Analysis of cardiolipin in human muscle biopsy

Principles of Exercise Prescription, and How They Influence Exercise-Induced Changes of Transcription Factors and Other Regulators of Mitochondrial Biogenesis

Physical inactivity represents the fourth leading risk factor for mortality, and it has been linked with a series of chronic disorders, the treatment of which absorbs ~ 85% of healthcare costs in developed countries. Conversely, physical activity promotes many health benefits; endurance exercise in particular represents a powerful stimulus to induce mitochondrial biogenesis, and it is routinely used to prevent and treat chronic metabolic disorders linked with sub-optimal mitochondrial characteristics. Given the importance of maintaining a healthy mitochondrial pool, it is vital to better characterize how manipulating the endurance exercise dose affects cellular mechanisms of exercise-induced mitochondrial biogenesis. Herein, we propose a definition of mitochondrial biogenesis and the techniques available to assess it, and we emphasize the importance of standardizing biopsy timing and the determination of relative exercise intensity when comparing different studies. We report an intensity-dependent regulation of exercise-induced increases in nuclear peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) protein content, nuclear phosphorylation of p53 (serine 15), and PGC-1α messenger RNA (mRNA), as well as training-induced increases in PGC-1α and p53 protein content. Despite evidence that PGC-1α protein content plateaus within a few exercise sessions, we demonstrate that greater training volumes induce further increases in PGC-1α (and p53) protein content, and that short-term reductions in training volume decrease the content of both proteins, suggesting training volume is still a factor affecting training-induced mitochondrial biogenesis. Finally, training-induced changes in mitochondrial transcription factor A (TFAM) protein content are regulated in a training volume-dependent manner and have been linked with training-induced changes in mitochondrial content.

Calorie Restriction-induced Weight Loss and Exercise Have Differential Effects on Skeletal Muscle Mitochondria Despite Similar Effects on Insulin Sensitivity

Background

Skeletal muscle insulin resistance and reduced mitochondrial capacity have both been reported to be affected by aging. The purpose of this study was to compare the effects of calorie restriction-induced weight loss and exercise on insulin resistance, skeletal muscle mitochondrial content, and mitochondrial enzyme activities in older overweight to obese individuals.

Methods

Insulin-stimulated rates of glucose disposal (Rd) were determined using the hyperinsulinemic euglycemic clamp before and after completing 16 weeks of either calorie restriction to induce weight loss (N = 7) or moderate exercise (N = 10). Mitochondrial volume density, mitochondria membrane content (cardiolipin), and activities of electron transport chain (rotenone-sensitive NADH-oxidase), tricarboxylic acid (TCA) cycle (citrate synthase) and β-oxidation pathway (β-hydroxyacyl CoA dehydrogenase; β-HAD) were measured in percutaneous biopsies of the vastus lateralis before and after the interventions.

Results

Rd improved similarly (18.2% ± 9.0%, p < .04) with both weight loss and exercise. Moderate exercise significantly increased mitochondrial volume density (14.5% ± 2.0%, p < .05), cardiolipin content (22.5% ± 13.4%, p < .05), rotenone-sensitive NADH-oxidase (65.7% ± 13.2%, p = .02) and β-HAD (30.7% ± 6.8%, p ≤ .03) activity, but not citrate synthase activity (10.1% ± 4.0%). In contrast, calorie restriction-induced weight loss did not affect mitochondrial content, NADH-oxidase or β-HAD, yet increased citrate synthase activity (44.1% ± 21.1%, p ≤ .04). Exercise (increase) or weight loss (decrease) induced a remodeling of cardiolipin with a small (2%-3%), but significant change in the relative content of tetralinoleoyl cardiolipin.

Conclusion

Exercise increases both mitochondria content and mitochondrial electron transport chain and fatty acid oxidation enzyme activities within skeletal muscle, while calorie restriction-induced weight loss did not, despite similar improvements in insulin sensitivity in overweight older adults.

