Prolactin stimulates maturation and function of rat thymic dendritic cells

The effect of prolactin on immune cell subsets involved in SLE pathogenesis

The higher frequency of autoimmune diseases in the female population compared to males suggests that certain hormones, such as prolactin (PRL), play a role in determining the prevalence of autoimmunity in women, particularly during childbearing age. PRL can act not only as a hormone but also as a cytokine, being able to modulate immune responses. Hyperprolactinemia has been implicated in the pathogenesis of various autoimmune diseases where it may affect disease activity. One of the conditions where PRL has such a role is systemic lupus erythematosus (SLE). PRL regulates the proliferation and survival of both lymphoid and myeloid cells. It also affects the selection of T-cell repertoires by influencing the thymic microenvironment. In autoimmune conditions, PRL interferes with the activity of regulatory T cells. It also influences B cell tolerance by lowering the activation threshold of anergic B cells. The production of CD40L and cytokines, such as interleukin IL-6, are also promoted by PRL. This, in turn, leads to the production of autoantibodies, one of the hallmarks of SLE. PRL increases the cytotoxic activity of T lymphocytes and the secretion of proinflammatory cytokines. The production of proinflammatory cytokines, particularly those belonging to the type 1 interferon (IFN) family, is part of the SLE characteristic genetic signature. PRL also participates in the maturation and differentiation of dendritic cells, promoting the presentation of autoantigens and high IFNα secretion. It also affects neutrophil function and the production of neutrophil traps. Macrophages and dendritic cells can also be affected by PRL, linking this molecule to the abnormal behavior of both innate and adaptive immune responses.This review aimed to highlight the importance of PRL and its actions on the cells of innate and adaptive immune responses. Additionally, by elucidating the role of PRL in SLE etiopathogenesis, this work will contribute to a better understanding of the factors involved in SLE development and regulation.

Modulatory role of prolactin in type 1 diabetes

Objectives

Patients with type 1 diabetes mellitus have been reported to have elevated prolactin levels and a possible relationship between prolactin levels and the development of the disease has been proposed. However, some studies show that prolactin mediates beneficial functions in beta cells. Therefore, we review information on the roles of prolactin in type 1 diabetes mellitus.

Content

Here we summarize the functions of prolactin in the immune system and in pancreatic beta cells, in addition, we describe studies related to PRL levels, its regulation and alterations of secretion in patients with type 1 diabetes mellitus.

Summary

Studies in murine models have shown that prolactin protects beta cells from apoptosis, stimulates their proliferation and promotes pancreatic islet revascularization. In addition, some studies in patients with type 1 diabetes mellitus have shown that elevated prolactin levels correlate with better disease control.

Outlook

Prolactin treatment appears to be a promising strategy to improve beta-cell vascularization and proliferation in transplantation and immunotherapies.

Sex-dependent pain trajectories induced by prolactin require an inflammatory response for pain resolution

Pain development and resolution patterns in many diseases are sex-dependent. This study aimed to develop pain models with sex-dependent resolution trajectories, and identify factors linked to resolution of pain in females and males. Using different intra-plantar (i.pl.) treatment protocols with prolactin (PRL), we established models with distinct, sex-dependent patterns for development and resolution of pain. An acute PRL-evoked pain trajectory, in which hypersensitivity is fully resolved within 1 day, showed substantial transcriptional changes after pain-resolution in female and male hindpaws and in the dorsal root ganglia (DRG). This finding supports the notion that pain resolution is an active process. Prolonged treatment with PRL high dose (1 μg) evoked mechanical hypersensitivity that resolved within 5-7 days in mice of both sexes and exhibited a pro-inflammatory transcriptional response in the hindpaw, but not DRG, at the time point preceding resolution. Flow cytometry analysis linked pro-inflammatory responses in female hindpaws to macrophages/monocytes, especially CD11b⁺/CD64⁺/MHCII⁺ cell accumulation. Prolonged low dose PRL (0.1 μg) treatment caused non-resolving mechanical hypersensitivity only in females. This effect was independent of sensory neuronal PRLR and was associated with a lack of immune response in the hindpaw, although many genes underlying tissue damage were affected. We conclude that different i.pl. PRL treatment protocols generates distinct, sex-specific pain hypersensitivity resolution patterns. PRL-induced pain resolution is preceded by a pro-inflammatory macrophage/monocyte-associated response in the hindpaws of mice of both sexes. On the other hand, the absence of a peripheral inflammatory response creates a permissive condition for PRL-induced pain persistency in females.

