p38 MAPK is involved in activin A- and hepatocyte growth factor-mediated expression of pro-endocrine gene neurogenin 3 in AR42J-B13 cells

Activins and Inhibins in Cardiovascular Pathophysiology

Activins and inhibins, members of the transforming growth factor β (TGFβ) superfamily, were initially recognized for their opposing effects on the secretion of follicle-stimulating hormone. Subsequent research has demonstrated their broader biological roles across various tissue types. Primarily, activins and inhibins function through the classical TGFβ SMAD signaling pathway, but studies suggest that they also act through other pathways, with their specific signaling being complex and context-dependent. Recent research has identified significant roles for activins and inhibins in the cardiovascular system. Their actions in other systems and their signaling pathways show strong correlations with the development and progression of cardiovascular diseases, indicating potential broader roles in the cardiovascular system. This review summarizes the progress in research on the biological functions and mechanisms of activins and inhibins and their signaling pathways in cardiovascular diseases, offering new insights for the prevention and treatment of cardiovascular diseases.

MAPK and GSK3/ß-TRCP-mediated degradation of the maternal Ets domain transcriptional repressor Yan/Tel controls the spatial expression of nodal in the sea urchin embryo

In the sea urchin embryo, specification of the dorsal-ventral axis critically relies on the spatially restricted expression of nodal in the presumptive ventral ectoderm. The ventral restriction of nodal expression requires the activity of the maternal TGF-β ligand Panda but the mechanism by which Panda restricts nodal expression is unknown. Similarly, what initiates expression of nodal in the ectoderm and what are the mechanisms that link patterning along the primary and secondary axes is not well understood. We report that in Paracentrotus lividus, the activity of the maternally expressed ETS-domain transcription factor Yan/Tel is essential for the spatial restriction of nodal. Inhibiting translation of maternal yan/tel mRNA disrupted dorsal-ventral patterning in all germ layers by causing a massive ectopic expression of nodal starting from cleavage stages, mimicking the phenotype caused by inactivation of the maternal Nodal antagonist Panda. We show that like in the fly or in vertebrates, the activity of sea urchin Yan/Tel is regulated by phosphorylation by MAP kinases. However, unlike in the fly or in vertebrates, phosphorylation by GSK3 plays a central role in the regulation Yan/Tel stability in the sea urchin. We show that GSK3 phosphorylates Yan/Tel in vitro at two different sites including a β-TRCP ubiquitin ligase degradation motif and a C-terminal Ser/Thr rich cluster and that phosphorylation of Yan/Tel by GSK3 triggers its degradation by a β-TRCP/proteasome pathway. Finally, we show that, Yan is epistatic to Panda and that the activity of Yan/Tel is required downstream of Panda to restrict nodal expression. Our results identify Yan/Tel as a central regulator of the spatial expression of nodal in Paracentrotus lividus and uncover a key interaction between the gene regulatory networks responsible for patterning the embryo along the dorsal-ventral and animal-vegetal axes.

Specification of the embryonic axes is an essential step during early development of metazoa. In the sea urchin embryo, specification of the dorsal-ventral axis critically relies on the spatial restriction of the expression of the TGF-ß family member Nodal in ventral cells, a process that requires the activity of the maternal determinant Panda. How the spatially restricted expression of nodal is established downstream of Panda is not well understood. We have discovered that, in the Mediterranean sea urchin Paracentrotus lividus, the spatial restriction of nodal on the ventral side of the embryo requires the inhibitory activity of a transcriptional repressor named Yan/Tel. This finding suggests a molecular mechanism for the control of nodal expression by the release of a repression. We found that this release requires the activity of two families of kinases that we identified as the MAP kinases and GSK3, a kinase which, intriguingly, was previously known as a key regulator of patterning along the animal-vegetal axis. We discovered that phosphorylation by MAPK and GSK3 triggers degradation of Yan/Tel by a β-TRCP proteasome pathway. Finally, we find that Yan/Tel likely acts downstream of Panda in the hierarchy of genes required for nodal restriction. Our study therefore identifies Yan/Tel as a new essential regulator of nodal expression downstream of Panda and identifies a novel key interaction between the gene regulatory networks responsible for patterning along the primary and secondary axis of polarity.

Connexin 32 and connexin 43 are involved in lineage restriction of hepatic progenitor cells to hepatocytes

BACKGROUND

Bi-potential hepatic progenitor cells can give rise to both hepatocytes and cholangiocytes, which is the last phase and critical juncture in terms of sequentially hepatic lineage restriction from any kind of stem cells. If their differentiation can be controlled, it might access to functional hepatocytes to develop pharmaceutical and biotechnology industries as well as cell therapies for end-stage liver diseases.

METHODS

In this study, we investigated the influence of Cx32 and Cx43 on hepatocyte differentiation of WB-F344 cells by in vitro gain and loss of function analyses. An inhibitor of Cx32 was also used to make further clarification. To reveal p38 MAPK pathway is closely related to Cxs, rats with 70% partial hepatectomy were injected intraperitoneally with a p38 inhibitor, SB203580. Besides, the effects of p38 MAPK pathway on differentiation of hepatoblasts isolated from fetal rat livers were evaluated by addition of SB203580 in culture medium.

RESULTS

In vitro gain and loss of function analyses showed overexpression of Connexin 32 and knockdown of Connexin 43 promoted hepatocytes differentiation from hepatic progenitor cells. In addition, in vitro and ex vivo research revealed inhibition of p38 mitogen-activated protein kinase pathway can improve hepatocytes differentiation correlating with upregulation of Connexin 32 expression and downregulation of Connexin 43 expression.

