Mechanisms of glucose-induced expression of pancreatic-derived factor in pancreatic beta-cells

Contribution of Liver and Pancreatic Islet Crosstalk to β-Cell Function/Dysfunction in the Presence of Fatty Liver

Tissue-to-tissue crosstalk regulates organ function, according to growing data. This phenomenon is relevant for pancreatic β-cells and the liver, as both tissues are involved in glucose homeostasis and lipid metabolism. The ability to fine-tune regulation and adaptive responses is enabled through communication between pancreatic β-cells and the liver. However, the crosstalk between both tissues changes when metabolic dysregulation is present. Factors and cargo from extracellular vesicles (EVs) released by liver and pancreatic β-cells that reach the circulation form the words of this interaction. The molecules released by the liver are called hepatokines and are usually secreted in response to the metabolic state. When hepatokines reach the pancreatic islets several mechanisms are initiated for their protection or damage. In the case of the crosstalk between pancreatic β-cells and the liver, only one factor has been found to date. This protein, pancreatic derived factor (PANDER) has been proposed as a novel linker between insulin resistance (IR) and type 2 diabetes mellitus (T2D) and could be considered a biomarker for non-alcoholic fatty liver disease (NAFLD) and T2D. Furthermore, the cargo released by EVs, mainly miRNAs, plays a significant role in this crosstalk. A better knowledge of the crosstalk between liver and pancreatic β-cells is essential to understand both diseases and it could lead to better prevention and new therapeutic options.

FAM3 gene family: A promising therapeutical target for NAFLD and type 2 diabetes

Non-alcoholic fatty liver disease (NAFLD) and diabetes are severe public health issues worldwide. The Family with sequence similarity 3 (FAM3) gene family consists of four members designated as FAM3A, FAM3B, FAM3C and FAM3D, respectively. Recently, there had been increasing evidence that FAM3A, FAM3B and FAM3C are important regulators of glucose and lipid metabolism. FAM3A expression is reduced in the livers of diabetic rodents and NAFLD patients. Hepatic FAM3A restoration activates ATP-P2 receptor-Akt and AMPK pathways to attenuate steatosis and hyperglycemia in obese diabetic mice. FAM3C expression is also reduced in the liver under diabetic condition. FAM3C is a new hepatokine that activates HSF1-CaM-Akt pathway and represses mTOR-SREBP1-FAS pathway to suppress hepatic gluconeogenesis and lipogenesis. In contrast, hepatic expression of FAM3B, also called PANDER, is increased under obese state. FAM3B promotes hepatic lipogenesis and gluconeogenesis by repressing Akt and AMPK activities, and activating lipogenic pathway. Under obese state, the imbalance among hepatic FAM3A, FAM3B and FAM3C signaling networks plays important roles in the pathogenesis of NAFLD and type 2 diabetes. This review briefly discussed the latest research progress on the roles and mechanisms of FAM3A, FAM3B and FAM3C in the regulation of hepatic glucose and lipid metabolism.

Pancreatic-derived factor impaired glucagon-like Peptide-1 production from GLUTag enterendorine L-cell line and intestines

PURPOSE

Pancreatic-derived factor (PANDER) is a pancreatic islet-specific cytokine that co-secretes with insulin. However, its biological function remains largely unknown. We have recently shown that the intestine might be its novel target tissue. The aim of this study was to clarify whether PANDER impacts the production of glucagon-like peptide-1 (GLP-1).

METHODS

We treated GLUTag cells from the mouse intestine L cell line with recombinant PANDER protein and hepatic overexpression of PANDER in an obese murine model.

RESULTS

In GLUTag cells, PANDER exposure led to decreased proglucagon gene mRNA expression and GLP-1 secretion without affecting cell viability or caspase-3 activation. Overexpression of PANDER in mice induced glucose intolerance and impaired glucose-stimulated GLP-1 secretion Moreover, PANDER blocked insulin-induced GLP-1 secretion by inhibiting the insulin signalling-Wnt pathway and directly inhibited the cAMP/PKA pathway.

CONCLUSIONS

Our findings indicate that intestinal L cells are responsive to PANDER, and elevated PANDER levels impair GLP-1 production in vitro and in vivo.

FAM3B mediates high glucose-induced vascular smooth muscle cell proliferation and migration via inhibition of miR-322-5p

The proliferation and migration of vascular smooth muscle cells (VSMCs) play an essential role during the development of cardiovascular diseases (CVDs). While many factors potentially contribute to the abnormal activation of VSMCs, hyperglycemia is generally believed to be a major causative factor. On the other hand, FAM3B (named PANDER for its secretory form) is a uniquely structured protein strongly expressed within and secreted from the endocrine pancreas. FAM3B is co-secreted with insulin from the β-cell upon glucose stimulation and regulates glucose homeostasis. In the present study, we sought to determine the roles of FAM3B in the regulation of VSMC physiology, especially under the hyperglycemic condition. We found that FAM3B expression was induced by hyperglycemia both in vivo and in vitro. FAM3B knockdown inhibited, whereas FAM3B overexpression accelerated VSMC proliferation and migration. At the molecular level, FAM3B inhibited miR-322-5p expression, and enforced expression of miR-322-5p antagonized FAM3B-induced VSMC proliferation and migration, suggesting that FAM3B facilitated VSMC pathological activation via miR-322-5p. Taken together, FAM3B mediates high glucose-induced VSMC proliferation and migration via inhibition of miR-322-5p. Thus, FAM3B may therefore serve as a novel therapeutic target for diabetes-related CVDs.

