Effects of gonadal hormones on thymus gland after bilateral ovariectomy and orchidectomy in rats

Effects of 12 Weeks of Daily Melatonin Administration on Inflammatory Markers and Adipose Tissue Mass of Rats under Hypoestrogenism

Background and Objectives: The hormonal state of hypoestrogenism is associated with the accumulation of white adipose tissue, which can induce an increase in pro-inflammatory markers, leading to progressive health complications. Melatonin can act on adipose tissue mass, promoting its reduction and influencing inflammation, reducing IL-6 and releasing IL-10, pro- and anti-inflammatory markers, respectively. However, the role of melatonin regarding such parameters under the context of hypoestrogenism remains unknown. The aim of this study was to determine the effect of 12 weeks of hypoestrogenism and melatonin on white adipose tissue mass and circulating levels of IL-6, IL-10, TGF-β-1, and leukotriene C4 (LTC4). Materials and Methods: The animals (Wistar rats with sixteen weeks of age at the beginning of the experiment) under hypoestrogenism were submitted to the surgical technique of bilateral ovariectomy. The animals received melatonin (10 mg·kg-1) or vehicles by orogastric gavage every day for 12 weeks and administration occurred systematically 1 h after the beginning of the dark period. White adipose tissue (perigonadal, peritoneal, and subcutaneous) was collected for mass recording, while blood was collected for the serum determination of IL-6, IL-10, TGF-β-1, and LTC4. Results: Hypoestrogenism increased the perigonadal and subcutaneous mass and IL-6 levels. Melatonin kept hypoestrogenic animals in physiological conditions similar to the control group and increased thymus tissue mass. Conclusions: Hypoestrogenism appears to have a negative impact on white adipose tissue mass and IL-6 and although melatonin commonly exerts a significant effect in preventing these changes, this study did not have a sufficiently negative impact caused by hypoestrogenism for melatonin to promote certain benefits.

Sex differences in neuroimmunoendocrine communication. Involvement on longevity

Endocrine, nervous, and immune systems work coordinately to maintain the global homeostasis of the organism. They show sex differences in their functions that, in turn, contribute to sex differences beyond reproductive function. Females display a better control of the energetic metabolism and improved neuroprotection and have more antioxidant defenses and a better inflammatory status than males, which is associated with a more robust immune response than that of males. These differences are present from the early stages of life, being more relevant in adulthood and influencing the aging trajectory in each sex and may contribute to the different life lifespan between sexes.

The potential role of the thymus in immunotherapies for acute myeloid leukemia

Understanding the factors which shape T-lymphocyte immunity is critical for the development and application of future immunotherapeutic strategies in treating hematological malignancies. The thymus, a specialized central lymphoid organ, plays important roles in generating a diverse T lymphocyte repertoire during the infantile and juvenile stages of humans. However, age-associated thymic involution and diseases or treatment associated injury result in a decline in its continuous role in the maintenance of T cell-mediated anti-tumor/virus immunity. Acute myeloid leukemia (AML) is an aggressive hematologic malignancy that mainly affects older adults, and the disease's progression is known to consist of an impaired immune surveillance including a reduction in naïve T cell output, a restriction in T cell receptor repertoire, and an increase in frequencies of regulatory T cells. As one of the most successful immunotherapies thus far developed for malignancy, T-cell-based adoptive cell therapies could be essential for the development of a durable effective treatment to eliminate residue leukemic cells (blasts) and prevent AML relapse. Thus, a detailed cellular and molecular landscape of how the adult thymus functions within the context of the AML microenvironment will provide new insights into both the immune-related pathogenesis and the regeneration of a functional immune system against leukemia in AML patients. Herein, we review the available evidence supporting the potential correlation between thymic dysfunction and T-lymphocyte impairment with the ontogeny of AML (II-VI). We then discuss how the thymus could impact current and future therapeutic approaches in AML (VII). Finally, we review various strategies to rejuvenate thymic function to improve the precision and efficacy of cancer immunotherapy (VIII).

Thymus Degeneration and Regeneration

The immune system’s ability to resist the invasion of foreign pathogens and the tolerance to self-antigens are primarily centered on the efficient functions of the various subsets of T lymphocytes. As the primary organ of thymopoiesis, the thymus performs a crucial role in generating a self-tolerant but diverse repertoire of T cell receptors and peripheral T cell pool, with the capacity to recognize a wide variety of antigens and for the surveillance of malignancies. However, cells in the thymus are fragile and sensitive to changes in the external environment and acute insults such as infections, chemo- and radiation-therapy, resulting in thymic injury and degeneration. Though the thymus has the capacity to self-regenerate, it is often insufficient to reconstitute an intact thymic function. Thymic dysfunction leads to an increased risk of opportunistic infections, tumor relapse, autoimmunity, and adverse clinical outcome. Thus, exploiting the mechanism of thymic regeneration would provide new therapeutic options for these settings. This review summarizes the thymus’s development, factors causing thymic injury, and the strategies for improving thymus regeneration.

