A Disturbance in the Force: Cellular Stress Sensing by the Mitochondrial Network

Mitochondrial dysfunction: A fatal blow in depression

Mitochondria maintain the normal physiological function of nerve cells by producing sufficient cellular energy and performing crucial roles in maintaining the metabolic balance through intracellular Ca2+ homeostasis, oxidative stress, and axonal development. Depression is a prevalent psychiatric disorder with an unclear pathophysiology. Damage to the hippocampal neurons is a key component of the plasticity regulation of synapses and plays a critical role in the mechanism of depression. There is evidence suggesting that mitochondrial dysfunction is associated with synaptic impairment. The maintenance of mitochondrial homeostasis includes quantitative maintenance and quality control of mitochondria. Mitochondrial biogenesis produces new and healthy mitochondria, and mitochondrial dynamics cooperates with mitophagy to remove damaged mitochondria. These processes maintain mitochondrial population stability and exert neuroprotective effects against early depression. In contrast, mitochondrial dysfunction is observed in various brain regions of patients with major depressive disorders. The accumulation of defective mitochondria accelerates cellular nerve dysfunction. In addition, impaired mitochondria aggravate alterations in the brain microenvironment, promoting neuroinflammation and energy depletion, thereby exacerbating the development of depression. This review summarizes the influence of mitochondrial dysfunction and the underlying molecular pathways on the pathogenesis of depression. Additionally, we discuss the maintenance of mitochondrial homeostasis as a potential therapeutic strategy for depression.

An OMA1 redox site controls mitochondrial homeostasis, sarcoma growth, and immunogenicity

Aggressive tumors often display mitochondrial dysfunction. Upon oxidative stress, mitochondria undergo fission through OMA1-mediated cleavage of the fusion effector OPA1. In yeast, a redox-sensing switch participates in OMA1 activation. 3D modeling of OMA1 comforted the notion that cysteine 403 might participate in a similar sensor in mammalian cells. Using prime editing, we developed a mouse sarcoma cell line in which OMA1 cysteine 403 was mutated in alanine. Mutant cells showed impaired mitochondrial responses to stress including ATP production, reduced fission, resistance to apoptosis, and enhanced mitochondrial DNA release. This mutation prevented tumor development in immunocompetent, but not nude or cDC1 dendritic cell-deficient, mice. These cells prime CD8+ lymphocytes that accumulate in mutant tumors, whereas their depletion delays tumor control. Thus, OMA1 inactivation increased the development of anti-tumor immunity. Patients with complex genomic soft tissue sarcoma showed variations in the level of OMA1 and OPA1 transcripts. High expression of OPA1 in primary tumors was associated with shorter metastasis-free survival after surgery, and low expression of OPA1, with anti-tumor immune signatures. Targeting OMA1 activity may enhance sarcoma immunogenicity.

Extracellular Vesicles Derived From Neural Stem Cells, Astrocytes, and Microglia as Therapeutics for Easing TBI-Induced Brain Dysfunction

Extracellular vesicles (EVs) derived from neural stem cells (NSC-EVs), astrocytes (ADEVs), and microglia (MDEVs) have neuroregenerative properties. This review discusses the therapeutic efficacy of NSC-EVs, ADEVs, and MDEVs in traumatic brain injury (TBI) models. The translational value and future directions for such EV therapy are also deliberated. Studies have demonstrated that NSC-EV or ADEV therapy can mediate neuroprotective effects and improve motor and cognitive function after TBI. Furthermore, NSC-EVs or ADEVs generated after priming parental cells with growth factors or brain-injury extracts can mediate improved therapeutic benefits. However, the therapeutic effects of naïve MDEVs are yet to be tested rigorously in TBI models. Studies using activated MDEVs have reported both adverse and beneficial effects. NSC-EV, ADEV, or MDEV therapy for TBI is not ready for clinical translation. Rigorous testing of their efficacy for preventing chronic neuroinflammatory cascades and enduring motor and cognitive impairments after treatment in the acute phase of TBI, an exhaustive evaluation of their miRNA or protein cargo, and the effects of delayed EV administration post-TBI for reversing chronic neuroinflammation and enduring brain impairments, are needed. Moreover, the most beneficial route of administration for targeting EVs into different neural cells in the brain after TBI and the efficacy of well-characterized EVs from NSCs, astrocytes, or microglia derived from human pluripotent stem cells need to be evaluated. EV isolation methods for generating clinical-grade EVs must also be developed. Overall, NSC-EVs and ADEVs promise to mitigate TBI-induced brain dysfunction, but additional preclinical studies are needed before their clinical translation.

