Mitochondrial dynamics in type 2 diabetes: Pathophysiological implications

Reduced Levels of Drp1 Protect against Development of Retinal Vascular Lesions in Diabetic Retinopathy

High glucose (HG)-induced Drp1 overexpression contributes to mitochondrial dysfunction and promotes apoptosis in retinal endothelial cells. However, it is unknown whether inhibiting Drp1 overexpression protects against the development of retinal vascular cell loss in diabetes. To investigate whether reduced Drp1 level is protective against diabetes-induced retinal vascular lesions, four groups of mice: wild type (WT) control mice, streptozotocin (STZ)-induced diabetic mice, Drp1^+/− mice, and STZ-induced diabetic Drp1^+/− mice were examined after 16 weeks of diabetes. Western Blot analysis indicated a significant increase in Drp1 expression in the diabetic retinas compared to those of WT mice; retinas of diabetic Drp1^+/− mice showed reduced Drp1 level compared to those of diabetic mice. A significant increase in the number of acellular capillaries (AC) and pericyte loss (PL) was observed in the retinas of diabetic mice compared to those of the WT control mice. Importantly, a significant decrease in the number of AC and PL was observed in retinas of diabetic Drp1^+/− mice compared to those of diabetic mice concomitant with increased expression of pro-apoptotic genes, Bax, cleaved PARP, and increased cleaved caspase-3 activity. Preventing diabetes-induced Drp1 overexpression may have protective effects against the development of vascular lesions, characteristic of diabetic retinopathy.

Mitochondrial protein IF1 is a potential regulator of glucagon-like peptide (GLP-1) secretion function of the mouse intestine

IF1 (ATPIF1) is a nuclear DNA-encoded mitochondrial protein whose activity is inhibition of the F1Fo-ATP synthase to control ATP production. IF1 activity remains unknown in the regulation of GLP-1 activity. In this study, IF1 was examined in the diet-induced obese mice using the gene knockout (If1-KO) mice. The mice gained more body weight on a high fat diet without a change in food intake. Insulin tolerance was impaired, but the oral glucose tolerance was improved through an increase in GLP-1 secretion. The KO mice exhibited an improved intestine structure, mitochondrial superstructure, enhanced mitophagy, reduced apoptosis and decreased adenine nucleotide translocase 2 (ANT2) protein in the intestinal epithelial cells together with preserved gut microbiota. The data suggest that GLP-1 secretion was enhanced in the obese If1-KO mice to preserve glucose tolerance through a signaling pathway of ANT2/mitochondria/L-cells/GLP-1/insulin. IF1 is a potential mitochondrial target for induction of GLP-1 secretion in L-cells.

Interplay Between Reactive Oxygen/Reactive Nitrogen Species and Metabolism in Vascular Biology and Disease

Reactive oxygen species (ROS; e.g., superoxide [O₂^•-] and hydrogen peroxide [H₂O₂]) and reactive nitrogen species (RNS; e.g., nitric oxide [NO^•]) at the physiological level function as signaling molecules that mediate many biological responses, including cell proliferation, migration, differentiation, and gene expression. By contrast, excess ROS/RNS, a consequence of dysregulated redox homeostasis, is a hallmark of cardiovascular disease. Accumulating evidence suggests that both ROS and RNS regulate various metabolic pathways and enzymes. Recent studies indicate that cells have mechanisms that fine-tune ROS/RNS levels by tight regulation of metabolic pathways, such as glycolysis and oxidative phosphorylation. The ROS/RNS-mediated inhibition of glycolytic pathways promotes metabolic reprogramming away from glycolytic flux toward the oxidative pentose phosphate pathway to generate nicotinamide adenine dinucleotide phosphate (NADPH) for antioxidant defense. This review summarizes our current knowledge of the mechanisms by which ROS/RNS regulate metabolic enzymes and cellular metabolism and how cellular metabolism influences redox homeostasis and the pathogenesis of disease. A full understanding of these mechanisms will be important for the development of new therapeutic strategies to treat diseases associated with dysregulated redox homeostasis and metabolism. Antioxid. Redox Signal. 34, 1319-1354.

Mechanism of insulin resistance in obesity: a role of ATP

Obesity increases the risk of type 2 diabetes through the induction of insulin resistance. The mechanism of insulin resistance has been extensively investigated for more than 60 years, but the essential pathogenic signal remains missing. Existing hypotheses include inflammation, mitochondrial dysfunction, hyperinsulinemia, hyperglucagonemia, glucotoxicity, and lipotoxicity. Drug discoveries based on these hypotheses are unsuccessful in the development of new medicines. In this review, multidisciplinary literature is integrated to evaluate ATP as a primary signal for insulin resistance. The ATP production is elevated in insulin-sensitive cells under obese conditions independent of energy demand, which we have named "mitochondrial overheating." Overheating occurs because of substrate oversupply to mitochondria, leading to extra ATP production. The ATP overproduction contributes to the systemic insulin resistance through several mechanisms, such as inhibition of AMPK, induction of mTOR, hyperinsulinemia, hyperglucagonemia, and mitochondrial dysfunction. Insulin resistance represents a feedback regulation of energy oversupply in cells to control mitochondrial overloading by substrates. Insulin resistance cuts down the substrate uptake to attenuate mitochondrial overloading. The downregulation of the mitochondrial overloading by medicines, bypass surgeries, calorie restriction, and physical exercise leads to insulin sensitization in patients. Therefore, ATP may represent the primary signal of insulin resistance in the cellular protective response to the substrate oversupply. The prevention of ATP overproduction represents a key strategy for insulin sensitization.

Mitochondrial Targeting of Herbal Medicine in Chronic Kidney Disease

Chronic kidney disease (CKD) is a common progressive disease that is typically characterized by the permanent loss of nephrons and an eventual decline in glomerular filtration rate. CKD increases mortality and has a significant impact on the quality of life and the economy, which is becoming a major public health issue worldwide. Since current conventional-medicine treatment options for CKD are not satisfactory, many patients seek complementary and alternative medicine treatments including Traditional Chinese Medicine. Herbal medicine is often used to relieve symptoms of renal diseases in the clinic. The kidney is abundant in the number of mitochondria, which provide enough energy for renal function and metabolism. In recent years, a vital role for mitochondrial dysfunction has been suggested in CKD. Mitochondria have become a new target for the treatment of diseases. A growing number of studies have demonstrated herbal medicine could restore mitochondrial function and alleviate renal injury both in vivo and in vitro. In this review, we sum up the therapeutic effect of herbal medicine in CKD via targeting mitochondrial function. This implies future strategies in preventing CKD.

Tang Luo Ning, a Traditional Chinese Compound Prescription, Ameliorates Schwannopathy of Diabetic Peripheral Neuropathy Rats by Regulating Mitochondrial Dynamics In Vivo and In Vitro

