Mitochondrial dynamics as a bridge between mitochondrial dysfunction and insulin resistance

MitoNEET preserves muscle insulin sensitivity during iron overload by regulating mitochondrial iron, reactive oxygen species and fission

Iron overload (IO) is known to contribute to metabolic dysfunctions such as type 2 diabetes and insulin resistance. Using L6 skeletal muscle cells overexpressing the CDGSH iron-sulfur domain-containing protein 1 (CISD1, also known as mitoNEET) (mitoN) protein, we examined the potential role of MitoN in preventing IO-induced insulin resistance. In L6 control cells, IO resulted in insulin resistance which could be prevented by MitoN as demonstrated by western blot of p-Akt and Akt biosensor cells. Mechanistically, IO increased; mitochondrial iron accumulation, mitochondrial reactive oxygen species (ROS), Fis1-dependent mitochondrial fission, mitophagy, FUN14 domain-containing protein 1 (FUNDC1) expression, and decreased Parkin. MitoN overexpression was able to reduce increases in mitochondrial iron accumulation, mitochondrial ROS, mitochondrial fission, mitophagy and FUNDC1 upregulation due to IO. MitoN did not have any effect on the IO-induced downregulation of Parkin. MitoN alone also upregulated peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC1α) protein levels, a master regulator of mitochondrial biogenesis. The use of mitochondrial antioxidant, Skq1, or fission inhibitor, Mdivi-1, prevented IO-induced insulin resistance implying both mitochondrial ROS and fission play a causal role in the development of insulin resistance. Taken together, MitoN is able to confer protection against IO-induced insulin resistance in L6 skeletal muscle cells through regulation of mitochondrial iron content, mitochondrial ROS, and mitochondrial fission.

Construction and evaluation of a metabolic correlation diagnostic model for diabetes based on machine learning algorithms

BACKGROUND

Diabetes mellitus (DM) is a prevalent chronic disease marked by significant metabolic dysfunctions. Understanding its molecular mechanisms is vital for early diagnosis and treatment strategies.

METHODS

We used datasets GSE7014, GSE25724, and GSE156248 from the GEO database to build a diagnostic model for DM using Random Forest (RF) and LASSO regression models. GSE20966 served as a validation cohort. DM patients were classified into two subtypes for functional enrichment analysis. Expression levels of key diagnostic genes were validated using quantitative real-time PCR (qRT-PCR) on Peripheral Blood Mononuclear Cells (PBMCs) from DM patients and healthy controls, focusing on CXCL12 and PPP1R12B with GAPDH as the internal control.

RESULTS

After de-batching the datasets, we identified 131 differentially expressed genes (DEGs) between DM and control groups, with 70 up-regulated and 61 down-regulated. Enrichment analysis revealed significant down-regulation in the IL-12 signaling pathway, JAK signaling post-IL-12 stimulation, and the ferroptosis pathway in DM. Five genes (CXCL12, MXRA5, UCHL1, PPP1R12B, and C7) were identified as having diagnostic value. The diagnostic model showed high accuracy in both the training and validation cohorts. The gene set also enabled the subclassification of DM patients into groups with distinct functional traits. qRT-PCR results confirmed the bioinformatics findings, particularly the up-regulation of CXCL12 and PPP1R12B in DM patients.

CONCLUSION

Our study pinpointed seven energy metabolism-related genes differentially expressed in DM and controls, with five holding diagnostic value. Our model accurately diagnosed DM and facilitated patient subclassification, offering new insights into DM pathogenesis.

Mitochondrial damage-associated molecular patterns: A new insight into metabolic inflammation in type 2 diabetes mellitus

The pathogenesis of diabetes is accompanied by increased levels of inflammatory factors, also known as "metabolic inflammation", which runs through the whole process of the occurrence and development of the disease. Mitochondria, as the key site of glucose and lipid metabolism, is often accompanied by mitochondrial function damage in type 2 diabetes mellitus (T2DM). Damaged mitochondria release pro-inflammatory factors through damage-related molecular patterns that activate inflammation pathways and reactions to oxidative stress, further aggravate metabolic disorders, and form a vicious circle. Currently, the pathogenesis of diabetes is still unclear, and clinical treatment focuses primarily on symptomatic intervention of the internal environment of disorders of glucose and lipid metabolism with limited clinical efficacy. The proinflammatory effect of mitochondrial damage-associated molecular pattern (mtDAMP) in T2DM provides a new research direction for exploring the pathogenesis and intervention targets of T2DM. Therefore, this review covers the most recent findings on the molecular mechanism and related signalling cascades of inflammation caused by mtDAMP in T2DM and discusses its pathogenic role of it in the pathological process of T2DM to search potential intervention targets.

Intergenerational Hyperglycemia Impairs Mitochondrial Function and Follicular Development and Causes Oxidative Stress in Rat Ovaries Independent of the Consumption of a High-Fat Diet

We analyzed the influence of maternal hyperglycemia and the post-weaning consumption of a high-fat diet on the mitochondrial function and ovarian development of the adult pups of diabetic rats. Female rats received citrate buffer (Control-C) or Streptozotocin (for diabetes induction-D) on postnatal day 5. These adult rats were mated to obtain female pups (O) from control dams (OC) or from diabetic dams (OD), and they received a standard diet (SD) or high-fat diet (HFD) from weaning to adulthood and were distributed into OC/SD, OC/HFD, OD/SD, and OD/HFD. In adulthood, the OGTT and AUC were performed. These rats were anesthetized and euthanized for sample collection. A high percentage of diabetic rats were found to be in the OD/HFD group (OD/HFD 40% vs. OC/SD 0% p < 0.05). Progesterone concentrations were lower in the experimental groups (OC/HFD 0.40 ± 0.04; OD/SD 0.30 ± 0.03; OD/HFD 0.24 ± 0.04 vs. OC/SD 0.45 ± 0.03 p < 0.0001). There was a lower expression of MFF (OD/SD 0.34 ± 0.33; OD/HFD 0.29 ± 0.2 vs. OC/SD 1.0 ± 0.41 p = 0.0015) and MFN2 in the OD/SD and OD/HFD groups (OD/SD 0.41 ± 0.21; OD/HFD 0.77 ± 0.18 vs. OC/SD 1.0 ± 0.45 p = 0.0037). The number of follicles was lower in the OD/SD and OD/HFD groups. A lower staining intensity for SOD and Catalase and higher staining intensity for MDA were found in ovarian cells in the OC/HFD, OD/SD, and OD/HFD groups. Fetal programming was responsible for mitochondrial dysfunction, ovarian reserve loss, and oxidative stress; the association of maternal diabetes with an HFD was responsible for the higher occurrence of diabetes in female adult pups.

Mechanisms of Modulation of Mitochondrial Architecture

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

Decreased MFN2 activates the cGAS-STING pathway in diabetic myocardial ischaemia-reperfusion by triggering the release of mitochondrial DNA

BACKGROUND

The cause of aggravation of diabetic myocardial damage is yet to be elucidated; damage to mitochondrial function has been a longstanding focus of research. During diabetic myocardial ischaemia-reperfusion (MI/R), it remains unclear whether reduced mitochondrial fusion exacerbates myocardial injury by generating free damaged mitochondrial DNA (mitoDNA) and activating the cGAS-STING pathway.

METHODS

In this study, a mouse model of diabetes was established (by feeding mice a high-fat diet (HFD) plus a low dose of streptozotocin (STZ)), a MI/R model was established by cardiac ischaemia for 2 h and reperfusion for 30 min, and a cellular model of glycolipid toxicity induced by high glucose (HG) and palmitic acid (PA) was established in H9C2 cells.

RESULTS

We observed that altered mitochondrial dynamics during diabetic MI/R led to increased mitoDNA in the cytosol, activation of the cGAS-STING pathway, and phosphorylation of the downstream targets TBK1 and IRF3. In the cellular model we found that cytosolic mitoDNA was the result of reduced mitochondrial fusion induced by HG and PA, which also resulted in cGAS-STING signalling and activation of downstream targets. Moreover, inhibition of STING by H-151 significantly ameliorated myocardial injury induced by MFN2 knockdown in both the cell and mouse models. The use of a fat-soluble antioxidant CoQ10 improved cardiac function in the mouse models.

CONCLUSIONS

Our study elucidated the critical role of cGAS-STING activation, triggered by increased cytosolic mitoDNA due to decreased mitochondrial fusion, in the pathogenesis of diabetic MI/R injury. This provides preclinical insights for the treatment of diabetic MI/R injury. Video Abstract.

