Faculty Bibliography

Astrocytes are a heterogeneous population of central nervous system glial cells that respond to pathological insults and injury by undergoing a transformation called "reactivity." Reactive astrocytes exhibit distinct and context-dependent cellular, molecular, and functional state changes that can either support or disturb tissue homeostasis. We recently identified a reactive astrocyte sub-state defined by interferon-responsive genes like Igtp, Ifit3, Mx1, and others, called interferon-responsive reactive astrocytes (IRRAs). To further this transcriptomic definition of IRRAs, we wanted to define the proteomic changes that occur in this reactive sub-state. We induced IRRAs in immunopanned rodent astrocytes and human iPSC-differentiated astrocytes using TNF, IL1α, C1Q, and IFNβ and characterized their proteomic profile (both cellular and secreted) using unbiased quantitative proteomics. We identified 2335 unique cellular proteins, including IFIT2/3, IFITM3, OASL1/2, MX1/2/3, and STAT1. We also report that rodent and human IRRAs secrete PAI1, a serine protease inhibitor which may influence reactive states and functions of nearby cells. Finally, we evaluated how IRRAs are distinct from neurotoxic reactive astrocytes (NRAs). While NRAs are described by expression of the complement protein C3, it was not upregulated in IRRAs. Instead, we found ~90 proteins unique to IRRAs not identified in NRAs, including OAS1A, IFIT3, and MX1. Interferon signaling in astrocytes is critical for the antiviral immune response and for regulating synaptic plasticity and glutamate transport mechanisms. How IRRAs contribute to these functions is unknown. This study provides the basis for future experiments to define the functional roles of IRRAs in the context of neurodegenerative disorders.

Microsporidia are eukaryotic, obligate intracellular parasites that infect a wide range of hosts, leading to health and economic burdens worldwide. Microsporidia use an unusual invasion organelle called the polar tube (PT), which is ejected from a dormant spore at ultra-fast speeds, to infect host cells. The mechanics of PT ejection are impressive. Anncaliia algerae microsporidia spores (3-4 μm in size) shoot out a 100-nm-wide PT at a speed of 300 μm/s, creating a shear rate of 3000 s^-1. The infectious cargo, which contains two nuclei, is shot through this narrow tube for a distance of ∼60-140 μm (Jaroenlak et al, 2020) and into the host cell. Considering the large hydraulic resistance in an extremely thin tube and the low-Reynolds-number nature of the process, it is not known how microsporidia can achieve this ultrafast event. In this study, we use Serial Block-Face Scanning Electron Microscopy to capture 3-dimensional snapshots of A. algerae spores in different states of the PT ejection process. Grounded in these data, we propose a theoretical framework starting with a systematic exploration of possible topological connectivity amongst organelles, and assess the energy requirements of the resulting models. We perform PT firing experiments in media of varying viscosity, and use the results to rank our proposed hypotheses based on their predicted energy requirement. We also present a possible mechanism for cargo translocation, and quantitatively compare our predictions to experimental observations. Our study provides a comprehensive biophysical analysis of the energy dissipation of microsporidian infection process and demonstrates the extreme limits of cellular hydraulics.

The ongoing transmission of influenza A viruses (IAV) for the past century continues to be a burden to humans. IAV binds terminal sialic acids (SA) of sugar molecules present within the upper respiratory tract (URT) in order to successfully infect hosts. The two most common SA structures that are important for IAV infection are those with α2,3- and α2,6-linkages. While mice were once considered to be an unsuitable system for studying IAV transmission due to their lack of α2,6-SA in the trachea, we have successfully demonstrated that IAV transmission in infant mice is remarkably efficient. This finding led us to re-evaluate the SA composition of the URT of mice using in situ immunofluorescence and examine its in vivo contribution to transmission for the first time. We demonstrate that mice express both α2,3- and α2,6-SA in the URT and that the difference in expression between infants and adults contributes to the variable transmission efficiencies observed. Furthermore, selectively blocking α2,3-SA or α2,6-SA within the URT of infant mice using lectins was necessary but insufficient at inhibiting transmission, and simultaneous blockade of both receptors was crucial in achieving the desired inhibitory effect. By employing a broadly acting neuraminidase to indiscriminately remove both SA moieties in vivo, we effectively suppressed viral shedding and halted the transmission of different strains of influenza viruses. These results emphasize the utility of the infant mouse model for studying IAV transmission and strongly indicate that broadly targeting host SA is an effective approach that inhibits IAV contagion.IMPORTANCEInfluenza virus transmission studies have historically focused on viral mutations that alter hemagglutinin binding to sialic acid (SA) receptors in vitro. However, SA binding preference does not fully account for the complexities of influenza A virus transmission in humans. Our previous findings reveal that viruses that are known to bind α2,6-SA in vitro have different transmission kinetics in vivo, suggesting that diverse SA interactions may occur during their life cycle. In this study, we examine the role of host SA on viral replication, shedding, and transmission in vivo. We highlight the critical role of SA presence during virus shedding, such that attachment to SA during virion egress is equally important as detachment from SA during virion release. These insights support the potential of broadly acting neuraminidases as therapeutic agents capable of restraining viral transmission in vivo. Our study unveils intricate virus-host interactions during shedding, highlighting the necessity to develop innovative strategies to effectively target transmission.

β-Carotene oxygenase 1 (BCO1) catalyzes the cleavage of β-carotene to form vitamin A. Besides its role in vision, vitamin A regulates the expression of genes involved in lipid metabolism and immune cell differentiation. BCO1 activity is associated with the reduction of plasma cholesterol in humans and mice, while dietary β-carotene reduces hepatic lipid secretion and delays atherosclerosis progression in various experimental models. Here we show that β-carotene also accelerates atherosclerosis resolution in two independent murine models, independently of changes in body weight gain or plasma lipid profile. Experiments in Bco1^-/-