Paclitaxel induces peripheral neuropathy as a side effect of cancer treatment. The underlying causes are unclear, but epidermal, unmyelinated axons have been shown to be the first to degenerate. We previously utilized an in vivo zebrafish model to show that the epidermal matrix-metalloproteinase 13 (MMP-13) induces degeneration of unmyelinated axons, whereas pharmacological inhibition of MMP-13 prevented axon degeneration. However, the precise functions by which MMP-13 is regulated and affects axons remained elusive. In this study, we assessed mitochondrial damage and reactive oxygen species (ROS) formation as possible inducers of MMP-13, and we analyzed MMP-13-dependent damage. We show that the small ROS, H₂O₂, is increased in basal keratinocytes following treatment with paclitaxel. Cytoplasmic H₂O₂ appears to derive, at least in part, from mitochondrial damage, leading to upregulation of MMP-13, which in turn underlies increased epidermal extracellular matrix degradation. Intriguingly, also axonal mitochondria show signs of damage, such as fusion/fission defects and vacuolation, but axons do not show increased levels of H₂O₂. Since MMP-13 inhibition prevents axon degeneration but does not prevent mitochondrial vacuolation, we suggest that vacuolization occurs independently of axonal damage. Finally, we show that MMP-13 dysregulation also underlies paclitaxel-induced peripheral neuropathy in mammals, indicating that epidermal mitochondrial H₂O₂ and its effectors could be targeted for therapeutic interventions.

Paclitaxel-induced peripheral neuropathy is a condition of nerve degeneration induced by chemotherapy, which afflicts up to 70% of treated patients. Therapeutic interventions are unavailable due to an incomplete understanding of the underlying mechanisms. We previously discovered that major physiological changes in the skin underlie paclitaxel-induced peripheral neuropathy in zebrafish and rodents. The precise molecular mechanisms are only incompletely understood. For instance, paclitaxel induces the upregulation of MMP-13, which, when inhibited, prevents axon degeneration. To better understand other gene regulatory changes induced by paclitaxel, we induced peripheral neuropathy in mice following intraperitoneal injection either with vehicle or paclitaxel every other day four times total. Skin and dorsal root ganglion neurons were collected based on distinct behavioural responses categorised as “pain onset” (d4), “maximal pain” (d7), “beginning of pain resolution” (d11), and “recovery phase” (d23) for comparative longitudinal RNA sequencing. The generated datasets validate previous discoveries and reveal additional gene expression changes that warrant further validation with the goal to aid in the development of drugs that prevent or reverse paclitaxel-induced peripheral neuropathy.

Taxanes are chemotherapeutic agents that induce microtubule modifications in cancer cells, resulting in cell cycle modifications and tumor remission. Here we show that paclitaxel, a widely used taxane, also induces microtubule modifications in healthy epidermal keratinocytes leading to chemotherapy-induced peripheral neuropathy (CIPN). Paclitaxel activates the cell cycle regulator, Kinesin-5 (Eg5), which promotes microtubule detyrosination and fasciculation (dfMT). Eg5 loss protects neurons from paclitaxel neurotoxicity, whereas keratinocyte-specific overexpression promotes axon degeneration. In vivo imaging and 3D reconstructions of dfMTs and nuclei, combined with mechanotransduction studies further show that dfMTs constrict keratinocyte nuclei, leading to nuclear Nox-dependent reactive oxygen species (X-ROS) formation upstream of MMP-13 and cutaneous sensory axon degeneration. This new insight facilitates our understanding of chemotherapy side effects and highlights the need for targeted therapies.

Paclitaxel is a chemotherapeutic agent that causes peripheral neuropathy (PIPN) as a side effect of cancer treatment. Severely affected patients need to terminate chemotherapy, diminishing their chance of survival. The underlying causes of PIPN are unclear, but epidermal, unmyelinated axons have been shown to be the first to degenerate. We previously utilized a zebrafish in vivo model to show that the epidermal matrix-metalloproteinase 13 (MMP-13) induces degeneration of unmyelinated axons, whereas pharmacological inhibition of MMP-13 prevented axon degeneration. The precise functions by which MMP-13 is regulated and affects axons, however, remained elusive. In this study, we assessed mitochondrial damage and reactive oxygen species (ROS) formation as possible inducers of MMP-13, and we analyzed MMP-13-dependent damage. We show that the small ROS, H ₂ O ₂ , is increased in keratinocytes following treatment with paclitaxel. Epidermal mitochondrial damage appears to be a source of ROS leading to cytoplasmic H ₂ O ₂ elevation, upregulation of MMP-13, and increased matrix degradation. Intriguingly, although axonal mitochondria also show aberrant morphologies and are vacuolized, as shown in other neuropathies, these axonal mitochondria do not produce increased H ₂ O ₂ levels. We suggest that mitochondrial vacuolization occurs independently of axonal damage given that MMP-13 inhibition prevents axon degeneration, though vacuoles persist. We further show that MMP-13 dysregulation also underlies PIPN in rodent paclitaxel models, and that this function appears to be DRG neuron-extrinsic. These findings suggest that vacuolization is not a cause of paclitaxel-induced neuropathy, and that epidermal MMP-13 is a strong candidate for therapeutic interventions in cancer patients with neuropathy.