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Principal Investigator: Daniel K Mulkey
Organization: UNIVERSITY OF CONNECTICUT STORRS
Fiscal Year: 2024
Award: $511,535
Funding agency: National Heart Lung and Blood Institute
SUMMARY
Rett syndrome (RTT) (OMIM #312750) is a severe X-linked neurodevelopmental disorder caused by mutations
in the methyl-CpG-binding protein 2 (MECP2). Although RTT patients suffer from many co-morbid phenotypes,
wake disordered breathing has a major negative impact quality of life and is associated with high mortality rate
in this patient population. Evidence from murine models of RTT suggest disordered breathing results in part
from a disrupted ability to regulate breathing in response to changes in tissue CO2/H+ (i.e., central
chemoreflex). The retrotrapezoid nucleus (RTN) is a critical chemosensitive brainstem nucleus, contains
CO2/H+-sensitive neurons and astrocytes that together produce a CO2/H+-dependent drive to breath. Previous
and preliminary data identify heteromeric Kir4.1/5.1 channels as key determinants of RTN astrocyte CO2/H+
chemosensitivity. However, homomeric Kir4.1 and heteromeric Kir4.1/5.1 are differentially CO2/H+ sensitive
and regulate divergent astrocyte processes including membrane potential and clearance of neuronally
released extracellular K+, and it is not clear which of these mechanisms contributes to RTN chemoreception
and disordered breathing in RTT. Our previous work showed that MeCP2 deficient mice have reduced levels
of Kir4.1 and 5.1 channels, diminished astrocytic Kir4.1/5.1-like currents, dysregulated extracellular K+. MeCP2
deficient mice also show a blunted ventilatory response to CO2. Similarly, preliminary results show that global
deletion of astrocyte Kir4.1 channels also blunts the ventilatory response to CO2. Importantly targeted
(re)expression of Kir4.1 specifically in RTN astrocytes rescued disordered breathing in both Kir4.1 cKO and
MeCP2 deficient mice. Preliminary data also show that RTN astrocytes from Kir5.1 KO animals lack CO2/H+
sensitivity, thus suggesting heteromeric Kir4.1/5.1 channels regulate RTN astrocyte chemosensitivity.
Recent ultrastructural studies indicate reduced astrocytic coverage of neuronal elements during sleep together
with increased extracellular space; thus necessitating state-dependent changes in astrocyte ion and transmitter
homeostasis, that may account for a reduced ventilatory response to CO2 during sleep. Consistent with this,
preliminary results show that RTN astrocytes undergo a ~25% volume increase in the wake state as compared
to sleep. Based on this, we hypothesize that Kir4.1/5.1 deficiency and compromised astrocyte
chemoreception are responsible for state-dependent disordered breathing in RTT. In this proposal, we
use an established mouse model of RTT, an inducible astrocyte specific Kir4.1 knockout mouse in conjunction
with astrocyte targeted AAV, astrocyte volume and morphological complexity measurements, slice
electrophysiology, and whole-animal plethysmography to explore the sleep-wake state-dependent
contributions of Kir4.1/5.1 channels to RTN chemoreception and respiratory activity in RTT. Understanding
how Kir4.1 and Kir5.1 contribute to RTN chemoreception across sleep-wake states and disordered breathing
may provide mechanistic insight for targeted treatment of disordered breathing in RTT.
Terms: <AAV delivered><AAV delivery><AAV-based delivery><AAV-based viral delivery><AAV-mediated delivery><Adeno-associated-virus-based delivery><Affect><Animal Model><Animal Models and Related Studies><Animals><Astrocytes><Astrocytus><Astroglia><Autoregulation><Behavior><Body Tissues><Brain><Brain Nervous System><Brain Stem><Brain region><Brainstem><Breathing><CO2><Carbon Dioxide><Carbonic Anhydride><Cell Nucleus><Cerebroatrophic Hyperammonemia><Cessation of life><Communication><Data><Death><Death Rate><Electrophysiology><Electrophysiology (science)><Elements><Encephalon><Extracellular Space><Failure><Genes><Genetic Alteration><Genetic Change><Genetic defect><Goals><Grant><Homeostasis><In Vitro><Intercellular Space><Ions><KO mice><Knock-out Mice><Knockout Mice><Link><MeCP-2 protein><MeCP2><MeCP2 protein><Measurement><Mediating><Membrane Potentials><Methyl CpG Binding Protein 2><Methyl CpG binding protein MeCP2><Methyl-CpG binding protein 2><Methyl-CpG-Binding Protein 2><Methyl-DNA binding protein MECP2><Mice><Mice Mammals><Molecular><Morphology><Murine><Mus><Mutation><Nerve Cells><Nerve Unit><Neural Cell><Neurocyte><Neurodevelopmental Disorder><Neurological Development Disorder><Neurons><Neurophysiology / Electrophysiology><Nucleus><Null Mouse><OMIM><Online Mendelian Inheritance In Man><Patients><Phenotype><Physiological Homeostasis><Plethysmography><Process><QOL><Quality of life><Reflex><Reflex action><Regulation><Respiration Disorders><Respiratory Aspiration><Respiratory Disorder><Respiratory Inspiration><Resting Potentials><Rett Disorder><Rett Syndrome><Role><Seizures><Site><Sleep><Slice><Symptoms><Testing><Tissues><Transmembrane Potentials><Viral><Wakefulness><Work><adeno-associated viral vector delivery><adeno-associated virus delivery><adeno-associated virus mediated delivery><adenovirus mediated delivery><astrocytic glia><autistic behavior><autistic behaviour><autistic-like behavior><breathing disorder><co-morbid><co-morbidity><comorbidity><delivered with AAV><delivery with AAV><electrophysiological><extracellular><genome mutation><human model><improved><in vivo><insight><inspiration><loss of function mutation><model of animal><model of human><mortality rate><mortality ratio><mouse model><murine model><neurodevelopmental disease><neuronal><novel><patient population><premature><prematurity><respiratory><respiratory dysfunction><response><social role><targeted drug therapy><targeted drug treatments><targeted therapeutic><targeted therapeutic agents><targeted therapy><targeted treatment><therapeutic target>