Crosstalk among COVID-19, STRA6, Retinol, and G protein-coupled receptor may explain the novel hypothesis of Retinol depletion and retinoid signaling disorder of COVID-19 pathogenesis

Abstract

More than two years have passed since the pandemic and despite all the efforts of researchers, the pathogenesis of COVID-19 has not yet been resolved. Multisystem involvement, neuroendocrine involvement, and pathophysiological changes caused by SARS-CoV-2 in peripheral organs have been shown in many studies. However, the molecular mechanism of these pathophysiological changes caused by COVID-19 has not been elucidated. The frequent mutations of SARS-CoV-2 and the change in the interaction of the virus with host cells have further complicated the pathogenetic mechanism in COVID-19. Unfortunately, the mechanism determined at the beginning of the pandemic and based on the single receptor tropism of ACE2 was insufficient to explain the pathogenesis of COVID-19. It is known that SARS-CoV-2 causes retinoid signaling defects and chemosensory receptor disorders and exerts its pathogenic effects through these mechanisms. Multisystem involvement and different clinical presentations in COVID-19 suggest that virus-host interaction develops through multiple receptors and signaling pathways. The previous mechanism described via ACE2, based on single-receptor tropism, was insufficient to elucidate the pathogenesis of COVID-19 due to the absence of ACE2 receptors in most of the affected organs. In addition, there is no satisfactory explanation for the mechanism by which ACE2-free organs are affected in COVID-19. In this regard, we think that ACE2 is not a true binding receptor for the SARS-CoV-2 spike protein. With our recent molecular docking studies, STRA6 and its GPCRs were identified as new binding receptors of the SARS-CoV-2 spike protein. These studies have brought a multi-receptor mechanism to the pathogenesis of COVID-19. The multi-receptor mechanism clearly illuminates the complex pathogenesis of retinoid signaling disorder, systemic organ involvement, neuroendocrine involvement, loss of smell and taste, and many other peripheral symptoms and signs, which are considered an enigma in the pathogenesis of COVID-19. Therefore, we suggest retinoid signaling defect as the main pathogenetic disorder in COVID-19 and STRA6 and GPCRs as the main binding receptors of SARS-CoV-2 spike protein. This new mechanism also clarifies the changing symptoms and findings in COVID-19 with each new variant. Moreover, these studies have explained the novel hypothesis for COVID-19 pathogenesis: Retinol depletion and retinoid signaling disorder and have revealed new drug targets for the treatment and prophylaxis of COVID-19.