Experimental upregulation of developmentally downregulated ribosomal protein large subunits 7 and 7A promotes axon regeneration after injury in vivo [bulk RNA-Seq]

Ribosomal proteins are involved in neurodevelopment and central nervous system (CNS) disease and injury. However, the roles of specific ribosomal protein subunits in developmental axon growth, and their potential as therapeutic targets for treating CNS injuries, are still poorly understood. Here, we show that ribosomal protein large (Rpl) and small (Rps) subunit genes are substantially (56-fold) enriched amongst the genes, which are downregulated during maturation of retinal ganglion cell (RGC) CNS projection neuron. We also show that RGC subtype-specific Rpl and Rps subunits are highly co-regulated, and partially re-upregulated after optic nerve crush (ONC). Because developmental downregulation of ribosomal proteins coincides with developmental decline in neuronal intrinsic axon growth capacity, we hypothesized that Rpl/Rps incomplete re-upregulation after injury may be a part of the cellular response which attempts to reactivate intrinsic axon growth mechanism. We found that experimentally upregulating Rpl7 and Rpl7A promoted axon regeneration after ONC in vivo. Finally, we characterized gene networks associated with Rpl/Rps, and showed that Rpl7 and Rpl7A belong to the cluster of genes, which are shared between translational and neurodevelopmental biological processes (based on gene-ontology) that are co-downregulated in maturing RGC during the decline in intrinsic axon growth capacity. Bulk-mRNA-seq samples from different age RGCs were purified by immunopanning for Thy1 (after immunopanning depletion of macrophages), cDNA libraries prepared using polyA-selected RNA (TruSeq RNA Library Prep Kit, Illumina), paired reads sequenced 100 bp from each end on HiSeq 2000 Sequencer (Illumina), passed QC filters, mapped to the mm10 genome and transcriptome by Hisat2, and analyzed by Cufflinks/CuffDiff, as we previously described.