Mitochondria-Based Model for Fetal Origin of Adult Disease and Insulin Resistance

Relationships among Dioxin-like Mitochondria Inhibitor Substances (MIS)-Mediated Mitochondria Dysfunction, Obesity, and Lung Function in a Korean Cohort

Mitochondrial dysfunction is closely linked to obesity and diabetes, with declining lung function in aging increasing diabetes risk, potentially due to elevated serum levels of dioxin-like mitochondria inhibitor substances (MIS) from prolonged exposure to environmental pollutants. However, the mechanisms connecting MIS, mitochondria, lung function, and metabolic disorder remain unclear. In this study, we analyzed data from 1371 adults aged 40-69 years in the 2008 Korean Genome Epidemiologic Study (KoGES) Ansung cohort. We indirectly estimated dioxin-like MIS levels by measuring intracellular ATP (MISATP) and reactive oxygen species (MISROS) in cultured cells treated with the serum of participants. Using correlation analysis and structural equation modeling (SEM), we explored the relationships among MIS, mitochondrial function, body mass index (BMI), and lung function (FEV1 and FVC). Our findings revealed that MISATP was associated with BMI in females and with FVC in males, while MISROS correlated with both BMI and FVC in males, not in females. Significant associations between BMI and FVC were found in the highest MIS subgroup in both sexes. SEM analyses demonstrated that MIS negatively influenced mitochondrial function, which in turn affected BMI and lung function. Age-related declines in lung function were also linked to mitochondrial dysfunction. This study underscores the potential of MIS assays as alternatives for assessing mitochondrial function and highlights the importance of mitochondrial health in metabolic disorders and lung function.

The Cord Blood Insulin and Mitochondrial DNA Content Related Methylome

Mitochondrial dysfunction seems to play a key role in the etiology of insulin resistance. At birth, a link has already been established between mitochondrial DNA (mtDNA) content and insulin levels in cord blood. In this study, we explore shared epigenetic mechanisms of the association between mtDNA content and insulin levels, supporting the developmental origins of this link. First, the association between cord blood insulin and mtDNA content in 882 newborns of the ENVIRONAGE birth cohort was assessed. Cord blood mtDNA content was established via qPCR, while cord blood levels of insulin were determined using electrochemiluminescence immunoassays. Then the cord blood DNA methylome and transcriptome were determined in 179 newborns, using the human 450K methylation Illumina and Agilent Whole Human Genome 8 × 60 K microarrays, respectively. Subsequently, we performed an epigenome-wide association study (EWAS) adjusted for different maternal and neonatal variables. Afterward, we focused on the 20 strongest associations based on p-values to assign transcriptomic correlates and allocate corresponding pathways employing the R packages ReactomePA and RDAVIDWebService. On the regional level, we examined differential methylation using the DMRcate and Bumphunter packages in R. Cord blood mtDNA content and insulin were significantly correlated (r = 0.074, p = 0.028), still showing a trend after additional adjustment for maternal and neonatal variables (p = 0.062). We found an overlap of 33 pathways which were in common between the association with cord blood mtDNA content and insulin levels, including pathways of neurodevelopment, histone modification, cytochromes P450 (CYP)-metabolism, and biological aging. We further identified a DMR annotated to Repulsive Guidance Molecule BMP Co-Receptor A (RGMA) linked to cord blood insulin as well as mtDNA content. Metabolic variation in early life represented by neonatal insulin levels and mtDNA content might reflect or accommodate alterations in neurodevelopment, histone modification, CYP-metabolism, and aging, indicating etiological origins in epigenetic programming. Variation in metabolic hormones at birth, reflected by molecular changes, might via these alterations predispose children to metabolic diseases later in life. The results of this study may provide important markers for following targeted studies.

Mitochondrial Dysfunction Linking Obesity and Asthma

The bidirectional epidemiological association between asthma and obesity is well known. Recent evidence suggests that there is an intersection of the pathophysiological molecular pathways leading to either obesity or asthma, at the level of mitochondria. This is not surprising, because mitochondria, beyond their roles as the metabolic powerhouses of the cell, serve as sensors of threats, regulators of stress signaling, and effectors of cytotoxicity. Reduced mitochondrial function and low metabolic activity are well-recognized features of obesity. Three distinct lines of experimental evidences connect mitochondrial dysfunction with asthma. First, asthma is associated with aberrant mitochondrial metabolism. Second, mitochondrial dysfunction may either induce asthma-like features or increase asthma severity. Third, mitochondria-targeted therapies appear effective in preventing or reversing asthma features. Importantly, mitochondrial dysfunction in airway epithelial cells appears to be a powerful trigger for airway remodeling that is independent of cellular inflammation. This is clinically relevant to the obese-asthma phenotype, with exaggerated symptoms despite apparently low levels of inflammation, and poor response to antiinflammatory treatment. In summary, mitochondrial dysfunction is a common thread tying together the twin epidemics of obesity and asthma. Environmental and lifestyle factors leading to primary mitochondrial dysfunction may be increasing the risk for either disease. Further, secondary mitochondrial dysfunction emerging from the pathogenesis of either obesity or asthma may increase the risk of the other. Mitochondrial health-centric strategies may be relevant to prevention and treatment of both obesity and asthma, and should be actively considered.

