Mitochondria and the dynamic control of stem cell homeostasis

Harmonization of experimental procedures to assess mitochondrial respiration in human permeabilized skeletal muscle fibers

AIM

High-resolution respirometry in human permeabilized muscle fibers is extensively used for analysis of mitochondrial adaptions to nutrition and exercise interventions, and is linked to athletic performance. However, the lack of standardization of experimental conditions limits quantitative inter- and intra-laboratory comparisons.

METHODS

In our study, an international team of investigators measured mitochondrial respiration of permeabilized muscle fibers obtained from three biopsies (vastus lateralis) from the same healthy volunteer to avoid inter-individual variability. High-resolution respirometry assays were performed together at the same laboratory to assess whether the heterogenity in published results are due to the effects of respiration media (MiR05 versus Z) with or without the myosin inhibitor blebbistatin at low- and high-oxygen regimes.

RESULTS

Our findings reveal significant differences between respiration media for OXPHOS and ETcapacities supported by NADH&succinate-linked substrates at different oxygen concentrations. Respiratory capacities were approximately 1.5-fold higher in MiR05 at high-oxygen regimes compared to medium Z near air saturation. The presence or absence of blebbistatin in human permeabilized muscle fiber preparations was without effect on oxygen flux.

CONCLUSION

Our study constitutes a basis to harmonize and establish optimum experimental conditions for respirometric studies of permeabilized human skeletal muscle fibers to improve reproducibility.

Cpt1a Drives primed-to-naïve pluripotency transition through lipid remodeling

Metabolism has been implicated in cell fate determination, particularly through epigenetic modifications. Similarly, lipid remodeling also plays a role in regulating cell fate. Here, we present comprehensive lipidomics analysis during BMP4-driven primed to naive pluripotency transition or BiPNT and demonstrate that lipid remodeling plays an essential role. We further identify Cpt1a as a rate-limiting factor in BiPNT, driving lipid remodeling and metabolic reprogramming while simultaneously increasing intracellular acetyl-CoA levels and enhancing H3K27ac at chromatin open sites. Perturbation of BiPNT by histone acetylation inhibitors suppresses lipid remodeling and pluripotency transition. Together, our study suggests that lipid remodeling promotes pluripotency transitions and further regulates cell fate decisions, implicating Cpt1a as a critical regulator between primed-naive cell fate control.

piRNAs are regulators of metabolic reprogramming in stem cells

Stem cells preferentially use glycolysis instead of oxidative phosphorylation and this metabolic rewiring plays an instructive role in their fate; however, the underlying molecular mechanisms remain largely unexplored. PIWI-interacting RNAs (piRNAs) and PIWI proteins have essential functions in a range of adult stem cells across species. Here, we show that piRNAs and the PIWI protein Aubergine (Aub) are instrumental in activating glycolysis in Drosophila female germline stem cells (GSCs). Higher glycolysis is required for GSC self-renewal and aub loss-of-function induces a metabolic switch in GSCs leading to their differentiation. Aub directly binds glycolytic mRNAs and Enolase mRNA regulation by Aub depends on its 5'UTR. Furthermore, mutations of a piRNA target site in Enolase 5'UTR lead to GSC loss. These data reveal an Aub/piRNA function in translational activation of glycolytic mRNAs in GSCs, and pinpoint a mechanism of regulation of metabolic reprogramming in stem cells based on small RNAs.

Mitochondrial metabolism regulation and epigenetics in hypoxia

The complex and dynamic interaction between cellular energy control and gene expression modulation is shown by the intersection between mitochondrial metabolism and epigenetics in hypoxic environments. Poor oxygen delivery to tissues, or hypoxia, is a basic physiological stressor that sets off a series of reactions in cells to adapt and endure oxygen-starved environments. Often called the "powerhouse of the cell," mitochondria are essential to cellular metabolism, especially regarding producing energy through oxidative phosphorylation. The cellular response to hypoxia entails a change in mitochondrial metabolism to improve survival, including epigenetic modifications that control gene expression without altering the underlying genome. By altering the expression of genes involved in angiogenesis, cell survival, and metabolism, these epigenetic modifications help cells adapt to hypoxia. The sophisticated interplay between mitochondrial metabolism and epigenetics in hypoxia is highlighted by several important points, which have been summarized in the current article. Deciphering the relationship between mitochondrial metabolism and epigenetics during hypoxia is essential to understanding the molecular processes that regulate cellular adaptation to reduced oxygen concentrations.

Rbm46 inhibits reactive oxygen species in mouse embryonic stem cells through modulating BNIP3-mediated mitophagy

Embryonic stem cells (ESCs) exhibit a metabolic preference for glycolysis over oxidative phosphorylation to meet their substantial adenosine triphosphate (ATP) demands during self-renewal. This metabolic choice inherently maintains low mitochondrial activity and minimal reactive oxygen species (ROS) generation. Nonetheless, the intricate molecular mechanisms governing the restraint of ROS production and the mitigation of cellular damage remain incompletely elucidated. In this study, we reveal the pivotal role of RNA-binding motif protein 46 (RBM46) in ESCs, acting as a direct post transcriptional regulator of ROS levels by modulating BCL2/adenovirus E1B 19 kDa protein-interacting protein 3 (Bnip3) mRNA expression. Rbm46 knockout lead to diminished mitochondrial autophagy, culminating in elevated ROS within ESCs, disrupting the delicate balance required for healthy self-renewal. These findings provide insights into a novel mechanism governing ROS regulation in ESCs.

Nanodrug Delivery Systems for Myasthenia Gravis: Advances and Perspectives

Myasthenia gravis (MG) is a rare chronic autoimmune disease caused by the production of autoantibodies against the postsynaptic membrane receptors present at the neuromuscular junction. This condition is characterized by fatigue and muscle weakness, including diplopia, ptosis, and systemic impairment. Emerging evidence suggests that in addition to immune dysregulation, the pathogenesis of MG may involve mitochondrial damage and ferroptosis. Mitochondria are the primary site of energy production, and the reactive oxygen species (ROS) generated due to mitochondrial dysfunction can induce ferroptosis. Nanomedicines have been extensively employed to treat various disorders due to their modifiability and good biocompatibility, but their application in MG management has been rather limited. Nevertheless, nanodrug delivery systems that carry immunomodulatory agents, anti-oxidants, or ferroptosis inhibitors could be effective for the treatment of MG. Therefore, this review focuses on various nanoplatforms aimed at attenuating immune dysregulation, restoring mitochondrial function, and inhibiting ferroptosis that could potentially serve as promising agents for targeted MG therapy.

Extracellular matrix stiffness as an energy metabolism regulator drives osteogenic differentiation in mesenchymal stem cells

The biophysical factors of biomaterials such as their stiffness regulate stem cell differentiation. Energy metabolism has been revealed an essential role in stem cell lineage commitment. However, whether and how extracellular matrix (ECM) stiffness regulates energy metabolism to determine stem cell differentiation is less known. Here, the study reveals that stiff ECM promotes glycolysis, oxidative phosphorylation, and enhances antioxidant defense system during osteogenic differentiation in MSCs. Stiff ECM increases mitochondrial fusion by enhancing mitofusin 1 and 2 expression and inhibiting the dynamin-related protein 1 activity, which contributes to osteogenesis. Yes-associated protein (YAP) impacts glycolysis, glutamine metabolism, mitochondrial dynamics, and mitochondrial biosynthesis to regulate stiffness-mediated osteogenic differentiation. Furthermore, glycolysis in turn regulates YAP activity through the cytoskeletal tension-mediated deformation of nuclei. Overall, our findings suggest that YAP is an important mechanotransducer to integrate ECM mechanical cues and energy metabolic signaling to affect the fate of MSCs. This offers valuable guidance to improve the scaffold design for bone tissue engineering constructs.

Mitochondria in Mesenchymal Stem Cells: Key to Fate Determination and Therapeutic Potential

Mesenchymal stem cells (MSCs) have become popular tool cells in the field of transformation and regenerative medicine due to their function of cell rescue and cell replacement. The dynamically changing mitochondria serve as an energy metabolism factory and signal transduction platform, adapting to different cell states and maintaining normal cell activities. Therefore, a clear understanding of the regulatory mechanism of mitochondria in MSCs is profit for more efficient clinical transformation of stem cells. This review highlights the cutting-edge knowledge regarding mitochondrial biology from the following aspects: mitochondrial morphological dynamics, energy metabolism and signal transduction. The manuscript mainly focuses on mitochondrial mechanistic insights in the whole life course of MSCs, as well as the potential roles played by mitochondria in MSCs treatment of transplantation, for seeking pivotal targets of stem cell fate regulation and stem cell therapy.

