Prolactin-modulated gene expression profiles in pancreatic islets from adult female rats

The adaptation of maternal energy metabolism to lactation and its underlying mechanisms

Maternal energy metabolism undergoes a singular adaptation during lactation that allows for the caloric enrichment of milk. Changes in the mammary gland, changes in the white adipose tissue, brown adipose tissue, liver, skeletal muscles and endocrine pancreas are pivotal for this adaptation. The present review details the landmark studies describing the enzymatic modulation and the endocrine signals behind these metabolic changes. We will also update this perspective with data from recent studies showing transcriptional and post-transcriptional mechanisms that mediate the adaptation of the maternal metabolism to lactation. The present text will also bring experimental and observational data that describe the long-term consequences that short periods of lactation impose to maternal metabolism.

Association between variations of physiological prolactin serum levels and the risk of type 2 diabetes: A systematic review and meta-analysis

AIM

To determine the pooled association between variations of prolactin serum levels within the physiological range and the risk of type 2 diabetes mellitus (T2D).

METHODS

Pubmed, Scopus, Web of Science, and grey literature were searched for studies investigating the association between variations of prolactin serum levels in the normal range and the risk of T2D in adults. The risk of prevalent and incident T2D was summarized as the odds ratio or relative risk according to the quartile of prolactin serum concentration, using random-effects meta-analysis.

RESULTS

Of 2,014 articles identified, 6 met the inclusion criteria. Data were pooled from cross-sectional studies including 6,670 subjects and longitudinal studies involving 13,203 subjects. Men with prolactin levels in the fourth quartile versus those in the first quartile had decreased risk of prevalent T2D (OR 0.52; 95%CI 0.35-077). The same association was seen in women (OR 0.46; 95%CI 0.30-0.73). Conversely, prolactin levels in the fourth versus first quartile were not associated with the risk of incident T2D in men (RR 1.21; 95%CI 0.79-1.87) or women (RR 0.77; 95%CI 0.48-1.22).

CONCLUSION

Higher prolactin serum levels within the normal range were associated with reduced risk of prevalent but not incident T2D. Further studies are necessary to address whether this association is causal, but these findings raise the discussion regarding the optimal level of prolactin suppression in subjects undergoing therapy with dopaminergic agonists.

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.

Metabolic profile and prolactin serum levels in men with type 2 diabetes mellitus: Old-new rubric

Background:

Prolactin (PRL) is involved in the regulation of glucose metabolism since high PRL serum levels are associated with low incidence of type 2 diabetes mellitus (T2DM). Therefore, the aim of the present study was to assess the metabolic effects of PRL on glucose homeostasis in men with T2DM.

Methods:

Eighty male patients with T2DM compared with 25 male healthy controls matched with patients for age and weight were divided into four groups: Group (A): patients with T2DM on metformin (n = 29), Group (B): patients with T2DM on glyburide (n = 30), Group (C): patients with T2DM on glyburide plus metformin (n = 21), and Group (D): healthy male subjects as control (n = 25). Body mass index (BMI) and blood pressure measurements were determined. Fasting blood glucose (FBG), glycated hemoglobin, total cholesterol, triglyceride (TG), high-density lipoprotein, low-density lipoprotein, atherogenic index, fasting serum insulin, insulin resistance (IR), and β-cell function of the pancreas were determined by homeostatic model assessment-2 (HOMA-IR). Furthermore, C-reactive protein and PRL serum level were determined in patients with T2DM and healthy control men.

Results:

BMI of T2DM patients was higher as compared with control (P = 0.003). Combination therapy (glyburide plus metformin) in patients with T2DM showed better effect on most of glycemic indices and lipid profile than glyburide or metformin monotherapy (P < 0.05). PRL serum level was higher in patients with T2DM as compared with control (P = 0.001). PRL serum level was high in glyburide-treated patients as compared with metformin-treated patients (P = 0.002).

Conclusion:

This study concludes that elevated PRL serum level in patients with T2DM is associated with diabetic complications. Diabetic pharmacotherapy mainly metformin reduced PRL serum level in patients with T2DM through amelioration of IR.

Transcriptomic analysis reveals new hippocampal gene networks induced by prolactin

Prolactin (Prl) is a pleiotropic hormone with multiple functions in several tissues and organs, including the brain. In the hippocampus, Prl has been implicated in several functions, including neuroprotection against excitotoxicity in lactating rats and in Prl-treated ovariectomized animals. However, the molecular mechanisms involved in Prl actions in the hippocampus have not been completely elucidated. The aim of this study was to analyse the hippocampal transcriptome of female Prl-treated ovariectomized rats. Transcriptomic analysis by RNASeq revealed 162 differentially expressed genes throughout 24 h of Prl treatment. Gene Ontology analysis of those genes showed that 37.65% were involved in brain processes that are regulated by the hippocampus, such as learning, memory and behaviour, as well as new processes that we did not foresee, such as glial differentiation, axogenesis, synaptic transmission, postsynaptic potential, and neuronal and glial migration. Immunodetection analysis demonstrated that Prl significantly modified microglial morphology, reduced the expression of Cd11b/c protein, and altered the content and location of the neuronal proteins Tau, Map2 and Syp, which are involved in axogenic and synaptic functions. This novel delineation of Prl activity in the hippocampus highlights its importance as a neuroactive hormone, opens a new avenue for understanding its actions and supports its participation in neuronal plasticity of this brain area.