miR-24-mediated knockdown of H2AX damages mitochondria and the insulin signaling pathway

Mitochondrial deficits or altered expressions of microRNAs are associated with the pathogenesis of various diseases, and microRNA-operated control of mitochondrial activity has been reported. Using a retrovirus-mediated short-hairpin RNA (shRNA) system, we observed that miR-24-mediated H2AX knockdown (H2AX-KD) impaired both mitochondria and the insulin signaling pathway. The overexpression of miR-24 decreased mitochondrial H2AX and disrupted mitochondrial function, as indicated by the ATP content, membrane potential and oxygen consumption. Similar mitochondrial damage was observed in shH2AX-mediated specific H2AX-KD cells. The H2AX-KD reduced the expression levels of mitochondrial transcription factor A (TFAM) and mitochondrial DNA-dependent transcripts. H2AX-KD mitochondria were swollen, and their cristae were destroyed. H2AX-KD also blocked the import of precursor proteins into mitochondria and the insulin-stimulated phosphorylation of IRS-1 (Y632) and Akt (S473 and T308). The rescue of H2AX, but not the nuclear form of ΔC24-H2AX, restored all features of miR-24- or shH2AX-mediated impairment of mitochondria. Hepatic miR-24 levels were significantly increased in db/db and ob/ob mice. A strong feedback loop may be present among miR-24, H2AX, mitochondria and the insulin signaling pathway. Our findings suggest that H2AX-targeting miR-24 may be a novel negative regulator of mitochondrial function and is implicated in the pathogenesis of insulin resistance.

Review: Genetics of the cardiometabolic syndrome: new insights and therapeutic implications

Although the definition of the phenotype is imprecise, cardiometabolic syndrome (CMS) includes a constellation of complex diseases such as type 2 diabetes, dislipidemias, central obesity and hypertension, proinflammatory and prothrombotic states, ovarian polycystosis and fatty liver. The genetics of each disease is complex in itself and varies in spectrum from monogenic and syndromic models of inheritance, usually rare, to the most common polygenic and multifactorial forms. In addition, human studies using the candidate-gene approach indicate that common genetic variants of several genes are associated with the development of CMS. Genome-wide scans have also provided several chromosomal regions associated with some of the components of CMS. In addition, through comparative genomics animal models can generate a map for candidate loci in humans and a promising approach is offered by bioinformatic tools for gene prioritization. Lastly, the involvement of genes whose products are already the targets for approved drugs, such as SLC6A4, PPARα and PPARγ , in the development of CMS suggests new avenues for CMS pharmacological treatment.

In utero Undernutrition Programs Skeletal and Cardiac Muscle Metabolism

In utero undernutrition is associated with increased risk for insulin resistance, obesity, and cardiovascular disease during adult life. A common phenotype associated with low birth weight is reduced skeletal muscle mass. Given the central role of skeletal muscle in whole body metabolism, alterations in its mass as well as its metabolic characteristics may contribute to disease risk. This review highlights the metabolic alterations in cardiac and skeletal muscle associated with in utero undernutrition and low birth weight. These tissues have high metabolic demands and are known to be sites of major metabolic dysfunction in obesity, type 2 diabetes, and cardiovascular disease. Recent research demonstrates that mitochondrial energetics are decreased in skeletal and cardiac muscles of adult offspring from undernourished mothers. These effects apparently lead to the development of a thrifty phenotype, which may represent overall a compensatory mechanism programmed in utero to handle times of limited nutrient availability. However, in an environment characterized by food abundance, the effects are maladaptive and increase adulthood risks of metabolic disease.

Mitochondrial DNA content and function, childhood obesity, and insulin resistance

OBJECTIVES

The objectives of our study were to compare the mitochondrial enzyme activity between obese and non-obese children and to assess the association between mitochondrial DNA content and function and markers of metabolic syndrome.

METHODS

Clinical and anthropometric data of obese and normal-weight children ages 2-18 years were collected. We collected buccal swabs for mitochondrial respiratory enzymes (complex I, IV, and Citrate Synthase). In obese children only, serum levels of metabolic parameters and mitochondrial DNA from mononuclear cells were quantitated.

