Hyperphosphorylation of tau protein (tau) causes neurodegenerative diseases such as Alzheimer's disease (AD). Recent studies of the physiological correlation between tau and a-synuclein (a-SN) have demonstrated that: (a) phosphorylated tau is also present in Lewy bodies, which are cytoplasmic inclusions formed by abnormal aggregation of a-SN; and (b) the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) increases the phosphorylation of tau as well as the protein level of a-SN in cultured neuronal cells, and also in mice. However, the molecular mechanism responsible for the a-SN-mediated hyperphosphorylation of tau remains to be elucidated. In this in vitro study, we found that: (a) a-SN directly stimulates the phosphorylation of tau by glycogen synthase kinase-3b (GSK-3b), (b) a-SN forms a heterotrimeric complex with tau and GSK-3b, and (c) the nonamyloid beta component (NAC) domain and an acidic region of a-SN are responsible for the stimulation of GSK-3b-mediated tau phosphorylation. Thus, it is concluded that a-SN functions as a connecting mediator for tau and GSK-3b, resulting in GSK-3b-mediated tau phosphorylation. Because the expression of a-SN is promoted by oxidative stress, the accumulation of a-SN induced by such stress may directly induce the hyperphosphorylation of tau by GSK-3b. Furthermore, we found that heat shock protein 70 (Hsp70) suppresses the a-SN-induced phosphorylation of tau by GSK-3b through its direct binding to a-SN, suggesting that Hsp70 acts as a physiological suppressor of a-SN-mediated tau hyperphosphorylation. These results suggest that the cellular level of Hsp70 may be a novel therapeutic target to counteract a-SN-mediated tau phosphorylation in the initial stage of neurodegenerative disease. Structured digital abstractl GSK3B phosphorylates GSK3B by protein kinase assay (View interaction) l TAU binds to a-SN by pull down (View interaction) l GSK3B phosphorylates TAU by protein kinase assay (View Interaction: 1, 2, 3, 4) l TAU physically interacts with a-SN and HSP70 by pull down (View interaction) l TAU physically interacts with a-SN and GSK3B by pull down (View interaction) l GSK3B binds to a-SN by pull down (View interaction) Abbreviations GSK-3b, glycogen synthase kinase-3b; GST, glutathione S-transferase; Hsp70, heat shock protein 70; NAC, nonamyloid beta component; a-SN, alpha-synuclein; tau, microtubule-associated protein tau.

Leucine-rich repeat kinase 2 (LRRK2) has been identified as the causal molecule for autosomal-dominant Parkinson's disease (PD). Experimental evidence indicates that LRRK2 may play an important role in the pathology induced by abnormal phosphorylation of tau. In the present study, we demonstrated that LRRK2 directly associates with GSK-3b, and that this interaction enhances the kinase activity of GSK-3b. Furthermore, we found that LRRK2-mediated activation of GSK-3b induces high phosphorylation of tau at Ser396 in SH-SY5Y cells. From our present findings, we conclude that LRRK2 may function as a novel enhancer for GSK-3b and as a physiological regulator of neurite outgrowth and axonal transport through regulation of the GSK-3b-mediated phosphorylation of tau at the cellular level. Since LRRK2 is detected in tau-positive inclusions in brain tissue affected by various neurodegenerative disorders, including PD, LRRK2-stimulated phosphorylation of tau by GSK-3b may be involved in development of pathological features in the initial stage of PD. Structured digital abstract• LRKK2 physically interacts with GSK-3B by anti bait coimmunoprecipitation (View interaction)• LRRK2 physically interacts with GSK-3B by anti tag coimmunoprecipitation (View interaction)• LRRK2 binds to GSK-3B by pull down (View interaction)• GSK-3B physically interacts with LRRK2 and TAU by pull down (View interaction)

This enhancement could be useful for ultrasound-mediated gene therapy in the future since both treatments for membrane modification could be directly applied to the living body.

A sensitively responsive promoter to radiation could be constructed using this method, possibly leading to the construction of a promoter of interest that could be applied for clinical use.