Peripheral neuropathy is a common side effect of chemotherapy characterized by paraesthesia (tingling), numbness, pain, temperature sensitivity, and motor weakness. Paclitaxel (Taxol) is one of the most widely used chemotherapeutic agents, which primarily affects the somatosensory neurons innervating the skin1–3. Pathological examinations suggest that intraepidermal unmyelinated axons are the first to degenerate upon paclitaxel treatment4–8. Thus, understanding the genetic mechanisms underlying the earliest manifestations of the disease will be essential to develop therapies that allow chemotherapy patients to complete cancer treatment without disruption, and prevent irreversible long-term symptoms.
Few studies have established expression profiles of chemotherapy-induced peripheral neuropathy. In one study, parallel gene expression profiles from dorsal root ganglion (DRG) neurons in mice were established following injection with the chemotherapeutic agents, oxaliplatin, vincristine, and cisplatin9. This comparative study revealed that only few genes were common among these data sets, suggesting that fundamental differences in the aetiology of chemotherapy-induced peripheral neuropathy (CIPN) must exist. This may not be surprising given the differences in the mechanisms of action for each of these chemotherapeutic agents, leading to potentially different off-target effects. In addition, the investigation of dorsal root ganglion (DRG) neurons may have obscured common upstream mechanisms. For instance, we previously showed that sensory neurons are secondarily affected by earlier epidermal damage, which promotes the degeneration of intraepidermal nerve endings in zebrafish, rats, and mice treated with paclitaxel. Epidermal keratinocytes are damaged due to increased reactive oxygen species formation and upregulation of matrix metalloproteinases, such as MMP-13, leading to extracellular matrix damage that ultimately affects the axons, leading to their degeneration8. Epidermal damage can be prevented when animals are treated with pharmacological MMP-13 inhibitors10. Therefore, the skin plays a crucial role in sensory axon homeostasis.
Existing genomic studies have focused on single time point analyses and single cell types11,12. For instance, RNA sequencing was used to analyse blood samples of breast cancer survivors who suffered from long-term paclitaxel-induced peripheral neuropathy and these samples were compared to breast cancer survivors without neuropathy13. This study identified changes in mitochondrial genes that had been previously identified in preclinical CIPN models as differentially regulated, validating the importance of these models in studying the human pathology13. Potentially, mitochondrial dysfunction might play a role in the deficiency of some patients to resolve their neuropathy symptoms. Despite these findings, longitudinal studies to detect changes in affected tissues over prolonged time periods have not been conducted, and thus no data is available on gene expression changes prior to the onset of neuropathic symptoms. This information, however, will be critical to understand the molecular gene expression networks involved in the onset, progression, and resolution of neuropathy.
To address this need, we performed a comprehensive RNAseq study using skin and DRG neuron samples of vehicle and paclitaxel-treated mice. We compared gene expression profiles according to pain profiles generated in these mice. Mice were injected 4 times every other day with either vehicle or paclitaxel and subsequently underwent a recovery period between day 7 and day 23. Tissues were collected and analysed during these time points, which were categorized as “pain onset” on day 4, “maximal pain sensitivity” on day 7, “beginning of pain resolution” at day 11, and “post pain” on day 23. The generated data sets will be useful for the research community to further validate the genes implicated in paclitaxel-induced peripheral neuropathy.