Changes in Gene Expression Following Acute and Chronic Denervation in Humans and Rats

Introduction: Rodent models are typically used to investigate the cellular pathways following nerve injury. However, delayed coaptation for as little as 8 weeks in rodents significantly impairs recovery, whereas humans can withstand longer durations of denervation. Hence, little is known about how the gene expression profile of rodents following denervation maps temporally onto humans. Here, we compared mRNA expression in denervated humans (RNA-seq) and rats (microarrays).

Methods: Humans: Seventy-three patients underwent peripheral nerve surgery at Johns Hopkins Hospital (duration of denervation: control, 3mo, 6-8mo, 12mo-5yr). RNA-seq was performed.

Rats: the sciatic nerve was transected (duration of denervation: control, 1d, 3d, 7d, 14d, 1mo, 6mo) and distal sciatic nerve samples were analysed using DNA microarrays and qPCR.

Results: The majority of patients were male (76.9%), white (65.2%) and underwent traumatic mechanisms of nerve injury (65.6%), of which most were vehicular accidents (61.9%). Median duration until surgery was 7.0mo.

In human denervation, RUV analysis revealed a triphasic temporal pattern of RNA expression. The 3mo denervation group showed an increased innate immune response and reduced energy production, whereas 6-8mo denervation had an increased adaptive immune response. Finally, 12mo-5yr denervation showed somewhat reversion to the original state, with increased energy production, but reduced neurogenesis.

Gene ontology pathway analysis revealed persistent downregulation of biosynthetic pathways involved in cholesterol, lipid, secondary alcohol and acetyl coenzyme A metabolism in both humans and rats. In rats, cellular proliferation and immune signalling were upregulated between days 1 and 14 of denervation, with ficolin-1 RNA upregulated between day 1 and 7, whilst pyroptosis was upregulated at day 14.

Overlap analysis showed 3 months of denervation in humans corresponded most significantly to 3-7 days of denervation in rats. Six months of human denervation corresponded to 7-14 days rat denervation, and 12mo-5yrs of human denervation corresponded to 6 months in rats.

Conclusion : Denervation induces a differential RNA expression profile that maps temporally between humans and rodents. We will now perform snRNA-seq on acute and chronically denervated tissue to further characterise these changes.