RESULTS

We recruited 75 obese and 65 normal-weight children. There was no difference in respiratory complex enzyme activity levels between obese and normal-weight subjects. In obese subjects, mitochondrial to nuclear DNA (mt/nDNA) ratio was significantly correlated with BMI Z-score and BMI percentile (p < 0.05, and p < 0.01, respectively), and the strength of this correlation was proportionate to the degree of obesity. We did not find any association between mt/nDNA ratio and metabolic parameters. We observed a significant positive association between complex IV activity and fasting insulin level (p < 0.05). Finally, fasting insulin explained 45% of the variation in the complex IV activity level (p < 0.05).

CONCLUSION

Our findings indicate that mitochondrial DNA content is directly related to obesity, but not to the markers of metabolic syndrome/insulin resistance in children. Longitudinal studies involving larger samples are needed to confirm our findings and help elucidate the relationship between mitochondrial function, adiposity, and insulin resistance.

Dynamic comparisons of high-resolution expression profiles highlighting mitochondria-related genes between in vivo and in vitro fertilized early mouse embryos

STUDY QUESTION

Does in vitro fertilization (IVF) induce comprehensive and consistent changes in gene expression associated with mitochondrial biogenesis and function in mouse embryos from the pre- to post-implantation stage?

SUMMARY ANSWER

IVF-induced consistent mitochondrial dysfunction in early mouse embryos by altering the expression of a number of mitochondria-related genes.

WHAT IS KNOWN ALREADY

Although IVF is generally safe and successful for the treatment of human infertility, there is increasing evidence that those conceived by IVF suffer increased health risks. The mitochondrion is a multifunctional organelle that plays a crucial role in early development. We hypothesized that mitochondrial dysfunction is associated with increased IVF-induced embryonic defects and risks in offspring.

STUDY DESIGN, SIZE, DURATION

After either IVF and development (IVO groups as control) or IVF and culture (IVF groups), blastocysts were collected and transferred to pseudo-pregnant recipient mice. Both IVO and IVF embryos were sampled at E3.5, E7.5 and E10.5, and the expression profiles of mitochondria-related genes from the pre- to post-implantation stage were compared.

PARTICIPANTS/MATERIALS, SETTING, METHODS

ICR mice (5- to 6-week-old males and 8- to 9-week-old females) were used to generate IVO and IVF blastocysts. Embryo day (E) 3.5 blastocysts were transferred to pseudo-pregnant recipient mice. Both IVO and IVF embryos were sampled at E3.5, E7.5 and E10.5 for generating transcriptome data. Mitochondria-related genes were filtered for dynamic functional profiling. Mitochondrial dysfunctions indicated by bioinformatic analysis were further validated using cytological and molecular detection, morphometric and phenotypic analysis and integrated analysis with other high-throughput data.

MAIN RESULTS AND THE ROLE OF CHANCE

A total of 806, 795 and 753 mitochondria-related genes were significantly (P < 0.05) dysregulated in IVF embryos at E3.5, E7.5 and E10.5, respectively. Dynamic functional profiling, together with cytological and molecular investigations, indicated that IVF-induced mitochondrial dysfunctions mainly included: (i) inhibited mitochondrial biogenesis and impaired maintenance of DNA methylation of mitochondria-related genes during the post-implantation stage; (ii) dysregulated glutathione/glutathione peroxidase (GSH/Gpx) system and increased mitochondria-mediated apoptosis; (iii) disturbed mitochondrial β-oxidation, oxidative phosphorylation and amino acid metabolism; and (iv) disrupted mitochondrial transmembrane transport and membrane organization. We also demonstrated that some mitochondrial dysfunctions in IVF embryos, including impaired mitochondrial biogenesis, dysregulated GSH homeostasis and reactive oxygen species-induced apoptosis, can be rescued by treatment with melatonin, a mitochondria-targeted antioxidant, during in vitro culture.

LIMITATIONS, REASONS FOR CAUTION

Findings in mouse embryos and fetuses may not be fully transferable to humans. Further studies are needed to confirm these findings and to determine their clinical significance better.

WIDER IMPLICATIONS OF THE FINDINGS

The present study provides a new insight in understanding the mechanism of IVF-induced aberrations during embryonic development and the increased health risks in the offspring. In addition, we highlighted the possibility of improving existing IVF systems by modulating mitochondrial functions.

Obesity, metabolic syndrome, and airway disease: a bioenergetic problem?

Multiple studies have determined that obesity increases asthma risk or severity. Metabolic changes of obesity, such as diabetes or insulin resistance, are associated with asthma and poorer lung function. Insulin resistance is also found to increase asthma risk independent of body mass. Conversely, asthma is associated with abnormal glucose and lipid metabolism, insulin resistance, and obesity. Here we review our current understanding of how dietary and lifestyle factors lead to changes in mitochondrial metabolism and cellular bioenergetics, inducing various components of the cardiometabolic syndrome and airway disease.

