Impact of modeled microgravity stress on innate immunity in a beneficial animal-microbe symbiosis

The innate immune response is the first line of defense for all animals to not only detect invading microbes and toxins but also sense and interface with the environment. One such environment that can significantly affect innate immunity is spaceflight. In this study, we explored the impact of microgravity stress on key elements of the NFκB innate immune pathway. The symbiosis between the bobtail squid Euprymna scolopes and its beneficial symbiont Vibrio fischeri was used as a model system under a simulated microgravity environment. The expression of genes associated with the NFκB pathway was monitored over time as the symbiosis progressed. Results revealed that although the onset of the symbiosis was the major driver in the differential expression of NFκB signaling, the stress of simulated low-shear microgravity also caused a dysregulation of expression. Several genes were expressed at earlier time points suggesting that elements of the E. scolopes NFκB pathway are stress-inducible, whereas expression of other pathway components was delayed. The results provide new insights into the role of NFκB signaling in the squid-vibrio symbiosis, and how the stress of microgravity negatively impacts the host immune response. Together, these results provide a foundation to develop mitigation strategies to maintain host-microbe homeostasis during spaceflight. To begin to explore how simulated microgravity alters the expression of the NFκB pathway in the E. scolopes light organ, hatchling animals were incubated in the HARVs in both the LSMMG and gravity control positions in the presence and absence of the symbiotic V. fischeri for 2, 6, 8, 10, 12, 16, 18, 24 h. Total RNA extracted from host light organs was then screened for differential expression of 33 genes associated with the NFκB pathway using NanoString nCounter direct transcript counts (Table 1; Dataset S2) (Goytain & Ng, 2020). Genes were considered significantly differentially expressed (DEGs) at an adjusted p-value cutoff of 0.10, and highly significant at a cutoff of 0.05 (Dataset S3).