Increase In Mitochondrial Biogenesis Research Articles

Effects of exercise and body temperature on eNOS, SIRT1, SIRT3 and Hsp70 expression in rat plantaris muscles (1164.6)

Previously, we have demonstrated a dramatic increase in mitochondrial biogenesis in skeletal muscle of rats exercise trained while maintaining a constant core temperature. In this study, we explored the role of body temperature during exercise on the expression of multiple proteins (eNOS, SIRT1, SIRT3, and Hsp70) believed to play a role in mitochondrial biogenesis. Female, Sprague‐Dawley rats (5 mos of age) were divided into three groups sedentary (S), exercise in 22°C room (ET), and exercise while maintaining core temperature (E). Exercised animals trained for 5 weeks on a motor‐driven treadmill at 30 m/min, 60 min/day, 5 days/wk during final 2 wks. Core temperature was held constant in E by reducing room temp to 6‐8°C. Plantaris cytochrome oxidase activity (μmoles O2/min/g wet wt) was significantly (P<0.05) elevated in both ET (37.00±2.10) and E (47.14±4.11) versus S (24.15±1.37) and significantly greater in E versus ET. Preliminary results reveal no significant differences in SIRT1, SIRT3, or eNOS expression in the soleus muscles of S, E, or ET. Hsp70 was significantly (P<0.05) elevated in the ET group. These data suggest that although mitochondrial biogenesis increases in this model, eNOS, SIRT1 and SIRT3 do not parallel this increase and may not play a role in this process.

Effect of resveratrol on mitochondrial function: Implications in parkin-associated familiar Parkinson's disease

Mitochondrial dysfunction and oxidative stress occur in Parkinson's disease (PD), but the molecular mechanisms controlling these events are not completely understood. Peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α) is a transcriptional coactivator known as master regulator of mitochondrial functions and oxidative metabolism. Recent studies, including one from our group, have highlighted altered PGC-1α activity and transcriptional deregulation of its target genes in PD pathogenesis suggesting it as a new potential therapeutic target. Resveratrol, a natural polyphenolic compound proved to improve mitochondrial activity through the activation of several metabolic sensors resulting in PGC-1α activation. Here we have tested in vitro the effect of resveratrol treatment on primary fibroblast cultures from two patients with early-onset PD linked to different Park2 mutations. We show that resveratrol regulates energy homeostasis through activation of AMP-activated protein kinase (AMPK) and sirtuin 1 (SIRT1) and raise of mRNA expression of a number of PGC-1α's target genes resulting in enhanced mitochondrial oxidative function, likely related to a decrease of oxidative stress and to an increase of mitochondrial biogenesis. The functional impact of resveratrol treatment encompassed an increase of complex I and citrate synthase activities, basal oxygen consumption, and mitochondrial ATP production and a decrease in lactate content, thus supporting a switch from glycolytic to oxidative metabolism. Moreover, resveratrol treatment caused an enhanced macro-autophagic flux through activation of an LC3-independent pathway. Our results, obtained in early-onset PD fibroblasts, suggest that resveratrol may have potential clinical application in selected cases of PD-affected patients.

Inorganic nitrite supplementation for healthy arterial aging.

