Altered circulating mitochondrial DNA and increased inflammation in patients with diabetic retinopathy

Cell-Free DNA as a Biomarker in a Rodent Model of Chlorpyrifos Poisoning Causing Mitochondrial Dysfunction

INTRODUCTION

Organophosphates (OPs) are a major public health problem worldwide due to ease of access and high toxicity lacking effective biomarkers and treatment. Cholinergic agents such as OPs and carbamates are responsible for many pesticide-related deaths. While the inhibition of AChE is thought to be the main mechanism of injury, there are other important pathways that contribute to the overall toxicity of OPs such as mitochondrial dysfunction. An existing gap in OP poisoning are biomarkers to gauge severity and prognosis. Cell-free DNA (cfDNA) are novel biomarkers that have gained increased attention as a sensitive biomarker of disease with novel use in acute poisoning. This study investigates alterations in cerebral mitochondrial function in a rodent model of chlorpyrifos poisoning with the use of cfDNA as a potential biomarker.

METHODS

Twenty rodents were divided into two groups: Control (n = 10) and Chlorpyrifos (n = 10). Chlorpyrifos was administered through the venous femoral line with a Harvard Apparatus 11 Elite Syringe pump (Holliston, MA, USA) at 2 mg/kg. Animals were randomized to receive chlorpyrifos versus the vehicle (10% DMSO) for 60 min which would realistically present an acute exposure with continued absorption. At the end of the exposure (60 min), isolated mitochondria were measured for mitochondrial respiration along with measures of acetylcholinesterase activity, cfDNA, cytokines and western blot.

RESULTS

The Chlorpyrifos group showed a significant decrease in heart rate but no change in the blood pressure. There was a significant increase in bulk cfDNA concentrations and overall decrease in mitochondrial respiration from brain tissue obtained from animals in the Chlorpyrifos group when compared to the Control group with no difference in acetylcholinesterase activity. In addition, there was a significant increase in both IL-2 and IL-12 in the Chlorpyrifos group.

CONCLUSIONS

In our study, we found that the total cfDNA concentration may serve as a more accurate biomarker of OP exposure compared to acetylcholinesterase activity. In addition, there was an overall decrease in cerebral mitochondrial function in the Chlorpyrifos group when compared to the Control group.

The Diagnostic, Prognostic, and Therapeutic Potential of Cell-Free DNA with a Special Focus on COVID-19 and Other Viral Infections

Cell-free DNA (cfDNA) in human blood serum, urine, and other body fluids recently became a commonly used diagnostic marker associated with various pathologies. This is because cfDNA enables a much higher sensitivity than standard biochemical parameters. The presence of and/or increased level of cfDNA has been reported for various diseases, including viral infections, including COVID-19. Here, we review cfDNA in general, how it has been identified, where it can derive from, its molecular features, and mechanisms of release and clearance. General suitability of cfDNA for diagnostic questions, possible shortcomings and future directions are discussed, with a special focus on coronavirus infection.

Increased levels of circulating oxidized mitochondrial DNA contribute to chronic inflammation in metabolic syndrome, and MitoQ-based antioxidant therapy alleviates this DNA-induced inflammation

Here, the aim was to investigate the role of circulating oxidized mitochondrial DNA (ox-mtDNA) in metabolic syndrome (MetS)-associated chronic inflammation and evaluate the effect of Mito-Quinone (MitoQ)-based antioxidant therapy on inflammation. A total of 112 MetS patients and 111 healthy control individuals (HCs) were recruited. Peripheral blood was collected, and mononuclear cells (PBMCs) were separated. In a preclinical study, MitoQ, a mitochondrial-targeted antioxidant, was administered to Sprague-Dawley (SD) rats fed a high-fat diet (HFD). In vitro, H₂O₂- or MitoQ-treated HUVECs served as the oxidative or antioxidative cell models to detect the cell-free ox-mtDNA level. Plasma or cell-free ox-mtDNA levels were measured by qPCR. Additionally, THP-1 cells were incubated with plasma cell-free DNA (cfDNA) from MetS patients and HCs or cell-free ox-mtDNA to detect TLR9-NF-κB pathway activation. Plasma ox-mtDNA levels and TLR9 expression levels in PBMCs were increased in MetS patients. In vivo, HFD-fed rats showed elevated plasma ox-mtDNA and TLR9 expression levels in cardiac-residing immune cells, but MitoQ administration attenuated these increases. In vitro, a significant lower level of cell-free ox-mtDNA was detected in MitoQ-treated cells, compared with H₂O₂-treated cells. Coincubation of plasma cfDNA from MetS patients or cell-free ox-mtDNA and THP-1 cells increased TLR9-NF-κB p65 expression, and promoted IL-1β, IL-6 and IL-8 secretion in THP-1 cells. In conclusion, increased circulating ox-mtDNA contributes to chronic inflammation in MetS by activating the TLR9-NF-κB pathway. MitoQ-based antioxidant therapy effectively alleviates inflammation by reducing ox-mtDNA release.

The role of inflammation in immune system of diabetic retinopathy: Molecular mechanisms, pathogenetic role and therapeutic implications

Diabetic retinopathy is one of the most common complications of diabetes mellitus and the leading cause of low vision and blindness worldwide. Mounting evidence demonstrates that inflammation is a key mechanism driving diabetes-associated retinal disturbance, yet the pathophysiological process and molecular mechanisms of inflammation underlying diabetic retinopathy are not fully understood. Cytokines, chemokines, and adhesion molecules interact with each other to form a complex molecular network that propagates the inflammatory and pathological cascade of diabetic retinopathy. Therefore, it is important to understand and elucidate inflammation-related mechanisms behind diabetic retinopathy progression. Here, we review the current understanding of the pathology and pathogenesis of inflammation in diabetic retinopathy. In addition, we also summarize the relevant clinical trials to further suggest inflammation-targeted therapeutics for prevention and management of diabetic retinopathy.

Platelets, Macrophages, and Thromboinflammation in Chagas Disease

Chagas disease (CD) is a major health problem in the Americas and an emerging health problem in Europe and other nonendemic countries. Several studies have documented persistence of the protozoan parasite Trypanosoma cruzi, and oxidative and inflammatory stress are major pathogenic factor. Mural and cardiac thrombi, cardiac arrhythmias, and cardiomyopathy are major clinical features of CD. During T. cruzi infection, parasite-released factors induce endothelial dysfunction along with platelet (PLT) and immune-cell activation. PLTs have a fundamental role in maintaining hemostasis and preventing bleeding after vascular injury. Excessive activation of PLTs and coagulation cascade can result in thrombosis and thromboembolic events, which are recognized to occur in seropositive individuals in early stages of CD when clinically symptomatic heart disease is not apparent. Several host and parasite factors have been identified to signal hypercoagulability and increase the risk of ischemic stroke in early phases of CD. Further, PLT interaction with immune cells and their role in host defense against pathogens and inflammatory processes have only recently been recognized and evolving. In the context of parasitic diseases, PLTs function in directly responding to T. cruzi infection, and PLT interactions with immune cells in shaping the proinflammatory or immunoregulatory function of monocytes, macrophages, and neutrophils remains elusive. How T. cruzi infection alters systemic microenvironment conditions to influence PLT and immune-cell interactions is not understood. In this review, we discuss the current literature, and extrapolate the mechanistic situations to explain how PLT and innate immune cell (especially monocytes and macrophages) interactions might be sustaining hypercoagulability and thromboinflammation in chronic CD.

The SNPs of mitochondrial DNA displacement loop region and mitochondrial DNA copy number associated with risk of polymyositis and dermatomyositis

Oxidative damage-induced mitochondrial dysfunction may activate muscle catabolism and autophagy pathways to initiate muscle weakening in idiopathic inflammatory myopathies (IIMs). In this study, Single nucleotide polymorphisms (SNPs) in the mitochondrial displacement loop (D-loop) and mitochondrial DNA (mtDNA) copy number were assessed and their association with the risk of polymyositis and dermatomyositis (PM/DM) was evaluated. Excessive D-loop SNPs (8.779 ± 1.912 vs. 7.972 ± 1.903, p = 0.004) correlated positively with mtDNA copy number (0.602 ± 0.457 vs. 0.300 ± 0.118, p < 0.001). Compared with that of the controls, the mtDNA of PM/DM patients showed D-loop SNP accumulation. In addition, the distribution frequencies of 16304C (p = 0.047) and 16519C (p = 0.043) were significantly higher in the patients with PM/DM. Subsequent analysis showed that reactive oxygen species (ROS) generation was increased in PM/DM patients compared with that in the controls (18,477.756 ± 13,574.916 vs. 14,484.191 ± 5703.097, p = 0.012). Further analysis showed that the PM/DM risk-related allele 16304C was significantly associated with lower IL-4 levels (p = 0.021), while 16519C had a trend to be associated with higher IL-2 expression (p = 0.064). The allele 16519C was associated with a positive antinuclear antibody (ANA) status in PM/DM patients (p = 0.011). Our findings suggest that mitochondrial D-loop SNPs could be potential biomarkers for PM/DM risk and these SNPs associated with cytokine expression may be involved in the development of PM/DM. Further, mtDNA copy number-mediated mitochondrial dysfunction may precede the onset of PM/DM.

