Neuroprotective Effect of 4-Phenylbutyric Acid against Photo-Stress in the Retina

Sustained feeding of a diet high in fat resulted in a decline in the liver's insulin-degrading enzyme levels in association with the induction of oxidative and endoplasmic reticulum stress in adult male rats: Evaluation of 4-phenylbutyric acid

The current study explored the impact of high fat diet (HFD) on hepatic oxidative and endoplasmic reticulum (ER) stress and its insulin degrading enzyme (IDE) content with the injection of 4-phenyl butyric acid (4-PBA) in adult male rats. Following the weaning period, male offspring were distributed among six distinct groups. The corresponding diet was used for 20 weeks, subsequently 4-PBA was administered for three consecutive days. Plasma glucose and insulin levels, HOMA-β (homeostasis model assessment of β-cell), hepatic ER and oxidative stress biomarkers and IDE protein content were assessed. Long-term ingestion of HFD (31 % cow butter) induced oxidative and ER stress in the liver tissue. Accordingly, a rise in the malondialdehyde (MDA) content and catalase enzyme activity and a decrease in the glutathione (GSH) content were detected within the liver of the HFD and HFD + DMSO groups. Consumption of this diet elevated the liver expression of binding immunoglobulin protein (BIP) and C/enhancer-binding protein homologous protein (CHOP) levels while reduced its IDE content. The HOMA-β decreased significantly. The injection of the 4-PBA moderated all the induced changes. Findings from this study indicated that prolonged HFD consumption led to a reduction in plasma insulin levels, likely attributed to pancreatic β cell malfunction, as evidenced by a decline in the HOMA-β index. Also, the HFD appears to have triggered oxidative and ER stress in the liver, along with a decrease in its IDE content.

Can endoplasmic reticulum stress observed in the PTZ-kindling model seizures be prevented with TUDCA and 4-PBA?

Epilepsy is a chronic neurological disease with recurrent seizures. Increasing evidence suggests that endoplasmic reticulum (ER) stress may play a role in the pathogenesis of epilepsy. We aimed to investigate the effects of Tauroursodeoxycholic acid (TUDCA) and 4-phenyl-butyric acid (4-PBA), which are known to suppress ER stress, on developed seizures in terms of markers of ER stress, oxidative stress, and apoptosis. The pentylenetetrazole (PTZ) kindling model was induced in Wistar albino rats (n = 48) by administering 35 mg/kg PTZ intraperitoneally (I.P.) every other day for 1 month. TUDCA and 4-PBA were administered via I.P. at a dose of 500 mg/kg dose. ER stress, apoptosis, and oxidative stress were determined in the hippocampus tissues of animals in all groups. Immunohistochemistry, qRT-PCR, ELISA, and Western Blot analyzes were performed to determine the efficacy of treatments. Expressions of ATF4, ATF6, p-JNK1/2, Cleaved-Kaspase3, and Caspase12 significantly increased in PTZ-kindled seizures compared to the control group. Increased NOX2 and MDA activity in the seizures were measured. In addition, stereology analyzes showed an increased neuronal loss in the PTZ-kindled group. qRT-PCR examination showed relative mRNA levels of CHOP. Accordingly, TUDCA and 4-PBA treatment suppressed the expressions of ATF4, ATF6, Cleaved-Caspase3, Kaspase12, NOX2, MDA, and CHOP in TUDCA + PTZ and 4-PBA + PTZ groups. ER stress-induced oxidative stress and apoptosis by reducing neuronal loss and degeneration were also preserved in these groups. Our data show molecularly that TUDCA and 4-PBA treatment can suppress the ER stress process in epileptic seizures.

Endoplasmic Reticulum Stress Disrupts Mitochondrial Bioenergetics, Dynamics and Causes Corneal Endothelial Cell Apoptosis

Purpose

Endoplasmic reticulum (ER) and mitochondrial stress are independently associated with corneal endothelial cell (CEnC) loss in many corneal diseases, including Fuchs' endothelial corneal dystrophy (FECD). However, the role of ER stress in mitochondrial dysfunction contributing to CEnC apoptosis is unknown. The purpose of this study is to explore the crosstalk between ER and mitochondrial stress in CEnC.

