Regulation of Nucleocytoplasmic Partitioning and Proteostasis of Substrates and Chemokine Signaling by Ran-binding protein 2 (Ranbp2) in Thy1⁺-Ganglionic Neurons

Abstract

Purpose: Retinal ganglionic neurons present well-discerned spatiotemporal compartmentation of subcellular processes. Retinal and other types of ganglionic neurons are cellular targets of disparate neurological diseases with ill-defined pathomechanisms, but often presenting derangement of intracellular trafficking events. The multifunctional nucleoporin, Ranbp2, is most abundant in ganglionic neurons owing to the very high-density of nuclear pore complexes (NPC) and localization of Ranbp2 at their cytoplasmic face. This study tests the hypothesis that Ranbp2 plays a central role in the integration of nucleocytoplasmic trafficking processes and function of ganglionic neurons.

Methods: We generated mice harboring the conditional deletion of Ranbp2 in Thy1⁺-ganglionic neurons (Thy1-CreER^T2::Ranbp2^flox/flox) upon administration of tamoxifen. Loss of Ranbp2 in Thy1⁺-ganglionic neurons of Thy1-CreER^T2::Ranbp2^-/- mice were analyzed by immunohistochemistry, electron microscopy, electrophysiology, RNA-Seq and proteomics before and after induction.

Results: Thy1-CreER^T2::Ranbp2^-/- mice develop severe hind limb paralysis, ataxia, seizures and respiratory distress which culminates with death 10 days after the end of tamoxifen induction. These effects are accompanied by the suppression of amplitudes and delayed of implicit times of the visual evoked potential, but without loss of Thy1+-ganglionic neurons. Loss of Ranbp2 promotes the hypermyelination of the sciatic and phrenic, but not optic nerves. Thy1⁺-neurons of Thy1-CreER^T2::Ranbp2^-/- present severe impairment of the nucleocytoplasmic partitioning and proteostasis of nuclear import and export receptors, Ran GTPase, HDAC4, vimentin, myelin basic protein, an hnRNP member and massive redistribution of pre-induced Ranbp2 to the mitochondria. Transcriptome and proteomic analyses identified a set of overlapping and unique genes and proteins and the deregulation of unique chemokine signaling between Thy1⁺-neurons of the retina and spinal horns.

Conclusions: This study unveils that Ranbp2 is critical to the function of Thy1⁺-ganglionic neurons, but without compromising their survival. The data support that Ranbp2 controls intrinsically and differentially cell type-dependent manifestations among Thy1⁺-ganglionic neurons that stem from the regulation of shared and unique cell-type selective factors by Ranbp2.

Keywords: 531 ganglion cells • 740 transgenics/knock-outs • 636 pathobiology