Low Protein Programming Causes Increased Mitochondrial Fusion and Decreased Oxygen Consumption in the Hepatocytes of Female Rats

The liver is one of the major organs involved in the regulation of glucose and lipid homeostasis. The effectiveness of metabolic activity in hepatocytes is determined by the quality and quantity of its mitochondria. Mitochondrial function is complex, and they act via various dynamic networks, which rapidly adapt to changes in the cellular milieu. Our present study aims to investigate the effects of low protein programming on the structure and function of mitochondria in the hepatocytes of adult females. Pregnant rats were fed with a control or isocaloric low-protein diet from gestational day 4 until delivery. A normal laboratory chow was given to all dams after delivery and to pups after weaning. The rats were euthanized at 4 months of age and the livers were collected from female offspring for investigating the mitochondrial structure, mtDNA copy number, mRNA, and proteins expression of genes associated with mitochondrial function. Primary hepatocytes were isolated and used for the analysis of the mitochondrial bioenergetics profiles. The mitochondrial ultrastructure showed that the in utero low-protein diet exposure led to increased mitochondrial fusion. Accordingly, there was an increase in the mRNA and protein levels of the mitochondrial fusion gene Opa1 and mitochondrial biogenesis genes Pgc1a and Essra, but Fis1, a fission gene, was downregulated. Low protein programming also impaired the mitochondrial function of the hepatocytes with a decrease in basal respiration ATP-linked respiration and proton leak. In summary, the present study suggests that the hepatic mitochondrial dysfunction induced by an in utero low protein diet might be a potential mechanism linking glucose intolerance and insulin resistance in adult offspring.

A Glimpse into Milestones of Insulin Resistance and an Updated Review of Its Management

Insulin is the main metabolic regulator of fuel molecules in the diet, such as carbohydrates, lipids, and proteins. It does so by facilitating glucose influx from the circulation into the liver, adipose tissue, and skeletal myocytes. The outcome of which is subjected to glycogenesis in skeletal muscle and lipogenesis in adipose tissue, as well as in the liver. Therefore, insulin has an anabolic action while, on the contrary, hypoinsulinemia promotes the reverse process. Protein breakdown in myocytes is also encountered during the late stages of diabetes mellitus. The balance of the blood glucose level in physiological conditions is maintained by virtue of the interactive functions of insulin and glucagon. In insulin resistance (IR), the balance is disturbed because glucose transporters (GLUTs) of cell membranes fail to respond to this peptide hormone, meaning that glucose molecules cannot be internalized into the cells, the consequence of which is hyperglycemia. To develop the full state of diabetes mellitus, IR should be associated with the impairment of insulin release from beta-cells of the pancreas. Periodic screening of individuals of high risk, such as those with obesity, hypercholesterolemia, and pregnant nulliparous women in antenatal control, is vital, as these are important checkpoints to detect cases of insulin resistance. This is pivotal as IR can be reversed, provided it is detected in its early stages, through healthy dietary habits, regular exercise, and the use of hypoglycemic agents. In this review, we discuss the pathophysiology, etiology, diagnosis, preventive methods, and management of IR in brief.

F1Fo adenosine triphosphate (ATP) synthase is a potential drug target in non-communicable diseases

F₁F_o adenosine triphosphate (ATP) synthase, also known as the complex V, is the central ATP-producing unit in the cells arranged in the mitochondrial and plasma membranes. F₁F_o ATP synthase also regulates the central metabolic processes in the human body driven by proton motive force (Δp). Numerous studies have immensely contributed toward highlighting its regulation in improving energy homeostasis and maintaining mitochondrial integrity, which otherwise gets compromised in illnesses. Yet, its role in the implication of non-communicable diseases remains unknown. F₁F_o ATP synthase dysregulation at gene level leads to reduced activity and delocalization in the cristae and plasma membranes, which is directly associated with non-communicable diseases: cardiovascular diseases, diabetes, neurodegenerative disorders, cancer, and renal diseases. Individual subunits of the F₁F_o ATP synthase target ligand-based competitive or non-competitive inhibition. After performing a systematic literature review to understand its specific functions and its novel drug targets, the present article focuses on the central role of F₁F_o ATP synthase in primary non-communicable diseases. Next, it discusses its involvement through various pathways and the effects of multiple inhibitors, activators, and modulators specific to non-communicable diseases with a futuristic outlook.

Oxidative stress: The nexus of obesity and cognitive dysfunction in diabetes

Obesity has been associated with oxidative stress. Obese patients are at increased risk for diabetic cognitive dysfunction, indicating a pathological link between obesity, oxidative stress, and diabetic cognitive dysfunction. Obesity can induce the biological process of oxidative stress by disrupting the adipose microenvironment (adipocytes, macrophages), mediating low-grade chronic inflammation, and mitochondrial dysfunction (mitochondrial division, fusion). Furthermore, oxidative stress can be implicated in insulin resistance, inflammation in neural tissues, and lipid metabolism disorders, affecting cognitive dysfunction in diabetics.

Rhodiola pre-conditioning reduces exhaustive exercise-induced myocardial injury of insulin resistant mice

Myocardial injury reduction and recovery under acute cardiac stress are adversely impacted by insulin resistance (IR). We previously demonstrated that Rhodiola improved cardiac anti-stress capacity in mice. Thus, this study focuses on the preventive efficacy of Rhodiola on exhaustive exercise (EE)-induced myocardial injury of IR mice. An 8-week high-fat diet (HFD) model of IR mice was established. Rhodiola was administrated by garaging. After the 8-week intervention, half of the mice performed EE to simulate acute cardiac stress, and determine myocardial injury; The remaining mice were sacrificed following fasting to assess metabolic disorder. We found myocardial injury induced by EE in IR mice was worse and was alleviated by Rhodiola pre-conditioning. Further, the nuclear factor erythroid 2-related factor 2 (Nrf2)-related antioxidant system was impaired by HFD, while mitochondrial dynamic fusion and fission were activated by HFD as a physiological protective compensation. The Rhodiola administration rescued Nrf2 impairment and further facilitated mitochondrial fusion and fission. All these results indicate that Rhodiola is a potential treatment for the prevention of cardiac events in type 2 diabetes mellitus and metabolic syndrome patients, and the Nrf2-related antioxidant activity and mitochondrial dynamics are the proposed mechanisms.

Berberine mitigates hepatic insulin resistance by enhancing mitochondrial architecture via the SIRT1/Opa1 signalling pathway

The aberrant changes of fussion/fission-related proteins can trigger mitochondrial dynamics imbalance, which cause mitochondrial dysfunctions and result insulin resistance (IR). However, the relationship between the inner mitochondrial membrane fusion protein optic atrophy 1 (Opa1) and hepatic IR as well as the specific molecular mechanisms of signal transduction has not been fully elucidated. In this study, we explore whether abnormalities in the Opa1 cause hepatic IR and whether berberine (BBR) can prevent hepatic IR through the SIRT1/Opa1 signalling pathway. High-fat diet (HFD)-fed mice and db/db mice are used as animal models to study hepatic IR in vivo. IR, morphological changes, and mitochondrial injury of the liver are examined to explore the effects of BBR. SIRT1/Opa1 protein expression is determined to confirm whether the signalling pathway is damaged in the model animals and is involved in BBR treatment-mediated mitigation of hepatic IR. A palmitate (PA)-induced hepatocyte IR model is established in HepG2 cells in vitro. Opa1 silencing and SIRT1 overexpression are induced to verify whether Opa1 deficiency causes hepatocyte IR and whether SIRT1 improves this dysfunction. BBR treatment and SIRT1 silencing are employed to confirm that BBR can prevent hepatic IR by activating the SIRT1/Opa1 signalling pathway. Western blot analysis and JC-1 fluorescent staining results show that Opa1 deficiency causes an imbalance in mitochondrial fusion/fission and impairs insulin signalling in HepG2 cells. SIRT1 and BBR overexpression ameliorates PA-induced IR, increases Opa1, and improves mitochondrial function. SIRT1 silencing partly reverses the effects of BBR on HepG2 cells. SIRT1 and Opa1 expressions are downregulated in the animal models. BBR attenuates hepatic IR and enhances SIRT1/Opa1 signalling in db/db mice. In summary, Opa1 silencing-mediated mitochondrial fusion/fission imbalance could lead to hepatocyte IR. BBR may improve hepatic IR by regulating the SIRT1/Opa1 signalling pathway, and thus, it may be used to treat type-2 diabetes.

The Role of Mitochondrial Dynamic Dysfunction in Age-Associated Type 2 Diabetes

Mitochondrial dynamics, such as fusion and fission, play a critical role in maintaining cellular metabolic homeostasis. The molecular mechanisms underlying these processes include fusion proteins (Mitofusin 1 [MFN1], Mitofusin 2 [MFN2], and optic atrophy 1 [OPA1]) and fission mediators (mitochondrial fission 1 [FIS1] and dynamin-related protein 1 [DRP1]), which interact with each other to ensure mitochondrial quality control. Interestingly, defects in these proteins can lead to the loss of mitochondrial DNA (mtDNA) integrity, impairment of mitochondrial function, a severe alteration of mitochondrial morphology, and eventually cell death. Emerging evidence has revealed a causal relationship between dysregulation of mitochondria dynamics and age-associated type 2 diabetes, a metabolic disease whose rates have reached an alarming epidemic-like level with the majority of cases (59%) recorded in men aged 65 and over. In this sense, fragmentation of mitochondrial networks is often associated with defects in cellular energy production and increased apoptosis, leading, in turn, to excessive reactive oxygen species release, mitochondrial dysfunction, and metabolic alterations, which can ultimately contribute to β-cell dysfunction and insulin resistance. The present review discusses the processes of mitochondrial fusion and fission and their dysfunction in type 2 diabetes, with special attention given to the therapeutic potential of targeting mitochondrial dynamics in this complex metabolic disorder.

