Over-expression of GRP75 inhibits liver injury induced by oxidative damage

Mitochondrial heterogeneity in diseases

As key organelles involved in cellular metabolism, mitochondria frequently undergo adaptive changes in morphology, components and functions in response to various environmental stresses and cellular demands. Previous studies of mitochondria research have gradually evolved, from focusing on morphological change analysis to systematic multiomics, thereby revealing the mitochondrial variation between cells or within the mitochondrial population within a single cell. The phenomenon of mitochondrial variation features is defined as mitochondrial heterogeneity. Moreover, mitochondrial heterogeneity has been reported to influence a variety of physiological processes, including tissue homeostasis, tissue repair, immunoregulation, and tumor progression. Here, we comprehensively review the mitochondrial heterogeneity in different tissues under pathological states, involving variant features of mitochondrial DNA, RNA, protein and lipid components. Then, the mechanisms that contribute to mitochondrial heterogeneity are also summarized, such as the mutation of the mitochondrial genome and the import of mitochondrial proteins that result in the heterogeneity of mitochondrial DNA and protein components. Additionally, multiple perspectives are investigated to better comprehend the mysteries of mitochondrial heterogeneity between cells. Finally, we summarize the prospective mitochondrial heterogeneity-targeting therapies in terms of alleviating mitochondrial oxidative damage, reducing mitochondrial carbon stress and enhancing mitochondrial biogenesis to relieve various pathological conditions. The possibility of recent technological advances in targeted mitochondrial gene editing is also discussed.

Hepatic heat shock proteins, antioxidant-related genes, and immunocompetence of heat-stressed broilers in response to short periods of incubation during egg storage and thermal conditioning

Short Periods of Incubation During Egg Storage (SPIDES) approach improves chick quality and hatching rates. Also, embryonic thermal conditioning (TC) is a strategy for enhancing thermotolerance in avian species. Until now, evaluating the effect of either SPIDES or embryonic TC effects has only been separately conducted, so we hypothesized that combining TC and SPIDES may enhance the response of broilers to thermal stress. Eight hundred Ross broiler eggs were divided into two groups; the first one was kept under appropriate storage room conditions, S0 (control) The 2nd was subjected to SPIDES for 5 h at 37.8 ○C ± 0.1 three times at days 5, 10, and 15 (S1) after egg collection respectively. On the 14th day of incubation (DOI) each of the two main groups was randomly divided into two equal subgroups; the control one was left under the appropriate incubation settings (TC0) whereas the other received prenatal heat conditioning (TC1) at 39.5 ○C ± 0.1 for 6 h/d from the 14th to the 18th embryonic day (E), resulting finally in four experimental subgroups (S0TC0, S1TC0, S0TC1 & S1TC1). RESULTS: showed that SPIDES treatment improved the hatchability of the stored eggs by almost 20% compared to untreated eggs. A combination of SPIDES and TC (S1TC1) increased significantly the levels of Immunoglobulin (IgG and IgM) production at hatch and heat-stressed birds. Our findings revealed that the hepatic heat shock proteins (hsp70, 90 A,90 B, 60 and hspA9), antioxidants-related genes (CAT, and SOD2), and NADPH4 were significantly downregulated in the thermally conditioned group that challenged with thermal stress conditions. As opposed to that, the SPIDES group showed a significant increase in hepatic heat shock proteins, antioxidants-related genes, and NADPH4 when subjected to thermal-stress conditions. In conclusion, the combination of SPIDES and TC has a positive effect on some pre and post-hatch traits of broiler chicks. Under heat stress challenge, thermal conditioning can modify the expression of antioxidant-related genes and Hsps, leading to the enhanced acquisition of thermotolerance as evidenced by lower expression of Hsps and NADPH4. While SPIDES does not have a significant role in thermotolerance acquisition.

Dose-Dependent Response to the Environmental Pollutant Dichlorodipheniletylhene (DDE) in HepG2 Cells: Focus on Cell Viability and Mitochondrial Fusion/Fission Proteins

Dichlorodiphenyldichloroethylene (DDE), the primary persistent metabolite of dichlorodiphenyltrichloroethane (DDT), has toxic effects on cells, but its dose-dependent impact on mitochondrial proteins involved in mitochondrial fusion and fission processes associated with cell viability impairment has not yet been analysed. Mitochondrial fusion and fission processes are critical to maintaining the mitochondrial network and allowing the cell to respond to external stressors such as environmental pollutants. Fusion processes are associated with optimizing mitochondrial function, whereas fission processes are associated with removing damaged mitochondria. We assessed the effects of different DDE doses, ranging between 0.5 and 100 µM, on cell viability and mitochondrial fusion/fission proteins in an in vitro hepatic cell model (human hepatocarcinomatous cells, HepG2); the DDE induced a decrease in cell viability in a dose-dependent manner, and its effect was enhanced in conditions of coincubation with dietary fatty acids. Fusion protein markers exhibited an inverted U-shape dose-response curve, showing the highest content in the 2.5–25 μM DDE dose range. The fission protein marker was found to increase significantly, leading to an increased fission/fusion ratio with high DDE doses. The low DDE doses elicited cell adaption by stimulating mitochondrial dynamics machinery, whereas high DDE doses induced cell viability loss associated with mitochondrial dynamics to shift toward fission. Present results are helpful to clarify the mechanisms underlying the cell fate towards survival or death in response to increasing doses of environmental pollutants.