Thymus-Pineal Gland Axis: Revisiting Its Role in Human Life and Ageing

For years the thymus gland (TG) and the pineal gland (PG) have been subject of increasingly in-depth studies, but only recently a link that can associate the activities of the two organs has been identified. Considering, on the one hand, the well-known immune activity of thymus and, on the other, the increasingly emerging immunological roles of circadian oscillators and the rhythmically secreted main pineal product, melatonin, many studies aimed to analyse the possible existence of an interaction between these two systems. Moreover, data confirmed that the immune system is functionally associated with the nervous and endocrine systems determining an integrated dynamic network. In addition, recent researches showed a similar, characteristic involution process both in TG and PG. Since the second half of the 20th century, evidence led to the definition of an effectively interacting thymus-pineal axis (TG-PG axis), but much has to be done. In this sense, the aim of this review is to summarize what is actually known about this topic, focusing on the impact of the TG-PG axis on human life and ageing. We would like to give more emphasis to the implications of this dynamical interaction in a possible therapeutic strategy for human health. Moreover, we focused on all the products of TG and PG in order to collect what is known about the role of peptides other than melatonin. The results available today are often unclear and not linear. These peptides have not been well studied and defined over the years. In this review we hope to awake the interest of the scientific community in them and in their future pharmacological applications.

CD8 T-cell Recruitment Into the Central Nervous System of Cuprizone-Fed Mice: Relevance to Modeling the Etiology of Multiple Sclerosis

Cuprizone (CPZ)-feeding in mice induces atrophy of peripheral immune organs (thymus and spleen) and suppresses T-cell levels, thereby limiting its use as a model for studying the effects of the immune system in demyelinating diseases such as Multiple Sclerosis (MS). To investigate whether castration (Cx) can protect the peripheral immune organs from CPZ-induced atrophy and enable T-cell recruitment into the central nervous system (CNS) following a breach of the blood-brain barrier (BBB), three related studies were carried out. In Study 1, Cx prevented the dose-dependent reductions (0.1% < 0.2% CPZ) in thymic and splenic weight, size of the thymic medulla and splenic white pulp, and CD4 and CD8 (CD4/8) levels remained comparable to gonadally intact (Gi) control males. Importantly, 0.1% and 0.2% CPZ were equipotent at inducing central demyelination and glial activation. In Study 2, combining Cx with 0.1% CPZ-feeding and BBB disruption with pertussis toxin (PT) enhanced CD8⁺ T-cell recruitment into the CNS. The increased CD8⁺ T-cell level observed in the parenchyma of the cerebrum, cerebellum, brainstem and spinal cord were confirmed by flow cytometry and western blot analyses of CNS tissue. In Study 3, PT+0.1% CPZ-feeding to Gi female mice resulted in similar effects on the peripheral immune organs, CNS demyelination, and gliosis comparable to Gi males, indicating that testosterone levels alone were not responsible for the immune response seen in Study 2. The combination of Cx+0.1% CPZ-feeding+PT indicates that CPZ-induced demyelination can trigger an “inside-out” immune response when the peripheral immune system is spared and may provide a better model to study the initiating events in demyelinating conditions such as MS.

Pregnancy protects against the pro-inflammatory respiratory responses induced by particulate matter exposure

BACKGROUND

Little is known about the effect of pregnancy on the response to particulate matter. The aim of this study was to determine if pregnancy increases the susceptibility to PM from different sources using a mouse model.

METHODS

Pregnant, eight-week-old C57BL/6J mice were exposed intranasally to 50 μg of diesel exhaust particles (DEP), iron oxide (Fe₂O₃) or silica (SiO₂) in 50 μL of saline, or saline alone, on gestational day (E)7.5, E12.5 and E17.5. Groups of non-pregnant mice were exposed on day (D)0, D5 and D10. Biological samples were collected 24 h after the last exposure. Serum IL-4 and IL-6 levels were quantified by ELISA. Bronchoalveolar lavage (BAL) fluid was collected for inflammatory cells counts and assessment of IFN-ɣ, IL-4, IL-5, IL-6, IL-8 and IL-10 levels by ELISA. The spleen and thymus were also collected and the percentage of B cells and CD4⁺, CD8⁺ and CD4⁺CD25 ⁺ T cells were determined by flow cytometry.

RESULTS

Exposure to silica caused an influx of lymphocytes, eosinophils and neutrophils into the lung. The magnitude of this response was suppressed by pregnancy. Pregnancy also enhanced the production of CD4⁺CD25 ⁺ T cells in response to DEP and silica exposure.

CONCLUSIONS

Collectively, our data suggest that pregnancy reduces the inflammatory response to silica and alters the immune response to DEP. These responses were accompanied by pregnancy related changes including increased IL-4 production, reduced IL-8 production and an increase in the proportion of CD4⁺CD25 ⁺ T cells in response to PM exposure.

