Circadian disruption upon painful peripheral nerve injury in mice: Temporal effects on transcriptome in pain-regulating sensory tissues.

BACKGROUND

Neuropathic pain (NP) resulting from nerve damage shows diurnal fluctuation of intensity in patients, indicating circadian regulation. However, mechanisms linking NP and circadian regulation remain unclear. This study aimed to investigate time-dependent transcriptomic changes during a 24-hour period using a spared nerve injury (SNI) mouse model of NP.

METHODS

Pain-related behaviours were assessed at baseline and on days 7, 14, and 21 after SNI and control sham surgeries in C57BL/6JRJ mice. Spinal cord (SC) and periaqueductal gray (PAG) were collected 4-hourly over 24 h upon completion of behavioural testing.

RESULTS

RNA sequencing revealed 111 up- and 21 downregulated differentially expressed genes (DEGs) in the SC, and 35 up- and 33 downregulated DEGs in the PAG, across all six time points. The large majority of DEGs, 245 in the SC and 191 in the PAG, are involved in regulation of immunity. Among the top expressed genes, five DEGs in the SC, Atf3, Anxa10, Gpr151, Cxcl10, Sprr1a, and two DEGs in the PAG, Igf2 and Wnt6, were previously reported to regulate pain. Circadian analysis using CircaCompare identified 383 SC transcripts and 261 PAG transcripts with altered rhythmicity. Variability of gene expression during circadian day was increased in the SC and decreased in the PAG from the SNI mice.

CONCLUSION

These findings suggest that NP disrupts the circadian expression of rhythmic transcripts in the SC and PAG, potentially revealing new targets for chronotherapy of NP.