Trigeminal sensory neurons of transgenic knock-in (KI) mice expressing the R192Q missense mutation in the alpha 1A subunit of neuronal voltage-gated Ca(V)2.1 Ca2+ channels, which leads to familial... Show moreTrigeminal sensory neurons of transgenic knock-in (KI) mice expressing the R192Q missense mutation in the alpha 1A subunit of neuronal voltage-gated Ca(V)2.1 Ca2+ channels, which leads to familial hemiplegic migraine type 1 (FHM1) in patients, exhibit a hyperexcitability phenotype. Here, we show that the expression of Na(V)1.7 channels, linked to pain states, is upregulated in KI primary cultures of trigeminal ganglia (TG), as shown by increased expression of its alpha 1 subunit. In the majority of TG neurons, Na(V)1.7 channels are co-expressed with ATP-gated P2X3 receptors (P2X3R), which are important nociceptive sensors. Reversing the trigeminal phenotype with selective Ca(V)2.1 channel inhibitor omega-agatoxin IVA inhibited Na(V)1.7 overexpression. Functionally, KI neurons revealed a TTX-sensitive inward current of larger amplitude that was partially inhibited by selective Na(V)1.7 blocker Tp1a. Under current-clamp condition, Tp1a raised the spike threshold of both wild-type (WT) and KI neurons with decreased firing rate in KI cells. Na(V)1.7 activator OD1 accelerated firing in WT and KI neurons, a phenomenon blocked by Tp1a. Enhanced expression and function of Na(V)1.7 channels in KI TG neurons resulted in higher excitability and facilitated nociceptive signaling. Co-expression of Na(V)1.7 channels and P2X3Rs in TGs may explain how hypersensitivity to local stimuli can be relevant to migraine. Show less
Eroli, F.; Loonen, I.C.M.; Maagdenberg, A.M.J.M. van den; Tolner, E.A.; Nistri, A. 2018
Background: The R192Q mutation of the CACNA1A gene, encoding for the alpha 1 subunit of voltage-gated P/Q Ca2+ channels (Ca(v)2.1), is associated with familial hemiplegic migraine-1. We... Show moreBackground: The R192Q mutation of the CACNA1A gene, encoding for the alpha 1 subunit of voltage-gated P/Q Ca2+ channels (Ca(v)2.1), is associated with familial hemiplegic migraine-1. We investigated whether this gain-of-function mutation changed the structure and function of trigeminal neuron P2X(3) receptors that are thought to be important contributors to migraine pain. Results: Using in vitro trigeminal sensory neurons of a mouse genetic model knockin for the CACNA1A R192Q mutation, we performed patch clamp recording and intracellular Ca2+ imaging that showed how these knockin ganglion neurons generated P2X(3) receptor-mediated responses significantly larger than wt neurons. These enhanced effects were reversed by the Cav2.1 blocker.-agatoxin. We, thus, explored intracellular signalling dependent on kinases and phosphatases to understand the molecular regulation of P2X(3) receptors of knockin neurons. In such cells we observed strong activation of CaMKII reversed by.-agatoxin treatment. The CaMKII inhibitor KN-93 blocked CaMKII phosphorylation and the hyperesponsive P2X(3) phenotype. Although no significant difference in membrane expression of knockin receptors was found, serine phosphorylation of knockin P2X(3) receptors was constitutively decreased and restored by KN-93. No change in threonine or tyrosine phosphorylation was detected. Finally, pharmacological inhibitors of the phosphatase calcineurin normalized the enhanced P2X(3) receptor responses of knockin neurons and increased their serine phosphorylation. Conclusions: The present results suggest that the CACNA1A mutation conferred a novel molecular phenotype to P2X3 receptors of trigeminal ganglion neurons via CaMKII-dependent activation of calcineurin that selectively impaired the serine phosphorylation state of such receptors, thus potentiating their effects in transducing trigeminal nociception. Show less