Extension of the mitochondria dysfunction hypothesis of metabolic syndrome to atherosclerosis with emphasis on the endocrine-disrupting chemicals and biophysical laws

Metabolic syndrome and its component phenotypes, hyperglycemia, hypertension, (abdominal) obesity and hypertriglyceridemia, are major risk factors for atherosclerosis. Recently, associations between exposure to endocrine‐disrupting chemicals (EDCs), mitochondrial dysfunction, metabolic syndrome and atherosclerosis have been established, suggesting a possible common mechanism underlying these phenomena. Extending a previously proposed mitochondria dysfunction theory of metabolic syndrome and using biophysical laws, such as metabolic scaling, Murray's law and fractal geometry of the vascular branching system, we propose that atherosclerosis could be explained as an ill‐adaptive change occurring in nutrient‐supplying arteries in response to the decreasing tissue energy demand caused by tissue mitochondrial dysfunction. Various aspects of this new hypothesis are discussed.

Systemic modelling of human bioenergetics and blood circulation

This work reviews the main aspects of human bioenergetics and the dynamics of the cardiovascular system, with emphasis on modelling their physiological characteristics. The methods used to study human bioenergetics and circulation dynamics, including the use of mathematical models, are summarised. The main characteristics of human bioenergetics, including mitochondrial metabolism and global energy balance, are first described, and the systemic aspects of blood circulation and related physiological issues are introduced. The authors also discuss the present status of studies of human bioenergetics and blood circulation. Then, the limitations of the existing studies are described in an effort to identify directions for future research towards integrated and comprehensive modelling. This review emphasises that a multi-scale and multi-physical approach to bioenergetics and blood circulation that considers multiple scales and physiological factors are necessary for the appropriate clinical application of computational models.

Perinatal taurine exposure affects adult arterial pressure control

Taurine is an abundant, free amino acid found in mammalian cells that contributes to many physiologic functions from that of a simple cell osmolyte to a programmer of adult health and disease. Taurine's contribution extends from conception throughout life, but its most critical exposure period is during perinatal life. In adults, taurine supplementation prevents or alleviates cardiovascular disease and related complications. In contrast, low taurine consumption coincides with increased risk of cardiovascular disease, obesity and type II diabetes. This review focuses on the effects that altered perinatal taurine exposure has on long-term mechanisms that control adult arterial blood pressure and could thereby contribute to arterial hypertension through its ability to program these cardiovascular regulatory mechanisms very early in life. The modifications of these mechanisms can last a lifetime and transfer to the next generation, suggesting that epigenetic mechanisms underlie the changes. The ability of perinatal taurine exposure to influence arterial pressure control mechanisms and hypertension in adult life appears to involve the regulation of growth and development, the central and autonomic nervous system, the renin-angiotensin system, glucose-insulin interaction and changes to heart, blood vessels and kidney function.

T16189C mitochondrial DNA variant is associated with metabolic syndrome in Caucasian subjects

OBJECTIVES

Different nuclear genes are thought to be involved in the regulation of the complex phenotype of metabolic syndrome (MS) and their number is increasing. A mutation in mitochondrial DNA (mtDNA), T4291C in transfer RNA isoleucine (tRNAile), has been associated with MS in a large American family. In addition, a mtDNA T16189C variant, already known to be associated with insulin resistance and type 2 diabetes mellitus in Caucasians, seems to underlie susceptibility to MS in the Chinese population. Our aim was to verify the T4291C and T16189C variants in subjects affected by different phenotypes of MS.

METHODS

Seventy patients with MS and 35 healthy individuals were investigated for the presence of the mtDNA variants by polymerase chain reaction-restriction fragment length polymorphism analysis.

RESULTS

The T4291C variant was absent in patients and in controls. The T16189C variant was more frequent in patients with MS than in control subjects (21.4% versus 5.7%, P<0.04) and was associated with hypertension (P=0.01), waist circumference (P=0.02), body mass index (P=0.009), visceral fat thickness (P=0.04), homeostasis model assessment (P=0.03), and the number of MS diagnostic criteria (P=0.01).

CONCLUSION

The mtDNA T16189C variant is associated with MS and its different clinical expressions. Prospective studies are warranted to establish the clinical relevance of this association.

Liver-specific reduction of Mfn2 protein by RNAi results in impaired glycometabolism and lipid homeostasis in BALB/c mice

