Modulating mitochondrial dynamics ameliorates left ventricular dysfunction by suppressing diverse cell death pathways after diabetic cardiomyopathy.

Diabetic cardiomyopathy (DCM) triggers a detrimental shift in mitochondrial dynamics, characterized by increased fission and decreased fusion, contributing to cardiomyocyte apoptosis and cardiac dysfunction. This study investigated the impact of modulating mitochondrial dynamics on DCM outcomes and underlying mechanisms in a mouse model. DCM induction led to upregulation of fission genes (Drp1, Mff, Fis1) and downregulation of fusion genes (Mfn1, Mfn2, Opa1). Inhibiting fission with Mdivi-1 or promoting fusion with Ginsenoside Rg1 preserved cardiac function, as evidenced by improved left ventricular ejection fraction (LVEF), fractional shortening (FS), and E/A ratio. Both treatments also reduced infarct size and attenuated cardiomyocyte apoptosis, indicated by decreased caspase-3 activity. Mechanistically, Mdivi-1 enhanced mitochondrial function by improving mitochondrial membrane potential, reducing reactive oxygen species (ROS) production, and increasing ATP generation. Ginsenoside Rg1 also preserved mitochondrial integrity and function under hypoxic conditions in HL-1 cardiomyocytes. These findings suggest that restoring the balance of mitochondrial dynamics through pharmacological interventions targeting either fission or fusion may offer a promising therapeutic strategy for mitigating MI-induced cardiac injury and improving patient outcomes.

Bcl-2 Orthologues, Buffy and Debcl, Can Suppress Drp1-Dependent Age-Related Phenotypes in Drosophila.

The relationship of Amyotrophic Lateral Sclerosis, Parkinson's disease, and other age-related neurodegenerative diseases with mitochondrial dysfunction has led to our study of the mitochondrial fission gene Drp1 in Drosophila melanogaster and aspects of aging. Previously, the Drp1 protein has been demonstrated to interact with the Drosophila Bcl-2 mitochondrial proteins, and Drp1 mutations can lead to mitochondrial dysfunction and neuronal loss. In this study, the Dopa decarboxylase-Gal4 (Ddc-Gal4) transgene was exploited to direct the expression of Drp1 and Drp1-RNAi transgenes in select neurons. Here, the knockdown of Drp1 seems to compromise locomotor function throughout life but does not alter longevity. The co-expression of Buffy suppresses the poor climbing induced by the knockdown of the Drp1 function. The consequences of Drp1 overexpression, which specifically reduced median lifespan and diminished climbing abilities over time, can be suppressed through the directed co-overexpression of pro-survival Bcl-2 gene Buffy or by the co-knockdown of the pro-cell death Bcl-2 homologue Debcl. Alteration of the expression of Drp1 acts to phenocopy neurodegenerative disease phenotypes in Drosophila, while overexpression of Buffy can counteract or rescue these phenotypes to improve overall health. The diminished healthy aging due to either the overexpression of Drp1 or the RNA interference of Drp1 has produced novel Drosophila models for investigating mechanisms underlying neurodegenerative disease.

N6-Methyladenosine-mediated phase separation suppresses NOTCH1 expression and promotes mitochondrial fission in diabetic cardiac fibrosis.