Methods

Human corneal endothelial cell line (HCEnC-21T) and human corneal endothelial tissues were treated with ER stressor tunicamycin. ER stress-reducing chemical 4-phenyl butyric acid (4-PBA) was used in HCEnC-21T after tunicamycin. Fuchs' corneal endothelial cell line (F35T) was used to determine differential activation of ER stress with respect to HCEnC-21T at the baseline. ER stress, mitochondrial-mediated intrinsic apoptotic, mitochondrial fission, and fusion proteins were determined using immunoblotting and immunohistochemistry. Mitochondrial bioenergetics were assessed by mitochondrial membrane potential (MMP) loss and ATP production at 48 hours after tunicamycin. Mitochondria dynamics (shape, area, perimeter) were also analyzed at 24 hours using transmission electron microscopy.

Results

Treatment of HCEnC-21T cell line with tunicamycin activated three ER stress pathways (PERK-eIF2α-CHOP, IRE1α-XBP1, and ATF6), reduced cell viability, upregulated mitochondrial-mediated intrinsic apoptotic molecules (cleaved caspase 9, caspase 3, PARP, Bax, cytochrome C), downregulated anti-apoptotic Bcl-2 protein, initiated mitochondrial dysfunction by loss of MMP and lowering of ATP production, and caused mitochondrial swelling and fragmentation with increased expression of mitochondrial fission proteins (Fis1 and p-Drp1). Fuchs' CEnC (F35T) cell line also showed activation of the ER stress-related proteins (p-eIF2α, GRP78, CHOP, XBP1) compared to HCEnC-21T at the baseline. The 4-PBA ameliorated cell loss and reduced cleaved caspase 3 and 9, thereby rescuing tunicamycin-induced cell death but not mitochondrial bioenergetics in HCEnC-21T cell line.

Conclusions

Tunicamycin-induced ER stress disrupts mitochondrial bioenegetics, dynamics and contributes to the loss of CEnC viability. This novel study highlights the importance of ER-mitochondria crosstalk and its contribution to CEnCs apoptosis, seen in many corneal diseases, including FECD.

4-PBA Attenuates Fat Accumulation in Cultured Spotted Seabass Fed High-Fat-Diet via Regulating Endoplasmic Reticulum Stress

Excessive fat accumulation is a common phenomenon in cultured fish, which can cause metabolic disease such as fatty liver. However, the relative regulatory approach remains to be explored. Based on this, two feeding trials were conducted. Firstly, fish were fed either a normal-fat diet (NFD) or a high-fat diet (HFD) for eight weeks and sampled at the 2nd, 4th, 6th, and 8th week after feeding (Experiment I). In the first four weeks, fish fed an HFD grew faster than those fed an NFD. Conversely, the body weight and weight gain were higher in the NFD group at the 6th and 8th weeks. Under light and transmission electron microscopes, fat accumulation of the liver was accompanied by an obvious endoplasmic reticulum (ER) swell. Accordingly, the expressions of atf-6, ire-1, perk, eif-2α, atf-4, grp78, and chop showed that ER stress was activated at the 6th and 8th weeks. In Experiment II, 50 mg/kg 4-PBA (an ERs inhibitor) was supplemented to an HFD; this was named the 4-PBA group. Then, fish was fed with an NFD, an HFD, and a 4-PBA diet for eight weeks. As the result, the excessive fat deposition caused by an HFD was reversed by 4-PBA. The expression of ER stress-related proteins CHOP and GRP78 was down-regulated by 4-PBA, and the transmission electron microscope images also showed that 4-PBA alleviated ER stress induced by the feeding of an HFD. Furthermore, 4-PBA administration down-regulated SREBP-1C/ACC/FAS, the critical pathways of fat synthesis. In conclusion, the results confirmed that ER stress plays a contributor role in the fat deposition by activating the SREBP-1C/ACC/FAS pathway. 4-PBA as an ER stress inhibitor could reduce fat deposition caused by an HFD via regulating ER stress.

