Mitochondria Lead the Way: Mitochondrial Dynamics and Function in Cellular Movements in Development and Disease

TNFα-mediated subcellular heterogeneity of succinate dehydrogenase activity in human airway smooth muscle cells

Tumor necrosis factor-α (TNFα) is a pro-inflammatory cytokine, which mediates acute inflammatory effects in response to allergens, pollutants, and respiratory infections. Previously, we reported that TNFα increased maximum O2 consumption rate (OCR) and mitochondrial volume density (MVD) in human airway smooth muscle (hASM) cells. However, TNFα decreased maximum OCR when normalized to mitochondrial volume. In addition, TNFα altered mitochondrial distribution and motility within hASM cells. Although high-resolution respirometry is valuable for assessing mitochondrial function, it overlooks mitochondrial structural and functional heterogeneity within cells. Therefore, a direct measurement of cellular mitochondrial function provides valuable information. Previously, we developed a confocal-based quantitative histochemical technique to determine the maximum velocity of the succinate dehydrogenase (SDH) reaction (SDHmax) in single cells and observed that cellular SDHmax corresponds with MVD. Therefore, we hypothesized that TNFα decreases SDHmax per mitochondrion in hASM cells. The hASM cells were treated with TNFα (20 ng/mL, 6 h, and 24 h) or untreated (time-matched control). Using three-dimensional (3-D) confocal imaging of labeled mitochondria and a concentric shell method for analysis, we quantified MVD, mitochondrial complexity index (MCI) and SDHmax relative to the nuclear membrane. Within each shell, SDHmax and MVD peaked in the perinuclear compartments and decreased toward the distal compartments of the cell. When normalized to mitochondrial volume, SDHmax decreased in the perinuclear compartments compared with distal compartments. TNFα caused a significant shift in mitochondrial morphometry and function compared to control. In conclusion, mitochondria within individual cells exhibit distinct morphological and functional heterogeneity, which is disrupted during acute inflammation.NEW & NOTEWORTHY Mitochondria show context-specific heterogeneity in their morphometry. Previously, we reported that acute TNFα exposure increased O2 consumption rate (OCR) and mitochondrial volume density, but decreased OCR per mitochondrion. TNFα also altered mitochondrial distribution and motility. To assess TNFα-mediated subcellular mitochondrial structural and functional heterogeneity, we used a confocal-based quantitative histochemical technique to determine the maximum velocity of succinate dehydrogenase reaction. Our findings highlight that mitochondria within cells exhibit functional heterogeneity, which is disrupted during inflammation.

Mitochondrial aldehyde dehydrogenase restores the migratory capacity inhibited by high glucose-induced hyperosmolality

Cell migration, which is often impaired under high glucose (HG) conditions, plays a crucial role in the pathogenesis of various diabetic complications. This study investigates the role of mitochondrial aldehyde dehydrogenase (ALDH2) in the HG-induced migratory inhibition. Using fibroblasts sub-cultured in HG medium as a cell model of chronic hyperglycemia, we found that prolonged exposure to HG stress inhibited cell migration via a novel mechanism independent of oxidative stress or cell death. By increasing osmolality, HG induced perinuclear clustering of mitochondria, enhanced focal adhesion maturation, and caused the cells to be less responsive to migratory cues. The pharmacological inhibition of ALDH2 exaggerated this phenomenon, while ALDH2 overexpression protected cells from the migratory impairment caused by HG-induced hyperosmolality. Cells with ALDH2 overexpression exhibited less mature focal adhesions and longer mitochondrial network, suggesting that ALDH2 might preserve mitochondrial integrity to facilitate the focal adhesion turnover during cell migration.

Protective Action of 3,5-Diiodo-L-Thyronine on Cigarette Smoke-Induced Mitochondrial Dysfunction in Human Alveolar Epithelial Cells

Background: Cigarette smoke (CS) is a major risk factor for chronic lung conditions. Oxidative stress and mitochondrial dysfunction play a crucial role in CS-induced pulmonary injury. 3,5-Diiodothyronine (T2) affects energy metabolism, having mitochondria as a major target. However, the underlying mechanisms of T2 related to lung diseases are poorly understood. Aims: To investigate the protective action of T2 on CS-induced mitochondrial dysfunction in an in vitro model of human epithelial alveolar cells. Methods: ATP synthesis and cytochrome c oxidase (COX) activity, as a marker of mitochondrial function, was assessed in A549 cells pretreated with T2 and exposed to CS using a bioluminescence assay and an Oroboros 2k-Oxygraph system, respectively. An evaluation of the oxidative status was conducted by assessing superoxide radical production, superoxide dismutase (SOD) activity, and H2O2 levels. Moreover, we investigated the mitochondrial mass via Mito-Tracker Green (MTG) staining and flow cytometry analysis. Results: CS significantly reduced ATP production. T2 pretreatment was found to prevent CS-induced impairments in ATP synthesis, enhancing COX activity. Additionally, the 2 h T2 pretreatment of CS-exposed cells mitigated CS-induced oxidative stress, thereby enhancing SOD activity and reducing the superoxide anion and H2O2 levels. Finally, MTG labeling was correlated with CS-induced mitochondrial mass gain, which is associated with cell senescence. Unexpectedly, T2 was not able to significantly prevent this mass increment, probably due to its rapid mode of action. Conclusions: Our results provide new insights into the protective effects of T2 against CS-induced mitochondrial damage.

Elevating VAPB-PTPIP51 integration repairs damaged mitochondria-associated endoplasmic reticulum membranes and inhibits lung fibroblasts activation

Long-term silica exposure to silica dust leads to irreversible pulmonary fibrosis, during which lung fibroblast activation plays an essential role. Mitochondria-associated endoplasmic reticulum membranes (MAMs) is a structural interface for communication between the outer mitochondrial membrane and the endoplasmic reticulum. VAPB-PTPIP51 is a key complex on MAMs. However, the role of VAPB-PTPIP51-linked MAMs in lung fibroblast activation remains under investigation. In this study, we observed mitochondrial damage and endoplasmic reticulum stress in a SiO2-induced lung fibrosis model using C57BL/6J mice. In the model of TGF-β1-induced mouse lung fibroblast (MLG) activation, interventions with Dioscin and TUDCA reduced mitochondrial damage and alleviated endoplasmic reticulum stress by repairing damaged MAMs. Additionally, TUDCA may restore the MAMs structure by enhancing the interaction between VAPB and PTPIP51. Our findings indicate that MAMs may play a crucial role in linking mitochondrial damage and endoplasmic reticulum stress, suggesting their potential involvement in fibroblast activation.

