Altered Expression of Connexin43 in Rats Incisors with Dental Fluorosis

Excessive intake of fluoride (F^-) during tooth mineralization causes alterations of the cellular structure and function. Intercellular junction molecules, including, connexin 43 (Cx43), are important for dental development as control growth and cell differentiation. Furthermore, alkaline phosphatase (AP) contributes to mineralization process. In previous work we demonstrated that the F^- alters the expression of tight junctions molecules. Objective: To study the effect of chronic exposure to F^- upon the expression of Cx43 and other morphological and functional parameters in rat incisors. Methods: Male Wistar rats drank from 22 days of age, for 8 weeks, water with different concentrations of NaF: a) 0.3 mg/L (control), b) 10 mg/L (T₁) and c) 50 mg/L (T₂). The animal body weights were recorded at the beginning and at the end of treatment, and water intake was measured daily. The urine F^- was measured with an ion selective electrode. In digitized images of radiographs were analyzed morphometric parameters in mandible and diameter of incisors. In the pulp tissue of upper teeth AP activity was determined and Cx43 gene expression analyzed by RT-PCR. Results: There were no differences in daily water intake or body weight gain between groups. Urine F^- values were higher in T₁ and T₂ animals compared to control (p<0.01). None of mandibular growth parameters were affected by treatment. The diameter of the lower incisor in T₂ rats was lower compared to control (p=0.0047). The AP activity was higher in incisor pulp of treated rat respect to control (p<0.05). Cx43 gene expression increased by exposure to F^- in dose-dependent manner (p<0.05). Conclusion: fluorotic lesions in dental tissue are associated to alterations in AP activity and Cx43 expression, both molecules involved in dental tissue mineralization. It is possible that the observed changes are part of the molecular mechanism triggered by F^- during dental fluorosis development.