Visual analysis on ferroptosis and its cross-talk to coronavirus disease 2019 (COVID-19).

Background: Ferroptosis is a new type of programmed cell death. Although ferroptosis has been studied in various aspects, there has been no visual analysis of ferroptosis in coronavirus disease 2019 (COVID-19) to date. It is still a global health concern of the COVID-19 pandemic worldwide, three years after its outbreak. Yet the emergence of the mutant strain Omicron has caused a fourth wave of infections in many countries. The pathogenesis of COVID-19 is still undergoing extensive exploration, which holds paramount importance in mitigating future epidemics. Methods: For this study, CiteSpace 6.2 R4 software was used for bibliometric and visual atlas analysis of ferroptosis-related research, and the Genecards database was used to mine ferroptosis and COVID-19-related genes. Results: We found increasing studies about ferroptosis. China and the United States have demonstrated robust scientific innovation over recent years, with extensive collaboration between their institutions and authors. Ferroptosis and COVID-19 were seen to have 13 shared genes, which may be new targets for the treatment of COVID-19 in the future. Most of the shared genes are enriched in tumor necrosis factor (TNF) pathways. The majority of those genes are up-regulated under the cellular response to oxidative stress. Genes including Tumour necrosis factor (TNF), RELA proto-oncogene (RELA), Activating transcription factor 4 (ATF4), Cytochrome b-245 beta chain (CYBB), Jun proto-oncogene (JUN), Mitogen-activated protein kinase 1 (MAPK1) and Heme oxygenase 1 (HMOX1), maybe a breakthrough for ferroptosis and COVID-19. Whilst previous research has shown there to be a relationship between ferroptosis and COVID-19, the specific role of ferroptosis remained unclear. Our study aimed to analyze the research status of ferroptosis and its relationship with COVID-19, to provide a useful reference for further prevention and treatment of COVID-19. Overall, uncovering the role of ferroptosis in SARS-CoV-2 infection is important for the development of new treatment strategies for COVID-19.

Vaccination with Span, an antigen guided by SARS-CoV-2 S protein evolution, protects against challenge with viral variants in mice.

SARS-CoV-2 continues to accumulate mutations to evade immunity, leading to breakthrough infections after vaccination. How researchers can anticipate the evolutionary trajectory of the virus in advance in the design of next-generation vaccines requires investigation. Here, we performed a comprehensive study of 11,650,487 SARS-CoV-2 sequences, which revealed that the SARS-CoV-2 spike (S) protein evolved not randomly but into directional paths of either high infectivity plus low immune resistance or low infectivity plus high immune resistance. The viral infectivity and immune resistance of variants are generally incompatible, except for limited variants such as Beta and Kappa. The Omicron variant has the highest immune resistance but showed high infectivity in only one of the tested cell lines. To provide cross-clade immunity against variants that undergo diverse evolutionary pathways, we designed a new pan-vaccine antigen (Span). Span was designed by analyzing the homology of 2675 SARS-CoV-2 S protein sequences from the NCBI database before the Delta variant emerged. The refined Span protein harbors high-frequency residues at given positions that reflect cross-clade generality in sequence evolution. Compared with a prototype wild-type (Swt) vaccine, which, when administered to mice, induced serum with decreased neutralization activity against emerging variants, Span vaccination of mice elicited broad immunity to a wide range of variants, including those that emerged after our design. Moreover, vaccinating mice with a heterologous Span booster conferred complete protection against lethal infection with the Omicron variant. Our results highlight the importance and feasibility of a universal vaccine to fight against SARS-CoV-2 antigenic drift.

Hemocytin facilitates host immune responses against Nosema bombycis.

Invertebrates lack an adaptive immune response and thus are reliant on their innate immune response for eliminating invading pathogens. The innate immune responses of silkworms against the pathogen Nosema bombycis include: hemocyte aggregation, melanization, antimicrobial peptides, etc. In our current study, we discovered that a silkworm hemostasis-related protein, hemocytin, is up-regulated after Nosema bombycis infection. This novel finding lead to our hypothesis that hemocytin participates in immune responses against N. bombycis. We investigated this hypothesis by analyzing the adhesive effects of hemocytin to invading N. bombycis, and the hemocytin-mediated hemocyte aggregation and hemolymph melanization. We showed that hemocytin can adhere to the surface of N. bombycis, which facilitates the agglutination of N. bombycis and hemocytes as well as the subsequent melanization. Moreover, when we utilize RNAi technology to decrease in vivo hemocytin expression, we found that the proliferation of N. bombycis within the host significantly increased. These results support our hypothesis that hemocytin exerts pro-inflammatory effects by facilitating pathogen agglutination, along with hemocyte aggregation and melanization, to combat N. bombycis. Our study is the first to determine a function of hemocytin in innate immunity against N. bombycis. Moreover, our findings are of great importance to provide potential targets for developing novel strategy against microsporidia infection.

Nosema bombycis suppresses host hemolymph melanization through secreted serpin 6 inhibiting the prophenoloxidase activation cascade.

Nosema bombycis is a pathogen of the silkworm that belongs to the microsporidia, a group of obligate intracellular parasites related to fungi. N. bombycis infection causes the disease pébrine in silkworms. Insects utilize hemolymph melanization as part of the innate immune response to fight against pathogens, and melanization relies on a serine protease-mediated prophenoloxidase (PPO) activation cascade that is tightly regulated by serine protease inhibitors (serpins). Previous studies showed that N. bombycis infection suppressed silkworm hemolymph melanization, however the mechanism has not been elucidated. We hypothesize that N. bombycis can secret serpins (NbSPNs) to inhibit host serine proteases in the PPO activation cascade, thus suppressing phenoloxidase (PO) activity and the consequent melanization. We demonstrated in this study that N. bombycis infection suppressed silkworm PO activity and melanization and we identified the expression of N. bombycis serpin 6 (NbSPN6) in the hemolymph of the infected host. When recombinant NbSPN6 was added to normal hemolymph, PO activity was inhibited in a dose-dependent manner. Moreover, in vivo analysis by RNA interference technology showed that when NbSPN6 expression is blocked, the inhibitory effects on PO activity can be reversed and the proliferation of N. bombycis within host can be suppressed. These results demonstrated the indispensable role of NbSPN6 in successful pathogen infection. To further elucidate the molecular basis of NbSPN6 suppressing host defense, we determined that the host serine protease prophenoloxidase-activating enzyme (PPAE) is the direct target of NbSPN6 inhibition. Taken together, our novel study is the first to elucidate the molecular mechanism of pathogen-derived serpin inhibiting hemolymph melanization and, thus, regulating host innate immune responses. This study may also provide novel strategies for preventing microsporidia infection.