Age-related mitochondrial DNA depletion and the impact on pancreatic Beta cell function

Disruption of perinatal myeloid niches impacts the aging clock of pancreatic β cells

Perinatal expansion of pancreatic β cells is critical to metabolic adaptation. Yet, mechanisms surveying the fidelity by which proliferative events generate functional β cell pools remain unknown. We have previously identified a CCR2+ myeloid niche required for peri-natal β cell replication, with β cells dynamically responding to loss and repopulation of these myeloid cells with growth arrest and rebound expansion, respectively. Here, using a timed single-cell RNA-sequencing approach, we show that transient disruption of perinatal CCR2+ macrophages change islet β cell repertoires in young mice to resemble those of aged mice. Gene expression profiling and functional assays disclose prominent mitochondrial defects in β cells coupled to impaired redox states, NAD depletion, and DNA damage, leading to accelerated islets' dysfunction with age. These findings reveal an unexpected vulnerability of mitochondrial β cells' bioenergetics to the disruption of perinatal CCR2+ macrophages, implicating these cells in surveying early in life both the size and energy homeostasis of β cells populations.

Attenuating mitochondrial dysfunction and morphological disruption with PT320 delays dopamine degeneration in MitoPark mice

BACKGROUND

Mitochondria are essential organelles involved in cellular energy production. Changes in mitochondrial function can lead to dysfunction and cell death in aging and age-related disorders. Recent research suggests that mitochondrial dysfunction is closely linked to neurodegenerative diseases. Glucagon-like peptide-1 receptor (GLP-1R) agonist has gained interest as a potential treatment for Parkinson's disease (PD). However, the exact mechanisms responsible for the therapeutic effects of GLP-1R-related agonists are not yet fully understood.

METHODS

In this study, we explores the effects of early treatment with PT320, a sustained release formulation of the GLP-1R agonist Exenatide, on mitochondrial functions and morphology in a progressive PD mouse model, the MitoPark (MP) mouse.

RESULTS

Our findings demonstrate that administration of a clinically translatable dose of PT320 ameliorates the reduction in tyrosine hydroxylase expression, lowers reactive oxygen species (ROS) levels, and inhibits mitochondrial cytochrome c release during nigrostriatal dopaminergic denervation in MP mice. PT320 treatment significantly preserved mitochondrial function and morphology but did not influence the reduction in mitochondria numbers during PD progression in MP mice. Genetic analysis indicated that the cytoprotective effect of PT320 is attributed to a reduction in the expression of mitochondrial fission protein 1 (Fis1) and an increase in the expression of optic atrophy type 1 (Opa1), which is known to play a role in maintaining mitochondrial homeostasis and decreasing cytochrome c release through remodeling of the cristae.

CONCLUSION

Our findings suggest that the early administration of PT320 shows potential as a neuroprotective treatment for PD, as it can preserve mitochondrial function. Through enhancing mitochondrial health by regulating Opa1 and Fis1, PT320 presents a new neuroprotective therapy in PD.

Gene dosage adaptations to mtDNA depletion and mitochondrial protein stress in budding yeast

Mitochondria contain a local genome (mtDNA) comprising a small number of genes necessary for respiration, mitochondrial transcription and translation, and other vital functions. Various stressors can destabilize mtDNA leading to mtDNA loss. While some cells can survive mtDNA loss, they exhibit various deficiencies. Here, we investigated the impact of proteotoxicity on mitochondrial function by inducing mitochondrial unfolded protein stress in budding yeast. This led to rapid mtDNA loss, but aerobic conditioning imparted transient resistance to mitochondrial protein stress. We present a quantitative model of mtDNA loss in a growing cell population and measure its parameters. To identify genetic adaptations to mtDNA depletion, we performed a genome-wide screen for gene dosage increases that affect the growth of cells lacking mtDNA. The screen revealed a set of dosage suppressors that alleviate the growth impairment in mtDNA-deficient cells. Additionally, we show that these suppressors of mtDNA stress both bolster cell proliferation and prevent mtDNA loss during mitochondrial protein stress.

Interactions between mitochondrial dysfunction and other hallmarks of aging: Paving a path toward interventions that promote healthy old age

Current research on human aging has largely been guided by the milestone paper "hallmarks of aging," which were first proposed in the seminal 2013 paper by Lopez-Otin et al. Most studies have focused on one aging hallmark at a time, asking whether the underlying molecular perturbations are sufficient to drive the aging process and its associated phenotypes. More recently, researchers have begun to investigate whether aging phenotypes are driven by concurrent perturbations in molecular pathways linked to not one but to multiple hallmarks of aging and whether they present different patterns in organs and systems over time. Indeed, preliminary results suggest that more complex interactions between aging hallmarks must be considered and addressed, if we are to develop interventions that successfully promote healthy aging and/or delay aging-associated dysfunction and diseases. Here, we summarize some of the latest work and views on the interplay between hallmarks of aging, with a specific focus on mitochondrial dysfunction. Indeed, this represents a significant example of the complex crosstalk between hallmarks of aging and of the effects that an intervention targeted to a specific hallmark may have on the others. A better knowledge of these interconnections, of their cause-effect relationships, of their spatial and temporal sequence, will be very beneficial for the whole aging research field and for the identification of effective interventions in promoting healthy old age.

