Early ERK1/2 activation promotes DRP1-dependent mitochondrial fission necessary for cell reprogramming

Emerging Functional Connections Between Metabolism and Epigenetic Remodeling in Neural Differentiation

Stem cells possess extraordinary capacities for self-renewal and differentiation, making them highly valuable in regenerative medicine. Among these, neural stem cells (NSCs) play a fundamental role in neural development and repair processes. NSC characteristics and fate are intricately regulated by the microenvironment and intracellular signaling. Interestingly, metabolism plays a pivotal role in orchestrating the epigenome dynamics during neural differentiation, facilitating the transition from undifferentiated NSC to specialized neuronal and glial cell types. This intricate interplay between metabolism and the epigenome is essential for precisely regulating gene expression patterns and ensuring proper neural development. This review highlights the mechanisms behind metabolic regulation of NSC fate and their connections with epigenetic regulation to shape transcriptional programs of stemness and neural differentiation. A comprehensive understanding of these molecular gears appears fundamental for translational applications in regenerative medicine and personalized therapies for neurological conditions.

Resveratrol stimulates brown of white adipose via regulating ERK/DRP1-mediated mitochondrial fission and improves systemic glucose homeostasis

PURPOSE

Diabetes mellitus and metabolic homeostasis disorders may benefit from white adipose tissue (WAT) browning, which is associated with mitochondrial fission. Resveratrol, a dietary polyphenol, exhibits beneficial effects against abnormalities related to metabolic diseases. However, it remains unknown whether resveratrol contributes to WAT browning by regulating mitochondrial fission.

METHODS

We administered resveratrol (0.4% mixed with control) to db/db mice for 12 weeks, measuring body weight, oral glucose tolerance, insulin tolerance, and histological changes. The uncoupling protein 1 (UCP1) and dynamin-related protein 1 (DRP1) expressions in the epididymal WAT were assessed via immunoblotting.

RESULTS

We found that resveratrol improved systemic glucose homeostasis and insulin resistance in db/db mice, which was associated with increased UCP1 in epididymal WAT. Resveratrol-treated mice exhibited more fragmented mitochondria and increased phosphorylation of DRP1 in the epididymal WAT of the db/db mice. These results were further confirmed in vitro, where resveratrol induced extracellular signal-regulated kinase (ERK) signaling activation, leading to phosphorylation of DRP1 at the S616 site (p-DRP1S616) and mitochondrial fission, which was reversed by an ERK inhibitor in 3T3-L1 adipocytes.

CONCLUSION

Resveratrol plays a role in regulating the phosphorylation of ERK and DRP1, resulting in the promotion of beige cells with epididymal WAT and the improvement of glucose homeostasis. Our present study provides novel insights into the potential mechanism of resveratrol-mediated effects on WAT browning, suggesting that it is, at least in part, mediated through ERK/DRP1-mediated mitochondrial fission.

GPx1-ERK1/2-CREB pathway regulates the distinct vulnerability of hippocampal neurons to oxidative stress via modulating mitochondrial dynamics following status epilepticus

Glutathione peroxidase-1 (GPx1) and cAMP/Ca2+ responsive element (CRE)-binding protein (CREB) regulate neuronal viability by maintaining the redox homeostasis. Since GPx1 and CREB reciprocally regulate each other, it is likely that GPx1-CREB interaction may play a neuroprotective role against oxidative stress, which are largely unknown. Thus, we investigated the underlying mechanisms of the reciprocal regulation between GPx1 and CREB in the male rat hippocampus. Under physiological condition, L-buthionine sulfoximine (BSO)-induced oxidative stress increased GPx1 expression, extracellular signal-regulated kinase 1/2 (ERK1/2) activity and CREB serine (S) 133 phosphorylation in CA1 neurons, but not dentate granule cells (DGC), which were diminished by GPx1 siRNA, U0126 or CREB knockdown. GPx1 knockdown inhibited ERK1/2 and CREB activations induced by BSO. CREB knockdown also decreased the efficacy of BSO on ERK1/2 activation. BSO facilitated dynamin-related protein 1 (DRP1)-mediated mitochondrial fission in CA1 neurons, which abrogated by GPx1 knockdown and U0126. CREB knockdown blunted BSO-induced DRP1 upregulation without affecting DRP1 S616 phosphorylation ratio. Following status epilepticus (SE), GPx1 expression was reduced in CA1 neurons and DGC. SE also decreased CREB activity CA1 neurons, but not DGC. SE degenerated CA1 neurons, but not DGC, accompanied by mitochondrial elongation. These post-SE events were ameliorated by N-acetylcysteine (NAC, an antioxidant), but deteriorated by GPx1 knockdown. These findings indicate that a transient GPx1-ERK1/2-CREB activation may be a defense mechanism to protect hippocampal neurons against oxidative stress via maintenance of proper mitochondrial dynamics.

Association between mitochondrial DNA copy number and production traits in pigs

Mitochondria are essential organelles in the regulation of cellular energetic metabolism. Mitochondrial DNA copy number (mtDNA_CN) can be used as a proxy for mitochondria number, size, and activity. The aims of our study are to evaluate the effect of mtDNA_CN and mitochondrial haploblocks on production traits in pigs, and to identify the genetic background of this cellular phenotype. We collected performance data of 234 pigs and extracted DNA from skeletal muscle. Whole-genome sequencing data was used to determine mtDNA_CN. We found positive correlations of muscle mtDNA_CN with backfat thickness at 207 d (+0.14; p-value = 0.07) and negative correlations with carcase loin thickness (-0.14; p-value = 0.03). Pigs with mtDNA_CN values below the lower quartile had greater loin thickness (+4.1 mm; p-value = 0.01) and lower backfat thickness (-1.1 mm; p-value = 0.08), which resulted in greater carcase lean percentage (+2.4%; p-value = 0.04), than pigs with mtDNA_CN values above the upper quartile. These results support the hypothesis that a reduction of mitochondrial activity is associated with greater feed efficiency. Higher mtDNA_CN was also positively correlated with higher meat ultimate pH (+0.19; p-value <0.01) but we did not observe significant difference for meat ultimate pH between the two groups with extreme mtDNA_CN. We found no association of the most frequent mitochondrial haploblocks with mtDNA_CN or the production traits, but several genomic regions that harbour potential candidate genes with functions related to mitochondrial biogenesis and homeostasis were associated with mtDNA_CN. These regions provide new insights into the genetic background of this cellular phenotype but it is still uncertain if such associations translate into noticeable effects on the production traits.

MitoTempo protects against nε-carboxymethyl lysine-induced mitochondrial dyshomeostasis and neuronal cells injury

Enhanced formation of advanced glycation end products (AGEs) is a pivotal factor in diabetes pathophysiology, increasing the risk of diabetic complications. Nε-carboxy-methyl-lysine (CML) is one of the most relevant AGEs found in several tissues including the peripheral blood of diabetic subjects. Despite recognizing diabetes as a risk factor for neurodegenerative diseases and the documented role of mitochondrial abnormalities in this connection, the impact of CML on neuronal mitochondria and its contribution to diabetes-related neurodegeneration remain uncertain. Here, we evaluated the effects of CML in differentiated SH-SY5Y human neuroblastoma cells. Due to the association between mitochondrial dysfunction and increased production of reactive oxygen species (ROS), the possible protective effects of MitoTempo, a mitochondria-targeted antioxidant, were also evaluated. Several parameters were assessed namely cells viability, mitochondrial respiration and membrane potential, ATP and ROS production, Ca2+ levels, mitochondrial biogenesis and dynamics, mito/autophagy, endoplasmic reticulum (ER) stress and amyloidogenic and synaptic integrity markers. CML caused pronounced mitochondrial defects characterized by a significant decrease in mitochondrial respiration, membrane potential, and ATP production and an increase in ROS production. An accumulation of individual mitochondria associated with disrupted mitochondrial networks was also observed. Furthermore, CML caused mitochondrial fusion and a decrease in mitochondrial mass and induced ER stress associated with altered unfolded protein response and Ca2+ dyshomeostasis. Moreover, CML increased the protein levels of β-secretase-1 and amyloid precursor protein, key proteins involved in Alzheimer's Disease pathophysiology. All these effects contributed to the decline in neuronal cells viability. Notable, MitoTempo was able to counteract most of CML-mediated mitochondrial defects and neuronal cells injury and death. Overall, these findings suggest that CML induces pronounced defects in neuronal mitochondria and ER stress, predisposing to neurodegenerative events. More, our observations suggest that MitoTempo holds therapeutic promise in mitigating CML-induced mitochondrial imbalance and neuronal damage and death.

