Mitochondrial fragmentation and network architecture in degenerative diseases

Using C. elegans as a model for neurodegenerative diseases: Methodology and evaluation

Caenorhabditis elegans is a nematode that has been used as an animal model for almost 50years. It has primitive and simple tissues and organs, making it an ideal model for studying neurological pathways involved in neurodegenerative diseases like Alzheimer's disease (AD) and Parkinson's disease (PD). C. elegans has conserved neurological pathways and is able to mimic human diseases, providing valuable insights into the human disease phenotype. This methodological review presents current approaches to generate neurodegenerative-like models of AD and PD in C. elegans, and evaluates the experiments commonly used to validate the diseases. These experimental approaches include assessing survival, fertility, mobility, electropharyngeogram assays, confocal mitochondrial imaging, RNA extraction for qRT-PCR or RT-PCR, and rate of defecation. This review also summarizes the current knowledge acquired on AD and PD using the aforementioned experimental approaches. Additionally, gaps in knowledge and future directions for research are also discussed in the review.

The crude extract obtained from Cinnamomum macrostemon Hayata regulates oxidative stress and mitophagy in keratinocytes

Four ethanol fractionated crude extracts (EFCEs [A-D]) purified from the leaves of Cinnamomum macrostemon Hayata were screened for antioxidative effects and mitochondrial function in HaCaT cells. The higher cell viability indicated that EFCE C was mildly toxic. Under the treatment of 50 ng/mL EFCE C, the hydrogen peroxide (H2O2)-induced cytosolic and mitochondrial reactive oxygen species levels were reduced as well as the H2O2-impaired cell viability, mitochondrial membrane potential (MMP), ATP production, and mitochondrial mass. The conversion of globular mitochondria to tubular mitochondria is coincident with EFCE C-restored mitochondrial function. The mitophagy activator rapamycin showed similar effects to EFCE C in recovering the H2O2-impaired cell viability, MMP, ATP production, mitochondrial mass, and also mitophagic proteins such as PINK1, Parkin, LC3 II, and biogenesis protein PGC-1α. We thereby propose the application of EFCE C in the prevention of oxidative stress in skin cells.

Mitochondrial heterogeneity in diseases

As key organelles involved in cellular metabolism, mitochondria frequently undergo adaptive changes in morphology, components and functions in response to various environmental stresses and cellular demands. Previous studies of mitochondria research have gradually evolved, from focusing on morphological change analysis to systematic multiomics, thereby revealing the mitochondrial variation between cells or within the mitochondrial population within a single cell. The phenomenon of mitochondrial variation features is defined as mitochondrial heterogeneity. Moreover, mitochondrial heterogeneity has been reported to influence a variety of physiological processes, including tissue homeostasis, tissue repair, immunoregulation, and tumor progression. Here, we comprehensively review the mitochondrial heterogeneity in different tissues under pathological states, involving variant features of mitochondrial DNA, RNA, protein and lipid components. Then, the mechanisms that contribute to mitochondrial heterogeneity are also summarized, such as the mutation of the mitochondrial genome and the import of mitochondrial proteins that result in the heterogeneity of mitochondrial DNA and protein components. Additionally, multiple perspectives are investigated to better comprehend the mysteries of mitochondrial heterogeneity between cells. Finally, we summarize the prospective mitochondrial heterogeneity-targeting therapies in terms of alleviating mitochondrial oxidative damage, reducing mitochondrial carbon stress and enhancing mitochondrial biogenesis to relieve various pathological conditions. The possibility of recent technological advances in targeted mitochondrial gene editing is also discussed.

RUNX1 Upregulation Causes Mitochondrial Dysfunction via Regulating the PI3K-Akt Pathway in iPSC from Patients with Down Syndrome

