Dehydroascorbic acid-induced endoplasmic reticulum stress and leptin resistance in neuronal cells

Stress granules inhibit endoplasmic reticulum stress-mediated apoptosis during hypoxia-induced injury in acute liver failure

BACKGROUND

Stress granules (SGs) could be formed under different stimulation to inhibit cell injury.

AIM

To investigate whether SGs could protect hepatocytes from hypoxia-induced damage during acute liver failure (ALF) by reducing endoplasmic reticulum stress (ERS) mediated apoptosis.

METHODS

The agonist of SGs, arsenite (Ars) was used to intervene hypoxia-induced hepatocyte injury cellular model and ALF mice models. Further, the siRNA of activating transcription factor 4 (ATF4) and SGs inhibitor anisomycin was then used to intervene in cell models.

RESULTS

With the increase of hypoxia time from 4 h to 12 h, the levels of HIF-1α, ERS and apoptosis gradually increased, and the expression of SGs marker G3BP1 and TIA-1 was increased and then decreased. Compared with the hypoxia cell model group and ALF mice model, the levels of HIF-1α, apoptosis and ERS were increased in the Ars intervention group. After siRNA-ATF4 intervention, the level of SGs in cells increased, and the levels of HIF-1α, ERS and apoptosis decreased. Compared with the siRNA-ATF4 group, the levels of G3BP1 in the siRNA-ATF4+anisomycin group were decreased, and the levels of HIF-1α, ERS and apoptosis were increased. Moreover, compared with the ALF group, the degree of liver injury and liver function, the levels of HIF-1α, ERS and apoptosis in the Ars intervention group were decreased, the level of SGs was increased.

CONCLUSION

SGs could protect hepatocytes from hypoxia-induced damage during ALF by reducing ERS-mediated apoptosis.

SVCT2 Overexpression and Ascorbic Acid Uptake Increase Cortical Neuron Differentiation, Which Is Dependent on Vitamin C Recycling between Neurons and Astrocytes

During brain development, sodium–vitamin C transporter (SVCT2) has been detected primarily in radial glial cells in situ, with low-to-absent expression in cerebral cortex neuroblasts. However, strong SVCT2 expression is observed during the first postnatal days, resulting in increased intracellular concentration of vitamin C. Hippocampal neurons isolated from SVCT2 knockout mice showed shorter neurites and low clustering of glutamate receptors. Other studies have shown that vitamin C-deprived guinea pigs have reduced spatial memory, suggesting that ascorbic acid (AA) and SVCT2 have important roles in postnatal neuronal differentiation and neurite formation. In this study, SVCT2 lentiviral overexpression induced branching and increased synaptic proteins expression in primary cultures of cortical neurons. Analysis in neuroblastoma 2a (Neuro2a) and human subventricular tumor C3 (HSVT-C3) cells showed similar branching results. SVCT2 was mainly observed in the cell membrane and endoplasmic reticulum; however, it was not detected in the mitochondria. Cellular branching in neuronal cells and in a previously standardized neurosphere assay is dependent on the recycling of vitamin C or reduction in dehydroascorbic acid (DHA, produced by neurons) by glial cells. The effect of WZB117, a selective glucose/DHA transporter 1 (GLUT1) inhibitor expressed in glial cells, was also studied. By inhibiting GLUT1 glial cells, a loss of branching is observed in vitro, which is reproduced in the cerebral cortex in situ. We concluded that vitamin C recycling between neurons and astrocyte-like cells is fundamental to maintain neuronal differentiation in vitro and in vivo. The recycling activity begins at the cerebral postnatal cortex when neurons increase SVCT2 expression and concomitantly, GLUT1 is expressed in glial cells.

