DADLE promotes motor function recovery by inhibiting cytosolic phospholipase A₂ mediated lysosomal membrane permeabilization after spinal cord injury

Background and purpose: Autophagy is a protective factor for controlling neuronal damage, while necroptosis promotes neuroinflammation after spinal cord injury (SCI). DADLE (D-Ala² , D-Leu⁵ ]-enkephalin) is a selective agonist for delta (δ) opioid receptor and has been identified as a promising drug for neuroprotection. The aim of this study was to investigate the mechanism/s by which DADLE causes locomotor recovery following SCI.

Experimental approach: Spinal cord contusion model was used and DADLE was given by i.p. (16 mg·kg^-1 ) in mice for following experiments. Motor function was assessed by footprint and Basso mouse scale (BMS) score analysis. Western blotting used to evaluate related protein expression. Immunofluorescence showed the protein expression in each cell and its distribution. Network pharmacology analysis was used to find the related signalling pathways.

Key results: DADLE promoted functional recovery after SCI. In SCI model of mice, DADLE significantly increased autophagic flux and inhibited necroptosis. Concurrently, DADLE restored autophagic flux by decreasing lysosomal membrane permeabilization (LMP). Additionally, chloroquine administration reversed the protective effect of DADLE to inhibit necroptosis. Further analysis showed that DADLE decreased phosphorylated cPLA₂ , overexpression of cPLA₂ partially reversed DADLE inhibitory effect on LMP and necroptosis, as well as the promotion autophagy. Finally, AMPK/SIRT1/p38 pathway regulating cPLA₂ is involved in the action DADLE on SCI and naltrindole inhibited DADLE action on δ receptor and on AMPK signalling pathway.

Conclusion and implication: DADLE causes its neuroprotective effects on SCI by promoting autophagic flux and inhibiting necroptosis by decreasing LMP via activating δ receptor/AMPK/SIRT1/p38/cPLA₂ pathway.