Lactogens protect rodent and human beta cells against glucolipotoxicity-induced cell death through Janus kinase-2 (JAK2)/signal transducer and activator of transcription-5 (STAT5) signalling

LGR4 is essential for maintaining β-cell homeostasis through suppression of RANK

Pancreatic β-cell stress contributes to diabetes progression. This study demonstrates that Leucine-rich repeat-containing G-protein-coupled-receptor-4 (LGR4) is critical for maintaining β-cell health and is modulated by stressors. In vitro , Lgr4 knockdown decreases proliferation and survival in rodent β-cells, while overexpression protects against cytokine-induced cell death in rodent and human β-cells. Mechanistically, LGR4 suppresses Receptor Activator of Nuclear Factor Kappa B (NFκB) (RANK) and its subsequent activation of NFκB to protect β-cells. β-cell-specific Lgr4 -conditional knockout (cko) mice exhibit normal glucose homeostasis but increased β-cell death in both sexes and decreased proliferation only in females. Male Lgr4 cko mice under stress display reduced β-cell proliferation and a further increase in β-cell death. Upon aging, both male and female Lgr4 cko mice display impaired β-cell homeostasis, however, only female mice are glucose intolerant with decreased plasma insulin. We show that LGR4 is required for maintaining β-cell health under basal and stress-induced conditions, through suppression of RANK.

Teaser

LGR4 receptor is critical for maintaining β-cell health under basal and stressed conditions, through suppression of RANK.

Magnetogenetic cell activation using endogenous ferritin

The ability to precisely control the activity of defined cell populations enables studies of their physiological roles and may provide therapeutic applications. While prior studies have shown that magnetic activation of ferritin-tagged ion channels allows cell-specific modulation of cellular activity, the large size of the constructs made the use of adeno-associated virus, AAV, the vector of choice for gene therapy, impractical. In addition, simple means for generating magnetic fields of sufficient strength have been lacking. Toward these ends, we first generated a novel anti-ferritin nanobody that when fused to transient receptor potential cation channel subfamily V member 1, TRPV1, enables direct binding of the channel to endogenous ferritin in mouse and human cells. This smaller construct can be delivered in a single AAV and we validated that it robustly enables magnetically induced cell activation in vitro . In parallel, we developed a simple benchtop electromagnet capable of gating the nanobody-tagged channel in vivo . Finally, we showed that delivering these new constructs by AAV to pancreatic beta cells in combination with the benchtop magnetic field delivery stimulates glucose-stimulated insulin release to improve glucose tolerance in mice in vivo . Together, the novel anti-ferritin nanobody, nanobody-TRPV1 construct and new hardware advance the utility of magnetogenetics in animals and potentially humans.

RANKL/RANK is required for cytokine-induced beta cell death; osteoprotegerin, a RANKL inhibitor, reverses rodent type 1 diabetes

Treatment for type 1 diabetes (T1D) requires stimulation of functional β cell regeneration and survival under stress. Previously, we showed that inhibition of the RANKL/RANK [receptor activator of nuclear factor kappa Β (NF-κB) ligand] pathway, by osteoprotegerin and the anti-osteoporotic drug denosumab, induces rodent and human β cell proliferation. We demonstrate that the RANK pathway mediates cytokine-induced rodent and human β cell death through RANK-TRAF6 interaction and induction of NF-κB activation. Osteoprotegerin and denosumab protected β cells against this cytotoxicity. In human immune cells, osteoprotegerin and denosumab reduce proinflammatory cytokines in activated T-cells by inhibiting RANKL-induced activation of monocytes. In vivo, osteoprotegerin reversed recent-onset T1D in nonobese diabetic/Ltj mice, reduced insulitis, improved glucose homeostasis, and increased plasma insulin, β cell proliferation, and mass in these mice. Serum from T1D subjects induced human β cell death and dysfunction, but not α cell death. Osteoprotegerin and denosumab reduced T1D serum-induced β cell cytotoxicity and dysfunction. Inhibiting RANKL/RANK could have therapeutic potential.