Prolactin protects against cytokine-induced beta-cell death by NFκB and JNK inhibition

Type 1 diabetes is caused by an autoimmune assault that induces progressive beta-cell dysfunction and dead. Pro-inflammatory cytokines, such as interleukin 1 beta (IL1B), tumor necrosis factor (TNF) and interferon gamma (IFNG) contribute for beta-cell death, which involves the activation of the nuclear factor kappa B (NFκB) and c- Jun N-terminal kinase (JNK). Prolactin (PRL), a physiological mediator for beta-cell proliferation, was shown to protect beta cells against cytokines pro-apoptotic effects. We presently investigated the mechanisms involved in the protective effects of prolactin against cytokine-induced beta-cell death. The findings obtained indicate that STAT3 activation is involved in the anti-apoptotic role of PRL in rat beta cells. PRL prevents the activation of JNK via AKT and promotes a shift from expression of pro- to anti-apoptotic proteins downstream of the JNK cascade. Furthermore, PRL partially prevents the activation of NFκB and the transcription of its target genes IkBa, Fas, Mcp1, A20 and Cxcl10 and also decreases NO production. On the other hand, the pro-survival effects of PRL do not involve modulation of cytokine-induced endoplasmic reticulum stress. These results suggest that the beneficial effects of PRL in beta cells involve augmentation of anti-apoptotic mechanisms and, at the same time, reduction of pro-apoptotic effectors, rendering beta cells better prepared to deal with inflammatory insults. The better understanding of the pro-survival mechanisms modulated by PRL in beta cells can provide tools to prevent cell demise during an autoimmune attack or following islet transplantation.

Autocrine Prolactin Stimulates Endometrial Carcinoma Growth and Metastasis and Reduces Sensitivity to Chemotherapy

Advanced and recurrent endometrial carcinoma (EC) exhibits a poor response to chemotherapy and low survival rates. It has been previously reported that human prolactin (hPRL) is upregulated in endometrial cancer and is associated with worse survival outcomes. We provide evidence for the functional role of hPRL in EC progression. We generated a model for the study of autocrine hPRL-mediated cell functional effects through the forced expression of hPRL in human EC cells. Autocrine hPRL expression stimulated cell proliferation, anchorage-independent growth, migration, and invasion of EC cells and promoted tumor growth, local invasion, and metastatic colonization in xenograft models. In addition, forced expression of hPRL decreased sensitivity of EC cells to chemotherapeutic drugs (i.e., doxorubicin and paclitaxel), both in vitro and in vivo. Consistently, small interfering RNA-mediated depletion of hPRL significantly reduced oncogenicity and enhanced the chemosensitivity of EC cells. As CD24 is hPRL-regulated and has been implicated in drug resistance in EC, we further showed that CD24 is a critical mediator of hPRL-stimulated reduced sensitivity to doxorubicin and paclitaxel in EC cells. Therefore, inhibition of hPRL signaling is a potential therapeutic strategy for the treatment of late-stage EC, which can be used in combination with chemotherapy to improve the chemotherapeutic response.

Prolactin-induced neuroprotection against glutamate excitotoxicity is mediated by the reduction of [Ca2+]i overload and NF-κB activation

Prolactin (PRL) is a peptidic hormone that displays pleiotropic functions in the organism including different actions in the brain. PRL exerts a neuroprotective effect against excitotoxicity produced by glutamate (Glu) or kainic acid in both in vitro and in vivo models. It is well known that Glu excitotoxicity causes cell death through apoptotic or necrotic pathways due to intracellular calcium ([Ca²⁺] i) overload. Therefore, the aim of the present study was to assess the molecular mechanisms by which PRL maintains cellular viability of primary cultures of rat hippocampal neurons exposed to Glu excitotoxicity. We determined cell viability by monitoring mitochondrial activity and using fluorescent markers for viable and dead cells. The intracellular calcium level was determined by a fluorometric assay and proteins involved in the apoptotic pathway were determined by immunoblot. Our results demonstrated that PRL afforded neuroprotection against Glu excitotoxicity, as evidenced by a decrease in propidium iodide staining and by the decrease of the LDH activity. In addition, the MTT assay shows that PRL maintains normal mitochondrial activity even in neurons exposed to Glu. Furthermore, the Glu-induced intracellular [Ca²⁺]i overload was attenuated by PRL. These data correlate with the reduction found in the level of active caspase-3 and the pro-apoptotic ratio (Bax/Bcl-2). Concomitantly, PRL elicited the nuclear translocation of the transcriptional factor NF-κB, which was detected by immunofluorescence and confocal microscopy. To our knowledge, this is the first report demonstrating that PRL prevents Glu excitotoxicity by a mechanism involving the restoration of the intracellular calcium homeostasis and mitochondrial activity, as well as an anti-apoptotic action possibly mediated by the activity of NF-κB. Overall, the current results suggest that PRL could be of potential therapeutic advantage in the treatment of neurodegenerative diseases.