GJA1-20k, a Short Isoform of Connexin43, from Its Discovery to Its Potential Implication in Cancer Progression

The Connexin43 transmembrane protein (Cx43), encoded by the GJA1 gene, is a member of a multigenic family of proteins that oligomerize to form hemichannels and intercellular channels, allowing gap junctional intercellular communication between adjacent cells or communication between the intracellular and extracellular compartments. Cx43 has long been shown to play a significant but complex role in cancer development, acting as a tumor suppressor and/or tumor promoter. The effects of Cx43 are associated with both channel-dependent and -independent functionalities and differ depending on the expression level, subcellular location and the considered stage of cancer progression. Recently, six isoforms of Cx43 have been described and one of them, called GJA1-20k, has also been found to be expressed in cancer cells. This isoform is generated by alternative translation and corresponds to the end part of the fourth transmembrane domain and the entire carboxyl-terminal (CT) domain. Initial studies in the cardiac model implicated GJA1-20k in the trafficking of full-length Cx43 to the plasma membrane, in cytoskeletal dynamics and in mitochondrial fission and subcellular distribution. As these processes are associated with cancer progression, a potential link between Cx43 functions, mitochondrial activity and GJA1-20k expression can be postulated in this context. This review synthetizes the current knowledge on GJA1-20k and its potential involvement in processes related to epithelial-to-mesenchymal transition (EMT) and the proliferation, dissemination and quiescence of cancer cells. Particular emphasis is placed on the putative roles of GJA1-20k in full-length Cx43 exportation to the plasma membrane, mitochondrial activity and functions originally attributed to the CT domain.

Disrupted mitochondrial morphology and function exacerbate inflammation in elderly-onset ulcerative colitis

BACKGROUND

The characteristics of ulcerative colitis (UC) in the elderly are quite different from the young population. Mitochondrial injury is a key mechanism regulating both aging and inflammation. This study aims to reveal the role of mitochondrial damage in the pathogenesis of adult- and elderly-onset UC.

METHODS

RNA-sequencing of colonic mucosa from adult- and elderly-onset UC patients was performed. Mitochondria-related differentially expressive genes (mDEGs) and immune cell infiltration analysis were identified and performed in colonic tissues from UC patients. Mice aged 6-8 weeks and 20-24 months were administered 2% dextran sodium sulphate (DSS) for 7 days to induce colitis. Mitochondrial morphological changes and ATP levels were evaluated in the colons of mice. Mechanistically, we explored the association of key mDEG with reactive oxygen species (ROS), oxygen consumption rates, NLRP3/IL-1β pathway in HCT116 cell line.

RESULTS

Thirty mDEGs were identified between adult- and elderly-onset UC, which were related primarily to mitochondrial respiratory function and also had significant correlation with different infiltrates of immune cells. Compared with young colitis mice, DSS-induced colitis in the aged mice exhibited more severe inflammation, damaged mitochondrial structure and lower ATP levels in colonic tissues. ALDH1L1 was identified as a hub DEG through protein-protein interaction networks of RNA-seq, which was downregulated in UC patients or colitis mice versus healthy controls. In tumor necrosis factor-alpha-stimulated HCT116 cells, mitochondrial ROS, NLRP3 and IL-1β expression increased less and mitochondrial respiration had an upregulated trend after knocking down ALDH1L1.

CONCLUSION

There are significant differences in mitochondrial structure, ATP production and mitochondria-related gene expression between adult- and elderly-onset UC, which have a potential link with cytokine pathways and immune microenvironment. The more prominent mitochondrial injury may be a key factor for more severe inflammatory response and poorer outcome in elderly-onset UC.

Twist-Induced Epithelial-to-Mesenchymal Transition Confers Specific Metabolic and Mitochondrial Alterations

Cells undergo significant epigenetic and phenotypic change during the epithelial-to-mesenchymal transition (EMT), a process observed in development, wound healing, and cancer metastasis. EMT confers several advantageous characteristics, including enhanced migration and invasion, resistance to cell death, and altered metabolism. In disease, these adaptations could be leveraged as therapeutic targets. Here, we analyze Twist-induced EMT in non-transformed HMLE cells as well as a breast cancer cell line with (MDA-MB-231) and without (MCF7) EMT features to compare differences in metabolic pathways and mitochondrial morphology. Analysis of oxidative and glycolytic metabolism reveals a general EMT-associated glycolytic metabolic phenotype accompanied by increased ATP production. Furthermore, a decrease in mitochondrial size was also associated with EMT-positive cells. However, mitochondrial elongation and spatial dynamics were not consistently altered, as HMLE Twist cells exhibit more rounded and dispersed mitochondria compared to control, while MDA-MB-231 cells exhibit more elongated and clustered mitochondria compared to MCF7 cells. These results provide further insight as to the contextual nature of EMT conferred properties.

Rlip76 in ageing and Alzheimer's disease: Focus on oxidative stress and mitochondrial mechanisms

RLIP76 (Rlip), a stress-responsive protein, plays a multifaceted role in cellular function. This protein acts primarily as a glutathione-electrophile conjugate (GS-E) transporter, crucial for detoxifying hazardous compounds and converting them into mercapturic acids. RLIP76 also modulates cytoskeletal motility and membrane plasticity through its role in the Ral-signaling pathway, interacting with RalA and RalB, key small GTPases involved in growth and metastasis. Beyond its ATP-dependent transport functions in various tissues, RLIP76 also demonstrates GTPase Activating Protein (GAP) activity towards Rac1 and Cdc42, with a preference for Ral-GTP over Ral-GDP. Its functions span critical physiological processes including membrane dynamics, oxidative stress response, and mitochondrial dynamics. The protein's widespread expression and evolutionary conservation underscore its significance. Our lab discovered that Rlip interacts with Alzheimer's disease (AD) proteins, amyloid beta and phosphorylated and induce oxidative stress, mitochondrial dysfnction and synaptic damage in AD. Our in vitro studies revealed that overexpression of Rlip reduces mitochondrial abnormalities. Further, our in vivo studies (Rlip+/- mice) revealed that a partial reduction of Rlip in mice (Rlip+/-), leads to mitochondrial abnormalities, elevated oxidative stress, and cognitive deficits resembling late-onset AD, emphasizing the protein's crucial role in neuronal health and disease. Finally, we discuss the experimental cross-breedings of overexpression of mice Rlip TG/TG or Rlip + /- mice with Alzheimer's disease models - earlyonset 5XFAD, late-onset APPKI and Tau transgenic mice, providing new insights into RLIP76's role in AD progression and development. This review summarizes RLIP76's structure, function, and cellular pathways, highlighting its implications in AD and its potential as a therapeutic target.

