ORLANDO — “,” said Delia Marias Talos, MD, at a session of the annual meeting of the American Epilepsy Society (AES).
A Closer Look at the Brain
“Phosphorylated tau correlates with cognitive function and executive function recorded presurgery, but it looks like the generative changes are more associated with temporal lobe and aging.”
Alzheimer’s disease is a degenerative condition marked by progressive memory deficits and cognitive decline noted by amyloid plaques and a formation of neurofibrillary tangles resulting from tau hyperphosphorylation.
Epilepsy, on the other hand, is a multifactorial condition with causes ranging from metabolic disorders, structural defects, infections, genetic mutations, and autoimmune disorders. In addition, nearly 50% of all epileptic seizures are idiopathic in nature.
Dr. Talos, professor of neurology at the University of Pennsylvania Perlman School of Medicine in Philadelphia, and her team did not see neurofibrillary tangles in the presurgical brains of epilepsy patients they studied; however, they saw tau plaques. In the future, they seek to investigate the features that distinguish epilepsy from Alzheimer’s disease.
Toxic fragments are probably there because amyloid precursor protein is highly upregulated, she told conference attendees. “We hypothesized that amyloid plaque is cleared but not impaired in epilepsy.”
The prognosis looks comparatively worse for patients who have Alzheimer’s disease and comorbid epilepsy than for patients who have only epilepsy. In addition, Dr. Talos stated that seizures appear to have an additive effort on Alzheimer’s disease.
Fyn-disruptive Therapy
Marson Putra, MD, PhD, a neuroscientist and postdoctoral researcher at Iowa State in Ames, Iowa, presented on the potential impact of a novel fyn-tau interaction as an unexplored target for epileptogensis and epilepsy.
Dr. Putra studied whether fyn-tau interactions exist in epilepsy. In both Alzheimer’s disease and epilepsy, Fyn belongs to the Src family of nonreceptor tyrosine kinases (SFKs), which are involved in cell proliferation and migration. Fyn contains an SH3 domain, which serves as a target for tau’s proline-rich (PxxP) motif. Fyn phosphorylates tau, specifically at tyrosine residue Y18, making fyn-disruptive therapy worth exploring.
Dr. Putra shared several currently proposed mechanisms of action regarding the pathogenesis of the tau plaque. In the first theory, the tau protein assumes a closed conformation in its normal state, thereby concealing the PxxP motif. However, in the second theory, pathogenesis causes the tau protein to assume an open conformation in the disease state, exposing pAT8 sites and making them available to fyn phosphorylation. In the second scenario, which involves Alzheimer’s disease, the fyn-tau interaction still occurs in open conformation state and is thought to occur in the postsynaptic terminal of the dendritic spine.
To investigate the proposed disease-causing mechanisms, Dr. Putra and her team studied status epilepticus in a rodent model of status epilepticus (SE). They used proximity ligation assay to measure interactions between Fyn and tau. They found AT8 and Y18 Fyn and N-methyl-D-aspartate (NMDA) receptor activation in a rat model and increased Fyn interaction. In addition, neuronal nitric oxide synthase levels were elevated 24 hours post-status. When investigating the fyn activity and interactions in the human brain, they found fyn phosphorylation – something that had never been reported before.
From there, Dr. Putra’s team sought to answer whether manipulating fyn-tau interactions could modify epilepsy. To do so, they conducted an experiment using the pharmacological Fyn inhibitor sarcatinib (SAR) and found it modified dysregulated postsynaptic proteins 24 hours post-SE in rat models. Longer exposure also bore a positive effect on epileptic rats.
After treating epileptic rats with SAR for 7 weeks, Dr. Putra found that SAR therapy reduces convulsive seizures during 7 weeks post-SE in rats. Recruiting pharmacological Fyn inhibition sufficiently decreased Fyn-tau interaction, NR-PSD95 complex, and convulsive seizures in chronic epilepsy.
Ultimately, her findings showed that SE exacerbates fyn-tau interactions, with chronic epilepsy modeling showing sustained elevation. In addition, fyn-tau interactions mediate and sustain neuronal hyperexcitability in the epileptic population.
“The impact on clinical care will be bidirectional relevant therapeutic targets in epilepsy and Alzheimer’s disease,” Dr. Putra told the audience.