Impact of Roux-en-Y Gastric Bypass on Mitochondrial Biogenesis and Dynamics in Leukocytes of Obese Women

The chronic low-grade inflammation widely associated with obesity can lead to a prooxidant status that triggers mitochondrial dysfunction. To date, Roux-en-Y gastric bypass (RYGB) is considered the most effective strategy for obese patients. However, little is known about its molecular mechanisms. This interventional study aimed to investigate whether RYGB modulates oxidative stress, inflammation and mitochondrial dynamics in the leukocytes of 47 obese women at one year follow-up. We evaluated biochemical parameters and serum inflammatory cytokines -TNFα, IL6 and IL1β- to assess systemic status. Total superoxide production -dHe-, mitochondrial membrane potential -TMRM-, leucocyte protein expression of inflammation mediators -MCP1 and NF-kB-, antioxidant defence -GPX1-, mitochondrial regulation—PGC1α, TFAM, OXPHOS and MIEAP- and dynamics -MFN2, MNF1, OPA1, FIS1 and p-DRP1- were also determined. After RYGB, a significant reduction in superoxide and mitochondrial membrane potential was evident, while GPX1 content was significantly increased. Likewise, a marked upregulation of the transcription factors PGC1α and TFAM, complexes of the oxidative phosphorylation chain (I–V) and MIEAP and MFN1 was observed. We conclude that women undergoing RYGB benefit from an amelioration of their prooxidant and inflammatory status and an improvement in mitochondrial dynamics of their leukocytes, which is likely to have a positive effect on clinical outcome.

SIRT3 regulates mitochondrial biogenesis in aging-related diseases

Sirtuin 3 (SIRT3), the main family member of mitochondrial deacetylase, targets the majority of substrates controlling mitochondrial biogenesis via lysine deacetylation and modulates important cellular functions such as energy metabolism, reactive oxygen species production and clearance, oxidative stress, and aging. Deletion of SIRT3 has a deleterious effect on mitochondrial biogenesis, thus leading to the defect in mitochondrial function and insufficient ATP production. Imbalance of mitochondrial dynamics leads to excessive mitochondrial biogenesis, dampening mitochondrial function. Mitochondrial dysfunction plays an important role in several diseases related to aging, such as cardiovascular disease, cancer and neurodegenerative diseases. Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) launches mitochondrial biogenesis through activating nuclear respiratory factors. These factors act on genes, transcribing and translating mitochondrial DNA to generate new mitochondria. PGC1α builds a bridge between SIRT3 and mitochondrial biogenesis. This review described the involvement of SIRT3 and mitochondrial dynamics, particularly mitochondrial biogenesis in aging-related diseases, and further illustrated the role of the signaling events between SIRT3 and mitochondrial biogenesis in the pathological process of aging-related diseases.

Mitofusin 1 and 2 regulation of mitochondrial DNA content is a critical determinant of glucose homeostasis

The dynamin-like GTPases Mitofusin 1 and 2 (Mfn1 and Mfn2) are essential for mitochondrial function, which has been principally attributed to their regulation of fission/fusion dynamics. Here, we report that Mfn1 and 2 are critical for glucose-stimulated insulin secretion (GSIS) primarily through control of mitochondrial DNA (mtDNA) content. Whereas Mfn1 and Mfn2 individually were dispensable for glucose homeostasis, combined Mfn1/2 deletion in β-cells reduced mtDNA content, impaired mitochondrial morphology and networking, and decreased respiratory function, ultimately resulting in severe glucose intolerance. Importantly, gene dosage studies unexpectedly revealed that Mfn1/2 control of glucose homeostasis was dependent on maintenance of mtDNA content, rather than mitochondrial structure. Mfn1/2 maintain mtDNA content by regulating the expression of the crucial mitochondrial transcription factor Tfam, as Tfam overexpression ameliorated the reduction in mtDNA content and GSIS in Mfn1/2-deficient β-cells. Thus, the primary physiologic role of Mfn1 and 2 in β-cells is coupled to the preservation of mtDNA content rather than mitochondrial architecture, and Mfn1 and 2 may be promising targets to overcome mitochondrial dysfunction and restore glucose control in diabetes.

Mitophagy and mitochondrial dynamics in type 2 diabetes mellitus treatment

The prevalence of type 2 diabetes is associated with inflammatory bowels diseases, nonalcoholic steatohepatitis and even a spectrum of cancer such as colon cancer and liver cancer, resulting in a substantial healthcare burden on our society. Autophagy is a key regulator in metabolic homeostasis such as lipid metabolism, energy management and the balance of cellular mineral substances. Mitophagy is selective autophagy for clearing the damaged mitochondria and dysfunctional mitochondria. A myriad of evidence has demonstrated a major role of mitophagy in the regulation of type 2 diabetes and metabolic homeostasis. It is well established that defective mitophagy has been linked to the development of insulin resistance. Moreover, insulin resistance is further progressed to various diseases such as nephropathy, retinopathy and cardiovascular diseases. Concordantly, restoration of mitophagy will be a reliable and therapeutic target for type 2 diabetes. Recently, various phytochemicals have been proved to prevent dysfunctions of β-cells by mitophagy inductions during diabetes developments. In agreement with the above phenomenon, mitophagy inducers should be warranted as potential and novel therapeutic agents for treating diabetes. This review focuses on the role of mitophagy in type 2 diabetes relevant diseases and the pharmacological basis and therapeutic potential of autophagy regulators in type 2 diabetes.

Prenatal Low-Protein Diet Affects Mitochondrial Structure and Function in the Skeletal Muscle of Adult Female Offspring

Gestational low-protein (LP) diet leads to glucose intolerance and insulin resistance in adult offspring. We had earlier demonstrated that LP programming affects glucose disposal in females. Mitochondrial health is crucial for normal glucose metabolism in skeletal muscle. In this study, we sought to analyze mitochondrial structure, function, and associated genes in skeletal muscles to explore the molecular mechanism of insulin resistance LP-programmed female offspring. On day four of pregnancy, rats were assigned to a control diet containing 20% protein or an isocaloric 6% protein-containing diet. Standard laboratory diet was given to the dams after delivery until the end of weaning and to pups after weaning. Gestational LP diet led to changes in mitochondrial ultrastructure in the gastrocnemius muscles, including a nine-fold increase in the presence of giant mitochondria along with unevenly formed cristae. Further, functional analysis showed that LP programming caused impaired mitochondrial functions. Although the mitochondrial copy number did not show significant changes, key genes involved in mitochondrial structure and function such as Fis1, Opa1, Mfn2, Nrf1, Nrf2, Pgc1b, Cox4b, Esrra, and Vdac were dysregulated. Our study shows that prenatal LP programming induced disruption in mitochondrial ultrastructure and function in the skeletal muscle of female offspring.

Mitochondrial haplogroups have a better correlation to insulin requirement than nuclear genetic variants for type 2 diabetes mellitus in Taiwanese individuals

AIMS/INTRODUCTION

Identifying diabetes-susceptible genetic variants will help to provide personalized therapy for the management of type 2 diabetes. Previous studies have reported a genetic risk score (GRS), computed by the sum of nuclear DNA (nDNA) risk alleles, that may predict the future requirement for insulin therapy. Although mitochondrial dysfunction has a close association with insulin resistance (IR), there are few studies investigating whether genetic variants of mitochondrial DNA (mtDNA) will affect the clinical characteristics of type 2 diabetes.

MATERIALS AND METHODS

Mitochondrial haplogroups were determined using mtDNA whole genome next generation sequencing and 13 single nucleotide polymorphisms (SNPs) in nDNA susceptibility loci of 13 genes in 604 Taiwanese subjects with type 2 diabetes. A GRS of nDNA was computed by summation of the number of risk alleles. The correlation between the mtDNA haplogroup and the clinical characteristics of type 2 diabetes was assessed by logistic regression analysis. The results were compared with the GRS subgroups for the risk of insulin requirement.

RESULTS

Mitochondrial haplogroups modulate the clinical characteristics of type 2 diabetes, in which patients harboring haplogroup D4, compared with those harboring non-D4 haplotypes, were less prone to require insulin treatment, after adjusting for age, gender, and diabetes duration. However, there was no association between insulin requirement and GRS calculated from nuclear genetic variants.

CONCLUSIONS

Mitochondrial haplogroups, but not nuclear genetic variants, have a better association with the insulin requirement. The results highlight the role of mitochondria in the management of common metabolic diseases.

