TLR4 and ischemia: Similarly, the degeneration of retinal ganglion cells (RGCs) induced by ischemia and axotomy could be reduced in TLR4-knockout mice, and the phosphorylation levels of ERK-1/-2, c-Jun N-terminal kinase (JNK)-1/-1, and p38 were significantly decreased, with a low level of inducible NO synthase [48].