Mitochondrial Diabetes Is Associated with the ND4 G11696A Mutation

Type 2 diabetes mellitus (T2DM) is a common endocrine disorder which remains a large challenge for clinicians. Previous studies have suggested that mitochondrial dysfunction plays an active role in T2DM progression, but a detailed mechanism is still elusive. In the current study, two Han Chinese families with maternally inherited T2DM were evaluated using clinical, genetic, molecular, and biochemical analyses. The mitochondrial genomes were PCR amplified and sequenced. Phylogenetic and bioinformatic analyses were used to assess the potential pathogenicity of mitochondrial DNA (mtDNA) mutations. Interestingly, the matrilineal relatives of these pedigrees exhibited variable severity of T2DM, in particular, the age at onset of T2DM varied from 26 to 65 years, with an average of 49 years. Sequence analysis revealed the presence of ND4 G11696A mutation, which resulted in the substitution of an isoleucine for valine at amino acid (AA) position 312. Indeed, this mutation was present in homoplasmy only in the maternal lineage, not in other members of these families, as well as 200 controls. Furthermore, the m.C5601T in the tRNA^Ala and novel m.T5813C in the tRNA^Cys, showing high evolutional conservation, may contribute to the phenotypic expression of ND4 G11696A mutation. In addition, biochemical analysis revealed that cells with ND4 G11696A mutation exhibited higher levels of reactive oxygen species (ROS) productions than the controls. In contrast, the levels of mitochondrial membrane potential (MMP), ATP, mtDNA copy number (mtDNA-CN), Complex I activity, and NAD⁺/NADH ratio significantly decreased in cell lines carrying the m.G11696A and tRNA mutations, suggesting that these mutations affected the respiratory chain function and led to mitochondrial dysfunction that was involved in T2DM. Thus, our study broadened the clinical phenotypes of m.G11696A mutation.

Assessment of the bi-directional relationship between blood mitochondrial DNA copy number and type 2 diabetes mellitus: a multivariable-adjusted regression and Mendelian randomisation study

AIMS/HYPOTHESIS

Mitochondrial dysfunction, which can be approximated by blood mitochondrial DNA copy number (mtDNA-CN), has been implicated in the pathogenesis of type 2 diabetes mellitus. Thus far, however, insights from prospective cohort studies and Mendelian randomisation (MR) analyses on this relationship are limited. We assessed the association between blood mtDNA-CN and incident type 2 diabetes using multivariable-adjusted regression analyses, and the associations between blood mtDNA-CN and type 2 diabetes and BMI using bi-directional MR.

METHODS

Multivariable-adjusted Cox proportional hazard models were used to estimate the association between blood mtDNA-CN and incident type 2 diabetes in 285,967 unrelated European individuals from UK Biobank free of type 2 diabetes at baseline. Additionally, a cross-sectional analysis was performed to investigate the association between blood mtDNA-CN and BMI. We also assessed the potentially causal relationship between blood mtDNA-CN and type 2 diabetes (N=898,130 from DIAGRAM, N=215,654 from FinnGen) and BMI (N=681,275 from GIANT) using bi-directional two-sample MR.

RESULTS

During a median follow-up of 11.87 years, 15,111 participants developed type 2 diabetes. Participants with a higher level of blood mtDNA-CN are at lower risk of developing type 2 diabetes (HR 0.90 [95% CI 0.89, 0.92]). After additional adjustment for BMI and other confounders, these results attenuated moderately and remained present. The multivariable-adjusted cross-sectional analyses showed that higher blood mtDNA-CN was associated with lower BMI (-0.12 [95% CI -0.14, -0.10]) kg/m2. In the bi-directional MR analyses, we found no evidence for causal associations between blood mtDNA-CN and type 2 diabetes, and blood mtDNA-CN and BMI in either direction.

CONCLUSIONS/INTERPRETATION

The results from the present study indicate that the observed association between low blood mtDNA-CN and higher risk of type 2 diabetes is likely not causal.

Glyoxalase 1 knockdown induces age-related β-cell dysfunction and glucose intolerance in mice

Tight control of glycemia is a major treatment goal for type 2 diabetes mellitus (T2DM). Clinical studies indicated that factors other than poor glycemic control may be important in fostering T2DM progression. Increased levels of methylglyoxal (MGO) associate with complications development, but its role in the early steps of T2DM pathogenesis has not been defined. Here, we show that MGO accumulation induces an age-dependent impairment of glucose tolerance and glucose-stimulated insulin secretion in mice knockdown for glyoxalase 1 (Glo1KD). This metabolic alteration associates with the presence of insular inflammatory infiltration (F4/80-positive staining), the islet expression of senescence markers, and higher levels of cytokines (MCP-1 and TNF-α), part of the senescence-activated secretory profile, in the pancreas from 10-month-old Glo1KD mice, compared with their WT littermates. In vitro exposure of INS832/13 β-cells to MGO confirms its casual role on β-cell dysfunction, which can be reverted by senolytic treatment. These data indicate that MGO is capable to induce early phenotypes typical of T2D progression, paving the way for novel prevention approaches to T2DM.

Endocrine Manifestations and New Developments in Mitochondrial Disease

Mitochondrial diseases are a group of common inherited diseases causing disruption of oxidative phosphorylation. Some patients with mitochondrial disease have endocrine manifestations, with diabetes mellitus being predominant but also include hypogonadism, hypoadrenalism, and hypoparathyroidism. There have been major developments in mitochondrial disease over the past decade that have major implications for all patients. The collection of large cohorts of patients has better defined the phenotype of mitochondrial diseases and the majority of patients with endocrine abnormalities have involvement of several other systems. This means that patients with mitochondrial disease and endocrine manifestations need specialist follow-up because some of the other manifestations, such as stroke-like episodes and cardiomyopathy, are potentially life threatening. Also, the development and follow-up of large cohorts of patients means that there are clinical guidelines for the management of patients with mitochondrial disease. There is also considerable research activity to identify novel therapies for the treatment of mitochondrial disease. The revolution in genetics, with the introduction of next-generation sequencing, has made genetic testing more available and establishing a precise genetic diagnosis is important because it will affect the risk for involvement for different organ systems. Establishing a genetic diagnosis is also crucial because important reproductive options have been developed that will prevent the transmission of mitochondrial disease because of mitochondrial DNA variants to the next generation.