Phosphatases are predicted to govern prolactin-mediated JAK–STAT signaling in pancreatic beta cells

Patients with diabetes are unable to produce a sufficient amount of insulin to properly regulate their blood glucose levels. One potential method of treating diabetes is to increase the number of insulin-secreting beta cells in the pancreas to enhance insulin secretion. It is known that during pregnancy, pancreatic beta cells proliferate in response to the pregnancy hormone, prolactin (PRL). Leveraging this proliferative response to PRL may be a strategy to restore endogenous insulin production for patients with diabetes. To investigate this potential treatment, we previously developed a computational model to represent the PRL-mediated JAK–STAT signaling pathway in pancreatic beta cells. Here, we applied the model to identify the importance of particular signaling proteins in shaping the response of a population of beta cells. We simulated a population of 10 000 heterogeneous cells with varying initial protein concentrations responding to PRL stimulation. We used partial least squares regression to analyze the significance and role of each of the varied protein concentrations in producing the response of the cell. Our regression models predict that the concentrations of the cytosolic and nuclear phosphatases strongly influence the response of the cell. The model also predicts that increasing PRL receptor strengthens negative feedback mediated by the inhibitor suppressor of cytokine signaling. These findings reveal biological targets that can potentially be used to modulate the proliferation of pancreatic beta cells to enhance insulin secretion and beta cell regeneration in the context of diabetes.

Exogenous Lactogenic Signaling Stimulates Beta Cell Replication In Vivo and In Vitro

As patients recently diagnosed with T1D and patients with T2D have residual beta cell mass, there is considerable effort in beta cell biology to understand the mechanisms that drive beta cell regeneration as a potential cellular therapy for expanding patients’ residual beta cell population. Both mouse and human studies have established that beta cell mass expansion occurs rapidly during pregnancy. To investigate the mechanisms of beta cell mass expansion during pregnancy, we developed a novel in vivo and in vitro models of pseudopregnancy. Our models demonstrate that pseudopregnancy promotes beta cell mass expansion in parous mice, and this expansion is driven by beta cell proliferation rather than hypertrophy. Importantly, estrogen, progesterone, and placental lactogen induce STAT5A signaling in the pseudopregnancy model, demonstrating that this model successfully recapitulates pregnancy-induced beta cell replication. We then created an in vitro model of pseudopregnancy and found that the combination of estrogen and placental lactogen induced beta cell replication in human islets and rat insulinoma cells. Therefore, beta cells both in vitro and in vivo increase proliferation when subjected to the pseudopregnancy cocktail compared to groups treated with estradiol or placental lactogen alone. The pseudopregnancy models described here may help inform novel methods of inducing beta cell replication in patients with diabetes.

The Human Islet: Mini-Organ With Mega-Impact

This review focuses on the human pancreatic islet-including its structure, cell composition, development, function, and dysfunction. After providing a historical timeline of key discoveries about human islets over the past century, we describe new research approaches and technologies that are being used to study human islets and how these are providing insight into human islet physiology and pathophysiology. We also describe changes or adaptations in human islets in response to physiologic challenges such as pregnancy, aging, and insulin resistance and discuss islet changes in human diabetes of many forms. We outline current and future interventions being developed to protect, restore, or replace human islets. The review also highlights unresolved questions about human islets and proposes areas where additional research on human islets is needed.

Extracellular vesicles and their potential role inducing changes in maternal insulin sensitivity during gestational diabetes mellitus

Gestational diabetes mellitus (GDM) is one of the most common endocrine disorders during gestation and affects around 15% of all pregnancies worldwide, paralleling the global increase in obesity and type 2 diabetes. Normal pregnancies are critically dependent on the development of maternal insulin resistance balanced by an increased capacity to secrete insulin, which allows for the allocation of nutrients for adequate foetal growth and development. Several factors including placental hormones, inflammatory mediators and nutrients have been proposed to alter insulin sensitivity and insulin response and underpin the pathological outcomes of GDM. However, other factors may also be involved in the regulation of maternal metabolism and a complete understanding of GDM pathophysiology requires the identification of these factors, and the mechanisms associated with them. Recent studies highlight the potential utility of tissue-specific extracellular vesicles (EVs) in the diagnosis of disease onset and treatment monitoring for several pregnancy-related complications, including GDM. To date, there is a paucity of data defining changes in the release, content, bioactivity and diagnostic utility of circulating EVs in pregnancies complicated by GDM. Placental EVs may engage in paracellular interactions including local cell-to-cell communication between the cell constituents of the placenta and contiguous maternal tissues, and/or distal interactions involving the release of placental EVs into biological fluids and their transport to a remote site of action. Hence, the aim of this review is to discuss the biogenesis, isolation methods and role of EVs in the physiopathology of GDM, including changes in maternal insulin sensitivity during pregnancy.