Non-cell autonomous regulation of cell-cell signaling and differentiation by mitochondrial ROS

Mitochondrial reactive oxygen species (ROS) function intrinsically within cells to induce cell damage, regulate transcription, and cause genome instability. However, we know little about how mitochondrial ROS production non-cell autonomously impacts cell-cell signaling. Here, we show that mitochondrial dysfunction inhibits the plasma membrane localization of cell surface receptors that drive cell-cell communication during oogenesis. Within minutes, we found that mitochondrial ROS impairs exocyst membrane binding and leads to defective endosomal recycling. This endosomal defect impairs the trafficking of receptors, such as the Notch ligand Delta, during oogenesis. Remarkably, we found that overexpressing RAB11 restores ligand trafficking and rescues the developmental defects caused by ROS production. ROS production from adjacent cells acutely initiates a transcriptional response associated with growth and migration by suppressing Notch signaling and inducing extra cellualr matrix (ECM) remodeling. Our work reveals a conserved rapid response to ROS production that links mitochondrial dysfunction to the non-cell autonomous regulation of cell-cell signaling.

Biofunctionalization of dental abutments by a zinc/chitosan/gelatin coating to optimize fibroblast behavior and antibacterial properties

Tightly sealed peri-implant gingival tissue provides a barrier against oral bacterial invasion, protecting the alveolar bone and maintaining long-term implant survival. To investigate if zinc can enhance the integration between peri-implant gingival tissue and abutment surface, we herein present novel zinc/chitosan/gelatin (Zn/CS/Gel) coatings prepared using the electrophoretic deposition (EPD) technique. The effect of these coatings on human gingival fibroblasts (hGFs) was investigated by culturing these cells on top of the EPD coatings. Surface characterization demonstrated that Zn2+ were released in a sustained and pH-responsive manner. The preclinical cell culture evaluation of these coatings indicated that the zinc-containing coatings enhanced cell migration, adhesion and collagen secretion of hGFs. Moreover, the zinc-containing coatings exhibited antibacterial efficacy by inhibiting the growth of Porphyromonas gingivalis and reducing attachment of Staphylococcus aureus. Notably, zinc-free CS/Gel coatings prevented attachment of P. gingivalis as well. The coatings were also shown to be cytocompatible with epithelial cells and osteoblasts, which are other relevant cell types which surround dental implants after clinical placement. Based on our findings, it can be concluded that Zn-containing coatings hold promise to enhance the adhesion of gingival tissue to the implant surface, which may potentially contribute to the formation of a robust peri-implant soft sealing counteracting bacterial invasion.

Normothermic ex vivo kidney perfusion preserves mitochondrial and graft function after warm ischemia and is further enhanced by AP39

We previously reported that normothermic ex vivo kidney  perfusion (NEVKP) is superior in terms of organ protection compared to static cold storage (SCS), which is still the standard method of organ preservation, but the mechanisms are incompletely understood. We used a large animal kidney autotransplant model to evaluate mitochondrial function during organ preservation and after kidney transplantation, utilizing live cells extracted from fresh kidney tissue. Male porcine kidneys stored under normothermic perfusion showed preserved mitochondrial function and higher ATP levels compared to kidneys stored at 4 °C (SCS). Mitochondrial respiration and ATP levels were further enhanced when AP39, a mitochondria-targeted hydrogen sulfide donor, was administered during warm perfusion. Correspondingly, the combination of NEVKP and AP39 was associated with decreased oxidative stress and inflammation, and with improved graft function after transplantation. In conclusion, our findings suggest that the organ-protective effects of normothermic perfusion are mediated by maintenance of mitochondrial function and enhanced by AP39 administration. Activation of mitochondrial function through the combination of AP39 and normothermic perfusion could represent a new therapeutic strategy for long-term renal preservation.

UVB radiation exposure modulates mitophagy in embryonic cells of freshwater prawn Macrobrachium olfersii: Exploring a protective organelle quality control mechanism

Aquatic environments are subject to ultraviolet B (UVB) radiation incidence, and its effects on organisms are dose-dependent. Besides DNA, mitochondria are an important target of this radiation that causes structural damage and impairs its functional dynamics. Here, we hypothesize that mitophagy acts as an organelle quality control mechanism to mitigate UVB impacts in embryonic cells. Then, freshwater prawn Macrobrachium olfersii embryos was used as a model to investigate the effects of UVB on genes (Tomm20, Opa1, Pink, Prkn, Sqstm1, and Map1lc3) and proteins (TOM20, PINK1, p62 and LC3B) involved in mitophagy modulation. The choice of genes and proteins was based on the identification of mitochondrial membrane (Tomm20, Opa1 and TOM20), mediation of mitophagy (Pink1, Prkn and PINK1), and recognition of mitochondria by the autophagosome membrane (Sqstm1, Map1lc3, p62 and LC3B). First, the phylogeny of all genes presented bootstrap values >80 and conserved domains among crustacean species. Gene expression was inherently modulated during development, with transcripts (Tomm20, Opa1, Pink, Prkn, Sqstm1, and Map1lc3) overexpressed in the initial and final stages of development. Moreover, UVB radiation induced upregulation of Tomm20, Opa1, Pink, Prkn, Sqstm1, and Map1lc3 genes at 6 h after exposure. Interestingly, after 12 h, the protein content of PINK1, p62, and LC3B increased, while TOM20 was not responsive. Despite UVB radiation's harmful effects on embryonic cells, the chronology of gene expression and protein content indicates rapid activation of mitophagy, serving as an organelle quality control mechanism, given the analyzed cells' integrity.

Cellular and Molecular Responses to Mitochondrial DNA Deletions in Kearns-Sayre Syndrome: Some Underlying Mechanisms

Kearns-Sayre syndrome (KSS) is a rare multisystem mitochondrial disorder. It is caused by mitochondrial DNA (mtDNA) rearrangements, mostly large-scale deletions of 1.1-10 kb. These deletions primarily affect energy supply through impaired oxidative phosphorylation and reduced ATP production. This impairment gives rise to dysfunction of several tissues, in particular those with high energy demand like brain and muscles. Over the past decades, changes in respiratory chain complexes and energy metabolism have been emphasized, whereas little attention has been paid to other reports on ROS overproduction, protein synthesis inhibition, myelin vacuolation, demyelination, autophagy, apoptosis, and involvement of lipid raft and oligodendrocytes in KSS. Therefore, this paper draws attention towards these relatively underemphasized findings that might further clarify the pathologic cascades following deletions in the mtDNA.