Mitochondrial Displacement Loop Region SNPs Modify Sjögren’s Syndrome Development by Regulating Cytokines Expression in Female Patients

Mitochondrial dysfunction could induce innate immune response with cytokines releasing to initiate Sjögren’s syndrome (SS) onset. Single nucleotide polymorphisms (SNPs) in the mitochondrial displacement loop (D-loop) and mitochondrial DNA (mtDNA) copy number of female SS patients were evaluated for their association with SS in female patients. At the nucleotide site of 152, 16304, 16311 and 16362 in the D-loop, the frequencies for the minor alleles of 152C (p = 0.040, odds ratio [OR] = 0.504), 16304C (p = 0.045, OR = 0.406), 16311C (p = 0.045, OR = 0.406) and 16362C (p = 0.028, OR = 0.519) were significantly higher in the SS patients than those in the female controls, which indicated that 152,C, 16304C, 16311C, and 16362C allele in the D-loop of mtDNA were associated with the risk of SS. Meanwhile, the excessive SNPs were accumulated in D-loop region of SS patients (8.955 ± 2.028 versus 7.898 ± 1.987, p < 0.001, 95% confidence interval [CI]: 0.477–1.637) and mtDNA copy number increased in SS patients (1.509 ± 0.836 versus 1.221 ± 0.506, p = 0.006, 95% CI: 0.086–0.490) by a case-control analysis. The subsequent analysis showed that SS risk-related allele 16311C was associated with higher IL-2 levels (p = 0.010) at significantly statistical level whereas 152C associated with lower IL-10 levels (p = 0.058) at a borderline statistical levels. Our findings suggest that mitochondrial D-loop SNPs are predictors for SS risk, it might modify the SS development by regulating cytokine expression.

Circulating cell-free mitochondrial DNA in brain health and disease: A systematic review and meta-analysis

OBJECTIVES

Circulating cell-free mitochondrial DNA (ccf-mtDNA) are detectable fragments of mtDNA released from the cell as a result of mitochondrial dysfunction or apoptosis. The brain is one of the most energy demanding organs in the human body, and many neuropsychiatric and non-psychiatric neurological diseases have mitochondrial dysfunction associated with disease pathophysiology. Thus, we aimed to assess ccf-mtDNA as a potential biomarker for brain diseases.

METHODS

We conducted a systematic review and meta-analyses of studies that examined peripheral and/or cerebrospinal fluid (CSF) ccf-mtDNA relevant to neuropsychiatric conditions, which we define as disorders of affect, behaviour and mood, and non-psychiatric neurological diseases, which consist of neurological diseases not related to psychiatry including neurodegenerative diseases.

RESULTS

The results of the sensitivity analysis investigating the levels of peripheral ccf-mtDNA in neuropsychiatric studies showed no significant difference between cases and controls (Z = 1.57; p = 0.12), whereas the results of the sensitivity analysis investigating the levels of CSF ccf-mtDNA in non-psychiatric neurological diseases showed a decreasing trend in cases compared with controls (Z = 2.32; p = 0.02). Interestingly, the results indicate an overall mitochondrial stress associated mainly with non-psychiatric neurological diseases.

CONCLUSIONS

Our study supports the involvement of mitochondrial stress, here defined as ccf-mtDNA, in brain diseases and encourage further investigation of ccf-mtDNA among patients with brain diseases.

Reduced Maternal Circulating Cell-Free Mitochondrial DNA Is Associated With the Development of Preeclampsia

Background Circulating cell-free mitochondrial DNA (ccf-mtDNA) is a damage-associated molecular pattern that reflects cell stress responses and tissue damage, but little is known about ccf-mtDNA in preeclampsia. The main objectives of this study were to determine (1) absolute concentrations of ccf-mtDNA in plasma and mitochondrial DNA content in peripheral blood mononuclear cells and (2) forms of ccf-mtDNA transport in blood from women with preeclampsia and healthy controls. In addition, we sought to establish the association between aberrance in circulating DNA-related metrics, including ccf-mtDNA and DNA clearance mechanisms, and the clinical diagnosis of preeclampsia using bootstrapped penalized logistic regression. Methods and Results Absolute concentrations of ccf-mtDNA were reduced in plasma from women with preeclampsia compared with healthy controls (P≤0.02), while mtDNA copy number in peripheral blood mononuclear cells did not differ between groups (P>0.05). While the pattern of reduced ccf-mtDNA in patients with preeclampsia remained, DNA isolation from plasma using membrane lysis buffer resulted in 1000-fold higher ccf-mtDNA concentrations in the preeclampsia group (P=0.0014) and 430-fold higher ccf-mtDNA concentrations in the control group (P<0.0001). Plasma from women with preeclampsia did not induce greater Toll-like receptor-9-induced nuclear factor kappa-light-chain enhancer of activated B cells-dependent responses in human embryonic kidney 293 cells overexpressing the human TLR-9 gene (P>0.05). Penalized regression analysis showed that women with preeclampsia were more likely to have lower concentrations of ccf-mtDNA as well as higher concentrations of nuclear DNA and DNase I compared with their matched controls. Conclusions Women with preeclampsia have aberrant circulating DNA dynamics, including reduced ccf-mtDNA concentrations and DNA clearance mechanisms, compared with gestational age-matched healthy pregnant women.

Preclinical evidence for mitochondrial DNA as a potential blood biomarker for chemotherapy-induced peripheral neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a serious dose-limiting side effect of several first-line chemotherapeutic agents including paclitaxel, oxaliplatin and bortezomib, for which no predictive marker is currently available. We have previously shown that mitochondrial dysfunction is associated with the development and maintenance of CIPN. The aim of this study was to evaluate the potential use of mitochondrial DNA (mtDNA) levels and complex I enzyme activity as blood biomarkers for CIPN. Real-time qPCR was used to measure mtDNA levels in whole blood collected from chemotherapy- and vehicle-treated rats at three key time-points of pain-like behaviour: prior to pain development, at the peak of mechanical hypersensitivity and at resolution of pain-like behaviour. Systemic oxaliplatin significantly increased mtDNA levels in whole blood prior to pain development. Furthermore, paclitaxel- and bortezomib-treated animals displayed significantly higher levels of mtDNA at the peak of mechanical hypersensitivity. Mitochondrial complex I activity in whole blood was assessed with an ELISA-based Complex I Enzyme Activity Dipstick Assay. Complex I activity was not altered by any of the three chemotherapeutic agents, either prior to or during pain-like behaviour. These data demonstrate that blood levels of mtDNA are altered after systemic administration of chemotherapy. Oxaliplatin, in particular, is associated with higher mtDNA levels before animals show any pain-like behaviour, thus suggesting a potential role for circulating mtDNA levels as non-invasive predictive biomarker for CIPN.

Cell-Free Mitochondrial DNA as a Potential Biomarker for Astronauts' Health

Background

Space travel–associated stressors such as microgravity or radiation exposure have been reported in astronauts after short‐ and long‐duration missions aboard the International Space Station. Despite risk mitigation strategies, adverse health effects remain a concern. Thus, there is a need to develop new diagnostic tools to facilitate early detection of physiological stress.

Methods and Results

We measured the levels of circulating cell‐free mitochondrial DNA in blood plasma of 14 astronauts 10 days before launch, the day of landing, and 3 days after return. Our results revealed a significant increase of cell‐free mitochondrial DNA in the plasma on the day of landing and 3 days after return with vast ~2 to 355‐fold interastronaut variability. In addition, gene expression analysis of peripheral blood mononuclear cells revealed a significant increase in markers of inflammation, oxidative stress, and DNA damage.

Conclusions

Our study suggests that cell‐free mitochondrial DNA abundance might be a biomarker of stress or immune response related to microgravity, radiation, and other environmental factors during space flight.