Skeletal muscle cellular metabolism in older HIV-infected men

Skeletal muscle mitochondrial dysfunction may contribute to low aerobic capacity. We previously reported 40% lower aerobic capacity in HIV-infected men compared to noninfected age-matched men. The objective of this study was to compare skeletal muscle mitochondrial enzyme activities in HIV-infected men on antiretroviral therapy (55 ± 1 years of age, n = 10 African American men) with age-matched controls (55 ± 1 years of age, n = 8 Caucasian men), and determine their relationship with aerobic capacity. Activity assays for mitochondrial function including enzymes involved in fatty acid activation and oxidation, and oxidative phosphorylation, were performed in homogenates prepared from vastus lateralis muscle. Hydrogen peroxide (H2O2), cardiolipin, and oxidized cardiolipin were also measured. β-hydroxy acyl-CoA dehydrogenase (β-HAD) (38%) and citrate synthase (77%) activities were significantly lower, and H2O2 (1.4-fold) and oxidized cardiolipin (1.8-fold) were significantly higher in HIV-infected men. VO2peak (mL/kg FFM/min) was 33% lower in HIV-infected men and was directly related to β-HAD and citrate synthase activity and inversely related to H2O2 and oxidized cardiolipin. Older HIV-infected men have reduced oxidative enzyme activity and increased oxidative stress compared to age-matched controls. Further research is crucial to determine whether an increase in aerobic capacity by exercise training will be sufficient to restore mitochondrial function in older HIV-infected individuals.

Effects of aging on mitochondrial function in skeletal muscle of American American Quarter Horses

Skeletal muscle function, aerobic capacity, and mitochondrial (Mt) function have been found to decline with age in humans and rodents. However, not much is known about age-related changes in Mt function in equine skeletal muscle. Here, we compared fiber-type composition and Mt function in gluteus medius and triceps brachii muscle between young (age 1.8 ± 0.1 yr, n = 24) and aged (age 17-25 yr, n = 10) American Quarter Horses. The percentage of myosin heavy chain (MHC) IIX was lower in aged compared with young muscles (gluteus, P = 0.092; triceps, P = 0.012), while the percentages of MHC I (gluteus; P < 0.001) and MHC IIA (triceps; P = 0.023) were increased. Mass-specific Mt density, indicated by citrate synthase activity, was unaffected by age in gluteus, but decreased in aged triceps (P = 0.023). Cytochrome-c oxidase (COX) activity per milligram tissue and per Mt unit decreased with age in gluteus (P < 0.001 for both) and triceps (P < 0.001 and P = 0.003, respectively). Activity of 3-hydroxyacyl-CoA dehydrogenase per milligram tissue was unaffected by age, but increased per Mt unit in aged gluteus and triceps (P = 0.023 and P < 0.001, respectively). Mt respiration of permeabilized muscle fibers per milligram tissue was unaffected by age in both muscles. Main effects of age appeared when respiration was normalized to Mt content, with increases in LEAK, oxidative phosphorylation capacity, and electron transport system capacity (P = 0.038, P = 0.045, and P = 0.007, respectively), independent of muscle. In conclusion, equine skeletal muscle aging was accompanied by a shift in fiber-type composition, decrease in Mt density and COX activity, but preserved Mt respiratory function.

Renal 2',3'-Cyclic Nucleotide 3'-Phosphodiesterase Is an Important Determinant of AKI Severity after Ischemia-Reperfusion

