Induction of an inflammatory loop by interleukin-1ß and tumor necrosis factor-α involves NF-kB and STAT-1 in differentiated human neuroprogenitor cells.

Proinflammatory cytokines secreted from microglia are known to induce a secondary immune response in astrocytes leading to an inflammatory loop. Cytokines also interfere with neurogenesis during aging and in neurodegenerative diseases. The present study examined the mechanism of induction of inflammatory mediators at the transcriptional level in human differentiated neuroprogenitor cells (NPCs). Interleukin-1ß (IL-1ß) and tumor necrosis factor-α (TNF-α) induced the expression of cytokines and chemokines in differentiated human NPCs as shown by an immune pathway-specific array. Network motif (NM) analysis of these genes revealed 118 three-node NMs, suggesting complex interactions between inflammatory mediators and transcription factors. Immunofluorescent staining showed increases in the levels of IL-8 and CXCL10 proteins in neurons and glial cells. Findings from Taqman low density array suggested the synergistic actions of IL-1ß and TNF-α in the induction of a majority of inflammatory genes by a mechanism involving NF-kB and STAT-1. Nuclear localization of these transcription factors in differentiated NPCs was observed following exposure to IL-1α and TNF-α. Further studies on CXCL10, a chemokine known to be elevated in the Alzheimer's brain, showed that TNF-α is a stronger inducer of CXCL10 promoter when compared to IL-1ß. The synergy between these cytokines was lost when ISRE or kB elements in CXCL10 promoter were mutated. Our findings suggest that the activation of inflammatory pathways in neurons and astrocytes through transcription factors including NF-kB and STAT-1 play important roles in neuroglial interactions and in sustaining the vicious cycle of inflammatory response.

Neuroprotective actions of glucagon-like peptide-1 in differentiated human neuroprogenitor cells.

Glucagon-like peptide-1 (GLP-1)-based therapies are currently available for the treatment of type 2 diabetes, based on their actions on pancreatic ß cells. GLP-1 is also known to exert neuroprotective actions. To determine its mechanism of action, we developed a neuron-rich cell culture system by differentiating human neuroprogenitor cells in the presence of a combination of neurotrophins and retinoic acid. The neuronal nature of these cells was characterized by neurogenesis pathway-specific array. GLP-1 receptor expression was seen mainly in the neuronal population. Culture of neurons in the presence of Aß oligomers resulted in the induction of apoptosis as shown by the activation of caspase-3 and caspase-6. Exendin-4, a long-acting analog of GLP-1, protected the neurons from apoptosis induced by Aß oligomers. Exendin-4 stimulated cyclic AMP response element binding protein phosphorylation, a regulatory step in its activation. A transient transfection assay showed induction of a reporter linked to CRE site-containing human brain-derived neurotrophic factor promoter IV, by the growth factor through multiple signaling pathways. The anti-apoptotic action of exendin-4 was lost following down-regulation of cAMP response element binding protein. Withdrawal of neurotrophins resulted in the loss of neuronal phenotype of differentiated neuroprogenitor cells, which was prevented by incubation in the presence of exendin-4. Diabetes is a risk factor in the pathogenesis of Alzheimer's disease. Our findings suggest that GLP-1-based therapies can decrease the incidence of Alzheimer's disease among aging diabetic population.

A synthetic chalcone as a potent inducer of glutathione biosynthesis.

Chalcones continue to attract considerable interest due to their anti-inflammatory and antiangiogenic properties. We recently reported the ability of 2',5'-dihydroxychalcone (2',5'-DHC) to induce both breast cancer resistance protein-mediated export of glutathione (GSH) and c-Jun N-terminal kinase-mediated increased intracellular GSH levels. Herein, we report a structure-activity relationship study of a series of 30 synthetic chalcone derivatives with hydroxyl, methoxyl, and halogen (F and Cl) substituents and their ability to increase intracellular GSH levels. This effect was drastically improved with one or two electrowithdrawing groups on phenyl ring B and up to three methoxyl and/or hydroxyl groups on phenyl ring A. The optimal structure, 2-chloro-4',6'-dimethoxy-2'-hydroxychalcone, induced both a potent NF-E2-related factor 2-mediated transcriptional response and an increased formation of glutamate cysteine ligase holoenzyme, as shown using a human breast cancer cell line stably expressing a luciferase reporter gene driven by antioxidant response elements.