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

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

Prescription Drugs and Mitochondrial Metabolism

Mitochondria are central to the physiology and survival of nearly all eukaryotic cells and house diverse metabolic processes including oxidative phosphorylation, reactive oxygen species buffering, metabolite synthesis/exchange, and Ca2+ sequestration. Mitochondria are phenotypically heterogeneous and this variation is essential to the complexity of physiological function among cells, tissues, and organ systems. As a consequence of mitochondrial integration with so many physiological processes, small molecules that modulate mitochondrial metabolism induce complex systemic effects. In the case of many common prescribed drugs, these interactions may contribute to drug therapeutic mechanisms, induce adverse drug reactions, or both. The purpose of this article is to review historical and recent advances in the understanding of the effects of prescription drugs on mitochondrial metabolism. Specific 'modes' of xenobiotic-mitochondria interactions are discussed to provide a set of qualitative models that aid in conceptualizing how the mitochondrial energy transduction system may be affected. Findings of recent in vitro high-throughput screening studies are reviewed, and a few candidate drug classes are chosen for additional brief discussion (i.e. antihyperglycemics, antidepressants, antibiotics, and antihyperlipidemics). Finally, recent improvements in pharmacokinetic models that aid in quantifying systemic effects of drug-mitochondria interactions are briefly considered.

TAL effectors and the predicted host targets of pomegranate bacterial blight pathogen Xanthomonas citri pv. punicae

The molecular mechanism of pomegranate susceptibility to bacterial blight, a serious threat to pomegranate production in India, is largely unknown. In the current study, we have used PacBio and Illumina sequencing of Xanthomonas citri pv. punicae (Xcp) strain 119 genome to identify tal genes and RNA-Seq analysis to identify putative host targets in the susceptible pomegranate variety Bhagwa challenged with Xcp119. Xcp119 genome encodes seven transcription activator-like effectors (TALEs), three of which are harbored by a plasmid. RVD-based phylogenetic analysis of TALEs of Xanthomonas citri pathovars indicate the TALEs of Xcp as evolutionarily and functionally close to Xanthomonas citri pv. malvacearum and Xanthomonas citri pv. glycines. Comparative RNA-Seq of Xcp and mock-inoculated leaf tissues revealed Xcp-induced pomegranate transcription modulation. The prediction of TALE binding elements (EBEs) in the promoters of up-regulated genes identified a set of TALE-targeted candidate genes in pomegranate-Xcp interaction. The predicted candidate susceptibility genes include two oxoglutarate-dependent dioxygenase gene, ethylene-responsive transcription factor and flavanone 3-hydroxylase-like gene, and the further characterization of these would enable blight resistance engineering in pomegranate.

Complete genome sequence of Microbulbifer sp. YPW1 from mangrove sediments in Yanpu harbor, China

In this work, a strain named YPW1 was isolated from the sediments of an artificial mangrove in Yanpu harbor, China. A complete genome of YPW1 was sequenced and assembled. The 16S rRNA gene assigned strain YPW1 into genus Microbulbifer, and the maximum values of average nucleotide identity and digital DNA-DNA hybridization of ZHDP1 genome were 90.36 and 68.1, respectively, indicating that YPW1 was a potential new species in genus Microbulbifer. A total of 10 representative genomes from genus Microbulbifer were selected to compare with YPW1. The results showed that the genome of strain YPW1 possessed more carbohydrate-active enzyme genes to transform various recalcitrant polysaccharides into bioavailable monosaccharides than those of the selected genomes. Furthermore, among the selected genomes, YPW1 was the only strain with nitrate, nitrite, and nitric oxide reductases which could appoint nitrous oxide, a powerful greenhouse gas, as the end-product of its denitrification process. Therefore, strain YPW1 was a potential novel member of genus Microbulbifer with special ecological roles in the cycles of carbon and nitrogen in mangrove ecosystems.

Association of mitochondrial DNA copy number with metabolic syndrome and type 2 diabetes in 14 176 individuals

BACKGROUND

Mitochondria play an important role in cellular metabolism, and their dysfunction is postulated to be involved in metabolic disturbances. Mitochondrial DNA is present in multiple copies per cell. The quantification of mitochondrial DNA copy number (mtDNA-CN) might be used to assess mitochondrial dysfunction.

OBJECTIVES

We aimed to investigate the cross-sectional association of mtDNA-CN with type 2 diabetes and the potential mediating role of metabolic syndrome.

METHODS

We examined 4812 patients from the German Chronic Kidney Disease (GCKD) study and 9364 individuals from the Cooperative Health Research in South Tyrol (CHRIS) study. MtDNA-CN was measured in whole blood using a plasmid-normalized qPCR-based assay.

RESULTS

In both studies, mtDNA-CN showed a significant correlation with most metabolic syndrome parameters: mtDNA-CN decreased with increasing number of metabolic syndrome components. Furthermore, individuals with low mtDNA-CN had significantly higher odds of metabolic syndrome (OR = 1.025; 95% CI = 1.011-1.039, P = 3.19 × 10-4 , for each decrease of 10 mtDNA copies) and type 2 diabetes (OR = 1.027; 95% CI = 1.012-1.041; P = 2.84 × 10-4 ) in a model adjusted for age, sex, smoking and kidney function in the meta-analysis of both studies. Mediation analysis revealed that the association of mtDNA-CN with type 2 diabetes was mainly mediated by waist circumference in the GCKD study (66%) and by several metabolic syndrome parameters, especially body mass index and triglycerides, in the CHRIS study (41%).

CONCLUSIONS

Our data show an inverse association of mtDNA-CN with higher risk of metabolic syndrome and type 2 diabetes. A major part of the total effect of mtDNA-CN on type 2 diabetes is mediated by obesity parameters.

Inhibition of glycolysis and mitochondrial respiration promotes radiosensitisation of neuroblastoma and glioma cells

BACKGROUND

Neuroblastoma accounts for 7% of paediatric malignancies but is responsible for 15% of all childhood cancer deaths. Despite rigorous treatment involving chemotherapy, surgery, radiotherapy and immunotherapy, the 5-year overall survival rate of high-risk disease remains < 40%, highlighting the need for improved therapy. Since neuroblastoma cells exhibit aberrant metabolism, we determined whether their sensitivity to radiotherapy could be enhanced by drugs affecting cancer cell metabolism.

METHODS

Using a panel of neuroblastoma and glioma cells, we determined the radiosensitising effects of inhibitors of glycolysis (2-DG) and mitochondrial function (metformin). Mechanisms underlying radiosensitisation were determined by metabolomic and bioenergetic profiling, flow cytometry and live cell imaging and by evaluating different treatment schedules.

