Rett syndrome (RTT) is a neurodevelopmental disorder caused by loss-of-function mutations in the gene encoding methyl-CpG-binding protein 2 (MECP2). Symptoms of RTT include mental disability, autistic behavior, and seizures. In addition, severe respiratory dysfunction contributes significantly to poor quality of life and is associated with high mortality rate in this population. Evidence from RTT mouse models suggest that disordered breathing in RTT may result from disruption of central chemoreceptors (neurons that regulate breathing in response to CO2/H+), yet the cellular and molecular basis of MeCP2-dependent control of breathing remains largely unknown. MeCP2 is highly expressed throughout the nervous system and recent evidence shows that loss of MeCP2 from astrocytes contributes to symptoms of RTT including disordered breathing. Astrocytes in a brainstem region called the retrotrapezoid nucleus (RTN) are known to control breathing by sensing CO2/H+ by inhibition of inward rectifying K+ channels (Kir4.1) and releasing ATP to stimulate nearby chemosensitive neurons. Preliminary data presented here demonstrates Kir4.1 expression is significantly decreased in multiple brain regions in MeCP2 deficient mice, suggesting expression of this channel is regulated by MeCP2. Therefore, we hypothesize that MeCP2 is required for expression of Kir4.1 in RTN astrocytes and loss of MeCP2 from astrocytes disrupts RTN chemoreceptor function and contributes to disordered breathing in RTT. In this proposal, we use an established mouse model of RTT and the newly developed inducible astrocyte specific Kir4.1 knockouts in conjunction with molecular, genetics, slice electrophysiology, and whole-animal plethysmography to determine if MeCP2 and Kir4.1 in astrocytes are essential for control of breathing. The three Specific Aims of this project are: 1) determine whether MeCP2 is required for expression of Kir4.1 in RTN astrocytes; 2) determine if loss of MeCP2 affects excitability chemosensitive RTN neurons; 3) determine the essential roles of Kir4.1 in RTN astrocytes for control of breathing. By understanding contributions of MeCP2 and Kir4.1 in astrocytes to RTN physiology in vitro and in vivo, we will provide insight into the cellular and molecular basis of disordered breathing in RTT and in doing so create new avenues for treatment of life-threatening symptoms of this disease.
Rett syndrome (RTT) is a neurodevelopmental disorder that is a leading cause of cognitive and motor impairment in females. One of the most disturbing and life- threatening presentations of RTT is disordered breathing, which is thought to contribute to the high mortality rate in this patient population. RTT is caused by mutations in the gene encoding methyl-CpG-binding protein 2 (MECP2); however, it is not known how disruption of MeCP2 disrupts breathing. This project seeks to establish novel roles MeCP2 and Kir4.1 channels in astrocytes as the cellular and molecular basis of respiratory problems in a mouse model of RTT.
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