Single-Cell and Neuronal Network Alterations in an In Vitro Model of Fragile X Syndrome

Abstract

The Fragile X mental retardation protein (FMRP) is involved in many cellular processes and it regulates synaptic and network development in neurons. Its absence is known to lead to intellectual disability, with a wide range of comorbidities including autism. Over the past decades, FMRP research focused on abnormalities both in glutamatergic and GABAergic signaling, and an altered balance between excitation and inhibition has been hypothesized to underlie the clinical consequences of absence of the protein. Using Fmrp knockout mice, we studied an in vitro model of cortical microcircuitry and observed that the loss of FMRP largely affected the electrophysiological correlates of network development and maturation but caused less alterations in single-cell phenotypes. The loss of FMRP also caused a structural increase in the number of excitatory synaptic terminals. Using a mathematical model, we demonstrated that the combination of an increased excitation and reduced inhibition describes best our experimental observations during the ex vivo formation of the network connections.

Hyperexcitability of Sensory Neurons in Fragile X Mouse Model

“…The age-dependent changes in excitability have been reported in central neurons of Fmr1 KO mice: the CA3 pyramidal neurons show increased excitability in young Fmr1 KO mice (3–4 weeks) ( Deng et al, 2019 ; Dwivedi et al, 2019 ), but this was not seen in the older animals (6–8 weeks) ( Dwivedi et al, 2019 ). Further, a delay in neuronal maturation and immature state of dendritic spines is widely documented in central neurons of Fmr1 KO mice ( Comery et al, 1997 ; Harlow et al, 2010 ; Guo et al, 2015 ; Moskalyuk et al, 2020 ), resulting in delayed maturation of local networks ( Vislay et al, 2013 ; Nomura et al, 2017 ) and a developmental delay in somatosensory map formation ( Till et al, 2012 ). This is also consistent with abnormal neurogenesis and altered differentiation of neural stem cells in Fmr1 KOs, leading to poor neuronal maturation and high gliogenic development ( Castren et al, 2005 ; Telias et al, 2013 , 2015 ).…”

The potential of in vitro neuronal networks cultured on micro electrode arrays for biomedical research

“…Similarly to disease models based on genetic manipulation of healthy neuronal cultures, this approach is clearly more suitable for modeling genetic disorders. Examples of neurological disorders which have been modeled on MEAs by isolating and culturing neuronal cultures from rodents carrying specific pathogenic mutations include Autosomal Dominant Sleep-related Hypermotor Epilepsy (ADSHE) [228,255] (formerly known as Autosomal Dominant Nocturnal Frontal Lobe Epilepsy, ADNFLE), Epilepsy Aphasia Syndromes (EAS) [235], PCDH19-Clustering Epilepsy (PCDH19-CE) [234], ASD [237], FXS [240,241], and Niemann-Pick Type C1 (NPC1) disease [242].…”

Human-Derived Cortical Neurospheroids Coupled to Passive, High-Density and 3D MEAs: A Valid Platform for Functional Tests

“…Microelectrode arrays (MEAs) technology is a well-established tool to study how cellular composition, connectivity, genetic, and epigenetic expression correlate with the functional electrical activity expressed by in-vitro neuronal models [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ]. MEAs applicability ranges from drug/toxicological screening [ 1 , 5 , 9 ] to the characterization of various neuronal disorders [ 3 , 8 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ]. In particular, with the introduction of human-induced pluripotent stem cells (hiPSCs) and differentiation protocols, human-derived neuronal models could be created, potentially making the in-vitro approach more reliable and representative of in-vivo conditions.…”