Mitochondrial Membrane Potential-dependent Endoplasmic Reticulum Fragmentation is an Important Step in Neuritic Degeneration

The neurotoxicity of pesticides: Implications for Parkinson's disease

Parkinson's disease (PD) is the fastest-growing neurodegenerative disorder worldwide, and no effective cure is currently available. Neuropathologically, PD is characterized by the selective degeneration of dopaminergic neurons in the substantia nigra and by the accumulation of alpha-synuclein (aSyn)-rich proteinaceous inclusions within surviving neurons. As a multifactorial disorder, approximately 85 % of PD cases are sporadic with unknown etiology. Among the many risk factors implicated in PD, exposure to neurotoxic pesticides stands out as a significant contributor. While the effects of many are still uncharacterized, it has already been shown that rotenone, paraquat, maneb, and dieldrin affect critical cellular pathways, including mitochondrial and proteasomal dysfunction, aSyn aggregation, autophagy dysregulation, and disruption of dopamine metabolism. With the constant rise in pesticide usage to meet the demands of a growing human population, the risk of environmental contamination and subsequent PD development is also increasing. This review explores the molecular mechanisms by which pesticide exposure influences PD development, shedding light on their role in the pathogenesis of PD and highlighting the need for preventative measures and regulatory oversight to mitigate these risks.

Inhibition of SGLT2 protects podocytes in diabetic kidney disease by rebalancing mitochondria-associated endoplasmic reticulum membranes

BACKGROUND

Sodium-glucose cotransporter 2 (SGLT2) inhibitors have changed the therapeutic landscape for diabetic kidney disease (DKD) patients, but their underlying mechanisms are complicated and not fully understood. Mitochondria-associated endoplasmic reticulum membranes (MAMs), the dynamic contact sites between mitochondria and the endoplasmic reticulum (ER), serve as intracellular platforms important for regulating cellular fate and function. This study explored the roles and mechanisms of SGLT2 inhibitors in regulating MAMs formation in diabetic podocytes.

METHODS

We assessed MAMs formation in podocytes from DKD patients' renal biopsy samples and induced an increase in MAMs formation in cultured human podocytes by transfecting OMM-ER linker plasmid to investigate the effects of MAMs imbalance on podocyte injury. Empagliflozin-treated diabetic mice and podocyte-specific SGLT2 knockout diabetic mice (diabetic states were induced by streptozotocin and a high-fat diet), empagliflozin-treated podocytes, SGLT2-downregulated podocytes, and SGLT2-overexpressing podocytes were used to investigate the effects and mechanisms of SGLT2 inhibitors on MAMs formation in diabetic podocytes.

RESULTS

MAMs were increased in podocytes and were associated with renal dysfunction in DKD patients. Increased MAMs aggravated HG-induced podocyte injury. The expression of SGLT2 was increased in diabetic podocytes. In addition, empagliflozin-treatment and podocyte-specific SGLT2 knockout attenuated MAMs formation and podocyte injury in diabetic mice. Empagliflozin treatment and SGLT2 knockdown decreased podocyte MAMs formation by activating the AMP-activated protein kinase (AMPK) pathway, while SGLT2 overexpression had the opposite effect.

CONCLUSIONS

Inhibition of SGLT2 attenuates MAMs imbalance in diabetic podocytes by activating the AMPK pathway. This study expands our knowledge of the roles of SGLT2 inhibitors in improving DKD podocyte injury and provides new insights into DKD treatment.

A novel protein CYTB-187AA encoded by the mitochondrial gene CYTB modulates mammalian early development

The mitochondrial genome transcribes 13 mRNAs coding for well-known proteins essential for oxidative phosphorylation. We demonstrate here that cytochrome b (CYTB), the only mitochondrial-DNA-encoded transcript among complex III, also encodes an unrecognized 187-amino-acid-long protein, CYTB-187AA, using the standard genetic code of cytosolic ribosomes rather than the mitochondrial genetic code. After validating the existence of this mtDNA-encoded protein arising from cytosolic translation (mPACT) using mass spectrometry and antibodies, we show that CYTB-187AA is mainly localized in the mitochondrial matrix and promotes the pluripotent state in primed-to-naive transition by interacting with solute carrier family 25 member 3 (SLC25A3) to modulate ATP production. We further generated a transgenic knockin mouse model of CYTB-187AA silencing and found that reduction of CYTB-187AA impairs females' fertility by decreasing the number of ovarian follicles. For the first time, we uncovered the novel mPACT pattern of a mitochondrial mRNA and demonstrated the physiological function of this 14th protein encoded by mtDNA.