Immunity and longevity

The role of immune system is to protect the organism from the not built-in program-like alterations inside and against the agents penetrating from outside (bacteria, viruses, and protozoa). These functions were developed and formed during the evolution. Considering these functions, the immune system promotes the lengthening of lifespan and helps longevity. However, some immune functions have been conveyed by men to medical tools (e.g., pharmaceuticals, antibiotics, and prevention), especially in our modern age, which help the struggle against microbes, but evolutionarily weaken the immune system. Aging is a gradual slow attrition by autoimmunity, directed by the thymus and regulated by the central nervous system and pineal gland. Considering this, thymus could be a pacemaker of aging. The remodeling of the immune system, which can be observed in elderly people and centenarians, is probably not a cause of aging, but a consequence of it, which helps to suit immunity to the requirements. Oxidative stress also helps the attrition of the immune cells and antioxidants help to prolong lifespan. There are gender differences in the aging of the immune system as well as in the longevity. There is an advantage for women in both cases. This can be explained by hormonal differences (estrogens positively influences both processes); however, social factors are also not excluded. The endocrine disruptor chemicals act similar to estrogens, like stimulating or suppressing immunity and provoking autoimmunity; however, their role in longevity is controversial. There are some drugs (rapamycin, metformin, and selegiline) and antioxidants (as vitamins C and E) that prolong lifespan and also improve immunity. It is difficult to declare that longevity is exclusively dependent on the state of the immune system; however, there is a parallelism between the state of immune system and lifespan. It seems likely that there is not a real decline of immunity during aging, but there is a remodeling of the system according to the claims of senescence. This is manifested in the remaining (sometimes stronger) function of memory cells in contrast to the production and number of the new antigen-reactive naive T-cells.

Oestrogen receptor distribution related to functional thymus anatomy of the European sea bass, Dicentrarchus labrax

In jawed vertebrates, the crosstalk between immune and endocrine system as well as many fundamental mechanisms of T cell development are evolutionary conserved. Oestrogens affect mammalian thymic function and plasticity, but the mechanisms of action and the oestrogen receptors involved remain unclear. To corroborate the oestrogenic regulation of thymic function in teleosts and to identify the implicated oestrogen receptor subtypes, we examined the distribution of nuclear and membrane oestrogen receptors within the thymus of the European Sea bass, Dicentrarchus labrax, in relation to its morpho-functional organisation. Immunohistological analysis specified thymus histology and organisation in teleosts and described, for the first time, Hassall's corpuscle like structures in the medulla of sea bass. All oestrogen receptors were expressed at the transcript and protein level, both in T cells and in stromal cells belonging to specific functional areas. These observations suggest complex regulatory actions of oestrogen on thymic function, notably through the stromal microenvironment, comprising both, genomic and non-genomic pathways that are likely to affect T cell maturation and trafficking processes. Comparison with birds, rodents and humans supports the thymic localization of oestrogen receptors and suggests that oestrogens modulate T cell maturation in all gnathostomes.

Peripubertal ovariectomy influences thymic adrenergic network plasticity in adult rats

The study investigated the influence of peripubertal ovariectomy on the thymic noradrenaline (NA) concentration, and the thymocyte NA content and β2- and α1-adrenoceptor (AR) expression in adult 2- and 11-month-old rats. In control rats, the thymic NA concentration increased with age. This increase reflected rise in the density of catecholamine (CA)-containing fluorescent nerve fibers and cells and their CA content. Additionally, the average β2- and α1-AR thymocyte surface density changed in the opposite direction with age; the density of β2-AR decreased, whereas that of α1-AR increased. Ovariectomy diminished the thymic NA concentration in 2-month-old rats. This reflected the decrease in the density of fluorescent nerve fibers, and CA content in fluorescent nerve fibers and non-lymphoid cells, since the thymocyte NA content was increased in ovariectomized (Ox) rats. Estrogen supplementation prevented the ovariectomy-induced changes. In Ox rats, the density of CA-synthesizing nerve fibers and non-lymphoid cells diminished with age. To the contrary, NA content in thymocytes increased with age, but it did not exceed that in 11-month-old controls. Additionally, ovariectomy diminished the average thymocyte surface density of β2-ARs, but it increased that of α1-ARs in 2-month-old-rats (due to estrogen, and estrogen and progesterone deficiency, respectively). These changes, despite of the rise in circulating estrogen level post-ovariectomy, remained stable with age. This most likely reflected a decreased sensitivity to estrogen action, as a consequence of the hormone misprinting in peripubertal age. The analysis of thymocyte proliferation in culture suggested that age- and ovariectomy-induced alterations in thymocyte NA synthesis and AR expression altered NA autocrine/paracrine action on thymocytes. In conclusion, the study indicates that the ovarian hormone deficiency in peripubertal age affects ovarian steroid-dependent remodeling of thymic adrenergic regulatory network in adult rats.

Sex steroid ablation: an immunoregenerative strategy for immunocompromised patients

Age-related decline in thymic function is a well-described process that results in reduced T-cell development and thymic output of new naïve T cells. Thymic involution leads to reduced response to vaccines and new pathogens in otherwise healthy individuals; however, reduced thymic function is particularly detrimental in clinical scenarios where the immune system is profoundly depleted such as after chemotherapy, radiotherapy, infection and shock. Poor thymic function and restoration of immune competence has been correlated with an increased risk of opportunistic infections, tumor relapse and autoimmunity. Apart from their primary role in sex dimorphism, sex steroid levels profoundly affect the immune system in general and, in fact, age-related thymic involution has been at least partially attributed to the increase in sex steroids at puberty. Subsequently it has been demonstrated that the removal of sex steroids, or sex steroid ablation (SSA), triggers physiologic changes that ultimately lead to thymic re-growth and improved T-cell reconstitution in settings of hematopoietic stem cell transplant (HSCT). Although the cellular and molecular process underlying these regenerative effects are still poorly understood, SSA clearly represents an attractive therapeutic approach to enhance thymic function and restore immune competence in immunodeficient individuals.

