Does prolactin play a role in skin biology and pathology?

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.

Neuroendocrine signaling in the skin with a special focus on the epidermal neuropeptides

The skin, which is comprised of the epidermis, dermis, and subcutaneous tissue, is the largest organ in the human body and it plays a crucial role in the regulation of the body's homeostasis. These functions are regulated by local neuroendocrine and immune systems with a plethora of signaling molecules produced by resident and immune cells. In addition, neurotransmitters, endocrine factors, neuropeptides, and cytokines released from nerve endings play a central role in the skin's responses to stress. These molecules act on the corresponding receptors in an intra-, juxta-, para-, or autocrine fashion. The epidermis as the outer most component of skin forms a barrier directly protecting against environmental stressors. This protection is assured by an intrinsic keratinocyte differentiation program, pigmentary system, and local nervous, immune, endocrine, and microbiome elements. These constituents communicate cross-functionally among themselves and with corresponding systems in the dermis and hypodermis to secure the basic epidermal functions to maintain local (skin) and global (systemic) homeostasis. The neurohormonal mediators and cytokines used in these communications regulate physiological skin functions separately or in concert. Disturbances in the functions in these systems lead to cutaneous pathology that includes inflammatory (i.e., psoriasis, allergic, or atopic dermatitis, etc.) and keratinocytic hyperproliferative disorders (i.e., seborrheic and solar keratoses), dysfunction of adnexal structure (i.e., hair follicles, eccrine, and sebaceous glands), hypersensitivity reactions, pigmentary disorders (vitiligo, melasma, and hypo- or hyperpigmentary responses), premature aging, and malignancies (melanoma and nonmelanoma skin cancers). These cellular, molecular, and neural components preserve skin integrity and protect against skin pathologies and can act as "messengers of the skin" to the central organs, all to preserve organismal survival.

Protecting the outside: biological tools to manipulate the skin microbiota

Interest surrounding the role that skin microbes play in various aspects of human health has recently experienced a timely surge, particularly among researchers, clinicians and consumer-focused industries. The world is now approaching a post-antibiotic era where conventional antibacterial therapeutics have shown a loss in effectiveness due to overuse, leading to the looming antibiotic resistance crisis. The increasing threat posed by antibiotic resistance is compounded by an inadequate discovery rate of new antibiotics and has, in turn, resulted in global interest for alternative solutions. Recent studies have demonstrated that imbalances in skin microbiota are associated with assorted skin diseases and infections. Specifically, restoration of this ecosystem imbalance results in an alleviation of symptoms, achieved simply by applying bacteria normally found in abundance on healthy skin to the skin of those deficient in beneficial bacteria. The aim of this review is to discuss the currently available literature on biological tools that have the potential to manipulate the skin microbiota, with particular focus on bacteriocins, phage therapy, antibiotics, probiotics and targets of the gut-skin axis. This review will also address how the skin microbiota protects humans from invading pathogens in the external environment while discussing novel strategies to manipulate the skin microbiota to avoid and/or treat various disease states.

Is prolactin a negative neuroendocrine regulator of human skin re-epithelisation after wounding?

Chronic wounds remain a major unmet healthcare challenge, associated with substantial morbidity and economic costs. Therefore, novel treatment strategies and therapeutic approaches need to be urgently developed. Yet, despite the increasingly recognized importance of neurohormonal signaling in skin physiology, the neuroendocrine regulation of cutaneous wound healing has received surprisingly little attention. Human skin, and its appendages, locally express the pleiotropic neurohormone prolactin (PRL), which not only regulates lactation but also hair follicle cycling, angiogenesis, keratinocyte proliferation, and epithelial stem cell functions. Therefore, we examined the effects of PRL in experimentally wounded female human skin organ culture. Overall, this revealed that PRL slightly, but significantly, inhibited epidermal regeneration (reepithelialisation), cytokeratin 6 protein expression and intraepidermal mitochondrial activity (MTCO1 expression), while it promoted keratinocyte terminal differentiation (i.e. involucrin expression) ex vivo. If the current pilot data are confirmed by further studies, PRL may serve as one of the-rarely studied-negative regulators of cutaneous wound healing that control excessive reepithelialisation. This raises the intriguing and clinically relevant question of whether PRL receptor antagonists could actually promote epidermal repair after human skin wounding.