Mitofusin-2 (Mfn2) gene expression is positively correlated with insulin sensitivity in patients with type 2 diabetes. However, it is unclear if Mfn2 is involved in carbohydrate metabolism and lipid homeostasis. In order to investigate the specific functions of Mfn2 in glycometabolism and lipid homeostasis in BALB/c mice, a RNA interference technique-mediated hydrodynamic injection was developed, in which short hairpin RNAs (shRNAs) were used to inhibit the Mfn2 expression in vivo. Seventy-two mice were randomly divided into two groups: the Mfn2 reduction group (Mfn2/shRNA) and the negative control group (NC). Intraperitoneal glucose tolerance tests and intraperitoneal insulin tolerance tests were used to evaluate glycometabolism and insulin sensitivity. D-(3-3H) glucose or 3H2O was injected into the tail vein or intraperitoneally to facilitate the calculation of the rate of hepatic glucose production and fatty acid synthesis in vivo. The results showed that, in Mfn2/shRNA mice, the liver Mfn2 protein was significantly decreased, and fasting blood glucose concentrations were increased by approximately 48%, when compared with the NC mice. In parallel with the changes in fasting glucose levels, hepatic glucose production was significantly elevated in Mfn2/shRNA mice. When insulin was administrated, these mice exhibited impaired insulin tolerance. It was also found that the reduction of Mfn2 markedly decreased the rate of fatty acid synthesis in the liver, and the Mfn2/shRNA mice exhibited hypertriglyceridema. Taken together, our results indicate that Mfn2 plays an important role in maintaining glucose and lipid homeostasis, and in the development of insulin resistance in vivo.

Changed mitochondrial function by pre- and/or postpartum diet alterations in sheep

In a sheep model, we investigated diet effects on skeletal muscle mitochondria to look for fetal programming. During pregnancy, ewes were fed normally (N) or were 50% food restricted (L) during the last trimester, and lambs born to these ewes received a normal (N) or a high-fat diet (H) for the first 6 mo of life. We examined mitochondrial function in permeabilized muscle fibers from the lambs at 6 mo of age (adolescence) and after 24 mo of age (adulthood). The postpartum H diet for the lambs induced an approximately 30% increase (P < 0.05) of mitochondrial VO(2max) and an approximately 50% increase (P < 0.05) of the respiratory coupling ratio (RCR) combined with lower levels of UCP3 and PGC-1alpha mRNA levels (P < 0.05). These effects proved to be reversible by a normal diet from 6 to 24 mo of age. However, at 24 mo, a long-term effect of the maternal gestational diet restriction (fetal programming) became evident as a lower VO(2max) (approximately 40%, P < 0.05), a lower state 4 respiration (approximately 40%, P < 0.05), and lower RCR ( approximately 15%, P < 0.05). Both PGC-1alpha and UCP3 mRNA levels were increased (P < 0.05). Two analyzed muscles were affected differently, and muscle rich in type I fibers was more susceptible to fetal programming. We conclude that fetal programming, seen as a reduced VO(2max) in adulthood, results from gestational undernutrition. Postnatal high-fat diet results in a pronounced RCR and VO(2max) increase in adolescence. However, these effects are reversible by diet correction and are not maintained in adulthood.

Mitochondrial dysfunction and metabolic syndrome-looking for environmental factors

The centerpiece of the pathophysiologic mechanism of metabolic syndrome is insulin resistance. Recently, it is becoming evident that mitochondrial dysfunction is closely related to insulin resistance and metabolic syndrome. The underlying mechanism of mitochondrial dysfunction is very complex, which includes genetic factors from both nuclear and mitochondrial genome and numerous environmental factors. Several mitochondrial DNA polymorphisms are associated with the components of metabolic syndrome. Numerous chemicals and drugs may cause mitochondrial dysfunction and insulin resistance. Notably, it was recently reported that serum levels of several mitochondrial toxins, such as persistent organic pollutants are associated with metabolic syndrome, which necessitates further investigation to reveal its precise mechanism. Given that the health impact of metabolic syndrome is tremendous, it is necessary to develop therapeutic modalities to correct mitochondrial dysfunction or at least to halt its aggravation. In this regard, exercise can improve both mitochondrial function and insulin sensitivity, and some pharmaceutical agents were reported to improve mitochondrial function. However, further studies are warranted to find more effective therapeutic strategies to treat mitochondrial dysfunction. By doing so, we can also shed light on the path of research for other diseases related to mitochondrial dysfunction.

Effects of ooplasm transfer on paternal genome function in mice

BACKGROUND

The ooplasm plays a central role in forming the paternal pronucleus, and subsequently in regulating the expression of paternally inherited chromosomes. Previous studies in mice have revealed genetic differences in paternal genome processing by ooplasm of different genotypes. Ooplasm donation coupled to intracytoplasmic sperm injection (ICSI) has been used in human assisted reproductive technology (ART). This procedure exposes the developing paternal pronucleus to 'foreign' ooplasm, which may direct aberrant epigenetic processing. The potential effects of the foreign ooplasm on epigenetic information in the paternal pronucleus are unknown; however, some human progeny from ooplasm donation procedures display abnormalities.

METHODS

In this study, we employed inter-genotype ooplasm transfer followed by ICSI using two mouse strains, C57BL/6 and DBA/2, to explore the influence of foreign ooplasm on paternal pronucleus function. In order to assay for effects on the paternal genome without masking effects of the maternal genome, we examined ooplasm effects in diploid androgenones, which are produced by pronuclear transfer to contain exclusively two paternal sets of chromosomes, in combination with ICSI.

