Synergistic Inhibition of ERK1/2 and JNK, Not p38, Phosphorylation Ameliorates Neuronal Damages After Traumatic Brain Injury

Mitogen-activated protein (MAP) kinases are serine/threonine protein kinases that play a critical role in signal transduction and are activated by phosphorylation in response to a variety of pathophysiology stimuli. While MAP kinase signaling has a significant role in the pathophysiology of several neurodegenerative diseases, the precise function of activation of MAP kinase in traumatic brain injury (TBI) is unknown. Therefore, it is important to study the role of MAP kinase signaling in TBI-associated neurological ailments. In this study, using an in vitro stretch injury model in rat embryo neuronal cultures and the in vivo fluid percussion injury (FPI) model in rats, we explored the role of MAP kinase signaling in the mechanisms of cell death in TBI. Our study demonstrated that the stretch injury in vitro and FPI in vivo upregulated the phosphorylation of MAP kinase proteins ERK1/2 and JNK, but not p38. Using ERK1/2 inhibitor U0126, JNK inhibitor SP600125, and p38 inhibitor SB203580, we validated the role of MAP kinase proteins in the activation of NF-kB and caspase-3. By immunofluorescence and western blotting, further, we demonstrated the role of ERK1/2 and JNK phosphorylation in neurodegeneration by analyzing cell death proteins annexin V and Poly-ADP-Ribose-Polymerase p85. Interestingly, combined use of ERK1/2 and JNK inhibitors further attenuated the cell death in stretch-injured neurons. In conclusion, this study could establish the significance of MAP kinase signaling in the pathophysiology of TBI and may have significant implications for developing therapeutic strategies using ERK1/2 and JNK inhibitors for TBI-associated neurological complications.