High Glucose Enhances Neurotoxicity and Inflammatory Cytokine Secretion by Stimulated Human Astrocytes.

BACKGROUND: Chronic neuroinflammation caused by activation of microglia and astrocytes in the brain contributes to neuronal loss and disease progression in Alzheimer's disease (AD). Recent research has identified type 2 diabetes mellitus (T2DM) as a risk factor for AD. High blood glucose (hyperglycemia) and the phenomenon of insulin resistance are being considered as the major factors contributing to an increased risk of AD. However, the mechanisms involved in this interaction remain unclear. OBJECTIVE: High glucose has been shown to increase release of pro-inflammatory mediators from various immune cells, including microglia. Since astrocytes are the most abundant glial cell type in the brain, we investigated the effects of elevated glucose concentrations (5.5-30.5 mM) on selected functions of cultured human astrocytes in the presence of inflammatory stimuli. METHOD: Experiments were conducted using primary human astrocytes and U-118 MG astrocytoma cells. RESULTS: High glucose (30.5 mM) increased mRNA expression of interleukin (IL)-6 and secretion of both IL-6 and IL-8 by astrocytes. This astrocytic inflammatory response to high glucose did not appear to be mediated by augmented p38 or p44/42 mitogen activated protein kinase (MAPK) signaling pathways. In addition, high glucose increased the susceptibility of undifferentiated human SH-SY5Y neuronal cells and retinoic-acid differentiated SH-SY5Y cells to injury by hydrogen peroxide (H2O2) and fibrillar amyloid beta-42 protein (Aß42), respectively. CONCLUSION: Our data indicate that hyperglycemia in T2DM may be one of the factors contributing to the observed increased risk of AD by exacerbating astrocyte-mediated neuroinflammation and neuronal injury caused by disease-associated agents.

Insulin Modulates In Vitro Secretion of Cytokines and Cytotoxins by Human Glial Cells.

Alzheimer's disease (AD) is the most common form of dementia worldwide. Type 2 diabetes (T2D) has been implicated as a risk factor for AD. Since T2D is a peripheral inflammatory condition, and AD brains exhibit exacerbated neuroinflammation, we hypothesized that inflammatory mechanisms could contribute to the observed link between T2D and AD. Abnormal peripheral and brain insulin concentrations have been reported in both T2D and AD. The neurotrophic role of insulin has been described; however, this hormone can also regulate inflammatory responses in the periphery. Therefore we used in vitro human cell culture systems to elucidate the possible effects of insulin on neuroinflammation. We show that human astrocytes and microglia express both isoforms of the insulin receptor as well as the insulin-like growth factor (IGF)-1 receptor. They also express insulin receptor substrate (IRS)-1 and IRS-2, which are required for propagation of insulin/IGF- 1 signaling. We show that at low nanomolar concentrations, insulin could be pro-inflammatory by upregulating secretion of interleukin (IL)-6 and IL-8 from stimulated human astrocytes and secretion of IL-8 from stimulated human microglia. This effect dissipates at higher insulin concentrations. In contrast, insulin at a broader concentration range (10 pM - 1 µM) reduces the toxicity of stimulated human microglia and THP-1 monocytic cells towards SH-SY5Y neuronal cells. These data show that insulin may regulate the inflammatory status of glial cells by modulating their select functions, which in turn can influence the survival of neurons contributing to the observed link between T2D and AD.

Improvement in generic problem-solving abilities of students by use of tutor-less problem-based learning in a large classroom setting.

Problem-based learning (PBL) was originally introduced in medical education programs as a form of small-group learning, but its use has now spread to large undergraduate classrooms in various other disciplines. Introduction of new teaching techniques, including PBL-based methods, needs to be justified by demonstrating the benefits of such techniques over classical teaching styles. Previously, we demonstrated that introduction of tutor-less PBL in a large third-year biochemistry undergraduate class increased student satisfaction and attendance. The current study assessed the generic problem-solving abilities of students from the same class at the beginning and end of the term, and compared student scores with similar data obtained in three classes not using PBL. Two generic problem-solving tests of equal difficulty were administered such that students took different tests at the beginning and the end of the term. Blinded marking showed a statistically significant 13% increase in the test scores of the biochemistry students exposed to PBL, while no trend toward significant change in scores was observed in any of the control groups not using PBL. Our study is among the first to demonstrate that use of tutor-less PBL in a large classroom leads to statistically significant improvement in generic problem-solving skills of students.

Moderate increase in temperature may exacerbate neuroinflammatory processes in the brain: human cell culture studies.

The effect of a moderate, physiologically relevant rise in temperature on several neuroinflammatory parameters was investigated in vitro using human cell lines and cultured human astrocytes. A two degree Celsius rise in temperature was found to enhance the neurotoxicity of microglia-like and astrocytic cells, increase the release of monocyte chemotactic protein (MCP)-1 by activated human monocytic THP-1 cells and amplify the generation of reactive oxygen intermediates by differentiated HL-60 myelocytic cells. Moderate increases in body temperature may exacerbate neuroinflammation and neuronal injury in chronic neurodegenerative disorders. Hence, therapies aimed at lowering the body temperature could be used to slow down the progression of such diseases.

Cultured adult porcine astrocytes and microglia express functional interferon-γ receptors and exhibit toxicity towards SH-SY5Y cells.

In vitro cultures of various glial cell types are common systems used to model neuroinflammatory processes associated with age-dependent human neurodegenerative diseases. Even though most researchers choose to use neonatal rodent brain tissues as the source of glial cells, there are significant variations in glial cell functions that are species and age dependent. It has been established that human and swine immune systems have a number of similarities, which suggests that cultured porcine microglia and astrocytes may be good surrogates for human glial cell types. Here we describe a method that could be used to prepare more than 90% pure microglia and astrocyte cultures derived from adult porcine tissues. We demonstrate that both microglia and astrocytes derived from adult porcine brains express functional interferon-γ receptors (IFN-γ-R) and CD14. They become toxic towards SH-SY5Y neuroblastoma cells when exposed to proinflammatory mediators. Upon such stimulation with lipopolysaccharide (LPS) and interferon-γ (IFN-γ), adult porcine microglia, but not astrocytes, secrete tumor necrosis factor-α (TNF-α) while both cell types do not secrete detectable levels of nitric oxide (NO). Comparison of our experimental data with previously published studies indicates that adult porcine glial cultures have certain functional characteristics that make them similar to human glial cells. Therefore adult porcine glial cells may be a useful model system for studies of human diseases associated with adulthood and advanced age. Adult porcine tissues are relatively easy to obtain in most countries and could be used as a reliable and inexpensive source of cultured cells.