CONCLUSIONS

Here we demonstrate that Connexins play crucial roles in facilitating differentiation of hepatic progenitors. Our work further implicates that regulators of Connexins and their related pathways might provide new insights to improve lineage restriction of stem cells to mature hepatocytes.

p38 MAPK as an essential regulator of dorsal-ventral axis specification and skeletogenesis during sea urchin development: a re-evaluation

Dorsal-ventral axis formation in the sea urchin embryo relies on the asymmetrical expression of the TGFβ Nodal. The p38-MAPK pathway has been proposed to be essential for dorsal-ventral axis formation by acting upstream of nodal expression. Here, we report that, in contrast to previous studies that used pharmacological inhibitors of p38, manipulating the activity of p38 by genetic means has no obvious impact on morphogenesis. Instead, we discovered that p38 inhibitors strongly disrupt specification of all germ layers by blocking signalling from the Nodal receptor and by interfering with the ERK pathway. Strikingly, while expression of a mutant p38 that is resistant to SB203580 did not rescue dorsal-ventral axis formation or skeletogenesis in embryos treated with this inhibitor, expression of mutant Nodal receptors that are resistant to SB203580 fully restored nodal expression in SB203580-treated embryos. Taken together, these results establish that p38 activity is not required for dorsal-ventral axis formation through nodal expression nor for skeletogenesis. Our results prompt a re-evaluation of the conclusions of several recent studies that linked p38 activity to dorsal-ventral axis formation and to patterning of the skeleton.

Activins and Inhibins: Roles in Development, Physiology, and Disease

Since their original discovery as regulators of follicle-stimulating hormone (FSH) secretion and erythropoiesis, the TGF-β family members activin and inhibin have been shown to participate in a variety of biological processes, from the earliest stages of embryonic development to highly specialized functions in terminally differentiated cells and tissues. Herein, we present the history, structures, signaling mechanisms, regulation, and biological processes in which activins and inhibins participate, including several recently discovered biological activities and functional antagonists. The potential therapeutic relevance of these advances is also discussed.

Swertisin an Anti-Diabetic Compound Facilitate Islet Neogenesis from Pancreatic Stem/Progenitor Cells via p-38 MAP Kinase-SMAD Pathway: An In-Vitro and In-Vivo Study

Transplanting islets serves best option for restoring lost beta cell mass and function. Small bio-chemical agents do have the potential to generate new islets mass, however lack of understanding about mechanistic action of these small molecules eventually restricts their use in cell-based therapies for diabetes. We recently reported "Swertisin" as a novel islet differentiation inducer, generating new beta cells mass more effectively. Henceforth, in the present study we attempted to investigate the molecular signals that Swertisin generate for promoting differentiation of pancreatic progenitors into islet cells. To begin with, both human pancreatic progenitors (PANC-1 cells) and primary cultured mouse intra-islet progenitor cells (mIPC) were used and tested for Swertisin induced islet neogenesis mechanism, by monitoring immunoblot profile of key transcription factors in time dependent manner. We observed Swertisin follow Activin-A mediated MEPK-TKK pathway involving role of p38 MAPK via activating Neurogenin-3 (Ngn-3) and Smad Proteins cascade. This MAP Kinase intervention in differentiation of cells was confirmed using strong pharmacological inhibitor of p38 MAPK (SB203580), which effectively abrogated this process. We further confirmed this mechanism in-vivo in partial pancreatectomised (PPx) mice model, where we could show Swertisin exerted potential increase in insulin transcript levels with persistent down-regulation of progenitor markers like Nestin, Ngn-3 and Pancreatic Duodenal Homeobox Gene-1 (PDX-1) expression, within three days post PPx. With detailed molecular investigations here in, we first time report the molecular mode of action of Swertisin for islet neogenesis mediated through MAP Kinase (MEPK-TKK) pathway involving Ngn-3 and Smad transcriptional regulation. These findings held importance for developing Swertisin as potent pharmacological drug candidate for effective and endogenous differentiation of islets in cell based therapy for diabetes.

Combination treatment of db/db mice with exendin-4 and gastrin preserves β-cell mass by stimulating β-cell growth and differentiation

Aim/Introduction:  Preservation of β‐cell mass is crucial for maintaining long‐term glucose homeostasis. Therapies based on incretin and its mimetics are expected to achieve this goal through various biological functions, particularly the restoration of β‐cell mass. Here we tested the effects of gastrin and exendin‐4 in type 2 diabetic animals.

Materials and Methods:  The effects of exendin‐4 and gastrin on β‐cell function and mass were examined in 8‐week‐old db/db mice. INS‐1 beta cells and AR42J cells were used to determine the molecular mechanism underlying the effects of the two agents. Immunohistochemistry, western blotting and RT‐PCR assays were used to assess the biological effects of the two agents.

Results:  Two weeks of combination administration of exendin‐4 plus gastrin resulted in a significant improvement of glucose tolerance associated with a marked preservation of β‐cell mass in db/db mice. Immunohistochemical analysis showed that such treatment resulted in the appearance of numerous irregularly‐shaped small islets and single insulin‐positive cells. While gastrin had little biological effect on INS‐1 β‐cells consistent with low expression of its intrinsic receptor on these cells, it caused differentiation of AR42J cells into insulin‐producing cells. Co‐stimulation with exendin‐4 significantly enhanced gastrin‐induced endocrine differentiation of AR42J precursor cells. These findings were further supported by enhanced expression of key genes involved in β‐cell differentiation and maturation, such as neurogenin3 (Ngn3) and MafA.

Conclusions:  These results suggest that combination treatment of db/db mice with exendin‐4 and gastrin preserves β‐cell mass by stimulating β‐cell growth and differentiation. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.00044.x, 2010)

Activin A, exendin-4, and glucose stimulate differentiation of human pancreatic ductal cells

Islet transplantation is one treatment option for diabetes mellitus. However, novel sources of pancreatic islets or insulin-producing cells are required because the amount of donor tissue available is severely limited. Pancreatic ductal cells are an alternative source of β-cells because they have the potential to differentiate into insulin-producing cells. We investigated whether treatment of human pancreatic ductal cells with activin A (ActA) and exendin-4 (EX-4) stimulated transdifferentiation of the cells, both in vitro and in vivo. We treated human pancreatic ductal cells with ActA and EX-4 in high-glucose media to induce differentiation into insulin-producing cells and transplanted the cells into streptozotocin-induced diabetic nude mice. Co-treatment of mice with ActA and EX-4 promoted cell proliferation, induced expression of pancreatic β-cell-specific markers, and caused glucose-induced insulin secretion compared with the ActA or EX-4 mono-treatment groups respectively. When pancreatic ductal cells treated with ActA and EX-4 in high-glucose media were transplanted into diabetic nude mice, their blood glucose levels normalized and insulin was detected in the graft. These findings suggest that pancreatic ductal cells have a potential to replace pancreatic islets for the treatment of diabetes mellitus when the ductal cells are co-treated with ActA, EX-4, and glucose to promote their differentiation into functional insulin-producing cells.

