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During tissue injury events, the innate immune system responds immediately to alarms sent from the injured cells, and the adaptive immune system subsequently joins in the inflammatory reaction. The control mechanism of each immune reaction relies on the orchestration of different types of T cells and the activators, antigen-presenting cells, co-stimulatory molecules, and cytokines. Mitochondria are an intracellular signaling organelle and energy plant, which supply the energy requirement of the immune system and maintain the system activation with the production of reactive oxygen species (ROS). Extracellular mitochondria can elicit regenerative effects or serve as an activator of the immune cells to eliminate the damaged cells. Recent clarification of the cytosolic escape of mitochondrial DNA triggering innate immunity underscores the pivotal role of mitochondria in inflammation-related diseases. Human mesenchymal stem cells could transfer mitochondria through nanotubular structures to defective mitochondrial DNA cells. In recent years, mitochondrial therapy has shown promise in treating heart ischemic events, Parkinson's disease, and fulminating hepatitis. Taken together, these results emphasize the emerging role of mitochondria in immune-cell-mediated tissue regeneration and ageing.

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., (Copyright © 2020 Chang, Lin, Shen, Su, Chuang, Lin, Liou, Lin, Weng and Wang.)

Aims: Obesity-induced excessive visceral fat (VF) accumulation is associated with insulin resistance (IR), systemic oxidative stress, and chronic inflammation. As toll-like receptor 4 (TLR4) plays an important role in innate immunity, we herein investigate the effect of TLR4 knockout (T4KO) in a high-fat high-sucrose diet (HFD)-induced obesity mouse model. Results: C57BL6 wild-type (WT) and T4KO mice were fed with either control diet (CD) or HFD for 12 months, rendering four experimental groups: WT+CD, WT+HFD, T4KO+CD, and T4KO+HFD. Compared with WT+CD, WT+HFD demonstrated significant increase in VF accumulation, oxidative damage, M1/M2 macrophage ratio, chronic inflammation, and development of IR. Compared with WT+HFD, T4KO+HFD presented increased BW and body fat with higher subcutaneous fat (SF)/VF ratio, but lower body temperature, as well as decreased oxidative damage, M1/M2 macrophage ratio, chronic inflammation, and IR. Unlike WT+HFD, T4KO+HFD exhibited an increase in mitochondrial electron transport chain activity but a decrease of uncoupling protein 2 (UCP2) level. While T4KO hindered HFD-induced increasing mitochondrial oxygen consumption rate, a shift toward a higher extracellular acidification rate in VF was observed. Notably, T4KO inhibits HFD-induced mitochondrial translocation of nuclear factor of activated T cells 2 (NFATC2), which contributed to mitochondrial metabolic reprogramming. Both fat distribution shifting from VF to SF and mitochondrial metabolic reprogramming may alleviate systemic oxidative stress and chronic inflammation. Innovation and Conclusion: Abrogation of TLR4 contributes to reduction of oxidative stress through metabolic reprogramming of mitochondria in VF, mitigating obesity-induced IR. The study provides critical insight into associating innate immunity-mitochondria interplay with prevention of diabetes.

