Spatiotemporal Quantification of Endosomal Acidification on the Viral Journey

Mapping Extracellular Space Features of Viral Encephalitis to Evaluate the Proficiency of Anti-Viral Drugs

The extracellular space (ECS) is an important barrier against viral attack on brain cells, and dynamic changes in ECS microstructure characteristics are closely related to the progression of viral encephalitis in the brain and the efficacy of antiviral drugs. However, mapping the precise morphological and rheological features of the ECS in viral encephalitis is still challenging so far. Here, a robust approach is developed using single-particle diffusional fingerprinting of quantum dots combined with machine learning to map ECS features in the brain and predict the efficacy of antiviral encephalitis drugs. These results demonstrated that this approach can characterize the microrheology and geometry of the brain ECS at different stages of viral infection and identify subtle changes induced by different drug treatments. This approach provides a potential platform for drug proficiency assessment and is expected to offer a reliable basis for the clinical translation of drugs.

Living virus-based nanohybrids for biomedical applications

Living viruses characterized by distinctive biological functions including specific targeting, gene invasion, immune modulation, and so forth have been receiving intensive attention from researchers worldwide owing to their promising potential for producing numerous theranostic modalities against diverse pathological conditions. Nevertheless, concerns during applications, such as rapid immune clearance, altering immune activation modes, insufficient gene transduction efficiency, and so forth, highlight the crucial issues of excessive therapeutic doses and the associated biosafety risks. To address these concerns, synthetic nanomaterials featuring unique physical/chemical properties are frequently exploited as efficient drug delivery vehicles or treatments in biomedical domains. By constant endeavor, researchers nowadays can create adaptable living virus-based nanohybrids (LVN) that not only overcome the limitations of virotherapy, but also combine the benefits of natural substances and nanotechnology to produce novel and promising therapeutic and diagnostic agents. In this review, we discuss the fundamental physiochemical properties of the viruses, and briefly outline the basic construction methodologies of LVN. We then emphasize their distinct diagnostic and therapeutic performances for various diseases. Furthermore, we survey the foreseeable challenges and future perspectives in this interdisciplinary area to offer insights. This article is categorized under: Biology-Inspired Nanomaterials > Protein and Virus-Based Structures Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Single-virus tracking with quantum dots in live cells

Single-virus tracking (SVT) offers the opportunity to monitor the journey of individual viruses in real time and to explore the interactions between viral and cellular structures in live cells, which can assist in characterizing the complex infection process and revealing the associated dynamic mechanisms. However, the low brightness and poor photostability of conventional fluorescent tags (e.g., organic dyes and fluorescent proteins) greatly limit the development of the SVT technique, and challenges remain in performing multicolor SVT over long periods of time. Owing to the outstanding photostability, high brightness and narrow emission with tunable color range of quantum dots (QDs), QD-based SVT (QSVT) enables us to follow the fate of individual viruses interacting with different cellular structures at the single-virus level for milliseconds to hours, providing more accurate and detailed information regarding viral infection in live cells. So far, the QSVT technique has yielded spectacular achievements in uncovering the mechanisms associated with virus entry, trafficking and egress. Here, we provide a detailed protocol for QSVT implementation using the viruses that we have previously studied systematically as an example. The specific procedures for performing QSVT experiments in live cells are described, including virus preparation, the QD labeling strategies, imaging approaches, image processing and data analysis. The protocol takes 1-2 weeks from the preparation of viruses and cellular specimens to image acquisition, and 1 d for image processing and data analysis.

Endosomes supporting fusion mediated by vesicular stomatitis virus glycoprotein have distinctive motion and acidification

Most enveloped viruses infect cells by binding receptors at the cell surface and undergo trafficking through the endocytic pathway to a compartment with the requisite conditions to trigger fusion with a host endosomal membrane. Broad categories of compartments in the endocytic pathway include early and late endosomes, which can be further categorized into subpopulations with differing rates of maturation and motility characteristics. Endocytic compartments have varying protein and lipid components, luminal ionic conditions and pH that provide uniquely hospitable environments for specific viruses to fuse. In order to characterize compartments that permit fusion, we studied the trafficking and fusion of viral particles pseudotyped with the vesicular stomatitis virus glycoprotein (VSV-G) on their surface and equipped with a novel pH sensor and a fluorescent content marker to measure pH, motion and fusion at the single particle level in live cells. We found that the VSV-G particles fuse predominantly from more acidic and more motile endosomes, and that a significant fraction of particles is trafficked to more static and less acidic endosomes that do not support their fusion. Moreover, the fusion-supporting endosomes undergo directed motion.