Enhanced expression of CD69 and CD25 antigen on human peripheral blood mononuclear cells by prolactin

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.

Prolactin promotes proliferation of germinal center B cells, formation of plasma cells, and elevated levels of IgG3 anti-dsDNA autoantibodies

Systemic lupus erythematosus (SLE) mainly affects females at reproductive age, which has been associated with hormones, such as prolactin (PRL). Different studies suggest that PRL exacerbates the clinical manifestations of SLE both in patients and in mouse models (e.g., the MRL/lpr strain), increasing the production of autoantibodies, which can be deposited as immune complexes and trigger inflammation and damage to different tissues. The objective of this work was to explore the potential mechanisms by which PRL increases the concentration of self-reactive antibodies in the MRL/lpr SLE model. To this end, we determined the role of PRL on the activation and proliferation of germinal center B cells (B-GCs) and their differentiation into antibody-secreting cells (ASCs). We show that the absolute number and percentage of B-GCs were significantly increased by PRL in vivo or upon in vitro treatment with anti-IgM and anti-CD40 antibodies and PRL. The augmented B-GC numbers correlated with enhanced proliferation, but we did not observe enhanced expression of CD80 and CD86 activation markers or the BCL6 transcription factor, arguing against a more effective differentiation. Nevertheless, we observed enhanced phosphorylation of STAT1, secretion of IL-6, expression of IRF4, numbers of ASCs, and levels of IgG3 antibodies directed against dsDNA. Altogether, these results support the hypothesis that a PRL-mediated expansion of B-GCs yields more self-reactive ASCs, potentially explaining the pathogenic immune complexes that steadily lead to tissue damage during SLE.

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.

Associations between Prolactin, Diabetes, and Cognitive Impairment: A Literature Review

BACKGROUND

Converging evidence indicates prolactin (PRL) and diabetes play an important role in the pathophysiology of cognitive impairment. However, little is known about the mechanisms responsible for the effects of PRL and diabetes on cognitive impairment.

SUMMARY

We summarize and review the available literature and current knowledge of the association between PRL and diabetes on aspects of cognitive impairment.

KEY MESSAGES

The phosphatidylinositol 3-kinase/protein kinase B pathway is central to the molecular mechanisms underlying how PRL and diabetes interact in cognitive impairment. Further work is needed to identify the interaction between PRL and diabetes, especially in the molecular aspects of cognitive impairment, which can suggest novel strategies for cognitive dysfunction treatment.

Prolactin and Its Altered Action in Alzheimer's Disease and Parkinson's Disease

BACKGROUND

Prolactin (PRL) is one of the most diverse pituitary hormones and is known to modulate normal neuronal function and neurodegenerative conditions. Many studies have described the influence that PRL has on the central nervous system and addressed its contribution to neurodegeneration, but little is known about the mechanisms responsible for the effects of PRL on neurodegenerative disorders, especially on Alzheimer's disease (AD) and Parkinson's disease (PD).

SUMMARY

We review and summarize the existing literature and current understanding of the roles of PRL on various PRL aspects of AD and PD.

KEY MESSAGES

In general, PRL is viewed as a promising molecule for the treatment of AD and PD. Modulation of PRL functions and targeting of immune mechanisms are needed to devise preventive or therapeutic strategies.

Prolactin enhances T regulatory cell promotion of breast cancer through the long form prolactin receptor

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Systemic knockdown of the long form prolactin receptor in vivo increases survival in an aggressive, immunocompetent model of stage IV, triple negative breast cancer.

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Knockdown of the long form prolactin receptor reduces Treg recruitment to tumors by reducing tumor parenchymal production of CCL-17.

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Those Tregs still recruited to primary tumors have a substantial reduction in their ability to promote epithelial to mesenchymal transition of tumor parenchyma.

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For the Tregs in the primary tumor, there is transcript downregulation of components of the T cell receptor complex and CTLA-4.