RESULTS

There was no significant effect of intra-strain ooplasm transfer among androgenones made with either C57BL/6 or DBA/2 oocytes. There was a significant negative effect on androgenone blastocyst development with inter-genotype transfer (10% volume) of DBA/2 ooplasm to C57BL/6 oocytes (P < 0.05). The reciprocal inter-genotype ooplasm transfer had no significant effect.

CONCLUSIONS

Thus, inter-genotype ooplasm transfer in conjunction with ICSI can alter the function of the paternal genome. However, the effect of foreign ooplasm is restricted to a negative effect, with no evidence of a positive effect. This study provides important new information about the possible consequences of ooplasm donation in human ART.

A decreased mitochondrial DNA content is related to insulin resistance in adolescents

The aim of this study was to investigate whether mitochondrial DNA (mtDNA) content is associated with insulin resistance (IR) in a sample of adolescents with features of metabolic syndrome. We further studied the link between polymorphisms in three genes involved in mitochondrial biogenesis and the presence of deleted mtDNA and mtDNA content. Data and blood samples were collected from 175 adolescents out of a cross-sectional, population-based study of 934 high school students. On the basis of the median value of homeostasis model assessment of IR (HOMA-IR) of the whole sample (2.2), the population was divided into two groups: noninsulin resistance (NIR) and IR. mtDNA quantification using nuclear DNA (nDNA) as a reference was carried out using a real-time quantitative PCR method. Genotyping for peroxisome proliferator-activated receptor-gamma (PPAR-gamma) (pro12Ala), PPAR- gamma coactivator-1alpha (PGC-1alpha) (Gly482Ser), and Tfam (rs1937 and rs12247015) polymorphisms was performed by PCR-based restriction fragment length polymorphism. Long-extension PCR was performed to amplify the whole mitochondrial genome. The mtDNA/nDNA ratio was significantly lower in the IR group (median: 9.08, range: 68.94) in comparison with the NIR group (12.24, 71.92) (P<0.03). Besides, the mtDNA/nDNA ratio was inversely correlated with HOMA (R: -0.18, P<0.02), glucose (R: -0.21, P<0.008), and uric acid (R: -0.18, P<0.03). Genotypes for the PPAR- gamma, PGC-1alpha, and Tfam variants were not associated with the mtDNA/nDNA ratio. Long-extension PCR did not show significant levels of mtDNA deletions. In conclusion, our findings indicate that reduced mtDNA content in peripheral leukocytes is associated with IR. This result seems not to be related with the previously mentioned variants in genes involved in the regulation of mitochondrial biogenesis.

AMP-activated protein kinase signalling pathways are down regulated and skeletal muscle development impaired in fetuses of obese, over-nourished sheep

Maternal obesity and over-nutrition give rise to both obstetric problems and neonatal morbidity. The objective of this study was to evaluate effects of maternal obesity and over-nutrition on signalling of the AMP-activated protein kinase (AMPK) pathway in fetal skeletal muscle in an obese pregnant sheep model. Non-pregnant ewes were assigned to a control group (Con, fed 100% of NRC nutrient recommendations, n = 7) or obesogenic group (OB, fed 150% of National Research Council (NRC) recommendations, n = 7) diet from 60 days before to 75 days after conception (term 150 days) when fetal semitendinosus skeletal muscle (St) was sampled. OB mothers developed severe obesity accompanied by higher maternal and fetal plasma glucose and insulin levels. In fetal St, activity of phosphoinositide-3 kinase (PI3K) associated with insulin receptor substrate-1 (IRS-1) was attenuated (P < 0.05), in agreement with the increased phophorylation of IRS-1 at serine 1011. Phosphorylation of AMP-activated protein kinase (AMPK) at Thr 172, acetyl-CoA carboxylase at Ser 79, tuberous sclerosis 2 at Thr 1462 and eukaryotic translation initiation factor 4E-binding protein 1 at Thr 37/46 were reduced in OB compared to Con fetal St. No difference in energy status (AMP/ATP ratio) was observed. The expression of protein phosphatase 2C was increased in OB compared to Con fetal St. Plasma tumour necrosis factor alpha (TNFalpha) was increased in OB fetuses indicating an increased inflammatory state. Expression of peroxisome proliferator-activated receptor gamma (PPARgamma) was higher in OB St, indicating enhanced adipogenesis. The glutathione: glutathione disulphide ratio was also lower, showing increased oxidative stress in OB fetal St. In summary, we have demonstrated decreased signalling of the AMPK system in skeletal muscle of fetuses of OB mothers, which may play a role in altered muscle development and development of insulin resistance in the offspring.