Association of serum pancreatic derived factor (PANDER) with beta-cell dysfunction in type 2 diabetes mellitus

AIM

Beta-cell dysfunction is the critical determinant for type 2 diabetes. The novel PANcreatic DERived factor (PANDER) has been identified as interesting islet-secreted cytokine that might be involved in beta-cell dysfunction, a role that has n"ot been clinically elucidated yet. Therefore, this study was designed to study the potential clinical association of this cytokine with beta-cell dysfunction in type 2 diabetes.

METHODS

Anthropometric parameters, routine biochemical markers and serum levels of PANDER were measured in 63 diabetic subjects including; recently diagnosed type 2 diabetic patients with duration of diabetes ≤6months and long-standing type 2 diabetic patients with duration of diabetes ≥5years then compared to 16 healthy control volunteers. Proinsulin, C-peptide, insulin and PANDER were measured by ELISA. Beta-cell dysfunction was assessed by HOMA2-%β, proinsulin, proinsulin-to-insulin (PI/I) ratio and proinsulin-to-C-peptide (PI/C-pep) ratio. Relations among various parameters were studied using simple and multiple linear regressions.

RESULTS

Serum PANDER levels were found to be significantly elevated in long-standing diabetics as compared to recently diagnosed diabetics and controls. In addition, PANDER was found to be significantly correlated negatively to HOMA2-%β, as well as positively to proinsulin, PI/I and PI/C-pep ratios.

CONCLUSION

PANDER is associated with beta-cell dysfunction in diabetic patients.

Quantitative proteomic profiling reveals hepatic lipogenesis and liver X receptor activation in the PANDER transgenic model

PANcreatic-DERived factor (PANDER) is a member of a superfamily of FAM3 proteins modulating glycemic levels by metabolic regulation of the liver and pancreas. The precise PANDER-induced hepatic signaling mechanism is still being elucidated and has been very complex due to the pleiotropic nature of this novel hormone. Our PANDER transgenic (PANTG) mouse displays a selective hepatic insulin resistant (SHIR) phenotype whereby insulin signaling is blunted yet lipogenesis is increased, a phenomena observed in type 2 diabetes. To examine the complex PANDER-induced mechanism of SHIR, we utilized quantitative mass spectrometry-based proteomic analysis using Stable Isotope Labeling by Amino Acids in Cell Culture (SILAC) to reveal the global hepatic proteome differences within the PANTG under the metabolic states of fasting, fed and insulin-stimulated conditions. Proteomic analysis identified lipid metabolism as one of the top cellular functions differentially altered in all metabolic states. Differentially expressed proteins within the PANTG having a lipid metabolic role included ACC, ACLY, CD36, CYP7A1, FASN and SCD1. Central to the differentially expressed proteins involved in lipid metabolism was the predicted activation of the liver X receptor (LXR) pathway. Western analysis validated the increased hepatic expression of LXRα along with LXR-directed targets such as FASN and CYP7A1 within the PANTG liver. Furthermore, recombinant PANDER was capable of inducing LXR promoter activity in-vitro as determined by luciferase reporter assays. Taken together, PANDER strongly impacts hepatic lipid metabolism across metabolic states and may induce a SHIR phenotype via the LXR pathway.

Hepatic nutrient and hormonal regulation of the PANcreatic-DERived factor (PANDER) promoter

PANcreatic-DERived factor (PANDER, FAM3B) has been shown to regulate glycemic levels via interactions with both pancreatic islets and the liver. Although PANDER is predominantly expressed from the endocrine pancreas, recent work has provided sufficient evidence that the liver may also be an additional tissue source of PANDER production. At physiological levels, PANDER is capable of disrupting insulin signaling and promoting increased hepatic glucose production. As shown in some animal models, strong expression of PANDER, induced by viral delivery within the liver, induces hepatic steatosis. However, no studies to date have explicitly characterized the transcriptional regulation of PANDER from the liver. Therefore, our investigation elucidated the nutrient and hormonal regulation of the hepatic PANDER promoter. Initial RNA-ligated rapid amplification of cDNA ends identified a novel transcription start site (TSS) approximately 26 bp upstream of the PANDER translational start codon not previously revealed in pancreatic β-cell lines. Western evaluation of various murine tissues demonstrated robust expression in the liver and brain. Promoter analysis identified strong tissue-specific activity of the PANDER promoter in both human and murine liver-derived cell lines. The minimal element responsible for maximal promoter activity within hepatic cell lines was located between -293 and -3 of the identified TSS. PANDER promoter activity was inhibited by both insulin and palmitate, whereas glucose strongly increased expression. The minimal element was responsible for maximal glucose-responsive and basal activity. Co-transfection reporter assays, chromatin-immunoprecipitation (ChIP) and site-directed mutagenesis revealed that the carbohydrate-responsive element binding protein (ChREBP) increased PANDER promoter activity and interacted with the PANDER promoter. E-box 3 was shown to be critical for basal and glucose responsive expression. In summary, in-vitro and in-vivo glucose is a potent stimulator of the PANDER promoter within the liver and this response may be facilitated by ChREBP.

The effect and action mechanism of resveratrol on the vascular endothelial cell by high glucose treatment

To investigate the effect and action mechanism of resveratrol on the vascular endothelial cell by high glucose treatment. Primarily cultured human umbilical vein endothelial cells (HUVECs) were pretreated by resveratrol (0.2 μmol/L) and holding for 6 h, and then cultured in Dulbecco Modified Eagle Medium (DMEM) within 0.45 mmol/L of palmimte acid and 32.8 mmol/L of glucose, which is holding for 12 h. The cells were collected to analyze the expression of E-selected element. Supernatant of cultured cells, induced by 100 nmol/L insulin for 30 min, was used to analyze the nitric oxide content. Compared with normal control cells, the secretion of nitric oxide is stimulated by insulin decrease, however, the expression of E-selected element increased in HUVEC. Resveratrol treatment increased the secretion of nitric oxide stimulated by insulin and decreased the expression of E-selected element and partly counteracts the impairment of high glucose and palmitate acid on the function of endothelial cells. Resveratrol can improve and protect the function of high glucose and fatty acid cultured endothelial cell, and therefore may be a promising medicine in the prevention or therapy of diabetic macrovascular diseases.

