Targeted inactivation of hepatocyte growth factor receptor c-met in beta-cells leads to defective insulin secretion and GLUT-2 downregulation without alteration of beta-cell mass

Neurotrophic modulation of motor neuron development

Neurotrophic factors (NTFs) are a pleiotropic group of secreted growth factors that regulate multiple aspects of neuronal development, including the regressive event of cell death. Skeletal muscleinnervating lower motoneurons (MNs) of the brain stem and spinal cord comprise one population of central neurons in which programmed cell death (PCD) during embryogenesis has been actively investigated, as much for reasons of technical facility as clinical relevance. The precise identity of NTF-dependent MNs has remained unclear, with most studies simply reporting losses or gains across the entire spinal cord or individual brain-stem nuclei. However, MNs are grouped into highly heterogenous populations based on transcriptional identity, target innervation, and physiological function. Therefore, recent work has focused on the effects of NTF overexpression or deletion on the survival of these MN subpopulations. Together with the recent progress attained in the generation of conditional mutant mice, in which the function of an NTF or its receptor can be eliminated specifically in MNs, these recent studies have begun to define the differential trophic requirements for MN subpopulations during PCD. The intent of this review is to summarize these recent findings and to discuss their significance with respect to neurotrophic theory.

Minireview: Meeting the demand for insulin: molecular mechanisms of adaptive postnatal beta-cell mass expansion

Type 2 diabetes results from pancreatic ss-cell failure in the setting of insulin resistance. This model of disease progression has received recent support from the results of genome-wide association studies that identify genes potentially regulating ss-cell growth and function as type 2 diabetes susceptibility loci. Normal ss-cell compensation for an increased insulin demand includes both enhanced insulin-secretory capacity and an expansion of morphological ss-cell mass, due largely to changes in the balance between ss-cell proliferation and apoptosis. Recent years have brought significant progress in the understanding of both extrinsic signals stimulating ss-cell growth as well as mediators intrinsic to the ss-cell that regulate the compensatory response. Here, we review the current knowledge of mechanisms underlying adaptive expansion of ss-cell mass, focusing on lessons learned from experimental models of physiologically occurring insulin-resistant states including diet-induced obesity and pregnancy, and highlighting the potential importance of interorgan cross talk. The identification of critical mediators of islet compensation may direct the development of future therapeutic strategies to enhance the response of ss-cells to insulin resistance.

c-Met-targeted RNA interference inhibits growth and metastasis of glioma U251 cells in vitro

Angiogenesis plays an essential role in tumor growth and metastasis and is a promising target for cancer therapy. c-Met, a receptor tyrosine kinase, and its ligand, hepatocyte growth factor (HGF), are critical in cellular proliferation, motility, invasion, and angiogenesis. The present study was designed to determine the role of c-Met in growth and metastasis of glioma U251 cells using RNA interference (RNAi) technology in vitro. We constructed three kinds of shRNA expression vectors aiming at the c-Met gene, then transfected them into glioma U251 cells by lipofectamine(TM) 2000. The level of c-Met mRNA was investigated by real-time polymerse chain reaction (RT-PCR). The protein expression of c-Met was observed by immunofluoresence staining and western blotting. U251 cell growth and adherence was detected by methyl thiazole tetrazolium assay. The apoptosis of U251 cells was examined with a flow cytometer. The adherence, invasion, and in vitro angiogenesis assays of U251 cells were done. We got three kinds of c-Met specific shRNA expression vectors which could efficiently inhibit the growth and metastasis of U251 cells and the expression of c-Met in U251 cells. RT-PCR, immunofluoresence staining and western blotting showed that inhibition rate for c-Met expression was up to 90%, 79% and 85%, respectively. The expression of c-Met can be inhibited by RNA interference in U251 cells, which can inhibit the growth and metastasis of U251 cell and induce cell apoptosis. These results indicate that RNAi of c-Met can be an effective antiangiogenic strategy for glioma.

