Evaluation of YAP signaling in a rat tympanic membrane under a continuous negative pressure load and in human middle ear cholesteatoma

Osteopontin-driven partial epithelial-mesenchymal transition governs the development of middle ear cholesteatoma

Cholesteatoma is a common disease of the middle ear. Currently, surgical removal is the only treatment option and patients face a high risk of relapse. The molecular basis of cholesteatoma remains largely unknown. Here, we show that Osteopontin (OPN), a predominantly secreted protein, plays a crucial role in the development of middle ear cholesteatoma. Global transcriptome analysis revealed the loss of epithelial features and an enhanced immune response in human cholesteatoma tissues. Quantitative RT-PCR and immunohistochemical staining of middle ear cholesteatoma validated the reduced expression of epithelial markers, as well as the elevated expression of mesenchymal markers including Vimentin and Fibronectin, but not N-Cadherin, α-smooth muscle actin (α-SMA) or ferroptosis suppressor protein 1 (FSP1), indicating a partial epithelial-mesenchymal transition (EMT) state. Besides, the expression of OPN was significantly elevated in human cholesteatoma tissues. Treatment with OPN promoted cell proliferation, survival and migration and led to a partial EMT in immortalized human keratinocyte cells. Importantly, blockade of OPN signaling could remarkably improve the cholesteatoma-like symptoms in SD rats. Our mechanistic study demonstrated that the AKT-zinc finger E-box binding homeobox 2 (ZEB2) axis mediated the effects of OPN. Overall, these findings suggest that targeting the OPN signaling represents a promising strategy for the treatment of middle ear cholesteatoma.

Analysis of mRNA m6A modification and mRNA expression profiles in middle ear cholesteatoma

Introduction: Middle ear cholesteatoma is characterized by the hyperproliferation of keratinocytes. In recent decades, N6-methyladenosine (m6A) modification has been shown to play an essential role in the pathogenesis of many proliferative diseases. However, neither the m6A modification profile nor its potential role in the pathogenesis of middle ear cholesteatoma has currently been investigated. Therefore, this study aimed to explore m6A modification patterns in middle ear cholesteatoma. Materials and methods: An m6A mRNA epitranscriptomic microarray analysis was performed to analyze m6A modification patterns in middle ear cholesteatoma tissue (n = 5) and normal post-auricular skin samples (n = 5). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed to predict the potential biological functions and signaling pathways underlying the pathogenesis of middle ear cholesteatoma. Subsequently, m6A modification levels were verified by methylated RNA immunoprecipitation-qPCR (MeRIP-qPCR) in middle ear cholesteatoma tissue and normal skin samples, respectively. Results: A total of 6,865 distinctive m6A-modified mRNAs were identified, including 4,620 hypermethylated and 2,245 hypomethylated mRNAs, as well as 9,162 differentially expressed mRNAs, including 4,891 upregulated and 4,271 downregulated mRNAs, in the middle ear cholesteatoma group relative to the normal skin group. An association analysis between methylation and gene expression demonstrated that expression of 1,926 hypermethylated mRNAs was upregulated, while expression of 2,187 hypomethylated mRNAs and 38 hypermethylated mRNAs was downregulated. Moreover, GO analysis suggested that differentially methylated mRNAs might influence cellular processes and biological behaviors, such as cell differentiation, biosynthetic processes, regulation of molecular functions, and keratinization. KEGG pathway analysis demonstrated that the hypermethylated transcripts were involved in 26 pathways, including the Hippo signaling pathway, the p53 signaling pathway, and the inflammatory mediator regulation of transient receptor potential (TRP) channels, while the hypomethylated transcripts were involved in 13 pathways, including bacterial invasion of epithelial cells, steroid biosynthesis, and the Hippo signaling pathway. Conclusion: Our study presents m6A modification patterns in middle ear cholesteatoma, which may exert regulatory roles in middle ear cholesteatoma. The present study provides directions for mRNA m6A modification-based research on the epigenetic etiology and pathogenesis of middle ear cholesteatoma.