RESULTS

The radiosensitising effects of 2-DG were greatly enhanced by combination with the antidiabetic biguanide, metformin. Metabolomic analysis and cellular bioenergetic profiling revealed this combination to elicit severe disruption of key glycolytic and mitochondrial metabolites, causing significant reductions in ATP generation and enhancing radiosensitivity. Combination treatment induced G2/M arrest that persisted for at least 24 h post-irradiation, promoting apoptotic cell death in a large proportion of cells.

CONCLUSION

Our findings demonstrate that the radiosensitising effect of 2-DG was significantly enhanced by its combination with metformin. This clearly demonstrates that dual metabolic targeting has potential to improve clinical outcomes in children with high-risk neuroblastoma by overcoming radioresistance.

Peroxisomes and pancreatic beta-cell lipo-dysfunction

AIMS

Pancreatic beta-cell lipo-dysfunction decreases insulin secretion and predisposes to the development of type 2 diabetes. Through targeted Pex11β knockdown and peroxisome depletion, our aim was to investigate the specific contribution of peroxisomes to palmitate mediated pancreatic beta-cell dysfunction.

METHODS

MIN6 cells were transfected with probes targeted against Pex11β, a regulator of peroxisome abundance, or with scrambled control probes. Peroxisome abundance was measured by PMP-70 protein expression. 48 h post transfection, cells were incubated with 250 μM palmitate or BSA control for a further 48 h before measurement of glucose stimulated insulin secretion and of reactive oxygen species.

RESULTS

Pex11β knockdown decreased target gene expression by >80% compared with the scrambled control (P<0.001). This led to decreased PMP-70 expression (p<0.01) and a 22% decrease in peroxisome number (p<0.05). At 25 mM glucose, palmitate treatment decreased insulin secretion by 64% in the scrambled control cells (2.54±0.25 vs 7.07±0.83 [mean±SEM] ng/h/μg protein; Palmitate vs BSA P<0.001), but by just 37% in the Pex11β knockdown cells. Comparing responses in the presence of palmitate, insulin secretion at 25 mM glucose was significantly greater in the Pex11β knockdown cells compared with the scrambled controls (4.04±0.46 vs 2.54±0.25 ng/h/μg protein; p<0.05). Reactive oxygen species generation with palmitate was lower in the Pex11β knockdown cells compared with the scrambled controls (P<0.001).

CONCLUSION

Pex11β knockdown decreased peroxisome abundance, decreased palmitate mediated reactive oxygen species generation, and reversed the inhibitory effect of palmitate on insulin secretion. These findings reveal a distinct role of peroxisomes in palmitate mediated beta-cell dysfunction.

Mannheimia bovis sp. nov., Isolated from a Dead Cow with Hemorrhagic Pneumonia

Strain ZY190616^T was isolated from lung of a dead cow with hemorrhagic pneumonia in Yunnan Province, China. The strain was Gram-stain-negative, facultatively anaerobic bacterium. Phylogenetic analysis based on 16S rRNA gene sequence indicated that the strain was closely related to species of the genus Mannheimia and formed an independent clade with M.varigena CCUG 38462 ^T (97.0% similarity). Phylogenetic analysis based on recN gene indicated that the strain formed a clade with M.caviae CCUG 59995 ^T (87.8% similarity). Phylogenetic analysis based on rpoB gene indicated that the strain formed a clade with M.varigena CCUG 38462 ^T (94.7% similarity). The genomic OrthoANI values between strain ZY190616^T and M. ovis, M.haemolytica and M.granulomatis were 84.5%, 82.7% and 81.9%, respectively. The genomic G + C content was 39.8 mol%. The predominant fatty acids (> 5%) of the strain were C_16:0, C_14:0, C_18:1ω7c, summed feature 3 (C_16:1 ω7c and/ or C_16:1ω6c) and summed feature 2 (C14:0 3OH/ C16:1 Iso). The major polar lipids were phosphatidylglycerol (PG), phosphatidylethanolamine (PE), monophosphatidylglycerol (MGDG), triacylglycerol (TAG) and diphosphatidylglycerol (DLCL). The sole respiratory quinone was CoQ-7. Based on evidence from the taxonomic study, strain ZY190616^T represents a novel species of the genus Mannheimia, for which the name Mannheimia bovis sp. nov. is proposed. The type strain is ZY190616^T (= CCTCC AB 2020168 ^T = KCTC 25018 ^T).

Age-induced mitochondrial DNA point mutations are inadequate to alter metabolic homeostasis in response to nutrient challenge

Mitochondrial dysfunction is frequently associated with impairment in metabolic homeostasis and insulin action, and is thought to underlie cellular aging. However, it is unclear whether mitochondrial dysfunction is a cause or consequence of insulin resistance in humans. To determine the impact of intrinsic mitochondrial dysfunction on metabolism and insulin action, we performed comprehensive metabolic phenotyping of the polymerase gamma (PolG) D257A "mutator" mouse, a model known to accumulate supraphysiological mitochondrial DNA (mtDNA) point mutations. We utilized the heterozygous PolG mutator mouse (PolG+/mut ) because it accumulates mtDNA point mutations ~ 500-fold > wild-type mice (WT), but fails to develop an overt progeria phenotype, unlike PolGmut/mut animals. To determine whether mtDNA point mutations induce metabolic dysfunction, we examined male PolG+/mut mice at 6 and 12 months of age during normal chow feeding, after 24-hr starvation, and following high-fat diet (HFD) feeding. No marked differences were observed in glucose homeostasis, adiposity, protein/gene markers of metabolism, or oxygen consumption in muscle between WT and PolG+/mut mice during any of the conditions or ages studied. However, proteomic analyses performed on isolated mitochondria from 12-month-old PolG+/mut mouse muscle revealed alterations in the expression of mitochondrial ribosomal proteins, electron transport chain components, and oxidative stress-related factors compared with WT. These findings suggest that mtDNA point mutations at levels observed in mammalian aging are insufficient to disrupt metabolic homeostasis and insulin action in male mice.