Deciphering tissue-specific expression profiles of mitochondrial genome-encoded tRNAs and rRNAs through transcriptomic profiling in buffalo

BACKGROUND

Mitochondria, essential for cellular energy production through oxidative phosphorylation (OXPHOS), integrate mt-DNA and nuclear-encoded genes. This cooperation extends to the mitochondrial translation machinery, involving crucial mtDNA-encoded RNAs: 22 tRNAs (mt-tRNAs) as adapters and two rRNAs (mt-rRNAs) for ribosomal assembly, enabling mitochondrial-encoded mRNA translation. Disruptions in mitochondrial gene expression can strongly impact energy generation and overall animal health. Our study investigates the tissue-specific expression patterns of mt-tRNAs and mt-rRNAs in buffalo.

MATERIAL AND METHODS

To investigate the expression patterns of mt-tRNAs and mt-rRNAs in different tissues and gain a better understanding of tissue-specific variations, RNA-seq was performed on various tissues, such as the kidney, heart, brain, and ovary, from post-pubertal female buffaloes. Subsequently, we identified transcripts that were differentially expressed in various tissue comparisons.

RESULTS

The findings reveal distinct expression patterns among specific mt-tRNA and mt-rRNA genes across various tissues, with some exhibiting significant upregulation and others demonstrating marked downregulation in specific tissue contexts. These identified variations reflect tissue-specific physiological roles, underscoring their significance in meeting the unique energy demands of each tissue. Notably, the brain exhibits the highest mtDNA copy numbers and an abundance of mitochondrial mRNAs of our earlier findings, potentially linked to the significant upregulation of mt-tRNAs in brain. This suggests a plausible association between mtDNA replication and the regulation of mtDNA gene expression.

CONCLUSION

Overall, our study unveils the tissue-specific expression of mitochondrial-encoded non-coding RNAs in buffalo. As we proceed, our further investigations into tissue-specific mitochondrial proteomics and microRNA studies aim to elucidate the intricate mechanisms within mitochondria, contributing to tissue-specific mitochondrial attributes. This research holds promise to elucidate the critical role of mitochondria in animal health and disease.

Deficiency of ValRS-m Causes Male Infertility in Drosophila melanogaster

Drosophila spermatogenesis involves the renewal of germline stem cells, meiosis of spermatocytes, and morphological transformation of spermatids into mature sperm. We previously demonstrated that Ocnus (ocn) plays an essential role in spermatogenesis. The ValRS-m (Valyl-tRNA synthetase, mitochondrial) gene was down-regulated in ocn RNAi testes. Here, we found that ValRS-m-knockdown induced complete sterility in male flies. The depletion of ValRS-m blocked mitochondrial behavior and ATP synthesis, thus inhibiting the transition from spermatogonia to spermatocytes, and eventually, inducing the accumulation of spermatogonia during spermatogenesis. To understand the intrinsic reason for this, we further conducted transcriptome-sequencing analysis for control and ValRS-m-knockdown testes. The differentially expressed genes (DEGs) between these two groups were selected with a fold change of ≥2 or ≤1/2. Compared with the control group, 4725 genes were down-regulated (dDEGs) and 2985 genes were up-regulated (uDEGs) in the ValRS-m RNAi group. The dDEGs were mainly concentrated in the glycolytic pathway and pyruvate metabolic pathway, and the uDEGs were primarily related to ribosomal biogenesis. A total of 28 DEGs associated with mitochondria and 6 meiosis-related genes were verified to be suppressed when ValRS-m was deficient. Overall, these results suggest that ValRS-m plays a wide and vital role in mitochondrial behavior and spermatogonia differentiation in Drosophila.

Mitochondrial inhibitors: a new horizon in breast cancer therapy

Breast cancer, due to resistance to standard therapies such as endocrine therapy, anti-HER2 therapy and chemotherapy, continues to pose a major health challenge. A growing body of research emphasizes the heterogeneity and plasticity of metabolism in breast cancer. Because differences in subtypes exhibit a bias toward metabolic pathways, targeting mitochondrial inhibitors shows great potential as stand-alone or adjuvant cancer therapies. Multiple therapeutic candidates are currently in various stages of preclinical studies and clinical openings. However, specific inhibitors have been shown to face multiple challenges (e.g., single metabolic therapies, mitochondrial structure and enzymes, etc.), and combining with standard therapies or targeting multiple metabolic pathways may be necessary. In this paper, we review the critical role of mitochondrial metabolic functions, including oxidative phosphorylation (OXPHOS), the tricarboxylic acid cycle, and fatty acid and amino acid metabolism, in metabolic reprogramming of breast cancer cells. In addition, we outline the impact of mitochondrial dysfunction on metabolic pathways in different subtypes of breast cancer and mitochondrial inhibitors targeting different metabolic pathways, aiming to provide additional ideas for the development of mitochondrial inhibitors and to improve the efficacy of existing therapies for breast cancer.

An aggregated mitochondrial distribution in preimplantation embryos disrupts nuclear morphology, function, and developmental potential

A dispersed cytoplasmic distribution of mitochondria is a hallmark of normal cellular organization. Here, we have utilized the expression of exogenous Trak2 in mouse oocytes and embryos to disrupt the dispersed distribution of mitochondria by driving them into a large cytoplasmic aggregate. Our findings reveal that aggregated mitochondria have minimal impact on asymmetric meiotic cell divisions of the oocyte. In contrast, aggregated mitochondria during the first mitotic division result in daughter cells with unequal sizes and increased micronuclei. Further, in two-cell embryos, microtubule-mediated centering properties of the mitochondrial aggregate prevent nuclear centration, distort nuclear shape, and inhibit DNA synthesis and the onset of embryonic transcription. These findings demonstrate the motor protein-mediated distribution of mitochondria throughout the cytoplasm is highly regulated and is an essential feature of cytoplasmic organization to ensure optimal cell function.

