Glucose and fatty acids synergize to promote B-cell apoptosis through activation of glycogen synthase kinase 3β independent of JNK activation

Background

The combination of elevated glucose and free-fatty acids (FFA), prevalent in diabetes, has been suggested to be a major contributor to pancreatic β-cell death. This study examines the synergistic effects of glucose and FFA on β-cell apoptosis and the molecular mechanisms involved. Mouse insulinoma cells and primary islets were treated with palmitate at increasing glucose and effects on apoptosis, endoplasmic reticulum (ER) stress and insulin receptor substrate (IRS) signaling were examined.

Principal Findings

Increasing glucose (5–25 mM) with palmitate (400 µM) had synergistic effects on apoptosis. Jun NH2-terminal kinase (JNK) activation peaked at the lowest glucose concentration, in contrast to a progressive reduction in IRS2 protein and impairment of insulin receptor substrate signaling. A synergistic effect was observed on activation of ER stress markers, along with recruitment of SREBP1 to the nucleus. These findings were confirmed in primary islets. The above effects associated with an increase in glycogen synthase kinase 3β (Gsk3β) activity and were reversed along with apoptosis by an adenovirus expressing a kinase dead Gsk3β.

Conclusions/Significance

Glucose in the presence of FFA results in synergistic effects on ER stress, impaired insulin receptor substrate signaling and Gsk3β activation. The data support the importance of controlling both hyperglycemia and hyperlipidemia in the management of Type 2 diabetes, and identify pancreatic islet β-cell Gsk3β as a potential therapeutic target.     

Plexin-B1 activates NF-κB and IL-8 to promote a pro-angiogenic response in endothelial cells

Background

The semaphorins and their receptors, the plexins, are proteins related to c-Met and the scatter factors that have been implicated in an expanding signal transduction network involving co-receptors, RhoA and Ras activation and deactivation, and phosphorylation events. Our previous work has demonstrated that Semaphorin 4D (Sema4D) acts through its receptor, Plexin-B1, on endothelial cells to promote angiogenesis in a RhoA and Akt-dependent manner. Since NF-κB has been linked to promotion of angiogenesis and can be activated by Akt in some contexts, we wanted to examine NF-κB in Sema4D treated cells to determine if there was biological significance for the pro-angiogenic phenotype observed in endothelium.

Methods/Principal Findings

Using RNA interference techniques, gel shifts and NF-κB reporter assays, we demonstrated NF-κB translocation to the nucleus in Sema4D treated endothelial cells occurring downstream of Plexin-B1. This response was necessary for endothelial cell migration and capillary tube formation and protected endothelial cells against apoptosis as well, but had no effect on cell proliferation. We dissected Plexin-B1 signaling with chimeric receptor constructs and discovered that the ability to activate NF-κB was dependent upon Plexin-B1 acting through Rho and Akt, but did not involve its role as a Ras inhibitor. Indeed, inhibition of Rho by C3 toxin and Akt by {"type":"entrez-nucleotide","attrs":{"text":"LY294002","term_id":"1257998346","term_text":"LY294002"}}LY294002 blocked Sema4D-mediated endothelial cell migration and tubulogenesis. We also observed that Sema4D treatment of endothelial cells induced production of the NF-κB downstream target IL-8, a response necessary for angiogenesis. Finally, we could show through co-immunofluorescence for p65 and CD31 that Sema4D produced by tumor xenografts in nude mice activated NF-κB in vessels of the tumor stroma.

Conclusion/Significance

These findings provide evidence that Sema4D/Plexin-B1-mediated NF-κB activation and IL-8 production is critical in the generation a pro-angiogenic phenotype in endothelial cells and suggests a new therapeutic target for the anti-angiogenic treatment of some cancers.     

Predominance of Th2 response in human abdominal aortic aneurysm: mistaken identity for IL-4-producing NK and NKT cells?

