Macrophage Depletion in CCR2-/- Mice Delays Bacterial Clearance and Enhances Neutrophil Infiltration in an Acute Otitis Media Model.

BACKGROUND: Otitis media (OM) is a common and potentially serious disease of childhood. Although OM is multifactorial on origin, bacterial infection is a unifying component. Many studies have established a critical role for innate immunity in bacterial clearance and OM resolution. A key component of innate immunity is the recruitment of immune and inflammatory cells, including macrophages. METHODS: To explore the role of macrophages in OM, we evaluated the expression of genes related to macrophage function during a complete episode of acute OM in the mouse caused by middle ear (ME) inoculation with Haemophilus influenzae. We also combined CCR2 deficiency with chlodronate liposome toxicity to deplete macrophages during OM. RESULTS: Macrophage genes were robustly regulated during OM. Moreover, macrophage depletion enhanced and prolonged the infiltration of neutrophils into the infected ME and increased the persistence of bacterial infection. CONCLUSIONS: The results illustrate the critical role played by macrophages in OM resolution.

Molecular Screening Strategy to Identify a Non-invasive Delivery Mechanism for the Treatment of Middle Ear Disorders.

Middle ear ailments include a broad range of pathological conditions. Otitis media is the leading middle ear disease of childhood, which incurs significant health care resources in developed countries and, in developing countries, causes significant mortality and morbidity. Recurrent and chronic infections of the middle ear lead to the prolonged presence of inflammatory factors and cellular infiltrates resulting in temporary hearing loss. However, long-term alteration of the middle ear space can pose the risk of permanent damage to the delicate ear structures and cause tissue remodeling. While the etiopathogenesis of middle ear diseases is multifactorial, targeting the biological mechanisms and molecular networks that drive disease development is critical. Yet, a pivotal step in realizing the potential of molecular therapies is the development of methods for local drug delivery, since systemic application risks side effects. Utilizing bacteriophage display in the rat, we discovered rare peptides that are able to transit the intact tympanic membrane from the external canal to the middle ear cavity by an active process. An in vitro assay demonstrated that transport occurs across the tympanic membranes of humans and that the peptides cross the membrane independent of phage. Transport of phage, which is ~900 nm in length, suggests that these peptides could non-invasively deliver drug packages or gene therapy vectors into the middle ear.

An RNA interference-based screen of transcription factor genes identifies pathways necessary for sensory regeneration in the avian inner ear.

Sensory hair cells of the inner ear are the mechanoelectric transducers of sound and head motion. In mammals, damage to sensory hair cells leads to hearing or balance deficits. Nonmammalian vertebrates such as birds can regenerate hair cells after injury. In a previous study, we characterized transcription factor gene expression during chicken hair cell regeneration. In those studies, a laser microbeam or ototoxic antibiotics were used to damage the sensory epithelia (SE). The current study focused on 27 genes that were upregulated in regenerating SEs compared to untreated SEs in the previous study. Those genes were knocked down by siRNA to determine their requirement for supporting cell proliferation and to measure resulting changes in the larger network of gene expression. We identified 11 genes necessary for proliferation and also identified novel interactive relationships between many of them. Defined components of the WNT, PAX, and AP1 pathways were shown to be required for supporting cell proliferation. These pathways intersect on WNT4, which is also necessary for proliferation. Among the required genes, the CCAAT enhancer binding protein, CEBPG, acts downstream of Jun Kinase and JUND in the AP1 pathway. The WNT coreceptor LRP5 acts downstream of CEBPG, as does the transcription factor BTAF1. Both of these genes are also necessary for supporting cell proliferation. This is the first large-scale screen of its type and suggests an important intersection between the AP1 pathway, the PAX pathway, and WNT signaling in the regulation of supporting cell proliferation during inner ear hair cell regeneration.