Inhibition of TGF-β signaling enables long-term proliferation of mouse primary epithelial stem/progenitor cells of the tympanic membrane and the middle ear mucosa

The surface of the middle ear is composed of the tympanic membrane (TM) and the middle ear mucosa (MEM). A number of diseases and conditions such as otitis media, middle ear cholesteatoma, and perforation of the TM have been reported to cause dysfunction of the middle ear, ultimately leading to high-frequency hearing loss. Despite its importance in repairing the damaged tissues, the stem/progenitor cells of the TM and the MEM epithelia remains largely uncharacterized due, in part, to the lack of an optimal methodology to expand and maintain stem/progenitor cells long-term. Here, we show that suppression of TGF-β signaling in a low Ca²⁺ condition enables long-term proliferation of p63-positive epithelial stem/progenitor cells of the TM and the MEM while avoiding their malignant transformation. Indeed, our data show that the expanded TM and MEM stem/progenitor cells respond to Ca²⁺ stimulation and differentiate into the mature epithelial cell lineages marked by cytokeratin (CK) 1/8/18 or Bpifa1, respectively. These results will allow us to expand epithelial stem/progenitor cells of the TM and MEM in quantity for large-scale analyses and will enhance the use of mouse models in developing stem cell-mediated therapeutic strategies for the treatment of middle ear diseases and conditions.

Keratinocyte Growth Factor Stimulates Growth of p75+ Neural Crest Lineage Cells During Middle Ear Cholesteatoma Formation in Mice

During development, cranial neural crest (NC) cells display a striking transition from collective to single-cell migration and undergo a mesenchymal-to-epithelial transformation to form a part of the middle ear epithelial cells (MEECs). While MEECs derived from NC are known to control homeostasis of the epithelium and repair from otitis media, paracrine action of keratinocyte growth factor (KGF) promotes the growth of MEECs and induces middle ear cholesteatoma (cholesteatoma). The animal model of cholesteatoma was previously established by transfecting a human KGF-expression vector. Herein, KGF-inducing cholesteatoma was studied in Wnt1-Cre/Floxed-enhanced green fluorescent protein (EGFP) mice that conditionally express EGFP in the NC lineages. The cytokeratin 14-positive NC lineage expanded into the middle ear and formed cholesteatoma. Moreover, the green fluorescent protein-positive NC lineages comprising the cholesteatoma tissue expressed p75, an NC marker, with high proliferative activity. Similarly, a large number of p75-positive cells were observed in human cholesteatoma tissues. Injections of the immunotoxin murine p75-saporin induced depletion of the p75-positive NC lineages, resulting in the reduction of cholesteatoma in vivo. The p75 knockout in the MEECs had low proliferative activity with or without KGF protein in vitro. Controlling p75 signaling may reduce the proliferation of NC lineages and may represent a new therapeutic target for cholesteatoma.

Analysis of the epidermal growth factor receptor/phosphoinositide‐dependent protein kinase‐1 axis in tumor of the external auditory canal in response to epidermal growth factor stimulation

Objectives

The epidermal growth factor receptor (EGFR) is related to the invasion and metastasis of external auditory canal (EAC) squamous cell carcinoma (SCC). The phosphoinositide‐dependent protein kinase‐1 (PDPK1) accelerates tumor cell growth through anti‐apoptotic signaling under the influence of downstream EGFR‐mediated signaling pathways. In this study, we investigated the EGFR/PDPK1 axis in the EAC under EGF stimulation.

Methods

We confirmed EGFR and PDPK1 expression in human EACSCC specimens immunohistochemically. We next transfected the EGF expression vector in the mouse EAC and then conducted a PDPK1 inhibitory experiment. Immunohistochemical analysis was performed in the mouse EAC, using anti‐EGF, anti‐EGFR, anti‐PDPK1, and anti‐Ki67 antibodies. Immunohistochemical analysis of cleaved caspase‐3 and terminal deoxy(d)‐UTP nick end labeling (TUNEL) detection assays were also performed for the assessment of apoptosis in the inhibitory experiment.

