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DISEASE ASSOCIATED CD46 SPLICING VARIANTS AND PATHOLOGIC BONE REMODELLING IN OTOSCLEROSIS
Tamás Karosi1, Anita Szalmás2, József Kónya2, Péter Csomor2, László Z. Szabó3, István Sziklai1
1University of Debrecen, Department of Otolaryngology Head and Neck Surgery, Debrecen, Hungary/2University of Debrecen, Department of Medical Microbiology, Debrecen, Hungary/3National Health Center, Department of Otorhinolaryngology, Budapest, Hungary.
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OBJECTIVES: Otosclerosis is a complex bone remodeling disorder of the human otic capsule which is associated to persisting measles virus infection. The general cellular receptor of measles virus is the CD46 molecule which has 14 known splicing isoforms. Otosclerotic stapes footplates have been supposed to show unique CD46 expression pattern which could be the basis of the pathogenesis of otosclerosis and decreased humoral immune response against measles virus.■
METHODS: After histologic pretreatment, nucleic acid was extracted from ankylotic stapes footplates (N=101) removed during stapedectomies. Consecutive histologic-, CD46 specific immunohistologic analysis and multiple PCR amplifications were performed. Measles virus was detected by seminested RT-PCR. Splicing variants of CD46 molecule were identified by nested RT-PCR and digestion by restriction endonucleases and finally determined by mass sequencing of DNA.■
RESULTS: Measles virus RNA was detectable only in histologically otosclerotic stapes footplates (N=71). Virus negative stapes specimens (N=29) represented degenerative disorders with variable histopathology. Otosclerosis was featured by increased numbers of osteoclasts showing strong CD46 immunoreaction in contrast to non-otosclerotic stapes fixation. Normal and pseudootosclerotic stapes footplates (N=30) showed consistent expression of “c”, “d”, “e”, “f” and “l” CD46 isoforms. However, four novel CD46 splicing variants were additionally detected in case of otosclerosis: os1, os2, os3 and os4. All of these isoforms were translated from the 1.-5. and 14. exons, furthermore os1 was additionally translated from the 6., 11. and 12. exons; os2 from a shorter 6. and 11. exons and the normal 12. exon; os3 from the 6. and a shorter 12. exons, while variant os4 was not translated from the variable region.■
CONCLUSIONS: Newly described CD46 isoforms have shorter or missing cytoplasmic domains with pathologic or uncommon signal transduction; however virus binding ability remains equal and invariable. Disturbed phosphorilation signals may be responsible for the smooth virus replication. A special expression pattern and altered functions of CD46 could explain the organ specific and virus associated pathogenesis of otosclerosis.