A positional isomer of 3',5'-cAMP, 2',3'-cAMP, is produced by kidneys in response to energy depletion, and renal 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) metabolizes 2',3'-cAMP to 2'-AMP; 2',3'-cAMP is a potent opener of mitochondrial permeability transition pores (mPTPs), which can stimulate autophagy. Because autophagy protects against AKI, it is conceivable that inhibition of CNPase protects against ischemia-reperfusion (IR) -induced AKI. Therefore, we investigated renal outcomes, mitochondrial function, number, area, and autophagy in CNPase-knockout (CNPase(-/-)) versus wild-type (WT) mice using a unique two-kidney, hanging-weight model of renal bilateral IR (20 minutes of ischemia followed by 48 hours of reperfusion). Analysis of urinary purines showed attenuated metabolism of 2',3'-cAMP to 2'-AMP in CNPase(-/-) mice. Neither genotype nor IR affected BP, heart rate, urine volume, or albumin excretion. In WT mice, renal IR reduced (14)C-inulin clearance (index of GFR) and increased renal vascular resistance (measured by transit time nanoprobes) and urinary excretion of kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin. IR did not affect these parameters in CNPase(-/-) mice. Histologic analysis revealed that IR induced severe damage in kidneys from WT mice, whereas histologic changes were minimal after IR in CNPase(-/-) mice. Measurements of renal cardiolipin levels, citrate synthase activity, rotenone-sensitive NADH oxidase activity, and proximal tubular mitochondrial and autophagosome area and number (by transmission electron microscopy) indicted accelerated autophagy/mitophagy in injured CNPase(-/-) mice. We conclude that CNPase deletion attenuates IR-induced AKI, in part by accelerating autophagy with targeted removal of damaged mitochondria.

pH-Driven Ordering Transitions in Liquid Crystal Induced by Conformational Changes of Cardiolipin

We report an investigation of interfacial phenomena occurring at aqueous-liquid crystal (LC) interfaces that triggers an orientational ordering transition of the LC in the presence of cardiolipin (CL) by varying pH, salt concentration and valence. In particular, the effects of three different conformational isomeric forms of the CL are observed to cause the response of the LC ordering to vary significantly from one to another at those interfaces. An ordering transition of the LC was observed when the CL is mostly in undissociated (at pH 2) and/or in bicyclic (at pH 4) conformation in which LC shows changes in the optical appearance from bright to dark. By contrast, no change in the optical appearance of the LC was observed when the pH of the system increases to 8 or higher in which the CL mostly exists in the open conformation. Fluorescence microscopy measurements further suggest that pH-dependent conformational forms of the CL have different ability to self-assemble (thus different packing efficiency) at aqueous-LC interfaces leading to dissimilar orientational behavior of the LC. Specifically, we found that change in headgroup-headgroup repulsion of the central phosphatidyl groups of the CL plays a key role in tuning the lipid packing efficiency and thus responses to interfacial phenomena. Orientational ordering transition of the LC was also observed as a function of increasing the ionic strength (buffer capacity) and strongly influenced in the presence of mono and divalent cations. Langmuir-Blodgett (LB) and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) measurements provide further insight in modulation of the lipid packing efficiency and alkyl chain conformation of the CL at different pH and ionic conditions. Overall, the results presented in this paper establish that LCs offer a promising approach to differentiate different conformations (label free detection) of the CL through ordering transition of the LC at aqueous-LC interfaces.

Reduced skeletal muscle oxidative capacity and elevated ceramide but not diacylglycerol content in severe obesity

OBJECTIVE

The link between a reduced capacity for skeletal muscle mitochondrial fatty acid oxidation (FAO) and lipotoxicity in human insulin resistance has been the subject of intense debate. The objective of this study was to investigate whether reduced FAO is associated with elevated acyl CoA, ceramide, and diacylglycerol (DAG) in severely obese insulin resistant subjects.

METHODS

Muscle biopsies were conducted in lean (L, 22.6 ± 0.5 kg/m(2) , n = 8), Class I (CI, 32.1 ± 0.4 kg/m(2) , n = 7) and Class II&III obese (CII&III, 45.6 ± 1.1 kg/m(2) , n = 15) women for acyl CoA, sphingolipid and DAG profiling. Intramyocellular triglyceride (IMTG) content was determined by histology. FAO was assessed by incubating muscle homogenates with [1-C]palmitate and measuring CO2 production. Cardiolipin content was quantified as an index of mitochondrial content. Lipid metabolism proteins, DGAT1, PLIN5, and PNPLA2 were quantified in biopsy samples by western blot.