Energy transfer between the mitochondrial network and lipid droplets in insulin resistant skeletal muscle

Mitochondria and lipid droplets in the insulin resistant skeletal muscle of type 2 diabetic individuals have both been heavily investigated independently and are characterized by more fragmented, dysfunctional mitochondrial networks and larger lipid droplets compared to skeletal muscle of healthy individuals. Specialized contacts between mitochondrial and lipid droplet membranes are known to decrease in diabetic muscle, though it remains unclear how energy transfer at the remaining mitochondria-lipid droplet contact sites may be altered by type 2 diabetes. The purpose of this review is to highlight recent data on mitochondrial structure and function and lipid droplet dynamics in type 2 diabetic skeletal muscle and to underscore the need for more detailed investigations into the functional nature of mitochondria-lipid droplet interactions in type 2 diabetes.

Influence of Obesity and Type 2 Diabetes on Calcium Handling by Skeletal Muscle: Spotlight on the Sarcoplasmic Reticulum and Mitochondria

Obesity and diabetes have been shown to interfere with energy metabolism and cause peripheral insulin resistance in skeletal muscle. However, recent studies have focused on the effect metabolic insult has on the loss of muscle size, strength, and physical function. Contractile dysfunction has been linked to impaired intracellular Ca²⁺ concentration ([Ca²⁺]_i) regulation. In skeletal muscle, [Ca²⁺]_i homeostasis is highly regulated by Ca²⁺ transport across the sarcolemma/plasma membrane, the golgi apparatus, sarcoplasmic reticulum (SR), and mitochondria. Particularly, the SR and or mitochondria play an important role in the fine-tuning of this metabolic process. Recent studies showed that obesity and insulin resistance are associated with interactions between the SR and mitochondrial networks (the dynamic tubular reticulum formed by mitochondria), suggesting that metabolic disorders alter Ca²⁺ handling by these organelles. These interactions are facilitated by specific membrane proteins, including ion channels. This review considers the impact of metabolic disorders, such as obesity and type 2 diabetes, on the regulation of [Ca²⁺]_i in skeletal muscle. It also discusses the mechanisms by which this occurs, focusing chiefly on the SR and mitochondria networks. A deeper understanding of the effect of metabolic disorders on calcium handling might be useful for therapeutic strategies.

Entresto protected the cardiomyocytes and preserved heart function in cardiorenal syndrome rat fed with high-protein diet through regulating the oxidative stress and Mfn2-mediated mitochondrial functional integrity

This study tested the hypothesis that Entresto (En) therapy protected the cardiomyocytes and heart function in cardiorenal syndrome (CRS) rats fed with high-protein diet (HPD) through regulating the oxidative-stress and Mfn2-mediated mitochondrial functional integrity. En (12.5 μM for the in-vitro study) protected the H9C2-cells against H₂O₂-induced cell apoptosis, whereas stepwise-increased H₂O₂ concentrations induced a significant increase in protein expressions of Mfn2/phosphorylated (p)-DRP1/mitochondrial-Bax in H9C2-cells. En downregulated H₂O₂-induced mitochondrial fission/upregulated mitochondrial fusion and deletion of Mfn2 gene (i.e., shMfn2) to significantly reduce H₂O₂-induced ROS production. En significantly suppressed and shMfn2 further significantly suppressed both H₂O₂-reduced mitochondrial-membrane potential and H₂O₂-induced ROS production/cell apoptosis/mitochondrial damage/mitochondrial-Bax released from mitochondria in H9C2 cells. En significantly reduced protein expressions of Mfn2 and p-DRP1. Additionally, En significantly suppressed and shMfn2 further significantly suppressed the protein expressions of mitochondrial-damaged (DRP1)/oxidative-stress (NOX-1/NOX-2)/apoptosis (mitochondrial-Bax/caspase-3/PARP)/autophagic (LC3B-II/LC3B-I) biomarkers (all p < 0.01). Rats were categorized into group 1 [sham-control + high-protein-diet (HPD)], group 2 (CRS + HPD) and group 3 (CRS+ HPD + En/100 mg/kg/day). By day 63 after CRS induction, the LVEF was significantly lower in group 3 and more significantly lower in group 2 than in group 1, whereas the protein expressions of oxidative-stress (NOX-1/NOX-2/p22phox/oxidized protein)/apoptotic (mitochondrial-Bax/caspase-3/PARP), fibrotic (Smad-3/TGF-ß), autophagic (Beclin-1/Atg5/ratio of LC3B-II/LC3B-I) and mitochondrial-damaged (DRP1/cyclophilin-D/cytosolic-cytochrome-C) biomarkers exhibited an opposite pattern of LVEF among the groups. Downregulation of Mfn2 by En or shMfn2 in cardiomyocytes avoided H₂O₂ damage and En improved the cardiac function in HPD-feeding CRS rat via adjusting Mfn2-mediated mitochondrial functional integrity.

Combinatorial peptides: A library that continuously probes low-abundance proteins

After a decade of experimental applications, it is the objective of this review to make a point on combinatorial peptide ligand libraries dedicated to low-abundance proteins from animals to plants and to microorganism proteomics. It is, thus, at the light of the recent technical developments and applications that we will examine the state of the art, its usage within the scientific community, and its openness to unexplored fields. The improvements of the methodology and its implementation in connection with analytical determinations of combinatorial peptide ligand library (CPLL)-treated samples are extensively reviewed and commented upon. Relevant examples covering few critical aspects describe the performance of the technology. Finally, a reflection on the technological future is attempted in particular by involving new concepts adapted to the limited availability of certain biological samples.

Mitochondrial Dysfunction and Mitophagy Closely Cooperate in Neurological Deficits Associated with Alzheimer's Disease and Type 2 Diabetes

Alzheimer's disease (AD) and type 2 diabetes (T2D) are known to be correlated in terms of their epidemiology, histopathology, and molecular and biochemical characteristics. The prevalence of T2D leading to AD is approximately 50-70%. Moreover, AD is often considered type III diabetes because of the common risk factors. Uncontrolled T2D may affect the brain, leading to memory and learning deficits in patients. In addition, metabolic disorders and impaired oxidative phosphorylation in AD and T2D patients suggest that mitochondrial dysfunction is involved in both diseases. The dysregulation of pathways involved in maintaining mitochondrial dynamics, biogenesis and mitophagy are responsible for exacerbating the impact of hyperglycemia on the brain and neurodegeneration under T2D conditions. The first section of this review describes the recent views on mitochondrial dysfunction that connect these two disease conditions, as the pathways are observed to overlap. The second section of the review highlights the importance of different mitochondrial miRNAs (mitomiRs) involved in the regulation of mitochondrial dynamics and their association with the pathogenesis of T2D and AD. Therefore, targeting mitochondrial biogenesis and mitophagy pathways, along with the use of mitomiRs, could be a potent therapeutic strategy for T2D-related AD. The last section of the review highlights the known drugs targeting mitochondrial function for the treatment of both disease conditions.

Sirt1 and Sirt3 Activation Improved Cardiac Function of Diabetic Rats via Modulation of Mitochondrial Function

In the present study, we aimed to evaluate the effect of Sirt1, Sirt3 and combined activation in high fructose diet-induced insulin resistance rat heart and assessed the cardiac function focusing on mitochondrial health and function. We administered the Sirt1 activator; SRT1720 (5 mg/kg, i.p.), Sirt3 activator; Oroxylin-A (10 mg/kg i.p.) and the combination; SRT1720 + Oroxylin-A (5 mg/kg and 10 mg/kg i.p.) daily from 12th week to 20th weeks of study. We observed significant perturbations of most of the cardiac structural and functional parameters in high fructose diet-fed animals. Administration of SRT1720 and Oroxylin-A improved perturbed cardiac structural and functional parameters by decreasing insulin resistance, oxidative stress, and improving mitochondrial function by enhancing mitochondrial biogenesis, OXPHOS expression and activity in high fructose diet-induced insulin-resistant rats. However, we could not observe the synergistic effect of SRT1720 and Oroxylin-A combination. Similar to in-vivo study, perturbed mitochondrial function and oxidative stress observed in insulin-resistant H9c2 cells were improved after activation of Sirt1 and Sirt3. We observed that Sirt1 activation enhances Sirt3 expression and mitochondrial biogenesis, and the opposite effects were observed after Sirt1 inhibition in cardiomyoblast cells. Taken together our results conclude that activation of Sirt1 alone could be a potential therapeutic target for diabetes-associated cardiovascular complications.

