Weighing up beta-cell mass in mice and humans: self-renewal, progenitors or stem cells?

Notch1 Has an Important Role in β-Cell Mass Determination and Development of Diabetes

BACKGROUND

Notch signaling pathway plays an important role in regulating pancreatic endocrine and exocrine cell fate during pancreas development. Notch signaling is also expressed in adult pancreas. There are few studies on the effect of Notch on adult pancreas. Here, we investigated the role of Notch in islet mass and glucose homeostasis in adult pancreas using Notch1 antisense transgenic (NAS).

METHODS

Western blot analysis was performed for the liver of 8-week-old male NAS mice. We also conducted an intraperitoneal glucose tolerance test (IPGTT) and intraperitoneal insulin tolerance test in 8-week-old male NAS mice and male C57BL/6 mice (control). Morphologic observation of pancreatic islet and β-cell was conducted in two groups. Insulin secretion capacity in islets was measured by glucose-stimulated insulin secretion (GSIS) and perifusion.

RESULTS

NAS mice showed higher glucose levels and lower insulin secretion in IPGTT than the control mice. There was no significant difference in insulin resistance. Total islet and β-cell masses were decreased in NAS mice. The number of large islets (≥250 µm) decreased while that of small islets (<250 µm) increased. Reduced insulin secretion was observed in GSIS and perifusion. Neurogenin3, neurogenic differentiation, and MAF bZIP transcription factor A levels increased in NAS mice.

CONCLUSION

Our study provides that Notch1 inhibition decreased insulin secretion and decreased islet and β-cell masses. It is thought that Notch1 inhibition suppresses islet proliferation and induces differentiation of small islets. In conclusion, Notch signaling pathway may play an important role in β-cell mass determination and diabetes.

Effects of Cyclocarya paliurus Aqueous and Ethanol Extracts on Glucolipid Metabolism and the Underlying Mechanisms: A Meta-Analysis and Systematic Review

Background and Aims:Cyclocarya paliurus (CP) has been used as an herbal tea to treat diabetes mellitus and obesity for hundreds of years. Previous research suggests that CP specifically restores glucolipid metabolic homeostasis, and the two most studied preparations are aqueous and ethanol extracts. In order to verify the effect of CP on glucolipid metabolism in animal models with metabolic syndrome, a meta-analysis was performed, and the active components and underlying mechanisms were systematically reviewed.

Methods: Four databases: PubMed, Web of Science, Embase, and Cochrane Library were searched to identify potential literature. Data of blood glucose (BG) level, area under curve (AUC) of oral glucose tolerance test (OGTT), total cholesterol (TC), triglyceride (TG), high-density lipoprotein (HDL), and low-density lipoprotein (LDL) levels were extracted as indicators of the assessment of CP's effects. Follow-up analyses including subgroup analysis, meta-regressions, and publication bias were also conducted.

Results: A total of 96 papers were identified from the databases and 11 papers including 31 data reports were involved in the meta-analysis. CP had a positive effect in down-regulating BG, AUC of OGTT, TC, TG, and LDL, and up-regulating HDL (P < 0.001, 95% confidence interval of standard mean difference did not incorporate the null value 0).

Conclusion: CP showed definite activity of regulating glucolipid metabolism in animal models, and it exerted its function through multiple mechanisms including but not limited to: (1) improving insulin resistance; (2) protecting pancreatic β cells; (3) decreasing inflammatory infiltration; and (4) anti-oxidative stress.

Liraglutide Therapy in a Prediabetic State: Rethinking the Evidence

BACKGROUND

Prediabetes is defined as a state of glucose metabolism between normal glucose tolerance and type 2 diabetes. Continuous β-cell failure and death are the reasons for the evolution from normal glucose tolerance to prediabetes and finally type 2 diabetes.

INTRODUCTION

The necessity of new therapeutic approaches in order to prevent or delay the development of type 2 diabetes is obligatory. Liraglutide, a long-acting GLP-1 receptor agonist, has 97% homology for native GLP-1. Identification of the trophic and antiapoptotic properties of liraglutide in preclinical studies, together with evidence of sustained β-cell function longevity during its administration in type 2 diabetes individuals, indicated its earliest possible administration during this disease, or even before its development, so as to postpone or delay its onset.