Protective effects of 2,4-dinitrophenol in okadaic acid-induced cellular model of Alzheimer's disease

Alzheimer's disease (AD) research started several decades ago and despite the many efforts employed to develop new treatments or approaches to slow and/or revert disease progression, AD treatment remains an unsolved issue. Knowing that mitochondria loss of function is a central hub for many AD-associated pathophysiological processes, there has been renewed interest in exploring mitochondria as targets for intervention. In this perspective, the present study was aimed to investigate the possible beneficial effects of 2,4 dinitrophenol (DNP), a mitochondrial uncoupler agent, in an in vitro model of AD. Retinoic acid-induced differentiated SH-SY5Y cells were incubated with okadaic acid (OA), a neurotoxin often used as an AD experimental model, and/or with DNP. OA caused a decrease in neuronal cells viability, induced multiple mitochondrial anomalies including increased levels of reactive oxygen species, decreased bioenergetics and mitochondria content markers, and an altered mitochondria morphology. OA-treated cells also presented increased lipid peroxidation levels, and overactivation of tau related kinases (GSK3β, ERK1/2 and AMPK) alongside with a significant augment in tau protein phosphorylation levels. Interestingly, DNP co-treatment ameliorated and rescued OA-induced detrimental effects not only on mitochondria but also but also reinstated signaling pathways homeostasis and ameliorated tau pathology. Overall, our results show for the first time that DNP has the potential to preserve mitochondria homeostasis under a toxic insult, like OA exposure, as well as to reestablish cellular signaling homeostasis. These observations foster the idea that DNP, as a mitochondrial modulator, might represent a new avenue for treatment of AD.

Cell-free ascites from ovarian cancer patients induces Warburg metabolism and cell proliferation through TGFβ-ERK signaling

Ascites plays a key role in supporting the metastatic potential of ovarian cancer cells. Shear stress and carry-over of cancer cells by ascites flow support carcinogenesis and metastasis formation. In addition, soluble factors may participate in the procarcinogenic effects of ascites in ovarian cancer. This study aimed to determine the biological effects of cell-free ascites on carcinogenesis in ovarian cancer cells. Cell-free ascites from ovarian cancer patients (ASC) non-selectively induced cell proliferation in multiple models of ovarian cancer and untransformed primary human dermal fibroblasts. Furthermore, ASC induced a Warburg-type rearrangement of cellular metabolism in A2780 ovarian cancer cells characterized by increases in cellular oxygen consumption and glycolytic flux; increases in glycolytic flux were dominant. ASC induced mitochondrial uncoupling and fundamentally reduced fatty acid oxidation. Ascites-elicited effects were uniform among ascites specimens. ASC-elicited transcriptomic changes in A2780 ovarian cancer cells included induction of the TGFβ-ERK/MEK pathway, which plays a key role in inducing cell proliferation and oncometabolism. ASC-induced gene expression changes, as well as the overexpression of members of the TGFβ signaling system, were associated with poor survival in ovarian cancer patients. We provided evidence that the activation of the autocrine/paracrine of TGFβ signaling system may be present in bladder urothelial carcinoma and stomach adenocarcinoma. Database analysis suggests that the TGFβ system may feed forward bladder urothelial carcinoma and stomach adenocarcinoma. Soluble components of ASC support the progression of ovarian cancer. These results suggest that reducing ascites production may play an essential role in the treatment of ovarian cancer by inhibiting the progression and reducing the severity of the disease.

Deoxynivalenol Induces Drp-1-Mediated Mitochondrial Dysfunction via Elevating Oxidative Stress

Mitochondrial dysfunction is often linked to neurotoxicity and neurological diseases and stems from oxidative stress, yet effective therapies are lacking. Deoxynivalenol (DON or vomitoxin) is one of the most common and hazardous type-B trichothecene mycotoxins, which contaminates crops used for food and animal feed. Despite the abundance of preliminary reports, comprehensive investigations are scarce to explore the relationship between these fungal metabolites and neurodegenerative disorders. The present study aimed to elucidate the precise role of DON in mitochondrial dynamics and cell death in neuronal cells. Excessive mitochondrial fission is associated with the pathology of several neurodegenerative diseases. Human SH-SY5Y cells were treated with different concentrations of DON (250-1000 ng/mL). Post 24 and 48 h DON treatment, the indexes were measured as follows: generation of reactive oxygen species (ROS), ATP levels, mitochondrial membrane potential, calcium levels, and cytotoxicity in SH-SY5Y cells. The results showed that cytotoxicity, intracellular calcium levels, and ROS in the DON-treated group increased, while the ATP levels and mitochondrial membrane potential decreased in a dose-dependent manner. With increasing DON concentrations, the expression levels of P-Drp-1, mitochondrial fission proteins Mff, and Fis-1 were elevated with reduced activities of MFN1, MFN2, and OPA1, further resulting in an increased expression of autophagic marker LC3 and beclin-1. The reciprocal relationship between mitochondrial damage and ROS generation is evident as ROS can instigate structural and functional deficiencies within the mitochondria. Consequently, the impaired mitochondria facilitate the release of ROS, thereby intensifying the cycle of damage and exacerbating the overall process. Using specific hydroxyl, superoxide inhibitors, and calcium chelators, our study confirmed that ROS and Ca2+-mediated signaling pathways played essential roles in DON-induced Drp1 phosphorylation. Therefore, ROS and mitochondrial fission inhibitors could provide critical research tools for drug development in mycotoxin-induced neurodegenerative diseases.

Korean red ginseng alleviates benign prostatic hyperplasia by dysregulating androgen receptor signaling and inhibiting DRP1-mediated mitochondrial fission

Panax ginseng (C.A. Mey.) has been traditionally employed in Korea and China to alleviate fatigue and digestive disorders. In particular, Korean red ginseng (KRG), derived from streamed and dried P. ginseng, is known for its anti-aging and anti-inflammatory properties. However, its effects on benign prostatic hyperplasia (BPH), a representative aging-related disease, and the underlying mechanisms remain unclear. This study aims to elucidate the therapeutic effects of KRG on BPH, with a particular focus on mitochondrial dynamics, including fission and fusion processes. The effects of KRG on cell proliferation, apoptosis, and mitochondrial dynamics and morphology were evaluated in a rat model of testosterone propionate (TP)-induced BPH and TP-treated LNCaP cells, with mdivi-1 as a control. The results revealed that KRG treatment reduced the levels of androgen receptors (AR) and prostate-specific antigens in the BPH group. KRG inhibited cell proliferation by downregulating cyclin D and proliferating cell nuclear antigen (PCNA) levels, and it promoted apoptosis by increasing the ratio of B-cell lymphoma protein 2 (Bcl-2)-associated X protein (Bax) to Bcl-2 expression. Notably, KRG treatment enhanced the phosphorylation of dynamin-related protein 1 (DRP-1, serine 637) compared with that in the BPH group, which inhibited mitochondrial fission and led to mitochondrial elongation. This modulation of mitochondrial dynamics was associated with decreased cell proliferation and increased apoptosis. By dysregulating AR signaling and inhibiting mitochondrial fission through enhanced DRP-1 (ser637) phosphorylation, KRG effectively reduced cell proliferation and induced apoptosis. These findings suggest that KRG's regulation of mitochondrial dynamics offers a promising clinical approach for the treatment of BPH.

Insulin signaling and mitochondrial phenotype of skeletal muscle are programmed in utero by maternal diabetes

Maternal diabetes may influence glucose metabolism in adult offspring, an area with limited research on underlying mechanisms. Our study explored the impact of maternal hyperglycemia during pregnancy on insulin resistance development. Adult female Sprague-Dawley rats from control and diabetic mothers were mated, and their female offspring were monitored for 150 days. The rats were euthanized for blood and muscle samples. Maternal diabetes led to heightened insulin levels, increased HOMA-IR, elevated triglycerides, and a raised TyG index in adult offspring. Muscle samples showed a decreased protein expression of AMPK, PI3K, MAPK, DRP1, and MFF. These changes induced intergenerational metabolic programming in female pups, resulting in insulin resistance, dyslipidemia, and glucose intolerance by day 150. Findings highlight the offspring's adaptation to maternal hyperglycemia, involving insulin resistance, metabolic alterations, the downregulation of insulin signaling sensors, and disturbed mitochondrial morphology. Maintaining maternal glycemic control emerges as crucial in mitigating diabetes-associated disorders in adult offspring.

ROS-mediated cytoplasmic localization of CARM1 induces mitochondrial fission through DRP1 methylation

The dynamic regulation of mitochondria through fission and fusion is essential for maintaining cellular homeostasis. In this study, we discovered a role of coactivator-associated arginine methyltransferase 1 (CARM1) in mitochondrial dynamics. CARM1 methylates specific residues (R403 and R634) on dynamin-related protein 1 (DRP1). Methylated DRP1 interacts with mitochondrial fission factor (Mff) and forms self-assembly on the outer mitochondrial membrane, thereby triggering fission, reducing oxygen consumption, and increasing reactive oxygen species (ROS) production. This sets in motion a feedback loop that facilitates the translocation of CARM1 from the nucleus to the cytoplasm, enhancing DRP1 methylation and ROS production through mitochondrial fragmentation. Consequently, ROS reinforces the CARM1-DRP1-ROS axis, resulting in cellular senescence. Depletion of CARM1 or DRP1 impedes cellular senescence by reducing ROS accumulation. The uncovering of the above-described mechanism fills a missing piece in the vicious cycle of ROS-induced senescence and contributes to a better understanding of the aging process.