Suberoylanilide hydroxamic acid upregulates reticulophagy receptor expression and promotes cell death in hepatocellular carcinoma cells

BACKGROUND

Hepatocellular carcinoma (HCC) is a common clinical condition with a poor prognosis and few effective treatment options. Potent anticancer agents for treating HCC must be identified. Epigenetics plays an essential role in HCC tumorigenesis. Suberoylanilide hydroxamic acid (SAHA), the most common histone deacetylase inhibitor agent, triggers many forms of cell death in HCC. However, the underlying mechanism of action remains unclear. Family with sequence similarity 134 member B (FAM134B)-induced reticulophagy, a selective autophagic pathway, participates in the decision of cell fate and exhibits anticancer activity. This study focused on the relationship between FAM134B-induced reticulophagy and SAHA-mediated cell death.

AIM

To elucidate potential roles and underlying molecular mechanisms of reticulophagy in SAHA-induced HCC cell death.

METHODS

The viability, apoptosis, cell cycle, migration, and invasion of SAHA-treated Huh7 and MHCC97L cells were measured. Proteins related to the reticulophagy pathway, mitochondria-endoplasmic reticulum (ER) contact sites, intrinsic mitochondrial apoptosis, and histone acetylation were quantified using western blotting. ER and lysosome colocalization, and mitochondrial Ca2+ levels were characterized via confocal microscopy. The level of cell death was evaluated through Hoechst 33342 staining and propidium iodide colocalization. Chromatin immunoprecipitation was used to verify histone H4 lysine-16 acetylation in the FAM134B promoter region.

RESULTS

After SAHA treatment, the proliferation of Huh7 and MHCC97L cells was significantly inhibited, and the migration and invasion abilities were greatly blocked in vitro. This promoted apoptosis and caused G1 phase cells to increase in a concentration-dependent manner. Following treatment with SAHA, ER-phagy was activated, thereby triggering autophagy-mediated cell death of HCC cells in vitro. Western blotting and chromatin immunoprecipitation assays confirmed that SAHA regulated FAM134B expression by enhancing the histone H4 lysine-16 acetylation in the FAM134B promoter region. Further, SAHA disturbed the Ca2+ homeostasis and upregulated the level of autocrine motility factor receptor and proteins related to mitochondria-endoplasmic reticulum contact sites in HCC cells. Additionally, SAHA decreased the mitochondrial membrane potential levels, thereby accelerating the activation of the reticulophagy-mediated mitochondrial apoptosis pathway and promoting HCC cell death in vitro.

CONCLUSION

SAHA stimulates FAM134B-mediated ER-phagy to synergistically enhance the mitochondrial apoptotic pathway, thereby enhancing HCC cell death.

Mitochondria-associated endoplasmic reticulum membranes promote mitochondrial fission through AKAP1-Drp1 pathway in podocytes under high glucose conditions

