Extracellular α-Synuclein Leads to Microtubule Destabilization via GSK-3β-Dependent Tau Phosphorylation in PC12 Cells

Abstract

α-Synuclein (ASN) plays an important role in pathogenesis of Parkinson's disease (PD) and other neurodegenerative disorders. Novel and most interesting data showed elevated tauopathy in PD and suggested relationship between ASN and Tau protein. However, the mechanism of ASN-evoked Tau protein modification is not fully elucidated. In this study we investigated the role of extracellular ASN in Tau hyperphosphorylation in rat pheochromocytoma (PC12) cells and the involvement of glycogen synthase kinase-3β (GSK-3β) and cyclin-dependent kinase 5 (CDK5) in ASN-dependent Tau modification. Our results indicated that exogenously added ASN increases Tau phosphorylation at Ser396. Accordingly, the GSK-3β inhibitor (SB-216763) prevented ASN-evoked Tau hyperphosphorylation, but the CDK5 inhibitor had no effect. Moreover, western blot analysis showed that ASN affected GSK-3β via increasing of protein level and activation of this enzyme. GSK-3β activity evaluated by its phosphorylation status assay showed that ASN significantly increased the phosphorylation of this enzyme at Tyr216 with parallel decrease in phosphorylation at Ser9, indicative of stimulation of GSK-3β activity. Moreover, the effect of ASN on microtubule (MT) destabilization and cell death with simultaneous the involvement of GSK-3β in these processes were analyzed. ASN treatment increased the amount of free tubulin and concomitantly reduced the amount of polymerized tubulin and SB-216763 suppressed these ASN-induced changes in tubulin, indicating that GSK-3β is involved in ASN-evoked MT destabilization. ASN-induced apoptotic processes lead to decrease in PC12 cells viability and SB-216763 protected those cells against ASN-evoked cytotoxicity. Concluding, extracellular ASN is involved in GSK-3β-dependent Tau hyperphosphorylation, which leads to microtubule destabilization. GSK-3β inhibition may be an effective strategy for protecting against ASN-induced cytotoxicity.

Glycogen synthase kinase-3 beta (GSK-3β) signaling: Implications for Parkinson's disease

“…On the other hand, by decreasing Ser9 phosphorylation and elevating Tyr216 phosphorylation, ␣-Synuclein stimulates GSK-3␤ activity and inhibition of GSK-3␤ abrogates ␣-Synuclein mediated neurotoxicity (Fig. 2) [123]. In addition, GSK-3␤ also phosphorylates synphilin-1 (␣-Synucleininteracting protein) and decreases its ubiquitylation, mediated degradation [124], therefore it is suggested that this phosphorylation of synphilin-1/alpha-synuclein or direct activation of intrinsic cascades might be implicated in the GSK-3␤ induced toxicity [88].…”

Human Basic Fibroblast Growth Factor Inhibits Tau Phosphorylation via the PI3K/Akt-GSK3β Signaling Pathway in a 6-Hydroxydopamine-Induced Model of Parkinson's Disease

“…The kinases regulating phosphorylated (p)-tau include GSK3 [54,55], CDK5 [56], casein kinase 1 [54,55], PKA [54,55], p38 mitogen-activated protein kinase [57], SAPK4/p38 [58], and c-Jun N-terminal kinase families [59]. Previous studies have provided evidence that MPTP/MPP+ leads to the hyperphosphorylation of tau at Ser 396/404 both in vivo and in vitro by inducing a significant accumulation of α - Syn [7,60]. In an SH-SY5Y cell model of parkinsonism induced by MPP+, time- and dose-dependent increases in tau hyperphosphorylation at Ser 396/404 were observed [61].…”

“…GSK3, a major tau protein kinase, catalyzed and regulated tau phosphorylation at Ser 262 and Ser 396/404 [7,63,64,65]. The phosphorylation of GSK3β at Ser 9 or Tyr 216 was primarily targeted by the Akt signaling pathway [8,9].…”

“…Increased phosphorylation of tau at Ser 396 has also been discovered in synapse-enriched fractions from PD brains [6]. This phenomenon is blocked by the inhibition of GSK3β (glycogen synthase kinase-3β), which mediates tau hyperphosphorylation in PC12 cell models of PD [7]. GSK3 activity is most commonly inhibited by phosphorylation at Ser 21 in GSK3α and Ser 9 in GSK3β.…”

Selenium in the therapy of neurological diseases. Where is it going?

“…Extracellular SelP binds to ApoER2, which initiates endocytosis and enables the selenocysteine supply. Presumably, in those conditions astrocytes are the main source of extracellular SelP, which in turn is taken up by neurons using the ApoER2 [57,33]. Aside from evidence that SelP serves to transport Se to brain tissue and to maintain its homeostasis, other suggesting function is a survival factor for neurons [58] as well as microtubule stabiliser.…”