Systemic phospho-defective and phospho-mimetic Drp1 mice exhibit normal growth and development with altered anxiety-like behavior

Mitochondrial division controls the size, distribution, and turnover of this essential organelle. A dynamin-related GTPase, Drp1, drives membrane division as a force-generating mechano-chemical enzyme. Drp1 is regulated by multiple mechanisms, including phosphorylation at two primary sites: serine 579 and serine 600. While previous studies in cell culture systems have shown that Drp1 S579 phosphorylation promotes mitochondrial division, its physiological functions remained unclear. Here, we generated phospho-mimetic Drp1 S579D and phospho-defective Drp1 S579R mice using the CRISPR-Cas system. Both mouse models exhibited normal growth, development, and breeding. We found that Drp1 is highly phosphorylated at S579 in brain neurons. Notably, the Drp1 S579D mice showed decreased anxiety-like behaviors, whereas the Drp1 S579R mice displayed increased anxiety-like behaviors. These findings suggest a critical role for Drp1 S579 phosphorylation in brain function. The Drp1 S579D and S579R mice thus offer valuable in vivo models for specific analysis of Drp1 S579 phosphorylation.

Is mitochondrial morphology important for cellular physiology?

Mitochondria are double membrane-bound organelles the network morphology of which in cells is shaped by opposing events of fusion and fission executed by dynamin-like GTPases. Mutations in these genes can perturb the form and functions of mitochondria in cell and animal models of mitochondrial diseases. An expanding array of chemical, mechanical, and genetic stressors can converge on mitochondrial-shaping proteins and disrupt mitochondrial morphology. In recent years, studies aimed at disentangling the multiple roles of mitochondrial-shaping proteins beyond fission or fusion have provided insights into the homeostatic relevance of mitochondrial morphology. Here, I review the pleiotropy of mitochondrial fusion and fission proteins with the aim of understanding whether mitochondrial morphology is important for cell and tissue physiology.

Modulation of mitochondrial function by extracellular acidosis in tumor cells and normal fibroblasts: Role of signaling pathways

In many tumors pronounced extracellular acidosis resulting from glycolytic metabolism is found. Since several environmental stress factors affect the mitochondrial activity the aim of the study was to analyze the impact of acidosis on cellular oxygen consumption and which signaling pathways may be involved in the regulation. In two tumor cell lines and normal fibroblasts cellular oxygen consumption rate (OCR) and mitochondrial function were measured after 3 h at pH 6.6. Besides the activation of ERK1/2, p38 and PI3K signaling in the cytosolic and mitochondrial compartment, the mitochondrial structure and proteins related to mitochondria fission were analyzed. The acidic extracellular environment increased OCR in tumor cells but not in fibroblasts. In parallel, the mitochondrial membrane potential increased at low pH. In both tumor lines (but not in fibroblasts), the phosphorylation of ERK1/2 and PI3K/Akt was significantly increased, and both cascades were involved in OCR modulation. The activation of signaling pathways was located predominantly in the mitochondrial compartment of the cells. At low pH, the mitochondrial structure in tumor cells showed structural changes related to elongation whereas mitochondria fragmentation was reduced indicating mitochondria fusion. However, these morphological changes were not related to ERK1/2 or PI3K signaling. Acidic stress seems to induce an increased oxygen consumption, which might further aggravate tumor hypoxia. Low pH also induces mitochondria fusion that is not mediated by ERK1/2 or PI3K signaling. The mechanism by which these signaling cascades modulate the respiratory activity of tumor cells needs further investigation.

A novel MTORC2-AKT-ROS axis triggers mitofission and mitophagy-associated execution of colorectal cancer cells upon drug-induced activation of mutant KRAS

RAS is one of the most commonly mutated oncogenes associated with multiple cancer hallmarks. Notably, RAS activation induces intracellular reactive oxygen species (ROS) generation, which we previously demonstrated as a trigger for autophagy-associated execution of mutant KRAS-expressing cancer cells. Here we report that drug (merodantoin; C1)-induced activation of mutant KRAS promotes phospho-AKT S473-dependent ROS-mediated S616 phosphorylation and mitochondrial localization of DNM1L/DRP1 (dynamin 1 like) and cleavage of the fusion-associated protein OPA1 (OPA1 mitochondrial dynamin like GTPase). Interestingly, accumulation of the outer mitochondrial membrane protein VDAC1 (voltage dependent anion channel 1) is observed in mutant KRAS-expressing cells upon exposure to C1. Conversely, silencing VDAC1 abolishes C1-induced mitophagy, and gene knockdown of either KRAS, AKT or DNM1L rescues ROS-dependent VDAC1 accumulation and stability, thus suggesting an axis of mutant active KRAS-phospho-AKT S473-ROS-DNM1L-VDAC1 in mitochondrial morphology change and cancer cell execution. Importantly, we identified MTOR (mechanistic target of rapamycin kinsase) complex 2 (MTORC2) as the upstream mediator of AKT phosphorylation at S473 in our model. Pharmacological or genetic inhibition of MTORC2 abrogated C1-induced phosphorylation of AKT S473, ROS generation and mitophagy induction, as well as rescued tumor colony forming ability and migratory capacity. Finally, increase in thermal stability of KRAS, AKT and DNM1L were observed upon exposure to C1 only in mutant KRAS-expressing cells. Taken together, our work has unraveled a novel mechanism of selective targeting of mutant KRAS-expressing cancers via MTORC2-mediated AKT activation and ROS-dependent mitofission, which could have potential therapeutic implications given the relative lack of direct RAS-targeting strategies in cancer.Abbreviations: ACTB/ß-actin: actin beta; AKT: AKT serine/threonine kinase; C1/merodantoin: 1,3-dibutyl-2-thiooxo-imidazoldine-4,5-dione; CAT: catalase; CETSA: cellular thermal shift assay; CHX: cycloheximide; DKO: double knockout; DNM1L/DRP1: dynamin 1 like; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; H2O2: hydrogen peroxide; HSPA1A/HSP70-1: heat shock protein family A (Hsp70) member 1A; HSP90AA1/HSP90: heat shock protein 90 alpha family class A member 1; KRAS: KRAS proto-oncogene, GTPase; MAP1LC3B/LC3B, microtubule associated protein 1 light chain 3 beta; LC3B-I: unlipidated form of LC3B; LC3B-II: phosphatidylethanolamine-conjugated form of LC3B; MAPKAP1/SIN1: MAPK associated protein 1; MAPK1/ERK2: mitogen-activated protein kinase 1; MAPK3/ERK1: mitogen-activated protein kinase 3; MFI: mean fluorescence intensity; MiNA: Mitochondrial Network Analysis; MTOR: mechanistic target of rapamycin kinase; MTORC1: mechanistic target of rapamycin kinase complex 1; MTORC2: mechanistic target of rapamycin kinase complex 2; O2.-: superoxide; OMA1: OMA1 zinc metallopeptidase; OPA1: OPA1 mitochondrial dynamin like GTPase; RICTOR: RPTOR independent companion of MTOR complex 2; ROS: reactive oxygen species; RPTOR/raptor: regulatory associated protein of MTOR complex 1; SOD1: superoxide dismutase 1; SOD2: superoxide dismutase 2; SQSTM1/p62: sequestosome 1; VDAC1: voltage dependent anion channel 1; VDAC2: voltage dependent anion channel 2.

Mitochondrial metallopeptidase OMA1 in cancer

Our understanding of the roles that mitochondria play in cellular physiology has evolved drastically-from a mere cellular energy supplier to a crucial regulator of metabolic and signaling processes, particularly in the context of development and progression of human diseases such as cancers. The present review examines the role of OMA1, a conserved, redox-sensitive metallopeptidase in cancer biology. OMA1's involvement in mitochondrial quality control, redox activity, and stress responses underscores its potential as a novel target in cancer diagnosis and treatment. However, our incomplete understanding of OMA1's regulation and structural detail presents ongoing challenges to target OMA1 for therapeutic purposes. Further exploration of OMA1 holds promise in uncovering novel insights into cancer mechanisms and therapeutic strategies. In this chapter, we briefly summarize our current knowledge about OMA1, its redox-regulation, and emerging role in certain cancers.

Environmental cadmium inhibits testicular testosterone synthesis via Parkin-dependent MFN1 degradation

Low testosterone (T) levels are associated with many common diseases, such as obesity, male infertility, depression, and cardiovascular disease. It is well known that environmental cadmium (Cd) exposure can induce T decline, but the exact mechanism remains unclear. We established a murine model in which Cd exposure induced testicular T decline. Based on the model, we found Cd caused mitochondrial fusion disorder and Parkin mitochondrial translocation in mouse testes. MFN1 overexpression confirmed that MFN1-dependent mitochondrial fusion disorder mediated the Cd-induced T synthesis suppression in Leydig cells. Further data confirmed Cd induced the decrease of MFN1 protein by increasing ubiquitin degradation. Testicular specific Parkin knockdown confirmed Cd induced the ubiquitin-dependent degradation of MFN1 protein through promoting Parkin mitochondrial translocation in mouse testes. Expectedly, testicular specific Parkin knockdown also mitigated testicular T decline. Mito-TEMPO, a targeted inhibitor for mitochondrial reactive oxygen species (mtROS), alleviated Cd-caused Parkin mitochondrial translocation and mitochondrial fusion disorder. As above, Parkin mitochondrial translocation induced mitochondrial fusion disorder and the following T synthesis repression in Cd-exposed Leydig cells. Collectively, our study elucidates a novel mechanism through which Cd induces T decline and provides a new treatment strategy for patients with androgen disorders.