An aldose reductase inhibitor, WJ-39, ameliorates renal tubular injury in diabetic nephropathy by activating PINK1/Parkin signaling

Renal tubular injury is a critical factor during the early stages of diabetic nephropathy (DN). Proximal tubular epithelial cells, which contain abundant mitochondria essential for intracellular homeostasis, are susceptible to disruptions in the intracellular environment, making them especially vulnerable to diabetic state disorders, which may be attributed to their elevated energy requirements and reliance on aerobic metabolism. It is widely thought that overactivation of the polyol pathway is implicated in DN pathogenesis, and inhibition of aldose reductase (AR), the rate-limiting enzyme in this pathway, represents a promising therapeutic avenue. WJ-39, a novel aldose reductase inhibitor, was investigated in this study for its protective effects on renal tubules in DN and the underlying mechanisms. Our findings revealed that WJ-39 significantly ameliorated the renal tubular morphology in high-fat diet (HFD)/streptozotocin (STZ)-induced DN rats, concurrently inhibiting fibrosis. Notably, WJ-39 safeguarded the structure and function of renal tubular mitochondria by enhancing mitochondrial dynamics. This involved the regulation of mitochondrial fission and fusion proteins and the promotion of PTEN-induced putative kinase 1 (PINK1)/Parkin-mediated mitophagy. Furthermore, WJ-39 demonstrated the inhibition of endogenous apoptosis by mitigating the production of mitochondrial reactive oxygen species (ROS). The protective effects of WJ-39 on mitochondria and apoptosis were countered in high glucose-treated HK-2 cells upon transfection with PINK1 siRNA. Overall, our findings suggest that WJ-39 protects the structural and functional integrity of renal tubules in DN, which may be attributed to its capacity to inhibit aldose reductase activity, activate the PINK1/Parkin signaling pathway, promote mitophagy, and alleviate apoptosis.

YAP/TAZ as Molecular Targets in Skeletal Muscle Atrophy and Osteoporosis

Skeletal muscles and bones are closely connected anatomically and functionally. Age-related degeneration in these tissues is associated with physical disability in the elderly and significantly impacts their quality of life. Understanding the mechanisms of age-related musculoskeletal tissue degeneration is crucial for identifying molecular targets for therapeutic interventions for skeletal muscle atrophy and osteoporosis. The Hippo pathway is a recently identified signaling pathway that plays critical roles in development, tissue homeostasis, and regeneration. The Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are key downstream effectors of the mammalian Hippo signaling pathway. This review highlights the fundamental roles of YAP and TAZ in the homeostatic maintenance and regeneration of skeletal muscles and bones. YAP/TAZ play a significant role in stem cell function by relaying various environmental signals to stem cells. Skeletal muscle atrophy and osteoporosis are related to stem cell dysfunction or senescence triggered by YAP/TAZ dysregulation resulting from reduced mechanosensing and mitochondrial function in stem cells. In contrast, the maintenance of YAP/TAZ activation can suppress stem cell senescence and tissue dysfunction and may be used as a basis for the development of potential therapeutic strategies. Thus, targeting YAP/TAZ holds significant therapeutic potential for alleviating age-related muscle and bone dysfunction and improving the quality of life in the elderly.

Mitochondrial DNA integrity and metabolome profile are preserved in the human induced pluripotent stem cell reference line KOLF2.1J

Quality control of human induced pluripotent stem cells (iPSCs) is critical to ensure reproducibility of research. Recently, KOLF2.1J was characterized and published as a male iPSC reference line to study neurological disorders. Emerging evidence suggests potential negative effects of mtDNA mutations, but its integrity was not analyzed in the original publication. To assess mtDNA integrity, we conducted a targeted mtDNA analysis followed by untargeted metabolomics analysis. We found that KOLF2.1J mtDNA integrity was intact at the time of publication and is still preserved in the commercially distributed cell line. In addition, the basal KOLF2.1J metabolome profile was similar to that of the two commercially available iPSC lines IMR90 and iPSC12, but clearly distinct from an in-house-generated ERCC6R683X/R683X iPSC line modeling Cockayne syndrome. Conclusively, we validate KOLF2.1J as a reference iPSC line, and encourage scientists to conduct mtDNA analysis and unbiased metabolomics whenever feasible.

Mitochondria at the Nanoscale: Physics Meets Biology-What Does It Mean for Medicine?

Mitochondria are commonly perceived as "cellular power plants". Intriguingly, power conversion is not their only function. In the first part of this paper, we review the role of mitochondria in the evolution of eukaryotic organisms and in the regulation of the human body, specifically focusing on cancer and autism in relation to mitochondrial dysfunction. In the second part, we overview our previous works, revealing the physical principles of operation for proton-pumping complexes in the inner mitochondrial membrane. Our proposed simple models reveal the physical mechanisms of energy exchange. They can be further expanded to answer open questions about mitochondrial functions and the medical treatment of diseases associated with mitochondrial disorders.

Glutathione safeguards TET-dependent DNA demethylation and is critical for the acquisition of totipotency and pluripotency during preimplantation development

During early development, both genome-wide epigenetic reprogramming and metabolic remodeling are hallmark changes of normal embryogenesis. However, little is known about their relationship and developmental functions during the preimplantation window, which is essential for the acquisition of totipotency and pluripotency. Herein, we reported that glutathione (GSH), a ubiquitous intracellular protective antioxidant that maintains mitochondrial function and redox homeostasis, plays a critical role in safeguarding postfertilization DNA demethylation and is essential for establishing developmental potential in preimplantation embryos. By profiling mitochondria-related transcriptome that coupled with different pluripotency, we found GSH is a potential marker that is tightly correlated with full pluripotency, and its beneficial effect on prompting developmental potential was functionally conformed using in vitro fertilized mouse and bovine embryos as the model. Mechanistic study based on preimplantation embryos and embryonic stem cells further revealed that GSH prompts the acquisition of totipotency and pluripotency by facilitating ten-eleven-translocation (TET)-dependent DNA demethylation, and ascorbic acid (AsA)-GSH cycle is implicated in the process. In addition, we also reported that GSH serves as an oviductal paracrine factor that supports development potential of preimplantation embryos. Thus, our results not only advance the current knowledge of functional links between epigenetic reprogramming and metabolic remodeling during preimplantation development but also provided a promising approach for improving current in vitro culture system for assisted reproductive technology.

Orientation-invariant autoencoders learn robust representations for shape profiling of cells and organelles

Cell and organelle shape are driven by diverse genetic and environmental factors and thus accurate quantification of cellular morphology is essential to experimental cell biology. Autoencoders are a popular tool for unsupervised biological image analysis because they learn a low-dimensional representation that maps images to feature vectors to generate a semantically meaningful embedding space of morphological variation. The learned feature vectors can also be used for clustering, dimensionality reduction, outlier detection, and supervised learning problems. Shape properties do not change with orientation, and thus we argue that representation learning methods should encode this orientation invariance. We show that conventional autoencoders are sensitive to orientation, which can lead to suboptimal performance on downstream tasks. To address this, we develop O2-variational autoencoder (O2-VAE), an unsupervised method that learns robust, orientation-invariant representations. We use O2-VAE to discover morphology subgroups in segmented cells and mitochondria, detect outlier cells, and rapidly characterise cellular shape and texture in large datasets, including in a newly generated synthetic benchmark.

Mechanical activation of mitochondria in germ cell differentiation

Mitochondria are activated during stem cell differentiation. Recently, Wang et al. found that mechanical stimulation from tissue surrounding differentiating germ cells in the female fly ovary is necessary to sustain intracellular calcium levels, promoting mitochondrial activity. This suggests a molecular link between cell mechanics and developmental metabolic transitions in eukaryotes.

Characteristics and Comparative Analysis of the Special-Structure (Non-Single-Circle) Mitochondrial Genome of Capsicum pubescens Ruiz & Pav

Chilean peppers, cultivated from Capsicum pubescens, are globally renowned as popular vegetable and spice crops. C. pubescens belongs to the Capsicum L. (pepper) family and is one of the five pepper cultivars grown in China. In this study, we assembled and annotated the complete mt genome of C. pubescens. We investigated several aspects of its genome, including characteristics, codon usage, RNA editing sites, repeat sequences, selective pressure, gene clusters, and phylogenetic relationships. Furthermore, we compared it with other plant mt genomes. The data we obtained will provide valuable information for studying evolutionary processes in the Capsicum genus and will assist in the functional analysis of Capsicum mitogenomes.

