FK506-DEPENDENT NEUROREGENERATION RESEMBLES THE EARLY STEPS OF NEURONAL DIFFERENTIATION

QUINTA HR; GALIGNIANA MD

Buenos Aires

Workshop; 3rd South American Workshop & International Gregorio Weber Conference on New trends in Advanced Fluorescence Microscopy Techniques; 2011

BACKGROUND AND PURPOSE The immunosuppressive macrolide FK506 (tacrolimus) shows neuroregenerative action by a mechanism that appears to involve the Hsp90-binding immunophilin FKBP52. This study analyzes some aspects of the early steps of neuronal differentiation and neuroregeneration. EXPERIMENTAL APPROACH Undifferentiated murine neuroblastoma cells and hippocampal neurons isolated from embryonic day-17 rat embryos were induced to differentiate with FK506. The subcellular relocalization of FKBP52, Hsp90 and its cochaperone p23 was analyzed by indirect immunofluorescence confocal microscopy and by Western blots of axonal fractions isolated from cells grown on a porous transwell cell culture chamber. Neuroregeneration was evaluated using a scratch-wound assay. KEY RESULTS In undifferentiated cells, FKBP52, Hsp90 and p23 are located in the cell nucleus forming an annular structure that disassembles as soon as the differentiation process is triggered by the macrolide FK506. This observation is valid for the N2a cell line as well as for hippocampal neurons, but not for astrocytic glial cells. Importantly, the annular structure of chaperones is reassembled after damaging the neurons, whereas FK506 prompts their rapid regeneration, a process that is linked to the subcellular redistribution of the heterocomplex. CONCLUSIONS AND IMPLICATIONS There is a direct relationship between the disassembly of the chaperone complex and the progression of neuronal differentiation upon stimulation with the immunophilin ligand FK506. Both neuronal differentiation and neuroregeneration appear to be mechanistically linked, so the elucidation of one mechanism may lead to unravel the properties of the other. The study also implies that the generation of FK506 derivatives devoid of immunosuppressive action would be therapeutically significant for neurotrophic use.