Metaplastic regeneration in the mouse stomach requires a reactive oxygen species pathway

In pyloric metaplasia, mature gastric chief cells reprogram via an evolutionarily conserved process termed paligenosis to re-enter the cell cycle and become spasmolytic polypeptide-expressing metaplasia (SPEM) cells. Here, we use single-cell RNA sequencing (scRNA-seq) following injury to the murine stomach to analyze mechanisms governing paligenosis at high resolution. Injury causes induced reactive oxygen species (ROS) with coordinated changes in mitochondrial activity and cellular metabolism, requiring the transcriptional mitochondrial regulator Ppargc1a (Pgc1α) and ROS regulator Nf2el2 (Nrf2). Loss of the ROS and mitochondrial control in Ppargc1a-/- mice causes the death of paligenotic cells through ferroptosis. Blocking the cystine transporter SLC7A11(xCT), which is critical in lipid radical detoxification through glutathione peroxidase 4 (GPX4), also increases ferroptosis. Finally, we show that PGC1α-mediated ROS and mitochondrial changes also underlie the paligenosis of pancreatic acinar cells. Altogether, the results detail how metabolic and mitochondrial changes are necessary for injury response, regeneration, and metaplasia in the stomach.

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.

Mitochondrial dysfunction induced by HIF-1α under hypoxia contributes to the development of gastric mucosal lesions

INTRODUCTION

Hypoxia is an important characteristic of gastric mucosal diseases, and hypoxia-inducible factor-1α (HIF-1α) contributes to microenvironment disturbance and metabolic spectrum abnormalities. However, the underlying mechanism of HIF-1α and its association with mitochondrial dysfunction in gastric mucosal lesions under hypoxia have not been fully clarified.

OBJECTIVES

To evaluate the effects of hypoxia-induced HIF-1α on the development of gastric mucosal lesions.

METHODS

Portal hypertensive gastropathy (PHG) and gastric cancer (GC) were selected as representative diseases of benign and malignant gastric lesions, respectively. Gastric tissues from patients diagnosed with the above diseases were collected. Portal hypertension (PHT)-induced mouse models in METTL3 mutant or NLRP3-deficient littermates were established, and nude mouse gastric graft tumour models with relevant inhibitors were generated. The mechanisms underlying hypoxic condition, mitochondrial dysfunction and metabolic alterations in gastric mucosal lesions were further analysed.

RESULTS

HIF-1α, which can mediate mitochondrial dysfunction via upregulation of METTL3/IGF2BP3-dependent dynamin-related protein 1 (Drp1) N6-methyladenosine modification to increase mitochondrial reactive oxygen species (mtROS) production, was elevated under hypoxic conditions in human and mouse portal hypertensive gastric mucosa and GC tissues. While blocking HIF-1α with PX-478, inhibiting Drp1-dependent mitochondrial fission via mitochondrial division inhibitor 1 (Mdivi-1) treatment or METTL3 mutation alleviated this process. Furthermore, HIF-1α influenced energy metabolism by enhancing glycolysis via lactate dehydrogenase A. In addition, HIF-1α-induced Drp1-dependent mitochondrial fission also enhanced glycolysis. Drp1-dependent mitochondrial fission and enhanced glycolysis were associated with alterations in antioxidant enzyme activity and dysfunction of the mitochondrial electron transport chain, resulting in massive mtROS production, which was needed for activation of NLRP3 inflammasome to aggravate the development of the PHG and GC.

CONCLUSIONS

Under hypoxic conditions, HIF-1α enhances mitochondrial dysfunction via Drp1-dependent mitochondrial fission and influences the metabolic profile by altering glycolysis to increase mtROS production, which can trigger NLRP3 inflammasome activation and mucosal microenvironment alterations to contribute to the development of benign and malignant gastric mucosal lesions.

Mitochondria in the Central Nervous System in Health and Disease: The Puzzle of the Therapeutic Potential of Mitochondrial Transplantation

Mitochondria, the energy suppliers of the cells, play a central role in a variety of cellular processes essential for survival or leading to cell death. Consequently, mitochondrial dysfunction is implicated in numerous general and CNS disorders. The clinical manifestations of mitochondrial dysfunction include metabolic disorders, dysfunction of the immune system, tumorigenesis, and neuronal and behavioral abnormalities. In this review, we focus on the mitochondrial role in the CNS, which has unique characteristics and is therefore highly dependent on the mitochondria. First, we review the role of mitochondria in neuronal development, synaptogenesis, plasticity, and behavior as well as their adaptation to the intricate connections between the different cell types in the brain. Then, we review the sparse knowledge of the mechanisms of exogenous mitochondrial uptake and describe attempts to determine their half-life and transplantation long-term effects on neuronal sprouting, cellular proteome, and behavior. We further discuss the potential of mitochondrial transplantation to serve as a tool to study the causal link between mitochondria and neuronal activity and behavior. Next, we describe mitochondrial transplantation's therapeutic potential in various CNS disorders. Finally, we discuss the basic and reverse-translation challenges of this approach that currently hinder the clinical use of mitochondrial transplantation.

Profibrogenic macrophage-targeted delivery of mitochondrial protector via exosome formula for alleviating pulmonary fibrosis

Pulmonary fibrosis (PF) is a devastating lung disease with limited treatment options. During this pathological process, the profibrogenic macrophage subpopulation plays a crucial role, making the characterization of this subpopulation fundamentally important. The present study revealed a positive correlation between pulmonary macrophages with higher mitochondrial mass (Mømitohigh) and fibrosis. Among the Mømitohigh subpopulation of CD206+ M2, characterized by higher expression of dynamin 1-like (Drp1), as determined by flow cytometry and RNA-seq analysis, a therapeutic intervention was developed using an exosome-based formula composed of pathfinder and therapeutics. A pathfinder exosome called "exosomeMMP19 (ExoMMP19)", was constructed to display matrix metalloproteinase-19 (MMP19) on the surface to locally break down the excessive extracellular matrix (ECM) in the fibrotic lung. A therapeutic exosome called "exosome therapeutics (ExoTx)", was engineered to display D-mannose on the surface while encapsulating siDrp1 inside. Prior delivery of ExoMMP19 degraded excessive ECM and thus paved the way for ExoTx to be delivered into Mømitohigh, where ExoTx inhibited mitochondrial fission and alleviated PF. This study has not only identified Mømitohigh as profibrotic macrophages but it has also provided a potent strategy to reverse PF via a combination of formulated exosomes.

Kinase signalling adaptation supports dysfunctional mitochondria in disease

Mitochondria form a critical control nexus which are essential for maintaining correct tissue homeostasis. An increasing number of studies have identified dysregulation of mitochondria as a driver in cancer. However, which pathways support and promote this adapted mitochondrial function? A key hallmark of cancer is perturbation of kinase signalling pathways. These pathways include mitogen activated protein kinases (MAPK), lipid secondary messenger networks, cyclic-AMP-activated (cAMP)/AMP-activated kinases (AMPK), and Ca2+/calmodulin-dependent protein kinase (CaMK) networks. These signalling pathways have multiple substrates which support initiation and persistence of cancer. Many of these are involved in the regulation of mitochondrial morphology, mitochondrial apoptosis, mitochondrial calcium homeostasis, mitochondrial associated membranes (MAMs), and retrograde ROS signalling. This review will aim to both explore how kinase signalling integrates with these critical mitochondrial pathways and highlight how these systems can be usurped to support the development of disease. In addition, we will identify areas which require further investigation to fully understand the complexities of these regulatory interactions. Overall, this review will emphasize how studying the interaction between kinase signalling and mitochondria improves our understanding of mitochondrial homeostasis and can yield novel therapeutic targets to treat disease.

Phosphorylation of INF2 by AMPK promotes mitochondrial fission and oncogenic function in endometrial cancer

Mitochondria are highly dynamic organelles capable of altering their sizes and shapes to maintain metabolic balance through coordinated fission and fusion processes. In various cancer types, mitochondrial hyperfragmentation has been frequently observed, contributing to the progression of cancer toward metastasis. Inverted formin 2 (INF2), which resides in the endoplasmic reticulum (ER), has been found to accelerate actin polymerization and drive mitochondrial fission. In this study, we demonstrate that INF2 expression is significantly upregulated in endometrial cancer (EC) and is associated with a poor prognosis in EC patients. INF2 promotes anchorage-dependent and independent EC cell growth in part by facilitating mitochondrial fission. Furthermore, in conditions of energy stress, AMP-activated protein kinase (AMPK) phosphorylates INF2 at Ser1077, leading to increased localization of INF2 to the ER and enhanced recruitment of the dynamin-related protein 1 (DRP1) to mitochondria. This AMPK-mediated phosphorylation of INF2 at Ser1077 facilitates mitochondrial division and promotes EC cell growth. Pathological examination using immunohistochemical analyses revealed a positive correlation between AMPK activity and phosphorylated INF2 (Ser1077) in EC specimens. Collectively, our findings uncover novel molecular mechanisms involving the AMPK-INF2 axis, which regulates mitochondrial dynamics and malignant cell growth in EC.