Moderate aerobic exercise training ameliorates impairment of mitochondrial function and dynamics in skeletal muscle of high-fat diet-induced obese mice

The purpose of this study is to determine whether moderate aerobic exercise training improves high-fat diet-induced alterations in mitochondrial function and structure in the skeletal muscle. Male 4-week-old C57BL/6 mice were randomly divided into four groups: control (CON), control plus exercise (CON + EX), high-fat diet (HFD), and high-fat diet plus exercise (HFD + EX). After obesity was induced by 20 weeks of 60% HFD, treadmill exercise training was performed at 13-16 m/min, 40-50 min/day, and 6 days/week for 12 weeks. Mitochondrial structure, function, and dynamics, and mitophagy were analyzed in the skeletal muscle fibers from the red gastrocnemius. Exercise training increased mitochondrial number and area and reduced high-fat diet-induced obesity and hyperglycemia. In addition, exercise training attenuated mitochondrial dysfunction in the permeabilized myofibers, indicating that HFD-induced decrease of mitochondrial O₂ respiration and Ca²⁺ retention capacity and increase of mitochondrial H₂ O₂ emission were attenuated in the HFD + EX group compared to the HFD group. Exercise also ameliorated HFD-induced imbalance of mitochondrial fusion and fission, demonstrating that HFD-induced decrease in fusion protein levels was elevated, and increase in fission protein levels was reduced in the HFD + EX groups compared with the HFD group. Moreover, dysregulation of mitophagy induced by HFD was mitigated in the HFD + EX group, indicating a decrease in PINK1 protein level. Our findings demonstrated that moderate aerobic exercise training mitigated obesity-induced insulin resistance by improving mitochondrial function, and reversed obesity-induced mitochondrial structural damage by improving mitochondrial dynamics and mitophagy, suggesting that moderate aerobic exercise training may play a therapeutic role in protecting the skeletal muscle against mitochondrial impairments and insulin resistance induced by obesity.

Mitochondrial Dynamics in Adult Cardiomyocytes and Heart Diseases

Mitochondria are the powerhouse organelles of cells; they participate in ATP generation, calcium homeostasis, oxidative stress response, and apoptosis. Thus, maintenance of mitochondrial function is critical for cellular functions. As highly dynamic organelles, the function of mitochondria is dynamically regulated by their fusion and fission in many cell types, which regulate mitochondrial morphology, number, distribution, metabolism, and biogenesis in cells. Mature rod-shaped cardiomyocytes contain thousands of end-to-end contacted spheroid mitochondria. The movement of mitochondria in these cells is limited, which hinders the impetus for research into mitochondrial dynamics in adult cardiomyocytes. In this review, we discuss the most recent progress in mitochondrial dynamics in mature (adult) cardiomyocytes and the relationship thereof with heart diseases.

Diabetes exacerbates brain pathology following a focal blast brain injury: New role of a multimodal drug cerebrolysin and nanomedicine

Blast brain injury (bBI) is a combination of several forces of pressure, rotation, penetration of sharp objects and chemical exposure causing laceration, perforation and tissue losses in the brain. The bBI is quite prevalent in military personnel during combat operations. However, no suitable therapeutic strategies are available so far to minimize bBI pathology. Combat stress induces profound cardiovascular and endocrine dysfunction leading to psychosomatic disorders including diabetes mellitus (DM). This is still unclear whether brain pathology in bBI could exacerbate in DM. In present review influence of DM on pathophysiology of bBI is discussed based on our own investigations. In addition, treatment with cerebrolysin (a multimodal drug comprising neurotrophic factors and active peptide fragments) or H-290/51 (a chain-breaking antioxidant) using nanowired delivery of for superior neuroprotection on brain pathology in bBI in DM is explored. Our observations are the first to show that pathophysiology of bBI is exacerbated in DM and TiO₂-nanowired delivery of cerebrolysin induces profound neuroprotection in bBI in DM, not reported earlier. The clinical significance of our findings with regard to military medicine is discussed.

Loss of metabolic flexibility as a result of overexpression of pyruvate dehydrogenase kinases in muscle, liver and the immune system: Therapeutic targets in metabolic diseases

Good health depends on the maintenance of metabolic flexibility, which in turn is dependent on the maintenance of regulatory flexibility of a large number of regulatory enzymes, but especially the pyruvate dehydrogenase complex (PDC), because of its central role in carbohydrate metabolism. Flexibility in regulation of PDC is dependent on rapid changes in the phosphorylation state of PDC determined by the relative activities of the pyruvate dehydrogenase kinases (PDKs) and the pyruvate dehydrogenase phosphatases. Inactivation of the PDC by overexpression of PDK4 contributes to hyperglycemia, and therefore the serious health problems associated with diabetes. Loss of regulatory flexibility of PDC occurs in other disease states and pathological conditions that have received less attention than diabetes. These include cancers, non‐alcoholic fatty liver disease, cancer‐induced cachexia, diabetes‐induced nephropathy, sepsis and amyotrophic lateral sclerosis. Overexpression of PDK4, and in some situations, the other PDKs, as well as under expression of the pyruvate dehydrogenase phosphatases, leads to inactivation of the PDC, mitochondrial dysfunction and deleterious effects with health consequences. The possible basis for this phenomenon, along with evidence that overexpression of PDK4 results in phosphorylation of “off‐target” proteins and promotes excessive transport of Ca²⁺ into mitochondria through mitochondria‐associated endoplasmic reticulum membranes are discussed. Recent efforts to find small molecule PDK inhibitors with therapeutic potential are also reviewed.

Organelle Stress and Crosstalk in Kidney Disease

Organelles play important roles in maintaining cellular homeostasis. Organelle stress responses, especially in mitochondria, endoplasmic reticula (ER), and primary cilia, are deeply involved in kidney disease pathophysiology. Mitochondria are the center of energy production in most eukaryotic cells. Renal proximal tubular cells are highly energy demanding and abundant in mitochondria. Mitochondrial dysfunctions in association with energy metabolism alterations produce reactive oxygen species and promote inflammation in proximal tubular cells, resulting in progression of kidney disease. The ER play critical roles in controlling protein quality. Unfolded protein response (UPR) pathways are the adaptive response to ER stress for maintaining protein homeostasis. UPR pathway dysregulation under pathogenic ER stress often occurs in glomerular and tubulointerstitial cells and promotes progression of kidney disease. The primary cilia sense extracellular signals and maintain calcium homeostasis in cells. Dysfunction of the primary cilia in autosomal dominant polycystic kidney disease reduces the calcium concentration in proximal tubular cells, leading to increased cell proliferation and retention of cyst fluid. In recent years, the direct interaction at membrane contact sites has received increased attention in association with the development of imaging technologies. The part of the ER that is directly connected to mitochondria is termed the mitochondria-associated ER membrane (MAM), which regulates calcium homeostasis and phospholipid metabolism in cells. Disruption of MAM integrity collapses cellular homeostasis and leads to diseases such as diabetes and Alzheimer disease. This review summarizes recent research on organelle stress and crosstalk, and their involvement in kidney disease pathophysiology. In addition, potential treatment options that target organelle stress responses are discussed.

Nuclear Factor-Erythroid 2-Related Factor 2 (Nrf2) and Mitochondrial Dynamics/Mitophagy in Neurological Diseases

Mitochondria play an essential role in bioenergetics and respiratory functions for cell viability through numerous biochemical processes. To maintain mitochondria quality control and homeostasis, mitochondrial morphologies change rapidly in response to external insults and changes in metabolic status through fusion and fission (so called mitochondrial dynamics). Furthermore, damaged mitochondria are removed via a selective autophagosomal process, referred to as mitophagy. Although mitochondria are one of the sources of reactive oxygen species (ROS), they are themselves vulnerable to oxidative stress. Thus, endogenous antioxidant defense systems play an important role in cell survival under physiological and pathological conditions. Nuclear factor-erythroid 2-related factor 2 (Nrf2) is a redox-sensitive transcription factor that maintains redox homeostasis by regulating antioxidant-response element (ARE)-dependent transcription and the expression of antioxidant defense enzymes. Although the Nrf2 system is positively associated with mitochondrial biogenesis and mitochondrial quality control, the relationship between Nrf2 signaling and mitochondrial dynamics/mitophagy has not been sufficiently addressed in the literature. This review article describes recent clinical and experimental observations on the relationship between Nrf2 and mitochondrial dynamics/mitophagy in various neurological diseases.

TLR4 knockout upregulates the expression of Mfn2 and PGC-1α in a high-fat diet and ischemia-reperfusion mice model of liver injury

AIMS

Patients with nonalcoholic fatty liver disease (NAFLD) have less tolerance to ischemia-reperfusion injury (IRI) of the liver than those with the healthy liver; hence have a higher incidence of severe complications after surgery. This study aimed to investigate the dynamics of the liver and mitochondrial damage and the impact of TLR4 knockout (TLR4KO) on Mfn2 expression in the composite model of NAFLD and IRI.

MAIN METHODS

We performed high-fat diet (HFD) feeding and ischemia reperfusion (IR) on wild type (WT) and TLR4 knockout TLR4KO mice.

KEY FINDINGS

The degree of structural and functional injuries to the liver and mitochondria (NAFLD and IRI) is greater than that caused by a single factor (NAFLD or IRI) or a simple superposition of both. The IL-6 and TNF-α expressions were significantly suppressed (P < .05), while PGC-1α and Mfn2 expressions were up-regulated considerably (P < .05) after TLR4KO. Furthermore, mitochondrial fusion increased, while ATP consumption and ROS production decreased significantly after TLR4KO (P < .05). The degree of reduction of compound injury by TLR4KO is more significant than the reduction degree of single factor injury. Also, TNF-α and IL-6 levels can be used predictive markers for mitochondrial damage and liver tolerance to NAFLD and IRI.