RESULTS

CII&III were more insulin resistant (HOMA-IR: 4.5 ± 0.5 vs. 1.1 ± 0.1, P < 0.001), and had lower FAO (∼58%, P = 0.007) and cardiolipin content (∼31%, P = 0.013) compared to L. IMTG was elevated in CI (P = 0.04) and CII&III (P = 0.04) compared to L. Sphingolipid content was higher in CII&III compared to L (13.6 ± 1.1 vs. 10.3 ± 0.5 pmol/mg, P = 0.031) whereas DAG content was not different among groups. DGAT1 was elevated in CII&III, and PLIN5 was elevated in CI compared to L.

CONCLUSIONS

Severe obesity is associated with reduced muscle oxidative capacity and occurs concomitantly with elevated IMTG, ceramide and insulin resistance.

Biomarkers of mitochondrial content in skeletal muscle of healthy young human subjects

Skeletal muscle mitochondrial content varies extensively between human subjects. Biochemical measures of mitochondrial proteins, enzyme activities and lipids are often used as markers of mitochondrial content and muscle oxidative capacity (OXPHOS). The purpose of this study was to determine how closely associated these commonly used biochemical measures are to muscle mitochondrial content and OXPHOS. Sixteen young healthy male subjects were recruited for this study. Subjects completed a graded exercise test to determine maximal oxygen uptake (VO2peak) and muscle biopsies were obtained from the vastus lateralis. Mitochondrial content was determined using transmission electron microscopy imaging and OXPHOS was determined as the maximal coupled respiration in permeabilized fibres. Biomarkers of interest were citrate synthase (CS) activity, cardiolipin content, mitochondrial DNA content (mtDNA), complex I–V protein content, and complex I–IV activity. Spearman correlation coefficient tests and Lin's concordance tests were applied to assess the absolute and relative association between the markers and mitochondrial content or OXPHOS. Subjects had a large range of VO2peak (range 29.9–71.6ml min−1 kg−1) and mitochondrial content (4–15% of cell volume).Cardiolipin content showed the strongest association with mitochondrial content followed by CS and complex I activities. mtDNA was not related to mitochondrial content. Complex IV activity showed the strongest association with muscle oxidative capacity followed by complex II activity.We conclude that cardiolipin content, and CS and complex I activities are the biomarkers that exhibit the strongest association with mitochondrial content, while complex IV activity is strongly associated with OXPHOS capacity in human skeletal muscle.

Age-related decline in mitochondrial bioenergetics: does supercomplex destabilization determine lower oxidative capacity and higher superoxide production?

Mitochondrial decay plays a central role in the aging process. Although certainly multifactorial in nature, defective operation of the electron transport chain (ETC) constitutes a key mechanism involved in the age-associated loss of mitochondrial energy metabolism. Primarily, mitochondrial dysfunction affects the aging animal by limiting bioenergetic reserve capacity and/or increasing oxidative stress via enhanced electron leakage from the ETC. Even though the important aging characteristics of mitochondrial decay are known, the molecular events underlying inefficient electron flux that ultimately leads to higher superoxide appearance and impaired respiration are not completely understood. This review focuses on the potential role(s) that age-associated destabilization of the macromolecular organization of the ETC (i.e. supercomplexes) may be important for development of the mitochondrial aging phenotype, particularly in post-mitotic tissues.

Role of mitochondrial function in insulin resistance

The obesity pandemic increases the prevalence of type 2 diabetes (DM2).DM2 develops when pancreatic β-cells fail and cannot compensate for the decrease in insulin sensitivity. How excessive caloric intake and weight gain cause insulin resistance has not completely been elucidated.Skeletal muscle is responsible for a major part of insulin stimulated whole-body glucose disposal and, hence, plays an important role in the pathogenesis of insulin resistance.It has been hypothesized that skeletal muscle mitochondrial dysfunction is involved in the accumulation of intramyocellular lipid metabolites leading to lipotoxicity and insulin resistance. However, findings on skeletal muscle mitochondrial function in relation to insulin resistance in human subjects are inconclusive. Differences in mitochondrial activity can be the result of several factors, including a reduced mitochondrial density, differences in insulin stimulated mitochondrial respiration, lower energy demand or reduced skeletal muscle perfusion, besides an intrinsic mitochondrial defect. The inconclusive results may be explained by the use of different techniques and study populations. Also, mitochondrial capacity is in far excess to meet energy requirements and therefore it may be questioned whether a reduced mitochondrial capacity limits mitochondrial fatty acid oxidation. Whether reduced mitochondrial function is causally related to insulin resistance or rather a consequence of the sedentary lifestyle remains to be elucidated.