Beta-cell failure as a complication of diabetes

Type 2 diabetes mellitus is a complex disease characterized by beta-cell failure in the setting of insulin resistance. In early stages of the disease, pancreatic beta-cells adapt to insulin resistance by increasing mass and function. As nutrient excess persists, hyperglycemia and elevated free fatty acids negatively impact beta-cell function. This happens by numerous mechanisms, including the generation of reactive oxygen species, alterations in metabolic pathways, increases in intracellular calcium and the activation of endoplasmic reticulum stress. These processes adversely affect beta-cells by impairing insulin secretion, decreasing insulin gene expression and ultimately causing apoptosis. In this review, we will first discuss the regulation of beta-cell mass during normal conditions. Then, we will discuss the mechanisms of beta-cell failure, including glucotoxicity, lipotoxicity and endoplasmic reticulum stress. Further research into mechanisms will reveal the key modulators of beta-cell failure and thus identify possible novel therapeutic targets. Type 2 diabetes mellitus is a multifactorial disease that has greatly risen in prevalence in part due to the obesity and inactivity that characterize the modern Western lifestyle. Pancreatic beta-cells possess the potential to greatly expand their function and mass in both physiologic and pathologic states of nutrient excess and increased insulin demand. beta-cell response to nutrient excess occurs by several mechanisms, including hypertrophy and proliferation of existing beta-cells, increased insulin production and secretion, and formation of new beta-cells from progenitor cells [1, 2]. Failure of pancreatic beta-cells to adequately expand in settings of increased insulin demand results in hyperglycemia and diabetes. In this review, we will first discuss the factors involved in beta-cell growth and then discuss the mechanisms by which beta-cell expansion fails and leads to beta-cell failure and diabetes (Fig. 1).

Bipartite adenoviral vector encoding hHGF and hIL-1Ra for improved human islet transplantation

PURPOSE

Ex vivo gene therapy can improve the outcome of islet transplantation for treating type I diabetes. Hepatocyte growth factor (HGF) increases beta-cell proliferation and promotes revascularization of islets, while interleukin-1 receptor antagonist (hIL-1Ra) inhibits islet cell apoptosis.

METHODS

We constructed Adv-hHGF-hIL-1Ra by cloning hHGF and hIL-1Ra coding sequences and polyA signal under separate CMV promoters in Adenoquick plasmid.

RESULTS

There was dose and time dependent expression of these genes after transduction of Adv-hHGF-hIL-1Ra into human islets. Compared to un-transduced islets, hHGF and hIL-1Ra gene expression at protein levels was more than 60 and 40 times higher at 1,000 MOI, respectively. Transduced islets were viable after incubation with the cocktail of TNF-alpha, IL-1beta and IFN-gamma, as evidenced by insulin release in response to glucose concentration. Co-expression of hHGF and hIL-1Ra led to significant decrease in caspase-3 induced by the cytokines. Compared to un-transduced islets, transduction of islets with Adv-hHGF-hIL-1Ra at 1,000 MOI prior to transplantation under the kidney capsules of streptozotocin-induced-diabetic NOD-SCID mice reduced blood glucose levels, and increased serum insulin and c-peptide levels.

CONCLUSIONS

Transduction of islets with Adv-hHGF-hIL-1Ra efficiently expresses both growth factor and antiapoptotic genes, decreases caspase-3 and improves the outcome of islet transplantation.

Developmental biology of the pancreas: a comprehensive review

Pancreatic development represents a fascinating process in which two morphologically distinct tissue types must derive from one simple epithelium. These two tissue types, exocrine (including acinar cells, centro-acinar cells, and ducts) and endocrine cells serve disparate functions, and have entirely different morphology. In addition, the endocrine tissue must become disconnected from the epithelial lining during its development. The pancreatic development field has exploded in recent years, and numerous published reviews have dealt specifically with only recent findings, or specifically with certain aspects of pancreatic development. Here I wish to present a more comprehensive review of all aspects of pancreatic development, though still there is not a room for discussion of stem cell differentiation to pancreas, nor for discussion of post-natal regeneration phenomena, two important fields closely related to pancreatic development.

Screening of genes differentially expressed in HepG2 cells transfected with human hepatocyte growth factor

AIM: To construct the eukaryotic expression vector of pcDNA3.1(-)-hHGF, and to screen the differentially expressed genes in HepG2 cells transfected with the vector.

METHODS: We constructed the expression vector of pcDNA3.1(-)-hHGF, which was confirmed by restriction enzyme digestion and DNA sequencing, and then transfected it into HepG2 cell line. The expression of HGF protein was observed by Western blotting. At last, we compared the differentially expressed genes between HepG2 cells transfected with pcDNA3.1(-)-hHGF and pcDNA3.1(-) respectively by cDNA microarray technique.

RESULTS: The expression vector was constructed successfully and confirmed by restriction enzyme digestion and DNA sequencing analysis. The expression of hHGF protein was confirmed by Western blotting. High quality mRNA and cDNA had been prepared and successful microarray screening had been conducted. From the scanning results, we found 430 genes that were up-regulated and 88 genes down-regulated in HepG2 cells transfected with hHGF.