Dynamic Regulation of JAK-STAT Signaling Through the Prolactin Receptor Predicted by Computational Modeling

Introduction

The expansion of insulin-producing beta cells during pregnancy is critical to maintain glucose homeostasis in the face of increasing insulin resistance. Prolactin receptor (PRLR) signaling is one of the primary mediators of beta cell expansion during pregnancy, and loss of PRLR signaling results in reduced beta cell mass and gestational diabetes. Harnessing the proliferative potential of prolactin signaling to expand beta cell mass outside of the context of pregnancy requires quantitative understanding of the signaling at the molecular level.

Methods

A mechanistic computational model was constructed to describe prolactin-mediated JAK-STAT signaling in pancreatic beta cells. The effect of different regulatory modules was explored through ensemble modeling. A Bayesian approach for likelihood estimation was used to fit the model to experimental data from the literature.

Results

Including receptor upregulation, with either inhibition by SOCS proteins, receptor internalization, or both, allowed the model to match experimental results for INS-1 cells treated with prolactin. The model predicts that faster dimerization and nuclear import rates of STAT5B compared to STAT5A can explain the higher STAT5B nuclear translocation. The model was used to predict the dose response of STAT5B translocation in rat primary beta cells treated with prolactin and reveal possible strategies to modulate STAT5 signaling.

Conclusions

JAK-STAT signaling must be tightly controlled to obtain the biphasic response in STAT5 activation seen experimentally. Receptor up-regulation, combined with SOCS inhibition, receptor internalization, or both is required to match experimental data. Modulating reactions upstream in the signaling can enhance STAT5 activation to increase beta cell survival.

Electronic supplementary material

The online version of this article (10.1007/s12195-020-00647-8) contains supplementary material, which is available to authorized users.

Lactogens Reduce Endoplasmic Reticulum Stress-Induced Rodent and Human β-Cell Death and Diabetes Incidence in Akita Mice

Diabetes occurs due to a loss of functional β-cells, resulting from β-cell death and dysfunction. Lactogens protect rodent and human β-cells in vitro and in vivo against triggers of β-cell cytotoxicity relevant to diabetes, many of which converge onto a common pathway of endoplasmic reticulum (ER) stress. However, whether lactogens modulate the ER stress pathway is unknown. This study examines whether lactogens can protect β-cells against ER stress and mitigate diabetes incidence in Akita (Ak) mice, a rodent model of ER stress-induced diabetes, akin to neonatal diabetes in humans. We show that lactogens protect INS-1 cells, primary rodent and human β-cells in vitro against two distinct ER stressors, tunicamycin and thapsigargin, through activation of the JAK2/STAT5 pathway. Lactogens mitigate expression of proapoptotic molecules in the ER stress pathway that are induced by chronic ER stress in INS-1 cells and rodent islets. Transgenic expression of placental lactogen in β-cells of Ak mice drastically reduces the severe hyperglycemia, diabetes incidence, hypoinsulinemia, β-cell death, and loss of β-cell mass observed in Ak littermates. These are the first studies in any cell type demonstrating that lactogens modulate the ER stress pathway, causing enhanced β-cell survival and reduced diabetes incidence in the face of chronic ER stress.

Placental Lactogen as a Marker of Maternal Obesity, Diabetes, and Fetal Growth Abnormalities: Current Knowledge and Clinical Perspectives

Placental lactogen (PL) is a peptide hormone secreted throughout pregnancy by both animal and human specialized endocrine cells. PL plays an important role in the regulation of insulin secretion in pancreatic β-cells, stimulating their proliferation and promoting the expression of anti-apoptotic proteins. Cases of pregnancy affected by metabolic conditions, including obesity and diabetes, are related to alterations in the PL secretion pattern. Whereas obesity is most often associated with lower PL serum concentrations, diabetes results in increased PL blood levels. Disruptions in PL secretion are thought to be associated with an increased prevalence of gestational complications, such as placental dysfunction, diabetic retinopathy, and abnormalities in fetal growth. PL is believed to be positively correlated with birth weight. The impaired regulation of PL secretion could contribute to an increased incidence of both growth retardation and fetal macrosomia. Moreover, the dysregulation of PL production during the intrauterine period could affect the metabolic status in adulthood. PL concentration measurement could be useful in the prediction of fetal macrosomia in women with normal oral glucose tolerance test (OGTT) results or in evaluating the risk of fetal growth restriction, but its application in standard clinical practice seems to be limited in the era of ultrasonography.