Abdominal aortic aneurysm (AAA) is a complex remodeling process that involves both synthesis and degradation of extracellular matrix proteins in the aortic wall, leading to decreased tensile strength, progressive dilation and eventual rupture. Chronic inflammation, increased local production of elastin-degrading proteases by inflammatory cells and destruction of medial elastic lamellae play important roles in aneurysm progression. Neovascularization in all layers of the arterial wall is prominent and angiogenesis can facilitate chronic inflammation. It is still unclear what initiates aneurysmal dilation and what determines its progression. The complex nature of the process has defied elucidation. Apart from macrophages, the predominant immune cell infiltrates reported so far are CD3(+)T cells that express CD4 and CD8. Infiltrates of type 2 Th cells and their production of IL-4 and IL-5 have been implicated in AAA development. However, NKT and NK cells have a Th0 cytokine profile and can also produce type 2 as well as type 1 (IL-2 and IFNgamma) cytokines. We have demonstrated the presence of NK and NKT cells in AAA tissue. With their growing importance in autoimmunity and transplantation, they may play a role in AAA development. Therefore, there is a need to use a combination of T and NK markers to fully characterize both innate and adaptive lymphoid cell subsets in local inflammatory infiltrates in order to elucidate their roles in AAA progression.     

LXRs regulate the balance between fat storage and oxidation

Despite the well-established role of liver X receptors (LXRs) in regulating cholesterol homeostasis, their contribution to lipid homeostasis remains unclear. Here we show that LXR null mice are defective in hepatic lipid metabolism and are resistant to obesity when challenged with a diet containing both high fat and cholesterol. This phenotype is dependent on the presence of dietary cholesterol and is accompanied by the aberrant production of thyroid hormone in liver. Interestingly, the inability of LXR-/- mice to induce SREBP-1c-dependent lipogenesis does not explain the LXR-/- phenotype, since SREBP-1c null mice are not obesity resistant. Instead, the LXR-/- response is due to abnormal energy dissipation resulting from uncoupled oxidative phosphorylation and ectopic expression of uncoupling proteins in muscle and white adipose. These studies suggest that, by selectively sensing the cholesterol component of a lipid-rich diet, LXRs govern the balance between storage and oxidation of dietary fat.     

Matrix metalloproteinase secretion by gastric epithelial cells is regulated by E prostaglandins and MAPKs

Because matrix metalloproteinases (MMPs) play roles in inflammatory tissue injury, we asked whether MMP secretion by gastric epithelial cells may contribute to gastric injury in response to signals involved in Helicobacter pylori-induced inflammation and/or cyclooxygenase inhibition. Tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and epidermal growth factor (EGF) stimulated gastric cell MMP-1 secretion, indicating that MMP-1 secretion occurs in inflammatory as well as non-inflammatory situations. MMP-1 secretion required activation of the MAPK Erk and subsequent protein synthesis but was down-regulated by the alternate MAPK, p38. In contrast, secretion of MMP-13 was stimulated by TNF-alpha/IL-1beta but not EGF and was Erk-independent and mediated by p38. MMP-13 secretion was more rapid (peak, 6 h) than MMP-1 (peak > or =30 h) and only partly depended on protein synthesis, suggesting initial release of a pre-existing MMP-13 pool. Therefore, MMP-1 and MMP-13 secretion are differentially regulated by MAPKs. MMP-1 secretion was regulated by E prostaglandins (PGEs) in an Erk-dependent manner. PGEs enhanced Erk activation and MMP-1 secretion in response to EGF but inhibited Erk and MMP-1 when TNF-alpha and IL-1beta were the stimuli, indicating that the effects of PGEs on gastric cell responses are context-dependent. These data show that secretion of MMPs is differentially regulated by MAPKs and suggest mechanisms through which H. pylori infection and/or cyclooxygenase inhibition may induce epithelial cell signaling to contribute to gastric ulcerogenesis.     

Phagocytic functions of microglial cells in the central nervous system and their importance in two neurodegenerative diseases: multiple sclerosis and Alzheimer’s disease

Microglial cells are the resident phagocytic cells of the central nervous system (CNS). They possess a wide range of receptors allowing them to identify and internalize numerous pathogens. We will discuss here the role of the most important receptors of microglia involved in non-opsonin-dependent phagocytosis (mannose receptor, β-glucan receptor, scavenger receptor) and that of receptors involved in the opsonin-dependent phagocytosis, namely the complement 3 (CR3) and the Fcγ receptors (FcγR). First, the molecular and cellular mechanisms induced when these receptors are conducting a phagocytic event are presented. In the second part, we will discuss the role these receptors may play in multiple sclerosis and Alzheimer’s disease, in the elimination by phagocytosis of myelin and beta amyloid peptide respectively. The first two authors contributed equally to this work.     