F3MB(PANDER) decreases mice hepatic triglyceride and is associated with decreased DGAT1 expression

OBJECTIVE

Pancreatic-derived factor (PANDER, also named as FAM3B) is secreted by pancreatic α and β cells. Increasing evidence suggests that it may serve a hormonal function related to glycemic and lipid metabolism. In this study, we investigated the effects of PANDER overexpression on hepatic and adipose triglyceride metabolism in high-fat diet-fed male C57BL/6 mice.

METHODS

PANDER overexpression was achieved by tail-vein injection of recombinant Ad-PANDER and Ad-GFP injected mice served as a control. The TG metabolism in both groups were compared.

RESULTS

Adenoviral-mediated overexpression of PANDER did not affect body weight, food consumption, or liver enzymes. The triglyceride (TG) content of both liver and adipose tissue was significantly decreased in Ad-PANDER mice (liver: 6.16±1.89 mg/g vs. control 14.95±2.27 mg/g, P<0.05; adipose: 39.31±1.99 mg/100mg vs. 47.22±2.21 mg/100mg, P<0.05). The free fatty acid (FFA) content of adipose tissue in Ad-PANDER mice was also decreased (1.38±0.18 mg/g vs. 2.77±0.31 mg/g, P<0.01). The investigation of key enzymes of triglyceride hydrolysis and FFA oxidation in liver and adipose tissue showed that p-HSL/HSL was significantly increased and that DGAT1 gene and protein expression were significantly reduced in the liver of PANDER-overexpressing mice. PKA phosphorylation was also significantly increased in the livers of Ad-PANDER mice. No differences in ATGL, CPT1, ACOX1, or DGAT2 expression were observed.

CONCLUSION

Overexpression of PANDER is associated with observable decreases in TG, increases in PKA phosphorylation, and decreased DGAT1 expression, suggesting a possible interrelationship. The mechanisms by which this occurs remain to be elucidated.

Enhanced glucose tolerance in pancreatic-derived factor (PANDER) knockout C57BL/6 mice

Pancreatic-derived factor (PANDER; also known as FAM3B) is a uniquely structured protein strongly expressed within and secreted from the endocrine pancreas. PANDER has been hypothesized to regulate fasting and fed glucose homeostasis, hepatic lipogenesis and insulin signaling, and to serve a potential role in the onset or progression of type 2 diabetes (T2D). Despite having potentially pivotal pleiotropic roles in glycemic regulation and T2D, there has been limited generation of stable animal models for the investigation of PANDER function, and there are no models on well-established genetic murine backgrounds for T2D. Our aim was to generate an enhanced murine model to further elucidate the biological function of PANDER. Therefore, a pure-bred PANDER knockout C57BL/6 (PANKO-C57) model was created and phenotypically characterized with respect to glycemic regulation and hepatic insulin signaling. The PANKO-C57 model exhibited an enhanced metabolic phenotype, particularly with regard to enhanced glucose tolerance. Male PANKO-C57 mice displayed decreased fasting plasma insulin and C-peptide levels, whereas leptin levels were increased as compared with matched C57BL/6J wild-type mice. Despite similar peripheral insulin sensitivity between both groups, hepatic insulin signaling was significantly increased during fasting conditions, as demonstrated by increased phosphorylation of hepatic PKB/Akt and AMPK, along with mature SREBP-1 expression. Insulin stimulation of PANKO-C57 mice resulted in increased hepatic triglyceride and glycogen content as compared with wild-type C57BL/6 mice. In summary, the PANKO-C57 mouse represents a suitable model for the investigation of PANDER in multiple metabolic states and provides an additional tool to elucidate the biological function and potential role in T2D.

PANDER transgenic mice display fasting hyperglycemia and hepatic insulin resistance

PANcreatic-DERived factor (PANDER, FAM3B) is a novel protein that is highly expressed within the endocrine pancreas and to a lesser degree in other tissues. Under glucose stimulation, PANDER is co-secreted with insulin from the β-cell. Despite prior creation and characterization of acute hepatic PANDER animal models, the physiologic function remains to be elucidated from pancreas-secreted PANDER. To determine this, in this study, a transgenic mouse exclusively overexpressing PANDER from the endocrine pancreas was generated. PANDER was selectively expressed by the pancreatic-duodenal homeobox-1 (PDX1) promoter. The PANDER transgenic (PANTG) mice were metabolically and proteomically characterized to evaluate effects on glucose homeostasis, insulin sensitivity, and lipid metabolism. Fasting glucose, insulin and C-peptide levels were elevated in the PANTG compared with matched WT mice. Younger PANTG mice also displayed glucose intolerance in the absence of peripheral insulin sensitivity. Hyperinsulinemic-euglycemic clamp studies revealed that hepatic glucose production and insulin resistance were significantly increased in the PANTG with no difference in either glucose infusion rate or rate of disappearance. Fasting glucagon, corticosterones, resistin and leptin levels were also similar between PANTG and WT. Stable isotope labeling of amino acids in cell culture revealed increased gluconeogenic and lipogenic proteomic profiles within the liver of the PANTG with phosphoenol-pyruvate carboxykinase demonstrating a 3.5-fold increase in expression. This was matched with increased hepatic triglyceride content and decreased p-AMPK and p-acetyl coenzyme A carboxylase-1 signaling in the PANTG. Overall, our findings support a role of pancreatic β-cell-secreted PANDER in the regulation of hepatic insulin and lipogenenic signaling with subsequent impact on overall glycemia.

