2016: A 'Mitochondria' Odyssey

The three-dimensional conformation and activity of mitochondria in syncytial male germ line-cysts of medicinal leeches

We studied the spatial conformation and activity of mitochondria in the developing syncytial male germline cysts during spermatogenesis of the medicinal leeches using light, fluorescent, transmission electron microscopy, and serial block-face scanning electron microscopy. In cysts with spermatogonia and spermatocytes, mitochondria form networks and are in a dynamic hyperfusion state, while in cysts with spermatids, a single huge mitochondrion is observed. As spermiogenesis progresses, this huge mitochondrion is finally located in the future midpiece. The highest activity, in terms of membrane potential, of the mitochondria in H. medicinalis germline cysts was observed in cysts with spermatocytes; the lowest was in cysts with late elongated spermatids.

NecroX Improves Polyhexamethylene Guanidine-induced Lung Injury by Regulating Mitochondrial Oxidative Stress and Endoplasmic Reticulum Stress

Various environmental compounds are inducers of lung injury. Mitochondria are crucial organelles that can be affected by many lung diseases. NecroX is an indole-derived antioxidant that specifically targets mitochondria. We aimed to evaluate the therapeutic potential and related molecular mechanisms of NecroX in preclinical models of fatal lung injury. We investigated the therapeutic effects of NecroX on two different experimental models of lung injury induced by polyhexamethylene guanidine (PHMG) and bleomycin, respectively. We also performed transcriptome analysis of lung tissues from PHMG-exposed mice and compared the expression profiles with those from dozens of bleomycin-induced fibrosis public data sets. Respiratory exposure to PHMG and bleomycin led to fatal lung injury manifesting extensive inflammation followed by fibrosis. These specifically affected mitochondria regarding biogenesis, mitochondrial DNA integrity, and the generation of mitochondrial reactive oxygen species in various cell types. NecroX significantly improved the pathobiologic features of the PHMG- and bleomycin-induced lung injuries through regulation of mitochondrial oxidative stress. Endoplasmic reticulum stress was also implicated in PHMG-associated lung injuries of mice and humans, and NecroX alleviated PHMG-induced lung injury and the subsequent fibrosis, in part, via regulation of endoplasmic reticulum stress in mice. Gene expression profiles of PHMG-exposed mice were highly consistent with public data sets of bleomycin-induced lung injury models. Pathways related to mitochondrial activities, including oxidative stress, oxidative phosphorylation, and mitochondrial translation, were upregulated, and these patterns were significantly reversed by NecroX. These findings demonstrate that NecroX possesses therapeutic potential for fatal lung injury in humans.

Mitochondrial Metabolism in Pancreatic Ductal Adenocarcinoma: From Mechanism-Based Perspectives to Therapy

Pancreatic ductal adenocarcinoma (PDAC), the fourteenth most common malignancy, is a major contributor to cancer-related death with the utmost case fatality rate among all malignancies. Functional mitochondria, regardless of their complex ecosystem relative to normal cells, are essential in PDAC progression. Tumor cells' potential to produce ATP as energy, despite retaining the redox potential optimum, and allocating materials for biosynthetic activities that are crucial for cell growth, survival, and proliferation, are assisted by mitochondria. The polyclonal tumor cells with different metabolic profiles may add to carcinogenesis through inter-metabolic coupling. Cancer cells frequently possess alterations in the mitochondrial genome, although they do not hinder metabolism; alternatively, they change bioenergetics. This can further impart retrograde signaling, educate cell signaling, epigenetic modifications, chromatin structures, and transcription machinery, and ultimately satisfy cancer cellular and nuclear demands. To maximize the tumor microenvironment (TME), tumor cells remodel nearby stromal cells and extracellular matrix. These changes initiate polyclonality, which is crucial for growth, stress response, and metastasis. Here, we evaluate all the intrinsic and extrinsic pathways drawn by mitochondria in carcinogenesis, emphasizing the perspectives of mitochondrial metabolism in PDAC progression and treatment.

Variants in the Control Region of Mitochondrial Genome Associated with type 2 Diabetes in a Cohort of Mexican Mestizos

BACKGROUND

According to the International Diabetes Federation, Mexico is seventh place in the prevalence of type 2 diabetes (T2D) worldwide. Mitochondrial DNA variant association studies in multifactorial diseases like T2D are scarce in Mexican populations.

AIM OF THE STUDY

The objective of this study was to analyze the association between 18 variants in the mtDNA control region and T2D and related metabolic traits in a Mexican mestizo population from Mexico City.

METHODS

This study included 1001 participants divided into 477 cases with T2D and 524 healthy controls aged between 42 and 62 years and 18 mtDNA variants with frequencies >15%.