Mitochondrial DNA-Mediated Inflammation in Acute Kidney Injury and Chronic Kidney Disease

The integrity and function of mitochondria are essential for normal kidney physiology. Mitochondrial DNA (mtDNA) has been widely a concern in recent years because its abnormalities may result in disruption of aerobic respiration, cellular dysfunction, and even cell death. Particularly, aberrant mtDNA copy number (mtDNA-CN) is associated with the development of acute kidney injury and chronic kidney disease, and urinary mtDNA-CN shows the potential to be a promising indicator for clinical diagnosis and evaluation of kidney function. Several lines of evidence suggest that mtDNA may also trigger innate immunity, leading to kidney inflammation and fibrosis. In mechanism, mtDNA can be released into the cytoplasm under cell stress and recognized by multiple DNA-sensing mechanisms, including Toll-like receptor 9 (TLR9), cytosolic cGAS-stimulator of interferon genes (STING) signaling, and inflammasome activation, which then mediate downstream inflammatory cascades. In this review, we summarize the characteristics of these mtDNA-sensing pathways mediating inflammatory responses and their role in the pathogenesis of acute kidney injury, nondiabetic chronic kidney disease, and diabetic kidney disease. In addition, we highlight targeting of mtDNA-mediated inflammatory pathways as a novel therapeutic target for these kidney diseases.

Increase of Neutrophil Extracellular Traps, Mitochondrial DNA and Nuclear DNA in Newly Diagnosed Type 1 Diabetes Children but Not in High-Risk Children

Neutrophil extracellular traps (NETs) and mitochondrial DNA (mtDNA) are inflammatory mediators involved in the development of type 1 diabetes (T1D). Pancreas-infiltrating neutrophils can release NETs, contributing to the inflammatory process. Levels of NETs are increased in serum from patients with T1D and mtDNA is increased in adult T1D patients. Our aim was to investigate extracellular DNA (NETs, mtDNA and nuclear DNA) in children with newly diagnosed T1D and in children at high risk of the disease. We also elucidated if extracellular DNA short after diagnosis could predict loss of endogenous insulin production. Samples were analysed for mtDNA and nuclear DNA using droplet digital PCR and NETs were assessed by a NET-remnants ELISA. In addition, in vitro assays for induction and degradation of NETs, as well as analyses of neutrophil elastase, HLA genotypes, levels of c-peptide, IL-1beta, IFN and autoantibodies (GADA, IA-2A, IAA and ZnT8A) were performed. In serum from children 10 days after T1D onset there was an increase in NETs (p=0.007), mtDNA (p<0.001) and nuclear DNA (p<0.001) compared to healthy children. The elevated levels were found only in younger children. In addition, mtDNA increased in consecutive samples short after onset (p=0.017). However, levels of extracellular DNA short after onset did not reflect future loss of endogenous insulin production. T1D serum induced NETs in vitro and did not deviate in the ability to degrade NETs. HLA genotypes and autoantibodies, except for ZnT8A, were not associated with extracellular DNA in T1D children. Serum from children with high risk of T1D showed fluctuating levels of extracellular DNA, sometimes increased compared to healthy children. Therefore, extracellular DNA in serum from autoantibody positive high-risk children does not seem to be a suitable biomarker candidate for prediction of T1D. In conclusion, we found increased levels of extracellular DNA in children with newly diagnosed T1D, which might be explained by an ongoing systemic inflammation.

Donor plasma mitochondrial DNA is associated with antibody-mediated rejection in renal allograft recipients

We previously showed that donor plasma mitochondrial DNA (dmtDNA) levels were correlated with renal allograft function. The aim of the current study was to determine whether dmtDNA levels are associated with the occurrence of antibody-mediated rejection (ABMR). This is a retrospective open cohort study comprised of 167 donors and 323 recipients enrolled from January 2015 to December 2017. We quantified the mtDNA level present in donor plasma using quantitative real-time polymerase chain reaction. The average plasma dmtDNA level in the acute rejection (AR) group was higher than that of the control group (0.156 versus 0.075, p<0.001). Multivariate logistic regression analysis showed that dmtDNA levels were also significantly associated with AR (OR=1.588, 95% CI 1.337-4.561, p<0.001). When the dmtDNA level was >0.156, the probability of AR was 62.9%. The plasma dmtDNA level in the ABMR group was significantly higher than that of the T cell-mediated rejection group (0.185 versus 0.099, p=0.032). The area under the receiver operating characteristic curve of dmtDNA for prediction of ABMR was as high as 0.910 (95% CI 0.843-0.977). We demonstrated that plasma dmtDNA was an independent risk factor for ABMR, which is valuable in organ evaluation. dmtDNA level is a possible first predictive marker for ABMR.

The effects of Bushen Yiqi Huoxue prescription and its disassembled prescriptions on a diabetic retinopathy model in Sprague Dawley rats

BACKGROUND

Diabetic retinopathy (DR) is one of the most serious complications in the late stages of diabetes, with a complex mechanism. As a complication affecting local lesions, few studies have compared differences of cytokine expression in the serum and retina. Owing to the specific value of traditional Chinese medicine (TCM) to complex diseases, TCM research has recently boomed in the prevention and treatment of diabetes. Bushen Yiqi Huoxue (BYH) prescription is a Chinese herbal compound that has been independently developed by our research group and has been proved to have a positive effect on DR; however, its specific mechanism and compatibility rule remain to be further explored.

OBJECTIVE

To construct a DR model of Sprague Dawley (SD) rats, simultaneously detect multiple factor expression in the serum and retina of rats, explore the effect of BYH prescription and its disassembled prescriptions on DR, and discuss the influence of various compatibility combinations.

METHODS

BYH prescription was disassembled into two new compatibilities in the absence of Rehmanniae Radix (Yiqi Huoxue prescription, YH prescription) or Ginseng Radix et Rhizoma (Bushen Huoxue prescription, BH prescription). Male SD rats were induced using streptozotocin + high-fat and high-sugar diet to establish DR models and were divided into groups, then the intragastric administration and sampling. The body weight and fasting blood glucose of rats were continuously recorded during feeding; pathophysiological status observation of the retina by haematoxylin and eosin (HE) staining; advanced glycation end products (AGEs) and haemoglobin A1c (HbA1c) level detection in the rat serum by enzyme-linked immunosorbent assay; and the Luminex technique was used to detect the ICAM-1, IL-1β, IL-6, TNF-α and vascular endothelial growth factor (VEGF) expression concentrations in the retinal tissue and serum.

RESULTS

The results of blood glucose, body weight and HE staining proved that the model was successfully constructed, and the three combinations could reduce the retinal injury in DR rats. Serum AGEs and HbA1c levels of the model group increased compared with the control group (CG). Compared with the DR model group, only AGEs decreased in the BYH group, while the AGEs and HbA1c levels were significantly inhibited in the YH and BH groups, showing a significant correlation between the expression of AGEs and HbA1c in the serum of DR rats. In the serum of rats, IL-1β, IL-6, TNF-α and VEGF concentrations in the DR model group increased, although no statistical difference was observed in the ICAM-1 data compared with the CG. Compared with the DR model group, the IL-1β, IL-6 and TNF-α expression decreased in the BYH group. Moreover, the IL-6 and TNF-α expression decreased in the YH group and only the IL-6 expression decreased in the BH group. In the retina tissue, the model group had higher ICAM-1, IL-1β, IL-6, TNF-α and VEGF levels than the CG. Compared with the DR model group, TNF-α in the BYH group rats decreased, and the ICAM-1, IL-6 and TNF-α concentrations decreased in the YH and BH groups. Furthermore, differences in the ICAM-1 and VEGF expression in the serum and retina existed.

CONCLUSION

BYH compound and its disassembled prescriptions could improve the DR model rats induced with streptozotocin + high-fat and high-sugar diet, respectively, by inhibiting chronic blood glucose, AGEs, or inflammation response. The expression level and location of each factor are different, confirming that the effect of TCM prescriptions is not the simple addition of each single drug or its chemical components, but the rationality of its internal compatibility combination. Further, ICAM-1 and VEGF have exactly different expression levels, suggesting more attention to be paid by other researchers or doctors in future studies.

Supplementation with a prebiotic (polydextrose) in obese mouse pregnancy improves maternal glucose homeostasis and protects against offspring obesity

OBJECTIVES

We hypothesised that maternal diet-induced-obesity has adverse consequences for offspring energy expenditure and susceptibility to obesity in adulthood, and that the prebiotic polydextrose (PDX) would prevent the consequences of programming by maternal obesity.

