MKK3 signalling plays an essential role in leukocyte-mediated pancreatic injury in the multiple low-dose streptozotocin model

Pancreatic β-Cell-Derived IP-10/CXCL10 Isletokine Mediates Early Loss of Graft Function in Islet Cell Transplantation

Pancreatic islets produce and secrete cytokines and chemokines in response to inflammatory and metabolic stress. The physiological role of these "isletokines" in health and disease is largely unknown. We observed that islets release multiple inflammatory mediators in patients undergoing islet transplants within hours of infusion. The proinflammatory cytokine interferon-γ-induced protein 10 (IP-10/CXCL10) was among the highest released, and high levels correlated with poor islet transplant outcomes. Transgenic mouse studies confirmed that donor islet-specific expression of IP-10 contributed to islet inflammation and loss of β-cell function in islet grafts. The effects of islet-derived IP-10 could be blocked by treatment of donor islets and recipient mice with anti-IP-10 neutralizing monoclonal antibody. In vitro studies showed induction of the IP-10 gene was mediated by calcineurin-dependent NFAT signaling in pancreatic β-cells in response to oxidative or inflammatory stress. Sustained association of NFAT and p300 histone acetyltransferase with the IP-10 gene required p38 and c-Jun N-terminal kinase mitogen-activated protein kinase (MAPK) activity, which differentially regulated IP-10 expression and subsequent protein release. Overall, these findings elucidate an NFAT-MAPK signaling paradigm for induction of isletokine expression in β-cells and reveal IP-10 as a primary therapeutic target to prevent β-cell-induced inflammatory loss of graft function after islet cell transplantation.

Protein kinase STK25 aggravates the severity of non-alcoholic fatty pancreas disease in mice

Characterising the molecular networks that negatively regulate pancreatic β-cell function is essential for understanding the underlying pathogenesis and developing new treatment strategies for type 2 diabetes. We recently identified serine/threonine protein kinase 25 (STK25) as a critical regulator of ectopic fat storage, meta-inflammation, and fibrosis in liver and skeletal muscle. Here, we assessed the role of STK25 in control of progression of non-alcoholic fatty pancreas disease in the context of chronic exposure to dietary lipids in mice. We found that overexpression of STK25 in high-fat-fed transgenic mice aggravated diet-induced lipid storage in the pancreas compared with that of wild-type controls, which was accompanied by exacerbated pancreatic inflammatory cell infiltration, stellate cell activation, fibrosis and apoptosis. Pancreas of Stk25 transgenic mice also displayed a marked decrease in islet β/α-cell ratio and alteration in the islet architecture with an increased presence of α-cells within the islet core, whereas islet size remained similar between genotypes. After a continued challenge with a high-fat diet, lower levels of fasting plasma insulin and C-peptide, and higher levels of plasma leptin, were detected in Stk25 transgenic vs wild-type mice. Furthermore, the glucose-stimulated insulin secretion was impaired in high-fat-fed Stk25 transgenic mice during glucose tolerance test, in spite of higher net change in blood glucose concentrations compared with wild-type controls, suggesting islet β-cell dysfunction. In summary, this study unravels a role for STK25 in determining the susceptibility to diet-induced non-alcoholic fatty pancreas disease in mice in connection to obesity. Our findings highlight STK25 as a potential drug target for metabolic disease.

Though Active on RINm5F Insulinoma Cells and Cultured Pancreatic Islets, Recombinant IL-22 Fails to Modulate Cytotoxicity and Disease in a Protocol of Streptozotocin-Induced Experimental Diabetes

