Aberrant neuronal activity-induced signaling and gene expression in a mouse model of RASopathy

Abstract

Noonan syndrome (NS) is characterized by reduced growth, craniofacial abnormalities, congenital heart defects, and variable cognitive deficits. NS belongs to the RASopathies, genetic conditions linked to mutations in components and regulators of the Ras signaling pathway. Approximately 50% of NS cases are caused by mutations in PTPN11. However, the molecular mechanisms underlying cognitive impairments in NS patients are still poorly understood. Here, we report the generation and characterization of a new conditional mouse strain that expresses the overactive Ptpn11D61Y allele only in the forebrain. Unlike mice with a global expression of this mutation, this strain is viable and without severe systemic phenotype, but shows lower exploratory activity and reduced memory specificity, which is in line with a causal role of disturbed neuronal Ptpn11 signaling in the development of NS-linked cognitive deficits. To explore the underlying mechanisms we investigated the neuronal activity-regulated Ras signaling in brains and neuronal cultures derived from this model. We observed an altered surface expression and trafficking of synaptic glutamate receptors, which are crucial for hippocampal neuronal plasticity. Furthermore, we show that the neuronal activity-induced ERK signaling, as well as the consecutive regulation of gene expression are strongly perturbed. Microarray-based hippocampal gene expression profiling revealed profound differences in the basal state and upon stimulation of neuronal activity. The neuronal activity-dependent gene regulation was strongly attenuated in Ptpn11D61Y neurons. In silico analysis of functional networks revealed changes in the cellular signaling beyond the dysregulation of Ras/MAPK signaling that is nearly exclusively discussed in the context of NS at present. Importantly, changes in PI3K/AKT/mTOR and JAK/STAT signaling were experimentally confirmed. In summary, this study uncovers aberrant neuronal activity-induced signaling and regulation of gene expression in Ptpn11D61Y mice and suggests that these deficits contribute to the pathophysiology of cognitive impairments in NS.

Noonan Syndrome-Associated SHP2 Dephosphorylates GluN2B to Regulate NMDA Receptor Function

“…By contrast, CA1 EPSCs in NS mice were initially potentiated to levels lower than WT and decayed to baseline 30 min after TBS ( Figure 1D ). Our findings agree with and extend previous reports that several N-SH2 D61 mutant animals fail other hippocampus-dependent memory tasks and cannot stably express TBS-induced LTP ( Altmüller et al, 2017 ; Lee et al, 2014 ).…”

“…Our findings of disrupted novel object recognition and NMDAR-dependent hippocampal plasticity in NS mice agree with and extend previous reports ( Altmüller et al, 2017 ; Lee et al, 2014 ), and our result that LTP is absent in whole-cell recordings also confirms previous work using extracellular field recordings ( Lee et al, 2014 ). Together, these results strongly affirm that NS-associated mutations of SHP2 D61 in mice cause behavioral and plasticity defects.…”

“…Mutation of N-SH2 D61 in NS causes greater phosphatase hyperactivation and is associated with more severe cognitive symptoms than another common NS mutation, N308D ( Keilhack et al, 2005 ; Pierpont et al, 2009 ). In mice, heterozygous knockin of D61G or brain-specific overexpression of SHP2 D61G or D61Y causes learning and memory deficits ( Altmüller et al, 2017 ; Lee et al, 2014 ), whereas these phenotypes are milder in N308D mutants ( Lee et al, 2014 ). These results suggest that increased SHP2 phosphatase activity itself underlies cognitive problems in NS patients.…”

The Forebrain-Specific Overexpression of Acid Sphingomyelinase Induces Depressive-Like Symptoms in Mice

“…Here, we report the generation and characterization of a conditional transgenic mouse model in which the expression of Asm is restricted to the forebrain (Asm-tg fb ). Restriction to the forebrain is possible via the Emx1-cre mouse strain [22], a widely used strain to generate conditional transgenic mouse models [23]. Emx1 encodes a transcription factor and is expressed in the developing forebrain [24], specifically in the excitatory neurons and astrocytes [22].…”

Advancing RAS/RASopathy therapies: An NCI‐sponsored intramural and extramural collaboration for the study of RASopathies

“…Despite the advantages of zebrafish models, mouse models more accurately represent human organ function and the size of a mouse allows for a more detailed analysis of organ structures to be performed. Multiple mouse models with Ras/MAPK activating variants have been established for NS (Altmuller et al, ), CS (Oba et al, ), and CFC (Aoidi et al, ). Selection of a preclinical model, then, is guided by ease and cost of use, ability to provide drug exposure at the appropriate time and dosage, and availability of outcome measures for drug effects.…”