MUC5AC and chronic obstructive pulmonary disease: Mucin secretion is regulated by a variety of signaling pathways, and the mitogen-activated protein kinase (MAPK) phosphorylation cascade plays an important role in regulating the expression of MUC5AC. As a member of the MAPK family, p38 MAPK can play an important role in the acute exacerbation of COPD by activating key transcription factors and inducing increases in the release of various cytokines, as confirmed by our previous research (Xue et al., 2021).