Espressione e localizzazione del gene TAS2R38 in relazione agli aspetti clinici

Taste plays a crucial role in life and in survival of all living organisms. Taste perception means, from a physiological point of view, having receptors on the tongue and at the level of the palate, capable of binding to specific molecules and sending the message to the central nervous system. Among bitter taste receptor genes, particular attention has been given to the TAS2R38 gene. The genetic variability of TAS2R38 gene family, that encodes for bitter taste receptors, includes two haplotypes: PAV, that determines the synthesis of functional TAS2R38 receptors, and AVI, the non-functional variant. The expression of bitter taste receptors was found not only in the oral cavity but also in the respiratory tract. In this extraoral tissue, bitter taste receptors play a role in physiological processes that are not related to taste perception. In particular, in a study conducted on epithelial sinonasal cells, TAS2R38 receptors were found in cilia of cells that, if stimulated by bacterial agonists, produce nitric oxide (NO) in a TAS2R38-dependant manner. NO is believed to be important for preventing airway infections by damaging bacterial structures and increasing ciliary beat frequency. It was demonstrated that individuals with one or both non-functional alleles of TAS2R38 gene (haplotypes AVI) are more prone to bacterial infections than individuals with both functional alleles (haplotypes PAV). Finally, in the present thesis, I examined the possible implications of TAS2R38 gene expression in relationship to classic symptoms of COVID-19 (anosmia and ageusia). I analysed a study of Barham et al (2021) that showed a correlation between seriousness / duration of the symptoms and TAS2R38 phenotype. This study suggested that homozygous individuals AVI/AVI (called ‘‘nontasters’’) were more likely to be infected with COVID-19 than PAV/PAV or PAV/AVI individuals (called ‘‘supertasters’’ and ‘‘tasters’’, respectively).