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Tregs outside of the tumor have normal ability to suppress T effector cell proliferation after 1–5 months of treatment.

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Knockdown of the long form of the prolactin receptor therefore seems to have an intra-tumor immunotherapeutic effect without effect on peripheral Treg function.

Previous work has shown systemic knockdown of the long form prolactin receptor (LFPRLR) in vivo markedly reduced metastasis in mouse models of breast cancer, but whether this translated to prolonged survival was unknown. Here we show that LFPRLR knockdown in the highly metastatic, immunocompetent 4T1 model prolonged survival and reduced recruitment of T regulatory cells (Tregs) to the tumor through effects on the production of CCL17. For the Tregs still recruited to the primary tumor, LFPRLR knockdown both directly and indirectly reduced their ability to promote tumor parenchymal epithelial to mesenchymal transition. Importantly, effects of prolactin on expression of mesenchymal genes by the tumor parenchyma were very different in the absence and presence of Tregs. While systemic knockdown of the LFPRLR downregulated transcripts important for immune synapse function in the remaining tumor Tregs, splenic Tregs seemed unaffected by LFPRLR knockdown, as demonstrated by their continued ability to suppress anti-CD3/CD28-stimulated effector cell proliferation at 1–5 months. These results demonstrate that knockdown of the LFPRLR achieves intra-tumor immunotherapeutic effects and suggest this occurs with reduced likelihood of peripheral inflammatory/autoimmune sequelae.

Prolactin Increases the Frequency of Follicular T Helper Cells with Enhanced IL21 Secretion and OX40 Expression in Lupus-Prone MRL/lpr Mice

Systemic lupus erythematosus is characterized by high levels of IgG class autoantibodies that contribute to the pathophysiology of the disease. The formation of these autoantibodies occurs in the germinal centers, where there is cooperation between follicular T helper cells (T_FH) and autoreactive B cells. Prolactin has been reported to exacerbate the clinical manifestations of lupus by increasing autoantibody concentrations. The objective of this study was to characterize the participation of prolactin in the differentiation and activation of T_FH cells, by performing in vivo and in vitro tests with lupus-prone mice, using flow cytometry and real-time PCR. We found that T_FH cells express the long isoform of the prolactin receptor and promoted STAT3 phosphorylation. Receptor expression was higher in MRL/lpr mice and correlative with the manifestations of the disease. Although prolactin does not intervene in the differentiation of T_FH cells, it does favor their activation by increasing the percentage of T_FH OX40⁺ and T_FH IL21⁺ cells, as well as leading to high serum concentrations of IL21. These results support a mechanism in which prolactin participates in the emergence of lupus by inducing overactive T_FH cells and perhaps promoting dysfunctional germinal centers.

Involvement of miR-106b in tumorigenic actions of both prolactin and estradiol

Prolactin promotes a variety of cancers by an array of different mechanisms. Here, we have investigated prolactin's inhibitory effect on expression of the cell cycle-regulating protein, p21. Using a miRNA array, we identified a number of miRNAs upregulated by prolactin treatment, but one in particular that was strongly induced by prolactin and predicted to bind to the 3′UTR of p21 mRNA, miR-106b. By creating a p21 mRNA 3′UTR-luciferase mRNA construct, we demonstrated degradation of the construct in response to prolactin in human breast, prostate and ovarian cancer cell lines. Increased expression of miR-106b replicated, and anti-miR-106b counteracted, the effects of prolactin on degradation of the 3′UTR construct, p21 mRNA levels, and cell proliferation in breast (T47D) and prostate (PC3) cancer cells. Increased expression of miR-106b also stimulated migration of the very epithelioid T47D cell line. By contrast, anti-miR-106b dramatically decreased expression of the mesenchymal markers, SNAIL-2, TWIST-2, VIMENTIN, and FIBRONECTIN. Using signaling pathway inhibitors and the 3′UTR construct, induction of miR-106b by prolactin was determined to be mediated through the MAPK/ERK and PI3K/Akt pathways and not through Jak2/Stat5 in both T47D and PC3 cells. Prolactin activation of MAPK/ERK and PI3K/Akt also activates ERα in the absence of an ERα ligand. 17β-estradiol promoted degradation of the construct in both cell lines and pre-incubation in the estrogen antagonist, Fulvestrant, blocked the ability of both prolactin and 17β-estradiol to induce the construct-degrading activity. Together, these data support a convergence of the prolactin and 17β-estradiol miR-106b-elevating signaling pathways at ERα.