Interleukin (IL)-22 is a cytokine displaying tissue protective and pro-regenerative functions in various preclinical disease models. Anti-bacterial, pro-proliferative, and anti-apoptotic properties mediated by activation of the transcription factor signal transducer and activator of transcription (STAT)-3 are key to biological functions of this IL-10 family member. Herein, we introduce RINm5F insulinoma cells as rat β-cell line that, under the influence of IL-22, displays activation of STAT3 with induction of its downstream gene targets Socs3, Bcl3, and Reg3b. In addition, IL-22 also activates STAT1 in this cell type. To refine those observations, IL-22 biological activity was evaluated using ex vivo cultivated murine pancreatic islets. In accord with data on RINm5F cells, islet exposure to IL-22 activated STAT3 and upregulation of STAT3-inducible Socs3, Bcl3, and Steap4 was evident under those conditions. As these observations supported the hypothesis that IL-22 may exert protective functions in toxic β-cell injury, application of IL-22 was investigated in murine multiple-low-dose streptozotocin (STZ)-induced diabetes. For that purpose, recombinant IL-22 was administered thrice either immediately before and at disease onset (at d4, d6, d8) or closely thereafter (at d8, d10, d12). These two IL-22-treatment periods coincide with two early peaks of β-cell injury detectable in this model. Notably, none of the two IL-22-treatment strategies affected diabetes incidence or blood glucose levels in STZ-treated mice. Moreover, pathological changes in islet morphology analyzed 28 days after disease induction were not ameliorated by IL-22 administration. Taken together, despite being active on rat RINm5F insulinoma cells and murine pancreatic islets, recombinant IL-22 fails to protect pancreatic β-cells in the tested protocols from toxic effects of STZ and thus is unable to ameliorate disease in the widely used model of STZ-induced diabetes.

Evidence for a role of mitogen-activated protein kinases in the treatment of experimental acute pancreatitis

Acute pancreatitis (AP) is an inflammatory disease characterized by acute inflammation and necrosis of the pancreatic parenchyma. AP is often associated with organ failure, sepsis, and high mortality. The pathogenesis of AP is still not well understood. In recent years several papers have highlighted the cellular and molecular events of acute pancreatitis. Pancreatitis is initiated by activation of digestive enzymes within the acinar cells that are involved in autodigestion of the gland, followed by a massive infiltration of neutrophils and macrophages and release of inflammatory mediators, responsible for the local and systemic inflammatory response. The hallmark of AP is parenchymal cell necrosis that represents the cause of the high morbidity and mortality, so that new potential therapeutic approaches are indispensable for the treatment of patients at high risk of complications. However, not all factors that determine the onset and course of the disease have been explained. Aim of this article is to review the role of mitogen-activated protein kinases in pathogenesis of acute pancreatitis.

Comparative efficacy of 3 soluble epoxide hydrolase inhibitors in rat neuropathic and inflammatory pain models

Epoxy-fatty acids have been recognized as important cell signaling molecules with multiple biological effects including anti-nociception. The main degradation pathway of these signaling molecules is via the soluble epoxide hydrolase (sEH) enzyme. Inhibitors of sEH extend the anti-nociceptive effects of fatty acid epoxides. In this study two models of pain with different etiology, streptozocin induced type I diabetic neuropathic pain and lipopolysaccharide induced inflammatory pain were employed to test sEH inhibitors. A dose range of three sEH inhibitors with the same central pharmacophore but varying substituent moieties was used to investigate maximal anti-allodynic effects in these two models of pain. Inhibiting the sEH enzyme in these models successfully blocked pain related behavior in both models. The sEH inhibitors were more potent and more efficacious than celecoxib in reducing both diabetic neuropathic pain and lipopolysaccharide induced inflammatory pain. Because of their ability to block diabetic neuropathic pain sEH inhibition is a promising new approach to treat chronic pain conditions.