RESULTS

Association analyses matched by age and sex showed differences in the distribution between cases and controls for variants m.315_316insC (p = 1.18 × 10^-6), m.489T>C (p = 0.009), m.16362T>C (p = 0.001), and m.16519T>C (p = 0.004). The associations between T2D and variants m.315_316ins (OR = 6.13, CI = 3.42-10.97, p = 1.97 × 10^-6), m.489T>C (OR = 1.45, CI = 1.00-2.11, p = 0.006), m.16362T>C (OR = 2.17, CI = 1.57-3.00, p = 0.001), and m.16519T>C (OR = 1.69, CI = 1.23-2.33, p = 0.006) were significant after performing logistic regression models adjusted for age, sex, and diastolic blood pressure. Metabolic traits in the control group through linear regressions, adjusted for age, sex and BMI, and corrected for multiple comparisons showed nominal association between glucose and variants m.263A>G (p <0.050), m.16183A>C (p <0.010), m.16189T>C (p <0.020), and m.16223C>T (p <0.024); triglycerides, and cholesterol and variant m.309_310insC (p <0.010 and p <0.050 respectively); urea, and creatinine, and variant m.315_316insC (p <0.007, and p <0.004 respectively); diastolic blood pressure and variants m.235A>G (p <0.016), m.263A>G (p <0.013), m.315_316insC (p <0.043), and m.16111C>T (p <0.022).

CONCLUSION

These results demonstrate a strong association between variant m.315_316insC and T2D and a nominal association with T2D traits.

Gemigliptin Alleviates Succinate-Induced Hepatic Stellate Cell Activation by Ameliorating Mitochondrial Dysfunction

BACKGRUOUND

Dipeptidyl peptidase-4 inhibitors (DPP-4Is) are used clinically as oral antidiabetic agents. Although DPP-4Is are known to ameliorate liver fibrosis, the protective mechanism of DPP-4Is in liver fibrosis remains obscure. In this study, gemigliptin was used to investigate the potential of DPP-4Is to alleviate the progression of liver fibrosis.

METHODS

To clarify the effects and mechanisms of gemigliptin, we conducted various experiments in LX-2 cells (immortalized human hepatic stellate cells [HSCs], the principal effectors of hepatic fibrogenesis), which were activated by succinate and exhibited elevated expression of α-smooth muscle actin, collagen type 1, and pro-inflammatory cytokines and increased cell proliferation. In vivo, we examined the effects and mechanisms of gemigliptin on a high-fat, high-cholesterol-induced mouse model of nonalcoholic steatohepatitis (NASH).

RESULTS

Gemigliptin decreased the expression of fibrogenesis markers and reduced the abnormal proliferation of HSCs. In addition, gemigliptin reduced the succinate-induced production of mitochondrial reactive oxygen species (ROS), intracellular ROS, and mitochondrial fission in HSCs. Furthermore, in the mouse model of NASH-induced liver fibrosis, gemigliptin alleviated both liver fibrosis and mitochondrial dysfunction.

CONCLUSION

Gemigliptin protected against HSC activation and liver fibrosis by alleviating mitochondrial dysfunction and ROS production, indicating its potential as a strategy for preventing the development of liver disease.

Isolation and Quality Control of Functional Mitochondria

Even in times, when the study of mitochondria in their natural cellular context is becoming more and more popular, some scientific questions still require the preparation of isolated mitochondria. Numerous protocols are available being adapted for different cell or tissue types allowing isolation of "pure" mitochondria trying to preserve their "structural and functional" integrity. In this chapter, we intend to provide a more general framework introducing differential isopycnic density gradient centrifugation strategy with a special focus sensitizing for the specific challenges coming along with this method and how to obtain "functional," enriched, "intact" mitochondria. Due to the fact that in any study dealing with these organelles standardized processing is mandatory, here we describe a strategy addressing quality control of prepared intact mitochondria. The quality control should be an integrated part of all isolation processes. The underlying protocol should be seen as starting point and has to be carefully adjusted to cover different sample types used for the diverse research questions.

Preparation of "Functional" Mitochondria: A Challenging Business

As the powerhouse of the cell, mitochondria, plays a crucial role in many aspects of life, whereby mitochondrial dysfunctions are associated with pathogenesis of many diseases, like neurodegenerative diseases, obesity, cancer, and metabolic as well as cardiovascular disorders. Mitochondria analysis frequently starts with isolation and enrichment procedures, which have become increasingly important in biomedical research. Unfortunately, isolation procedures can easily cause changes in the structural integrity of mitochondria during in vitro handling having impact on their function. This carries the risk that conclusions about isolated mitochondria may be drawn on the basis of experimental artifacts. Here we critically review a commonly used isolation procedure for mitochondria utilizing differential (gradient) centrifugation and depict major challenges to achieve "functional" mitochondria as basis for comprehensive physiological studies.

Mitotherapy as a Novel Therapeutic Strategy for Mitochondrial Diseases

BACKGROUND

The mitochondrion is a multi-functional organelle that is mainly responsible for energy supply in the mammalian cells. Over 100 human diseases are attributed to mitochondrial dysfunction. Mitochondrial therapy (mitotherapy) aims to transfer functional exogenous mitochondria into mitochondria-defective cells for recovery of the cell viability and consequently, prevention of the disease progress.

OBJECTIVE

The review summarizes the evidence on exogenous mitochondria that can directly enter mammalian cells for disease therapy following local and intravenous administration, and suggests that when healthy cells donate their mitochondria to damaged cells, the mitochondrial transfer between cells serve as a new mode of cell rescue. Then the transferred mitochondria play their roles in recipient cells, including energy production and maintenance of cell function.

CONCLUSION

Mitotherapy makes the of modulation of cell survival possible, and it would be a potential therapeutic strategy for mitochondrial diseases.