The nascent polypeptide-associated complex subunit Egd1 is required for efficient selective mitochondrial degradation in budding yeast

Selective degradation of dysfunctional or excess mitochondria is a fundamental process crucial for cell homeostasis in almost all eukaryotes. This process relies on autophagy, an intracellular self-eating system conserved from yeast to humans and is thus called mitophagy. Detailed mechanisms of mitophagy remain to be fully understood. Here we show that mitochondrial degradation in budding yeast, which requires the pro-mitophagic protein Atg32, is strongly reduced in cells lacking Egd1, a beta subunit of the nascent polypeptide-associated complex acting in cytosolic ribosome attachment and protein targeting to mitochondria. By contrast, loss of the sole alpha subunit Egd2 or the beta subunit paralogue Btt1 led to only a partial or slight reduction in mitophagy. We also found that phosphorylation of Atg32, a crucial step for priming mitophagy, is decreased in the absence of Egd1. Forced Atg32 hyperphosphorylation almost completely restored mitophagy in egd1-null cells. Together, we propose that Egd1 acts in Atg32 phosphorylation to facilitate mitophagy.

Mitophagy induction improves salivary gland stem/progenitor cell function by reducing senescence after irradiation

BACKGROUND AND PURPOSE

Patients undergoing radiotherapy for head and neck cancer often experience a decline in their quality of life due to the co-irradiation of salivary glands. Radiation-induced cellular senescence is a key factor contributing to salivary gland dysfunction. Interestingly, mitochondrial dysfunction and cellular senescence have been reported to be strongly interconnected and thus implicated in several aging-related diseases. This study aims to investigate the role of mitochondrial dysfunction in senescence induction in salivary gland stem/progenitor cells after irradiation.

MATERIALS AND METHODS

A dose of 7 Gy photons was used to irradiate mouse salivary gland organoids. Senescent markers and mitochondrial function were assessed using rt-qPCR, western blot analysis, SA-β-Gal staining and flow cytometry analysis. Mitochondrial dynamics-related proteins were detected by western blot analysis while Mdivi-1 and MFI8 were used to modulate the mitochondrial fission process. To induce mitophagy, organoids were treated with Urolithin A and PMI and subsequently stem/progenitor cell self-renewal capacity was assessed as organoid forming efficiency.

RESULTS

Irradiation led to increased senescence and accumulation of dysfunctional mitochondria. This was accompanied by a strong downregulation of mitochondrial fission-related proteins and mitophagy-related genes. After irradiation, treatment with the mitophagy inducer Urolithin A attenuated the senescent phenotype and improved organoid growth and stem/progenitor cell self-renewal capacity.

CONCLUSION

This study shows the important interplay between senescence and mitochondrial dysfunction after irradiation. Importantly, activation of mitophagy improved salivary gland stem/progenitor cell function thereby providing a novel therapeutic strategy to restore the regenerative capacity of salivary glands following irradiation.

Autologous non-invasively derived stem cells mitochondria transfer shows therapeutic advantages in human embryo quality rescue

BACKGROUND

The decline in the quantity and quality of mitochondria are closely associated with infertility, particularly in advanced maternal age. Transferring autologous mitochondria into the oocytes of infertile females represents an innovative and viable strategy for treating infertility, with no concerns regarding ethical considerations. As the donor cells of mitochondria, stem cells have biological advantages but research and evidence in this area are quite scarce.

METHODS

To screen out suitable human autologous ooplasmic mitochondrial donor cells, we performed comprehensive assessment of mitochondrial physiology, function and metabolic capacity on a varity of autologous adipose, marrow, and urine-derived mesenchymal stromal cells (ADSC, BMSC and USC) and ovarian germline granulosa cells (GC). Further, to explore the biosafety, effect and mechanism of stem cell-derived mitochondria transfer on human early embryo development, randomized in-vitro basic studies were performed in both of the young and aged oocytes from infertile females.

RESULTS

Compared with other types of mesenchymal stromal cells, USC demonstrated a non-fused spherical mitochondrial morphology and low oxidative stress status which resembled the oocyte stage. Moreover, USC mitochondrial content, activity and function were all higher than other cell types and less affected by age, and it also exhibited a biphasic metabolic pattern similar to the pre-implantation stage of embryonic development. After the biosafety identification of the USC mitochondrial genome, early embryos after USC mitochondrial transfer showed improvements in mitochondrial content, activity, and cytoplasmic Ca2+ levels. Further, aging embryos also showed improvements in embryonic morphological indicators, euploidy rates, and oxidative stress status.

CONCLUSION

Autologous non-invasively derived USC mitochondria transfer may be an effective strategy to improve embryonic development and metabolism, especially in infertile females with advanced age or repeated pregnancy failure. It provides evidence and possibility for the autologous treatment of infertile females without invasive and ethical concerns.

Induced pluripotent stem cells derived from patients carrying mitochondrial mutations exhibit altered bioenergetics and aberrant differentiation potential

BACKGROUND

Human mitochondrial DNA mutations are associated with common to rare mitochondrial disorders, which are multisystemic with complex clinical pathologies. The pathologies of these diseases are poorly understood and have no FDA-approved treatments leading to symptom management. Leigh syndrome (LS) is a pediatric mitochondrial disorder that affects the central nervous system during early development and causes death in infancy. Since there are no adequate models for understanding the rapid fatality associated with LS, human-induced pluripotent stem cell (hiPSC) technology has been recognized as a useful approach to generate patient-specific stem cells for disease modeling and understanding the origins of the phenotype.

METHODS

hiPSCs were generated from control BJ and four disease fibroblast lines using a cocktail of non-modified reprogramming and immune evasion mRNAs and microRNAs. Expression of hiPSC-associated intracellular and cell surface markers was identified by immunofluorescence and flow cytometry. Karyotyping of hiPSCs was performed with cytogenetic analysis. Sanger and next-generation sequencing were used to detect and quantify the mutation in all hiPSCs. The mitochondrial respiration ability and glycolytic function were measured by the Seahorse Bioscience XFe96 extracellular flux analyzer.

RESULTS

Reprogrammed hiPSCs expressed pluripotent stem cell markers including transcription factors POU5F1, NANOG and SOX2 and cell surface markers SSEA4, TRA-1-60 and TRA-1-81 at the protein level. Sanger sequencing analysis confirmed the presence of mutations in all reprogrammed hiPSCs. Next-generation sequencing demonstrated the variable presence of mutant mtDNA in reprogrammed hiPSCs. Cytogenetic analyses confirmed the presence of normal karyotype in all reprogrammed hiPSCs. Patient-derived hiPSCs demonstrated decreased maximal mitochondrial respiration, while mitochondrial ATP production was not significantly different between the control and disease hiPSCs. In line with low maximal respiration, the spare respiratory capacity was lower in all the disease hiPSCs. The hiPSCs also demonstrated neural and cardiac differentiation potential.

CONCLUSION

Overall, the hiPSCs exhibited variable mitochondrial dysfunction that may alter their differentiation potential and provide key insights into clinically relevant developmental perturbations.

Augmenting Mitochondrial Respiration in Immature Smooth Muscle Cells with an ACTA2 Pathogenic Variant Mitigates Moyamoya-like Cerebrovascular Disease

ACTA2 pathogenic variants altering arginine 179 cause childhood-onset strokes due to moyamoya disease (MMD)-like occlusion of the distal internal carotid arteries. A smooth muscle cell (SMC)-specific knock-in mouse model (Acta2SMC-R179C/+) inserted the mutation into 67% of aortic SMCs, whereas explanted SMCs were uniformly heterozygous. Acta2R179C/+ SMCs fail to fully differentiate and maintain stem cell-like features, including high glycolytic flux, and increasing oxidative respiration (OXPHOS) with nicotinamide riboside (NR) drives the mutant SMCs to differentiate and decreases migration. Acta2SMC-R179C/+ mice have intraluminal MMD-like occlusive lesions and strokes after carotid artery injury, whereas the similarly treated WT mice have no strokes and patent lumens. Treatment with NR prior to the carotid artery injury attenuates the strokes, MMD-like lumen occlusions, and aberrant vascular remodeling in the Acta2SMC-R179C/+ mice. These data highlight the role of immature SMCs in MMD-associated occlusive disease and demonstrate that altering SMC metabolism to drive quiescence of Acta2R179C/+ SMCs attenuates strokes and aberrant vascular remodeling in the Acta2SMC-R179C/+ mice.