METHODS

Female mice were fed a control (Con) or obesogenic diet (Ob) for 6 weeks prior to mating and throughout pregnancy and lactation. Half the obese dams were supplemented with 5% PDX (ObPDX) in drinking water throughout pregnancy and lactation. Offspring were weaned onto standard chow. At 3 and 6 months, offspring energy intake (EI) and energy expenditure (EE by indirect calorimetry) were measured, and a glucose-tolerance test performed. Offspring of control (OffCon), obese (OffOb) and PDX supplemented (OffObP) dams were subsequently challenged for 3 weeks with Ob, and energy balanced reassessed. Potential modifiers of offspring energy balance including gut microbiota and biomarkers of mitochondrial activity were also evaluated.

RESULTS

Six-month-old male OffOb demonstrated increased bodyweight (BW, P < 0.001) and white adipose tissue mass (P < 0.05), decreased brown adipose tissue mass (BAT, P < 0.01), lower night-time EE (P < 0.001) versus OffCon, which were prevented in OffObP. Both male and female OffOb showed abnormal glucose-tolerance test (peak [Glucose] P < 0.001; AUC, P < 0.05) which was prevented by PDX. The Ob challenge resulted in greater BW gain in both male and female OffOb versus OffCon (P < 0.05), also associated with increased EI (P < 0.05) and reduced EE in females (P < 0.01). OffObP were protected from accelerated BW gain on the OB diet compared with controls, associated with increased night-time EE in both male (P < 0.05) and female OffObP (P < 0.001). PDX also prevented an increase in skeletal muscle mtDNA copy number in OffOb versus OffCon (P < 0.01) and increased the percentage of Bacteroides cells in faecal samples from male OffObP relative to controls.

CONCLUSIONS

Maternal obesity adversely influences adult offspring energy balance and propensity for obesity, which is ameliorated by maternal PDX treatment with associated changes in gut microbiota composition and skeletal muscle mitochondrial function.

Protective role of mitoquinone against impaired mitochondrial homeostasis in metabolic syndrome

Mitochondria control various processes in cellular metabolic homeostasis, such as adenosine triphosphate production, generation and clearance of reactive oxygen species, control of intracellular Ca²⁺ and apoptosis, and are thus a critical therapeutic target for metabolic syndrome (MetS). The mitochondrial targeted antioxidant mitoquinone (MitoQ) reduces mitochondrial oxidative stress, prevents impaired mitochondrial dynamics, and increases mitochondrial turnover by promoting autophagy (mitophagy) and mitochondrial biogenesis, which ultimately contribute to the attenuation of MetS conditions, including obesity, insulin resistance, hypertension and cardiovascular disease. The regulatory effect of MitoQ on mitochondrial homeostasis is mediated through AMPK and its downstream signaling pathways, including MTOR, SIRT1, Nrf2 and NF-κB. However, there are few reviews focusing on the critical role of MitoQ as a therapeutic agent in the treatment of MetS. The purpose of this review is to summarize the mitochondrial role in the pathogenesis of MetS, especially in obesity and type 2 diabetes, and discuss the effect and underlying mechanism of MitoQ on mitochondrial homeostasis in MetS.

A case for measuring both cellular and cell-free mitochondrial DNA as a disease biomarker in human blood

Circulating mitochondrial DNA (mtDNA), widely studied as a disease biomarker, comprises of mtDNA located within mitochondria, indicative of mitochondrial function, and cell-free (cf) mtDNA linked to inflammation. The purpose of this study was to determine the ranges of, and relationship between, cellular and cf mtDNA in human blood. Whole blood from 23 controls (HC) and 20 patients with diabetes was separated into peripheral blood mononuclear cells (PBMCs), plasma, and serum. Total DNA was isolated and mtDNA copy numbers were determined using absolute quantification. Cellular mtDNA content in PBMCs was higher than in peripheral blood and a surprisingly high level of cf mtDNA was present in serum and plasma of HC, with no direct relationship between cellular and cf mtDNA content within individuals. Diabetes patients had similar levels of cellular mtDNA compared to healthy participants but a significantly higher cf mtDNA content. Furthermore, only in patients with diabetes, we observed a correlation between whole blood and plasma mtDNA levels, indicating that the relationship between cellular and cf mtDNA content is affected by disease status. In conclusion, when evaluating mtDNA in human blood as a biomarker of mitochondrial dysfunction, it is important to measure both cellular and cf mtDNA.

Blood contains circulating cell-free respiratory competent mitochondria

Mitochondria are considered as the power-generating units of the cell due to their key role in energy metabolism and cell signaling. However, mitochondrial components could be found in the extracellular space, as fragments or encapsulated in vesicles. In addition, this intact organelle has been recently reported to be released by platelets exclusively in specific conditions. Here, we demonstrate for the first time, that blood preparation with resting platelets, contains whole functional mitochondria in normal physiological state. Likewise, we show, that normal and tumor cultured cells are able to secrete their mitochondria. Using serial centrifugation or filtration followed by polymerase chain reaction-based methods, and Whole Genome Sequencing, we detect extracellular full-length mitochondrial DNA in particles over 0.22 µm holding specific mitochondrial membrane proteins. We identify these particles as intact cell-free mitochondria using fluorescence-activated cell sorting analysis, fluorescence microscopy, and transmission electron microscopy. Oxygen consumption analysis revealed that these mitochondria are respiratory competent. In view of previously described mitochondrial potential in intercellular transfer, this discovery could greatly widen the scope of cell-cell communication biology. Further steps should be developed to investigate the potential role of mitochondria as a signaling organelle outside the cell and to determine whether these circulating units could be relevant for early detection and prognosis of various diseases.

Mitochondrial DNA Promotes NLRP3 Inflammasome Activation and Contributes to Endothelial Dysfunction and Inflammation in Type 1 Diabetes

Background: NLRP3 inflammasome activation in response to several signals, including mitochondrial DNA (mDNA), regulates inflammatory responses by caspase-1 activation and interleukin-1β (IL-1β) release. Circulating mDNA is linked to micro and macrovascular complications in diabetes. However, a role for mDNA in endothelial dysfunction is not clear. We tested the hypothesis that mDNA contributes to diabetes-associated endothelial dysfunction and vascular inflammation via NLRP3 activation. Methods: Vascular reactivity, reactive oxygen species (ROS) generation, calcium (Ca²⁺) influx and caspase-1 and IL-1β activation were determined in mesenteric resistance arteries from normoglicemic and streptozotocin-induced diabetic C57BL/6 and NLRP3 knockout (Nlrp3^-/- ) mice. Endothelial cells and mesenteric arteries were stimulated with mDNA from control (cmDNA) and diabetic (dmDNA) mice. Results: Diabetes reduced endothelium-dependent vasodilation and increased vascular ROS generation and caspase-1 and IL-1β activation in C57BL/6, but not in Nlrp3^-/- mice. Diabetes increased pancreatic cytosolic mDNA. dmDNA decreased endothelium-dependent vasodilation. In endothelial cells, dmDNA activated NLRP3 via mitochondrial ROS and Ca²⁺ influx. Patients with type 1 diabetes exhibited increased circulating mDNA as well as caspase-1 and IL-1β activation. Conclusion: dmDNA activates endothelial NLRP3 inflammasome by mechanisms that involve Ca²⁺ influx and mitochondrial ROS generation. NLRP3 deficiency prevents diabetes-associated vascular inflammatory damage and endothelial dysfunction. Our study highlights the importance of NLRP3 inflammasome in diabetes-associated vascular dysfunction, which is key to diabetic complications.

Endothelial Dysfunction in Diabetic Retinopathy

Diabetic retinopathy (DR) is a diabetic complication which affects retinal function and results in severe loss of vision and relevant retinal diseases. Retinal vascular dysfunction caused by multifactors, such as advanced glycosylation end products and receptors, pro-inflammatory cytokines and chemokines, proliferator-activated receptor-γ disruption, growth factors, oxidative stress, and microRNA. These factors promote retinal endothelial dysfunction, which results in the development of DR. In this review, we summarize the contributors in the pathophysiology of DR for a better understanding of the molecular and cellular mechanism in the development of DR with a special emphasis on retinal endothelial dysfunction.

de Menezes E, Tamang P, Hamid Z, Naik A, Parsade CK, Sivaprasad S. The Detection and Partial Localisation of Heteroplasmic Mutations in the Mitochondrial Genome of Patients with Diabetic Retinopathy

Diabetic retinopathy (DR) is a common complication of diabetes and a major cause of acquired blindness in adults. Mitochondria are cellular organelles involved in energy production which contain mitochondrial DNA (mtDNA). We previously showed that levels of circulating mtDNA were dysregulated in DR patients, and there was some evidence of mtDNA damage. In the current project, our aim was to confirm the presence of, and determine the location and prevalence of, mtDNA mutation in DR. DNA isolated from peripheral blood from diabetes patients (n = 59) with and without DR was used to amplify specific mtDNA regions which were digested with surveyor nuclease S1 to determine the presence and location of heteroplasmic mtDNA mutations were present. An initial screen of the entire mtDNA genome of 6 DR patients detected a higher prevalence of mutations in amplicon P, covering nucleotides 14,443 to 1066 and spanning the control region. Further analysis of 42 subjects showed the presence of putative mutations in amplicon P in 36% (14/39) of DR subjects and in 10% (2/20) non-DR subjects. The prevalence of mutations in DR was not related to the severity of the disease. The detection of a high-prevalence of putative mtDNA mutations within a specific region of the mitochondrial genome supports the view that mtDNA damage contributes to DR. The exact location and functional impact of these mutations remains to be determined.

