Understanding and Enhancing Repair of the Ear Drum

Tympanic membrane (ear drum) perforation (TMP) is a highly prevalent clinical problem, particularly common in young children. TMPs can result from physical trauma, pressure changes and, most commonly, from acute otitis media (AOM) a disease which almost all children will suffer from before the age of three (1). TMPs occur in 29.5% of children with AOM, with increased incidence associated with a previous history of OM (2). Although the majority of TMPs spontaneously heal within 2 weeks, approximately 6% do not heal and become chronic. In patients, TMPs can fail to spontaneously heal due to a range of factors. The hole may be too large to allow repair (3) or may form an epithelial ridge preventing further healing (4). Infectious factors, involved with AOM, also inhibit healing. Perforations involving the malleus also appear to be problematic (5). Chronic TMPs lead to complications including recurrent infections, middle ear cysts, otalgia, tinnitus and conductive hearing loss and have to be treated surgically (Type 1 Tympanoplasty or Myringoplasty).

This proposal aims to uncover the mechanisms involved in perforation healing in order to enhance healing in TMPs that do not heal naturally.

Due to the ability of the TM to spontaneously heal it has been suggested that the membrane must harbour its own stem/progenitor cell populations. Several groups have used the epidermal SC markers a6-integrin, B1 -integrin and cytokeratin 19 (CK19) to look for SCs in human and rat TMs. Positive staining for these markers was observed along the manubrium and around the annulus, at the edge of the membrane and after perforation a significant increase in expression of these markers was observed [6].

Wnt signalling is central to the control of stem/progenitor cell activity in a number of organs and may act as a niche factor to maintain stem cells in a self-renewing state. In addition, As part of a preliminary study to investigate whether Wnts may play a role in control of the stem/progenitor cells in the TM we looked at Wnt activity in the TM using the Axin2lacZ reporter mouse. Cells responding to Wnt activity were located in the annulus region of the TM and around the manubrium, matching the general pattern of other putative stem cell markers. Wnt signalling is therefore active in a discrete population of cells within the membrane.

The Tucker lab has developed a TMP protocol for studying ear drum perforations in mice in vivo and in explant culture and has a collection of transgenic models for studying the problem. The research is supported by a postdoc on an MRC funded project grant on ear drum repair. The Tucker lab has particular expertise in middle and external ear development and repair and have published a number of papers in this area. Prof Jiang is an ear surgeon and will provide his expertise in dealing with chronic TMPs in patients.

We aim to understand how the ear drum repairs itself during injury (the cells and signalling pathways involved) and how to enhance healing of problematic holes.



Homeostasis: what cells contribute to turnover in the ear drum?

Wnt responding cells (Axin2creERT2Tom label)



Lineage tracing repair. What cells respond to injury?

Neural crest, endoderm, mesoderm, ectoderm?

Cres: Wnt1cre, Mesp1cre, Sox17icre, Sox2ert2cre, K14cre, K14ert2cre, Axin2ert2cre



How does manipulating Wnt signalling impact on repair?

Overexpresssion GOF mice, Axin2 mice, loss of function Wntless mice

Cres: Pcagcre, K14ert2cre, Sox2ert2cre



How does manipulating signalling pathways impact repair in vitro: use of explant cultures?

Effect on vasculature Mesp1cretom mice

Pharmacological impact on repair