Tang Luo Ning (TLN), a traditional Chinese compound prescription, has been used clinically to treat diabetic peripheral neuropathy (DPN) in China. However, the exact mechanisms remain unclear. The objective of this study is to unravel the effects of TLN on mitochondrial dynamics of DPN in streptozotocin-induced rat models and Schwann cells cultured in 150 mM glucose. Mitochondrial function was determined by Ca²⁺ and ATP levels of streptozotocin (STZ)-induced DPN rats and mitochondria structure, mitochondrial membrane potential (MMP), and mtDNA of high glucose incubated SCs. Mitochondrial dynamics protein including mitofusin 1 (Mfn1), mitofusin 2 (Mfn2), optic atrophy 1 (Opa1), and dynamin-related protein 1 (Drp1) were investigated using Western blot or immunofluorescence. Myelin basic protein (MBP), myelin protein zero (MPZ), and sex-determining region Y (SRY)-box 10 (Sox10) were measured to represent schwannopathy. Our results showed that TLN increased ATP levels (0.38 of model, 0.69 of HTLN, 0.61 of LTLN, P＜0.01; 0.52 of 150 mM glucose, 1.00 of 10% TLN, P＜0.01, 0.94 of 1% TLN, P＜0.05), MMP (0.56 of 150 mM glucose, P＜0.01, 0.75 of 10% TLN, P＜0.05, 0.83 of 1% TLN, P＜0.01), and mtDNA (0.32 of 150 mM glucose, 0.43 of 10% TLN, P＜0.01) while decreased Ca²⁺ (1.54 of model, 1.06 of HTLN, 0.96 of LTLN, P＜0.01) to improve mitochondrial function in vivo and in vitro. TLN helps maintain balance of mitochondrial dynamics: it reduces the mitochondria number (1.60 of 150 mM glucose, 1.10 of 10% TLN, P＜0.01) and increases the mitochondria coverage (0.51 of 150 mM glucose, 0.80 of 10% TLN, 0.87 of 1% TLN, P＜0.01), mitochondrial network size (0.51 of 150 mM glucose, 0.95 of 10% TLN, 0.94 of 1% TLN, P＜0.01), and branch length (0.63 of 150 mM glucose, P＜0.01, 0.73 of 10% TLN, P＜0.05, 0.78 of 1% TLN, P＜0.01). Further, mitochondrial dynamics–related Mfn1 (0.47 of model, 0.82 of HTLN, 0.77 of LTLN, P＜0.01; 0.42 of 150 mM glucose, 0.56 of 10% TLN, 0.57 of 1% TLN, P＜0.01), Mfn2 (0.40 of model, 0.84 of HTLN, 0.63 of LTLN, P＜0.01; 0.46 of 150 mM glucose, 1.40 of 10% TLN, 1.40 of 1% TLN, P＜0.01), and Opa1 (0.58 of model, 0.71 of HTLN, 0.90 of LTLN, P＜0.01; 0.69 of 150 mM glucose, 0.96 of 10% TLN, 0.98 of 1% TLN, P＜0.05) were increased, while Drp1 (1.39 of model, 0.96 of HTLN, 1.18 of LTLN, P＜0.01; 1.70 of 150 mM glucose, 1.20 of 10% TLN, 1.10 of 1% TLN, P＜0.05), phosphorylated Drp1 (2.61 of model, 1.44 of HTLN, P＜0.05; 2.80 of 150 mM glucose, 1.50 of 10% TLN, 1.30 of 1% TLN, P＜0.01), and Drp1 located in mitochondria (1.80 of 150 mM glucose, 1.00 of 10% TLN, P＜0.05) were decreased after treatment with TLN. Additionally, TLN improved schwannopathy by increasing MBP (0.50 of model, 1.05 of HTLN, 0.94 of HTLN, P＜0.01; 0.60 of 150 mM glucose, 0.78 of 10% TLN, P＜0.01, 0.72 of 1% TLN, P＜0.05), Sox101 (0.41 of model, 0.99 of LTLN, P＜0.01; 0.48 of 150 mM glucose, 0.65 of 10% TLN, P＜0.05, 0.69 of 1% TLN, P＜0.01), and MPZ (0.48 of model, 0.66 of HTLN, 0.55 of HTLN, P＜0.01; 0.60 of 150 mM glucose, 0.78 of 10% TLN, P＜0.01, 0.75 of 1% TLN, P＜0.05) expressions. In conclusion, our study indicated that TLN’s function on DPN may link to the improvement of the mitochondrial dynamics, which provides scientific evidence for the clinical application.

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

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

Mitofusin-2 boosts innate immunity through the maintenance of aerobic glycolysis and activation of xenophagy in mice

Mitochondrial function and innate immunity are intimately linked; however, the mechanisms how mitochondrion-shaping proteins regulate innate host defense remains largely unknown. Herein we show that mitofusin-2 (MFN2), a mitochondrial fusion protein, promotes innate host defense through the maintenance of aerobic glycolysis and xenophagy via hypoxia-inducible factor (HIF)-1α during intracellular bacterial infection. Myeloid-specific MFN2 deficiency in mice impaired the antimicrobial and inflammatory responses against mycobacterial and listerial infection. Mechanistically, MFN2 was required for the enhancement of inflammatory signaling through optimal induction of aerobic glycolysis via HIF-1α, which is activated by mitochondrial respiratory chain complex I and reactive oxygen species, in macrophages. MFN2 did not impact mitophagy during infection; however, it promoted xenophagy activation through HIF-1α. In addition, MFN2 interacted with the late endosomal protein Rab7, to facilitate xenophagy during mycobacterial infection. Our findings reveal the mechanistic regulations by which MFN2 tailors the innate host defense through coordinated control of immunometabolism and xenophagy via HIF-1α during bacterial infection.

Ablation of dynamin-related protein 1 promotes diabetes-induced synaptic injury in the hippocampus

Dynamin-related protein 1 (Drp1)-mediated mitochondrial dysfunction is associated with synaptic injury in the diabetic brain. However, the dysfunctional mitochondria by Drp1 deletion in the diabetic brain are poorly understood. Here, we investigated the effects of neuron-specific Drp1 deletion on synaptic damage and mitophagy in the hippocampus of a high-fat diet (HFD)/streptozotocin (STZ)-induced diabetic mice. HFD/STZ-induced diabetic mice exhibited metabolic disturbances and synaptic damages. Floxed Drp1 mice were crossed with Ca²⁺/calmodulin-dependent protein kinase IIα (CaMKIIα)-Cre mice, to generate neuron-specific Drp1 knockout (Drp1cKO) mice, which showed marked mitochondrial swelling and dendritic spine loss in hippocampal neurons. In particular, diabetic Drp1cKO mice exhibited an increase in dendritic spine loss and higher levels of oxidative stress and neuroinflammation compared with diabetic wild-type (WT) mice. Diabetic WT mice generally displayed increased Drp1-induced small mitochondrial morphology in hippocampal neurons, but large mitochondria were prominently observed in diabetic Drp1cKO mice. The levels of microtubule-associated protein 1 light-chain 3 and lysosomal-associated membrane protein 1 proteins were significantly increased in the hippocampus of diabetic Drp1cKO mice compared with diabetic WT mice. The inhibition of Drp1 adversely promotes synaptic injury and neurodegeneration in the diabetic brain. The findings suggest that the exploratory mechanisms behind Drp1-mediated mitochondrial dysfunction could provide a possible therapeutic target for diabetic brain complications.

Protective effects of a mitochondria-targeted small peptide SS31 against hyperglycemia-induced mitochondrial abnormalities in the liver tissues of diabetic mice, Tallyho/JngJ mice

Type 2 Diabetes mellitus (T2DM) has become a major public health issue associated with a high risk of late-onset Alzheimer's disease (LOAD). Mitochondrial dysfunction is one of the molecular events that occur in the LOAD pathophysiology. The present study was planned to investigate the molecular alterations induced by hyperglycemia in the mitochondria of diabetic mice and further explore the possible ameliorative role of the mitochondria-targeted small peptide, SS31 in diabetic mice. For this purpose, we used a polygenic mouse model of type 2 diabetes, TALLYHO/JngJ (TH), and nondiabetic, SWR/J mice strains. The diabetic status in TH mice was confirmed at 8 weeks of age. The 24 weeks old experimental animals were segregated into three groups: Non-diabetic controls (SWR/J mice), diabetic (TH mice) and, SS31 treated diabetic TH mice. The mRNA and protein expression levels of mitochondrial proteins were investigated in all the study groups in the liver tissues using qPCR and immunoblot analysis. Also, the mitochondrial functions including H2O2 production, ATP generation, and lipid peroxidation were assessed in all the groups. Mitochondrial dysfunction was observed in TH mice as evident by significantly elevated H2O2 production, lipid peroxidation, and reduced ATP production. The mRNA expression and Western blot analysis of mitochondrial dynamics (Drp1 and Fis1 - fission; Mfn1, Mfn2, and Opa1 -fusion), and biogenesis (PGC-1α, Nrf1, Nrf2, and TFAM) genes were significantly altered in diabetic TH mice. Furthermore, SS31 treatment significantly reduced the mitochondrial abnormalities and restore mitochondrial functions in diabetic TH mice.

Drp1-dependent mitochondrial fission in cardiovascular disease

Mitochondria are highly dynamic organelles undergoing cycles of fusion and fission to modulate their morphology, distribution, and function, which are referred as 'mitochondrial dynamics'. Dynamin-related protein 1 (Drp1) is known as the major pro-fission protein whose activity is tightly regulated to clear the damaged mitochondria via mitophagy, ensuring a strict control over the intricate process of cellular and organ dynamics in heart. Various posttranslational modifications (PTMs) of Drp1 have been identified including phosphorylation, SUMOylation, palmitoylation, ubiquitination, S-nitrosylation, and O-GlcNAcylation, which implicate a role in the regulation of mitochondrial dynamics. An intact mitochondrial homeostasis is critical for heart to fuel contractile function and cardiomyocyte metabolism, while defects in mitochondrial dynamics constitute an essential part of the pathophysiology underlying various cardiovascular diseases (CVDs). In this review, we summarize current knowledge on the critical role of Drp1 in the pathogenesis of CVDs including endothelial dysfunction, smooth muscle remodeling, cardiac hypertrophy, pulmonary arterial hypertension, myocardial ischemia-reperfusion, and myocardial infarction. We also highlight how the targeting of Drp1 could potentially contribute to CVDs treatments.

