ABT1 modifies SMARD1 pathology via interactions with IGHMBP2 and stimulation of ATPase and helicase activity
Gangadhar P. Vadla, … , Kamal Singh, Monique A. Lorson
Gangadhar P. Vadla, … , Kamal Singh, Monique A. Lorson
Published December 8, 2022
Citation Information: JCI Insight. 2023;8(2):e164608. https://doi.org/10.1172/jci.insight.164608.
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Research Article Genetics Neuroscience

ABT1 modifies SMARD1 pathology via interactions with IGHMBP2 and stimulation of ATPase and helicase activity

Abstract

SMA with respiratory distress type 1 (SMARD1) and Charcot-Marie-Tooth type 2S (CMT2S) are results of mutations in immunoglobulin mu DNA binding protein 2 (IGHMBP2). IGHMBP2 is a UPF1-like helicase with proposed roles in several cellular processes, including translation. This study examines activator of basal transcription 1 (ABT1), a modifier of SMARD1-nmd disease pathology. Microscale thermophoresis and dynamic light scattering demonstrate that IGHMBP2 and ABT1 proteins directly interact with high affinity. The association of ABT1 with IGHMBP2 significantly increases the ATPase and helicase activity as well as the processivity of IGHMBP2. The IGHMBP2/ABT1 complex interacts with the 47S pre-rRNA 5′ external transcribed spacer and U3 small nucleolar RNA (snoRNA), suggesting that the IGHMBP2/ABT1 complex is important for pre-rRNA processing. Intracerebroventricular injection of scAAV9-Abt1 decreases FVB-Ighmbp2nmd/nmd disease pathology, significantly increases lifespan, and substantially decreases neuromuscular junction denervation. To our knowledge, ABT1 is the first disease-modifying gene identified for SMARD1. We provide a mechanism proposing that ABT1 decreases disease pathology in FVB-Ighmbp2nmd/nmd mutants by optimizing IGHMBP2 biochemical activity (ATPase and helicase activity). Our studies provide insight into SMARD1 pathogenesis, suggesting that ABT1 modifies IGHMBP2 activity as a means to regulate pre-rRNA processing.

Authors

Gangadhar P. Vadla, Sara M. Ricardez Hernandez, Jiude Mao, Mona O. Garro-Kacher, Zachary C. Lorson, Ronin P. Rice, Sarah A. Hansen, Christian L. Lorson, Kamal Singh, Monique A. Lorson

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Figure 8

scAAV9-Abt1 delivery reduces NMJ denervation in FVB-nmd mutant mice.

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scAAV9-Abt1 delivery reduces NMJ denervation in FVB-nmd mutant mice. Tis...
Tissue from P12 WT (+/+), Ighmbp2nmd/nmd, and Ighmbp2nmd/nmd mice injected with scAAV9-Abt1 (4 × 1011 viral genomes) was evaluated. (A) Quantification of the percentage of end plates of gastrocnemius neuromuscular junctions (NMJs). Assessment of fully denervated (dark gray), partially innervated (light gray), or fully innervated (black) end plates. Statistical significance was determined by 2-way ANOVA with a Tukey’s multiple-comparison post hoc test; ****P ≤ 0.0001. Greater than 100 end plates per cohort were counted and averaged. Data points on graphs represent the average per animal with statistical analysis comparing the average of each animal. (B) Quantification of the percentage of end plates of tibialis anterior NMJs. Assessment of fully denervated (dark gray), partially innervated (light gray), or fully innervated (black) end plates. Statistical significance was determined by 2-way ANOVA with a Tukey’s multiple-comparison post hoc test; *P ≤ 0.0331, ****P ≤ 0.0001. Greater than 100 end plates per cohort were counted and averaged. Data points on graphs represent the average per animal with statistical analysis comparing the average of each animal. (C) Microscopic images of gastrocnemius tissue sections. (D) Microscopic images of tibialis anterior tissue sections. Tissue was assessed by neurofilament heavy chain (NF-H) and synaptic vesicle type 2 (SV2) to label axons and synaptic terminals. bungarotoxin labeled acetylcholine receptors (AChRs). Original magnification, 40×. Analyses were performed with GraphPad Prism software. Data are shown as mean ± SEM. Data points on graph represent the average per animal with statistical analysis comparing the average of each animal. Scale bars: 50 μm.