Redox and Inflammatory Signaling, the Unfolded Protein Response, and the Pathogenesis of Pulmonary Hypertension

Protein folding overload and oxidative stress disrupt endoplasmic reticulum (ER) homeostasis, generating reactive oxygen species (ROS) and activating the unfolded protein response (UPR). The altered ER redox state induces further ROS production through UPR signaling that balances the cell fates of survival and apoptosis, contributing to pulmonary microvascular inflammation and dysfunction and driving the development of pulmonary hypertension (PH). UPR-induced ROS production through ER calcium release along with NADPH oxidase activity results in endothelial injury and smooth muscle cell (SMC) proliferation. ROS and calcium signaling also promote endothelial nitric oxide (NO) synthase (eNOS) uncoupling, decreasing NO production and increasing vascular resistance through persistent vasoconstriction and SMC proliferation. C/EBP-homologous protein further inhibits eNOS, interfering with endothelial function. UPR-induced NF-κB activity regulates inflammatory processes in lung tissue and contributes to pulmonary vascular remodeling. Conversely, UPR-activated nuclear factor erythroid 2-related factor 2-mediated antioxidant signaling through heme oxygenase 1 attenuates inflammatory cytokine levels and protects against vascular SMC proliferation. A mutation in the bone morphogenic protein type 2 receptor (BMPR2) gene causes misfolded BMPR2 protein accumulation in the ER, implicating the UPR in familial pulmonary arterial hypertension pathogenesis. Altogether, there is substantial evidence that redox and inflammatory signaling associated with UPR activation is critical in PH pathogenesis.

Neurobiology of vitamin C: Expanding the focus from antioxidant to endogenous neuromodulator

Ascorbic acid (AA) is a water-soluble vitamin (C) found in all bodily organs. Most mammals synthesize it, humans are required to eat it, but all mammals need it for healthy functioning. AA reaches its highest concentration in the brain where both neurons and glia rely on tightly regulated uptake from blood via the glucose transport system and sodium-coupled active transport to accumulate and maintain AA at millimolar levels. As a prototype antioxidant, AA is not only neuroprotective, but also functions as a cofactor in redox-coupled reactions essential for the synthesis of neurotransmitters (e.g., dopamine and norepinephrine) and paracrine lipid mediators (e.g., epoxiecoisatrienoic acids) as well as the epigenetic regulation of DNA. Although redox capacity led to the promotion of AA in high doses as potential treatment for various neuropathological and psychiatric conditions, ample evidence has not supported this therapeutic strategy. Here, we focus on some long-neglected aspects of AA neurobiology, including its modulatory role in synaptic transmission as demonstrated by the long-established link between release of endogenous AA in brain extracellular fluid and the clearance of glutamate, an excitatory amino acid. Evidence that this link can be disrupted in animal models of Huntington´s disease is revealing opportunities for new research pathways and therapeutic applications (e.g., epilepsy and pain management). In fact, we suggest that improved understanding of the regulation of endogenous AA and its interaction with key brain neurotransmitter systems, rather than administration of AA in excess, should be the target of future brain-based therapies.

Chemical Similarity Enrichment Analysis (ChemRICH) as alternative to biochemical pathway mapping for metabolomic datasets

Metabolomics answers a fundamental question in biology: How does metabolism respond to genetic, environmental or phenotypic perturbations? Combining several metabolomics assays can yield datasets for more than 800 structurally identified metabolites. However, biological interpretations of metabolic regulation in these datasets are hindered by inherent limits of pathway enrichment statistics. We have developed ChemRICH, a statistical enrichment approach that is based on chemical similarity rather than sparse biochemical knowledge annotations. ChemRICH utilizes structure similarity and chemical ontologies to map all known metabolites and name metabolic modules. Unlike pathway mapping, this strategy yields study-specific, non-overlapping sets of all identified metabolites. Subsequent enrichment statistics is superior to pathway enrichments because ChemRICH sets have a self-contained size where p-values do not rely on the size of a background database. We demonstrate ChemRICH’s efficiency on a public metabolomics data set discerning the development of type 1 diabetes in a non-obese diabetic mouse model. ChemRICH is available at www.chemrich.fiehnlab.ucdavis.edu