When the Balance Tips: Dysregulation of Mitochondrial Dynamics as a Culprit in Disease

Mitochondria are dynamic organelles, the morphology of which is tightly linked to their functions. The interplay between the coordinated events of fusion and fission that are collectively described as mitochondrial dynamics regulates mitochondrial morphology and adjusts mitochondrial function. Over the last few years, accruing evidence established a connection between dysregulated mitochondrial dynamics and disease development and progression. Defects in key components of the machinery mediating mitochondrial fusion and fission have been linked to a wide range of pathological conditions, such as insulin resistance and obesity, neurodegenerative diseases and cancer. Here, we provide an update on the molecular mechanisms promoting mitochondrial fusion and fission in mammals and discuss the emerging association of disturbed mitochondrial dynamics with human disease.

Design, synthesis and antitumor activity evaluation of Chrysamide B derivatives

Marine natural products derived from special or extreme environment provide an important source for the development of anti-tumor drugs due to their special skeletons and functional groups. In this study, based on our previous work on the total synthesis and structure revision of the novel marine natural product Chrysamide B, a group of its derivatives were designed, synthesized, and subsequently of which the anti-cancer activity, structure-activity relationships and cellular mechanism were explored for the first time. Compared with Chrysamide B, better anti-cancer performance of some derivatives against five human cancer cell lines (SGC-7901, MGC-803, HepG2, HCT-116, MCF-7) was observed, especially for compound b-9 on MGC-803 and SGC-7901 cells with the IC ₅₀ values of 7.88 ± 0.81 and 10.08 ± 1.08 μM, respectively. Subsequently, cellular mechanism study suggested that compound b-9 treatment could inhibit the cellular proliferation, reduce the migration and invasion ability of cells, and induce mitochondrial-dependent apoptosis in gastric cancer MGC-803 and SGC-7901 cells. Furthermore, the mitochondrial-dependent apoptosis induced by compound b-9 is related with the JAK2/STAT3/Bcl-2 signaling pathway. To conclude, our results offer a new structure for the discovery of anti-tumor lead compounds from marine natural products.

Exercise intervention under hypoxic condition as a new therapeutic paradigm for type 2 diabetes mellitus: A narrative review

This review aims to summarize the health benefits of exposure to hypoxic conditions during exercise in patients with type 2 diabetes mellitus (T2DM). Exposure to hypoxic conditions during exercise training positively changes the physiological response in healthy subjects. Exposure to hypoxic conditions during exercise could markedly increase skeletal muscle glucose uptake compared to that in normoxic conditions. Furthermore, post-exercise insulin sensitivity of T2DM patients increases more when exercising under hypoxic than under normoxic conditions. Regular exercise under short-term hypoxic conditions can improve blood glucose control at lower workloads than in normoxic conditions. Additionally, exercise training under short-term hypoxic conditions can maximize weight loss in overweight and obese patients. Previous studies on healthy subjects have reported that regular exercise under hypoxic conditions had a more positive effect on vascular health than exercising under normoxic conditions. However, currently, evidence indicating that exposure to hypoxic conditions could positively affect T2DM patients in the long-term is lacking. Therefore, further evaluations of the beneficial effects of exercise under hypoxic conditions on the human body, considering different cycle lengths, duration of exposures, sessions per day, and the number of days, are necessary. In this review, we conclude that there is evidence that exercise under hypoxic conditions can yield health benefits, which is potentially valuable in terms of clinical care as a new intervention for T2DM patients.

Mitophagy in Human Diseases

Mitophagy is a selective autophagic process, essential for cellular homeostasis, that eliminates dysfunctional mitochondria. Activated by inner membrane depolarization, it plays an important role during development and is fundamental in highly differentiated post-mitotic cells that are highly dependent on aerobic metabolism, such as neurons, muscle cells, and hepatocytes. Both defective and excessive mitophagy have been proposed to contribute to age-related neurodegenerative diseases, such as Parkinson's and Alzheimer's diseases, metabolic diseases, vascular complications of diabetes, myocardial injury, muscle dystrophy, and liver disease, among others. Pharmacological or dietary interventions that restore mitophagy homeostasis and facilitate the elimination of irreversibly damaged mitochondria, thus, could serve as potential therapies in several chronic diseases. However, despite extraordinary advances in this field, mainly derived from in vitro and preclinical animal models, human applications based on the regulation of mitochondrial quality in patients have not yet been approved. In this review, we summarize the key selective mitochondrial autophagy pathways and their role in prevalent chronic human diseases and highlight the potential use of specific interventions.

Stressed mitochondria: A target to intrude alzheimer's disease

Alzheimer's disease (AD) is the inoperable, incapacitating, neuropsychiatric, and degenerative manifestation that drastically affects human life quality. The current medications target extra-neuronal senile plaques, oxidative stress, neuroinflammation, intraneuronal neurofibrillary tangles, cholinergic deficits, and excitotoxicity. Among novel pathways and targets, bioenergetic and resultant mitochondrial dysfunction has been recognized as essential factors that decide the neuronal fate and consequent neurodegeneration in AD. The crucial attributes of mitochondria, including bioenergesis, signaling, sensing, integrating, and transmitting biological signals contribute to optimum networking of neuronal dynamics and make them indispensable for cell survival. In AD, mitochondrial dysfunction and mitophagy are a preliminary and critical event that aggravates the pathological cascade. Stress is known to promote and exaggerate the neuropathological alteration during neurodegeneration and metabolic impairments, especially in the cortico-limbic system, besides adversely affecting the normal physiology and mitochondrial dynamics. Stress involves the allocation of energy resources for neuronal survival. Chronic and aggravated stress response leads to excessive release of glucocorticoids by activation of the hypothalamic-pituitaryadrenal (HPA) axis. By acting through their receptors, glucocorticoids influence adverse mitochondrial changes and alter mtDNA transcription, mtRNA expression, hippocampal mitochondrial network, and ultimately mitochondrial physiology. Chronic stress also affects mitochondrial dynamics by changing metabolic and neuro-endocrinal signalling, aggravating oxidative stress, provoking inflammatory mediators, altering tropic factors, influencing gene expression, and modifying epigenetic pathways. Thus, exploring chronic stress-induced glucocorticoid dysregulation and resultant bio-behavioral and psychosomatic mitochondrial alterations may be a feasible narrative to investigate and unravel the mysterious pathobiology of AD.

NGBR is required to ameliorate type 2 diabetes in mice by enhancing insulin sensitivity

The reduction of insulin resistance or improvement of insulin sensitivity is the most effective treatment for type 2 diabetes (T2D). We previously reported that Nogo-B receptor (NGBR), encoded by the NUS1 gene, is required for attenuating hepatic lipogenesis by blocking nuclear translocation of liver X receptor alpha, suggesting its important role in regulating hepatic lipid metabolism. Herein, we demonstrate that NGBR expression was decreased in the liver of obesity-associated T2D patients and db/db mice. NGBR knockout in mouse hepatocytes resulted in increased blood glucose, insulin resistance, and beta-cell loss. High-fat diet (HFD)/streptozotocin (STZ)-treated mice presented the T2D phenotype by showing increased nonesterified fatty acid (NEFA) and triglyceride (TG) in the liver and plasma and increased insulin resistance and beta-cell loss. AAV-mediated NGBR overexpression in the liver reduced NEFA and TG in the liver and circulation and improved liver functions. Consequently, HFD/STZ-treated mice with hepatic NGBR overexpression had increased insulin sensitivity and reduced beta-cell loss. Mechanistically, NGBR overexpression restored insulin signaling of AMPKα1-dependent phosphorylation of AKT and GSK3β. NGBR overexpression also reduced expression of endoplasmic reticulum stress-associated genes in the liver and skeletal muscle to improve insulin sensitivity. Together, our results reveal that NGBR is required to ameliorate T2D in mice, providing new insight into the role of hepatic NGBR in insulin sensitivity and T2D treatment.

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.

Mitochondrial Fission Protein 1: Emerging Roles in Organellar Form and Function in Health and Disease

Mitochondrial fission protein 1 (Fis1) was identified in yeast as being essential for mitochondrial division or fission and subsequently determined to mediate human mitochondrial and peroxisomal fission. Yet, its exact functions in humans, especially in regard to mitochondrial fission, remains an enigma as genetic deletion of Fis1 elongates mitochondria in some cell types, but not others. Fis1 has also been identified as an important component of apoptotic and mitophagic pathways suggesting the protein may have multiple, essential roles. This review presents current perspectives on the emerging functions of Fis1 and their implications in human health and diseases, with an emphasis on Fis1's role in both endocrine and neurological disorders.

