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ASEMV 2019 Annual Meeting on Exosomes & Microvesicles—Day 3, Tuesday October 8

Tuesday’s sessions of the annual ASEMV 2019 meeting at Asilomar, California, featured many exciting presentations. Among the 16 talks of the day, five were of particular interest. The first was by Ryan McNamara, PhD, of University of North Carolina-Chapel Hill, whose presentation was titled “EVs from Kaposi Sarcoma-Associated Herpes Lymphoma Induce Long-Term Endothelial Cell Reprogramming.” Dr. McNamara noted that extracellular communication is critical for organismal homeostasis, and thus presents as a major network for viruses to usurp for viral pathogenesis. EVs package contents from a donor cell to communicate with its surroundings, and evolutionarily diverse viruses have been shown to hijack this communication axis to promote pathogenesis. Previously, Dr. McNamara and colleagues had showd that the oncovirus Kaposi’s Sarcoma-Associated Herpes Virus (KSHV) incorporates viral miRNA into EVs secreted from infected cells during the “latency stage” of the viral life cycle. They hypothesized that these modified EVs, termed KSHV-EVs, aid in the establishment of a more favorable niche for disease/tumor progression. Their current results demonstrate that KSHV can modify the local environment using EVs. The group currently proposes that oncoviruses such as KSHV utilize the extracellular communications network through EVs to establish a niche favorable for disease progression and tissue transformation. This allows for the virus to reshape the local environment with minimal spread of the infectious agent, and without tripping immune alarms. In a following presentation, Jeffrey Savas, PhD, from Northwestern University, spoke on how “Viral Scission Factor Alix Tunes Neuronal Communication Through EVs.” Dr. Savas began by noting that synaptic plasticity is a dynamic process facilitating adaptable and flexible communication. He further remarked that N-methyl-d-aspartate (NMDA) receptors play a key role in long-term potentiation (LTP), and that chemical activation of synaptic NMDARs mimics many hallmarks of LTP. Using multiplexed quantitative proteomics, Dr. Savas and colleagues identified EVs as important modulators of neuronal communication. NMDAR activation triggered acute translation, increased phosphorylation, and promoted synaptic localization of the viral membrane scission factor Alix. They found that Alix protein levels increased within 5 minutes after stimulation, while mRNA levels were not significantly increased. This suggests, Dr. Savas said, that increased Alix levels are occurring through a rapid burst of translation. Current experiments indicate that Alix-mediated EV release represents an unexpected mechanism underlying neuronal communication during synaptic plasticity, which provides additional support for convergent mechanisms in viral budding and neural communication.

Association of ABeta with Astrocyte-Derived and Ceramide-Enriched Exosomes

In a third, very interesting presentation, Simone Crivelli, PhD, of the University of Kentucky, gave a talk entitled “Association of ABeta with Astrocyte-Derived and Ceramide-Enriched Exosomes Mediates ABeta Microtoxicity in Neurons, Which Is Prevented by Novel Ceramide Analogs.” Dr. Crivelli began by noting that the neurotoxicity of ABeta in Alzheimer’s disease (AD) is still not clear. In their current work, Dr. Crivelli and colleagues report showing that serum from 5xFAD mice and AD patients, but not serum from wild-type mice or healthy human controls, contains a proportion of ceramide-enriched and astocyte-derived (GFAP-positive) exosomes, termed “astrosomes,” that are associated with ABeta. The novel ceramide analog N-oleoyl Betaserinol (S18) prevented ABeta association with astrosomes, suggesting that ceramide mediated binding of ABeta to astrosomes. In contrast to ABeta alone, ABeta-associated astrosomes increased neurite fragmentation and neuronal cell death by three-fold, suggesting that association with astrosomes enhanced ABeta neurotoxicity. Dr. Crivelli concluded by stating that her group’s data suggests that association of ABeta with ceramide in astrosomes enhances ABeta interaction with VDAC1 and mediates ABeta neurotoxicity in AD, which can be prevented by novel ceramide analogs.

EVS AND THEIR miRNA CARGO IN MILK PLAY A ROLE IN OPTIMAL POST-NATAL GROWTH & GUT HEALTH DURING LACTATION IN MOUSE PUPS

In a fourth presentation, Janos Zemplani, PhD, of the University of Nebraska-Lincoln, spoke on how “Knockout of Maternal Tsg101 and Dicer Impair Gut Health in Suckling Wild-Type Pups.” Dr. Zemplani noted at the outset that EVs, endogenously labeled with a CD63-eGFP fusion protein are absorbed from maternal milk and accumulate primarily in intestinal mucosa, kidneys, and brain in wild-type (WT) c57/B6 pups. Tsg101 and Dicer are known to play roles in exosome and miRNA biogenesis. Dr. Zemplani’s group began with the hypothesis that loss of maternal exosome and miRNA biogenesis impairs post-natal growth and gut health in suckling WT pups. In their experiments, the scientists showed that the body weight of WT pups fostered to Tsg101 and Dicer knockout (KO) dams was 20% and 40%-50% lower, respectively, compared to WT pups fostered to WT dams. In addition, total body fat was 75% lower in WT pups fostered to Dicer KO dams compared to WT pups fostered to WT dams. Villus height was 30% less in WT pups fostered to Dicer KO dams compared to WT pups fostered to WT dams, whereas the effect on crypt depth was modest. WT pups fostered to Dicer KO dams appeared to be lethargic and consumed 50% (males) and 70% (females) less milk than WT pups fostered to WT dams, whereas Tsg101 KO had no effect on milk consumption. Tsg101 KO caused an 80% drop in exosome-sized EVs. TSG101 and Dicer KO did not affect total protein in milk. Based on these results, Dr. Zempleni said that his group has concluded that EVs and their miRNA cargos in milk play a role in optimal post-natal growth and gut health during lactation.