Ethyl pyruvate does not require microglia for mediating neuroprotection after excitotoxic injury

Role of Toll-like receptor mediated signaling in traumatic brain injury

The mechanisms underlying secondary brain damage following traumatic brain injury (TBI) remain unclear. A great many studies have demonstrated that inflammatory cascades contribute to brain damage through the activation of immune/inflammatory responses, including the increased release of cytokines and chemokines, and the recruitment of leukocytes. The cells and tissues damaged by primary mechanical injury release a number of endogenous factors acting as damage-associated molecular patterns (DAMPs), which initiate and perpetuate noninfectious inflammatory responses through transduction signaling pathways. Toll-like receptors (TLRs) are a transmembrane receptor family that can recognize the specific DAMPs released from damaged cells and recruit a set of adaptors leading to the activation of downstream kinases and nuclear factors which regulate the expression of inflammatory genes. The activation of inflammatory responses mediated by TLR signaling is closely associated with brain tissue damage and neurological dysfunction following TBI. TLRs and their downstream protein kinases may be potential targets for the treatment of TBI. Modulation of TLR-mediated signaling may attenuate brain damage and improve TBI outcome. In this review, we briefly discuss the role of TLR-mediated signaling in TBI and the new treatments targeting TLR signaling. This article is part of the Special Issue entitled "Novel Treatments for Traumatic Brain Injury".

Ethyl pyruvate does not require microglia for mediating neuroprotection after excitotoxic injury

AIMS

Ethyl pyruvate (EP) mediates protective effects after neuronal injury. Besides a direct conservation of damaged neurons, the modulation of indigenous glial cells has been suggested as one important mechanism for EP-related neuroprotection. However, the specific contribution of glial cells is still unknown.

METHODS

Organotypic hippocampal slice cultures (OHSC) were excitotoxically lesioned by 50 μmol/L N-methyl-D-aspartate (NMDA, for 4 hours) or left untreated. In an additional OHSC subset, microglia was depleted using the bisphosphonate clodronate (100 μg/mL) before lesion. After removal of NMDA, EP containing culture medium (0.84 μmol/L, 8.4 μmol/L, 42 μmol/L, 84 μmol/L, 168 μmol/L) was added and incubated for 72 hours. OHSC were stained with propidium iodide to visualize degenerating neurons and isolectin IB₄ -FITC to identify microglia. Effects of EP at concentrations of 0.84, 8.4, and 84 μmol/L (0-48 hours) were analyzed in the astrocytic scratch wound assay.

RESULTS

EP significantly reduced neurodegeneration following induced excitotoxicity except for 168 μmol/L. For 84 μmol/L, a reduction in the microglia cells was observed. Microglia depletion did not affect neuronal survival after EP treatment. EP decelerated astrocytic wound closure at 48 hours after injury.

CONCLUSION

EP-mediated neuroprotection seems to be mediated by astrocytes and/or neurons.