Arterial Stiffness Index and Exercise Tolerance in Patients Undergoing Cardiac Rehabilitation

Arterial stiffness contributes to the development of cardiovascular disease (CVD). However, the relationship between the arterial stiffness and exercise tolerance in CVD patients with preserved ejection fraction (pEF) and those with reduced EF (rEF) is unclear. We enrolled 358 patients who participated in cardiac rehabilitation and underwent cardiopulmonary exercise testing at Juntendo University Hospital. After excluding 195 patients who had undergone open heart surgery and 20 patients with mid-range EF, the patients were divided into pEF (n = 99) and rEF (n = 44) groups. Arterial stiffness was assessed using arterial velocity pulse index (AVI) and arterial pressure volume index (API) at rest. The patients in the pEF group were significantly older and had a higher prevalence of coronary artery disease than the rEF group. The pEF group had significantly lower AVI levels and higher API levels than the rEF group. In the pEF group, the peak oxygen uptake (peak VO₂) and the anaerobic threshold was significantly higher than those in the rEF group. The peak VO₂ was significantly and negatively correlated with AVI and API in the pEF group (All, P < 0.05), but not in the rEF group. Multivariate linear regression analyses demonstrated that AVI was independently associated with peak VO₂ (β = -0.34, P < 0.05) in the pEF group. In conclusion, AVI may be a useful factor for assessing exercise tolerance, particularly in CVD patients with pEF.

Crocin Improves Endothelial Mitochondrial Dysfunction via GPx1/ROS/KCa3.1 Signal Axis in Diabetes

Mitochondrial dysfunction contributes to excessive reactive oxygen species (ROS) generation, which is a dramatic cause to promote endothelial dysfunction in diabetes. It was previously demonstrated that crocin protected the endothelium based on its diverse medicinal properties, but its effect on the mitochondrion and the potential mechanism are not fully understood. In this study, mitochondrial function was analyzed during the process of excessive ROS generation in high glucose (HG)-cultured human umbilical vein endothelial cells (HUVECs). The role played by KCa3.1 was further investigated by the inhibition and/or gene silence of KCa3.1 in this process. In addition, nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase 2 (NOX2), superoxide dismutase 1 (SOD1), and glutathione peroxidase 1 (GPx1) were also detected in this study. Our data showed that crocin improved mitochondrial dysfunction and maintained normal mitochondrial morphology by enhancing the mitochondrial membrane potential (MMP), mitochondrial mass, and mitochondrial fusion. Furthermore, KCa3.1 was confirmed to be located in the mitochondrion, and the blockade and/or silencing of KCa3.1 improved mitochondrial dysfunction and reduced excessive ROS generation but did not affect NOX2 and/or the SOD1 system. Intriguingly, it was confirmed that KCa3.1 expression was elevated by ROS overproduction in the endothelium under HG and/or diabetes conditions, while crocin significantly suppressed this elevation by promoting GPx1 and subsequently eliminating ROS generation. In addition, crocin enhanced CD31, thrombomodulin (TM), and p-/t-endothelial nitric oxide synthase (eNOS) expressions as well as NO generation and decreased vascular tone. Hence, crocin improved mitochondrial dysfunction through inhibiting ROS-induced KCa3.1 overexpression in the endothelium, which in turn reduced more ROS generation and final endothelial dysfunction in diabetes.

Schisandrin Restores the Amyloid β-Induced Impairments on Mitochondrial Function, Energy Metabolism, Biogenesis, and Dynamics in Rat Primary Hippocampal Neurons

INTRODUCTION

Schisandrin which is derived from Schisandra chinensis has shown multiple pharmacological effects on various diseases including Alzheimer's disease (AD). It is demonstrated that mitochondrial dysfunction plays an essential role in the pathogenesis of neurodegenerative disorders.

OBJECTIVE

Our study aims to investigate the effects of schisandrin on mitochondrial functions and metabolisms in primary hippocampal neurons.

METHODS

In our study, rat primary hippocampal neurons were isolated and treated with indicated dose of amyloid β1-42 (Aβ1-42) oligomer to establish a cell model of AD in vitro. Schisandrin (2 μg/mL) was further subjected to test its effects on mitochondrial function, energy metabolism, mitochondrial biogenesis, and dynamics in the Aβ1-42 oligomer-treated neurons.

RESULTS AND CONCLUSIONS

Our findings indicated that schisandrin significantly alleviated the Aβ1-42 oligomer-induced loss of mitochondrial membrane potential and impaired cytochrome c oxidase activity. Additionally, the opening of mitochondrial permeability transition pore and release of cytochrome c were highly restricted with schisandrin treatment. Alterations in cell viability, ATP production, citrate synthase activity, and the expressions of glycolysis-related enzymes demonstrated the relief of defective energy metabolism in Aβ-treated neurons after the treatment of schisandrin. For mitochondrial biogenesis, elevated expression of peroxisome proliferator-activated receptor γ coactivator along with promoted mitochondrial mass was found in schisandrin-treated cells. The imbalance in the cycle of fusion and fission was also remarkably restored by schisandrin. In summary, this study provides novel mechanisms for the protective effect of schisandrin on mitochondria-related functions.

Mitophagy: An Emerging Target in Ocular Pathology

Mitochondrial function is essential for the viability of aerobic eukaryotic cells, as mitochondria provide energy through the generation of adenosine triphosphate (ATP), regulate cellular metabolism, provide redox balancing, participate in immune signaling, and can initiate apoptosis. Mitochondria are dynamic organelles that participate in a cyclical and ongoing process of regeneration and autophagy (clearance), termed mitophagy specifically for mitochondrial (macro)autophagy. An imbalance in mitochondrial function toward mitochondrial dysfunction can be catastrophic for cells and has been characterized in several common ophthalmic diseases. In this article, we review mitochondrial homeostasis in detail, focusing on the balance of mitochondrial dynamics including the processes of fission and fusion, and provide a description of the mechanisms involved in mitophagy. Furthermore, this article reviews investigations of ocular diseases with impaired mitophagy, including Fuchs endothelial corneal dystrophy, primary open-angle glaucoma, diabetic retinopathy, and age-related macular degeneration, as well as several primary mitochondrial diseases with ocular phenotypes that display impaired mitophagy, including mitochondrial encephalopathy lactic acidosis stroke, Leber hereditary optic neuropathy, and chronic progressive external ophthalmoplegia. The results of various studies using cell culture, animal, and human tissue models are presented and reflect a growing awareness of mitophagy impairment as an important feature of ophthalmic disease pathology. As this review indicates, it is imperative that mitophagy be investigated as a targetable mechanism in developing therapies for ocular diseases characterized by oxidative stress and mitochondrial dysfunction.

Can N-3 polyunsaturated fatty acids be considered a potential adjuvant therapy for COVID-19-associated cardiovascular complications?

Coronavirus disease 2019 (COVID-19), caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), has currently led to a global pandemic with millions of confirmed and increasing cases around the world. The novel SARS-CoV-2 not only affects the lungs causing severe acute respiratory dysfunction but also leads to significant dysfunction in multiple organs and physiological systems including the cardiovascular system. A plethora of studies have shown the viral infection triggers an exaggerated immune response, hypercoagulation and oxidative stress, which contribute significantly to poor cardiovascular outcomes observed in COVID-19 patients. To date, there are no approved vaccines or therapies for COVID-19. Accordingly, cardiovascular protective and supportive therapies are urgent and necessary to the overall prognosis of COVID-19 patients. Accumulating literature has demonstrated the beneficial effects of n-3 polyunsaturated fatty acids (n-3 PUFA) toward the cardiovascular system, which include ameliorating uncontrolled inflammatory reactions, reduced oxidative stress and mitigating coagulopathy. Moreover, it has been demonstrated the n-3 PUFAs, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are precursors to a group of potent bioactive lipid mediators, generated endogenously, which mediate many of the beneficial effects attributed to their parent compounds. Considering the favorable safety profile for n-3 PUFAs and their metabolites, it is reasonable to consider n-3 PUFAs as potential adjuvant therapies for the clinical management of COVID-19 patients. In this article, we provide an overview of the pathogenesis of cardiovascular complications secondary to COVID-19 and focus on the mechanisms that may contribute to the likely benefits of n-3 PUFAs and their metabolites.

Elevated Lactate by High-Intensity Interval Training Regulates the Hippocampal BDNF Expression and the Mitochondrial Quality Control System

High-intensity interval training (HIIT) is reported to be beneficial to brain-derived neurotrophic factor (BDNF) biosynthesis. A key element in this may be the existence of lactate, the most obvious metabolic product of exercise. In vivo, this study investigated the effects of a 6-week HIIT on the peripheral and central lactate changes, mitochondrial quality control system, mitochondrial function and BDNF expression in mouse hippocampus. In vitro, primary cultured mice hippocampal cells were used to investigate the role and the underlying mechanisms of lactate in promoting mitochondrial function during HIIT. In vivo studies, we firstly reported that HIIT can potentiate mitochondrial function [boost some of the mitochondrial oxidative phosphorylation (OXPHOS) genes expression and ATP production], stimulate BDNF expression in mouse hippocampus along with regulating the mitochondrial quality control system in terms of promoting mitochondrial fusion and biogenesis, and suppressing mitochondrial fission. In parallel to this, the peripheral and central lactate levels elevated immediately after the training. In vitro study, our results revealed that lactate was in charge of regulating mitochondrial quality control system for mitochondrial function and thus may contribute to BDNF expression. In conclusion, our study provided the mitochondrial mechanisms of HIIT enhancing brain function, and that lactate itself can mediate the HIIT effect on mitochondrial quality control system in the hippocampus.