Dynamic regulation of cardiolipin by the lipid pump Atp8b1 determines the severity of lung injury in experimental pneumonia

Pneumonia remains the leading cause of infectious deaths and yet fundamentally new conceptual models underlying its pathogenesis have not emerged. Patients and mice with bacterial pneumonia have marked elevations of cardiolipin in lung fluid, a rare, mitochondrial-specific phospholipid that potently disrupts surfactant function. Intratracheal cardiolipin in mice recapitulates the clinical phenotype of pneumonia including impaired lung mechanics, modulation of cell survival and cytokine networks, and lobar consolidation. We have identified and characterized the activity of a novel cardiolipin transporter, ATP8b1, a mutant version of which is associated with severe pneumonia in humans and mice. ATP8b1 bound and internalized cardiolipin from extracellular fluid via a basic residue-enriched motif. Administration of cardiolipin binding motif peptide or ATP8b1 gene transfer in mice lessened lung injury and improved survival. The results unveil a new paradigm whereby ATP8b1 is a cardiolipin importer but its capacity to remove cardiolipin from lung fluid is exceeded during inflammation or ATP8b1 inefficiency. This discovery opens the door for new therapeutic strategies directed at modulating cardiolipin levels or its molecular interactions in pneumonia.

Methylation of TFAM gene promoter in peripheral white blood cells is associated with insulin resistance in adolescents

PURPOSE

To explore whether DNA methylation of the mitochondrial transcription factor A (TFAM) promoter is associated with insulin resistance in a sample of adolescents with features of metabolic syndrome.

METHODS

The data and blood samples were collected from 122 adolescents out of a cross-sectional study of 934 high-school students. The population was divided into two groups: noninsulin resistance (NIR) and insulin resistance (IR). After bisulfite treatment of genomic DNA from peripheral leukocytes, we used methylation-specific polymerase chain reaction (PCR) to assess DNA methylation of three putative methylation target sites (CpG) in the TFAM promoter.

RESULTS

The ratio of the promoter methylated DNA/unmethylated DNA was 0.012+/-0.0009 (1.2% of alleles), and inversely correlated with the biochemical features of insulin resistance (plasma fasting insulin R: -0.26, p<0.004 and homeostasis model assessment (HOMA) index R: -0.27, p<0.002), and obesity (R: -0.27, p<0.002). Multiple regression analysis showed that the log-transformed HOMA index correlated with the status of promoter methylation of TFAM, independently of body mass index (BMI) Z score (beta: -0.33+/-0.094, p=0.00094). Finally, the TFAM promoter methylated DNA/unmethylated DNA ratio was found to be significantly associated with insulin resistance as dichotomous variable (NIR n=45, 0.014+/-0.002 and IR n=77, 0.011+/-0.001, respectively, p<0.016).

CONCLUSION

Our findings suggest a potential role of promoter TFAM methylation in the pathogenesis of insulin resistance in adolescents.