Roles of activin family in pancreatic development and homeostasis

The transforming growth factor-beta (TGF-β) superfamily of ligands have been recognized as important signals in vertebrate embryonic development from the blastula stage to adulthood. In addition to roles in early development, TGF-β superfamily ligands, and particularly activin family ligands, are involved in specification, differentiation, and proliferation of multiple organ systems, including the pancreas. More recently, research has suggested that activin family ligands, binding proteins, receptors, and Smad signal transducers and modulators are involved in regulating adult pancreatic function and maintaining pancreatic islet homeostasis in the adult. This article will focus on outlining common themes in activin family regulation of embryonic pancreatic development and adult pancreatic homeostasis, particularly in activin family involvement in setting and maintaining populations of islet cells such as β-cells.

The many faces of p38 mitogen-activated protein kinase in progenitor/stem cell differentiation

Regulation of stem cells is essential for development and adult tissue homoeostasis. The proper control of stem cell self-renewal and differentiation maintains organ physiology, and disruption of such a balance results in disease. There are many mechanisms that have been established as stem cell regulators, such as Wnt or Notch signals. However, the intracellular mechanisms that mediate and integrate these signals are not well understood. A new intracellular pathway that has been reported to be involved in the regulation of many stem cell types is that of p38 MAPK (mitogen-activated protein kinase). In particular, p38α is essential for the proper differentiation of many haematopoietic, mesenchymal and epithelial stem/progenitor cells. Many reports have shown that disruption of this kinase pathway has pathological consequences in many organs. Understanding the extracellular cues and downstream targets of p38α in stem cell regulation may help to tackle some of the pathologies associated with improper differentiation and regulation of stem cell function. In the present review we present a vision of the current knowledge on the roles of the p38α signal as a regulator of stem/progenitor cells in different tissues in physiology and disease.

Activin A Stimulates Mouse APCs to Express BAFF via ALK4-Smad3 Pathway

Background

B cell-activating factor belonging to the TNF family (BAFF) is primarily expressed by macrophages and dendritic cells, and stimulates B cell proliferation, differentiation, survival, and Ig production. In the present study, we explored the effect of activin A on BAFF expression by APCs.

Methods

To investigate the effect of activin A on BAFF expression by mouse APCs, we measured the level of BAFF expression at the transcriptional and protein levels using RT-PCR and ELISA.

Results

Activin A markedly enhanced BAFF expression in mouse macrophages and dendritic cells at both the transcriptional and protein levels. SB431542, an activin receptor-like kinase 4 (ALK4) inhibitor, completely abrogated activin A-induced BAFF transcription. Furthermore, overexpression of DN-Smad3 abolished activin-induced BAFF expression at the transcriptional and protein levels.

Conclusion

These results demonstrate that activin A can enhance BAFF expression through ALK4-Smad3 pathway.

Extracellular matrix modulates insulin production during differentiation of AR42J cells: functional role of Pax6 transcription factor

Extracellular matrix (ECM) modulates differentiation of pancreatic β-cells during development. However, the mechanism by which ECM proteins modulate differentiation is not totally clear. We investigated the effect of ECM proteins on differentiation β-cells in vitro. We investigated the effect of basement membrane ECM on differentiation of AR42J cells and rat ductal cells. First, we examined the effect of reconstituted basement membrane, Matrigel on differentiation of AR42J cells induced by activin and betacellulin. Matrigel augmented insulin production and increased the expression of GLUT2, SUR1, and glucokinase. Among various transcription factors investigated, Matrigel markedly upregulated the expression of Pax6. When Pax6 was overexpressed in cells treated with activin and betacellulin, the expression of insulin was upregulated. Conversely, knockdown of Pax6 significantly reduced the insulin expression in cells cultured on Matrigel. The effects of Matrigel on insulin-production and induction of Pax6 were reproduced partially by laminin-1, a major component of Matrigel, and inhibited by anti-integrin-β1 antibody. Matrigel also enhanced the activation of p38 mitogen-activated kinase induced by activin and betacellulin, which was inhibited by anti-β1 antibody. Finally, the effect of Matrigel on differentiation was reproduced in rat cultured ductal cells, and Matrigel also increased the expression of Pax6. These results indicate that basement membrane ECM augments differentiation of pancreatic progenitor cells to insulin-secreting cells by upregulating the expression of Pax6. .

Activin A stimulates mouse macrophages to express APRIL via the Smad3 and ERK/CREB pathways

A proliferation-inducing ligand (APRIL) is primarily expressed by macrophages and dendritic cells, and stimulates B cell proliferation, differentiation, survival, and Ig production. In the present study, we investigated the role and signaling mechanisms of activin A in APRIL expression by mouse macrophages. Activin A markedly enhanced APRIL expression in mouse macrophages at both the transcriptional and protein levels. Overexpression of dominant-negative (DN)-Smad3 and SB431542 abrogated activin-induced APRIL transcription. Furthermore, activin A induced Smad3 phosphorylation. These results indicate that activin A enhances APRIL expression through both activin receptor-like kinase 4 (ALK4) and Smad3. In a subsequent analysis of activin A signaling, it was found that PD98059, an extracellular signal-related kinase (ERK) inhibitor, eliminated activin A-induced APRIL expression. On the other hand, overexpression of cAMP responsive element-binding protein (CREB), a molecule downstream of ERK, augmented activin A-induced APRIL expression, and this effect could be abolished by PD98059. This finding that activin A induces ERK and CREB phosphorylation suggests that ERK and CREB act as intermediates in APRIL expression. Taken together, these results demonstrate that activin A can enhance APRIL expression through two different pathways, Smad3 and ERK/CREB.