Interleukin-10 Protects against Ureteral Obstruction-Induced Kidney Fibrosis by Suppressing Endoplasmic Reticulum Stress and Apoptosis

Fibrosis is a common final pathway of chronic kidney disease, which is a major incurable disease. Although fibrosis has an irreversible pathophysiology, the molecular and cellular mechanisms responsible remain unclear and no specific treatment is available to halt the progress of renal fibrosis. Thus, an improved understanding of the cellular mechanism involved and a novel therapeutic approach are urgently required for end-stage renal disease (ESRD). We investigated the role played by interleukin-10 (IL-10, a potent anti-inflammatory cytokine) in kidney fibrosis and the mechanisms involved using IL-10^−/− mice and TCMK-1 cells (mouse kidney tubular epithelial cell line). Endoplasmic reticulum stress (ERS), apoptosis, and fibrosis in IL-10^−/− mice were more severe than in IL-10^+/+ mice after unilateral ureteral obstruction (UUO). The 4-Phenylbutyrate (an ERS inhibitor) treatment induced dramatic reductions in ERS, apoptosis, and fibrosis-associated factors in the renal tissues of IL-10^−/− mice, compared to wild-type controls after UUO. On the other hand, in cultured TCMK-1 cells, the ERS inducers (tunicamycin, thapsigargin, or brefeldin A) enhanced the expressions of proapoptotic and profibrotic factors, though these effects were mitigated by IL-10. These results were supported by the observation that IL-10 siRNA transfection aggravated tunicamycin-induced CHOP and a-SMA expressions in TCMK-1 cells. We conclude that the anti-fibrotic effects of IL-10 were attributable to the inhibition of ERS-mediated apoptosis and believe that the results of this study improve the understanding of the cellular mechanism responsible for fibrosis and aid in the development of novel therapeutic approaches.

Endoplasmic Reticulum Stress, Oxidative Stress, and Rheumatic Diseases

Background: The endoplasmic reticulum (ER) is a multi-functional organelle responsible for cellular homeostasis, protein synthesis, folding and secretion. It has been increasingly recognized that the loss of ER homeostasis plays a central role in the development of autoimmune inflammatory disorders, such as rheumatic diseases. Purpose/Main contents: Here, we review current knowledge of the contribution of ER stress to the pathogenesis of rheumatic diseases, with a focus on rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE). We also review the interplay between protein folding and formation of reactive oxygen species (ROS), where ER stress induces oxidative stress (OS), which further aggravates the accumulation of misfolded proteins and oxidation, in a vicious cycle. Intervention studies targeting ER stress and oxidative stress in the context of rheumatic diseases are also reviewed. Conclusions: Loss of ER homeostasis is a significant factor in the pathogeneses of RA and SLE. Targeting ER stress, unfolded protein response (UPR) pathways and oxidative stress in these diseases both in vitro and in animal models have shown promising results and deserve further investigation.

Inherited Retinal Dystrophies: Role of Oxidative Stress and Inflammation in Their Physiopathology and Therapeutic Implications

Inherited retinal dystrophies (IRDs) are a large group of genetically and clinically heterogeneous diseases characterized by the progressive degeneration of the retina, ultimately leading to loss of visual function. Oxidative stress and inflammation play fundamental roles in the physiopathology of these diseases. Photoreceptor cell death induces an inflammatory state in the retina. The activation of several molecular pathways triggers different cellular responses to injury, including the activation of microglia to eliminate debris and recruit inflammatory cells from circulation. Therapeutical options for IRDs are currently limited, although a small number of patients have been successfully treated by gene therapy. Many other therapeutic strategies are being pursued to mitigate the deleterious effects of IRDs associated with oxidative metabolism and/or inflammation, including inhibiting reactive oxygen species’ accumulation and inflammatory responses, and blocking autophagy. Several compounds are being tested in clinical trials, generating great expectations for their implementation. The present review discusses the main death mechanisms that occur in IRDs and the latest therapies that are under investigation.

