Cannabinoid receptor‐1 expressing interneurons require postsynaptic dystroglycan for targeting during postnatal brain development

Abstract

Dystroglycan is a transmembrane glycoprotein highly expressed in muscle and brain that links the extracellular matrix to the actin cytoskeleton through its two subunits, a heavily glycosylated extracellular subunit alpha dystroglycan (a‐DG), and the membrane spanning beta‐dystroglycan (b‐DG). Glycosylation of dystroglycan by at least 18 enzymes is essential for its ability to bind extracellular ligands throughout development. Mutations in genes encoding glycosyltransferases such as B4gat1 and ISPD reduce dystroglycan function and cause a spectrum of congenital muscular dystrophies characterized by muscle weakness, brain malformations, and cognitive deficits. In the brain, dystroglycan is expressed by both glia and excitatory neurons, but its specific function in neurons has remained elusive. Recently, neuronal dystroglycan was discovered to be important for the formation of presynaptic cannabinoid receptor 1 (CB1R) synapses derived from cholecystokinin (CCK) interneurons, a population of inhibitory cells in the forebrain. However, the mechanism by which dystroglycan regulates the development of CCK/CB1R+ inhibitory synapses remains unknown. In the present study, we use multiple mouse lines to determine how dystroglycan regulates CB1R+ synapse development, including mouse models of dystroglycanopathy (B4gat1, ISPD), conditional genetic deletion of dystroglycan from neurons and glia (Dag1‐cKO: Nex‐Cre, Emx‐Cre, Nestin‐Cre), and a mouse lacking the intracellular signaling domain of dystroglycan (Dag1ICD). We found that deletion of dystroglycan specifically from excitatory neurons resulted in the loss of nearly all presynaptic CB1R+ terminals within the first week after birth. Surprisingly, deletion of dystroglycan from both neurons and glia using Nestin‐Cre or Emx‐Cre resulted in abnormal targeting of CB1R+ terminals. We also find that maintenance of CB1R+ terminals in adulthood does not require full glycosylation of a‐DG or the intracellular signaling domain of b‐DG. Collectively, these results suggest that dystroglycan may be required for the proper targeting of CB1R+ synapses during postnatal brain development.Support or Funding InformationNINDS R01 NS091027 (KMW)NINDS F31 NS108522 (DSM)ARCS Fellowship (DSM)Tartar Fellowship (DSM)