Expression and regulation of ATF6α in the mouse uterus during embryo implantation

VIP conditions human endometrial receptivity by privileging endoplasmic reticulum stress through ATF6α pathway

Endometrial stromal cells undergo endoplasmic reticulum (ER) stress and unfolded protein response (UPR) during the decidualization linked with the inflammation and angiogenesis processes. Considering VIP (vasoactive intestinal peptide) induces the decidualization program, we studied whether modulates the ER/UPR pathways to condition both processes for embryo implantation. When Human Endometrial Stromal Cell line (HESC) were decidualized by VIP we observed an increased expression of ATF6α, an ER stress-sensor, and UPR markers, associated with an increase in IL-1β production. Moreover, AEBSF (ATF6α -inhibitor pathway) prevented this effect and decreased the expansion index in the in vitro model of implantation. VIP-decidualized cells also favor angiogenesis accompanied by a strong downregulation in thrombospondin-1. Finally, ATF6α, VIP and VPAC2-receptor expression were reduced in endometrial biopsies from women with recurrent implantation failures in comparison with fertile. In conclusion, VIP privileged ATF6α-pathway associated with a sterile inflammatory response and angiogenesis that might condition endometrial receptivity.

ALA protects against ERS-mediated apoptosis in a cochlear cell model with low citrate synthase expression

A/J mouse is a model of age-related hearing loss (AHL). Mutation in the citrate synthase (Cs) gene of the mouse plays an important role in the hearing loss and degeneration of cochlear cells. To investigate the pathogenesis of cochlear cell damage in A/J mice resulted from Cs mutation, we downregulated the expression level of CS in HEI-OC1, a cell line of mouse cochlea, by shRNA. The results showed that low CS expression led to low ability of cell proliferation. Further study revealed an increase level of reactive oxygen species (ROS), activation of ATF6 mediated endoplasmic reticulum stress (ERS) and high expression levels of caspase12 and Bax in the cells. Moreover, the AEBSF, an ATF6 inhibitor, could reduce the expression levels of caspase-12 and Bax by inhibiting the hydrolysis of ATF6 in the cells. Finally, antioxidant alpha-lipoic acid (ALA) reduced the ROS levels and the apoptotic signals in the cell model with low CS expression. We therefore conclude that the ERS mediated apoptosis, which is triggered by ROS, may be involved in the cell degeneration in the cochleae of A/J mice.

Establishment and validation of an endoplasmic reticulum stress reporter to monitor zebrafish ATF6 activity in development and disease

Induction of endoplasmic reticulum (ER) stress is associated with diverse developmental and degenerative diseases. Modified ER homeostasis causes activation of conserved stress pathways at the ER called the unfolded protein response (UPR). ATF6 is a transcription factor activated during ER stress as part of a coordinated UPR. ATF6 resides at the ER and, upon activation, is transported to the Golgi apparatus, where it is cleaved by proteases to create an amino-terminal cytoplasmic fragment (ATF6f). ATF6f translocates to the nucleus to activate transcriptional targets. Here, we describe the establishment and validation of zebrafish reporter lines for ATF6 activity. These transgenic lines are based on a defined and multimerized ATF6 consensus site, which drives either eGFP or destabilized eGFP, enabling dynamic study of ATF6 activity during development and disease. The results show that the reporter is specific for the ATF6 pathway, active during development and induced in disease models known to engage UPR. Specifically, during development, ATF6 activity is highest in the lens, skeletal muscle, fins and gills. The reporter is also activated by common chemical inducers of ER stress, including tunicamycin, thapsigargin and brefeldin A, as well as by heat shock. In models for amyotrophic lateral sclerosis and cone dystrophy, ATF6 reporter expression is induced in spinal cord interneurons or photoreceptors, respectively, suggesting a role for ATF6 response in multiple neurodegenerative diseases. Collectively our results show that these ATF6 reporters can be used to monitor ATF6 activity changes throughout development and in zebrafish models of disease.

This article has an associated First Person interview with the first author of the paper.

Summary: In this study, we validate transgenic zebrafish generated to specifically report the activity of ATF6, representing a major branch of the endoplasmic reticulum stress pathway with functions in development and disease.

Endoplasmic reticulum stress is involved in lipopolysaccharide-induced inflammatory response and apoptosis in goat endometrial stromal cells

Endoplasmic reticulum (ER) stress is involved in regulating cell metabolism, apoptosis, autophagy, and survival. However, there is not enough information about the role of ER stress in lipopolysaccharide (LPS)-induced apoptosis and inflammatory cytokine secretion in the uterus. In this study, we found that LPS induced apoptosis and inflammation in goat endometrial stromal cells (ESCs). LPS treatment inhibited cell viability and cell proliferation. In addition, the genes associated with proliferation, such as proliferating cell nuclear antigen and MKI67, were affected by LPS treatment. Moreover, LPS increased the secretion of interleukin (IL)-1β and IL-8, promoting the levels of MYD88, caspase1, and TRL4. The 4-phenylbutyric acid pretreatment inhibited the expression of unfolded protein response proteins and the secretion of inflammatory cytokines in LPS-treated cells. However, blockage of inositol-requiring enzyme 1 and activating transcription factor 6 did not significantly reduce apoptosis and inflammatory cytokine secretion. Collectively, ER stress involved in LPS-induced apoptosis and inflammatory cytokine increased in goat ESCs. This study provides new insight into the function of ER stress in the pathological process.

A lifetime of stress: ATF6 in development and homeostasis

BACKGROUND

Activating transcription factor 6 (ATF6) is an endoplasmic reticulum (ER)-localised protein and member of the leucine zipper family of transcription factors. Best known for its role in transducing signals linked to stress to the endoplasmic reticulum, the 50 kDa activated form of ATF6 is now emerging as a major regulator of organogenesis and tissue homeostasis. Responsible for the correct folding, secretion and membrane insertion of a third of the proteome in eukaryotic cells, the ER encompasses a dynamic, labyrinthine network of regulators, chaperones, foldases and cofactors. Such structures are crucial to the extensive protein synthesis required to undergo normal development and maintenance of tissue homeostasis. When an additional protein synthesis burden is placed on the ER, ATF6, in tandem with ER stress transducers inositol requiring enzyme 1 (IRE1) and PKR-like endoplasmic reticulum kinase (PERK), slows the pace of protein translation and induces the production of stress-reducing chaperones and foldases.

MAIN TEXT

In the context of development and tissue homeostasis, however, distinct cellular impacts have been attributed to ATF6. Drawing on data published from human, rodent, fish, goat and bovine research, this review first focuses on ATF6-mediated regulation of osteo- and chondrogenesis, ocular development as well as neuro- and myelinogenesis. The purported role of ATF6 in development of the muscular and reproductive systems as well as adipo- and lipogenesis is then described. With relevance to cardiac disease, cancer and brain disorders, the importance of ATF6 in maintaining tissue homeostasis is the subject of the final section.

CONCLUSION

In conclusion, the review encourages further elucidation of ATF6 regulatory operations during organogenesis and tissue homeostasis, to spawn the development of ATF6-targeted therapeutic strategies.