Functional changes in beta cells during ageing and senescence

Insulin secretion from beta cells is crucial for maintaining euglycaemia and preventing type 2 diabetes, a disease correlated with ageing. Therefore, understanding the functional changes that beta cell function undergoes with age can reveal new therapeutic targets and strategies to delay or revert the disease. Herein, a systematic review of the literature agrees that, as humans age, their beta cell function declines, independently of peripheral insulin resistance, BMI and waist circumference. Rodent studies reveal that, with age, basal insulin secretion increases with either no change or an increase in stimulated insulin secretion, but the biological significance of this is unclear. The accumulation of senescent beta cells could explain some of these functional changes: transcriptional analysis of senescent and aged beta cells revealed parallel downregulation of several steps along the pathway linking glucose stimulation and insulin secretion. Moreover, specific deletion of senescent cells (senolysis) improved residual beta cell function, gene expression profile and blood glucose levels. In conclusion, cellular senescence could underlie the functional decline of beta cells during ageing and could represent a novel and promising approach for recovering insulin secretion. Graphical abstract.

Altered Transcription Factor Binding and Gene Bivalency in Islets of Intrauterine Growth Retarded Rats

Intrauterine growth retardation (IUGR), which induces epigenetic modifications and permanent changes in gene expression, has been associated with the development of type 2 diabetes. Using a rat model of IUGR, we performed ChIP-Seq to identify and map genome-wide histone modifications and gene dysregulation in islets from 2- and 10-week rats. IUGR induced significant changes in the enrichment of H3K4me3, H3K27me3, and H3K27Ac marks in both 2-wk and 10-wk islets, which were correlated with expression changes of multiple genes critical for islet function in IUGR islets. ChIP-Seq analysis showed that IUGR-induced histone mark changes were enriched at critical transcription factor binding motifs, such as C/EBPs, Ets1, Bcl6, Thrb, Ebf1, Sox9, and Mitf. These transcription factors were also identified as top upstream regulators in our previously published transcriptome study. In addition, our ChIP-seq data revealed more than 1000 potential bivalent genes as identified by enrichment of both H3K4me3 and H3K27me3. The poised state of many potential bivalent genes was altered by IUGR, particularly Acod1, Fgf21, Serpina11, Cdh16, Lrrc27, and Lrrc66, key islet genes. Collectively, our findings suggest alterations of histone modification in key transcription factors and genes that may contribute to long-term gene dysregulation and an abnormal islet phenotype in IUGR rats.

Leukocyte Telomere Length Independently Predicts 3-Year Diabetes Risk in a Longitudinal Study of Chinese Population

Cellular aging markers, including telomere length and mitochondrial function, as well as oxidative stress and inflammation markers influence each other and form a complex network, which is affected in diabetes. However, it remains unknown whether these markers could independently predict future diabetes after adjustment for their mutual effects. We conducted a 3-year longitudinal study in a Chinese cohort that comprised 108 nondiabetic individuals at baseline. The 2-hour 75 g oral glucose tolerance tests were performed at baseline and at 3-year follow-up. At baseline, leukocyte telomere length (LTL) and mitochondrial DNA copy number (mtDNAcn) in leukocytes were determined using the polymerase chain reaction method. Tumor necrosis factor (TNF-α), interleukin-6, 8-hydroxy-2-deoxyguanosine levels, and superoxide dismutase (SOD) activity were measured by the enzyme-linked immunosorbent assay. Participants who developed diabetes at the 3-year follow-up (n = 28) had shorter LTL and higher levels of TNF-α and SOD activity at baseline. Baseline LTL was found to be independently associated with the development of diabetes at the 3-year follow-up after the adjustment for mtDNAcn, markers of oxidative stress and inflammation, and conventional diabetes risk factors. Our findings suggest that LTL is an independent predictor for 3-year diabetes risk, which might inform timely prevention and treatment of diabetes. Telomere shortening might be involved in the pathogenesis of diabetes independently of conventional diabetes risk factors, mtDNAcn, or oxidative stress and inflammation pathways.

Optimizing beta cell function through mesenchymal stromal cell-mediated mitochondria transfer

Pretransplant islet culture is associated with the loss of islet cell mass and insulin secretory function. Insulin secretion from islet β‐cells is primarily controlled by mitochondrial ATP generation in response to elevations in extracellular glucose. Coculture of islets with mesenchymal stromal cells (MSCs) improves islet insulin secretory function in vitro, which correlates with superior islet graft function in vivo. This study aimed to determine whether the improved islet function is associated with mitochondrial transfer from MSCs to cocultured islets. We have demonstrated mitochondrial transfer from human adipose MSCs to human islet β‐cells in coculture. Fluorescence imaging showed that mitochondrial transfer occurs, at least partially, through tunneling nanotube (TNT)‐like structures. The extent of mitochondrial transfer to clinically relevant human islets was greater than that to experimental mouse islets. Human islets are subjected to more extreme cellular stressors than mouse islets, which may induce “danger signals” for MSCs, initiating the donation of MSC‐derived mitochondria to human islet β‐cells. Our observations of increased MSC‐mediated mitochondria transfer to hypoxia‐exposed mouse islets are consistent with this and suggest that MSCs are most effective in supporting the secretory function of compromised β‐cells. Ensuring optimal MSC‐derived mitochondria transfer in preculture and/or cotransplantation strategies could be used to maximize the therapeutic efficacy of MSCs, thus enabling the more widespread application of clinical islet transplantation.

Mitochondrial DNA copy number associates with insulin sensitivity and aerobic capacity, and differs between sedentary, overweight middle-aged males with and without type 2 diabetes

BACKGROUND/OBJECTIVES

Increased risk of type 2 diabetes mellitus (T2DM) is linked to impaired muscle mitochondrial function and reduced mitochondrial DNA copy number (mtDNA^num). However, studies have failed to control for habitual physical activity levels, which directly influences both mtDNA copy number and insulin sensitivity. We, therefore, examined whether physical conditioning status (maximal oxygen uptake, V̇O_2max) was associated with skeletal muscle mitochondrial volume and mtDNA^num, and was predictive of T2DM in overweight, middle-aged men.