CONCLUSION: cDNA microarray technology is successfully used to screen the genes differentially expressed in HepG2 cells transfected with hHGF, which brings some new clues for studying the regulatory mechanism of hHGF in liver cells.

Resolving the conundrum of islet transplantation by linking metabolic dysregulation, inflammation, and immune regulation

Although type 1 diabetes cannot be prevented or reversed, replacement of insulin production by transplantation of the pancreas or pancreatic islets represents a definitive solution. At present, transplantation can restore euglycemia, but this restoration is short-lived, requires islets from multiple donors, and necessitates lifelong immunosuppression. An emerging paradigm in transplantation and autoimmunity indicates that systemic inflammation contributes to tissue injury while disrupting immune tolerance. We identify multiple barriers to successful islet transplantation, each of which either contributes to the inflammatory state or is augmented by it. To optimize islet transplantation for diabetes reversal, we suggest that targeting these interacting barriers and the accompanying inflammation may represent an improved approach to achieve successful clinical islet transplantation by enhancing islet survival, regeneration or neogenesis potential, and tolerance induction. Overall, we consider the proinflammatory effects of important technical, immunological, and metabolic barriers including: 1) islet isolation and transplantation, including selection of implantation site; 2) recurrent autoimmunity, alloimmune rejection, and unique features of the autoimmune-prone immune system; and 3) the deranged metabolism of the islet transplant recipient. Consideration of these themes reveals that each is interrelated to and exacerbated by the other and that this connection is mediated by a systemic inflammatory state. This inflammatory state may form the central barrier to successful islet transplantation. Overall, there remains substantial promise in islet transplantation with several avenues of ongoing promising research. This review focuses on interactions between the technical, immunological, and metabolic barriers that must be overcome to optimize the success of this important therapeutic approach.

Embryonic stem cells to beta-cells by understanding pancreas development

Insulin injections treat but do not cure Type 1 diabetes (T1DM). The success of islet transplantation suggests cell replacement therapies may offer a curative strategy. However, cadaver islets are of insufficient number for this to become a widespread treatment. To address this deficiency, the production of beta-cells from pluripotent stem cells offers an ambitious far-sighted opportunity. Recent progress in generating insulin-producing cells from embryonic stem cells has shown promise, highlighting the potential of trying to mimic normal developmental pathways. Here, we provide an overview of the current methodology that has been used to differentiate stem cells toward a beta-cell fate. Parallels are drawn with what is known about normal development, especially regarding the human pancreas.

Hepatocyte growth factor is a novel stimulator of glucose uptake and metabolism in skeletal muscle cells

Skeletal muscle plays a major role in glucose and lipid metabolism. Active hepatocyte growth factor (HGF) is present in the extracellular matrix in skeletal muscle. However, the effects of HGF on glucose and lipid metabolism in skeletal muscle are completely unknown. We therefore examined the effects of HGF on deoxyglucose uptake (DOGU), glucose utilization, and fatty acid oxidation (FAO) in skeletal muscle cells. HGF significantly enhanced DOGU in mouse soleus muscles in vitro. Furthermore, HGF significantly increased: (i) DOGU in a time- and dose-dependent manner; (ii) glucose utilization; and (iii) plasma membrane expression of Glut-1 and Glut-4 in the rat skeletal muscle model of L6 myotubes. HGF-mediated effect on DOGU was dependent on the activation of phosphatidylinositol 3-kinase signaling pathway. On the other hand, HGF markedly and significantly decreased FAO in L6 myotubes without affecting the activities of carnitine palmitoyltransferase I and II. Collectively, these results indicate that HGF is a potent activator of glucose transport and metabolism and also a strong inhibitor of FAO in rodent myotubes. HGF, through its ability to stimulate glucose transport and metabolism and to impair FAO, may participate in the regulation of glucose disposal in skeletal muscle.

Stromal cell derived factor-1 (SDF-1)/CXCL12 attenuates diabetes in mice and promotes pancreatic beta-cell survival by activation of the prosurvival kinase Akt

OBJECTIVE

Diabetes is caused by a deficiency of pancreatic beta-cells that produce insulin. Approaches to enhance beta-cell mass by increasing proliferation and survival are desirable. We determined whether stromal cell-derived factor (SDF)-1/CXCL12 and its receptor, CX chemokine receptor (CXCR)4, are important for the survival of beta-cells.