Metabolic control of induced pluripotency

Pluripotent stem cells of the mammalian epiblast and their cultured counterparts-embryonic stem cells (ESCs) and epiblast stem cells (EpiSCs)-have the capacity to differentiate in all cell types of adult organisms. An artificial process of reactivation of the pluripotency program in terminally differentiated cells was established in 2006, which allowed for the generation of induced pluripotent stem cells (iPSCs). This iPSC technology has become an invaluable tool in investigating the molecular mechanisms of human diseases and therapeutic drug development, and it also holds tremendous promise for iPSC applications in regenerative medicine. Since the process of induced reprogramming of differentiated cells to a pluripotent state was discovered, many questions about the molecular mechanisms involved in this process have been clarified. Studies conducted over the past 2 decades have established that metabolic pathways and retrograde mitochondrial signals are involved in the regulation of various aspects of stem cell biology, including differentiation, pluripotency acquisition, and maintenance. During the reprogramming process, cells undergo major transformations, progressing through three distinct stages that are regulated by different signaling pathways, transcription factor networks, and inputs from metabolic pathways. Among the main metabolic features of this process, representing a switch from the dominance of oxidative phosphorylation to aerobic glycolysis and anabolic processes, are many critical stage-specific metabolic signals that control the path of differentiated cells toward a pluripotent state. In this review, we discuss the achievements in the current understanding of the molecular mechanisms of processes controlled by metabolic pathways, and vice versa, during the reprogramming process.

Role of bio-flavonols and their derivatives in improving mitochondrial dysfunctions associated with pancreatic tumorigenesis

Mitochondria, a cellular metabolic center, efficiently fulfill cellular energy needs and regulate crucial metabolic processes, including cellular proliferation, differentiation, apoptosis, and generation of reactive oxygen species. Alteration in the mitochondrial functions leads to metabolic imbalances and altered extracellular matrix dynamics in the host, utilized by solid tumors like pancreatic cancer (PC) to get energy benefits for fast-growing cancer cells. PC is highly heterogeneous and remains unidentified for a longer time because of its complex pathophysiology, retroperitoneal position, and lack of efficient diagnostic approaches, which is the foremost reason for accounting for the seventh leading cause of cancer-related deaths worldwide. PC cells often respond poorly to current therapeutics because of dense stromal barriers in the pancreatic tumor microenvironment, which limit the drug delivery and distribution of antitumor immune cell populations. As an alternative approach, various natural compounds like flavonoids are reported to possess potent antioxidant and anticancerous properties and are less toxic than current chemotherapeutic drugs. Therefore, we aim to summarize the current state of knowledge regarding the pharmacological properties of flavonols in PC in this review from the perspective of mitigating mitochondrial dysfunctions associated with cancer cells. Our literature survey indicates that flavonols efficiently regulate cellular metabolism by scavenging reactive oxygen species, mitigating inflammation, and arresting the cell cycle to promote apoptosis in tumor cells via intrinsic mitochondrial pathways. In particular, flavonols proficiently inhibit the cancer-associated proliferation and inflammatory pathways such as EGFR/MAPK, PI3K/Akt, and nuclear factor κB in PC. Overall, this review provides in-depth evidence about the therapeutic potential of flavonols for future anticancer strategies against PC; still, more multidisciplinary human interventional studies are required to dissect their pharmacological effect accurately.

Significance of quantitative analyses of the impact of heterogeneity in mitochondrial content and shape on cell differentiation

Mitochondria, classically known as the powerhouse of cells, are unique double membrane-bound multifaceted organelles carrying a genome. Mitochondrial content varies between cell types and precisely doubles within cells during each proliferating cycle. Mitochondrial content also increases to a variable degree during cell differentiation triggered after exit from the proliferating cycle. The mitochondrial content is primarily maintained by the regulation of mitochondrial biogenesis, while damaged mitochondria are eliminated from the cells by mitophagy. In any cell with a given mitochondrial content, the steady-state mitochondrial number and shape are determined by a balance between mitochondrial fission and fusion processes. The increase in mitochondrial content and alteration in mitochondrial fission and fusion are causatively linked with the process of differentiation. Here, we critically review the quantitative aspects in the detection methods of mitochondrial content and shape. Thereafter, we quantitatively link these mitochondrial properties in differentiating cells and highlight the implications of such quantitative link on stem cell functionality. Finally, we discuss an example of cell size regulation predicted from quantitative analysis of mitochondrial shape and content. To highlight the significance of quantitative analyses of these mitochondrial properties, we propose three independent rationale based hypotheses and the relevant experimental designs to test them.

Mitochondria act as a key regulatory factor in cancer progression: Current concepts on mutations, mitochondrial dynamics, and therapeutic approach

The diversified impacts of mitochondrial function vs. dysfunction have been observed in almost all disease conditions including cancers. Mitochondria play crucial roles in cellular homeostasis and integrity, however, mitochondrial dysfunctions influenced by alterations in the mtDNA can disrupt cellular balance. Many external stimuli or cellular defects that cause cellular integrity abnormalities, also impact mitochondrial functions. Imbalances in mitochondrial activity can initiate and lead to accumulations of genetic mutations and can promote the processes of tumorigenesis, progression, and survival. This comprehensive review summarizes epigenetic and genetic alterations that affect the functionality of the mitochondria, with considerations of cellular metabolism, and as influenced by ethnicity. We have also reviewed recent insights regarding mitochondrial dynamics, miRNAs, exosomes that play pivotal roles in cancer promotion, and the impact of mitochondrial dynamics on immune cell mechanisms. The review also summarizes recent therapeutic approaches targeting mitochondria in anti-cancer treatment strategies.

Tangeretin attenuates acute lung injury in septic mice by inhibiting ROS-mediated NLRP3 inflammasome activation via regulating PLK1/AMPK/DRP1 signaling axis

OBJECTIVE

NLRP3 inflammasome-mediated pyroptosis of macrophage acts essential roles in the progression of sepsis-induced acute lung injury (ALI). Tangeretin (TAN), enriched in citrus fruit peel, presents anti-oxidative and anti-inflammatory effects. Here, we aimed to explore the potentially protective effect of TAN on sepsis-induced ALI, and the underlying mechanism of TAN in regulating NLRP3 inflammasome.

MATERIAL AND METHODS

The effect of TAN on sepsis-induced ALI and NLRP3 inflammasome-mediated pyroptosis of macrophage were examined in vivo and in vitro using a LPS-treated mice model and LPS-induced murine macrophages, respectively. The mechanism of TAN regulating the activation of NLRP3 inflammasome in sepsis-induced ALI was investigated with HE staining, Masson staining, immunofluorescent staining, ELISA, molecular docking, transmission electron microscope detection, qRT-PCR, and western blot.

RESULTS

TAN could evidently attenuate sepsis-induced ALI in mice, evidenced by reducing pulmonary edema, pulmonary congestion and lung interstitial fibrosis, and inhibiting macrophage infiltration in the lung tissue. Besides, TAN significantly suppressed inflammatory cytokine IL-1β and IL-18 expression in the serum or bronchoalveolar lavage fluid (BALF) samples of mice with LPS-induced ALI, and inhibited NLRP3 inflammasome-mediated pyroptosis of macrophages. Furthermore, we found TAN inhibited ROS production, preserved mitochondrial morphology, and alleviated excessive mitochondrial fission in LPS-induced ALI in mice. Through bioinformatic analysis and molecular docking, Polo-like kinase 1 (PLK1) was identified as a potential target of TAN for treating sepsis-induced ALI. Moreover, TAN significantly inhibited the reduction of PLK1 expression, AMP-activated protein kinase (AMPK) phosphorylation, and Dynamin related protein 1 (Drp1) phosphorylation (S637) in LPS-induced ALI in mice. In addition, Volasertib, a specific inhibitor of PLK1, abolished the protective effects of TAN against NLRP3 inflammasome-mediated pyroptosis of macrophage and lung injury in the cell and mice septic models.

CONCLUSION

TAN attenuates sepsis-induced ALI by inhibiting ROS-mediated NLRP3 inflammasome activation via regulating PLK1/AMPK/DRP1 signaling axis, and TAN is a potentially therapeutic candidate against ALI through inhibiting pyroptosis.

Restoring AIBP expression in the retina provides neuroprotection in glaucoma

Glaucoma is a neurodegenerative disease manifested in retinal ganglion cell (RGC) death and irreversible blindness. While lowering intraocular pressure (IOP) is the only proven therapeutic strategy in glaucoma, it is insufficient for preventing disease progression, thus justifying the recent focus on targeting retinal neuroinflammation and preserving RGCs. We have identified apolipoprotein A-I binding protein (AIBP) as the protein regulating several mechanisms of retinal neurodegeneration. AIBP controls excessive cholesterol accumulation via upregulating the cholesterol transporter ATP-binding cassette transporter 1 (ABCA1) and reduces inflammatory signaling via toll-like receptor 4 (TLR4) and mitochondrial dysfunction. ABCA1, TLR4 and oxidative phosphorylation components are genetically linked to primary open-angle glaucoma. Here we demonstrated that AIBP and ABCA1 expression was decreased, while TLR4, interleukin 1 beta (IL-1 beta), and the cholesterol content increased in the retina of patients with glaucoma and in mouse models of glaucoma. Restoring AIBP expression by a single intravitreal injection of adeno-associated virus (AAV)-AIBP protected RGCs in glaucomatous DBA/2J mice, in mice with microbead-induced chronic IOP elevation, and optic nerve crush. In addition, AIBP expression attenuated TLR4 and IL-1 beta expression, localization of TLR4 to lipid rafts, reduced cholesterol accumulation, and ameliorated visual dysfunction. These studies collectively indicate that restoring AIBP expression in the glaucomatous retina reduces neuroinflammation and protects RGCs and Muller glia, suggesting the therapeutic potential of AAV-AIBP in human glaucoma.

