Fyn-tau Ablation Modifies PTZ-Induced Seizures and Post-seizure Hallmarks of Early Epileptogenesis

Abstract

Both Fyn and tau have been associated with neuronal hyperexcitability and neurotoxicity in many tauopathies, including Alzheimer's disease (AD). Individual genetic ablation of fyn or tau appears to be protective against aberrant excitatory neuronal activities in AD and epilepsy models. It is, however, still unknown whether ablation of both Fyn and tau can likely elicit more profound anti-seizure and neuroprotective effects. Here, we show the effects of genetic deletion of Fyn and/or tau on seizure severity in response to pentylenetetrazole (PTZ)-induced seizure in mouse models and neurobiological changes 24 h post-seizures. We used Fyn KO (fyn−/−), tau KO (tau−/−), double knockout (DKO) (fyn−/−/tau−/−), and wild-type (WT) mice of the same genetic background. Both tau KO and DKO showed a significant increase in latency to convulsive seizures and significantly decreased the severity of seizures post-PTZ. Although Fyn KO did not differ significantly from WT, in response to PTZ, Fyn KO still had 36 ± 8% seizure reduction and a 30% increase in seizure latency compared to WT. Surprisingly, in contrast to WT, Fyn KO mice showed higher mortality in <20 min of seizure induction; these mice had severe hydrocephalous. None of the tau−/− and DKO died during the study. In response to PTZ, all KO groups showed a significant reduction in neurodegeneration and gliosis, in contrast to WT, which showed increased neurodegeneration [especially, parvalbumin (PV)-GABAergic interneurons] and gliosis. DKO mice had the most reduced gliosis. Immunohistochemically, phospho-tau (AT8, pS199/S202), Fyn expression, as well as Fyn-tau interaction as measured by PLA increased in WT post-PTZ. Moreover, hippocampal Western blots revealed increased levels of AT8, tyrosine phospho-tau (pY18), and phosphorylated Src tyrosine family kinases (pSFK) in PTZ-treated WT, but not in KO, compared to respective controls. Furthermore, PV interneurons were protected from PTZ-induced seizure effects in all KO mice. The levels of inwardly rectifying potassium (Kir 4.1) channels were also downregulated in astrocytes in the WT post-PTZ, while its levels did not change in KO groups. Overall, our results demonstrated the role of Fyn and tau in seizures and their impact on the mediators of early epileptogenesis in PTZ model.

Differential Impact of Severity and Duration of Status Epilepticus, Medical Countermeasures, and a Disease-Modifier, Saracatinib, on Brain Regions in the Rat Diisopropylfluorophosphate Model

“…Our work showed that fyn knockout mice had reduced SE severity following repeated low doses of KA although there was no difference in the amount of KA needed to initiate the first CS (Sharma et al, 2018). In the mouse pentylenetetrazole model, our lab showed that fyn knockout mice had a reduction in SE severity compared to wild type mice though the difference was not significant (Putra et al, 2020b). Importantly, the fyn knockout mice treated with pentylenetetrazole did not have significant neurodegeneration compared to fyn knockout mice without pentylenetetrazole which suggests mitigation of Fyn is neuroprotective.…”

“…Following neurological insult, SFKs, more specifically Fyn and Src, are upregulated and can initiate signaling cascades that contribute to neuroinflammation and hyper-excitability (Kaufman et al, 2015;Liu et al, 2016;Nygaard, 2018;Panicker et al, 2019). In neurons, Fyn can modulate both NMDARs, metabotropic glutamatergic receptors, and gamma aminobutyric acid receptors (GABAR) (Salter and Kalia, 2004;Knox and Jiang, 2015;Wang et al, 2016;Jin et al, 2017;Putra et al, 2020b). This regulation can lead to excitotoxicity and to the development of epilepsy.…”

“…SFKs have been implicated in a variety of neurological diseases, including Parkinson's and Alzheimer's diseases (PD, AD), stroke, chronic pain and epilepsy (Lee et al, 2004;Kaufman et al, 2015;Knox and Jiang, 2015;Miyamoto et al, 2017;Sharma et al, 2018Sharma et al, , 2021Panicker et al, 2019;Ge et al, 2020;Yang et al, 2020). In neurons, phosphorylated Fyn, a SFK, interacts with tau in response to seizures and can lead to phosphorylation of N-methyl D-aspartate receptors (NMDAR) and contribute to glutamatergic toxicity (Nakazawa et al, 2001;Yang and Leonard, 2001;Ittner et al, 2010;Trepanier et al, 2012;Putra et al, 2020b). Phosphorylated Fyn can also regulate the expression of metabotropic glutamatergic receptors (Jin et al, 2017).…”

Mechanisms of disease-modifying effect of saracatinib (AZD0530), a Src/Fyn tyrosine kinase inhibitor, in the rat kainate model of temporal lobe epilepsy

“…The role of a non-receptor Src/Fyn tyrosine kinase in neuroinflammation and neuronal hyperexcitability is emerging as a new mechanistic target for the development of drugs for epilepsy and Alzheimer’s disease ( Nygaard et al, 2014 ; Sharma et al, 2018a ; Smith et al, 2017 ). We have recently shown that Fyn, protein kinase C delta (PKCδ), NADPH oxidase 2 (NOX2), and inducible nitric oxide synthase (iNOS) were upregulated during epileptogenesis ( Putra et al, 2019 ; Putra et al, 2020b ; Sharma et al, 2018a ), and in a Parkinson’s disease model ( Gordon et al, 2016 ; Panicker et al, 2015 ). The Fyn-PKCδ-NOX2-iNOS signaling is a novel pathway in epilepsy.…”

“…Interestingly, NFkB also transcriptionally regulates PKCδ and gp91 phox ( Anrather et al, 2006 ; Gordon et al, 2016 ) implying that it can be a self-perpetuating neuroinflammatory signaling pathway, which could potentially exacerbate seizures ( Gage and Thippeswamy, 2021 ; Vezzani et al, 2011 ). Recently, we demonstrated increased hyperphosphorylated Tau and phosphorylated Src/Fyn and Fyn-tau interaction, using the Proximity Ligation Assay, in neurons at 24 h post-seizure in a mouse model ( Putra et al, 2020b ).…”