Viral Infection of the Reproductive System in Times of COVID-19

Cellular Entry Mechanism Of The Virus

A novel CoV emerged in December 2019, termed SARS-CoV-2 by the International Virus Taxonomy Committee (Gorbalenya et al., 2020) due to its genetic similarities to the SARS-CoV-1 virus (79.5%) (Guo et al., 2020). The infection has been termed “COVID-19” (coronavirus disease-19), as this is a CoV-related disease that was discovered originally in 2019 (Ashour et al., 2020; Guarner, 2020) SARS-CoV-2 has been identified as a member of the β-coronavirus subgroup, with a positive-sense single-strand RNA, located within a nucleocapsid contained in an envelope Ashour et al., 2020; Lu et al., 2020; Zhou, 2020). The viral structure includes characteristic spike (S) proteins that are projected from the virion surface and assist viral cell entry, membrane (M) and envelope (E) proteins that assist in viral assembly, and the N protein which forms the nucleocapsid (Ashour et al., 2020). The S protein mediates viral transfer into host cells and is composed of two unique subunits, S1 and S2. The S1 domain functions in virus binding to the host cell membrane, while the S2 domain is responsible for the fusion of the virus to host cell membranes to facilitate the viral genome in entering the host cell. Viral S proteins undergo proteolytic priming by the transmembrane protease, serine 2 (TMPRSS2) (Hoffmann et al., 2020). Many receptors on the human cell membrane are identified which are involved in S1 protein binding to host cells (Ashour et al., 2020). The SARS-CoV-2 may gain access to host cells through the angiotensin-converting enzyme 2 (ACE2) receptor, with a higher affinity than reported in SARS-CoV-1 (Ashour et al., 2020; Gheblawi et al., 2020) (Fig.1). These receptors are widely expressed in the lungs (particularly type II pneumocytes and macrophages), cardiovascular system, gastrointestinal system, kidneys, neurological tissues, and the testes (Guo et al., 2020, Verdecchia et al., 2020; Fu et al., 2020). Here, the viruses replicate within the cells, releasing mature virions, which in turn infect new target cells (Margone et al., 2020).