Lrrc55 is a novel prosurvival factor in pancreatic islets

Pancreatic islets adapt to the increase in insulin demand during pregnancy by upregulating β-cell number, insulin synthesis, and secretion. These changes require prolactin receptor (PrlR) signaling, as mice with PrlR deletion are glucose intolerant with a lower β-cell mass. Prolactin also prevents β-cell apoptosis. Many genes participate in these adaptive changes in the islet, and Lrrc55 is one of the most upregulated genes with unknown function in islets. Because Lrrc55 expression increases in parallel to the increase in β-cell number and insulin production during pregnancy, we hypothesize that Lrrc55 might regulate β-cell proliferation/apoptosis (thus β-cell number) and insulin synthesis. Here, we found that Lrrc55 expression was upregulated by >60-fold during pregnancy in a PrlR-dependent manner, and this increase was restricted only to the islets. Overexpression of Lrrc55 in β-cells had minimal effect on β-cell proliferation and glucose-stimulated insulin secretion but protected β-cells from glucolipotoxicity-induced reduction in insulin gene expression. Moreover, Lrrc55 protects β-cells from glucolipotoxicity-induced apoptosis, with upregulation of prosurvival signals and downregulation of proapoptotic signals of the endoplasmic reticulum (ER) stress pathway. Furthermore, Lrrc55 attenuated calcium depletion induced by glucolipotoxicity, which may contribute to its antiapoptotic effect. Hence our findings suggest that Lrrc55 is a novel prosurvival factor that is upregulated specifically in islets during pregnancy, and it prevents conversion of adaptive unfolded protein response to unresolved ER stress and apoptosis in β-cells. Lrrc55 could be a potential therapeutic target in diabetes by reducing ER stress and promoting β-cell survival.

Stigmasterol prevents glucolipotoxicity induced defects in glucose-stimulated insulin secretion

Type 2 diabetes results from defects in both insulin sensitivity and insulin secretion. Elevated cholesterol content within pancreatic β-cells has been shown to reduce β-cell function and increase β-cell apoptosis. Hyperglycemia and dyslipidemia contribute to glucolipotoxicity that leads to type 2 diabetes. Here we examined the capacity of glucolipotoxicity to induce free cholesterol accumulation in human pancreatic islets and the INS-1 insulinoma cell line. Glucolipotoxicity treatment increased free cholesterol in β-cells, which was accompanied by increased reactive oxygen species (ROS) production and decreased insulin secretion. Addition of AAPH, a free radical generator, was able to increase filipin staining indicating a link between ROS production and increased cholesterol in β-cells. We also showed the ability of stigmasterol, a common food-derived phytosterol with anti-atherosclerotic potential, to prevent the increase in both free cholesterol and ROS levels induced by glucolipotoxicity in INS-1 cells. Stigmasterol addition also inhibited early apoptosis, increased total insulin, promoted actin reorganization, and improved insulin secretion in cells exposed to glucolipotoxicity. Overall, these data indicate cholesterol accumulation as an underlying mechanism for glucolipotoxicity-induced defects in insulin secretion and stigmasterol treatment as a potential strategy to protect β-cell function during diabetes progression.

Suppressor of cytokine signaling 2 (SOCS2) deletion protects against multiple low dose streptozotocin-induced type 1 diabetes in adult male mice

BACKGROUND

Diabetes type 1 is characterized by the failure of beta cells to produce insulin. Suppressor of cytokine signaling (SOCS) proteins are important regulators of the Janus kinase/signal transducer and activator of transcription (JAK-STAT) pathway. Previous studies have shown that GH can prevent the development of type I diabetes in mice and that SOCS2 deficiency mimics a state of increased GH sensitivity.

METHODOLOGY

The elevated sensitivity of SOCS2-/- mice to GH and possibly to PRL was the rationale to analyze the effects of multiple low dose streptozotocin (MLDSTZ)-induced diabetes in SOCS2-/- mice.