Excessive mitochondrial fission in podocytes is a critical feature of diabetic nephropathy (DN). Mitochondria-associated endoplasmic reticulum membranes (MAMs) are contact sites between the endoplasmic reticulum (ER) and mitochondria, which are suggested to be related to mitochondrial function. However, the role of MAMs in mitochondrial dynamics disorder in podocytes remains unknown. Here, we firstly reported a novel mechanism of MAMs' effects on mitochondrial dynamics in podocytes under diabetic conditions. Increased MAMs were found in diabetic podocytes in vivo and in vitro, which were positively correlated with excessive mitochondrial fission. What's more, we also found that A-kinase anchoring protein 1 (AKAP1) was located in MAMs, and its translocation to MAMs was increased in podocytes cultured with high glucose (HG). In addition, AKAP1 knockdown significantly reduced mitochondrial fission and attenuated high glucose induced-podocyte injury through regulating phosphorylation of dynamin-related protein 1 (Drp1) and its subsequent mitochondrial translocation. On the contrary, AKAP1 overexpression in these podocytes showed the opposite effect. Finally, pharmacological inhibition of Drp1 alleviated excessive mitochondrial fission and podocyte damage in AKAP1 overexpressed podocytes. Our data suggest that MAMs were increased in podocytes under diabetic conditions, leading to excessive mitochondrial fission and podocyte damage through AKAP1-Drp1 signaling.

Advances in Human Mitochondria-Based Therapies

Mitochondria are the key biological generators of eukaryotic cells, controlling the energy supply while providing many important biosynthetic intermediates. Mitochondria act as a dynamic, functionally and structurally interconnected network hub closely integrated with other cellular compartments via biomembrane systems, transmitting biological information by shuttling between cells and tissues. Defects and dysregulation of mitochondrial functions are critically involved in pathological mechanisms contributing to aging, cancer, inflammation, neurodegenerative diseases, and other severe human diseases. Mediating and rejuvenating the mitochondria may therefore be of significant benefit to prevent, reverse, and even treat such pathological conditions in patients. The goal of this review is to present the most advanced strategies using mitochondria to manage such disorders and to further explore innovative approaches in the field of human mitochondria-based therapies.

Mitochondrial abnormalities in neurodegenerative models and possible interventions: Focus on Alzheimer's disease, Parkinson's disease, Huntington's disease

Mitochondrial abnormalities in the brain are considered early pathological changes in neurogenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD) and Huntington's disease (HD). The mitochondrial dysfunction in the brain can be induced by toxic proteins, including amyloid-beta (Aβ), phosphorylated tau, alpha-synuclein (α-syn) and mutant huntingtin (mtHTT). These proteins cause mitochondrial genome damage, increased oxidative stress, decreased mitochondrial membrane permeability, and diminished ATP production. Consequently, synaptic dysfunction, synaptic loss, neuronal apoptosis, and ultimately cognitive impairment are exhibited. Therefore, the restoration of mitochondrial abnormalities in the brain is an alternative intervention to delay the progression of neurodegenerative diseases in addition to reducing the level of toxic proteins, especially Aβ, and restored synaptic dysfunction by interventions. Here we comprehensively review mitochondrial alterations in the brain of neurodegenerative models, specifically AD, PD and HD, from both in vitro and in vivo studies. Additionally, the correlation between mitochondrial changes, cognitive function, and disease progression from in vivo studies is described. This review also summarizes interventions that possibly attenuate mitochondrial abnormalities in AD, PD and HD models from both in vitro and in vivo studies. This may lead to the introduction of novel therapies that target on brain mitochondria to delay the progression of AD, PD and HD.

Topology-dependent, bifurcated mitochondrial quality control under starvation

Selective elimination of mitochondria by autophagy is a critical strategy for a variety of physiological processes, including development, cell-fate determination and stress response. Although several mechanisms have been identified as responsible for selective degradation of mitochondria, such as the PINK1-PRKN/PARKIN- and receptor-dependent pathways, aspects of the mechanisms and particularly the principles underlying the selection process of mitochondria remain obscure. Here, we addressed a new selection strategy in which the selective elimination of mitochondria is dependent on organellar topology. We found that populations of mitochondria undergo different topological transformations under serum starvation, either swelling or forming donut shapes. Swollen mitochondria are associated with mitochondrial membrane potential dissipation and PRKN recruitment, which promote their selective elimination, while the donut topology maintains mitochondrial membrane potential and helps mitochondria resist autophagy. Mechanistic studies show that donuts resist autophagy even after depolarization through preventing recruitment of autophagosome receptors CALCOCO2/NDP52 and OPTN even after PRKN recruitment. Our results demonstrate topology-dependent, bifurcated mitochondrial recycling under starvation, that is swollen mitochondria undergo removal by autophagy, while donut mitochondria undergo fission and fusion cycles for reintegration. This study reveals a novel morphological selection for control of mitochondrial quality and quantity under starvation.