The prolactin receptor: Diverse and emerging roles in pathophysiology

Investigations over two decades have revised understanding of the prolactin hormone. Long thought to be merely a lactogenic hormone, its list of functions has been extended to include: reproduction, islet differentiation, adipocyte control and immune modulation. Prolactin functions by binding cell-surface expressed prolactin receptor, initiating signaling cascades, primarily utilizing Janus kinase-signal transducer and activator of transcription (JAK-STAT). Pathway disruption has been implicated in tumorigenesis, reproductive abnormalities, and diabetes. Prolactin can also be secreted from extrapituitary sources adding complexity to understanding of its physiological functions. This review aims to describe how prolactin exerts its pathophysiological roles by endocrine and autocrine means.

Downregulation of CD94/NKG2A inhibitory receptor on decreased γδ T cells in patients with systemic lupus erythematosus

γδ T cells are characterized by recognizing conserved endogenous and stress-induced antigens without antigen presentation. It has been show that γδ T cells play an important role in anti-tumour/microbe responses, but their function in autoimmune diseases is yet not clear. Here, we reported the quantity and phenotype of peripheral blood γδ T cells from systemic lupus erythematosus (SLE). Both the percentages of γδ T cells in peripheral blood and among CD3(+) T cells of patients with SLE were significantly decreased, regardless of disease activity. However, activating marker CD69 and HLA-DR was upregulated, while inhibiting receptor CD94/NKG2A was downregulated in γδ T cells of patients with SLE. The expression of CD69 is negatively correlated with the quantity of γδ T cells. Moreover, the expression of CD94/NKG2A remained low even with antigen stimulation on those γδ T cells. Our results suggested that the low expression level of CD94/NKG2A upon γδ T cell activation might lead to the over-activation of γδ T cells in patients with SLE. These findings will be useful in elucidating the roles of γδ T cells in SLE pathogenesis.

Prolactin down-regulates CD4+CD25hiCD127low/- regulatory T cell function in humans

Among its many functions, prolactin (PRL) participates in immune responses and promotes the activation, differentiation and proliferation of T cells. However, the mechanisms by which PRL regulates regulatory T (T(reg)) cells are still unknown. Our goal was to determine whether PRL plays a role in T(reg) function. We measured the expression of PRL and its receptor in T(reg) and effector T (T(eff)) cells from 15 healthy individuals. We also evaluated the functional activity of T(reg) cells by examining proliferation and cytokine secretion in cells activated with anti-CD3/CD28 in the presence or absence of PRL. We report that T(reg) cells constitutively expressed PRL receptor, whereas T(eff) cells required stimulation with anti-CD3/CD28 to induce PRL receptor expression. Expression of PRL was constitutive in both populations. We found that the addition of PRL inhibited the suppressor effect (proliferation) mediated by T(reg) cells in vitro, reducing suppression from 37.4 to 13% when PRL was added to co-cultures of T(reg) and T(eff) cells (P<0.05). Cultures treated with PRL favoured a Th1 cytokine profile, with increased production of TNF and IFNγ. We report for the first time that PRL receptor expression was constitutive in T(reg) cells but not in T(eff) cells, which require stimulation to induce PRL receptor expression. PRL inhibited the suppressive function of T(reg) cells, apparently through the induced secretion of Th1 cytokines.