METHODS

Pubmed and Google databases have been thoroughly searched and relevant studies were selected.

RESULTS

This paper explores the current evidence of liraglutide administration both in humans and animal models with prediabetes. Also, it investigates the safety profile of liraglutide treatment and its future role to postpone or delay the evolution of type 2 diabetes.

CONCLUSION

Liralgutide remains a valuable tool in our therapeutic armamentarium for individuals who are overweight or obese and have prediabetes. Future well designed studies will give valuable information that will help clinicians to stratify individuals who will derive the most benefit from this agent, achieving targeted therapeutic strategies.

Phospho‑regulation of Cdc14A by polo‑like kinase 1 is involved in β‑cell function and cell cycle regulation

The objective of the present study was to investigate the effects of polo‑like kinase 1 (PLK1) and the phosphorylation of human cell division cycle protein 14A (Cdc14A) by PLK1 on β‑cell function and cell cycle regulation. Mouse β‑TC3 cells were incubated with small interfering RNA (siRNA) to knock down the expression of PLK1. Cell cycle analysis was performed using flow cytometry, and cell proliferation and apoptosis was determined. Insulin secretion was evaluated by a radioimmunoassay under both low and high glucose conditions. Mouse β‑TC3 cells were transfected with a wild type or a non‑phosphorylatable Cdc14A mutant (Cdc14AS351A/363A; Cdc14AAA) to investigate whether the phosphorylation of Cdc14A is involved in cellular regulation of PLK1 under high glucose conditions. It was found that PLK1 siRNA significantly promoted cellular apoptosis, inhibited cell proliferation, decreased insulin secretion and reduced Cdc14A expression under both low and high glucose conditions. Cdc14A overexpression promoted β‑TC3 cell proliferation and insulin secretion, while Cdc14AAA overexpression inhibited cell proliferation and insulin secretion under high glucose conditions. PLK1 siRNA partially reversed the proliferation‑promoting effects of Cdc14A and further intensified the inhibition of proliferation by Cdc14AAA under high glucose conditions. Similarly, Cdc14A overexpression partially reversed the insulin‑inhibiting effects of PLK1 siRNA, while Cdc14AAA overexpression showed a synergistic inhibitory effect on insulin secretion with PLK1 siRNA under high glucose conditions. In conclusion, PLK1 promoted cell proliferation and insulin secretion while inhibiting cellular apoptosis in β‑TC3 cell lines under both low and high glucose conditions. In addition, the phospho‑regulation of Cdc14A by PLK1 may be involved in β‑TC3 cell cycle regulation and insulin secretion under high glucose conditions.

Pancreatic β-cell identity in diabetes

Recovery of functional β-cell mass continues to be an ongoing challenge in treating diabetes. Initial work studying β-cells suggested apoptotic β-cell death as a main contributor for the loss of β-cell mass in diabetes. Restoration of β-cells either by transplant or stimulating proliferation of remaining β-cells or precursors would then logically be a viable therapeutic option for diabetes. However, recent work has highlighted the inherent β-cell plasticity and the critical role of loss of β-cell identity in diabetes, and has suggested that β-cells fail to maintain a fully differentiated glucose-responsive and drug-responsive state, particularly in diabetic individuals with poorly controlled, long-lasting periods of hyperglycaemia. Understanding the underlying mechanisms of loss of β-cell identity and conversion in other cell types, as well as how to regain their mature differentiated functional state, is critical to develop novel therapeutic strategies to prevent or reverse these processes. In this review, we discuss the role of plasticity and loss of β-cell identity in diabetes, the current understanding of mechanisms involved in altering this mature functional β-cell state and potential progresses to identify novel therapeutic targets providing better opportunities for slowing or preventing diabetes progression.

