ORF8 protein of SARS-CoV-2 reduces male fertility in mice.

As one of the most rapidly evolving proteins of the genus Betacoronavirus, open reading frames (ORF8's) function and potential pathological consequence in vivo are still obscure. In this study, we show that the secretion of ORF8 is dependent on its N-terminal signal peptide sequence and can be inhibited by reactive oxygen species scavenger and endoplasmic reticulum-Golgi transportation inhibitor in cultured cells. To trace the effect of its possible in vivo secretion, we examined the plasma samples of coronavirus disease 2019 (COVID-19) convalescent patients and found that the patients aged from 40 to 60 had higher antibody titers than those under 40. To explore ORF8's in vivo function, we administered the mice with ORF8 via tail-vein injection to simulate the circulating ORF8 in the patient. Although no apparent difference in body weight, food intake, and vitality was detected between vehicle- and ORF8-treated mice, the latter displayed morphological abnormalities of testes and epididymides, as indicated by the loss of the central ductal lumen accompanied by a decreased fertility in 5-week-old male mice. Furthermore, the analysis of gene expression in the testes between vehicle- and ORF8-treated mice identified a decreased expression of Col1a1, the loss of which is known to be associated with mice's infertility. Although whether our observation in mice could be translated to humans remains unclear, our study provides a potential mouse model that can be used to investigate the impact of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection on the human reproductive system.

Oxidative stress transforms 3CLpro into an insoluble and more active form to promote SARS-CoV-2 replication.

3CLpro is a key proteinase for SARS-CoV-2 replication and serves as an important target for antiviral drug development. However, how its activity is regulated intracellularly is still obscure. In this study, we developed a 3CLpro protease activity reporter system to examine the impact of various factors, including nutrient supplements, ions, pHs, or oxidative stress inducers, on 3CLpro protease activity. We found that oxidative stress could increase the overall activity of 3CLpro. Not altering the expression, oxidative stress decreased the solubility of 3CLpro in the lysis buffer containing 1% Triton-X-100. The Triton-X-100-insoluble 3CLpro was correlated with aggregates' formation and responsible for the increased enzymatic activity. The disulfide bonds formed between Cys85 sites of 3CLpro protomers account for the insolubility and the aggregation of 3CLpro. Besides being regulated by oxidative stress, 3CLpro impaired the cellular antioxidant capacity by regulating the cleavage of GPx1 at its N-terminus. This cleavage could further elevate the 3CLpro-proximate oxidative activity, favor aggregation and activation of 3CLpro, and thus lead to a positive feedback loop. In summary, we reported that oxidative stress transforms 3CLpro into a detergent-insoluble form that is more enzymatically active, leading to increased viral replication/transcription. Our study provided mechanistic evidence that suggests the therapeutic potential of antioxidants in the clinical treatment of COVID-19 patients.