Family with sequence similarity 3 gene family and nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) comprises a disease spectrum ranging from simple steatosis (fatty liver) and nonalcoholic steatohepatitis to fibrosis and cirrhosis. NAFLD has become the leading cause of chronic liver diseases as well as liver-related morbidity and mortality worldwide. NAFLD is also associated with increased risk of cardiovascular diseases, hyperlipidemia, and type 2 diabetes. Insulin resistance in adipose tissues and the liver plays crucial roles in the progression of NAFLD. The family with sequence similarity 3 (FAM3) gene family is a cytokine-like gene family with four members designated FAM3A, FAM3B, FAM3C, and FAM3D, respectively. Increasing evidence suggests that the FAM3 gene family members are involved in the pathogenesis of NAFLD. In particular, FAM3B, also called pancreatic-derived factor, is an important regulator of glucose and lipid metabolism. In obesity status, increased expression and secretion of FAM3B in pancreatic islets and liver may induce lipid accumulation in the liver via the induction of hepatic insulin resistance and lipogenesis. FAM3A and FAM3D may also participate in the regulation of lipid and energy metabolism. In this brief review, we discussed the latest findings regarding the role of FAM3 gene family members, in particular FAM3B, in the pathogenesis of NAFLD.

Resveratrol protects vascular endothelial cells from high glucose-induced apoptosis through inhibition of NADPH oxidase activation-driven oxidative stress

INTRODUCTION

Hyperglycemia-induced oxidative stress has been implicated in diabetic vascular complications in which NADPH oxidase is a major source of reactive oxygen species (ROS) generation. Resveratrol is a naturally occurring polyphenol, which has vasoprotective effects in diabetic animal models and inhibits high glucose (HG)-induced oxidative stress in endothelial cells.

AIMS

We aimed to examine whether HG-induced NADPH oxidase activation and ROS production contribute to glucotoxicity to endothelial cells and the effect of resveratrol on glucotoxicity.

RESULTS

Using a murine brain microvascular endothelial cell line bEnd3, we found that NADPH oxidase inhibitor (apocynin) and resveratrol both inhibited HG-induced endothelial cell apoptosis. HG-induced elevation of NADPH oxidase activity and production of ROS were inhibited by apocynin, suggesting that HG induces endothelial cell apoptosis through NADPH oxidase-mediated ROS production. Mechanistic studies revealed that HG upregulated NADPH oxidase subunit Nox1 but not Nox2, Nox4, and p22(phox) expression through NF-κB activation, which resulted in elevation of NADPH oxidase activity and consequent ROS production. Resveratrol prevented HG-induced endothelial cell apoptosis through inhibiting HG-induced NF-κB activation, NADPH oxidase activity elevation, and ROS production.

CONCLUSIONS

HG induces endothelial cell apoptosis through NF-κB/NADPH oxidase/ROS pathway, which was inhibited by resveratrol. Our findings provide new potential therapeutic targets against brain vascular complications of diabetes.

Signal transduction via TRPM3 channels in pancreatic β-cells

Transient receptor potential melastatin 3 (TRPM3) channels are non-selective cation channels that are expressed in insulinoma cells and pancreatic β-cells. Stimulation of TRPM3 with the neurosteroid pregnenolone sulfate induces an intracellular signaling cascade, involving a rise in intracellular Ca(2)(+) concentration, activation of the protein kinases Raf and ERK, and a change in the gene expression pattern of the cells. In particular, biosynthesis of insulin is altered following activation of TRPM3 by pregnenolone sulfate. Moreover, a direct effect of TRPM3 stimulation on insulin secretion has been reported. The fact that stimulation of TRPM3 induces a signaling cascade that is very similar to the signaling cascade induced by glucose in β-cells suggests that TRPM3 may influence main functions of pancreatic β-cells. The view that TRPM3 represents an ionotropic steroid receptor of pancreatic β-cells linking insulin release with steroid hormone signaling is discussed.

A non-secretory form of FAM3B promotes invasion and metastasis of human colon cancer cells by upregulating Slug expression

FAM3B mRNA has been predicted to have multiple splicing forms. Its secretory form PANDER is decreased in gastric cancers with high invasiveness and metastasis. Here we found that its non-secretory form FAM3B-258 was highly expressed in most colon cancer cell lines and colorectal adenocarcinoma tissues but not hepatocellular carcinoma, lung carcinoma and pancreatic adenocarcinoma cell lines. Elevation of FAM3B-258 was associated with poor cancer cell differentiation. Stable overexpression of FAM3B-258 in colon cancer cells downregulated adhesion proteins, upregulated Slug and Cdc42, promoted cell migration and invasion in vitro and metastasis in nude mice. Slug mediated FAM3B-258-induced downregulation of adhesion molecules, upregulation of Cdc42, and invasion of colon cancer cells. The expression of FAM3B-258 in human colorectal adenocarcinomas was positively correlated with Slug. These results suggest that FAM3B-258 promotes colon cancer cell invasion and metastasis through upregulation of Slug.