Huangkui capsule attenuates diabetic kidney disease through the induction of mitophagy mediated by STING1/PINK1 signaling in tubular cells

BACKGROUND

Mitochondria is critic to tubulopathy, especially in diabetic kidney disease (DKD). Huangkui capsule (HKC; a new ethanol extract from the dried corolla of Abelmoschus manihot) has significant clinical effect on DKD. Previous studies have shown that HKC protects kidney by regulating mitochondrial function, but its mechanism is still unclear. The latest research found that the stimulator of interferon genes (STING1) signal pathway is closely related to mitophagy. However, whether HKC induces mitophagy through targeting STING1/PTEN-Induced putative kinase (PINK1) in renal tubular remains elusive.

OBJECTIVE

This study aims to clarify the therapeutic effect of HKC on renal tubular mitophagy in DKD and its potential mechanism in vivo and in vitro.

METHODS

Forty male C57BL/6 mice were randomly divided into 5 groups: CON group, DKD group, HKC-L (1.0 g/kg/day, by gavage), HKC-H (2.0 g/kg/day), and LST group. Diabetes model was induced by high-fat diet (HFD) combined with intraperitoneal injection of Streptozotocin (STZ). LST (losartan) is used as a positive control drug. Then, the glomeruli, renal tubular lesions, mitochondrial morphology and function of renal tubular cells and mitophagy levels were detected in mice. In addition, a high glucose injury model was established using HK2 human renal tubular cells. Pretreate HK2 cells with HKC or LST and detect mitochondrial function, mitophagy level, and autophagic flux. In addition, small interfering RNAs (siRNAs) of STING1 and PINK1 and overexpressing pcDNA3.1 plasmids were transfected into HK-2 cells to validate the mitophagy mechanism regulated by STING1/PINK1 signaling.

RESULTS

The ratio of urinary albumin to creatinine (ACR), fasting blood glucose, body weight in the early DKD mice model was increased, with damage to the glomerulus and renal tubules, mitochondrial structure and dysfunction in the renal tubules, and inhibition of STING1/PINK1 mediated mitophagy. Although the fasting blood glucose, body weight and serum creatinine levels were hardly ameliated, high dose HKC (2.0 g/kg/day) treatment significantly reduced ACR in the DKD mice to some extent, improved renal tubular injury, accurately upregulated STING1/PINK1 signaling mediated mitophagy levels, improved autophagic flux, and restored healthy mitochondrial pools. In vitro, an increase in mitochondrial fragments, fusion to fission, ROS and apoptosis, and a decrease in respiratory function, mtDNA, and membrane potential were observed in HK2 cells exposed to high glucose. HKC treatment significantly protected mitochondrial dynamics and function, which is consistent with in vivo results. Further research has shown that HKC can increase the level of mitophagy mediated by STING1/PINK1 in HK2 cells.

CONCLUSIONS

Our results suggest that HKC ameliorates renal tubulopathy in DKD and induces mitophagy partly through the up-regulation of the STING1/PINK1 pathway. These findings may provide an innovative therapeutic basis for DKD treatment.

Insights on the role of L-lactate as a signaling molecule in skin aging

L-lactate is a catabolite from the anaerobic metabolism of glucose, which plays a paramount role as a signaling molecule in various steps of the cell survival. Its activity, as a master tuner of many mechanisms underlying the aging process, for example in the skin, is still presumptive, however its crucial position in the complex cross-talk between mitochondria and the process of cell survival, should suggest that L-lactate may be not a simple waste product but a fine regulator of the aging/survival machinery, probably via mito-hormesis. Actually, emerging evidence is highlighting that ROS are crucial in the signaling of skin health, including mechanisms underlying wound repair, renewal and aging. The ROS, including superoxide anion, hydrogen peroxide, and nitric oxide, play both beneficial and detrimental roles depending upon their levels and cellular microenvironment. Physiological ROS levels are essential for cutaneous health and the wound repair process. Aberrant redox signaling activity drives chronic skin disease in elderly. On the contrary, impaired redox modulation, due to enhanced ROS generation and/or reduced levels of antioxidant defense, suppresses wound healing via promoting lymphatic/vascular endothelial cell apoptosis and death. This review tries to elucidate this issue.

Bioenergetic profile and redox tone modulate in vitro osteogenesis of human dental pulp stem cells: new perspectives for bone regeneration and repair

BACKGROUND

Redox signaling and energy metabolism are known to be involved in controlling the balance between self-renewal and proliferation/differentiation of stem cells. In this study we investigated metabolic and redox changes occurring during in vitro human dental pulp stem cells (hDPSCs) osteoblastic (OB) differentiation and tested on them the impact of the reactive oxygen species (ROS) signaling.

METHODS

hDPSCs were isolated from dental pulp and subjected to alkaline phosphatase and alizarin red staining, q-RT-PCR, and western blotting analysis of differentiation markers to assess achievement of osteogenic/odontogenic differentiation. Moreover, a combination of metabolic flux analysis and confocal cyto-imaging was used to profile the metabolic phenotype and to evaluate the redox tone of hDPSCs.

RESULTS

In differentiating hDPSCs we observed the down-regulation of the mitochondrial respiratory chain complexes expression since the early phase of the process, confirmed by metabolic flux analysis, and a reduction of the basal intracellular peroxide level in its later phase. In addition, dampened glycolysis was observed, thereby indicating a lower energy-generating phenotype in differentiating hDPSCs. Treatment with the ROS scavenger Trolox, applied in the early-middle phases of the process, markedly delayed OB differentiation of hDPSCs assessed as ALP activity, Runx2 expression, mineralization capacity, expression of stemness and osteoblast marker genes (Nanog, Lin28, Dspp, Ocn) and activation of ERK1/2. In addition, the antioxidant partly prevented the inhibitory effect on cell metabolism observed following osteogenic induction.

CONCLUSIONS

Altogether these results provided evidence that redox signaling, likely mediated by peroxide species, influenced the stepwise osteogenic expansion/differentiation of hDPSCs and contributed to shape its accompanying metabolic phenotype changes thus improving their efficiency in bone regeneration and repair.

Mitochondria in cancer stem cells: Achilles heel or hard armor

Previous studies have shown that mitochondria play core roles in not only cancer stem cell (CSC) metabolism but also the regulation of CSC stemness maintenance and differentiation, which are key regulators of cancer progression and therapeutic resistance. Therefore, an in-depth study of the regulatory mechanism of mitochondria in CSCs is expected to provide a new target for cancer therapy. This article mainly introduces the roles played by mitochondria and related mechanisms in CSC stemness maintenance, metabolic transformation, and chemoresistance. The discussion mainly focuses on the following aspects: mitochondrial morphological structure, subcellular localization, mitochondrial DNA, mitochondrial metabolism, and mitophagy. The manuscript also describes the recent clinical research progress on mitochondria-targeted drugs and discusses the basic principles of their targeted strategies. Indeed, an understanding of the application of mitochondria in the regulation of CSCs will promote the development of novel CSC-targeted strategies, thereby significantly improving the long-term survival rate of patients with cancer.

Role of SH3GLB1 in the regulation of CD133 expression in GBM cells

BACKGROUND

Glioblastoma (GBM), a malignant brain tumor, has poor survival outcomes due to recurrence or drug resistance. We found that SH3GLB1 is a crucial factor for cells to evade temozolomide (TMZ) cytotoxicity through autophagy-mediated oxidative phosphorylation, which is associated with CD133 levels. Therefore, we propose that SH3GLB1 participate in the impact on tumor-initiating cells (TICs).

METHODS

The parental, the derived resistant cell lines and their CD133⁺ cells were used, and the levels of the proteins were compared by western blotting. Then RNA interference was applied to observe the effects of the target protein on TIC-related features. Finally, in vitro transcription assays were used to validate the association between SH3GLB1 and CD133.

RESULTS

The CD133⁺ cells from resistant cells with enhanced SH3GLB1 levels more easily survived cytotoxic treatment than those from the parental cells. Inhibition of SH3GLB1 attenuated frequency and size of spheroid formation, and the levels of CD133 and histone 4 lysine 5 (H4K5) acetylation can be simultaneously regulated by SH3GLB1 modification. The H4K5 acetylation of the CD133 promoter was later suggested to be the mediating mechanism of SH3GLB1.

CONCLUSIONS

These data indicate that SH3GLB1 can regulate CD133 expression, suggesting that the protein plays a crucial role in TICs. Our findings on the effects of SH3GLB1 on the cells will help explain tumor resistance formation.

