Angiotensin II influences ovarian follicle development in the transgenic (mRen-2)27 and Sprague-Dawley rat

Exploration of multifaceted molecular mechanism of angiotensin-converting enzyme 2 (ACE2) in pathogenesis of various diseases

Angiotensin converting enzyme 2 (ACE2) is a homolog of ACE (a transmembrane bound dipeptidyl peptidase enzyme). ACE2 converts angiotensinogen to the heptapeptide angiotensin-(1-7). ACE2 and its product, angiotensin-(1-7), have counteracting effects against the adverse actions of other members of renin-angiotensin system (RAS). ACE2 and its principal product, angiotensin-(1-7), were considered an under recognized arm of the RAS. The COVID-19 pandemic brought to light this arm of RAS with special focus on ACE2. Membrane bound ACE2 serves as a receptor for SARS-CoV-2 viral entry through spike proteins. Apart from that, ACE2 is also involved in the pathogenesis of various other diseases like cardiovascular disease, cancer, respiratory diseases, neurodegenerative diseases and infertility. The present review focuses on the molecular mechanism of ACE2 in neurodegenerative diseases, cancer, cardiovascular disease, infertility and respiratory diseases, including SARS-CoV-2. This review summarizes unveiled roles of ACE2 in the pathogenesis of various diseases which further provides intriguing possibilities for the use of ACE2 activators and RAS modulating agents for various diseases.

Angiotensin-converting enzymes play a dominant role in fertility

According to the World Health Organization, infertility, associated with metabolic syndrome, has become a global issue with a 10%-20% incidence worldwide. An accumulating body of evidence has shown that the renin-angiotensin system is involved in the fertility problems observed in some populations. Moreover, alterations in the expression of angiotensin-converting enzyme-1, angiotensin-converting enzyme-2, and angiotensin-converting enzyme-3 might be one of the most important mechanisms underlying both female and male infertility. However, as a pseudogene in humans, further studies are needed to explore whether the abnormal angiotensin-converting enzyme-3 gene could result in the problems of human reproduction. In this review, the relationship between angiotensin-converting enzymes and fertile ability is summarized, and a new procedure for the treatment of infertility is discussed.

Local Renin-Angiotensin system in the reproductive system

The renin-angiotensin system (RAS) is well known as regulator of electrolytes and blood pressure. Besides this function, there are numerous studies supporting the idea of a local tissue RAS. This system controls the local activity of the different RAS family members, especially of the functional proteins Angiotensin II and Angiotensin (1-7). Those antagonistically acting proteins have been described to be expressed in different organ systems including the human reproductive tract. Therefore, this local RAS has been suspected to be involved in the control and regulation of physiological and pathological conditions in the female reproduction tract. This review of the available literature summarizes the physiological influence of the RAS on the follicular development, ovarian angiogenesis, and placental- and uterine function. In addition, in the second part the role of the RAS concerning ovarian- and endometrial cancer becomes elucidated. This section includes possible novel therapeutic strategies via inhibition of RAS-mediated tumor growth and angiogenesis. Looking at a very complex system of agonistic and antagonistic tissue factors, it may be supposed that the RAS in the female reproduction tract will be of rising scientific interest in the upcoming years.

Prevention of metabolic disorders and reproductive performance deficits by the blockade of Angiotensin II AT1 receptor in female rats fed with cafeteria diet

Besides the well-known detrimental effects of obesity on cardiovascular and metabolic function, studies have shown that obesity is also associated with impaired reproductive function in women. Alterations in Angiotensin II (Ang II) have been associated with obesity and with female reproduction. The aim of the present study was to evaluate the reproductive and metabolic effects of Ang II AT1 receptor blockade with losartan in an animal model of obesity, in which female rats were offered a palatable, high calorie diet from weaning to adulthood. Sexual behavior, ovulation rates and preovulatory levels of the hormones estradiol, progesterone, LH and prolactin were analyzed. Retroperitoneal and perigonadal fat pads, triglycerides and cholesterol (total, HDL and LDL), and insulin resistance were analyzed. Losartan prevented increases in fat pad storage, insulin resistance, as well as triglycerides and LDL levels induced by cafeteria diet intake. Losartan also prevented ovulatory deficits and loss of preovulatory surges of progesterone and LH in cafeteria-fed female rats probably through the prevention of the increase in body weight and body fat. No alterations in sexual behavior were observed. These results suggest, for the first time, that Ang II contributes to the development of the deleterious effects of obesity on preovulatory surges of LH and progesterone and on the reduction of ovulation in obese female rats.

