The role of ASAH1-driven ceramide metabolism in EBV B-cell transformation under physiologically relevant germinal center hypoxia

About This Grant

Abstract Epstein Barr virus (EBV)-driven lymphomagenesis significantly burdens immunocompromised individuals. EBV- related lymphomas are aggressive and often untreatable. Current treatments use high-intense chemotherapy and rituximab lacking specificity and often causing severe side effects. This emphasizes the need for novel therapies targeting EBV or EBV-driven pathways. EBV reprograms B-cell metabolism for transformation, highlighting the potential of targeting these virus-driven metabolic pathways. Most EBV-associated lymphomas originate from the germinal center (GC) in the secondary lymphoid organs where B cells undergo activation and differentiation. A key characteristic of the GC is its severe hypoxic state (<1% O2 tension). The traditional in vitro model of EBV transformation overlooks the GC hypoxia. Consequently, most current studies of EBV-driven metabolic reprogramming that are performed under standard 20% O2 conditions, may not allow for the discovery of changes to cellular metabolism that are truly essential for EBV-driven lymphomagenesis in vivo. To address this, my research group has developed an ex vivo model that replicates the hypoxic conditions of the GC, allowing us to study EBV-driven metabolic reprogramming in human primary B cells at 1% O2 tension. We found that under these hypoxic conditions, ASAH1—an acidic ceramidase that can be targeted pharmacologically—emerges as a critical dependent factor in EBV-transformed B-cells. ASAH1 regulates the balance between ceramide and sphingosine-1-phosphate (S1P), two pivotal bioactive sphingolipids. Ceramide and S1P have opposing roles in regulating cell fate: ceramide promotes cell death and stress responses, whereas S1P enhances cell survival and proliferation. Hence, ASAH1 is often described as a "sphingolipid rheostat" due to its role in modulating this critical balance. In various cancers, an abnormal increase in ASAH1 activity shifts this balance towards S1P and its associated pro-survival signaling. Our central hypothesis is that EBV upregulates ASAH1 to shift the ceramide-S1P balance towards S1P production, enhancing survival and oncogenic signaling in B-cells transformed by EBV under the physiologically relevant GC hypoxia. We are testing this hypothesis by determining the mechanisms by which EBV and hypoxia cooperate to activate ASAH1(Aim 1), defining the role of ASAH1 in the ceramide-S1P axis in supporting the survival of EBV transformed B-cells under GC hypoxia (Aim 2), and defining the therapeutic potential by targeting ASAH1 in EBV hypoxically transformed tumors using mouse xenograft models (Aim 3). By underscoring the significant impact of the hypoxic microenvironment on viral oncogenesis, our study aims to pioneer more effective strategies to halt EBV transformation in immunocompromised individuals at high risk of developing EBV-related lymphomas.