Down syndrome (DS) is the most common autosomal aneuploidy caused by trisomy of chromosome 21. Previous studies demonstrated that DS affected mitochondrial functions, which may be associated with the abnormal development of the nervous system in patients with DS. Runt-related transcription factor 1 (RUNX1) is an encoding gene located on chromosome 21. It has been reported that RUNX1 may affect cell apoptosis via the mitochondrial pathway. The present study investigated whether RUNX1 plays a critical role in mitochondrial dysfunction in DS and explored the mechanism by which RUNX1 affects mitochondrial functions. Expression of RUNX1 was detected in induced pluripotent stem cells of patients with DS (DS-iPSCs) and normal iPSCs (N-iPSCs), and the mitochondrial functions were investigated in the current study. Subsequently, RUNX1 was overexpressed in N-iPSCs and inhibited in DS-iPSCs. The mitochondrial functions were investigated thoroughly, including reactive oxygen species levels, mitochondrial membrane potential, ATP content and lysosomal activity. Finally, RNA-sequencing was used to explore the global expression pattern. It was observed that the expression levels of RUNX1 in DS-iPSCs were significantly higher than those in normal controls. Impaired mitochondrial functions were observed in DS-iPSCs. Of note, overexpression of RUNX1 in N-iPSCs resulted in mitochondrial dysfunction, while inhibition of RUNX1 expression could improve the mitochondrial function in DS-iPSCs. Global gene expression analysis indicated that overexpression of RUNX1 may promote the induction of apoptosis in DS-iPSCs by activating the PI3K/Akt signaling pathway. The present findings indicate that abnormal expression of RUNX1 may play a critical role in mitochondrial dysfunction in DS-iPSCs.

Mitochondrial Dysfunction in Down Syndrome: From Pathology to Therapy

Mitochondrial dysfunctions have been described in Down syndrome (DS) caused by either partial or full trisomy of chromosome 21 (HSA21). Mitochondria play a crucial role in various vital functions in eukaryotic cells, especially in energy production, calcium homeostasis and programmed cell death. The function of mitochondria is primarily regulated by genes encoded in the mitochondrion and nucleus. Many genes on HSA21 are involved in oxidative phosphorylation (OXPHOS) and regulation of mitochondrial functions. This review highlights the HSA21 dosage-sensitive nuclear-encoded mitochondrial genes associated with overexpression-related phenotypes seen in DS. This includes impaired mitochondrial dynamics, structural defects and dysregulated bioenergetic profiles such as OXPHOS deficiency and reduced ATP production. Various therapeutic approaches for modulating energy deficits in DS, effects and molecular mechanism of gene therapy and drugs that exert protective effects through modulation of mitochondrial function and attenuation of oxidative stress in DS cells were discussed. It is prudent that improving DS pathophysiological conditions or quality of life may be feasible by targeting something as simple as cellular mitochondrial biogenesis and function.

Potential Diets to Improve Mitochondrial Activity in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is an incurable neurodegenerative disease, the pathogenesis of which is based on alternations in the mitochondria of motor neurons, causing their progressive death. A growing body of evidence shows that more efficient mitophagy could prevent and/or treat this disorder by suppressing mitochondrial dysfunction-induced oxidative stress and inflammation. Mitophagy has been considered one of the main mechanisms responsible for mitochondrial quality control. Since ALS is characterized by enormous oxidative stress, several edible phytochemicals that can activate mitophagy to remove damaged mitochondria could be considered a promising option to treat ALS by providing neuroprotection. Therefore, it is of great significance to explore the mechanisms of mitophagy in ALS and to understand the effects and/or molecular mechanisms of phytochemical action, which could translate into a treatment for neurodegenerative diseases, including ALS.

Oxidation of DJ-1 Cysteines in Retinal Pigment Epithelium Function

The retina and RPE cells are regularly exposed to chronic oxidative stress as a tissue with high metabolic demand and ROS generation. DJ-1 is a multifunctional protein in the retina and RPE that has been shown to protect cells from oxidative stress in several cell types robustly. Oxidation of DJ-1 cysteine (C) residues is important for its function under oxidative conditions. The present study was conducted to analyze the impact of DJ-1 expression changes and oxidation of its C residues on RPE function. Monolayers of the ARPE-19 cell line and primary human fetal RPE (hfRPE) cultures were infected with replication-deficient adenoviruses to investigate the effects of increased levels of DJ-1 in these monolayers. Adenoviruses carried the full-length human DJ-1 cDNA (hDJ) and mutant constructs of DJ-1, which had all or each of its three C residues individually mutated to serine (S). Alternatively, endogenous DJ-1 levels were decreased by transfection and transduction with shPARK7 lentivirus. These monolayers were then assayed under baseline and low oxidative stress conditions. The results were analyzed by immunofluorescence, Western blot, RT-PCR, mitochondrial membrane potential, and viability assays. We determined that decreased levels of endogenous DJ-1 levels resulted in increased levels of ROS. Furthermore, we observed morphological changes in the mitochondria structure of all the RPE monolayers transduced with all the DJ-1 constructs. The mitochondrial membrane potential of ARPE-19 monolayers overexpressing all DJ-1 constructs displayed a significant decrease, while hfRPE monolayers only displayed a significant decrease in their ΔΨm when overexpressing the C2S mutation. Viability significantly decreased in ARPE-19 cells transduced with the C53S construct. Our data suggest that the oxidation of C53 is crucial for regulating endogenous levels of ROS and viability in RPE cells.

Biomarkers of mitochondrial origin: a futuristic cancer diagnostic

Cancer is a highly fatal disease without effective early-stage diagnosis and proper treatment. Along with the oncoproteins and oncometabolites, several organelles from cancerous cells are also emerging as potential biomarkers. Mitochondria isolated from cancer cells are one such biomarker candidates. Cancerous mitochondria exhibit different profiles compared with normal ones in morphology, genomic, transcriptomic, proteomic and metabolic landscape. Here, the possibilities of exploring such characteristics as potential biomarkers through single-cell omics and Artificial Intelligence (AI) are discussed. Furthermore, the prospects of exploiting the biomarker-based diagnosis and its futuristic utilization through circulatory tumor cell technology are analyzed. A successful alliance of circulatory tumor cell isolation protocols and a single-cell omics platform can emerge as a next-generation diagnosis and personalized treatment procedure.

Targeting mitochondria in dermatological therapy: Beyond oxidative damage and skin aging

INTRODUCTION

The analysis of the role of the mitochondria in oxidative damage and skin aging is a significant aspect of dermatological research. Mitochondria generate most reactive oxygen species (ROS); however, excessive ROS are cytotoxic and DNA-damaging and promote (photo-)aging. ROS also possesses key physiological and regulatory functions and mitochondrial dysfunction is prominent in several skin diseases including skin cancers. Although many standard dermatotherapeutics modulate mitochondrial function, dermatological therapy rarely targets the mitochondria. Accordingly, there is a rationale for "mitochondrial dermatology"-based approaches to be applied to therapeutic research.

AREAS COVERED

This paper examines the functions of mitochondria in cutaneous physiology beyond energy (ATP) and ROS production. Keratinocyte differentiation and epidermal barrier maintenance, appendage morphogenesis and homeostasis, photoaging and skin cancer are considered. Based on related PubMed search results, the paper evaluates thyroid hormones, glucocorticoids, Vitamin D3 derivatives, retinoids, cannabinoid receptor agonists, PPARγ agonists, thyrotropin, and thyrotropin-releasing hormone as instructive lead compounds. Moreover, the mitochondrial protein MPZL3 as a promising new drug target for future "mitochondrial dermatology" is highlighted.

EXPERT OPINION

Future dermatological therapeutic research should have a mitochondrial medicine emphasis. Focusing on selected lead agents, protein targets, in silico drug design, and model diseases will fertilize a mito-centric approach.

The dynamin-related protein 1 is decreased and the mitochondrial network is altered in Friedreich's ataxia cardiomyopathy

Friedreich ataxia is an autosomal recessive congenital neurodegenerative disease caused by a deficiency in the frataxin protein and is often diagnosed in young adulthood. An expansion of guanine-adenine-adenine repeats in the first intron of the FXN gene leads to decreased frataxin expression. Frataxin plays an essential role in mitochondrial metabolism. Most Friedreich ataxia patients are diagnosed with left ventricular hypertrophic cardiomyopathy, and 60% of patients die with hypertrophic cardiomyopathy. However, the mitochondrial anatomy in Friedreich ataxia hypertrophic cardiomyopathy is still poorly understood. We investigated mitochondrial fission, fusion, and function using biochemical, microscopy, and computational stochastic analysis in human induced pluripotent stem cell derived cardiomyocytes from a patient with Friedreich ataxia hypertrophic cardiomyopathy and a healthy individual. We found a significantly higher mitochondrial footprint, decreased mitochondrial fission protein dynamin-related protein, and mitochondrial fission rate over fusion with more giant mitochondrial clusters in human induced pluripotent stem cell derived cardiomyocytes from a patient with Friedreich ataxia hypertrophic cardiomyopathy, compared to an unaffected individual. We also found significantly depolarized mitochondrial membrane potential and higher reactive oxygen species levels in Friedreich ataxia human induced pluripotent stem cell cardiomyocytes. Our results show that frataxin's depletion may dampen the mitochondrial fission machinery by reducing dynamin-related protein1. The loss of mitochondrial fission might lead to elevated reactive oxygen species and depolarized mitochondrial membrane potential, which may cause oxidative damage in Friedreich ataxia hypertrophic cardiomyopathy. Further investigations are needed to identify the mechanism of downregulating dynamin-related protein1 due to the frataxin deficiency in Friedreich ataxia hypertrophic cardiomyopathy.

Increased ROS-Dependent Fission of Mitochondria Causes Abnormal Morphology of the Cell Powerhouses in a Murine Model of Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is the most common motor neuron disease in humans and remains to have a fatal prognosis. Recent studies in animal models and human ALS patients indicate that increased reactive oxygen species (ROS) play an important role in the pathogenesis. Considering previous studies revealing the influence of ROS on mitochondrial physiology, our attention was focused on mitochondria in the murine ALS model, wobbler mouse. The aim of this study was to investigate morphological differences between wild-type and wobbler mitochondria with aid of superresolution structured illumination fluorescence microscopy, TEM, and TEM tomography. To get an insight into mitochondrial dynamics, expression studies of corresponding proteins were performed. Here, we found significantly smaller and degenerated mitochondria in wobbler motor neurons at a stable stage of the disease. Our data suggest a ROS-regulated, Ox-CaMKII-dependent Drp1 activation leading to disrupted fission-fusion balance, resulting in fragmented mitochondria. These changes are associated with numerous impairments, resulting in an overall self-reinforcing decline of motor neurons. In summary, our study provides common pathomechanisms with other ALS models and human ALS cases confirming mitochondria and related dysfunctions as a therapeutic target for the treatment of ALS.

Subcellular Specialization of Mitochondrial Form and Function in Skeletal Muscle Cells

Across different cell types and within single cells, mitochondria are heterogeneous in form and function. In skeletal muscle cells, morphologically and functionally distinct subpopulations of mitochondria have been identified, but the mechanisms by which the subcellular specialization of mitochondria contributes to energy homeostasis in working muscles remains unclear. Here, we discuss the current data regarding mitochondrial heterogeneity in skeletal muscle cells and highlight potential new lines of inquiry that have emerged due to advancements in cellular imaging technologies.

Role of the lipid transport protein StarD7 in mitochondrial dynamics

Mitochondria are dynamic organelles crucial for cell function and survival implicated in oxidative energy production whose central functions are tightly controlled by lipids. StarD7 is a lipid transport protein involved in the phosphatidylcholine (PC) delivery to mitochondria. Previous studies have shown that StarD7 knockdown induces alterations in mitochondria and endoplasmic reticulum (ER) with a reduction in PC content, however whether StarD7 modulates mitochondrial dynamics remains unexplored. Here, we generated HTR-8/SVneo stable cells expressing the precursor StarD7.I and the mature processed StarD7.II isoforms. We demonstrated that StarD7.I overexpression altered mitochondrial morphology increasing its fragmentation, whereas no changes were observed in StarD7.II-overexpressing cells compared to the control (Ct) stable cells. StarD7.I (D7.I) stable cells were able to transport higher fluorescent PC analog to mitochondria than Ct cells, yield mitochondrial fusions, maintained the membrane potential, and produced lower levels of reactive oxygen species (ROS). Additionally, the expression of Dynamin Related Protein 1 (Drp1) and Mitofusin (Mfn2) proteins were increased, whereas the amount of Mitofusin 1 (Mfn1) decreased. Moreover, transfections with plasmids encoding Drp1-K38A, Drp1-S637D or Drp1-S637A mutants indicated that mitochondrial fragmentation in D7.I cells occurs in a fission-dependent manner via Drp1. In contrast, StarD7 silencing decreased Mfn1 and Mfn2 fusion proteins without modification of Drp1 protein level. These cells increased ROS levels and presented donut-shape mitochondria, indicative of metabolic stress. Altogether our findings provide novel evidence indicating that alterations in StarD7.I expression produce significant changes in mitochondrial morphology and dynamics.

DRP1 Inhibition Rescues Mitochondrial Integrity and Excessive Apoptosis in CS-A Disease Cell Models

Cockayne syndrome group A (CS-A) is a rare recessive progeroid disorder characterized by sun sensitivity and neurodevelopmental abnormalities. Cells derived from CS-A patients present as pathological hallmarks excessive oxidative stress, mitochondrial fragmentation and apoptosis associated with hyperactivation of the mitochondrial fission dynamin related protein 1 (DRP1). In this study, by using human cell models we further investigated the interplay between DRP1 and CSA and we determined whether pharmacological or genetic inhibition of DRP1 affects disease progression. Both reactive oxygen and nitrogen species are in excess in CS-A cells and when the mitochondrial translocation of DRP1 is inhibited a reduction of these species is observed together with a recovery of mitochondrial integrity and a significant decrease of apoptosis. This study indicates that the CSA-driven modulation of DRP1 pathway is key to control mitochondrial homeostasis and apoptosis and suggests DRP1 as a potential target in the treatment of CS patients.

Mitoprotective Effects of Centella asiatica (L.) Urb.: Anti-Inflammatory and Neuroprotective Opportunities in Neurodegenerative Disease

Natural products remain a crucial source of drug discovery for accessible and affordable solutions for healthy aging. Centella asiatica (L.) Urb. (CA) is an important medicinal plant with a wide range of ethnomedicinal uses. Past in vivo and in vitro studies have shown that the plant extract and its key components, such as asiatic acid, asiaticoside, madecassic acid and madecassoside, exhibit a range of anti-inflammatory, neuroprotective, and cognitive benefits mechanistically linked to mitoprotective and antioxidant properties of the plant. Mitochondrial dysfunction and oxidative stress are key drivers of aging and neurodegenerative disease, including Alzheimer’s disease and Parkinson’s disease. Here we appraise the growing body of evidence that the mitoprotective and antioxidative effects of CA may potentially be harnessed for the treatment of brain aging and neurodegenerative disease.

All-Trans Retinoic Acid Increases DRP1 Levels and Promotes Mitochondrial Fission

In the heart, mitochondrial homeostasis is critical for sustaining normal function and optimal responses to metabolic and environmental stressors. Mitochondrial fusion and fission are thought to be necessary for maintaining a robust population of mitochondria, and disruptions in mitochondrial fission and/or fusion can lead to cellular dysfunction. The dynamin-related protein (DRP1) is an important mediator of mitochondrial fission. In this study, we investigated the direct effects of the micronutrient retinoid all-trans retinoic acid (ATRA) on the mitochondrial structure in vivo and in vitro using Western blot, confocal, and transmission electron microscopy, as well as mitochondrial network quantification using stochastic modeling. Our results showed that ATRA increases DRP1 protein levels, increases the localization of DRP1 to mitochondria in isolated mitochondrial preparations. Our results also suggested that ATRA remodels the mitochondrial ultrastructure where the mitochondrial area and perimeter were decreased and the circularity was increased. Microscopically, mitochondrial network remodeling is driven by an increased rate of fission over fusion events in ATRA, as suggested by our numerical modeling. In conclusion, ATRA results in a pharmacologically mediated increase in the DRP1 protein. It also results in the modulation of cardiac mitochondria by promoting fission events, altering the mitochondrial network, and modifying the ultrastructure of mitochondria in the heart.

Sestrin2 and mitochondrial quality control: Potential impact in myogenic differentiation

Mitochondria are highly dynamic organelles capable of adapting their network, morphology, and function, playing a role in oxidative phosphorylation and many cellular processes in most cell types. Skeletal muscle is a very plastic tissue, subjected to many morphological changes following diverse stimuli, such as during myogenic differentiation and regenerative myogenesis. For some time now, mitochondria have been reported to be involved in myogenesis by promoting a bioenergetic remodeling and assisting myoblasts in surviving the process. However, not much is known about the interplay between mitochondrial quality control and myogenic differentiation. Sestrin2 (SESN2) is a well described regulator of autophagy and antioxidant responses and has been gaining attention due to its role in aging-associated pathologies and redox signaling promoted by reactive oxygen species (ROS) in many tissues. Current evidence involving SESN2-associated pathways suggest that it can act as a potential regulator of mitochondrial quality control following induction by ROS under stress conditions, such as during myogenesis. Yet, there are no studies directly assessing SESN2 involvement in myogenic differentiation. This review provides novel insights pertaining the involvement of SESN2 in myogenic differentiation by analyzing the interactions between ROS and mitochondrial remodeling.

Suppression of PGC-1α Drives Metabolic Dysfunction in TGFβ2-Induced EMT of Retinal Pigment Epithelial Cells

PGC-1α, a key orchestrator of mitochondrial metabolism, plays a crucial role in governing the energetically demanding needs of retinal pigment epithelial cells (RPE). We previously showed that silencing PGC-1α induced RPE to undergo an epithelial-mesenchymal-transition (EMT). Here, we show that induction of EMT in RPE using transforming growth factor-beta 2 (TGFβ2) suppressed PGC-1α expression. Correspondingly, TGFβ2 induced defects in mitochondrial network integrity with increased sphericity and fragmentation. TGFβ2 reduced expression of genes regulating mitochondrial dynamics, reduced citrate synthase activity and intracellular ATP content. High-resolution respirometry showed that TGFβ2 reduced mitochondrial OXPHOS levels consistent with reduced expression of NDUFB5. The reduced mitochondrial respiration was associated with a compensatory increase in glycolytic reserve, glucose uptake and gene expression of glycolytic enzymes (PFKFB3, PKM2, LDHA). Treatment with ZLN005, a selective small molecule activator of PGC-1α, blocked TGFβ2-induced upregulation of mesenchymal genes (αSMA, Snai1, CTGF, COL1A1) and TGFβ2-induced migration using the scratch wound assay. Our data show that EMT is accompanied by mitochondrial dysfunction and a metabolic shift towards reduced OXPHOS and increased glycolysis that may be driven by PGC-1α suppression. ZLN005 effectively blocks EMT in RPE and thus serves as a novel therapeutic avenue for treatment of subretinal fibrosis.

A Perspective on Accelerated Aging Caused by the Genetic Deficiency of the Metabolic Protein, OPA1

Autosomal Dominant Optic Atrophy (ADOA) is an ophthalmological condition associated primarily with mutations in the OPA1 gene. It has variable onset, sometimes juvenile, but in other patients, the disease does not manifest until adult middle age despite the presence of a pathological mutation. Thus, individuals carrying mutations are considered healthy before the onset of clinical symptoms. Our research, nonetheless, indicates that on the cellular level pathology is evident from birth and mutant cells are different from controls. We argue that the adaptation and early recruitment of cytoprotective responses allows normal development and functioning but leads to an exhaustion of cellular reserves, leading to premature cellular aging, especially in neurons and skeletal muscle cells. The appearance of clinical symptoms, thus, indicates the overwhelming of natural cellular defenses and break-down of native protective mechanisms.

The Function of Mitochondrial Calcium Uniporter at the Whole-Cell and Single Mitochondrion Levels in WT, MICU1 KO, and MICU2 KO Cells

Mitochondrial Ca2+ ([Ca2+]M) uptake through its Ca2+ uniporter (MCU) is central to many cell functions such as bioenergetics, spatiotemporal organization of Ca2+ signals, and apoptosis. MCU activity is regulated by several intrinsic proteins including MICU1, MICU2, and EMRE. While significant details about the role of MICU1, MICU2, and EMRE in MCU function have emerged recently, a key challenge for the future experiments is to investigate how these regulatory proteins modulate mitochondrial Ca2+ influx through MCU in intact cells under pathophysiological conditions. This is further complicated by the fact that several variables affecting MCU function change dynamically as cell functions. To overcome this void, we develop a data-driven model that closely replicates the behavior of MCU under a wide range of cytosolic Ca2+ ([Ca2+]C), [Ca2+]M, and mitochondrial membrane potential values in WT, MICU1 knockout (KO), and MICU2 KO cells at the single mitochondrion and whole-cell levels. The model is extended to investigate how MICU1 or MICU2 KO affect mitochondrial function. Moreover, we show how Ca2+ buffering proteins, the separation between mitochondrion and Ca2+-releasing stores, and the duration of opening of Ca2+-releasing channels affect mitochondrial function under different conditions. Finally, we demonstrate an easy extension of the model to single channel function of MCU.

Mitochondrial function in immune cells in health and disease

One of the main functions of mitochondria is production of ATP for cellular energy needs, however, it becomes more recognized that mitochondria are involved in differentiation and activation processes of immune cells. Upon activation, immune cells have a high need for energy. Immune cells have different strategies to generate this energy. In pro-inflammatory cells, such as activated monocytes and activated T and B cells, the energy is generated by increasing glycolysis, while in regulatory cells, such as regulatory T cells or M2 macrophages, energy is generated by increasing mitochondrial function and beta-oxidation. Except for being important for energy supply during activation, mitochondria also induce immune responses. During an infection, they release mitochondrial danger associated molecules (DAMPs) that resemble structures of bacterial derived pathogen associated molecular patterns (PAMPs). Such mitochondrial DAMPS are for instance mitochondrial DNA with hypomethylated CpG motifs or a specific lipid that is only present in prokaryotic bacteria and mitochondria, i.e. cardiolipin. Via release of such DAMPs, mitochondria guide the immune response towards an inflammatory response against pathogens. This is an important mechanism in early detection of an infection and in stimulating and sustaining immune responses to fight infections. However, mitochondrial DAMPs may also have a negative impact. If mitochondrial DAMPs are released by damaged cells, without the presence of an infection, such as after a trauma, mitochondrial DAMPs may induce an undesired inflammatory response, resulting in tissue damage and organ dysfunction. Thus, immune cells have developed mechanisms to prevent such undesired immune activation by mitochondrial components. In the present narrative review, we will describe the current view of mitochondria in regulation of immune responses. We will also discuss the current knowledge on disturbed mitochondrial function in immune cells in various immunological diseases.

The role of cell type-specific mitochondrial dysfunction in the pathogenesis of Alzheimer's disease

The decrease of metabolism in the brain has been observed as the important lesions of Alzheimer’s disease (AD) from the early stages of diagnosis. The cumulative evidence has reported that the failure of mitochondria, an organelle involved in diverse biological processes as well as energy production, maybe the cause or effect of the pathogenesis of AD. Both amyloid and tau pathologies have an impact upon mitochondria through physical interaction or indirect signaling pathways, resulting in the disruption of mitochondrial function and dynamics which can trigger AD. In addition, mitochondria are involved in different biological processes depending on the specific functions of each cell type in the brain. Thus, it is necessary to understand mitochondrial dysfunction as part of the pathological phenotypes of AD according to each cell type. In this review, we summarize that 1) the effects of AD pathology inducing mitochondrial dysfunction and 2) the contribution of mitochondrial dysfunction in each cell type to AD pathogenesis.

The ubiquitous role of mitochondria in Parkinson and other neurodegenerative diseases

Orderly mitochondrial life cycle, plays a key role in the pathology of neurodegenerative diseases. Mitochondria are ubiquitous in neurons as they respond to an ever-changing demand for energy supply. Mitochondria constantly change in shape and location, feature of their dynamic nature, which facilitates a quality control mechanism. Biological studies in mitochondria dynamics are unveiling the mechanisms of fission and fusion, which essentially arrange morphology and motility of these organelles. Control of mitochondrial network homeostasis is a critical factor for the proper function of neurons. Disease-related genes have been reported to be implicated in mitochondrial dysfunction. Increasing evidence implicate mitochondrial perturbation in neuronal diseases, such as AD, PD, HD, and ALS. The intricacy involved in neurodegenerative diseases and the dynamic nature of mitochondria point to the idea that, despite progress toward detecting the biology underlying mitochondrial disorders, its link to these diseases is difficult to be identified in the laboratory. Considering the need to model signaling pathways, both in spatial and temporal level, there is a challenge to use a multiscale modeling framework, which is essential for understanding the dynamics of a complex biological system. The use of computational models in order to represent both a qualitative and a quantitative structure of mitochondrial homeostasis, allows to perform simulation experiments so as to monitor the conformational changes, as well as the intersection of form and function.