Ascending dorsal column sensory neurons respond to spinal cord injury and downregulate genes related to lipid metabolism

Abstract

Regeneration failure after spinal cord injury (SCI) results in part from the lack of a pro-regenerative response in injured neurons, but the response to SCI has not been examined specifically in injured sensory neurons. Using RNA sequencing of dorsal root ganglion, we determined that thoracic SCI elicits a transcriptional response distinct from sciatic nerve injury (SNI). Both SNI and SCI induced upregulation of ATF3 and Jun, yet this response failed to promote growth in sensory neurons after SCI. RNA sequencing of purified sensory neurons one and three days after injury revealed that unlike SNI, the SCI response is not sustained. Analysis of differentially expressed genes revealed that lipid biosynthetic pathways, including fatty acid biosynthesis, were differentially regulated after SCI and SNI. Pharmacologic inhibition of fatty acid synthase, the enzyme generating fatty acid, decreased axon growth in vitro. These findings suggest that decreased fatty acid synthesis inhibits axon regeneration after SCI.

Profiling sensory neuron microenvironment after peripheral and central axon injury reveals key pathways for neural repair

“…Our single cell approach does not allow recovery of many neurons and thus limits the depth of our neuronal analysis. However, our results support our previous studies showing that SCI and nerve injury elicits very distinct responses in sensory neurons 19 . Our results expand these findings and reveal that dorsal root crush leads to key RAG expression similar to nerve injury, suggesting that differential gene expression beyond RAGs and/or non-neuronal cells contribute to an axon generation speed that is half that of the peripheral nerve.…”

“…We then determined the number of differentially expressed genes in six major cell types. Heat map of differential gene expression in the indicated cell types revealed that the magnitude of gene expression changes was the largest after SNC, but also occurred after DRC and SCI (Fig 1i), as previously suggested 19, 35 . We focused our analyses on neurons, endothelial cells, pericytes, Schwann cells, macrophages and SGC.…”

“…However, a small proportion of neurons (5%) which include both nociceptors (TrkA positive) and LTMRs (TrkB positive), expressed Atf3 after SCI ( Fig. 2d,e), consistent with prior findings 19 . KEGG pathway [38][39][40] analysis of DE genes in each condition identified distinct and shared pathways enriched after SNC, DRC and SCI injuries (Fig 2f).…”

“…2a). Since the injured state induced by peripheral nerve injury is similar across neuronal subtypes 16 19 , we pooled neuronal subtypes for each condition in our analyses and examined the differentially expressed genes in each injury condition (Supplementary Table2). There was little overlap in upregulated genes between the three injury conditions and more overlap in downregulated genes (Fig 2b).…”

“…Interestingly, dorsal root injury causes up-regulation of the pro-regenerative gene Atf3 14 , but only in large diameter neurons, whereas Atf3 and Jun are upregulated in a majority of neurons after peripheral nerve injury [15][16][17][18] . Spinal cord injury also leads to activation of Atf3 in large diameter neurons, but this is not sufficient to promote regenerative growth 19 . Another possibility explaining the slow growth capacity of axons in the injured dorsal root, is the contribution of nonneuronal cells.…”