The regulation and functions of activin and follistatin in inflammation and immunity

The activins are members of the transforming growth factor β superfamily with broad and complex effects on cell growth and differentiation. Activin A has long been known to be a critical regulator of inflammation and immunity, and similar roles are now emerging for activin B, with which it shares 65% sequence homology. These molecules and their binding protein, follistatin, are widely expressed, and their production is increased in many acute and chronic inflammatory conditions. Synthesis and release of the activins are stimulated by inflammatory cytokines, Toll-like receptor ligands, and oxidative stress. The activins interact with heterodimeric serine/threonine kinase receptor complexes to activate SMAD transcription factors and the MAP kinase signaling pathways, which mediate inflammation, stress, and immunity. Follistatin binds to the activins with high affinity, thereby obstructing the activin receptor binding site, and targets them to cell surface proteoglycans and lysosomal degradation. Studies on transgenic mice and those with gene knockouts, together with blocking studies using exogenous follistatin, have established that activin A plays critical roles in the onset of cachexia, acute and chronic inflammatory responses such as septicemia, colitis and asthma, and fibrosis. However, activin A also directs the development of monocyte/macrophages, myeloid dendritic cells, and T cell subsets to promote type 2 and regulatory immune responses. The ability of both endogenous and exogenous follistatin to block the proinflammatory and profibrotic actions of activin A has led to interest in this binding protein as a potential therapeutic for limiting the severity of disease and to improve subsequent damage associated with inflammation and fibrosis. However, the ability of activin A to sculpt the subsequent immune response as well means that the full range of effects that might arise from blocking activin bioactivity will need to be considered in any therapeutic applications.

Comprehending the complex connection between PKCbeta, TAK1, and IKK in BCR signaling

The transcription factor nuclear factor-kappaB (NF-kappaB) contributes to many events in the immune system. Characterization of NF-kappaB has facilitated our understanding of immune cell differentiation, survival, proliferation, and effector functions. Intense research continues to elucidate the role of NF-kappaB, which is shared in several receptor signaling pathways, such as Toll-like receptors, the tumor necrosis factor receptor, and antigen receptors. The specificity of cellular responses emanating from stimulation of these receptors is determined by post-translational modification, or 'fine tuning', which regulates spatiotemporal dynamics of downstream signaling. Understanding the fine tuning mechanisms of NF-kappaB activation is crucial for insights into biological regulation and for understanding how cellular signaling pathways are tightly regulated to guide different cell fates. In this review, we focus on recent advances that illuminate the fine tuning mechanisms of NF-kappaB activation by BCR signaling and have increased our comprehension of complex signal systems.

Liver X receptor agonists augment human islet function through activation of anaplerotic pathways and glycerolipid/free fatty acid cycling

Recent studies in rodent models suggest that liver X receptors (LXRs) may play an important role in the maintenance of glucose homeostasis and islet function. To date, however, no studies have comprehensively examined the role of LXRs in human islet biology. Human islets were isolated from non-diabetic donors and incubated in the presence or absence of two synthetic LXR agonists, TO-901317 and GW3965, under conditions of low and high glucose. LXR agonist treatment enhanced both basal and stimulated insulin secretion, which corresponded to an increase in the expression of genes involved in anaplerosis and reverse cholesterol transport. Furthermore, enzyme activity of pyruvate carboxylase, a key regulator of pyruvate cycling and anaplerotic flux, was also increased. Whereas LXR agonist treatment up-regulated known downstream targets involved in lipogenesis, we observed no increase in the accumulation of intra-islet triglyceride at the dose of agonist used in our study. Moreover, LXR activation increased expression of the genes encoding hormone-sensitive lipase and adipose triglyceride lipase, two enzymes involved in lipolysis and glycerolipid/free fatty acid cycling. Chronically, insulin gene expression was increased after treatment with TO-901317, and this was accompanied by increased Pdx-1 nuclear protein levels and enhanced Pdx-1 binding to the insulin promoter. In conclusion, our data suggest that LXR agonists have a direct effect on the islet to augment insulin secretion and expression, actions that should be considered either as therapeutic or unintended side effects, as these agents are developed for clinical use.

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.

Combined expression of transcription factors induces AR42J-B13 cells to differentiate into insulin-producing cells

Neurogenin 3 (Ngn3) is a transcription factor that regulates an initial step of differentiation from uncommitted pancreatic progenitors into endocrine cells. Additional transcription factors are required for complete differentiation into mature pancreatic beta cells. In this study, we established an in vitro model system of beta-cell differentiation by adenovirus-mediated expression of several transcription factors in AR42J-B13 cells, a pancreatic progenitor-like cell line derived from exocrine pancreas. Exogenous expression of Ngn3 in AR42J-B13 cells induced expression of Nkx2.2, Pax4, and Pax6, which are all essential for beta-cell differentiation in mouse embryos. However, Ngn3 did not induce more downstream regulators of beta-cell differentiation, Nkx6.1 and Maf A. Coexpression of Nkx6.1 and Ngn3 induced endogenous expression of the insulin 2 gene, while coexpression of Maf A and Ngn3 induced both insulin 1 and 2 genes in AR42J-B13 cells. Our data demonstrated that Ngn3 expressed together with Nkx6.1 or MafA induces AR42J-B13 cells to differentiate into insulin-producing cells, supporting the use of these cells as a model system for studying beta-cell differentiation in vitro.

Impact of oxidative stress and peroxisome proliferator-activated receptor gamma coactivator-1alpha in hepatic insulin resistance

OBJECTIVE

Recent studies identified accumulation of reactive oxygen species (ROS) as a common pathway causing insulin resistance. However, whether and how the reduction of ROS levels improves insulin resistance remains to be elucidated. The present study was designed to define this mechanism.

RESEARCH DESIGN AND METHODS

We investigated the effect of overexpression of superoxide dismutase (SOD)1 in liver of obese diabetic model (db/db) mice by adenoviral injection.

