Project 1: Determine how epidermal oxidative stress as a result of chemotherapy and diabetes leads to peripheral neuropathy and to develop treatments for these conditions

We previously established zebrafish in vivo models to study mechanisms of paclitaxel and glucose-induced somatosensory axon degeneration (Lisse et al., PNAS 2016, Waldron et al., Journal of Diabetic Complications 2018). These models revealed that the epidermis undergoes rapid phenotypic changes upon paclitaxel and glucose treatment prior to the onset of axon degeneration. We find increased levels of the reactive oxygen species, hydrogen peroxide (H2O2) in epidermal keratinocytes, which leads to a specific upregulation of the Matrix-metalloproteinase, MMP-13. Excitingly, administration of MMP-13 inhibitory compounds shows significant beneficial effects in the prevention and reversal of neuropathy in zebrafish and rodent models (patent pending). We argue that not axons but rather keratinocytes are the primary target of paclitaxel and glucose toxicity and that increased MMP-13-dependent matrix degradation in the epidermis induces the degeneration of unmyelinated nerve endings. We are collaborating with Nathan Staff, MD/PhD at Mayo Clinic to further explore the role of MMP-13 in human paclitaxel-treated patients. In addition, we are using genomic technologies in collaboration with Ben Harrison at the University of New England to identify global regulatory networks in skin and DRG neurons that are altered. We are currently also conducting pre-clinical studies in collaboration with Dr. Jacqueline Sagen at the Miller School of Medicine to translate our findings into therapies.

Project 2: Microbial contributions to appendage regeneration

This project is concerned with an intriguing finding in our lab whereby microbial populations influence appendage regeneration. We are characterizing microbial populations following amputation using microbiome studies followed by their manipulation to address their function in regeneration. We are also interested in the communication between nerve signals and amputation wounds through microbial populations present at the wound and possibly in the gut.

Project 3: Identify H2O2-dependent wound repair mechanisms

H2O2 has been well studied for its role in wound repair and appendage regeneration whereby it promotes the migration of inflammatory cells. We are specifically interested in its role during wound re-epithelialization. We are using in vivo time-lapse imaging to study H2O2-dependent keratinocyte migration mechanisms after injury.

Project 4: Define molecular mechanisms that promote cutaneous sensory axon regeneration following injury

Injury-induced sensory axon regeneration in the epidermis is conserved among vertebrates but despite this conservation, we do not understand the basic mechanisms underlying this process. This is however of interest considering that axon regeneration is critical to restore skin function after injury and to prevent wound healing complications, such as present in patients with diabetic peripheral neuropathy. We previously showed that H2O2 released by wound keratinocytes stimulates axon regeneration (Rieger & Sagasti, PLoS Biology 2011). We are currently analyzing downstream factors that are targeted by H2O2 for oxidation in this process, and we are defining the specific mechanisms by which these molecules promote axon regeneration. We have found a particular role for the epidermis in this process.