DO CONVERGENT OR DIVERGENT PROTEOMIC EFFECTS UNDERLY ALTERED NEURONAL EXCITABILITY OF CORTICAL EXCITATORY AND INHIBITORY CELLULAR MODELS OF MYOCLONUS DYSTONIA?

Dystonia is a hyperkinetic movement disorder estimated to affect 1.2% of the population and characterised by involuntary muscle contractions, resulting in abnormal postures, repetitive movements, pain and reduced quality of life (PMID:34543508). Evidence supports dystonia to arise from cortico-thalamo-basal ganglia-cerebello neural network dysfunction, with cortical excitatory/inhibitory imbalance considered key. Myoclonus Dystonia is a genetic form of dystonia caused by dominantly inherited SGCE mutations which impair ε-sarcoglycan protein production (PMID:17200151). Cortical excitatory and inhibitory neurons generated from induced pluripotent stem cell (iPSC) models of Myoclonus Dystonia exhibit hyperactive and hypoactive functional phenotypes, respectively, compared to isogenic controls (PMID:36204995, 40711998). This work sought to investigate the mechanisms underlying these cellular phenotypes, by performing unbiased liquid chromatography-mass spectrometry (LC-MS) to characterise proteomic alterations associated with SGCE mutations.
Excitatory and inhibitory neurons were generated separately from patient-derived and isogenic control iPSCs using dual-smad inhibition protocols (PMID:30661995). At 80 days differentiation, membrane-bound and cytosolic protein fractions were isolated and analysed using LC-MS. Differential expression was assessed using the R Limma package, with log2(fold-change) > 1.5 and false discovery rate < 0.05 considered significant.
We identified 148 and 369 differentially expressed proteins in excitatory and inhibitory neurons, respectively. Upregulated proteins in both cell types included, potassium channel auxiliary subunit, DPP6, axon guidance protein, SLIT1, and synaptic proteins, vGlut2, PSD-93, synapsin-3. Divergently regulated proteins included axon guidance proteins, SLIT2 and ROBO2, and GABA transporters, GAT-3 and VGAT. These findings further implicate altered synaptic function, particularly GABAergic signalling, in Myoclonus Dystonia pathophysiology and highlight potential pharmacological targets.