BACKGROUND: N6-methyladenosine (m6A) modification of messenger RNA (mRNA) is crucial for liquid-liquid phase separation in mammals. Increasing evidence indicates that liquid-liquid phase separation in proteins and RNAs affects diabetic cardiomyopathy. However, the molecular mechanism by which m6A-mediated phase separation regulates diabetic cardiac fibrosis remains elusive. METHODS: Leptin receptor-deficient mice (db/db), cardiac fibroblast-specific Notch1 conditional knockout (POSTN-Cre × Notch1flox/flox) mice, and Cre mice were used to induce diabetic cardiac fibrosis. Adeno-associated virus 9 carrying cardiac fibroblast-specific periostin (Postn) promoter-driven small hairpin RNA targeting Alkbh5, Ythdf2, or Notch1, and the phase separation inhibitor 1,6-hexanediol were administered to investigate their roles in diabetic cardiac fibrosis. Histological and biochemical analyses were performed to determine how Alkbh5 and Ythdf2 regulate Notch1 expression in diabetic cardiac fibrosis. NOTCH1 was reconstituted in ALKBH5- and YTHDF2-deficient cardiac fibroblasts and mouse hearts to study its effects on mitochondrial fission and diabetic cardiac fibrosis. Heart tissue samples from patients with diabetic cardiomyopathy were used to validate our findings. RESULTS: In mice with diabetic cardiac fibrosis, decreased Notch1 expression was accompanied by high m6A mRNA levels and mitochondrial fission. Fibroblast-specific deletion of Notch1 enhanced mitochondrial fission and cardiac fibroblast proliferation and induced diabetic cardiac fibrosis in mice. Notch1 downregulation was associated with Alkbh5-mediated m6A demethylation in the 3'UTR of Notch1 mRNA and elevated m6A mRNA levels. These elevated m6A levels in Notch1 mRNA markedly enhanced YTHDF2 phase separation, increased the recognition of m6A residues in Notch1 mRNA by YTHDF2, and induced Notch1 degradation. Conversely, epitranscriptomic downregulation rescues Notch1 expression, resulting in the opposite effects. Human heart tissues from patients with diabetic cardiomyopathy were used to validate the findings in mice with diabetic cardiac fibrosis. CONCLUSIONS: We identified a novel epitranscriptomic mechanism by which m6A-mediated phase separation suppresses Notch1 expression, thereby promoting mitochondrial fission in diabetic cardiac fibrosis. Our findings provide new insights for the development of novel treatment approaches for patients with diabetic cardiac fibrosis.

How mitochondrial dynamics imbalance affects the progression of breast cancer:a mini review.

Despite the high incidence of breast cancer in women worldwide, there are still great challenges in the treatment process. Mitochondria are highly dynamic organelles, and their dynamics involve cellular energy conversion, signal conduction and other processes. In recent years, an increasing number of studies have affirmed the dynamics of mitochondria as the basis for cancer progression and metastasis; that is, an imbalance between mitochondrial fission and fusion may lead to the progression and metastasis of breast cancer. Here, we review the latest insights into mitochondrial dynamics in the progression of breast cancer and emphasize the clinical value of mitochondrial dynamics in diagnosis and prognosis, as well as important advances in clinical research.

Dihydrotestosterone induces reactive oxygen species accumulation and mitochondrial fission leading to apoptosis of granulosa cells.

Dihydrotestosterone (DHT), which has significant androgenic activity，is a major player in follicle development and ovary function in females. However, an excess of androgens may result in increased follicular apoptosis with adverse effects on female fertility. This study aimed to explore the mechanism by which DHT induces apoptosis in human ovarian granulosa cells (GCs). The association between DHT and GC apoptosis was explored by the construction of rat models of polycystic ovary syndrome (PCOS). It was found that serum DHT levels were negatively correlated with thickness of the GC layer in PCOS model rats (R2=0.8342, p＜0.0001), compared with control rats, together with significant increases in cofactors (Fis1: p=0.008; MFF: p=0.044). The GC SVOG cell line was used to clarify the mechanism by which DHT influenced GC apoptosis in in vitro experiments. The results confirmed that apoptosis in SVOG cells was positively associated with the DHT dose. The expression of the autophagy-related proteins LC3A/B (p=0.027) and the proapoptotic protein Bax (p=0.0095) were increased, while that of the anti-apoptotic protein Bcl-2 (p=0.0005) was decreased in the high-dose DHT group. ROS levels were significantly increased (p=0.0237) and the mitochondrial membrane potential ΔΨm was decreased (p=0.0194). Moreover, ultrastructural analysis of the mitochondria indicated significant damage. The results of RT-qPCR and western blotting showed that two fission cofactor-Fis1（p=0.034） and MFF (p=0.039) were significantly increased after treatment with high doses of DHT. Even though the overall expression of Drp1 did not change significantly (p=0.5961), that of activated Phosphor-Drp1(Ser616) was significantly increased (p=0.046), while the expression of Phosphor-Drp1 (Ser637) was markedly reduced (p=0.007) following exposure to high concentrations of DHT. All these effects could be reversed by the Drp1 inhibitor Mdivi-1. These findings indicated the impact of DHT on ROS aggregation and mitochondrial fission, resulting in GC apoptosis. An imbalance in Drp1 phosphorylation may be the key link in DHT-induced excessive mitochondrial fission.

