Mutations in α and β Subunits of Voltage-Gated Sodium Channels in Neuropathic Pain: Functional Assessment in Rodent and Human iPSC-Derived Sensory Neurons
Date of Award
Doctor of Philosophy (PhD)
Interdepartmental Neuroscience Program
Voltage-gated sodium (NaV) channels are key mediators of excitability in dorsal root ganglion (DRG) neurons, the primary afferents responsible for transmitting pain signals into the central nervous system. NaV channels are found as heterotrimeric complexes in humans, comprised of one pore-forming α-subunit and two non-ion conducting β-subunits. Gain-of-function mutations in NaV1.7, NaV1.8, and NaV1.9, the NaV channels preferentially expressed in the peripheral nervous system, confer hyperexcitability to DRG neurons and have been linked to the development of neuropathic pain. In this dissertation, I utilize dynamic clamp electrophysiology to precisely quantify the contribution of NaV1.8 and NaV1.9 to neuronal excitability. Furthermore, I then quantify the levels of NaV1.7 current reduction necessary to normalize excitability in human induced pluripotent stem-cell derived sensory neurons (iPSC-SNs) with gain-of-function mutations in NaV1.7, showing that reduction of approximately 50% of NaV1.7 currents is sufficient to reverse hyperexcitability in these iPSC-SNs.While sodium channel β-subunits play integral roles in modulating the trafficking and function of the α-subunits, and have been linked to the development of other diseases, their role in neuropathic pain has been less clear. In this dissertation, I also identify two novel mutations in the SCN2B gene, encoding the β2-subunit, in patients with two different neuropathic pain conditions. In a patient with diabetic neuropathy, I identify the β2-D109N mutation and show that this mutation renders DRG neurons hyperexcitable by depolarizing the voltage-dependence of fast-inactivation and reducing the use-dependent inhibition of NaV1.7. In a patient with small-fiber neuropathy, I identify the β2-Y69H mutation. This mutation does not affect the biophysical properties of NaV channels, but increases the current density of tetrodotoxin-sensitive current in DRG neurons. Altogether, we indict gain-of-function mutations in the SCN2B gene as potential contributors to the development of neuropathic pain.
Alsaloum, Matthew, "Mutations in α and β Subunits of Voltage-Gated Sodium Channels in Neuropathic Pain: Functional Assessment in Rodent and Human iPSC-Derived Sensory Neurons" (2021). Yale Graduate School of Arts and Sciences Dissertations. 291.