Mice That Express a KCNQ2 Channel Gain‐of‐Function Variant (R201C) Exhibit a Blunted Ventilatory Response to CO 2

Abstract

The KCNQ1-5 (Kv7)family of voltage gated K+ channels activate at subthreshold voltages and are important determinants of resting membrane potential. In particular, both loss- and gain-of-function KCNQ2 pathogenic variants are associated with neurodevelopmental disorders characterized by seizures, myoclonus, disordered breathing and early mortality. To understand how KCNQ2 channels regulate breathing and contribute to mortality, we developed a conditional mouse line that expresses a KCNQ2 gain-of-function mutation (R201C) that in humans causes severe respiratory problems reminiscent of congenital central hypoventilation syndrome (CCHS). Considering CCHS involves disruption of neurons in the retrotrapezoid nucleus (RTN) that regulate breathing in response to changes in CO2/H+ (i.e., function as respiratory chemoreceptors), we first used fluorescent in situ hybridization to confirm that Kcnq2 channels are expressed by chemosensitive RTN neurons identified based on location and expression of Phox2b. Next, we used whole-body plethysmography to characterize baseline breathing and the ventilatory response to CO2 or low O2 in control (N=6) and Phox2bcre::Kcnq2R201C/+ (N=4) mice (P30; mixed sex). We found that Phox2bcre::Kcnq2R201C/+ mice show diminished ventilatory response to graded increases in CO2. In 7% CO2 (balance O2), Phox2bcre::Kcnq2R201C/+ mice show noticeably reduced respiratory frequency (283.9 ± 26.8 bpm for Phox2bcre::Kcnq2R201C/+ compared to 359.5 ± 16.86 bpm for controls); tidal volume (0.024 ± 0.005 ml/g for Phox2bcre::Kcnq2R201C/+ compared to 0.031 ± 0.003 ml/g for control), and minute ventilation (6.9 ± 1.97 ml/min/g for Phox2bcre::Kcnq2R201C/+ compared to 11.08 ± 1.58 ml/min/g for control). Interestingly, Phox2bcre::Kcnq2R201C/+ mice also show an augmented ventilatory response to hypoxia compared to control mice. In 10% O2 (5 min exposure), Phox2bcre::Kcnq2R201C/+ mice show increased respiratory frequency (Phox2bcre::Kcnq2R201C/+ 268.5 ± 5.073 bpm compared to 223.4 ± 15.84 bpm for controls); tidal volume (0.014 ± 0.001 ml/g for Phox2bcre::Kcnq2R201C/+ compared to control 0.013 ± 0.001 ml/g), and minute ventilation (3.81 ± 0.361 ml/min/g for Phox2bcre::Kcnq2R201C/+ compared to 2.95 ± 0.235 ml/min/g for control). These results suggest mice expressing the KCNQ2 variant R201C in Phox2b expressing neurons recapitulate the hypoventilatory phenotype exhibited by patients caring this variant. Our results also suggest peripheral chemoreceptor drive partially compensates for diminished central drive in Phox2bcre::Kcnq2R201C/+ mice.