An epilepsy‐associated ACTL6B variant captures neuronal hyperexcitability in a human induced pluripotent stem cell model

Abstract

ACTL6B is a component of the neuronal BRG1/brm‐associated factor (nBAF) complex, which is required for chromatin remodeling in postmitotic neurons. We recently reported biallelic pathogenic variants in ACTL6B in patients diagnosed with early infantile epileptic encephalopathy, subtype 76 (EIEE‐76), presenting with severe, global developmental delay, epileptic encephalopathy, cerebral atrophy, and abnormal central nervous system myelination. However, the pathophysiological mechanisms underlying their phenotype is unknown. Here, we investigate the molecular pathogenesis of ACTL6B p.(Val421_Cys425del) using in silico 3D protein modeling predictions and patient‐specific induced pluripotent stem cell‐derived neurons. We found neurons derived from EIEE‐76 patients showed impaired accumulation of ACTL6B compared to unaffected relatives, caused by reduced protein stability. Furthermore, EIEE‐76 patient‐derived neurons had dysregulated nBAF target gene expression, including genes important for neuronal development and disease. Multielectrode array system analysis unveiled elevated electrophysiological activity of EIEE‐76 patients‐derived neurons, consistent with the patient phenotype. Taken together, our findings validate a new model for EIEE‐76 and reveal how reduced ACTL6B expression affects neuronal function.

Secondary thalamic neuroinflammation after focal cortical stroke and traumatic injury mirrors corticothalamic functional connectivity

“…The GFAP antibody was made against recombinant full‐length human GFAP (1:1000, chicken, Abcam, ab4674, AB_304558) has been used extensively in previous reports (Ahn et al., 2021; Suarez‐Mier & Buckwalter, 2015; Worker et al., 2020). Previous studies have validated its specificity by demonstrating that the antibody recognized cells with astrocyte morphology in controlled cocultures, and that antibody labeling of astrocytes coincided with genetic modes of astrocyte identification (Müller et al., 2015).…”

Using Human‐Induced Pluripotent Stem Cell Derived Neurons on Microelectrode Arrays to Model Neurological Disease: A Review

“…The iPSC-DNs stemmed from epilepsy patients can be used to establish specific epilepsy models on MEA in vitro. [155][156][157] Patientspecific models can simulate the in vitro electrophysiological activity of neurons after epilepsy related gene modifications. They also facilitate in vitro drug screening for individual patients.…”

Aberrant Local Synchrony in Distinct Mouse Models of Epileptic Encephalopathy

“…Aberrant neuronal synchrony is a definitive phenotype for epileptic encephalopathies; however, identifying robust synchrony phenotypes in vitro remains a significant challenge. Reports often do not identify specific synchrony differences or only identify them in genetically modified mouse genotypes that do not reflect those of patients (Shore 2020, Ahn 2021, Amador 2020). Further, more complex synchrony phenotypes, such as topological phenotypes that assess how groups of spatially organized neurons interact with each other can be especially difficult to identify in cultured networks.…”

“…More recently, multi-well MEA systems have been developed that are capable of recording simultaneously from a number of neuronal networks, ranging from 6-well to 96-well plates. While lacking direct evidence of synchrony phenotypes in genotypes that match patients, such MEA systems have identified aberrant network activity using in vitro models of certain epileptic encephalopathies (‘EEs’) (Gullo 2014, Raghavan 2012, Shore 2020, Ahn 2021, Amador 2020). Interestingly, network activity of wild-type cultures shows a limited number of active electrodes (Ahn 2021) or highly synchronized activity in primary neuronal cultures (Shore 2020, Guiberson 2018, Lignani 2013) inconsistent with in vivo activity patterns, where networks begin to desynchronize by the end of the second postnatal week (Golshani 2009).…”

“…While lacking direct evidence of synchrony phenotypes in genotypes that match patients, such MEA systems have identified aberrant network activity using in vitro models of certain epileptic encephalopathies (‘EEs’) (Gullo 2014, Raghavan 2012, Shore 2020, Ahn 2021, Amador 2020). Interestingly, network activity of wild-type cultures shows a limited number of active electrodes (Ahn 2021) or highly synchronized activity in primary neuronal cultures (Shore 2020, Guiberson 2018, Lignani 2013) inconsistent with in vivo activity patterns, where networks begin to desynchronize by the end of the second postnatal week (Golshani 2009). Thus, one hypothesis for limitations of existing in vitro evidence is that maintained high levels of synchrony may be confounding.…”