Authors :
Presenting Author: Marson Putra, MD, PhD – Iowa State University
Nikhil Rao, DVM – Graduate Student, Biomedical Sciences, Iowa State University; Cara Gardner, MS – Biomedical Sciences – Iowa State University; Guanghao liu, MD, PhD – Internal Medicine – University of Iowa; Marco Hefti, MD – Pathology – University of Iowa; Alexander Bassuk, MD, PhD – Pediatrics and Neurology – University of Iowa; Gloria Lee, PhD – Internal Medicine – University of Iowa
Rationale:
Epilepsy and Alzheimer's Disease (AD) have been reported to share common neurological deficits involving seizures and impaired cognition. Fyn, the Src-family tyrosine kinase, is known to interact with cytoskeletal protein tau, leading to NMDAR-mediated excitotoxicity in AD. Recently, we found that Fyn-tau interactions were significantly increased following seizures. However, the role of Fyn-tau interaction-mediated neuronal excitotoxicity and hyperexcitability in epilepsy remains elusive as to whether it involves postsynaptic excitotoxic signaling complexes similar to AD. Here, we investigate the Fyn-tau and NR2B-PSD95-nNOS mediated pathology and their interactions in kainic acid (KA) rodent models of epilepsy.
Methods:
We injected a repeated low dose of KA (5 mg/kg, i.p., at 30 min intervals) to induce status epilepticus (SE) in adult C57BL/6/S129 mice and SD rats. Brains were collected at 24h post-SE for acute study. In the mouse study, we used proximity ligation assay (PLA) to identify interactions between Fyn and tau and/or NR2B and PSD-95 following SE at 24hr. Subcellular PSD fractionation of mouse hippocampus was used to evaluate the expression of proteins at postsynaptic levels. Immunohistochemistry (IHC) was used for tau phosphorylation markers. In rats, co-immunoprecipitation was conducted to evaluate the binding between Fyn and tau, and NR2B, PSD-95, and nNOS signaling molecules following SE at 24hr.
Results:
Here, we report that fyn-tau coupling was significantly increased following KA-induced SE at 24hrs in mice. The interaction between NR2B and PSD95 was also enhanced after SE and shown to positively correlate with the increase of Fyn-tau interactions. PSD-enriched fraction of the hippocampus revealed a significant increase in phosphorylation of NMDAR (pNR2B), tau (AT8, Y18), Fyn activation (pSFK), and the levels of nNOS but not total Fyn, total Tau, PSD-95 in KA-treated mice relative to controls. Similarly, we show elevated co-immunoprecipitation between Fyn/tau/NR2B/PSD95/nNOS upon status epilepticus (SE) at 24hr in KA-treated rats compared to controls.
Conclusions:
Our study demonstrates the enhanced complexes of Fyn-tau and NR2B-PSD95-nNOS following SE. Fyn-tau interactions may mediate neurotoxicity and neuronal hyperexcitability during the acute phase of epileptogenesis through NMDAR-induced excitotoxicity, as in AD. Therefore, strategies intervening Fyn-tau interactions could modify seizure progression and associated brain pathology in epilepsy.
Funding:
This project was supported by ISU-UI seed grant, Iowa, USA, NIH/NIA R01 AG017753, NIH R21 NS112779, and W.E. Lloyd Endowment fund (SG2200008).