β-Cell regeneration through the transdifferentiation of pancreatic cells: Pancreatic progenitor cells in the pancreas

Pancreatic progenitor cell research has been in the spotlight, as these cells have the potential to replace pancreatic β‐cells for the treatment of type 1 and 2 diabetic patients with the absence or reduction of pancreatic β‐cells. During the past few decades, the successful treatment of diabetes through transplantation of the whole pancreas or isolated islets has nearly been achieved. However, novel sources of pancreatic islets or insulin‐producing cells are required to provide sufficient amounts of donor tissues. To overcome this limitation, the use of pancreatic progenitor cells is gaining more attention. In particular, pancreatic exocrine cells, such as duct epithelial cells and acinar cells, are attractive candidates for β‐cell regeneration because of their differentiation potential and pancreatic lineage characteristics. It has been assumed that β‐cell neogenesis from pancreatic progenitor cells could occur in pancreatic ducts in the postnatal stage. Several studies have shown that insulin‐producing cells can arise in the duct tissue of the adult pancreas. Acinar cells also might have the potential to differentiate into insulin‐producing cells. The present review summarizes recent progress in research on the transdifferentiation of pancreatic exocrine cells into insulin‐producing cells, especially duct and acinar cells.

Liraglutide improves pancreatic Beta cell mass and function in alloxan-induced diabetic mice

Glucagon-like peptide-1 (GLP-1) receptor agonists potentiate glucose-induced insulin secretion. In addition, they have been reported to increase pancreatic beta cell mass in diabetic rodents. However, the precise mode of action of GLP-1 receptor agonists still needs to be elucidated. Here we clarify the effects of the human GLP-1 analog liraglutide on beta cell fate and function by using an inducible Cre/loxP-based pancreatic beta cell tracing system and alloxan-induced diabetic mice. Liraglutide was subcutaneously administered once daily for 30 days. The changes in beta cell mass were examined as well as glucose tolerance and insulin secretion. We found that chronic liraglutide treatment improved glucose tolerance and insulin response to oral glucose load. Thirty-day treatment with liraglutide resulted in a 2-fold higher mass of pancreatic beta cells than that in vehicle group. Liraglutide increased proliferation rate of pancreatic beta cells and prevented beta cells from apoptotic cells death. However, the relative abundance of YFP-labeled beta cells to total beta cells was no different before and after liraglutide treatment, suggesting no or little contribution of neogenesis to the increase in beta cell mass. Liraglutide reduced oxidative stress in pancreatic islet cells of alloxan-induced diabetic mice. Furthermore, the beneficial effects of liraglutide in these mice were maintained two weeks after drug withdrawal. In conclusion, chronic liraglutide treatment improves hyperglycemia by ameliorating beta cell mass and function in alloxan-induced diabetic mice.

Diabetes enhances the proliferation of adult pancreatic multipotent progenitor cells and biases their differentiation to more β-cell production

Endogenous pancreatic multipotent progenitors (PMPs) are ideal candidates for regenerative approaches to compensate for β-cell loss since their β-cell-producing capacities as well as strategic location would eliminate unnecessary invasive manipulations. However, little is known about the status and potentials of PMPs under diabetic conditions. Here we show that β-cell metabolic stress and hyperglycemia enhance the proliferation capacities of adult PMP cells and bias their production of progeny toward β-cells in mouse and human. These effects are dynamic and correlate with functional β-cell regeneration when conditions allow.

Are we overestimating the loss of beta cells in type 2 diabetes?

AIMS/HYPOTHESIS

Previous work has demonstrated that beta cell amount (whether measured as beta cell mass, beta cell volume or insulin-positive area) is decreased in type 2 diabetes; however, recent findings suggest that mechanisms other than death may contribute to beta cell failure in this disease. To better characterise beta cell mass and function in type 2 diabetes, we performed morphological, ultra-structural and functional studies using histological samples and isolated islets.

METHODS

Pancreases from ten non-diabetic (ND) and ten matched type 2 diabetic organ donors were studied by insulin, glucagon and chromogranin A immunocytochemistry and electron microscopy (EM). Glucose-stimulated insulin secretion was assessed using isolated islets and studies were performed using independent ND islet preparations after 24 h exposure to 22.2 mmol/l glucose.

RESULTS

Immunocytochemistry showed that the fractional islet insulin-positive area was lower in type 2 diabetic islets (54.9 ± 6.3% vs 72.1 ± 8.7%, p < 0.01), whereas glucagon (23.3 ± 5.4% vs 20.2 ± 5.3%) and chromogranin A (86.4 ± 6.1% vs 89.0 ± 5.5%) staining was similar between the two groups. EM showed that the proportion of beta cells in type 2 diabetic islets was only marginally decreased; marked beta cell degranulation was found in diabetic beta cells; these findings were all reproduced after exposing isolated ND islets to high glucose. Glucose-stimulated insulin secretion was 40–50% lower from type 2 diabetic islets (p < 0.01), which again was mimicked by culturing non-diabetic islets in high glucose.

