Background & Aims

Paclitaxel (PTX) is a chemotherapy drug used primarily for treating solid cancer. However, it causes peripheral sensory neuropathy, resulting in sensory abnormalities and pain in patients receiving this treatment (1). Mechanistically, PTX interrupts axonal transport, leading to an insufficient supply of ATP and increased oxidative stress (2). Mitochondria are critical organelles to supply the cellular energy demand and continuously undergo fusion and fission processes, which are regulated by GTPases, such as mitofusin (Mfn2) and dynamin-related protein 1 (Drp1), respectively. Studies demonstrate a correlation between the impairment of mitochondrial bioenergetics metabolism and the development of peripheral neuropathy (3). However, whether mitochondrial dynamics regulate neuropathic pain is unknown. We aimed to investigate the role of mitochondrial dynamics in paclitaxel-induced neuropathy.

Methods

Neuropathy was induced by PTX (4mg/kg, ip.). The mechanical nociceptive threshold was assessed by von Frey filaments and cold allodynia by the acetone test, in wild type (WT) and conditional transgenic mice (Mfn2f/f or Drp1f/fNav1.8Cre), which have removal of mitochondrial fission and fusion proteins (Mfn2 and Drp1) exclusively in the nociceptive neurons (Nav1.8 positive neurons). To assess motor function and coordination the rotarod test was performed. The protein levels of mitochondrial Mfn-2, OPA1, and, Drp-1 were detected by Western Blot in samples from the dorsal ganglion of the spinal cord (DRG). Mitochondrial morphology was evaluated by transmission electron microscopy. The behavioral, biochemical, and imaging assays were performed at 7, 28, and 42 days after PTX.

Results

PTX reduces the mechanical nociceptive threshold (hypernociception) in WT mice when compared to vehicle-treated mice, peak at day 28 (80±7,5*%), returning to baseline levels at day 42 after treatment. Moreover, PTX induces cold allodynia with peak at day 21 (93±42%). No alterations in motor coordination were observed during the study. The electron microscopy of the DRG demonstrates extensive vacuolization, abnormal shape, and reduction in the number and area of mitochondria on day 28 after PTX when compared to the vehicle group. Mild mitochondrial alterations were detected at days 7 and 42. Supporting the imaging data, the expression levels of the Drp1 (fission) in DRG increase at 28 after PTX (54±16*%). No changes were detected in Mfn2 (fusion) levels. The Mfn2 deletion in the nociceptor lowers the baseline threshold and potentiates PTX-induced neuropathy at day 28 (95±15*%). Conversely, the Drp1 removal from Nav1.8 positive neurons decreases PTX-induced hypernociception.

Conclusions

Using in vivo loss-of-function genetic tools and biochemical assays we show for the first time that excessive mitochondrial fission in the primary sensory neurons contributes to the development of chemotherapy-induced neuropathic pain. This study reveals Drp1 as a potential target for the neuropathic pain treatment.

References

(1) Ann Oncol. 1995 May;6(5):489-94. doi: 10.1093/oxfordjournals.annonc.a059220.
(2) Eur J Med Res. 2024 Jan 30;29(1):90. doi: 10.1186/s40001-024-01657-2.
(3) Exp Neurol. 2020 Feb;324:113121. doi: 10.1016/j.expneurol.2019.113121. Epub 2019 Nov 21.

Presenting Author

Natalia Gabriele Hosch

Poster Authors

Vanessa Zambelli PhD

PhD

Butantan Institute

Lead Author

Bárbara Martins Msc

Laboratory of Pain and Signaling, Butantan Institute, São Paulo, SP, Brazil.

Lead Author

Natalia Gabriele Hösch

Butantan Institute

Lead Author

Thiago Cunha

University of Sao Paulo

Lead Author

Marcos Chiaratti

Federal University of Sao Carlos

Lead Author

Julio Ferreira

University of Sao Paulo

Lead Author

Topics

  • Mechanisms: Biological-Molecular and Cell Biology