Reproductive dysfunction in female rats with renovascular hypertension

BACKGROUND

Hypertension is a major public health epidemic that is highly associated with sexual dysfunction in both men and women. Despite its high prevalence, clinical and animal literature on the underlying mechanisms of sexual dysfunction in hypertensive women is remarkably limited.

METHODS

Using a well-established rodent model of renovascular hypertension-the 2-kidney, 1-clip (2K1C) Goldblatt model-we investigated possible reproductive deficits in female rats. We evaluated several aspects of reproductive function in hypertensive female rats: estrous cycle, sexual behavior, ovulation, and plasma levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and estradiol at proestrus afternoon.

RESULTS

Clipping of the left renal artery resulted in dramatic elevations in systolic blood pressure and heart rate. Renovascular hypertension was associated with a delay for reestablishing estrous cyclicity (50% of 2K1C rats failed to resume cycling by 15 days after surgery). In rats that resumed cycling, 2K1C female rats showed a decrease in sexual behavior, evidenced by a decreased lordosis quotient and a reduction in ovulation, as demonstrated by a decreased number of oocytes. Moreover, plasma levels of LH on the proestrus afternoon were reduced in hypertensive female rats, but no changes in estradiol or FSH were observed.

CONCLUSIONS

Our results demonstrate that renovascular hypertension induces an overall decrease in reproductive function in female rats. Most important, our results indicate that the animal model of renovascular hypertension could be used as a relevant tool to understand better the pathophysiological mechanisms involved in the reproductive deficits in women with renovascular hypertension.

Role of angiotensin in ovarian follicular development and ovulation in mammals: a review of recent advances

Angiotensin (Ang) II is widely known for its role in the control of systemic blood vessels. Moreover, Ang II acts on the vascular control of ovarian function, corpus luteum formation, and luteolysis. Over the past 10 years, our research group has been studying the new concept of the renin–angiotensin system (RAS) as an autocrine/paracrine factor regulating steroidogenesis and promoting different cellular responses in the ovary, beyond vascular function. We have developed and used differentin vivoandin vitroexperimental models to study the role of RAS in the ovary and a brief overview of our findings is presented here. It is widely accepted that there are marked species differences in RAS function in follicle development. Examples of species-specific functions of the RAS in the ovary include the involvement of Ang II in the regulation of follicle atresia in rats vs the requirement of this peptide for the dominant follicle development and ovulation in rabbits and cattle. More recently, Ang-(1–7), its receptor, and enzymes for its synthesis (ACE2, NEP, and PEP) were identified in bovine follicles, implying that Ang-(1–7) has an ovarian function. Other novel RAS components (e.g. (pro)renin receptor and renin-binding protein) recently identified in the bovine ovary show that ovarian RAS is poorly understood and more complex than previously thought. In the present review, we have highlighted the progress toward understanding the paracrine and autocrine control of ovarian antral follicle development and ovulation by ovarian tissue RAS, focusing onin vivostudies using cattle as a model.

Angiotensin II signaling promotes follicle growth and dominance in cattle

It is generally understood that angiotensin II (AngII) promotes follicle atresia in rats, although recent data suggested that this may not be true in cattle. In this study, we aimed to determine in vivo whether AngII alters follicle development in cattle, using intrafollicular injection of AngII or antagonist into the growing dominant follicle or the second largest subordinate follicle. Injection of saralasin, an AngII antagonist, into the growing dominant follicle inhibited follicular growth, and this inhibitory effect was overcome by systemic FSH supplementation. Injection of AngII into the dominant follicle did not affect follicular growth, whereas injection of AngII into the second largest follicle prevented the expected atresia of this subordinate follicle, and the treated follicle grew at the same rate as the dominant follicle for the next 24 h. Inhibition of AngII action in the dominant follicle decreased estradiol concentrations in follicular fluid and the abundance of mRNA encoding aromatase, 3β-hydroxysteroid dehydrogenase, LH receptor, and cyclinD2 in granulosa cells, with minimal effects on theca cells. The effect of AngII on aromatase mRNA levels was confirmed using an in vitro granulosa cell culture system. In conclusion, these data suggest that AngII signaling promotes follicle growth in cattle and does so by regulating genes involved in estradiol secretion and granulosa cell proliferation and differentiation.

