Background & Aims
Paclitaxel is an antineoplastic agent used to treat cancer, including breast and lung carcinomas. The main side effect induced by paclitaxel is painful neuropathy. The mechanisms involved in paclitaxel-induced axonal degeneration leading to neuropathy are poorly understood. Mitochondria are a dynamic and heterogeneous network that undergoes continuous fusion and fission process. This mitochondrial plasticity is regulated by GTPases, such as Mfn2 and Drp1, which are important for mitochondrial fusion and fission, respectively. Considering that neurons have a high metabolic demand and substantial mitochondria density, and that chemotherapy-induced neuropathy often occurs with mitochondrial dysfunction, we hypothesized that an imbalance between the levels of fusion and fission proteins contributes to the development of axonal degeneration. Therefore, we investigated the involvement of mitochondrial dynamics in the axonal degeneration of mice submitted to paclitaxel-induced neuropathy.
Methods
To induce neuropathy, mice were treated with paclitaxel (4g/kg, i.p.), on alternative days (1, 3, 5 and 7). Previous studies from our group showed that paclitaxel reduces mechanical threshold (i.e. mechanical hypersensitivity) on day 7, reaching chronicity 28 days after treatment. The nociceptive threshold returns to baseline values at day 42 (remission of neuropathic pain). Therefore, sciatic nerve collection was performed during these periods. Western blot assay was used to evaluate the levels of proteins related to mitochondrial fusion (Mfn2 and Opa1) and fission (Drp1), lipid peroxidation (4-hydroxy-2-nonenal – 4HNE), apoptosis (Calpain-2 and Calpastatin, a calpain inhibitor) and myelin integrity (Myelin Basic Protein – MBP). The sciatic nerve from mice treated with vehicle (cremophor, ethanol and 0.9% sterile saline, 1:1:18) was used as control. One-way ANOVA with post hoc testing by Tukey was performed. A value of P<0.05 was considered significant. n=4-7.
Results
Paclitaxel treatment increased the levels of Mfn2 on days 7 (23.6%) and 42 (28.5%), while the expression of Opa-1 was reduced on days 28 (30.57%) and 42 (52.73%). Drp1 levels were reduced on days 7 (34.86%) and 42 (38.33%). Considering that impaired mitochondrial dynamics is associated with oxidative stress and lipid peroxidation, we checked 4-HNE levels. Paclitaxel treatment upregulated 4-HNE levels in the chronic (41.85%) and remission (37.69%) phases. We next checked the calpain-2 levels, which is involved in mitochondrial dysfunction-induced axonal degeneration. Paclitaxel increased calpain-2 on day 7 (44.90%). We also analyzed the expression of calpastatin and the levels of this inhibitor were downregulated from day 7 to day 42 (7D: 360.99%; 28D: 68.2%; 42D: 34.32%). Lipid peroxidation and calpain-2 are associated with myelin degeneration. Therefore, the expression of MBP was evaluated. Paclitaxel reduced MBP levels from day 7 to day 42 (7D: 42.37%; 28D: 46.11%; 42D: 47.42%).
Conclusions
Together, these results indicate that paclitaxel induces an imbalance in the expression of fusion and fission proteins that may contribute to mitochondrial dysfunction leading to axonal degeneration. This study contributes to a better understanding of mitochondrial processes and open perspectives for new approaches to minimize the risks related to chemotherapy-induced axonal degeneration. Financial Support: FAPESP (2021/14831-8); FAPESP (2023/05626-7)
References
Kun-Long Zhang et al. Redox Biol 2022. Targeted up-regulation of Drp1 in dorsal horn attenuates neuropathic pain hypersensitivity by increasing mitochondrial fission. DOI: 10.1016/j.redox.2021.102216
Ilja Bobylev et al. Neurobiol Dis. 2015. Paclitaxel inhibits mRNA transport in axons. DOI: 10.1016/j.nbd.2015.07.006
Annalisa Canta et al. Toxics. 2015. Mitochondrial Dysfunction in Chemotherapy-Induced Peripheral Neuropathy (CIPN) DOI: 10.3390/toxics3020198
Erica L Gornstein et al. Exp Neurol. 2017. Neurotoxic mechanisms of paclitaxel are local to the distal axon and independent of transport defects DOI: 10.1016/j.expneurol.2016.11.015
Jack T Wang et al. J Cell Biol. 2012. Axon degeneration: molecular mechanisms of a self-destruction pathway DOI: 10.1083/jcb.201108111
Antonio Ayala et al. Oxid Med Cell Longev. 2014. Lipid peroxidation: production, metabolism, and signaling mechanisms of malondialdehyde and 4-hydroxy-2-nonenal DOI: 10.1155/2014/360438
Presenting Author
Natália Gabriele Hösch
Poster Authors
Topics
- Mechanisms: Biological-Molecular and Cell Biology