ERK1/2 Regulates Epileptic Seizures by Modulating the DRP1-Mediated Mitochondrial Dynamic.

After seizures, the hyperactivation of extracellular signal-regulated kinases (ERK1/2) causes mitochondrial dysfunction. Through the guidance of dynamin-related protein 1 (DRP1), ERK1/2 plays a role in the pathogenesis of several illnesses. Herein, we speculate that ERK1/2 affects mitochondrial division and participates in the pathogenesis of epilepsy by regulating the activity of DRP1. LiCl-Pilocarpine was injected intraperitoneally to establish a rat model of status epilepticus (SE) for this study. Before SE induction, PD98059 and Mdivi-1 were injected intraperitoneally. The number of seizures and the latency period before the onset of the first seizure were then monitored. The analysis of Western blot was also used to measure the phosphorylated and total ERK1/2 and DRP1 protein expression levels in the rat hippocampus. In addition, immunohistochemistry revealed the distribution of ERK1/2 and DRP1 in neurons of hippocampal CA1 and CA3. Both PD98059 and Mdivi-1 reduced the susceptibility of rats to epileptic seizures, according to behavioral findings. By inhibiting ERK1/2 phosphorylation, the Western blot revealed that PD98059 indirectly reduced the phosphorylation of DRP1 at Ser616 (p-DRP1-Ser616). Eventually, the ERK1/2 and DRP1 were distributed in the cytoplasm of neurons by immunohistochemistry. Inhibition of ERK1/2 signaling pathways downregulates p-DRP1-Ser616 expression, which could inhibit DRP1-mediated excessive mitochondrial fission and then regulate the pathogenesis of epilepsy.

Inhibition of DRP-1 mitochondrial mitophagy and fission by novel α-aminophosphonates bearing pyridine: synthesis, biological evaluations, and computer-aided design.

Heterocyclic compounds play a crucial role in the drug discovery process and development due to their significant presence and importance. Here, we report a comprehensive analysis of α-aminophosphonates containing pyridine (3a-g), prepared according to a clear-cut, uncomplicated procedure. The phosphonates are thoroughly characterized using various methods, such as elemental analysis, mass spectrometry, proton and carbon NMR, and FT-IR. The molecular docking interactions between the phosphonate and DRP-1 target protein observed that compound 3d had the top-ranked binding energy towards DRP-1 with a value equal to - 9.54 kcal/mol and this theoretically proves its inhibitory efficacy against DRP-1 arbitrated mitochondrial fission. Besides, the anticancer characteristics of compound 3d showed the best IC50 against HepG-2, MCF-7, and Caco-2 which confirmed our results towards suppressing DRP-1 protein (in-silico), and it elucidated no cytotoxic effects against human normal cell line (WI-38). Further, its pharmacokinetics were observed theoretically using ADMET. Moreover,compound 3d investigated the most potent antimicrobial ability against two pathological fungal strains, A. flavus and C. albicans, and four bacterial strains, E. coli, B. subtillis, S. aureus, and P. aregeunosa. Additionally, compound 3d clarified a powerful antioxidant scavenging activity against DPPH and ABTS free radicals (in-vitro). Furthermore, Density functional theory (DFT) was used to study the molecular structures of the synthesized compounds 3a-g, utilizing 6-311++G(d,p) as the basis set and to learn more about the molecules' reactive sites, the energies of the molecular electrostatic potential (MEP), the lowest unoccupied molecular orbital (LUMO), and the highest occupied molecular orbital (HOMO) were observed. Theoretically, FT-IR and Nuclear magnetic resonance (NMR) measurements are calculated for every compound under investigation to show how theory and experiment relate. It was found that there was an excellent agreement between the theoretical and experimental data. Conclusively, all novel synthesized phosphonates could be used as pharmaceutical agents against pathogenic microbial strains and as anticancer candidates by inhibiting DRP-1-mediated mitochondrial mitophagy.