Endothelial MKK3 is a critical mediator of lethal murine endotoxemia and acute lung injury

Sepsis is a leading cause of intensive care unit admissions, with high mortality and morbidity. Although outcomes have improved with better supportive care, specific therapies are limited. Endothelial activation and oxidant injury are key events in the pathogenesis of sepsis-induced lung injury. The signaling pathways leading to these events remain poorly defined. We sought to determine the role of MAPK kinase 3 (MKK3), a kinase of the p38 group, in the pathogenesis of sepsis. We used a murine i.p. LPS model of systemic inflammation to mimic sepsis. Lung injury parameters were assessed in lung tissue and bronchoalveolar lavage specimens. Primary lung endothelial cells were cultured and assessed for mediators of inflammation and injury, such as ICAM-1, AP-1, NF-κB, and mitochondrial reactive oxygen species. Our studies demonstrate that MKK3 deficiency confers virtually complete protection against organ injury after i.p. LPS. Specifically, MKK3(-/-) mice were protected against acute lung injury, as assessed by reduced inflammation, mitochondrial reactive oxygen species generation, endothelial injury, and ICAM-1 expression after LPS administration. Our results show that endothelial MKK3 is required for inflammatory cell recruitment to the lungs, mitochondrial oxidant-mediated AP-1, NF-κB activation, and ICAM-1 expression during LPS challenge. Collectively, these studies identify a novel role for MKK3 in lethal LPS responses and provide new therapeutic targets against sepsis and acute lung injury.

Beneficial effects of inhibition of soluble epoxide hydrolase on glucose homeostasis and islet damage in a streptozotocin-induced diabetic mouse model

Soluble epoxide hydrolase (sEH) is an enzyme involved in the metabolism of endogenous inflammatory and anti-apoptotic mediators. In the present study, we determined the effects of the inhibition of sEH on glucose homeostasis and islet damage in mice treated with streptozotocin (STZ), a model of chemical-induced diabetes. STZ increased daily water intake and decreased visceral (spleen and pancreas) weight in mice; sEH inhibition in STZ mice decreased water intake, but did not affect visceral weight. Hyperglycemia induced by STZ treatment in mice was attenuated by inhibiting sEH. The beneficial effects of sEH inhibition were accompanied, after 2 and 4 weeks of initial administration, by improving glucose tolerance. In contrast, sEH inhibition did not affect insulin tolerance. Using LC/MS analysis, neither STZ nor STZ plus sEH inhibition affected pancreatic and plasma ratios of epoxyeicosatrienoic acids (EETs) to dihydroxyeicosatrienoic acids (DHETs), an index of EETs levels. Western blot analysis showed that mouse cytochrome P450 (CYP) 2C enzymes are the major epoxygenases in islets. On day 5 after initial STZ treatment, STZ induced islet cell apoptosis, while sEH inhibition in STZ mice significantly reduced islet cell apoptosis. These studies provide pharmacological evidence that inhibiting sEH activity provides significant protection against islet β-cell damage and improves glucose homeostasis in STZ-induced diabetes.

p38MAPK suppresses chronic pancreatitis by regulating HSP27 and BAD expression

Mitogen-activated protein kinases (MAPKs) are ubiquitous proteins that function in both normal and stress-related pathophysiological states of the cell. This study aimed to analyze the importance of p38MAPK in pancreatic injury using WBN/Kob rats with spontaneous chronic pancreatitis. Male WBN/Kob rats were injected with the p38MAPK inhibitor SB203580, starting at the age of 4 weeks, and sacrificed 6 weeks later. Compared with vehicle-treated rats, p38 inhibitor-treated rats exhibited a significant increase in pancreatic cell death and inflammation as assessed by histologic examination and myeloperoxidase activity, respectively. p38 inhibition decreased the expression of heat shock protein 27 (HSP27), an antioxidant protein, and enhanced accumulation of reactive oxygen species (ROS). In addition, the proapoptotic protein BAD was increased in the pancreas of rats treated with p38 inhibitor. In a pancreatic cell line (PANC-1), HSP27 knockdown augmented reactive oxygen species accumulation and cell death induced by tumor necrosis factor-α plus actinomycin D. In conclusion, p38MAPK suppresses chronic pancreatitis by upregulating HSP27 expression and downregulating BAD expression.