Serum prolactin levels in psoriasis and its association with disease activity: a case-control study

Background:

Psoriasis is a T-cell-mediated autoimmune chronic skin disorder in which an environmental factor, perhaps a viral antigen, induces T cells to produce cytokines. These cytokines stimulate keratinocyte proliferation and production of antigenic adhesion molecules in the dermal blood vessels. Several mediators and hormones have been implicated in keratinocyte hyperproliferation and among these hormones, prolactin (PRL) has been found to have an effect on epithelial cells, lymphocytes and keratinocytes, thus an effect on the etiopathogenesis of psoriasis.

Aim:

The present study was designed to compare serum PRL levels in psoriatic patients with a control group.

Settings and Design:

This study was a hospital-based case control study, conducted in the department of Dermatology, STD and Leprosy, SMHS Hospital (Associated teaching hospital of Government Medical College Srinagar) over a period of 1 year, from September 2012 to 2013.

Materials and Methods:

The present study included 60 patients of psoriasis (42 males and 18 females) and 60 controls matched for age and sex. Serum PRL levels of patients and controls were measured by ECLIA and inferences were drawn.

Statistical Analysis Used:

Statistical significance of the results was carried out by the Chi-square test and the independent samples t-test. Statistical significance was determined at a level of P < 0.05.

Results:

Serum PRL levels were significantly increased in patients as compared to the control group (P value: 0.002). There was a positive correlation between pretreatment serum PRL levels and PASI score (r value: 0.379; P value: 0.003). An insignificant association was found between the pretreatment PRL level and serum PRL level after treatment (P value: 0.22). Also, a negative correlation between the duration of psoriasis and serum PRL was seen (r value: -0.008; P value: 0.954).

Conclusion:

PRL may have a role to play in the etiopathogenesis of psoriasis. However, further studies with large sample size should be carried out so as to validate this hypothesis.

Serum prolactin levels in psoriasis vulgaris

Background. Psoriasis is a chronic inflammatory skin disease affecting approximately 1–3% of Caucasians. Prolactin has proliferative effects on human keratinocytes, a dominant feature of psoriasis, and it is thought that this hormone may play a role in the pathogenesis of the disease. This study was conducted to confirm or refute these findings in order to better understand the disease pathogenesis. Methods. The subjects were 90 individuals aged between 15 and 47 years. They were divided into three groups of 30 individuals each: psoriatic patients, atopic dermatitis patients, and control group. A questionnaire was filled regarding their demographic and medical history. All of the study subjects underwent venous blood sampling (5 mL), and serum TSH and prolactin levels were checked. Subjects with abnormal TSH were omitted. Results. None of the patients in the study had raised prolactin, and there was no significant difference in the serum prolactin level between patients with psoriasis and atopic dermatitis and the control group. There was no relationship between the severity of psoriasis and serum levels of prolactin. Conclusion. Prolactin does not seem to play a role in the pathogenesis of psoriasis as its serum levels are comparable with atopic dermatitis patients and that of the normal population.

Prolactin induces the production of Th17 and Th1 cytokines/chemokines in murine Imiquimod-induced psoriasiform skin

BACKGROUND

Prolactin (PRL) is a pituitary-derived neuropeptide hormone that has been suggested to promote the development of psoriasis, a Th17/Th1-mediated inflammatory dermatosis. PRL increases the expression of Th1 cytokines; however, its effects on Th17 responses are unknown.

OBJECTIVE

This study aims to determine the in vivo effects of PRL on the expression of Th17 cytokines/chemokines in imiquimod-induced psoriasiform skin inflammation in mice.

METHODS

BALB/c mice were intraperitoneally injected with PRL or phosphate-buffered saline, and imiquimod cream or Vaseline was applied to the shaved back skin for six consecutive days.