DNA-PKcs modulates mouse lung homeostasis via the regulation of mitochondrial fission.

BACKGROUND: The role of DNA-dependent protein kinase catalytic subunit (DNA-PKcs) is multifaceted, paradoxically promoting both cell survival and cell death across multiple organs. However, its impact on lung homeostasis remains elusive. Here, we investigate the function of DNA-PKcs in mouse lungs, aiming to elucidate its role for lung abnormalities associated with DNA-PKcs deficiency. MATERIALS AND METHODS: Histological assessment and immunohistochemistry were used to reveal the pathological changes of the lungs in DNA-PKcs-deficient mice. Transcriptomic analysis identified differentially expressed genes and pathways in DNA-PKcs-deficient lungs. Furthermore, mitochondrial dysfunction induced by DNA-PKcs deficiency was investigated by qPCR and immunoblotting. Mouse primary lung fibroblasts were used to evaluate the potential therapeutic effect of inhibiting mitochondrial fission with Mdivi-1. KEY FINDINGS: In DNA-PKcs-deficient mouse lungs, we observed pathological changes including alveolar septal thickening, capillary congestion and hemorrhage, along with lung cell proliferation. Transcriptome analysis revealed an upregulation of the reactive oxygen species (ROS) biosynthesis process and the apoptotic signaling pathway caused by DNA-PKcs deficiency. Further investigations demonstrated that DNA-PKcs deficiency led to mitochondrial dysfunction and increased oxidative stress, along with increased cell apoptosis in the mouse lungs. Notably, we detected enhanced phosphorylation of the mitochondrial fission protein DRP1 in DNA-PKcs-deficient mouse lungs. Intriguingly, inhibiting mitochondrial fission using Mdivi-1 suppressed cell death in primary mouse lung fibroblasts with siRNA-mediated DNA-PKcs knockdown. SIGNIFICANCE: Our study provides insights into the crucial role of DNA-PKcs in sustaining lung homeostasis via the maintenance of mitochondrial functionality and provides a therapeutic strategy targeting mitochondrial fission against DNA-PKcs deficiency-associated lung diseases.

GPRASP2 deficiency contributes to apoptosis in the spiral ganglion cells via the AMPK/DRP1 signaling pathway.

G protein-coupled receptor-associated sorting protein 2 (GPRASP2) deficiency has been implicated in immunological inflammation, cancers, and neurological disorders. Our previous work revealed that the pathogenic mutation in GPRASP2 was responsible for X-linked recessive syndromic hearing loss (SHL). Given the specific high expression of GPRASP2 in the spiral ganglion, GPRASP2 likely contributes to the maintenance and functionality of neurons, potentially playing a role in synaptic transmission. The impact of GPRASP2 deficiency on spiral ganglion cells (SGCs) and their underlying pathogenic mechanisms will be investigated in this study. The primary culture of SGCs obtained from mouse cochleae was treated with Gprasp2-targeting short hairpin RNA (Gprasp2-shRNA) via lentivirus infection. The results showed that GPRASP2 deficiency enhanced SGCs apoptosis and decreased cell viability. Meanwhile, a significant abnormality of mitochondrial morphology and decreased membrane potential were observed in GPRASP2-deficient SGCs. These effects could be mitigated by treatment with the mitochondrial division inhibitor 1 (Mdivi-1). In addition to enhancing SGCs apoptosis and decreasing cell viability, GPRASP2 deficiency also inhibited the development of SGCs in mouse cochlear explant culture. Our study further revealed that this deficiency resulted in increased phosphorylation of AMPK and activation of the AMPK/DRP1 pathway, promoting SGCs apoptosis. These findings provide insight into the pathogenic mechanisms by which GPRASP2 deficiency is implicated in auditory dysfunction.

