MMP9 and Alzheimer disease: A recently investigated etiopathogenic link between epigenetics and the skin microbiome in AD involves miR-939, suggesting a crucial regulatory role through increased expression of matrix metalloproteinase (MMP)1, MMP3, MMP9, and Intercellular Adhesion Molecule 1 (ICAM1) in human keratinocytes, promoting S. aureus colonization and the subsequent exacerbation of S. aureus-induced AD-like skin inflammation [67].