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A Variant in Human AIOLOS Impairs Adaptive Immunity by Interfering with IKAROS

ABSTRACT: A missense mutation (G158R) in Aiolos, encoded by Ikzf3 gene, resulted in defective generation of B cells in mice. Pre-B cells were profoundly decreased in homozygous mutant mice. Heterozygous mutant mice showed milder B cell developmental defects, and B cells in the secondary lymphoid organs decreased. Genome-wide binding of Aiolos and Ikaros were altered in the thymus of homozygous Ikzf3 G158R mice. Our findings indicate that Aiolos-G158R hinders B cell development by interfering Ikaros' function via formation of heterodimers. A heterozygous missense variant (G159R) in AIOLOS, encoded by IKZF3 gene, resulted in impaired adaptive immunity, which predominantly manifested as profound B cell developmental defect. Genome-wide binding of wild-type AIOLOS and AIOLOS G159R mutant were examined in IKZF3 knock-out human pre-B cell line NALM-6, retrovirally transduced with doxycycline inducible wild-type AIOLOS or AIOLOS G159R. Changes in genome-wide binding and binding motif were observed for AIOLOS G159R mutant.

ORGANISM(S): Mus musculus Homo sapiens

PROVIDER: GSE167487 | GEO | 2021/05/01

REPOSITORIES: GEO

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Project description:Aims: Pathogenic truncating variants in the largest human protein TITIN are a leading cause of dilated cardiomyopathy. Because of the size of the gene encoding TITIN, many missense variations are identified. These are difficult to evaluate in genetic testing, as even individually rare variants are common in aggregate in normal populations. While the majority will be benign, a small subset is pathogenic, but distinction is challenging. Here, we describe the generation of a mouse model to investigate the underlying disease mechanism of a previously reported TITIN A178D missense variant identified in a family with non-compaction and dilated cardiomyopathy. Methods and Results: Heterozygous and homozygous mice carrying the TITIN A178D missense variant were characterised in vivo. Heterozygous mice had no detectable phenotype at any time point observed (up to 1 year). By contrast, homozygous mice developed dilated cardiomyopathy from 3 months. Chronic adrenergic stimulation aggravated the phenotype. Targeted transcript profiling revealed induction of the fetal gene programme and hypertrophic signalling pathways in homozygous mice, and these were confirmed at the protein level. Unsupervised proteomics identified down-regulation of TELETHONIN and FOUR-AND-A-HALF LIM DOMAIN 2, as well as the up-regulation of heat shock proteins and MYELOID LEUKEMIA FACTOR 1. Loss of TELETHONIN from the cardiac Z-disc was accompanied by proteasomal degradation; however, TELETHONIN also accumulated in the cytoplasm. In parallel, a proteo-toxic response was observed in the mice. Conclusions: We have shown that the TITIN A178D missense variant is pathogenic in homozygous mice, resulting in cardiomyopathy. We also provide evidence of the disease mechanism. Because the TITIN A178D variant abolishes binding of TELETHONIN, this leads to its abnormal cytoplasmic accumulation. Subsequent degradation of TELETHONIN by the proteasome results in proteasomal overload, and activation of a proteo-toxic response. The latter appears to be a driving factor for the cardiomyopathy observed in the mouse model.

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A Variant in Human AIOLOS Impairs Adaptive Immunity by Interfering with IKAROS

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