VPS13D affects epileptic seizures by regulating mitochondrial fission and autophagy in epileptic rats.

Abnormal mitochondrial dynamics can lead to seizures, and improved mitochondrial dynamics can alleviate seizures. Vacuolar protein sorting 13D (VPS13D) is closely associated with regulating mitochondrial homeostasis and autophagy. However, further investigation is required to determine whether VPS13D affects seizures by influencing mitochondrial dynamics and autophagy. We aimed to investigate the influence of VPS13D on behavior in a rat model of acute epileptic seizures. Hence, we established an acute epileptic seizure rat model and employed the CRISPR/CAS9 technology to construct a lentivirus to silence the Vps13d gene. Furthermore, we used the HT22 mouse hippocampal neuron cell line to establish a stable strain with suppressed expression of Vps13d in vitro. Then, we performed quantitative proteomic and bioinformatics analyses to confirm the mechanism by which VPS13D influences mitochondrial dynamics and autophagy, both in vitro and in vivo using the experimental acute epileptic seizure model. We found that knockdown of Vps13d resulted in reduced seizure latency and increased seizure frequency in the experimental rats. Immunofluorescence staining and western blot analysis revealed a significant increase in mitochondrial dynamin-related protein 1 expression following Vps13d knockdown. Moreover, we observed a significant reduction in LC3II protein expression levels and the LC3II/LC3I ratio (indicators for autophagy) accompanied by a significant increase in P62 expression (an autophagy adaptor protein). The proteomic analysis confirmed the up-regulation of P62 protein expression. Therefore, we propose that VPS13D plays a role in modulating seizures by influencing mitochondrial dynamics and autophagy.

Silencing of PCK1 mitigates the proliferation and migration of vascular smooth muscle cells and vascular intimal hyperplasia by suppressing STAT3/DRP1-mediated mitochondrial fission.

The pathological proliferation and migration of vascular smooth muscle cells (VSMCs) are key processes during vascular neointimal hyperplasia (NIH) and restenosis. Phosphoenolpyruvate carboxy kinase 1 (PCK1) is closely related to a variety of malignant proliferative diseases. However, the role of PCK1 in VSMCs has rarely been investigated. This study aims to examine the role of PCK1 in the proliferation and migration of VSMCs and vascular NIH after injury. In vivo, extensive NIH and increased expression of PCK1 within the neointima are observed in injured arteries. Interestingly, the administration of adeno-associated virus-9 (AAV-9) carrying Pck1 short hairpin RNA (sh Pck1) significantly attenuates NIH and stenosis of the vascular lumen. In vitro, Pck1 small interfering RNA (si Pck1)-induced PCK1 silencing inhibits VSMC proliferation and migration. Additionally, silencing of PCK1 leads to reduced expression of dynamin-related protein 1 (DRP1) and attenuated mitochondrial fission. Lentivirus-mediated DRP1 overexpression markedly reverses the inhibitory effects of PCK1 silencing on VSMC proliferation, migration, and mitochondrial fission. Finally, PCK1 inhibition attenuates the phosphorylation of signal transducer and activator of transcription 3 (STAT3). Activation of STAT3 abolishes the suppressive effects of PCK1 silencing on DRP1 expression, mitochondrial fission, proliferation, and migration in VSMCs. In conclusion, PCK1 inhibition attenuates the mitochondrial fission, proliferation, and migration of VSMCs by inhibiting the STAT3/DRP1 axis, thereby suppressing vascular NIH and restenosis.

DRP1 Association in Inflammation and Metastasis: A Review.

