PGC-1alpha-induced mitochondrial alterations in 3T3 fibroblast cells

The Pattern of Peroxisome Proliferator-activated Receptor Gamma Coactivator 1-alpha Gene Expression in Type-2 Diabetes Mellitus Rat Model Liver: Focus on Exercise

BACKGROUND: Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) has an important role in mitochondria biogenesis which generated cellular metabolism. Carbohydrate metabolism in the liver is crucial to maintain plasma blood glucose. AIM: This research aimed to determine the expression of PGC-1α gene in the liver type-2 diabetes mellitus (T2DM) rat model, after treatment with a focus on exercise. METHODS: We used 25 healthy male Wistar rats as subjects. Rats were modified to T2DM models by feeding a high-fat diet and low-dose streptozotocin injection. We divided the rats into five groups, that is, sedentary group as a control and four others as treatment groups. The exercise was assigned for treatment groups by a run on the treadmill as moderate intensity continuous (MIC), highintensity continuous (HIC), slow interval (SI), and fast interval (FI). The treatment groups were exercise throughout 8 weeks with a frequency of 3 times a week. RESULTS: The results showed that expression of PGC-1α gene was lower in all treatment groups compared to controls (p < 0.05). Expression in HIC was higher than MIC (p < 0.05), so was the expression in FI more than SI (p < 0.05). CONCLUSIONS: Exercise affected PGC-1α gene expression in the liver of the T2DM rat model. The expression of PGC-1α was linear with exercise intensity.

SIRT1 promotes lipid metabolism and mitochondrial biogenesis in adipocytes and coordinates adipogenesis by targeting key enzymatic pathways

The NAD⁺-dependent deacetylase SIRT1 controls key metabolic functions by deacetylating target proteins and strategies that promote SIRT1 function such as SIRT1 overexpression or NAD⁺ boosters alleviate metabolic complications. We previously reported that SIRT1-depletion in 3T3-L1 preadipocytes led to C-Myc activation, adipocyte hyperplasia, and dysregulated adipocyte metabolism. Here, we characterized SIRT1-depleted adipocytes by quantitative mass spectrometry-based proteomics, gene-expression and biochemical analyses, and mitochondrial studies. We found that SIRT1 promoted mitochondrial biogenesis and respiration in adipocytes and expression of molecules like leptin, adiponectin, matrix metalloproteinases, lipocalin 2, and thyroid responsive protein was SIRT1-dependent. Independent validation of the proteomics dataset uncovered SIRT1-dependence of SREBF1c and PPARα signaling in adipocytes. SIRT1 promoted nicotinamide mononucleotide acetyltransferase 2 (NMNAT2) expression during 3T3-L1 differentiation and constitutively repressed NMNAT1 and 3 levels. Supplementing preadipocytes with the NAD⁺ booster nicotinamide mononucleotide (NMN) during differentiation increased expression levels of leptin, SIRT1, and PGC-1α and its transcriptional targets, and reduced levels of pro-fibrotic collagens (Col6A1 and Col6A3) in a SIRT1-dependent manner. Investigating the metabolic impact of the functional interaction of SIRT1 with SREBF1c and PPARα and insights into how NAD⁺ metabolism modulates adipocyte function could potentially lead to new avenues in developing therapeutics for obesity complications.

