FASEB journal : official publication of the Federation of American Societies for Experimental Biology
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Increased expression of the astrocytic intermediate filament protein glial fibrillary acidic protein (GFAP) is a characteristic of astrogliosis. This process occurs in the brain during aging and neurodegeneration and coincides with impairment of the ubiquitin proteasome system. Inhibition of the proteasome impairs protein degradation; therefore, we hypothesized that the increase in GFAP may be the result of impaired proteasomal activity in astrocytes. ⋯ We show that the proteasome alters GFAP promoter activity, possibly mediated by transcription factors as demonstrated by a GFAP promoter-luciferase assay and RT(2) Profiler PCR array for human transcription factors. Most important, we demonstrate that proteasome inhibitors also reduce GFAP and vimentin expression in a rat model for induced astrogliosis in vivo. Therefore, proteasome inhibitors could serve as a potential therapy to modulate astrogliosis associated with CNS injuries and disease.
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The receptor for advanced glycation end products (RAGE) is a multiligand cell surface receptor, and amyloid beta peptide (Abeta) is one of the ligands for RAGE. Because RAGE is a transporter of Abeta from the blood to the brain, RAGE is believed to play an important role in Alzheimer's disease (AD) pathogenesis. In the present study, the role of RAGE in Abeta production was examined in the brain tissue of an AD animal model, Tg2576 mice, as well as cultured cells. ⋯ NFAT1 was activated following RAGE-induced BACE1 expression followed by Abeta generation. Injection of soluble RAGE (sRAGE), which acts as a competitor with full-length RAGE (fRAGE), into aged Tg2576 mouse brains reduced the levels of plaques, Abeta, BACE1, and the active form of NFAT1 compared with fRAGE-injected Tg2576 mice. Taken together, RAGE stimulates functional BACE1 expression through NFAT1 activation, resulting in more Abeta production and deposition in the brain.
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Tolerance to morphine-induced analgesia is a well-established phenomenon, often limiting its usefulness in the long-term treatment of pain. The mechanisms underlying tolerance are not well understood. We previously suggested a possible role for spinal calcitonin gene-related peptide (CGRP) in the development of tolerance to morphine-induced analgesia. ⋯ Interestingly, the inhibition of the ERK pathway suppressed the development of tolerance and morphine-induced up-regulation of IL-1beta, TNF-alpha, and mPGES-1. Blockade of p38 activity also inhibited the development of tolerance and morphine-induced IL-6 up-regulation. Taken together, these data suggest that chronic morphine induces the synthesis of CGRP, which in turn acts on CGRP receptors located on astrocytes and microglia to stimulate ERK and p38, respectively, leading to increased synthesis and release of proinflammatory mediators resulting in tolerance to morphine-induced analgesia.
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T-cell activation requires the influx of extracellular calcium, although mechanistic details regarding such activation are not fully defined. Here, we show that P2X(7) receptors play a key role in calcium influx and downstream signaling events associated with the activation of T cells. By real-time PCR and immunohistochemistry, we find that Jurkat T cells and human CD4(+) T cells express abundant P2X(7) receptors. ⋯ Removal of extracellular ATP by apyrase or alkaline phosphatase treatment, inhibition of ATP release with the maxi-anion channel blocker gadolinium chloride, or siRNA silencing of P2X(7) receptors blocks calcium entry and inhibits T-cell activation. Moreover, lymphocyte activation is impaired in C57BL/6 mice that express poorly functional P2X(7) receptors, compared to control BALB/c mice, which express fully functional P2X(7) receptors. We conclude that ATP release and autocrine, positive feedback through P2X(7) receptors is required for the effective activation of T cells.
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Calsequestrin-1 (CASQ1) is a moderate-affinity, high-capacity Ca(2+)-binding protein in the sarcoplasmic reticulum (SR) terminal cisternae of skeletal muscle. CASQ1 functions as both a Ca(2+)-binding protein and a luminal regulator of ryanodine receptor (RYR1)-mediated Ca(2+) release. Mice lacking skeletal CASQ1 are viable but exhibit reduced levels of releasable Ca(2+) and altered contractile properties. ⋯ The characteristics of these events are remarkably similar to analogous episodes observed in humans with malignant hyperthermia (MH) and animal models of MH and environmental heat stroke (EHS). In vitro studies indicate that CASQ1-null muscle exhibits increased contractile sensitivity to temperature and caffeine, temperature-dependent increases in resting Ca(2+), and an increase in the magnitude of depolarization-induced Ca(2+) release. These results demonstrate that CASQ1 deficiency alters proper control of RYR1 function and suggest CASQ1 as a potential candidate gene for linkage analysis in families with MH/EHS where mutations in the RYR1 gene are excluded.