Mitochondrial transfer from mesenchymal stem cells improves neuronal metabolism after oxidant injury in vitro: The role of Miro1

Stroke-induced cerebral ischemia is a major cause of death and disability. The disruption of blood flow results in neuronal and glial cell death leading to brain injury. Reperfusion restores oxygen to the affected tissue, but can also cause damage through an enhanced oxidative stress and inflammatory response. This study examines mitochondrial transfer from MSC to neurons and the role it plays in neuronal preservation after oxidant injury. We observed the transfer of mitochondria from MSC to mouse neurons in vitro following hydrogen peroxide exposure. The observed transfer was dependent on cell-to-cell contact and led to increased neuronal survival and improved metabolism. A number of pro-inflammatory and mitochondrial motility genes were upregulated in neurons after hydrogen peroxide exposure. This included Miro1 and TNFAIP2, linking inflammation and mitochondrial transfer to oxidant injury. Increasing Miro1 expression in MSC improved the metabolic benefit of mitochondrial transfer after neuronal oxidant injury. Decreasing Miro1 expression had the opposite effect, decreasing the metabolic benefit of MSC co-culture. MSC transfer of mitochondria to oxidant-damaged neurons may help improve neuronal preservation and functional recovery after stroke.

Energy Metabolism During Osteogenic Differentiation: The Role of Akt

Osteogenic differentiation, the process by which bone marrow mesenchymal stem/stromal (a.k.a. skeletal stem) cells and osteoprogenitors form osteoblasts, is a critical event for bone formation during development, fracture repair, and tissue maintenance. Extra cellular and intracellular signaling pathways triggering osteogenic differentiation are relatively well known; however, the ensuing change in cell energy metabolism is less clearly defined. We and others have previously reported activation of mitochondria during osteogenic differentiation. To further elucidate the involved bioenergetic mechanisms and triggers, we tested the effect of osteogenic media containing ascorbate and β-glycerol phosphate, or various osteogenic hormones and growth factors on energy metabolism in long bone (ST2)- and calvarial bone (MC3T3-E1)-derived osteoprogenitors. We show that osteogenic media and differentiation factors, Wnt3a and BMP2, stimulate mitochondrial oxidative phosphorylation (OxPhos) with little effect on glycolysis. The activation of OxPhos occurs acutely, suggesting a metabolic signaling change rather than protein expression change. To this end, we found that the observed mitochondrial activation is Akt dependent. Akt is activated by osteogenic media, Wnt3a, and BMP2, leading to increased phosphorylation of various mitochondrial Akt targets, a phenomenon known to stimulate OxPhos. In sum, our data provide comprehensive analysis of cellular bioenergetics during osteoinduction in cells of two different origins (mesenchyme vs neural crest) and identify Wnt3a and BMP2 as physiological stimulators of mitochondrial respiration through Akt activation.

Inhibition of the mitochondrial permeability transition improves bone fracture repair

Bone fracture is accompanied by trauma, mechanical stresses, and inflammation - conditions known to induce the mitochondrial permeability transition. This phenomenon occurs due to opening of the mitochondrial permeability transition pore (MPTP) promoted by cyclophilin D (CypD). MPTP opening leads to more inflammation, cell death and potentially to disruption of fracture repair. Here we performed a proof-of-concept study and tested a hypothesis that protecting mitochondria from MPTP opening via inhibition of CypD improves fracture repair. First, our in vitro experiments indicated pro-osteogenic and anti-inflammatory effects in osteoprogenitors upon CypD knock-out or pharmacological inhibition. Using a bone fracture model in mice, we observed that bone formation and biomechanical properties of repaired bones were significantly increased in CypD knock-out mice or wild type mice treated with a CypD inhibitor, NIM811, when compared to controls. These effects were evident in young male but not female mice, however in older (13 month-old) female mice bone formation was also increased during fracture repair. In contrast to global CypD knock-out, mesenchymal lineage-specific (Prx1-Cre driven) CypD deletion did not result in improved fracture repair. Our findings implicate MPTP in bone fracture and suggest systemic CypD inhibition as a modality to promote fracture repair.

Clinical Phenotype and Genetic Features of a Pair of Chinese Twins with Kearns-Sayre Syndrome

Kearns-Sayre Syndrome (KSS) is a severe mitochondrial disorder involving the central nervous system, eyes, ears, skeletal muscles, and heart. The mitochondrial DNA (mtDNA) rearrangements, especially the deletions, are present in almost all KSS patients and considered as the disease-causing factor. However, the size and position of mtDNA deletions are distinct in different individuals. In this study, we report the case of a pair of Chinese twins with KSS. The twin patients revealed typical KSS clinical symptoms, including heart block, bilateral sensorineural hearing loss, progressive external ophthalmoplegia, exercise intolerance, proximal limb weakness, and endocrine disorders. Using long-range polymerase chain reactions (long-range PCR) and next-generation sequencing (NGS), the genetic features of the twin patients were investigated. A large 6600 bp mtDNA deletion, ranging from position 8702 to 15,302, was detected in both patients. To our knowledge, this kind of mtDNA deletion has never been described previously. Our study enriched the mutation spectrum of KSS and showed that NGS is a powerful tool for detecting mtDNA large variants.