Sex-Specific Negative Association between Iron Intake and Cellular Aging Markers: Mediation Models Involving TNFα

Background

Given that the dysregulation of iron homeostasis leads to genomic instability, iron has been linked to cellular aging. However, epidemiological research on dietary iron intake and cellular aging markers is scarce. The aim of this study was to explore the relationship between dietary iron intake and cellular aging markers and to investigate whether tumor necrosis factor-α (TNFα) mediated this relationship.

Methods

We conducted a cross-sectional analysis with a total of 467 subjects. Detailed dietary data were obtained using 24 h food recalls. Peripheral blood leukocyte telomere length (LTL) and mitochondrial DNA copy number (mtDNAcn) were assessed using real-time PCR assay. The association between dietary iron intake and cellular aging markers and TNFα and superoxide dismutase (SOD) was analyzed by Pearson correlation analysis and regression models adjusted by covariates. Simple mediation models were generated to examine whether TNFα mediated the association between iron intake and cellular aging markers using PROCESS macro Version 3.3.

Results

The study population contained more women than men, but their basic demographic and metabolic characteristics did not differ. After adjusting for age, LTL was the same for men and women, while mtDNAcn was lower in men. Multiple linear regression adjusted for confounding factors found that iron intake was negatively associated with LTL only in women and negatively associated with mtDNAcn only in men. Moreover, iron intake was positively associated with TNFα in both women and men but positively associated with SOD only in men. Path modeling showed that TNFα significantly mediated the indirect detrimental effect of iron intake on LTL only in women; in men, mediation of the indirect effect of iron intake on mtDNAcn by TNFα did not reach significance.

Conclusions

The study found sex-specific negative associations between dietary iron intake and cellular aging markers in that iron intake had deleterious effects on LTL attrition in women and mtDNAcn in men; only the former was partly mediated by TNFα. Consequently, when dietary iron intake and iron supplementation is recommended, the effects of iron imbalance on genomic stability and cellular aging markers must be considered.

A Diet Induced Maladaptive Increase in Hepatic Mitochondrial DNA Precedes OXPHOS Defects and May Contribute to Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD), an increasingly prevalent and underdiagnosed disease, is postulated to be caused by hepatic fat mediated pathological mechanisms. Mitochondrial dysfunction is proposed to be involved, but it is not known whether this is a pathological driver or a consequence of NAFLD. We postulate that changes to liver mitochondrial DNA (mtDNA) are an early event that precedes mitochondrial dysfunction and irreversible liver damage. To test this hypothesis, we evaluated the impact of diet on liver steatosis, hepatic mtDNA content, and levels of key mitochondrial proteins. Liver tissues from C57BL/6 mice fed with high fat (HF) diet (HFD) and Western diet (WD, high fat and high sugar) for 16 weeks were used. Steatosis/fibrosis were assessed using haematoxylin and eosin (H&E) Oil Red and Masson’s trichome staining and collagen content. Total DNA was isolated, and mtDNA content was determined by quantifying absolute mtDNA copy number/cell using quantitative PCR. Selected mitochondrial proteins were analysed from a proteomics screen. As expected, both HFD and WD resulted in steatosis. Mouse liver contained a high mtDNA content (3617 ± 233 copies per cell), which significantly increased in HFD diet, but this increase was not functional, as indicated by changes in mitochondrial proteins. In the WD fed mice, liver dysfunction was accelerated alongside downregulation of mitochondrial oxidative phosphorylation (OXPHOS) and mtDNA replication machinery as well as upregulation of mtDNA-induced inflammatory pathways. These results demonstrate that diet induced changes in liver mtDNA can occur in a relatively short time; whether these contribute directly or indirectly to subsequent mitochondrial dysfunction and the development of NAFLD remains to be determined. If this hypothesis can be substantiated, then strategies to prevent mtDNA damage in the liver may be needed to prevent development and progression of NAFLD.

Imaging and Biomarkers in Diabetic Macular Edema and Diabetic Retinopathy

PURPOSE OF REVIEW

Diabetic retinopathy (DR) is the leading cause of acquired vision loss in adults across the globe. Early identification and treatment of patients with DR is paramount for vision preservation. The aim of this review paper is to outline current and new imaging techniques and biomarkers that are valuable for clinical diagnosis and management of DR.

RECENT FINDINGS

Ultrawide field imaging and automated deep learning algorithms are recent advancements on traditional fundus photography and fluorescein angiography. Optical coherence tomography (OCT) and OCT angiography are techniques that image retinal anatomy and vasculature and OCT is routinely used to monitor response to treatment. Many circulating, vitreous, and genetic biomarkers have been studied to facilitate disease detection and development of new treatments. Recent advancements in retinal imaging and identification of promising new biomarkers for DR have the potential to increase detection, risk stratification, and treatment for patients with DR.

Regional mitochondrial DNA and cell-type changes in post-mortem brains of non-diabetic Alzheimer's disease are not present in diabetic Alzheimer's disease

Diabetes increases the risk of Alzheimer's disease (AD), and mitochondrial dysfunction is implicated in both diseases, however the impact of both diabetes and AD on brain mitochondria is not known. We measured mitochondrial DNA (mtDNA), an indicator of mitochondrial function, in frontal, parietal, and cerebellar regions of post-mortem human brains (n = 74) from non-cognitively impaired controls (NCI), mild-cognitively impaired (MCI) and AD cases. In a subset of parietal cortices, we measured mRNAs corresponding to cell types and mitochondrial function and semi-automated stereological assessment was performed on immune-staining of parietal cortex sections. mtDNA showed significant regional variation, highest in parietal cortex, and lowest in cerebellum. Irrespective of cognitive status, all brain regions had significantly higher mtDNA in diabetic cases. In the absence of diabetes, AD parietal cortices had decreased mtDNA, reduced MAP2 (neuronal) and increased GFAP (astrocyte) mRNA, relative to NCI. However, in the presence of diabetes, we did not observe these AD-related changes, suggesting that the pathology observed in diabetic AD may be different to that seen in non-diabetic AD. The lack of clear functional changes in mitochondrial parameters in diabetic AD suggest different cellular mechanisms contributing to cognitive impairment in diabetes which remain to be fully understood.

IL-1 Family Members Mediate Cell Death, Inflammation and Angiogenesis in Retinal Degenerative Diseases

Inflammation underpins and contributes to the pathogenesis of many retinal degenerative diseases. The recruitment and activation of both resident microglia and recruited macrophages, as well as the production of cytokines, are key contributing factors for progressive cell death in these diseases. In particular, the interleukin 1 (IL-1) family consisting of both pro- and anti-inflammatory cytokines has been shown to be pivotal in the mediation of innate immunity and contribute directly to a number of retinal degenerations, including Age-Related Macular Degeneration (AMD), diabetic retinopathy, retinitis pigmentosa, glaucoma, and retinopathy of prematurity (ROP). In this review, we will discuss the role of IL-1 family members and inflammasome signaling in retinal degenerative diseases, piecing together their contribution to retinal disease pathology, and identifying areas of research expansion required to further elucidate their function in the retina.

Deletion of OGG1 Results in a Differential Signature of Oxidized Purine Base Damage in mtDNA Regions

Mitochondrial oxidative stress accumulates with aging and age-related diseases and induces alterations in mitochondrial DNA (mtDNA) content. Since mtDNA qualitative alterations are also associated with aging, repair of mtDNA damage is of great importance. The most relevant form of DNA repair in this context is base excision repair (BER), which removes oxidized bases such as 8-oxoguanine (8-oxoG) and thymine glycol through the action of the mitochondrial isoform of the specific 8-oxoG DNA glycosylase/apurinic or apyrimidinic (AP) lyase (OGG1) or the endonuclease III homolog (NTH1). Mouse strains lacking OGG1 (OGG1^−/−) or NTH1 (NTH1^−/−) were analyzed for mtDNA alterations. Interestingly, both knockout strains presented a significant increase in mtDNA content, suggestive of a compensatory mtDNA replication. The mtDNA “common deletion” was not detected in either knockout mouse strain, likely because of the young age of the mice. Formamidopyrimidine DNA glycosylase (Fpg)-sensitive sites accumulated in mtDNA from OGG1^−/− but not from NTH1^−/− mice. Interestingly, the D-loop region was most severely affected by the absence of OGG1, suggesting that this region may be a hotspot for oxidative damage. Thus, we speculate that mtDNA alterations may send a stress message to evoke cell changes through a retrograde mitochondrial–nucleus communication.

