Abstract 1986 Analyzing the Effects of Repetitive and Chronic Stress in FicD Knock-out Mice

The proper synthesis, folding, modification, and degradation of proteins are critical processes for maintaining cellular health and function. These processes, collectively known as protein homeostasis, are regulated by intricate molecular mechanisms within the cell. The unfolded protein response (UPR) is one such adaptive pathway that safeguards cells against the accumulation of unfolded proteins in the endoplasmic reticulum (ER). Precise management of this pathway is crucial, as improper UPR signaling is implicated in numerous diseases, including metabolic and inflammatory diseases. We previously uncovered a novel method of UPR regulation through the post-translational modification of BiP. FicD is an enzyme that AMPylates and deAMPylates BiP in response to changes in ER stress. AMPylation of BiP results in inactivation of BiP's chaperone activity. Furthermore, loss of FicD results in increased UPR signaling in response to physiologic stress in both Drosophila and mice. We propose that FicD's AMPylation/deAMPylation of BiP acts as a molecular rheostat for the activation of the UPR. Based on our previous studies we predicted that chronic and repetitive ER stressors would be deleterious to FicD-/- animals which should lack adaptation resiliency to continued stress. In this study, we utilize an ATF4 translational reporter mouse (UMAI-LUC) to analyze the effects of UPR activation in wildtype and FicD-/- mice under acute, repetitive, and chronic ER stress-inducing conditions. Using both in vivo and ex vivo bioluminescence imaging, we found significant differences in ATF4 reporter expression over the course of these stresses. Taken together, our findings indicate that FicD is required for proper regulation of UPR signaling in mammalian cells and may play a role in the adaption of UPR signaling to both repetitive and chronic stress. Funding was provided by a Welch Foundation grant I-1561, Once Upon a TimeFoundation, NIH R35GM134945 to K.O. and the UTSW NORC Pilot and Feasibility grant under NIDDK/NIH award number P30DK127984 to A.C.