ATG4B antagonizes antiviral immunity by GABARAP-directed autophagic degradation of TBK1.

ABBREVIATIONS: Baf A1: bafilomycin A1; GABARAP: GABA type A receptor-associated protein; GFP: green fluorescent protein; IFN: interferon; IKBKE/IKKi: inhibitor of nuclear factor kappa B kinase subunit epsilon; IRF3: interferon regulatory factor 3; ISG: interferon-stimulated gene; ISRE: IFN-stimulated response element; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MAVS: mitochondrial antiviral signaling protein; MOI: multiplicity of infection; PAMPs: pathogen-associated molecule patterns; RIGI/DDX58: RNA sensor RIG-I; SeV: Sendai virus; siRNA: small interfering RNA; TBK1: TANK binding kinase 1; WT: wild-type; VSV: vesicular stomatitis virus.

Molecular mechanisms and cellular functions of liquid-liquid phase separation during antiviral immune responses.

Spatiotemporal separation of cellular components is vital to ensure biochemical processes. Membrane-bound organelles such as mitochondria and nuclei play a major role in isolating intracellular components, while membraneless organelles (MLOs) are accumulatively uncovered via liquid-liquid phase separation (LLPS) to mediate cellular spatiotemporal organization. MLOs orchestrate various key cellular processes, including protein localization, supramolecular assembly, gene expression, and signal transduction. During viral infection, LLPS not only participates in viral replication but also contributes to host antiviral immune responses. Therefore, a more comprehensive understanding of the roles of LLPS in virus infection may open up new avenues for treating viral infectious diseases. In this review, we focus on the antiviral defense mechanisms of LLPS in innate immunity and discuss the involvement of LLPS during viral replication and immune evasion escape, as well as the strategy of targeting LLPS to treat viral infectious diseases.

Modulation of virus-induced neuroinflammation by the autophagy receptor SHISA9 in mice.

Microglia and astrocytes are subgroups of brain glia cells that support and protect neurons within the central nervous system (CNS). At early stages of viral infection in the CNS, they are predominant responding cells and lead to recruitment of peripheral immune cells for viral clearance. Inhibitor of nuclear factor κB kinase subunit epsilon (IKKi) is critical for type I interferon signalling and inflammation, which modulate heterogenic immune responses during CNS infection. Balanced autophagy is vital to maintain brain integrity, yet regulation of autophagy and immune activity within brain glia cells is poorly understood. Here we identify SHISA9 as an autophagy cargo receptor that mediates the autophagy-dependent degradation of IKKi during herpes simplex virus type 1 infection. IKKi is recognized by SHISA9 through unanchored K48-linked poly-ubiquitin chains and bridged to autophagosome membrane components GABARAPL1. Single-cell RNA sequencing analysis shows that SHISA9 has temporal characteristics while modulating both antiviral and inflammatory responses in microglia and astrocytes at different stages during viral infection. We found that Shisa9-/- mice are highly susceptible to herpes simplex virus encephalitis, have pathogenic astrocytes and display more severe neuroinflammation compared with wild-type mice. Taken together, our study unravels a critical role of selective autophagy by orchestrating immune heterogeneity of different CNS resident cells through the SHISA9-IKKi axis.

Phase-separated nucleocapsid protein of SARS-CoV-2 suppresses cGAS-DNA recognition by disrupting cGAS-G3BP1 complex.

Currently, the incidence and fatality rate of SARS-CoV-2 remain continually high worldwide. COVID-19 patients infected with SARS-CoV-2 exhibited decreased type I interferon (IFN-I) signal, along with limited activation of antiviral immune responses as well as enhanced viral infectivity. Dramatic progresses have been made in revealing the multiple strategies employed by SARS-CoV-2 in impairing canonical RNA sensing pathways. However, it remains to be determined about the SARS-CoV-2 antagonism of cGAS-mediated activation of IFN responses during infection. In the current study, we figure out that SARS-CoV-2 infection leads to the accumulation of released mitochondria DNA (mtDNA), which in turn triggers cGAS to activate IFN-I signaling. As countermeasures, SARS-CoV-2 nucleocapsid (N) protein restricts the DNA recognition capacity of cGAS to impair cGAS-induced IFN-I signaling. Mechanically, N protein disrupts the assembly of cGAS with its co-factor G3BP1 by undergoing DNA-induced liquid-liquid phase separation (LLPS), subsequently impairs the double-strand DNA (dsDNA) detection ability of cGAS. Taken together, our findings unravel a novel antagonistic strategy by which SARS-CoV-2 reduces DNA-triggered IFN-I pathway through interfering with cGAS-DNA phase separation.

Selective autophagy controls the stability of TBK1 via NEDD4 to balance host defense.