PGC-1α-Derived Peptide Influences Energy in Normal Human Dermal Fibroblasts

Mitochondrial energy metabolism declines during aging. PGC-1α is a transcription coactivator that plays a key role in the regulation of energetic metabolism and mitochondrial biogenesis in the cells. The aim of this study was to compare the PPARGC1A gene expression level in normal human dermal fibroblasts (NHDF) derived from young and old donors. A PGC-1α-derived peptide was then synthetized and its ability to affect the PPARGC1A gene expression and mitochondrial function was tested. We assessed changes in PPARGC1A gene expression using quantitative RT-PCR. The effect of the PGC-1α-derived peptide on energy production was determined using an ATP bioluminescent assay kit. We also studied changes in mitochondrial membrane potential using JC-1 fluorescent dye and the level of reactive oxygen species (ROS) using DCFH-DA dye in NHDF cells after UVA/B irradiation alone and in combination with a peptide treatment. The PPARGC1A gene expression decreased in an aged human dermal fibroblast. The PGC-1α-derived peptide was synthetized and increased the PPARGC1A gene expression and ATP levels in cells. Furthermore, the mitochondrial membrane potential in UVA/B irradiated cells treated with the tested PGC-1α-derived peptide was increased compared to irradiated controls. Moreover, the ROS levels in UVA/B irradiated cells treated with the PGC-1α-derived peptide decreased. On the basis of our results, PGC-1α emerges as an interesting target to combat decreasing energetic metabolism in aging skin cells. Indeed, the PGC-1α-derived peptide increasing the PPARGC1A gene expression improved the mitochondrial function and increased energy production in the cells.

Tissue-specific implications of mitochondrial alterations in aging

Aging is a multifactorial process during which physiological alterations occur in all tissues. A decline in mitochondrial function plays an important role in the process of aging and in aging-associated diseases. The mitochondrial genome encodes 13 essential subunits of protein complexes belonging to the oxidative phosphorylation system, while most of the mitochondria-related genes are encoded by the nuclear genome. Coordination between the nucleus and mitochondria is crucial for the regulation of mitochondrial biogenesis and function. In this review, we will discuss aging-related mitochondrial dysfunction in various tissues and its implication in aging-related diseases and the aging process.

The interactive effect of SIRT1 promoter region polymorphism on type 2 diabetes susceptibility in the North Indian population

Our previous studies have implicated genes mainly involved in the activity of pancreatic β cells in type 2 diabetes (T2D) susceptibility in the North Indian population. Recent literature on the role of SIRT1 as a potential master switch modulating insulin secretion and regulating gene expression in pancreatic β cells has warranted an evaluation of SIRT1 promoter region polymorphisms in the North Indian population, which is the main focus of the present study. 1542 samples (692 T2D patients and 850 controls) were sequenced for the 1.46 kb region upstream the translation start site of the SIRT1 gene. We performed a functional characterization of the SIRT1 promoter region polymorphisms using luciferase assay and observed a single-nucleotide polymorphism (SNP), rs12778366, in association with SIRT1 expression. We propose that TT, the high-expressing genotype of SNP rs12778366 in the SIRT1 promoter region and present in >80% of the North Indian population, was favored under conditions of feast-famine cycles in evolution, which has turned out to be a cause of concern in the present sedentary lifestyle under ad libitum conditions. Case-control association analysis did not implicate rs12778366 in T2DM per se in the studied population. However, our earlier reported risk genotype combinations of mt-ND3, PGC1α, and UCP2-866, when compared with the protective genotype combinations, in the background of the high-expressing TT genotype of SIRT1 SNP rs12778366, showed a very high additive risk [corrected odd ratio (OR) = 8.91; p = 6.5×10(-11)]. The risk level was considerably low in the genotype backgrounds of TX (OR = 6.68; p = 2.71×10(-12)) and CX (OR = 3.74; p = 4.0×10(-3)). In addition, we screened other reported T2D-associated polymorphisms: PIK3R1 rs3730089, IRS1 rs1801278, and PPP1R3 rs1799999, which did not show any significant association in North Indian population. The present paper emphasizes the importance of gene interactions in the biological pathways of T2D, a complex lifestyle disease.