Aging is the major risk factor for cardiovascular diseases (CVD). This is attributable primarily to adverse changes in arteries, notably, increases in large elastic artery stiffness and endothelial dysfunction mediated by inadequate concentrations of the vascular-protective molecule, nitric oxide (NO), and higher levels of oxidative stress and inflammation. Inorganic nitrite is a promising precursor molecule for augmenting circulating and tissue NO bioavailability because it requires only a one-step reduction to NO. Nitrite also acts as an independent signaling molecule, exerting many of the effects previously attributed to NO. Results of recent studies indicate that nitrite may be effective in the treatment of vascular aging. In old mice, short-term oral sodium nitrite supplementation reduces aortic pulse wave velocity, the gold-standard measure of large elastic artery stiffness, and ameliorates endothelial dysfunction, as indicated by normalization of NO-mediated endothelium-dependent dilation. These improvements in age-related vascular dysfunction with nitrite are mediated by reductions in oxidative stress and inflammation, and may be linked to increases in mitochondrial biogenesis and health. Increasing nitrite levels via dietary intake of nitrate appears to have similarly beneficial effects in many of the same physiological and clinical settings. Several clinical trials are being performed to determine the broad therapeutic potential of increasing nitrite bioavailability on human health and disease, including studies related to vascular aging. In summary, inorganic nitrite, as well as dietary nitrate supplementation, represents a promising therapy for treatment of arterial aging and prevention of age-associated CVD in humans.

Biphasic Response of Mitochondrial Biogenesis to Oxidative Stress in Visceral Fat of Diet-Induced Obesity Mice

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

Mitochondrial dysfunction in cancer.

Mitochondria are semi-autonomous organelles of eukaryotic cells. They perform crucial functions such as generating most of the cellular energy through the oxidative phosphorylation (OXPHOS) system and some other metabolic processes. In addition, mitochondria are involved in regulation of cell death and reactive oxygen species (ROS) generation. Also, mitochondria play important roles in carcinogenesis via altering energy metabolism, resistance to apoptosis, increase of production of ROS and mtDNA (mitochondrial genome) changes. Studies have suggested that aerobic glycolysis is high in malignant tumors. Probably, it correlates with high glucose intake of cancerous tissues. This observation is contrary to Warburg's theory that the main way of energy generation in cancer cells is non-oxidative glycolysis. Further studies have suggested that in tumor cells both oxidative phosphorylation and glycolysis were active at various rates.An increase of intracellular oxidative stress induces damage of cellular structure and somatic mutations. Further studies confirmed that permanent activity of oxidative stress and the influence of chronic inflammation damage the healthy neighboring epithelium and may lead to carcinogenesis. For instance, chronic inflammatory bowel disease could be related to high risk of colon adenocarcinoma.The data have shown a role of ROS generation, mtDNA or nDNA alterations and abnormal apoptotic machinery in endometrial cancer progress. Recent studies suggest that mtDNA mutations might play a potential role in endometrial cancer progress and indicate an increase of mitochondrial biogenesis in this cancer. The investigators suggested that MtCOI and MtND6 alteration has an influence on assembly of respiratory complexes in endometrial cancer.In many human cancers, there is a deregulation of the balance between cell growth and death. The tumor cells can avoid apoptosis through a loss of balance between anti- and pro-apoptotic proteins, reduced caspase function and impaired death receptor signaling. Over-expression of the anti-apoptotic BCL-2 gene has also been identified in numerous cancers including colon, thyroid, breast and endometrial cancer. Most studies have found low BCL-2 family gene expression, which could be a sign of blocking apoptosis in breast and endometrial cancer. Moreover, BCL-2 gene expression is correlated with the degree of aggressiveness and differentiation in endometrial cancer. As a result, it could be a valuable predictor of disease progression.

Length variation in the mouse mitochondrial tRNAArg DHU loop size promotes oxidative phosphorylation functional differences

The efficiency of the cellular oxidative phosphorylation system was recently shown to be modulated by common mitochondrial tRNA(A) (rg) haplotypes. The molecular mechanism by which some mt-Tr haplotypes induce these functional differences remains undetermined. Common polymorphisms in mouse mt-Tr genes affect the size of the dihydrouridine loop in the mature tRNA, producing loops of between five and seven nucleotides, the largest being a rare variant among mammals. Here, we analyzed a new mt-Tr variant identified in C3H mice, and found that it is mitochondrial tRNA loop size, but not the specific sequence, that is responsible for the observed differences in cellular respiration. We further found that the sensitivity of mitochondrial protein synthesis to specific inhibitors is dependent on the mt-Tr gene haplotype, and confirmed that the differences in oxidative phosphorylation performance are masked by a reactive oxygen species-induced compensatory increase in mitochondrial biogenesis.