CXCL12-driven thymocyte migration is increased by thymic epithelial cells treated with prolactin in vitro

The prolactin hormone (PRL), in addition to its known effects on breast development and lactation, exerts effects on the immune system, including pleiotropic effects on the thymus. The aim of this study was to evaluate the influence of PRL on the epithelial compartment of the thymus. Thymic epithelial cells (TECs) (2BH4 cells) and fresh thymocytes were used. Immunofluorescence assay revealed that PRL treatment (10 ng/mL) increases the deposition of laminin and expression of the chemokine CXCL12 in 2BH4 cells. However, no change was observed in the deposition of fibronectin. Moreover, PRL altered F-actin polymerisation, allowing the formation of focal adhesion complexes in treated cells. When 2BH4 cells were pre-treated with PRL, thymocyte adhesion was not altered. However, in the cell migration assay, pre-treatment with PRL potentiated the chemotactic effect of CXCL12 on the migration of total, double-positive, CD4-positive, and CD8-positive thymocytes. Together, the results of this study demonstrate the effect of PRL on thymic epithelial cells, particularly on CXCL12-driven thymocyte migration, confirming that this hormone is a regulator of thymic physiology.

The Functional Significance of Endocrine-immune Interactions in Health and Disease

Hormones are known to influence various body systems that include skeletal, cardiac, digestive, excretory, and immune systems. Emerging investigations suggest the key role played by secretions of endocrine glands in immune cell differentiation, proliferation, activation, and memory attributes of the immune system. The link between steroid hormones such as glucocorticoids and inflammation is widely known. However, the role of peptide hormones and amino acid derivatives such as growth and thyroid hormones, prolactin, dopamine, and thymopoietin in regulating the functioning of the immune system remains unclear. Here, we reviewed the findings pertinent to the functional role of hormone-immune interactions in health and disease and proposed perspective directions for translational research in the field.

CXCL12-driven thymocyte migration is increased by thymic epithelial cells treated with prolactin in vitro

The prolactin hormone (PRL), in addition to its known effects on breast development and lactation, exerts effects on the immune system, including pleiotropic effects on the thymus. The aim of this study was to evaluate the influence of PRL on the epithelial compartment of the thymus. Thymic epithelial cells (TECs) (2BH4 cells) and fresh thymocytes were used. Immunofluorescence assay revealed that PRL treatment (10 ng/ mL) increases the deposition of laminin and expression of the chemokine CXCL12 in 2BH4 cells. However, no change was observed in the deposition of fibronectin. Moreover, PRL altered F-actin polymerisation, allowing the formation of focal adhesion complexes in treated cells. When 2BH4 cells were pre-treated with PRL, thymocyte adhesion was not altered. However, in the cell migration assay, pre-treatment with PRL potentiated the chemotactic effect of CXCL12 on the migration of total, double-positive, CD4-positive, and CD8-positive thymocytes. Together, the results of this study demonstrate the effect of PRL on thymic epithelial cells, particularly on CXCL12-driven thymocyte migration, confirming that this hormone is a regulator of thymic physiology.

Prolactin, a potential biomarker for chronic GVHD activity

INTRODUCTION

The polypeptide prolactin (PRL) is a peptide hormone and a cytokine mostly secreted from the anterior pituitary gland. PRL is also synthesized in extra pituitary tissues including thymocytes and T lymphocytes. Considering the need for chronic GVHD (cGVHD) biomarkers, we explored the relationship between hyperprolactinemia and active cGVHD in a cohort of long-term post-alloHCT survivors.

METHODS

Three-hundred sixteen adults underwent alloHCT between 2010 and 2016, survived more than 1 year and were included. All patients underwent a regular annual assessment that includes a hormone profile with serum PRL levels.

