Endothelial progenitor cells populate the stromal stem niche of tympanum.

The tympanic membrane (TM) integrity is of utmost integrity for the sense of hearing. Therefore, the intrinsic potential of the TM to regenerate and repair deserves complete characterization. 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 with 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 so as a distinctive contributor during physiologial and pathological processes of the TM, such as is the cholesteatoma formation, at least as a biological support for processes of vasculogenesis. However, further characterization of the molecular pattern of the stromal stem niche of the TM is mandatory.