Boosting mitochondrial biogenesis in white adipocytes: A route towards improved insulin sensitivity?

Boosting mitochondrial biogenesis in white adipocytes: A route towards improved insulin sensitivity?

Hibernation: The search for treatments to prevent disuse-induced skeletal muscle atrophy

Loss of skeletal muscle mass is a serious consequence of multiple diseases and conditions for which there is limited treatment options. Disuse-induced muscle atrophy occurs as the result of both reduced mechanical loading and decreased neural activity. Hibernation represents a unique physiological state where skeletal muscles are protected from unloading, inactivity and nutritional deprivation. A recent study published in Experimental Neurology (Xu et al., 2013) utilized the thirteen-lined ground squirrel, a natural hibernator, to specifically examine whether peroxisome proliferator-activated receptor γ (PPARγ) coactivator 1-α (PGC-1α) and its associated upstream and downstream signaling partners were increased during hibernation. The results showed an increase in PGC-1α expression as well as increases in mitochondrial biogenesis, oxidative capacity, and antioxidant capacity in hibernating animals. It was suggested that upregulation of PCG-1α could be a viable strategy for the treatment of disuse-induced atrophy in humans. This commentary discusses the results of Xu et al. in the context of other studies that have examined muscle sparing in hibernating mammals, and compares these findings to what is known about disuse-induced atrophy in nonhibernating rodents and humans.

Antiobesity effects of a–lipoic acid supplementation

The incidence of obesity is increasing worldwide and concerns about its association with comorbidities such as cardiovascular disease or Type 2 diabetes led to research into alternative therapies to modulate bodyweight and adiposity. α-lipoic acid is a natural antioxidant with potential beneficial effects on obesity and its related disorders. This article aims to review the evidence from animal studies, with particular reference to trials in humans. Moreover, the putative mechanisms mediating the antiobesity properties of α-lipoic acid, including inhibition of food intake, stimulation of energy expenditure, increase of mitochondrial biogenesis, inhibition of lipogenesis and promotion of fat oxidation, among others, will be evaluated.

Induction of mitochondrial biogenesis protects against caspase-dependent and caspase-independent apoptosis in L6 myoblasts

Apoptotic signaling plays an important role in skeletal muscle degradation, atrophy, and dysfunction. Mitochondria are central executers of apoptosis by directly participating in caspase-dependent and caspase-independent cell death signaling. Given the important apoptotic role of mitochondria, altering mitochondrial content could influence apoptosis. Therefore, we examined the direct effect of modest, but physiological increases in mitochondrial biogenesis and content on skeletal muscle apoptosis using a cell culture approach. Treatment of L6 myoblasts with SNAP or AICAR (5h/day for 5days) significantly increased PGC-1, AIF, cytochrome c, and MnSOD protein content as well as MitoTracker staining. Following induction of mitochondrial biogenesis, L6 myoblasts displayed decreased sensitivity to apoptotic cell death as well as reduced caspase-3 and caspase-9 activation following exposure to staurosporine (STS) and C2-ceramide. L6 myoblasts with higher mitochondrial content also exhibited reduced apoptosis and AIF release following exposure to hydrogen peroxide (H2O2). Analysis of several key apoptosis regulatory proteins (ARC, Bax, Bcl-2, XIAP), antioxidant proteins (catalase, MnSOD, CuZnSOD), and reactive oxygen species (ROS) measures (DCF and MitoSOX fluorescence) revealed that these mechanisms were not responsible for the observed cellular protection. However, myoblasts with higher mitochondrial content were less sensitive to Ca2+-induced mitochondrial permeability transition pore formation (mPTP) and mitochondrial membrane depolarization. Collectively, these data demonstrate that increased mitochondrial content at physiological levels provides protection against apoptotic cell death by decreasing caspase-dependent and caspase-independent signaling through influencing mitochondrial Ca2+-mediated apoptotic events. Therefore, increasing mitochondrial biogenesis/content may represent a potential therapeutic approach in skeletal muscle disorders displaying increased apoptosis.

