Postnatal Gene Therapy Improves Spatial Learning Despite the Presence of Neuronal Ectopia in a Model of Neuronal Migration Disorder

Inhibitory CCK+ basket synapse defects in mouse models of dystroglycanopathy

Dystroglycan (Dag1) is a transmembrane glycoprotein that links the extracellular matrix to the actin cytoskeleton. Mutations in Dag1 or the genes required for its glycosylation result in dystroglycanopathy, a type of congenital muscular dystrophy characterized by a wide range of phenotypes including muscle weakness, brain defects, and cognitive impairment. We investigated interneuron (IN) development, synaptic function, and associated seizure susceptibility in multiple mouse models that reflect the wide phenotypic range of dystroglycanopathy neuropathology. Mice that model severe dystroglycanopathy due to forebrain deletion of Dag1 or Pomt2, which is required for Dystroglycan glycosylation, show significant impairment of CCK+/CB1R+ IN development. CCK+/CB1R+ IN axons failed to properly target the somatodendritic compartment of pyramidal neurons in the hippocampus, resulting in synaptic defects and increased seizure susceptibility. Mice lacking the intracellular domain of Dystroglycan have milder defects in CCK+/CB1R+ IN axon targeting, but exhibit dramatic changes in inhibitory synaptic function, indicating a critical postsynaptic role of this domain. In contrast, CCK+/CB1R+ IN synaptic function and seizure susceptibility was normal in mice that model mild dystroglycanopathy due to partially reduced Dystroglycan glycosylation. Collectively, these data show that inhibitory synaptic defects and elevated seizure susceptibility are hallmarks of severe dystroglycanopathy, and show that Dystroglycan plays an important role in organizing functional inhibitory synapse assembly.

Large1 gene transfer in older myd mice with severe muscular dystrophy restores muscle function and greatly improves survival

Muscular dystrophy is a progressive and ultimately lethal neuromuscular disease. Although gene editing and gene transfer hold great promise as therapies when administered before the onset of severe clinical symptoms, it is unclear whether these strategies can restore muscle function and improve survival in the late stages of muscular dystrophy. Largemyd/Largemyd (myd) mice lack expression of like-acetylglucosaminyltransferase-1 (Large1) and exhibit severe muscle pathophysiology, impaired mobility, and a markedly reduced life span. Here, we show that systemic delivery of AAV2/9 CMV Large1 (AAVLarge1) in >34-week-old myd mice with advanced disease restores matriglycan expression on dystroglycan, attenuates skeletal muscle pathophysiology, improves motor and respiratory function, and normalizes systemic metabolism, which collectively and markedly extends survival. Our results in a mouse model of muscular dystrophy demonstrate that skeletal muscle function can be restored, illustrating its remarkable plasticity, and that survival can be greatly improved even after the onset of severe muscle pathophysiology.

Decreased Expression of Protein O-linked Mannose β 1,2-N-Acetylglucosaminyltransferase 1 Contributes to Alzheimer's Disease-like Pathologies

Alzheimer's disease (AD) is pathologically characterized by senile plaques and neurofibrillary tangles composed of β-amyloid peptide (Aβ) and tau hyperphosphorylation, respectively. Mannosylation, a particular type of post-translational modification, may be involved in the pathogenesis of AD. However, its underlying mechanism remains unclear. Protein O-linked mannose β 1,2-N-acetylglucosaminyltransferase 1 (POMGnT1) catalyzes the formation of the N-acetylglucosamine β-1,2-Man linkage of O-mannosylglycan, which can increase the protein post-translational mannosylation level. The defective POMGnT1 gene leads to the hypomannosylation of proteins, which may cause cognitive decline in aged people. This study aimed to investigate whether POMGnT1 participated in the pathogenesis of AD and explore its underlying role using AD mouse and cell models. In this study, the expression of POMGnT1 was measured in AD models [β-amyloid precursor protein (APP)/presenilin-1 (PS1) transgenic mice, an AD mouse model; N2a cells stably transfected with Swedish mutant APP (N2a/APP), an AD cell model]. The results revealed that the expression of POMGnT1 decreased in AD mouse and cell models. Additionally, POMGnT1-overexpressing N2a/APP cells were built by retroviral transfection. POMGnT1 overexpression may lower Aβ levels by reducing APP production and downregulating β-and γ-secretase activities. It also promoted clearance of Aβ by upregulating insulin-degrading enzymes and ameliorated tau hyperphosphorylation. Hence, it was concluded that POMGnT1 was involved in the pathogenic process of AD. The decreased expression of POMGnT1 contributes to AD-like pathologies.

The roles of dystroglycan in the nervous system: insights from animal models of muscular dystrophy

Dystroglycan is a cell membrane protein that binds to the extracellular matrix in a variety of mammalian tissues. The α-subunit of dystroglycan (αDG) is heavily glycosylated, including a special O-mannosyl glycoepitope, relying upon this unique glycosylation to bind its matrix ligands. A distinct group of muscular dystrophies results from specific hypoglycosylation of αDG, and they are frequently associated with central nervous system involvement, ranging from profound brain malformation to intellectual disability without evident morphological defects. There is an expanding literature addressing the function of αDG in the nervous system, with recent reports demonstrating important roles in brain development and in the maintenance of neuronal synapses. Much of these data are derived from an increasingly rich array of experimental animal models. This Review aims to synthesize the information from such diverse models, formulating an up-to-date understanding about the various functions of αDG in neurons and glia of the central and peripheral nervous systems. Where possible, we integrate these data with our knowledge of the human disorders to promote translation from basic mechanistic findings to clinical therapies that take the neural phenotypes into account.

Summary: Dystroglycan is a ubiquitous matrix receptor linked to brain and muscle disease. Unraveling the functions of this protein will inform basic and translational research on neural development and muscular dystrophies.