Dystroglycan Mediates Clustering of Essential GABAergic Components in Cerebellar Purkinje Cells

Abstract

Muscle dystrophin–glycoprotein complex (DGC) links the intracellular cytoskeleton to the extracellular matrix. In neurons, dystroglycan and dystrophin, two major components of the DGC, localize in a subset of GABAergic synapses, where their function is unclear. Here we used mouse models to analyze the specific role of the DGC in the organization and function of inhibitory synapses. Loss of full-length dystrophin in mdx mice resulted in a selective depletion of the transmembrane β-dystroglycan isoform from inhibitory post-synaptic sites in cerebellar Purkinje cells. Remarkably, there were no differences in the synaptic distribution of the extracellular α-dystroglycan subunit, of GABA A receptors and neuroligin 2. In contrast, conditional deletion of the dystroglycan gene from Purkinje cells caused a disruption of the DGC and severely impaired post-synaptic clustering of neuroligin 2, GABA A receptors and scaffolding proteins. Accordingly, whole-cell patch-clamp analysis revealed a significant reduction in the frequency and amplitude of spontaneous IPSCs recorded from Purkinje cells. In the long-term, deletion of dystroglycan resulted in a significant decrease of GABAergic innervation of Purkinje cells and caused an impairment of motor learning functions. These results show that dystroglycan is an essential synaptic organizer at GABAergic synapses in Purkinje cells.

Gephyrin-Lacking PV Synapses on Neocortical Pyramidal Neurons

“…In addition, α2- and γ2 -GABA A Rs and miniature IPSC frequency are normal in hippocampal cultures from the gephyrin knock-out [ 85 ]. Gephyrin-independent clustering of GABA A Rs has been observed in other brain areas, including α1-containing GABA A Rs on Purkinje cell somas [ 86 , 87 , 88 , 89 ], perisomatic α1-containing GABA A Rs on hippocampal Pyr cells [ 90 , 91 , 92 ], and α2/α3/α5/β3-containing GABA A Rs on sensory afferents [ 93 ]. Our data indicate that gephyrin may be a particularly unreliable marker for PV-type inhibitory synapses and suggest that other types of inhibitory inputs be carefully evaluated for gephyrin colocalization.…”

Calsyntenin-3, an atypical cadherin, suppresses inhibitory basket- and stellate-cell synapses but boosts excitatory parallel-fiber synapses in cerebellum

“…Clstn3 protein was localized to parallel-fiber synapses by immunoelectron microscopy (Hintsch et al, 2002). Moreover, other genetic manipulations that cause a decrease in inhibitory synaptic transmission in cerebellar cortex, such as deletions of Nlgn2 or of GABA A -receptors (Briatore et al, 2020; Fritschy et al, 2006; Meng et al, 2019; Zhang et al, 2015), do not induce an increase in excitatory parallel-fiber synapses. Finally and probably most importantly, although competition between synapses using the same transmitters is well-described (e.g., competition between glutamatergic parallel- and climbing-fiber synapses on Purkinje cells; Cesa and Strata, 2009; Miyazaki et al, 2012; Strata et al, 1997), no such competition has been observed between GABAergic and glutamatergic synapses, such that the decrease in one of them would lead to the increase of the other.…”

“…The interaction of presynaptic neurexins with cerebellins and postsynaptic GluD receptors plays a major role in shaping parallel-fiber synapses (Yuzaki and Aricescu, 2017), and the binding of C1ql1 to postsynaptic Bai3 has a prominent function in climbing-fiber synapses (Kakegawa et al, 2015; Sigoillot et al, 2015). Postsynaptic Nlgn2 and Nlgn3 are major contributors to the function of GABAergic synapses in Purkinje cells (Zhang et al, 2015), as is dystroglycan (Briatore et al, 2020). How can we envision the collaboration of various synaptic adhesion complexes in establishing and shaping the different types of synapses on Purkinje cells?…”

The Synaptic Extracellular Matrix: Long-Lived, Stable, and Still Remarkably Dynamic

“…While this is the only demonstration, to our knowledge, of a complete recycling loop of an ECM molecule, many additional studies also add credence to the concept of ECM recycling at synapses. These include reports of ECM molecules that undergo internalization (e.g., Coopman et al, 1996 ; Tammi et al, 2001 ; Shi and Sottile, 2008 ; Lobert et al, 2010 ; Leonoudakis et al, 2014 ), demonstrations that ECM receptors are present at synapses (e.g., Kramár et al, 2002 ; Huang et al, 2006 ; Roszkowska et al, 2016 ; Izumi et al, 2017 ; Apóstolo et al, 2020 ; Briatore et al, 2020 ), and reports that synapses contain the machinery for trafficking recycling molecules in an activity-dependent manner (Tang, 2008 ; Gürth et al, 2020 ; Helm et al, 2021 ). Nevertheless, additional demonstrations of the recycling of ECM molecules in neurons are anticipated in the future.…”