Mechanisms underlying developmental programming of elevated blood pressure and vascular dysfunction: evidence from human studies and experimental animal models

Cardiovascular-related diseases are the leading cause of death in the world in both men and women. In addition to the environmental and genetic factors, early life conditions are now also considered important contributing elements to these pathologies. The concept of 'fetal' or 'developmental' origins of adult diseases has received increased recognition over the last decade, yet the mechanism by which altered perinatal environment can lead to dysfunction mostly apparent in the adult are incompletely understood. This review will focus on the mechanisms and pathways that epidemiological studies and experimental models have revealed underlying the adult cardiovascular phenotype dictated by the perinatal experience, as well as the probable key causal or triggering elements. Programmed elevated blood pressure in the adult human or animal is characterized by vascular dysfunction and microvascular rarefaction. Developmental mechanisms that have been more extensively studied include glucocorticoid exposure, the role of the kidneys and the renin-angiotensin system. Other pathophysiological pathways have been explored, such as the role of the brain and the sympathetic nervous system, oxidative stress and epigenetic changes. As with many complex diseases, a unifying hypothesis linking the perinatal environment to elevated blood pressure and vascular dysfunction in later life cannot be presumed, and a better understanding of those mechanisms is critical before clinical trials of preventive or 'deprogramming' measures can be designed.

Acetaminophen normalizes glucose homeostasis in mouse models for diabetes

Loss of pancreatic beta cell insulin secretion is the most important element in the progression of type 1 and type 2 diabetes. Since oxidative stress is involved in the progressive loss of beta cell function, we evaluated the potential for the over-the-counter analgesic drug and antioxidant, acetaminophen (APAP), to intervene in the diabetogenic process. We used mouse models for type 1 diabetes (streptozotocin) and type 2 diabetes (high-fat diet) to examine the ability of APAP to intervene in the progression of diabetes. In C57BL/6J mice, streptozotocin caused a dosage dependent increase in fasting blood glucose (FBG), from 100 to >600mg/dl. Daily APAP (20mg/kg BW, gastric gavage), significantly prevented and partially reversed the increase in FBG levels produced by streptozotocin. After 10 weeks on a high-fat diet, mice developed fasting hyperinsulemia and impaired glucose tolerance compared to animals fed a control diet. APAP largely prevented these changes in insulin and glucose tolerance. Furthermore, APAP prevented most of the increase in body fat in mice fed the high-fat diet. One protective mechanism for APAP is suggested by studies using isolated liver mitochondria, where low micromolar concentrations abolished the production of reactive oxygen that might otherwise contribute to the destruction of pancreatic beta-cells. These findings suggest that administration of APAP to mice, in a dosage used safely by humans, reduces the production of mitochondrial reactive oxygen and concomitantly prevents the development of type 1 and type 2 diabetes in established animal models.

Techniques used in studies of epigenome dysregulation due to aberrant DNA methylation: an emphasis on fetal-based adult diseases

Epigenetic changes are heritable modifications that do not involve alterations in the primary DNA sequence. They regulate crucial cellular functions such as genome stability, X-chromosome inactivation, and gene imprinting. Epidemiological and experimental observations now suggest that such changes may also explain the fetal basis of adult diseases such as cancer, obesity, diabetes, cardiovascular disorders, neurological diseases, and behavioral modifications. The main molecular events known to initiate and sustain epigenetic modifications are histone modification and DNA methylation. This review specifically focuses on existing and emerging technologies used in studying DNA methylation, which occurs primarily at CpG dinucleotides in the genome. These include standard exploratory tools used for global profiling of DNA methylation and targeted gene investigation: methylation sensitive restriction fingerprinting (MSRF), restriction landmark genomic scanning (RLGS), methylation CpG island amplification-representational difference analysis (MCA-RDA), differential methylation hybridization (DMH), and cDNA microarrays combined with treatment with demethylating agents and inhibitors of histone deacetylase. The basic operating principals, resource requirements, applications, and benefits and limitations of each methodology are discussed. Validation methodologies and functional assays needed to establish the role of a CpG-rich sequence in regulating the expression of a target or candidate gene are outlined. These include in silico database searches, methylation status studies (bisulfite genomic sequencing, COBRA, MS-PCR, MS-SSCP), gene expression studies, and promoter activity analyses. Our intention is to give readers a starting point for choosing methodologies and to suggest a workflow to follow during their investigations. We believe studies of epigenetic changes such as DNA methylation hold great promise in understanding the early origins of adult diseases and in advancing their diagnosis, prevention, and treatment.

