Opposing roles of ERK and p38 MAP kinases in FGF2-induced astroglial process extension.
ABSTRACT The stellate processes of astroglial cells undergo extensive remodeling in response to neural injury. Little is known about intracellular signaling mechanisms controlling process extension. We tested roles for the ERK and p38 MAP kinase pathways in a simplified culture model. FGF2-induced process extension was preceded by a strong and transient phosphorylation of ERK, and a modest activation of p38 MAP kinase, which exhibited significant basal activity. Phosphorylated ERK was found predominantly in the cytoplasm, whereas activated p38 MAP kinase was nuclear. Process extension was completely blocked by the specific MEK inhibitor U0126. Conversely, inhibition of the p38 MAP kinase pathway with SB202190 stimulated spontaneous process growth and greatly potentiated FGF2-induced process extension. The p38 inhibitor effect was reproduced with an adenovirus expressing dominant-negative p38 MAP kinase. Selective pharmacological blockade of MAP kinase pathways may enable modulation of the astroglial response to injury so as to promote neural regeneration.
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ABSTRACT: Brain-specific angiogenesis inhibitor-1 (BAI1) is a transmembrane protein highly expressed in normal brain that has been ascribed two apparently distinct functions: inhibition of angiogenesis and recognition and engulfment of apoptotic cells by phagocytes. A previous localization study reported BAI1 expression only in neurons. Because a phagocytic function of BAI1 could be important for neuroglial antigen processing and presentation, we performed immunolocalization studies in adult mouse brain and cultured neural cells, using a pair of antibodies directed against N- and C-terminal epitopes. BAI1 immunoreactivity is enriched in gray matter structures and largely excluded from myelinated axon tracts. Neuronal BAI1 expression was readily detectable in the cerebellar molecular layer as well as in primary hippocampal cultures. In some brain regions, especially olfactory bulb glomeruli, BAI1 was expressed by GFAP-positive astrocytes. Cultured cortical astrocytes show small (∼0.4μm(2)) BAI1 immunoreactive membrane puncta as well as prominent focal adhesion localization in a subset of cells. In mixed neuronal-glial cultures, BAI1-expressing astrocytes frequently contained engulfed apoptotic debris. Cultured astrocytes engulfed apoptotic targets, and BAI1 showed accumulation within the phagocytic cup. We hypothesize that glial BAI1 may subserve an engulfment function in adult brain regions such as olfactory bulb with ongoing apoptotic turnover, whereas neuronal-derived BAI1 may serve primarily as an anti-angiogenic factor in the mature neuropil.Brain Behavior and Immunity 09/2010; 25(5):915-21. DOI:10.1016/j.bbi.2010.09.021 · 6.13 Impact Factor
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ABSTRACT: Numerous studies have implicated spinal extracellular signal-regulated kinases (ERKs) as mediators of nociceptive plasticity. These studies have utilized pharmacological inhibition of MEK to demonstrate a role for ERK signaling in pain, but this approach cannot distinguish between effects of ERK in neuronal and non-neuronal cells. The present studies were undertaken to test the specific role of neuronal ERK in formalin-induced inflammatory pain. Dominant negative MEK (DN MEK) mutant mice in which MEK function is suppressed exclusively in neurons were tested in the formalin model of inflammatory pain. Formalin-induced second phase spontaneous pain behaviors as well as thermal hyperalgesia measured 1 - 3 hours post-formalin were significantly reduced in the DN MEK mice when compared to their wild type littermate controls. In addition, spinal ERK phosphorylation following formalin injection was significantly reduced in the DN MEK mice. This was not due to a reduction of the number of unmyelinated fibers in the periphery, since these were almost double the number observed in wild type controls. Further examination of the effects of suppression of MEK function on a downstream target of ERK phosphorylation, the A-type potassium channel, showed that the ERK-dependent modulation of the A-type currents is significantly reduced in neurons from DN MEK mice compared to littermate wild type controls. Our results demonstrate that the neuronal MEK-ERK pathway is indeed an important intracellular cascade that is associated with formalin-induced inflammatory pain and thermal hyperalgesia.Molecular Pain 02/2006; 2:2. DOI:10.1186/1744-8069-2-2 · 3.53 Impact Factor