Effect of PANDER in βTC6-cell lipoapoptosis and the protective role of exendin-4

Chronic exposure to high concentrations of saturated fatty acids, such as palmitic acid (PA), leads to apoptosis of pancreatic β-cells through the activation of the c-Jun N-terminal kinase (JNK) signaling pathway. This study of β-cell lipoapoptosis was designed to investigate the roles of pancreatic-derived factor (PANDER), a pro-apoptosis cytokine-like peptide, and exendin-4, a long-acting agonist of the hormone glucagon-like peptide-1 (GLP-1) receptor and anti-apoptosis factor. The glucose-sensitive mouse β-pancreatic cell line, βTC6, was used to investigate the mechanisms of PA-induced apoptosis. Twenty-four hours of PA exposure led to increased PANDER expression in a dose- and time-dependent manner, and significantly increased phosphorylation of JNK. Treatment with the JNK-specific inhibitor SP600125 reduced the PA-induced PANDER expression. After the 24h of PA exposure, cells also underwent marked apoptosis and showed increased activation of the apoptosis protease, caspase-3. The small interfering (si)RNA-mediated silencing of PANDER gene expression significantly reduced both of these effects. When PA-treated βTC6 cells were exposed to exogenous exendin-4, JNK activation was inhibited, PANDER expression was decreased, and the numbers of apoptotic cells were reduced. Collectively, these results demonstrated that the JNK-mediated signaling mechanism of PA-induced β-cell apoptosis involves up-regulated expression of PANDER and activation of caspase-3. Exendin-4 may protect against lipoapoptosis by interfering with the JNK-PANDER pathway.

Role of pancreatic-derived factor in type 2 diabetes: evidence from pancreatic β cells and liver

Pancreatic-derived factor (PANDER) is a cytokine-like protein that is highly expressed in pancreatic islets. In vitro, PANDER pretreatment or viral-mediated overexpression promotes apoptosis of islet β cells. Under conditions of insulin resistance, chronic hyperglycemia potently activates PANDER expression and stimulates the cosecretion of insulin and PANDER in β cells. PANDER binds to the liver cell membrane and induces insulin resistance, resulting in increased gluconeogenesis. Recently, PANDER was found to be expressed in rodent and human liver, and its expression is increased in the liver of diabetic mice and rats. Hepatic overexpression of PANDER promotes lipogenesis in the liver and induces insulin resistance in C57BL/6 mice, whereas the inactivation of hepatic PANDER markedly reduces steatosis, insulin resistance, and hyperglycemia in db/db mice. PANDER deficiency protects mice from high-fat-diet-induced hyperglycemia by decreasing gluconeogenesis in the liver. In summary, PANDER plays an important role in the progression of type 2 diabetes by negatively regulating islet β-cell function and insulin sensitivity in the liver.

Pregnenolone sulfate activates basic region leucine zipper transcription factors in insulinoma cells: role of voltage-gated Ca2+ channels and transient receptor potential melastatin 3 channels

The neurosteroid pregnenolone sulfate activates a signaling cascade in insulinoma cells involving activation of extracellular signal-regulated protein kinase and enhanced expression of the transcription factor Egr-1. Here, we show that pregnenolone sulfate stimulation leads to a significant elevation of activator protein-1 (AP-1) activity in insulinoma cells. Expression of the basic region leucine zipper (bZIP) transcription factors c-Jun and c-Fos is up-regulated in insulinoma cells and pancreatic β-cells in primary culture after pregnenolone sulfate stimulation. Up-regulation of a chromatin-embedded c-Jun promoter/luciferase reporter gene transcription in pregnenolone sulfate-stimulated insulinoma cells was impaired when the AP-1 binding sites were mutated, indicating that these motifs function as pregnenolone sulfate response elements. In addition, phosphorylation of cAMP response element (CRE)-binding protein is induced and transcription of a CRE-controlled reporter gene is stimulated after pregnenolone sulfate treatment, indicating that the CRE functions as a pregnenolone sulfate response element as well. Pharmacological and genetic experiments revealed that both L-type Ca(2+) channels and transient receptor potential melastatin 3 (TRPM3) channels are essential for connecting pregnenolone sulfate stimulation with enhanced AP-1 activity and bZIP-mediated transcription in insulinoma cells. In contrast, pregnenolone sulfate stimulation did not enhance AP-1 activity or c-Jun and c-Fos expression in pituitary corticotrophs that express functional L-type Ca(2+) channels but only trace amounts of TRPM3. We conclude that expression of L-type Ca(2+) channels is not sufficient to activate bZIP-mediated gene transcription by pregnenolone sulfate. Rather, additional expression of TRPM3 or depolarization of the cells is required to connect pregnenolone sulfate stimulation with enhanced gene transcription.

Upregulation of pancreatic derived factor (FAM3B) expression in pancreatic β-cells by MCP-1 (CCL2)

Pancreatic derived factor (PANDER, FAM3B) is a peptide mainly synthesized and secreted by pancreatic β-cells. PANDER is proposed to be involved in regulation of β-cell function under physiological conditions and impairment of β-cell function under pathological conditions. MCP-1 (CCL2) is expressed by normal pancreatic islets and has been implicated in inflammation related pancreatic disorders. We examined the effect of MCP-1 on PANDER expression by using murine pancreatic β-cell line MIN6 and pancreatic islets. We found that MCP-1 induced PANDER mRNA transcription and protein synthesis in MIN6 cells and islets. By using calcium chelator (EGTA); inhibitors for PKC (Go6976), MEK1/2 (PD98059) or c-Jun-N-terminal kinase (JNK) (SP600125); c-Jun dominant-negative construct; PANDER promoter luciferase constructs; and islets isolated from Fos knockout mice; we demonstrated that MCP-1 induced PANDER gene expression in β-cells through Ca(2+)-ERK1/2-AP-1 and PKC-JNK-AP-1 signaling pathways. Our findings suggest a new link between the endocrine and immune systems and provide useful information for further investigating the physiological functions of PANDER and its involvement in inflammation-related pancreatic disorders.