Results

Immunohistochemical analysis revealed overexpression and colocalization of EGFR and PDPK1 in human EACSCC specimens. The growth of a protuberant tumor was observed in the mouse EAC in which EGF expression vector was transfected, and EGF, EGFR, PDPK1, and Ki67 labeling indexes (LIs) were significantly increased. PDPK1 inhibition then induced normal epithelial appearance in the EAC. Moreover, EGF, EGFR, PDPK1, and Ki67 LIs were decreased, and cleaved caspase‐3 and TUNEL LIs were increased in the EAC.

Conclusion

We demonstrated the possibility that PDPK1 plays an important role in EACSCC.

Level of Evidence: NA.

L1CAM-ILK-YAP Mechanotransduction Drives Proliferative Activity of Epithelial Cells in Middle Ear Cholesteatoma

Middle-ear cholesteatoma (cholesteatoma) is a chronic otitis media with an enhanced proliferation of epithelial cells. Negative pressure in the middle ear is thought to be important for the etiology of cholesteatoma. However, the mechanism of cholesteatoma formation remains unclear. Integrin-linked protein kinase (ILK), an important modulator of actin cytoskeletal dynamics, interacts with extracellular matrix and results in the up-regulation of mechanotransduction effector Yes-associated protein (YAP). The L1 cell adhesion molecule (L1CAM) has recently been reported as an activator of the mechanotransduction effectors related to cell proliferation and migration. In this study, we demonstrated a stretch assay for middle-ear cultured cells and performed immunohistochemistry using antibodies against Ilk, Yap, and L1cam. The tympanic membrane was also analyzed within a new middle-ear negative-pressure animal model and human cholesteatoma tissues, using immunohistochemistry with antibodies against ILK, YAP, Ki-67, and L1CAM. The expression of cytoplasmic ILK and nuclear shift of YAP increased in the thickened epithelium of the tympanic membrane under a negative-pressure load and the cholesteatoma. The expression of L1CAM was detected in the stromal cells, which enhanced epithelial cell proliferation depending on ILK signaling events. In conclusion, we demonstrated the possibility that the stromal L1CAM and epithelial ILK-YAP signaling played an important role in epithelial growth under mechanotransduction in cholesteatoma formation.

Regulation of DNA methylation levels in the process of oral mucosal regeneration in a rat oral ulcer model

DNA methylation is an important epigenetic mechanism for cellular maintenance. However, the methylation pattern and the key molecule regulated epigenetically in oral mucosal regeneration is unclear. In this study, we generated a rat oral ulcer model and investigated the cell proliferative activities and DNA methylation patterns immunohistochemically. We also performed immunohistochemical analysis of a regulator of epithelial stem/progenitor cell differentiation in the rat model. We demonstrated immunohistochemistry using antibodies for the molecules as follows: Ki-67, a marker of cellular proliferation; 5-methylcytosine (5-mC), a marker of DNA methylation; 5-hydroxymethylcytosine (5-hmC), a marker of DNA demethylation; Dnmt1, a maintenance DNA methyltransferase; Dnmt3a and Dnmt3b, de novo DNA methyltransferases; and Wnt5a, a regulator of stem/progenitor cell differentiation. In this model, re-epithelialization was completed at Day 4 after ulceration. Regenerating mucosal hypertrophy reached a peak at Day 5 and appeared normal at Day 14. Ki-67-positive cells increased at Day 2 and returned to normal at Day 6 after ulceration. The ratio of the expression level of 5-mC to 5-hmC declined at Day 5 and returned to normal at Day 6. The expression level of Dnmt1 had not changed compared to the normal control at every time point. On the other hand, the expression levels of Dnmt3a and Dnmt3b had decreased significantly at Day 5 and returned to normal at Day 6. Moreover, Wnt5a-positive cells increased at Day 5. In conclusion, oral mucosal regeneration was strictly regulated by DNA methylation. Moreover, Wnt5a might play a critical role in oral mucosal regeneration.