Regulation of angiotensin type 2 receptor in bovine granulosa cells

Angiotensin II (AngII) is best known for its role in blood pressure regulation, but it also has documented actions in the reproductive system. There are two AngII receptors, type 1 (AGTR1) and type 2 (AGTR2). AGTR2 mediates the noncardiovascular effects of AngII and is expressed in the granulosa cell layer in rodents and is associated with follicle atresia. In contrast, expression of AGTR2 is reported to occur only in theca cells in cattle. The objective of the present study was to determine whether AngII also plays a role in follicle atresia in cattle. RT-PCR demonstrated AGTR2 mRNA in both granulosa and theca cells of bovine follicles. The presence of AGTR2 protein was confirmed by immunofluorescence. Abundance of AGTR2 mRNA in granulosa cells was higher in healthy compared with atretic follicles, whereas in theca cells, it did not change. Granulosa cells were cultured in serum-free medium, and treatment with hormones that increase estradiol secretion (FSH, IGF-I, and bone morphogenetic protein-7) increased AGTR2 mRNA and protein levels, whereas fibroblast growth factors inhibited estradiol secretion and AGTR2 protein levels. The addition of AngII or an AGTR2-specific agonist to granulosa cells in culture did not affect estradiol secretion or cell proliferation but inhibited abundance of mRNA encoding serine protease inhibitor E2, a protein involved in tissue remodeling. Because estradiol secretion is a major marker of nonatretic granulosa cells, these data suggest that AngII is not associated with follicle atresia in cattle but may have other specific roles during follicle growth.

Changes in the Messenger RNA Expressions of the Endothelin-1 and Angiotensin Systems in Mature Follicles of the Superovulated Bovine Ovary

The aim of the present study was to examine the messenger RNA expressions of the endothelin and angiotensin systems during the periovulatory phase in gonadotrophin releasing hormone (GnRH)-treated cows. Ovaries were collected by transvaginal ovariectomy (n=5 cows/group), and the follicles (n=5, one follicle/cow) were classified into the following groups: before GnRH administration (control, before LH surge), 3-5 h after GnRH (during LH surge), 10 h after GnRH; 20 h after GnRH, 25 h after GnRH (peri-ovulation), and early corpus luteum (CL) (Days 2-3). Expression of mRNA was investigated using quantitative real-time PCR. The expression of angiotensin converting enzyme (ACE) mRNA significantly decreased immediately after onset of the LH surge and remained at low levels. The levels of angiotensin II receptor type 1 (AT1R) and type 2 (AT2R) expression during the periovulatory period significantly decreased compared with other periods. The concentration of angiotensin II in follicular fluid began to increase 10 h after GnRH treatment and further increased as ovulation approached. The level of ET-1 mRNA significantly decreased 10 h after GnRH treatment compared with the levels before GnRH treatment and those of the early CL period. The expression of ETR-A and ETR-B mRNA during the periovulatory period were lower than in other periods. The expression of ECE-1 mRNA began to decrease in the LH surge period and significantly decrease in the periovulatory period compared with other periods. These results suggest that the vasoactive peptides angiotensin and endothelin may be associated with final maturation of follicles.

Mouse ovary developmental RNA and protein markers from gene expression profiling

To identify genes involved in morphogenetic events during mouse ovary development, we started with microarray analyses of whole organ RNA. Transcripts for 60% of the 15,000 gene NIA panel were detected, and about 2000 were differentially expressed in nascent newborn compared to adult ovary. Highly differentially expressed transcripts included noncoding RNAs and newly detected genes involved in transcription regulation and signal transduction. The phased pattern of newborn mouse ovary differentiation allowed us to (1) extend information on activity and stage specificity of cell type-specific genes; and (2) generate a list of candidate genes involved in primordial follicle formation, including podocalyxin (Podxl), PDGFR-beta, and a follistatin-domain-encoding gene Flst1. Oocyte-specific transcripts included many (e.g., Deltex2, Bicd2, and Zfp37) enriched in growing oocytes, as well as a novel family of untranslated RNA's (RLTR10) that is selectively expressed in early stage follicles. The results indicate that global expression profiling of whole organ RNA provides sensitive first-line information about ovarian histogenesis for which no in vitro cell models are currently available.