YY1 control of mitochondrial-related genes does not account for regulation of immunoglobulin class switch recombination in mice

Immunoglobulin class switch recombination (CSR) occurs in activated B cells with increased mitochondrial mass and membrane potential. Transcription factor Yin Yang 1 (YY1) is critical for CSR and for formation of the DNA loops involved in this process. We therefore sought to determine if YY1 knockout impacts mitochondrial gene expression and mitochondrial function in murine splenic B cells, providing a potential mechanism for regulating CSR. We identified numerous genes in splenic B cells differentially regulated when cells are induced to undergo CSR. YY1 conditional knockout caused differential expression of 1129 genes, with 59 being mitochondrial-related genes. ChIP-seq analyses showed YY1 was directly bound to nearly half of these mitochondrial-related genes. Surprisingly, at the time when YY1 knockout dramatically reduces DNA loop formation and CSR, mitochondrial mass and membrane potential were not significantly impacted, nor was there a significant change in mitochondrial oxygen consumption, extracellular acidification rate, or mitochondrial complex I or IV activities. Our results indicate that YY1 regulates numerous mitochondrial-related genes in splenic B cells, but this does not account for the impact of YY1 on CSR or long-distance DNA loop formation.

A Systematic Pan-Cancer Analysis of Genetic Heterogeneity Reveals Associations with Epigenetic Modifiers

Intratumor genetic heterogeneity (ITH) is the main obstacle to effective cancer treatment and a major mechanism of drug resistance. It results from the continuous evolution of different clones of a tumor over time. However, the molecular features underlying the emergence of genetically-distinct subclonal cell populations remain elusive. Here, we conducted an exhaustive characterization of ITH across 2807 tumor samples from 16 cancer types. Integration of ITH scores and somatic variants detected in each tumor sample revealed that mutations in epigenetic modifier genes are associated with higher ITH levels. In particular, genes that regulate genome-wide histone and DNA methylation emerged as being determinant of high ITH. Indeed, the knockout of histone methyltransferase SETD2 or DNA methyltransferase DNMT3A using the CRISPR/Cas9 system on cancer cells led to significant expansion of genetically-distinct clones and culminated in highly heterogeneous cell populations. The ITH scores observed in knockout cells recapitulated the heterogeneity levels observed in patient tumor samples and correlated with a better mitochondrial bioenergetic performance under stress conditions. Our work provides new insights into tumor development, and discloses new drivers of ITH, which may be useful as either predictive biomarkers or therapeutic targets to improve cancer treatment.

Oxygen Tension Strongly Influences Metabolic Parameters and the Release of Interleukin-6 of Human Amniotic Mesenchymal Stromal Cells In Vitro

The human amniotic membrane (hAM) has been used for tissue regeneration for over a century. In vivo (in utero), cells of the hAM are exposed to low oxygen tension (1-4% oxygen), while the hAM is usually cultured in atmospheric, meaning high, oxygen tension (20% oxygen). We tested the influence of oxygen tensions on mitochondrial and inflammatory parameters of human amniotic mesenchymal stromal cells (hAMSCs). Freshly isolated hAMSCs were incubated for 4 days at 5% and 20% oxygen. We found 20% oxygen to strongly increase mitochondrial oxidative phosphorylation, especially in placental amniotic cells. Oxygen tension did not impact levels of reactive oxygen species (ROS); however, placental amniotic cells showed lower levels of ROS, independent of oxygen tension. In contrast, the release of nitric oxide was independent of the amniotic region but dependent on oxygen tension. Furthermore, IL-6 was significantly increased at 20% oxygen. To conclude, short-time cultivation at 20% oxygen of freshly isolated hAMSCs induced significant changes in mitochondrial function and release of IL-6. Depending on the therapeutic purpose, cultivation conditions of the cells should be chosen carefully for providing the best possible quality of cell therapy.

The landscape of mitochondrial small non-coding RNAs in the PGCs of male mice, spermatogonia, gametes and in zygotes

Background

Mitochondria are organelles that fulfill a fundamental role in cell bioenergetics, as well as in other processes like cell signaling and death. Small non-coding RNAs (sncRNA) are now being considered as pivotal post-transcriptional regulators, widening the landscape of their diversity and functions. In mammalian cells, small RNAs encoded by the mitochondrial genome, mitosRNAs were discovered recently, although their biological role remains uncertain.

Results

Here, using specific bioinformatics analyses, we have defined the diversity of mitosRNAs present in early differentiated germ cells of male mice (PGCs and spermatogonia), and in the gametes of both sexes and in zygotes. We found strong transcription of mitosRNAs relative to the size of the mtDNA, and classifying these mitosRNAs into different functional sncRNA groups highlighted the predominance of Piwi-interacting RNAs (piRNAs) relative to the other types of mitosRNAs. Mito-piRNAs were more abundant in oocytes and zygotes, where mitochondria fulfill key roles in fecundation process. Functional analysis of some particular mito-piRNAs (mito-piR-7,456,245), also expressed in 3T3-L1 cells, was assessed after exposure to RNA antagonists.

Conclusions

As far as we are aware, this is the first integrated analysis of sncRNAs encoded by mtDNA in germ cells and zygotes. The data obtained suggesting that mitosRNAs fulfill key roles in gamete differentiation and fertilization.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5020-3) contains supplementary material, which is available to authorized users.

