Hyperphosphorylation of tau leading to neurofibrillary tangles (NFT) is a key pathological hallmarks in neurodegenerative disorders such as Alzheimer’s disease (AD) (1). Peptidyl-prolyl cis-trans isomerase (Pin1) regulates the phosphorylation of Ser/Thr sites of tau protein, and promote microtubule assembly (2). In this study, we aimed to determine the interaction between Pin1 expression and tau hyperphosphorylation in primary cortical neurons using okadaic acid (OKA) model (3) utilized to study AD.

Cortical neurons were obtained from embryonic day 16(E16) Sprague Dawley rat embryos. The neurons were treated with 25 nM OKA on day 7 of culture. Then at 4, 8 and 24 hours after treatment OKA, tau phosphorylation was analyzed by western blot using anti-tau antibodies including Thr231 and Tau-1. Immunocytochemistry was used for Pin1 protein expression and localization.  Pin1 mRNA expression was determined by qRT-PCR at 4, 8 and 24 hours. For cytotoxicity LDH analysis was performed by ELISA. At 8 hours with OKA, tau phosphorylation at Thr231 was increased and non-phosphorylated Tau-1 was decreased compared with the untreated control. Pin1 mRNA expression levels at both 4 and 8 hours post-OKA treatment were lower than the control group.  No significant differences at Pin1 mRNA and protein expression levels were observed between the OKA-treated group and the untreated control group at 24 hours of treatment. Pin1 was mainly localized in the nucleus of control groups, whereas was found in cytoplasm of OKA-treated group. Apoptotic nuclear morphology in OKA-treated group was detected more than the control neurons. In OKA-treated group the LDH release was not significantly different than the other groups at 4 and 8 hours, whereas it significantly increased at 24 hours.

Our study indicates that OKA induces the tau-hyperphosphorylation, affects Pin-1 expression, and causes to translocation of Pin-1 proteins into cytoplasm from nucleus. This study will provide a new approach for AD molecular pathophysiology of in OKA- induced AD model.

References:

1-Iqbal K et al:  Curr Alzheimer Res 2010,7(8):656–664

2-Lu KP, Zhou XZ: Nat Rev Mol Cell Biol 2007,8(11):904–916

3-Martin L, Page G, Terro F: Neurochem Int 2011,59(2):235-250

Figures:

Figure 1: Immunoflourescence staining. In control group, Pin1 localization is mainly in the nucleus in the neurons (A-D), whereas is localized in cytoplasm in OKA-treated group (E-H). (A and E; DAPI, B and F; Pin-1, C and G; Pan neuronal marker, D and H; Merge images)

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EMC Abstracts - https://emc-proceedings.com/abstract/the-effect-of-tau-hyperphosphorylation-on-pin1-expression-in-primary-cortical-neurons-in-okadaic-acid-induced-ad-model/