RESULTS

Intraperitoneal PRL increased the mRNA levels of IL-17A, IL-17F, IL-22, IL-23p19, IL-12p40, CCL20 and STAT3 in imiquimod-treated skin. Mice treated with imiquimod plus PRL, but not those treated with imiquimod plus phosphate-buffered saline, showed significantly increased mRNA levels of TNF-α, IFN-γ, IL-12p35 and CXCL2 compared with controls. Intraperitoneal PRL increased the numbers of CD3(+) and GR-1(+) cells in the dermis of imiquimod-treated skin.

CONCLUSIONS

These results suggest that intraperitoneal PRL enhances the expression of Th17 and Th1 cytokines/chemokines, and augments inflammation in imiquimod-induced psoriasiform skin. Prolactin may thus exacerbate psoriasis through the enhancement of Th17/Th1 responses.

Pathophysiology of the Behçet's Disease

Behçet's disease (BD) is a multisystemic disease of unknown etiology characterized by chronic relapsing oral-genital ulcers and uveitis. Multiple systemic associations including articular, gastrointestinal, cardiopulmonary, neurologic, and vascular involvement are also observed in BD. Although the etiopathogenesis of the disease remains unknown, increased neutrophil functions such as chemotaxis, phagocytosis, and excessive production of reactive oxygen species (ROS), including superoxide anion, which may be responsible for oxidative tissue damage seen in BD, and also immunological alterations, T lymphocyte abnormalities in both subpopulation and function have been considered to be correlated with the etiopathogenesis of BD. There is some clinical evidence suggesting that emotional stress and hormonal alterations can influence the course and disease activity of BD.

Clinical efficacy of propylthiouracil and its influence on prolactin in psoriatic patients

OBJECTIVE

Propylthiouracil (PTU) is an effective drug for psoriasis treatment. Prolactin (PRL) is increased during psoriasis which has hyperproliferative effect on keratinocytes. Hence, the objective is to find the effect of PTU on PRL level in psoriatic patients.

DESIGN AND METHODS

25 psoriatic patients and 10 control subjects were involved in the study. Serum PRL, hematological and biochemical parameters, thyroid profile and histopathological examination were performed.

RESULTS

PTU treatment for 6 weeks and 12 weeks cleared psoriatic lesions indicated by decreased PASI score (p<0.001). Patients before treatment showed significantly increased PRL levels (male p<0.01, female p<0.001) when compared to controls, which was found to decrease significantly (male p<0.01, female p<0.001) after 12 weeks. Hematological and biochemical parameters showed no significant change. Histopathology showed reduced thickening of the epidermis and acanthosis after PTU treatment.

CONCLUSION

Since PRL is a growth hormone involved in hyperproliferation of keratinocytes, this study reveals the antiproliferative effect of PTU. Furthermore, no major side effects were observed following PTU treatment.

Prolactin: an emerging force along the cutaneous-endocrine axis

Prolactin (PRL), one of the most diverse regulators in mammalian biology, is produced in both human skin and hair follicles. Important advances in our understanding of the intracutaneous regulation and functions of PRL have recently been made using the serum-free skin and hair follicle organ culture technique. Given that human skin is the largest peripheral endocrine organ and a key interface between the endocrine, nervous and immune systems, a detailed understanding of PRL in the cutaneous context promises to have far-reaching implications beyond the skin. The current review presents a timely cutaneous perspective on the production, regulation and functions of PRL and summarizes the key questions facing extrapituitary PRL research in general and cutaneous PRL research in particular.

Dermatologic manifestations of hypopituitarism

Hypopituitarism is characterized by diminished or absent secretion of one or more pituitary hormones. The clinical features of hypopituitarism vary depending on age, rapidity of onset, hormones involved, and degree of deficiency. Dermatologic signs of hypopituitarism may involve alterations in pigmentation, the epidermal and dermal skin structures, and the pilosebaceous unit. We describe the causes and presentation of hypopituitarism with an emphasis on its dermatologic manifestations.