Active mitochondria support osteogenic differentiation by stimulating β-catenin acetylation

Bone marrow stromal (a.k.a. mesenchymal stem) cells (BMSCs) can differentiate into osteoblasts (OBs), adipocytes, or chondrocytes. As BMSCs undergo OB differentiation, they up-regulate mitochondrial oxidative phosphorylation (OxPhos). Here, we investigated the mechanism(s) connecting mitochondrial OxPhos to OB differentiation. First, we found that treating BMSC-like C3H10T1/2 cells with an OxPhos inhibitor reduces their osteogenic potential. Interestingly, ATP levels were not reduced, as glycolysis compensated for the decreased OxPhos. Thus, mitochondria support OB differentiation not only by supplying ATP, but also by other mechanisms. To uncover these mechanisms, we stimulated OxPhos in C3H10T1/2 cells by replacing media glucose with galactose and observed that this substitution increases both OxPhos and osteogenesis even in the absence of osteoinducers. β-Catenin, an important signaling pathway in osteogenesis, was found to be responsive to OxPhos stimulation. β-Catenin activity is maintained by acetylation, and mitochondria generate the acetyl donor acetyl-CoA, which upon entering the Krebs cycle is converted to citrate capable of exiting mitochondria. Cytosolic citrate is converted back to acetyl-CoA by ATP citrate lyase (ACLY). We found that inhibiting ACLY with SB204990 (SB) reverses the galactose-induced β-catenin activity and OB differentiation. This suggested that acetylation is involved in β-catenin activation after forced OxPhos stimulation, and using immunoprecipitation, we indeed detected SB-sensitive β-catenin acetylation. Both β-catenin acetylation and activity increased during osteoinduction coincident with OxPhos activation. These findings suggest that active mitochondria support OB differentiation by promoting β-catenin acetylation and thus activity.

Low mitochondrial activity within developing earthworm male germ-line cysts revealed by JC-1

The male germ-line cysts that occur in annelids appear to be a very convenient model for spermatogenesis studies. Germ-line cysts in the studied earthworm are composed of two compartments: (1) germ cells, where each cell is connected via one intercellular bridge to (2) an anuclear central cytoplasmic mass, the cytophore. In the present paper, confocal and transmission electron microscopy were used to follow the changes in the mitochondrial activity and ultrastructure within the cysts during spermatogenesis. JC-1 was used to visualize the populations of mitochondria with a high and low membrane potential. We used the spot detection Imaris software module to obtain the quantitative data. We counted and compared the 'mitochondrial spots' - the smallest detectable signals from mitochondria. It was found that in all of the stages of cyst development, the majority of mitochondria spots showed a green fluorescence, thus indicating a low mitochondrial membrane potential (MMP). Moreover, the number of active mitochondria spots that were visualized by red JC-1 fluorescence (high MMP) drastically decreased as spermatogenesis progressed. As much as 26% of the total number of mitochondrial spots in the spermatogonial cysts showed a high MMP - 19% in the spermatocytes, 24% in the isodiametric spermatids and 3% and 6%, respectively, in the cysts that were holding early and late elongate spermatids. The mitochondria were usually thread-like and had an electron-dense matrix and lamellar cristae. Then, during spermiogenesis, the mitochondria within both the spermatids and the cytophore had a tendency to form aggregates in which the mitochondria were cemented by an electron-dense material.

Epigenetic Treatment of Neurodegenerative Ophthalmic Disorders: An Eye Toward the Future

Eye disease is one of the primary medical conditions that requires attention and therapeutic intervention in ageing populations worldwide. Further, the global burden of diabetes and obesity, along with heart disease, all lead to secondary manifestations of ophthalmic distress. Therefore, there is increased interest in developing innovative new approaches that target various mechanisms and sequelae driving conditions that result in adverse vision. The research challenge is even greater given that the terrain of eye diseases is difficult to landscape into a single therapeutic theme. This report addresses the burden of eye disease due to mitochondrial dysfunction, including antioxidant, autophagic, epigenetic, mitophagic, and other cellular processes that modulate the biomedical end result. In this light, we single out lipoic acid as a potent known natural activator of these pathways, along with alternative and potentially more effective conjugates, which together harness the necessary potency, specificity, and biodistribution parameters required for improved therapeutic outcomes.

Succinate promotes stem cell migration through the GPR91-dependent regulation of DRP1-mediated mitochondrial fission

The role of metabolites produced from stem cell metabolism has been emerged as signaling molecules to regulate stem cell behaviors such as migration. The mitochondrial morphology is closely associated with the metabolic balance and stem cell function. However, the physiological role of succinate on human mesenchymal stem cell (hMSC) migration by regulating the mitochondrial morphology remains unclear. Here, we investigate the effect of succinate on hMSC migration via regulation of mitochondrial dynamics and its related signaling pathway. Succinate (50 μM) significantly accelerates hMSC migration. Succinate increases phosphorylation of pan-PKC, especially the atypical PKCζ level which was blocked by the knockdown of Gα_q and Gα_12. Activated PKCζ subsequently phosphorylates p38 MAPK. Cytosolic DRP1 is phosphorylated by p38 MAPK and results in DRP1 translocation to the mitochondria outer membrane, eventually inducing mitochondrial fragmentation. Mitochondrial fission-induced mitochondrial function elevates mitochondrial ROS (mtROS) levels and activates Rho GTPases, which then induces F-actin formation. Furthermore, in a skin excisional wound model, we found the effects of succinate-pretreated hMSC enhanced wound closure, vascularization and re-epithelialization and confirmed that DRP1 has a vital role in injured tissue regeneration. Overall, succinate promotes DRP1-mediated mitochondrial fission via GPR91, consequently stimulating the hMSC migration through mtROS-induced F-actin formation.