Therapeutic Potential of Mesenchymal Stem Cells in a Pre-Clinical Model of Diabetic Kidney Disease and Obesity

Diabetic kidney disease (DKD) is a worldwide microvascular complication of type 2 diabetes mellitus (T2DM). From several pathological mechanisms involved in T2DM-DKD, we focused on mitochondria damage induced by hyperglycemia-driven reactive species oxygen (ROS) accumulation and verified whether mesenchymal stem cells (MSCs) anti-oxidative, anti-apoptotic, autophagy modulation, and pro-mitochondria homeostasis therapeutic potential curtailed T2DM-DKD progression. For that purpose, we grew immortalized glomerular mesangial cells (GMCs) in hyper glucose media containing hydrogen peroxide. MSCs prevented these cells from apoptosis-induced cell death, ROS accumulation, and mitochondria membrane potential impairment. Additionally, MSCs recovered GMCs' biogenesis and mitophagy-related gene expression that were downregulated by stress media. In BTBRob/ob mice, a robust model of T2DM-DKD and obesity, MSC therapy (1 × 106 cells, two doses 4-weeks apart, intra-peritoneal route) led to functional and structural kidney improvement in a time-dependent manner. Therefore, MSC-treated animals exhibited lower levels of urinary albumin-to-creatinine ratio, less mesangial expansion, higher number of podocytes, up-regulation of mitochondria-related survival genes, a decrease in autophagy hyper-activation, and a potential decrease in cleaved-caspase 3 expression. Collectively, these novel findings have important implications for the advancement of cell therapy and provide insights into cellular and molecular mechanisms of MSC-based therapy in T2DM-DKD setting.

Pathophysiology linking depression and type 2 diabetes: Psychotherapy, physical exercise, and fecal microbiome transplantation as damage control

Diabetes increases the likelihood of developing depression and vice versa. Research on this bidirectional association has somewhat managed to delineate the interplay among implicated physiological processes. Still, further exploration is required in this context. This review addresses the comorbidity by investigating suspected common pathophysiological mechanisms. One such factor is psychological stress which disturbs the hypothalamic-pituitary-adrenal axis causing hormonal imbalance. This includes elevated cortisol levels, a common biomarker of both depression and diabetes. Disrupted insulin signaling drives the hampered neurotransmission of serotonin, dopamine, and norepinephrine. Also, adipokine hormones such as adiponectin, leptin, and resistin and the orexigenic hormone, ghrelin, are involved in both depression and T2DM. This disarray further interferes with physiological processes encompassing sleep, the gut-brain axis, metabolism, and mood stability. Behavioral coping mechanisms, such as unhealthy eating, mediate disturbed glucose homeostasis, and neuroinflammation. This is intricately linked to oxidative stress, redox imbalance, and mitochondrial dysfunction. However, interventions such as psychotherapy, physical exercise, fecal microbiota transplantation, and insulin-sensitizing agents can help to manage the distressing condition. The possibility of glucagon-like peptide 1 possessing a therapeutic role has also been discussed. Nonetheless, there stands an urgent need for unraveling new correlating targets and biological markers for efficient treatment.

Mitochondria-Targeted Small Peptide, SS31 Ameliorates Diabetes Induced Mitochondrial Dynamics in Male TallyHO/JngJ Mice

The escalating burden of type 2 diabetes (T2D) and its related complications has become a major public health challenge worldwide. Substantial evidence indicates that T2D is one of the culprits for the high prevalence of Alzheimer's disease (AD) in diabetic subjects. This study aimed to investigate the possible mitochondrial alterations in the pancreas induced by hyperglycemia in diabetes. We used a diabetic TallyHO/JngJ (TH) and non-diabetic, SWR/J mice strains. The diabetic and non-diabetic status in animals was assessed by performing intraperitoneal glucose tolerance test at four time points, i.e., 4, 8, 16, and 24 weeks of age. We divided 24-week-old TH and SWR/J mice into 3 groups: controls, diabetic TH mice, and diabetic TH mice treated with SS31 peptide. After the treatment of male TH mice with SS31, intraperitoneally, for 4 weeks, we studied mitochondrial dynamics, biogenesis, and function. The mRNA and protein expression levels of mitochondrial proteins were evaluated using qPCR and immunoblot analysis. The diabetic mice after 24 weeks of age showed overt pancreatic injury as demonstrated by disintegration and atrophy of β cells with vacuolization and reduced islet size. Mitochondrial dysfunction was observed in TH mice, as evidenced by significantly elevated H2O2 production, lipid peroxidation, and reduced ATP production. Furthermore, mRNA expression and immunoblot analysis of mitochondrial dynamics genes were significantly affected in diabetic mice, compared with controls. However, treatment of animals with SS31 reduced mitochondrial dysfunction and restored most of the mitochondrial functions and mitochondrial dynamics processes to near normal in TH mice. In conclusion, mitochondrial dysfunction is established as one of the molecular events that occur in the pathophysiology of T2D. Further, SS31 treatment may confer protection against the mitochondrial alterations induced by hyperglycemia in diabetic TallyHO/JngJ mice.

Human ClpP protease, a promising therapy target for diseases of mitochondrial dysfunction

Human caseinolytic protease P (HsClpP), an ATP-dependent unfolding peptidase protein in the mitochondrial matrix, controls protein quality, regulates mitochondrial metabolism, and maintains the integrity and enzyme activity of the mitochondrial respiratory chain (RC). Studies show that abnormalities in HsClpP lead to mitochondrial dysfunction and various human diseases. In this review, we provide a comprehensive overview of the structure and biological function of HsClpP, and the involvement of its dysexpression or mutation in mitochondria for a panel of important human diseases. We also summarize the structural types and binding modes of known HsClpP modulators. Finally, we discuss the challenges and future directions of HsClpP targeting as promising approach for the treatment of human diseases of mitochondrial origin.

Skeletal muscle proteins important for work capacity are altered with type 2 diabetes - Effect of 10-20-30 training

The study examined whether men with type 2 diabetes exhibit lower expression of muscle proteins important for exercise capacity, and whether exercise training promotes adaptations in these proteins. In a cross-sectional and longitudinal study, conducted at the University of Copenhagen. Twelve men with type 2 diabetes (T2D) were compared to eleven nondiabetes counterparts (ND) matched for age and body composition (body fat percentage). T2D underwent 10 weeks of high-intensity interval exercise training (10-20-30 training). T2D had lower expression of SOD1 (-62%; p < 0.001) and ETC complex V (-34%; p = 0.003), along with higher expression of ETC complex IV (+66%; p = 0.007), MFN2 (+62%; p = 0.001), and DRP1 (+30%; p = 0.028) compared to ND. T2D had higher (p < 0.001) expression of Na⁺ /K⁺ α1 (+98%), α2 (+114%), and NHE1 (+144%) than ND. In T2D, training increased exercise capacity (+9%; p < 0.001) as well as expression of SOD2 (+44%; p = 0.029), ETC complex II (+25%; p = 0.035), III (+52%; p = 0.041), IV (+23%; p = 0.005), and V (+21%; p = 0.035), CS activity (+32%; p = 0.006) as well as Na⁺ /K⁺ α1 (+24%; p = 0.034), Kir6.2 (+36%; p = 0.029), and MCT1 (+20%; p = 0.007). Men with type 2 diabetes exhibited altered expression of a multitude of skeletal muscle proteins important for exercise capacity. Ten weeks of 10-20-30 training upregulated expression of muscle proteins regulating antioxidant defense, mitochondrial function, and ion handling while enhancing exercise capacity in men with type 2 diabetes.

Huidouba Improved Podocyte Injury by Down-Regulating Nox4 Expression in Rats With Diabetic Nephropathy

Diabetic nephropathy (DN), as the most common microvascular complication of diabetes mellitus (DM), has become one of the leading causes of end-stage renal disease (ESRD). Numerous studies have indicated that podocyte loss plays an important role in the development of DN and can even cause proteinuria in the early stage of DN. In the study, we found that Huidouba (HDB) significantly decreased the level of fasting blood glucose (FBG), the ratio of microalbumin to urine creatine (mAlb/Ucr), serum creatine (Scr), serum urea nitrogen (BUN), and malondialdehyde (MDA) in the kidney and downregulated the expression of Nox4 predominantly located in glomerular tissue while upregulating nephrin and WT1 expression in DN rats. In addition, HDB could also reduce podocyte damage and glomerular basement membrane (GBM) pathologic changes, as shown by transmission electron microscopy (TEM). In vitro study showed that HDB could inhibit high glucose (HG)-induced Reactive Oxygen Species (ROS) production and protect against podocyte apoptosis by downregulated Nox4 expression in podocytes. These results may provide a scientific basis for developing HDB as a potential folk medicine for the treatment of DN.

