Islets 1:1, 34-41; July/August 2009; © 2009 Landes Bioscience
Expression and regulation of osteopontin in type 1 diabetes Qiaoke Gong, Galina Chipitsyna, Chancellor F. Gray, Rathai Anandanadesan and Hwyda A. Arafat* Department of Surgery; Thomas Jefferson University; Philadelphia, PA USA
Keywords: osteopontin, NOD mice, islets, type 1 diabetes, cytokines
Osteopontin (OPN) is a secreted acidic phosphoprotein that is involved in many inflammatory and immune-modulating disorders. We previously demonstrated that OPN is a novel islet protein and a pro survival factor that may serve as an intrinsic feedback regulator of nitric oxide signaling in b-cells. Here, we investigated the endogenous expression of pancreatic OPN in non obese diabetic (NOD) mice and explored its regulation in the islets and b-cells. High levels of pancreatic OPN mRNA and protein were seen in the prediabetic NOD mice pancreata.The temporal pattern of OPN expression inversely correlated with progression of insulitis and b-cell destruction. Immunostaining of pancreatic serial sections showed co localization of OPN with most of the islet hormones. Next we investigated the regulation of OPN in the islets and b-cells. Naturally occurring early upregulation of OPN transcription was seen after exposure of native normoglycemic NOD islets and b-cells to a high-dose combination of IL-1β, TNF-α and IFN-γ. To distinguish between the effect of cytokines and high glucose on OPN transcription, RINm5F cells were transfected with luciferase-labeled rat OPN promoter and treated with cytokines or glucose. Cytokines induced upregulation of OPN promoter activity within one hour, while glucose induced a dose-dependent upregulation of OPN promoter activity after 24 hrs. Long-term exposures to cytokines or glucose reduced OPN expression and promoter activity. Our data provide the first observations into the presence of a positive intrinsic mechanism that regulates pancreatic OPN expression. Based upon previous studies that support a protective role of OPN in the islets, our data suggest that exhaustion of this local OPN system is implicated in the associated loss of endogenous islet protection and progression of the destructive insulitis and diabetes severity in the NOD mouse model.
Introduction Type 1 diabetes develops as a consequence of autoimmunity, leading to b-cell destruction.1 In the early stages of insulitis, activated macrophages and T-cells are attracted to the islets and produce cytokines and free radicals, which contribute to b-cell dysfunction and death.2,3 However, the defense mechanisms through which b-cells respond to the early destructive signals are unidentified and poorly investigated. Osteopontin (OPN) is an integrin- and calcium-binding phosphoprotein produced by a limited set of normal cells, including cells of mineralized tissue, epithelial cells, activated cells of the immune system and urinary tract smooth muscle cells.4-7 Soluble OPN can promote cell survival signaling, which is mediated by extracellular matrix (ECM) receptors. OPN is suggested to deliver an antiapoptotic “ECM-like” signal via multiple ligand-receptor interactions in bone metastasis and dermal melanocytes.8,9 Classical mediators of acute inflammation such as tumor necrosis factor-alpha (TNF-α) and interleukin-1β (IL-1β) strongly induce OPN expression.10,11,12 OPN protein is selectively upregulated in the serum of type 1 diabetic patients,13 in diabetic vascular walls,14,15 and in the diabetic kidneys,16 and was reported among the early genes specifically activated in the islets and lymph nodes in non obese diabetic
(NOD) mice.17 However, data concerning the temporal changes in OPN expression in correlation with destructive insulitis and hyperglycemia in type 1 diabetes, and the intrinsic mechanisms that contribute to its regulation have not been reported. Previously, we demonstrated that high levels of pancreatic OPN correlate with the acute response to streptozotocin (STZ) induced diabetes in rodents.18 Using an OPN knockout model, we showed that OPN is essential for polarizing the islet cytokine immune response towards the protective Th2 profile.19 We also demonstrated that OPN regulates NO signaling in the islets and b-cells via an RGD-mediated feedback regulation of IL-1βinduced nuclear factor-kB (NFκB) activation with consequent downregulation of induced nitric oxide synthase activity and increased b-cell survival.20 In this study, we used different age groups of the NOD mice, which spontaneously develop a form of type I diabetes and shares many features of the human disease.21 We examined the temporal expression of OPN in NOD mice in correlation with age, hyperglycemia and b-cell destruction, and explored its regulation in the islets and b-cells. Results Temporal reduction of pancreatic OPN protein and mRNA levels correlate with hyperglycemia and destructive insulitis. The