Multiplexed and Millimeter-Scale Fluorescence Nanoscopy of Cells and Tissue Sections via Prism-Illumination and Microfluidics-Enhanced DNA-PAINT

Fluorescence nanoscopy has become increasingly powerful for biomedical research, but it has historically afforded a small field-of-view (FOV) of around 50 μm × 50 μm at once and more recently up to ∼200 μm × 200 μm. Efforts to further increase the FOV in fluorescence nanoscopy have thus far relied on the use of fabricated waveguide substrates, adding cost and sample constraints to the applications. Here we report PRism-Illumination and Microfluidics-Enhanced DNA-PAINT (PRIME-PAINT) for multiplexed fluorescence nanoscopy across millimeter-scale FOVs. Built upon the well-established prism-type total internal reflection microscopy, PRIME-PAINT achieves robust single-molecule localization with up to ∼520 μm × 520 μm single FOVs and 25-40 nm lateral resolutions. Through stitching, nanoscopic imaging over mm2 sample areas can be completed in as little as 40 min per target. An on-stage microfluidics chamber facilitates probe exchange for multiplexing and enhances image quality, particularly for formalin-fixed paraffin-embedded (FFPE) tissue sections. We demonstrate the utility of PRIME-PAINT by analyzing ∼106 caveolae structures in ∼1,000 cells and imaging entire pancreatic cancer lesions from patient tissue biopsies. By imaging from nanometers to millimeters with multiplexity and broad sample compatibility, PRIME-PAINT will be useful for building multiscale, Google-Earth-like views of biological systems.

Dynamin-Related Protein 1 Binding Partners MiD49 and MiD51 Increased Mitochondrial Fission In Vitro and Atherosclerosis in High-Fat-Diet-Fed ApoE-/- Mice

Novel components of the mitochondrial fission machinery, mitochondrial dynamics proteins of 49 kDa (MiD49) and 51 kDa (MiD51), have been recently described, and their potential therapeutic targets for treating cardiovascular disease have been shown, including acute myocardial infarction (AMI), anthracycline cardiomyopathy and pulmonary arterial hypertension (PAH). Here, we examined the role of MiD49 and MiD51 in atherosclerosis. MiD49/51 expression was increased in the aortic valve endothelial cells (ECs) of high-fat diet-induced atherosclerosis in ApoE-/-mice and IL-8-induced human umbilical vein endothelial cells (HUVECs), which accelerated dynamin-related protein 1 (Drp1)-mediated mitochondrial fission. Silencing MiD49/51 reduced atherosclerotic plaque size, increased collagen content, and decreased the IL-8-induced adhesion and proliferation of HUVECs. MiD51 upregulation resulted from decreased microRNA (miR)-107 expression and increased hypoxia-inducible factor-1a (HIF-1a) expression. Treatment with miR-107 mimics decreased atherosclerotic plaque size by reducing HIF-1α and MiD51 production. Both MiD49 and MiD51 were involved in atherosclerotic plaque formation through Drp1-mediated mitochondrial fission, and the involvement of MiD51 in this process was the result of decreased miR-107 expression and increased HIF-1α expression. The miR-107-HIF-1α-MiD51 pathway might provide new therapeutic targets for atherosclerosis.

Types of Cell Death from a Molecular Perspective

The former conventional belief was that cell death resulted from either apoptosis or necrosis; however, in recent years, different pathways through which a cell can undergo cell death have been discovered. Various types of cell death are distinguished by specific morphological alterations in the cell's structure, coupled with numerous biological activation processes. Various diseases, such as cancers, can occur due to the accumulation of damaged cells in the body caused by the dysregulation and failure of cell death. Thus, comprehending these cell death pathways is crucial for formulating effective therapeutic strategies. We focused on providing a comprehensive overview of the existing literature pertaining to various forms of cell death, encompassing apoptosis, anoikis, pyroptosis, NETosis, ferroptosis, autophagy, entosis, methuosis, paraptosis, mitoptosis, parthanatos, necroptosis, and necrosis.

The mystery of phospho-Drp1 with four adaptors in cell cycle: when mitochondrial fission couples to cell fate decisions

Recent study had deepened our knowledge of the mitochondrial dynamics to classify mitochondrial fission into two types. To further clarify the relationship between the two distinct fission machinery and the four major adaptors of Drp1, we propose a model of mechanism elucidating the multiple functions of phospho-Drp1 with its adaptors during cell cycle and providing in-depth insights into the molecular basis and evolutionary implications in depth. The model highlights not only the clustering characteristics of different phospho-Drp1 with respective subsets of mitochondrial pro-fission adaptors but also the correlation, crosstalk and shifting between different clustering of phosphorylated Drp1-adaptors during different key fission situations. Particularly, phospho-Drp1 (Ser616) couples with Mff/MiD51 to exert mitochondrial division and phospho-Drp1 (Ser637) couples with MiD49/Fis1 to execute mitophagy in M-phase. We then apply the model to address the relationship of mitochondrial dynamics to Parkinson's disease (PD) and carcinogenesis. Our proposed model is indeed compatible with current research results and pathological observations, providing promising directions for future treatment design.

Carbon dioxide and MAPK signalling: towards therapy for inflammation

Inflammation, although necessary to fight infections, becomes a threat when it exceeds the capability of the immune system to control it. In addition, inflammation is a cause and/or symptom of many different disorders, including metabolic, neurodegenerative, autoimmune and cardiovascular diseases. Comorbidities and advanced age are typical predictors of more severe cases of seasonal viral infection, with COVID-19 a clear example. The primary importance of mitogen-activated protein kinases (MAPKs) in the course of COVID-19 is evident in the mechanisms by which cells are infected with SARS-CoV-2; the cytokine storm that profoundly worsens a patient's condition; the pathogenesis of diseases, such as diabetes, obesity, and hypertension, that contribute to a worsened prognosis; and post-COVID-19 complications, such as brain fog and thrombosis. An increasing number of reports have revealed that MAPKs are regulated by carbon dioxide (CO2); hence, we reviewed the literature to identify associations between CO2 and MAPKs and possible therapeutic benefits resulting from the elevation of CO2 levels. CO2 regulates key processes leading to and resulting from inflammation, and the therapeutic effects of CO2 (or bicarbonate, HCO3-) have been documented in all of the abovementioned comorbidities and complications of COVID-19 in which MAPKs play roles. The overlapping MAPK and CO2 signalling pathways in the contexts of allergy, apoptosis and cell survival, pulmonary oedema (alveolar fluid resorption), and mechanical ventilation-induced responses in lungs and related to mitochondria are also discussed. Video Abstract.

Mitochondrial Dynamics and Cristae Shape Changes During Metabolic Reprogramming

Significance: The architecture of the mitochondrial network and cristae critically impact cell differentiation and identity. Cells undergoing metabolic reprogramming to aerobic glycolysis (Warburg effect), such as immune cells, stem cells, and cancer cells, go through controlled modifications in mitochondrial architecture, which is critical for achieving the resulting cellular phenotype. Recent Advances: Recent studies in immunometabolism have shown that the manipulation of mitochondrial network dynamics and cristae shape directly affects T cell phenotype and macrophage polarization through altering energy metabolism. Similar manipulations also alter the specific metabolic phenotypes that accompany somatic reprogramming, stem cell differentiation, and cancer cells. The modulation of oxidative phosphorylation activity, accompanied by changes in metabolite signaling, reactive oxygen species generation, and adenosine triphosphate levels, is the shared underlying mechanism. Critical Issues: The plasticity of mitochondrial architecture is particularly vital for metabolic reprogramming. Consequently, failure to adapt the appropriate mitochondrial morphology often compromises the differentiation and identity of the cell. Immune, stem, and tumor cells exhibit striking similarities in their coordination of mitochondrial morphology with metabolic pathways. However, although many general unifying principles can be observed, their validity is not absolute, and the mechanistic links thus need to be further explored. Future Directions: Better knowledge of the molecular mechanisms involved and their relationships to both mitochondrial network and cristae morphology will not only further deepen our understanding of energy metabolism but may also contribute to improved therapeutic manipulation of cell viability, differentiation, proliferation, and identity in many different cell types. Antioxid. Redox Signal. 39, 684-707.

Ets1 facilitates EMT/invasion through Drp1-mediated mitochondrial fragmentation in ovarian cancer

Ovarian cancer has sustained as a major cause of cancer-related female mortality owing to its aggressive nature and a dearth of early detection markers. Ets1 oncoprotein, a transcription factor belonging to the Ets family, is a well-established promoter of epithelial to mesenchymal transition (EMT) and a prospective malignancy marker in ovarian cancer. Our study establishes Ets1 as a regulator of mitochondrial fission-fusion dynamics through Drp1 augmentation via direct binding at DNM1L (DRP1) promoter. Ets1 overexpression-mediated Drp1 increment resulted in mitochondrial load reduction and compromised OXPHOS Complex 5 (ATP synthase) expression, facilitating a greater reliance on glycolysis over OXPHOS. Furthermore, our work demonstrates that inhibition of mitochondrial fission through molecular or pharmacological inhibition of Drp1 successfully mitigates Ets1-associated EMT in both in vitro and in vivo syngeneic mice model. Collectively, our data highlight the role of Drp1-mediated mitochondrial fragmentation in driving Ets1-mediated bioenergetic alterations and EMT/invasion in ovarian cancer.