Diabetes diminishes a typical metabolite of litchi pericarp oligomeric procyanidins (LPOPC) in urine mediated by imbalanced gut microbiota

Animal studies and clinical trials have shown that dietary polyphenols and polyphenol-rich foods can reduce the risk of type 2 diabetes (T2D) and its complications, but how diabetes regulates the metabolism of polyphenol has not been fully elucidated. This study investigated the effects of diabetes on litchi pericarp oligomeric procyanidin (LPOPC) dynamic metabolism and its major static metabolites in urine. First, a high-fat and streptozotocin (STZ)-induced diabetic Sprague Dawley (SD) rat model was established. In the diabetic rat model, elevated fasting blood glucose, severely impaired glucose tolerance test, and increased reactive oxygen species (ROS) levels in serum and the liver were observed. Subsequently, 200 mg per kg body weight of LPOPC was administrated to control and diabetic SD rats, and the gastrointestinal tract was collected at 0.5 h, 1 h, 3 h, and 6 h. The results showed that the retention time of LPOPC was not changed in our diabetic rat model. However, the gut microbiota were significantly altered, with elevated Proteobacteria and Verrucomicrobia abundance in diabetic rats and decreased short chain fatty acid (SCFA)-producing bacteria. Interestingly, after one dose of 300 mg per kg body weight LPOPC, the total antioxidant capacity of urine in diabetic rats significantly decreased. We then tested the static metabolites of LPOPC, demonstrating that epicatechin had not changed in urine in diabetic rats, but that shikimic acid was significantly reduced in urine in diabetic rats. The changes in shikimic acid may be due to the alteration of gut microbiota and elevated ROS levels in serum.

Mitochondrial-induced Epigenetic Modifications: From Biology to Clinical Translation

Mitochondria are maternally inherited semi-autonomous organelles that play a central role in redox balance, energy metabolism, control of integrated stress responses, and cellular homeostasis. The molecular communication between mitochondria and the nucleus is intricate and bidirectional in nature. Though mitochondrial genome encodes for several key proteins involved in oxidative phosphorylation, several regulatory factors encoded by nuclear DNA are prominent contributors to mitochondrial biogenesis and function. The loss of synergy between this reciprocal control of anterograde (nuclear to mitochondrial) and retrograde (mitochondrial to nuclear) signaling, triggers epigenomic imbalance and affects mitochondrial function and global gene expressions. Recent expansions of our knowledge on mitochondrial epigenomics have offered novel perspectives for the study of several non-communicable diseases including cancer. As mitochondria are considered beacons for pharmacological interventions, new frontiers in targeted delivery approaches could provide opportunities for effective disease management and cure through reversible epigenetic reprogramming. This review focuses on recent progress in the area of mitochondrial-nuclear cross-talk and epigenetic regulation of mitochondrial DNA methylation, mitochondrial micro RNAs, and post-translational modification of mitochondrial nucleoid-associated proteins that hold major opportunities for targeted drug delivery and clinical translation.

Neuroprotective Effect of Syringic Acid by Modulation of Oxidative Stress and Mitochondrial Mass in Diabetic Rats

Diabetes is a metabolic complaint associated with oxidative stress and dysfunction of mitochondria. One of the most common complications of diabetes mellitus is neuropathy. This study evaluated the possible neuroprotective effects of syringic acid (SYR), a natural polyphenolic derivative of benzoic acid, on oxidative damage and mitochondria in the brain, spinal cord, and sciatic nerve of streptozotocin-induced diabetic rats. Different groups of rats including normal control, diabetics (induced by streptozotocin), diabetic groups treated with 25, 50, and 100 mg/kg of SYR, and non-diabetic group treated with only 100 mg/kg of SYR were treated for 6 weeks. Learning and memory function, physical coordination, and acetylcholinesterase (AChE) and antioxidant indexes, as well as mRNA expression of mitochondrial biogenesis, were measured in the brain, spinal cord, and sciatic nerves. Diabetic rats treated with 100 mg/kg SYR exhibited significantly improved learning, memory, and movement deficiency (p < 0.05). SYR 100 mg/kg also significantly upregulated the brain mRNA expression of PGC-1α and NRF-1, the key regulators of energy metabolism, oxidative phosphorylation, and mitochondrial biogenesis. In addition, SYR 100 mg/kg and SYR 50 mg/kg increased the mtDNA/nDNA ratio in the brain and the spinal cord of diabetic rats, respectively (p < 0.05). SYR attenuated the lipid peroxidation in all the tissues, but not significant effects were observed on GSH, AChE, catalase, and superoxide dismutase activity. In all the tests, nonsignificant differences were observed between the control and SYR 100 mg/kg groups. Moreover, SYR reduced inflammation and demyelination in sciatic nerves. This is the first study to reveal the regulation of mitochondrial biogenesis and energy metabolism by SYR, beyond its antioxidant role in the diabetic rats' brain and spinal tissues.

Interaction between magnesium and methylglyoxal in diabetic polyneuropathy and neuronal models

Objective

The lack of effective treatments against diabetic sensorimotor polyneuropathy demands the search for new strategies to combat or prevent the condition. Because reduced magnesium and increased methylglyoxal levels have been implicated in the development of both type 2 diabetes and neuropathic pain, we aimed to assess the putative interplay of both molecules with diabetic sensorimotor polyneuropathy.

Methods

In a cross-sectional study, serum magnesium and plasma methylglyoxal levels were measured in recently diagnosed type 2 diabetes patients with (n = 51) and without (n = 184) diabetic sensorimotor polyneuropathy from the German Diabetes Study baseline cohort. Peripheral nerve function was assessed using nerve conduction velocity and quantitative sensory testing. Human neuroblastoma cells (SH-SY5Y) and mouse dorsal root ganglia cells were used to characterize the neurotoxic effect of methylglyoxal and/or neuroprotective effect of magnesium.

Results

Here, we demonstrate that serum magnesium concentration was reduced in recently diagnosed type 2 diabetes patients with diabetic sensorimotor polyneuropathy and inversely associated with plasma methylglyoxal concentration. Magnesium, methylglyoxal, and, importantly, their interaction were strongly interrelated with methylglyoxal-dependent nerve dysfunction and were predictive of changes in nerve function. Magnesium supplementation prevented methylglyoxal neurotoxicity in differentiated SH-SY5Y neuron-like cells due to reduction of intracellular methylglyoxal formation, while supplementation with the divalent cations zinc and manganese had no effect on methylglyoxal neurotoxicity. Furthermore, the downregulation of mitochondrial activity in mouse dorsal root ganglia cells and consequently the enrichment of triosephosphates, the primary source of methylglyoxal, resulted in neurite degeneration, which was completely prevented through magnesium supplementation.

Conclusions

These multifaceted findings reveal a novel putative pathophysiological pathway of hypomagnesemia-induced carbonyl stress leading to neuronal damage and merit further investigations not only for diabetic sensorimotor polyneuropathy but also other neurodegenerative diseases associated with magnesium deficiency and impaired energy metabolism.

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Magnesium and methylglyoxal levels were inversely associated in individuals with type 2 diabetes and distal sensorimotor polyneuropathy.

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Magnesium, methylglyoxal, and their interaction were associated with methylglyoxal-dependent nerve dysfunction.

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Under experimental conditions, magnesium supplementation prevented methylglyoxal-mediated neurotoxicity.

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Magnesium downregulates intracellular methylglyoxal production.

Role of mitochondria in pathogenesis of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is global health problem. An estimated 425 million people in the world had diabetes in 2017. It is a major cause of morbidity and mortality worldwide. Although, pathogenesis of T2DM and its complications have been focus of medical research for long, much remains to be learned. A better understanding of molecular pathogenesis is essential for more effective preventive and therapeutic interventions. Role of mitochondria in pathogenesis of metabolic problems such as obesity, metabolic syndrome, and T2DM is the focus of many recent research studies. Mitochondrial dysfunction contributes to the oxidative stress and systemic inflammation leading to insulin resistance (IR). Mitochondria are also essential for pancreatic beta cell insulin secretion. Hence, mitochondria are important players in the pathogenesis of T2DM. In this article, pathogenesis of T2DM is examined from a mitochondrial perspective.