SIGNIFICANCE

TLR4KO upregulates the expression of Mfn2 and PGC-1α in the composite model of NAFLD and IRI. This pathway may be related to IL-6 and TNF-α. This evidence provides theoretical and experimental basis for the subsequent Toll-like receptor 4 (TLR4) receptor targeted therapy.

Modulation of mitochondria and NADPH oxidase function by the nitrate-nitrite-NO pathway in metabolic disease with focus on type 2 diabetes

Mitochondria play fundamental role in maintaining cellular metabolic homeostasis, and metabolic disorders including type 2 diabetes (T2D) have been associated with mitochondrial dysfunction. Pathophysiological mechanisms are coupled to increased production of reactive oxygen species and oxidative stress, together with reduced bioactivity/signaling of nitric oxide (NO). Novel strategies restoring these abnormalities may have therapeutic potential in order to prevent or even treat T2D and associated cardiovascular and renal co-morbidities. A diet rich in green leafy vegetables, which contains high concentrations of inorganic nitrate, has been shown to reduce the risk of T2D. To this regard research has shown that in addition to the classical NO synthase (NOS) dependent pathway, nitrate from our diet can work as an alternative precursor for NO and other bioactive nitrogen oxide species via serial reductions of nitrate (i.e. nitrate-nitrite-NO pathway). This non-conventional pathway may act as an efficient back-up system during various pathological conditions when the endogenous NOS system is compromised (e.g. acidemia, hypoxia, ischemia, aging, oxidative stress). A number of experimental studies have demonstrated protective effects of nitrate supplementation in models of obesity, metabolic syndrome and T2D. Recently, attention has been directed towards the effects of nitrate/nitrite on mitochondrial functions including beiging/browning of white adipose tissue, PGC-1α and SIRT3 dependent AMPK activation, GLUT4 translocation and mitochondrial fusion-dependent improvements in glucose homeostasis, as well as dampening of NADPH oxidase activity. In this review, we examine recent research related to the effects of bioactive nitrogen oxide species on mitochondrial function with emphasis on T2D.

Inter-organelle Communication in the Pathogenesis of Mitochondrial Dysfunction and Insulin Resistance

PURPOSE OF REVIEW

Impairments in mitochondrial function in patients with insulin resistance and type 2 diabetes have been disputed for decades. This review aims to briefly summarize the current knowledge on mitochondrial dysfunction in metabolic tissues and to particularly focus on addressing a new perspective of mitochondrial dysfunction, the altered capacity of mitochondria to communicate with other organelles within insulin-resistant tissues.

RECENT FINDINGS

Organelle interactions are temporally and spatially formed connections essential for normal cell function. Recent studies have shown that mitochondria interact with various cellular organelles, such as the endoplasmic reticulum, lysosomes and lipid droplets, forming inter-organelle junctions. We will discuss the current knowledge on alterations in these mitochondria-organelle interactions in insulin resistance and diabetes, with a focus on changes in mitochondria-lipid droplet communication as a major player in ectopic lipid accumulation, lipotoxicity and insulin resistance.

Decreased Mitochondrial Dynamics Is Associated with Insulin Resistance, Metabolic Rate, and Fitness in African Americans

CONTEXT

African American women (AAW) have a higher incidence of insulin resistance and are at a greater risk for the development of obesity and type 2 diabetes than Caucasian women (CW). Although several factors have been proposed to mediate these racial disparities, the mechanisms remain poorly defined. We previously demonstrated that sedentary lean AAW have lower peripheral insulin sensitivity, reduced maximal aerobic fitness (VO2max), and lower resting metabolic rate (RMR) than CW. We have also demonstrated that skeletal muscle mitochondrial respiration is lower in AAW and appears to play a role in these racial differences.

OBJECTIVE

The goal of this study was to assess mitochondrial pathways and dynamics to examine the potential mechanisms of lower insulin sensitivity, RMR, VO2max, and mitochondrial capacity in AAW.

DESIGN

To achieve this goal, we assessed several mitochondrial pathways in skeletal muscle using gene array technology and semiquantitative protein analysis.

RESULTS

We report alterations in mitochondrial pathways associated with inner membrane small molecule transport genes, fusion-fission, and autophagy in lean AAW. These differences were associated with lower insulin sensitivity, RMR, and VO2max.

CONCLUSIONS

Together these data suggest that the metabolic racial disparity of insulin resistance, RMR, VO2max, and mitochondrial capacity may be mediated by perturbations in mitochondrial pathways associated with membrane transport, fission-fusion, and autophagy. The mechanisms contributing to these differences remain unknown.

Perturbations in Mitochondrial Dynamics Are Closely Involved in the Progression of Alcoholic Liver Disease

BACKGROUND

Mitochondria play a fundamental role in the pathogenesis of alcoholic liver disease (ALD). The preservation of functional mitochondria during toxic alcohol insults is essential for cell survival and is maintained by key processes known as mitochondrial dynamics, including fragmentation and fusion, which are regulated by mitochondria-shaping proteins (MSP). We have shown mitochondrial dynamics to be distorted by alcohol in cellular and animal models, but the effect in humans remains unknown.

METHODS

Hepatic gene expression of the main MSP involved in the mitochondrial fusion and fragmentation pathways was evaluated in patients with alcoholic hepatitis (AH) by DNA microarray (n = 15) and Reverse Transcription Polymerase Chain Reaction (n = 32). The activation of dynamin-1-like protein (Drp1) was also investigated in mitochondria isolated from liver biopsies of ALD patients (n = 8). The effects of alcohol on mitochondrial dynamics and on MSP protein expression were studied in human precision-cut liver slices (PCLS) exposed for 24 hours to increasing doses of ethanol (EtOH; 50 to 250 mM).

RESULTS

A profound hyperactivation of the fragmentation pathway was observed in AH patients, with a significant increase in the expression of Drp1 and its adapters/receptors. The translocation of Drp1 to the mitochondria was also induced in patients with severe ALD and was affected in the PCLS with short-term exposure to EtOH but only mildly. The fusion pathway was not altered in ALD, and this was confirmed in the PCLS model.

CONCLUSIONS

The present study reveals the role of mitochondrial dynamics in human ALD, confirming our previous observations in animal and cell culture models of ALD. Taken together, we show that alcohol has a significant impact on the fragmentation pathway, and we confirm Drp1 as a potential therapeutic target in severe ALD.

Insulin resistance is improved in high-fat fed mice by photobiomodulation therapy at 630 nm

Photobiomodulation therapy (PBMT) in the infrared spectrum exerts positive effects on glucose metabolism, but the use of PBMT at the red spectrum has not been assessed. Male Swiss albino mice were divided into low-fat control and high-fat diet (HFD) for 12 weeks and were treated with red (630 nm) PBMT or no treatment (Sham) during weeks 9 to 12. PBMT was delivered at 31.19 J/cm² , 60 J total dose per day for 20 days. In HFD-fed mice, PBMT improved glucose tolerance, insulin resistance and fasting hyperinsulinemia. PBMT also reduced adiposity and inflammatory infiltrate in adipose tissue. Phosphorylation of Akt in epididymal adipose tissue and rectus femoralis muscle was improved by PBMT. In epididymal fat PBMT reversed the reduced phosphorylation of AS160 and the reduced Glut4 content. In addition, PBMT reversed the alterations caused by HFD in rectus femoralis muscle on proteins involved in mitochondrial dynamics and β-oxidation. In conclusion, PBMT at red spectrum improved insulin resistance and glucose metabolism in HFD-fed mice.

MiD51 Is Important for Maintaining Mitochondrial Health in Pancreatic Islet and MIN6 Cells

Background: Mitochondrial dynamics are important for glucose-stimulated insulin secretion in pancreatic beta cells. The mitochondrial elongation factor MiD51 has been proposed to act as an anchor that recruits Drp1 from the cytosol to the outer mitochondrial membrane. Whether MiD51 promotes mitochondrial fusion by inactivation of Drp1 is a controversial issue. Since both the underlying mechanism and the effects on mitochondrial function remain unknown, this study was conducted to investigate the role of MiD51 in beta cells. Methods: Overexpression and downregulation of MiD51 in mouse insulinoma 6 (MIN6) and mouse islet cells was achieved using the pcDNA expression vector and specific siRNA, respectively. Expression of genes regulating mitochondrial dynamics and autophagy was analyzed by quantitative Real-Time PCR, glucose-stimulated insulin secretion by ELISA, and cellular oxygen consumption rate by optode sensor technology. Mitochondrial membrane potential and morphology were visualized after TMRE and MitoTracker Green staining, respectively. Immunofluorescence analyses were examined by confocal microscopy. Results: MiD51 is expressed in insulin-positive mouse and human pancreatic islet and MIN6 cells. Overexpression of MiD51 resulted in mitochondrial fragmentation and cluster formation in MIN6 cells. Mitochondrial membrane potential, glucose-induced oxygen consumption rate and glucose-stimulated insulin secretion were reduced in MIN6 cells with high MiD51 expression. LC3 expression remained unchanged. Downregulation of MiD51 resulted in inhomogeneity of the mitochondrial network in MIN6 cells with hyperelongated and fragmented mitochondria. Mitochondrial membrane potential, maximal and glucose-induced oxygen consumption rate and insulin secretion were diminished in MIN6 cells with low MiD51 expression. Furthermore, reduced Mfn2 and Parkin expression was observed. Based on MiD51 overexpression and downregulation, changes in the mitochondrial network structure similar to those in MIN6 cells were also observed in mouse islet cells. Conclusion: We have demonstrated that MiD51 plays a pivotal role in regulating mitochondrial function and hence insulin secretion in MIN6 cells. We propose that this anchor protein of Drp1 is important to maintain a homogeneous mitochondrial network and to avoid morphologies such as hyperelongation and clustering which are inaccessible for degradation by autophagy. Assuming that insulin granule degradation frequently suppresses autophagy in beta cells, MiD51 could be a key element maintaining mitochondrial health.

