Endothelial progenitor cells populate the stromal stem niche of tympanum

The tympanic membrane (TM) integrity is of utmost importance for the sense of hearing. Therefore, the intrinsic potential of the TM to regenerate and repair deserves complete characterisation. Existing studies brought evidence on the epithelial stem niche of the TM. However, the stromal compartment was not evaluated for harbouring a distinctive stem, or progenitor, niche. We aimed doing this in transmission electron microscopy. We used TMs dissected out from 3 male Oryctolagus cuniculus rabbits. Evidence of stromal quiescent stem cells was gathered. Moreover, endothelial progenitor cells were found in the TM, being accurately identified by two specific ultrastructural markers of the endothelial lineage: the Weibel-Palade bodies and the stomatal diaphragms of the subplasmalemmal caveolae. The stromal stem niche of the TM appears to be a distinctive contributor during physiological and pathological processes of the TM, such as cholesteatoma formation, at least as a biological support for processes of vasculogenesis. However, further characterisation of the molecular pattern of the stromal stem niche of the TM is mandatory.