Balance between MKK6 and MKK3 mediates p38 MAPK associated resistance to cisplatin in NSCLC

The p38 MAPK signaling pathway has been proposed as a critical mediator of the therapeutic effect of several antitumor agents, including cisplatin. Here, we found that sensitivity to cisplatin, in a system of 7 non-small cell lung carcinoma derived cell lines, correlated with high levels of MKK6 and marked activation of p38 MAPK. However, knockdown of MKK6 modified neither the response to cisplatin nor the activation of p38 MAPK. Deeper studies showed that resistant cell lines also displayed higher basal levels of MKK3. Interestingly, MKK3 knockdown significantly decreased p38 phosphorylation upon cisplatin exposure and consequently reduced the response to the drug. Indeed, cisplatin poorly activated MKK3 in resistant cells, while in sensitive cell lines MKK3 showed the opposite pattern in response to the drug. Our data also demonstrate that the low levels of MKK6 expressed in resistant cell lines are the consequence of high basal activity of p38 MAPK mediated by the elevated levels of MKK3. This finding supports the existence of a regulatory mechanism between both MAPK kinases through their MAPK. Furthermore, our results were also mirrored in head and neck carcinoma derived cell lines, suggesting our observations boast a potential universal characteristic in cancer resistance of cisplatin. Altogether, our work provides evidence that MKK3 is the major determinant of p38 MAPK activation in response to cisplatin and, hence, the resistance associated with this MAPK. Therefore, these data suggest that the balance between both MKK3 and MKK6 could be a novel mechanism which explains the cellular response to cisplatin.

NOX2 deficiency protects against streptozotocin-induced beta-cell destruction and development of diabetes in mice

OBJECTIVE

The role of NOX2-containing NADPH oxidase in the development of diabetes is not fully understood. We hypothesized that NOX2 deficiency decreases reactive oxygen species (ROS) production and immune response and protects against streptozotocin (STZ)-induced β-cell destruction and development of diabetes in mice.

RESEARCH DESIGN AND METHODS

Five groups of mice--wild-type (WT), NOX2(-/-), WT treated with apocynin, and WT adoptively transferred with NOX2(-/-) or WT splenocytes--were treated with multiple-low-dose STZ. Blood glucose and insulin levels were monitored, and an intraperitoneal glucose tolerance test was performed. Isolated WT and NOX2(-/-) pancreatic islets were treated with cytokines for 48 h.

RESULTS

Significantly lower blood glucose levels, higher insulin levels, and better glucose tolerance was observed in NOX2(-/-) mice and in WT mice adoptively transferred with NOX2(-/-) splenocytes compared with the respective control groups after STZ treatment. Compared with WT, β-cell apoptosis, as determined by TUNEL staining, and insulitis were significantly decreased, whereas β-cell mass was significantly increased in NOX2(-/-) mice. In response to cytokine stimulation, ROS production was significantly decreased, and insulin secretion was preserved in NOX2(-/-) compared with WT islets. Furthermore, proinflammatory cytokine release induced by concanavalin A was significantly decreased in NOX2(-/-) compared with WT splenocytes.

CONCLUSIONS

NOX2 deficiency decreases β-cell destruction and preserves islet function in STZ-induced diabetes by reducing ROS production, immune response, and β-cell apoptosis.

Inhibition or deletion of soluble epoxide hydrolase prevents hyperglycemia, promotes insulin secretion, and reduces islet apoptosis