RESULTS

Overall, 236 (74.7%) patients had cGVHD, and in 199 (63%), the grade was moderate or severe. Sixty-five (21%) recipients had active cGVHD at the time of the annual evaluation, and hyperprolactinemia was documented in 63 (19.9%) patients. Hyperprolactinemia correlated with cGVHD activity (Odds Ratio 6.9 (95% CI; 3.6-13.1); P < .001) in the multivariate analysis. In conclusion, patients with hyperprolactinemia were 6.4 times more likely to have active cGVHD in comparison with those patients with normal levels of PRL (P < .001).

CONCLUSION

Prolactin may serve as a biomarker for cGVHD activity. Further studies are required to confirm these findings, and to explore if hyperprolactinemia has an impact on cGVHD severity and prognosis.

The tumour microenvironment of pituitary neuroendocrine tumours

The tumour microenvironment (TME) includes a variety of non-neoplastic cells and non-cellular elements such as cytokines, growth factors and enzymes surrounding tumour cells. The TME emerged as a key modulator of tumour initiation, progression and invasion, with extensive data available in many cancers, but little is known in pituitary tumours. However, the understanding of the TME of pituitary tumours has advanced thanks to active research in this field over the last decade. Different immune and stromal cell subpopulations, and several cytokines, growth factors and matrix remodelling enzymes, have been characterised in pituitary tumours. Studying the TME in pituitary tumours may lead to a better understanding of tumourigenic mechanisms, identification of biomarkers useful to predict aggressive disease, and development of novel therapies. This review summarises the current knowledge on the different TME cellular/non-cellular elements in pituitary tumours and provides an overview of their role in tumourigenesis, biological behaviour and clinical outcomes.

Prolactin and autoimmunity: The hormone as an inflammatory cytokine

Nowadays, more than 80 autoimmune disorders are recognized, in which an aberrant immune response against different organs and tissues plays a crucial role. Hormonal homeostasis has great influence in achieving competent and healthy immune system function. Prolactin has a bioactive function acting as a hormone and a cytokine. It influences the immune system modulation, mainly inhibiting the negative selection of autoreactive B lymphocytes. Hyperprolactinemia has been detected in many patients with different autoimmune diseases, such as rheumatoid arthritis, systemic lupus erythematosus, Sjögren syndrome, multiple sclerosis, autoimmune thyroid disease, systemic sclerosis, among others, and its believed to play a crucial role in disease pathogenesis. A direct correlation between prolactin levels and disease activity was not clear. Genetic factors may have a role in humans as in animal models. Dopamine agonists have proven to offer clinical benefits among autoimmune patients and represent a promising therapy to be explored. In this review, the authors attempt to provide a critical overview on the role of prolactin in the immune system, exploring its contribution to the development of autoimmune diseases.

Prolactin and Autoimmunity

The great asymmetry of autoimmune diseases between genders represents one of the most enigmatic observations among the mosaic of autoimmunity. Sex hormones are believed to play a crucial role on this dimorphism. The higher prevalence of autoimmunity among women at childbearing ages, disease onset/relapses during pregnancy, and post-partum are some of the arguments that support this hypothesis. Certainly, motherhood represents one of the most remarkable challenges for the immune system, which not only has to allow for the conceptus, but also has to deal with complex endocrine alterations. Hormonal homeostasis is known to exert a crucial influence in achieving a competent and healthy immune system. Prolactin (PRL) has a bioactive function acting as a hormone and a cytokine. It interferes with immune system modulation, mainly inhibiting the negative selection of autoreactive B lymphocytes. Likewise, hyperprolactinemia has been described in relation to the pathogenesis and activity of several autoimmune disorders. Dopamine is an effective inhibitor of PRL secretion due to either a direct influence on the hypophysis or stimulation of postsynaptic dopamine receptors in the hypothalamus, arousing the release of the PRL inhibitory factor. Hence, dopamine agonists have proven to offer clinical benefits among autoimmune patients and represent a promising therapy to be explored. In this review, we attempt to provide a critical overview of the link between PRL, autoimmune diseases, and motherhood.