*Correspondence to: Hwyda Arafat; Email:
[email protected] Submitted: 02/25/09; Revised: 04/02/09; Accepted: 04/03/09 Previously published online: www.landesbioscience.com/journals/islets/article/8629 34
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Research Paper
Research paper
Figure 1. Expression of OPN in NOD mice pancreata. (A) Expression of OPN protein. Representative Western immunoblot of protein extracts from NOD mice pancreata between 4 and 22 weeks of age. Pancreatic OPN protein is expressed as three bands at ~65, 50, and 45 kDa in the younger animals and one band at ~65kDa in the older ones. A decrease in OPN expression is seen in the 16 weeks diabetic group that became significant in the severely diabetic group (22 weeks). Blots were stripped and reprobed with actin antibody to control for loading errors. Average densitometry values of the samples were multiplied to obtain the arbitrary levels. Data are means ± SEM of n=5 in each group. *p < 0.05, #p< 0.02 vs. noromoglycemic mice (4 weeks). (B) OPN mRNA expression. Real time PCR analysis of OPN mRNA transcripts revealed the presence of considerable amount of OPN mRNA in normoglycemic pancreata. Significant downregulation of OPN mRNA levels is seen in the second group that became more significant in the older diabetic group. Data are means ± SEM of n = 5 in each group. *p < 0.05, #p< 0.02 vs. noromoglycemic mice (4 weeks). (C) Representative Western immunoblot of protein extracts from ICR mice pancreata between 4 and 22 weeks of age. Pancreatic OPN protein is expressed as one band at ~65kDa. Stable levels of OPN expression seen in the 4 and 22 weeks groups. Blots were stripped and reprobed with actin antibody to control for loading errors. Average densitometry values of the samples were multiplied to obtain the arbitrary levels. Data are means ± SEM of n = 3 in each group.
intrapancreatic levels of OPN in the three groups of female NOD mice were analyzed by western blotting and real time RT-PCR. Age-blood glucose dependent analyses showed that OPN protein is highly expressed in the female NOD mice at 4 weeks of age. As seen in Figure 1A, three OPN molecular weight isoforms at ~65, 50, and 45 kDa were recognized at 4 and 16 weeks. At 16 weeks, with onset of hyperglycemia, OPN protein levels in NOD pancreata were significantly reduced. With the establishment of hyperglycemia, although still detectable, OPN levels continued to decrease and its molecular weight isoforms expression was limited to the ~65 kDa band. OPN mRNA levels showed the same pattern seen with the protein (Fig. 1B). The mice were compared to age matched non prone diabetic ICR mice. Interestingly, in ICR mice, OPN protein was detected as a single ~65 kDa band (Fig. 1C). OPN levels were generally stable through the young (4 weeks) and older (22 weeks) ICR mice. These results demonstrate the importance of the NOD genetic background in the control of the patterns of OPN expression and show that the progression to destructive insulitis in NOD mice is associated with a lower intrapancreatic OPN mRNA and protein levels. OPN distribution in the NOD pancreas. Staining of serial sections showed clear OPN immunoreactivity in the islets colocalizing will almost all islet hormones (Fig. 2A). OPN immunoreactivity was distinctively intense in the 4-week NOD mice islets, clearly colocalizing with insulin secreting b-cells (Fig. 2B). In severely diabetic mice at 22 weeks of age, OPN immunoreactivity was substantially deminished (Fig. 2B). ICR mice between 4 and 22 weeks of age showed colocalization of OPN and insulin in the pancreatic islets with stable expression (Fig. 2C). The comparable expression pattern and close proximity between OPN and insulin suggests a potential paracrine/autocrine interaction and similar regulation. So, next we investigated the regulation of OPN in the pancreatic islets and b-cells.
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Cytokines induce of OPN mRNA and protein expression in the pancreatic islets. OPN mRNA steady state expression as percent of the internal standard GAPDH was evaluated by real time PCR in normoglycemic NOD mice islets exposed to a high-dose combination of IL-1β, TNF-α and IFN-γ. Statistically significant induction of OPN mRNA expression was observed after a 24 hr and 48 hr cytokine exposure (ANOVA p = 0.001 and p = 0.01, respectively Fig. 3A).
