Regeneration of the peripheral motor nerves and myelin sheath following hyperglycemic induction and recovery

Abstract

The peripheral nervous system is made up of motor and sensory neurons that allow the brain to sense and respond to the environment. Diabetes mellitus is a chronic metabolic condition that often results in damage to these nerves. Patients with diabetic peripheral neuropathy (DPN) present with numbness, paresthesia, and/or muscle weakness. Because the pathophysiology underlying DPN is not yet clear, treatment is limited to pain management. In the Clark lab, we have shown that incubation of larval zebrafish for five days in 60 mM glucose concentration negatively affects axon length and myelin sheath coverage. Due to the known regenerative capabilities of zebrafish, we hypothesize that after removing the larvae from hyperglycemic conditions, peripheral motor axons and myelin sheath will begin to regenerate. Tg(NBT:DsRed) and Tg(mbp:caaxEGFP) larval zebrafish were incubated in 120 mM glucose solution (treatment), or egg water (control), for seven days beginning five days postfertilization. Incubation time was increased from 5 to 7 days to allow for a more robust phenotype while maintaining survivability. To allow for regeneration, zebrafish were placed in normal egg water for an additional ten days, and control fish were kept in egg water for an equal amount of time. Motor axon length of zebrafish following 7-day incubation glucose solution was significantly shorter than controls of the same age (12dpf), p<0.0001****. Following the 10-day recovery period, there was no significant difference between the 22dpf control group and the 22dpf treatment group, p = 0.1489, suggesting that the motor axons regenerated back to original length. Similarly, the length of the myelin sheath at 12dpf was significantly shorter in the treatment group compared to controls, p<0.0001****. Following recovery, there was no significant difference in myelin sheath length between treatment and control groups at 22dpf, p = 0.8801. This suggests that both the motor axons and myelin sheath were able to regenerate to lengths similar to controls following a 10-day recovery period. Future experiments conducting drug screens on compounds known to impact regeneration may elucidate signaling pathways in the regeneration process. This discovery would guide further research into potential therapeutics for DPN, and may even be manipulated for allow for regeneration in the central nervous system.