Mitochondrial Dysfunction and Diabetes: Is Mitochondrial Transfer a Friend or Foe?

Obesity, insulin resistance and type 2 diabetes are accompanied by a variety of systemic and tissue-specific metabolic defects, including inflammation, oxidative and endoplasmic reticulum stress, lipotoxicity, and mitochondrial dysfunction. Over the past 30 years, association studies and genetic manipulations, as well as lifestyle and pharmacological invention studies, have reported contrasting findings on the presence or physiological importance of mitochondrial dysfunction in the context of obesity and insulin resistance. It is still unclear if targeting mitochondrial function is a feasible therapeutic approach for the treatment of insulin resistance and glucose homeostasis. Interestingly, recent studies suggest that intact mitochondria, mitochondrial DNA, or other mitochondrial factors (proteins, lipids, miRNA) are found in the circulation, and that metabolic tissues secrete exosomes containing mitochondrial cargo. While this phenomenon has been investigated primarily in the context of cancer and a variety of inflammatory states, little is known about the importance of exosomal mitochondrial transfer in obesity and diabetes. We will discuss recent evidence suggesting that (1) tissues with mitochondrial dysfunction shed their mitochondria within exosomes, and that these exosomes impair the recipient's cell metabolic status, and that on the other hand, (2) physiologically healthy tissues can shed mitochondria to improve the metabolic status of recipient cells. In this context the determination of whether mitochondrial transfer in obesity and diabetes is a friend or foe requires further studies.

An In Vitro Study on Mitochondrial Compensatory Response Induced by Gliadin Peptides in Caco-2 Cells

Dietary gliadin may show a broad spectrum of toxicity. The interplay between mitochondria and gliadin-induced oxidative stress has not been thoroughly examined in the intestinal epithelium. In this kinetic study, Caco-2 cells were exposed for 24 h to pepsin-trypsin-digested gliadin, alone or in combination with the antioxidant 2,6-di-tbutyl-p-cresol (BHT), and the effects on mitochondrial biogenesis and mtDNA were studied. Cells ability to recover from stress was determined after 24 h and 48 h of incubation in the culture medium. Gliadin-induced oxidative stress evoked a compensatory response. The stressor triggered a rapid and significant increase of Peroxisome proliferator-activated receptor γ coactivator-1alpha (PGC-1α) and Peroxiredoxin III (PrxIII) proteins, and mtDNA amount. As for the effects of gliadin on mtDNA integrity, strand breaks, abasic sites, and modified bases were analyzed in three mtDNA regions. D-loop appeared a more fragile target than Ori-L and ND1/ND2. The temporal trend of the damage at D-loop paralleled that of the amount of mtDNA. Overall, a trend toward control values was shown 48 h after gliadin exposure. Finally, BHT was able to counteract the effects of gliadin. Results from this study highlighted the effects of gliadin-induced oxidative stress on mitochondria, providing valuable evidence that might improve the knowledge of the pathophysiology of gluten-related disorders.

Quantifying circulating cell-free DNA in humans

To our knowledge, this is the first comprehensive study on the influence of several pre-analytical and demographic parameters that could be a source of variability in the quantification of nuclear and mitochondrial circulating DNA (NcirDNA and McirDNA). We report data from a total of 222 subjects, 104 healthy individuals and 118 metastatic colorectal cancer (mCRC) patients. Approximately 50,000 and 3,000-fold more mitochondrial than nuclear genome copies were found in the plasma of healthy individuals and mCRC patients, respectively. In healthy individuals, NcirDNA concentration was statistically influenced by age (p = 0.009) and gender (p = 0.048). Multivariate analysis with logistic regression specified that age over 47 years-old was predictive to have higher NcirDNA concentration (OR = 2.41; p = 0.033). McirDNA concentration was independent of age and gender in healthy individuals. In mCRC patients, NcirDNA and McirDNA levels were independent of age, gender, delay between food intake and blood collection, and plasma aspect, either with univariate or multivariate analysis. Nonetheless, ad hoc study suggested that menopause and blood collection time might have tendency to influence cirDNA quantification. In addition, high significant statistical differences were found between mCRC patients and healthy individuals for NcirDNA (p < 0.0001), McirDNA (p < 0.0001) and McirDNA/NcirDNA ratio (p < 0.0001). NcirDNA and McirDNA levels do not vary in the same way with regards to cancer vs healthy status, pre-analytical and demographic factors.

The co-activator-associated arginine methyltransferase 1 (CARM1) gene is overexpressed in type 2 diabetes

PURPOSE

We examined the expression of a panel of epigenetic enzymes catalyzing histone tails post-transcriptional modifications, together with effectors of metabolic and inflammatory alterations, in type 2 diabetes.

METHODS

Cross-sectional, case-control study of 21 people with type 2 diabetes and 21 matched controls. Total RNA was extracted from white cells and reverse transcribed. PCR primer assays for 84 key genes encoding enzymes known to modify genomic DNA and histones were performed. Western blot was performed on lysates using primary antibodies for abnormally expressed enzymes. Hormones and cytokines were measured by multiplex kits. A Bayesian network was built to investigate the relationships between epigenetic, cytokine, and endocrine variables.

RESULTS

Co-activator-associated aRginine Methyltransferase 1 (CARM1) expression showed a five-fold higher median value, matched by higher protein levels, among patients who also had increased GIP, IL-4, IL-7, IL-13, IL-17, FGF basic, G-CSF, IFN-γ, and TNFα and decreased IP-10. In a Bayesian network approach, CARM1 expression showed a conditional dependence on diabetes, but was independent of all other variables nor appeared to influence any.

CONCLUSIONS

Increased CARM1 expression in type 2 diabetes suggests that epigenetic mechanisms are altered in human diabetes. The impact of lifestyle and pharmacological treatment on regulation of this enzyme should be further investigated.

Implementing a new variant load model to investigate the role of mtDNA in oxidative stress and inflammation in a bi-ethnic cohort: the SABPA study

Mitochondrial DNA (mtDNA) variation has been implicated in several common complex and degenerative diseases, including cardiovascular disease. Inflammation is seen as part of many of these conditions. Mitochondria feature in inflammatory pathways and it has been suggested that mtDNA variation or released mtDNA might be important in this phenomenon. To determine if mtDNA is involved in the mechanisms leading up to cardiovascular disease, we investigated the role of these variants in seven indicators of oxidative stress and inflammation. This study was done in participants of the Sympathetic Activity and Ambulatory Blood Pressure in Africans (SABPA) cohort, a South African bi-ethnic cohort (N = 363). We applied a variant load hypothesis, which is an alternative approach to, and moves away from the classic haplogroup association approaches, to evaluate the cumulative effect of non-synonymous mtDNA variants on measurements of serum peroxides, nitric oxide metabolites, 8-hydroxy-deoxyguanosine, thiobarbituric acid reactive substances, whole blood reduced glutathione, C-reactive protein, and tumor necrosis factor alpha. We found no significant relationships between non-synonymous mtDNA variants and the seven biochemical parameters investigated here. Non-synonymous mtDNA variants are unlikely to impact on disease in this cohort, to an appreciable or measurable extent.

