Biogenesis Signaling Research Articles

PPARgamma agonist pioglitazone does not enhance performance in mice

Peroxisome-proliferator-activated receptor (PPAR) delta and adenosine monophosphate (AMP)-activated protein kinases (AMPKs) regulate the metabolic and contractile characteristics of myofibres. PPAR proteins are nuclear receptors that function as transcription factors and regulate the expression of multiple genes. AMPK has been described as a master metabolic regulator which also controls gene expression through the direct phosphorylation of some nuclear proteins. Since it was discovered that both PPARdelta agonists (GW1516) and AMPK activators (5-aminoimidazole-4-carboxamide-1-β-D-ribofuranoside, known as AICAR) are very effective performance-enhancing substances in sedentary mice, the World Anti-doping Agency (WADA) included AICAR and GW1516 in the prohibited list of substances as metabolic modulators in the class 'Hormone and metabolic modulators'. Thiazolidinediones are PPARgamma agonists that can induce similar biological effects to those of PPARdelta and PPARdelta-AMPK agonists. Thus in this study, the effects of pioglitazone on mitochondrial biogenesis and performance were evaluated. Blood glucose levels and the protein expression of the intermediates involved in the mitochondrial biogenesis pathway and the citrate synthase activity were determined in both gastrocnemius and soleus muscles. Maximal aerobic velocity (MAV), endurance capacity, and grip strength before and after the training period were also determined. The MAV endurance capacity and grip strength of trained animals significantly increased. We found that the peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) and the nuclear respiratory factor-1 (NRF-1) protein content and citrate synthase activity significantly increased in the soleus muscle of trained animals. No effect of treatment was found. Therefore in our study, pioglitazone administration did not affect mitochondrial biogenesis signaling pathway.

Effect of near-infrared light exposure on mitochondrial signaling in C2C12 muscle cells

Near-infrared (NIR) light is a complementary therapy used to treat musculoskeletal injuries but the underlying mechanisms are unclear. Acute NIR light treatment (~800–950nm; 22.8J/cm2) induced a dose-dependent increase in mitochondrial signaling (AMPK, p38 MAPK) in differentiated muscle cells. Repeated NIR light exposure (4days) appeared to elevate oxidative stress and increase the upstream mitochondrial regulatory proteins AMPK (3.1-fold), p38 (2.8-fold), PGC-1α (19.7%), Sirt1 (26.8%), and reduced RIP140 (23.2%), but downstream mitochondrial regulation/content (Tfam, NRF-1, Sirt3, cytochrome c, ETC subunits) was unaltered. Our data indicates that NIR light alters mitochondrial biogenesis signaling and may represent a mechanistic link to the clinical benefits.

Resveratrol protects cardiomyocytes from oxidative stress through SIRT1 and mitochondrial biogenesis signaling pathways

Reactive oxygen species (ROS) is generated by oxidative stress and plays an important role in various cardiac pathologies. The SIRT1 signaling pathway and mitochondrial biogenesis play essential roles in mediating the production of ROS. SIRT1 activated by resveratrol protects cardiomyocytes from oxidative stress, but the exact mechanisms by which SIRT1 prevents oxidative stress, and its relationship with mitochondrial biogenesis, remain unclear. In this study, it was observed that after stimulation with 50μMH2O2 for 6h, H9C2 cells produced excessive ROS and downregulated SIRT1. The mitochondrial protein NDUFA13 was also downregulated by ROS mediated by SIRT1. Resveratrol induced the expression of SIRT1 and mitochondrial genes NDUFA1, NDUFA2, NDUFA13 and Mn-SOD. However, the production of these genes was reversed by SIRT1 inhibitor nicotinamide. These results suggest that resveratrol inhibits ROS generation in cardiomyocytes via SIRT1 and mitochondrial biogenesis signaling pathways.

