Increased levels of COX‐2 in oral lichen planus supports an autoimmune cause of the disease

BACKGROUND: Oral lichen planus (OLP) is a chronic inflammatory disease for which the pathogenesis is not fully understood. OLP has autoimmune features and auto immunity has been suggested as a potential cause, whereas WHO has classified OLP as a premalignant condition. Association between chronic inflammation and cancer is known and chronic inflammation is one of the characteristics of OLP. A protein connected to inflammation and suggested to be involved in cancer development is cyclooxygenase-2 (COX-2) which can be inhibited by microRNA-26b (miR-26b). OBJECTIVE: The aim was to map levels of COX-2 and miR-26b in OLP lesions to see if there was any correlation between expression of COX-2 and its regulator miR-26b in OLP. METHODS: In biopsies from 20 OLP patients and 20 age and gender-matched controls laser- micro dissection of epithelium was performed. Quantitative RT-PCR, immunohistochemistry and Western blot were used in the analysis. RESULTS: Levels of COX-2 mRNA were significantly higher while levels of miR-26b were significantly lower in OLP lesions compared to controls. Using immunohistochemistry normal oral mucosa samples did not show any expression of COX-2 while OLP samples expressed the protein. No COX-2 protein was detectable with Western blot. CONCLUSION: Increased expression of COX-2 and decreased expression of miR-26b in OLP suggests both to play a role in OLP. COX-2 has been connected to both malignant development and autoimmunity but as malignant development of OLP is quite rare we suggest that the increased levels of COX-2 seen here support an autoimmune cause of the disease.