RESEARCH DESIGN AND METHODS

Mouse pancreata and clonal beta-cells were examined for expression of SDF-1 and CXCR4, activation of AKT and downstream signaling pathways by SDF-1, and protection against apoptosis and diabetes induced by streptozotocin (STZ).

RESULTS

CXCR4 is expressed in beta-cells, and SDF-1 is expressed in microvascular endothelial cells within the islets and in surrounding interstitial stromal tissue. Transgenic mice overexpressing SDF-1 within their beta-cells (RIP-SDF-1 mice) are resistant to STZ-induced beta-cell apoptosis and diabetes. In MIN6 beta-cells, a CXCR4 antagonist (AMD3100) induces apoptosis, increases reactive oxygen species, decreases expression levels of the anti-apoptotic protein Bcl-2, and reduces phosphorylation of the proapoptotic protein Bad. Active phosphorylated prosurvival kinase Akt is increased both in the beta-cells of RIP-SDF-1 mice and in INS-1 cells treated with SDF-1 and sensitive to AMD3100. Inhibition of AKT expression by small interfering RNA attenuates the ameliorative effects of SDF-1 on caspase-dependent apoptosis induced by thapsigargin or glucose deprivation in INS-1 beta-cells. Specific inhibition of Akt activation by a soluble inhibitor (SH-5) reverses the anti-apoptotic effects of SDF-1 in INS-1 cells and mouse islets.

CONCLUSIONS

SDF-1 promotes pancreatic beta-cell survival via activation of Akt, suggesting that SDF-1 agonists may prove beneficial for treatment of diabetes.

Protein kinase C-zeta activation markedly enhances beta-cell proliferation: an essential role in growth factor mediated beta-cell mitogenesis

OBJECTIVE

Diabetes results from a deficiency of functional beta-cells. Previous studies have identified hepatocyte growth factor (HGF) and parathyroid hormone-related protein (PTHrP) as two potent beta-cell mitogens. The objective of this study is to determine 1) whether HGF and PTHrP have additive/synergistic effects on beta-cell growth and proliferation; 2) the signaling pathways through which these growth factors mediate beta-cell mitogenesis; and 3) whether activation of this/these signaling pathway(s) enhances human beta-cell replication.

RESEARCH DESIGN AND METHODS

We generated and phenotypically analyzed doubly transgenic mice overexpressing PTHrP and HGF in the beta-cell. INS-1 and primary mouse and human islet cells were used to identify mitogenic signaling pathways activated by HGF and/or PTHrP.

RESULTS

Combined overexpression of HGF and PTHrP in the beta-cell of doubly transgenic mice did not result in additive/synergistic effects on beta-cell growth and proliferation, suggesting potential cross-talk between signaling pathways activated by both growth factors. Examination of these signaling pathways in INS-1 cells revealed atypical protein kinase C (PKC) as a novel intracellular target activated by both HGF and PTHrP in beta-cells. Knockdown of PKC zeta, but not PKC iota/lambda, expression using specific small-interfering RNAs blocked growth factor-induced INS-1 cell proliferation. Furthermore, adenovirus-mediated delivery of kinase-dead PKC zeta completely inhibited beta-cell proliferation in primary islet cells overexpressing PTHrP and/or HGF. Finally, adenovirus-mediated delivery of constitutively active PKC zeta in mouse and human primary islet cells significantly enhanced beta-cell proliferation.

CONCLUSIONS

PKC zeta is essential for PTHrP- and HGF-induced beta-cell proliferation. PKC zeta activation could be useful in therapeutic strategies for expanding beta-cell mass in vitro and in vivo.

Tyrosine kinase receptors are crucial for normal β-cell development and function

Signaling pathways play critical roles in most physiological and pathological processes and convert an extracellular stimulus into a change of function in the recipient cell. Intracellular messages originate from the activation of membrane receptors by a variety of ligands, such as hormones, nutrients or growth factors. The receptors subsequently interact with specific intracellular cascades, triggering the phosphorylation of cell effectors. In the pancreas, these processes control the organogenesis, maintenance and function of endocrine cells within the islets. Growth factors acting through tyrosine kinase receptors play a prominent role among the multitude of signaling pathways active in pancreatic β cells. Deregulation of these processes leads to the development of disorders such as hypoglycemia or diabetes. This review will describe recent advances made on the understanding of the roles of major tyrosine kinase receptors in pancreatic β-cell physiology.