METHODS

Whole-body physiological (ISI-insulin sensitivity index, HOMA-IR, V̇O_2max) and muscle biochemical/molecular (vastus lateralis; mtDNA^num, mitochondrial and glycolytic enzymes activity, lipid content and markers of lipid peroxidation) measurements were performed in three groups of overweight, middle-aged male volunteers (n = 10 per group): sedentary T2DM (ST2DM); sedentary control (SC) and non-sedentary control (NSC), who differed in aerobic capacity (ST2DM < SC < NSC).

RESULTS

mtDNA^num was greater in NSC versus SC and ST2DM (P < 0.001; P < 0.001), and less in ST2DM versus SC (P < 0.01). Across all groups, mtDNA^num positively correlated with ISI (P < 0.001; r = 0.688) and V̇O_2max (normalised to free fat mass; r = 0.684, P < 0.001), and negatively correlated to HOMA-IR (r = -0.544, P < 0.01). The activity of mitochondrial enzymes (GluDH, CS and β-HAD) was greater in NSC than ST2DM (P < 0.01, P < 0.001 and P < 0.05) and SC (P < 0.05, P < 0.01 and P < 0.05), but similar between ST2DM and SC. Intramuscular-free fatty acids, triglycerides and malondialdehyde contents were similar between ST2DM and SC.

CONCLUSIONS

Body composition and indices of muscle mitochondrial volume/function were similar between SC and ST2DM. However, mtDNA^num differed and was positively associated with ISI, HOMA-IR and V̇O_2max across all groups. Collectively, the findings support the contention that habitual physical activity is a key component of T2DM development, possibly by influencing mtDNA^num.

Role of mitochondria in diabetic peripheral neuropathy: Influencing the NAD+-dependent SIRT1-PGC-1α-TFAM pathway

Survival of human peripheral nervous system neurons and associated distal axons is highly dependent on energy. Diabetes invokes a maladaptation in glucose and lipid energy metabolism in adult sensory neurons, axons and Schwann cells. Mitochondrial (Mt) dysfunction has been implicated as an etiological factor in failure of energy homeostasis that results in a low intrinsic aerobic capacity within the neuron. Over time, this energy failure can lead to neuronal and axonal degeneration and results in increased oxidative injury in the neuron and axon. One of the key pathways that is impaired in diabetic peripheral neuropathy (DPN) is the energy sensing pathway comprising the nicotinamide-adenine dinucleotide (NAD⁺)-dependent Sirtuin 1 (SIRT1)/peroxisome proliferator-activated receptor-γ coactivator α (PGC-1α)/Mt transcription factor A (TFAM or mtTFA) signaling pathway. Knockout of PGC-1α exacerbates DPN, whereas overexpression of human TFAM is protective. LY379268, a selective metabolomic glutamate receptor 2/3 (mGluR2/3) receptor agonist, also upregulates the SIRT1/PGC-1α/TFAM signaling pathway and prevents DPN through glutamate recycling in Schwann/satellite glial (SG) cells and by improving dorsal root ganglion (DRG) neuronal Mt function. Furthermore, administration of nicotinamide riboside (NR), a precursor of NAD⁺, prevents and reverses DPN, in part by increasing NAD⁺ levels and SIRT1 activity. In summary, we review the role of NAD⁺, mitochondria and the SIRT1-PGC-1α-TFAM pathway both from the perspective of pathogenesis and therapy in DPN.

Urinary mitochondrial DNA: A potential early biomarker of diabetic nephropathy

BACKGROUND

Mitochondrial dysfunction and chronic sterile inflammation are common features of type 2 diabetes. Therefore, we aimed to investigate whether mitochondrial DNA (mtDNA) could be a biomarker implicated in the progression of type 2 diabetes and diabetic nephropathy and explore the underlying mechanism.

MATERIAL AND METHODS

We developed a method for relative quantification of mtDNA content in clinical practice. qRT-PCR was used to measure the mtDNA content both in vivo in CD-1 mice with diabetes induction by streptozotocin and in vitro in murine endothelial cells and conditionally immortalized mouse podocytes. By pumping mtDNA into the mouse circulation, the effect of mtDNA on the kidney was assessed in mice. In patients with type 2 diabetes (n = 42; 24 males; mean age 57.9 ± 12.00 years), plasma mtDNA was evaluated.

RESULTS

Plasma mtDNA content was significantly decreased in patients with type 2 diabetes, particularly those with significant proteinuria. In vitro, high glucose treatment suppressed intracellular mtDNA content and facilitated the extracellular release of mtDNA, so excessive circulatory mtDNA induced by high glucose might be filtered through the kidney and then into urine. Indeed, urinary mtDNA content was significantly increased in both diabetic patients and mice. Moreover, by pumping excess mtDNA into circulation in mice, filtered mtDNA could trigger inflammation and induce kidney injury.

CONCLUSION

Excessive mtDNA filtered through the kidney under diabetic conditions may be involved in chronic renal inflammation. Reduced plasma mtDNA content and increased urinary mtDNA/creatinine ratio might play a potential role as an early biomarker of diabetic nephropathy.

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.

Mitochondrial dysfunction in type 2 diabetes mellitus: an organ-based analysis

Type 2 diabetes mellitus (T2DM) is a systemic disease characterized by hyperglycemia, hyperlipidemia, and organismic insulin resistance. This pathological shift in both circulating fuel levels and energy substrate utilization by central and peripheral tissues contributes to mitochondrial dysfunction across organ systems. The mitochondrion lies at the intersection of critical cellular pathways such as energy substrate metabolism, reactive oxygen species (ROS) generation, and apoptosis. It is the disequilibrium of these processes in T2DM that results in downstream deficits in vital functions, including hepatocyte metabolism, cardiac output, skeletal muscle contraction, β-cell insulin production, and neuronal health. Although mitochondria are known to be susceptible to a variety of genetic and environmental insults, the accumulation of mitochondrial DNA (mtDNA) mutations and mtDNA copy number depletion is helping to explain the prevalence of mitochondrial-related diseases such as T2DM. Recent work has uncovered novel mitochondrial biology implicated in disease progressions such as mtDNA heteroplasmy, noncoding RNA (ncRNA), epigenetic modification of the mitochondrial genome, and epitranscriptomic regulation of the mtDNA-encoded mitochondrial transcriptome. The goal of this review is to highlight mitochondrial dysfunction observed throughout major organ systems in the context of T2DM and to present new ideas for future research directions based on novel experimental and technological innovations in mitochondrial biology. Finally, the field of mitochondria-targeted therapeutics is discussed, with an emphasis on novel therapeutic strategies to restore mitochondrial homeostasis in the setting of T2DM.