The over-expression of ERbeta modifies estradiol effects on mitochondrial dynamics in breast cancer cell line

Mitochondrial biogenesis and function are under the control of 17β-estradiol, which acts through two distinct estrogen receptors (alpha or beta), and the estrogen receptors ratio can determine the final effect of 17β-estradiol on mitochondria. Our aim was to study the effects of 17β-estradiol on mitochondrial biogenesis, dynamics and function in breast cancer cell lines with different estrogen receptors ratios. Mitochondrial biogenesis was increased in MDA-MB-231 (with only estrogen receptor beta expression), T47D (normal estrogen receptors ratio) and MCF-7 (highest estrogen receptors ratio) breast cancer cell lines, in response to different mitochondrial and cellular status. In fact, mitochondria of the MDA-MB-231 and T47D cell lines maintained their functionality, although, the MCF-7 cell line did suffer an important decrease in mitochondrial function. Thus, mitochondrial biogenesis increased in MCF-7 with the aim of mitigating these defective mitochondria. In normal conditions, mitophagic processes remove defective mitochondria to refresh the mitochondrial pool. Mitochondrial dynamics were also under control by 17β-estradiol, and showed modifications in the fusion/fission processes and the modulation of mitochondrial removal. In fact, cells with only estrogen receptor beta or with a low estrogen receptors ratio, such as MDA-MB-231 and T47D, showed an increase in fusion processes. However, the MCF-7 cell line, with more estrogen receptor alpha, also showed an increase in fusion processes, even though the fission processes were diminished and led to an accumulation of unfunctional mitochondria. Finally, the importance of estrogen receptor beta in mitochondrial biogenesis, function, as well as in mitochondrial dynamics was examined. Using the T47D-estrogen receptor beta tetracycline-inducible cell line, the results confirmed that when the overexpression of estrogen receptor beta was inhibited, there was an increase in mitochondrial biogenesis, although these mitochondria were less functional, and with fewer fission events, although there was an increase in fusion processes.

Cardiac ischemia reperfusion elicits increased mitochondrial mass but decreased mitochondrial respiration in mice

Modulation of mitochondrial biogenesis (MB) has been proposed to play a potentially critical role in the cardiac response to ischemia‐reperfusion (I/R), however, the specific effect of IR on MB has been little studied. We previously observed a significant increase in apparent cardiac mitochondrial mass after I/R in mice. Here we examined whether I/R‐induced increases in mitochondrial mass were associated with changes in mitochondrial respiratory activity. Mice were subjected to 30 occlusion of the left anterior descending coronary artery followed by 4 h reperfusion. Hearts were harvested for determination of both mitochondrial and nuclear DNA (mtDNA, nDNA, respectively) and measurement of respiratory activity in isolated mitochondria. The ratio of mtDNA/nDNA was increased 2–4‐fold by I/R. This was associated with significant decreases in both glutamate/malate‐ and succinate‐fueled oxygen consumption , as well as decreased respiratory control ratio (state3/state4). These results suggest that acute increases in mitochondrial biogenesis may be a compensatory but maladaptive response to I/R‐induced mitochondrial dysfunction, analogous to chronic mitochondrial cardiomyopathies. Supported by NIH AA‐014945 and HL‐095486.