RESULTS

We show that 6-month-old SOCS2-/- mice, but not 2-month-old mice, were less sensitive to MLDSTZ-induced diabetes, compared to controls. MLDSTZ treatment induced glucose intolerance in both SOCS2+/+ and SOCS2-/- mice, as shown by glucose tolerance tests, with SOCS2+/+ mice showing a more marked intolerance, compared to SOCS2-/- mice. Furthermore, insulin tolerance tests showed that the SOCS2-/- mice have an improved hypoglycemic response to exogenous insulin, compared to SOCS2+/+ mice. Moreover, in isolated islets, lipotoxic effects on insulin release could partly be overcome by ligands, which bind to GH or PRL receptors.

CONCLUSION

Knockdown of SOCS2 makes mice less sensitive to MLDSTZ. These results are consistent with the proposal that elimination of SOCS2 in pancreatic islets creates a state of β-cell hypersensitivity to GH/PRL that mimics events in pregnancy, and which is protective against MLDSTZ-induced type I diabetes in mice. SOCS2-dependent control of β-cell survival may be of relevance to islet regeneration and survival in transplantation.

Human Islets Have Fewer Blood Vessels than Mouse Islets and the Density of Islet Vascular Structures Is Increased in Type 2 Diabetes

Human and rodent islets differ substantially in several features, including architecture, cell composition, gene expression and some aspects of insulin secretion. Mouse pancreatic islets are highly vascularized with interactions between islet endothelial and endocrine cells being important for islet cell differentiation and function. To determine whether human islets have a similar high degree of vascularization and whether this is altered with diabetes, we examined the vascularization of islets from normal human subjects, subjects with type 2 diabetes (T2D), and normal mice. Using an integrated morphometry approach to quantify intra-islet capillary density in human and mouse pancreatic sections, we found that human islets have five-fold fewer vessels per islet area than mouse islets. Islets in pancreatic sections from T2D subjects showed capillary thickening, some capillary fragmentation and had increased vessel density as compared with non-diabetic controls. These changes in islet vasculature in T2D islets appeared to be associated with amyloid deposition, which was noted in islets from 8/9 T2D subjects (and occupied 14% ± 4% of islet area), especially around the intra-islet capillaries. The physiological implications of the differences in the angioarchitecture of mouse and human islets are not known. Islet vascular changes in T2D may exacerbate β cell/islet dysfunction and β cell loss.

Metabolic, anabolic, and mitogenic insulin responses: A tissue-specific perspective for insulin receptor activators

Insulin acts as the major regulator of the fasting-to-fed metabolic transition by altering substrate metabolism, promoting energy storage, and helping activate protein synthesis. In addition to its glucoregulatory and other metabolic properties, insulin can also act as a growth factor. The metabolic and mitogenic responses to insulin are regulated by divergent post-receptor signaling mechanisms downstream from the activated insulin receptor (IR). However, the anabolic and growth-promoting properties of insulin require tissue-specific inter-relationships between the two pathways, and the nature and scope of insulin-regulated processes vary greatly across tissues. Understanding the nuances of this interplay between metabolic and growth-regulating properties of insulin would have important implications for development of novel insulin and IR modulator therapies that stimulate insulin receptor activation in both pathway- and tissue-specific manners. This review will provide a unique perspective focusing on the roles of "metabolic" and "mitogenic" actions of insulin signaling in various tissues, and how these networks should be considered when evaluating selective pharmacologic approaches to prevent or treat metabolic disease.

Augmented Stat5 Signaling Bypasses Multiple Impediments to Lactogen-Mediated Proliferation in Human β-Cells

Pregnancy in rodents is associated with a two- to threefold increase in β-cell mass, which is attributable to large increases in β-cell proliferation, complimented by increases in β-cell size, survival, and function and mediated mainly by the lactogenic hormones prolactin (PRL) and placental lactogens. In humans, however, β-cell mass does not increase as dramatically during pregnancy, and PRL fails to activate proliferation in human islets in vitro. To determine why, we explored the human PRL-prolactin receptor (hPRLR)-Janus kinase 2 (JAK2)-signal transducer and activator of transcription 5 (STAT5)-cyclin-cdk signaling cascade in human β-cells. Surprisingly, adult human β-cells express little or no PRLR. As expected, restoration of the hPRLR in human β-cells rescued JAK2-STAT5 signaling in response to PRL. However, rescuing hPRLR-STAT5 signaling nevertheless failed to confer proliferative ability on adult human β-cells in response to PRL. Surprisingly, mouse (but not human) Stat5a overexpression led to upregulation of cyclins D1-3 and cdk4, as well as their nuclear translocation, all of which are associated with β-cell cycle entry. Collectively, the findings show that human β-cells fail to proliferate in response to PRL for multiple reasons, one of which is a paucity of functional PRL receptors, and that murine Stat5 overexpression is able to bypass these impediments.

