Meta-analysis of associations between functional prolactin −1149 G/T polymorphism and susceptibility to rheumatoid arthritis and systemic lupus erythematosus

Prolactin's paradox: Friend, foe, or both in immune regulation?

Over 100 diseases have been recognized as autoimmune in nature, collectively affecting ∼20 % of the population in industrialized countries. These conditions are more prevalent among women of childbearing age, reflecting the potential association between alterations in the immune-neuroendocrine network, on the one hand, and autoimmune conditions, on the other. Prolactin (PRL), a polypeptide hormone that is primarily (but not only) secreted by the lactotrophic cells of the pituitary gland, is a critical element of the immune-neuroendocrine network. Although this hormone has several nonimmune functions, its role in regulating immune responses and affecting autoimmune inflammation is particularly enigmatic and controversial. Indeed, PRL interacts with various immune cells to bolster the body defenses, but also potentially to exacerbate autoimmune conditions. Understanding how and when PRL acts as a 'friend or foe' is crucial for unraveling its role as a potential therapeutic target in the management of autoimmune diseases (AIDs). This review therefore provides a critical overview of PRL's role in the immune system, and of the influence of this pleiotropic hormone in the development of autoimmunity.

Prolactin: A Mammalian Stress Hormone and Its Role in Cutaneous Pathophysiology

The hormone prolactin (PRL) is best recognised for its indispensable role in mammalian biology, specifically the regulation of lactation. Bearing in mind that the mammary gland is a modified sweat gland, it is perhaps unsurprising to discover that PRL also plays a significant role in cutaneous biology and is implicated in the pathogenesis of a range of skin diseases, often those reportedly triggered and/or exacerbated by psychological stress. Given that PRL has been implicated in over 300 biological processes, spanning reproduction and hair growth and thermo- to immunoregulation, a comprehensive understanding of the relationship between PRL and the skin remains frustratingly elusive. In an historical curiosity, the first hint that PRL could affect skin biology came from the observation of seborrhoea in patients with post-encephalitic Parkinsonism as a result of another global pandemic, encephalitis lethargica, at the beginning of the last century. As PRL is now being postulated as a potential immunomodulator for COVID-19 infection, it is perhaps timeous to re-examine this pluripotent hormone with cytokine-like properties in the cutaneous context, drawing together our understanding of the role of PRL in skin disease to illustrate how targeting PRL-mediated signalling may represent a novel strategy to treat a range of skin diseases and hair disorders.

Interference of B lymphocyte tolerance by prolactin in rheumatic autoimmune diseases

Systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and systemic sclerosis (SSc) are the most common rheumatic autoimmune diseases/disorders (RADs) that affect autologous connective tissues as a result of the breakdown of the self-tolerance mechanisms of the immune system. Prolactin, a glycoprotein hormone, has been known for its crucial role in the pathogenesis of these rheumatic autoimmune diseases. In addition to regulating lymphocyte proliferation and antibody synthesis, prolactin is also responsible for regulating cytokine production. Moreover, it contributes to the breakdown of central and peripheral tolerance mechanisms of B lymphocytes. Given the crucial role of prolactin in the pathogenesis of the mentioned RADs, prolactin may contribute to their pathogenesis by the breakdown of tolerance. In the present study, the key role of prolactin to the breakdown of B lymphocyte tolerance and its possible implication for the pathogenesis of these diseases is discussed. Current literature supports prolactin's role in the breakdown of B lymphocyte central and peripheral tolerance mechanisms, such apoptosis, receptor editing, and also anergy. Therefore, prolactin may contribute to the pathogenesis of RADs by the breakdown of B lymphocyte tolerance. However, more investigations, particularly in RA and SSc animal models, are required to precisely address the pathologic role of prolactin.

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.

