Targeting ERK1/2-calpain 1-NF-κB signal transduction in secondary tissue damage and astrogliosis after spinal cord injury

Neuronal damage, glial inflammation, and astrogliosis/astroglial scar formation are major secondary injury mechanisms that are significant contributors to functional deficits after spinal cord injury (SCI). The objectives of the study were to evaluate the distinct roles of ERK2 vs. ERK1/2 and ERK1/2-calpain 1–NF-κB signal transduction in the tissue damage and astrogliosis/astroglial scar formation following SCI in rats. RNAi approaches, pharmacological intervention (U0126), Western blot analysis, immunofluorescence analysis, and histological assessment were used to target ERK1/2-calpain 1-NF-κB signal transduction pathway for neuroprotection. Histological staining analysis demonstrated that selectively reducing pERK2 using ERK2 siRNA, but not inhibition of pERK1/2 with U0126, significantly reduced lesion volume and improved total tissue sparing, white matter sparing, and gray matter sparing in spinal cord two weeks after contusive SCI. An ERK1/2-calpain 1-NF-κB signal transduction pathway was involved in the astroglial scar formation after SCI. Blockade of ERK1/2 by U0126 decreased calpain 1 expression 4 h following SCI. Selective calpain 1 reduction by lentiviral shRNA attenuated astroglial NF-κB activity and astroglial scar formation after SCI in rats. Taken together, these results demonstrate the involvement of individual ERK2 and calpain 1 signaling pathways in tissue damage and astrogliosis/astroglial scar formation in animal models of SCI. Therefore, targeting individual ERK and its downstream signal transduction of calpain 1-NF-κB may provide greater potential as novel therapeutics for minimizing tissue damage and astroglial scar formation following SCI.