The Causal Role of Mitochondrial Dynamics in Regulating Innate Immunity in Diabetes

Background: Plenty of evidence suggested that chronic low-grade inflammation triggered by innate immunity activation contributes to the pathogenesis of type 2 diabetes (T2D). Using the trans-mitochondrial cybrid cell model, we have demonstrated that mitochondria independently take part in the pathological process of insulin resistance (IR) and pro-inflammatory phenotype in cybrid cells harboring mitochondrial haplogroup B4, which are more likely to develop T2D. The mitochondrial network is more fragmented, and the expression of fusion-related proteins is low in Cybrid B4. We also discovered the causal role of mitochondrial dynamics (mtDYN) proteins in regulating IR in this cybrid model, and the bidirectional interaction between mtDYN and mitochondrial oxidative stress is considered etiologically important. In this study, we further investigated whether mtDYN bridges the gap between nutrient excess and chronic inflammation in T2D. Methods: Trans-mitochondrial cybrid cells derived from the 143B human osteosarcoma cell line were cultured in a medium containing glucose (25 mM) with or without saturated fatty acid (0.25 mM BSA-conjugated palmitate), and the expression of innate immunity/inflammasome molecules was compared between cybrid B4 (the major T2D-susceptible haplogroup among the Chinese population) and cybrid D4 (the major T2D-resistant haplogroup among the Chinese population). We investigated the causal relationship between mtDYN and nutrient excess-induced inflammation in cybrid B4 by genetic manipulation of mtDYN and by pharmacologically inhibiting mitochondrial fission using the Drp1 inhibitor, mdivi-1, and metformin. Results: Under nutrient excess with high fatty acid, cybrid B4 presented increased mitochondrial pro-fission profiles and enhanced chronic inflammation markers (RIG-I, MDA5, MAVS) and inflammasome (NLRP3, Caspase-1, IL-1β), whereas the levels in cybrid D4 were not or less significantly altered. In cybrid B4 under nutrient excess, overexpression of fusion proteins (Mfn1 or Mfn2) significantly repressed the expression of innate immunity/inflammasome-related molecules, while knockdown had a less significant effect. On the contrary, knockdown of fission proteins (Drp1 or Fis1) significantly repressed the expression of innate immunity/inflammasome-related molecules, while overexpression had a less significant effect. In addition, Drp1 inhibitor mdivi-1 and metformin inhibited mitochondrial fission and attenuated the pro-inflammation expression as well. Conclusion: Our results discovered the causal relationship between mtDYN and nutrient excess-induced chronic inflammation in a diabetes-susceptible cell model. Targeting mtDYN by direct interfering pro-fission can be a therapeutic intervention for chronic inflammation in T2D.

Mitochondrially-targeted treatment strategies

Disruption of mitochondrial function is a common feature of inherited mitochondrial diseases (mitochondriopathies) and many other infectious and non-infectious diseases including viral, bacterial and protozoan infections, inflammatory and chronic pain, neurodegeneration, diabetes, obesity and cardiovascular diseases. Mitochondria therefore become an attractive target for developing new therapies. In this review we describe critical mechanisms involved in the maintenance of mitochondrial functionality and discuss strategies used to identify and validate mitochondrial targets in different diseases. We also highlight the most recent preclinical and clinical findings using molecules targeting mitochondrial bioenergetics, morphology, number, content and detoxification systems in common pathologies.

The effect of endurance training with crocin consumption on the levels of MFN2 and DRP1 gene expression and glucose and insulin indices in the muscle tissue of diabetic rats

This study aimed to investigate the effect of crocin consumption, high-intensity interval training (HIIT), and low-intensity continuous training (LICT) and their interactive effect on the gene expression of Mfn2 and Drp1 in the skeletal muscle and serum glucose and insulin indices in high-fat diet (HFD) and streptozotocin (STZ)-induced diabetic rats. Fifty-six adult rats were divided into eight groups of seven subjects: crocin consumption, HIIT, LICT, HIIT with crocin, LICT with crocin, diabetic control, healthy control, and sham (placebo). At the end of the course (5 months), metabolic indices were measured. Moreover, the Mfn2 and Drp1 gene expression levels in all groups were measured using RT-PCR. The statistical analysis showed that in the exercise training (HIIT and LICT) and the crocin consumption groups, the glucose and insulin indices significantly improved (p = .005). Moreover, in these groups, the levels of gene expression of Mfn2 and Drp1 significantly increased and decreased, respectively (p = .001). Exercise training and crocin consumption appear to, either in combination or individually, have a beneficial effect on mitochondrial dynamics and diabetes by improving the mitochondrial fusion and fission indices (Mfn2 and Drp1), and by modifying the insulin resistance index and glucose homeostasis. PRACTICAL APPLICATIONS: Mfn2 and Drp1, as the main regulators of the mitochondrial fusion and fission, play an important role in maintaining mitochondrial dynamics and type 2 diabetes. Thus, the regulation of mitochondrial dynamics is an intricate process that retains the balance between mitochondrial fission and fusion, and any disturbance in this balance can lead to mitochondrial-associated diseases including insulin resistance and T2D. There is evidence that herbal antioxidants Including crocin and exercise training help improve the mitochondrial activity and insulin sensitivity in T2D. Considering the importance of the two Drp1 and Mfn1 genes in the mitochondrial dynamic pathway and coding the proteins that play a key role in relation to T2D, this study primarily examined the interactive effects of endurance training (HIIT and LICT) along with crocin consumption on the expression the genes mentioned above; the results obtained in this study can provide a new approach to the treatment of HFD + STZ-induced diabetic rats.

Cardiac Insulin Resistance in Heart Failure: The Role of Mitochondrial Dynamics

Heart failure (HF) frequently coexists with conditions associated with glucose insufficiency, such as insulin resistance and type 2 diabetes mellitus (T2DM), and patients with T2DM have a significantly high incidence of HF. These two closely related diseases cannot be separated on the basis of their treatment. Some antidiabetic drugs failed to improve cardiac outcomes in T2DM patients, despite lowering glucose levels sufficiently. This may be, at least in part, due to a lack of understanding of cardiac insulin resistance. Basic investigations have revealed the significant contribution of cardiac insulin resistance to the pathogenesis and progression of HF; however, there is no clinical evidence of the definition or treatment of cardiac insulin resistance. Mitochondrial dynamics play an important role in cardiac insulin resistance and HF because they maintain cellular homeostasis through energy production, cell survival, and cell proliferation. The innovation of diagnostic tools and/or treatment targeting mitochondrial dynamics is assumed to improve not only the insulin sensitivity of the myocardium and cardiac metabolism, but also the cardiac contraction function. In this review, we summarized the current knowledge on the correlation between cardiac insulin resistance and progression of HF, and discussed the role of mitochondrial dynamics on the pathogenesis of cardiac insulin resistance and HF. We further discuss the possibility of mitochondria-targeted intervention to improve cardiac metabolism and HF.