Associations of Mitochondrial and Nuclear Mitochondrial Variants and Genes with Seven Metabolic Traits

Mitochondria (MT), the major site of cellular energy production, are under dual genetic control by 37 mitochondrial DNA (mtDNA) genes and numerous nuclear genes (MT-nDNA). In the CHARGEmtDNA+ Consortium, we studied genetic associations of mtDNA and MT-nDNA associations with body mass index (BMI), waist-hip-ratio (WHR), glucose, insulin, HOMA-B, HOMA-IR, and HbA1c. This 45-cohort collaboration comprised 70,775 (insulin) to 170,202 (BMI) pan-ancestry individuals. Validation and imputation of mtDNA variants was followed by single-variant and gene-based association testing. We report two significant common variants, one in MT-ATP6 associated (p ≤ 5E-04) with WHR and one in the D-loop with glucose. Five rare variants in MT-ATP6, MT-ND5, and MT-ND6 associated with BMI, WHR, or insulin. Gene-based meta-analysis identified MT-ND3 associated with BMI (p ≤ 1E-03). We considered 2,282 MT-nDNA candidate gene associations compiled from online summary results for our traits (20 unique studies with 31 dataset consortia's genome-wide associations [GWASs]). Of these, 109 genes associated (p ≤ 1E-06) with at least 1 of our 7 traits. We assessed regulatory features of variants in the 109 genes, cis- and trans-gene expression regulation, and performed enrichment and protein-protein interactions analyses. Of the identified mtDNA and MT-nDNA genes, 79 associated with adipose measures, 49 with glucose/insulin, 13 with risk for type 2 diabetes, and 18 with cardiovascular disease, indicating for pleiotropic effects with health implications. Additionally, 21 genes related to cholesterol, suggesting additional important roles for the genes identified. Our results suggest that mtDNA and MT-nDNA genes and variants reported make important contributions to glucose and insulin metabolism, adipocyte regulation, diabetes, and cardiovascular disease.

A Monochrome Multiplex Real-Time Quantitative PCR Assay for the Measurement of Mitochondrial DNA Content

Mitochondrial DNA copies per cell (mtDNA content) can fluctuate with cellular aging, oxidative stress, and mitochondrial dysfunction, and has been investigated in cancer, diabetes, HIV, and metabolic disease. mtDNA content testing in both clinical and basic settings is expected to increase as research uncovers its biological relevance. Herein, we present a novel mtDNA content assay developed on monochrome multiplex real-time quantitative PCR (MMqPCR) principles. This assay offers a greater than twofold improvement on time effectiveness and cost-effectiveness over conventional (monoplex) qPCR, as well as improved reproducibility given the reduced effects of human pipetting errors. The new MMqPCR method was compared with the gold standard monoplex qPCR assay on DNA from a variety of sources, including human whole blood, skeletal muscle, and commercial cell lines. The MMqPCR assay is reproducible (n = 98, r = 0.99, P < 0.0001) and highly correlated to the monoplex qPCR assay (n = 160, r > 0.98, P < 0.0001). Intra-assay and interassay variabilities, as established independently by multiple operators, range between 4.3% and 7.9% and between 2.9% and 9.2%, respectively. This robust assay can quantify >82 pg of template DNA per reaction, with a minimum mtDNA/nuclear DNA ratio of 20, and is especially suitable for studies that require high throughput.

Promoter methylation of PGC1A and PGC1B predicts cancer incidence in a veteran cohort

AIM

Previous studies suggest telomere shortening represses PGC1A and PGC1B expression leading to mitochondrial dysfunction. Methylation of CpG sites within these genes may interact with these factors to affect cancer risk.

MATERIALS & METHODS

Among 385 men, we identified 84 incidents of cancers (predominantly prostate and nonmelanoma skin). We examined associations between leukocyte DNA methylation of 41 CpGs from PGC1A and PGC1B with telomere length, mitochondrial 8-OHdG lesions, mitochondrial abundance and cancer incidence.

RESULTS

Methylation of five and eight CpG sites were significantly associated with telomere length and mitochondrial abundance at p < 0.05. Two CpG sites were independently associated with cancer risk: cg27514608 (PGC1A, TSS1500; HR: 1.55, 95% CI: 1.19-2.03, FDR = 0.02), and cg15219393 (PGC1B, first exon/5'UTR; HR: 3.71, 95% CI: 1.82-7.58, FDR < 0.01). Associations with cg15219393 were observed primarily among men with shorter leukocyte telomeres.

CONCLUSION

PGC1A and PGC1B methylation may serve as early biomarkers of cancer risk.

Advances in PCOS Pathogenesis and Progression-Mitochondrial Mutations and Dysfunction

Polycystic ovary syndrome (PCOS) is a common female endocrine disorder, which still remains largely unsolved in terms of etiology and pathogenesis despite important advances in our understanding of its genetic, epigenetic, or environmental factor implications. It is a heterogeneous disease, frequently associated with insulin resistance, chronic inflammation, and oxidative stress and probably accompanied with subclinical cardiovascular disease (CVD) and some malignant lesions as well, such as endometrial cancer. Discrepancies in the clinical phenotype and progression of PCOS exist between different population groups, which nuclear genetic studies have so far failed to explain. Over the last years, mitochondrial dysfunction has been increasingly recognized as an important contributor to an array of diseases. Because mitochondria are under the dual genetic control of both the mitochondrial and nuclear genomes, mutations within either DNA molecule may result in deficiency in respiratory chain function that leads to a reduced ability to produce cellular adenosine-5'-triphosphate and to an excessive production of reactive oxygen species. However, the association between variants in mitochondrial genome, mitochondrial dysfunction, and PCOS has been investigated to a lesser extent. May mutations in mitochondrial DNA (mtDNA) become an additional target of investigations on the missing PCOS heritability? Are mutations in mtDNA implicated in the initiation and progression of PCOS complications, e.g., CVDs, diabetes mellitus, cancers?

Effects and Mechanisms of Taurine as a Therapeutic Agent

Taurine is an abundant, β-amino acid with diverse cytoprotective activity. In some species, taurine is an essential nutrient but in man it is considered a semi-essential nutrient, although cells lacking taurine show major pathology. These findings have spurred interest in the potential use of taurine as a therapeutic agent. The discovery that taurine is an effective therapy against congestive heart failure led to the study of taurine as a therapeutic agent against other disease conditions. Today, taurine has been approved for the treatment of congestive heart failure in Japan and shows promise in the treatment of several other diseases. The present review summarizes studies supporting a role of taurine in the treatment of diseases of muscle, the central nervous system, and the cardiovascular system. In addition, taurine is extremely effective in the treatment of the mitochondrial disease, mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), and offers a new approach for the treatment of metabolic diseases, such as diabetes, and inflammatory diseases, such as arthritis. The review also addresses the functions of taurine (regulation of antioxidation, energy metabolism, gene expression, ER stress, neuromodulation, quality control and calcium homeostasis) underlying these therapeutic actions.

Effect of TET2 on the pathogenesis of diabetic nephropathy through activation of transforming growth factor β1 expression via DNA demethylation

AIMS

Transforming growth factor β1 (TGFβ1) plays a pivotal role in the pathogenesis of diabetic nephropathy (DN). However, the mechanism of its expression and activation induced by high glucose (HG) is still unclear. We mainly explored the role of ten-eleven translocation enzyme-2 (TET2) in regulating TGFβ1 expression in the process of DN.

MAIN METHODS

Human mesangial cells (HMCs) and db/db mice were used to analyze the biological effects of hyperglycemia both in vivo and in vitro. Gene expression levels, cell proliferation, protein recruitment levels to TGFβ1 regulatory region, DNA methylation statues and pathological changes in kidney were tested in different groups. Short hairpin RNA(shRNA) and oral inhibitor were used to knock down or inhibit TET2 expression.

KEY FINDINGS

Our study demonstrated that TET2 expression was increased in the renal cortex of db/db mice and in HMCs inducing by HG. We also found that TET2 binding was increased while DNA methylation of CpG islands was reduced in the TGFβ1 regulation region in HG, resulting in the increased expression level of TGFβ1 and cell phenotype transformation. More importantly, clinical research revealed that gradually decreased DNA methylation in the TGFβ1 regulatory region was also present in patients with diabetes and DN.

SIGNIFICANCE

Our work suggests that TET2 plays an important role in the pathogenesis of DN by activating TGFβ1 expression through demethylation of CpG islands in the TGFβ1 regulatory region. This may provide a potential new therapeutic target for DN.

Mitochondria and redox balance in coeliac disease: A case-control study

BACKGROUND

Coeliac disease (CD) is a gluten-sensitive autoimmune disorder. Gluten toxicity encompasses a wide spectrum of target organ functions and pathologies, including the activation of the immune response and triggering of oxidative stress. The aim of this study was to investigate inflammation and the redox balance in patients with active CD, and to evaluate whether alteration of mitochondrial function is involved in the disease status.

DESIGN

In this prospective case-control study, blood samples from sixteen adult CD patients and sixteen healthy controls (HC) were investigated for IL-1β, IL-6 and IL-8 plasma concentrations, for serum PON1 arylesterase, total and MnSOD antioxidant enzyme activities, induced TBARs levels, and for lymphocyte mtDNA content.