CONCLUSIONS/INTERPRETATION

These results suggest that, at least in subgroups of type 2 diabetic patients, the loss of beta cells as assessed so far might be overestimated, possibly due to changes in beta cell phenotype other than death, also contributing to beta cell failure in type 2 diabetes.

Beta-cell imaging: call for evidence-based and scientific approach

INTRODUCTION

Advances in positron emission tomography (PET) imaging have provided opportunities to develop radiotracers specific for imaging insulin-producing pancreatic β-cells. However, a host of lingering questions should be addressed before these radiotracers are advocated for noninvasive quantification of β-cell mass (BCM) in vivo in the native pancreas.

METHOD

We provide an overview of tetrabenazine-based PET tracers developed to image and quantify BCM and discuss several theoretical, technical, and biological limitations of applying these tracers in clinical practice.

DISCUSSION

VMAT2, a transporter protein expressed on pancreatic β-cells, has been advocated as a promising target for PET imaging tracers, such as dihydrotetrabenazine. However, the lack of radiotracer specificity for these proteins hampers their clinical application. Another important argument against their use is a striking discrepancy between radiotracer uptake and BCM in subjects with type I diabetes mellitus and healthy controls. Additionally, technical issues, such as the finite spatial resolution of PET, partial volume effects, and movement of the pancreas during respiration, impede PET imaging as a viable option for BCM quantification in the foreseeable future.

CONCLUSION

The assertion that BCM can be accurately quantified by tetrabenazine derived β-cell-specific radiotracers as density per unit volume of pancreatic tissue is not justifiable at this time. The fallacy of these claims can be explained by technical as well as biological facts that have been disregarded and ignored in the literature.

Non-β-cell progenitors of β-cells in pregnant mice

Pregnancy is a normal physiological condition in which the maternal β-cell mass increases rapidly about two-fold to adapt to new metabolic challenges. We have used a lineage tracing of β-cells to analyse the origin of new β-cells during this rapid expansion in pregnancy. Double transgenic mice bearing a tamoxifen-dependent Cre-recombinase construct under the control of a rat insulin promoter, together with a reporter Z/AP gene, were generated. Then, in response to a pulse of tamoxifen before pregnancy, β-cells in these animals were marked irreversibly and heritably with the human placental alkaline phosphatase (HP AP). First, we conclude that the lineage tracing system was highly specific for β-cells. Secondly, we scored the proportion of the β-cells marked with HP AP during a subsequent chase period in pregnant and non-pregnant females. We observed a dilution in this labeling index in pregnant animal pancreata, compared to nonpregnant controls, during a single pregnancy in the chase period. To extend these observations we also analysed the labeling index in pancreata of animals during the second of two pregnancies in the chase period. The combined data revealed statistically-significant dilution during pregnancy, indicating a contribution to new beta cells from a non-β-cell source. Thus for the first time in a normal physiological condition, we have demonstrated not only β-cell duplication, but also the activation of a non-β-cell progenitor population. Further, there was no transdifferentiation of β-cells to other cell types in a two and half month period following labeling, including the period of pregnancy.

β-cell preservation and regeneration for diabetes treatment: where are we now?

Over the last decade, our knowledge of β-cell biology has expanded with the use of new scientific techniques and strategies. Growth factors, hormones and small molecules have been shown to enhance β-cell proliferation and function. Stem cell technology and research into the developmental biology of the pancreas have yielded new methods for in vivo and in vitro regeneration of β cells from stem cells and endogenous progenitors as well as transdifferentiation of non-β cells. Novel pharmacological approaches have been developed to preserve and enhance β-cell function. Strategies to increase expression of insulin gene transcription factors in dysfunctional and immature β cells have ameliorated these impairments. Hence, we suggest that strategies to minimize β-cell loss and to increase their function and regeneration will ultimately lead to therapy for both Type 1 and 2 diabetes.