Advances in β cell replacement and regeneration strategies for treating diabetes

In the past decade, new approaches have been explored that are aimed at restoring functional β cell mass as a treatment strategy for diabetes. The two most intensely pursued strategies are β cell replacement through conversion of other cell types and β cell regeneration by enhancement of β cell replication. The approach closest to clinical implementation is the replacement of β cells with human pluripotent stem cell-derived (hPSC-derived) cells, which are currently under investigation in a clinical trial to assess their safety in humans. In addition, there has been success in reprogramming developmentally related cell types into β cells. Reprogramming approaches could find therapeutic applications by inducing β cell conversion in vivo or by reprogramming cells ex vivo followed by implantation. Finally, recent studies have revealed novel pharmacologic targets for stimulating β cell replication. Manipulating these targets or the pathways they regulate could be a strategy for promoting the expansion of residual β cells in diabetic patients. Here, we provide an overview of progress made toward β cell replacement and regeneration and discuss promises and challenges for clinical implementation of these strategies.

Short-term low-protein diet during pregnancy alters islet area and protein content of phosphatidylinositol 3-kinase pathway in rats

The phosphatidylinositol 3-kinase and mitogen-activated protein kinase pathways mediate β cell growth, proliferation, survival and death. We investigated whether protein restriction during pregnancy alters islet morphometry or the expression and phosphorylation of several proteins involved in the phosphatidylinositol 3-kinase and mitogen-activated protein kinase pathways. As controls, adult pregnant and non-pregnant rats were fed a normal-protein diet (17%). Pregnant and non-pregnant rats in the experimental groups were fed a low-protein diet (6%) for 15 days. Low protein diet during pregnancy increased serum prolactin level, reduced serum corticosterone concentration and the expression of both protein kinase B/AKT1 (AKT1) and p70 ribosomal protein S6 kinase (p70S6K), as well as the islets area, but did not alter the insulin content of pancreatic islets. Pregnancy increased the expression of the Src homology/collagen (SHC) protein and the extracellular signal-regulated kinases 1/2 (ERK1/2) independent of diet. ERK1/2 phosphorylation (pERK1/2) was similar in islets from pregnant and non-pregnant rats fed a low-protein diet, and was higher in islets from pregnant rats than in islets from non-pregnant rats fed a normal-protein diet. Thus, a short-term, low-protein diet during pregnancy was sufficient to reduce the levels of proteins in the phosphatidylinositol 3-kinase pathway and affect islet morphometry.

Long-term disruption of maternal glucose homeostasis induced by prenatal glucocorticoid treatment correlates with miR-29 upregulation

Excess of glucocorticoids (GCs) during pregnancy is strongly associated with the programming of glucose intolerance in the offspring. However, the impact of high GC levels on maternal metabolism is not clearly documented. This study aimed to test the hypothesis that mothers exposed to elevated levels of GCs might also display long-term disturbances in glucose homeostasis. Dexamethasone (DEX) was administered noninvasively to the mothers via drinking water between the 14th and the 19th days of pregnancy. Mothers were subjected to glucose and insulin tolerance tests at 1, 2, 3, 6, and 12 mo postweaning. Pregnant rats not treated with DEX and age-matched virgin rats were used as controls. Pancreatic islets were isolated at the 20th day of pregnancy and 12 mo postweaning in order to evaluate glucose-stimulated insulin secretion. The expression of the miR-29 family was also studied due to its responsiveness to GCs and its well-documented role in the regulation of pancreatic β-cell function. Rats treated with DEX during pregnancy presented long-term glucose intolerance and impaired insulin secretion. These changes correlated with 1) increased expression of miR-29 and its regulator p53, 2) reduced expression of syntaxin-1a, a direct target of miR-29, and 3) altered expression of genes related to cellular senescence. Our data demonstrate that the use of DEX during pregnancy results in deleterious outcomes to the maternal metabolism, hallmarked by reduced insulin secretion and glucose intolerance. This maternal metabolic programming might be a consequence of time-sustained upregulation of miR-29s in maternal pancreatic islets.

