Loss of Ranbp2 in motor neurons causes the disruption of nucleocytoplasmic and chemokine signaling and proteostasis of hnRNPH3 and Mmp28, and the development of amyotrophic lateral sclerosis (ALS)-like syndromes

Abstract

The 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.

Differential activation of neuronal and glial STAT3 in the spinal cord of the SOD1G93A mouse model of amyotrophic lateral sclerosis

“…The nuclear labeling of pSTAT3 in neurons is also observed by this antibody in the mouse hypothalamus after leptin injection (Ernst et al ., ). Accumulation of pSTAT3 in the sciatic nerve is found in Ran‐binding proteins 2 knockout mice by the immunoblots using this antibody (Cho et al ., ). This antibody also shows that axotomy‐induced increase in the intensity of immunoblot bands corresponding to pSTAT3 is significantly lowered in conditional STAT3 knockout mice (Tyzack et al ., ).…”

Microglial activation in an amyotrophic lateral sclerosis-like model caused by Ranbp2 loss and nucleocytoplasmic transport impairment in retinal ganglion neurons

“…Ranbp2 genetic insults in RGNs and motoneurons trigger distinct paracrine signaling likely by the dysregulation of nucleocytoplasmic transport of neural-type selective substrates. Metabolic and immune-modulators underpinning RGN-tomicroglial signaling are regulated by Ranbp2, and this neuroglial system manifests endophenotypes that are likely useful in the prognosis and diagnosis of ALS.Ranbp2 triggers the dysregulation of neuroglia and chemokine signaling without apparent gliosis [34].Multiple lines of evidence indicate that ALS and Ranbp2 affect retinal ganglion neurons (RGNs). The nuclear envelopes of RGNs, like motoneurons, are highly enriched in nuclear pores and Ranbp2, a phenotype that appears related to the long-distance burden of transport of cargoes exiting the nucleus towards axons and synapses [35].…”

“…All transgenic lines were on a mixed genetic background and did not carry the rd1 and rd8 alleles. Tamoxifen (T5648; Sigma-Aldrich) was administered by oral gavage for 5 consecutive days (0.25 mg/g of body weight) to 4-6 week-old mice as described previously [34]. Mice were reared at <70 lux in a pathogen-free transgenic barrier facility at Duke University with a 12 h light-dark cycles (6:00 A.M. -6:00 P.M.) under humidity-and temperature-controlled conditions.…”

“…Ranbp2 triggers the dysregulation of neuroglia and chemokine signaling without apparent gliosis [34].…”

The roles of the nuclear pore complex in cellular dysfunction, aging and disease

“…A recent example of this connection is that a motor neuron specific knockout of Nup358 (also known as RanBP2), a cytoplasmic filament nucleoporin with known roles in oxidative stress response [50], causes a mouse ALS phenotype (Table 1). Conditional ablation of Nup358 in mouse motor neurons causes the onset of the ALS symptoms of hypoactivity, hind limb paralysis, respiratory distress, and eventually death [51]. The ubiquitous Nup358 heterozygous null mice suffer from increased severity of akinetic PD when they are exposed to the neurotoxin MPTP (Table 1) [52].…”