The study of women, infant feeding and type 2 diabetes after GDM pregnancy and growth of their offspring (SWIFT Offspring study): prospective design, methodology and baseline characteristics

BACKGROUND

Breastfeeding is associated with reduced risk of becoming overweight or obese later in life. Breastfed babies grow more slowly during infancy than formula-fed babies. Among offspring exposed in utero to maternal glucose intolerance, prospective data on growth during infancy have been unavailable. Thus, scientific evidence is insufficient to conclude that breastfeeding reduces the risk of obesity among the offspring of diabetic mothers (ODM). To address this gap, we devised the Study of Women, Infant Feeding and Type 2 Diabetes after GDM Pregnancy and Growth of their Offspring, also known as the SWIFT Offspring Study. This prospective, longitudinal study recruited mother-infant pairs from the SWIFT Study, a prospective study of women with recent gestational diabetes mellitus (GDM). The goal of the SWIFT Offspring Study is to determine whether breastfeeding intensity and duration, compared with formula feeding, are related to slower growth of GDM offspring during the first year life. This article details the study design, participant eligibility, data collection, and methodologies. We also describe the baseline characteristics of the GDM mother-infant pairs.

METHODS

The study enrolled 466 mother-infant pairs among GDM deliveries in northern California from 2009-2011. Participants attended three in-person study exams at 6-9 weeks, 6 months and 12 months after delivery for infant anthropometry (head circumference, body weight, length, abdominal circumference and skinfold thicknesses), as well as maternal anthropometry (body weight, waist circumference and percent body fat). Mothers also completed questionnaires on health and lifestyle behaviors, including infant diet, sleep and temperament. Breastfeeding intensity and duration were assessed via several sources (diaries, telephone interviews, monthly mailings and in-person exams) from birth through the first year of life. Pregnancy course, clinical perinatal and newborn outcomes were obtained from health plan electronic medical records. Infant saliva samples were collected and stored for genetics studies.

DISCUSSION

This large, racially and ethnically diverse cohort of GDM offspring will enable evaluation of the relationship of infant feeding to growth during infancy independent of perinatal characteristics, sociodemographics and other risk factors. The longitudinal design provides the first quantitative measures of breastfeeding intensity and duration among GDM offspring during early life.

Osteoprotegerin and Denosumab Stimulate Human Beta Cell Proliferation through Inhibition of the Receptor Activator of NF-κB Ligand Pathway

Diabetes results from a reduction of pancreatic β-cells. Stimulating replication could normalize β-cell mass. However, adult human β-cells are recalcitrant to proliferation. We identified osteoprotegerin, a bone-related decoy receptor, as a β-cell mitogen. Osteoprotegerin was induced by and required for lactogen-mediated rodent β-cell replication. Osteoprotegerin enhanced β-cell proliferation in young, aged, and diabetic mice. This resulted in increased β-cell mass in young mice and significantly delayed hyperglycemia in diabetic mice. Osteoprotegerin stimulated replication of adult human β-cells, without causing dedifferentiation. Mechanistically, osteoprotegerin induced human and rodent β-cell replication by modulating CREB and GSK3 pathways, through binding Receptor Activator of NF-κB (RANK) Ligand (RANKL), a brake in β-cell proliferation. Denosumab, an FDA-approved osteoporosis drug, and RANKL-specific antibody induced human β-cell proliferation in vitro, and in vivo, in humanized mice. Thus, osteoprotegerin and Denosumab prevent RANKL/RANK interaction to stimulate β-cell replication, highlighting the potential for repurposing an osteoporosis drug to treat diabetes.