The advantage of using a cytoplasmic hybrid (cybrid) model to study the genetic effects of mitochondria is that the cells have the same nuclear genomic background. We previously demonstrated the independent role of mitochondria in the pathogenesis of insulin resistance (IR) and pro-inflammation in type 2 diabetes. In this study, we compared mitochondrial dynamics and related physiological functions between cybrid cells harboring diabetes-susceptible (B4) and diabetes-protective (D4) mitochondrial haplogroups, especially the responses before and after insulin stimulation. Cybrid B4 showed a more fragmented mitochondrial network, impaired mitochondrial biogenesis and bioenergetics, increased apoptosis and ineffective mitophagy and a low expression of fusion-related molecules. Upon insulin stimulation, increases in network formation, mitochondrial DNA (mtDNA) content, and ATP production were observed only in cybrid D4. Insulin promoted a pro-fusion dynamic status in both cybrids, but the trend was greater in cybrid D4. In cybrid B4, the imbalance of mitochondrial dynamics and impaired biogenesis and bioenergetics, and increased apoptosis were significantly improved in response to antioxidant treatment. We concluded that diabetes-susceptible mtDNA variants are themselves resistant to insulin., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Aims: Studies in skeletal muscle demonstrate a strong association of mitochondrial dysfunction with insulin resistance (IR). However, there is still a paucity of knowledge regarding the alteration of mitochondria in adipose tissue (AT) in the pathogenesis of IR in obesity. We investigated the mitochondrial biogenesis in visceral fat (VF) and subcutaneous fat (SF) in C57BL/6J mice fed a high-fat high-sucrose diet for 12 months., Results: Impairment of glucose tolerance and insulin sensitivity developed after 1 month of the diet and was associated with a prompt increase of VF. The VF adipocytes were larger than those in the SF and had increased expressions of HIF-1α and p-NFκB p65. However, the alteration of mitochondrial biogenesis did not occur in the early stage when increased intracellular reactive oxygen species (ROS), mitochondrial oxygen consumption rate, and mitochondrial ROS emerged at the 1st, 2nd and 2nd month, respectively. Until the 6th month, the VF had markedly increased mitochondrial DNA content and expression of PGC-1α, Tfam, ATP5A, and MnSOD. This increase of mitochondrial biogenesis was followed by a generalized decrease at the 12th month and the mitochondrial morphology altered markedly. In the late stage, although mitochondrial ROS decreased, the increased expression of 8-OHdG in VF continued., Innovation and Conclusion: These data suggest that IR and ROS production occur before the biphasic changes of mitochondrial biogenesis in AT, and the VF plays a more crucial role.

The mitochondrial 13513G>A (D393N) mutation in the ND5 subunit of the respiratory chain complex I was initially described in association with MELAS syndrome. Recent observations have linked this mutation to Leigh disease. We screened for the 13513G>A mutation in a cohort of 265 patients with Leigh and Leigh-like disease. The mutation was found in a total of 5 patients. An additional patient who had clinical presentation consistent with a Leigh-like phenotype but with a normal brain MRI was added to the cohort. None of an additional 88 patients meeting MELAS disease criteria, nor 56 patients with respiratory chain deficiency screened for the 13513G>A were found positive for the mutation. The most frequent clinical manifestations in our patients were hypotonia, ocular and cerebellar involvement. Low mutation heteroplasmy in the range of 20-40% was observed in all 6 patients. This observation is consistent with the previously reported low heteroplasmy of this mutation in some patients with the 13513G>A mutation and complex I deficiency. However, normal complex I activity was observed in two patients in our cohort. As most patients with Leigh-like disease and the 13513G>A mutation have been described with complex I deficiency, this report adds to the previously reported subset of patients with normal respiratory complex function. We conclude that in any patient with Leigh or Leigh-like disease, testing for the 13513G>A mutation is clinically relevant and low mutant loads in blood or muscle may be considered pathogenic, in the presence of normal respiratory chain enzyme activities.

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. [ABSTRACT FROM AUTHOR]

Reactive oxygen species (ROS) plays a crucial role in pathogenesis of insulin resistance (IR) and type 2 diabetes. In the United Kingdom, Prospective Diabetes Study and its 10-year post-trial monitoring, a beneficial effect of early optimisation of blood glucose control is clearly demonstrated. In this study, we investigated whether ROS scavenger N-acetylcysteine (NAC) and the time point of intervention can affect IR in a diet-induced obesity mouse model. Male C57B/L6 mice were fed chow diet (CD), high-fat high-sucrose diet (HFD), CD + NAC1-6 (NAC intervention 1st to 6th month), HFD + NAC1-6, and HFD + NAC3-6 (NAC intervention 3rd to 6th month) for a 6-month treatment course. HFD group showed significantly increased body weight (BW) and body fat, decreased motor activity (MA), impaired intraperitoneal glucose tolerance test (IPGTT), and insulin tolerance test (IPITT) throughout the study. HFD + NAC1-6, as compared with HFD group, had increased MA, improved IPGTT and IPITT since first month, followed by decreased BW and body fat. HFD + NAC3-6 group, although showed improved IPGTT and IPITT than HFD group, still had higher BW, decreased MA, and impaired IPGTT and IPITT as compared with HFD + NAC1-6 at the end of the study. NAC significantly increased MA, and ameliorated the HFD-induced mitochondrial and intracellular ROS expression, DNA and protein oxidative damage, and adipose tissue inflammation. We concluded that ROS scavenger can improve IR and chronic inflammation in diet-induced obesity mice. This action is likely better expressed through early intervention. The mechanism is probably through a virtuous circle of suppressed oxidative stress, and increased motor activity, which helps to reduce body fat. [ABSTRACT FROM AUTHOR]