Soluble epoxide hydrolase (sEH) is an enzyme involved in the metabolism of endogenous inflammatory and antiapoptotic mediators. However, the roles of sEH in diabetes and the pancreas are unknown. Our aims were to determine whether sEH is involved in the regulation of hyperglycemia in diabetic mice and to investigate the reasons for the regulation of insulin secretion by sEH deletion or inhibition in islets. We used two separate approaches, targeted disruption of Ephx2 gene [sEH knockout (KO)] and a selective inhibitor of sEH [trans-4-[4-(3-adamantan-1-ylureido)-cyclohexyloxy]-benzoic acid (t-AUCB)], to assess the role of sEH in glucose and insulin homeostasis in streptozotocin (STZ) mice. We also examined the effects of sEH KO or t-AUCB on glucose-stimulated insulin secretion (GSIS) and intracellular calcium levels in islets. Hyperglycemia in STZ mice was prevented by both sEH KO and t-AUCB. In addition, STZ mice with sEH KO had improved glucose tolerance. More important, when insulin levels were assessed by hyperglycemic clamp study, sEH KO was found to promote insulin secretion. In addition, sEH KO and t-AUCB treatment augmented islet GSIS. Islets with sEH KO had a greater intracellular calcium influx when challenged with high glucose or KCl in the presence of diazoxide. Moreover, sEH KO reduced islet cell apoptosis in STZ mice. These results show not only that sEH KO and its inhibition prevent hyperglycemia in diabetes, but also that sEH KO enhances islet GSIS through the amplifying pathway and decreases islet cell apoptosis in diabetes.

Linoleic acid promotes mitochondrial biogenesis and maintains mitochondrial structure for prevention of streptozotocin damage in RIN-m5F cells

Linoleic acid (LA) improves insulin resistance and prevents diabetes. To investigate whether linoleic acid could protect against streptozotocin (STZ)-induced cell death, rat RIN-m5F cells were exposed to STZ. SL and SO groups consisted of cells treated with STZ and then LA or oleic acid (OA) respectively. STZ treatment decreased the mitochondrial membrane potential in the STZ, SO, and SL groups. Cells of the SL group had more intact mitochondria. Increased mRNA expression of mitochondrial DNA (mtDNA) and nuclear DNA (nDNA), as well as of the mitochondrial biogenesis regulators peroxisome proliferator activated receptor gamma coactivator-1alpha (PGC-1alpha), and mitochondrial transcription factor A (Tfam), were found in the LA group. The insulin content was significantly decreased in all three groups. These results suggest that the effects of LA on cell viability after STZ damage occur through maintenance of mitochondrial structure and increased mitochondrial biogenesis.

Role of MKK3-p38 MAPK signalling in the development of type 2 diabetes and renal injury in obese db/db mice

AIMS/HYPOTHESIS

Obesity and diabetes are associated with increased intracellular p38 mitogen-activated protein kinase (MAPK) signalling, which may promote tissue inflammation and injury. Activation of p38 MAPK can be induced by either of the immediate upstream kinases, MAP kinase kinase (MKK)3 or MKK6, and recent evidence suggests that MKK3 has non-redundant roles in the pathology attributed to p38 MAPK activation. Therefore, this study examined whether MKK3 signalling influences the development of obesity, type 2 diabetes and diabetic nephropathy.

METHODS

Wild-type and Mkk3 (also known as Map2k3) gene-deficient db/db mice were assessed for the development of obesity, type 2 diabetes and renal injury from 8 to 32 weeks of age.

RESULTS

Mkk3 (+/+) db/db and Mkk3 (-/-) db/db mice developed comparable obesity and were similar in terms of incidence and severity of type 2 diabetes. At 32 weeks, diabetic Mkk3 (+/+) db/db mice had increased kidney levels of phospho-p38 and MKK3 protein. In comparison, kidney levels of phospho-p38 in diabetic Mkk3 ( -/- ) db/db mice remained normal, despite a fourfold compensatory increase in MKK6 protein levels. The reduced levels of p38 MAPK signalling in the diabetic kidneys of Mkk3 ( -/- ) db/db mice was associated with protection against the following: declining renal function, increasing albuminuria, renal hypertrophy, podocyte loss, mesangial cell activation and glomerular fibrosis. Diabetic Mkk3 ( -/- ) db/db mice were also significantly protected from tubular injury and interstitial fibrosis, which was associated with reduced Ccl2 mRNA expression and interstitial macrophage accumulation.

CONCLUSIONS/INTERPRETATION

MKK3-p38 MAPK signalling is not required for the development of obesity or type 2 diabetes, but plays a distinct pathogenic role in the progression of diabetic nephropathy in db/db mice.