Macrophage Migration Inhibitory Factor Inhibition Is Deleterious for High-Fat Diet-Induced Cardiac Dysfunction

AimsDevelopment of metabolic syndrome is associated with impaired cardiac performance, mitochondrial dysfunction and pro-inflammatory cytokine increase, such as the macrophage migration inhibitory factor MIF. Depending on conditions, MIF may exert both beneficial and deleterious effects on the myocardium. Therefore, we tested whether pharmacological inhibition of MIF prevented or worsened metabolic syndrome-induced myocardial dysfunction.Methods and ResultsC57BL/6J mice were fed for ten weeks with 60% fat-enriched diet (HFD) or normal diet (ND). MIF inhibition was obtained by injecting mice twice a week with ISO-1, for three consecutive weeks. Then, triglycerides, cholesterol, fat mass, glucose intolerance, insulin resistance, ex vivo cardiac contractility, animal energetic substrate utilization assessed by indirect calorimetry and mitochondrial respiration and biogenesis were evaluated. HFD led to fat mass increase, dyslipidemia, glucose intolerance and insulin resistance. ISO-1 did not alter these parameters. However, MIF inhibition was responsible for HFD-induced cardiac dysfunction worsening. Mouse capacity to increase oxygen consumption in response to exercise was reduced in HFD compared to ND, and further diminished in ISO-1-treated HFD group. Mitochondrial respiration was reduced in HFD mice, treated or not with ISO-1. Compared to ND, mitochondrial biogenesis signaling was upregulated in the HFD as demonstrated by mitochondrial DNA amount and PGC-1α expression. However, this increase in biogenesis was blocked by ISO-1 treatment.ConclusionMIF inhibition achieved by ISO-1 was responsible for a reduction in HFD-induced mitochondrial biogenesis signaling that could explain majored cardiac dysfunction observed in HFD mice treated with MIF inhibitor.

Mitochondrial quality, dynamics and functional capacity in Parkinson’s disease cybrid cell lines selected for Lewy body expression

BackgroundLewy bodies (LB) are a neuropathological hallmark of Parkinson’s disease (PD) and other synucleinopathies. The role their formation plays in disease pathogenesis is not well understood, in part because studies of LB have been limited to examination of post-mortem tissue. LB formation may be detrimental to neuronal survival or merely an adaptive response to other ongoing pathological processes. In a human cytoplasmic hybrid (cybrid) neural cell model that expresses mitochondrial DNA from PD patients, we observed spontaneous formation of intracellular protein aggregates (“cybrid LB” or CLB) that replicate morphological and biochemical properties of native, cortical LB. We studied mitochondrial morphology, bioenergetics and biogenesis signaling by creating stable sub-clones of three PD cybrid cell lines derived from cells expressing CLB.ResultsCloning based on CLB expression had a differential effect on mitochondrial morphology, movement and oxygen utilization in each of three sub-cloned lines, but no long-term change in CLB expression. In one line (PD63CLB), mitochondrial function declined compared to the original PD cybrid line (PD63Orig) due to low levels of mtDNA in nucleoids. In another cell line (PD61Orig), the reverse was true, and cellular and mitochondrial function improved after sub-cloning for CLB expression (PD61CLB). In the third cell line (PD67Orig), there was no change in function after selection for CLB expression (PD67CLB).ConclusionsExpression of mitochondrial DNA derived from PD patients in cybrid cell lines induced the spontaneous formation of CLB. The creation of three sub-cloned cybrid lines from cells expressing CLB resulted in differential phenotypic changes in mitochondrial and cellular function. These changes were driven by the expression of patient derived mitochondrial DNA in nucleoids, rather than by the presence of CLB. Our studies suggest that mitochondrial DNA plays an important role in cellular and mitochondrial dysfunction in PD. Additional studies will be needed to assess the direct effect of CLB expression on cellular and mitochondrial function.