PANcreatic-DERived factor: novel hormone PANDERing to glucose regulation

PANcreatic-DERived factor (PANDER, FAM3B) is a member of the FAM3 family of cytokine molecules that were initially described in 2002. PANDER expression is primarily localized to the endocrine pancreas and is secreted from both pancreatic α and β-cells. Initial characterization of PANDER revealed a potential role in pancreatic islet apoptosis. However, recent animal models have indicated PANDER functions as a hormone by regulating glucose levels via interaction with both the liver and the endocrine pancreas. An understanding of the function of PANDER can further the insight into the mechanisms of glucose regulation and potentially provide additional therapeutic targets for the treatment of diabetes. This review details the supporting data demonstrating PANDER has a biological function in glycemic regulation.

MCP-1 upregulates amylin expression in murine pancreatic β cells through ERK/JNK-AP1 and NF-κB related signaling pathways independent of CCR2

Background

Amylin is the most abundant component of islet amyloid implicated in the development of type 2 diabetes. Plasma amylin levels are elevated in individuals with obesity and insulin resistance. Monocyte chemoattractant protein-1 (MCP-1, CCL2) is involved in insulin resistance of obesity and type 2 diabetes. We investigated the effect of MCP-1 on amylin expression and the underlying mechanisms with murine pancreatic β-cell line MIN6 and pancreatic islets.

Methodology/Principal Findings

We found that MCP-1 induced amylin expression at transcriptional level and increased proamylin and intermediate forms of amylin at protein level in MIN6 cells and islets. However, MCP-1 had no effect on the expressions of proinsulin 1 and 2, as well as prohormone convertase (PC) 1/3 and PC2, suggesting that MCP-1 specifically induces amylin expression in β-cells. Mechanistic studies showed that although there is no detectable CCR2 mRNA in MIN6 cells and islets, pretreatment of MIN6 cells with pertussis toxin inhibited MCP-1 induced amylin expression, suggesting that alternative Gi-coupled receptor(s) mediates the inductive effect of MCP-1. MCP-1 rapidly induced ERK1/2 and JNK phosphorylation. Inhibitors for MEK1/2 (PD98059), JNK (SP600125) or AP1 (curcumin) significantly inhibited MCP-1-induced amylin mRNA expression. MCP-1 failed to induce amylin expression in pancreatic islets isolated from Fos knockout mice. EMSA showed that JNK and ERK1/2 were involved in MCP-1-induced AP1 activation. These results suggest that MCP-1 induces murine amylin expression through AP1 activation mediated by ERK1/2 or JNK. Further studies showed that treatment of MIN6 cells with NF-κB inhibitor or overexpression of IκBα dominant-negative construct in MIN6 cells significantly inhibited MCP-1-induced amylin expression, suggesting that NF-κB related signaling also participates in MCP-1-induced murine amylin expression.

Conclusions/Significance

MCP-1 induces amylin expression through ERK1/2/JNK-AP1 and NF-κB related signaling pathways independent of CCR2. Amylin upregulation by MCP-1 may contribute to elevation of plasma amylin in obesity and insulin resistance.

TNF-α acutely upregulates amylin expression in murine pancreatic beta cells

AIMS/HYPOTHESIS

Amylin, a secretory protein mainly produced by pancreatic beta cells, is elevated in the circulation of patients with diseases related to acute and chronic inflammation, including acute pancreatitis, pancreas graft rejection, obesity and insulin resistance. TNF-α is involved in these disorders. We investigated the effect of TNF-α on amylin levels and the underlying mechanisms, using murine pancreatic beta cell line MIN6 and pancreatic islets.

METHODS

Amylin, proinsulin and prohormone convertase 1/3, 2 (Pc1/3, Pc2 [also known as Pcsk1/3 and Pcsk2, respectively]) mRNA levels, and amylin promoter and nuclear factor κB (NF-κB) activation were examined by real-time PCR and luciferase reporter assay, respectively. Amylin protein level and mitogen-activated protein kinase phosphorylation were detected by western blot. Activator protein 1 (AP1) activation was examined by electrophoretic mobility shift assay (EMSA).

RESULTS

TNF-α acutely induced amylin expression at the transcriptional level and increased proamylin and the intermediate form of amylin in MIN6 cells and islets. However, it had no effect on proinsulin, Pc1/3 and Pc2 expression. Studies with (1) MIN6 cells treated with inhibitors of MEK1/2, c-Jun-N-terminal kinase (JNK) or protein kinase Cζ (PKC(ζ)), (2) MIN6 cells expressing a c-Jun-dominant negative construct and (3) islets from Fos knockout mice demonstrated that TNF-α induced amylin expression through the PKC(ζ)-extracellular signal-regulated kinase (ERK)/JNK pathways. EMSA showed that (PKC(ζ)), JNK and ERK1/2 were involved in TNF-α-induced AP1 activation, suggesting that TNF-α induces murine amylin expression through the (PKC(ζ)) - ERK1/2 - AP and PKC(ζ) - JNK - AP1 pathways. Further studies showed that TNF-α also induced murine amylin expression through the phosphatidylinositol 3 kinase-NF-κB signalling pathway and enhanced human amylin promoter activation through NF-κB and AP1.

CONCLUSIONS/INTERPRETATION

TNF-α acutely induces amylin gene expression in beta cells through multiple signalling pathways, possibly contributing to amylin elevation in acute inflammation-related pancreatic disorders.

PP2A mediated AMPK inhibition promotes HSP70 expression in heat shock response

BACKGROUND

Under stress, AMP-activated protein kinase (AMPK) plays a central role in energy balance, and the heat shock response is a protective mechanism for cell survival. The relationship between AMPK activity and heat shock protein (HSP) expression under stress is unclear.

