DISRUPTION OF EXCITATORY-INHIBITORY BALANCE IN PURKINJE CELLS AFTER <EM>N</EM>-GLYCOSYLATION IMPAIRMENT

Alterations in N-glycosylation pathway lead to Congenital Disorders of Glycosylation (CDG). Among other symptoms, CDGs include cerebellar dysfunction causing severe ataxia. Despite the high prevalence of neurological symptoms in CDG-patients, the role of N-glycosylation in modulating nervous system proteins has been largely unexplored. Traditionally, N-glycosylation has been associated with protein folding and surface expression. However, recent studies have demonstrated that N-glycosylation also influences protein function, including cerebellar synaptic proteins. We hypothesize that the disruption of N-glycosylation impairs Purkinje cell (PC) function and, consequently, cerebellar circuit activity.
To investigate the modulation role of N-glycosylation in the cerebellar network, we used cerebellar organotypic cultures and applied the inhibitor Kifunensine (Kf) to block N-glycosylation maturation. Following several days of glycosylation impairment, we assessed the cerebellar network (dys)function using electrophysiological recordings to measure spontaneous firing activity, synaptic inputs onto the main inhibitory neurons from the cerebellum —PC and molecular layer interneurons— and their intrinsic membrane properties. In parallel, we performed immunolabeling analyses of neuronal populations and inhibitory synapses in our cultured cerebellar slices.
We observed a marked reduction of PC firing rate, accompanied by a disruption of the excitatory/inhibitory (E/I) balance, favouring the inhibitory transmission, consistent with observations reported in other ataxia mouse models.
Together, our findings indicate that N-glycosylation plays a critical role in modulating the function of excitatory and inhibitory synapses within the cerebellar circuit. Disruption of this process may lead to imbalances in synaptic transmission, aberrant PC firing patterns and ultimately contribute to the cerebellar dysfunction and ataxia observed in CDG-patients.