Contact sites between endoplasmic reticulum sheets and mitochondria regulate mitochondrial DNA replication and segregation

Mitochondria are multifaceted organelles crucial for cellular homeostasis that contain their own genome. Mitochondrial DNA (mtDNA) replication is a spatially regulated process essential for the maintenance of mitochondrial function, its defect causing mitochondrial diseases. mtDNA replication occurs at endoplasmic reticulum (ER)-mitochondria contact sites and is affected by mitochondrial dynamics: The absence of mitochondrial fusion is associated with mtDNA depletion whereas loss of mitochondrial fission causes the aggregation of mtDNA within abnormal structures termed mitobulbs. Here, we show that contact sites between mitochondria and ER sheets, the ER structure associated with protein synthesis, regulate mtDNA replication and distribution within mitochondrial networks. DRP1 loss or mutation leads to modified ER sheets and alters the interaction between ER sheets and mitochondria, disrupting RRBP1-SYNJ2BP interaction. Importantly, mtDNA distribution and replication were rescued by promoting ER sheets-mitochondria contact sites. Our work identifies the role of ER sheet-mitochondria contact sites in regulating mtDNA replication and distribution.

Dynamin-independent CaV1.2 and KCa1.1 channels regulation and vascular tone modulation by the mitochondrial fission inhibitors dynasore and dyngo-4a

A role for mitochondrial fission in vascular contraction has been proposed based on the vasorelaxant activity of the dynamin (and mitochondrial fission) inhibitors mdivi-1 and dynasore. However, mdivi-1 is capable to inhibit Ba2+ currents through CaV1.2 channels (IBa1.2), stimulate KCa1.1 channel currents (IKCa1.1), and modulate pathways key to the maintenance of vessel active tone in a dynamin-independent manner. Using a multidisciplinary approach, the present study demonstrates that dynasore, like mdivi-1, is a bi-functional vasodilator, blocking IBa1.2 and stimulating IKCa1.1 in rat tail artery myocytes, as well as promoting relaxation of rat aorta rings pre-contracted by either high K+ or phenylephrine. Conversely, its analogue dyngo-4a, though inhibiting mitochondrial fission triggered by phenylephrine and stimulating IKCa1.1, did not affect IBa1.2 but potentiated both high K+- and phenylephrine-induced contractions. Docking and molecular dynamics simulations identified the molecular basis supporting the different activity of dynasore and dyngo-4a at CaV1.2 and KCa1.1 channels. Mito-tempol only partially counteracted the effects of dynasore and dyngo-4a on phenylephrine-induced tone. In conclusion, the present data, along with previous observations (Ahmed et al., 2022) rise caution for the use of dynasore, mdivi-1, and dyngo-4a as tools to investigate the role of mitochondrial fission in vascular contraction: to this end, a selective dynamin inhibitor and/or a different experimental approach are needed.

Metformin impairs trophoblast metabolism and differentiation in a dose-dependent manner

Metformin is a widely prescribed medication whose mechanism of action is not completely defined and whose role in gestational diabetes management remains controversial. In addition to increasing the risk of fetal growth abnormalities and preeclampsia, gestational diabetes is associated with abnormalities in placental development including impairments in trophoblast differentiation. Given that metformin impacts cellular differentiation events in other systems, we assessed metformin's impact on trophoblast metabolism and differentiation. Using established cell culture models of trophoblast differentiation, oxygen consumption rates and relative metabolite abundance were determined following 200 µM (therapeutic range) and 2000 µM (supra-therapeutic range) metformin treatment using Seahorse and mass-spectrometry approaches. While no differences in oxygen consumption rates or relative metabolite abundance were detected between vehicle and 200 µM metformin-treated cells, 2000 µM metformin impaired oxidative metabolism and increased the abundance of lactate and TCA cycle intermediates, α-ketoglutarate, succinate, and malate. Examining differentiation, treatment with 2000 μM, but not 200 µM metformin, impaired HCG production and expression of multiple trophoblast differentiation markers. Overall, this work suggests that supra-therapeutic concentrations of metformin impair trophoblast metabolism and differentiation whereas metformin concentrations in the therapeutic range do not strongly impact these processes.

Mitochondrial citrate metabolism and efflux regulate BeWo differentiation

Cytotrophoblasts fuse to form and renew syncytiotrophoblasts necessary to maintain placental health throughout gestation. During cytotrophoblast to syncytiotrophoblast differentiation, cells undergo regulated metabolic and transcriptional reprogramming. Mitochondria play a critical role in differentiation events in cellular systems, thus we hypothesized that mitochondrial metabolism played a central role in trophoblast differentiation. In this work, we employed static and stable isotope tracing untargeted metabolomics methods along with gene expression and histone acetylation studies in an established BeWo cell culture model of trophoblast differentiation. Differentiation was associated with increased abundance of the TCA cycle intermediates citrate and α-ketoglutarate. Citrate was preferentially exported from mitochondria in the undifferentiated state but was retained to a larger extent within mitochondria upon differentiation. Correspondingly, differentiation was associated with decreased expression of the mitochondrial citrate transporter (CIC). CRISPR/Cas9 disruption of the mitochondrial citrate carrier showed that CIC is required for biochemical differentiation of trophoblasts. Loss of CIC resulted in broad alterations in gene expression and histone acetylation. These gene expression changes were partially rescued through acetate supplementation. Taken together, these results highlight a central role for mitochondrial citrate metabolism in orchestrating histone acetylation and gene expression during trophoblast differentiation.

Protective effect of resveratrol on mitochondrial biogenesis during hyperoxia-induced brain injury in neonatal pups

BACKGROUND

Neonatal hyperoxic brain injury is caused by exposure to hyperphysiological oxygen content during the period of incomplete development of the oxidative stress defence system, resulting in a large number of reactive oxygen species (ROS) and causing damage to brain tissue. Mitochondrial biogenesis refers to the synthesis of new mitochondria from existing mitochondria, mostly through the PGC-1α/Nrfs/TFAM signalling pathway. Resveratrol (Res), a silencing information regulator 2-related enzyme 1 (Sirt1) agonist, has been shown to upregulate the level of Sirt1 and the expression of peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α). We speculate that Res has a protective effect on hyperoxia-induced brain injury through mitochondrial biogenesis.

METHODS

Sprague-Dawley (SD) pups were randomly divided into the nonhyperoxia (NN) group, the nonhyperoxia with dimethyl sulfoxide (ND) group, the nonhyperoxia with Res (NR) group, the hyperoxia (HN) group, the hyperoxia with dimethyl sulfoxide (HD) group, and the hyperoxia with Res (HR) group within 12 h after birth. The HN, HD, and HR groups were placed in a high-oxygen environment (80‒85%), and the other three groups were placed in the standard atmosphere. The NR and HR groups were given 60 mg/kg Res every day, the ND and HD groups were given the same dose of dimethyl sulfoxide (DMSO) every day, and the NN and HN groups were given the same dose of normal saline every day. On postnatal day (PN) 1, PN7, and PN14, brain samples were acquired for HE staining to assess pathology, TUNEL to detect apoptosis, and real-time quantitative polymerase chain reaction and immunoblotting to detect the expression levels of Sirt1, PGC-1α, nuclear respiratory factor 1 (Nrf1), nuclear respiratory factor 2 (Nrf2) and mitochondrial transcription factor A (TFAM) in brain tissue.

RESULTS

Hyperoxia induced brain tissue injury; increased brain tissue apoptosis; inhibited Sirt1, PGC-1α, Nrf1, Nrf2, TFAM mRNA expression in mitochondria; diminished the ND1 copy number and ND4/ND1 ratio; and decreased Sirt1, PGC-1α, Nrf1, Nrf2, and TFAM protein levels in the brain. In contrast, Res reduced brain injury and attenuated brain tissue apoptosis in neonatal pups and increased the levels of the corresponding indices.

CONCLUSION

Res has a protective effect on hyperoxia-induced brain injury in neonatal SD pups by upregulating Sirt1 and stimulating the PGC-1α/Nrfs/TFAM signalling pathway for mitochondrial biogenesis.