Unraveling the NRF2 confusion: Distinguishing nuclear respiratory factor 2 from nuclear erythroid factor 2

In recent years, the acronym NRF2 has garnered significant attention in scientific discourse. However, this attention has occasionally led to confusion due to the existence of two distinct proteins sharing the same acronym: Nuclear Respiratory Factor 2 (NRF2), also known as GA-binding protein transcription factor subunit alpha (GABPA), and Nuclear Factor Erythroid 2-related Factor 2 (NFE2L2 or NRF2). This confusion has been highlighted in various scientific forums, including PubPeer and anonymous reader comments, where the confusion between the two proteins has been expressed. In this article, we aim to elucidate the disparities between these two proteins. Both are transcription factors that play pivotal roles in cellular homeostasis and response to stress, with some overlapping functional aspects. Nuclear Factor Erythroid 2-related Factor 2 (NFE2L2) is a key regulator of the antioxidant response element (ARE) pathway. It functions by binding to antioxidant response elements in the promoters of target genes, thereby orchestrating the expression of various cytoprotective enzymes and proteins involved in detoxification, redox balance, and cellular defense against oxidative stress. Conversely, Nuclear Respiratory Factor 2 (GABPA) is primarily associated with the regulation of mitochondrial biogenesis, in relation to PGC1α, and maintaining cellular energy metabolism. It is important to recognize and differentiate between these two proteins to avoid misconceptions and misinterpretations in scientific literature and discussions. Our laboratories (Arubala P Reddy and P. Hemachandra Reddy) focued on Nuclear Respiratory Factor 2 (NRF2), but not on Nuclear Factor Erythroid 2-related Factor 2 (NFE2L2). We hope that the facts, figures, and discussions presented in this article will clarify the current controversy regarding the sizes, structural features, and functional aspects of these proteins.

Heterogeneous distribution of mitochondria and succinate dehydrogenase activity in human airway smooth muscle cells

Succinate dehydrogenase (SDH) is a key mitochondrial enzyme involved in the tricarboxylic acid cycle, where it facilitates the oxidation of succinate to fumarate, and is coupled to the reduction of ubiquinone in the electron transport chain as Complex II. Previously, we developed a confocal-based quantitative histochemical technique to determine the maximum velocity of the SDH reaction (SDHmax) in single cells and observed that SDHmax corresponds with mitochondrial volume density. In addition, mitochondrial volume and motility varied within different compartments of human airway smooth muscle (hASM) cells. Therefore, we hypothesize that the SDH activity varies relative to the intracellular mitochondrial volume within hASM cells. Using 3D confocal imaging of labeled mitochondria and a concentric shell method for analysis, we quantified mitochondrial volume density, mitochondrial complexity index, and SDHmax relative to the distance from the nuclear membrane. The mitochondria within individual hASM cells were more filamentous in the immediate perinuclear region and were more fragmented in the distal parts of the cell. Within each shell, SDHmax also corresponded to mitochondrial volume density, where both peaked in the perinuclear region and decreased in more distal parts of the cell. Additionally, when normalized to mitochondrial volume, SDHmax was lower in the perinuclear region when compared to the distal parts of the cell. In summary, our results demonstrate that SDHmax measures differences in SDH activity within different cellular compartments. Importantly, our data indicate that mitochondria within individual cells are morphologically heterogeneous, and their distribution varies substantially within different cellular compartments, with distinct functional properties.

EP4-induced mitochondrial localization and cell migration mediated by CALML6 in human oral squamous cell carcinoma

Lymph node metastasis, primarily caused by the migration of oral squamous cell carcinoma (OSCC) cells, stands as a crucial prognostic marker. We have previously demonstrated that EP4, a subtype of the prostaglandin E2 (PGE2) receptor, orchestrates OSCC cell migration via Ca2+ signaling. The exact mechanisms by which EP4 influences cell migration through Ca2+ signaling, however, is unclear. Our study aims to clarify how EP4 controls OSCC cell migration through this pathway. We find that activating EP4 with an agonist (ONO-AE1-473) increased intracellular Ca2+ levels and the migration of human oral cancer cells (HSC-3), but not human gingival fibroblasts (HGnF). Further RNA sequencing linked EP4 to calmodulin-like protein 6 (CALML6), whose role remains undefined in OSCC. Through protein-protein interaction network analysis, a strong connection is identified between CALML6 and calcium/calmodulin-dependent protein kinase kinase 2 (CaMKK2), with EP4 activation also boosting mitochondrial function. Overexpressing EP4 in HSC-3 cells increases experimental lung metastasis in mice, whereas inhibiting CaMKK2 with STO-609 markedly lowers these metastases. This positions CaMKK2 as a potential new target for treating OSCC metastasis. Our findings highlight CALML6 as a pivotal regulator in EP4-driven mitochondrial respiration, affecting cell migration and metastasis via the CaMKK2 pathway.

New Insights in ATP Synthesis as Therapeutic Target in Cancer and Angiogenic Ocular Diseases

Lactate and ATP formation by aerobic glycolysis, the Warburg effect, is considered a hallmark of cancer. During angiogenesis in non-cancerous tissue, proliferating stalk endothelial cells (ECs) also produce lactate and ATP by aerobic glycolysis. In fact, all proliferating cells, both non-cancer and cancer cells, need lactate for the biosynthesis of building blocks for cell growth and tissue expansion. Moreover, both non-proliferating cancer stem cells in tumors and leader tip ECs during angiogenesis rely on glycolysis for pyruvate production, which is used for ATP synthesis in mitochondria through oxidative phosphorylation (OXPHOS). Therefore, aerobic glycolysis is not a specific hallmark of cancer but rather a hallmark of proliferating cells and limits its utility in cancer therapy. However, local treatment of angiogenic eye conditions with inhibitors of glycolysis may be a safe therapeutic option that warrants experimental investigation. Most types of cells in the eye such as photoreceptors and pericytes use OXPHOS for ATP production, whereas proliferating angiogenic stalk ECs rely on glycolysis for lactate and ATP production. (J Histochem Cytochem XX.XXX-XXX, XXXX).

Diversity of Intercellular Communication Modes: A Cancer Biology Perspective

From the moment a cell is on the path to malignant transformation, its interaction with other cells from the microenvironment becomes altered. The flow of molecular information is at the heart of the cellular and systemic fate in tumors, and various processes participate in conveying key molecular information from or to certain cancer cells. For instance, the loss of tight junction molecules is part of the signal sent to cancer cells so that they are no longer bound to the primary tumors and are thus free to travel and metastasize. Upon the targeting of a single cell by a therapeutic drug, gap junctions are able to communicate death information to by-standing cells. The discovery of the importance of novel modes of cell-cell communication such as different types of extracellular vesicles or tunneling nanotubes is changing the way scientists look at these processes. However, are they all actively involved in different contexts at the same time or are they recruited to fulfill specific tasks? What does the multiplicity of modes mean for the overall progression of the disease? Here, we extend an open invitation to think about the overall significance of these questions, rather than engage in an elusive attempt at a systematic repertory of the mechanisms at play.