In recent years, mitochondria have gained significant interest in the field of biomedical research due to their impact on aging, human health, and other advanced findings in metabolic functions. The latest finding shows that metabolic interventions are a leading cause of several diseases, which has sparked interest in finding new therapeutic treatments. Apart from this, the unique inheritance of genetic material from mother to offspring can help scientists find ways to prevent mitochondrial inherited diseases. Additionally, the anti-aging benefits of controlling mitochondrial functions are also being researched. The present study aims to provide a cohesive overview of the latest findings in mitochondrial research, focusing on the role of DRP1 (Dynamin- related protein 1), a member of the GTPase family, in mediating mitochondrial fission. The first section of this paper provides a concise explanation of how DRP1 controls processes such as mitophagy and mitochondrial fission. Subsequently, the paper delves into the topic of inflammation, discussing the current findings regarding the inflammatory response mediated by DRP1. Finally, the role of mitochondrial fission mediated by DRP1 in cancer is examined, reviewing ongoing research on various types of cancer and their recurrence. Moreover, this review also covers the epigenetic regulation of mitochondrial fission. The studies were selected, and evaluated, and the information was collected to present an overview of the key findings. By exploring various aspects of research and potential links, we hope to contribute to a deeper understanding of the intricate relationship between the fields of cancer research and inflammation studies with respect to mitochondrial- based research.

Acutely blocking excessive mitochondrial fission prevents chronic neurodegeneration after traumatic brain injury.

Progression of acute traumatic brain injury (TBI) into chronic neurodegeneration is a major health problem with no protective treatments. Here, we report that acutely elevated mitochondrial fission after TBI in mice triggers chronic neurodegeneration persisting 17 months later, equivalent to many human decades. We show that increased mitochondrial fission after mouse TBI is related to increased brain levels of mitochondrial fission 1 protein (Fis1) and that brain Fis1 is also elevated in human TBI. Pharmacologically preventing Fis1 from binding its mitochondrial partner, dynamin-related protein 1 (Drp1), for 2 weeks after TBI normalizes the balance of mitochondrial fission/fusion and prevents chronically impaired mitochondrial bioenergetics, oxidative damage, microglial activation and lipid droplet formation, blood-brain barrier deterioration, neurodegeneration, and cognitive impairment. Delaying treatment until 8 months after TBI offers no protection. Thus, time-sensitive inhibition of acutely elevated mitochondrial fission may represent a strategy to protect human TBI patients from chronic neurodegeneration.

Alternative splicing of Mff regulates AMPK-mediated phosphorylation, mitochondrial fission and antiviral response.

Mitochondrial morphology and function change dynamically in response to intracellular signaling and the surrounding environment. The mitochondrial fission factor Mff, which localizes to the outer mitochondrial membrane, mediates not only mitochondrial fission by recruiting the dynamin-related GTPase Drp1 to mitochondrial fission sites but also the double-stranded RNA-induced antiviral response on mitochondria through mitochondrial antiviral signaling (MAVS). Mff is reported to be regulated by AMP-activated protein kinase (AMPK)-mediated protein phosphorylation and alternative pre-mRNA splicing; however, the relationships among RNA splicing, phosphorylation, and multiple functions of Mff have not been fully understood. Here, we showed that mouse Mff has a tissue-specific splicing pattern, and at least eight Mff splice isoforms were expressed in mouse embryonic fibroblasts (MEFs). We introduced single Mff isoforms into Mff knockout MEFs and found that insertion of exon 6 just after the phosphorylation site, by the alternative splicing, reduced its phosphorylation by AMPK and its functions in mitochondrial fission and the antiviral response. In addition, the underlying mechanism repressing these functions was independent of phosphorylation. These results indicate that multiple functions of Mff on mitochondria are regulated by AMPK-mediated phosphorylation and alternative splicing, under the control of energy metabolism and cellular differentiation.

Melatonin regulates mitochondrial dynamics and mitophagy: Cardiovascular protection.