Gemfibrozil Pretreatment Resulted in a Sexually Dimorphic Outcome in the Rat Models of Global Cerebral Ischemia–Reperfusion via Modulation of Mitochondrial Pro-survival and Apoptotic Cell Death Factors as well as MAPKs

Inducers of mitochondrial biogenesis are widely under investigation for use in a novel therapeutic approach in neurodegenerative disorders. The ability of Gemfibrozil, a fibrate, is investigated for the first time to modulate mitochondrial pro-survival factors involved in the mitochondrial biogenesis signaling pathway, including peroxisome proliferator-activated receptor coactivator-1α (PGC-1α), nuclear respiratory factor (NRF-1), and mitochondrial transcription factor A (TFAM) in the brain. Gemfibozil is clinically administered to control hyperlipidemia. It secondarily prevents cardiovascular events such as cardiac arrest in susceptible patients. In this study, pretreatment of animals with gemfibrozil prior to ischemia-reperfusion (I/R) resulted in a sexually dimorphic outcome. While the expression of NRF-1 and TFAM were induced in gemfibrozil-pretreated met-estrous females, they were suppressed in males. Gemfibrozil also proved to be neuroprotective in met-estrous females, as it inhibited caspase-dependent apoptosis while in males it led to hippocampal neurodegeneration via activation of both the caspase-dependent and caspase-independent apoptosis. In the mitogen-activated protein kinase (MAPKs) pathway, gemfibrozil pretreatment induced the expression of extracellular signal-regulated kinases (ERK1/2) in met-estrous females and reduced it in males. These findings correlatively point to the sexual-dimorphic effects of gemfibrozil in global cerebral I/R context by affecting important factors involved in the mitochondrial biogenesis, MAPKs, and apoptotic cell death pathways.

Selenite Stimulates Mitochondrial Biogenesis Signaling and Enhances Mitochondrial Functional Performance in Murine Hippocampal Neuronal Cells

Supplementation of selenium has been shown to protect cells against free radical mediated cell damage. The objectives of this study are to examine whether supplementation of selenium stimulates mitochondrial biogenesis signaling pathways and whether selenium enhances mitochondrial functional performance. Murine hippocampal neuronal HT22 cells were treated with sodium selenite for 24 hours. Mitochondrial biogenesis markers, mitochondrial respiratory rate and activities of mitochondrial electron transport chain complexes were measured and compared to non-treated cells. The results revealed that treatment of selenium to the HT22 cells elevated the levels of nuclear mitochondrial biogenesis regulators PGC-1α and NRF1, as well as mitochondrial proteins cytochrome c and cytochrome c oxidase IV (COX IV). These effects are associated with phosphorylation of Akt and cAMP response element-binding (CREB). Supplementation of selenium significantly increased mitochondrial respiration and improved the activities of mitochondrial respiratory complexes. We conclude that selenium activates mitochondrial biogenesis signaling pathway and improves mitochondrial function. These effects may be associated with modulation of AKT-CREB pathway.

Carbon Monoxide Improves Cardiac Function and Mitochondrial Population Quality in a Mouse Model of Metabolic Syndrome

AimsMetabolic syndrome induces cardiac dysfunction associated with mitochondria abnormalities. As low levels of carbon monoxide (CO) may improve myocardial and mitochondrial activities, we tested whether a CO-releasing molecule (CORM-3) reverses metabolic syndrome-induced cardiac alteration through changes in mitochondrial biogenesis, dynamics and autophagy.Methods and ResultsMice were fed with normal diet (ND) or high-fat diet (HFD) for twelve weeks. Then, mice received two intraperitoneal injections of CORM-3 (10 mg.kg−1), with the second one given 16 hours after the first. Contractile function in isolated hearts and mitochondrial parameters were evaluated 24 hours after the last injection. Mitochondrial population was explored by electron microscopy. Changes in mitochondrial dynamics, biogenesis and autophagy were assessed by western-blot and RT-qPCR. Left ventricular developed pressure was reduced in HFD hearts. Mitochondria from HFD hearts presented reduced membrane potential and diminished ADP-coupled respiration. CORM-3 restored both cardiac and mitochondrial functions. Size and number of mitochondria increased in the HFD hearts but not in the CORM-3–treated HFD group. CORM-3 modulated HFD-activated mitochondrial fusion and biogenesis signalling. While autophagy was not activated in the HFD group, CORM-3 increased the autophagy marker LC3-II. Finally, ex vivo experiments demonstrated that autophagy inhibition by 3-methyladenine abolished the cardioprotective effects of CORM-3.ConclusionCORM-3 may modulate pathways controlling mitochondrial quality, thus leading to improvements of mitochondrial efficiency and HFD-induced cardiac dysfunction.

