Lipid Signaling Under Microgravity Conditions

Over the past decade, it has become increasingly clear that astronauts experience a number of physiological alterations related to the unique conditions of the Space environment, which include microgravity, altered nutrition, increased radiation exposure, confinement, and other stressors. In this context, a substantial body of literature has documented that the functional integrity of multiple tissues is compromised during Space missions. Epithelial barriers, whose primary role is the host defense, are among the first tissues to be affected by Space stressors. Intesti-nal epithelial cells (IECs), which form the intestinal lining, respond to environmental insults – including pathogens and other abiotic stressors – by interacting with the immune system and triggering inflammatory responses. Inflammation represents a well-conserved and tightly regulated biological process that allows tissues to remove harmful stimuli and restore homeostasis. This response involves a complex interplay among signaling molecules, most of which are represented by endogenous bioactive lipids such as endocannabinoids, sphingolipids, eicosanoids, and specialized pro-resolving mediators (SPMs). Each signal plays a role in different phases of the inflammatory response. Notably, our research group has previously demonstrated that both real and simulated mi-crogravity can modulate the metabolism of bioactive lipids. These findings prompted us to investigate whether similar metabolic changes occur in the intestinal system, especially since astronauts frequently report gastrointestinal problems at the end of their missions, including diarrhea and malnutrition. The aim of this project is to understand how IECs respond to Space-relevant environmental changes and whether the metabolism of bioactive lipids could be affected. To this end, we developed an in vitro model of IECs exposed to simulated microgravity. Briefly, we exposed human intestinal epithelial Caco-2 cells to microgravity, which was simu-lated by means of the NASA’s Rotary Cell Culture System (RCCS). Then, in these cells we characterized gene and protein expression of the main components of the endocannabinoid system (ECS) and of the sphingosine 1-phosphate (S1P) system, both essential for intestinal homeostasis, and we assessed inflammatory and functional markers. Finally, we treated Caco-2 cells with JWH-133, a selective cannabinoid receptor 2 (CB2) agonist, in order to determine whether it could reverse the observed changes of inflammatory and functional markers, and thus represent a potential countermeasure to Space-related gastrointestinal dysfunctions.