Hepatocyte growth factor induces glucose uptake in 3T3-L1 adipocytes through A Gab1/phosphatidylinositol 3-kinase/Glut4 pathway

Adipose tissue is a source of hepatocyte growth factor (HGF), and circulating HGF levels have been associated with elevated body mass index in human. However, the effects of HGF on adipocyte functions have not yet been investigated. We show here that in 3T3-L1 adipocytes HGF stimulates the phosphatidylinositol (PI) 3-kinase-dependent protein kinase B (PKB) activity, AS160 phosphorylation, Glut4 translocation, and consequently, glucose uptake. The initial steps involved in HGF- and insulin-induced glucose uptake are different. HGF enhanced the tyrosine phosphorylation of Gab1, leading to the recruitment of the p85-regulated subunit of PI 3-kinase, whereas p85 was exclusively recruited by IRS1 in response to insulin. In adipocytes rendered insulin-resistant by a long-lasting tumor necrosis factor alpha treatment, the protein level of Gab1 was strongly decreased, and HGF-stimulated PKB activation and glucose uptake were also altered. Moreover, treatment of 3T3-L1 adipocytes with thiazolidinedione, an anti-diabetic drug, enhanced the expression of both HGF and its receptor. These data provide the first evidence that in vitro HGF promotes glucose uptake through a Gab1/PI 3-kinase/PKB/AS160 pathway which was altered in tumor necrosis factor alpha-treated adipocytes.

Tissue-specific deletion of the retinoblastoma protein in the pancreatic beta-cell has limited effects on beta-cell replication, mass, and function

Animal studies show that G(1/S) regulatory molecules (D-cyclins, cdk-4, p18, p21, p27) are critical for normal regulation of beta-cell proliferation, mass, and function. The retinoblastoma protein, pRb, is positioned at the very end of a cascade of these regulatory proteins and is considered the final checkpoint molecule that maintains beta-cell cycle arrest. Logically, removal of pRb from the beta-cell should result in unrestrained beta-cell replication, increased beta-cell mass, and insulin-mediated hypoglycemia. Because global loss of both pRb alleles is embryonic lethal, this hypothesis has not been tested in beta-cells. We developed two types of conditional knockout (CKO) mice in which both alleles of the pRb gene were inactivated specifically in beta-cells. Surprisingly, although the pRb gene was efficiently recombined in beta-cells of both CKO models, changes in beta-cell mass, beta-cell replication rates, insulin concentrations, and blood glucose levels were limited or absent. Other pRb family members, p107 and p130, were not substantially upregulated. In contrast to dogma, the pRb protein is not essential to maintain cell cycle arrest in the pancreatic beta-cell. This may reflect fundamental inaccuracies in models of beta-cell cycle control or complementation for pRb by undefined proteins.

Long-term cultured neonatal porcine islet cell monolayers: a potential tissue source for transplant in diabetes

BACKGROUND

The restricted availability of cadaveric human donor pancreases mandates validation of possibly inexhaustible, alternative sources of insulin secretory cells in order to expand islet transplant for the therapy of insulin dependent diabetes mellitus (T1DM).

METHODS

Neonatal pig pancreatic islets (NPI), isolated and purified by our method, were specially cultured until confluent cell monolayers were obtained. Expression of several beta-cell phenotype transcriptional factors, under glucose and other stimuli, were examined throughout 90 days of culture.

RESULTS

High glucose concentration and glucagon-like peptide 1 (GLP-1) were associated with maintenance either of insulin secretory patterns from the incubated cell monolayers, or expression of transcriptional markers associated with beta-cell like phenotypes.

CONCLUSION

Morphological and molecular expression of beta-cell markers and products from NPI cell monolayers seem to identify a novel and potentially powerful source of insulin producing cells that might fulfill transplant needs for insulin substitution therapy.

Avenues for immunomodulation and graft protection by gene therapy in transplantation

Organ transplantation represents the only definitive therapy for many causes of end-organ failure. However, the universal success of this therapy is limited by chronic allograft rejection, the side effects of chronic immunosuppressive therapy, and a severe shortage of donor organs. Presently, the success of solid-organ transplantation depends on the continuous administration of toxic and nonspecific immunosuppressive agents, therapies that present risks for opportunistic infection, malignancy, and a variety of agent-specific side effects. To promote the use of transplantation with limited risk of long-term sequelae, three dominant research challenges emerge: (i) elimination of the need for exogenous immunosuppression by immunological tolerance induction; (ii) prevention of chronic rejection/graft dysfunction; and (iii) expansion of available organs for transplantation. Gene therapy may provide significant advances and solutions in each of these areas. Rejection of the graft in the immediate post-transplant period has been attacked through the transfer of immunomodulatory molecules in addition to tolerance inducing approaches. Chronic graft rejection may be similarly addressed through permanent tolerance induction or alternatively through the introduction of molecules to resist chronic graft damage. Genetic manipulation of stem cells may ultimately produce transgenic animals to serve as tissue donors to overcome the limited donor organ supply. This review will highlight ongoing developments in the translation of gene therapy approaches to the challenges inherent in transplantation.