Effects of Epigenetic Modification of PGC-1α by a Chemical Chaperon on Mitochondria Biogenesis and Visual Function in Retinitis Pigmentosa

Retinitis pigmentosa (RP) is a hereditary blinding disease characterized by gradual photoreceptor death, which lacks a definitive treatment. Here, we demonstrated the effect of 4-phenylbutyric acid (PBA), a chemical chaperon that can suppress endoplasmic reticulum (ER) stress, in P23H mutant rhodopsin knock-in RP models. In the RP models, constant PBA treatment led to the retention of a greater number of photoreceptors, preserving the inner segment (IS), a mitochondrial- and ER-rich part of the photoreceptors. Electroretinography showed that PBA treatment preserved photoreceptor function. At the early point, ER-associated degradation markers, xbp1s, vcp, and derl1, mitochondrial kinetic-related markers, fis1, lc3, and mfn1 and mfn2, as well as key mitochondrial regulators, pgc-1α and tfam, were upregulated in the retina of the models treated with PBA. In vitro analyses showed that PBA upregulated pgc-1α and tfam transcription, leading to an increase in the mitochondrial membrane potential, cytochrome c oxidase activity, and ATP levels. Histone acetylation of the PGC-1α promoter was increased by PBA, indicating that PBA affected the mitochondrial condition through epigenetic changes. Our findings constituted proof of concept for the treatment of ER stress-related RP using PBA and revealed PBA’s neuroprotective effects, paving the way for its future clinical application.

Inhibition of endoplasmic reticulum stress by 4-phenylbutyrate alleviates retinal inflammation and the apoptosis of retinal ganglion cells after ocular alkali burn in mice

OBJECTIVE

Retinal ganglion cell (RGC) apoptosis is one of the most severe complications that causes permanent visual impairment following ocular alkali burn (OAB). Currently, very few treatment options exist for this condition. This study was conducted to determine the effect of 4-phenylbutyric acid (4-PBA) on endoplasmic reticulum (ER) stress after OAB using a well-established OAB mouse model.

METHODS

Ocular alkali burn was induced in C57BL/6 mouse corneas using 1 M NaOH. 4-PBA (10 mg/kg; 250 μL per injection) or saline (250 μL per injection) was injected intraperitoneally once per day for 3 days before the establishment of the OAB model. The apoptosis of retinal ganglion cells (RGCs) was assessed by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay, and the histological damage was examined by hematoxylin and eosin and immunofluorescence assay on retinal flat mounts. The key inflammatory response and the expression of ER stress-related markers in the retinal tissues were assessed by real-time PCR, western blotting and histologic analyses.

RESULTS

4-PBA significantly alleviated the apoptosis of RGCs and prevented the structural damage of the retina, as determined by the evaluation of RGC density and retinal thickness. Inhibition of ER stress by 4-PBA decreased the expression of vital proinflammatory cytokines, tumor necrosis factor alpha, and interleukin-1 beta; and suppressed the activation of retinal microglial cells and nuclear factor-kappa B (NF-κB). 4-PBA reduced the expression of the ER stress molecules, glucose-regulated protein 78, activated transcription factor 6, inositol-requiring enzyme-1 (IRE1), X-box-binding protein 1 splicing, and CCAAT/enhancer-binding protein homologous protein, in the retinal tissues and RGCs of OAB mice.

CONCLUSIONS

The present study demonstrated that the inhibition of ER stress by 4-PBA alleviates the inflammatory response via the IRE1/NF-κB signaling pathway and protects the retina and RGCs from injury in an OAB mouse model. Such findings further suggest that 4-PBA might have potential therapeutic implications for OAB treatment.