RESULTS

db/db mice had high ROS levels in liver. Overexpression of SOD1 in liver of db/db mice reduced hepatic ROS and blood glucose level. These changes were accompanied by improvement in insulin resistance and reduction of hepatic gene expression of phosphoenol-pyruvate carboxykinase and peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha), which is the main regulator of gluconeogenic genes. The inhibition of hepatic insulin resistance was accompanied by attenuation of phosphorylation of cAMP-responsive element-binding protein (CREB), which is a main regulator of PGC-1alpha expression, and attenuation of Jun NH(2)-terminal kinase (JNK) phosphorylation. Simultaneously, overexpression of SOD1 in db/db mice enhanced the inactivation of forkhead box class O1, another regulator of PGC-1alpha expression, without the changes of insulin-induced Akt phosphorylation in liver. In hepatocyte cell lines, ROS induced phosphorylation of JNK and CREB, and the latter, together with PGC-1alpha expression, was inhibited by a JNK inhibitor.

CONCLUSIONS

Our results indicate that the reduction of ROS is a potential therapeutic target of liver insulin resistance, at least partly by the reduced expression of PGC-1alpha.

p38 mitogen-activated protein kinase is critical for synergistic induction of the FSH(beta) gene by gonadotropin-releasing hormone and activin through augmentation of c-Fos induction and Smad phosphorylation

GnRH and activin independently and synergistically activate transcription of the FSH beta-subunit gene, the subunit that provides specificity and is the limiting factor in the synthesis of the mature hormone. This synergistic interaction, as determined by two-way ANOVA, is specific for FSHbeta and may, therefore, contribute to differential expression of the two gonadotropin hormones, which is critical for the reproductive cycle. We find that the cross-talk between the GnRH and activin signaling pathways occurs at the level of p38 MAPK, because the synergy is dependent on p38 MAPK activity, which is activated by GnRH, and activin cotreatment augments p38 activation by GnRH. Both the Smad and activator protein-1 binding sites on the FSHbeta promoter are necessary and sufficient for synergy. After cotreatment, Smad 3 proteins are more highly phosphorylated on the activin-receptor signaling-dependent residues on the C terminus than with activin treatment alone, and c-Fos is more highly expressed than with GnRH treatment alone. Inhibition of p38 by either of two different inhibitors or a dominant-negative p38 kinase abrogates synergy on FSHbeta expression, reduces c-Fos induction by GnRH, and prevents the further increase in c-Fos levels that occurs with cotreatment. Additionally, p38 is necessary for maximal Smad 3 C-terminal phosphorylation by activin treatment alone and for the further increase caused by cotreatment. Thus, p38 is the pivotal signaling molecule that integrates GnRH and activin interaction on the FSHbeta promoter through higher induction of c-Fos and elevated Smad phosphorylation.

Effects of activin A on pancreatic ductal cells in streptozotocin-induced diabetic rats

BACKGROUND

The shortage of islets for transplantation has led to find alternative insulin producing cells. Pancreatic progenitor cells in the duct have the potential to grow and differentiate into endocrine cells. In this study, we examined whether activin A can promote the expansion and/or differentiation of ductal cells into insulin-producing cells.

METHODS

Pancreatic ductal cells were treated with activin A for differentiation into endocrine cells, and transplanted into the renal subcapsular space of streptozotocin (STZ)-induced diabetic rats. The identity of the endocrine cells was confirmed by immunostaining and analysis of the expression of transcription factors and endocrine genes by reverse-transcriptase polymerase chain reaction.

RESULTS

Activin A treatment significantly increased the DNA synthesis and the expression of insulin I, insulin II, PDX-1, Nkx 6.1, Glut-2, Pax-4, Pax-6, and Ngn-3. De novo synthesis of insulin in activin A-treated ductal cells was observed by the immunocytochemical detection of C-peptide and the differentiated ductal cells secreted significantly increased amount of insulin compared to nontreated ductal cells in response to glucose stimulation. When activin A-treated ductal cells were transplanted on STZ-induced diabetic rats, blood glucose levels were normalized and the removal of the transplanted kidney resulted in return to hyperglycemia.

CONCLUSIONS

The pancreatic ductal cells could be efficiently differentiated into insulin secreting cells by activin A treatment in vitro and normalize hyperglycemia in vivo.

Conophylline and betacellulin-delta4: an effective combination of differentiation factors for pancreatic beta cells

Conophylline and betacellulin-delta4 reproduce differentiation-inducing activity of activin A and betacellulin, respectively. We examined the effect of conophylline and betacellulin-delta4 on beta cell differentiation. In AR42J cells, conophylline and betacellulin-delta4 converted them into insulin-producing cells. Cells treated with conophylline and betacellulin-delta4 continued to grow after differentiation. Thus, cell number and insulin content were much greater compared to cells treated with activin A and betacellulin. Furthermore, cells treated with conophylline and betacellulin-delta4 secreted insulin in response to glucose. Likewise, conophylline and betacellulin-delta4 converted pancreatic ductal cells into insulin-producing cells. Insulin content, cell number and glucose-evoked insulin secretion were significantly greater than those in cells treated with activin A and betacellulin. Transplantation of pseudoislets prepared using ductal cells treated with conophylline and betacellulin-delta4 was able to reduce effectively the plasma glucose concentration in streptozotocin-treated nude mice. Conophylline and betacellulin-delta4 are effective in inducing differentiation of beta cells from progenitors.

Amelioration of glucose tolerance by hepatic inhibition of nuclear factor kappaB in db/db mice

AIMS/HYPOTHESIS

Recent studies have identified the involvement of inhibitor IkappaB kinase (IKK) in the pathogenesis of insulin resistance. To investigate the mechanism involved, we examined the role of nuclear factor kappaB (NF-kappaB), the distal target of IKK, in hepatic glucose metabolism.

METHODS

To inhibit NF-kappaB activity, db/db mice were infected with adenovirus expressing the IkappaBalpha super-repressor.

RESULTS

The IkappaBalpha super-repressor adenovirus infection caused a moderate reduction of NF-kappaB activity in liver. The treatment was associated with improved glucose tolerance, reduction in the serum insulin level, and increased hepatic triacylglycerol and glycogen contents, but had no effect on insulin-stimulated phosphorylation of Akt. On the other hand, quantification of mRNA in the liver revealed marked reduction of expression of gluconeogenic genes, such as those encoding phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase, concurrent with reduced expression of gene encoding peroxisome proliferator-activated receptor gamma coactivator-1alpha (PPARGC1A, also known as PGC-1alpha). Furthermore, the production of super-repressor IkappaBalpha suppressed the increase in blood glucose level after pyruvate injection.

