MMP1 and temporomandibular joint disorder: ERK is a key factor in inducing many MMP subtypes (e.g., MMP-1, -3, -13), and the upregulation of MMPs is closely related to temporomandibular joint disorders, which leads to loss of collagen and glycosaminoglycans.98–100 In a rat model of sleep deprivation, the MAPK/ERK pathway was activated, leading to enhanced phosphorylation of ERK, upregulation of downstream MMP-1, MMP-3, and MMP-13 mRNA and protein levels, finally resulting in temporomandibular joint damage.