Acetyl-l-Carnitine Activates the Peroxisome Proliferator-Activated Receptor-γ Coactivators PGC-1α/PGC-1β–Dependent Signaling Cascade of Mitochondrial Biogenesis and Decreases the Oxidized Peroxiredoxins Content in Old Rat Liver

The behavior of the peroxisome proliferator-activated receptor-γ coactivators PGC-1α/PGC-β-dependent mitochondrial biogenesis signaling pathway, as well as the level of some antioxidant enzymes and proteins involved in mitochondrial dynamics in the liver of old rats before and after 2 months of acetyl-L-carnitine (ALCAR) supplementation, was tested. The results reveal that ALCAR treatment is able to reverse the age-associated decline of PGC-1α, PGC-1β, nuclear respiratory factor 1 (NRF-1), mitochondrial transcription factor A (TFAM), nicotinamide adenine dinucleotide (NADH) dehydrogenase subunit 1 (ND1), and cytochrome c oxidase subunit IV (COX IV) protein levels, of mitochondrial DNA (mtDNA) content, and of citrate synthase activity. Moreover, it partially reverses the mitochondrial superoxide dismutase 2 (SOD2) decline and reduces the cellular content of oxidized peroxiredoxins. These data demonstrate that ALCAR treatment is able to promote in the old rat liver a new mitochondrial population that can contribute to the cellular oxidative stress reduction. Furthermore, a remarkable decline of Drp1 and of Mfn2 proteins is reported here for the first time, suggesting a reduced mitochondrial dynamics in aging liver with no effect of ALCAR treatment.

Effect of Exercise on the Mitochondrial Profile of Testicular Tumors in Aged Fischer 344 Rats

Tumors exhibit an altered mitochondrial metabolic profile and suppressed mitochondrial‐mediated apoptosis. Exercise improves mitochondrial function and reduces susceptibility to mitochondrial‐mediated apoptosis in a variety of tissues but its effect on aged tumorigenic testes is unexplored. Thus, we investigated whether key mitochondrial signaling markers, mitochondrial content, and/or apoptotic factors differed in, 1) young control testes (YC; 6m; Fischer 344; n=4 group), 2) young exercised‐trained testes (YE; 6m; 10 weeks treadmill training) 3) old control non‐tumorigenic testes (OC; 22–24m; Fischer 344), 4) old tumorigenic testes (OT), 5) old tumorigenic exercise‐trained (OT‐E) testes. OT and OT‐E testes mass were similar but significantly larger (1.5‐ fold) than YC, YE and OC. Mitochondrial content was significantly elevated by 70–80% in both OT and OT‐E testes when compared to YC, YE, and OC, and similar trends were evident in upstream mitochondrial biogenesis signaling markers LKB1, AMPK, p38 and PGC‐1á. Bax:Bcl‐2 ratio, an apoptotic index, was significantly reduced by 70–80% in both OT and OT‐E when compared to YC, YE, and OC. Our findings indicate old tumorigenic testes exhibit enhanced mitochondrial biogenesis signaling and mitochondrial content but have reduced mitochondrial apoptotic susceptibility when compared to young healthy testes and this was unaffected by exercise.