Heparan Sulfate Mimicking Glycopolymer Prevents Pancreatic β Cell Destruction and Suppresses Inflammatory Cytokine Expression in Islets under the Challenge of Upregulated Heparanase

Diabetes is a chronic disease in which the levels of blood glucose are too high because the body does not effectively produce insulin to meet its needs or is resistant to insulin. β Cells in human pancreatic islets produce insulin, which signals glucogen production by the liver and causes muscles and fat to uptake glucose. Progressive loss of insulin-producing β cells is the main cause of both type 1 and type 2 diabetes. Heparan sulfate (HS) is a ubiquitous polysaccharide found at the cell surface and in the extracellular matrix (ECM) of a variety of tissues. HS binds to and assembles proteins in ECM, thus playing important roles in the integrity of ECM (particularly basement membrane), barrier function, and ECM-cell interactions. Islet HS is highly expressed by the pancreatic β cells and critical for the survival of β cells. Heparanase is an endoglycosidase and cleaves islet HS in the pancreas, resulting in β-cell death and oxidative stress. Heparanase could also accelerate β-cell death by promoting cytokine release from ECM and secretion by activated inflammatory and endothelial cells. We demonstrate that HS-mimicking glycopolymer, a potent heparanase inhibitor, improves the survival of cultured mouse pancreatic β cells and protects HS contents under the challenge of heparanase in human pancreatic islets. Moreover, this HS-mimicking glycopolymer reduces the expression levels of cytokines (IL8, IL1β, and TNFα) and the gene encoding Toll-like Receptor 2 (TLR2) in human pancreatic islets.

Astrocyte-derived exosomes protect hippocampal neurons after traumatic brain injury by suppressing mitochondrial oxidative stress and apoptosis

In this study, we investigated the mechanisms through which astrocyte-derived exosomes (AS-Exos) alleviate traumatic brain injury (TBI)-induced neuronal defects in TBI model rats and mice. Treatment with AS-Exos alleviated neurobehavioral deficits, cognitive impairment, and brain edema in TBI rats. AS-Exos also significantly reduced neuronal cell loss and atrophy in the TBI rats. AS-Exos significantly reduced oxidative stress and mitochondrial H₂O₂ levels by increasing the activity of antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT) in the hippocampal neurons of TBI rats. TUNEL-staining assays showed that AS-Exos significantly reduced TBI-induced neuronal apoptosis. Mechanistically, AS-Exos ameliorated oxidative stress by activating Nrf2/HO-1 signaling in the hippocampus of TBI rats. In addition, the neuroprotective effects of AS-Exos were abrogated in brain-specific Nrf2-knockout mice subjected to TBI. These findings demonstrate that AS-Exos protects against TBI-induced oxidative stress and neuronal apoptosis by activating Nrf2 signaling in both rat and mouse models.

Melatonin prevents blood-retinal barrier breakdown and mitochondrial dysfunction in high glucose and hypoxia-induced in vitro diabetic macular edema model

Diabetic macular edema (DME) is a leading cause of blindness in diabetic retinopathy. Prolonged hyperglycemia plus hypoxia contributes to DME pathogenesis. Retinal pigmented epithelial cells comprise the outer blood-retinal barrier and are essential for maintaining physiological functioning of the retina. Melatonin acts as an antioxidant and regulator of mitochondrial bioenergetics and has a protective effect against ocular diseases. However, the role of mitochondrial dysfunction and the therapeutic potential of melatonin in DME remain largely unexplored. Here, we used an in vitro model of DME to investigate blood-retinal barrier integrity and permeability, angiogenesis, mitochondrial dynamics, and apoptosis signaling to evaluate the potential protective efficacy of melatonin in DME. We found that melatonin prevents cell hyper-permeability and outer barrier breakdown by reducing HIF-1α, HIF-1β and VEGF and VEGF receptor gene expression. In addition, melatonin reduced the expression of genes involved in mitochondrial fission (DRP1, hFis1, MIEF2, MFF), mitophagy (PINK, BNip3, NIX), and increased the expression of genes involved in mitochondrial biogenesis (PGC-1α, NRF2, PPAR-γ) to maintain mitochondrial homeostasis. Moreover, melatonin prevented apoptosis of retinal pigmented epithelial cells. Our results suggest that mitochondrial dysfunction may be involved in DME pathology, and melatonin may have therapeutic value in DME, by targeting signaling in mitochondria.