Pancreatic function, type 2 diabetes, and metabolism in aging

Aging is a risk factor for impaired glucose tolerance and diabetes. Of the reported 25.8 million Americans estimated to have diabetes, 26.9% are over the age of 65. In certain ethnic groups, the proportion is even higher; almost 1 in 3 older Hispanics and African Americans and 3 out of 4 Pima Indian elders have diabetes. As per the NHANES III (Third National Health and Nutrition Examination) survey, the percentage of physician-diagnosed diabetes increased from 3.9% in middle-aged adults (40-49 years) to 13.2% in elderly adults (≥75 years). The higher incidence of diabetes is especially alarming considering that diabetes in itself increases the risk for multiple other age-related diseases such as cancer, stroke, cardiovascular diseases, Parkinson's disease, and Alzheimer's disease (AD). In this review, we summarize the current evidence on how aging affects pancreatic β cell function, β cell mass, insulin secretion and insulin sensitivity. We also review the effects of aging on the relationship between insulin sensitivity and insulin secretion. Understanding the mechanisms that lead to impaired glucose homeostasis and T2D in the elderly will lead to development of novel treatments that will prevent or delay diabetes, substantially improve quality of life and ultimately increase overall life span.

Longevity of human islet α- and β-cells

Pancreatic islet cell regeneration is considered to be important in the onset and progression of diabetes and as a potential cell therapy. Current hypotheses, largely based on rodent studies, indicate continuous turnover and plasticity of α- and β-cells in adults; cell populations in rodents respond to increased secretory demand in obesity (30-fold β-cell increase) and pregnancy. Turnover and plasticity of islet cells decrease in mice within >1 year. In man, morphometric observations on postmortem pancreas have indicated that the cellular expansion is much smaller than the increased insulin secretion that accompanies obesity. Longevity of β-cells in humans >20-30 years has been shown by (14) C measurements and bromo-deoxyuridine (BrdU) incorporation and there is an age-related decline in the expression of proteins associated with cell division and regeneration including cyclin D3 and PDX-1. Quantitative estimation and mathematical modelling of the longevity marker, cellular lipofuscin body content, in islets of subjects aged 1-84 years indicated an age-related increase and that 97% of the human β-cell population was established by the age of 20. New data show that human α-cell lipofuscin content is less than that seen in β-cells, but the age-related accumulation is similar; lipofuscin-positive (aged) cells form ≥ 95% of the population after 20 years. Increased turnover of cellular organelles such as mitochondria and endoplasmic reticulum could contribute to lipofuscin accumulation with age in long-lived cells. Induction of regeneration of human islet cells will require understanding of the mechanisms associated with age-related senescence.

Oligodeoxynucleotide IMT504 induces a marked recovery in a streptozotocin-induced model of diabetes in rats: correlation with an early increase in the expression of nestin and neurogenin 3 progenitor cell markers

AIMS/HYPOTHESIS

IMT504 is an oligonucleotide that promotes tissue repair in bone injury and neuropathic pain models by stimulating progenitor cells. Here we evaluated the effect of IMT504 on the recovery of islet function in a streptozotocin (STZ)-induced model of diabetes in the rat.

METHODS

Male Sprague-Dawley rats were injected with STZ (60 mg/kg, i.p., day 1) or citrate buffer (Control). Animals with glycaemia between 11 and 20 mmol/l on day 4 were injected with IMT504 (4 mg/animal in saline, s.c., STZ-IMT504) or with saline (STZ-Saline) for 10 days. Glycaemia and water and food intake were recorded for 33 days. Intraperitoneal glucose tolerance tests (IPGTTs) were performed on day 30. On day 35, overnight-fasted animals were killed and blood samples and pancreases collected for hormonal and histological studies. A second group of STZ-IMT504 rats was killed, together with Control and STZ-Saline rats, after two consecutive days of blood glucose decreases after the beginning of IMT504 treatment. Pancreases were collected and proliferating cell nuclear antigen (PCNA), nestin and neurogenin 3 (NGN3) detected by immunohistochemistry.

RESULTS

IMT504 greatly improved blood glucose and food and water intakes in STZ-IMT504 rats by day 8, as well as IPGTTs on day 30. Significant increases in islet number and beta cell content were observed in STZ-IMT504 rats (day 33). Furthermore, after two to five IMT504 injections, blood glucose decreased, and an increase in pancreatic nestin (mainly in endothelial cells), PCNA and NGN3 production (in islets) was observed in STZ-IMT504 rats.

CONCLUSIONS/INTERPRETATION

IMT504 induced a marked recovery of STZ-induced diabetes that correlated with early production of progenitor cell markers, such as nestin and NGN3.