Synergistic Effects of Leucine and β‐Hydroxy‐β‐Methyl‐ Butyrate (HMB) with Phosphodiesterase (PDE) Inhibitors on Sirtuin Activation

We recently demonstrated leucine and HMB synergy with resveratrol and other polyphenols to activate sirtuin signaling and downstream pathways, including mitochondrial biogenesis and fatty acid oxidation (FAO). Since resveratrol also activates Sirt1 via PDE inhibition with AMPK activation, we determined synergy between leucine or HMB and low‐dose PDE inhibitors in stimulating aerobic metabolism in adipocytes and myotubes. PDE inhibitors were studied at concentrations that exerted no independent effects in the systems studied (0.1 – 10 nM); only PDE 5 inhibitors (sildenafil and icariin) exhibited synergy with leucine (0.5 mM) or HMB (5 μM) in stimulating fat oxidation in myotubes (~200%, p=0.003) and adipocytes (~100%, p<0.05). Both PDE inhibitors exhibited comparable synergy with leucine and HMB in increasing NO production (~50%: p<0.0003) and corresponding increases in mitochondrial biogenesis (~15–30%, p<0.01). Thus, leucine‐dependent Sirt1/AMPK signaling synergizes with PDE 5‐regulated cGMP signaling to stimulate mitochondrial biogenesis and aerobic metabolism, resulting in significant effects at concentrations that are ~1% of the therapeutically‐effective plasma concentrations of these drugs.

Facts and controversies in our understanding of how caloric restriction impacts the mitochondrion

Caloric restriction (CR) has pronounced benefits in promoting healthy aging. Amongst the most frequently implicated physiological mechanisms implicated in this benefit is altered mitochondrial function. Whereas a reduction in mitochondrial reactive oxygen species (ROS) production is a widely consistent effect of CR, an increase in mitochondrial biogenesis, which is accepted by many as fact, is contradicted on several levels, most critically by a lack of increase in mitochondrial protein synthesis rate in vivo. Furthermore, an increase in PGC-1α protein and markers of mitochondrial content with CR is a highly variable observation between studies. On the other hand, deacetylation of several mitochondrial proteins by the sirtuin, Sirt3, is an increasingly reported observation and at least so far, this observation is consistent between studies. Notwithstanding this point, the controversies evident in the published literature underscore the significant questions that remain in our understanding of how CR impacts the mitochondrion and suggest we have yet to fully understand the complexities herein.

Sustained Activation of Akt Elicits Mitochondrial Dysfunction to Block Plasmodium falciparum Infection in the Mosquito Host

The overexpression of activated, myristoylated Akt in the midgut of female transgenic Anopheles stephensi results in resistance to infection with the human malaria parasite Plasmodium falciparum but also decreased lifespan. In the present study, the understanding of mitochondria-dependent midgut homeostasis has been expanded to explain this apparent paradox in an insect of major medical importance. Given that Akt signaling is essential for cell growth and survival, we hypothesized that sustained Akt activation in the mosquito midgut would alter the balance of critical pathways that control mitochondrial dynamics to enhance parasite killing at some cost to survivorship. Toxic reactive oxygen and nitrogen species (RNOS) rise to high levels in the midgut after blood feeding, due to a combination of high NO production and a decline in FOXO-dependent antioxidants. Despite an apparent increase in mitochondrial biogenesis in young females (3 d), energy deficiencies were apparent as decreased oxidative phosphorylation and increased [AMP]/[ATP] ratios. In addition, mitochondrial mass was lower and accompanied by the presence of stalled autophagosomes in the posterior midgut, a critical site for blood digestion and stem cell-mediated epithelial maintenance and repair, and by functional degradation of the epithelial barrier. By 18 d, the age at which An. stephensi would transmit P. falciparum to human hosts, mitochondrial dysfunction coupled to Akt-mediated repression of autophagy/mitophagy was more evident and midgut epithelial structure was markedly compromised. Inhibition of RNOS by co-feeding of the nitric-oxide synthase inhibitor L-NAME at infection abrogated Akt-dependent killing of P. falciparum that begins within 18 h of infection in 3–5 d old mosquitoes. Hence, Akt-induced changes in mitochondrial dynamics perturb midgut homeostasis to enhance parasite resistance and decrease mosquito infective lifespan. Further, quality control of mitochondrial function in the midgut is necessary for the maintenance of midgut health as reflected in energy homeostasis and tissue repair and renewal.