Pharmacological inhibition of mitochondrial fission attenuates cardiac ischemia-reperfusion injury in pre-diabetic rats

An increase in the number of fragmented mitochondria contributes to the pathogenesis of ischemia-reperfusion (I/R) injury. Also, mitochondrial fission has shown an increase in obese condition. However, the cardioprotective roles of a mitochondrial fission inhibitor in obesity with cardiac I/R injury are unclear. We hypothesized that a fission inhibitor (Mdivi-1) reduces cardiac dysfunction during I/R injury in pre-diabetic rats. Male Wistar rats (n = 40) were received a high-fat diet for 12 weeks to induce prediabetes. Then, rats underwent a 30-min coronary artery ligation was performed followed by reperfusion for 120 min. These I/R rats were given either: (1) vehicle or Mdivi-1 treatment at 3 time points relative to onset of ischemia: (2) pre-ischemia; (3) during ischemia; and (4) at onset of reperfusion. Cardiac function, myocardial infarct size, mitochondrial function and dynamic balance were determined. Interestingly, Mdivi-1 given at any time points effectively attenuated mitochondrial reactive oxygen species production, depolarization, swelling, and dynamic imbalance, resulting in reduced arrhythmias, myocardial cell death, infarct size and enhanced cardiac performance during I/R injury in pre-diabetic rats. Taken together, inhibition of mitochondrial fission effectively protected the heart against cardiac I/R injury regardless of the time of administration in pre-diabetic rats.

D-allulose provides cardioprotective effect by attenuating cardiac mitochondrial dysfunction in obesity-induced insulin-resistant rats

PURPOSE

Obesity-induced insulin resistant is associated with cardiovascular diseases via impairing cardiac mitochondria. Recently, D-allulose could protect β-islets and improve insulin resistance. However, the effects of D-allulose on the heart and cardiac mitochondrial function under obesity-induced insulin-resistant condition has not been investigated. In this study, we aimed to investigate the effects of D-allulose on metabolic parameters, cardiac function, heart rate variability (HRV), cardiac mitochondrial function, and apoptosis in the heart of obesity-induced insulin-resistant rats induced by chronic high fat diet consumption.

METHODS

Male Wistar rats (n = 24) received a normal fat diet (ND) or high fat diet (HFD) for 12 weeks. Then, HFD group was randomly divided into three subgroups to receive (1) HFD with distilled water, (2) HFD with 3% D-allulose 1.9 g/ kg·BW/ day (HFR), and (3) HFD with metformin 300 mg/kg·BW/ day (HFM) by diluted in drinking water daily for 12 weeks. At week 24, proposed study parameters were investigated.

RESULTS

Chronic HFD consumption induced obesity-induced insulin resistant in rats and high fat diet impaired cardiac function and HRV. HFR rats had improved insulin sensitivity as indicated by decreasing HOMA index, plasma insulin, whereas HFM decreased body weight, visceral fat, plasma cholesterol, and plasma LDL. HFR and HFM provided similar efficacy in improving HRV and attenuating cardiac mitochondrial dysfunction, leading to improved cardiac function.

CONCLUSIONS

Even though this is the first investigation of the D-allulose impact on the heart with a relatively small sample size, it clearly demonstrated a beneficial effect on the heart. D-allulose exerted a therapeutic effect on metabolic parameters except for body weight and lipid profiles and provided cardioprotective effects similar to metformin via attenuating cardiac mitochondrial function in obesity-induced insulin-resistant rats.

Mechanisms of muscle insulin resistance and the cross-talk with liver and adipose tissue

Insulin resistance is a metabolic disorder affecting multiple tissues and is a precursor event to type 2 diabetes (T2D). As T2D affects over 425 million people globally, there is an imperative need for research into insulin resistance to better understand the underlying mechanisms. The proposed mechanisms involved in insulin resistance include both whole body aspects, such as inflammation and metabolic inflexibility; as well as cellular phenomena, such as lipotoxicity, ER stress, and mitochondrial dysfunction. Despite numerous studies emphasizing the role of lipotoxicity in the pathogenesis of insulin resistance, an understanding of the interplay between tissues and these proposed mechanisms is still emerging. Furthermore, the tissue-specific and unique responses each of the three major insulin target tissues and how each interconnect to regulate the whole body insulin response has become a new priority in metabolic research. With an emphasis on skeletal muscle, this mini-review highlights key similarities and differences in insulin signaling and resistance between different target-tissues, and presents the latest findings related to how these tissues communicate to control whole body metabolism.

Modulation of redox and insulin signaling underlie the anti-hyperglycemic and antioxidant effects of diphenyl diselenide in zebrafish

The organic selenium compound diphenyl diselenide (DD) has been recognized as an antioxidant and neuroprotective agent, exerting an anti-hyperglycemic effect in experimental models of diabetes. However, the precise mechanisms involved in the protection are unclear. Using the zebrafish (Danio rerio) as a model organism, here we investigated biomarkers underlying the protective effects of DD against hyperglycemia, targeting in a transcriptional approach the redox and insulin-signaling pathway. Fish were fed on a diet containing DD (3 mg/kg) for 74 days. In the last 14 days, they were exposed to a 111 mM glucose solution to induce a hyperglycemic state. DD reduced blood glucose levels as well as normalized the brain mRNA transcription of four insulin receptors-coding genes (Insra1, Insra2, Insrb1, Insrb2), which were down-regulated by glucose. DD alone caused an up-regulation of relative mRNA transcription in both Insra receptors and glucose transporter 3 genes. DD counteracted hyperglycemia-induced lipid peroxidation, protein and thiol depletion. Along with the decreased activity of antioxidant enzymes SOD and GPx, the brain of hyperglycemic fish presented a reduction in mRNA transcription of FoxO3A, FoxO3B, Nrf2, GPx3A, SOD1, and SOD2 genes. Besides normalizing the transcriptional levels, DD caused an up-regulation of relative mRNAs that encode Nrf2, FoxO1A, FOXO3A, GPx4A, PTP1B, AKT and SelP. Collectively, our findings suggest that the antioxidant and anti-hyperglycemic actions of DD in a zebrafish diabetes model are likely associated with the regulation of the oxidative stress resistance and the insulin-signaling pathway and that could be related to the modulation at mRNA level of two important transcription factors, Nrf2 and FoxO.

Hexavalent chromium induces mitochondrial dynamics disorder in rat liver by inhibiting AMPK/PGC-1α signaling pathway

Occupational exposure to hexavalent chromium (Cr(VI)) can cause cytotoxicity and carcinogenicity. In this study, we established a liver injury model in rats via intraperitoneal injection of potassium dichromate (0, 2, 4, and 6 mg/kg body weight) for 35 d to investigate the mechanism of Cr(VI)-induced liver injury. We found that Cr(VI) induced hepatic histopathological lesions, oxidative stress, and apoptosis and reduced the expression of mitochondrial-related regulatory factors such as adenosine 5'-monophosphate-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) in a dose-dependent manner. Furthermore, Cr(VI) promoted mitochondrial division and inhibited fusion, leading to increased expression of caspase-3 and production of mitochondrial reactive oxygen species. Our study demonstrates that long-term exposure to Cr(VI) induces mitochondrial dynamics disorder by inhibiting AMPK/PGC-1α signaling pathway in rat liver.

Mitochondria-derived methylmalonic acid, a surrogate biomarker of mitochondrial dysfunction and oxidative stress, predicts all-cause and cardiovascular mortality in the general population

BACKGROUND

Inherited methylmalonic acidemia is characterized by mitochondrial dysfunction, oxidative stress, and damage of mitochondria-rich organs in children. It is unclear whether methylmalonic acid (MMA) is related to poor prognosis in adults. The study aims to investigate the associations of MMA with all-cause and cause-specific mortality in the general population.

METHODS

Overall, 23,437 adults from the US National Health and Nutrition Examination Survey (NHANES) were enrolled. NHANES 1999-2004 and 2011-2014 were separately used as primary and validation subsets (median follow-up 13.5 and 2.8 years, respectively). Circulating MMA was measured with gas chromatography/mass spectrophotometry. Hazard ratios (HR) were estimated using weighted Cox regression models.

RESULTS

During 163,632 person-years of follow-up in NHANES 1999-2004, 3019 deaths occurred. Compared with participants with MMA <120 nmol/L, those with MMA≥250 nmol/L had increased all-cause and cardiovascular mortality in the multivariable-adjusted model [HR(95%CI), 1.62 (1.43-1.84) and 1.66 (1.22-2.27), respectively]. The association was especially significant among participants with normal cobalamin. MMA remained an independent predictor of all-cause mortality occurring whether within 5-year, 5-10 years, or beyond 10-year of follow-up (each p for trend≤0.007). That association was repeatable in NHANES 2011-2014. Moreover, baseline MMA improved reclassification for 10-year mortality in patients with cardiovascular disease (net reclassification index 0.239, integrated discrimination improvement 0.022), overmatched established cardiovascular biomarkers C-reactive protein or homocysteine.