RESULTS

Patients showed IL-8 and IL-1β concentrations significantly higher than HC counterparts. Patients had a significantly higher content of induced TBARS compared to HC value, indicating a shift in their serum redox balance towards pro-oxidant species. The assay of antioxidant enzyme activities showed a significant 25% increase in PON1, a higher total SOD, and a significant 21% higher MnSOD in patients compared to HC. Lymphocyte mtDNA content in patients was significantly twofold higher than in HC, supporting the induction of mitochondrial biogenesis. The patients' mitochondrial compensatory response may explain the correlation between MnSOD activity and mtDNA content. The patients' mitochondrial oxidative stress, cooperating to cytokines secretion, may justify the correlation between IL-1β concentration and mtDNA content.

CONCLUSIONS

These results highlight the mitochondrial involvement in CD and suggest the evaluation of the mtDNA content as a potential diagnostic and follow-up parameter.

The Role of Oxidative Stress, Mitochondrial Function, and Autophagy in Diabetic Polyneuropathy

Diabetic polyneuropathy (DPN) is the most frequent and prevalent chronic complication of diabetes mellitus (DM). The state of persistent hyperglycemia leads to an increase in the production of cytosolic and mitochondrial reactive oxygen species (ROS) and favors deregulation of the antioxidant defenses that are capable of activating diverse metabolic pathways which trigger the presence of nitro-oxidative stress (NOS) and endoplasmic reticulum stress. Hyperglycemia provokes the appearance of micro- and macrovascular complications and favors oxidative damage to the macromolecules (lipids, carbohydrates, and proteins) with an increase in products that damage the DNA. Hyperglycemia produces mitochondrial dysfunction with deregulation between mitochondrial fission/fusion and regulatory factors. Mitochondrial fission appears early in diabetic neuropathy with the ability to facilitate mitochondrial fragmentation. Autophagy is a catabolic process induced by oxidative stress that involves the formation of vesicles by the lysosomes. Autophagy protects cells from diverse stress factors and routine deterioration. Clarification of the mechanisms involved in the appearance of complications in DM will facilitate the selection of specific therapeutic options based on the mechanisms involved in the metabolic pathways affected. Nowadays, the antioxidant agents consumed exogenously form an adjuvant therapeutic alternative in chronic degenerative metabolic diseases, such as DM.

The aetiology of cardiovascular disease: a role for mitochondrial DNA?

Cardiovascular disease (CVD) is a world-wide cause of mortality in humans and its incidence is on the rise in Africa. In this review, we discuss the putative role of mitochondrial dysfunction in the aetiology of CVD and consequently identify mitochondrial DNA (mtDNA) variation as a viable genetic risk factor to be considered. We then describe the contribution and pitfalls of several current approaches used when investigating mtDNA in relation to complex disease. We also propose an alternative approach, the adjusted mutational load hypothesis, which would have greater statistical power with cohorts of moderate size, and is less likely to be affected by population stratification. We therefore address some of the shortcomings of the current haplogroup association approach. Finally, we discuss the unique challenges faced by studies done on African populations, and recommend the most viable methods to use when investigating mtDNA variation in CVD and other common complex disease.

Kinetic analysis, size profiling, and bioenergetic association of DNA released by selected cell lines in vitro

Although circulating DNA (cirDNA) analysis shows great promise as a screening tool for a wide range of pathologies, numerous stumbling blocks hinder the rapid translation of research to clinical practice. This is related directly to the inherent complexity of the in vivo setting, wherein the influence of complex systems of interconnected cellular responses and putative DNA sources creates a seemingly arbitrary representation of the quantitative and qualitative properties of the cirDNA in the blood of any individual. Therefore, to evaluate the potential of in vitro cell cultures to circumvent the difficulties encountered in in vivo investigations, the purpose of this work was to elucidate the characteristics of the DNA released [cell-free DNA (cfDNA)] by eight different cell lines. This revealed three different forms of cfDNA release patterns and the presence of nucleosomal fragments as well as actively released forms of DNA, which are not only consistently observed in every tested cell line, but also in plasma samples. Correlations between cfDNA release and cellular origin, growth rate, and cancer status were also investigated by screening and comparing bioenergetics flux parameters. These results show statistically significant correlations between cfDNA levels and glycolysis, while no correlations between cfDNA levels and oxidative phosphorylation were observed. Furthermore, several correlations between growth rate, cancer status, and dependency on aerobic glycolysis were observed. Cell cultures can, therefore, successfully serve as closed-circuit models to either replace or be used in conjunction with biofluid samples, which will enable sharper focus on specific cell types or DNA origins.

Origins, structures, and functions of circulating DNA in oncology

While various clinical applications especially in oncology are now in progress such as diagnosis, prognosis, therapy monitoring, or patient follow-up, the determination of structural characteristics of cell-free circulating DNA (cirDNA) are still being researched. Nevertheless, some specific structures have been identified and cirDNA has been shown to be composed of many “kinds.” This structural description goes hand-in-hand with the mechanisms of its origins such as apoptosis, necrosis, active release, phagocytosis, and exocytose. There are multiple structural forms of cirDNA depending upon the mechanism of release: particulate structures (exosomes, microparticles, apoptotic bodies) or macromolecular structures (nucleosomes, virtosomes/proteolipidonucleic acid complexes, DNA traps, links with serum proteins or to the cell-free membrane parts). In addition, cirDNA concerns both nuclear and/or mitochondrial DNA with both species exhibiting different structural characteristics that potentially reveal different forms of biological stability or diagnostic significance. This review focuses on the origins, structures and functional aspects that are paradoxically less well described in the literature while numerous reviews are directed to the clinical application of cirDNA. Differentiation of the various structures and better knowledge of the fate of cirDNA would considerably expand the diagnostic power of cirDNA analysis especially with regard to the patient follow-up enlarging the scope of personalized medicine. A better understanding of the subsequent fate of cirDNA would also help in deciphering its functional aspects such as their capacity for either genometastasis or their pro-inflammatory and immunological effects.

Peripheral Blood Mitochondrial DNA Damage as a Potential Noninvasive Biomarker of Diabetic Retinopathy

PURPOSE

In the development of diabetic retinopathy, retinal mitochondria become dysfunctional, and mitochondrial DNA (mtDNA) is damaged. Because retinopathy is a progressive disease, and circulating glucose levels are high in diabetes, our aim was to investigate if peripheral blood mtDNA damage can serve as a potential biomarker of diabetic retinopathy.

METHODS

Peripheral blood mtDNA damage was investigated by extended-length PCR in rats and mice, diabetic for 10 to 12 months (streptozotocin-induced, type 1 model), and in 12- and 40-week-old Zucker diabetic fatty rats (ZDF, type 2). Mitochondrial copy number (in gDNA) and transcription (in cDNA) were quantified by qPCR. Similar parameters were measured in blood from diabetic patients with/without retinopathy.

RESULTS

Peripheral blood from diabetic rodents had significantly increased mtDNA damage and decreased copy numbers and transcription. Lipoic acid administration in diabetic rats, or Sod2 overexpression or MMP-9 knockdown in mice, the therapies that prevent diabetic retinopathy, also ameliorated blood mtDNA damage and restored copy numbers and transcription. Although blood from 40-week-old ZDF rats had significant mtDNA damage, 12-week-old rats had normal mtDNA. Diabetic patients with retinopathy had increased blood mtDNA damage, and decreased transcription and copy numbers compared with diabetic patients without retinopathy and nondiabetic individuals.

CONCLUSIONS

Type 1 diabetic rodents with oxidative stress modulated by pharmacologic/genetic means, and type 2 animal model and patients with/without diabetic retinopathy, demonstrate a strong relation between peripheral blood mtDNA damage and diabetic retinopathy, and suggest the possibility of use of peripheral blood mtDNA as a noninvasive biomarker of diabetic retinopathy.

Immunostimulatory role of mitochondrial DAMPs: alarming for pre-eclampsia?

Mitochondria are critical signaling organelles that play an integral cellular role in the activation of diverse physiological responses to perturbation. Mitochondrial damage-associated molecular patterns (DAMPs) act as redox signaling nodes synchronizing mitochondrial metabolism with triggering of inflammation. Oxidative stress and inflammation are implicated in the pathogenesis of pre-eclampsia; however, the mechanisms involved in the novel crosstalk between these two pathogenic pathways are less well elucidated. In this review, we show that mitochondrial redox signals are paramount for regulating and maintaining the inflammatory response to danger signals. Mitochondrial DNA (mtDNA) represents a mitochondrial DAMP and is often liberated as signal of mitochondrial dysfunction. This review will explore the mechanistic role of mitochondrial DNA in directly coordinating adaptive changes in the maternal inflammatory status in pre-eclampsia through recruitment of innate immune cells and subsequent cytokine production. Finally, we provide emerging evidence of elevated circulating mitochondrial DAMPs in pre-eclampsia.