Mitofusins: Disease Gatekeepers and Hubs in Mitochondrial Quality Control by E3 Ligases

Mitochondria are dynamic organelles engaged in quality control and aging processes. They constantly undergo fusion, fission, transport, and anchoring events, which empower mitochondria with a very interactive behavior. The membrane remodeling processes needed for fusion require conserved proteins named mitofusins, MFN1 and MFN2 in mammals and Fzo1 in yeast. They are the first determinants deciding on whether communication and content exchange between different mitochondrial populations should occur. Importantly, each cell possesses hundreds of mitochondria, with a different severity of mitochondrial mutations or dysfunctional proteins, which potentially spread damage to the entire network. Therefore, the degree of their merging capacity critically influences cellular fitness. In turn, the mitochondrial network rapidly and dramatically changes in response to metabolic and environmental cues. Notably, cancer or obesity conditions, and stress experienced by neurons and cardiomyocytes, for example, triggers the downregulation of mitofusins and thus fragmentation of mitochondria. This places mitofusins upfront in sensing and transmitting stress. In fact, mitofusins are almost entirely exposed to the cytoplasm, a topology suitable for a critical relay point in information exchange between mitochondria and their cellular environment. Consistent with their topology, mitofusins are either activated or repressed by cytosolic post-translational modifiers, mainly by ubiquitin. Ubiquitin is a ubiquitous small protein orchestrating multiple quality control pathways, which is covalently attached to lysine residues in its substrates, or in ubiquitin itself. Importantly, from a chain of events also mediated by E1 and E2 enzymes, E3 ligases perform the ultimate and determinant step in substrate choice. Here, we review the ubiquitin E3 ligases that modify mitofusins. Two mitochondrial E3 enzymes—March5 and MUL1—one ligase located to the ER—Gp78—and finally three cytosolic enzymes—MGRN1, HUWE1, and Parkin—were shown to ubiquitylate mitofusins, in response to a variety of cellular inputs. The respective outcomes on mitochondrial morphology, on contact sites to the endoplasmic reticulum and on destructive processes, like mitophagy or apoptosis, are presented. Ultimately, understanding the mechanisms by which E3 ligases and mitofusins sense and bi-directionally signal mitochondria-cytosolic dysfunctions could pave the way for therapeutic approaches in neurodegenerative, cardiovascular, and obesity-linked diseases.

Mitochondrial Dynamics Impairment in Dexamethasone-Treated Neuronal Cells

Dexamethasone is an approved steroid for clinical use to activate or suppress cytokines, chemokines, inflammatory enzymes and adhesion molecules. It enters the brain, by-passing the blood brain barrier, and acts through genomic mechanisms. High levels of dexamethasone are able to induce neuronal cell loss, reduce neurogenesis and cause neuronal dysfunction. The exact mechanisms of steroid, especially the dexamethasone contribute to neuronal damage remain unclear. Therefore, the present study explored the mitochondrial dynamics underlying dexamethasone-induced toxicity of human neuroblastoma SH-SY5Y cells. Neuronal cells treatment with the dexamethasone resulted in a marked decrease in cell proliferation. Dexamethasone-induced neurotoxicity also caused upregulation of mitochondrial fusion and cleaved caspase-3 proteins expression. Mitochondria fusion was found in large proportions of dexamethasone-treated cells. These results suggest that dexamethasone-induced hyperfused mitochondrial structures are associated with a caspase-dependent death process in dexamethasone-induced neurotoxicity. These findings point to the high dosage of dexamethasone as being neurotoxic through impairment of mitochondrial dynamics.

Dysregulated Mitochondrial Dynamics and Metabolism in Obesity, Diabetes, and Cancer

Metabolism describes the life-sustaining chemical reactions in organisms that provide both energy and building blocks for cellular survival and proliferation. Dysregulated metabolism leads to many life-threatening diseases including obesity, diabetes, and cancer. Mitochondria, subcellular organelles, contain the central energy-producing metabolic pathway, the tricarboxylic acid (TCA) cycle. Also, mitochondria exist in a dynamic network orchestrated by extracellular nutrient levels and intracellular energy needs. Upon stimulation, mitochondria undergo consistent interchange through fusion (small to big) and fission (big to small) processes. Mitochondrial fusion is primarily controlled by three GTPases, mitofusin 1 (Mfn1), Mfn2, and optic atrophy 1 (Opa1), while mitochondrial fission is primarily regulated by GTPase dynamin-related protein 1 (Drp1). Dysregulated activity of these GTPases results in disrupted mitochondrial dynamics and cellular metabolism. This review will update the metabolic roles of these GTPases in obesity, diabetes, and cancer.

The Causal Role of Mitochondrial Dynamics in Regulating Insulin Resistance in Diabetes: Link through Mitochondrial Reactive Oxygen Species

Background

Mitochondrial dynamics (mtDYN) has been proposed as a bridge between mitochondrial dysfunction and insulin resistance (IR), which is involved in the pathogenesis of type 2 diabetes (T2D). Our previous study has identified that mitochondrial DNA (mtDNA) haplogroup B4 is a T2D-susceptible genotype. Using transmitochondrial cybrid model, we have confirmed that haplogroup B4 contributes to cellular IR as well as a profission mtDYN, which can be reversed by antioxidant treatment. However, the causal relationship between mtDYN and cellular IR pertaining to T2D-susceptible haplogroup B4 remains unanswered.

Methods

To dissect the mechanisms between mtDYN and IR, knockdown or overexpression of MFN1, MFN2, DRP1, and FIS1 was performed using cybrid B4. We then examined the mitochondrial network and mitochondrial oxidative stress (mtROS) as well as insulin signaling IRS-AKT pathway and glucose transporters (GLUT) translocation to plasma membrane stimulated by insulin. We employed Drp1 inhibitor, mdivi-1, to interfere with endogenous expression of fission to validate the pharmacological effects on IR.

Results

Overexpression of MFN1 or MFN2 increased mitochondrial network and reduced mtROS, while knockdown had an opposing effect. In contrast, overexpression of DRP1 or FIS1 decreased mitochondrial network and increased mtROS, while knockdown had an opposing effect. Concomitant with the enhanced mitochondrial network, activation of the IRS1-AKT pathway and GLUT translocation stimulated by insulin were improved. On the contrary, suppression of mitochondrial network caused a reduction of the IRS1-AKT pathway and GLUT translocation stimulated by insulin. Pharmacologically inhibiting mitochondrial fission by the Drp1 inhibitor, mdivi-1, also rescued mitochondrial network, reduced mtROS, and improved insulin signaling of diabetes-susceptible cybrid cells.

Conclusion

Our results discovered the causal role of mtDYN proteins in regulating IR resulted from diabetes-susceptible mitochondrial haplogroup. The existence of a bidirectional interaction between mtDYN and mtROS plays an important role. Direct intervention to reverse profission in mtDYN provides a novel therapeutic strategy for IR and T2D.

Adult skeletal muscle deletion of Mitofusin 1 and 2 impedes exercise performance and training capacity

Endurance exercise has been shown to be a positive regulator of skeletal muscle metabolic function. Changes in mitochondrial dynamics (fusion and fission) have been shown to influence mitochondrial oxidative capacity. We therefore tested whether genetic disruption of mitofusins (Mfns) affected exercise performance in adult skeletal muscle. We generated adult-inducible skeletal muscle-specific Mfn1 (iMS-Mfn1KO), Mfn2 (iMS-Mfn2KO), and Mfn1/2 (iMS-MfnDKO) knockout mice. We assessed exercise capacity by performing a treadmill time to exhaustion stress test before deletion and up to 8 wk after deletion. Analysis of either the iMS-Mfn1KO or the iMS-Mfn2KO did not reveal an effect on exercise capacity. However, analysis of iMS-MfnDKO animals revealed a progressive reduction in exercise performance. We measured individual electron transport chain (ETC) complex activity and observed a reduction in ETC activity in both the subsarcolemmal and intermyofibrillar mitochondrial fractions specifically for NADH dehydrogenase (complex I) and cytochrome- c oxidase (complex IV), which was associated with a decrease in ETC subunit expression for these complexes. We also tested whether voluntary exercise training would prevent the decrease in exercise capacity observed in iMS-MfnDKO animals ( n = 10/group). However, after 8 wk of training we did not observe any improvement in exercise capacity or ETC subunit parameters in iMS-MfnDKO animals. These data suggest that the decrease in exercise capacity observed in the iMS-MfnDKO animals is in part the result of impaired ETC subunit expression and ETC complex activity. Taken together, these results provide strong evidence that mitochondrial fusion in adult skeletal muscle is important for exercise performance. NEW & NOTEWORTHY This study is the first to utilize an adult-inducible skeletal muscle-specific knockout model for Mitofusin (Mfn)1 and Mfn2 to assess exercise capacity. Our findings reveal a progressive decrease in exercise performance with Mfn1 and Mfn2 deletion. The decrease in exercise capacity was accompanied by impaired oxidative phosphorylation specifically for complex I and complex IV. Furthermore, voluntary exercise training was unable to rescue the impairment, suggesting that normal fusion is essential for exercise-induced mitochondrial adaptations.

Physiological and pathophysiological role of reactive oxygen species and reactive nitrogen species in the kidney

End‐stage renal disease is a leading cause of morbidity and mortality worldwide. The prevalence of the disease and the number of patients who receive renal replacement therapy are expected to increase in the next decade. Accumulating evidence suggests that chronic hypoxia in the tubulointerstitium represents the final common pathway to end‐stage renal failure, and that reactive oxygen species (ROS) and reactive nitrogen species (RNS) are the key players in kidney injury. However, ROS and RNS that exceed the physiological levels associated with the pathophysiology of most kidney diseases. The molecules that comprise ROS and RNS play an important role in regulating solute and water reabsorption in the kidney, which is vital for maintaining electrolyte homeostasis and the volume of extracellular fluid. This article reviews the physiological and pathophysiological role of ROS and RNS in normal kidney function and in various kidney diseases.