Ranolazine promotes muscle differentiation and reduces oxidative stress in C2C12 skeletal muscle cells

PURPOSE

The purpose of this study is to investigate Ranolazine action on skeletal muscle differentiation and mitochondrial oxidative phenomena. Ranolazine, an antianginal drug, which acts blocking the late INaL current, was shown to lower hemoglobin A1c in patients with diabetes. In the present study, we hypothesized an action of Ranolazine on skeletal muscle cells regeneration and oxidative process, leading to a reduction of insulin resistance.

METHODS

10 μM Ranolazine was added to C2C12 murine myoblastic cells during proliferation, differentiation and newly formed myotubes.

RESULTS

Ranolazine promoted the development of a specific myogenic phenotype: increasing the expression of myogenic regulator factors and inhibiting cell cycle progression factor (p21). Ranolazine stimulated calcium signaling (calmodulin-dependent kinases) and reduced reactive oxygen species levels. Furthermore, Ranolazine maintained mitochondrial homeostasis. During the differentiation phase, Ranolazine promoted myotubes formation. Ranolazine did not modify kinases involved in skeletal muscle differentiation and glucose uptake (extracellular signal-regulated kinases 1/2 and AKT pathways), but activated calcium signaling pathways. During proliferation, Ranolazine did not modify the number of mitochondria while decreasing osteopontin protein levels. Lastly, neo-formed myotubes treated with Ranolazine showed typical hypertrophic phenotype.

CONCLUSION

In conclusion, our results indicate that Ranolazine stimulates myogenesis and reduces a pro-oxidant inflammation/oxidative condition, activating a calcium signaling pathway. These newly described mechanisms may partially explain the glucose lowering effect of the drug.

Mitochondrial-epigenetic crosstalk in environmental toxicology

Crosstalk between the nuclear epigenome and mitochondria, both in normal physiological function and in responses to environmental toxicant exposures, is a developing sub-field of interest in environmental and molecular toxicology. The majority (∼99%) of mitochondrial proteins are encoded in the nuclear genome, so programmed communication among nuclear, cytoplasmic, and mitochondrial compartments is essential for maintaining cellular health. In this review, we will focus on correlative and mechanistic evidence for direct impacts of each system on the other, discuss demonstrated or potential crosstalk in the context of chemical insult, and highlight biological research questions for future study. We will first review the two main signaling systems: nuclear signaling to the mitochondria [anterograde signaling], best described in regulation of oxidative phosphorylation (OXPHOS) and mitochondrial biogenesis in response to environmental signals received by the nucleus, and mitochondrial signals to the nucleus [retrograde signaling]. Both signaling systems can communicate intracellular energy needs or a need to compensate for dysfunction to maintain homeostasis, but both can also relay inappropriate signals in the presence of dysfunction in either system and contribute to adverse health outcomes. We will first review these two signaling systems and highlight known or biologically feasible epigenetic contributions to both, then briefly discuss the emerging field of epigenetic regulation of the mitochondrial genome, and finally discuss putative "crosstalk phenotypes", including biological phenomena, such as caloric restriction, maintenance of stemness, and circadian rhythm, and states of disease or loss of function, such as cancer and aging, in which both the nuclear epigenome and mitochondria are strongly implicated.

Mitochondria, Bioenergetics and Excitotoxicity: New Therapeutic Targets in Perinatal Brain Injury

Injury to the fragile immature brain is implicated in the manifestation of long-term neurological disorders, including childhood disability such as cerebral palsy, learning disability and behavioral disorders. Advancements in perinatal practice and improved care mean the majority of infants suffering from perinatal brain injury will survive, with many subtle clinical symptoms going undiagnosed until later in life. Hypoxic-ischemia is the dominant cause of perinatal brain injury, and constitutes a significant socioeconomic burden to both developed and developing countries. Therapeutic hypothermia is the sole validated clinical intervention to perinatal asphyxia; however it is not always neuroprotective and its utility is limited to developed countries. There is an urgent need to better understand the molecular pathways underlying hypoxic-ischemic injury to identify new therapeutic targets in such a small but critical therapeutic window. Mitochondria are highly implicated following ischemic injury due to their roles as the powerhouse and main energy generators of the cell, as well as cell death processes. While the link between impaired mitochondrial bioenergetics and secondary energy failure following loss of high-energy phosphates is well established after hypoxia-ischemia (HI), there is emerging evidence that the roles of mitochondria in disease extend far beyond this. Indeed, mitochondrial turnover, including processes such as mitochondrial biogenesis, fusion, fission and mitophagy, affect recovery of neurons after injury and mitochondria are involved in the regulation of the innate immune response to inflammation. This review article will explore these mitochondrial pathways, and finally will summarize past and current efforts in targeting these pathways after hypoxic-ischemic injury, as a means of identifying new avenues for clinical intervention.

