Growing evidence demonstrates circadian rhythms of
pain hypersensitivity in various chronic disorders. In
chemotherapy-induced
peripheral neuropathy (CIPN), agents such as
paclitaxel are known to elicit chronic
neuropathic pain in
cancer patients and seriously compromise their quality of life. Here, we report that the mechanical threshold for
allodynia in
paclitaxel-treated rats exhibited a robust circadian oscillation, reaching the nadir during the daytime (inactive phase). Using Per2::LucSV circadian reporter mice expressing a PER2::LUC fusion
protein, we isolated dorsal root ganglia (DRG), the primary sensory cell body for
peripheral nerve injury generated
hypersensitivity, and monitored ex vivo reporter bioluminescence. We observed strong circadian reporter rhythms in DRG neurons which are highly entrainable by external cues.
Paclitaxel treatment significantly lengthened DRG circadian periods, with little effects on the amplitude of oscillation. We further observed the core
protein BMAL1 and PER2 in DRG neurons and satellite cells. Using DRG and dorsal horn (DH; another key structure for CIPN
pain response) tissues from vehicle and
paclitaxel treated rats, we performed
RNA-sequencing and identified diurnal expression of core clock genes as well as clock-controlled genes in both sites. Interestingly, 20.1% and 30.4% of diurnal differentially expressed genes (DEGs) overlapped with
paclitaxel-induced DEGs in the DRG and the DH respectively. In contrast,
paclitaxel-induced DEGs displayed only a modest overlap between daytime and nighttime (Zeitgeber Time 8 and 20). Furthermore,
paclitaxel treatment induced de novo diurnal DEGs, suggesting reciprocal interaction of circadian rhythms and
chemotherapy. Our study therefore demonstrates a circadian oscillation of CIPN and its underlying transcriptomic landscape.