Polybrene induces neural degeneration by bidirectional Ca2+ influx-dependent mitochondrial and ER-mitochondrial dynamics

Hexadimethrine bromide (Polybrene) was once used clinically as a heparin neutralizer and has recently found use as a promoter in virus-mediated gene therapy trials and gene transfer in research. However, the potential for tissue-specific toxicity of polybrene at low doses has been ignored so far. Here, we found that after intracerebroventricular (ICV) polybrene injection, mice showed disability of movement accompanied neural death and gliosis in brain, and in human neurons, polybrene induces concentration-dependent neuritic beading and fragmentation. Mechanistically, polybrene induces a rapid voltage-dependent calcium channel (VDCC)-mediated influx of extracellular Ca²⁺. The elevated cytoplasmic Ca²⁺ activates DRP1, which leads to mitochondrial fragmentation and metabolic dysfunction. At the same time, Ca²⁺ influx induces endoplasmic reticulum (ER) fragmentation and tightened associations between ER and mitochondria, which makes mitochondria prone to Ca²⁺ overloading and ensuing permeability transition. These results reveal an unexpected neuronal toxicity of polybrene, wherein Ca²⁺ influx serves as a regulator for both mitochondrial dynamics and ER–mitochondrial remodeling.

Improved photodynamic effect through encapsulation of two photosensitizers in lipid nanocapsules

Photodynamic therapy (PDT) has developed into a new clinical and non-invasive treatment for cancer over the past 30 years. By the combination of three non-toxic partners, i.e. a photosensitizer (PS), molecular oxygen (O₂) and light, cytotoxic reactive oxygen species (ROS) are locally produced leading to irreversible vascular and cellular damage. In the present study, we report for the first time that the combination of two photosensitizers (2 PSs: Protoporphyrin IX, PpIX and Hypericin, Hy) loaded in the same lipid nanocapsules (LNCs) leads to enhanced photodynamic therapy efficiency when compared with previously reported systems. The 2 PS-loaded LNCs are shown to increase the in vitro phototoxicity at the nanomolar range (IC₅₀ = 274 and 278 nM on HeLa and MDA-MB-231 cell lines, respectively), whereas the corresponding single PS-loaded LNCs at the same concentration exhibit a phototoxicity two times lower. Intracellular localization in HeLa cells indicates a subcellular asymmetry of PpIX and Hy, in the plasma, ER membranes and round internal structures. The biodistribution of LNCs was studied upon different routes of injection into Swiss nude mice; based on the obtained data, LNCs were injected intratumorally and used to slow the growth of xenograft tumors in mice. The results obtained in this study suggest that the combination of two or more PSs may be a promising strategy to improve the efficacy of conventional photodynamic therapy as well as to reduce dark toxicity.

Combining autophagy-inducing peptides and brefeldin A delivered by perinuclear-localized mesoporous silica nanoparticles: a manipulation strategy for ER-phagy

Autophagic degradation of the endoplasmic reticulum (ER-phagy) has been found to play a critical role in human sensory neuropathy. So far, however, specific and efficient intervention means for ER-phagy remain unexplored. Herein, brefeldin A (BFA), a blocking agent on protein transport between the ER and Golgi, was screened from ER stress inducers. BFA was then delivered to the perinuclear area co-localized with the ER by a mesoporous silica nanoparticle-based drug-carrier functionalized with autophagy-inducing peptides of TAT-beclin 1 (MSNs-BFA), to evoke a perturbation of ER-phagy. The molecular mechanism of ER-phagy regulated by BFA was explored by biochemical evaluation including time-lapse live-cell fluorescence imaging. We found that MSNs-BFA treatment caused a lower mRNA/protein expression level of FAM134b even under a compensation of autophagic flux in U2OS cells, and resulted in ER-expansion. The fragmentation of the ER was blocked as a response to ER stress mediated by inactivation of the AKT/TSC/mTOR pathway. Our work developed an efficient external manipulation strategy to regulate ER-phagy and may contribute to the therapeutic application of autophagy-related major human diseases.