CONCLUSIONS/INTERPRETATION

Our results indicate that moderate inhibition of NF-kappaB improved glucose tolerance through decreased gluconeogenesis associated with reduced PGC-1alpha gene expression in db/db mice, and suggest that inhibition of NF-kappaB activity in liver is a potentially suitable strategy for the normalisation of blood glucose concentration in type 2 diabetes.

Repetitive fluctuations in blood glucose enhance monocyte adhesion to the endothelium of rat thoracic aorta

BACKGROUND

The aim of this study was to elucidate the effect of repetitive fluctuations in blood glucose concentrations on monocyte adhesion to the aortic endothelium.

METHODS AND RESULTS

Nonobese type 2 diabetes, Goto-Kakizaki (GK) rats were fed twice daily to induce repetitive postprandial glucose spikes. Then, we compared the number of monocytes adherent to the endothelium of thoracic aorta in these rats with that in rats fed ad libitum. To suppress the glucose spikes, rats were injected with an inhibitor of sodium-glucose transporter, phloridzin, just before each meal for 12 weeks. GK rats fed twice daily showed significantly lower HbA1c than GK rats fed ad libitum. However, the former group showed markedly higher number of monocytes adherent to the endothelium than the latter, together with increased arterial intimal thickening. Phloridzin significantly reduced the number of adherent monocytes in GK rats fed twice daily.

CONCLUSIONS

Our data demonstrated that repetitive postprandial fluctuation in glucose concentration evokes monocyte adhesion to endothelial cells that was worse than that induced by stable hyperglycemia in vivo. Suppression of such fluctuations efficiently suppressed monocyte adhesion to the aortic endothelium.

Activin signaling and its role in regulation of cell proliferation, apoptosis, and carcinogenesis

Activins, cytokine members of the transforming growth factor-beta superfamily, have various effects on many physiological processes, including cell proliferation, cell death, metabolism, homeostasis, differentiation, immune responses endocrine function, etc. Activins interact with two structurally related serine/threonine kinase receptors, type I and type II, and initiate downstream signaling via Smads to regulate gene expression. Understanding how activin signaling is controlled extracellularly and intracellularly would not only lead to more complete understanding of cell growth and apoptosis, but would also provide the basis for therapeutic strategies to treat cancer and other related diseases. This review focuses on the recent progress on activin-receptor interactions, regulations of activin signaling by ligand-binding proteins, receptor-binding proteins, and nucleocytoplasmic shuttling of Smad proteins.

In vivo disruption of TGF-beta signaling by Smad7 leads to premalignant ductal lesions in the pancreas

TGF-beta has been postulated to play an important role in the development of pancreatic cancers. More than 50% of human pancreatic cancers bear mutations of Sma- and Mad-related protein (Smad) 4, a critical protein required for TGF-beta signaling. To evaluate the in vivo function of TGF-beta in the development of pancreatic cancers, we generated a transgenic mouse model with pancreas-specific expression of Smad7, a specific inhibitor of TGF-beta signaling. Through the use of elastase I promoter, we directed the tissue specific expression of exogenous Smad7. Consistently, the exogenous Smad7 was detected only in the pancreas in the transgenic mice, and, furthermore, phosphorylation of Smad2 was blocked in the pancreatic tissues. At 6 months of age, most transgenic animals developed premalignant ductal lesions in the pancreas, with characteristics of pancreatic intraepithelial neoplasia (PanIN), a precursor to invasive pancreatic cancers. The premalignant lesions of the pancreas were accompanied by accelerated proliferation of the ductal epithelium and acinar cells, as well as increased fibrosis around the ductal lesions. This study not only demonstrated that in vivo inactivation of TGF-beta signaling is implicated in the development of early stage of pancreatic cancers, but also provided a promising animal model useful for the investigation and intervention of pancreatic cancers in humans.

Activin A-induced expression of PAX4 in AR42J-B13 cells involves the increase in transactivation of E47/E12

Pax4 is a paired-homeodomain containing transcriptional factor that controls the differentiation of pancreatic beta cells. The aim of this study was to investigate the mechanism of PAX4 expression by activin A. By reporter gene analysis using AR42J-B13 cells, in which treatment with activin A induced PAX4 mRNA expression, we identified that a short sequence located approximately 1930 bp upstream of the transcriptional start site is essential for activin A induced PAX4 promoter activation. This region contains an E box and binding sites for hepatocyte nuclear factor (HNF)-1alpha. Mutation introduced in each binding site markedly reduced activin A responsiveness. It has been reported that HNF-1alpha synergizes with basic helix-loop-helix (bHLH) proteins in activating the PAX4 promoter, and we demonstrated that activin A strongly enhanced the functional activity of E47/E12 without the increase in its binding ability. In addition, suppression of E47/E12 expression in AR42J-B13 cells using siRNA oligonucleotides results in the significant decrease in the intrinsic activin A-induced PAX4 expression. Our results suggest that activin A enhances PAX4 expression by enhanced transactivation of E47/E12 proteins and might result in a cumulative transactivation of the promoter.

Transforming growth factor beta-activated kinase 1 is a key mediator of ovine follicle-stimulating hormone beta-subunit expression

FSH, a key regulator of gonadal function, contains a beta-subunit (FSHbeta) that is transcriptionally induced by activin, a member of the TGFbeta-superfamily. This study used 4.7 kb of the ovine FSHbeta-promoter linked to luciferase (oFSHbetaLuc) plus a well-characterized activin-responsive construct, p3TPLuc, to investigate the hypothesis that Smad3, TGFbeta-activated kinase 1 (TAK1), or both cause activin-mediated induction of FSH. Overexpression of either Smad3 or TAK1 induced oFSHbetaLuc in gonadotrope-derived LbetaT2 cells as much as activin itself. Induction of p3TPLuc by activin is known to require Smad3 activation in many cell types, and this was true in LbetaT2 cells, where 10-fold induction by activin (2-8 h after activin treatment) was blocked more than 90% by two dominant negative (DN) inhibitors of Smad3 [DN-Smad3 (3SA) and DN-Smad3 (D407E)]. By contrast, 6.5-fold induction of oFSHbetaLuc by activin (10-24 h after activin treatment) was not blocked by either DN-Smad inhibitor, suggesting that activation of Smad3 did not trigger induction of oFSHbetaLuc. By contrast, inhibition of TAK1 by a DN-TAK1 construct led to a 50% decrease in activin-mediated induction of oFSHbetaLuc, and a specific inhibitor of TAK1 (5Z-7-Oxozeanol) blocked induction by 100%, indicating that TAK1 is necessary for activin induction of oFSHbetaLuc. Finally, inhibiting p38-MAPK (often activated by TAK1) blocked induction of oFSHbetaLuc by 60%. In conclusion, the data presented here indicate that activation of TAK1 (and probably p38-MAPK), but not Smad3, is necessary for triggering induction of oFSHbeta by activin.

