Abstract Background One evident hallmark of Alzheimer's Disease (AD) is the irregular accumulation of proteins such as Aβ and pTau. This accumulation could alleviate ER stress and trigger an integrated signaling cascade called the unfolded protein response (UPR). UPR reduces the number of misfolded proteins and further inhibits abnormal protein accumulation. Targeting ER stress may therefore be an effective treatment for AD. One protein of interest that plays a role in modulating ER stress is the Sigma‐1 receptor (Sig1R). Sig1R agonists have been shown to be neuroprotective and anti‐amnesic in AD mouse models. However, the mechanism of action remains largely unknown. Method In our study, we use primary MEF cells derived from Wild‐type and Knock‐out Sig1R mouse models to examine the role of Sig1R in ER stress. We treated cells with an acute ER stressor, DTT, and measured transcript levels of target genes under the UPR branches. Furthermore, we used Chromosomal Immunoprecipitation (ChIP) to identify regulators of SIG1R gene during stress. Result We observed that the loss of Sig1R compromised the PERK pathway. KO MEFs had a slow recovery from stress suggesting Sig1R plays a role in re‐establishing homeostasis following stress. Following DTT treatment, mRNA and protein levels of Sig1R increase significantly over the course of recovery. ChIP uncovered three CHOP, a major player in the UPR, binding sites within the promoter of SIG1R, and each site had a distinct temporal binding pattern over the course of cell recovery. This increase in binding correlates with an increase in Sig1R expression. This showed that Sig1R is a chaperone downstream of CHOP, and that the up‐regulation of Sig1R might be crucial in re‐establishing homeostasis. Finally, our imaging data showed an increase in localization of Sig1R with extracellular vesicles. We further hypothesized that the high expression of Sig‐1R may have a role in the removal of misfolded proteins, perhaps Aβ. Therefore, we have ongoing experiments looking at the effect of Aβ on our models. Conclusion Our study has the potential to unravel the implications of Sig1R in AD by showing that it is transcriptionally and translationally regulated in response to stress induced by misfolded proteins.