Asymmetrical positioning of cell organelles reflects the cell chirality of mouse myoblast cells

Cell chirality is crucial for the chiral morphogenesis of biological tissues, yet its underlying mechanism remains unclear. Cell organelle polarization along multiple axes in a cell body, namely, apical-basal, front-rear, and left-right, is known to direct cell behavior such as orientation, rotation, and migration. Among these axes, the left-right bias holds significant sway in determining the chiral directionality of these behaviors. Normally, mouse myoblast (C2C12) cells exhibit a strong counterclockwise chirality on a ring-shaped micropattern, whereas they display a clockwise dominant chirality under Latrunculin A treatment. To investigate the relationship between multicellular chirality and organelle positioning in single cells, we studied the left-right positioning of cell organelles under distinct cell chirality in single cells via micropatterning technique, fluorescent microscopy, and imaging analysis. We found that on a "T"-shaped micropattern, a C2C12 cell adopts a triangular shape, with its nucleus-centrosome axis pointing toward the top-right direction of the "T." Several other organelles, including the Golgi apparatus, lysosomes, actin filaments, and microtubules, showed a preference to polarize on one side of the axis, indicating the universality of the left-right asymmetrical organelle positioning. Interestingly, upon reversing cell chirality with Latrunculin A, the organelles correspondingly reversed their left-right positioning bias, as suggested by the consistently biased metabolism and contractile properties at the leading edge. This left-right asymmetry in organelle positioning may help predict cell migration direction and serve as a potential marker for identifying cell chirality in biological models.

Mitochondrial morphology dynamics and ROS regulate apical polarity and differentiation in Drosophila follicle cells

Mitochondrial morphology dynamics regulate signaling pathways during epithelial cell formation and differentiation. The mitochondrial fission protein Drp1 affects the appropriate activation of EGFR and Notch signaling-driven differentiation of posterior follicle cells in Drosophila oogenesis. The mechanisms by which Drp1 regulates epithelial polarity during differentiation are not known. In this study, we show that Drp1-depleted follicle cells are constricted in early stages and present in multiple layers at later stages with decreased levels of apical polarity protein aPKC. These defects are suppressed by additional depletion of mitochondrial fusion protein Opa1. Opa1 depletion leads to mitochondrial fragmentation and increased reactive oxygen species (ROS) in follicle cells. We find that increasing ROS by depleting the ROS scavengers, mitochondrial SOD2 and catalase also leads to mitochondrial fragmentation. Further, the loss of Opa1, SOD2 and catalase partially restores the defects in epithelial polarity and aPKC, along with EGFR and Notch signaling in Drp1-depleted follicle cells. Our results show a crucial interaction between mitochondrial morphology, ROS generation and epithelial cell polarity formation during the differentiation of follicle epithelial cells in Drosophila oogenesis.

Microfluidic devices for precise measurements of cell directionality reveal a role for glutamine during cell migration

Cancer cells that migrate from tumors into surrounding tissues are responsible for cancer dissemination through the body. Microfluidic devices have been instrumental in discovering unexpected features of cancer cell migration, including the migration in self-generated gradients and the contributions of cell-cell contact during collective migration. Here, we design microfluidic channels with five successive bifurcations to characterize the directionality of cancer cell migration with high precision. We uncover an unexpected role for glutamine in epithelial cancer cell orientation, which could be replaced by alfa-keto glutarate but not glucose.

Promotion of mitochondrial fragmentation suppresses the formation of mitochondrial spherical compartmentation in PINK1B9Drosophila melanogaster

Mitochondria undergo structural changes reflective of functional statuses. Ultrastructural characterizing of mitochondria is valuable for understanding mitochondrial dysfunction in various pathological conditions. PINK1, a Parkinson's disease (PD) associated gene, plays key roles in maintaining mitochondrial function and integrity. In Drosophila melanogaster, deficiency of PINK1 results in PD-like pathologies due to mitochondrial abnormalities. Here, we report the existence of a new type of mitochondrial-membrane deformity, mitochondrial spherical compartmentation (MSC), caused by PINK1 deficiency in Drosophila. The MSC is a three-dimensional spheroid-like mitochondrial membrane structure encompassing nonselective contents. Upregulation of dDrp1, downregulation of dMarf, and upregulation of dArgK1-A-all resulting in mitochondrial fragmentation-were able to suppress the formation of MSC. Furthermore, arginine kinase, only when localizing to the vicinity of mitochondria, induced mitochondrial fragmentation and reversed the MSC phenotype. In summary, this study demonstrates that loss of dPINK1 leads to the formation of mitochondrial-membrane deformity MSC, which responds to mitochondrial dynamics. In addition, our data suggest a new perspective of how phosphagen energy-buffer system might regulate mitochondrial dynamics.

Human fetal dermal fibroblast-myeloid cell diversity is characterized by dominance of pro-healing Annexin1-FPR1 signaling

Fetal skin achieves scarless wound repair. Dermal fibroblasts play a central role in extracellular matrix deposition and scarring outcomes. Both fetal and gingival wound repair share minimal scarring outcomes. We tested the hypothesis that compared to adult skin fibroblasts, human fetal skin fibroblast diversity is unique and partly overlaps with gingival skin fibroblasts. Human fetal skin (FS, n = 3), gingiva (HGG, n = 13), and mature skin (MS, n = 13) were compared at single-cell resolution. Dermal fibroblasts, the most abundant cluster, were examined to establish a connectome with other skin cells. Annexin1-FPR1 signaling pathway was dominant in both FS as well as HGG fibroblasts and related myeloid cells while scanty in MS fibroblasts. Myeloid-specific FPR1-ORF delivered in murine wound edge using tissue nanotransfection (TNT) technology significantly enhanced the quality of healing. Pseudotime analyses identified the co-existence of an HGG fibroblast subset with FPR1high myeloid cells of fetal origin indicating common underlying biological processes.