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Figure 2. Localization of OPN in NOD mice islets. (A) To identify which cells in the islets express OPN, paraffin embedded NOD pancreatic serial sections were stained with antibodies against insulin, glucagon and somatostatin. Representative sections from 16 week pancreata show that most islet cells express OPN. Negative control samples where the primary antibody was omitted did not show non-specific reaction. x200 original magnification. (B) Colocalization of OPN and insulin in the pancreatic islets in NOD mice. Progression of insulitis and hyperglycemia show correlation between reductions of OPN and insulin immunoreactivities. Negative control samples where the primary antibody was omitted did not show non-specific reaction. x200 original magnification. (C) Colocalization of OPN and insulin in the pancreatic islets in ICR mice islets. Representative sections from 22-week pancreata show strong immunoreactivities and colocalization of insulin OPN in the ICR islets. Negative control samples where the primary antibody was omitted did not show non-specific reaction. x200 original magnification.
Western blotting of the islets treated with the same doses of the cytokine cocktail revealed a time-dependent significant increase in OPN protein expression (Fig. 3B). To investigate whether OPN
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is also regulated by glucose in the islets, NOD islets were exposed to different doses of glucose (5–25 mM). Analysis of islet OPN mRNA indicated a dose-dependent increase in OPN mRNA by
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glucose at 24 hr (Fig. 3C). Next we determined whether of OPN regulation by cytokines or glucose is at the transcriptional level. Regulation of OPN promoter by cytokines and glucose. Previous studies have shown OPN promoter contains glucose responsive elements.14,15 To investigate the regulation of OPN by cytokines or glucose, RINm5F cells were transfected with rat OPN promoter/luciferase gene construct. After 24 hr of transfection, the cells were incubated with cytokines for 1, 6, 24, 48 and 96 h. Relative luciferase activity was calculated after deduction of the activity levels with pGL2 vector alone. Cytokines induced a significant activation of OPN promoter in RINm5F cells within 1h. Activation levels are decreased after 6, and 24 h, but were still significantly high (Fig. 4A). By 48 hr, promoter luciferase levels were back to control levels. However, at 96h, the promoter activity levels were significantly reduced (Fig. 4A). Cells were also incubated with glucose (5–50 mM) for 6, 24, 48, and 96 hr. Glucose induced a dose-dependent upregulation of OPN promoter activity after 24 hr (Fig. 4B). High glucose concentrations (50 mM) reduced OPN promoter activity at all time points of treatment. These data show that OPN promoter responds differentially, time-wise, to cytokines and glucose. Discussion
Figure 3. Cytokines induce OPN accumulation in cultured normoglycemic islets. (A) OPN mRNA Islets were incubated with high dose combination of cytokines IL-1β, TNF-α, and IFN-γ for 24 and 48 hours. ~Three-fold upregulation of OPN mRNA in the islets is seen after stimulation for 24 hr Levels were reduced at 48 hr.Values are expressed as mean ± SEM of three experiments. *p < 0.02, #p< 0.05 vs. control levels. (B) OPN protein. Representative Western immunoblot of protein extracts from islets treated with high dose cytokine combination. Significant increase in OPN protein is seen after 24 and 48 hr. Data are expressed as mean ± SEM of three experiments *p< 0.05 vs. control levels. (C) Dosedependent induction of OPN mRNA by glucose in the islets. Islets were incubated with glucose (5–25 mM) for 24 hours. Three to six-fold upregulation of OPN mRNA in the islets is seen with high glucose concentrations.Values are expressed as mean ± SEM of three experiments. * p < 0.05, # p< 0.02 vs. control levels.