Functional ability of the elderly in institutional and non-institutional care in Croatia

Gerontology-public health indicators of functional ability of the elderly in institutional and non-institutional health care in Croatia were determined by use of expert methodology developed at Department of Gerontology, Dr. Andrija Stampar Institute of Public Health in Zagreb, with the aim to upgrade the Program of Health Care Measures and Procedures in Health Care of the Elderly. Comparison of functional ability between the users of selected Old People's Homes (institutional care; N = 5030) and Gerontology Centers (non-institutional care; N = 2112) yielded highest between-group difference in the proportion of "fully movable" and "fully independent" categories in favor of the latter, thus steering the program of health care for the elderly accordingly. In addition, study results showed greater difference in the proportion of categories describing mental status of institutional and non-institutional care users as compared with the categories describing their physical status, suggesting that mental status plays a more important role than physical status in the geriatric user's stay in non-institutional care versus institutional care. This issue requires additional studies. The results obtained by this indicator analysis pointed to the preventive and geroprophylactic measures to ensure efficient health care for the elderly and to develop the program of mental health promotion and preservation. According to 2007 estimate, there were 759,318 (16.9%) persons aged > or = 65 in Croatia. Data collected at gerontology database kept at Department of Gerontology, Dr. Andrija Stampar Institute of Public Health (September 2008) showed 2% of the elderly (N = 14807) to be accommodated at Old People's Homes, which is below the European average of 4%.     

Quality of life of patients after stroke in county Osijek-Baranya

The purpose of this prospective study was to determine quality of life of patients after stroke in Osijek-Baranya County. The research included 161 patients (82 men and 79 women) who had their first acute stroke and were treated at Department of Neurology, Osijek University Hospital Center The Barthel Index (BI) was used to assess functional deficiency and SS-QOL (Stroke-Specific Quality of Life) questionnaire was used for self-evaluation of patients' physical and mental health. The first assessment was carried out in the acute phase of the disease, and control assessments 30, 90 and 180 days after the stroke. Mean Barthel Index score was higher at every successive measurement (55, 80, 95, 95). All BI items were statistically significant (Friedman, p < 0.001) apart from dressing and bowel control. BI score indicated greater dependence in women in all assessments except for those taken 90 days after onset of symptoms (chi2-test, p = 0.111). Mean values of SS-QOL for physical health were: 105.2, 98.3, 105.7, 117.5 and for mental health: 64.24, 57.9, 64.3, 68.1. Statistically significant difference was present in men, both for physical health (Friedman p = 0.009) and total SS-QOL (Friedman p = 0.014), while in women there was no statistically significant difference between the measurements (Friedman p = 0.719). The research showed that stroke has significant influence on basic and specific daily life activities and interferes with the quality of life of stroke patients. Women have lower level of independence. Patients who live with their families make better evaluation of their physical and mental health.     

Splenic hematoma as a first manifestation of cytomegalovirus infection

Splenic rupture is rare but life threatening complication of mononucleosis syndrome. It has been suggested that subcapsular splenic hematoma formation precedes rupture. The case of 44-year-old, previously healthy, male with splenic hematoma occurring after rising of heavy cargo is reported. Mononucleosis syndrome was suggested based on routine laboratory tests (elevated white blood cell count with predominance of lymphocytes and raised serum transaminases) and CMV infection was confirmed by serological test. Nonoperative management was used since the patient was hemodynamically stable with no further signs of splenic rupture. The same approach has been used in growing number of cases of patients with spontaneous splenic rupture in mononucleosis syndrome. Importance of considering splenic hematoma and/or rupture if abdominal pain occurs in the course of mononucleosis syndrome is outlined as well as importance of routine laboratory tests in suspecting mononucleosis syndrome in otherwise clinically silent patient.