Getting into mitochondria

The human mitochondrial glutamate dehydrogenase isoenzymes (hGDH1 and hGDH2) are abundant matrix-localized proteins encoded by nuclear genes. The proteins are synthesized in the cytoplasm, with an atypically long N-terminal mitochondrial targeting sequence (MTS). The results of secondary structure predictions suggest the presence of two α-helices within the N-terminal region of the MTS. Results from deletion analyses indicate that individual helices have limited ability to direct protein import and matrix localization, but that there is a synergistic interaction when both helices are present [Biochem. J. (2016) 473: , 2813-2829]. Mutagenesis of the MTS cleavage sites blocked post-import removal of the presequences, but did not impede import. The authors propose that the high matrix levels of hGDH can be attributed to the unusual length and secondary structure of the MTS.

Betaine promotes cell differentiation of human osteoblasts in primary culture

BACKGROUND

Betaine (BET), a component of many foods, is an essential osmolyte and a source of methyl groups; it also shows an antioxidant activity. Moreover, BET stimulates muscle differentiation via insulin like growth factor I (IGF-I). The processes of myogenesis and osteogenesis involve common mechanisms with skeletal muscle cells and osteoblasts sharing the same precursor. Therefore, we have hypothesized that BET might be effective on osteoblast cell differentiation.

METHODS

The effect of BET was tested in human osteoblasts (hObs) derived from trabecular bone samples obtained from waste material of orthopedic surgery. Cells were treated with 10 mM BET at 5, 15, 60 min and 3, 6 and 24 h. The possible effects of BET on hObs differentiation were evaluated by real time PCR, western blot and immunofluorescence analysis. Calcium imaging was used to monitor intracellular calcium changes.

RESULTS

Real time PCR results showed that BET stimulated significantly the expression of RUNX2, osterix, bone sialoprotein and osteopontin. Western blot and immunofluorescence confirmed BET stimulation of osteopontin protein synthesis. BET stimulated ERK signaling, key pathway involved in osteoblastogenesis and calcium signaling. BET induced a rise of intracellular calcium by means of the calcium ions influx from the extracellular milieu through the L-type calcium channels and CaMKII signaling activation. A significant rise in IGF-I mRNA at 3 and 6 h and a significant increase of IGF-I protein at 6 and 24 h after BET stimulus was detected. Furthermore, BET was able to increase significantly both SOD2 gene expression and protein content.

CONCLUSIONS

Our study showed that three signaling pathways, i.e. cytosolic calcium influx, ERK activation and IGF-I production, are enhanced by BET in human osteoblasts. These pathways could have synergistic effects on osteogenic gene expression and protein synthesis, thus potentially leading to enhanced bone formation. Taken together, these results suggest that BET could be a promising nutraceutical therapeutic agent in the strategy to counteract the concomitant and interacting impact of sarcopenia and osteoporosis, i.e. the major determinants of senile frailty and related mortality.

Mitophagy Transcriptome: Mechanistic Insights into Polyphenol-Mediated Mitophagy

Mitochondria are important bioenergetic and signalling hubs critical for myriad cellular functions and homeostasis. Dysfunction in mitochondria is a central theme in aging and diseases. Mitophagy, a process whereby damaged mitochondria are selectively removed by autophagy, plays a key homeostatic role in mitochondrial quality control. Upregulation of mitophagy has shown to mitigate superfluous mitochondrial accumulation and toxicity to safeguard mitochondrial fitness. Hence, mitophagy is a viable target to promote longevity and prevent age-related pathologies. Current challenge in modulating mitophagy for cellular protection involves identification of physiological ways to activate the pathway. Till date, mitochondrial stress and toxins remain the most potent inducers of mitophagy. Polyphenols have recently been demonstrated to protect mitochondrial health by facilitating mitophagy, thus suggesting the exciting prospect of augmenting mitophagy through dietary intake. In this review, we will first discuss the different surveillance mechanisms responsible for the removal of damaged mitochondrial components, followed by highlighting the transcriptional regulatory mechanisms of mitophagy. Finally, we will review the functional connection between polyphenols and mitophagy and provide insight into the underlying mechanisms that potentially govern polyphenol-induced mitophagy.

Neurons derived from different brain regions are inherently different in vitro: a novel multiregional brain-on-a-chip

