Alternative Splicing & Differential Expression of Lipases in Host-Microbe Interactions - ABSTRACT Lipids exert a profound influence on immune status providing bulk energy sources and mediating immune sig- naling. Indeed, host responses to microbiota and infection have immune and metabolic facets. But, mecha- nisms that govern immunometabolic remodeling are poorly understood and have been studied mostly in the context of transcriptional regulation. The role of post-transcriptional mechanisms such as Pre-mRNA splicing in host-bacteria conflict remains largely unknown. We have uncovered a novel, evolutionarily conserved and physiologically relevant mechanism by which alternative splicing (Alt-Spl) of lipases alters endocannabinoid (eCB) production and shapes the host response to intestinal bacterial infection. Here, we propose to study how infection-associated splicing links lipase activity, eCB biogenesis and immune response in vivo. In preliminary, unpublished studies, we discovered that Alt-Spl of DAGL-2, the sole C. elegans homolog of DAGLa & DAGLb enzymes that catalyze biogenesis of 2-Arachidonyl Glycerol (2-AG), the most abundant eCB in mammals, alters 2-AG production and influences host response to bacterial infection. We have identified analogous exons in DAGLB, the gene encoding DAGLb, cells. DAGL-2 Alt-Spl is regulated by TCER-1, a splicing and found them to undergo Alt-Spl in human immune factor that we previously discovered represses patho- gen resistance; we found this regulatory relationship to be maintained in mammals. Our data has identified ad- ditional lipid-catabolizing genes that undergo Alt-Spl upon infection and revealed broad infection-induced splic- ing alterations suggesting that Pre-mRNA splicing is a key regulatory step at the host-bacteria interface. We also found that TCER-1 modulates infection-induced fat loss and, in a partly independent pathway, regulates overall gene expression of a family of ‘LIPL’ triglyceride lipases, homologs of human lysosomal acid lipase A (LIPA), to shape host response. Hence, we hypothesize that infection-induced Alt-Spl and differential expression of conserved lipases dictates fat mobilization and shapes host response. To test this, we will conduct in vivo mechanistic studies to elucidate how DAGL-2/DAGLB splicing alters 2-AG biogenesis and how 2-AG/its derivatives shape immune outcomes (Aim 1). We will define the spatiotemporal expression and func- tion dynamics of the ‘LIPL’ enzymes, identify their downstream metabolites and the mechanism(s) by which they shape immunometabolism (Aim 2). These studies combine in vivo molecular genetic approaches with advanced lipidomics, protein modeling and mammalian cell studies. They address topics of broad significance in host-bacteria interactions: (a) Pre-mRNA splicing, (b) eCB pathway, (c) immune-activating host lipases. This work will potentially establish splicing as a conserved regulatory feature of host-bacteria conflict and fulfill a fundamental knowledge gap in immunome- tabolism to establish splicing as a target for non-antibiotic therapies for infections and inflammatory diseases.
