Baculovirus Transduction in Mammalian Cells Is Affected by the Production of Type I and III Interferons, Which Is Mediated Mainly by the cGAS-STING Pathway

Regulation of type I and type III interferon induction in response to pathogen sensing

Type I and III interferons (IFN-I and IFN-III) have a central role in the early antimicrobial response against invading pathogens. Induction of IFN-Is and IFN-IIIs arises due to the sensing by pattern recognition receptors of pathogen-associated molecular patterns (from micro-organisms) or of damage-associated molecular patterns (DAMPs; produced by host cells). Here, we review recent developments on how IFN-I and IFN-III expression is stimulated by different pathogens and how the signalling pathways leading to IFN induction are tightly regulated. We also summarise the growing knowledge of the sensing pathways that lead to IFN-I and IFN-III induction in response to severe acute respiratory syndrome coronavirus 2.

The cGAS-STING pathway: a therapeutic target in diabetes and its complications

Diabetic wound healing (DWH) represents a major complication of diabetes where inflammation is a key impediment to proper healing. The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway has emerged as a central mediator of inflammatory responses to cell stress and damage. However, the contribution of cGAS-STING activation to impaired healing in DWH remains understudied. In this review, we examine the evidence that cGAS-STING-driven inflammation is a critical factor underlying defective DWH. We summarize studies revealing upregulation of the cGAS-STING pathway in diabetic wounds and discuss how this exacerbates inflammation and senescence and disrupts cellular metabolism to block healing. Partial pharmaceutical inhibition of cGAS-STING has shown promise in damping inflammation and improving DWH in preclinical models. We highlight key knowledge gaps regarding cGAS-STING in DWH, including its relationships with endoplasmic reticulum stress and metal-ion signaling. Elucidating these mechanisms may unveil new therapeutic targets within the cGAS-STING pathway to improve healing outcomes in DWH. This review synthesizes current understanding of how cGAS-STING activation contributes to DWH pathology and proposes future research directions to exploit modulation of this pathway for therapeutic benefit.

P26 enhances baculovirus gene delivery by modulating the mammalian antiviral response

Poxins are poxviral proteins that act by degrading 2´3´-cGAMP, a key molecule of cGAS-STING axis that drives and amplifies the antiviral response. Previous works have described some poxin homologous among lepidopteran and baculoviral genes. In particular, P26, a poxin homologous from AcMNPV retains the 2´3´-cGAMP degradation activity in vitro. In this work, we demonstrated that the antiviral activity triggered by baculovirus was disrupted by the transient expression of P26 in murine and human cell lines, and the effect of this action is not only on IFN-β production but also on the induction of IFN-λ. Besides, we proved P26 functionality in a stable-transformed cell line where the protein was constitutively expressed, preventing the production of IFN-β induced by baculovirus and resulting in an improvement in the transduction efficiency by the attenuation of the antiviral activity. Finally, we incorporated P26 into budded virions by capsid display or passive incorporation, and the results showed that both strategies resulted in an improvement of 3-17 times in the efficiency of transgene expression in murine fibroblasts. Our results suggest that the incorporation of P26 to budded baculoviral vectors is a very promising tool to modulate negatively the innate antiviral cellular response and to improve the efficiency of gene delivery in mammalian cells. KEY POINTS: • P26 affects baculovirus-induced IFN-β and IFN-λ production in mammalian cells. • Murine fibroblasts expressing P26 are more susceptible to transduction by baculovirus. • Incorporation of P26 into the virion improves gene delivery efficiency of baculovirus.

The DEAD/H-box helicase DHX9 contributes to suppression of Bombyx mori nucleopolyhedrovirus propagation in B. mori cells

Antiviral immune responses are mainly triggered through the recognition of virus-derived nucleic acids by host-specific pattern recognition receptors (PRRs). Here, we identified and characterized homologs of human PRRs for virus-derived DNA in Bombyx mori upon infection with a nucleopolyhedrovirus (NPV), a member of the family Baculoviridae. We found that progeny virus production of B. mori NPV was promoted in B. mori cells silenced with B. mori homolog of DEAD/H box polypeptide 9 gene (Bm-DHX9), but not in cells silenced with the other examined genes. Silencing of Bm-DHX9 expression has no effect on apoptosis induction, one of the major antiviral responses in B. mori cells. We also showed that Bm-DHX9 has the ability to bind DNA containing unmethylated C-phosphate-G-motif, which are characteristic of microbial pathogens and contained in the NPV genome with high frequency. Our findings suggest that Bm-DHX9 has the potential for sensing NPV-derived DNA to induce antiviral immune responses.

