative stress, caspase-3 activation and cytoplasmic fragmentation while increasing developmental competence, LC3-II contents, LC3-II/I ratio, mitochondrial membrane potential, spindle/chromosome integrity and normal cortical granule distribution. Downregulating autophagy with 3-methyladenine (3-MA) produced opposite effects on all these parameters except cytoplasmic fragmentation. After 12 h of aging culture, however, regulating autophagy with either rapamycin/lithium chloride or 3-MA had no impact on oocyte activation susceptibility. It is concluded that autophagy plays an important role in regulating PMOA. Thus, during the early stage of PMOA, autophagy increases as an adaptive response to prevent further apoptosis, but by the late stage of PMOA, the activation of more caspases blocks the autophagic process leading to severer apoptosis.

Paraptosis-like cell death in Wistar rat granulosa cells

Follicular atresia, a common process present in all mammals, involves apoptotic and autophagic cell death. However, the participation of paraptosis, a type of caspase-independent cell death, during follicular atresia is unknown. This study found swollen endoplasmic reticulum in the granulosa cells of adult Wistar rats. Calnexin was used as a marker of the endoplasmic reticulum at the ultrastructural and optical levels. The cells with swelling of the endoplasmic reticulum were negative to the TUNEL assay and active caspase-3 immunodetection, indicating that this swelling is not part of any apoptotic or autophagic process. Additionally, immunodetection of the CHOP protein was used as a marker of endoplasmic reticulum stress, and this confirmed the presence of the paraptosis process. These data suggest that paraptosis-like cell death is associated with the death of granulosa cells during follicular atresia in adult Wistar rats.

Immunohistochemical and ultrastructural study of the lamellae of oocytes in atretic follicles in relation to different processes of cell death

Atresia is the process through which non-selectable oocytes are eliminated; it involves apoptosis and/or autophagy. This study used immunohistochemical and ultrastructural techniques to characterize the lamellae present in the cytoplasm of oocytes in follicles in the process of atresia in prepubertal and adult Wistar rats. The results indicate that the lamellae are positive to tubulin and myosin immunodetection under light and electron microscopy. Labeling is greater with anti-tubulin and lesser with anti-myosin. Our observations indicate that lamellae are present in oocytes at the initial antral stage in prepubertal rats; that is, from day 14 post-birth to adult age. We were able to determine that the increase in altered lamellae principally occurs in the apoptotic cells rather than in the autophagic cells.

IL-33 is required for disposal of unnecessary cells during ovarian atresia through regulation of autophagy and macrophage migration

Physiological processes such as ovarian follicle atresia generate large amounts of unnecessary cells or tissue detritus, which needs to be disposed of rapidly. IL-33 is a member of the IL-1 cytokine gene family. Constitutive expression of IL-33 in a wide range of tissues has hinted at its role beyond immune defense. We have previously reported a close correlation between IL-33 expression patterns and ovarian atresia. In this study, we demonstrated that IL-33 is required for disposal of degenerative tissue during ovarian atresia using Il33(-/-) mice. Deletion of the Il33 gene impaired normal disposal of atretic follicles, resulting in massive accumulations of tissue wastes abundant with aging-related catabolic wastes such as lipofuscin. Accumulation of tissue wastes in Il33(-/-) mice, in turn, accelerated ovarian aging and functional decline. Thus, their reproductive life span was shortened to two thirds of that for Il33(+/-) littermates. IL-33 orchestrated disposal mechanism through regulation of autophagy in degenerating tissues and macrophage migration into the tissues. Our study provides direct evidence supporting an expanded role of IL-33 in tissue integrity and aging through regulating disposal of unnecessary tissues or cells.

Impact of Histochemistry on biomedical research: looking through the articles published in a long-established histochemical journal

Histochemistry provides the unique opportunity to detect single molecules in the very place where they exert their structural roles or functional activities: this makes it possible to correlate structural organization and function, and may be fruitfully exploited in countless biomedical research topics. Aiming to estimate the impact of histochemical articles in the biomedical field, the last few years citations of articles published in a long-established histochemical journal have been considered. This brief survey suggests that histochemical journals, especially the ones open to a large spectrum of research subjects, do represent an irreplaceable source of information not only for cell biologists, microscopists or anatomists, but also for biochemists, molecular biologists and biotechnologists.

Histochemistry as an irreplaceable approach for investigating functional cytology and histology

In agreement with the evolution of histochemistry over the last fifty years and thanks to the impressive advancements in microscopy sciences, the application of cytochemical techniques to light and electron microscopy is more and more addressed to elucidate the functional characteristics of cells and tissue under different physiological, pathological or experimental conditions. Simultaneously, the mere description of composition and morphological features has become increasingly sporadic in the histochemical literature. Since basic research on cell functional organization is essential for understanding the mechanisms responsible for major biological processes such as differentiation or growth control in normal and tumor tissues, histochemical Journals will continue to play a pivotal role in the field of cell and tissue biology in all its structural and functional aspects.

On the future contents of a small journal of histochemistry

In the last three years, more than 70,000 scientific articles have been published in peer reviewed journals on the application of histochemistry in the biomedical field: most of them did not appear in strictly histochemical journals, but in others dealing with cell and molecular biology, medicine or biotechnology. This proves that histochemistry is still an active and innovative discipline with relevance in basic and applied biological research, but also demonstrates that especially the small histochemical journals should likely reconsider their scopes and strategies to preserve their authorship. A review of the last three years volumes of the European Journal of Histochemistry, taken as an example of a long-time established small journal, confirmed that the published articles were widely heterogeneous in their topics and experimental models, as in this journal's tradition. This strongly suggests that a journal of histochemistry should keep its role as a forum open to an audience as broad as possible, publishing papers on cell and tissue biology in a wide variety of models. This will improve knowledge of the basic mechanisms of development and differentiation, while helping to increase the number of potential authors since scientists who generally do not use histochemistry in their research will find hints for the applications of histochemical techniques to novel still unexplored subjects.