Age-Dependent Protection of Insulin Secretion in Diet Induced Obese Mice

Type 2 diabetes is an age-and-obesity associated disease driven by impairments in glucose homeostasis that ultimately result in defective insulin secretion from pancreatic β-cells. To deconvolve the effects of age and obesity in an experimental model of prediabetes, we fed young and aged mice either chow or a short-term high-fat/high-sucrose Western diet (WD) and examined how weight, glucose tolerance, and β-cell function were affected. Although WD induced a similar degree of weight gain in young and aged mice, a high degree of heterogeneity was found exclusively in aged mice. Weight gain in WD-fed aged mice was well-correlated with glucose intolerance, fasting insulin, and in vivo glucose-stimulated insulin secretion, relationships that were not observed in young animals. Although β-cell mass expansion in the WD-fed aged mice was only three-quarters of that observed in young mice, the islets from aged mice were resistant to the sharp WD-induced decline in ex vivo insulin secretion observed in young mice. Our findings demonstrate that age is associated with the protection of islet function in diet-induced obese mice, and furthermore, that WD challenge exposes variability in the resilience of the insulin secretory pathway in aged mice.

Reversing wrinkled skin and hair loss in mice by restoring mitochondrial function

Mitochondrial DNA (mtDNA) depletion is involved in mtDNA depletion syndromes, mitochondrial diseases, aging and aging-associated chronic diseases, and other human pathologies. To evaluate the consequences of depletion of mtDNA in the whole animal, we created an inducible mtDNA-depleter mouse expressing, in the polymerase domain of POLG1, a dominant-negative mutation to induce depletion of mtDNA in various tissues. These mice showed reduced mtDNA content, reduced mitochondrial gene expression, and instability of supercomplexes involved in oxidative phosphorylation (OXPHOS) resulting in reduced OXPHOS enzymatic activities. We demonstrate that ubiquitous depletion of mtDNA in mice leads to predominant and profound effects on the skin resulting in wrinkles and visual hair loss with an increased number of dysfunctional hair follicles and inflammatory responses. Development of skin wrinkle was associated with the significant epidermal hyperplasia, hyperkeratosis, increased expression of matrix metalloproteinases, and decreased expression of matrix metalloproteinase inhibitor TIMP1. We also discovered markedly increased skin inflammation that appears to be a contributing factor in skin pathology. Histopathologic analyses revealed dysfunctional hair follicles. mtDNA-depleter mice also show changes in expression of aging-associated markers including IGF1R, KLOTHO, VEGF, and MRPS5. mtDNA-repleter mice showed that, by turning off the mutant POLG1 transgene expression, mitochondrial function, as well as the skin and hair pathology, is reversed to wild-type level. To our knowledge that restoration of mitochondrial functions can reverse the skin and hair pathology is unprecedented.

Prolonged Activation of the Htr2b Serotonin Receptor Impairs Glucose Stimulated Insulin Secretion and Mitochondrial Function in MIN6 Cells

Aims

Pancreatic β-cells synthesize and release serotonin (5 hydroxytryptamine, 5HT); however, the role of 5HT receptors on glucose stimulated insulin secretion (GSIS) and the mechanisms mediating this function is not fully understood. The aims of this study were to determine the expression profile of 5HT receptors in murine MIN6 β-cells and to examine the effects of pharmacological activation of 5HT receptor Htr2b on GSIS and mitochondrial function.

Materials and Methods

mRNA levels of 5HT receptors in MIN6 cells were quantified by RT qPCR. GSIS was assessed in MIN6 cells in response to global serotonergic activation with 5HT and pharmacological Htr2b activation or inhibition with BW723C86 or SB204741, respectively. In response to Htr2b activation also was evaluated the mRNA and protein levels of PGC1α and PPARy by RT-qPCR and western blotting and mitochondrial function by oxygen consumption rate (OCR) and ATP cellular content.

Results

We found that mRNA levels of most 5HT receptors were either very low or undetectable in MIN6 cells. By contrast, Htr2b mRNA was present at moderate levels in these cells. Preincubation (6 h) of MIN6 cells with 5HT or BW723C86 reduced GSIS and the effect of 5HT was prevented by SB204741. Preincubation with BW723C86 increased PGC1α and PPARy mRNA and protein levels and decreased mitochondrial respiration and ATP content in MIN6 cells.

Conclusions

Our results indicate that prolonged Htr2b activation in murine β-cells decreases glucose-stimulated insulin secretion and mitochondrial activity by mechanisms likely dependent on enhanced PGC1α/PPARy expression.

Reduced peripheral blood mtDNA content is associated with impaired glucose-stimulated islet β cell function in a Chinese population with different degrees of glucose tolerance

AIMS

Our aim is to explore the associations between mitochondrial DNA (mtDNA) content and basal plasma glucose, plasma glucose after oral glucose administration and oxidative stress in a Chinese population with different levels of glucose tolerance. We also aimed to investigate the effect of mtDNA content on basal and oral glucose-stimulated insulin secretion.

METHODS

Five hundred and fifty-six Chinese subjects underwent a 75-g, 2-h oral glucose tolerance test. Subjects with diabetes (n = 159), pre-diabetes (n = 197) and normal glucose tolerance (n = 200) were screened. Blood lipid profile was assessed, and levels of the oxidative stress indicators superoxide dismutase, glutathione reductase (GR) and 8-oxo-2'-deoxyguanosine (8-oxo-dG) were measured. Levels of HbA_1c , plasma glucose, insulin and C-peptide were also determined. Measurements were taken at 0, 30, 60 and 120 min after 75 g oral glucose tolerance test. Peripheral blood mtDNA content was assessed using a real-time polymerase chain reaction assay. Insulin sensitivity was evaluated by homeostatic model assessment of insulin resistance and Matsuda index (ISI_M ). Basal insulin secretion index (HOMA-β), early phase disposition index (DI₃₀ ) and total phase disposition index (DI₁₂₀ ) indicate insulin levels at different phases of insulin secretion.