LRP130 protein remodels mitochondria and stimulates fatty acid oxidation

Impaired oxidative phosphorylation (OXPHOS) is implicated in several metabolic disorders. Even though mitochondrial DNA encodes several subunits critical for OXPHOS, the metabolic consequence of activating mitochondrial transcription remains unclear. We show here that LRP130, a protein involved in Leigh syndrome, increases hepatic β-fatty acid oxidation. Using convergent genetic and biochemical approaches, we demonstrate LRP130 complexes with the mitochondrial RNA polymerase to activate mitochondrial transcription. Activation of mitochondrial transcription is associated with increased OXPHOS activity, increased supercomplexes, and denser cristae, independent of mitochondrial biogenesis. Consistent with increased oxidative phosphorylation, ATP levels are increased in both cells and mouse liver, whereas coupled respiration is increased in cells. We propose activation of mitochondrial transcription remodels mitochondria and enhances oxidative metabolism.

Fatty liver is associated with impaired activity of PPARγ-coactivator 1α (PGC1α) and mitochondrial biogenesis in mice

Accumulating evidence indicates that mitochondria have a key role in non-alcoholic fatty liver disease (NAFLD). C57BL/6J mice were fed a choline-deficient, ethionine-supplemented (CDE) diet. Histological studies demonstrated accumulation of fat vacuoles in up to 90% of hepatocytes in mice fed the CDE diet for 14 days. In addition, a decrease in mitochondrial levels, together with an increase in superoxide radicals' levels were observed, indicating elevation of oxidative stress in hepatocytes. ATP levels were decreased in livers from CDE-fed mice after overnight fasting. This was accompanied by a compensative and significant increase in peroxisome-proliferator-activated receptor-γ coactivator 1α (PGC1α) mRNA levels in comparison to control livers. However, there was a reduction in PGC1α protein levels in CDE-treated mice. Moreover, the expression of mitochondrial biogenesis genes nuclear respiratory factor 1 (NRF-1), mitochondrial transcription factor A (TFAM), mitochondrial transcription factor B1 (TFB1M) and mitochondrial transcription factor B2 (TFB2M), which are all regulated by PGC1α activity, remained unchanged in fasted CDE-treated mice. These results indicate impaired activity of PGC1α. The impaired activity was further confirmed by chromatin immunoprecipitation analysis, which demonstrated decreased interaction of PGC1α with promoters containing NRF-1 and NRF-2 response elements in mice fed the CDE diet. A decrease in PGC1α ability to activate the expression of the gluconeogenic gene phosphoenol-pyruvate carboxykinase was also observed. This study demonstrates, for the first time, that attenuated mitochondrial biogenesis in steatotic livers is associated with impaired biological activity of PGC1α.

The Pim protein kinases regulate energy metabolism and cell growth

The serine/threonine Pim kinases are overexpressed in solid cancers and hematologic malignancies and promote cell growth and survival. Here, we find that a novel Pim kinase inhibitor, SMI-4a, or Pim-1 siRNA blocked the rapamycin-sensitive mammalian target of rapamycin (mTORC1) activity by stimulating the phosphorylation and thus activating the mTORC1 negative regulator AMP-dependent protein kinase (AMPK). Mouse embryonic fibroblasts (MEFs) deficient for all three Pim kinases [triple knockout (TKO) MEFs] demonstrated activated AMPK driven by elevated ratios of AMPATP relative to wild-type MEFs. Consistent with these findings, TKO MEFs were found to grow slowly in culture and have decreased rates of protein synthesis secondary to a diminished amount of 5'-cap-dependent translation. Pim-3 expression alone in TKO MEFs was sufficient to reverse AMPK activation, increase protein synthesis, and drive MEF growth similar to wild type. Pim-3 expression was found to markedly increase the protein levels of both c-Myc and the peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α), enzymes capable of regulating glycolysis and mitochondrial biogenesis, which were diminished in TKO MEFs. Overexpression of PGC-1α in TKO MEFs elevated ATP levels and inhibited the activation of AMPK. These results demonstrate the Pim kinase-mediated control of energy metabolism and thus regulation of AMPK activity. We identify an important role for Pim-3 in modulating c-Myc and PGC-1α protein levels and cell growth.