Deficiency of electron transport chain in human skeletal muscle mitochondria in type 2 diabetes mellitus and obesity

Insulin resistance in skeletal muscle in obesity and T2DM is associated with reduced muscle oxidative capacity, reduced expression in nuclear genes responsible for oxidative metabolism, and reduced activity of mitochondrial electron transport chain. The presented study was undertaken to analyze mitochondrial content and mitochondrial enzyme profile in skeletal muscle of sedentary lean individuals and to compare that with our previous data on obese or obese T2DM group. Frozen skeletal muscle biopsies obtained from lean volunteers were used to estimate cardiolipin content, mtDNA (markers of mitochondrial mass), NADH oxidase activity of mitochondrial electron transport chain (ETC), and activity of citrate synthase and beta-hydroxyacyl-CoA dehydrogenase (beta-HAD), key enzymes of TCA cycle and beta-oxidation pathway, respectively. Frozen biopsies collected from obese or T2DM individuals in our previous studies were used to estimate activity of beta-HAD. The obtained data were complemented by data from our previous studies and statistically analyzed to compare mitochondrial content and mitochondrial enzyme profile in lean, obese, or T2DM cohort. The total activity of NADH oxidase was reduced significantly in obese or T2DM subjects. The cardiolipin content for lean or obese group was similar, and although for T2DM group cardiolipin showed a tendency to decline, it was statistically insignificant. The total activity of citrate synthase for lean and T2DM group was similar; however, it was increased significantly in the obese group. Activity of beta-HAD and mtDNA content was similar for all three groups. We conclude that the total activity of NADH oxidase in biopsy for lean group is significantly higher than corresponding activity for obese or T2DM cohort. The specific activity of NADH oxidase (per mg cardiolipin) and NADH oxidase/citrate synthase and NADH oxidase/beta-HAD ratios are reduced two- to threefold in both T2DM and obesity.

Separation and characterization of cardiolipin molecular species by reverse-phase ion pair high-performance liquid chromatography-mass spectrometry

An improved high-performance liquid chromatography-mass spectrometry method for the separation and characterization of cardiolipin molecular species is presented. Reverse-phase ion pair chromatography with acidified triethylamine resulted in increased chromatographic retention and resolution when compared with chromatography without acidified triethylamine. Using a hybrid triple quadrupole linear ion trap mass spectrometer to generate MS/MS spectra revealed three regions within each spectrum that could be used to deduce the structure of the cardiolipin molecular species: the diacylglycerol phosphate region, the monoacylglycerol phosphate region, and the fatty acid region. Cardiolipin standards of known composition were analyzed and exhibited expected chromatographic and mass spectral results. Two minor components in commercial bovine heart cardiolipin, (with the same molecular weight but different chromatographic retention times), were shown to differ by fatty acid composition: (C18:2)(2)(C18:1)(2) versus (C18:2)(3)(C18:0)(1). These compounds were then analyzed by HPLC-MS(3) to examine specific diacylglycerol phosphate generated fatty acid fragmentation. Also, two commercial sources of bovine heart cardiolipin were shown to have minor differences in cardiolipin species content. Cardiolipin isolated from rat liver, mouse heart, and dog heart mitochondria were then characterized and the relative distributions of the major cardiolipin species were determined.

New method for GC/FID and GC-C-IRMS analysis of plasma free fatty acid concentration and isotopic enrichment

A simple, direct and accurate method for the determination of concentration and enrichment of free fatty acids (FFAs) in human plasma was developed. The validation and comparison to a conventional method are reported. Three amide derivatives, dimethyl, diethyl and pyrrolidide, were investigated in order to achieve optimal resolution of the individual fatty acids. This method involves the use of dimethylamine/Deoxo-Fluor to derivatize plasma free fatty acids to their dimethylamides. This derivatization method is very mild and efficient, and is selective only towards FFAs so that no separation from a total lipid extract is required. The direct method gave lower concentrations for palmitic acid and stearic acid and increased concentrations for oleic acid and linoleic acid in plasma as compared to methyl ester derivative after thin-layer chromatography. The [(13)C]palmitate isotope enrichment measured using direct method was significantly higher than that observed with the BF(3)/MeOH-TLC method. The present method provided accurate and precise measures of concentration as well as enrichment when analyzed with gas chromatography combustion-isotope ratio-mass spectrometry.