Despite extensive progress in the knowledge and understanding of cardiovascular diseases and significant advances in pharmacological treatments and procedural interventions, cardiovascular diseases (CVD) remain the leading cause of death globally. Mitochondrial dynamics refers to the repetitive cycle of fission and fusion of the mitochondrial network. Fission and fusion balance regulate mitochondrial shape and influence physiology, quality and homeostasis. Mitophagy is a process that eliminates aberrant mitochondria. Melatonin (Mel) is a pineal-synthesized hormone with a range of pharmacological properties. Numerous nonclinical trials have demonstrated that Mel provides cardioprotection against ischemia/reperfusion, cardiomyopathies, atherosclerosis and cardiotoxicity. Recently, interest has grown in how mitochondrial dynamics contribute to melatonin cardioprotective effects. This review assesses the literature on the protective effects of Mel against CVD via the regulation of mitochondrial dynamics and mitophagy in both in-vivo and in-vitro studies. The signalling pathways underlying its cardioprotective effects were reviewed. Mel modulated mitochondrial dynamics and mitophagy proteins by upregulation of mitofusin, inhibition of DRP1 and regulation of mitophagy-related proteins. The evidence supports a significant role of Mel in mitochondrial dynamics and mitophagy quality control in CVD.

[Retracted] SFRP2 modulates non­small cell lung cancer A549 cell apoptosis and metastasis by regulating mitochondrial fission via Wnt pathways.

Following the publication of this paper, it was drawn to the Editor's attention by a concerned reader that certain of the JC1­stained cellular images shown in Fig. 2C on p. 1928 were strikingly similar to data that had already been published in different form in another article written by different authors at different research institutes [Yao S and Yan W: Overexpression of Mst1 reduces gastric cancer cell viability by repressing the AMPK­Sirt3 pathway and activating mitochondrial fission. Onco Targets Ther 11: 8465­8479, 2019]. Owing to the fact that the contentious data in the above article had already been published prior to its submission to Molecular Medicine Reports, the Editor has decided that this paper should be retracted from the Journal. The authors were asked for an explanation to account for these concerns, but the Editorial Office did not receive a satisfactory reply. The Editor apologizes to the readership for any inconvenience caused. [Molecular Medicine Reports 20: 1925­1932, 2019; DOI: 10.3892/mmr.2019.10393].

Targeting TGR5 to mitigate liver fibrosis: Inhibition of hepatic stellate cell activation through modulation of mitochondrial fission.

Chronic hepatitis B virus (HBV) infection continues to be a prominent cause of liver fibrosis and end-stage liver disease in China, necessitating the development of effective therapeutic strategies. This study investigated the potential of targeting TGR5 to alleviate liver fibrosis by impeding the activation of hepatic stellate cells (HSCs), which play a pivotal role in fibrotic progression. Using the human hepatic stellate cell line LX-2 overexpressing hepatitis B virus X protein (HBX), this study revealed that TGR5 activation through INT-777 inhibits HBX-induced LX-2 cell activation, thereby ameliorating liver fibrosis, which is associated with the attenuation of mitochondrial fission and introduces a novel regulatory pathway in liver fibrosis. Additional experiments with mitochondrial fission inducers and inhibitors confirm the crucial role of mitochondrial dynamics in TGR5-mediated effects. In vivo studies using TGR5 knockout mice substantiate these findings, demonstrating exacerbated fibrosis in the absence of TGR5 and its alleviation with the mitochondrial fission inhibitor Mdivi-1. Overall, this study provides insights into TGR5-mediated regulation of liver fibrosis through the modulation of mitochondrial fission in HSCs, suggesting potential therapeutic strategies for liver fibrosis intervention.

Real-time assessment of mitochondrial DNA heteroplasmy dynamics at the single-cell level.