Human islet preparations distributed for research exhibit a variety of insulin-secretory profiles

Human islet research is providing new insights into human islet biology and diabetes, using islets isolated at multiple US centers from donors with varying characteristics. This creates challenges for understanding, interpreting, and integrating research findings from the many laboratories that use these islets. In what is, to our knowledge, the first standardized assessment of human islet preparations from multiple isolation centers, we measured insulin secretion from 202 preparations isolated at 15 centers over 11 years and noted five distinct patterns of insulin secretion. Approximately three quarters were appropriately responsive to stimuli, but one quarter were dysfunctional, with unstable basal insulin secretion and/or an impairment in stimulated insulin secretion. Importantly, the patterns of insulin secretion by responsive human islet preparations (stable Baseline and Fold stimulation of insulin secretion) isolated at different centers were similar and improved slightly over the years studied. When all preparations studied were considered, basal and stimulated insulin secretion did not correlate with isolation center, biological differences of the islet donor, or differences in isolation, such as Cold Ischemia Time. Dysfunctional islet preparations could not be predicted from the information provided by the isolation center and had altered expression of genes encoding components of the glucose-sensing pathway, but not of insulin production or cell death. These results indicate that insulin secretion by most preparations from multiple centers is similar but that in vitro responsiveness of human islets cannot be predicted, necessitating preexperimental human islet assessment. These results should be considered when one is designing, interpreting, and integrating experiments using human islets.

Milk consumption during pregnancy increases birth weight, a risk factor for the development of diseases of civilization

Antenatal dietary lifestyle intervention and nutrition during pregnancy and early postnatal life are important for appropriate lifelong metabolic programming. Epidemiological evidence underlines the crucial role of increased birth weight as a risk factor for the development of chronic diseases of civilization such as obesity, diabetes and cancer. Obstetricians and general practitioners usually recommend milk consumption during pregnancy as a nutrient enriched in valuable proteins and calcium for bone growth. However, milk is not just a simple nutrient, but has been recognized to function as an endocrine signaling system promoting anabolism and postnatal growth by activating the nutrient-sensitive kinase mTORC1. Moreover, pasteurized cow’s milk transfers biologically active exosomal microRNAs into the systemic circulation of the milk consumer apparently affecting more than 11 000 human genes including the mTORC1-signaling pathway. This review provides literature evidence and evidence derived from translational research that milk consumption during pregnancy increases gestational, placental, fetal and birth weight. Increased birth weight is a risk factor for the development of diseases of civilization thus involving key disciplines of medicine. With regard to the presented evidence we suggest that dietary recommendations promoting milk consumption during pregnancy have to be re-evaluated.

Knockdown of prolactin receptors in a pancreatic beta cell line: effects on DNA synthesis, apoptosis, and gene expression

Prolactin (PRL) and placental lactogen stimulate beta cell replication and insulin production in vitro and in vivo. The molecular mechanisms by which lactogens promote beta cell expansion are unclear. We treated rat insulinoma cells with a PRL receptor (PRLR) siRNA to determine if PRLR signaling is required for beta cell DNA synthesis and cell survival and to identify beta cell cycle genes whose expression depends upon lactogen action. Effects of PRLR knockdown were compared with those of PRL treatment. PRLR knockdown (-80 %) reduced DNA synthesis, increased apoptosis, and inhibited expression of cyclins D2 and B2, IRS-2, Tph1, and the anti-apoptotic protein PTTG1; p21 and BCL6 mRNAs increased. Conversely, PRL treatment increased DNA synthesis, reduced apoptosis, and enhanced expression of A, B and D2 cyclins, CDK1, IRS-2, FoxM1, BCLxL, and PTTG1; BCL6 declined. PRLR signaling is required for DNA synthesis and survival of rat insulinoma cells. The effects of lactogens are mediated by down-regulation of cell cycle inhibitors (BCL6, p21) and induction of A, B, and D2 cyclins, IRS-2, Tph1, FoxM1, and the anti-apoptotic proteins BCLxL and PTTG1.

The regulation of pre- and post-maturational plasticity of mammalian islet cell mass

Regeneration of mature cells that produce functional insulin represents a major focus and a challenge of current diabetes research aimed at restoring beta cell mass in patients with most forms of diabetes, as well as in ageing. The capacity to adapt to diverse physiological states during life and the consequent ability to cope with increased metabolic demands in the normal regulation of glucose homeostasis is a distinctive feature of the endocrine pancreas in mammals. Both beta and alpha cells, and presumably other islet cells, are dynamically regulated via nutrient, neural and/or hormonal activation of growth factor signalling and the post-transcriptional modification of a variety of genes or via the microbiome to continually maintain a balance between regeneration (e.g. proliferation, neogenesis) and apoptosis. Here we review key regulators that determine islet cell mass at different ages in mammals. Understanding the chronobiology and the dynamics and age-dependent processes that regulate the relationship between the different cell types in the overall maintenance of an optimally functional islet cell mass could provide important insights into planning therapeutic approaches to counter and/or prevent the development of diabetes.