Mitochondrial capacity in skeletal muscle is not stimulated by weight loss despite increases in insulin action and decreases in intramyocellular lipid content

OBJECTIVE

In obesity and type 2 diabetes, exercise combined with weight loss increases skeletal muscle mitochondrial capacity. It remains unclear whether mitochondrial capacity increases because of weight loss, improvements in insulin resistance, or physical training. In this study, we examined the effects of an intervention of weight loss induced by diet and compared these with those of a similar intervention of weight loss by diet with exercise. Both are known to improve insulin resistance, and we tested the hypothesis that physical activity, rather than improved insulin resistance, is required to increase mitochondrial capacity of muscle.

RESEARCH DESIGN AND METHODS

Sixteen sedentary overweight/obese volunteers were randomized to a 16-week intervention of diet (n = 7) or diet plus exercise (n = 9). Insulin sensitivity was measured using euglycemic clamps. Mitochondria were examined in muscle biopsies before and after intervention. We measured mitochondrial content and size by electron microscopy, electron transport chain (ETC) activity, cardiolipin content, and mitochondrial DNA content. Intramyocellular content of lipid (IMCL) and fiber-type distribution were determined by histology.

RESULTS

The diet-only and diet plus exercise groups achieved similar weight loss (10.8 and 9.2%, respectively); only the diet plus exercise group improved aerobic capacity. Insulin sensitivity improved similarly in both groups. Mitochondrial content and ETC activity increased following the diet plus exercise intervention but remained unchanged following the diet-only intervention, and mitochondrial size decreased with weight loss despite improvement in insulin resistance. IMCL decreased in the diet-only but not in the diet plus exercise intervention.

CONCLUSIONS

Despite similar effects to improve insulin resistance, these interventions had differential effects on mitochondria. Clinically significant weight loss in the absence of increased physical activity ameliorates insulin resistance and IMCL but does not increase muscle mitochondrial capacity in obesity.

Selective early cardiolipin peroxidation after traumatic brain injury: an oxidative lipidomics analysis

OBJECTIVE

Enhanced lipid peroxidation is well established in traumatic brain injury. However, its molecular targets, identity of peroxidized phospholipid species, and their signaling role have not been deciphered.

METHODS

Using controlled cortical impact as a model of traumatic brain injury, we employed a newly developed oxidative lipidomics approach to qualitatively and quantitatively characterize the lipid peroxidation response.

RESULTS

Electrospray ionization and matrix-assisted laser desorption/ionization mass spectrometry analysis of rat cortical mitochondrial/synaptosomal fractions demonstrated the presence of highly oxidizable molecular species containing C(22:6) fatty acid residues in all major classes of phospholipids. However, the pattern of phospholipid oxidation at 3 hours after injury displayed a nonrandom character independent of abundance of oxidizable species and included only one mitochondria-specific phospholipid, cardiolipin (CL). This selective CL peroxidation was followed at 24 hours by peroxidation of other phospholipids, most prominently phosphatidylserine, but also phosphatidylcholine and phosphatidylethanolamine. CL oxidation preceded appearance of biomarkers of apoptosis (caspase-3 activation, terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling-positivity) and oxidative stress (loss of glutathione and ascorbate).

INTERPRETATION

The temporal sequence combined with the recently demonstrated role of CL hydroperoxides (CL-OOH) in in vitro models of apoptosis suggest that CL-OOH may be both a key in vivo trigger of apoptotic cell death and a therapeutic target in experimental traumatic brain injury.

Effects of physical activity and weight loss on skeletal muscle mitochondria and relationship with glucose control in type 2 diabetes

OBJECTIVE

Reduced mitochondrial capacity in skeletal muscle occurs in type 2 diabetic patients and in those at increased risk for this disorder, but the extent to which mitochondrial dysfunction in type 2 diabetic patients is remediable by physical activity and weight loss intervention is uncertain. We sought to address whether an intervention of daily moderate-intensity exercise combined with moderate weight loss can increase skeletal muscle mitochondrial content in type 2 diabetic patients and to address the relationship with amelioration of insulin resistance and hyperglycemia.