P21WAF1/CIP1 deficiency induces mitochondrial dysfunction in HCT116 colon cancer cells

p21WAF1/CIP1 is a critical regulator of cell cycle progression. However, the role of p21 in mitochondrial function remains poorly understood. In this study, we examined the effect of p21 deficiency on mitochondrial function in HCT116 human colon cancer cells. We found that there was a significant increase in the mitochondrial mass of p21−/− HCT116 cells, as measured by 10-N-nonyl-acridine orange staining, as well as an increase in the mitochondrial DNA content. In contrast, p53−/− cells had a mitochondrial mass comparable to that of wild-type HCT116 cells. In addition, the expression levels of the mitochondrial biogenesis regulators PGC-1α and TFAM and AMPK activity were also elevated in p21−/− cells, indicating that p21 deficiency induces the rate of mitochondrial biogenesis through the AMPK-PGC-1α axis. However, the increase in mitochondrial biogenesis in p21−/− cells did not accompany an increase in the cellular steady-state level of ATP. Furthermore, p21−/− cells exhibited significant proliferation impairment in galactose medium, suggesting that p21 deficiency induces a defect in the mitochondrial respiratory chain in HCT116 cells. Taken together, our results suggest that the loss of p21 results in an aberrant increase in the mitochondrial mass and in mitochondrial dysfunction in HCT116 cells, indicating that p21 is required to maintain proper mitochondrial mass and respiratory function.

Regulation of Mitochondrial Oxidative Metabolism by Tumor Suppressor FLCN

Birt-Hogg-Dubé (BHD) syndrome is a hereditary hamartoma syndrome that predisposes patients to develop hair follicle tumors, lung cysts, and kidney cancer. Genetic studies of BHD patients have uncovered the causative gene, FLCN, but its function is incompletely understood. Mice with conditional alleles of FLCN and/or peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PPARGC1A), a transcriptional coactivator that regulates mitochondrial biogenesis, were crossbred with mice harboring either muscle creatine kinase (CKM) -Cre or myogenin (MYOG) -Cre transgenes to knock out FLCN and/or PPARGC1A in muscle, or cadherin 16 (CDH16)- Cre transgenes to knock out FLCN and/or PPARGC1A in kidney. Real-time polymerase chain reaction, immunoblotting, electron microscopy, and metabolic profiling assay were performed to evaluate mitochondrial biogenesis and function in muscle. Immunoblotting, electron microscopy, and histological analysis were used to investigate expression and the pathological role of PPARGC1A in FLCN-deficient kidney. Real-time polymerase chain reaction, oxygen consumption measurement, and flow cytometry were carried out using a FLCN-null kidney cancer cell line. All statistical analyses were two-sided. Muscle-targeted FLCN knockout mice underwent a pronounced metabolic shift toward oxidative phosphorylation, including increased mitochondrial biogenesis (FLCN ( f/f ) vs FLCN ( f/f ) /CKM-Cre: % mitochondrial area mean = 7.8% vs 17.8%; difference = 10.0%; 95% confidence interval = 5.7% to 14.3%; P < .001), and the observed increase in mitochondrial biogenesis was PPARGC1A dependent. Reconstitution of FLCN-null kidney cancer cells with wild-type FLCN suppressed mitochondrial metabolism and PPARGC1A expression. Kidney-targeted PPARGC1A inactivation partially rescued the enlarged kidney phenotype and abrogated the hyperplastic cells observed in the FLCN-deficient kidney. FLCN deficiency and subsequent increased PPARGC1A expression result in increased mitochondrial function and oxidative metabolism as the source of cellular energy, which may give FLCN-null kidney cells a growth advantage and drive hyperplastic transformation.