Loss and gain of function of Grp75 or mitofusin 2 distinctly alter cholesterol metabolism, but all promote triglyceride accumulation in hepatocytes

In the liver, contact sites between the endoplasmic reticulum (ER) and mitochondria (named MAMs) may be crucial hubs for the regulation of lipid metabolism, thus contributing to the exacerbation or prevention of fatty liver. We hypothesized that tether proteins located at MAMs could play a key role in preventing triglyceride accumulation in hepatocytes and nonalcoholic fatty liver disease (NAFLD) occurrence. To test this, we explored the role of two key partners in building MAM integrity and functionality, the glucose-regulated protein 75 (Grp75) and mitofusin 2 (Mfn2), which liver contents are altered in obesity and NAFLD. Grp75 or Mfn2 expression was either silenced using siRNA or overexpressed with adenoviruses in Huh7 cells. Silencing of Grp75 and Mfn2 resulted in decreased ER-mitochondria interactions, mitochondrial network fusion state and mitochondrial oxidative capacity, while overexpression of the two proteins induced mirror impacts on these parameters. Furthermore, Grp75 or Mfn2 silencing decreased cellular cholesterol content and enhanced triglyceride secretion in ApoB100 lipoproteins, while their overexpression led to reverse effects. Cellular phosphatidylcholine/phosphatidylethanolamine ratio was decreased only upon overexpression of the proteins, potentially contributing to altered ApoB100 assembly and secretion. Despite the opposite differences, both silencing and overexpression of Grp75 or Mfn2 induced triglyceride storage, although a fatty acid challenge was required to express the alteration upon protein silencing. Among the mechanisms potentially involved in this phenotype, ER stress was closely associated with altered triglyceride metabolism after Grp75 or Mfn2 overexpression, while blunted mitochondrial FA oxidation capacity may be the main defect causing triglyceride accumulation upon Grp75 or Mfn2 silencing. Further studies are required to decipher the link between modulation of Grp75 or Mfn2 expression, change in MAM integrity and alteration of cholesterol content of the cell. In conclusion, Grp75 or Mfn2 silencing and overexpression in Huh7 cells contribute to altering MAM integrity and cholesterol storage in opposite directions, but all promote triglyceride accumulation through distinct cellular pathways. This study also highlights that besides Mfn2, Grp75 could play a central role in hepatic lipid and cholesterol metabolism in obesity and NAFLD.

Transcriptome Analysis of Yamame (Oncorhynchus masou) in Normal Conditions after Heat Stress

Understanding the mechanism of high-temperature tolerance in cold-freshwater fish is crucial for predicting how certain species will cope with global warming. In this study, we investigated temperature tolerance in masu salmon (Oncorhynchus masou, known in Japan as ‘yamame’), an important aquaculture species. By selective breeding, we developed a group of yamame (F2) with high-temperature tolerance. This group was subjected to a high-temperature tolerance test and divided into two groups: High-temperature tolerant (HT) and non-high-temperature tolerant (NT). RNA was extracted from the gill and adipose fin tissues of each group, and the mRNA expression profiles were analyzed using RNA sequencing. A total of 2893 differentially expressed genes (DEGs) from the gill and 836 from the adipose fin were identified by comparing the HT and NT groups. Functional analyses were then performed to identify associated gene ontology (GO) terms and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. The HT group showed a high expression of heat shock protein 70 (HSP70) gene and enriched gene expression in the extracellular matrix (ECM), cell junction, and adhesion pathways in gill tissues compared to the NT group. The HT group also exhibited highly expressed genes in glycolysis and showed lower expression of the genes in the p53 signaling pathway in adipose fin tissues. Taken together, the difference of expression of some genes in the normal condition may be responsible for the difference in heat tolerance between the HT and NT yamame in the heat stress condition.

