FL/FLT3 signaling enhances mechanical pain hypersensitivity through Interleukin-1 beta (IL-1β) in male mice

The timeline of the experimental design and the graphical abstract were created with BioRender.com • Cytokines are known to engage in complex interactions and regulate each other. • FL increases IL-1β in DRG and DSC within 4 h, but IL-1β does not affect FL levels. • FL modulates capsaicin-induced Ca 2+ influx via IL-1β/IL-1R signalling in DRG neurons. • IL-1R inhibition delays or abolishes FL-induced mechanical hypersensitivity in vivo. Fms-like tyrosine kinase 3 (FLT3) plays a critical role in chronic pain through its ligand FL, a cytokine that triggers mechanical pain hypersensitivity. However, the underlying molecular mechanisms remain unclear. Here, we investigate the potential interplay between FL and IL-1β a key cytokine in DRG neurons sensitization and mechanical hyperalgesia through both in vitro and in vivo approaches. ELISA assays reveal that intrathecal FL administration significantly increases IL-1β protein levels in both the DRG and dorsal spinal cord of mice, by four hours post-injection. Using video microscopy and [Ca 2+ ] 1 fluorescence imaging in primary DRG neuron cultures, we demonstrate that FL potentiation of TRPV1 receptor responses to capsaicin is partially mediated by IL-1β signalling, as evidenced by a significant reduction in this potentiation in the presence of the IL-1 receptor antagonist, IL-1Ra. Furthermore, FLT3-driven acute mechanical pain hypersensitivity in vivo is reduced both by prior administration of IL-1Ra and in IL-1 receptor knockout mice. Importantly, IL-1β-induced mechanical pain hypersensitivity remains independent of FLT3 signalling as shown in Flt3 knockout mice. Collectively our findings expand the understanding of neuro-immune interactions by demonstrating a potential functional link between FL/FLT3 and IL-1β/IL-1R signalling in nociceptive processing.