The production of alpha/beta and gamma/delta double negative (DN) T-cells and their role in the maintenance of pregnancy

The ability of the thymus gland to convert bone marrow-derived progenitor cells into single positive (SP) T-cells is well known. In this review we present evidence that the thymus, in addition to producing SP T-cells, also has a pathway for the production of double negative (DN) T-cells. The existence of this pathway was noted during our examination of relevant literature to determine the cause of sex steroid-induced thymocyte loss. In conducting this search our objective was to answer the question of whether thymocyte loss is the end product of a typical interaction between the reproductive and immune systems, or evidence that the two systems are incompatible. We can now report that "thymocyte loss" is a normal process that occurs during the production of DN T-cells. The DN T-cell pathway is unique in that it is mediated by thymic mast cells, and becomes functional following puberty. Sex steroids initiate the development of the pathway by binding to an estrogen receptor alpha located in the outer membrane of the mast cells, causing their activation. This results in their uptake of extracellular calcium, and the production and subsequent release of histamine and serotonin. Lymphatic vessels, located in the subcapsular region of the thymus, respond to the two vasodilators by undergoing a substantial and preferential uptake of gamma/delta and alpha/beta DN T- cells. These T- cells exit the thymus via efferent lymphatic vessels and enter the lymphatic system.The DN pathway is responsible for the production of three subsets of gamma/delta DN T-cells and one subset of alpha/beta DN T-cells. In postpubertal animals approximately 35 % of total thymocytes exit the thymus as DN T-cells, regardless of sex. In pregnant females, their levels undergo a dramatic increase. Gamma/delta DN T-cells produce cytokines that are essential for the maintenance of pregnancy.

Reshaping of T-lymphocyte compartment in adult prepubertaly ovariectomised rats: a putative role for progesterone deficiency

This study explores the role of ovarian hormones in the phenotypic shaping of peripheral T-cell pool over the reproductive lifespan of rats. For this purpose, 2-month-old prepubertally ovariectomised (Ox) rats, showing oestrogen and progesterone deficiency, and 11-month-old Ox rats, exhibiting only progesterone deficiency, were examined for thymus output, and cellularity and composition of major TCRαβ+ peripheral blood lymphocyte (PBL) and splenocyte subsets. Although ovariectomy increased thymic output in both 2- and 11-month-old rats, the count of both CD4+ and CD8+ PBLs and splenocytes increased only in the former. In the blood and spleen of 11-month-old Ox rats only the count of CD8+ cells increased. Although ovariectomy affected the total CD4+ count in none of the examined compartments from the 11-month-old rats, it increased CD4+FoxP3+ PBL and splenocyte relative proportions over those in the age-matched controls. The age-related differences in the cellularity and the major subset composition in Ox rats were linked to the differences in the ovarian steroid hormone levels registered in 2- and 11-month-old rats. The administration of progesterone to Ox rats during the seven days before the sacrificing confirmed contribution of this hormone deficiency to the ovariectomy-induced changes in the TCRαβ+ PBL and splenocyte pool from 11-month-old rats. The expansion of the CD8+ splenocyte subset in the 11-month-old Ox rats reflected increases in cellularity of memory and, particularly, naïve cells. This was due to greater thymic output of CD8+ cells and homeostatic proliferation than apoptosis in 11-month-old Ox rats when compared with age-matched sham-Ox control rats. The homeostatic changes within CD8+ splenocyte pool from 11-month-old Ox rats, most likely, reflected the enhanced splenic IL-7 and TGF-β mRNA expression. Overall, in adult female rats, circulating oestrogen and progesterone provide maintenance of T-cell counts, a diversity of T-cell repertoire, and the main T-cell subset composition in the periphery. Progesterone deficiency affects mainly the CD8+ lymphocyte compartment through increasing thymic CD8+ cell export and upsetting homeostatic regulation within the CD8+ splenocyte pool. These alterations were reversible through progesterone supplementation.

Ovarian hormone withdrawal in prepubertal developmental stage does not prevent thymic involution in rats

The study was undertaken to assess the effects of ovarian hormone withdrawal in prepubertal age on thymopoiesis in 2- (young) and 11-month-old (middle-aged) rats. In ovariectomized (Ox) rats, irrespective of age, thymic weight and cellularity were greater than in age-matched controls, but the values of both parameters exhibited the age-related decline. In addition, although thymopoietic efficiency was increased in both groups of Ox rats when compared with age-matched controls, thymopoiesis exhibited the age-related decline mirrored in the lower numbers of both CD4+ and CD8+ recent thymic emigrants in peripheral blood. This reflected the prethymic changes affecting bone marrow progenitor generation/entry and the thymic alterations encompassing the impaired progenitor progression through early pre-T-cell receptor developmental stages (defined by CD45RC/CD2 expression) and, possibly, a more pronounced decrease in the proliferation of the most mature thymocytes. Apart from the changes at thymocyte level, in Ox rats the age-related alterations in thymic stroma (substantiated in a prominent loss of thymic epithelial cells) were registered. Ovariectomy-induced changes in thymic lymphoid and epithelial component, most probably, influenced each other leading to the increase in thymic expression of interleukin-6 and interleukin-7 mRNAs along with time after ovariectomy. Collectively, the study showed that the withdrawal of ovarian hormones in prepubertal age increases the efficiency of thymopoiesis in young adult rats, but does not prevent decline in thymopoiesis occurring with age.

