Loss of Ranbp2 in motoneurons causes disruption of nucleocytoplasmic and chemokine signaling, proteostasis of hnRNPH3 and Mmp28, and development of amyotrophic lateral sclerosis-like syndromes.

Kyoung-In Cho,Dosuk Yoon,William C Wetsel,Paulo A Ferreira,Zachary Danziger,Warren M Grill,Sunny Qiu

doi:10.1242/dmm.027730

Kyoung-In Cho, Dosuk Yoon + Show 5 more

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https://doi.org/10.1242/dmm.027730

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Abstract

ABSTRACTThe pathogenic drivers of sporadic and familial motor neuron disease (MND), such amyotrophic lateral sclerosis (ALS), are unknown. MND impairs the Ran GTPase cycle, which controls nucleocytoplasmic transport, ribostasis and proteostasis; however, cause-effect mechanisms of Ran GTPase modulators in motoneuron pathobiology have remained elusive. The cytosolic and peripheral nucleoporin Ranbp2 is a crucial regulator of the Ran GTPase cycle and of the proteostasis of neurological disease-prone substrates, but the roles of Ranbp2 in motoneuron biology and disease remain unknown. This study shows that conditional ablation of Ranbp2 in mouse Thy1 motoneurons causes ALS syndromes with hypoactivity followed by hindlimb paralysis, respiratory distress and, ultimately, death. These phenotypes are accompanied by: a decline in the nerve conduction velocity, free fatty acids and phophatidylcholine of the sciatic nerve; a reduction in the g-ratios of sciatic and phrenic nerves; and hypertrophy of motoneurons. Furthermore, Ranbp2 loss disrupts the nucleocytoplasmic partitioning of the import and export nuclear receptors importin β and exportin 1, respectively, Ran GTPase and histone deacetylase 4. Whole-transcriptome, proteomic and cellular analyses uncovered that the chemokine receptor Cxcr4, its antagonizing ligands Cxcl12 and Cxcl14, and effector, latent and activated Stat3 all undergo early autocrine and proteostatic deregulation, and intracellular sequestration and aggregation as a result of Ranbp2 loss in motoneurons. These effects were accompanied by paracrine and autocrine neuroglial deregulation of hnRNPH3 proteostasis in sciatic nerve and motoneurons, respectively, and post-transcriptional downregulation of metalloproteinase 28 in the sciatic nerve. Mechanistically, our results demonstrate that Ranbp2 controls nucleocytoplasmic, chemokine and metalloproteinase 28 signaling, and proteostasis of substrates that are crucial to motoneuronal homeostasis and whose impairments by loss of Ranbp2 drive ALS-like syndromes.

Highlights

Motoneuron disease (MND) encompasses neurodegenerative disorders of familial and sporadic origins that affect predominantly motoneurons, but they have varied syndromic presentations (Finsterer and Burgunder, 2014)
Generation of mice with conditional ablation of Ranbp2 in Thy1+ motoneurons To assess the role of Ranbp2 in Thy1+ neurons, we genetically excised exon 2 (ΔE2) from the Ranbp2 floxed gene (Patil et al, 2014; Cho et al, 2013; Dawlaty et al, 2008) by crossing these mice with the single-neuron labeling with inducible Cre-mediated knockout V (SLICK-V) or H transgenic lines (SLICK-H) lines (Young et al, 2008)
These SLICK lines co-express the yellow fluorescent protein (YFP) and tamoxifen-inducible Cre recombinase (CreERT2) under the control of two oppositely oriented Thy1 neural-selective promoters that drive the expression of the cell surface glycoprotein Thy1 (CD90) and that are differentially expressed among Thy1 neurons of the central and peripheral nervous system of the SLICK-V and SLICK-H lines (Fig. 1A) (Young et al, 2008)

Summary

Introduction

Motoneuron disease (MND) encompasses neurodegenerative disorders of familial and sporadic origins that affect predominantly motoneurons, but they have varied syndromic presentations (Finsterer and Burgunder, 2014). Regardless, mounting evidence in mice and humans indicates that sporadic and familial ALS promote impairments of multiple components that are dependent on the Ran GTPase cycle (Jovicić et al, 2015; Freibaum et al, 2015; Zhang et al, 2015; Kim et al, 2013; Boeynaems et al, 2016; Xiao et al, 2015a; Zhang et al, 2006; Kinoshita et al, 2009), which controls nucleocytoplasmic trafficking of substrates implicated in ribostasis (Kim et al, 2013; Dickmanns et al, 2015; Cautain et al, 2015) These impairments lead to pathological imbalances in ribostasis, protein homeostasis ( known as ‘proteostasis’) and toxic aggregation of selective shuttling substrates that are thought to lead to motoneuron dysfunction and degeneration (Ramaswami et al, 2013; Ling et al, 2013). Some mouse models of ALS that affect components of the Ran GTPase cycle do not cause motoneuron degeneration for reasons that remain to be elucidated (Koppers et al, 2015; Peters et al, 2015; O’Rourke et al, 2015, 2016)

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