A New Mouse Strain to Study Motoneurons in Pompe Disease

Pompe disease is a lysosomal storage disorder resulting from a deficiency in the lysosomal enzyme acid α‐glucosidase (GAA). The most severe form of the disease is associated with complete or near complete absence of functional GAA which results in cardiorespiratory failure and death within the first year of life. The only approved treatment for Pompe disease is human recombinant GAA (enzyme replacement therapy (ERT)) which improves overall survival rates but the recombinant protein does not reach the central nervous system. Respiratory impairment in Pompe disease has historically been attributed to muscle weakness but an accumulation of studies of Pompe patients and animal models indicate that motoneuron pathology is functionally relevant. In an effort to better understand the role of motoneurons in Pompe disease, we used breeding strategies to create a new mouse model with motoneuron histopathology features seen in Pompe disease while also allowing easy visualization of motoneurons via a fluorescent tag. Chat‐cre mice (Jackson) were crossed with Gaa −/− mice (Taconic). The resulting heterozygous strain were crossed with eYFP +/+ mice (courtesy Dr. Brian Harfe). Further breeding resulted in homozygous mice which were Chat‐cre +/+ /Gaa −/− /eYFP +/+ . These mice were then crossed to a Flox‐Gaa +/+ (Taconic) to create a heterozygous strain (Chat‐cre +/− /Gaa +/− /eYFP +/− /Flox‐Gaa +/− ). Further inbreeding produced mice that were Chat‐cre +/+ /Gaa +/− /eYFP +/+ /Flox‐Gaa +/+ . The intent of this final cross was to produce mice in which alpha motoneurons express eYFP but do not express GAA. Histological evaluation of the brainstem and spinal cord of these mice showed robust eYFP expression in the brainstem including the hypoglossal motor nucleus, nucleus ambiguous, and facial motor nucleus. In the cervical spinal cord, alpha motoneurons throughout the ventral horn also had robust fluorescence. This included putative phrenic motoneurons as determined based on location and size. The robust eYFP expression was restricted to motoneurons which indicates that motoneurons are Gaa −/− (based on the breeding scheme). Ongoing studies are evaluating GAA protein expression in peripheral tissues, glycogen accumulation in motoneurons, and also brainstem and spinal cord motoneuron loss over the lifespan. In addition, the eYFP signal in motoneurons will permit rigorous evaluation of motoneuron transduction efficacy in gene therapy experiments. Support or Funding Information 2R01HD052682‐11A1 (DDF/BJB)