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The molecular changes of the islets and their microenvironment represent a major feature of the diabetic islet injury. The final islet response to cytotoxic signals is regulated by an intricate pattern of differentially regulated genes that decide the fate of b-cells whether to apoptosis or survival, with or without complete functional recovery.22,23 We have recently introduced OPN as a new player in the acute islet response to experimentally induced diabetes18 and identified it as a novel islet protein that functions as an endogenous negative feedback inhibitor for IL-1β-induced nitric oxide synthase through regulation of NFκB.20 Since overexpression of OPN in the islets and b-cells make them more resistant to cytokine-induced islet dysfunction,20 we sought to understand the in vivo regulation of pancreatic OPN during the early and late stages of type 1 diabetes as a means to understand the early islet response mechanisms that might contribute to islet defense and protection during the early stages of this disease. In the present study we show for the first time that progression of destructive insulitis and diabetes severity are associated with exhaustion of pancreatic OPN. We demonstrate that as early as 4 weeks of age, OPN expression levels were enhanced in the pre diabetic pancreas (Fig. 1 and 2). We also show that OPN levels were still high with insulitis and during the early stages of hyperglycemia. Our results correlate with other studies that analyzed OPN expression in several diabetic animal models,16,17,24 suggesting that the upregulation of OPN expression with diabetes is a general phenomenon observed across the different tissues. We also show that OPN is constitutively expressed in the NOD mice pancreatic islets colocalizing with insulin (Fig. 2), and their expression levels were weakened at the later stages of hyperglycemia. Although we are yet to explore the paracrine/autocrine interaction between OPN and insulin, it appears that the expression of the two molecules
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Figure 4. (A) Cytokines induce OPN promoter activity in RINm5F cells. After 24 hr of transfection, the cells were incubated with high dose combination of cytokines IL-1β, TNF-α and IFN-γ at different times. After incubation, the luciferase activity in the cell lysates was measured. Cytokines cause significant increase in OPN promoter activity within 1 hour. Relative luciferase activity was calculated after deduction of the activity levels with pGL2 vector alone. Results represent mean ± SEM of triplicate determinations. All experiments were repeated at least three times to confirm the reproducibility of the observations. *p < 0.02, #p < 0.05. vs. control levels, **p < 0.02 vs. 1h levels. (B) Glucose induces OPN promoter activity in RINm5F cells. After 24 hr of transfection, the cells were incubated with different concentrations of glucose for different times. After incubation, the luciferase activity in the cell lysates was measured. Glucose induces a dose-dependent increase in OPN promoter activity at 24 hr. At 48 hr levels were reduced. High glucose concentrations (50 mM) reduced OPN promoter activity at all time points. Relative luciferase activity was calculated after deduction of the activity levels with pGL2 vector alone. Results represent mean ± SEM of triplicate determinations. All experiments were repeated at least three times to confirm the reproducibility of the observations. *p < 0.02, #p < 0.05. vs. control levels.
correlate in the islets, where strong OPN expression is associated with strong insulin expression, and exhaustion of insulin is correlated with exhaustion of OPN in the islets. Western blotting showed that OPN protein is highly expressed at 4 weeks with three molecular weight isoform at 65, 50 and 45 kDa at 4 and 16 weeks (prediabetic status) and Only 65 kDa band was expressed at the age of 22 weeks (hyperglycemia status) (Fig. 1A). When aged-matched non
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prone diabetic ICR were compared, only the 65 kDa band was detected (Fig. 1C). Multiple forms of osteopontin have been described, including differentially glycosylated, phosphorylated and sulphated isoforms, as well as naturally occurring proteolytic fragments.5 In our study, the changes in OPN isoform expression in the diabetic animals, occurring at the time of diabetes incidence may indicate that different osteopontin isoforms play functional roles involving islet protection. The absence of the
