UC San Diego

Paclitaxel is a common chemotherapeutic that often causes peripheral sensory neuropathy. Paclitaxel binds to and stabilizes microtubules, preventing their depolymerizaiton. Through unknown mechanisms, paclitaxel treatment causes bundling and altered organization axonal microtubules. In neurons, microtubules serve several roles, including facilitating axonal transport, and supporting axonal structure. In addition, peripheral nerves exist in a dynamic biomechanical environment and undergo significant strain during joint motion. Given the structural and functional roles of microtubules, this dissertation explores the effects of paclitaxel on nerve biomechanics and the ability of neurons to properly accommodate tensile loading. Chapter 2 explores experiments testing the hypothesis that axonal stretch magnifies disruptions in axonal transport in paclitaxel treated neurons. Results indicated that stretch alone minimally altered axonal transport, paclitaxel treatment alone significantly decreased transport velocity and frequency, and the combination of both paclitaxel and stretch together led to the largest disruptions in the transport of multiple different cargoes. Chapter 3 discusses whether microtubule bundling observed in paclitaxel treated axons leads to changes in the tissue level mechanical properties of whole nerves. In this experiment, the mechanical properties of nerves bathed in paclitaxel were compared to control nerves. Results showed that paclitaxel significantly stiffened nerves. Chapter 4 investigates the role of tau in inducing microtubule bundling following paclitaxel treatment. In this study, nervous tissue from tau knockout mice exhibited significantly less microtubule bundling than tissue from wild type mice, indicating that tau may play a role aberrant microtubule bundle formation following paclitaxel treatment. Collectively, results from chapters 2-4 show that paclitaxel treatment leads to microtubule bundling, partially due to tau, which leads to tissue level mechanical changes and an inability of neurons to successfully accommodate mechanical loading. Chapter 5 is unrelated to the effects of paclitaxel on neurons, but is related to the theme of determining the effects of cytoskeletal perturbations on neuronal function. This chapter discusses the effects of actin and myosin on osmotic regulation of SH-SY5Y neuroblastoma cells. Results indicated that actin and myosin disruption differentially altered the normal cellular response to osmotic loading, and neuronal cells were unable to restore normal morphology 30 minutes after osmotic insult