S-adenosyl-L-methionine increases skeletal muscle mitochondrial DNA density and whole body insulin sensitivity in OLETF rats

Both mitochondrial dysfunction and alterations in mitochondrial DNA (mtDNA) are implicated in type 2 diabetes mellitus and insulin resistance. Evidence also suggests that metabolism of S-adenosyl-L-methionine (SAM), the universal methyl donor for biological methylation, is associated with mitochondrial dysfunction and insulin resistance. We investigated the effect of SAM on mtDNA density and insulin sensitivity using the Otsuka Long-Evans Tokushima Fatty (OLETF) rat, an animal model of type 2 diabetes mellitus and insulin resistance. To determine the short-term effect on mtDNA density, SAM (15 mg.kg-1.d-1) was administered intraperitoneally for 7 d to 6 male, 57-wk-old OLETF rats and 6 Long-Evans Tokushima Otsuka (LETO) rats of the same age as a nondiabetic control. To determine the long-term effect, the same dose of SAM was administered daily to 5 male, 6-wk-old OLETF rats until the age of 25 wk; 7 control OLETF rats received vehicle and 7 LETO rats were untreated. Skeletal muscle mtDNA density was measured by either competitive or multiplex PCR and insulin sensitivity was measured by hyperinsulinemic-euglycemic clamp. SAM treatment for 1 wk increased skeletal muscle mtDNA density of both OLETF and LETO rats. The long-term SAM treatment significantly reduced body weight gain as well as increased skeletal muscle mtDNA density and whole body insulin sensitivity in OLETF rats compared with their vehicle-treated controls. Furthermore, in all 3 groups, skeletal muscle mtDNA density correlated with insulin sensitivity (r=0.752, P<0.001). In conclusion, SAM treatment increased mtDNA density in the skeletal muscle, improved whole body insulin sensitivity, and prevented body weight gain in OLETF rats.

Hyperlipidemic mice present enhanced catabolism and higher mitochondrial ATP-sensitive K+ channel activity

BACKGROUND & AIMS

Changes in mitochondrial energy metabolism promoted by uncoupling proteins (UCPs) are often found in metabolic disorders. We have recently shown that hypertriglyceridemic (HTG) mice present higher mitochondrial resting respiration unrelated to UCPs. Here, we disclose the underlying mechanism and consequences, in tissue and whole body metabolism, of this mitochondrial response to hyperlipidemia.

METHODS

Oxidative metabolism and its response to mitochondrial adenosine triphosphate (ATP)-sensitive K+ channel (mitoK(ATP)) agonists and antagonists were measured in isolated mitochondria, livers, and mice.

RESULTS

Mitochondria isolated from the livers of HTG mice presented enhanced respiratory rates compared with those from wild-type mice. Changes in oxygen consumption were sensitive to adenosine triphosphate (ATP), diazoxide, and 5-hydroxydecanoate, indicating they are attributable to mitochondrial ATP-sensitive K+ channel (mitoK(ATP)) activity. Indeed, mitochondria from HTG mice presented enhanced swelling in the presence of K+ ions, sensitive to mitoK(ATP) agonists and antagonists. Furthermore, mitochondrial binding to fluorescent glibenclamide indicates that HTG mice expressed higher quantities of mitoK(ATP). The higher content and activity of liver mitoK(ATP) resulted in a faster metabolic state, as evidenced by increased liver oxygen consumption and higher body CO(2) release and temperature in these mice. In agreement with higher metabolic rates, food ingestion was significantly larger in HTG mice, without enhanced weight gain.

CONCLUSIONS

These results show that primary hyperlipidemia leads to an elevation in liver mitoK(ATP) activity, which may represent a regulated adaptation to oxidize excess fatty acids in HTG mice. Furthermore, our data indicate that mitoK(ATP), in addition to UCPs, may be involved in the control of energy metabolism and body weight.

Drug-induced mitochondrial toxicity

Mitochondria play a critical role in generating most of the cell's energy as ATP. They are also involved in other metabolic processes such as urea generation, haem synthesis and fatty acid beta-oxidation. Disruption of mitochondrial function by drugs can result in cell death by necrosis or can signal cell death by apoptosis (e.g., following cytochrome c release). Drugs that injure mitochondria usually do so by inhibiting respiratory complexes of the electron chain; inhibiting or uncoupling oxidative phosphorylation; inducing mitochondrial oxidative stress; or inhibiting DNA replication, transcription or translation. It is important to test for mitochondrial toxicity early in drug development as impairment of mitochondrial function can induce various pathological conditions that are life threatening or can increase the progression of existing mitochondrial diseases.

Fetal origins of adult disease

The term 'fetal origins of adult disease' was coined on the basis of the inverse association between low birth weight and blood pressure, adult-onset diabetes, coronary heart disease, and stroke seen in numerous epidemiological studies. However, it seems unlikely that birth weight is involved in causal pathways underlying these observations, and if it were then the significance to public health of these findings is very limited because of our inability to modify birth weight to a relevant extent in humans. There has been a major focus on maternal nutrition. Despite evidence that experimental manipulation of maternal nutrition in animals influences offspring birth weight and programme measures related to cardiovascular disease, human studies in general provide limited and unconvincing evidence that differences in maternal macronutrient intake are important. Nevertheless there is a need to understand the underlying causal pathways, and the utility of studies of twins and possible mechanisms are discussed.