Emerging use of stem cells in regenerative medicine

Stem cells represent a unique opportunity for regenerative medicine to cure a broad number of diseases for which current treatment only alleviates symptoms or retards further disease progression. However, the number of stem cells available has speedily increased these past 10 years and their diversity presents new challenges to clinicians and basic scientists who intend to use them in clinics or to study their unique properties. In addition, the recent possibility to derive pluripotent stem cells from somatic cells using epigenetic reprogramming has further increased the clinical interest of stem cells since induced pluripotent stem cells could render personalized cell-based therapy possible. The present review will attempt to summarize the advantages and challenges of each type of stem cell for current and future clinical applications using specific examples.

Regenerating pancreatic beta-cells: plasticity of adult pancreatic cells and the feasibility of in-vivo neogenesis

PURPOSE OF REVIEW

Diabetes results from inadequate functional mass of pancreatic beta-cells and therefore replenishing with new glucose-responsive beta-cells is an important therapeutic option. In addition to replication of pre-existing beta-cells, new beta-cells can be produced from differentiated adult cells using in-vitro or in-vivo approaches. This review will summarize recent advances in in-vivo generation of beta-cells from cells that are not beta-cells (neogenesis) and discuss ways to overcome the limitations of this process.

RECENT FINDINGS

Multiple groups have shown that adult pancreatic ducts, acinar and even endocrine cells exhibit cellular plasticity and can differentiate into beta-cells in vivo. Several different approaches, including misexpression of transcription factors and tissue injury, have induced neogenesis of insulin-expressing cells in vivo and ameliorated diabetes.

SUMMARY

Recent breakthroughs demonstrating cellular plasticity of adult pancreatic cells to form new beta-cells are a positive first step towards developing in-vivo regeneration-based therapy for diabetes. Currently, neogenesis processes are inefficient and do not generate sufficient amounts of beta-cells required to normalize hyperglycemia. However, an improved understanding of mechanisms regulating neogenesis of beta-cells from adult pancreatic cells and of their maturation into functional glucose-responsive beta-cells can make therapies based on in-vivo regeneration a reality.

Molecular regulation of pancreas development in zebrafish

The pancreas is a vertebrate-specific organ of endodermal origin which is responsible for production of digestive enzymes and hormones involved in regulating glucose homeostasis, in particular insulin, deficiency of which results in diabetes. Basic research on the genetic and molecular pathways regulating pancreas formation and function has gained major importance for the development of regenerative medical approaches aimed at improving diabetes treatment. Among the different model organisms that are currently used to elucidate the basic pathways of pancreas development and regeneration, the zebrafish is distinguished by its unique opportunities to combine genetic and pharmacological approaches with sophisticated live-imaging methodology, and by its ability to regenerate the pancreas within a short time. Here we review current perspectives and present methods for studying two important processes contributing to pancreas development and regeneration, namely cell migration via time-lapse micropscopy and cell proliferation via incorporation of nucleotide analog EdU, with a focus on the insulin-producing beta cells of the islet.

Cellular origins of beta-cell regeneration: a legacy view of historical controversies

Beta-cell regeneration represents a major goal of therapy for diabetes. Unravelling the origin of beta cells during pancreatic regeneration could help restore a functional beta-cell mass in diabetes patients. This scientific question has represented a longstanding interest still intensively investigated today. This review focuses on pioneering observations and subsequent theories made 100 years ago and describes how technical innovation helped resolve some, but not all, of the controversies generated by these early investigators. At the end of the 19th century, complete pancreatectomy demonstrated the crucial physiological role of the pancreas and its link with diabetes. Pancreatic injury models, including pancreatectomy and ductal ligation, allowed investigators to describe islet function and to assess the regenerative capacity of the pancreas. Three main theories were proposed to explain the origins of newly formed islets: (i) transdifferentiation of acinar cells into islets, (ii) islet neogenesis, a process reminiscent of islet formation during embryonic development, and (iii) replication of preexisting islet cells. Despite considerable technical innovation in the last 50 years, the origin of new adult beta cells remains highly controversial and the same three theories are still debated today.