Brain in vitro models are critically important to developing our understanding of basic nervous system cellular physiology, potential neurotoxic effects of chemicals, and specific cellular mechanisms of many disease states. In this study, we sought to address key shortcomings of current brain in vitro models: the scarcity of comparative data for cells originating from distinct brain regions and the lack of multiregional brain in vitro models. We demonstrated that rat neurons from different brain regions exhibit unique profiles regarding their cell composition, protein expression, metabolism, and electrical activity in vitro. In vivo, the brain is unique in its structural and functional organization, and the interactions and communication between different brain areas are essential components of proper brain function. This fact and the observation that neurons from different areas of the brain exhibit unique behaviors in vitro underline the importance of establishing multiregional brain in vitro models. Therefore, we here developed a multiregional brain-on-a-chip and observed a reduction of overall firing activity, as well as altered amounts of astrocytes and specific neuronal cell types compared with separately cultured neurons. Furthermore, this multiregional model was used to study the effects of phencyclidine, a drug known to induce schizophrenia-like symptoms in vivo, on individual brain areas separately while monitoring downstream effects on interconnected regions. Overall, this work provides a comparison of cells from different brain regions in vitro and introduces a multiregional brain-on-a-chip that enables the development of unique disease models incorporating essential in vivo features.NEW & NOTEWORTHY Due to the scarcity of comparative data for cells from different brain regions in vitro, we demonstrated that neurons isolated from distinct brain areas exhibit unique behaviors in vitro. Moreover, in vivo proper brain function is dependent on the connection and communication of several brain regions, underlining the importance of developing multiregional brain in vitro models. We introduced a novel brain-on-a-chip model, implementing essential in vivo features, such as different brain areas and their functional connections.

Epigenetic Treatment of Persistent Viral Infections

Preclinical Research Approximately 2,500 years ago, Hippocrates used the word herpes as a medical term to describe lesions that appeared to creep or crawl on the skin, advocating heat as a possible treatment. During the last 50 years, pharmaceutical research has made great strides, and therapeutic options have expanded to include small molecule antiviral agents, protease inhibitors, preventive vaccines for a handful of the papillomaviruses, and even cures for hepatitis C virus infections. However, effective treatments for persistent and recurrent viral infections, particularly the highly prevalent herpesviruses, continue to represent a significant unmet medical need, affecting the majority of the world's population. Exploring the population diversity of the human microbiome and the effects its compositional variances have on the immune system, health, and disease are the subjects of intense investigational research and study. Among the collection of viruses, bacteria, fungi, and single-cell eukaryotes that comprise the human microbiome, the virome has been grossly understudied relative to the influence it exerts on human pathophysiology, much as mitochondria have until recently failed to receive the attention they deserve, given their critical biomedical importance. Fortunately, cellular epigenetic machinery offers a wealth of druggable targets for therapeutic intervention in numerous disease indications, including those outlined above. With advances in synthetic biology, engineering our body's commensal microorganisms to seek out and destroy pathogenic species is clearly on the horizon. This is especially the case given recent breakthroughs in genetic manipulation with tools such as the CRISPR/Cas (clustered regularly interspaced short palindromic repeats/CRISPR-associated) gene-editing platforms. Tying these concepts together with our previous work on the microbiome and neurodegenerative and neuropsychiatric diseases, we suggest that, because mammalian cells respond to a viral infection by triggering a cascade of antiviral innate immune responses governed substantially by the cell's mitochondria, small molecule carnitinoids represent a new class of therapeutics with potential widespread utility against many infectious insults. Drug Dev Res 78 : 24-36, 2017.   © 2016 Wiley Periodicals, Inc.

Targeting cancer cells through antibiotics-induced mitochondrial dysfunction requires autophagy inhibition

A significant part of current research studies utilizes various cellular models which imply specific antibiotics-containing media as well as antibiotics used for clonal selection or promoter de/activation. With the great success of developing such tools, mitochondria, once originated from bacteria, can be effectively targeted by antibiotics. For that reason, some studies propose antibiotics-targeting of mitochondria as part of anticancer therapy. Here, we have focused on the effects of various classes of antibiotics on mitochondria in cancer and non-cancer cells and demonlow mitochondrial membrane potential, reduced ATP production, altered morphology and lowered respiration rate which altogether suggested mitochondrial dysfunction (MDF). This was in parallel with increased level of reactive oxygen species (ROS) and decreased activity of mitochondrial respiration complexes. However, both survival and repopulation capacity of cancer cells was not significantly affected by the antibiotics, perhaps due to a glycolytic shift or activated autophagy. In turn, simultaneous inhibition of autophagy and treatment with antibiotics largely reduced tumorigenic properties of cancer cells suggesting potential strategy for anticancer therapy.

Proteomics of human mitochondria

Proteomics have passed through a tremendous development in the recent years by the development of ever more sensitive, fast and precise mass spectrometry methods. The dramatically increased research in the biology of mitochondria and their prominent involvement in all kinds of diseases and ageing has benefitted from mitochondrial proteomics. We here review substantial findings and progress of proteomic analyses of human cells and tissues in the recent past. One challenge for investigations of human samples is the ethically and medically founded limited access to human material. The increased sensitivity of mass spectrometry technology aids in lowering this hurdle and new approaches like generation of induced pluripotent cells from somatic cells allow to produce patient-specific cellular disease models with great potential. We describe which human sample types are accessible, review the status of the catalog of human mitochondrial proteins and discuss proteins with dual localization in mitochondria and other cellular compartments. We describe the status and developments of pertinent mass spectrometric strategies, and the use of databases and bioinformatics. Using selected illustrative examples, we draw a picture of the role of proteomic analyses for the many disease contexts from inherited disorders caused by mutation in mitochondrial proteins to complex diseases like cancer, type 2 diabetes and neurodegenerative diseases. Finally, we speculate on the future role of proteomics in research on human mitochondria and pinpoint fields where the evolving technologies will be exploited.