C-Met antisense oligodeoxynucleotide inhibits growth of glioma cells

BACKGROUND

C-Met, a receptor tyrosine kinase, and its ligand, hepatocyte growth factor, are critical in cellular proliferation, motility, and invasion and are known to be overexpressed in gliomas. The aim of our study was therefore to investigate the effect of transfected caroboxyfluorescein-5-succimidyl ester (FAM)-labeled c-Met antisense oligonucleotide (ASODN) on growth of glioma cells.

METHODS

Conjugated FAM-labeled c-Met ASODN was encapsulated by LIPOFECTAMINE PLUS Reagent and then added into the human glioma cell line U251. Cultured cells were divided into 5 groups: control group, 500 nmol/L nonsense oligonucleotide (NSODN) group, 250 nmol/L ASODN group, 500 nmol/L ASODN group, and 750 nmol/L ASODN group. The intracellular distribution of c-Met ASODN was observed with fluorescence microscopy; cell growth was detected by methyl thiazole tetrazolium assay. The apoptosis of U251 cells was also examined with a flow cytometer. Semiquantitative reverse transcriptase polymerase chain reaction and Western blot examinations were carried for expression of c-Met messenger RNA (mRNA) and protein.

RESULTS

The blue fluorescence was seen in the cytoplast and nuclei of cells of FAM-labeled c-Met ASODN groups with fluorescence microscopy after the cells were treated with FAM-labeled c-Met ASODN-LIPOFECTAMINE PLUS Reagent complex for 3 hours. Antisense (AS) oligonucleotide caused a statistically significant reduction of cell viability (P < .05), whereas NSODN had no such changes. The cell growth was also significantly inhibited by ASODN (P < .05). After transfection, 250, 500, and 750 nmol/L ASODN induced significant apoptotic response, about 4.67% +/- 2.86%, 8.65% +/- 3.18%, and 12.76% +/- 3.15% for 24 hours (P < .05) and 7.79% +/- 1.92%, 11.43% +/- 1.54%, and 15.78% +/- 1.86% for 48 hours (P < .01), respectively. However, 500 nmol/L NSODN did not induce any significant apoptotic response until 48 hours after transfection (P > .05). A significant loss of c-Met mRNA was presented in ASODN-treated cells, and this was not seen in treatment with NSODN. Protein level was significantly decreased 48 hours after c-Met ASODN transfected.

CONCLUSIONS

Antisense oligonucleotide targeting c-Met can be identified as a most potent AS compound, which can inhibit cell growth and induce cell apoptosis. This provides evidence that c-Met plays a role in tumor progression of glioma by acting as an oncogene and suggests that c-Met ASODN may provide a novel approach to therapy for human glioma.

Growth factors and beta cell replication

Recent studies have demonstrated that human islet allograft transplantation can be a successful therapeutic option in the treatment of patients with Type I diabetes. However, this impressive recent advance is accompanied by a very important constraint. There is a critical paucity of pancreatic islets or pancreatic beta cells for islet transplantation to become a large-scale therapeutic option in patients with diabetes. This has prompted many laboratories around the world to invigorate their efforts in finding ways for increasing the availability of beta cells or beta cell surrogates that potentially could be transplanted into patients with diabetes. The number of studies analyzing the mechanisms that govern beta cell proliferation and growth in physiological and pathological conditions has increased exponentially during the last decade. These studies exploring the role of growth factors, intracellular signaling molecules and cell cycle regulators constitute the substrate for future strategies aimed at expanding human beta cells in vitro and/or in vivo after transplantation. In this review, we describe the current knowledge on the effects of several beta cell growth factors that have been shown to increase beta cell proliferation and expand beta cell mass in vitro and/or in vivo and that they could be potentially deployed in an effort to increase the number of patients transplanted with islets. Furthermore, we also analyze in this review recent studies deciphering the relevance of these specific islet growth factors as physiological and pathophysiological regulators of beta cell proliferation and islet growth.