UVB-induced eIF2α phosphorylation in keratinocytes depends on decreased ATF4, GADD34 and CReP expression levels

ATF4 regulates mitochondrial dysfunction, mitophagy, and autophagy, contributing to corneal endothelial apoptosis under chronic ER stress in Fuchs' dystrophy

Purpose

Endoplasmic reticulum (ER) stress, mitochondrial dysfunction, mitophagy/autophagy are known to contribute independently to corneal endothelial (CE) apoptosis in Fuchs' endothelial corneal dystrophy (FECD). However, the role of a well-studied specific ER stress pathway (PERK-ATF4-CHOP) in regulating mitochondrial dysfunction, mitophagy/autophagy, and apoptosis is unknown. The purpose of this study is to explore the role of ATF4 in regulating mitochondrial dysfunction and mitophagy/autophagy, leading to CEnC apoptosis in FECD.

Methods

Human corneal endothelial cell line (HCEnC-21T), Fuchs' corneal endothelial cell line (F35T), and primary human corneal endothelial cells were treated with ER stressor tunicamycin (0.01, 0.1, 1, 10 μg/mL) for 24 and/or 48 hours. ATF4 siRNA was used to knock down ATF4 in 21T cell line and primary corneal endothelial cells. Cell viability was measured using an MTT assay (10 μg/mL tunicamycin for 24 hours). Mitochondrial bioenergetics was analyzed by measuring mitochondria membrane potential (MMP) loss using TMRE assay and ATP production using mitochondrial complex V assay kit at 48 hours post tunicamycin. Mitochondrial-mediated intrinsic apoptotic pathway proteins, mitophagy, and autophagy marker proteins were analyzed using Western blotting (10 μg/mL tunicamycin for 24 hours). ATF4 +/- and ATF4 +/+ mice were irradiated with UVA to assess pro-apoptotic ER stress and corneal endothelial cell death in vivo .

Results

F35T cell line had a significantly increased expression of ER stress pathway molecules (eIF2α, ATF4, CHOP) and mitochondrial-mediated intrinsic apoptotic molecules (cleaved PARP, caspase 9, caspase 3) along with mitochondrial fragmentation compared to 21T cells at the baseline, which further increased after treatment with tunicamycin. Mitochondrial membrane potential also significantly decreased in F35T compared to 21T after tunicamycin. ATF4 knockdown after tunicamycin significantly attenuated pro-apoptotic ER and mitochondrial stress molecules, rescued MMP loss, and reduced mitochondrial fragmentation in the 21T cell line and primary corneal endothelial cells. ATF4 knockdown post tunicamycin treatment also downregulated altered/excessive Parkin-mediated mitophagy and Akt/mTOR-mediated autophagy pathway with reduction of caspases, leading to increased cellular viability. ATF4+/-mice had significantly increased CE numbers with improved cellular morphology and decreased CHOP expression compared to ATF4+/+ post-UVA.

Conclusions

Pro-apoptotic ATF4 induction under tunicamycin-induced ER stress disrupts mitochondrial bioenergetics and dynamics, leading to activation of excessive autophagy/mitophagy. ATF4-induced activation of CHOP plays a key role in switching excessive autophagy to CEnC apoptosis. This study highlights the importance of ATF4 in ER-mitochondrial crosstalk and its contribution to CEnC apoptosis in FECD.

Lysine demethylase KDM3A alleviates hyperoxia-induced bronchopulmonary dysplasia in mice by promoting ETS1 expression

Bronchopulmonary dysplasia (BPD) is the most common chronic lung disease among neonates, with increasing morbidity and mortality. This study aims to investigate the effect and mechanism of lysine demethylase 3A (KDM3A) on hyperoxia-induced BPD. Hyperoxia-induced BPD mouse and alveolar epithelial cell models were constructed. The effects of hyperoxia on lung development were evaluated by histological and morphological analysis. The levels of KDM3A, E26 transformation specific-1 (ETS1), H3 lysine 9 dimethylation (H3K9me2), and endoplasmic reticulum (ER) stress-related indexes were quantified by RT-qPCR, Western blot, and IF staining. Cell apoptosis was assessed by flow cytometry and TUNEL staining. Transfection of oe-ETS1, oe-KDM3A, and sh-ETS1 was applied in hyperoxia-induced alveolar epithelial cells to explore the mechanism of the KDM3A/ETS1 axis in hyperoxia-induced apoptosis. KDM3A inhibitor IOX1 was applied to validate the in vivo effect of KDM3A in hyperoxia-induced BPD mice. The results displayed that hyperoxia-induced BPD mice showed reduced body weight, severe destruction of alveolar structure, decreased radial alveolar count (RAC), and increased mean linear intercept (MLI) and mean alveolar diameter (MAD). Further, hyperoxia induction down-regulated ETS1 expression, raised ER stress levels, and increased apoptosis rate in BPD mice and alveolar epithelial cells. However, transfection of oe-ETS1 improved the above changes in hyperoxia-induced alveolar epithelial cells. Moreover, transfection of oe-KDM3A up-regulated ETS1 expression, down-regulated H3K9me2 expression, inhibited ER stress, and reduced apoptosis rate in hyperoxia-induced alveolar epithelial cells. In addition, transfection of sh-ETS1 reversed the inhibitory effect of KDM3A on hyperoxia-induced apoptosis by regulating ER stress. In vivo experiments, KDM3A inhibitor IOX1 intervention further aggravated BPD in newborn mice. In a word, KDM3A alleviated hyperoxia-induced BPD in mice by promoting ETS1 expression.

