Epithelial rests of Malassez form a mechanoresponsive network within the periodontal ligament space

The epithelial rests of Malassez (ERMs) constitute a three-dimensional epithelial meshwork that is embedded in the periodontal ligament (PDL) space and extends coronally to the junctional epithelium (JE). We hypothesized that ERMs are a candidate tissue for coordinating mechanosensitive responses in the PDL and JE. To test this hypothesis, we performed in finite element (FE) modeling to predict strain states in the PDL in response to normal and increased masticatory loading. These in silico data were combined with in vivo data from a mouse model of normal, hyper-loading and hypo-loading, and data from human tissues. Murine and human tissues were analyzed using histology, quantitative immunohistochemistry, single-cell RNA sequencing, and transmission electron microscopy. We found that the highest distortional strains in the PDL space correlated with load-enlargement of ERMs; conversely, ERMs were significantly smaller in cases of hypo-loading. Load-induced ERM enlargement was accompanied by a significant increase in expression of mechanosensitive proteins including Piezo1, β4 integrin, Plectin, and phosphorylated focal adhesion kinase (p-FAK). Human ERMs expressed the same mechanosensitive proteins. The ERM meshwork closest to the JE was enveloped by picrosirius red-stained collagen and oxytalan-stained fibers, both of which became disorganized under conditions of hyper-loading. Collectively, these data support a conclusion that the 3D ERM meshwork functions as a mechanosensory organ and may be a critical part of how periodontal tissues cope with functional changes in their mechanical environment.