Short-term Stimulation Studies on Neonatal Pig Pancreatic Duct-derived Cell Monolayers

Short-term stimulation with insulinotropic factors may induce morphologic and functional changes in primary ductal cell cultures as a potential source of stem cells. We sought to assess the capacity of hepatocyte growth factor (HGF) to induce expression and maturation of proteins--PDX-1 and GLUT-2--and the subsequent beta-cell secretory profiles. HGF, which is involved in pancreatic development, may induce islet beta-cell neogenesis. Primary ductal cell monolayers were cultured in Click's + FBS 10% at 37 degrees C until tissue confluence. The medium was enriched with HGF (10 ng/mL for different periods); controls were treated for similar times with normal culture medium. At the end of the study, three-dimensional islet-like cell aggregates were observed in both conditions. In all conditions immunostaining studies showed positivity for the major endocrine-phenotype cell markers: insulin, PDX-1, glucokinase, and GLUT-2. Furthermore, treatment with HGF for short periods induced the expression of a functionally active, phosphorylated isoform of PDX-1. Finally, we observed that under basal conditions the cells initially and progressively released proinsulin throughout 5 days in all settings. Thereafter proinsulin was gradually replaced by insulin in the culture medium, reflecting a maturation progress. This pattern of insulin maturation and release was more evident when the cells were continuously stimulated with HGF for 12 days. The employed stimuli seemed to differentiate the original ductal cell layers toward endocrine cell phenotypes that synthesize and release proinsulin and subsequently insulin. HGF seems to provide a more efficient differentiation.

Regulation of p38 MAPK by MAPK kinases 3 and 6 in fibroblast-like synoviocytes

The p38 MAPK signal transduction pathway is a key regulator of IL-1 and TNF-alpha production in rheumatoid arthritis. Previous studies demonstrated that upstream MAPK kinases (MKK3 and MKK6) that regulate p38 are activated in rheumatoid arthritis synovium. However, their functional relevance in fibroblast-like synoviocytes (FLS) has not been determined. To investigate the relative contribution of MKK3 and MKK6 to p38 activation, the effect of dominant-negative (DN) MKK3 and MKK6 constructs on cultured FLS was evaluated. Cultured FLS were stimulated with medium or IL-1beta, and immunoblotting was performed. In some experiments, cells were lysed and immunoprecipitated with anti-p38 Ab, followed by in vitro kinase assay with [gamma-(32)P]ATP and GST-activating transcription factor-2 as substrate. IL-1beta rapidly induced p38 phosphorylation in cells transfected with empty vector (pcDNA3.1), but was inhibited by 25% in cells expressing DN MKK3 or DN MKK6. Cotransfection with both DN plasmids decreased phospho-p38 by almost 75%. In vitro kinase assays on IL-1-stimulated FLS also showed that the combination of DN MKK3 and DN MKK6 markedly decreased kinase activity compared with empty vector or the individual DN plasmids. Furthermore, IL-1beta-induced IL-8, IL-6, and matrix metalloproteinase-3 protein production was significantly inhibited in DN MKK3/DN MKK6-transfected cells. The constructs had no effect on the respective mediator mRNA levels. These data demonstrate that MKK3 and MKK6 make individual contributions to p38 activation in FLS after cytokine stimulation, but that both must be blocked for maximum inhibition.

Expression of progenitor cell markers during expansion of sorted human pancreatic beta cells

Functional pancreatic beta cell mass is dynamic and although fully differentiated, beta cells are capable of reentering the cell cycle upon appropriate stimuli. Stimulating regeneration-competent cells in situ is clearly the most desirable way to restore damaged tissue. Regeneration by dedifferentiation and transdifferentiation is a potential source of cells exhibiting a more developmentally immature phenotype and a wide differentiation potential. In this context and to gain a better understanding of the transformation induced in human beta cells during forced in vitro expansion, we focused on identifying differences in gene expression along with phenotypical transformation between proliferating and quiescent human beta cells. FACS-purified beta cells from three different human pancreata were cultured during 3-4 months (8-10 subcultures) on HTB-9 cell matrix with hepatocyte growth factor. Gene expression profiling was performed on cells from each subculture on "in-house" pancreas-specific microarrays consisting of 218 genes and concomitant morphological transformations were studied by immunocytochemistry. Immunocytochemical studies indicated a shift from epithelial to neuroepithelial cell phenotype, including progenitor cell features such as protein gene product 9.5 (PGP 9.5), Reg, vimentin, and neurogenin 3 protein expression. The expression of 49 genes was downregulated, including several markers of endocrine differentiation while 76 were induced by cell expansion including several markers of progenitor cells. Their pattern also argues for the transdifferentiation of beta cells into progenitor cells, demonstrating neuroepithelial features and overexpressing both PBX1, a homeodomain protein that can bind as a heterodimer with PDX1 and could switch the nature of its transcriptional activity, and neurogenin 3, a key factor for the generation of endocrine islet cells. Our study of the machinery that regulates human beta cell expansion and dedifferentiation may help elucidate some of the critical genes that control the formation of adult pancreatic progenitor cells and hence design targets to modify their expression in view of the production of insulin-secreting cells.