METHODOLOGY/PRINCIPAL FINDINGS

We found that heat stress induced dephosphorylation of AMPKα subunit (AMPKα) in various cell types from human and rodent. In HepG2 cells, the dephosphorylation of AMPKα under heat stress in turn caused dephosphorylation of acetyl-CoA carboxylase and upregulation of phosphoenolpyruvate carboxykinase, two downstream targets of AMPK, confirming the inhibition of AMPK activity by heat stress. Treatment of HepG2 cells with phosphatase 2A (PP2A) inhibitor okadaic acid or inhibition of PP2A expression by RNA interference efficiently reversed heat stress-induced AMPKα dephosphorylation, suggesting that heat stress inhibited AMPK through activation of PP2A. Heat stress- and other HSP inducer (CdCl(2), celastrol, MG132)-induced HSP70 expression could be inhibited by AICAR, an AMPK specific activator. Inhibition of AMPKα expression by RNA interference reversed the inhibitory effect of AICAR on HSP70 expression under heat stress. These results indicate that AMPK inhibition under stress contribute to HSP70 expression. Mechanistic studies showed that activation of AMPK by AICAR had no effect on heat stress-induced HSF1 nuclear translocation, phosphorylation and binding with heat response element in the promoter region of HSP70 gene, but significantly decreased HSP70 mRNA stability.

CONCLUSIONS/SIGNIFICANCE

These results demonstrate that during heat shock response, PP2A mediated AMPK inhibition upregulates HSP70 expression at least partially through stabilizing its mRNA, which suggests a novel mechanism for HSP induction under stress.

Norepinephrine promotes microglia to uptake and degrade amyloid beta peptide through upregulation of mouse formyl peptide receptor 2 and induction of insulin-degrading enzyme

Locus ceruleus (LC) is the main subcortical site of norepinephrine synthesis. In Alzheimer's disease (AD) patients and rodent models, degeneration of LC neurons and reduced levels of norepinephrine in LC projection areas are significantly correlated with the increase in amyloid plaques, neurofibrillary tangles, and severity of dementia. Activated microglia play a pivotal role in the progression of AD by either clearing amyloid beta peptide (Abeta) deposits through uptake of Abeta or releasing cytotoxic substances and proinflammatory cytokines. Here, we investigated the effect of norepinephrine on Abeta uptake and clearance by murine microglia and explored the underlying mechanisms. We found that murine microglia cell line N9 and primary microglia expressed beta(2) adrenergic receptor (AR) but not beta(1) and beta(3)AR. Norepinephrine and isoproterenol upregulated the expression of Abeta receptor mFPR2, a mouse homolog of human formyl peptide receptor FPR2, through activation of beta(2)AR in microglia. Norepinephrine also induced mFPR2 expression in mouse brain. Activation of beta(2)AR in microglia promoted Abeta(42) uptake through upregulation of mFPR2 and enhanced spontaneous cell migration but had no effect on cell migration in response to mFPR2 agonists. Furthermore, activation of beta(2)AR on microglia induced the expression of insulin-degrading enzyme and increased the degradation of Abeta(42). Mechanistic studies showed that isoproterenol induced mFPR2 expression through ERK1/2-NF-kappaB and p38-NF-kappaB signaling pathways. These findings suggest that noradrenergic innervation from LC is needed to maintain adequate Abeta uptake and clearance by microglia, and norepinephrine is a link between neuron and microglia to orchestrate the host response to Abeta in AD.

Targeted disruption of pancreatic-derived factor (PANDER, FAM3B) impairs pancreatic beta-cell function

OBJECTIVE

Pancreatic-derived factor (PANDER, FAM3B) is a pancreatic islet-specific cytokine-like protein that is secreted from beta-cells upon glucose stimulation. The biological function of PANDER is unknown, and to address this we generated and characterized a PANDER knockout mouse.

RESEARCH DESIGN AND METHODS

To generate the PANDER knockout mouse, the PANDER gene was disrupted and its expression was inhibited by homologous recombination via replacement of the first two exons, secretion signal peptide and transcriptional start site, with the neomycin gene. PANDER(-/-) mice were then phenotyped by a number of in vitro and in vivo tests to evaluate potential effects on glucose regulation, insulin sensitivity, and beta-cell morphology and function.

RESULTS

Glucose tolerance tests demonstrated significantly higher blood glucose levels in PANDER(-/-) versus wild-type male mice. To identify the mechanism of the glucose intolerance, insulin sensitivity and pancreatic beta-cell function were examined. Hyperinsulinemic-euglycemic clamps and insulin tolerance testing showed similar insulin sensitivity for both the PANDER(-/-) and wild-type mice. The in vivo insulin response following intraperitoneal glucose injection surprisingly produced significantly higher insulin levels in the PANDER(-/-) mice, whereas insulin release was blunted with arginine administration. Islet perifusion and calcium imaging studies showed abnormal responses of the PANDER(-/-) islets to glucose stimulation. In contrast, neither islet architecture nor insulin content was impacted by the loss of PANDER. Interestingly, the elevated insulin levels identified in vivo were attributed to decreased hepatic insulin clearance in the PANDER(-/-) islets. Taken together, these results demonstrated decreased pancreatic beta-cell function in the PANDER(-/-) mouse.

CONCLUSIONS

These results support a potential role of PANDER in the pancreatic beta-cell for regulation or facilitation of insulin secretion.

