Abstracts

Rationale:
The phosphoinositide-3 kinase (PI3K)-AKT pathway is a central regulator of intracellular signaling, conserved from yeast to mammals. Activating mutations of this pathway, especially PIK3CA, encoding the catalytic subunit of PI3K, are common cause of cancers as well as a spectrum of brain overgrowth disorders. Patients with these mutations often suffer from forms of epilepsy, which are largely non-responsive to currently available seizure medications. Studying the underlying physiology of PIK3CA-related epilepsy may provide us with potential translational significance. Previously, we recapitulated the key human pathological features including brain enlargement, neocortical malformations and epilepsy in mouse models of patient–related Pik3ca mutations (Roy et al., 2015). We also demonstrated acute treatment of epileptic seizures in these mice with BKM120, a Pik3ca inhibitor, thus promising a new effective anti-epileptic therapy for intractable epilepsy patients. Currently, we sought to determine the role of PI3K activation in the physiology of seizures.
Method:
Following approved institutional ethical guidelines, we developed a conditional mouse model expressing patient-related activating PIK3CAE545K mutation; and used embryonically active Nestin-cre driving expression in neural progenitors through brain development. We performed in vivo and in vitro (acute brain slice) electrophysiological recordings on juvenile and young adult mice. Different channel blockers and pathway inhibitors were used to dissect mechanisms underlying PIK3CA-related epilepsy.
Results:
Biochemical and electrocorticographic analyses showed enhanced downstream signaling and neural activity in the mutant hippocampus, compared to neocortex. Thereafter, we determined the PIK3CA-dependent neurophysiology in detail, using hippocampus as our region of interest. Whole-cell patch clamp recordings from pyramidal neurons of hippocampal CA1 and CA3 demonstrated significantly higher excitability in mutant cells than in controls. This included increased tonic frequency, spontaneous bursts and paroxysmal plateaus, very similar to the pattern found in epilepsy patients. Direct administration of PI3K signaling inhibitors onto brain slices acutely altered the intrinsic spike/burst pattern of mutant cells towards ‘normal’, in 30 mins or less. Finally, experimentation with channel blockers indicated a largely cell-intrinsic mechanism behind the PI3K-related epileptiform activity.
Conclusion:
Our study concludes that hippocampus of PIK3CAE545K mutant mice is more excitable than neocortex. The mutant cells displayed aberrant intrinsic physiological patterns, that were significantly corrected by acute administration of PI3K pathway inhibitors. This study determines PIK3CA-related epileptic pathophysiology and provides a novel avenue for translational research. Reference: Roy A, Skibo J, Kalume F, Ni J, Rankin S, Lu Y, Dobyns WB, Mills GB, Zhao JJ, Baker SJ, Millen KJ. (2015) Mouse models of human PIK3CA-related brain overgrowth have acutely treatable epilepsy. eLife 4:e12703
Funding:
:This study is supported by funding from National Institutes of Health, USA (1R01NS099027, KJM).