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.

The regulation of Rasd1 expression by glucocorticoids and prolactin controls peripartum maternal insulin secretion

The transition from gestation to lactation is characterized by a robust adaptation of maternal pancreatic β-cells. Consistent with the loss of β-cell mass, glucose-induced insulin secretion is down-regulated in the islets of early lactating dams. Extensive experimental evidence has demonstrated that the surge of prolactin is responsible for the morphofunctional remodeling of the maternal endocrine pancreas during pregnancy, but the precise molecular mechanisms by which this phenotype is rapidly reversed after delivery are not completely understood. This study investigated whether glucocorticoid-regulated expression of Rasd1/Dexras, a small inhibitory G protein, is involved in this physiological plasticity. Immunofluorescent staining demonstrated that Rasd1 is localized within pancreatic β-cells. Rasd1 expression in insulin-secreting cells was increased by dexamethasone and decreased by prolactin. In vivo data confirmed that Rasd1 expression is decreased in islets from pregnant rats and increased in islets from lactating mothers. Knockdown of Rasd1 abolished the inhibitory effects of dexamethasone on insulin secretion and the protein kinase A, protein kinase C, and ERK1/2 pathways. Chromatin immunoprecipitation experiments revealed that glucocorticoid receptor (GR) and signal transducer and activator of transcription 5b (STAT5b) cooperatively mediate glucocorticoid-induced Rasd1 expression in islets. Prolactin inhibited the stimulatory effect of GR/STAT5b complex on Rasd1 transcription. Overall, our data indicate that the stimulation of Rasd1 expression by glucocorticoid at the end of pregnancy reverses the increased insulin secretion that occurs during pregnancy. Prolactin negatively regulates this pathway by inhibiting GR/STAT5b transcriptional activity on the Rasd1 gene.

Quercetin decreases inflammatory response and increases insulin action in skeletal muscle of ob/ob mice and in L6 myotubes

Quercetin is a potent anti-inflammatory flavonoid, but its capacity to modulate insulin sensitivity in obese insulin resistant conditions is unknown. This study investigated the effect of quercetin treatment upon insulin sensitivity of ob/ob mice and its potential molecular mechanisms. Obese ob/ob mice were treated with quercetin for 10 weeks, and L6 myotubes were treated with either palmitate or tumor necrosis factor-α (TNFα) plus quercetin. Cells and muscles were processed for analysis of glucose transporter 4 (GLUT4), TNFα and inducible nitric oxide synthase (iNOS) expression, and c-Jun N-terminal kinase (JNK) and inhibitor of nuclear factor-κB (NF-κB) kinase (IκK) phosphorylation. Myotubes were assayed for glucose uptake and NF-κB translocation. Chromatin immunoprecipitation assessed NF-κB binding to GLUT4 promoter. Quercetin treatment improved whole body insulin sensitivity by increasing GLUT4 expression and decreasing JNK phosphorylation, and TNFα and iNOS expression in skeletal muscle. Quercetin suppressed palmitate-induced upregulation of TNFα and iNOS and restored normal levels of GLUT4 in myotubes. In parallel, quercetin suppressed TNFα-induced reduction of glucose uptake in myotubes. Nuclear accumulation of NF-κB in myotubes and binding of NF-κB to GLUT4 promoter in muscles of ob/ob mice were also reduced by quercetin. We demonstrated that quercetin decreased the inflammatory status in skeletal muscle of obese mice and in L6 myotubes. This effect was followed by increased muscle GLUT4, with parallel improvement of insulin sensitivity. These results point out quercetin as a putative strategy to manage inflammatory-related insulin resistance.

Prolactin promotes oxytocin and vasopressin release by activating neuronal nitric oxide synthase in the supraoptic and paraventricular nuclei

Prolactin (PRL) stimulates the secretion of oxytocin (OXT) and arginine AVP as part of the maternal adaptations facilitating parturition and lactation. Both neurohormones are under the regulation of nitric oxide. Here, we investigate whether the activation of neuronal nitric oxide synthase (nNOS) in the hypothalamo-neurohypophyseal system mediates the effect of PRL on OXT and AVP release and whether these effects operate in males. Plasma levels of OXT and AVP were measured in male rats after the intracerebroventricular injection of PRL or after inducing hyperprolactinemia by placing two anterior pituitary glands under the kidney capsule. NOS activity was evaluated in the paraventricular (PVN) and supraoptic (SON) hypothalamic nuclei by NADPH-diaphorase histochemistry and in hypothalamic extracts by the phosphorylation/inactivation of nNOS at Ser847. Elevated central and systemic PRL correlated with increased NOS activity in the PVN and SON and with higher OXT and AVP circulating levels. Notably, treatment with 7-nitroindazole, a selective inhibitor of nNOS, prevented PRL-induced stimulation of the release of both neurohormones. Also, phosphorylation of nNOS was reduced in hyperprolactinemic rats, and treatment with bromocriptine, an inhibitor of anterior pituitary PRL secretion, suppressed this effect. These findings suggest that PRL enhances nNOS activity in the PVN and SON, thereby contributing to the regulation of OXT and AVP release. This mechanism likely contributes to the regulation of processes beyond those of female reproduction.