Increasing Nrf2 Activity as a Treatment Approach in Neuropsychiatry

Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor encoded by NFE2L2. Under oxidative stress, Nrf2 does not undergo its normal cytoplasmic degradation but instead travels to the nucleus, where it binds to a DNA promoter and initiates transcription of anti-oxidative genes. Nrf2 upregulation is associated with increased cellular levels of glutathione disulfide, glutathione peroxidase, glutathione transferases, thioredoxin and thioredoxin reductase. Given its key role in governing the cellular antioxidant response, upregulation of Nrf2 has been suggested as a common therapeutic target in neuropsychiatric illnesses such as major depressive disorder, bipolar disorder and schizophrenia, which are associated with chronic oxidative and nitrosative stress, characterised by elevated levels of reactive oxygen species, nitric oxide and peroxynitrite. These processes lead to extensive lipid peroxidation, protein oxidation and carbonylation, and oxidative damage to nuclear and mitochondrial DNA. Intake of N-acetylcysteine, coenzyme Q₁₀ and melatonin is accompanied by increased Nrf2 activity. N-acetylcysteine intake is associated with improved cerebral mitochondrial function, decreased central oxidative and nitrosative stress, reduced neuroinflammation, alleviation of endoplasmic reticular stress and suppression of the unfolded protein response. Coenzyme Q₁₀, which acts as a superoxide scavenger in neuroglial mitochondria, instigates mitohormesis, ameliorates lipid peroxidation in the inner mitochondrial membrane, activates uncoupling proteins, promotes mitochondrial biogenesis and has positive effects on the plasma membrane redox system. Melatonin, which scavenges mitochondrial free radicals, inhibits mitochondrial nitric oxide synthase, restores mitochondrial calcium homeostasis, deacetylates and activates mitochondrial SIRT3, ameliorates increased permeability of the blood-brain barrier and intestine and counters neuroinflammation and glutamate excitotoxicity.

Differential expression of nuclear genes encoding mitochondrial proteins from urban and rural populations in Morocco

Urbanization in low-income countries represents an important inflection point in the epidemiology of disease, with rural populations experiencing high rates of chronic and recurrent infections and urban populations displaying a profile of noncommunicable diseases. To investigate if urbanization alters the expression of genes encoding mitochondrial proteins, we queried gene microarray data from rural and urban populations living in Morocco (GSE17065). The R Bioconductor packages edgeR and limma were used to identify genes with different expression. The experimental design was modeled upon location and sex. Nuclear genes encoding mitochondrial proteins were identified from the MitoCarta2.0 database. Of the 1158 genes listed in the MitoCarta2.0 database, 847 genes (73%) were available for analysis in the Moroccan dataset. The urban-rural comparison with the greatest environmental differences showed that 76.5% of the MitoCarta2.0 genes were differentially expressed, with 97% of the genes having an increased expression in the urban area. Enrichment analysis revealed 367 significantly enriched pathways (adjusted p value < 0.05), with oxidative phosphorylation, insulin secretion and glucose regulations (adj.p values = 6.93E-16) being the top three. Four significantly perturbed KEGG disease pathways were associated with urbanization-three degenerative neurological diseases (Huntington's, Alzheimer's, and Parkinson's diseases) and herpes simplex infection (false discover rate corrected p value (PGFdr) < 0.2). Mitochondrial RNA metabolic processing and translational elongation were the biological processes that had the greatest enrichment (enrichment ratios 14.0 and 14.8, respectively, FDR < 0.5). Our study links urbanization in Morocco with changes in the expression of the nuclear genes encoding mitochondrial proteins.

