No abstract

Motor axons in peripheral nerves have the capacity to regenerate after injury. However, full functional motor recovery rarely occurs clinically, and this depends on the nature and location of the injury. Recent preclinical findings suggest that there may be a time after nerve injury where, while regrowth to the muscle successfully occurs, there is nevertheless a failure to reestablish motor function, suggesting a possible critical period for synapse reformation. We have now examined the temporal and anatomical determinants for the reestablishment of motor function after prolonged neuromuscular junction (NMJ) denervation in rats and mice. Using both sciatic transection-resuture and multiple nerve crush models in rats and mice to produce prolonged delays in reinnervation, we show that regenerating fibers reach motor endplates and anatomically fully reform the NMJ even after extended periods of denervation. However, in spite of this remarkably successful anatomical regeneration, after 1 month of denervation there is a consistent failure to reestablish functional recovery, as assessed by behavioral and electrophygiological assays. We conclude that this represents a failure in reestablishment of synaptic function, and the possible mechanisms responsible are discussed, as are their clinical implications.

The newly identified thirteen-series Resolvins (RvTs) regulate phagocyte functions and accelerate resolution of infectious inflammation. Since SARS-CoV-2 elicits uncontrolled inflammation involving neutrophil extracellular traps (NETs), we tested whether stereochemically defined RvTs regulate NET formation. Using microfluidic devices capturing NETs in PMA-stimulated human whole blood, the RvTs, RvT1-RvT4, 2.5 nM each, potently reduced NETs. With IL-1b-stimulated human neutrophils, each RvT dose- and time-dependently decreased NETosis giving ~50% potencies at 10 nM, compared to the known NETosis inhibitors [10 mM]. In mouse Staphylococcus aureus infection, RvTs [50 ng each] limited neutrophil infiltration, bacterial titers and NETs. Additionally, each RvT enhanced NET uptake by human macrophages; RvT2 was the most potent of the four RvTs, giving >50% increase in NET-phagocytosis. As part of the intracellular signaling mechanism, RvT2 increased cAMP and phospho-AMPK within human macrophages, and RvT2-stimulated NET uptake was abolished by PKA and AMPK inhibition. RvT2 also stimulated NET clearance by mouse macrophages in vivo. Together, these results provide evidence for novel pro-resolving functions of RvTs, namely reducing NETosis and enhancing macrophage NET clearance via a cAMP-PKA-AMPK axis. Thus, RvTs open opportunities for regulating NET-mediated collateral tissue damage during infection as well as monitoring NETs.