Hyperprolactinemia is associated with a high prevalence of serum autoantibodies, high levels of inflammatory cytokines and an abnormal distribution of peripheral B-cell subsets

PURPOSE

Hyperprolactinemia (HPRL) has been reported in many autoimmune diseases. However, the serum autoantibody profile and peripheral B-cell subset distribution in women with HPRL are largely unknown. The current study aimed to investigate the autoantibody prevalence and cytokine levels as well as to further explore the B-cell subset distribution in women with HPRL.

METHODS

Sera from 202 women with HPRL and 97 healthy women were included in this study. All sera were examined for prolactin (PRL), anti-nuclear antibody (ANA), rheumatoid factor, anticardiolipin (ACL), immunoglobulin G, immunoglobulin M, complement 3, complement 4, interleukin 4 (IL-4) and interleukin 6 (IL-6). Peripheral blood was collected from 22 women with HPRL and 19 healthy women, and B-cell subsets were measured by flow cytometry.

RESULTS

At least one autoantibody was found in 47 out of 202 women with HPRL compared with 9 of 97 healthy women (p < 0.001). The levels of IL-4 (p < 0.0001) and IL-6 (p < 0.0001) were significantly higher in women with HPRL than in healthy women. The percentages of naive IgD⁺IgM^- B cells (B_ND cells, p < 0.0001), antibody-secreting cells (p = 0.007) and unswitched memory B cells (p = 0.004) among the total B cells from HPRL women were significantly higher than those from healthy women.

CONCLUSIONS

Women with HPRL had a higher prevalence of autoantibodies, higher serum levels of IL-4 and IL-6, and more B_ND cells, antibody-secreting B cells and unswitched memory B cells than healthy women. These data imply that a high level of PRL is associated with autoimmune diseases.

Insight into the Endocrine System and the Immune System: A Review of the Inflammatory Role of Prolactin in Rheumatoid Arthritis and Psoriatic Arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease that affects females three times more frequently than males. A potential role for hormones, such as prolactin (PRL), may in part explain this phenomenon. The risk of developing RA is increased in women who are lactating after the first pregnancy, which might be related to breastfeeding and the release of PRL. Other studies found a protective effect of PRL on RA development. Some studies have reported that hyperprolactinemia is more common in RA and serum PRL levels are correlated with several disease parameters, although others could not confirm these findings. Overall the plasma PRL levels are on average not elevated in RA. Previously, a small number of open-label clinical trials using bromocriptine, which indirectly decreases PRL levels, were performed in RA patients and showed clinical benefit, although others found the opposite effect. Locally produced PRL at the site of inflammation may have a crucial role in RA as well, as it has been shown that PRL can be produced by synovial macrophages. Locally produced PRL has both pro-inflammatory and anti-inflammatory effects in arthritis. Psoriatic arthritis (PsA) is also an autoinflammatory disease, in which the prolactin receptor is also expressed in macrophages. The aim of this review is to provide an overview of the potential role of PRL signaling in inflammatory joint diseases (RA and PsA) and its potential as a therapeutic target.

Prolactin gene polymorphism (-1149 G/T) is associated with hyperprolactinemia in patients with schizophrenia treated with antipsychotics

BACKGROUND

Antipsychotic drugs can cause hyperprolactinemia. However, hyperprolactinemia was also observed in treatment-naive patients with a first schizophrenic episode. This phenomenon might be related to the role of prolactin as a cytokine in autoimmune diseases. Extrapituitary prolactin production is regulated by an alternative promoter, which contains the functional single nucleotide polymorphism -1149 G/T (rs1341239). We examined whether this polymorphism was associated with hyperprolactinemia in patients with schizophrenia.

METHOD

We recruited 443 patients with schizophrenia and 126 healthy controls. The functional polymorphism -1149 G/T (rs1341239) in the prolactin gene was genotyped with multiplexed primer extension, combined with MALDI-TOF mass spectrometry. Genotype and allele frequencies were compared between groups with the χ² test and logistic regression models adjusting for covariates.

