ZC4H2 gene: opposite synaptic defects in mice, KIZ study

A team led by Sheng Nengyin at the Kunming Institute of Zoology of the Chinese Academy of Sciences has described ZC4H2-associated rare disorder (ZARD) as a spectrum of mechanisms rather than a single one. According to EurekAlert, the work was published in Neuron on November 5. ZARD is marked by intellectual disability, developmental delay, muscle weakness and other neurological or physical abnormalities. eurekalert.org

Earlier, the same group showed that ZC4H2 is a postsynaptic regulator of excitatory synaptic activity and cognition: it controls the protein stability of the AMPA receptor subunits GluA1 and GluA2. It remained unclear whether the same mechanism operates in patients with different ZC4H2 variants. eurekalert.org

Two classes of mutations

The researchers expressed wild-type ZC4H2 and 23 pathogenic mutants in N2A cells. They identified two classes. The first lost the ability to regulate GluA1/GluA2 (loss of function). The second retained AMPA regulation but abnormally suppressed the inhibitory GABAA receptor subunits α1/β1 (gain of function). Recordings in hippocampal slices showed that the two classes specifically disrupted inhibitory and excitatory transmission, respectively. eurekalert.org

The team then created two knock-in mouse models with representative patient mutations, ZC4H2 L66H/y and ZC4H2 R213W/y. Both showed comparable cognitive deficits: impaired novel-object recognition, loss of social memory and defective spatial learning, without obvious motor or anxiety abnormalities. eurekalert.org

Different ubiquitin ligase pathways

In L66H mice, GABAergic inhibitory transmission and inhibitory long-term potentiation (LTP) were weakened. In R213W mice, AMPAR-mediated excitatory transmission was heightened and excitatory LTP was impaired. eurekalert.org

Using TurboID proximity labeling, the authors traced the divergence to two E3 ubiquitin ligases. The L66H mutant gained an interaction with MKRN2, which promotes polyubiquitination and destabilization of GABAA receptor subunits. The R213W mutant disrupted the interaction of ZC4H2 with RNF220, which reduced RNF220 stability and lowered ubiquitination of AMPA receptor subunits, leaving excitatory synapses overactive. eurekalert.org

Genetic rescue was specific. Knockout of MKRN2 in forebrain excitatory neurons rescued only the L66H model, while a degradation-resistant RNF220 variant rescued only the R213W model. eurekalert.org

Two clinically used drugs were also tested in mice. The GABAA agonist muscimol restored inhibitory transmission and cognition in L66H mice but had no effect in R213W mice. The AMPAR antagonist perampanel produced the opposite result. The authors conclude that intervention should be guided by the specific mutation rather than the diagnosis alone. The results were obtained in cells and mice. eurekalert.org

KIZ: mutations in the ZC4H2 gene cause similar deficits in mice through opposite synaptic defects

Two classes of mutations

Different ubiquitin ligase pathways

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