Characterization of the expression, localization, and secretion of PANDER in alpha-cells

The novel islet-specific protein PANcreatic DERived Factor (PANDER; FAM3B) has been extensively characterized with respect to the beta-cell, and these studies suggest a potential function for PANDER in the regulation of glucose homeostasis. Little is known regarding PANDER in pancreatic -cells, which are critically involved in maintaining euglycemia. Here we present the first report elucidating the expression and regulation of PANDER within the alpha-cell. Pander mRNA and protein are detected in alpha-cells, with primary localization to a glucagon-negative granular cytosolic compartment. PANDER secretion from alpha-cells is nutritionally and hormonally regulated by l-arginine and insulin, demonstrating similarities and differences with glucagon. Signaling via the insulin receptor (IR) through the PI3K and Akt/PKB node is required for insulin-stimulated PANDER release. The separate localization of PANDER and glucagon is consistent with their differential regulation, and the effect of insulin suggests a paracrine/endocrine effect on PANDER release. This provides further insight into the potential glucose-regulatory role of PANDER.

Cytokines in the Progression of Pancreatic β-Cell Dysfunction

The dysfunction of pancreatic β-cell and the reduction in β-cell mass are the decisive events in the progression of type 2 diabetes. There is increasing evidence that cytokines play important roles in the procedure of β-cell failure. Cytokines, such as IL-1β, IFN-γ, TNF-α, leptin, resistin, adiponectin, and visfatin, have been shown to diversely regulate pancreatic β-cell function. Recently, islet-derived cytokine PANcreatic DERived factor (PANDER or FAM3B) has also been demonstrated to be a regulator of islet β-cell function. The change in cytokine profile in islet and plasma is associated with pancreatic β-cell dysfunction and apoptosis. In this paper, we summarize and discuss the recent studies on the effects of certain important cytokines on pancreatic β-cell function. The imbalance in deleterious and protective cytokines plays pivotal roles in the development and progression of pancreatic β-cell dysfunction under insulin-resistant conditions.

Fatty acids induce amylin expression and secretion by pancreatic beta-cells

Amylin is the major component of pancreatic amyloid, which is implicated in the development of type 2 diabetes. It is costored with insulin in the secretory granules of pancreatic beta-cells and cosecreted with insulin following stimulation with glucose. Here, we investigate the effect of fatty acids (FAs) on amylin expression and secretion by beta-cells and explore the underlying mechanisms. Palmitate and oleate dose-dependently induced amylin mRNA accumulation in murine pancreatic beta-cell line MIN6 and primary pancreatic islets. the inductive effect of FAs on amylin expression is independent of glucose concentration. FAs upregulated amylin expression at the transcriptional level, and FAs must be metabolized to induce amylin expression. FAs also significantly induced human amylin promoter activation. Pretreatment of MIN6 cells with Ca(2+) chelator (EGTA, BAPTA-AM) PKC inhibitor Gö-6976 or protein synthesis inhibitor cycloheximide significantly inhibited FA-induced amylin mRNA expression. Transcription factors cAMP-responsive element-binding protein, pancreatic and duodenal homeobox factor-1, and peroxisome proliferator-activated receptor were not involved in FA-induced amylin expression. Palmitate and oleate both increased amylin and insulin release from MIN6 cells and stimulated amylin expression but had no effect on insulin expression. Mice refed with Intralipid had significantly higher levels of plasma FFA, amylin, and insulin than those refed with saline. These data demonstrate that FAs differently regulate amylin and insulin expression and induce both amylin and insulin release. Ca(2+) and PKC signaling pathways and de novo-synthesized protein(s) were involved in FA-induced amylin expression. Induction of amylin production and release by FA may contribute to its biological functions under physiological conditions.

PANDER binds to the liver cell membrane and inhibits insulin signaling in HepG2 cells

PANDER is a cytokine co-secreted with insulin from islet beta-cells. To date, the physiological function of PANDER remains largely unknown. Here we show that PANDER binds to the liver membrane by (125)I-PANDER saturation and competitive binding assays. In HepG2 cells, pre-treatment with PANDER ranging from 4 pM to 4 nM for 8h resulted in a maximal inhibition of insulin-stimulated activation of insulin receptor and insulin receptor substrate 1 by 52% and 63%, respectively. Moreover, PANDER treatment also reduced insulin-stimulated PI3K and pAkt levels by 55% and 48%, respectively. In summary, we have identified the liver as a novel target for PANDER, and PANDER may be involved in the progression of diabetes by regulating hepatic insulin signaling pathways.

PDX-1 interaction and regulation of the Pancreatic Derived Factor (PANDER, FAM3B) promoter

Pancreatic Derived Factor (PANDER) is a novel cytokine-like protein dominantly expressed within the endocrine pancreas. Our previous study demonstrated that the PANDER promoter was both tissue-specific and glucose-responsive. Surrounding the PANDER transcriptional start site are several putative A- and E-Box elements that may bind to the various pancreatic transcriptional factors of MafA, BETA2/NeuroD, and Pancreatic Duodenal Homeobox-1 (PDX-1). To characterize the transcriptional regulatory factors involved in PANDER gene expression, we performed co-transfection reporter gene analysis and demonstrated upregulation by all three transcription factors, with the greatest individual increase stemming from PDX-1. Potential binding of PDX-1 to A box (TAAT) regions of the PANDER promoter was demonstrated by chromatin immunoprecipitation (ChIP) and further corroborated by electrophoretic mobility shift assay (EMSA). Binding of PDX-1 to the A box regions was inhibited by mutagenized (TAGT) oligonucleotides. Site-directed mutagenesis of the three PDX-1 A box binding motifs revealed that A box sites 2 and 3 in combination were critical for maximal gene expression and deletion resulted in a 82% reduction in promoter activity. Furthermore, deletion of A box sites 2 and 3 completely diminished the glucose-responsiveness of the PANDER promoter. Our findings demonstrate that PANDER is a potential PDX-1 target gene and the A box sites within the promoter region are critical for basal and glucose-stimulated PANDER expression.