Analysis of beta cell proliferation dynamics in zebrafish

Among the different mechanisms invoked to explain the beta cell mass expansion during postnatal stages and adulthood, self-replication is being considered the major cellular event occurring both under physiological conditions and in regenerating pancreas after partial pancreactomy. Neogenesis, i.e. differentiation from pancreatic progenitors, has been demonstrated to act concurrently with beta cell replication during pancreatic regeneration. Both phenomena have been largely elucidated in higher vertebrates (mouse, rat and guinea pig), but an extensive description of beta cell dynamics in other animal models is currently lacking. We, therefore, explored in zebrafish the cellular origins of new beta cells in both adult and larval stages. By integrating the results from in vivo time lapse analysis and immunostaining, we provide a detailed reconstruction of the major processes involved in fish beta cell genesis and maintenance. Moreover, by establishing the selective ablation of proliferating beta cells, through the ganciclovir-HSVTK system, we could show that in larval stages self-replication is the main mechanism of beta cells expansion. Since the same mechanism of proliferation has been observed to occur during early and late life stages, we suggest that zebrafish larvae can be used as an alternative tool for an in vivo exploration and screening of new potential mitogens specifically targeting beta cells.

Adaptive beta-cell proliferation is severely restricted with advanced age

OBJECTIVE

Regeneration of the insulin-secreting beta-cells is a fundamental research goal that could benefit patients with either type 1 or type 2 diabetes. beta-Cell proliferation can be acutely stimulated by a variety of stimuli in young rodents. However, it is unknown whether this adaptive beta-cell regeneration capacity is retained into old age.

RESEARCH DESIGN AND METHODS

We assessed adaptive beta-cell proliferation capacity in adult mice across a wide range of ages with a variety of stimuli: partial pancreatectomy, low-dose administration of the beta-cell toxin streptozotocin, and exendin-4, a glucagon-like peptide 1 (GLP-1) agonist. beta-Cell proliferation was measured by administration of 5-bromo-2'-deoxyuridine (BrdU) in the drinking water.

RESULTS

Basal beta-cell proliferation was severely decreased with advanced age. Partial pancreatectomy greatly stimulated beta-cell proliferation in young mice but failed to increase beta-cell replication in old mice. Streptozotocin stimulated beta-cell replication in young mice but had little effect in old mice. Moreover, administration of GLP-1 agonist exendin-4 stimulated beta-cell proliferation in young but not in old mice. Surprisingly, adaptive beta-cell proliferation capacity was minimal after 12 months of age, which is early middle age for the adult mouse life span.

CONCLUSIONS

Adaptive beta-cell proliferation is severely restricted with advanced age in mice, whether stimulated by partial pancreatectomy, low-dose streptozotocin, or exendin-4. Thus, beta-cells in middle-aged mice appear to be largely postmitotic. Young rodents may not faithfully model the regenerative capacity of beta-cells in mature adult mice.

GABA's control of stem and cancer cell proliferation in adult neural and peripheral niches

Aside from traditional neurotransmission and regulation of secretion, gamma-amino butyric acid (GABA) through GABA(A) receptors negatively regulates proliferation of pluripotent and neural stem cells in embryonic and adult tissue. There has also been evidence that GABAergic signaling and its control over proliferation is not only limited to the nervous system, but is widespread through peripheral organs containing adult stem cells. GABA has emerged as a tumor signaling molecule in the periphery that controls the proliferation of tumor cells and perhaps tumor stem cells. Here, we will discuss GABA's presence as a near-universal signal that may be altered in tumor cells resulting in modified mitotic activity.

Human pancreatic islets and diabetes research

Human islet research is crucial to understanding the cellular biology of the pancreas in developing therapeutic options for diabetes patients and in attempting to prevent the development of this disease. The national Islet Cell Resource Center Consortium provides human pancreatic islets for diabetes research while simultaneously addressing the need to improve islet isolation and transplantation technologies. Since its inception in 2001, the consortium has supplied 297.6 million islet equivalents to 151 national and international scientists for use in clinical and laboratory projects. Data on the volume, quality, and frequency of shipments substantiate the importance of human islets for diabetes research, as do the number of funded grants for beta-cell projects and publications produced as a direct result of islets supplied by this resource. Limitations in using human islets are discussed, along with the future of islet distribution centers. The information presented here is instructive to clinicians, basic science investigators, and policy makers who determine the availability of funding for such work. Organ procurement coordinators also may find the information useful in explaining to donor families why research consent is so valuable.

