Pituitary adenylate cyclase-activating polypeptide prevents the effects of ceramides on migration, neurite outgrowth, and cytoskeleton remodeling

Abstract

During neuronal migration, cells that do not reach their normal destination or fail to establish proper connections are eliminated through an apoptotic process. Recent studies have shown that the proinflammatory cytokine tumor necrosis factor ␣ (and its second messengers ceramides) and the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) play a pivotal role in the histogenesis of the cerebellar cortex. However, the effects of ceramides and PACAP on migration of cerebellar granule cells have never been investigated. Time-lapse videomicroscopy recording showed that C2-ceramide, a cell-permeable ceramide analog, and PACAP induced opposite effects on cell motility and neurite outgrowth. C2-ceramide markedly stimulated cell movements during the first hours of treatment and inhibited neuritogenesis, whereas PACAP reduced cell migration and promoted neurite outgrowth. These actions of C2-ceramide on cell motility and neurite outgrowth were accompanied by a disorganization of the actin filament network, depolarization of tubulin, and alteration of the microtubule-associated protein Tau. In contrast, PACAP strengthened the polarization of actin at the emergence cone, increased Tau phosphorylation, and abolished C2-ceramide-evoked alterations of the cytoskeletal architecture. The caspase-inhibitor Z-VAD-FMK, like PACAP, suppressed the ''dance of the death'' provoked by C2-ceramide. Finally, Z-VAD-FMK and the PP2A inhibitor okadaic acid both prevented the impairment of Tau phosphorylation induced by C2-ceramide. Taken together, these data indicate that the reverse actions of C2-ceramide and PACAP on cerebellar granule cell motility and neurite outgrowth are attributable to their opposite effects on actin distribution, tubulin polymerization, and Tau phosphorylation.neuronal migration ͉ sphingolipid D uring neurodevelopment, newly generated neurons migrate to reach their appropriate location in the brain and undergo neurite outgrowth to establish cell connections. Cell migration and synaptogenesis thus represent pivotal phases in maturation of the central nervous system. Neurons that have not established proper connection will be eliminated through apoptosis (1), and defects in the differentiation processes can lead to severe neuronal malformations. For instance, in the developing cerebellum, overexpression of the cytokine TNF␣ markedly alters granule cell migration and induces aberrant cerebellar cytoarchitecture (2). TNF stimulates the biosynthesis of ceramides, a class of second messengers that play a pivotal role during neurodevelopment (3, 4). In cerebellar granule neurons, ceramides trigger cell death through activation of the mitochondrial apoptotic pathway (5). Invalidation of acid sphingomyelinase, which catalyses the formation of ceramides, causes cerebellar axonal dystrophy and neurodegeneration (6), indicating that ceramides are involved in the control of neurogenesis and programmed cell death.Pituitary adenylate cyclase-activating polypeptide (PACAP) is a 38-aa neuropeptide that belongs t...

Phosphorylation of Doublecortin by Protein Kinase A Orchestrates Microtubule and Actin Dynamics to Promote Neuronal Progenitor Cell Migration

“…1H. In contrast to our results, previous reports showed that PACAP inhibits the migration of immature granule neurons in the Purkinje cell layer at the postnatal stage (43,44). On the other hand, it has been reported that a high concentration of PACAP induces G q signaling (45), and G q signaling induced by the endothelin receptor inhibits the migration of NPCs (9).…”

Pituitary Adenylate Cyclase-Activating Polypeptide and Its Receptors: 20 Years after the Discovery

“…In cultured granule neurons, PACAP, acting through the PAC1-R (short and hop variants), stimulates cAMP production and polyphosphoinositide hydrolysis Basille et al, 1995;Favit et al, 1995;Villalba et al, 1997). The effect of PACAP on granule cell differentiation is associated with accumulation of actin at the emergence cone and phosphorylation of Tau protein (Falluel-Morel et al, 2005). The neuroprotective effect of PACAP on granule neurons involves AC activity and is blocked by a dominant-negative mutant of PKA (Kienlen Campard et al, 1997).…”

Effets du PACAP et du C2- céramide sur la motilité des neurones en grain du cervelet : Rien ne sert de courir, il faut partir à point

“…Il a été montré que les céramides peuvent induire des effets pro-apoptotiques au cours du neurodéveloppement suggérant une interaction avec le neuropeptide PACAP lors de la corticogenèse du cervelet [7,8]. L'analyse de la motilité des cellules en grain en culture révèle que ces neurones se déplacent régulièrement par nucleokinesis [9]. La distance au point d'origine parcourue par les neurones pendant les 12 premières heures de culture est de l'ordre de 15 µm, soit une vitesse moyenne de 20 nm par minute environ (Figure 2).…”

“…Le C2-céramide réduit fortement la neuritogenèse en agissant à la fois sur l'initiation et sur l'élongation des prolongements cellulaires alors que le PACAP abolit l'effet inhibiteur du C2-céra-mide sur la croissance des neurites sans modifier l'initiation, suggérant que ces deux processus sont régulés par des mécanismes distincts. Les effets du C2-céramide et du PACAP sur la morphogenèse du neurone en grain ne résultent pas de modifications d'expression de l'actine ni de la tubuline [9]. En revanche, la distribution cellulaire de ces deux protéines du cytosquelette est fortement modifiée.…”

“…Le PACAP est exprimé in situ dans les cellules de Purkinje et l'administration de PACAP à la surface du cortex cérébelleux immature induit une augmentation significative du nombre de neurones en grain dans la couche granulaire interne [12], suggérant un rôle du peptide endogène dans les processus de survie neuronale. Pour la première fois, les effets du C2-céramide et du PACAP sur la motilité des neurones en grain ont pu être visualisés et caractérisés par vidéomicroscopie [9]. Ces effets sont associés à des modifications morphologiques particulièrement marquées en ce qui concerne la croissance neuritique et à des régulations différentes des protéines du cytosquelette.…”