Lipotoxicity in the pancreatic beta cell: not just survival and function, but proliferation as well?

Free fatty acids (FFAs) exert both positive and negative effects on beta cell survival and insulin secretory function, depending on concentration, duration, and glucose abundance. Lipid signals are mediated not only through metabolic pathways, but also through cell surface and nuclear receptors. Toxicity is modulated by positive signals arising from circulating factors such as hormones, growth factors and incretins, as well as negative signals such as inflammatory mediators and cytokines. Intracellular mechanisms of lipotoxicity include metabolic interference and cellular stress responses such as oxidative stress, endoplasmic reticulum (ER) stress, and possibly autophagy. New findings strengthen an old hypothesis that lipids may also impair compensatory beta cell proliferation. Clinical observations continue to support a role for lipid biology in the risk and progression of both type 1 (T1D) and type 2 diabetes (T2D). This review summarizes recent work in this important, rapidly evolving field.

Defective prolactin signaling impairs pancreatic β-cell development during the perinatal period

Prolactin (PRL) and placental lactogens stimulate β-cell replication and insulin production in pancreatic islets and insulinoma cells through binding to the PRL receptor (PRLR). However, the contribution of PRLR signaling to β-cell ontogeny and function in perinatal life and the effects of the lactogens on adaptive islet growth are poorly understood. We provide evidence that expansion of β-cell mass during both embryogenesis and the postnatal period is impaired in the PRLR(-/-) mouse model. PRLR(-/-) newborns display a 30% reduction of β-cell mass, consistent with reduced proliferation index at E18.5. PRL stimulates leucine incorporation and S6 kinase phosphorylation in INS-1 cells, supporting a role for β-cell mTOR signaling in PRL action. Interestingly, a defect in the development of acini is also observed in absence of PRLR signaling, with a sharp decline in cellular size in both endocrine and exocrine compartments. Of note, a decrease in levels of IGF-II, a PRL target, in the Goto-Kakizaki (GK) rat, a spontaneous model of type 2 diabetes, is associated with a lack of PRL-mediated β-cell proliferation in embryonic pancreatic buds. Reduced pancreatic IGF-II expression in both rat and mouse models suggests that this factor may constitute a molecular link between PRL signaling and cell ontogenesis. Together, these results provide evidence that PRL signaling is essential for pancreas ontogenesis during the critical perinatal window responsible for establishing functional β-cell reserve.

CCAAT-enhancer-binding protein β (C/EBPβ) and downstream human placental growth hormone genes are targets for dysregulation in pregnancies complicated by maternal obesity

Human chorionic somatomammotropin (CS) and placental growth hormone variant (GH-V) act as metabolic adaptors in response to maternal insulin resistance, which occurs in "normal" pregnancy. Maternal obesity can exacerbate this "resistance," suggesting that CS, GH-V, or transcription factors that regulate their production might be targets. The human CS genes, hCS-A and hCS-B, flank the GH-V gene. A significant decrease in pre-term placental CS/GH-V RNA levels was observed in transgenic mice containing the CS/GH-V genes in a model of high fat diet (HFD)-induced maternal obesity. Similarly, a decrease in CS/GH-V RNA levels was detected in term placentas from obese (body mass index (BMI) ≥ 35 kg/m(2)) versus lean (BMI 20-25 kg/m(2)) women. A specific decrease in transcription factor CCAAT-enhancer-binding protein β (C/EBPβ) RNA levels was also seen with obesity; C/EBPβ is required for mouse placenta development and is expressed, like CS and GH-V, in syncytiotrophoblasts. Binding of C/EBPβ to the CS gene downstream enhancer regions, which by virtue of their position distally flank the GH-V gene, was reduced in placenta chromatin from mice on a HFD and in obese women; a corresponding decrease in RNA polymerase II associated with CS/GH-V promoters was also observed. Detection of decreased endogenous CS/GH-V RNA levels in human placental tumor cells treated with C/EBPβ siRNA is consistent with a direct effect. These data provide evidence for CS/GH-V dysregulation in acute HFD-induced obesity in mouse pregnancy and chronic obesity in human pregnancy and implicate C/EBPβ, a factor associated with CS regulation and placental development.