As a core kinase of antiviral immunity, the activity and stability of TANK-binding kinase 1 (TBK1) is tightly controlled by multiple post-translational modifications. Although it has been demonstrated that TBK1 stability can be regulated by ubiquitin-dependent proteasome pathway, it is unclear whether another important protein degradation pathway, autophagosome pathway, can specifically affect TBK1 degradation by cargo receptors. Here we report that E3 ubiquitin ligase NEDD4 functions as a negative regulator of type I interferon (IFN) signaling by targeting TBK1 for degradation at the late stage of viral infection, to prevent the host from excessive immune response. Mechanically NEDD4 catalyzes the K27-linked poly-ubiquitination of TBK1 at K344, which serves as a recognition signal for cargo receptor NDP52-mediated selective autophagic degradation. Taken together, our study reveals the regulatory role of NEDD4 in balancing TBK1-centered type I IFN activation and provides insights into the crosstalk between selective autophagy and antiviral signaling.

Osteogenic effects of antihypertensive drug benidipine on mouse MC3T3-E1 cells in vitro.

Hypertension is a prevalent systemic disease in the elderly, who can suffer from several pathological skeletal conditions simultaneously, including osteoporosis. Benidipine (BD), which is widely used to treat hypertension, has been proved to have a beneficial effect on bone metabolism. In order to confirm the osteogenic effects of BD, we investigated its osteogenic function using mouse MC3T3-E1 preosteoblast cells in vitro. The proliferative ability of MC3T3-E1 cells was significantly associated with the concentration of BD, as measured by methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay and cell cycle assay. With BD treatment, the osteogenic differentiation and maturation of MC3T3-E1 cells were increased, as established by the alkaline phosphatase (ALP) activity test, matrix mineralized nodules formation, osteogenic genetic test, and protein expression analyses. Moreover, our data showed that the BMP2/Smad pathway could be the partial mechanism for the promotion of osteogenesis by BD, while BD might suppress the possible function of osteoclasts through the OPG/RANKL/RANK (receptor activator of nuclear factor-κB (NF-κB)) pathway. The hypothesis that BD bears a considerable potential in further research on its dual therapeutic effect on hypertensive patients with poor skeletal conditions was proved within the limitations of the present study.

Early bone formation in mini-lateral window sinus floor elevation with simultaneous implant placement: An in vivo experimental study.

OBJECTIVE: To investigate the early bone formation in beagles with mini-lateral window sinus floor elevation and simultaneous implant placement. MATERIAL AND METHODS: Six beagles were selected for the split-mouth design procedures. In each animal, one maxillary recess received a 5 mm-diameter mini-round lateral osteotomy (test group), and the contralateral maxillary recess received a large rectangular osteotomy (10 mm long and 8 mm wide), (control group). Simultaneous implant installation was executed on bilateral maxillary recesses. Tetracycline and calcein dyes were administered on the 14th, 13th days and the 4th, 3rd days prior to sacrifice, respectively. After 8 weeks of healing, the beagles were euthanized for fluorescent labeling and histomorphometric analyses. RESULTS: In both groups, new bone formation initiated from the circumferential native bone of the maxillary recesses and extended toward the central sub-recess cavities. The maxillary recesses with the mini-window procedures exhibited superior mineral apposition rate, bone formation rate, and the percentage of new bone area to those of the group exposed to large osteotomy procedure (p < .05). While there was no significant difference in the value of bone-to-implant contact, the mini-window group displayed a tendency for an increase in this aspect (p > .05). Bone formation rate and new bone amount were not statistically correlated with bone-to-implant contact (p > .05). CONCLUSION: The hypothesis that mini-lateral window sinus floor elevation with simultaneous implant placement would improve early new bone formation in augmented sinus compared with large lateral window procedure is accepted.

Optimized beagle model for maxillary sinus floor augmentation via a mini-lateral window with simultaneous implant placement.

OBJECTIVE: This study was performed to establish an optimized beagle model for maxillary sinus floor augmentation via a mini-lateral window with simultaneous implant placement. METHODS: Twelve beagles underwent maxillary sinus floor augmentation via a mini-lateral window with simultaneous implant placement through sites selected by analyzing preoperative cone beam computed tomography (CBCT) images. During the experiment, no maxillary teeth were extracted and the infraorbital nerve was not severed. The osteotomy was only 5 mm in diameter. The implant stability quotient was measured, and postoperative CBCT was used to detect the condition of the sinus membrane and bone augmentation. RESULTS: The site corresponding to the tip of the highest dental cusp of the maxillary fourth premolar was suitable for the procedure, and the implant site was on the palatal bone plate. All implants achieved good primary stability. Postoperative CBCT showed no sinus membrane perforation, and the implants penetrated into the sinus cavity surrounded by bone substitute. CONCLUSION: The herein-described optimized model with mini-lateral osteotomy and without extraction or severing of the infraorbital nerve was minimally invasive, retained more lateral bone of the sinus, and achieved good sinus floor-lifting results. This model is highly reproducible and merits wider application.