Human scalp hair follicles are both a target and a source of prolactin, which serves as an autocrine and/or paracrine promoter of apoptosis-driven hair follicle regression

The prototypic pituitary hormone prolactin (PRL) exerts a wide variety of bioregulatory effects in mammals and is also found in extrapituitary sites, including murine skin. Here, we show by reverse transcriptase-polymerase chain reaction and immunohistology that, contrary to a previous report, human skin and normal human scalp hair follicles (HFs), in particular, express both PRL and PRL receptors (PRL-R) at the mRNA and protein level. PRL and PRL-R immunoreactivity can be detected in the epithelium of human anagen VI HFs, while the HF mesenchyme is negative. During the HF transformation from growth (anagen) to apoptosis-driven regression (catagen), PRL and PRL-R immunoreactivity appear up-regulated. Treatment of organ-cultured human scalp HFs with high-dose PRL (400 ng/ml) results in a significant inhibition of hair shaft elongation and premature catagen development, along with reduced proliferation and increased apoptosis of hair bulb keratinocytes (Ki-67/terminal dUTP nick-end labeling immunohistomorphometry). This shows that PRL receptors, expressed in HFs, are functional and that human skin and human scalp HFs are both direct targets and sources of PRL. Our data suggest that PRL acts as an autocrine hair growth modulator with catagen-promoting functions and that the hair growth-inhibitory effects of PRL demonstrated here may underlie the as yet ill-understood hair loss in patients with hyper-prolactinemia.

Prolactin and its receptor are expressed in murine hair follicle epithelium, show hair cycle-dependent expression, and induce catagen

Here, we provide the first study of prolactin (PRL) and prolactin receptor (PRLR) expression during the nonseasonal murine hair cycle, which is, in contrast to sheep, comparable with the human scalp and report that both PRL and PRLR are stringently restricted to the hair follicle epithelium and are strongly hair cycle-dependent. In addition we show that PRL exerts functional effects on anagen hair follicles in murine skin organ culture by down-regulation of proliferation in follicular keratinocytes. In telogen follicles, PRL-like immunoreactivity was detected in outer root sheath (ORS) keratinocytes. During early anagen (III to IV), the developing inner root sheath (IRS) and the surrounding ORS were positive for PRL. In later anagen stages, PRL could be detected in the proximal IRS and the inner layer of the ORS. The regressing (catagen) follicle showed a strong expression of PRL in the proximal ORS. In early anagen, PRLR immunoreactivity occurred in the distal part of the ORS around the developing IRS, and subsequently to a restricted area of the more distal ORS during later anagen stages and during early catagen. The dermal papilla (DP) stayed negative for both PRL and PRLR throughout the cycle. Telogen follicles showed only a very weak PRLR staining of ORS keratinocytes. The long-form PRLR transcript was shown by real-time polymerase chain reaction to be transiently down-regulated during early anagen, whereas PRL transcripts were up-regulated during mid anagen. Addition of PRL (400 ng/ml) to anagen hair follicles in murine skin organ culture for 72 hours induced premature catagen development in vitro along with a decline in the number of proliferating hair bulb keratinocytes. These data support the intriguing concept that PRL is generated locally in the hair follicle epithelium and acts directly in an autocrine or paracrine manner to modulate the hair cycle.

Prolactin signaling influences the timing mechanism of the hair follicle: analysis of hair growth cycles in prolactin receptor knockout mice

Pituitary PRL regulates seasonal hair follicle growth cycles in many mammals. Here we present the first evidence implicating PRL in the nonseasonal, wave-like pelage replacement of laboratory mice. In this study we show that messenger RNA transcripts encoding the one long and two short forms of PRL receptor are present in the skin of adult and neonate mice. The receptor protein was immunolocalized to the hair follicle as well as the epidermis and sebaceous glands. Furthermore, PRL messenger RNA was detected within skin extracts, suggesting a possible autocrine/paracrine role. Analysis of the hair growth phenotype of PRL gene-disrupted mice (PRLR(-/-)) revealed a change in the timing of hair cycling events. Although no hair follicle development differences were noted in PRLR(-/-) neonates, observations of the second generation of hair growth revealed PRLR(-/-) mice molted earlier than wild types (PRLR(+/+)). The advance was greater in females (29 days) than in males (4 days), resulting in the elimination of the sexual dimorphism associated with murine hair replacement. Heterozygotes were intermediate between PRLR(-/-) and PRLR(+/+) mice in molt onset. Once initiated, the pattern and progression of the molt across the body were similar in all genotypes. Although all fiber types were present and appeared structurally normal, PRLR(-/-) mice had slightly longer and coarser hair than wild types. These findings demonstrate that PRL has an inhibitory effect on murine hair cycle events. The pituitary PRL regulation of hair follicle cycles observed in seasonally responsive mammals may be a result of pituitary PRL interacting with a local regulatory mechanism.