UPR induces transient burst of apoptosis in islets of early lactating rats through reduced AKT phosphorylation via ATF4/CHOP stimulation of TRB3 expression

Endocrine pancreas from pregnant rats undergoes several adaptations that comprise increase in β-cell number, mass and insulin secretion, and reduction of apoptosis. Lactogens are the main hormones that account for these changes. Maternal pancreas, however, returns to a nonpregnant state just after the delivery. The precise mechanism by which this reversal occurs is not settled but, in spite of high lactogen levels, a transient increase in apoptosis was already reported as early as the 3rd day of lactation (L3). Our results revealed that maternal islets displayed a transient increase in DNA fragmentation at L3, in parallel with decreased RAC-alpha serine/threonine-protein kinase (AKT) phosphorylation (pAKT), a known prosurvival kinase. Wortmannin completely abolished the prosurvival action of prolactin (PRL) in cultured islets. Decreased pAKT in L3-islets correlated with increased Tribble 3 (TRB3) expression, a pseudokinase inhibitor of AKT. PERK and eIF2α phosphorylation transiently increased in islets from rats at the first day after delivery, followed by an increase in immunoglobulin heavy chain-binding protein (BiP), activating transcription factor 4 (ATF4), and C/EBP homologous protein (CHOP) in islets from L3 rats. Chromatin immunoprecipitation (ChIP) and Re-ChIP experiments further confirmed increased binding of the heterodimer ATF4/CHOP to the TRB3 promoter in L3 islets. Treatment with PBA, a chemical chaperone that inhibits UPR, restored pAKT levels and inhibited the increase in apoptosis found in L3. Moreover, PBA reduced CHOP and TRB3 levels in β-cell from L3 rats. Altogether, our study collects compelling evidence that UPR underlies the physiological and transient increase in β-cell apoptosis after delivery. The UPR is likely to counteract prosurvival actions of PRL by reducing pAKT through ATF4/CHOP-induced TRB3 expression.

Smad5 regulates Akt2 expression and insulin-induced glucose uptake in L6 myotubes

Insulin-induced glucose uptake by skeletal muscle results from Akt2 activation and is severely impaired during insulin resistance. Recently, we and others have demonstrated that BMP9 improves glucose homeostasis in diabetic and non-diabetic rodents. However, the mechanism by which BMP9 modulates insulin action remains unknown. Here we demonstrate that Smad5, a transcription factor activated by BMP9, and Akt2, are upregulated in differentiated L6 myotubes. Smad5, rather than Smad1/8, is downregulated "in vivo" and "in vitro" by dexamethasone. Smad5 knockdown decreased Akt2 expression and serine phosphorylation and insulin-induced glucose uptake, and increased the expression of the lipid phosphatase Ship2. Additionally, binding of Smad5 to Akt2 gene is decreased in dexamethasone-treated rats and increased in L6 myotubes compared to myoblasts. The present study indicates that Smad5 regulates glucose uptake in skeletal muscle by controlling Akt2 expression and phosphorylation. These finding reveals Smad5 as a potential target for the therapeutic of type 2 diabetes.

Pregnancy restores insulin secretion from pancreatic islets in cafeteria diet-induced obese rats

Insulin resistance during pregnancy is counteracted by enhanced insulin secretion. This condition is aggravated by obesity, which increases the risk of gestational diabetes. Therefore, pancreatic islet functionality was investigated in control nonpregnant (C) and pregnant (CP), and cafeteria diet-fed nonpregnant (Caf), and pregnant (CafP) obese rats. Isolated islets were used for measurements of insulin secretion (RIA), NAD(P)H production (MTS), glucose oxidation (14CO2 production), intracellular Ca2+ levels (fura-2 AM), and gene expression (real-time PCR). Impaired glucose tolerance was clearly established in Caf and CafP rats at the 14th wk on a diet. Insulin secretion induced by direct depolarizing agents such as KCl and tolbutamide and increasing concentrations of glucose was significantly reduced in Caf, compared with C islets. This reduction was not observed in islets from CP and CafP rats. Accordingly, the glucose oxidation and production of reduced equivalents were increased in CafP islets. The glucose-induced Ca2+ increase was significantly lower in Caf and higher in CafP, compared with all other groups. CP and CafP islets demonstrated an increased Ca2+ oscillation frequency, compared with both C and Caf islets, and the amplitude of oscillations was augmented in CafP, compared with Caf islets. In addition, Cavα1.2 and SERCA2a mRNA levels were reduced in Caf islets. Cavα1.2, but not SERCA2a, mRNA was normalized in CafP islets. In conclusion, cafeteria diet-induced obesity impairs insulin secretion. This alteration is related to the impairment of Ca2+ handling in pancreatic islets, in especial Ca2+ influx, a defect that is reversed during pregnancy allowing normalization of insulin secretion.