RESULTS

Peripheral blood mtDNA content was positively associated with DI₃₀ and DI₁₂₀ and was negatively associated with plasma glucose measured 30, 60 and 120 min after oral glucose administration. However, there was no correlation between mtDNA content and basal insulin secretion (HOMA-β), serum lipid or oxidative stress indicators (8-oxo-dG, superoxide dismutase, GR). HbA_1c was negatively associated with GR (r = -0.136, p = 0.001). Multiple linear regression analysis showed that reduced peripheral blood mtDNA content increased the risk of impaired glucose-stimulated β cell function (DI₃₀ : β = 0.104, p = 0.019; DI₁₂₀ : β = 0.116, p = 0.009).

CONCLUSIONS

Decreased peripheral blood mtDNA content was more closely associated with glucose-stimulated insulin secretion than with basal secretion. Reduction in glucose-stimulated insulin secretion causes postprandial hyperglycaemia. The oxidative stress was probably largely influenced by hyperglycaemia; it was probably that the decreased mt DNA content led to hyperglycaemia, which caused elevated oxidative stress. © 2016 The Authors. Diabetes/Metabolism Research and Reviews Published by John Wiley & Sons Ltd.

When two obese parents are worse than one! Impacts on embryo and fetal development

The prevalence of overweight and obesity in reproductive-age adults is increasing worldwide. While the effects of either paternal or maternal obesity on gamete health and subsequent fertility and pregnancy have been reported independently, the combination of having both parents overweight/obese on fecundity and offspring health has received minimal attention. Using a 2 × 2 study design in rodents we established the relative contributions of paternal and maternal obesity on fetal and embryo development and whether combined paternal and maternal obesity had an additive effect. Here, we show that parental obesity reduces fetal and placental weights without altering pregnancy establishment and is not dependent on an in utero exposure to a high-fat diet. Interestingly combined parental obesity seemed to accumulate both the negative influences of paternal and maternal obesity had alone on embryo and fetal health rather than an amplification, manifested as reduced embryo developmental competency, reduced blastocyst cell numbers, impaired mitochondrial function, and alterations to active and repressive embryonic chromatin marks, resulting in aberrant placental gene expression and reduced fetal liver mtDNA copy numbers. Further understanding both the maternal cytoplasmic and paternal genetic interactions during this early developmental time frame will be vital for understanding how developmental programming is regulated and for the proposition of interventions to mitigate their effects.

Mitochondrial transcription factor A regulation of mitochondrial degeneration in experimental diabetic neuropathy

Oxidative stress-induced mitochondrial dysfunction and mitochondrial DNA (mtDNA) damage in peripheral neurons is considered to be important in the development of diabetic neuropathy. Mitochondrial transcription factor A (TFAM) wraps mtDNA and promotes mtDNA replication and transcription. We studied whether overexpression of TFAM reverses experimental peripheral diabetic neuropathy using TFAM transgenic mice (TFAM Tg) that express human TFAM (hTFAM). Levels of mouse mtDNA and the total TFAM (mouse TFAM + hTFAM) in the dorsal root ganglion (DRG) increased by approximately twofold in the TFAM Tg mice compared with control (WT) mice. WT and TFAM Tg mice were made diabetic by the administration of streptozotocin. Neuropathy end points were motor and sensory nerve conduction velocities, mechanical allodynia, thermal nociception, and intraepidermal nerve fiber density (IENFD). In the DRG neurons, mtDNA copy number and damage to mtDNA were quantified by qPCR, and TFAM levels were measured by Western blot. Mice with 16-wk duration of diabetes developed motor and sensory nerve conduction deficits, behavioral deficits, and intraepidermal nerve fiber loss. All of these changes were mostly prevented in diabetic TFAM Tg mice and were independent of changes in blood parameters. Mice with 16 wk of diabetes had a 40% decrease in mtDNA copy number compared with nondiabetic mice (P < 0.01). Importantly, the mtDNA copy number in diabetic TFAM Tg mice reached the same level as that of WT nondiabetic mice. In comparison, there was upregulation of mtDNA and TFAM in 6-wk diabetic mice, suggesting that TFAM activation could be a therapeutic strategy to treat peripheral neuropathy.

Circulating cell-free mitochondrial DNA as the probable inducer of early endothelial dysfunction in the prediabetic patient

Recent evidence has shown that 346million people in the world have diabetes mellitus (DM); this number will increase to 439million by 2030. In addition, current data indicate an increase in DM cases in the population between 40 and 59years of age. Diabetes is associated with the development of micro- and macro-vascular complications, derived from chronic hyperglycemia on the endothelium. Some reports demonstrate that people in a prediabetic state have a major risk of developing early endothelial dysfunction (ED). Today, it is accepted that individuals considered as prediabetic patients are in a pro-inflammatory state associated with endothelial and mitochondrial dysfunction. It is important to mention that impaired mitochondrial functionality has been linked to endothelial apoptosis and release of mitochondrial DNA (mtDNA) in patients with sepsis, cardiac disease, or atherosclerosis. This free mtDNA could promote ED, as well as other side effects on the vascular system through the activation of the toll-like receptor 9 (TLR9). TLR9 is expressed in different cell types (e.g., T or B lymphocytes, mastocytes, and epithelial and endothelial cells). It is localized intracellularly and recognizes non-methylated dinucleotides of viral, bacterial, and mitochondrial DNA. Recently, it has been reported that TLR9 is associated with the pathogenesis of lupus erythematosus, rheumatoid arthritis, and autoimmune diabetes. In this work, it is hypothesized that the increase in the levels of circulating mtDNA is the trigger of early ED in the prediabetic patient, and later on in the older patient with diabetes, through activation of the TLR9 present in the endothelium.