Mitochondria-associated membranes (MAMs): An emerging platform connecting energy and immune sensing to metabolic flexibility

Living organisms have the capacity to sense both nutrients and immune signals in order to adapt their metabolism to the needs, and both metabolic inflexibility and exacerbated immune responses are associated with metabolic diseases. Over the past decade, mitochondria emerged as key nutrient and immune sensors regulating numerous signalling pathways, and mitochondria dysfunction has been extensively implicated in metabolic diseases. Interestingly, mitochondria interact physically and functionally with the endoplasmic reticulum (ER, in contact sites named mitochondria-associated membranes (MAMs), in order to exchange metabolites and calcium and regulate cellular homeostasis. Emerging evidences suggest that MAMs provide a platform for hormone and nutrient signalling pathways and for innate immune responses, then regulating mitochondrial bioenergetics and apoptosis. Here, I thus propose the concept that MAMs could be attractive nutrient and immune sensors that regulate mitochondria physiology in order to adapt metabolism and cell fate, and that organelle miscommunication could be involved in the metabolic inflexibility and the pro-inflammatory status associated with metabolic diseases.

Neurotropin® alleviates hippocampal neuron damage through a HIF-1α/MAPK pathway

AIMS

The main purpose was to verify the potent capacity of Neurotropin® against neuronal damage in hippocampus and to explore its underlying mechanisms.

METHODS

HT22 cells were treated with 40 μmol/L Aβ_25-35 in the presence of various concentrations of Neurotropin® or in its absence. The cell viability was assessed with a CCK-8 assay, and flow cytometry was used to measure cell apoptosis, intracellular ROS levels, and mitochondrial membrane potential. Aβ plaques were examined by Bielschowsky silver staining, and the activities of antioxidants were detected in hippocampus of APP/PS1 mice after Neurotropin® treatment. The expression of proteins, including HIF-1α, Bcl-2, Bax, and MAPKs signaling molecules was evaluated by Western blot.

RESULTS

Neurotropin® significantly reversed the cell injury induced by Aβ_25-35 through increasing cell viability and mitochondrial membrane potential, decreasing intracellular ROS and cell apoptosis of HT22 cells (P<.05). Furthermore, Neurotropin® markedly reduced the formation of Aβ plaques and upregulated the activities of antioxidants (P<.05). Additionally, the protein expression of HIF-1α, p-ERK1/2, p-JNK, and p-P38 was significantly inhibited in hippocampus of APP/PS1 mice.

CONCLUSIONS

Neurotropin® exhibited a potent neuroprotective effect on inhibiting Aβ-induced oxidative damage and alleviating Aβ deposition in hippocampus via modulation of HIF-1α/MAPK signaling pathway.

Endoplasmic reticulum-mitochondria calcium signaling in hepatic metabolic diseases

The liver plays a central role in glucose homeostasis, and both metabolic inflexibility and insulin resistance predispose to the development of hepatic metabolic diseases. Mitochondria and endoplasmic reticulum (ER), which play a key role in the control of hepatic metabolism, also interact at contact points defined as mitochondria-associated membranes (MAM), in order to exchange metabolites and calcium (Ca²⁺) and regulate cellular homeostasis and signaling. Here, we overview the role of the liver in the control of glucose homeostasis, mainly focusing on the independent involvement of mitochondria, ER and Ca²⁺ signaling in both healthy and pathological contexts. Then we focus on recent data highlighting MAM as important hubs for hormone and nutrient signaling in the liver, thus adapting mitochondria physiology and cellular metabolism to energy availability. Lastly, we discuss how chronic ER-mitochondria miscommunication could participate to hepatic metabolic diseases, pointing MAM interface as a potential therapeutic target for metabolic disorders. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech.