Microbiota and mitobiota. Putting an equal sign between mitochondria and bacteria

Association Between the Gut Microbiota and Alzheimer's Disease: An Update on Signaling Pathways and Translational Therapeutics

Alzheimer's disease (AD) is a cognitive disease with high morbidity and mortality. In AD patients, the diversity of the gut microbiota is altered, which influences pathology through the gut-brain axis. Probiotic therapy alleviates pathological and psychological consequences by restoring the diversity of the gut microbial flora. This study addresses the role of altered gut microbiota in the progression of neuroinflammation, which is a major hallmark of AD. This process begins with the activation of glial cells, leading to the release of proinflammatory cytokines and the modulation of cholinergic anti-inflammatory pathways. Short-chain fatty acids, which are bacterial metabolites, provide neuroprotective effects and maintain blood‒brain barrier integrity. Furthermore, the gut microbiota stimulates oxidative stress and mitochondrial dysfunction, which promote AD progression. The signaling pathways involved in gut dysbiosis-mediated neuroinflammation-mediated promotion of AD include cGAS-STING, C/EBPβ/AEP, RAGE, TLR4 Myd88, and the NLRP3 inflammasome. Preclinical studies have shown that natural extracts such as Ganmaidazao extract, isoorentin, camelia oil, Sparassis crispa-1, and xanthocerasides improve gut health and can delay the worsening of AD. Clinical studies using probiotics such as Bifidobacterium spp., yeast beta-glucan, and drugs such as sodium oligomannate and rifaximine have shown improvements in gut health, resulting in the amelioration of AD symptoms. This study incorporates the most current research on the pathophysiology of AD involving the gut microbiota and highlights the knowledge gaps that need to be filled to develop potent therapeutics against AD.

Telomere Length and Telomerase Activity as Potential Biomarkers for Gastrointestinal Cancer

Gastrointestinal (GI) cancers, such as colorectal and gastric cancers, pose significant global health challenges due to their high rates of incidence and mortality. Even with advancements in treatment and early detection, many patients still face poor outcomes, highlighting the critical need for new biomarkers and therapeutic targets. Telomere length (TL) and telomerase activity (TA) have gained attention in this context. Telomeres, protective nucleotide sequences at chromosome ends, shorten with each cell division, leading to cellular aging. Telomerase, a ribonucleoprotein enzyme, counteracts this shortening by adding telomeric repeats, a process tightly regulated in normal cells but often dysregulated in cancer. This review critically evaluates the role of TL and TA in the pathogenesis of GI cancers, examining their potential as diagnostic, prognostic, and predictive biomarkers. It explores how alterations in telomere biology contribute to the initiation and progression of GI tumors and assesses the therapeutic implications of targeting telomerase. By integrating findings from diverse studies, this review aims to elucidate the intricate relationship between telomere dynamics and gastrointestinal carcinogenesis, offering insights into how TL and TA could be leveraged to enhance the early detection, treatment, and prognosis of GI cancers.

The relationship between oxidative balance scores and chronic diarrhea and constipation: a population-based study

BACKGROUND

Oxidative stress is closely related to gut health. Exposures to oxidative stress in one's diet and lifestyle can be evaluated by the oxidative balance score (OBS). However, the relationship between OBS and intestinal habits is unknown. This study aimed to investigate the relationships between OBS and intestinal habits (chronic diarrhea and chronic constipation) and the underlying mechanisms involved.

METHODS

Using data from the National Health and Nutrition Examination Survey (NHANES) database from 2005 to 2010, we included a total of 8065 participants. Twenty dietary and lifestyle factors were selected for the OBS calculates. Chronic constipation and chronic diarrhea were defined using the Bristol stool form scale (BSFS) types 1 and 2 and the BSFS 6 and 7, respectively. Multivariate logistic regression, subgroup analysis, and restricted cubic splines (RCS) analysis were used to evaluate the relationship between OBS and defecation habits. Finally, we used mediation analysis to explore the indirect effects of oxidative stress and inflammatory markers on these associations.

RESULTS

After adjusting for all the covariates, multivariate logistic regression analysis revealed that OBS was negatively correlated with diarrhea (OR = 0.57; 95%CI = 0.39-0.83; P = 0.008)and positively correlated with constipation (OR = 1.75; 95%CI = 1.19-2.25; P = 0.008). The RCS showed a nonlinear relationship between OBS and diarrhea (P for nonlinearity = 0.02) and a linear relationship between OBS and constipation (P for nonlinearity = 0.19). Mediation analysis showed that the C-reactive protein (CRP) concentration and white blood cell (WBC) count mediated the correlation between OBS and diarrhea by 6.28% and 6.53%, respectively (P < 0.05).

CONCLUSIONS

OBS is closely related to changes in patients' defecation habits. Oxidative stress and inflammation may play a role in the relationship between the two. This result emphasizes the importance of the public adjusting their lifestyle and dietary habits according to their own situation. However, further prospective studies are needed to analyze the relationship between oxidative stress and changes in defecation habits.

Mitocentricity

Worldwide, interest in mitochondria is constantly growing, as evidenced by scientific statistics, and studies of the functioning of these organelles are becoming more prevalent than studies of other cellular structures. In this analytical review, mitochondria are conditionally placed in a certain cellular center, which is responsible for both energy production and other non-energetic functions, without which the existence of not only the eukaryotic cell itself, but also the entire organism is impossible. Taking into account the high multifunctionality of mitochondria, such a fundamentally new scheme of cell functioning organization, including mitochondrial management of processes that determine cell survival and death, may be justified. Considering that this issue is dedicated to the memory of V. P. Skulachev, who can be called mitocentric, due to the history of his scientific activity almost entirely aimed at studying mitochondria, this work examines those aspects of mitochondrial functioning that were directly or indirectly the focus of attention of this outstanding scientist. We list all possible known mitochondrial functions, including membrane potential generation, synthesis of Fe-S clusters, steroid hormones, heme, fatty acids, and CO2. Special attention is paid to the participation of mitochondria in the formation and transport of water, as a powerful biochemical cellular and mitochondrial regulator. The history of research on reactive oxygen species that generate mitochondria is subject to significant analysis. In the section "Mitochondria in the center of death", special emphasis is placed on the analysis of what role and how mitochondria can play and determine the program of death of an organism (phenoptosis) and the contribution made to these studies by V. P. Skulachev.

The potential mechanism of gut microbiota-microbial metabolites-mitochondrial axis in progression of diabetic kidney disease

Diabetic kidney disease (DKD), has become the main cause of end-stage renal disease (ESRD) worldwide. Lately, it has been shown that the onset and advancement of DKD are linked to imbalances of gut microbiota and the abnormal generation of microbial metabolites. Similarly, a body of recent evidence revealed that biological alterations of mitochondria ranging from mitochondrial dysfunction and morphology can also exert significant effects on the occurrence of DKD. Based on the prevailing theory of endosymbiosis, it is believed that human mitochondria originated from microorganisms and share comparable biological characteristics with the microbiota found in the gut. Recent research has shown a strong correlation between the gut microbiome and mitochondrial function in the occurrence and development of metabolic disorders. The gut microbiome's metabolites may play a vital role in this communication. However, the relationship between the gut microbiome and mitochondrial function in the development of DKD is not yet fully understood, and the role of microbial metabolites is still unclear. Recent studies are highlighted in this review to examine the possible mechanism of the gut microbiota-microbial metabolites-mitochondrial axis in the progression of DKD and the new therapeutic approaches for preventing or reducing DKD based on this biological axis in the future.

Unraveling the Gut-Brain Axis in Multiple Sclerosis: Exploring Dysbiosis, Oxidative Stress, and Therapeutic Insights

This comprehensive review delves into the intricate relationship between the gut microbiota and multiple sclerosis (MS), shedding light on the potential therapeutic avenues for this complex autoimmune disease. It emphasizes the multifactorial nature of MS, including genetic, environmental, and gender-related factors. Furthermore, the article highlights the emerging role of gut microbiota in MS pathophysiology, particularly in terms of gut dysbiosis, oxidative stress, and inflammasome activation within the gut-brain axis. This interplay raises intriguing questions about how the gut microbiota influences the onset and progression of MS. Environmental factors, such as diet and pollutants, add further layers of complexity to the connection between gut health and MS risk. This review also discusses promising therapeutic interventions, such as fecal microbiota transplantation, probiotics, dietary adjustments, and gut-derived metabolites that offer potential avenues for managing MS. It underscores the need for ongoing research to fully unravel the complexities of the role of the gut-brain axis in MS. Ultimately, this article provides a comprehensive exploration of the topic, offering hope for novel preventive and therapeutic strategies that could significantly improve the lives of individuals affected by this challenging autoimmune condition.

Mitochondrial Network: Electric Cable and More

Mitochondria in a cell can unite and organize complex, extended structures that occupy the entire cellular volume, providing an equal supply with energy in the form of ATP synthesized in mitochondria. In accordance with the chemiosmotic concept, the oxidation energy of respiratory substrates is largely stored in the form of an electrical potential difference on the inner membrane of mitochondria. The theory of the functioning of extended mitochondrial structures as intracellular electrical wires suggests that mitochondria provide the fastest delivery of electrical energy through the cellular volume, followed by the use of this energy for the synthesis of ATP, thereby accelerating the process of ATP delivery compared to the rather slow diffusion of ATP in the cell. This analytical review gives the history of the cable theory, lists unsolved critical problems, describes the restructuring of the mitochondrial network and the role of oxidative stress in this process. In addition to the already proven functioning of extended mitochondrial structures as electrical cables, a number of additional functions are proposed, in particular, the hypothesis is put forth that mitochondrial networks maintain the redox potential in the cellular volume, which may vary depending on the physiological state, as a result of changes in the three-dimensional organization of the mitochondrial network (fragmentation/fission-fusion). A number of pathologies accompanied by a violation of the redox status and the participation of mitochondria in them are considered.

The opening of mitochondrial permeability transition pore (mPTP) and the inhibition of electron transfer chain (ETC) induce mitophagy in wheat roots under waterlogging stress

Mitochondria are crucial for the regulation of intracellular energy metabolism, biosynthesis, and cell survival. And studies have demonstrated the role of mitochondria in oxidative stress-induced autophagy in plants. Previous studies found that waterlogging stress can induce the opening of mitochondrial permeability transition pore (mPTP) and the release of cytochrome c in endosperm cells, which proved that mPTP plays an important role in the programmed cell death of endosperm cells under waterlogging stress. This study investigated the effects of the opening of mPTP and the inhibition of ETC on mitophagy in wheat roots under waterlogging stress. The results showed that autophagy related genes in the mitochondria of wheat root cells could respond to waterlogging stress; waterlogging stress led to the degradation of the characteristic proteins cytochrome c and COXII in the mitochondria of root cells. With the prolongation of waterlogging time, the protein degradation degree and the occurrence of mitophagy gradually increased. Under waterlogging stress, exogenous mPTP opening inhibitor CsA inhibited mitophagy in root cells and alleviated mitophagy induced by flooding stress, while exogenous mPTP opening inducer CCCP induced mitophagy in root cells; exogenous mPTP opening inducer CCCP induced mitophagy in root cells. The electron transfer chain inhibitor antimycin A induces mitophagy in wheat root cells and exacerbates mitochondrial degradation. In conclusion, waterlogging stress led to the degradation of mitochondrial characteristic proteins and the occurrence of mitophagy in wheat root cells, and the opening of mPTP and the inhibition of ETC induced the occurrence of mitophagy.

Hydroxytyrosol attenuates diquat-induced oxidative stress by activating Nrf2 pathway and modulating colonic microbiota in mice

This study was conducted to investigate the antioxidant effects of hydroxytyrosol (HT) administration in diquat (DQ)-challenged mice. The results showed that HT treatment markedly alleviated DQ-induced oxidative stress, which was indicated by the enhanced total antioxidant capacity (T-AOC), increased activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase and decreased malondialdehyde (MDA) concentration in serum. Additionally, HT increased the mRNA expression levels of NF-E2-related factor 2 (Nrf2) and its downstream genes, including NADPH quinone oxidoreductase 1 (NQO1) and catalase (CAT) in the small intestine of DQ-challenged mice. 16S rRNA gene sequencing results showed that HT treatment increased the relative abundance of Firmicutes and Lactobacillus and decreased the relative abundance of Bacteroidetes. Interestingly, Pearson correlation analysis showed that there were strong association between colonic Firmicutes, Lactobacillus, and Bacteroidetes and the activities of serum antioxidant enzymes. Meanwhile, HT significantly enhanced the colonic butyrate concentration in DQ-challenged mice. Additionally, HT treatment decreased the serum metabolites involving in glycerophospholipid metabolism, pentose, and glucuronate interconversions, which were associated with alleviated oxidative stress. These results indicate that oral administration of 100 mg/kg body weight HT alleviates oxidative stress in DQ-challenged mice, which may involve Nrf2 signaling pathways via modulation of colonic microbiota.

Antimutagenic Activity as a Criterion of Potential Probiotic Properties

The antimutagenic activity of probiotic strains has been reported over several decades of studying the effects of probiotics. However, this activity is rarely considered an important criterion when choosing strains to produce probiotic preparations and functional food. Meanwhile, the association of antimutagenic activity with the prevention of oncological diseases, as well as with a decrease in the spread of resistant forms in the microbiota, indicates its importance for the selection of probiotics. Besides, an antimutagenic activity can be associated with probiotics' broader systemic effects, such as geroprotective activity. The main mechanisms of such effects are considered to be the binding of mutagens, the transformation of mutagens, and inhibition of the transformation of promutagens into antimutagens. Besides, we should consider the possibility of interaction of the microbiota with regulatory processes in eukaryotic cells, in particular, through the effect on mitochondria. This work aims to systematize data on the antimutagenic activity of probiotics and emphasize antimutagenic activity as a significant criterion for the selection of probiotic strains.

Isn't It Time for Establishing Mitochondrial Nomenclature Breaking Mitochondrial Paradigm?

In this work, we decided to initiate a discussion concerning heterogeneity of mitochondria, suggesting that it is time to build classification of mitochondria, like the one that exists for their progenitors, α-proteobacteria, proposing possible separation of mitochondrial strains and maybe species. We continue to adhere to the general line that mitochondria are friends and foes: on the one hand, they provide the cell and organism with the necessary energy and signaling molecules, and, on the other hand, participate in destruction of the cell and the organism. Current understanding that the activity of mitochondria is not only limited to energy production, but also that these alternative non-energetic functions are unique and irreplaceable in the cell, allowed us to speak about the strong subordination of the entire cellular metabolism to characteristic functional manifestations of mitochondria. Mitochondria are capable of producing not only ATP, but also iron-sulfur clusters, steroid hormones, heme, reactive oxygen and nitrogen species, participate in thermogenesis, regulate cell death, proliferation and differentiation, participate in detoxification, etc. They are a mandatory attribute of eukaryotic cells, and, so far, no eukaryotic cells performing a non-parasitic or non-symbiotic life style have been found that lack mitochondria. We believe that the structural-functional intracellular, intercellular, inter-organ, and interspecific diversity of mitochondria is large enough to provide grounds for creating a mitochondrial nomenclature. The arguments for this are given in this analytical work.

Gut microbiota in ischemic stroke: Where we stand and challenges ahead

Gut microbiota is increasingly recognized to affect host health and disease, including ischemic stroke (IS). Here, we systematically review the current understanding linking gut microbiota as well as the associated metabolites to the pathogenesis of IS (e.g., oxidative stress, apoptosis, and neuroinflammation). Of relevance, we highlight that the implications of gut microbiota-dependent intervention could be harnessed in orchestrating IS.

New Insights into the Gut Microbiota in Neurodegenerative Diseases from the Perspective of Redox Homeostasis

An imbalance between oxidants and antioxidants in the body can lead to oxidative stress, which is one of the major causes of neurodegenerative diseases. The gut microbiota contains trillions of beneficial bacteria that play an important role in maintaining redox homeostasis. In the last decade, the microbiota-gut-brain axis has emerged as a new field that has revolutionized the study of the pathology, diagnosis, and treatment of neurodegenerative diseases. Indeed, a growing number of studies have found that communication between the brain and the gut microbiota can be accomplished through the endocrine, immune, and nervous systems. Importantly, dysregulation of the gut microbiota has been strongly associated with the development of oxidative stress-mediated neurodegenerative diseases. Therefore, a deeper understanding of the relationship between the gut microbiota and redox homeostasis will help explain the pathogenesis of neurodegenerative diseases from a new perspective and provide a theoretical basis for proposing new therapeutic strategies for neurodegenerative diseases. In this review, we will describe the role of oxidative stress and the gut microbiota in neurodegenerative diseases and the underlying mechanisms by which the gut microbiota affects redox homeostasis in the brain, leading to neurodegenerative diseases. In addition, we will discuss the potential applications of maintaining redox homeostasis by modulating the gut microbiota to treat neurodegenerative diseases, which could open the door for new therapeutic approaches to combat neurodegenerative diseases.

The Emerging Role of the Aging Process and Exercise Training on the Crosstalk between Gut Microbiota and Telomere Length

Aging is a natural process of organism deterioration, which possibly impairs multiple physiological functions. These harmful effects are linked to an accumulation of somatic mutations, oxidative stress, low-grade inflammation, protein damage, and mitochondrial dysfunction. It is known that these factors are capable of inducing telomere shortening, as well as intestinal dysbiosis. Otherwise, among the biological mechanisms triggered by physical exercise, the attenuation of pro-inflammatory mediators accompanied by redox state improvement can be the main mediators for microbiota homeostasis and telomere wear prevention. Thus, this review highlights how oxidative stress, inflammation, telomere attrition, and gut microbiota (GM) dysbiosis are interconnected. Above all, we provide a logical foundation for unraveling the role of physical exercise in this process. Based on the studies summarized in this article, exercise training can increase the biodiversity of beneficial microbial species, decrease low-grade inflammation and improve oxidative metabolism, these factors together possibly reduce telomeric shortening.

Gut Dysbiosis and Kidney Diseases

Gut dysbiosis is defined as disorders of gut microbiota and loss of barrier integrity, which are ubiquitous on pathological conditions and associated with the development of various diseases. Kidney diseases are accompanied with gut dysbiosis and metabolic disorders, which in turn contribute to the pathogenesis and progression of kidney diseases. Microbial alterations trigger production of harmful metabolites such as uremic toxins and a decrease in the number of beneficial ones such as SCFAs, which is the major mechanism of gut dysbiosis on kidney diseases according to current studies. In addition, the activation of immune responses and mitochondrial dysfunction by gut dysbiosis, also lead to the development of kidney diseases. Based on the molecular mechanisms, modification of gut dysbiosis via probiotics, prebiotics and synbiotics is a potential approach to slow kidney disease progression. Fecal microbiota transplantation (FMT) and genetic manipulation of the gut microbiota are also promising choices. However, the clinical use of probiotics in kidney disease is not supported by the current clinical evidence. Further studies are necessary to explore the causal relationships of gut dysbiosis and kidney diseases, the efficiency and safety of therapeutic strategies targeting gut-kidney axis.

Searching for female reproductive aging and longevity biomarkers

Female reproductive aging is, in a way, a biological phenomenon that develops along canonical molecular pathways; however, it has particular features. Recent studies revealed complexity of the interconnections between reproductive aging and aging of other systems, and even suggested a cause-effect uncertainty between them. It was also shown that reproductive aging can impact aging processes in an organism at the level of cells, tissues, organs, and systems. Women at the end of their reproductive lives are characterized by the accelerated incidence of age-related diseases. Timing of the onset of menarche and menopause and variability in the duration of reproductive life carry a latent social risk: not having enough information about the reproductive potential, women keep on postponing childbirth. Identification and use of the most accurate and sensitive aging biomarkers enable the prediction of menopause timing and quantification of the true biological and reproductive ages of an organism. We discuss current views on reproductive aging and peculiarities of using available biomarkers of aging. We also consider latest advances in the search for potential genetic markers of reproductive aging. Finally, we posit the importance of determining the female biological age and highlight potential research directions in this area.

Mitochondrial Superoxide Dismutase: What the Established, the Intriguing, and the Novel Reveal About a Key Cellular Redox Switch

Significance: Reactive oxygen species (ROS) are now widely recognized as central mediators of cell signaling. Mitochondria are major sources of ROS. Recent Advances: It is now clear that mitochondrial ROS are essential to activate responses to cellular microenvironmental stressors. Mediators of these responses reside in large part in the cytosol. Critical Issues: The primary form of ROS produced by mitochondria is the superoxide radical anion. As a charged radical anion, superoxide is restricted in its capacity to diffuse and convey redox messages outside of mitochondria. In addition, superoxide is a reductant and not particularly efficient at oxidizing targets. Because there are many opportunities for superoxide to be neutralized in mitochondria, it is not completely clear how redox cues generated in mitochondria are converted into diffusible signals that produce transient oxidative modifications in the cytosol or nucleus. Future Directions: To efficiently intervene at the level of cellular redox signaling, it seems that understanding how the generation of superoxide radicals in mitochondria is coupled with the propagation of redox messages is essential. We propose that mitochondrial superoxide dismutase (SOD2) is a major system converting diffusion-restricted superoxide radicals derived from the electron transport chain into highly diffusible hydrogen peroxide (H₂O₂). This enables the coupling of metabolic changes resulting in increased superoxide to the production of H₂O₂, a diffusible secondary messenger. As such, to determine whether there are other systems coupling metabolic changes to redox messaging in mitochondria as well as how these systems are regulated is essential.

Mitochondrial Dynamic Dysfunction as a Main Triggering Factor for Inflammation Associated Chronic Non-Communicable Diseases

Mitochondria are organelles with highly dynamic ultrastructure maintained by flexible fusion and fission rates governed by Guanosine Triphosphatases (GTPases) dependent proteins. Balanced control of mitochondrial quality control is crucial for maintaining cellular energy and metabolic homeostasis; however, dysfunction of the dynamics of fusion and fission causes loss of integrity and functions with the accumulation of damaged mitochondria and mitochondrial deoxyribose nucleic acid (mtDNA) that can halt energy production and induce oxidative stress. Mitochondrial derived reactive oxygen species (ROS) can mediate redox signaling or, in excess, causing activation of inflammatory proteins and further exacerbate mitochondrial deterioration and oxidative stress. ROS have a deleterious effect on many cellular components, including lipids, proteins, both nuclear and mtDNA and cell membrane lipids producing the net result of the accumulation of damage associated molecular pattern (DAMPs) capable of activating pathogen recognition receptors (PRRs) on the surface and in the cytoplasm of immune cells. Chronic inflammation due to oxidative damage is thought to trigger numerous chronic diseases including cardiac, liver and kidney disorders, neurodegenerative diseases (Parkinson's disease and Alzheimer's disease), cardiovascular diseases/atherosclerosis, obesity, insulin resistance, and type 2 diabetes mellitus.

Mitochondrial function and abnormalities implicated in the pathogenesis of ASD

Mitochondria are the powerhouse that generate over 90% of the ATP produced in cells. In addition to its role in energy production, the mitochondrion also plays a major role in carbohydrate, fatty acid, amino acid and nucleotide metabolism, programmed cell death (apoptosis), generation of and protection against reactive oxygen species (ROS), immune response, regulation of intracellular calcium ion levels and even maintenance of gut microbiota. With its essential role in bio-energetic as well as non-energetic biological processes, it is not surprising that proper cellular, tissue and organ function is dependent upon proper mitochondrial function. Accordingly, mitochondrial dysfunction has been shown to be directly linked to a variety of medical disorders, particularly neuromuscular disorders and increasing evidence has linked mitochondrial dysfunction to neurodegenerative and neurodevelopmental disorders such as Alzheimer's Disease (AD), Parkinson's Disease (PD), Rett Syndrome (RS) and Autism Spectrum Disorders (ASD). Over the last 40 years there has been a dramatic increase in the diagnosis of ASD and, more recently, an increasing body of evidence indicates that mitochondrial dysfunction plays an important role in ASD development. In this review, the latest evidence linking mitochondrial dysfunction and abnormalities in mitochondrial DNA (mtDNA) to the pathogenesis of autism will be presented. This review will also summarize the results of several recent `approaches used for improving mitochondrial function that may lead to new therapeutic approaches to managing and/or treating ASD.

Mitochondrial membrane potential

The mitochondrial membrane potential (ΔΨm) generated by proton pumps (Complexes I, III and IV) is an essential component in the process of energy storage during oxidative phosphorylation. Together with the proton gradient (ΔpH), ΔΨm forms the transmembrane potential of hydrogen ions which is harnessed to make ATP. The levels of ΔΨm and ATP in the cell are kept relatively stable although there are limited fluctuations of both these factors that can occur reflecting normal physiological activity. However, sustained changes in both factors may be deleterious. A long-lasting drop or rise of ΔΨm vs normal levels may induce unwanted loss of cell viability and be a cause of various pathologies. Among other factors, ΔΨm plays a key role in mitochondrial homeostasis through selective elimination of dysfunctional mitochondria. It is also a driving force for transport of ions (other than H+) and proteins which are necessary for healthy mitochondrial functioning. We propose additional potential mechanisms for which ΔΨm is essential for maintenance of cellular health and viability and provide recommendations how to accurately measure ΔΨm in a cell and discuss potential sources of artifacts.