Single-Cell RNA-Seq Reveals LRRC75A-Expressing Cell Population Involved in VEGF Secretion of Multipotent Mesenchymal Stromal/Stem Cells Under Ischemia

Human multipotent mesenchymal stromal/stem cells (MSCs) have been utilized in cell therapy for various diseases and their clinical applications are expected to increase in the future. However, the variation in MSC-based product quality due to the MSC heterogeneity has resulted in significant constraints in the clinical utility of MSCs. Therefore, we hypothesized that it might be important to identify and ensure/enrich suitable cell subpopulations for therapies using MSC-based products. In this study, we aimed to identify functional cell subpopulations to predict the efficacy of angiogenic therapy using bone marrow-derived MSCs (BM-MSCs). To assess its angiogenic potency, we observed various levels of vascular endothelial growth factor (VEGF) secretion among 11 donor-derived BM-MSC lines under in vitro ischemic culture conditions. Next, by clarifying the heterogeneity of BM-MSCs using single-cell RNA-sequencing analysis, we identified a functional cell subpopulation that contributed to the overall VEGF production in BM-MSC lines under ischemic conditions. We also found that leucine-rich repeat-containing 75A (LRRC75A) was more highly expressed in this cell subpopulation than in the others. Importantly, knockdown of LRRC75A using small interfering RNA resulted in significant inhibition of VEGF secretion in ischemic BM-MSCs, indicating that LRRC75A regulates VEGF secretion under ischemic conditions. Therefore, LRRC75A may be a useful biomarker to identify cell subpopulations that contribute to the angiogenic effects of BM-MSCs. Our work provides evidence that a strategy based on single-cell transcriptome profiles is effective for identifying functional cell subpopulations in heterogeneous MSC-based products.

Microfluidic Devices for Precise Measurements of Cell Directionality Reveal a Role for Glutamine during Cell Migration

Cancer cells that migrate from tumors into surrounding tissues are responsible for cancer dissemination through the body. Microfluidic devices have been instrumental in discovering unexpected features of cancer cell migration, including the migration in self-generated gradients and the contributions of cell-cell contact during collective migration. Here, we design microfluidic channels with five successive bifurcations to characterize the directionality of cancer cell migration with high precision. We find that the directional decisions of cancer cells moving through bifurcating channels in response to self-generated epidermal growth factor (EGF) gradients require the presence of glutamine in the culture media. A biophysical model helps quantify the contribution of glucose and glutamine to cancer cell orientation during migration in self-generated gradients. Our study uncovers an unexpected interplay between cancer cell metabolism and cancer cell migration studies and may eventually lead to new ways to delay cancer cell invasion.

Rapamycin ameliorates brain damage and maintains mitochondrial dynamic balance in diabetic rats subjected to middle cerebral artery occlusion

To investigate the effect of rapamycin on mitochondrial dynamic balance in diabetic rats subjected to cerebral ischemia-reperfusion injury. Male Sprague Dawley (SD) rats (n = 78) were treated with high fat diet combined with streptozotocin injection to construct diabetic model in rats. Transient middle cerebral artery occlusion (MCAO) of 2 hours was induced and the brains were harvested after 1 and 3 days of reperfusion. Rapamycin was injected intraperitoneally for 3 days prior to and immediately after operation, once a day. The neurological function was assessed, infarct volumes were measured and HE staining as well as immunohistochemistry were performed. The protein of hippocampus was extracted and Western blotting were performed to detect the levels of mTOR, mitochondrial dynamin related proteins (DRP1, p-DRP1, OPA1), SIRT3, and Nix/BNIP3L. Diabetic hyperglycemia worsened the neurological function performance (p < 0.01), enlarged infarct size (p < 0.01) and increased ischemic neuronal cell death (p < 0.01). The increased damage was associated with elevations of p-mTOR, p-S6, and p-DRP1; and suppressions of SIRT3 and Nix/BNIP3L. Rapamycin ameliorated diabetes-enhanced ischemic brain damage and reversed the biomarker alterations caused by diabetes. High glucose activated mTOR pathway and caused mitochondrial dynamics toward fission. The protective effect of rapamycin against diabetes-enhanced ischemic brain damage was associated with inhibiting mTOR pathway, redressing mitochondrial dynamic imbalance, and elevating SIRT3 and Nix/BNIP3L expression.

gp130 Activates Mitochondrial Dynamics for Hepatocyte Survival in a Model of Steatohepatitis

Obesity is the main cause of metabolic complications. Fatty liver infiltration is a companion of obesity. NAFLD is associated with impaired energy metabolism with an excess of nutrients. Mitochondrial dynamics are important for the regulation of energy balance, which regulates mitochondrial function, apoptosis, and mitophagy. The aim of this study was to investigate the effect of gp130 on the components of mitochondrial dynamics in a cellular model of steatohepatitis. Addition of IL-6/gp130 contributed to an increase in the percentage of live cells and a decrease in the percentage of dead and apoptotic cells. Addition of IL-6/gp130 increased the expression of NF-kB1 gene and mitochondrial dynamics markers (MFN2 and TFAM) in HepG2 with tBHP/Oleic. Addition of IL-6 or gp130 reduced the expression of cytoprotector genes (HSF1 and HSP70) in HepG2 cell cultures with tBHP/Oleic. Increased mitochondrial dynamics gene activity protected against HepG2 cell death in the steatohepatitis model. Trans-signaling resulted in increased TFAM and MAPLC3B, and decreased DNM1L gene expression in HepG2 with tBHP/Oleic.

Mitochondrial network expansion and dynamic redistribution during islet morphogenesis in zebrafish larvae

Mitochondria, organelles critical for energy production, modify their shape and location in response to developmental state and metabolic demands. Mitochondria are altered in diabetes, but the mechanistic basis is poorly defined, due to difficulties in assessing mitochondria within an intact organism. Here, we use in vivo imaging in transparent zebrafish larvae to demonstrate filamentous, interconnected mitochondrial networks within islet cells. Mitochondrial movements highly resemble what has been reported for human islet cells in vitro, showing conservation in behaviour across species and cellular context. During islet development, mitochondrial content increases with emergence of cell motility, and mitochondria disperse within fine protrusions. Overall, this work presents quantitative analysis of mitochondria within their native environment and provides insights into mitochondrial behaviour during organogenesis.