Glutaminolysis and the Control of Neural Progenitors in Neocortical Development and Evolution

Multiple types of neural progenitor cells (NPCs) contribute to the development of the neocortex, a brain region responsible for our higher cognitive abilities. Proliferative capacity of NPCs varies among NPC types, developmental stages, and species. The higher proliferative capacity of NPCs in the developing human neocortex is thought to be a major contributing factor why humans have the most expanded neocortex within primates. Recent studies have shed light on the importance of cell metabolism in the neocortical NPC proliferative capacity. Specifically, glutaminolysis, a metabolic pathway that converts glutamine to glutamate and then to α-ketoglutarate, has been shown to play a critical role in human NPCs, both in apical and basal progenitors. In this review, we summarize our current knowledge of NPC metabolism, focusing especially on glutaminolysis, and discuss the role of NPC metabolism in neocortical development, evolution, and neurodevelopmental disorders, providing a broader perspective on a newly emerging research field.

Modeling mitochondrial DNA diseases: from base editing to pluripotent stem-cell-derived organoids

Mitochondrial DNA (mtDNA) diseases are multi-systemic disorders caused by mutations affecting a fraction or the entirety of mtDNA copies. Currently, there are no approved therapies for the majority of mtDNA diseases. Challenges associated with engineering mtDNA have in fact hindered the study of mtDNA defects. Despite these difficulties, it has been possible to develop valuable cellular and animal models of mtDNA diseases. Here, we describe recent advances in base editing of mtDNA and the generation of three-dimensional organoids from patient-derived human-induced pluripotent stem cells (iPSCs). Together with already available modeling tools, the combination of these novel technologies could allow determining the impact of specific mtDNA mutations in distinct human cell types and might help uncover how mtDNA mutation load segregates during tissue organization. iPSC-derived organoids could also represent a platform for the identification of treatment strategies and for probing the in vitro effectiveness of mtDNA gene therapies. These studies have the potential to increase our mechanistic understanding of mtDNA diseases and may open the way to highly needed and personalized therapeutic interventions.

Melatonin-mediated malic enzyme 2 orchestrates mitochondrial fusion and respiratory functions to promote odontoblastic differentiation during tooth development

Tooth development is a complex process that is tightly controlled by circadian rhythm. Melatonin (MT) is a major hormonal regulator of the circadian rhythm, and influences dentin formation and odontoblastic differentiation during tooth development; however, the underlying mechanism remains elusive. This study investigated how MT regulates odontoblastic differentiation, with a special focus on its regulation of mitochondrial dynamics. In rat dental papilla cells (DPCs), we found that MT promotes odontoblastic differentiation concurrently with enhanced mitochondrial fusion, while disruption of mitochondrial fusion by depleting optic atrophy 1 (OPA1) impairs MT-mediated differentiation and mitochondrial respiratory functions. Through RNA sequencing, we discovered that MT significantly upregulated malic enzyme 2 (ME2), a mitochondrial NAD(P)⁺ -dependent enzyme, and identified ME2 as a critical MT downstream effector that orchestrates odontoblastic differentiation, mitochondrial fusion, and respiration functions. By detecting the spatiotemporal expression of ME2 in developing tooth germs, and using tooth germ reconstituted organoids, we also provided in vivo and ex vivo evidence that ME2 promotes dentin formation, indicating a possible involvement of ME2 in MT-modulated tooth development. Collectively, our findings offer novel understandings regarding the molecular mechanism by which MT affects cell differentiation and organogenesis, meanwhile, the critical role of ME2 in MT-regulated mitochondrial functions is also highlighted.

Metformin impairs trophoblast metabolism and differentiation in dose dependent manner

Metformin is a widely prescribed medication whose mechanism of action is not completely defined and whose role in gestational diabetes management remains controversial. In addition to increasing risks of fetal growth abnormalities and preeclampsia, gestational diabetes is associated with abnormalities in placental development including impairments in trophoblast differentiation. Given that metformin impacts cellular differentiation events in other systems, we assessed metformin's impact on trophoblast metabolism and differentiation. Using established cell culture models of trophoblast differentiation, oxygen consumption rates and relative metabolite abundance were determined following 200 μM (therapeutic range) and 2000 μM (supra-therapeutic range) metformin treatment using Seahorse and mass-spectrometry approaches. While no differences in oxygen consumption rates or relative metabolite abundance were detected between vehicle and 200 μM metformin treated cells, 2000 μM metformin impaired oxidative metabolism and increased abundance of lactate and TCA cycle intermediates, α-ketoglutarate, succinate, and malate. Examining differentiation, treatment with 2000 μM, but not 200 μM metformin, impaired HCG production and expression of multiple trophoblast differentiation markers. Overall, this work suggests that supra-therapeutic concentrations of metformin impairs trophoblast metabolism and differentiation whereas metformin concentrations in the therapeutic range do not strongly impact these processes.

Transcriptome analysis of the response to thyroid hormone in Xenopus neural stem and progenitor cells

BACKGROUND

The thyroid hormones-thyroxine (T4) and 3,5,3'triiodothyronine (T3)-regulate the development of the central nervous system (CNS) in vertebrates by acting in different cell types. Although several T3 target genes have been identified in the brain, the changes in the transcriptome in response to T3 specifically in neural stem and progenitor cells (NSPCs) during the early steps of NSPCs activation and neurogenesis have not been studied in vivo. Here, we characterized the transcriptome of FACS-sorted NSPCs in response to T3 during Xenopus laevis metamorphosis.

RESULTS

We identified 1252 upregulated and 726 downregulated genes after 16 hours of T3 exposure. Gene ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that T3-upregulated genes were significantly enriched in rRNA processing and maturation, protein folding, ribosome biogenesis, translation, mitochondrial function, and proteasome. These results suggest that NSPCs activation induced by T3 is characterized by an early proteome remodeling through the synthesis of the translation machinery and the degradation of proteins by the proteasome.

CONCLUSION

This work provides new insights into the dynamics of activation of NPSCs in vivo in response to T3 during a critical period of neurogenesis in the metamorphosis.

Mitochondrial remodelling is essential for female germ cell differentiation and survival

Stem cells often possess immature mitochondria with few inner membrane invaginations, which increase as stem cells differentiate. Despite this being a conserved feature across many stem cell types in numerous organisms, how and why mitochondria undergo such remodelling during stem cell differentiation has remained unclear. Here, using Drosophila germline stem cells (GSCs), we show that Complex V drives mitochondrial remodelling during the early stages of GSC differentiation, prior to terminal differentiation. This endows germline mitochondria with the capacity to generate large amounts of ATP required for later egg growth and development. Interestingly, impairing mitochondrial remodelling prior to terminal differentiation results in endoplasmic reticulum (ER) lipid bilayer stress, Protein kinase R-like ER kinase (PERK)-mediated activation of the Integrated Stress Response (ISR) and germ cell death. Taken together, our data suggest that mitochondrial remodelling is an essential and tightly integrated aspect of stem cell differentiation. This work sheds light on the potential impact of mitochondrial dysfunction on stem and germ cell function, highlighting ER lipid bilayer stress as a potential major driver of phenotypes caused by mitochondrial dysfunction.

Mitochondrial citrate metabolism and efflux regulates trophoblast differentiation

Cytotrophoblasts fuse to form and renew syncytiotrophoblasts necessary to maintain placental health throughout gestation. During cytotrophoblast to syncytiotrophoblast differentiation, cells undergo regulated metabolic and transcriptional reprogramming. Mitochondria play a critical role in differentiation events in cellular systems, thus we hypothesized that mitochondrial metabolism played a central role in trophoblast differentiation. In this work, we employed static and stable isotope tracing untargeted metabolomics methods along with gene expression and histone acetylation studies in an established cell culture model of trophoblast differentiation. Trophoblast differentiation was associated with increased abundance of the TCA cycle intermediates citrate and α-ketoglutarate. Citrate was preferentially exported from mitochondria in the undifferentiated state but was retained to a larger extent within mitochondria upon differentiation. Correspondingly, differentiation was associated with decreased expression of the mitochondrial citrate transporter (CIC). CRISPR/Cas9 disruption of the mitochondrial citrate carrier showed that CIC is required for biochemical differentiation of trophoblasts. Loss of CIC resulted in broad alterations in gene expression and histone acetylation. These gene expression changes were partially rescued through acetate supplementation. Taken together, these results highlight a central role for mitochondrial citrate metabolism in orchestrating histone acetylation and gene expression during trophoblast differentiation.