Prolactin treatment improves engraftment and function of transplanted pancreatic islets

Transplantation of pancreatic islets is clinically used to treat type 1 diabetes but requires multiple donors. Previous experimental studies demonstrated that transplanted islets have a low blood vessel density, which leads to a hypoxic microenvironment. The present study tested the hypothesis that experimental prolactin pretreatment, a substance that seems to stimulate angiogenesis in endogenous islets, would increase graft blood vessel density, thereby improving transplantation outcome. Pancreatic islets from C57BL/6 mice were incubated with prolactin (500 ng/ml) or vehicle during the last 24 h of culture before syngeneic transplantation beneath the renal capsule, or recipients were injected with prolactin or vehicle for the first 7 d after transplantation. One month after transplantation, graft vascular density, blood flow, oxygen tension, endocrine volume, and function were evaluated. Also, human islets were incubated with prolactin or vehicle before experimental transplantation and investigated for vascular engraftment. Vascular engraftment of syngeneically transplanted mouse islets was improved by both in vivo and in vitro prolactin pretreatment. Moreover, prolactin pretreatment in vitro of islets used for transplantation improved recovery from diabetes in a minimal islet mass model. Interestingly, also human islets subjected to prolactin treatment before experimental transplantation demonstrated improved revascularization, blood perfusion, and oxygen tension when evaluated 1 month after transplantation. We conclude that prolactin may improve engraftment of transplanted pancreatic islets. The protocol with pretreatment of islets ex vivo could minimize the risk of side effects when used in the clinical setting.

Modulation of bone morphogenetic protein-9 expression and processing by insulin, glucose, and glucocorticoids: possible candidate for hepatic insulin-sensitizing substance

Bone morphogenetic protein 9 (BMP-9), a member of the TGF-beta superfamily predominantly expressed in nonparenchymal liver cells, has been demonstrated to improve glucose homeostasis in diabetic mice. Along with this therapeutic effect, BMP-9 was proposed as a candidate for the hepatic insulin-sensitizing substance (HISS). Whether BMP-9 plays a physiological role in glucose homeostasis is still unknown. In the present study, we show that BMP-9 expression and processing is severely reduced in the liver of insulin-resistant rats. BMP-9 expression and processing was directly stimulated by in situ exposition of the liver to the combination of glucose and insulin and oral glucose in overnight fasted rats. Additionally, prolonged fasting (72 h) abrogated refeeding-induced BMP-9 expression and processing. Previous exposition to dexamethasone, a known inductor of insulin resistance, reduced BMP-9 processing stimulated by the combination of insulin and glucose. Finally, we show that neutralization of BMP-9 with an anti-BMP-9 antibody induces glucose intolerance and insulin resistance in 12-h fasted rats. Collectively, the present results demonstrate that BMP-9 plays an important role in the control of glucose homeostasis of the normal rat. Additionally, BMP-9 is expressed and processed in an HISS-like fashion, which is impaired in the presence of insulin resistance. BMP-9 regulation according to the feeding status and the presence of diabetogenic factors reinforces the hypothesis that BMP-9 might exert the role of HISS in glucose homeostasis physiology.

STAT5 activity in pancreatic β-cells

Signal transducer and activator of transcription (STAT)5A and -5B are latent transcription factors activated by cytokines and hormones of the cytokine family. In pancreatic insulin-secreting β-cells, STAT5A and -5B are activated primarily by prolactin and growth hormone stimulation and are important mediators of the potent stimulation of proliferation and insulin production caused by these hormones. STAT5A and -5B are both expressed in β-cells and control the expression of a number of mRNAs implicated in cell replication control, insulin biosynthesis and secretion. In addition to STAT5A and -5B being transcriptional activators, they may also repress gene transcription. By these means, STAT5 proteins increase the levels of anti-apoptotic transcripts in β-cells and repress expression of pro-apoptotic genes. This review focuses on the anti-apoptotic role of STAT5 signaling, providing a mechanism for β-cell resistance to pro-apoptotic cytokines, Type 1 diabetes mellitus and obesity-associated β-cell stress. It is clear from studies of STAT5 signaling in pancreatic β-cells that STAT5 is important for postnatal β-cell compensatory growth (as in pregnancy or obesity) and in the defense against β-cell stress factors.

What can we learn from rodents about prolactin in humans?

Prolactin (PRL) is a 23-kDa protein hormone that binds to a single-span membrane receptor, a member of the cytokine receptor superfamily, and exerts its action via several interacting signaling pathways. PRL is a multifunctional hormone that affects multiple reproductive and metabolic functions and is also involved in tumorigenicity. In addition to being a classical pituitary hormone, PRL in humans is produced by many tissues throughout the body where it acts as a cytokine. The objective of this review is to compare and contrast multiple aspects of PRL, from structure to regulation, and from physiology to pathology in rats, mice, and humans. At each juncture, questions are raised whether, or to what extent, data from rodents are relevant to PRL homeostasis in humans. Most current knowledge on PRL has been obtained from studies with rats and, more recently, from the use of transgenic mice. Although this information is indispensable for understanding PRL in human health and disease, there is sufficient disparity in the control of the production, distribution, and physiological functions of PRL among these species to warrant careful and judicial extrapolation to humans.

Lactogens promote beta cell survival through JAK2/STAT5 activation and Bcl-XL upregulation

One of the goals in the treatment for diabetes is to enhance pancreatic beta cell function, proliferation, and survival. This study explores the role of lactogenic hormones, prolactin (PRL) and placental lactogen (PL), in beta cell survival. We have previously shown that transgenic mice expressing mouse placental lactogen-1 (mPL1) in beta cells under the rat insulin II promoter (RIP) are resistant to the diabetogenic and cytotoxic effects of streptozotocin (STZ) in vivo. The current study demonstrates that lactogens protect rat insulinoma (INS-1) cells and primary mouse beta cells against two distinct beta cell death inducers, STZ and dexamethasone (DEX), in vitro. Further, we identify the mechanism through which lactogens protect beta cells against DEX-induced death. The signaling pathway mediating this protective effect is the janus-activated-kinase-2/signal transducer and activator of transcription-5 (JAK2/STAT5) pathway. This is demonstrated in INS-1 cells and primary mouse beta cells using three separate approaches, pharmacological inhibitors, JAK2-specific siRNAs and a dominant-negative STAT5 mutant. Furthermore, lactogens specifically and significantly increase the anti-apoptotic protein Bcl-XL in insulinoma cells and mouse islets. Bcl-XL-specific siRNA significantly inhibits lactogen-mediated protection against DEX-induced beta cell death. We believe this is the first direct demonstration of lactogens mediating their protective effect through the JAK2/STAT5 pathway in the beta cell and through Bcl-XL in any cell type.

Ontogenesis of the Expression of Prolactin Receptor Messenger Ribonucleic Acid During Late Embryogenesis in Turkeys and Chickens

Changes in circulating levels of prolactin (PRL) and tissue content of PRL receptor (PRLR) messenger RNA (mRNA) in the liver, pancreas, kidney, and gonads (testis/ovary) were measured in turkey and chicken embryos from embryonic day (ED) 21 or ED15, respectively, to 1 d after hatch by real-time PCR. There were no differences between the sexes in chickens or turkeys. Both species had very similar patterns of PRL release and expression of PRLR mRNA, and no major differences were observed between turkey or chicken embryos. Plasma levels of PRL increased from low levels during the last week of embryonic development and were at significantly higher levels (about 4-fold) by 1 d after hatch. Similarly, in all tissues the content of PRLR mRNA was minimal at the outset and increased to reach maxima about the time of hatch. In both species, the highest levels of transcript were observed in the kidney followed by the gonad, liver, and pancreas. The tissue content of PRLR was correlated (0.6 to 0.8 dependent on the tissue) to circulating levels of PRL, which suggested that PRL may be associated with an increase in its receptor number around the time of hatch. Because levels of PRL and tissue content of PRLR mRNA increased around the time of hatch, this suggests that these tissues may be targets for PRL and may be involved in the physiologic changes occurring in embryos around the time of hatching.

Postpartum glycemic homeostasis in early lactating rats is accompanied by transient and specific increase of soleus insulin response through IRS2/AKT pathway

It is known that at the moment of delivery immediate lost of conceptus (main site of glucose disposal in late pregnancy) is not able to disturb glucose homeostasis in early lactating mothers. However, the mechanism by which this adaptation takes place in early lactation is still unknown. Most studies concerning insulin sensitivity in lactating rats were carried out at 11–13 days postpartum and did not describe functional changes in insulin response in early lactation. Here we show that lactation hypersensitivity to insulin is observed as early as 3 days after delivery (L3). We show that the oxidative soleus muscle displays a transient increased maximal insulin-induced glucose uptake and CO2production, which is temporally limited to L3. Response of soleus muscle was accompanied by an increase in glucose transporter 4 (GLUT4) content at L3. This adaptive response was not detected in the glycolytic plantaris muscle, which displayed lower content of GLUT4. We also found that soleus muscle from early lactating rats have higher insulin receptor expression and tyrosine phosphorylation. Downstream steps of insulin signaling pathway; e.g., insulin receptor substrate 2 tyrosine phosphorylation and its association with phosphatidylinositol 3-kinase were also upregulated in soleus muscle. In parallel, protein tyrosine phosphatase 1B expression, a negative regulator of insulin signal, was reduced. Importantly, all of these molecular alterations were time limited to L3 and were not observed in plantaris muscle. These results suggest that improved insulin action in oxidative, but not in glycolytic muscle might contribute to achievement of glucose homeostasis postpartum.

