Diadenosine-Polyphosphate Analogue AppCH2ppA Suppresses Seizures by Enhancing Adenosine Signaling in the Cortex

Abstract

Epilepsy is a multifactorial disorder associated with neuronal hyperexcitability that affects more than 1% of the human population. It has long been known that adenosine can reduce seizure generation in animal models of epilepsies. However, in addition to various side effects, the instability of adenosine has precluded its use as an anticonvulsant treatment. Here we report that a stable analogue of diadenosine-tetraphosphate: AppCH2ppA effectively suppresses spontaneous epileptiform activity in vitro and in vivo in a Tuberous Sclerosis Complex (TSC) mouse model (Tsc1+/−), and in postsurgery cortical samples from TSC human patients. These effects are mediated by enhanced adenosine signaling in the cortex post local neuronal adenosine release. The released adenosine induces A1 receptor-dependent activation of potassium channels thereby reducing neuronal excitability, temporal summation, and hypersynchronicity. AppCH2ppA does not cause any disturbances of the main vital autonomous functions of Tsc1+/− mice in vivo. Therefore, we propose this compound to be a potent new candidate for adenosine-related treatment strategies to suppress intractable epilepsies.

Retrograde adenosine/A2Areceptor signaling facilitates excitatory synaptic transmission and seizures

“…Presynaptic A2ARs are required for activity-dependent strengthening of MC-GC synapses Presynaptic PKA signaling is necessary and sufficient to induce LTP of MC-GC synaptic transmission 6 , raising the possibility that the retrograde messenger induces LTP by activating Gs-coupled GPCRs located on MC axon terminals. The Gs-coupled adenosine A2A receptor (A2AR) is a good candidate as it has been implicated in BDNF-mediated plasticity at other synapses [17][18][19] , and the endogenous ligand adenosine can be released from neurons upon activity [20][21][22][23][24] . To test whether adenosine mediates MC-GC LTP by activating presynaptic A2ARs, we first examined whether LTP induction requires A2ARs.…”

“…Adenosine can be released from neurons upon activity 20,[22][23][24] via equilibrative nucleoside transporters (ENTs) 21 . Our results strongly suggest that presynaptic A2ARs are activated by endogenous adenosine during MC-GC LTP (Fig.…”

“…To avoid adenosine tonic activity due to extracellular accumulation, we employed a singlecell approach and selectively blocked ENTs in a single GC. Similarly to previous studies 22,24 , we loaded inosine (100 µM) intracellularly, a competitive blocker of adenosine efflux through ENTs 21 , via the recording pipette. We found that intracellular inosine abolished TBF-LTP (Fig.…”

“…Using the genetically encoded adenosine sensor GRABAdo1.0m 27 , we detected a phasic increase in extracellular adenosine following both LTP induction ex vivo and during epileptic activity in vivo. Previous studies have shown that adenosine can be released from neurons upon activity via ENTs [20][21][22][23][24] . In support of this mechanism, we found that interfering with ENT-mediated release of adenosine from a single postsynaptic GC abolished MC-GC LTP, indicating that passive release of adenosine from GCs is crucial for this form of plasticity.…”

“…Presynaptic A2ARs are required for MC-GC LTP Presynaptic PKA signaling is necessary and sufficient to induce LTP of MC-GC synaptic transmission (Hashimotodani et al, 2017), raising the possibility that the retrograde messenger induces LTP by activating a Gs-coupled G protein-coupled receptor (GPCR) located on MC axon terminals. The Gs-coupled adenosine A2A receptor (A2AR) is a good candidate as it has been implicated in BDNF-mediated plasticity at other synapses (Diogenes et al, 2004;Fontinha et al, 2008;Sebastiao and Ribeiro, 2009b), and the endogenous ligand adenosine can be released from neurons upon activity (King et al, 2006;Latini and Pedata, 2001;Lovatt et al, 2012;Pons-Bennaceur et al, 2019;Wall and Dale, 2013). To test whether adenosine mediates MC-GC LTP by activating presynaptic A2ARs, we first examined whether A2AR antagonism impaired this plasticity.…”