Endoplasmic reticulum stress participates in apoptosis of HeLa cells exposed to TPHP and OH-TPHP via the eIF2α-ATF4/ATF3-CHOP-DR5/P53 signaling pathway

Purpose

Triphenyl phosphate (TPHP) is a widely used organophosphate flame retardant, which can be transformed in vivo into diphenyl phosphate (DPHP) and 4-hydroxyphenyl phosphate (diphenyl) ester (OH-TPHP) through biotransformation process. Accumulation of TPHP and its derivatives in biological tissues makes it necessary to investigate their toxicity and molecular mechanism.

Methods

The present study evaluated the cellular effects of TPHP, DPHP, and OH-TPHP on cell survival, cell membrane damage, oxidative damage, and cell apoptosis using HeLa cells as in vitro model. RNA sequencing and bioinformatics analysis were conducted to monitor the differently expressed genes, and then RT-qPCR and Western bolt were used to identify potential molecular mechanisms and key hub genes.

Results

Results showed that OH-TPHP had the most significant cytotoxic effect in HeLa cells, followed by TPHP; and no significant cytotoxic effects were observed for DPHP exposure within the experimental concentrations. Biological function enrichment analysis suggested that TPHP and OH-TPHP exposure may induce endoplasmic reticulum stress (ERS) and cell apoptosis. The nodes filtering revealed that ERS and apoptosis related genes were involved in biological effects induced by TPHP and OH-TPHP, which may be mediated through the eukaryotic translation initiation factor 2α/activating transcription factor 4 (ATF4)/ATF3- CCAAT/ enhancer-binding protein homologous protein (CHOP) cascade pathway and death receptor 5 (DR5) /P53 signaling axis.

Conclusion

Above all, these findings indicated that ERS-mediated apoptosis might be one of potential mechanisms for cytotoxicity of TPHP and OH-TPHP.

Ultraviolet Light, Unfolded Protein Response and Autophagy†

The endoplasmic reticulum (ER) plays an important role in the regulation of protein synthesis. Alterations in the folding capacity of the ER induce stress, which activates three ER sensors that mediate the unfolded protein response (UPR). Components of the pathways regulated by these sensors have been shown to regulate autophagy. The last corresponds to a mechanism of self-eating and recycling important for proper cell maintenance. Ultraviolet radiation (UV) is an external damaging stimulus that is known for inducing oxidative stress, and DNA, lipid and protein damage. Many controversies exist regarding the role of UV-inducing ER stress or autophagy. However, a connection between the three of them has not been addressed. In this review, we will discuss the contradictory theories regarding the relationships between UV radiation with the induction of ER stress and autophagy, as well as hypothetic connections between UV, ER stress and autophagy.

Characterization of UVB and UVA-340 Lamps and Determination of Their Effects on ER Stress and DNA Damage

Ultraviolet B-light (UVB) has been often used as a "physiological" UV in photobiology studies. How representative and equivalent these studies are compared to the effect of the sunlight is always of great interest. We now characterized the spectrum and intensity of two commonly used UV sources, a UVB lamp and a UVA-340 lamp which simulate the solar spectrum in the UVB/UVA range in the presence or absence of a UVB band pass filter that reduces >80% UVA from the UVA-340 lamp. The spectrum of each lamp was used in computational modeling for skin penetration. The effects of the lamps on endoplasmic reticulum (ER)-stress response and DNA damage in cultured keratinocytes HaCaT cells were analyzed. Our data show that the UVB lamp is a better inducer for both eIF2α phosphorylation and PERK modification, as well as a better reducer of ATF6 expression. The UVB lamp is also the best inducer of gamma-H2AX expression and cyclobutane pyrimidine dimers formation. However, the UVA-340 lamp is a better inducer for ATF4 expression. Our results indicate that different spectral characteristics of UV lamps can produce different results for the activation of the ER-stress responses and the differences do not always follow a defined pattern.