Plpp3, a novel regulator of pluripotency exit and endodermal differentiation of mouse embryonic stem cells

In recent decades, study of the actions of bioactive lipids such as lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) has increased since they are involved in regulating many processes, including self-renewal of embryonic stem cells, embryo development and cancer. Phospholipid phosphatase type 3 (PLPP3) has been shown to be a key player in regulating the balance of these lipids and, in consequence, their signaling. Different lines of evidence suggest that PLPP3 could play a role in endoderm development. To approach this hypothesis, we used mouse embryonic stem cells (ESC) as a model to study Plpp3 function in self-renewal and the transition towards differentiation. We found that lack of PLPP3 mainly affects endoderm formation during differentiation of suspension-formed embryoid bodies. PLPP3-deficient ESC strongly decrease the amount of FOXA2-expressing cells and fail to properly downregulate the expression of pluripotency factors when subjected to an endoderm-directed differentiation protocol. Impaired endoderm differentiation correlated with a transient reduction in nuclear localization of YAP1. These phenotypes were rescued by transiently restoring the expression of catalytically active hPLPP3. In conclusion, PLPP3 plays a role in downregulating pluripotency-associated factors and in endodermal differentiation. PLPP3 regulates proper lipid/YAP1 signaling required for endodermal differentiation.

Teriflunomide as a therapeutic means for myelin repair

BACKGROUND

Promotion of myelin repair in the context of demyelinating diseases such as multiple sclerosis (MS) still represents a clinical unmet need, given that this disease is not only characterized by autoimmune activities but also by impaired regeneration processes. Hence, this relates to replacement of lost oligodendrocytes and myelin sheaths-the primary targets of autoimmune attacks. Endogenous remyelination is mainly mediated via activation and differentiation of resident oligodendroglial precursor cells (OPCs), whereas its efficiency remains limited and declines with disease progression and aging. Teriflunomide has been approved as a first-line treatment for relapsing remitting MS. Beyond its role in acting via inhibition of de novo pyrimidine synthesis leading to a cytostatic effect on proliferating lymphocyte subsets, this study aims to uncover its potential to foster myelin repair.

METHODS

Within the cuprizone mediated de-/remyelination model teriflunomide dependent effects on oligodendroglial homeostasis and maturation, related to cellular processes important for myelin repair were analyzed in vivo. Teriflunomide administration was performed either as pulse or continuously and markers specific for oligodendroglial maturation and mitochondrial integrity were examined by means of gene expression and immunohistochemical analyses. In addition, axon myelination was determined using electron microscopy.

RESULTS

Both pulse and constant teriflunomide treatment efficiently boosted myelin repair activities in this model, leading to accelerated generation of oligodendrocytes and restoration of myelin sheaths. Moreover, teriflunomide restored mitochondrial integrity within oligodendroglial cells.

CONCLUSIONS

The link between de novo pyrimidine synthesis inhibition, oligodendroglial rescue, and maintenance of mitochondrial homeostasis appears as a key for successful myelin repair and hence for protection of axons from degeneration.

Flavonoids as new regulators of mitochondrial potassium channels: contribution to cardioprotection

Objectives

Acute myocardial ischemia is one of the major causes of illness in western society. Reduced coronary blood supply leads to cell death and loss of cardiomyocyte population, resulting in serious and often irreversible consequences on myocardial function. Mitochondrial potassium (mitoK) channels have been identified as fine regulators of mitochondrial function and, consequently, in the metabolism of the whole cell, and in the mechanisms underlying the cardioprotection. Interestingly, mitoK channels represent a novel putative target for treating cardiovascular diseases, particularly myocardial infarction, and their modulators represent an interesting tool for pharmacological intervention. In this review, we took up the challenge of selecting flavonoids that show cardioprotective properties through the activation of mitoK channels.

Key findings

A brief overview of the main information on mitoK channels and their participation in the induction of cytoprotective processes was provided. Then, naringenin, quercetin, morin, theaflavin, baicalein, epigallocatechin gallate, genistein, puerarin, luteolin and proanthocyanidins demonstrated to be effective modulators of mitoK channels activity, mediating many beneficial effects.

Summary

The pathophysiological role of mitoK channels has been investigated as well as the impact of flavonoids on this target with particular attention to their potential role in the prevention of cardiovascular disorders.

Learning from magnetotactic bacteria: mms6 protects stem cells from oxidative damage

Oxidative damage generally exists in stroke and impairs stem cells' survival; however, the problem is difficult to treat. In order to help stem cells to resist this damage, we inserted a magnetotactic bacteria (MB) gene, mms6, into the neural stem cell genome by lentiviral transfection. It was found that the transfection of mms6 significantly improved the survival rate of stem cells in the condition of iron overload but not hypoxia. The bioenergetic profile also revealed that iron overloading weakened the mitochondrial respiration and spare respiration capacity of stem cells, but that these were enhanced after the expression of mms6. Additionally, Western blotting (WB) data revealed that mms6 upregulated the expression of glutathione peroxidase (GPX4), which protected stem cells from oxidative damage and ferroptosis. In order to determine the possible mechanisms, we analyzed the interactions between the MMS6 protein, Fe2+, and GPX4 via analog computation. The predicted models found that the MMS6 protein had a direct chelating site in the region of M6A with divalent iron; it also had weak binding with GPX4. Taken together, the magnetotactic bacterial gene mms6 protected stem cells from oxidative damage via binding with Fe2+, which could help them adapt to the microenvironment of stroke.

Disrupting metformin adaptation of liver cancer cells by targeting the TOMM34/ATP5B axis

Metformin, a well-known antidiabetic drug, has been repurposed for cancer treatment; however, recently observed drug resistance and tumor metastasis have questioned its further application. Here, we found that long-term metformin exposure led to metabolic adaptation of hepatocellular carcinoma (HCC) cells, which was characterized by an obvious epithelial-mesenchymal transition (EMT) phenotype and compensatory elevation of oxidative phosphorylation (OXPHOS). TOMM34, a translocase of the outer mitochondrial membrane, was upregulated to promote tumor metastasis in response to metformin-induced metabolic stress. Mechanistically, TOMM34 interacted with ATP5B to preserve F₁ F_O -ATPase activity, which conferred mitochondrial OXPHOS and ATP production. This metabolic preference for OXPHOS suggested a large requirement of energy supply by cancer cells to survive and spread in response to therapeutic stress. Notably, disturbing the interaction between TOMM34 and ATP5B using Gboxin, a specific OXPHOS inhibitor, increased sensitivity to metformin and suppressed tumor progression both in vitro and in vivo. Overall, this study demonstrates a molecular link of the TOMM34/ATP5B-ATP synthesis axis during metformin adaptation and provides promising therapeutic targets for metformin sensitization in cancer treatment.

Plin2-mediated lipid droplet mobilization accelerates exit from pluripotency by lipidomic remodeling and histone acetylation

Metabolic switch is critical for cell fate determination through metabolic functions, epigenetic modifications, and gene expression. However, the mechanisms underlying these alterations and their functional roles remain unclear. Here, we show that Plin2-mediated moderate lipid hydrolysis is critical for pluripotency of embryonic stem cells (ESCs). Upon exit from pluripotency, lipid droplet (LD)-associated protein Plin2 is recognized by Hsc70 and degraded via chaperone-mediated autophagy to facilitate LD mobilization. Enhancing lipid hydrolysis by Plin2 knockout promotes pluripotency exit, which is recovered by ATGL inhibition. Mechanistically, excessive lipid hydrolysis induces a dramatic lipidomic remodeling characterized by decreased cardiolipin and phosphatidylethanolamine, which triggers defects in mitochondrial cristae and fatty acid oxidation, resulting in reduced acetyl-CoA and histone acetylation. Our results reveal how LD mobilization is regulated and its critical role in ESC pluripotency, and indicate the mechanism linking LD homeostasis to mitochondrial remodeling and epigenetic regulation, which might shed light on development and diseases.

Hyperhomocysteinemia exacerbates acute kidney injury via increased mitochondrial damage

Acute kidney injury (AKI) is a complex and common set of multifactorial clinical syndromes, and associated with increased in-hospital mortality. There is increasing evidence that Hyperhomocysteinemia (HHcy) is highly associated with the development of a variety of kidney diseases, including AKI. However, the pathogenesis of HHcy in AKI remains unclear. In this study, we investigated the effect and mechanism of HHcy on cisplatin-induced AKI in mice and NRK-52E cells cultured with HHcy. We confirmed that mice with HHcy had higher serum levels of creatinine and more severe renal tubule injury after cisplatin injection. We found that HHcy aggravated renal mitochondrial damage, mainly manifested as decreased ATP β, significantly increased cytoplasmic Cyt C expression and the ADP/ATP ratio, and a significantly decreased mitochondrial DNA (mtDNA) copy number. In addition, we found that HHcy accelerated cisplatin-induced renal DNA damage; culturing NRK-52E cells with homocysteine (Hcy) could significantly increase apoptosis and mitochondrial damage. Interestingly, we found that Mdivi-1 reduced Hcy-induced mitochondrial damage, thereby reducing the level of apoptosis. In conclusion, these results suggest that HHcy might aggravate the development of AKI by increasing mitochondrial damage and that reducing Hcy levels or inhibiting mitochondrial damage may be a potential therapeutic strategy to delay the development of AKI.