Role of ovarian hormones in T-cell homeostasis: from the thymus to the periphery

The study explored the putative role of ovarian hormones in the peripubertal remodelling of peripheral T-cell compartment. Ovariectomy at age of 1 month enhanced the peripubertal rise in CD4+ and CD8+ cell numbers in peripheral blood (PB) and spleen from 2-month-old rats. This reflected maintenance of thymopoietic efficiency at the prepubertal level (judging by numbers of the most mature CD4+ and CD8+ thymocytes and recent thymic emigrants) and alterations in T-cell survival/proliferation in the periphery. Compared with age-matched controls, the frequency of apoptotic cells among CD8+ peripheral blood lymphocytes (PBLs) and CD4+ and CD8+ splenocytes was diminished in ovariectomized (Ox) rats, at least partly, due to lower CD95 surface density. The diminished frequency of the apoptotic T splenocytes could also be associated with the rise in the amount of splenic IL-7 mRNA. Additionally, the latter finding was consistent with the augmented proliferation of CD4+ and CD8+ splenocytes. However, the enhanced proliferation of these cells could also be linked to the rise in IL-2 receptor surface density. This increase was related to the enhanced splenic TNF-α mRNA expression. Additionally, ovariectomy led to the phenotypic alterations in the major PBL and splenic T-cell subsets by diminishing/preventing the peripubertal changes in the frequency of cells at distinct stages of post-thymic differentiation/maturation (recent thymic emigrants, mature naïve and memory cells), and by decreasing the frequency of NKT cells within peripheral CD8+ subsets. In addition to numerical and phenotypic changes in T-cell compartment (due to the lack of ovarian hormone action at both the thymic and peripheral level), Ox rats exhibited a much larger delayed-type hypersensitivity (DTH) response compared with age-matched controls. This suggested the augmented T-cell-mediated immune response in Ox rats compared with aged-matched controls.

Reversal of age-related thymic involution by an LHRH agonist in miniature swine

BACKGROUND AND AIMS OF STUDY: We have previously demonstrated a requirement for the presence of a juvenile thymus for the induction of transplantation tolerance to renal allografts by a short-course of calcineurin inhibition in miniature swine. We have also shown that aged, involuted thymi can be rejuvenated when transplanted as vascularized thymic lobes into juvenile swine recipients. The present studies were aimed at elucidating the extrinsic factors facilitating this restoration of function in the aged thymus. In particular, we tested the impact of sex steroid blockade by Luteinizing Hormone-Releasing Hormone (LHRH).

MATERIALS AND METHODS

30 naive animals (25 males and 5 females) were used for measurement of serum testosterone levels. 3 mature male pigs (aged at 22, 22 and 29 months old) were used to test the effects of Lupron (LHRH analog) injection at 45 mg (per 70-80 kg body weight) as a 3-month depot on testosterone levels and thymic rejuvenation. Thymic rejuvenation was assessed by histology, flow cytometric analysis, morphometric analysis and TREC assays.

RESULTS

Hormonal alterations were induced by Lupron and resulted in macroscopic and histologic regeneration of the thymus of aged animals within 2 months, as evidenced by restoration of juvenile thymus architecture and increased cellularity. Two animals that were evaluated for TREC both showed increased levels in the periphery following Lupron treatment.

CONCLUSION

Treatment of aged animals with Lupron leads to thymic rejuventaion in adult miniature swine. This result could expand the applicability of thymus-dependent tolerance-inducing regimens to adult recipients.

Role of testosterone in mediating prenatal ethanol effects on hypothalamic-pituitary-adrenal activity in male rats

Prenatal ethanol (E) exposure programs the fetal hypothalamic-pituitary-adrenal (HPA) and -gonadal (HPG) axes such that E rats show HPA hyperresponsiveness to stressors and altered HPG and reproductive function in adulthood. Importantly, prenatal ethanol may differentially alter stress responsiveness in adult male and female offspring compared to their control counterparts. To test the hypothesis that alterations in HPA activity in E males are mediated, at least in part, by ethanol-induced changes in the capacity of testosterone to regulate HPA activity, we explored dose-related effects of testosterone on HPA and HPG function in adult male offspring from prenatal E, pair-fed (PF) and ad libitum-fed control (C) dams. Our data suggest that E males show changes in both HPA and HPG regulation, as well as altered sensitivity to the inhibitory effects of testosterone. While gonadectomy (GDX) reduced weight gain in all animals, low testosterone replacement restored body weights in PF and C but not E males. Further, sensitivity of the thymus and adrenal to circulating testosterone was reduced in E rats. In addition, stress-induced corticosterone (CORT) levels were increased in PF and C but not E males following GDX, and while low dose testosterone replacement restored CORT levels for PF and C, high testosterone levels were needed to normalize CORT levels for E males. A negative correlation between pre-stress testosterone and post-stress CORT levels in C but not in E and PF males further supports the finding of reduced sensitivity to testosterone. Importantly, testosterone appeared to have reduced effects on central corticotrophin releasing hormone (CRH) pathways in E, but greater effects on central arginine vasopressin (AVP) pathways in E and/or PF compared to C males. Testosterone also had less of an inhibitory effect on stress-induced luteinizing hormone increases in E than in PF and C males following GDX. In addition, androgen receptor mRNA levels in the medial preoptic nucleus and the principal nucleus of posterior bed nucleus of the stria terminalis were lower in E and PF compared to C males under intact conditions. Together, these data support our previous work suggesting altered sensitivity to testosterone in E males. Furthermore, differential effects of testosterone on the complex balance between central CRH and central AVP pathways may play a role in the HPA alterations observed. That some findings were similar in E and PF males suggest that nutritional effects of diet may have played a role in mediating at least some of the changes seen in E animals.

Role of ovarian hormones in age-associated thymic involution revisited

A commonly held view that ovarian hormones are causally involved in age-associated thymic involution has been recently challenged. In particular, their relevance in the progression of thymic involution has been disputed. To reassess this issue 10-month-old rats with well advanced thymic involutive changes were ovariectomized (Ovx), and after 1 month thymic cellularity, thymocyte development and levels of recent thymic emigrants (RTEs) were examined in peripheral blood and spleen. In addition, the distribution of major conventional and regulatory T-cell subsets was analyzed in the same peripheral lymphocyte compartments. Ovariectomy increased thymic weight and cellularity above the levels in both 10-month-old and age-matched controls indicating that ovarian hormone ablation not only prevented further progression of thymic involution, but also reversed it. The increased thymic cellularity was accompanied by altered thymocyte differentiation/maturation culminating in increased thymic output of naïve T cells as indicated by elevated levels of both CD4+ and CD8+ RTEs in peripheral blood and spleen. The changes in T-cell development produced: (i) a disproportional increase in cellularity across thymocyte subsets, so that relative proportions of cells at all maturational stages preceding the CD4+CD8+ T cell receptor (TCR)alphabeta(low) stage were reduced; the relative numbers of CD4+CD8+ TCRalphabeta(low) cells entering positive selection and their immediate CD4+CD8+ TCRalphabeta(high) descendents were increased, while those of the most mature CD4+CD8- and CD4-CD8+ TCRalphabeta(high) cells remained unaltered; (ii) enhanced cell proliferation across all thymocyte subsets and (iii) reduced apoptosis of cells within the CD4+CD8+ thymocyte subset. The augmented thymic output of naïve T cells in Ovx rats most likely reflected an early disinhibition of thymocyte development followed by increased positive/reduced negative selection, at least partly, due to raised thymocyte surface Thy-1 expression. The greater number of CD4+CD25+Foxp3+ cells in both thymus and peripheral blood suggested augmented thymic production of these cells. In addition, an increased CD4+/CD8+ cell ratio was found in the spleen of Ovx rats. Thus, ovarian hormone ablation led not only to increased diversity of the T-cell repertoire, but also to a new balance among distinct T-cell subsets in the periphery.

The estrogen-injected female mouse: new insight into the etiology of PCOS

BACKGROUND

Female mice and rats injected with estrogen perinatally become anovulatory and develop follicular cysts. The current consensus is that this adverse response to estrogen involves the hypothalamus and occurs because of an estrogen-induced alteration in the GnRH delivery system. Whether or not this is true has yet to be firmly established. The present study examined an alternate possibility in which anovulation and cyst development occurs through an estrogen-induced disruption in the immune system, achieved through the intermediation of the thymus gland.

METHODS, RESULTS AND CONCLUSION

A putative role for the thymus in estrogen-induced anovulation and follicular cyst formation (a model of PCOS) was examined in female mice by removing the gland prior to estrogen injection. Whereas all intact, female mice injected with 20 microg estrogen at 5-7 days of age had ovaries with follicular cysts, no cysts were observed in animals in which thymectomy at 3 days of age preceded estrogen injection. In fact, after restoring immune function by thymocyte replacement, the majority of thymectomized, estrogen-injected mice had ovaries with corpora lutea. Thus, when estrogen is unable to act on the thymus, ovulation occurs and follicular cysts do not develop. This implicates the thymus in the cysts' genesis and discounts the role of the hypothalamus. Subsequent research established that the disease is transferable by lymphocyte infusion. Transfer took place between 100-day-old estrogen-injected and 15-day-old naïve mice only when recipients were thymectomized at 3 days of age. Thus, a prerequisite for cyst formation is the absence of regulatory T cells. Their absence in donor mice was judged to be the result of an estrogen-induced increase in the thymus' vascular permeability, causing de facto circumvention of the final stages of regulatory T cell development. The human thymus has a similar vulnerability to steroid action during the fetal stage. We propose that in utero exposure to excessive levels of steroids such as estrogen has a long-term effect on the ability of the thymus to produce regulatory T cells. In female offspring this can lead to PCOS.

Activation of STAT3 in thymic epithelial tumours correlates with tumour type and clinical behaviour

The STAT3 (signal transducers and activators of transcription 3) signalling pathway plays a pivotal role in oncogenesis and appears essential for postnatal maintenance of thymic architecture and thymocyte survival. The association of STAT3 activation with thymic epithelial tumours (TETs) and myasthenia gravis (MG) has not been elucidated. In this study, 118 cases of TET and 25 non-neoplastic thymic tissue samples were evaluated for STAT3 and phospho-STAT3 (pSTAT3) expression immunohistochemically. In addition, 44 normal thymuses of different ages were included for comparison. It was found that STAT3 activation in thymic epithelial cells (TECs), as evidenced by pSTAT3 expression and/or nuclear STAT3, was present in the majority of non-neoplastic thymuses (88%, 22/25), including those from young children, but not in fetal thymus. In thymoma (n = 73), activated STAT3 was noted at a significantly higher frequency in the cases of lymphocyte-rich thymoma (ie types AB, B1, and B2, 46%, 23/50) in comparison with lymphocyte-depleted thymoma (types A and B3, 1/23) (p = 0.009). Thymoma with activated STAT3 tended to present at an earlier stage, show complete resectability and less aggressive behaviour, and have a higher correlation with MG than the STAT3-negative/inactive group (p < 0.05). In contrast, thymic carcinoma with activated STAT3 (14/45, 31%) had significantly higher rates of unresectability, vascular invasion, and regional lymph node metastasis (p < 0.05). These data provide the first evidence that constitutive STAT3 activation is seen in both benign and neoplastic thymic tissue and is associated with the persistence of thymic tissue and the presence of MG. It is likely to be induced by different factors in thymoma and thymic carcinoma.

Antiarthritic Effects of Relaxin, in Combination with Estrogen, in Rat Adjuvant-Induced Arthritis

The incidence and severity of rheumatoid arthritis (RA) are reduced during pregnancy. Estradiol-17beta and relaxin (RLX), hormones of pregnancy, are implicated in decreased immune responsiveness. The aim of this study was to determine the effects of estrogen and RLX, alone or in combination, on the development of adjuvant-induced arthritis (AIA) in ovariectomized (OVX) Lewis rats. Arthritis was induced on day 0 by adjuvant injection in the left hind paw. Rats were treated with estradiol valerate (E), porcine RLX, E + RLX, or vehicle. Healthy OVX control animals were used for comparison. Treatment with RLX or E alone decreased adjuvant-induced inflammation in both the injected (primary) and noninjected (secondary) hind paws. Combined treatment with E and RLX was more effective than either hormone alone in blocking secondary paw inflammation. Furthermore, E plus RLX reduced changes to spleen and thymus weights induced by adjuvant injection. Both E and RLX alone decreased circulating tumor necrosis factor (TNF) alpha. The combination of E and RLX resulted in a greater decline in TNFalpha than treatment with either hormone alone. There was no effect of hormones on the proinflammatory cytokine, interleukin (IL)-1beta. The anti-inflammatory cytokine IL-10 increased in response to E and E plus RLX. In conclusion, combined therapy with E and RLX was more effective than either hormone alone in reducing chronic inflammation, joint changes, and high circulating TNFalpha associated with AIA in rats. Accordingly, these hormones could play a role in reducing RA-induced inflammation during pregnancy by an effect on the immune system.

Thymic rejuvenation and the induction of tolerance by adult thymic grafts

The thymus, the site of origin of T cell immunity, shapes the repertoire of T cell reactivity through positive selection of developing T cells and prevents autoimmunity through negative selection of autoreactive T cells. Previous studies have demonstrated an important role for the thymus not only in central deletional tolerance, but also in the induction of peripheral tolerance by vascularized renal allografts in juvenile miniature swine recipients. The same protocol did not induce tolerance in thymectomized recipients nor in recipients beyond the age of thymic involution. We subsequently reported that vascularized thymic lobe grafts from juvenile donors were capable of inducing tolerance in thymectomized juvenile hosts. However, the important question remained whether aged, involuted thymus could also induce tolerance if transplanted into thymectomized hosts, which, if true, would imply that thymic involution is not an intrinsic property of thymic tissue but is rather determined by host factors extrinsic to the thymus. We report here that aged, involuted thymus transplanted as a vascularized graft into juvenile recipients leads to rejuvenation of both thymic structure and function, suggesting that factors extrinsic to the thymus are capable of restoring juvenile thymic function to aged recipients. We show furthermore that rejuvenated aged thymus has the ability to induce transplant tolerance across class I MHC barriers. These findings indicate that it may be possible to manipulate thymic function in adults to induce transplantation tolerance after the age of thymic involution.

Cellular mechanism of estrogen-induced thymic involution in wall lizard: caspase-dependent action

The present study, for the first time in an ectothermic vertebrate, demonstrates the cellular mechanism of estrogen-induced thymic involution. Ovariectomy in lizards during the preparatory phase of the reproductive cycle resulted in distinct differentiation of cortico-medullary regions and increase in cellularity, especially in the cortical region. The ovariectomy-induced changes were reversed following administration of 17-estradiol (E2), suggesting a primary role of E2 in causing thymic atrophy. To understand the cellular mechanism of E2-induced thymic atrophy, in vitro effect of E2 was investigated on thymocyte proliferation and apoptosis. E2 decreased the uptake of tritiated thymidine (3H-TdR) by thymocytes in a dose-dependent manner, suggesting that estrogen directly inhibits the thymocyte proliferation. Unlike proliferation, E2 did not have any direct effect on thymocyte apoptosis, as evident by DNA gel electrophoretic, flow cytometric or fluorescence microscopic studies. However, in the presence of thymic epithelial cell-rich stromal components (TEC), E2 treatment at low or high concentrations resulted in depolarization of plasma membrane, DNA fragmentation and decrease in DNA content. This suggests that E2 indirectly, through TEC-secreted factors, controls thymocyte apoptosis. Similar result was observed following fluorescence microscopy. The indirect effect of E2 was further ascertained with the findings that E2-pretreated TEC-conditioned medium accelerated the thymocyte apoptosis. Nevertheless, exposure of thymocytes to E2 was seen to be inevitable for the apoptotic action of TEC-secreted paracrine factors. In the presence of TEC, a positive reaction for caspase-3, -7 and -9 and enzyme substrate, poly(ADP-ribose) polymerase (PARP) in response to E2 suggests the caspase-dependent thymocyte apoptosis in the wall lizard Hemidactylus flaviviridis. Further, E2 was shown to act through genomic pathway, since the receptor antagonist tamoxifen and transcription/translation inhibitors blocked its apoptotic action. Interestingly, the apoptotic effect of E2 was effectively decreased by progesterone.

What are the effects of maternal and pre-adult environments on ageing in humans, and are there lessons from animal models?

An open issue in research on ageing is the extent to which responses to the environment during development can influence variability in life span in animals, and the health profile of the elderly in human populations. Both affluence and adversity in human societies have profound impacts on survivorship curves, and some of this effect may be traceable to effects in utero or in infancy. The Barker Hypothesis that links caloric restriction in very early life to disruptions of glucose-insulin metabolism in later life has attracted much attention, as well as some controversy, in medical circles. It is only rarely considered by evolutionary biologists working on phenotypic plasticity, or by biogerontologists studying model organisms such as C. elegans or Drosophila. One crucial mechanism by which animals can respond in an adaptive manner to adverse conditions, for example in nutrition or infection, during development is phenotypic plasticity. Here we begin with a discussion of adaptive plasticity in animals before asking what such phenomena may reveal of relevance to rates of ageing in animals, and in humans. We survey the evidence for effects on adult ageing of environmental conditions during development across mammalian and invertebrate model organisms, and ask whether evolutionary conserved mechanisms might be involved. We conclude that the Barker Hypothesis is poorly supported and argue that more work in human populations should be integrated with multi-disciplinary studies of ageing-related phenomena in experimental populations of different model species that are subjected to nutritional challenges or infections during pre-adult development.

Thymic atrophy via estrogen-induced apoptosis is related to Fas/FasL pathway

A convincing body of evidence indicates that estrogen has significant immunomodulatory properties, including induction of thymic involution. However, it is unclear whether or not estrogen induces thymic involution by triggering apoptosis depended on Fas-FasL interactions. In the present study, estradiol-17beta (E(2)) was used to treat rats by gavages at 10, 1, 0.1, 0.01, and 0 ng/kg/day, respectively. Atrophy of thymus was determined by in situ morphological examination. Apoptotic cells were identified by terminal deoxynucleotide transferase-mediated deoxy-UTP nick end labeling (TUNEL) assay. A semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) method was used to analyze Fas and FasL mRNA levels. The results showed that E(2) induced thymic atrophy, increased the rates of apoptotic death, and enhanced the Fas/FasL mRNA levels. These findings suggested that Fas/FasL-mediated apoptosis involved in the induction of thymic atrophy by E(2).

Nonylphenol induces thymocyte apoptosis through Fas/FasL pathway by mimicking estrogen in vivo

Nonylphenol (NP) is the final biodegradation product of nonylphenol polyethoxylates, which are widely used surfactants in domestic and industrial products. Nonylphenol has been reported to have estrogenic activity and shown to have potential reproductive toxicity. However, its influence on immune system function remains unclear. In this study, we investigated the effects of nonylphenol on apoptosis and Fas/FasL gene expression in rat thymus. Nonylphenol were given orally by gavages at 125, 250, and 375mg/kg per day. Negative and positive controls were treated with the vehicle and E(2) 10ng/kg per day, respectively. Atrophy of thymus was determined by in situ morphological examination using hematoxylin and eosin staining. Apoptotic cells were identified by terminal deoxynucleotide transferase-mediated deoxy-UTP nick end labeling (TUNEL) assay. A semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) method was used to analyze Fas and FasL mRNA levels. The results showed that both nonylphenol and E(2) increased the rates of apoptotic death; reduced the expression of Fas; enhanced the expression of FasL. These findings demonstrated that nonylphenol with estrogen-like activity might affect the regulation of the immune function through thymocyte apoptosis. This apoptosis was mediated by altering the expression of Fas and FasL mRNA.