Laminar CD34+ membranous cells with mechanosensitive properties in subcutaneous fascia of the abdominal midline.

The study of soft, amorphous fascia has been constrained by definitional ambiguities regarding its fine structure, constituent and precise function. Here, a previously unrecognized CD34(+) membranous cell (CMC) population was identified by single-cell RNA sequencing, which displayed a distinct spatial distribution in UMAP coordinates in the subcutaneous fascia of rat abdominal midline. Constituting one of the predominant cell populations in the fascia, CMCs were further validated morphologically in situ and in vitro. They exhibited lamina shapes and distributed alternating with the collagen bundles. Equipped with mechanosensors (integrins, cadherins, PIEZOs), CMCs are intricately interwoven with matrix fibers, forming the tensile mechanical apparatuses in the fascia. Enriched with Cx43 + gap junctions, Cdh1 + adherens junctions, integrin β1 + focal adhesions, Tsg101 + extracellular vesicles, F-actin + cytoskeletons, and caveolae, CMCs with marginal process foaming possessed typical evidence of signal conversion and transduction. The extensive membrane architecture of CMCs easily enabled their interactions with nerves, blood vessels, immune cells and interstitial fluid, promoting the integrations among different systems. In addition, functioning as membranous boundaries and signaling hubs, sheeting-like CMCs incompletely encapsulated or separated some structures, creating unique microenvironments. Molecular function analyses aligned with the ultrastructural features, distinguishing CMCs from other flat cells like fibroblasts. This discovery highlights a previously overlooked cell subpopulation, advancing our understanding of the fascial biology.