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50 and 45 kDa isoforms in the diabetic ICR mice is suggestive that they are related to the protective functions of OPN. Nonetheless, the individual function(s) of each OPN isoform are not clear and may differ according to the cell that expresses them. For example, recent studies in cancer cells revealed a specific 5 kDa isoform is related to tumor cell invasion (Weber GF et al., 2006, 2007).25,26 Further functional studies are needed to elaborate on the functions of OPN isoforms in pancreatic islets. During the prediabetic state, the pancreatic islets are exposed to elevated levels of proinflammatory cytokines27,28 with subsequent increase of local oxidative stress and b-cell damage.3,29 We used an in vitro system of cytokine-induced cytotoxicity to mimic these conditions. We show here that addition of cytokines to normoglycemic NOD mice islets induced a significant upregulation of OPN mRNA and protein levels (Fig. 3) through activation of its promoter activity (Fig. 4). It is noteworthy to mention that the different micro array analysis studies on the islets and b-cells30-33 could not recognize OPN among the early genes upregulated by cytokines. This could be attributed to the possible insensitivity of the affymetrix probes34 that could not detect OPN expression. Since glucotoxcitiy represents a potent contributing factor that could influence b-cell response mechanisms,23 we evaluated the effects of high glucose levels on OPN expression. We found that OPN levels are increased by glucose through regulation of its promoter activity. It was interesting to show that OPN promoter was differentially regulated by cytokine and glucose. We used a combination of IL-1β(5 ng/ml), TNF-α (30 ng/ml) and INF-γ (30 ng/ml), all cytokines that have been shown to play a role in the pathogenesis of type 1 diabetes.27 While cytokines induced an early (1 hr) upregulation, glucose induced a late (24 hr) upregulation. High doses of glucose and longer times of exposure to glucose and cytokines reduced OPN expression and reduced its promoter activity. Thus, it is reasonable to propose that the initial high levels of pancreatic OPN during the early prediabetic stages were cytokine-induced, while the continuous drop in OPN levels at the later stages might be due to a combination of glucose- and cytokine-induced toxicity. It is not to be excluded though that glucose-mediated induction of OPN could be through an indirect effect. Nonetheless, there are multiple aspects of OPN regulation in the islets and b-cells that are yet to be clarified. For example, it is not clear whether the cytokine-induced upregulation of OPN is mediated through NO, since cytokines in general and IL-1β in particular induce iNOS and NO in the islets and b-cells,2,22,27 and OPN expression itself is induced by NO and classical NO donor compounds.20,35 Furthermore, the signaling pathways through which glucose regulate OPN expression in b-cells are unknown, and how this regulation is involved in the diabetogenic process. Studies addressing these questions are ongoing in our laboratory. Based upon previous data supporting the protective and pro survival role of OPN in various tissues10,11,36 and in the pancreatic islets and b-cells,18,19,20 we propose that the high levels of islet OPN during the early stages of autoimmune diabetes might
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constitute a unique intercellular negative feedback mechanism. The early cytokine- and later glucose-mediated induction of OPN serve to protect the islets and b-cells against cytokinemediated cytotoxicity. At this stage the islets and b-cells are in a state of “compensation,” where the islets and b-cells are recoverable. However, at the later stages, with the long exposure of the islets to cytokines and glucose, OPN levels are reduced, rendering the islets and b-cells vulnerable and in a state of “decompensation,” where the islets and b-cells undergo a process of irreversible destruction. Studies to verify the protective role of OPN against type 1 diabetes are currently ongoing in our lab. In summary, we provide the first observations into the presence of positive intrinsic mechanisms that regulate pancreatic OPN expression and could be utilized to regulate cytokine action and thus the cellular fate after cytokine exposure in type 1 diabetes. Materials and Methods Mice. Female NOD mice were purchased from Taconic Farm, Hudson, NY. The incidence of diabetes in our colony is about 50% at 20 weeks of age in the females. The animals had free access to tap water and pelleted food. All animal studies were performed in accordance with guidelines set forth by the Animal Care Committee of Thomas Jefferson University. Fasting blood glucose (FBG) was monitored using a glucometer (accu-check, Roche, Indianapolis, IN). Mice with a reading of FBG > 200 mg/dl on two consecutive occasions were diagnosed as being positive for type 1 diabetes. According to age and blood glucose level, animals were divided into three main groups (n = 5): 4 week (normoglycemic), 16 week (FBG 200–250 g/dl), and 22 weeks (FBG > 350 g/ dl). The NOD mouse strain is derived from the ICR mouse strain. As non-diabetic prone controls, two groups of matching age (4 and 22 weeks) ICR mice (n = 3) were studied. Pancreata were isolated, cleaned from surrounding fat and lymph nodes and were either fixed in neutral formaline, snap frozen in liquid nitrogen, or incubated in RNA Later (Ambion; Austin, TX). Protein isolation and western blot analysis. Pancreata or islets were lysed in modified RIPA lysis buffer,37 and the protein concentrations in the supernatant were determined using the BCA protein assay reagent (Pierce; Rockford, IL). Equal protein concentrations (50 µg) were denatured in a gel loading buffer at 85oC for 5 minutes and then loaded onto 10 % SDS-polyacrylamide slab gels and transferred to polyvinylidene difluoride membranes and incubated at 4oC overnight with primary mouse monoclonal osteopontin antibody, 1:150 diluted in PBST (Santa Cruz Biotechnology, Santa Cruz, CA). To avoid sample loading errors, β-actin expression was determined in the blots to adjust and normalize the amount of sample loaded. The protein bands were visualized with enhanced chemiluminescence reagents (ECL Plus Western Blotting Detection System, Amersham Pharmacia Biotech), analyzed and intensity quantified using Kodak Electrophoresis Documentation and Analysis System 290 (EDAS 290). RNA extraction and real time Reverse Transcription Polymerase Chain Reaction (RT-PCR). Total RNA was
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isolated from pancreata, islets or b-cells using Trizol reagent (Life Technologies, Gaitherburg, MD), according to the manufacturer’s protocol. RNAs were quantified and input amounts were optimized for each amplicon. Primers and probes were designed with the help of Primer Express Software (Applied Biosystems, Foster City, CA). The specificity of OPN primers were validated using semi quantitative PCR. GAPDH was used as the house keeping gene, since it showed relative stable gene expression. RNA samples were DNase-digested and cDNA was prepared, diluted, and subjected to real-time PCR using the TaqMan technology (7500 Sequence Detector, Applied Biosystems). Probes were labeled with a reporter and a quencher. Each sample was analyzed in at least two independent assays with duplicate samples and the corresponding no-reverse transcriptase (RT) mRNA sample was included as a negative control. The GAPDH primers were included in every plate to avoid sample variations. The mRNA level of each sample for each gene was normalized to that of the GAPDH mRNA. The relative mRNA levels were presented as unit values of 2^[CT(GAPDH)- CT(OPN)], where CT is the threshold cycle value defined as the fractional cycle number at which the target fluorescent signal passes a fixed threshold above baseline. Immunohistochemistry. To localize OPN in the pancreas and study the changes in its expression with the development of insulitis, formaline fixed, paraffin embedded tissue blocks were prepared from pancreata of the different groups. Serial sections at 5 µm were stained with a monoclonal antibody against OPN (2A1, Santa Cruz) (1:100). To identify where this protein is expressed in the islet cells, we used ready to use antibodies against insulin, glucagon (BioGenex, San Ramon, CA) and somatostatin (Accurate Chemical, Westbury, NY) (1:200). A vectastain universal elite ABC kit and diaminobenzedine (DAB) chromogenic substrate (Vector Laboratories Inc.) were used according to the manufacturer protocol to visualize the tissue reaction to the antibodies. Insulin was visualized by alkaline phosphatase reaction (red), while DAB was used to visualize the rest of the islet hormones in addition to OPN (brown). Antibody specificities were validated with nonimmune isotype serum. Negative control sections, where the primary or secondary antibodies were omitted were also prepared. Islet isolation and treatment. Islets were isolated from normoglycemic 4- to 6-week-old female NOD mice as previously described.18 Briefly, 20 ml cold Hank’s buffer/Type IV collagenase solution was infused into the bile duct. The inflated pancreas was cleaned from the surrounding fat and lymph nodes, minced, and digested in a shaker-type water bath at 37°C. Islets were recognized and handpicked under the stereomicroscope after their staining with dithiazone (DTZ). Islets were aliquoted and cultured in RPMI medium containing 5 mmol/l glucose and supplemented with 10 mmol/l HEPES, 1% L-Glutamine and penicillin/streptomycin. Islets were allowed to equilibrate overnight before their treatment. A combination of IL-1β (5 ng/ml), TNF-α (30ng/ml), and INF-γ (30 ng/ml) (R & D, Minneapolis, MN) was added for 24 and 48 hours after which the islets were harvested. To examine the effect of high glucose concentration on OPN expression, glucose (5–25 mM) was added to the islets. All concentrations were