Mitochondrial DNA (mtDNA) is present in multiple copies within cells and is required for mitochondrial ATP generation. Even within individual cells, mtDNA copies can differ in their sequence, a state known as heteroplasmy. The principles underlying dynamic changes in the degree of heteroplasmy remain incompletely understood, due to the inability to monitor this phenomenon in real time. Here, we employ mtDNA-based fluorescent markers, microfluidics, and automated cell tracking, to follow mtDNA variants in live heteroplasmic yeast populations at the single-cell level. This approach, in combination with direct mtDNA tracking and data-driven mathematical modeling reveals asymmetric partitioning of mtDNA copies during cell division, as well as limited mitochondrial fusion and fission frequencies, as critical driving forces for mtDNA variant segregation. Given that our approach also facilitates assessment of segregation between intact and mutant mtDNA, we anticipate that it will be instrumental in elucidating the mechanisms underlying the purifying selection of mtDNA.

Inhibiting the NF-κB/DRP1 Axis Affords Neuroprotection after Spinal Cord Injury via Inhibiting Polarization of Pro-Inflammatory Microglia.

BACKGROUND: Spinal cord injury (SCI) is considered a central nervous system (CNS) disorder. Nuclear factor kappa B (NF-κB) regulates inflammatory responses in the CNS and is implicated in SCI pathogenesis. The mechanism(s) through which NF-κB contributes to the neuroinflammation observed during SCI however remains unclear. METHODS: SCI rat models were created using the weight drop method and separated into Sham, SCI and SCI+NF-κB inhibitor groups (n = 6 rats per-group). We used Hematoxylin-Eosin Staining (H&E) and Nissl staining for detecting histological changes in the spinal cord. Basso-Beattie-Bresnahan (BBB) behavioral scores were utilized for assessing functional locomotion recovery. Mouse BV2 microglia were exposed to lipopolysaccharide (LPS) to mimic SCI-induced microglial inflammation in vitro. RESULTS: Inhibition of NF-κB using JSH-23 alleviated inflammation and neuronal injury in SCI rats' spinal cords, leading to improved locomotion recovery (p < 0.05). NF-κB inhibition reduced expression levels of CD86, interleukin-6 (IL-6), IL-1ß, and inducible Nitric Oxide Synthase (iNOS), and improved expression levels of CD206, IL-4, and tissue growth factor-beta (TGF-ß) in both LPS-treated microglia and SCI rats' spinal cords (p < 0.05). Inhibition of NF-κB also effectively suppressed mitochondrial fission, evidenced by the reduced phosphorylation of dynamin-related protein 1 (DRP1) at Ser616 (p < 0.001). CONCLUSION: We show that inhibition of the NF-κB/DRP1 axis prevents mitochondrial fission and suppresses pro-inflammatory microglia polarization, promoting neurological recovery in SCI. Targeting the NF-κB/DRP1 axis therefore represents a novel approach for SCI.

Drp1 splice variants regulate ovarian cancer mitochondrial dynamics and tumor progression.

Aberrant mitochondrial fission/fusion dynamics are frequently associated with pathologies, including cancer. We show that alternative splice variants of the fission protein Drp1 (DNM1L) contribute to the complexity of mitochondrial fission/fusion regulation in tumor cells. High tumor expression of the Drp1 alternative splice variant lacking exon 16 relative to other transcripts is associated with poor outcome in ovarian cancer patients. Lack of exon 16 results in Drp1 localization to microtubules and decreased association with mitochondrial fission sites, culminating in fused mitochondrial networks, enhanced respiration, changes in metabolism, and enhanced pro-tumorigenic phenotypes in vitro and in vivo. These effects are inhibited by siRNAs designed to specifically target the endogenously expressed transcript lacking exon 16. Moreover, lack of exon 16 abrogates mitochondrial fission in response to pro-apoptotic stimuli and leads to decreased sensitivity to chemotherapeutics. These data emphasize the pathophysiological importance of Drp1 alternative splicing, highlight the divergent functions and consequences of changing the relative expression of Drp1 splice variants in tumor cells, and strongly warrant consideration of alternative splicing in future studies focused on Drp1.