Glucose-regulated protein 75 determines ER-mitochondrial coupling and sensitivity to oxidative stress in neuronal cells

The crosstalk between different organelles allows for the exchange of proteins, lipids and ions. Endoplasmic reticulum (ER) and mitochondria are physically linked and signal through the mitochondria-associated membrane (MAM) to regulate the transfer of Ca²⁺ from ER stores into the mitochondrial matrix, thereby affecting mitochondrial function and intracellular Ca²⁺ homeostasis. The chaperone glucose-regulated protein 75 (GRP75) is a key protein expressed at the MAM interface which regulates ER–mitochondrial Ca²⁺ transfer. Previous studies revealed that modulation of GRP75 expression largely affected mitochondrial integrity and vulnerability to cell death. In the present study, we show that genetic ablation of GRP75, by weakening ER–mitochondrial junctions, provided protection against mitochondrial dysfunction and cell death in a model of glutamate-induced oxidative stress. Interestingly, GRP75 silencing attenuated both cytosolic and mitochondrial Ca²⁺ overload in conditions of oxidative stress, blocked the formation of reactive oxygen species and preserved mitochondrial respiration. These data revealed a major role for GRP75 in regulating mitochondrial function, Ca²⁺ and redox homeostasis. In line, GRP75 overexpression enhanced oxidative cell death induced by glutamate. Overall, our findings suggest weakening ER–mitochondrial connectivity by GRP75 inhibition as a novel protective approach in paradigms of oxidative stress in neuronal cells.

An investigation of methyl tert‑butyl ether‑induced cytotoxicity and protein profile in Chinese hamster ovary cells

Methyl tert-butyl ether (MTBE) is widely used as an oxygenating agent in gasoline to reduce harmful emissions. However, previous studies have demonstrated that MTBE is a cytotoxic substance that has harmful effects in vivo and in vitro. Although remarkable progress has been made in elucidating the mechanisms underlying the MTBE-induced reproductive toxicological effect in different cell lines, the precise mechanisms remain far from understood. The present study aimed to evaluate whether mammalian ovary cells were sensitive to MTBE exposure in vitro by assessing cell viability, lactate dehydrogenase (LDH) leakage, malondialdehyde (MDA) content and antioxidant enzyme activities. In addition, the effect of MTBE exposure on differential protein expression profiles was examined by two-dimensional electrophoresis and matrix-assisted laser desorption/ionization-time of flight mass spectrometry. MTBE exposure induced significant effects on cell viability, LDH leakage, plasma membrane damage and the activity of antioxidant enzymes. In the proteomic analysis, 24 proteins were demonstrated to be significantly affected by MTBE exposure. Functional analysis indicated that these proteins were involved in catalytic activity, binding, structural molecule activity, metabolic processes, cellular processes and localization, highlighting the fact that the cytotoxic mechanisms resulting from MTBE exposure are complex and diverse. The altered expression levels of two representative proteins, heat shock protein family A (Hsp70) members 8 and 9, were further confirmed by western blot analysis. The results revealed that MTBE exposure affects protein expression in Chinese hamster ovary cells and that oxidative stress and altered protein levels constitute the mechanisms underlying MTBE-induced cytotoxicity. These findings provided novel insights into the biochemical mechanisms involved in MTBE-induced cytotoxicity in the reproductive system.

Reduced levels of Hspa9 attenuate Stat5 activation in mouse B cells

HSPA9 is located on chromosome 5q31.2 in humans, a region that is commonly deleted in patients with myeloid malignancies [del(5q)], including myelodysplastic syndrome (MDS). HSPA9 expression is reduced by 50% in patients with del(5q)-associated MDS, consistent with haploinsufficient levels. Zebrafish mutants and knockdown studies in human and mouse cells have implicated a role for HSPA9 in hematopoiesis. To comprehensively evaluate the effects of Hspa9 haploinsufficiency on hematopoiesis, we generated an Hspa9 knockout mouse model. Although homozygous knockout of Hspa9 is embryonically lethal, mice with heterozygous deletion of Hspa9 (Hspa9(+/-)) are viable and have a 50% reduction in Hspa9 expression. Hspa9(+/-) mice have normal basal hematopoiesis and do not develop MDS. However, Hspa9(+/-) mice have a cell-intrinsic reduction in bone marrow colony-forming unit-PreB colony formation without alterations in the number of B-cell progenitors in vivo, consistent with a functional defect in Hspa9(+/-) B-cell progenitors. We further reduced Hspa9 expression (<50%) using RNA interference and observed reduced B-cell progenitors in vivo, indicating that appropriate levels (≥50%) of Hspa9 are required for normal B lymphopoiesis in vivo. Knockdown of Hspa9 in an interleukin 7 (IL-7)-dependent mouse B-cell line reduced signal transducer and activator of transcription 5 (Stat5) phosphorylation following IL-7 receptor stimulation, supporting a role for Hspa9 in Stat5 signaling in B cells. Collectively, these data imply a role for Hspa9 in B lymphopoiesis and Stat5 activation downstream of IL-7 signaling.