Effect of Photo‐Irradiation on Mitochondrially‐Associated Signaling in C2C12 Muscle Cells

Laser therapy (phototherapy) is a clinical treatment used to promote tissue healing and improve muscle function in patients with musculoskeletal injury. However, the underlying cellular and molecular mechanisms responsible for the positive clinical outcomes are poorly understood. One proposed mechanism suggests specific wavelengths (710–1100‐nm) of light are preferentially absorbed by, and activate mitochondria in skeletal muscle to alter mitochondrial bioenergetics/biogenesis and potentially improve muscle regeneration post‐injury. To elucidate the underlying mechanisms, we applied varying treatment doses of phototherapy (0.42, 2.57, 8.14, 14.85, 22.80 and 29.60 J/cm2; 810–935nm; LiteCure LCT‐1000) to cultured muscle cells (C2C12 myotubes) and examined the activation of key mitochondrial biogenesis signalling proteins (AMPK, p38). Laser treatment caused phosphorylated‐AMPK (P‐AMPK) to increase in a traditional dose‐dependent manner, while phosphorylated‐p38 (P‐p38) exhibited a biphasic dose‐response. Thus, our preliminary findings indicate laser therapy evokes differential alterations in mitochondrial‐associated signaling molecules in C2C12 cells. Whether these acute phototherapy‐induced signaling changes will lead to an increase in functional mitochondria with longer‐term phototherapy in C2C12 cells has yet to be determined and is a focus of our future work.

Endonuclease G: The Link Between Mitochondria and Cardiac Hypertrophy?

### Endonuclease G Is a Novel Determinant of Cardiac Hypertrophy and Mitochondrial Function McDermott-Roe et al Nature . 2011;478:114–118. A recent study proposes novel functions of the long known mitochondrial endonuclease, endonuclease G (ENDOG).1 ENDOG was identified via quantitative trait loci analysis as a mediator of blood-pressure–independent cardiac hypertrophy and identified as a novel component in the mitochondrial biogenesis signaling network. Blood pressure-independent cardiac hypertrophy is commonly observed in subjects with obesity and Type 2 diabetes mellitus.2 It is likely that multiple predisposing factors and genetic modifiers interact in a complex fashion, to induce left ventricular (LV) hypertrophy. In the study by McDermott-Roe et al, the authors analyzed quantitative trait loci for blood pressure-independent cardiac mass in rats using an intercross of spontaneously hypertensive rats (SHR) and Brown Norway rats and identified ENDOG as a novel determinant of LV mass and cardiac function.1 Expression of ENDOG was reduced in SHR rats due to a frame-shift insertion in exon 1 of ENDOG that correlated with LV hypertrophy and impaired cardiac function. In subsequent studies, the authors demonstrated that shRNA-mediated knockdown of ENDOG in isolated neonatal rat cardiomyocytes resulted in increased cardiomyocyte size and that cardiomyocyte area was increased in mice lacking ENDOG. Thus, ENDOG may be a novel determinant of blood pressure-independent LV hypertrophy in rodents. To determine the potential relevance to cardiac hypertrophy in humans, a genome-wide coexpression network analysis in a large human cardiac expression data set was performed. ENDOG was identified as participating in a network that was highly enriched for mitochondrial genes and oxidative metabolism processes. Subsequently, the authors demonstrated that ENDOG is a direct target of ERRα and PGC-1α, master regulators of mitochondrial biogenesis. Overexpression of ENDOG increased mitochondrial mass in HEK293 and H9C2 cardiomyocytes. ENDOG directly binds to mitochondrial DNA suggesting a role in the regulation of mitochondrial gene transcription. Functionally, ENDOG−/− mice showed impaired mitochondrial respiration rates and increased …

Purple sweet potato color attenuates domoic acid-induced cognitive deficits by promoting estrogen receptor-α-mediated mitochondrial biogenesis signaling in mice