GDF11 modulates NGN3+ islet progenitor cell number and promotes beta-cell differentiation in pancreas development

Identification of endogenous signals that regulate expansion and maturation of organ-specific progenitor cells is a major goal in studies of organ development. Here we provide evidence that growth differentiation factor 11 (GDF11), a member of the TGF-beta ligand family, governs the number and maturation of islet progenitor cells in mouse pancreas development. Gdf11 is expressed in embryonic pancreatic epithelium during formation of islet progenitor cells that express neurogenin 3. Mice deficient for Gdf11 harbor increased numbers of NGN3+ cells, revealing that GDF11 negatively regulates production of islet progenitor cells. Despite a marked expansion of these NGN3+ islet progenitors, mice lacking Gdf11 have reduced beta-cell numbers and evidence of arrested beta-cell development, indicating that GDF11 is also required for beta-cell maturation. Similar precursor and islet cell phenotypes are observed in mice deficient for SMAD2, an intracellular signaling factor activated by TGF-beta signals. Our data suggest that Gdf11 and Smad2 regulate islet cell differentiation in parallel to the Notch pathway, which previously has been shown to control development of NGN3+ cells. Thus, our studies reveal mechanisms by which GDF11 regulates the production and maturation of islet progenitor cells in pancreas development.

Inhibition of activin signaling induces pancreatic epithelial cell expansion and diminishes terminal differentiation of pancreatic beta-cells

Activins regulate the growth and differentiation of a variety of cells. During pancreatic islet development, activins are required for the specialization of pancreatic precursors from the gut endoderm during midgestation. In this study, we probed the role of activin signaling during pancreatic islet cell development and regeneration. Indeed, we found that both activins and activin receptors are upregulated in duct epithelial cells during islet differentiation. Interestingly, the expression of endogenous cellular inhibitors of activin signaling, follistatin and Cripto, were also found to be augmented. Inhibition of activins significantly enhanced survival and expansion of pancreatic epithelial cells but decreased the numbers of differentiated beta-cells. Our results suggest that the homeostasis of growth and terminal differentiation requires a precise context-dependent regulation of activin signaling. Follistatin participates in this process by promoting expansion of precursor cells during pancreas growth.

Reduction of insulin-stimulated glucose uptake by peroxynitrite is concurrent with tyrosine nitration of insulin receptor substrate-1

Inducible nitric oxide synthetase plays an essential role in insulin resistance induced by a high-fat diet. The reaction of nitric oxide with superoxide leads to the formation of peroxynitrite (ONOO-), which can modify several proteins. In this study, we investigated whether peroxynitrite impairs insulin-signalling pathway. Our experiments showed that 3-(4-morpholinyl)sydnonimine hydrochloride (SIN-1), a constitutive producer of peroxynitrite, dose-dependently inhibited insulin-stimulated glucose uptake. While SIN-1 did not affect the insulin receptor protein level and tyrosine phosphorylation, it reduced the insulin receptor substrate-1 (IRS-1) protein level, and IRS-1 associated phosphatidylinositol-3 kinase (PI-3 kinase) activity. Although SIN-1 did not induce Ser307 phosphorylation of IRS-1, tyrosine nitration of IRS-1 was detected in SIN-1-treated-Rat1 fibroblasts expressing human insulin receptors. Mass spectrometry showed that peroxynitrite induced at least four nitrated tyrosine residues in rat IRS-1, including Tyr939, which is critical for association of IRS-1 with the p85 subunit of PI-3 kinase. Our results suggest that peroxynitrite reduces the IRS-1 protein level and decreases phosphorylation of IRS-1 concurrent with nitration of its tyrosine residues.

TAB3, a new binding partner of the protein kinase TAK1

We have identified a new binding partner of the TGFbeta (transforming growth factor-beta)-activated protein kinase (TAK1), termed TAB3 (TAK1-binding protein-3), which shares 48% amino acid sequence identity with TAB2. Our results indicate that two distinct TAK1 complexes are present in cells. One comprises TAK1 complexed with TAB1 and TAB2, and the other TAK1 complexed with TAB1 and TAB3. Both complexes are activated in response to tumour necrosis factor-alpha or interleukin-1 in human epithelial KB cells or bacterial lipopolysaccharide in RAW264.7 macrophages, and are subject to feedback control by stress-activated protein kinase 2a (SAPK2a; also called p38alpha). The electrophoretic mobility of TAB2 and TAB3 decreases in response to these agonists or osmotic shock, and is reversed by treatment with protein phosphatase-1. The decrease in mobility of TAB3 is prevented if the cells are incubated with SB 203580 before stimulation, but treatment with SB 203580 produces forms of TAB2 with a mobility intermediate between that observed for TAB2 in unstimulated and stimulated cells. Similar results were obtained in embryonic fibroblasts from mice deficient in SAPK2a/p38alpha. Our results indicate that TAB3 is phosphorylated via the SAPK2a/p38alpha pathway, whereas TAB2 is phosphorylated at two or more sites by both an SAPK2a/p38alpha-dependent and an SB 203580-independent kinase. The SAPK2a/p38alpha-mediated phosphorylation of TAB2 and TAB3 may contribute to the SAPK2a/p38alpha-mediated feedback control of TAK1 activity that also involves the phosphorylation of TAB1. We also show that the agonist-induced activation of TAK1 complexes requires the phosphorylation of the TAK1 catalytic subunit at a serine/threonine residue(s).

Gene regulatory factors in pancreatic development

The intensity of research on pancreatic development has increased markedly in the past 5 years, primarily for two reasons: we now know that the insulin-producing beta-cells normally arise from an endodermally derived, pancreas-specified precursor cell, and successful transplants of islet cells have been performed, relieving patients with type I diabetes of symptoms for extended periods after transplantation. Combining in vitro beta-cell formation from a pancreatic biopsy of a diabetic patient or from other stem-cell sources followed by endocrine cell transplantation may be the most beneficial route for a future diabetes therapy. However, to achieve this, a thorough understanding of the genetic components regulating the development of beta-cells is required. The following review discusses our current understanding of the transcription factor networks necessary for pancreatic development and how several genetic interactions coming into play at the earliest stages of endodermal development gradually help to build the pancreatic organ. Developmental Dynamics 229:176-200, 2004.