RESEARCH DESIGN AND METHODS

Muscle biopsies were obtained before and after a 4-month intervention to assess mitochondrial morphology, mitochondrial DNA content, and mitochondrial enzyme activities. Glucose control, body composition, aerobic fitness, and insulin sensitivity were measured.

RESULTS

In response to a weight loss of 7.1 +/- 0.8% and a 12 +/- 1.6% improvement in Vo(2max) (P < 0.05), insulin sensitivity improved by 59 +/- 21% (P < 0.05). There were significant increases in skeletal muscle mitochondrial density (by 67 +/- 17%, P < 0.01), cardiolipin content (55 +/- 17%, P < 0.01), and mitochondrial oxidation enzymes. Energy expenditure during physical activity correlated with the degree of improvement in insulin sensitivity (r = 0.84, P < 0.01), and, in turn, improvement in mitochondrial content was a strong correlate of intervention-induced improvement in A1C and fasting plasma glucose.

CONCLUSIONS

Intensive short-term lifestyle modifications can restore mitochondrial content and functional capacity in skeletal muscle in type 2 diabetic patients. The improvement in the oxidative capacity of skeletal muscle may be a key component mediating salutary effects of lifestyle interventions on hyperglycemia and insulin resistance.

Characteristics of skeletal muscle mitochondrial biogenesis induced by moderate-intensity exercise and weight loss in obesity

There are fewer mitochondria and a reduced oxidative capacity in skeletal muscle in obesity. Moderate-intensity physical activity combined with weight loss increase oxidative enzyme activity in obese sedentary adults; however, this adaptation occurs without a significant increase in mitochondrial DNA (mtDNA), which is unlike the classic pattern of mitochondrial biogenesis induced by vigorous activity. The objective of this study was to examine the hypothesis that the mitochondrial adaptation to moderate-intensity exercise and weight loss in obesity induces increased mitochondrial cristae despite a lack of mtDNA proliferation. Content of cardiolipin and mtDNA and enzymatic activities of the electron transport chain (ETC) and tricarboxylic acid cycle were measured in biopsy samples of vastus lateralis muscle obtained from sedentary obese men and women before and following a 4-mo walking intervention combined with weight loss. Cardiolipin increased by 60% from 47 ± 4 to 74 ± 8 μg/mU CK ( P < 0.01), but skeletal muscle mtDNA content did not change significantly (1,901 ± 363 to 2,169 ± 317 Rc, where Rc is relative copy number of mtDNA per diploid nuclear genome). Enzyme activity of the ETC increased ( P < 0.01); that for rotenone-sensitive NADH-oxidase (96 ± 1%) increased more than for ubiquinol-oxidase (48 ± 6%). Activities for citrate synthase and succinate dehydrogenase increased by 29 ± 9% and 40 ± 6%, respectively. In conclusion, moderate-intensity physical activity combined with weight loss induces skeletal muscle mitochondrial biogenesis in previously sedentary obese men and women, but this response occurs without mtDNA proliferation and may be characterized by an increase in mitochondrial cristae.

Role of cardiolipin alterations in mitochondrial dysfunction and disease

Cardiolipin (CL) is a structurally unique dimeric phospholipid localized in the inner mitochondrial membrane where it is required for optimal mitochondrial function. In addition to its role in maintaining membrane potential and architecture, CL is known to provide essential structural and functional support to several proteins involved in mitochondrial bioenergetics. A loss of CL content, alterations in its acyl chain composition, and/or CL peroxidation have been associated with mitochondrial dysfunction in multiple tissues in a variety of pathological conditions, including ischemia, hypothyroidism, aging, and heart failure. Recently, aberrations in CL metabolism have been implicated as a primary causative factor in the cardioskeletal myopathy known as Barth syndrome, underscoring an important role of CL in human health and disease. The purpose of this review is to provide an overview of evidence that has linked changes in the CL profile to mitochondrial dysfunction in various pathological conditions. In addition, a brief overview of CL function and biosynthesis, and a discussion of methods used to examine CL in biological tissues are provided.