Spinal caspase-3 contributes to tibial fracture-associated postoperative allodynia via up-regulation of LRRTM1 expression in mice.

BACKGROUND

Bone fracture may subsequently cause chronic postoperative pain after orthopedic surgery, but mechanisms remain elusive. The necessity of caspase-3 in neuroinflammation and synaptic plasticity has been summarized in pathological pain. Leucine-rich repeat transmembrane protein 1 (LRRTM1) mediates synaptic delivery of AMPA receptor and synaptogenesis. This study evaluated whether caspase-3 and LRRTM1 are required for fracture-associated postoperative allodynia.

METHODS

A model of tibial fracture with intramedullary pinning in mice was established for the induction of postoperative pain, verified by measurement of mechanical paw withdrawal threshold and cold scores response to acetone. The caspase-3 specific inhibitor, recombinant caspase-3 and LRRTM1 knockdown by shRNA were utilized for the investigation of pathogenesis as well as the prevention of allodynia. Also, the activity of caspase-3 and the expression of LRRTM1 in the spinal dorsal horn were examined by Western blot and RT-qPCR.

RESULTS

This study reported that tibial fracture and orthopedic surgery produced long-lasting mechanical allodynia and cold allodynia, along with the up-modulation of spinal caspase-3 activity (but not caspase-3 expression) and LRRTM1 expression. Spinal caspase-3 inhibition prevented fracture-associated behavioral allodynia in a dose-dependent manner. Caspase-3 inhibitor also reduced the spinal increased LRRTM1 level after tibial fracture with pinning. Spinal LRRTM1 deficiency impaired fracture-caused postoperative pain. Intrathecal recombinant caspase-3 facilitated acute pain hypersensitivity and spinal LRRTM1 expression in naïve mice, reversing by LRRTM1 knockdown.

CONCLUSION

Our current results demonstrate the spinal up-regulation of LRRTM1 by caspase-3 activation in the development of tibial fracture-associated postoperative pain in mice.