TM perforations are an extremely common pathology of which patients present with conductive hearing loss. Perforations, in general, spontaneously close within 2-3 weeks. Though commonly repaired without intervention, 750,000 surgical procedures are performed each year to close chronic perforations, in which the wound remains open for unknown reasons. Despite this high prevalence, the cause of this condition is unclear. A further investigation into the basic biology of the TM is compulsory to understanding the wound healing of the TM and what is dysregulated in chronic perforations. Wounding in skin, a tissue comparable to the TM, has been heavily studied, but the same sort of in- depth investigation into the biology of TM wounding is required. From recent work of my mentor and colleagues, using 5-ethynyl-2?-deoxyuridine (EdU) labeling, the TM displays a characteristic proliferation pattern, focused predominantly at the handle of the malleus, the first ossicle embedded into the TM, and around the annulus, the outer ring of the TM. From these regions, keratinocytes (KCs) then migrate down and radially outward, but what proliferation looks like in response to injury is unknown. Preliminary single-cell RNA sequencing studies have identified cell populations in the homeostatic TM via transcriptional profiles, revealing populations with characteristics distinct from those seen in other epithelial tissues like skin. This includes a basal KC population with inherent migratory properties. However, how these identified populations of cells coordinate renewal, differentiation, and migration is undefined, but it is critical to understand this to comprehend how the TM maintains homeostasis and repairs itself under the circumstance of injury. Work of the lab has shown that upon wounding, the TM is able to recognize injury and generate a robust proliferative response within 24 hours. Moreover, this proliferative response is not limited to the keratinocyte layer, but also involves the mesenchymal and mucosal layers. Given these Preliminary Studies, my central hypothesis is that healing of the TM involves the coordinated activities of subtypes of cells that are not present under homeostatic conditions. In this proposal, my first Aim is to define the cellular dynamics of healing in the TM following perforation. For my second Aim, I will look to understand the role of Bone Morphogenic Protein (BMP) signaling in maintaining the proliferation of TM keratinocytes under homeostasis and in response to injury. In addition to my mentor?s and co-mentor?s expertise with TM studies, collaborations with Julie Sneddon, Max Krummel, and Sarah Knox support the feasibility of this work. The studies proposed here will aim to define the characteristic cell populations present in the injured TM and define their transcriptional profiles. This will provide crucial insight into how the TM responds to injury and heals. Moreover, potential mechanisms for wound healing will be investigated to inform future therapies for chronic perforation of TMs.
Although both surgical and medical interventions for disorders of the tympanic membrane are used, there is great room for therapeutic improvement since our understanding of TM biology and cellular physiology, especially in regard to how homeostasis is restored after perforation, is severely lacking. We have now identified resident stem cell populations on the TM and characterized their migration patterns, but we need to understand how these progenitor cell populations are maintained and the migratory patterns altered in injury and subsequent healing in order to improve our surgical and medical approaches for restoring the ear after injury. The studies proposed here aim to understand the physiological signals that regulate the maintenance of the proliferative stem cell population of keratinocytes on the TM in order to inform potential non-surgical treatments for chronic perforation.
