INSIGHT ON BORTEZOMIB INDUCED MICROTUBULES STABILITY AND MITOCHONDRIAL TRAFFICKING

Bortezomib (BTZ) is a proteasome inhibitor that represents the cornerstone in the treatment of multiple myeloma. Despite its efficacy, its clinical use is limited by severe painful peripheral neuropathy (BIPN) that occurs approximately in 50% of patients, impairing their life and representing a dose- imiting toxicity. There is increasing evidence that, instead of BTZ proteasome inhibition activity, BIPN may be due to BTZ off-targets. We focused our attention on tubulin and mitochondrial trafficking. In fact, on one hand, post-translational tubulin modification and Microtubule Associated Proteins MAPs) regulate microtubules (MTs) dynamics, fundamental for nervous system functions. On the other hand, axonal transport of mitochondria along the axons is essential for metabolic state and synaptic activity. Alterations of these two processes and modifications in their dynamics could lead to BIPN. In this work, we evaluated how these aspects take place in neurons isolated from adult mice dorsal root ganglia and treated with BTZ. MAP 2, delta2 tubulin a marker of hyperstable MTs) and tubulin acetylation were assessed through western blot analysis while the axonal mitochondrial trafficking as evaluated by time lapse confocal microscopy and kymograph analysis. We investigated the MTs stabilization by MAPs and by posttranslational modifications of tubulin and we found that BTZ treatment induced alterations of MAP2, delta2 tubulin and acetylated tubulin proteins quantity. After treatment for 24h with BTZ we also observed a loss of mitochondrial motility and dose-dependent reduction of transport speed, but no alterations were observed on the direction of the movement. Our results demonstrated that BTZ affect both mitochondrial trafficking and tubulin cytoskeleton in sensory neurons. Moreover, our data There is increasing evidence that, instead of BTZ proteasome inhibition activity, BIPN may be due to BTZ off-targets. We focused our attention on tubulin and mitochondrial trafficking. In fact, on one hand, post-translational tubulin modification and Microtubule Associated Proteins (MAPs) regulate microtubules (MTs) dynamics, fundamental for nervous system functions. On the other hand, axonal transport of mitochondria along the axons is essential for metabolic state and synaptic activity. Alterations of these two processes and modifications in their dynamics could lead to BIPN. This work was supported by Fondazione Cariplo, Grant # 2019-1482