Recent findings suggest that endoplasmic reticulum stress may be involved in the pathogenesis of domoic acid-induced neurodegeneration. Purple sweet potato color, a class of naturally occurring anthocyanins, has beneficial health and biological effects. Recent studies have also shown that anthocyanins have estrogenic activity and can enhance estrogen receptor-α expression. In this study, we evaluated the effect of purple sweet potato color on cognitive deficits induced by hippocampal mitochondrial dysfunction in domoic acid-treated mice and explored the potential mechanisms underlying this effect. Our results showed that the oral administration of purple sweet potato color to domoic acid-treated mice significantly improved their behavioral performance in a step-through passive avoidance task and a Morris water maze task. These improvements were mediated, at least in part, by a stimulation of estrogen receptor-α-mediated mitochondrial biogenesis signaling and by decreases in the expression of p47phox and gp91phox. Decreases in reactive oxygen species and protein carbonylation were also observed, along with a blockade of the endoplasmic reticulum stress pathway. Furthermore, purple sweet potato color significantly suppressed endoplasmic reticulum stress-induced apoptosis, which prevented neuron loss and restored the expression of memory-related proteins. However, knockdown of estrogen receptor-α using short hairpin RNA only partially blocked the neuroprotective effects of purple sweet potato color in the hippocampus of mice cotreated with purple sweet potato color and domoic acid, indicating that purple sweet potato color acts through multiple pathways. These results suggest that purple sweet potato color could be a possible candidate for the prevention and treatment of cognitive deficits in excitotoxic and other brain disorders.

Acetyl-l-Carnitine Supplementation to Old Rats Partially Reverts the Age-Related Mitochondrial Decay of Soleus Muscle by Activating Peroxisome Proliferator-Activated Receptor γ Coactivator-1α–Dependent Mitochondrial Biogenesis

The age-related decay of mitochondrial function is a major contributor to the aging process. We tested the effects of 2-month-daily acetyl-L-carnitine (ALCAR) supplementation on mitochondrial biogenesis in the soleus muscle of aged rats. This muscle is heavily dependent on oxidative metabolism. Mitochondrial (mt) DNA content, citrate synthase activity, transcript levels of some nuclear- and mitochondrial-coded genes (cytochrome c oxidase subunit IV [COX-IV], 16S rRNA, COX-I) and of some factors involved in the mitochondrial biogenesis signaling pathway (peroxisome proliferator-activated receptor gamma [PPARgamma] coactivator-1alpha [PGC-1alpha], mitochondrial transcription factor A mitochondrial [TFAM], mitochondrial transcription factor 2B [TFB2]), as well as the protein content of PGC-1alpha were determined. The results suggest that the ALCAR treatment in old rats activates PGC-1alpha-dependent mitochondrial biogenesis, thus partially reverting the age-related mitochondrial decay.

Inhibition of xanthine oxidase mediated reactive oxygen species during exercise attenuates mitochondrial biogenesis signalling in skeletal muscle

INTRODUCTION:We tested the hypothesis that blocking the xanthine oxidase (XO)‐mediated increase in reactive oxygen species (ROS) with allopurinol during treadmill running in rats would inhibit phosphorylation of several key mitochondrial biogenesis signalling proteins.METHODS:Sprague Dawley rats rested (rest), exercised (Ex) or exercised following 30min pretreatment with 32 mg/kg of allopurinol by IP injection (Ex+allo). The exercise groups ran on a treadmill for 60 min (25m/min, 5% incline). Mitochondrial biogenesis signalling proteins were examined in the whole cell (phosphorylated p38 MAPK and AMPK) and nuclear fraction (phosphorylated CREB and ATF‐2) of the gastrocnemius via immunoblotting.RESULTS:Allopurinol treatment abolished the exercise‐induced phosphorylation of p38MAPK and ATF‐2 (P<0.05). There was a tendency (P=0.07) for exercise to increase phosphorylation of AMPK and allopurinol had no effect on this. CREB phosphorylation was not significantly different between groups.CONCLUSION:This data suggests that XO‐mediated increases in ROS during exercise are involved in some aspects of mitochondrial biogenesis signalling following exercise in skeletal muscle. Further studies are needed to examine if other aspects of the mitochondrial biogenesis pathway (eg PGC‐1 and NRF‐1) are also are also inhibited by allopurinol treatment during exercise.