Mitochondrial fragmentation and ROS signaling in wound response and repair

Mitochondria are organelles that serve numerous critical cellular functions, including energy production, Ca2+ homeostasis, redox signaling, and metabolism. These functions are intimately linked to mitochondrial morphology, which is highly dynamic and capable of rapid and transient changes to alter cellular functions in response to environmental cues and cellular demands. Mitochondrial morphology and activity are critical for various physiological processes, including wound healing. In mammals, wound healing is a complex process that requires coordinated function of multiple cell types and progresses in partially overlapping but distinct stages: hemostasis and inflammation, cell proliferation and migration, and tissue remodeling. The repair process at the single-cell level forms the basis for wound healing and regeneration in tissues. Recent findings reveal that mitochondria fulfill the intensive energy demand for wound repair and aid wound closure by cytoskeleton remodeling via morphological changes and mitochondrial reactive oxygen species (mtROS) signaling. In this review, we will mainly elucidate how wounding induces changes in mitochondrial morphology and activity and how these changes, in turn, contribute to cellular wound response and repair.

Mitochondrial Control in Inflammatory Gastrointestinal Diseases

Mitochondria play a central role in the pathophysiology of inflammatory bowel disease (IBD) and colorectal cancer (CRC). The maintenance of mitochondrial function is necessary for a stable immune system. Mitochondrial dysfunction in the gastrointestinal system leads to the excessive activation of multiple inflammatory signaling pathways, leading to IBD and increased severity of CRC. In this review, we focus on the mitochondria and inflammatory signaling pathways and its related gastrointestinal diseases.

Simple to Complex: The Role of Actin and Microtubules in Mitochondrial Dynamics in Amoeba, Yeast, and Mammalian Cells

Mitochondria are complex organelles that provide energy for the cell in the form of adenosine triphosphate (ATP) and have very specific structures. For most organisms, this is a reticular or tubular mitochondrial network, while others have singular oval-shaped organelles. Nonetheless, maintenance of this structure is dependent on the mitochondrial dynamics, fission, fusion, and motility. Recently, studies have shown that the cytoskeleton has a significant role in the regulation of mitochondrial dynamics. In this review, we focus on microtubules and actin filaments and look at what is currently known about the cytoskeleton’s role in mitochondrial dynamics in complex models like mammals and yeast, as well as what is known in the simple model system, Dictyostelium discoideum. Understanding how the cytoskeleton is involved in mitochondrial dynamics increases our understanding of mitochondrial disease, especially neurodegenerative diseases. Increases in fission, loss of fusion, and fragmented mitochondria are seen in several neurodegenerative diseases such as Parkinson’s, Alzheimer’s, and Huntington’s disease. There is no known cure for these diseases, but new therapeutic strategies using drugs to alter mitochondrial fusion and fission activity are being considered. The future of these therapeutic studies is dependent on an in-depth understanding of the mechanisms of mitochondrial dynamics. Understanding the cytoskeleton’s role in dynamics in multiple model organisms will further our understanding of these mechanisms and could potentially uncover new therapeutic targets for these neurodegenerative diseases.

Mitochondrial trafficking and redox/phosphorylation signaling supporting cell migration phenotypes

Regulation of cell signaling cascades is critical in making sure the response is activated spatially and for a desired duration. Cell signaling cascades are spatially and temporally controlled through local protein phosphorylation events which are determined by the activation of specific kinases and/or inactivation of phosphatases to elicit a complete and thorough response. For example, A-kinase-anchoring proteins (AKAPs) contribute to the local regulated activity protein kinase A (PKA). The activity of kinases and phosphatases can also be regulated through redox-dependent cysteine modifications that mediate the activity of these proteins. A primary example of this is the activation of the epidermal growth factor receptor (EGFR) and the inactivation of the phosphatase and tensin homologue (PTEN) phosphatase by reactive oxygen species (ROS). Therefore, the local redox environment must play a critical role in the timing and magnitude of these events. Mitochondria are a primary source of ROS and energy (ATP) that contributes to redox-dependent signaling and ATP-dependent phosphorylation events, respectively. The strategic positioning of mitochondria within cells contributes to intracellular gradients of ROS and ATP, which have been shown to correlate with changes to protein redox and phosphorylation status driving downstream cellular processes. In this review, we will discuss the relationship between subcellular mitochondrial positioning and intracellular ROS and ATP gradients that support dynamic oxidation and phosphorylation signaling and resulting cellular effects, specifically associated with cell migration signaling.

Synthesis and in Vivo Evaluation of Triphenylphosphonium Conjugated Trimetazidine with Enhanced Cardioprotection and Ability to Restore Mitochondrial Function

Trimetazidine exhibits great therapeutic potential in cardiovascular diseases and mitochondria-mediated cardioprotection by trimetazidine has been widely reported. In this study, to enhance its cardioprotection, the triphenylphosphonium-based modification of trimetazidine was conducted to deliver it specifically to mitochondria. Fifteen triphenylphosphonium (TPP) conjugated trimetazidine analogs were designed and synthesized. Their protective effects were evaluated in vivo using a tert-butyl hydroperoxide (t-BHP) induced zebrafish injury model. Structure-activity relationship correlations revealed the best way to couple the TPP moiety to trimetazidine, and led to a new conjugate (18a) with enhanced therapeutic properties. Compared to trimetazidine, 18a effectively protects against heart injury in the zebrafish model at a much lower concentration. Further study in t-BHP treated zebrafish and H9c2 cells demonstrated that 18a protects against cardiomyocyte death and damage by inhibiting excessive production of ROS, maintaining mitochondrial morphology, and preventing mitochondrial dysfunction. Consequently, 18a can be regarded as a potential therapeutic agent for cardioprotection.

Mitofusins: from mitochondria to fertility

Germ cell formation and embryonic development require ATP synthesized by mitochondria. The dynamic system of the mitochondria, and in particular, the fusion of mitochondria, are essential for the generation of energy. Mitofusin1 and mitofusin2, the homologues of Fuzzy onions in yeast and Drosophila, are critical regulators of mitochondrial fusion in mammalian cells. Since their discovery mitofusins (Mfns) have been the source of significant interest as key influencers of mitochondrial dynamics, including membrane fusion, mitochondrial distribution, and the interaction with other organelles. Emerging evidence has revealed significant insight into the role of Mfns in germ cell formation and embryonic development, as well as the high incidence of reproductive diseases such as asthenospermia, polycystic ovary syndrome, and gestational diabetes mellitus. Here, we describe the key mechanisms of Mfns in mitochondrial dynamics, focusing particularly on the role of Mfns in the regulation of mammalian fertility, including spermatogenesis, oocyte maturation, and embryonic development. We also highlight the role of Mfns in certain diseases associated with the reproductive system and their potential as therapeutic targets.