Proteomic, Transcriptomic, Mutational, and Functional Assays Reveal the Involvement of Both THF and PLP Sites at the GmSHMT08 in Resistance to Soybean Cyst Nematode

The serine hydroxymethyltransferase (SHMT; E.C. 2.1.2.1) is involved in the interconversion of serine/glycine and tetrahydrofolate (THF)/5,10-methylene THF, playing a key role in one-carbon metabolism, the de novo purine pathway, cellular methylation reactions, redox homeostasis maintenance, and methionine and thymidylate synthesis. GmSHMT08 is the soybean gene underlying soybean cyst nematode (SCN) resistance at the Rhg4 locus. GmSHMT08 protein contains four tetrahydrofolate (THF) cofactor binding sites (L129, L135, F284, N374) and six pyridoxal phosphate (PLP) cofactor binding/catalysis sites (Y59, G106, G107, H134, S190A, H218). In the current study, proteomic analysis of a data set of protein complex immunoprecipitated using GmSHMT08 antibodies under SCN infected soybean roots reveals the presence of enriched pathways that mainly use glycine/serine as a substrate (glyoxylate cycle, redox homeostasis, glycolysis, and heme biosynthesis). Root and leaf transcriptomic analysis of differentially expressed genes under SCN infection supported the proteomic data, pointing directly to the involvement of the interconversion reaction carried out by the serine hydroxymethyltransferase enzyme. Direct site mutagenesis revealed that all mutated THF and PLP sites at the GmSHMT08 resulted in increased SCN resistance. We have shown the involvement of PLP sites in SCN resistance. Specially, the effect of the two Y59 and S190 PLP sites was more drastic than the tested THF sites. This unprecedented finding will help us to identify the biological outcomes of THF and PLP residues at the GmSHMT08 and to understand SCN resistance mechanisms.

AIFM1 beyond cell death: An overview of this OXPHOS-inducing factor in mitochondrial diseases

Apoptosis-inducing factor (AIF) is a mitochondrial intermembrane space flavoprotein with diverse functions in cellular physiology. In this regard, a large number of studies have elucidated AIF's participation to chromatin condensation during cell death in development, cancer, cardiovascular and brain disorders. However, the discovery of rare AIFM1 mutations in patients has shifted the interest of biomedical researchers towards AIF's contribution to pathogenic mechanisms underlying inherited AIFM1-linked metabolic diseases. The functional characterization of AIF binding partners has rapidly advanced our understanding of AIF biology within the mitochondria and beyond its widely reported role in cell death. At the present time, it is reasonable to assume that AIF contributes to cell survival by promoting biogenesis and maintenance of the mitochondrial oxidative phosphorylation (OXPHOS) system. With this review, we aim to outline the current knowledge around the vital role of AIF by primarily focusing on currently reported human diseases that have been linked to AIFM1 deficiency.

A regeneration-triggered metabolic adaptation is necessary for cell identity transitions and cell cycle re-entry to support blastema formation and bone regeneration

Regeneration depends on the ability of mature cells at the injury site to respond to injury, generating tissue-specific progenitors that incorporate the blastema and proliferate to reconstitute the original organ architecture. The metabolic microenvironment has been tightly connected to cell function and identity during development and tumorigenesis. Yet, the link between metabolism and cell identity at the mechanistic level in a regenerative context remains unclear. The adult zebrafish caudal fin, and bone cells specifically, have been crucial for the understanding of mature cell contribution to tissue regeneration. Here, we use this model to explore the relevance of glucose metabolism for the cell fate transitions preceding new osteoblast formation and blastema assembly. We show that injury triggers a modulation in the metabolic profile at early stages of regeneration to enhance glycolysis at the expense of mitochondrial oxidation. This metabolic adaptation mediates transcriptional changes that make mature osteoblast amenable to be reprogramed into pre-osteoblasts and induces cell cycle re-entry and progression. Manipulation of the metabolic profile led to severe reduction of the pre-osteoblast pool, diminishing their capacity to generate new osteoblasts, and to a complete abrogation of blastema formation. Overall, our data indicate that metabolic alterations have a powerful instructive role in regulating genetic programs that dictate fate decisions and stimulate proliferation, thereby providing a deeper understanding on the mechanisms regulating blastema formation and bone regeneration.

Nestin-dependent mitochondria-ER contacts define stem Leydig cell differentiation to attenuate male reproductive ageing

Male reproductive system ageing is closely associated with deficiency in testosterone production due to loss of functional Leydig cells, which are differentiated from stem Leydig cells (SLCs). However, the relationship between SLC differentiation and ageing remains unknown. In addition, active lipid metabolism during SLC differentiation in the reproductive system requires transportation and processing of substrates among multiple organelles, e.g., mitochondria and endoplasmic reticulum (ER), highlighting the importance of interorganelle contact. Here, we show that SLC differentiation potential declines with disordered intracellular homeostasis during SLC senescence. Mechanistically, loss of the intermediate filament Nestin results in lower differentiation capacity by separating mitochondria-ER contacts (MERCs) during SLC senescence. Furthermore, pharmacological intervention by melatonin restores Nestin-dependent MERCs, reverses SLC differentiation capacity and alleviates male reproductive system ageing. These findings not only explain SLC senescence from a cytoskeleton-dependent MERCs regulation mechanism, but also suggest a promising therapy targeting SLC differentiation for age-related reproductive system diseases.

The regulatory mechanisms contributing to male reproductive ageing are unknown. Here, the authors show that Nestin-dependent mito-ER contacts (MERCs) regulate stem Leydig cell (SLC) senescence and provide insights into SLCs-targeting therapies.

LncRNA LOC105378097 inhibits cardiac mitophagy in natural ageing mice

BACKGROUND

The development of heart ageing is the main cause of chronic disability, disease and death in the elderly. Ample evidence has established a pivotal role for significantly reduced mitophagy in the ageing heart. However, the underlying mechanisms of mitophagy deficiency in ageing heart are little known. The present study aimed to explore the underlying mechanisms of lncRNA LOC105378097 (Senescence-Mitophagy Associated LncRNA, lncR-SMAL) actions on mitophagy in the setting of heart ageing.

METHODS

The expression of lncR-SMAL was measured in serum from different ages of human and heart from different ages of mice through a quantitative real-time polymerase chain reaction. The effects of lncR-SMAL on heart function of mice were assessed by echocardiography and pressure-volume measurements system. Cardiac senescence was evaluated by hematoxylin-eosin staining, senescence-associated β-galactosidase staining, flow cytometry and western blot analysis of expression of ageing related markes p53 and p21. Cardiomyocyte mitophagy was assessed by western blot, mRFP-GFP-LC3 adenovirus particles transfection and mito-Keima staining. Interaction between lncR-SMAL and Parkin was validated through molecular docking, RNA immunoprecipitation (RIP) and RNA pull-down assay. Ubiquitination assay was performed to explore the molecular mechanism of Parkin inhibition. The effects of lncR-SMAL on mitochondrial function were investigated through electron microscopic examination, JC-1 staining and oxygen consumption rates analysis.

RESULTS

The heart-enriched lncR-SMAL reached the expression crest in the serum of human at an age of 60. Exogenously overexpression of lncRNA SMAL deteriorated cardiac function exactly as natural ageing and inhibited the associated cardiomyocytes mitophagy by depressing Parkin protein level. Improved heart ageing and mitophagy caused by Parkin overexpression were reversed by lncR-SMAL in mice. In contrast, the loss of lncR-SMAL in AC16 cells induced the upregulation of Parkin protein and ameliorated mitophagy and mitochondrial dysfunction, resulting in alleviated cardiac senescence. Besides, we found the interaction between lncR-SMAL and Parkin protein through computational docking analysis, pull-down and RIP assay. This would contribute to the promotive effect of lncR-SMAL on Parkin ubiquitination and decrease Parkin protein stability.

CONCLUSIONS

The present study for the first time demonstrates a heart-enriched lncRNA, SMAL, that inhibits the mitophagy of cardiomyocytes via the downregulation of Parkin protein, which further contributes to heart ageing and cardiac dysfunction in natural ageing mice.