Parathyroid Hormone-related Peptide (hPTHrP) and Parathyroid Hormone-related Peptide Receptor Type 1 (PTHR1) Expression in Human Thymus

Parathyroid hormone-related peptide (hPTHrP) is expressed in human tissues and regulates cellular proliferation, differentiation, and apoptosis by an autocrine/paracrine loop. In rodent thymus, both parathormone and parathyroid hormone-related peptide (PTHrP) are expressed by thymic epithelial cells (TECs). The present study demonstrated by RT-PCR and immunohistochemistry that hPTHrP and parathyroid hormone-related peptide receptor type 1 (PTHR1) were expressed in human thymus at both RNA and protein levels. hPTHrP was expressed mainly in the thymic medulla by epithelial (cytokeratin-positive), mature dendritic (CD40+/86+) and plasmacytoid interleukin (IL)-3Rα+ cells. This protein was also present in some cells forming Hassall's bodies and a few subcapsular and cortical TECs. PTHR1 was expressed by scattered subcapsular and cortical TECs and by rare TECs in the medulla. Thymocytes did not express either hPTHrP or PTHR1. Primary cultures of human TECs revealed the presence of both hPTHrP and PTHR1 mRNAs, confirming the capacity of TECs to synthesize both peptides. Moreover, synthetic (1–39) hPTHrP peptide administered on cultured TECs induced the expression of IL-6 mRNA, suggesting that hPTHrP can regulate thymic functions by inducing in TECs the expression of IL-6, which is involved in the development and maturation of thymocytes.

Hormonal control of T-cell development in health and disease

The physiology of the thymus, the primary lymphoid organ in which T cells are generated, is controlled by hormones. Data from animal models indicate that several peptide and nonpeptide hormones act pleiotropically within the thymus to modulate the proliferation, differentiation, migration and death by apoptosis of developing thymocytes. For example, growth hormone and prolactin can enhance thymocyte proliferation and migration, whereas glucocorticoids lead to the apoptosis of these developing cells. The thymus undergoes progressive age-dependent atrophy with a loss of cells being generated and exported, therefore, hormone-based therapies are being developed as an alternative strategy to rejuvenate the organ, as well as to augment thymocyte proliferation and the export of mature T cells to peripheral lymphoid organs. Some hormones (such as growth hormone and progonadoliberin-1) are also being used as therapeutic agents to treat immunodeficiency disorders associated with thymic atrophy, such as HIV infection. In this Review, we discuss the accumulating data that shows the thymus gland is under complex and multifaceted hormonal control that affects the process of T-cell development in health and disease.

Tumor associated release of interleukin-10 alters the prolactin receptor and down-regulates prolactin responsiveness of immature cortical thymocytes

The soluble factors produced either by Ehrlich's ascites carcinoma (EAC) or thymic adherent cells (TAC) of tumor-bearing mice comprising of CD11b(+) and CD11c(+) antigen-presenting cells caused a sharp decrease in prolactin (PRL)-induced ConA-mediated effect on survival of PNA(+) thymocytes. Similar suppression of PRL-induced effect was observed when the cells were cocultured with TAC of EAC-bearing mice. Anti-IL-10 antibody could reverse the PRL inability to induce ConA-mediated effect on PNA(+) thymocyte survival, indicating the presence of IL-10 in EAC culture supernatant (EAC sup) and thymic microenvironment. IL-10 could block PRL-induced proliferation of PNA(+) thymocytes without affecting spontaneous apoptosis. IL-10 altered the expression of the long-form (LF) of PRL-R and reduced the PRL binding of the cells, suggesting down-regulation of the PRL effect on PNA(+) thymocyte by the cytokine. Induction of tumor, which was found to increase the IL-10 secretion by TAC, also modified the PRL-R (LF) to PRL-R (SF). Since PRL plays a role in survival, proliferation and differentiation of lymphoid progenitor cells, the tuning of PRL action by IL-10 may be a possible mechanism of depletion of immature cortical thymocytes and thymic atrophy in tumor-bearing mice.

p-Coumaric acid inhibits indoleamine 2, 3-dioxygenase expression in murine dendritic cells

Indoleamine 2, 3-dioxygenase (IDO), a key enzyme that catalyses the initial and rate-limiting step in the degradation of the tryptophan, is simultaneously expressed in murine dendritic cells and macrophages stimulated with interferon-gamma (IFN-gamma). In the present study, we investigated whether p-Coumaric acid (CA), which is suggested to exhibit antioxidant properties, could suppress the functional expression of IDO in murine bone marrow-derived dendritic cells (BMDCs) stimulated with IFN-gamma. Treatment with CA reduced intracellular expression of IDO mRNA and protein levels in IFN-gamma-activated murine BMDCs in vitro and in CD11c(+)CD8alpha(+) DCs of tumor-draining lymph node (TDLN) of tumor-bearing mice in vivo. Consequently, we obtained evidence that CA suppresses the functional activity of IDO, which catalyses oxidative catabolism of tryptophan, and significantly recovers the IDO-dependent T cell suppression. Activation of the signal transducer and activator of transcription 1 (STAT1) is important to be express IDO in IFN-gamma-stimulated murine BMDCs. To determine whether these inhibitory effects of CA are associated with the alteration of the signal transducer and activator of transcription 1 (STAT1) and IFN-gamma-inducible, dsRNA-activated serine/threonine protein kinase (PKR), BMDCs were pretreated with various concentrations of CA. We found that CA inhibited the activation of STAT1 in response to IFN-gamma. Based on our results, this study may account that CA could inhibit IDO expression by down-regulation of STAT1 activation in IFN-gamma-stimulated murine DCs.

Prolactin modulates the functions of murine spleen CD11c-positive dendritic cells

Prolactin (PRL), an anterior pituitary polypeptide hormone, has been shown to have a role in the immunomodulation. Some reports have shown the importance of PRL in activating lymphocytes and macrophages. To further investigate the effect of PRL on the immune system in vitro, murine spleen CD11c-positive dendritic cells (SDCs) were treated with various concentrations of PRL for 24 h, then their viability, phenotype, nuclear factor kappa B p65 (NF-kappaBp65), endocytosis, stimulatory capacity, and cytokine expression were analyzed. The results showed that PRL increased the viability and stimulatory capacity of SDCs, up-regulated the expressions of MHC-11 and CD40 while decreased the level of CD54 on SDCs. Furthermore, PRL decreased the level of NF-kappaBp65 and the endocytosis of SDCs. In addition, PRL increased the expressions of IL-6, IL-10, IL-12 and TNF-alpha in SDCs. These data suggested that PRL might regulate the physiological and pathological immune responses by changing the viability, phenotype, NF-kappaBp65, endocytosis, stimulatory capacity, and cytokine expression of SDCs.

Multiple cAMP-induced signaling cascades regulate prolactin expression in T cells

Beside its pivotal role in reproduction, the pituitary hormone prolactin (PRL) has been attributed an immunomodulatory function. Here we report that cAMP is an important stimulator of PRL transcription in primary human T lymphocytes. Inhibition of both protein kinase A (PKA) and p38 MAPK partially abrogated cAMP-induced PRL expression. In addition, cAMP-induced phosphorylation of p38 was shown to occur independently of PKA and could be mimicked by a methylated cAMP analogue which specifically activates the recently discovered cAMP receptor EPAC (exchange protein directly activated by cAMP). Our findings suggest that cAMP induces PRL expression in T lymphocytes via cooperation of at least two different signaling pathways: a PKA-dependent pathway leading to the phosphorylation of cAMP response element-binding protein, and a PKA-independent pathway leading to p38 phosphorylation.

Prolactin induced reversal of glucocorticoid mediated apoptosis of immature cortical thymocytes is abrogated by induction of tumor

Glucocorticoid (GC) and prolactin (PRL) are the two neuroendocrines that regulate thymocyte differentiation and maintain the immune homeostasis during stress. We found that dexamethasone (Dex), a synthetic GC, induced apoptosis in normal immature cortical thymocytes which remained unaltered in the presence of Elrich's ascitic carcinoma (EAC). PRL protected the normal CD4+ CD8+ cortical thymocytes from Dex-induced apoptosis but failed to alter the effect of Dex in tumor-bearing mice. Dex-treated normal thymocytes became unresponsive to PRL in presence of tumor cell culture supernatant. Low binding affinity of the microsomal membranes of thymocytes to PRL and absence of the mRNA of a particular form of prolactin receptor (PRL-R) suggest the presence of a different PRL-R in CD4+ CD8+ thymocytes of EAC-bearing mice. The induction of tumor may alter the PRL-R that can be correlated with the failure of PRL in rescuing CD4+ CD8+ immature cortical thymocytes from GC induced death.