IL-15Rα deficiency leads to mitochondrial and myofiber differences in fast mouse muscles

The purpose of this study was to determine mitochondrial changes in fast muscles from interleukin-15 receptor alpha knockout (IL-15RαKO) mice. We tested the hypothesis that fast muscles from IL-15RαKO mice would have a greater mitochondrial density and altered internal structure compared to muscles from control mice. In fast muscles from IL-15RαKO mice, mitochondrial density was 48% greater with a corresponding increase in mitochondrial DNA content. Although there were no differences in the relative size of isolated mitochondria, internal complexity was lower in mitochondria from IL-15RαKO mice. These data support an increase in mitochondrial biogenesis and provide direct evidence for a greater density and altered internal structure of mitochondria in EDL muscles deficient in IL-15Rα.

Dj-1β regulates oxidative stress, insulin-like signaling and development in Drosophila melanogaster

DJ-1 (or PARK-7) is a multifunctional protein implicated in numerous pathologies including cancer, sterility and Parkinson disease (PD). The popular genetic model Drosophila melanogaster has two orthologs, dj-1: α and β. Dysfunction of dj-1β strongly impairs fly mobility in an age-dependent manner. In this study, we analyze in detail the molecular mechanism underlying the dj-1β mutant phenotype. Mitochondrial hydrogen peroxide production, but not superoxide production, was increased in mutant flies. An increase in peroxide leak from mitochondria causes oxidative damage elsewhere and explains the strong reduction in mobility caused by dj-1β mutation. However, at the same time, increased levels of hydrogen peroxide activated a pro-survival program characterized by (1) an alteration in insulin-like signaling, (2) an increase in mitochondrial biogenesis and (3) an increase in the de-acetylase activity of sirtuins. The activation of this pro-survival program was associated with increased longevity under conditions of moderate oxidative stress. Additionally, the dj-1β mutation unexpectedly accelerated development, a phenotype not previously associated with this mutation. Our results reveal an important role of dj-1β in oxidative stress handling, insulin-like signaling and development in Drosophila melanogaster.

Augmentation of aerobic respiration and mitochondrial biogenesis in skeletal muscle by hypoxia preconditioning with cobalt chloride

High altitude/hypoxia training is known to improve physical performance in athletes. Hypoxia induces hypoxia inducible factor-1 (HIF-1) and its downstream genes that facilitate hypoxia adaptation in muscle to increase physical performance. Cobalt chloride (CoCl2), a hypoxia mimetic, stabilizes HIF-1, which otherwise is degraded in normoxic conditions. We studied the effects of hypoxia preconditioning by CoCl2 supplementation on physical performance, glucose metabolism, and mitochondrial biogenesis using rodent model. The results showed significant increase in physical performance in cobalt supplemented rats without (two times) or with training (3.3 times) as compared to control animals. CoCl2 supplementation in rats augmented the biological activities of enzymes of TCA cycle, glycolysis and cytochrome c oxidase (COX); and increased the expression of glucose transporter-1 (Glut-1) in muscle showing increased glucose metabolism by aerobic respiration. There was also an increase in mitochondrial biogenesis in skeletal muscle observed by increased mRNA expressions of mitochondrial biogenesis markers which was further confirmed by electron microscopy. Moreover, nitric oxide production increased in skeletal muscle in cobalt supplemented rats, which seems to be the major reason for peroxisome proliferator activated receptor-gamma coactivator-1α (PGC-1α) induction and mitochondrial biogenesis. Thus, in conclusion, we state that hypoxia preconditioning by CoCl2 supplementation in rats increases mitochondrial biogenesis, glucose uptake and metabolism by aerobic respiration in skeletal muscle, which leads to increased physical performance. The significance of this study lies in understanding the molecular mechanism of hypoxia adaptation and improvement of work performance in normal as well as extreme conditions like hypoxia via hypoxia preconditioning.