Pyrroloquinoline quinone stimulates mitochondrial biogenesis through cAMP response element-binding protein phosphorylation and increased PGC-1alpha expression

Bioactive compounds reported to stimulate mitochondrial biogenesis are linked to many health benefits such increased longevity, improved energy utilization, and protection from reactive oxygen species. Previously studies have shown that mice and rats fed diets lacking in pyrroloquinoline quinone (PQQ) have reduced mitochondrial content. Therefore, we hypothesized that PQQ can induce mitochondrial biogenesis in mouse hepatocytes. Exposure of mouse Hepa1-6 cells to 10-30 microm PQQ for 24-48 h resulted in increased citrate synthase and cytochrome c oxidase activity, Mitotracker staining, mitochondrial DNA content, and cellular oxygen respiration. The induction of this process occurred through the activation of cAMP response element-binding protein (CREB) and peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha), a pathway known to regulate mitochondrial biogenesis. PQQ exposure stimulated phosphorylation of CREB at serine 133, activated the promoter of PGC-1alpha, and increased PGC-1alpha mRNA and protein expression. PQQ did not stimulate mitochondrial biogenesis after small interfering RNA-mediated reduction in either PGC-1alpha or CREB expression. Consistent with activation of the PGC-1alpha pathway, PQQ increased nuclear respiratory factor activation (NRF-1 and NRF-2) and Tfam, TFB1M, and TFB2M mRNA expression. Moreover, PQQ protected cells from mitochondrial inhibition by rotenone, 3-nitropropionic acid, antimycin A, and sodium azide. The ability of PQQ to stimulate mitochondrial biogenesis accounts in part for action of this compound and suggests that PQQ may be beneficial in diseases associated with mitochondrial dysfunction.

Adipose tissue failure and mitochondria as a possible target for improvement by bioactive food components

PURPOSE OF REVIEW

Adipose tissue is an essential, highly dynamic and metabolically active tissue that vigorously communicates to support its primary function: the storage of lipids. It performs this function to secure energy supply and prevent lipotoxicity. Adipose tissue is essential for maintaining a healthy glucose and lipid homeostasis and failure results in disease. This review discusses causes of adipose tissue failure and four categories of bioactive food components that may help to prevent this.

RECENT FINDINGS

Based on recent findings, it is argued that initial adipose failure following long-term excess energy intake may be the result of reduced mitochondrial capacity associated with altered mitochondrial reactive oxygen species signaling and adipose tissue hypoxia. Current data suggest that different classes of bioactive food components, including vitamin B3, retinoids, fatty acids and polyphenols, may have the potential to modulate mitochondrial function and consequently prevent adipose dysfunction in obesity.

SUMMARY

It seems most attractive to aim nutritional intervention at the prevention of initial adipose dysfunction and hence to target dietary intervention at improvement of mitochondrial function.

Diet, energy metabolism and mitochondrial biogenesis

PURPOSE OF REVIEW

This review highlights some recent findings regarding nutritional and endocrine regulators of mitochondrial mass and function and their association with insulin resistance.

RECENT FINDINGS

Insulin resistance is central to many chronic metabolic diseases, including obesity, type 2 diabetes, dyslipidemia, and hypertension. Insulin resistance in skeletal muscle is associated with lower mitochondrial mass and reduced oxidative phosphorylation. Part of the mitochondrial dysfunction can be triggered by adverse nutrition. Increased fatty acid exposure, resulting from high fats diets or overfeeding, is linked to both decreased mitochondrial number and markers of oxidative phosphorylation. Caloric restriction and the adiponectin signaling pathway, however, can stimulate mitochondrial biogenesis by elevating the transcriptional machinery that regulates mitochondrial mass, improving mitochondrial efficiency, activating the peroxisome proliferator-activated receptor coactivator 1alpha mediated reactive oxygen species scavenging mechanism, and lowering reactive oxygen species production.

SUMMARY

States of insulin resistance are characterized by defects in lipid and carbohydrate metabolism. Abnormalities in oxidative capacity, however, can be partially normalized by caloric restriction by modulating mitochondrial mass in an insulin sensitizing manner.