STING signaling in inflammaging: a new target against musculoskeletal diseases

Stimulator of Interferon Gene (STING) is a critical signaling linker protein that plays a crucial role in the intrinsic immune response, particularly in the cytoplasmic DNA-mediated immune response in both pathogens and hosts. It is also involved in various signaling processes in vivo. The musculoskeletal system provides humans with morphology, support, stability, and movement. However, its aging can result in various diseases and negatively impact people's lives. While many studies have reported that cellular aging is a leading cause of musculoskeletal disorders, it also offers insight into potential treatments. Under pathological conditions, senescent osteoblasts, chondrocytes, myeloid cells, and muscle fibers exhibit persistent senescence-associated secretory phenotype (SASP), metabolic disturbances, and cell cycle arrest, which are closely linked to abnormal STING activation. The accumulation of cytoplasmic DNA due to chromatin escape from the nucleus following DNA damage or telomere shortening activates the cGAS-STING signaling pathway. Moreover, STING activation is also linked to mitochondrial dysfunction, epigenetic modifications, and impaired cytoplasmic DNA degradation. STING activation upregulates SASP and autophagy directly and indirectly promotes cell cycle arrest. Thus, STING may be involved in the onset and development of various age-related musculoskeletal disorders and represents a potential therapeutic target. In recent years, many STING modulators have been developed and used in the study of musculoskeletal disorders. Therefore, this paper summarizes the effects of STING signaling on the musculoskeletal system at the molecular level and current understanding of the mechanisms of endogenous active ligand production and accumulation. We also discuss the relationship between some age-related musculoskeletal disorders and STING, as well as the current status of STING modulator development.

Baculoviral COVID-19 Delta DNA vaccine cross-protects against SARS-CoV2 variants in K18-ACE2 transgenic mice

After severe acute respiratory syndrome coronavirus-2 (SARS-CoV2) made the world tremble with a global pandemic, SARS-CoV2 vaccines were developed. However, due to the coronavirus's intrinsic nature, new variants emerged, such as Delta and Omicron, refractory to the vaccines derived using the original Wuhan strain. We developed an HERV-enveloped recombinant baculoviral DNA vaccine against SARS-CoV2 (AcHERV-COVID19S). A non-replicating recombinant baculovirus that delivers the SARS-CoV2 spike gene showed a protective effect against the homologous challenge in a K18-hACE2 Tg mice model; however, it offered only a 50 % survival rate against the SARS-CoV2 Delta variant. Therefore, we further developed the AcHERV-COVID19 Delta vaccine (AcHERV-COVID19D). The AcHERV-COVID19D induced higher neutralizing antibodies against the Delta variant than the prototype or Omicron variant. On the other hand, cellular immunity was similarly high for all three SARS-CoV2 viruses. Cross-protection experiments revealed that mice vaccinated with the AcHERV-COVID19D showed 100 % survival upon challenge with Delta and Omicron variants and 71.4 % survival against prototype SARS-CoV2. These results support the potential of the viral vector vaccine, AcHERV-COVID19D, in preventing the spread of coronavirus variants such as Omicron and SARS-CoV2 variants.

Flow cytometric reporter assays provide robust functional analysis of signaling complexes

Conventional assays to probe signaling protein interactions and function involve measurement of luciferase reporter expression within the bulk cell population, with lack of control over target-protein expression level. To address this issue, we have developed a rapid and robust flow cytometric assay for analysis of signaling protein function. A fluorescent reporter and fluorescent tagging of the target protein enables simultaneous assessment of protein expression and signaling within individual cells. We have applied our technique to the analysis of variants of the lipopolysaccharide receptor Toll-like receptor 4 (TLR4) and its adapter protein MyD88, using a NF-кB-responsive promoter driving mScarlet-I expression. The assay enables exclusion of nontransfected cells and overexpressing cells that signal spontaneously. Additionally, our assay allows the identification of protein variants that fail to express. We found that the assays were highly sensitive, with cells expressing an appropriate level of GFP-MyD88 showing approximately 200-fold induction of mScarlet-I by lipopolysaccharide, and we can detect subtle protein concentration-dependent effects of mutations. Importantly, the assay is adaptable to various signaling pathways.