Syntaxin 17 Protects Against Heart Failure Through Recruitment of CDK1 to Promote DRP1-Dependent Mitophagy

Mitochondrial dysfunction is suggested to be a major contributor for the progression of heart failure (HF). Here we examined the role of syntaxin 17 (STX17) in the progression of HF. Cardiac-specific Stx17 knockout manifested cardiac dysfunction and mitochondrial damage, associated with reduced levels of p(S616)-dynamin-related protein 1 (DRP1) in mitochondria-associated endoplasmic reticulum membranes and dampened mitophagy. Cardiac STX17 overexpression promoted DRP1-dependent mitophagy and attenuated transverse aortic constriction-induced contractile and mitochondrial damage. Furthermore, STX17 recruited cyclin-dependent kinase-1 through its SNARE domain onto mitochondria-associated endoplasmic reticulum membranes, to phosphorylate DRP1 at Ser616 and promote DRP1-mediated mitophagy upon transverse aortic constriction stress. These findings indicate the potential therapeutic benefit of targeting STX17 in the mitigation of HF.

Mechanisms of Modulation of Mitochondrial Architecture

Mitochondrial network architecture plays a critical role in cellular physiology. Indeed, alterations in the shape of mitochondria upon exposure to cellular stress can cause the dysfunction of these organelles. In this scenario, mitochondrial dynamics proteins and the phospholipid composition of the mitochondrial membrane are key for fine-tuning the modulation of mitochondrial architecture. In addition, several factors including post-translational modifications such as the phosphorylation, acetylation, SUMOylation, and o-GlcNAcylation of mitochondrial dynamics proteins contribute to shaping the plasticity of this architecture. In this regard, several studies have evidenced that, upon metabolic stress, mitochondrial dynamics proteins are post-translationally modified, leading to the alteration of mitochondrial architecture. Interestingly, several proteins that sustain the mitochondrial lipid composition also modulate mitochondrial morphology and organelle communication. In this context, pharmacological studies have revealed that the modulation of mitochondrial shape and function emerges as a potential therapeutic strategy for metabolic diseases. Here, we review the factors that modulate mitochondrial architecture.

Prostaglandin F2α regulates mitochondrial dynamics and mitophagy in the bovine corpus luteum

Prostaglandins are arachidonic acid-derived lipid mediators involved in numerous physiological and pathological processes. PGF2α analogues are therapeutically used for regulating mammalian reproductive cycles and blood pressure, inducing term labor, and treating ocular disorders. PGF2α exerts effects via activation of calcium and PKC signaling, however, little is known about the cellular events imposed by PGF2α signaling. Here, we explored the early effects of PGF2α on mitochondrial dynamics and mitophagy in the bovine corpus luteum employing relevant and well characterized in vivo and in vitro approaches. We identified PKC/ERK and AMPK as critical protein kinases essential for activation of mitochondrial fission proteins, DRP1 and MFF. Furthermore, we report that PGF2α elicits increased intracellular reactive oxygen species and promotes receptor-mediated activation of PINK-Parkin mitophagy. These findings place the mitochondrium as a novel target in response to luteolytic mediator, PGF2α. Understanding intracellular processes occurring during early luteolysis may serve as a target for improving fertility.

Rapid degeneration of iPSC-derived motor neurons lacking Gdap1 engages a mitochondrial-sustained innate immune response

Charcot-Marie-Tooth disease is a chronic hereditary motor and sensory polyneuropathy targeting Schwann cells and/or motor neurons. Its multifactorial and polygenic origin portrays a complex clinical phenotype of the disease with a wide range of genetic inheritance patterns. The disease-associated gene GDAP1 encodes for a mitochondrial outer membrane protein. Mouse and insect models with mutations in Gdap1 have reproduced several traits of the human disease. However, the precise function in the cell types affected by the disease remains unknown. Here, we use induced-pluripotent stem cells derived from a Gdap1 knockout mouse model to better understand the molecular and cellular phenotypes of the disease caused by the loss-of-function of this gene. Gdap1-null motor neurons display a fragile cell phenotype prone to early degeneration showing (1) altered mitochondrial morphology, with an increase in the fragmentation of these organelles, (2) activation of autophagy and mitophagy, (3) abnormal metabolism, characterized by a downregulation of Hexokinase 2 and ATP5b proteins, (4) increased reactive oxygen species and elevated mitochondrial membrane potential, and (5) increased innate immune response and p38 MAP kinase activation. Our data reveals the existence of an underlying Redox-inflammatory axis fueled by altered mitochondrial metabolism in the absence of Gdap1. As this biochemical axis encompasses a wide variety of druggable targets, our results may have implications for developing therapies using combinatorial pharmacological approaches and improving therefore human welfare. A Redox-immune axis underlying motor neuron degeneration caused by the absence of Gdap1. Our results show that Gdap1^-/- motor neurons have a fragile cellular phenotype that is prone to degeneration. Gdap1^-/- iPSCs differentiated into motor neurons showed an altered metabolic state: decreased glycolysis and increased OXPHOS. These alterations may lead to hyperpolarization of mitochondria and increased ROS levels. Excessive amounts of ROS might be the cause of increased mitophagy, p38 activation and inflammation as a cellular response to oxidative stress. The p38 MAPK pathway and the immune response may, in turn, have feedback mechanisms, leading to the induction of apoptosis and senescence, respectively. CAC, citric acid cycle; ETC, electronic transport chain; Glc, glucose; Lac, lactate; Pyr, pyruvate.

The role of tumor microenvironment on cancer stem cell fate in solid tumors

In the last few decades, the role of cancer stem cells in initiating tumors, metastasis, invasion, and resistance to therapies has been recognized as a potential target for tumor therapy. Understanding the mechanisms by which CSCs contribute to cancer progression can help to provide novel therapeutic approaches against solid tumors. In this line, the effects of mechanical forces on CSCs such as epithelial-mesenchymal transition, cellular plasticity, etc., the metabolism pathways of CSCs, players of the tumor microenvironment, and their influence on the regulating of CSCs can lead to cancer progression. This review focused on some of these mechanisms of CSCs, paving the way for a better understanding of their regulatory mechanisms and developing platforms for targeted therapies. While progress has been made in research, more studies will be required in the future to explore more aspects of how CSCs contribute to cancer progression. Video Abstract.

Targeting Mitochondrial Metabolic Dysfunction in Pulmonary Hypertension: Toward New Therapeutic Approaches?

Pulmonary arterial hypertension (PAH) is a rare disease characterized by pulmonary vascular remodeling leading to right heart failure and death. To date, despite the three therapeutic approaches targeting the three major endothelial dysfunction pathways based on the prostacyclin, nitric oxide/cyclic guanosine monophosphate, and endothelin pathways, PAH remains a serious disease. As such, new targets and therapeutic agents are needed. Mitochondrial metabolic dysfunction is one of the mechanisms involved in PAH pathogenesis in part through the induction of a Warburg metabolic state of enhanced glycolysis but also through the upregulation of glutaminolysis, tricarboxylic cycle and electron transport chain dysfunction, dysregulation of fatty acid oxidation or mitochondrial dynamics alterations. The aim of this review is to shed light on the main mitochondrial metabolic pathways involved in PAH and to provide an update on the resulting interesting potential therapeutic perspectives.

MSCs Ameliorate Hepatic IR Injury by Modulating Phenotypic Transformation of Kupffer Cells Through Drp-1 Dependent Mitochondrial Dynamics

BACKGROUND

Hepatic ischemia and reperfusion (IR) injury, characterized by reactive oxygen species (ROS) production and immune disorders, leads to exogenous antigen-independent local inflammation and hepatocellular death. Mesenchymal stem cells (MSCs) have been shown to be immunomodulatory, antioxidative and contribute to liver regeneration in fulminant hepatic failure. We aimed to investigate the underlying mechanisms by which MSCs protect against liver IR injury in a mouse model.

METHODS

MSCs suspension was injected 30 min prior to hepatic warm IR. Primary kupffer cells (KCs) were isolated. Hepatic injury, inflammatory responses, innate immunity, KCs phenotypic polarization and mitochondrial dynamics were evaluated with or without KCs Drp-1 overexpression RESULTS: MSCs markedly ameliorated liver injury and attenuated inflammatory responses and innate immunity after liver IR injury. MSCs significantly restrained M1 phenotypic polarization but boosted M2 polarization of KCs extracted from ischemic liver, as demonstrated by lowered transcript levels of iNOS and IL-1β but raised transcript levels of Mrc-1 and Arg-1 combined with p-STAT6 up-regulation and p-STAT1 down-regulation. Moreover, MSCs inhibited KCs mitochondrial fission, as evidenced by decreased Drp1 and Dnm2 levels. We overexpressed Drp-1 in KCs which promote mitochondrial fission during IR injury. the regulation of MSCs towards KCs M1/M2 polarization was abrogated by Drp-1 overexpression after IR injury. Ultimately, in vivo Drp-1 overexpression in KCs hampered the therapeutic effects of MSCs against hepatic IR injury CONCLUSIONS: We revealed that MSCs facilitated M1-M2 phenotypic polarization through inhibiting Drp-1 dependent mitochondrial fission and further attenuated liver IR injury. These results add a new insight into regulating mechanisms of mitochondrial dynamics during hepatic IR injury and may offer novel opportunities for developing therapeutic targets to combat hepatic IR injury.