Controls of hair follicle cycling

Nearly 50 years ago, Chase published a review of hair cycling in which he detailed hair growth in the mouse and integrated hair biology with the biology of his day. In this review we have used Chase as our model and tried to put the adult hair follicle growth cycle in perspective. We have tried to sketch the adult hair follicle cycle, as we know it today and what needs to be known. Above all, we hope that this work will serve as an introduction to basic biologists who are looking for a defined biological system that illustrates many of the challenges of modern biology: cell differentiation, epithelial-mesenchymal interactions, stem cell biology, pattern formation, apoptosis, cell and organ growth cycles, and pigmentation. The most important theme in studying the cycling hair follicle is that the follicle is a regenerating system. By traversing the phases of the cycle (growth, regression, resting, shedding, then growth again), the follicle demonstrates the unusual ability to completely regenerate itself. The basis for this regeneration rests in the unique follicular epithelial and mesenchymal components and their interactions. Recently, some of the molecular signals making up these interactions have been defined. They involve gene families also found in other regenerating systems such as fibroblast growth factor, transforming growth factor-beta, Wnt pathway, Sonic hedgehog, neurotrophins, and homeobox. For the immediate future, our challenge is to define the molecular basis for hair follicle growth control, to regenerate a mature hair follicle in vitro from defined populations, and to offer real solutions to our patients' problems.

Human skin expresses growth hormone but not the prolactin gene

Using sensitive reverse transcriptase-polymerase chain reaction (RT-PCR) methods, we showed the expression of mRNA for growth hormone (GH) but not prolactin (PRL) in whole human skin (normal and basal cell carcinoma (BCC)). These RNAs for PRL and GH were below detectability in human epidermal keratinocytes and in human and hamster malignant melanocytes. This is in agreement with previous studies showing GH gene expression in dermal fibroblasts. GH peptide was not detected (by immunocytochemistry) in human skin specimens (normal and pathologic) in either dermal or epidermal compartments. The mRNA coding for the GH mediator insulin-like growth factor-1 (IGF-1) was detectable in whole skin and in malignant melanocytes. Therefore, in the present investigation of hormonal mediators of the cutaneous (epidermal) response to environmental stress, we have excluded the direct participation of PRL and GH in that reaction. Thus the analogy previously noted between the systemic (central) and skin responses to stress, as represented by cutaneous expression of hypothalamic-pituitary-adrenal axis components, does not extend to other pituitary hormones also involved in that response such as PRL and GH.

Neuroendocrinology of the skin

The classical observations of the skin as a target for melanotropins have been complemented by the discovery of their actual production at the local level. In fact, all of the elements controlling the activity of the hypothalamus-pituitary-adrenal axis are expressed in the skin including CRH, urocortin, and POMC, with its products ACTH, alpha-MSH, and beta-endorphin. Demonstration of the corresponding receptors in the same cells suggests para- or autocrine mechanisms of action. These findings, together with the demonstration of cutaneous production of numerous other hormones including vitamin D3, PTH-related protein (PTHrP), catecholamines, and acetylcholine that share regulation by environmental stressors such as UV light, underlie a role for these agents in the skin response to stress. The endocrine mediators with their receptors are organized into dermal and epidermal units that allow precise control of their activity in a field-restricted manner. The skin neuroendocrine system communicates with itself and with the systemic level through humoral and neural pathways to induce vascular, immune, or pigmentary changes, to directly buffer noxious agents or neutralize the elicited local reactions. Therefore, we suggest that the skin neuroendocrine system acts by preserving and maintaining the skin structural and functional integrity and, by inference, systemic homeostasis.