Characteristics of gastrin controlled ECL cell specific gene expression

BACKGROUND

The ECL cells are histamine-producing endocrine cells in the oxyntic mucosa that synthesize and secrete proteins and peptides. They are the primary target for gastrin and mediate the control of gastrin on acid secretion and oxyntic mucosal growth. Knowledge of the molecular biology of the ECL cell is therefore important for understanding gastric physiology. Accordingly, we wanted to identify genes that are characteristically expressed in the ECL cells and controlled by gastrin.

METHODS

Using Affymetrix GeneChips, RNA expression profiles were generated from ECL cells isolated by counterflow elutriation from hyper- or hypogastrinemic rats. Contamination from non-endocrine cells was eliminated by subtraction of the expression profiles of the fundic and antral mucosa.

RESULTS

The expression of 365 genes was ECL cell characteristic. Gastrin was found to control the expression of 120 which could be divided into two major groups depending on the known or anticipated biological function of the encoded protein: genes encoding proteins involved in the secretory process and genes encoding proteins needed to generate energy for secretion. Interestingly, gastrin stimulation also increased ECL cells expression of anti-apoptotic genes.

CONCLUSION

The ECL cell specific expression profile is reminiscent of that of neurons and other endocrine cells exhibiting high expression of genes encoding proteins involved in the synthesis, storage and secretion of neuropeptides or peptide hormones. Gastrin regulated the expression of one third of these genes and is thus involved in the control of secretion from the ECL cells.

Prolactin-induced changes in protein expression in human pancreatic islets

Ex vivo islet cell culture prior to transplantation appears as an attractive alternative for treatment of type 1 diabetes. Previous results from our laboratory have demonstrated beneficial effects of human prolactin (rhPRL) treatment on human islet primary cultures. In order to probe into the molecular events involved in the intracellular action of rhPRL in these cells, we set out to identify proteins with altered expression levels upon rhPRL cell treatment, using two-dimensional (2D) gel electrophoresis and mass spectrometry (MS). An average of 300 different protein spots were detected, 14 of which were modified upon rhPRL treatment (p<0.01), of which 12 were successfully identified using MS and grouped according to their biological functions. In conclusion, our study provides, for the first time, information about proteins that could be critically involved in PRL's action on human pancreatic islets, and facilitate identification of new and specific targets involved in islet cell function and proliferation.

ERK3 associates with MAP2 and is involved in glucose-induced insulin secretion

The adaptation of pancreatic islets to pregnancy includes increased beta cell proliferation, expansion of islet mass, and increased insulin synthesis and secretion. Most of these adaptations are induced by prolactin (PRL). We have previously described that in vitro PRL treatment increases ERK3 expression in isolated rat pancreatic islets. This study shows that ERK3 is also upregulated during pregnancy. Islets from pregnant rats treated with antisense oligonucleotide targeted to the PRL receptor displayed a significant reduction in ERK3 expression. Immunohistochemical double-staining showed that ERK3 expression is restricted to pancreatic beta cells. Transfection with antisense oligonucleotide targeted to ERK3 abolished the insulin secretion stimulated by glucose in rat islets and by PMA in RINm5F cells. Therefore, we examined the participation of ERK3 in the activation of a cellular target involved in secretory events, the microtubule associated protein MAP2. PMA induced ERK3 phosphorylation that was companied by an increase in ERK3/MAP2 association and MAP2 phosphorylation. These observations provide evidence that ERK3 is involved in the regulation of stimulus-secretion coupling in pancreatic beta cells.

Focus on prolactin as a metabolic hormone

New information about the effects of prolactin (PRL) on metabolic processes warrants re-evaluation of the overall metabolic actions of PRL. PRL affects metabolic homeostasis by regulating key enzymes and transporters that are associated with glucose and lipid metabolism in several target organs. In the lactating mammary gland, PRL increases the production of milk proteins, lactose and lipids. In adipose tissue, PRL generally suppresses lipid storage and adipokine release. PRL supports the growth of pancreatic islets, stimulates insulin secretion and increases citrate production in the prostate. A specific case is made for PRL in the human breast and adipose tissue, where it acts as a circulating hormone and an autocrine or paracrine factor. Although the overall effects of PRL on body composition are modest and species specific, PRL might be involved in the manifestation of insulin resistance.