Highly efficient CRISPR-mediated large DNA docking and multiplexed prime editing using a single baculovirus

CRISPR-based precise gene-editing requires simultaneous delivery of multiple components into living cells, rapidly exceeding the cargo capacity of traditional viral vector systems. This challenge represents a major roadblock to genome engineering applications. Here we exploit the unmatched heterologous DNA cargo capacity of baculovirus to resolve this bottleneck in human cells. By encoding Cas9, sgRNA and Donor DNAs on a single, rapidly assembled baculoviral vector, we achieve with up to 30% efficacy whole-exon replacement in the intronic β-actin (ACTB) locus, including site-specific docking of very large DNA payloads. We use our approach to rescue wild-type podocin expression in steroid-resistant nephrotic syndrome (SRNS) patient derived podocytes. We demonstrate single baculovirus vectored delivery of single and multiplexed prime-editing toolkits, achieving up to 100% cleavage-free DNA search-and-replace interventions without detectable indels. Taken together, we provide a versatile delivery platform for single base to multi-gene level genome interventions, addressing the currently unmet need for a powerful delivery system accommodating current and future CRISPR technologies without the burden of limited cargo capacity.

Baculovirus Vectors Induce the Production of Interferons in Swine: Their Potential in the Development of Antiviral Strategies

The huge variety of viruses affecting swine represents a global threat. Since vaccines against highly contagious viruses last several days to induce protective immune responses, antiviral strategies for rapid control of outbreak situations are needed. The baculovirus Autographa californica multiple nucleopolyhedrovirus (AcMNPV), an insect virus, has been demonstrated to be an effective vaccine vector for mammals. Besides the ability to display or transduce heterologous antigens, it also induces strong innate immune responses and provides IFN-mediated protection against lethal challenges with viruses like foot-and-mouth disease virus (FMDV) in mice. Thus, the aim of this study was to evaluate the ability of AcMNPV to induce IFN production and elicit antiviral activity in porcine peripheral blood mononuclear cells (PBMCs). Our results demonstrated that AcMNPV induced an IFN-α-mediated antiviral activity in PBMCs in vitro. Moreover, the inoculation of AcMNPV in piglets led to the production of type I and II IFNs in sera from inoculated animals and antiviral activities against vesicular stomatitis virus (VSV) and FMDV measured by in vitro assays. Finally, it was demonstrated that the pseudotyping of AcMNPV with VSV-G protein, but not the enrichment of the AcMNPV genome with specific immunostimulatory CpG motifs for the porcine TLR9, improved the ability to induce IFN-α production in PBMCs in vitro. Together, these results suggest that AcMNPV is a promising tool for the induction of IFNs in antiviral strategies, with the potential to be biotechnologically improved.

Solutions against emerging infectious and noninfectious human diseases through the application of baculovirus technologies

Abstract

Baculoviruses are insect pathogens widely used as biotechnological tools in different fields of life sciences and technologies. The particular biology of these entities (biosafety viruses 1; large circular double-stranded DNA genomes, infective per se; generally of narrow host range on insect larvae; many of the latter being pests in agriculture) and the availability of molecular-biology procedures (e.g., genetic engineering to edit their genomes) and cellular resources (availability of cell lines that grow under in vitro culture conditions) have enabled the application of baculoviruses as active ingredients in pest control, as systems for the expression of recombinant proteins (Baculovirus Expression Vector Systems—BEVS) and as viral vectors for gene delivery in mammals or to display antigenic proteins (Baculoviruses applied on mammals—BacMam). Accordingly, BEVS and BacMam technologies have been introduced in academia because of their availability as commercial systems and ease of use and have also reached the human pharmaceutical industry, as incomparable tools in the development of biological products such as diagnostic kits, vaccines, protein therapies, and—though still in the conceptual stage involving animal models—gene therapies. Among all the baculovirus species, the Autographa californica multiple nucleopolyhedrovirus has been the most highly exploited in the above utilities for the human-biotechnology field. This review highlights the main achievements (in their different stages of development) of the use of BEVS and BacMam technologies for the generation of products for infectious and noninfectious human diseases.

Key points

• Baculoviruses can assist as biotechnological tools in human health problems.

• Vaccines and diagnosis reagents produced in the baculovirus platform are described.

• The use of recombinant baculovirus for gene therapy–based treatment is reviewed.