Human epidermal keratinocytes upregulate expression of the prolactin receptor after the onset of terminal differentiation, but do not respond to prolactin

Growing and differentiating keratinocytes maintain the epidermal barrier. This is partly controlled by growth factors and hormones. Prolactin (PRL) is named after its hormonal role in mammals during lactation, but is found in all vertebrates where PRL exerts various effects. In serum-free keratinocyte cultures, PRL was thought to be the factor responsible for the proliferative effect of bovine pituitary extract. Here, we evaluated PRL as a clonogenic factor for keratinocytes and found no mitogenic activity. Studying the expression of the PRL receptor by keratinocytes, we found the receptor upregulated only after culture confluence, in differentiating keratinocytes, but we were unable to detect any cellular response to PRL. The hormone does not alter the gene expression of either early (suprabasal keratin) or late (involucrin) differentiation markers by keratinocytes. Accordingly, no activation of the transcription factor Stat5 by PRL can be detected in keratinocytes, Stat5 being nevertheless detected by Western blot.

Human dermal fibroblast cells express prolactin in vitro

This study demonstrates the synthesis and release of prolactin (PRL) from dermal fibroblasts (>98%) in vitro, suggesting a potential local source of PRL in skin. PRL release was first detected in confluent cultures (0.25 x 10(6) plated cells) on or before day 18 and increased to a maximal level of 2 ng/72 h by day 30. Medroxyprogesterone acetate and estradiol (E2) had no effect on PRL release, but prostaglandin E2 (PGE2) reduced the time required for PRL induction to 6-9 days. The steroids and PGE2 together were synergistic, reaching maximal values of approximately 10 ng/72 h after 2 or more weeks of treatment. Dibutyryl-cyclic AMP, a second messenger in prostaglandin signal transduction, was also synergistic with medroxyprogesterone acetate and E2, but induced significant PRL expression in the absence of the steroids (28 and 12 ng/72 h, respectively). The increase in PRL release was not a result of increased cell proliferation, because the PRL-secreting cultures had 32.2 +/- 8.8% less DNA (N = 3 individuals, 93% confidence limit) than control cultures after 3 weeks of treatment with dibutyryl-cyclic AMP, medroxyprogesterone acetate, and E2. Dermal fibroblast PRL was immunologically and electrophoretically identical to decidual and pituitary PR-Ls, and Northern blot analysis demonstrated a PRL mRNA size of 1.15 kb. Maximal PRL release from fibroblast cells was 32.0 +/- 6.1 ng/72 h (mean +/- SD at 95% confidence limit) for a donor population representing both males (n = 15) and females (n = 7) between the ages of 20-week gestation to 52 years. In contrast to term decidual fibroblast cells that also express PRL, dermal fibroblasts did not co-express insulin-like growth factor-binding protein-1.

Physiology of endocrine skin interrelations

Hormones influence the skin and play a role in normal biologic processes. Keratinocytes can convert and synthesize endocrine hormones. Endocrine dysregulation of the skin and abnormalities of endocrine functions of keratinocytes may produce abnormal changes in the skin. Knowledge of the cutaneous metabolism of thyroid hormones, steroids, peptide hormones, and vitamin A derivatives is being rapidly updated. Skin manifestations of endocrine disorders result from imbalance in feedback loops maintaining endocrine homeostasis. Define molecular mechanisms of hormonal action on target cells underlie functional agonism and antagonism of hormonal signals aimed at governing epidermal turnover. The molecular synergism between vitamin A and other hormones may explain the therapeutic efficiency of combining retinoids with other therapies.

On the potential role of proopiomelanocortin in skin physiology and pathology

Pro-opiomelanocortin (POMC) is the precursor of ACTH, alpha-MSH and beta-endorphin, neuropeptides with multiple regulatory functions. Both the pituitary gland and peripheral tissues such as mammalian skin are capable of generating POMC-derived neuropeptides. Mammalian skin is also a target for POMC products; their possible roles in skin physiology and pathology are discussed in this communication.