Bystin Expression In Reactive Astrocytes And Their Functions Study

Bystin has been identified as a protein which mediates cellular interactions between trophoblastic and endometrial epithelial cells by forming complexes with two partners, trophinin and tastin, during embryo implantation. In the present study, we report the expression of bystin in the adult rat brain and the levels of bystin expression were markedly up-regulated in the both 6-hydrodopamine-lesioned rat nigrostriatum and stab-lesioned cerebral cortex in adult rats. Double immunofluorescence staining revealed that most bystin-expressing glial cells were astrocytes. In primary cultures of postnatal cortical astrocytes, the expression of bystin was elevated by treatment with pro-inflammatory mediators lipopolysaccharide and interleukin-1β. Nerve growth factor known to be released after brain injury also induced bystin expression in the cultures. Exposure of astrocyte cultures to the differentiating agent forskolin, which elevated intracellular cAMP content, resulted in up-regulation of bystin followed by a pronounced astrocytic stellation.Immunohistochemical studies of the rat brain following cortical stab injury revealed that bystin was localized in proximal reactive astrocytes and the corpus callosum, implying that bystin is involved in the migration of these cells. siRNA-induced downregulation of bystin inhibited migration of astrocytes in transwell-based functional assay and scratch-induced migration. Depletion of bystin in astrocytes impaired lamellipodia formation and cell spreading. In migrating astrocytes, bystin was polarized to the leading edge of the lamellipodia and colocalized with F-actin. The direct association of bystin and F-actin at the leading edge was confirmed by using fluorescence resonance energy transfer (FRET). Bystin was also colocalized with F-actin along the stress fibers in stabilizing astrocytes. Cosedimentation experiments demonstrated that bystin bound to F-actin directly and the binding was mediated by the middle fragment (134-256 aa) and C-fragment...