Parkin Deficiency Reduces Hippocampal Glutamatergic Neurotransmission by Impairing AMPA Receptor Endocytosis

Abstract

Mutations in the gene encoding Parkin, an E3 ubiquitin ligase, lead to juvenile-onset Parkinson's disease by inducing the selective death of midbrain dopaminergic neurons. Accumulating evidence indicates that Parkin also has an important role in excitatory glutamatergic neurotransmission, although its precise mechanism of action remains unclear. Here, we investigate Parkin's role at glutamatergic synapses of rat hippocampal neurons. We find that Parkin-deficient neurons exhibit significantly reduced AMPA receptor (AMPAR)-mediated currents and cell-surface expression, and that these phenotypes result from decreased postsynaptic expression of the adaptor protein Homer1, which is necessary for coupling AMPAR endocytic zones with the postsynaptic density. Accordingly, Parkin loss of function leads to the reduced density of postsynaptic endocytic zones and to impaired AMPAR internalization. These findings demonstrate a novel and essential role for Parkin in glutamatergic neurotransmission, as a stabilizer of postsynaptic Homer1 and the Homer1-linked endocytic machinery necessary for maintaining normal cell-surface AMPAR levels.

Parkinson’s disease-linked Parkin mutations impair glutamatergic synaptic transmission and plasticity

“…8c, d). These data are consistent with our previous findings that Parkin regulates AMPAR endocytosis but not exocytosis (19).…”

“…We first assessed the expression and subcellular localization of these mutants in cultured hippocampal neurons from either the Parkin knockdown background (i.e. lentivirally transduced on 2 days in vitro (DIV) with an shRNA against rat Parkin (shParkin), previously shown to reduce Parkin levels by ~50% (19)), or Parkin knockout background (i.e. cultured from KO rats; SAGE/Horizon Discovery).…”

“…Parkin's mechanisms of action at excitatory synapses remain poorly understood, although its ubiquitinating activity has been found to regulate the stability and function of multiple synaptic substrates, including the presynaptic vesicle-associated protein synaptotagmins XI and IV, the postsynaptic scaffold PICK1, and the kainate receptor subunit GluK2 (21)(22)(23)(24)(25)(26). Furthermore, our recent work demonstrates that Parkin also has a structural role at the synapse, linking postsynaptic endocytic zones required for AMPA-type glutamate receptor (AMPAR) capture and internalization to the postsynaptic density through a direct interaction with the scaffold protein Homer1 (19). In Parkin deficient neurons, both the levels of postsynaptic Homer1 and the density of endocytic zones are significantly reduced, leading to impaired AMPAR retention at synapses and ultimately to decreased AMPAR-mediated currents (19).…”

“…However, Parkin is highly expressed throughout the brain and known to regulate other aspects of neuronal function, including glutamatergic neurotransmission (14). Indeed, defects in glutamatergic transmission and plasticity are reported at hippocampal and corticostriatal synapses deficient in Parkin (15)(16)(17)(18)(19)(20). Parkin's mechanisms of action at excitatory synapses remain poorly understood, although its ubiquitinating activity has been found to regulate the stability and function of multiple synaptic substrates, including the presynaptic vesicle-associated protein synaptotagmins XI and IV, the postsynaptic scaffold PICK1, and the kainate receptor subunit GluK2 (21)(22)(23)(24)(25)(26).…”

Cortical Overgrowth in a Preclinical Forebrain Organoid Model of CNTNAP2-Associated Autism Spectrum Disorder

“…Measurement of Electrophysiology Properties. Whole-cell patch-clamp recordings were performed as previously described (21). EBs were dissociated into single cells after rosettes were selected, plated onto glass coverslips coated with poly-L-ornithine (50µg/ml) and laminin (5µg/ml), and maintained in vitro for 60 days.…”