Effects of Mdivi-1 on Extending the Golden Treatment Time following Hemorrhagic Shock in Hot Environment in Rats

It is found that a hot environment aggravates hemorrhagic shock-induced internal environment and organ dysfunction. Meanwhile mitochondria show over-fission. Whether inhibition of mitochondrial fission benefits from the early treatment of hemorrhagic shock under a hot environment is unclear. An uncontrolled hemorrhagic shock model in rats is used, and the effects of mitochondrial fission inhibitor mdivi-1 on mitochondrial function, organ function, and survival rate of rats are measured. The results show that 0.1-3 mg/kg mdivi-1 antagonizes hemorrhagic shock-induced mitochondrial fragment. In addition, mdivi-1 improves mitochondrial function, and alleviates hemorrhagic shock-induced oxidative stress and inflammation under a hot environment. Further studies show that 0.1-3 mg/kg Mdivi-1 reduces blood loss, and maintains a mean artery pressure (MAP) of 50-60 mmHg before bleeding-stops after hemorrhagic shock, compared with single Lactate Ringer's (LR) resuscitation. Notably, 1 mg/kg of Mdivi-1 extends the time of hypotensive resuscitation to 2-3 h. During 1 or 2 h of ligation, Mdivi-1 prolongs survival time and protects vital organ function by rescuing mitochondrial morphology and improving mitochondrial function. These results suggest Mdivi-1 is suitable for the early treatment of hemorrhagic shock under a hot environment and can extend the golden treatment time to 2-3 hour for hemorrhagic shock under a hot environment.

MicroRNA-19b-3p dysfunction of mesenchymal stem cell-derived exosomes from patients with abdominal aortic aneurysm impairs therapeutic efficacy

Senescence of vascular smooth muscle cells (VSMCs) contributes to the formation of abdominal aortic aneurysm (AAA). Although mesenchymal stem cell exosomes (MSC-EXO) have been confirmed to restrict the development of AAA, their biological activity depends largely on the physiological state of the MSCs. This study aimed to compare the effects of adipose-derived MSC-EXO from healthy donors (HMEXO) and AAA patients (AMEXO) on senescence of VSMCs in AAA and explore the underlying mechanisms. An ApoE-/- mouse model of AAA was used to investigate the therapeutic effects of HMEXO, AMEXO or miR-19b-3p-AMEXO on AAA development. This in vitro model of AAA was established by treating VSMCs with Ang II (Angiotensin II). The senescence of VSMCs was determined by senescence-associated β-galactosidase (SA-β-gal) staining. The morphology of mitochondria in VSMCs was examined by MitoTracker staining. HMEXO exhibited superior capacity compared with AMEXO to inhibit VSMC senescence and attenuate AAA formation in Ang II-treated ApoE-/- mice. In vitro, both AMEXO and HMEXO inhibited Ang II-induced VSMC senescence via downregulation of mitochondrial fission. Notably, compared with HMEXO, the ability of AMEXO to inhibit VSMC senescence was significantly decreased. miRNA sequencing and the expression of miR-19b-3p was significantly decreased in AMEXO compared with HMEXO. Luciferase assay suggested that MST4 (Mammalian sterile-20-like kinase 4) is a potential target of miR-19b-3p. Mechanistically, miR-19b-3p in HMEXO ameliorated VSMC senescence by inhibiting mitochondrial fission via regulation of the MST4/ERK/Drp1 signaling pathway. Overexpression of miR-19b-3p in AMEXO improved their beneficial effect on AAA formation. Our study reveals that MSC-exosomal miR-19b-3p exerts protective effects against Ang II-induced AAA and VSMC senescence via regulation of the MST4/ERK/Drp1 pathway. The pathological state of AAA patients alters the miRNA components of AMEXO and impairs their therapeutic benefits.

EGCG Attenuates CA1 Neuronal Death by Regulating GPx1, NF-κB S536 Phosphorylation and Mitochondrial Dynamics in the Rat Hippocampus following Status Epilepticus

Epigallocatechin-3-gallate (EGCG) is an antioxidant that directly scavenges reactive oxygen species (ROS) and inhibits pro-oxidant enzymes. Although EGCG protects hippocampal neurons from status epilepticus (SE, a prolonged seizure activity), the underlying mechanisms are not fully understood. As the preservation of mitochondrial dynamics is essential for cell viability, it is noteworthy to elucidate the effects of EGCG on impaired mitochondrial dynamics and the related signaling pathways in SE-induced CA1 neuronal degeneration, which are yet unclear. In the present study, we found that EGCG attenuated SE-induced CA1 neuronal death, accompanied by glutathione peroxidase-1 (GPx1) induction. EGCG also abrogated mitochondrial hyperfusion in these neurons by the preservation of extracellular signal-regulated kinase 1/2 (ERK1/2)-dynamin-related protein 1 (DRP1)-mediated mitochondrial fission, independent of c-Jun N-terminal kinase (JNK) activity. Furthermore, EGCG abolished SE-induced nuclear factor-κB (NF-κB) serine (S) 536 phosphorylation in CA1 neurons. ERK1/2 inhibition by U0126 diminished the effect of EGCG on neuroprotection and mitochondrial hyperfusion in response to SE without affecting GPx1 induction and NF-κB S536 phosphorylation, indicating that the restoration of ERK1/2-DRP1-mediated fission may be required for the neuroprotective effects of EGCG against SE. Therefore, our findings suggest that EGCG may protect CA1 neurons from SE insults through GPx1-ERK1/2-DRP1 and GPx1-NF-κB signaling pathways, respectively.

Mitophagy regulation in aging and neurodegenerative disease

Mitochondria are the primary cellular energy generators, supplying the majority of adenosine triphosphate through oxidative phosphorylation, which is necessary for neuron function and survival. Mitophagy is the metabolic process of eliminating dysfunctional or redundant mitochondria. It is a type of autophagy and it is crucial for maintaining mitochondrial and neuronal health. Impaired mitophagy leads to an accumulation of damaged mitochondria and proteins leading to the dysregulation of mitochondrial quality control processes. Recent research shows the vital role of mitophagy in neurons and the pathogenesis of major neurodegenerative diseases. Mitophagy also plays a major role in the process of aging. This review describes the alterations that are being caused in the mitophagy process at the molecular level in aging and in neurodegenerative diseases, particularly Alzheimer's, Parkinson's, and Huntington's diseases and amyotrophic lateral sclerosis, also looks at how mitophagy can be exploited as a therapeutic target for these diseases.

Determinants and outcomes of mitochondrial dynamics

Mitochondria are not only central organelles in metabolism and energy conversion but are also platforms for cellular signaling cascades. Classically, the shape and ultrastructure of mitochondria were depicted as static. The discovery of morphological transitions during cell death and of conserved genes controlling mitochondrial fusion and fission contributed to establishing the concept that mitochondrial morphology and ultrastructure are dynamically regulated by mitochondria-shaping proteins. These finely tuned, dynamic changes in mitochondrial shape can in turn control mitochondrial function, and their alterations in human diseases suggest that this space can be explored for drug discovery. Here, we review the basic tenets and molecular mechanisms of mitochondrial morphology and ultrastructure, describing how they can coordinately define mitochondrial function.

Localization of Mitochondrial Nucleoids by Transmission Electron Microscopy Using the Transgenic Expression of the Mitochondrial Helicase Twinkle and APEX2

Reminiscent of their evolutionary origin, mitochondria contain their own genome (mtDNA) compacted into the mitochondrial chromosome or nucleoid (mt-nucleoid). Many mitochondrial disorders are characterized by disruption of mt-nucleoids, either by direct mutation of genes involved in mtDNA organization or by interfering with other vital proteins for mitochondrial function. Thus, changes in mt-nucleoid morphology, distribution, and structure are a common feature in many human diseases and can be exploited as an indicator of cellular fitness. Electron microscopy provides the highest possible resolution that can be achieved, delivering spatial and structural information about all cellular structures. Recently, the ascorbate peroxidase APEX2 has been used to increase transmission electron microscopy (TEM) contrast by inducing diaminobenzidine (DAB) precipitation. DAB has the ability to accumulate osmium during classical EM sample preparation and, due to its high electron density, provides strong contrast for TEM. Among the nucleoid proteins, the mitochondrial helicase Twinkle fused with APEX2 has been successfully used to target mt-nucleoids, providing a tool to visualize these subcellular structures with high contrast and with the resolution of an electron microscope. In the presence of H₂O₂, APEX2 catalyzes the polymerization of DAB, generating a brown precipitate that can be visualized in specific regions of the mitochondrial matrix. Here, we provide a detailed protocol to generate murine cell lines expressing a transgenic variant of Twinkle, suitable to target and visualize mt-nucleoids. We also describe all the necessary steps to validate the cell lines prior to electron microscopy imaging and offer examples of anticipated results.