Mutation in Phex Gene Predisposes BALB/c-PhexHyp-Duk/Y Mice to Otitis Media

Abstract

Genetic susceptibility underlying otitis media (OM) remains to be understood. We show in this study that mutation in Phex gene predisposes the BALB/c-PhexHyp-Duk/Y (abbreviated Hyp-Duk/Y) mice to OM, which occurs at post-natal day 21 (P21) with an average penetrance of 73%. The OM was identified by effusion in the middle ear cavity and/or thickening of middle ear mucosae, and was characterised by increase in goblet cells, deformity of epithelial cilia and higher expression of proliferating cell nuclear antigen (PCNA) in cells of the middle ear mucosae. Moreover, the transcription levels of Tlr2, Tlr4, Nfkb1, Ccl4, Il1b and Tnfα in the ears of the Hyp-Duk/Y mice at P35 were significantly upregulated, compared to those of the controls. Higher expression levels of TLR2, TLR4, NF-κB and TNF-α in the middle ears were demonstrated by immunohistochemistry (IHC). However, the OM in the mice was not prevented by azithromycin administration from gestational day 18 to P35. Further study showed that, in contrast to the low mRNA levels of Phex gene in the ears of the Hyp-Duk/Y mice, the mRNA level of Fgf23 was significantly elevated at P9, P14, P21 and P35. Meanwhile, mRNA levels of EP2 (PGE2 receptor), which expressed in the middle ear epithelia as demonstrated by IHC, were already increased at P14 even before the occurrence of OM, indicating that PGE2, an inflammatory mediator, is involved in the OM development in the mutants. Taking together, Phex mutation primarily up-regulates gene expression levels in FGF23 mediated pathways in the middle ears, resulting in cell proliferation and defence impairment at the mucosae and subsequently bacterial infection. The Hyp-Duk/Y mouse is a new genetic mouse model of OM.

Ectopic Mineralization and Conductive Hearing Loss in Enpp1asj Mutant Mice, a New Model for Otitis Media and Tympanosclerosis

“…PHEX mutations are associated with X-linked hypophosphatemic rickets in human patients, with hearing loss as one of the symptoms [32–34]. Mice with Phex mutations exhibit hypophospatemia-related abnormalities and hearing impairment [35], which recently was shown to be associated with middle ear effusion and ciliary defects [8]. Rpl38 (ribosomal protein L38) is not known to be directly involved in phosphate regulation; however, elevated organic phosphate levels in Rpl38 Ts mutant mice [4] suggest a potential but unknown function of Rpl38 in phosphate homeostasis.…”

“…Heritability studies have shown that genetic factors can play an important role in otitis media susceptibility, but few contributing genes have been identified in human populations [1]. In contrast to human studies, a growing number of mouse mutations have been identified that manifest a high incidence of otitis media, including Eya4 , Tlr4 , p73 , MyD88 , Fas , E2f4 , Plg , Fbxo11 , Evi1 [1,2], Sh3pxd2b [3], Rpl38 [4], Isl1 [5], Chd7 [6], Lmna1 [7], Phex [8], Oxgr1 [9], Tgif1 [10], and Mcph1 [11]. The wide diversity of these genes and their mutant pathologies, including craniofacial abnormalities with Eustachian tube malformations and innate immune response defects, underscores the complex nature of otitis media.…”

Understanding the aetiology and resolution of chronic otitis media from animal and human studies

“…Mcph1 mutant mice are also suspected to have cilia defects, as well as the null mutant at Porcn (porcupine O-acyltransferase), a gene involved in the processing of proteins by the endoplasmic reticulum ( Chen et al, 2013 ; Biechele et al, 2013 ). In Lmna , Chd7 , Eya4 and Phex (phosphate regulating endopeptidase homolog, X-linked) mutants, inflammation causes the loss of ciliated cells in the bulla epithelium, whereas perturbation of phosphorylation in the fibroblast growth factor (FGF)23/prostaglandin (PG)E2 pathways in the Phex hypomorph might also reduce the aqueous periciliary layer and impair the clearance of overlying mucus ( Han et al, 2012 ; Zhang et al, 2012 ; Tian et al, 2012 ; Depreux et al, 2008 ).…”

FGF23 and its role in X-linked hypophosphatemia-related morbidity

“…PHEX mutations can lead to retention of PHEX protein in the endoplasmic reticulum [60] and/or expression of truncated PHEX proteins which may retain some functions of the full-length protein [61, 62]. Identifying direct functions of PHEX that may be retained in truncated proteins would therefore contribute to our understanding of the aetiology of XLH.…”