RESULTS

The frequency of genotypes and alleles in patients with schizophrenia did not differ from those in control subjects. A comparison between patients with schizophrenia with and without hyperprolactinemia revealed significantly higher frequency of the G allele in patients with hyperprolactinemia than in patients without it (χ²=7.25; p=0.007; OR=1.44 [1.10-1.89]). Accordingly, patients with hyperprolactinemia carried the GG genotype more frequently than patients without hyperprolactinemia (χ²=9.49; p=0.009). This association remained significant after adjusting the estimates for such covariates as sex, age, duration of the diseases and the dose of chlorpromazine equivalents.

CONCLUSION

This study revealed a significant association between the polymorphic variant rs1341239 and the development of hyperprolactinemia in patients with schizophrenia. The serum prolactin concentration in patients with schizophrenia treated with antipsychotics may provide an indication of the activity of the gene that regulates extrapituitary prolactin production which is believed to play a role in the immune system.

Prolactin rs1341239 T allele may have protective role against the brick tea type skeletal fluorosis

Objective

Prolactin (PRL) has been reported to be associated with increased bone turnover, and increased bone turnover is also a feature of skeletal fluorosis (SF). Autocrine/paracrine production of PRL is regulated by the extrapituitary promoter and a polymorphism in the extrapituitary PRL promoter at -1149 (rs1341239) is associated with disturbances of bone metabolism in other diseases. Here, we have investigated the possibility that the rs1341239 polymorphism is associated with SF, which results from the consumption of brick tea.

Design

We conducted a cross-sectional study in Sinkiang, Qinghai, Inner Mongolia in China. Demography survey questionnaires were completed and physical examination and X-ray diagnoses were used to diagnose SF. Brick tea water fluoride intake (IF) and urinary fluoride (UF) were tested by an F-ion selective electrode method. A Sequenom MassARRAY system was used to determine PRL gene polymorphisms.

Results

Subjects who were younger than 45 years of age and carried the T allele had a significantly decreased risk of SF [OR = 0.279 (95%CI, 0.094–0.824)] compared to those carrying the homozygous G allele. This phenomenon was only observed in Kazakh subjects [OR = 0.127 (95%CI, 0.025–0.646)]. Kazakh females who carried T alleles has a decreased risk of SF [OR = 0.410 (95%CI, 0.199–0.847)]. For Kazakh subjects which IF is less than 3.5 mg/d, a decreased risk of SF was observed among the participants who carried T alleles [OR = 0.118 (95%CI, 0.029–0.472)]. Overall, subjects with 1.6–3.2 mg/L UF and carried T alleles had a significantly decreased risk of SF [OR = 0.476 (95%CI, 0.237–0.955)] compared to homozygous G allele carriers. This phenomenon was only observed in Kazakh subjects [OR = 0.324 (95%CI, 0.114–0.923)].

Conclusions

Our results suggested that the PRL rs1341239 T allele decreases the risk of brick tea SF.

Lectin, galactoside-binding, soluble, 3 rs4652 A/C gene variation and the risk for rheumatoid arthritis

Rheumatoid arthritis (RA) is a complex genetic disease. The lectin, galactoside-binding, soluble, 3 (LGALS3) gene, encodes a member of the galectin family of carbohydrate binding proteins, and is one of the best examples of a non-human leukocyte antigen gene associated with a risk for RA in various populations. In the current study, the association between LGALS3 rs4652 gene polymorphism and RA was examined. This case-control study was performed on the 120 patients with RA and 120 healthy subjects. Genomic DNA was extracted from whole blood, and gene polymorphism was tested using a tetra-primer amplification refractory mutation system-polymerase chain reaction. The results demonstrated that LGALS3 rs4652 AC genotype increased the risk of RA (OR=11.622, 95% CI=4.473-28.656; P=0.001) when compared with the AA genotype. However, the CC genotype and the C allele were not associated with RA. These findings indicated an association between LGALS3 rs4652 variation and the risk of RA in a sample of Iranian individuals. Further studies with larger sample sizes and populations of different ethnicities are required to validate our findings.