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used according to our preliminary concentration studies with references to the values of OPN mRNA. Cell culture and treatment. RIN, clone 5F (RINm5F), an insulinoma cell line derived from the NEDH rat islet cell tumor, were purchased from American Type Culture Collection and grown at 37oC under a humidified, 5% CO2 atmosphere in RPMI 1640 medium (Gibco BRL) supplemented with 10% fetal bovine serum and 2 mM glutamine, 100 units/ml of penicillin, 100 µg/ ml of streptomycin, and 2.5 µg/ml of amphotericin B. After overnight incubation in serum free medium, the cells were treated with the same cytokine combination for 6–48 hours after which the cells were harvested. Osteopontin promoter studies. To explore the regulation of OPN in b-cells, quiescent RINm5F cells were obtained after 18 hr incubation in serum free medium. The rat OPN promoter, (-1984luc) (GenBankTM accession number AF017274) in a luciferase expression vector pGL2 basic (Promega), was kindly provided by Dr. S Mori, Chiba University, Japan.14,15 Cells were seeded into 24-well culture plates (105). At ∼80% confluence they were co transfected by TransFast reagent (Promega) and 0.5 µg of pGL2 vectors containing the rat luciferase-labeled OPN promoter and 0.1 µg of GFP as transfection control. Two hours later, serumcontaining medium was overlaid and the cells will be incubated for additional 24 hr. The cells then were incubated with serum free medium for 16 hr followed by addition of the cytokine combination or different glucose concentrations (5–50 mM) for 1–48 hours. Luciferase activities were assayed with the Dual-Luciferase Reporter Assay System (Promega) in a TD-20/20 Luminometer (Turner Designs, Sunnyvale, CA). Transfection efficiency was normalized using the total protein concentration of the cell lysates. Statistical analysis. All experiments were performed four to six times. Data were analyzed for statistical significance by ANOVA with post-hoc student t test analysis. These analyses were performed with the assistance of a computer program (JMP 5 Software SAS Campus Drive; Cary, NC). Differences were considered significant at p ≤ 0.05. Acknowledgements
This study was supported by grants from the American Diabetes Association, Diabetes Transplant Fund, and Diabetes Action Research & Education Foundation. The authors wish to thank Dr. S. Mori, Chiba University, Japan, for providing the OPN promoter.
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References 1. Schranz DB, Lernmark A. Immunology in diabetes: an update. Diabete Metab Rev 1998; 14:3-29. 2. Mandrup-Poulsen T. The role of interleukin-1 in the pathogenesis of IDDM. Diabetologia 1996; 39: 1005-29. 3. Eizirik DL, Mandrup-Poulsen T. A choice of death— the signal-transduction of immune-mediated beta-cell apoptosis. Diabetologia 2001; 44:2115-33. 4. Denhardt DT, Noda M, O’Regan AW, Pavlin D, Berman JS. Osteopontin as a means to cope with environmental insults: regulation of inflammation, tissue remodeling and cell survival. J Clin Invest 2001; 107:1055-61. 5. Denhardt DT, Guo X. Osteopontin: a protein with diverse functions. FASEB J 1993; 7:1475-82. 6. Patarca R, Saavedra RA, Cantor H. Molecular and cellular basis of genetic resistance to bacterial infection: the role of the early T-lymphocyte activation-1/osteopontin gene. Crit Rev Immunol 1993; 13:225-46. 7. Arafat HA, Wein AJ, Chacko S. Osteopontin gene expression and immunolocalization in the rabbit urinary tract. J Urol 2002; 167:746-52. 8. Hotte SJ, Winquist EW, Stitt L, Wilson SM, Chambers AF. Plasma osteopontin: associations with survival and metastasis to bone in men with hormone-refractory prostate carcinoma. Cancer 2002; 95:506-12. 9. Geissinger E, Weisser C, Fischer P, Schartl M, Wellbrock C. Autocrine stimulation by osteopontin contributes to antiapoptotic signaling of melanocytes in dermal collagen. Cancer Res 2002; 62:4820-8. 10. Mazzali M, Kipari T, Ophascharoensuk V, Wesson JA, Johnson R, Hughes J. Osteopontin—a molecule for all seasons. QJM 2002; 95:3-13. 11. Ricardo SD, Franzoni DF, Roesener CD, Crisman JM, Diamond JR. Angiotensinogen and AT(1) antisense inhibition of osteopontin translation in rat proximal tubular cells. Am J Physiol Renal Physiol 2000; 278:708-16. 12. Yu XQ, Fan JM, Nikolic-Paterson DJ, Yang N, Mu W, Pichler R, et al. IL-1 upregulates osteopontin expression in experimental crescentic glomerulonephritis in the rat. Am J Pathol 1999; 154:833-41. 13. Fierabracci A, Biro PA, Yiangou Y, Mennuni C, Luzzago A, Ludvigsson J, et al. Osteopontin is an autoantigen of the somatostatin cells in human islets: identification by screening random peptide libraries with sera of patients with insulin-dependent diabetes mellitus. Vaccine 1999; 18:342-54.
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