Nutrigenomic Effects of Long-Term Grape Pomace Supplementation in Dairy Cows

Simple Summary

The aim of this study was to evaluate the effect of grape pomace (GP), the polyphenol-rich agricultural by-product, on dairy cows’ whole-blood transcriptome, milk production and composition. Twelve lactating Holstein-Friesian cows were randomly assigned to two groups; the first received a GP-supplemented diet for 60 days (group GP), whereas the second was given only a basal diet (CTR). The results reveal 40 protein-coding genes differentially expressed in the GP group when compared with the CTR group, but no effects were noticed on milk production, concentrations of crude protein, fat, casein, lactose and urea, or somatic cell count. Compared to CTR, GP had a transcriptomic signature mainly reflecting a reinforced immunogenic response.

Abstract

The increasing demand for more animal products put pressure on improving livestock production efficiency and sustainability. In this context, advanced animal nutrition studies appear indispensable. Here, the effect of grape pomace (GP), the polyphenol-rich agricultural by-product, was evaluated on Holstein-Friesian cows’ whole-blood transcriptome, milk production and composition. Two experimental groups were set up. The first one received a basal diet and served as a control, while the second one received a 7.5% GP-supplemented diet for a total of 60 days. Milk production and composition were not different between the group; however, the transcriptome analysis revealed a total of 40 genes significantly affected by GP supplementation. Among the most interesting down-regulated genes, we found the DnaJ heat-shock protein family member A1 (DNAJA1), the mitochondrial fission factor (MFF), and the impact RWD domain protein (IMPACT) genes. The gene set enrichment analysis evidenced the positive enrichment of ‘interferon alpha (IFN-α) and IFN-γ response’, ‘IL6-JAK-STAT3 signaling’ and ‘complement’ genes. Moreover, the functional analysis denoted positive enrichment of the ‘response to protozoan’ and ‘negative regulation of viral genome replication’ biological processes. Our data provide an overall view of the blood transcriptomic signature after a 60-day GP supplementation in dairy cows which mainly reflects a GP-induced immunomodulatory effect.

TRPV1 and TRPA1 in Lung Inflammation and Airway Hyperresponsiveness Induced by Fine Particulate Matter (PM2.5)

Exposure to fine particulate matter (PM_2.5) has been associated with lung inflammation and airway hyperresponsiveness (AHR). Transient receptor potential (TRP) vanilloid 1 (TRPV1) and ankyrin 1 (TRPA1) both may play important roles in lung inflammation and AHR. We investigated whether PM_2.5-induced lung inflammation and AHR could be prevented by blocking TRPV1 and TRPA1 channels. Mice were injected intraperitoneally with AMG9810 (30 mg/kg, a TRPV1 antagonist) or A967079 (30 mg/kg, a TRPA1 antagonist) or their combination or vehicle (PBS) one hour before intranasal instillation of PM_2.5 (7.8 mg/kg) or vehicle (PBS) for two consecutive days, and then the mice were studied 24 h later. All pretreatments inhibited PM_2.5-induced AHR and inflammatory infiltration in the lung tissue and decreased inflammatory cytokine levels in the bronchoalveolar lavage fluid, together with oxidant levels in the lung. AMG9810 inhibited MFF expression and increased MFN2 expression while A967079 inhibited DRP1 expression and increased OPA1 expression; combined pretreatment reduced MFF and DPR1 expression and increased MFN2 and OPA1 expression. All pretreatments inhibited the activation of the TLR4/NF-κB pathway, while A967079 alone, and combined with AMG9810 also reduced the activation of the NLRP3/caspase-1 pathway. Both TRPV1 and TRPA1 channels play an important role in PM_2.5-induced lung inflammation and AHR. However, inhibition of the TRPA1 channel or combined inhibition of TRPA1 and TRPV1 channels resulted in greater inhibitory effect on PM_2.5-induced lung injury through regulating the mitochondrial fission/fusion proteins and inhibiting the TLR4/NF-κB and NLRP3/caspase-1 pathways.