CONCLUSIONS

Circulating level of mitochondrial-derived MMA is strongly associated with elevated all-cause and cardiovascular mortality. Our results support MMA as a surrogate biomarker of mitochondrial dysfunction to predict poor prognosis in adults. The biological mechanisms under cardiovascular disease warrant further investigation.

HIF-1α ameliorates tubular injury in diabetic nephropathy via HO-1-mediated control of mitochondrial dynamics

Objectives

In diabetic nephropathy (DN), hypoxia‐inducible factor‐1α (HIF‐1α) activation in tubular cells plays an important protective role against kidney injury. The effects may occur via the target genes of HIF‐1α, such as haem oxygenase‐1 (HO‐1), but the exact mechanisms are incompletely understood.

Materials and methods

Mice with proximal tubule‐specific knockout of HIF‐1α (PT‐HIF‐1α^−/− mice) were generated, and diabetes was induced in these mice by streptozotocin (STZ) injection. In addition, to mimic a hypoxic state, cobaltous chloride (CoCl₂) was applied to HK‐2 cells.

Results

Our study first verified that conditional knockout of HIF‐1α worsened tubular injury in DN; additionally, aggravated kidney dysfunction, renal histopathological alterations, mitochondrial fragmentation, ROS accumulation and apoptosis were observed in diabetic PT‐HIF‐1α^−/− mice. In vitro study showed that compared to control group, HK‐2 cells cultured under hypoxic ambiance displayed increased mitochondrial fragmentation, ROS production, mitochondrial membrane potential loss and apoptosis. These increases were reversed by overexpression of HIF‐1α or treatment with a HO‐1 agonist. Importantly, cotreatment with a HIF‐1α inhibitor and a HO‐1 agonist rescued the HK‐2 cells from the negative impacts of the HIF‐1α inhibitor.

Conclusions

These data revealed that HIF‐1α exerted a protective effect against tubular injury in DN, which could be mediated via modulation of mitochondrial dynamics through HO‐1 upregulation.

Molecular insights of NADPH oxidases and its pathological consequences

Reactive oxygen species (ROS), formed by the partial reduction of oxygen, were for a long time considered to be a byproduct of cellular metabolism. Since, increase in cellular levels of ROS results in oxidative stress leading to damage of nucleic acids, proteins, and lipids resulting in numerous pathological conditions; ROS was considered a bane for aerobic species. Hence, the discovery of NADPH oxidases (NOX), an enzyme family that specifically generates ROS as its prime product came as a surprise to redox biologists. NOX family proteins participate in various cellular functions including cell proliferation and differentiation, regulation of genes and protein expression, apoptosis, and host defence immunological response. Balanced expression and activation of NOX with subsequent production of ROS are critically important to regulate various genes and proteins to maintain homeostasis of the cell. However, dysregulation of NOX activation leading to enhanced ROS levels is associated with various pathophysiologies including diabetes, cardiovascular diseases, neurodegenerative diseases, ageing, atherosclerosis, and cancer. Although our current knowledge on NOX signifies its importance in the normal functioning of various cellular pathways; yet the choice of ROS producing enzymes which can tip the scale from homeostasis toward damage, as mediators of biological functions remain an oddity. Though the role of NOX in maintaining normal cellular functions is now deemed essential, yet its dysregulation leading to catastrophic events cannot be denied. Hence, this review focuses on the involvement of NOX enzymes in various pathological conditions imploring them as possible targets for therapies. SIGNIFICANCE OF THE STUDY: The NOXs are multi-subunit enzymes that generate ROS as a prime product. NOX generated ROS are usually regulated by various molecular factors and play a vital role in different physiological processes. The dysregulation of NOX activity is associated with pathological consequences. Recently, the dynamic proximity of NOX enzymes with different molecular signatures of pathologies has been studied extensively. It is essential to identify the precise role of NOX machinery in its niche during the progression of pathology. Although inhibition of NOX could be a promising approach for therapeutic interventions, it is critical to expand the current understanding of NOX's dynamicity and shed light on their molecular partners and regulators.

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.

Diabetes Mellitus, Mitochondrial Dysfunction and Ca2+-Dependent Permeability Transition Pore

Diabetes mellitus is one of the most common metabolic diseases in the developed world, and is associated either with the impaired secretion of insulin or with the resistance of cells to the actions of this hormone (type I and type II diabetes, respectively). In both cases, a common pathological change is an increase in blood glucose-hyperglycemia, which eventually can lead to serious damage to the organs and tissues of the organism. Mitochondria are one of the main targets of diabetes at the intracellular level. This review is dedicated to the analysis of recent data regarding the role of mitochondrial dysfunction in the development of diabetes mellitus. Specific areas of focus include the involvement of mitochondrial calcium transport systems and a pathophysiological phenomenon called the permeability transition pore in the pathogenesis of diabetes mellitus. The important contribution of these systems and their potential relevance as therapeutic targets in the pathology are discussed.

Tunicamycin-Induced Endoplasmic Reticulum Stress Mediates Mitochondrial Dysfunction in Human Adipocytes

CONTEXT

Dysfunctional endoplasmic reticulum (ER) and mitochondria are known to contribute to the pathology of metabolic disease. This damage may occur, in part, as a consequence of ER-mitochondria cross-talk in conditions of nutrient excess such as obesity. To date, insight into this dynamic relationship has not been characterized in adipose tissue. Therefore, this study investigated whether ER stress contributes to the development of mitochondrial inefficiency in human adipocytes from lean and obese participants.

METHODS

Human differentiated adipocytes from Chub-S7 cell line and primary abdominal subcutaneous adipocytes from lean and obese participants were treated with tunicamycin to induce ER stress. Key parameters of mitochondrial function were assessed, including mitochondrial respiration, membrane potential (MMP), and dynamics.

RESULTS

ER stress led to increased respiratory capacity in a model adipocyte system (Chub-S7 adipocytes) in a concentration and time dependent manner (24 h: 23%↑; 48 h: 68%↑, P < 0.001; 72 h: 136%↑, P < 0.001). This corresponded with mitochondrial inefficiency and diminished MMP, highlighting the formation of dysfunctional mitochondria. Morphological analysis revealed reorganization of mitochondrial network, specifically mitochondrial fragmentation. Furthermore, p-DRP1, a key protein in fission, significantly increased (P < 0.001). Additionally, adipocytes from obese subjects displayed lower basal respiration (49%↓, P < 0.01) and were unresponsive to tunicamycin in contrast to their lean counterparts, demonstrating inefficient mitochondrial oxidative capacity.

CONCLUSION

These human data suggest that adipocyte mitochondrial inefficiency is driven by ER stress and exacerbated in obesity. Nutrient excess-induced ER stress leads to mitochondrial dysfunction that may therefore shift lipid deposition ectopically and thus have further implications on the development of related metabolic disorders.

Proteomic analysis of liver mitochondria of db/db mice treated with grape seed procyanidin B2

Hepatic damage has been recognized as one of the major complications in diabetes mellitus. Our previous studies have verified that grape seed procyanidin B2 (GSPB2) played a protective effect on hepatic damage of diabetes. We used isobaric tag for relative and absolute quantitation proteomics here to identify the alterant mitochondrial protein profile in diabetic liver and to seek the protective targets of GSPB2. Proteomics found that 171 proteins were upregulated or downregulated in the liver mitochondria of diabetic group compared to the control group. Of these proteins, 61 were normalized after GSPB2 treatment. These back-regulated proteins are involved in the process of fatty acid oxidation, tricarboxylic acid cycle, oxidative phosphorylation, oxidative stress, and apoptosis. Some differentially expressed proteins were confirmed by western blotting. Our study might help to better understand the mechanism of mitochondrial dysfunction in diabetic liver damage, and provide novel targets for estimating the protective effects of GSPB2. PRACTICAL APPLICATIONS: Grape seed procyanidin B2 (GSPB2), a polyphenolic component found in red wine and grapes, has beneficial effects such as antioxidative stress, antiapoptosis, and cardiovascular protection. We used proteomics here to identify the differentially expressed mitochondrial proteins in diabetic liver after GSPB2 treatment and to seek the protective targets of GSPB2. We found that the differentially expressed proteins were involved in carbon metabolism, oxidative phosphorylation, fatty acid metabolism, citrate cycle, oxidative stress, and apoptosis. These proteins may play a key role in diabetic hepatic damage as functional proteins. Targeting these proteins including apply of GSPB2 could potentially lead to an effective treatment in the diabetic hepatic disease.