HSP90-BINDING IMMUNOPHILIN FKBP52 MEDIATES NEURONAL DIFFERENTIATION AND ASTROCYTE TRANSDIFFERENTIATION INTO NEURONS

GALIGNIANA MD; DANERI-BECERRA C; PIWIEN PILIPUK G

Congreso; 2nd Experts Global Meeting on Frontiers in Cell & Stem Cell Research; 2021

Previously, we demonstrated that the macrolide FK506 (tacrolimus) promotes the differentiation into neurons of undifferentiated neuroblastoma cell lines and primary cultures of embryonic hippocampal cells. FKBP51 and FKBP52 are two immunophilins highly expressed in nervous cells that recognize FK506. Thus, FKBP52 overexpression or FKBP51 knock-down favored neurite outgrowth, whereas FKBP52 knock-down or FKBP51 overexpression impaired it. This indicates that both immunophilins play antagonistic roles during the early steps of neurodifferentiation. Inasmuch as the 5% unavoidable contaminant glial cells disappeared from primary cultures of neurons after 2-3 days with FK506, we evaluated two hypotheses: cell death or glial cell transdifferentiation. Therefore, astrocytic cells were purified from cerebral cortices of 2-day-old rat neonates and treated with FK506 in DMEM medium without serum. While DMSO-treated (control) astrocytes preserved their flat polygonal morphology with an actin network predominantly arranged as sub-cortical fibers just beneath the membrane, the FK506-treated cells adopted a bipolar morphology after 2 days, including cytoplasm retraction, nuclei elongation, and appearance of actin stress fibers. The GFAP astrocytic marker was sequentially replaced by nestin, a typical marker of neuronal stem cells. After 5-7 days cells adopted a neuronal-like phenotype associated to increased expression of neuronal markers (Tau1, III-tubulin), nestin expression gradually faded, and the GFAP marker was lost. Transdifferentiation of glial cells into neurons by FK506 was again assigned to FKBP52 since its overexpression accelerated this process, whereas FKBP51 impaired it. Actually, FKBP52-transfected cells already showed spontaneous neuronal-like phenotype, a phenomenon enhanced by FK506 treatment. Importantly, mice that had underwent spinal-cord injury, fully recovered the locomotor activity upon FK506 treatment, a process impaired in FKBP52-KO mice and enhanced in FKBP51-KO mice. Therefore, we conclude that FKBP52 is a key mediator of neuronal differentiation and astrocyte transdifferentiation, both processes being antagonized by FKBP51, and propose that FK506 is a potentially useful pharmacotherapeutic compound.