Reactive Oxygen Species and Mitochondrial Dynamics: The Yin and Yang of Mitochondrial Dysfunction and Cancer Progression

Mitochondria are organelles with a highly dynamic ultrastructure maintained by a delicate equilibrium between its fission and fusion rates. Understanding the factors influencing this balance is important as perturbations to mitochondrial dynamics can result in pathological states. As a terminal site of nutrient oxidation for the cell, mitochondrial powerhouses harness energy in the form of ATP in a process driven by the electron transport chain. Contemporaneously, electrons translocated within the electron transport chain undergo spontaneous side reactions with oxygen, giving rise to superoxide and a variety of other downstream reactive oxygen species (ROS). Mitochondrially-derived ROS can mediate redox signaling or, in excess, cause cell injury and even cell death. Recent evidence suggests that mitochondrial ultrastructure is tightly coupled to ROS generation depending on the physiological status of the cell. Yet, the mechanism by which changes in mitochondrial shape modulate mitochondrial function and redox homeostasis is less clear. Aberrant mitochondrial morphology may lead to enhanced ROS formation, which, in turn, may deteriorate mitochondrial health and further exacerbate oxidative stress in a self-perpetuating vicious cycle. Here, we review the latest findings on the intricate relationship between mitochondrial dynamics and ROS production, focusing mainly on its role in malignant disease.

Heat Stress Reduces Sperm Motility via Activation of Glycogen Synthase Kinase-3α and Inhibition of Mitochondrial Protein Import

The adverse effects of high environmental temperature exposure on animal reproductive functions have been concerned for many decades. However, the molecular basis of heat stress (HS)-induced decrease of sperm motility has not been entirely elucidated. We hypothesized that the deteriorate effects of HS may be mediated by damage of mitochondrial function and ATP synthesis. To test this hypothesis, we use mature boar sperm as model to explore the impacts of HS on mitochondrial function and sperm motility. A 6 h exposure to 42°C (HS) induced significant decrease in sperm progressive motility. Concurrently, HS induced mitochondrial dysfunction that is indicated by decreased of membrane potential, respiratory chain complex I and IV activities and adenosine triphosphate (ATP) contents. Exogenous ATP abolished this effect suggesting that reduced of ATP synthesis is the committed step in HS-induced reduction of sperm motility. At the molecular level, the mitochondrial protein contents were significantly decreased in HS sperm. Notably, the cytochrome c oxidase subunit 4, which was synthesized in cytoplasm and translocated into mitochondria, was significantly lower in mitochondria of HS sperm. Glycogen synthase kinase-3α (GSK3α), a negative regulator of sperm motility that is inactivated by Ser21 phosphorylation, was dephosphorylated after HS. The GSK3α inhibitor CHIR99021 was able to abolish the effects of HS on sperm and their mitochondria. Taken together, our results demonstrate that HS affects sperm motility through downregulation of mitochondrial activity and ATP synthesis yield, which involves dephosphorylation of GSK3α and interference of mitochondrial remodeling.

Mitochondrial Aging: Is There a Mitochondrial Clock?

Fragmentation (fission) of mitochondria, occurring in response to oxidative challenge, leads to heterogeneity in the mitochondrial population. It is assumed that fission provides a way to segregate mitochondrial content between the "young" and "old" phenotype, with the formation of mitochondrial "garbage," which later will be disposed. Fidelity of this process is the basis of mitochondrial homeostasis, which is disrupted in pathological conditions and aging. The asymmetry of the mitochondrial fission is similar to that of their evolutionary ancestors, bacteria, which also undergo an aging process. It is assumed that mitochondrial markers of aging are recognized by the mitochondrial quality control system, preventing the accumulation of dysfunctional mitochondria, which normally are subjected to disposal. Possibly, oncocytoma, with its abnormal proliferation of mitochondria occupying the entire cytoplasm, represents the case when segregation of damaged mitochondria is impaired during mitochondrial division. It is plausible that mitochondria contain a "clock" which counts the degree of mitochondrial senescence as the extent of flagging (by ubiquitination) of damaged mitochondria. Mitochondrial aging captures the essence of the systemic aging which must be analyzed. We assume that the mitochondrial aging mechanism is similar to the mechanism of aging of the immune system which we discuss in detail.

