Biallelic variants in TSPOAP1, encoding the active-zone protein RIMBP1, cause autosomal recessive dystonia
Niccolò E. Mencacci, … , Dimitri Krainc, Claudio Acuna
Niccolò E. Mencacci, … , Dimitri Krainc, Claudio Acuna
Published February 4, 2021
Citation Information: J Clin Invest. 2021;131(7):e140625. https://doi.org/10.1172/JCI140625.
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Biallelic variants in TSPOAP1, encoding the active-zone protein RIMBP1, cause autosomal recessive dystonia

Abstract

Dystonia is a debilitating hyperkinetic movement disorder, which can be transmitted as a monogenic trait. Here, we describe homozygous frameshift, nonsense, and missense variants in TSPOAP1, which encodes the active-zone RIM-binding protein 1 (RIMBP1), as a genetic cause of autosomal recessive dystonia in 7 subjects from 3 unrelated families. Subjects carrying loss-of-function variants presented with juvenile-onset progressive generalized dystonia, associated with intellectual disability and cerebellar atrophy. Conversely, subjects carrying a pathogenic missense variant (p.Gly1808Ser) presented with isolated adult-onset focal dystonia. In mice, complete loss of RIMBP1, known to reduce neurotransmission, led to motor abnormalities reminiscent of dystonia, decreased Purkinje cell dendritic arborization, and reduced numbers of cerebellar synapses. In vitro analysis of the p.Gly1808Ser variant showed larger spike-evoked calcium transients and enhanced neurotransmission, suggesting that RIMBP1-linked dystonia can be caused by either reduced or enhanced rates of spike-evoked release in relevant neural networks. Our findings establish a direct link between dysfunction of the presynaptic active zone and dystonia and highlight the critical role played by well-balanced neurotransmission in motor control and disease pathogenesis.

Authors

Niccolò E. Mencacci, Marisa M. Brockmann, Jinye Dai, Sander Pajusalu, Burcu Atasu, Joaquin Campos, Gabriela Pino, Paulina Gonzalez-Latapi, Christopher Patzke, Michael Schwake, Arianna Tucci, Alan Pittman, Javier Simon-Sanchez, Gemma L. Carvill, Bettina Balint, Sarah Wiethoff, Thomas T. Warner, Apostolos Papandreou, Audrey Soo, Reet Rein, Liis Kadastik-Eerme, Sanna Puusepp, Karit Reinson, Tiiu Tomberg, Hasmet Hanagasi, Thomas Gasser, Kailash P. Bhatia, Manju A. Kurian, Ebba Lohmann, Katrin Õunap, Christian Rosenmund, Thomas C. Südhof, Nicholas W. Wood, Dimitri Krainc, Claudio Acuna

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Figure 4

Impact of RIMBP1-p.Gly1808Ser variant on synaptic transmission.

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Impact of RIMBP1-p.Gly1808Ser variant on synaptic transmission. (A and B...
(A and B) Hippocampal autapses for assessing the role of p.Gly1808Ser on synaptic transmission in vitro. (A) Synaptic transmission in autapses was measured by whole-cell patch clamp recordings. Hippocampal autapses were prepared from RIMBP1, -2/RIM1, -2 quadruple conditional KO mice, and infected with lentiviruses expressing a recombinase-deficient version of Cre as control (ΔCre), Cre-recombinase (Cre), Cre+ RIMBP-WT, and Cre+ RIMBP-MUT constructs. (B) RIMBP levels in the presence of lentiviruses expressing ΔCre, Cre, Cre+ RIMBP-WT, and Cre+ RIMBP-MUT. In this experiment, α-tubulin was used as a loading control. (C) Representative recordings of single action potential–evoked release (EPSC) in hippocampal autapses. (D) Summary graphs of EPSC amplitudes rescued with either RIMBP-WT or with the pathogenic RIMBP-MUT construct. (E–G) Direct measurements of spike-triggered presynaptic calcium entry. (E) Fluorescence images of a representative hippocampal dendrite expressing SynGCaMP6f under basal conditions (0 AP), or after 1, 10, and 100 action potentials (APs). Scale bar: 2.5 μm. (F) Time course of presynaptic fluorescence signals (ΔF/F0) as a function of time following 1, 2, 5, or 10 APs. (G) Summary graph of presynaptic fluorescence signals for different AP frequencies in autaptic cultures infected with viruses expressing Cre+ RIMBP-WT and Cre+ RIMBP-MUT. (H–J) RIMBP pathogenic missense variant impacts RIMBP–Ca2+-channel interaction. (H) Experimental strategy for assessing the interaction of RIMBP with calcium channels using coimmunoprecipitations (co-IPs). (I) Cell lysates from HEK293T cells expressing CaV2.1-HA and RIMBP-WT–Myc, or CaV2.1-HA and RIMBP-MUT–Myc were immunoprecipitated with anti-Myc antibodies. Input fractions (left, 1% of total) and IPs were analyzed by immunoblotting with antibodies against the following: Myc epitope (RIMBP), HA epitope (CaV2.1), and GAPDH as a negative control. (J) Summary graph of 3 coimmunoprecipitation experiments performed as in I. Data are presented as the mean ± SEM. *P < 0.05; ***P < 0.001 by 1-way ANOVA with Tukey’s post hoc analysis (D and G) or Student’s t test (J). NS, not significant. Number of experiments (cells/cultures): (C and D) ΔCre (32/3), Cre (24/3), RIMBP-WT (43/3), RIMBP-MUT (35/3); (F and G) Cre+ RIMBP-WT (17/3), Cre+ RIMBP-MUT (16/3); (J) RIMBP-WT (3), Cre+ RIMBP-MUT (3).