Abstract: Aim: This study aims to elucidate the independent role of mitochondria in the pathogenesis of insulin resistance (IR). Methods: Cybrids derived from 143B osteosarcoma cell line and harboring the same nuclear DNA but different mitochondrial haplogroups were studied. Cybrid B4 (the major diabetes-susceptible haplogroup in Chinese population), cybrid D4 (the major diabetes-resistant haplogroup in Chinese population) and cybrid N9 (the diabetes-resistant haplogroup in Japanese population) were cultured in a medium containing 25mM glucose and stimulated with 0μM, 0.1μM, and 1.0μM insulin. We compared the insulin activation of PI3K–Akt (glucose uptake) and ERK–MAPK (pro-inflammation) signaling pathways, intracellular and mitochondrial oxidative stress (DCF and MitoSOX Red), and their responses to the antioxidant N-acetylcysteine (NAC). Results: Upon insulin treatment, the translocation of cytoplasmic GLUT1/GLUT4 to the cell membrane in cybrid D4 and N9 cells increased significantly, whereas the changes in B4 cells were not or less significant. On the contrary, the ratio of insulin-induced JNK and P38 to Akt phosphorylation was significantly greater in cybrid B4 cells than in cybrid D4 and N9 cells. The levels of DCF and MitoSOX Red, which are indicative of the oxidative stress, were significantly higher in the B4 cells in basal conditions and after insulin treatment. Following treatment with the antioxidant NAC, cybrid B4 cells showed significantly reduced insulin-induced phosphorylation of P38 and increased GLUT1/GLUT4 translocation to the cell membrane, suggesting that NAC may divert insulin signaling from pro-inflammation to glucose uptake. Conclusions: Mitochondria play an independent role in the pathogenesis of IR, possibly through altered production of intracellular ROS. [Copyright &y& Elsevier]

Abstract: Objective: The aim of this study was to examine the potential influence of insulin resistance (IR), hyperglycemia and oxidative stress on leucocytes mitochondrial DNA (mtDNA) content. Research design and method: One hundred twenty-five T2DM, 101 IFG and 70 normal subjects were enrolled in this study. The quantity of relative mtDNA content was measured by a real-time PCR and corrected by simultaneous measurement of the nuclear DNA. Parameters of lipid peroxidation, thiobarbituric acid reactive substance (TBARS), and total free thiols as antioxidative status were measured from serum samples. IR was assessed by homeostasis model assessment in the non-diabetic groups. Relationships among different variables were analyzed by general linear model correlation. Results: In all subjects, after correcting for age, sex and BMI, there were progressive increases of leucocyte mtDNA copy number, TBARS, and total reduced thiols with progressive dysregulation of glucose metabolism (normal vs. IFG vs. T2DM). Furthermore, correlation between mtDNA content and glucose dysregulation persisted after sequential correction for age, sex, BMI and TBARS. The independent predictor of mtDNA content by regression analysis was hyperglycemia. In non-diabetic group, influence of family history of diabetes on mtDNA content turned to non-significant after correcting for fasting plasma glucose (FPG). Correlation study revealed that mtDNA content was correlated with FPG (P < 0.001), but not IR. Conclusion: Our results indicate that hyperglycemia, not IR, is associated with an increase of leucocyte mtDNA copy number in cases of glucose dysregulation. [Copyright &y& Elsevier]

A letter to the editor is presented in response to the article "Neutrophil extracellular trap mitochondrial DNA and its autoantibody in systemic lupus erythematosus and a proof-of-concept trial of metformin," by H. Wang and colleagues in the 2015 issue.