Diseases and Aging: Gender Matters

At first glance, biological differences between male and female sex seem obvious, but, in fact, they affect a vast number of deeper levels apart from reproductive function and related physiological features. Such differences affect all organizational levels including features of cell physiology and even functioning of separate organelles, which, among other things, account for such global processes as resistance to diseases and aging. Understanding of mechanisms underlying resistance of one of the sexes to pathological processes and aging will allow taking into consideration gender differences while developing drugs and therapeutic approaches, and it will provide an opportunity to reproduce and enhance such resistance in the more vulnerable gender. Here we review physiological as well as cellular and biological features of disease course including aging that are affected by gender and discuss potential mechanisms behind these processes. Such mechanisms include features of oxidative metabolism and mitochondrial functioning.

[Intestinal microbiota and ageing: A new intervention route?]

Intestinal microbiota (IM) has continued to be the subject in all types of studies and publications. More is known on its different components and functions, as well as the changes that take place in IM through the life cycle, and the role of the factors involved in these changes. The aim of this review is to update the relationship between IM and aging. The presentation in 4 sections: (i)main factors of the human ageing process, underlining those related with gut changes; (ii)conceptual meaning of words like microbiota and other related terms; (iii)to comment on the most current findings as regards the changes in IM that occur in the ageing process, whether arising from the physiology or from disease situations, or other factors (environment, diet, drugs, etc.), and the health-consequences of these changes, and (iv)possibilities of different active positive interventions, with emphasis on diet measures.

Mitodiversity

Here, in addition to the previously coined term "mitobiota", we introduce the term "mitodiversity" for various phenotypic and genetic heterogeneities of mitochondria within the same cell or organ. Based on data on the mitochondrial transmembrane potential determined both in situ and in vitro under normal conditions and after organ ischemia/reperfusion, such heterogeneity is most evident under pathologic conditions. Herein, a part of the mitochondrial population with transmembrane potential typical of the normal state is sustained even under a pathological condition that, perhaps, underlies the development of ways of reversing pathology back to the normal state. The membrane potentials of isolated mitochondria were shown to directly correlate with the magnitude of side-scattered light depicting internal structure of mitochondria. We analyzed possible interpretations of data on mitochondrial membrane potential obtained using fluorescent probes. We suggest a possible mechanism underlying retention of fluorescent probes inside the cells and mitochondria.

Gastrointestinal dysfunction in autism spectrum disorder: the role of the mitochondria and the enteric microbiome

Autism spectrum disorder (ASD) affects a significant number of individuals worldwide with the prevalence continuing to grow. It is becoming clear that a large subgroup of individuals with ASD demonstrate abnormalities in mitochondrial function as well as gastrointestinal (GI) symptoms. Interestingly, GI disturbances are common in individuals with mitochondrial disorders and have been reported to be highly prevalent in individuals with co-occurring ASD and mitochondrial disease. The majority of individuals with ASD and mitochondrial disorders do not manifest a primary genetic mutation, raising the possibility that their mitochondrial disorder is acquired or, at least, results from a combination of genetic susceptibility interacting with a wide range of environmental triggers. Mitochondria are very sensitive to both endogenous and exogenous environmental stressors such as toxicants, iatrogenic medications, immune activation, and metabolic disturbances. Many of these same environmental stressors have been associated with ASD, suggesting that the mitochondria could be the biological link between environmental stressors and neurometabolic abnormalities associated with ASD. This paper reviews the possible links between GI abnormalities, mitochondria, and ASD. First, we review the link between GI symptoms and abnormalities in mitochondrial function. Second, we review the evidence supporting the notion that environmental stressors linked to ASD can also adversely affect both mitochondria and GI function. Third, we review the evidence that enteric bacteria that are overrepresented in children with ASD, particularly Clostridia spp., produce short-chain fatty acid metabolites that are potentially toxic to the mitochondria. We provide an example of this gut–brain connection by highlighting the propionic acid rodent model of ASD and the clinical evidence that supports this animal model. Lastly, we discuss the potential therapeutic approaches that could be helpful for GI symptoms in ASD and mitochondrial disorders. To this end, this review aims to help better understand the underlying pathophysiology associated with ASD that may be related to concurrent mitochondrial and GI dysfunction.