Blood glucose levels regulate pancreatic beta-cell proliferation during experimentally-induced and spontaneous autoimmune diabetes in mice

Background

Type 1 diabetes mellitus is caused by immune-mediated destruction of pancreatic β-cells leading to insulin deficiency, impaired intermediary metabolism, and elevated blood glucose concentrations. While at autoimmune diabetes onset a limited number of β-cells persist, the cells' regenerative potential and its regulation have remained largely unexplored. Using two mouse autoimmune diabetes models, this study examined the proliferation of pancreatic islet ß-cells and other endocrine and non-endocrine subsets, and the factors regulating that proliferation.

Methodology and Principal Findings

We adapted multi-parameter flow cytometry techniques (including DNA-content measurements and 5′-bromo-2′-deoxyuridine [BrdU] incorporation) to study pancreatic islet single cell suspensions. These studies demonstrate that β-cell proliferation rapidly increases at diabetes onset, and that this proliferation is closely correlated with the diabetic animals' elevated blood glucose levels. For instance, we show that when normoglycemia is restored by exogenous insulin or islet transplantation, the β-cell proliferation rate returns towards low levels found in control animals, yet surges when hyperglycemia recurs. In contrast, other-than-ß endocrine islet cells did not exhibit the same glucose-dependent proliferative responses. Rather, disease-associated alterations of BrdU-incorporation rates of δ-cells (minor decrease), and non-endocrine islet cells (slight increase) were not affected by blood glucose levels, or were inversely related to glycemia control after diabetes onset (α-cells).

Conclusion

We conclude that murine β-cells' ability to proliferate in response to metabolic need (i.e. rising blood glucose concentrations) is remarkably well preserved during severe, chronic β-cell autoimmunity. These data suggest that timely control of the destructive immune response after disease manifestation could allow spontaneous regeneration of sufficient β-cell mass to restore normal glucose homeostasis.

Regulation of beta cell replication

Beta cell mass, at any given time, is governed by cell differentiation, neogenesis, increased or decreased cell size (cell hypertrophy or atrophy), cell death (apoptosis), and beta cell proliferation. Nutrients, hormones and growth factors coupled with their signalling intermediates have been suggested to play a role in beta cell mass regulation. In addition, genetic mouse model studies have indicated that cyclins and cyclin-dependent kinases that determine cell cycle progression are involved in beta cell replication, and more recently, menin in association with cyclin-dependent kinase inhibitors has been demonstrated to be important in beta cell growth. In this review, we consider and highlight some aspects of cell cycle regulation in relation to beta cell replication. The role of cell cycle regulation in beta cell replication is mostly from studies in rodent models, but whether these findings can be extended to human beta cells remains to be shown.

Expression of the GLP-1 receptor in mouse, rat, and human pancreas

We studied the intra-islet localization of the glucagon-like peptide 1 receptor (GLP-1R) by colocalization studies of the GLP-1R mRNA and protein with islet cell hormones in mice, rats, and humans. In contrast to previous reports, we show that the GLP-1R is selectively located on the beta cells. The localization of GLP-1R in islets and ducts was studied using ISH and double and triple fluorescence microscopy. In normal pancreatic tissue from mice and rats, GLP-1R mRNA was only detectable in the beta cells. Double and triple immunofluorescence using two different GLP-1R antisera and combinations of insulin, glucagon, pancreatic polypeptide, and somatostatin showed that GLP-1R protein is almost exclusively colocalized with insulin. The same pattern was observed in human pancreas, but the GLP-1R expression was more heterogeneous, with populations of insulin immunoreactive cells with high and low expression. This is the first time that the GLP-1R has been localized in human islets. Furthermore, GLP-1R immunoreactivity was found in the pancreatic ducts in mouse, rat, and human pancreas. As an important confirmation of the specificity of our methods, we found no signals for GLP-1R mRNA or protein in pancreatic tissue from gene-targeted GLP-1R-deficient mice. In conclusion, our data suggest that the GLP-1 receptor is restricted to the pancreatic beta cells and the lack of receptor immunoreactivity on delta cells cannot be explained suitably to correspond with published in vivo and in vitro data. This manuscript contains online supplemental material at http://www.jhc.org. Please visit this article online to view these materials.