RESUMO
Diseases associated with mitochondrial DNA (mtDNA) mutations are highly variable in phenotype, in large part because of differences in the percentage of normal and mutant mtDNAs (heteroplasmy) present within the cell. For example, increasing heteroplasmy levels of the mtDNA tRNALeu(UUR) nucleotide (nt) 3243A > G mutation result successively in diabetes, neuromuscular degenerative disease, and perinatal lethality. These phenotypes are associated with differences in mitochondrial function and nuclear DNA (nDNA) gene expression, which are recapitulated in cybrid cell lines with different percentages of m.3243G mutant mtDNAs. Using metabolic tracing, histone mass spectrometry, and NADH fluorescence lifetime imaging microscopy in these cells, we now show that increasing levels of this single mtDNA mutation cause profound changes in the nuclear epigenome. At high heteroplasmy, mitochondrially derived acetyl-CoA levels decrease causing decreased histone H4 acetylation, with glutamine-derived acetyl-CoA compensating when glucose-derived acetyl-CoA is limiting. In contrast, α-ketoglutarate levels increase at midlevel heteroplasmy and are inversely correlated with histone H3 methylation. Inhibition of mitochondrial protein synthesis induces acetylation and methylation changes, and restoration of mitochondrial function reverses these effects. mtDNA heteroplasmy also affects mitochondrial NAD+/NADH ratio, which correlates with nuclear histone acetylation, whereas nuclear NAD+/NADH ratio correlates with changes in nDNA and mtDNA transcription. Thus, mutations in the mtDNA cause distinct metabolic and epigenomic changes at different heteroplasmy levels, potentially explaining transcriptional and phenotypic variability of mitochondrial disease.
Assuntos
Núcleo Celular/genética , DNA Mitocondrial/genética , Epigenoma , Acetilcoenzima A/metabolismo , Linhagem Celular , Histonas/metabolismo , Humanos , Metaboloma , Mitocôndrias/metabolismo , NAD/metabolismo , Transcrição GênicaRESUMO
Friedreich's ataxia (FRDA) is a progressive disorder caused by insufficient expression of frataxin, which plays a critical role in assembly of iron-sulfur centers in mitochondria. Individuals are cognitively normal but display a loss of motor coordination and cardiac abnormalities. Many ultimately develop heart failure. Administration of nicotinamide adenine dinucleotide-positive (NAD+) precursors has shown promise in human mitochondrial myopathy and rodent models of heart failure, including mice lacking frataxin in cardiomyocytes. We studied mice with systemic knockdown of frataxin (shFxn), which display motor deficits and early mortality with cardiac hypertrophy. Hearts in these mice do not "fail" per se but become hyperdynamic with small chamber sizes. Data from an ongoing natural history study indicate that hyperdynamic hearts are observed in young individuals with FRDA, suggesting that the mouse model could reflect early pathology. Administering nicotinamide mononucleotide or riboside to shFxn mice increases survival, modestly improves cardiac hypertrophy, and limits increases in ejection fraction. Mechanistically, most of the transcriptional and metabolic changes induced by frataxin knockdown are insensitive to NAD+ precursor administration, but glutathione levels are increased, suggesting improved antioxidant capacity. Overall, our findings indicate that NAD+ precursors are modestly cardioprotective in this model of FRDA and warrant further investigation.
Assuntos
Modelos Animais de Doenças , Frataxina , Ataxia de Friedreich , Proteínas de Ligação ao Ferro , NAD , Animais , Ataxia de Friedreich/metabolismo , Ataxia de Friedreich/patologia , Ataxia de Friedreich/genética , Proteínas de Ligação ao Ferro/genética , Proteínas de Ligação ao Ferro/metabolismo , Camundongos , Humanos , NAD/metabolismo , Fenótipo , Masculino , Cardiomegalia/metabolismo , Cardiomegalia/patologia , Mononucleotídeo de Nicotinamida/farmacologia , Niacinamida/análogos & derivados , Niacinamida/farmacologia , Feminino , Técnicas de Silenciamento de Genes , Compostos de Piridínio , Miócitos Cardíacos/metabolismo , Miócitos Cardíacos/patologiaRESUMO
Liver regeneration is critical to survival after traumatic injuries, exposure to hepatotoxins, or surgical interventions, yet the underlying signaling and metabolic pathways remain unclear. In this study, we show that hepatocyte-specific loss of the mitochondrial deacetylase SIRT3 drastically impairs regeneration and worsens mitochondrial function after partial hepatectomy. Sirtuins, including SIRT3, require NAD as a cosubstrate. We previously showed that the NAD precursor nicotinamide riboside (NR) promotes liver regeneration, but whether this involves sirtuins has not been tested. Here, we show that despite their NAD dependence and critical roles in regeneration, neither SIRT3 nor its nuclear counterpart SIRT1 is required for NR to enhance liver regeneration. NR improves mitochondrial respiration in regenerating WT or mutant livers and rapidly increases oxygen consumption and glucose output in cultured hepatocytes. Our data support a direct enhancement of mitochondrial redox metabolism as the mechanism mediating improved liver regeneration after NAD supplementation and exclude signaling via SIRT1 and SIRT3. Therefore, we provide the first evidence to our knowledge for an essential role for a mitochondrial sirtuin during liver regeneration and insight into the beneficial effects of NR.
Assuntos
Regeneração Hepática/fisiologia , Mitocôndrias Hepáticas/fisiologia , Niacinamida/análogos & derivados , Compostos de Piridínio/farmacologia , Sirtuína 3/metabolismo , Animais , Hepatócitos/efeitos dos fármacos , Hepatócitos/metabolismo , Regeneração Hepática/efeitos dos fármacos , Masculino , Camundongos Endogâmicos C57BL , Camundongos Knockout , Camundongos Transgênicos , Mitocôndrias Hepáticas/efeitos dos fármacos , Niacinamida/farmacologia , Oxirredução , Sirtuína 1/genética , Sirtuína 1/metabolismo , Sirtuína 3/genéticaRESUMO
Acetyl-CoA is a vitally important and versatile metabolite used for many cellular processes including fatty acid synthesis, ATP production, and protein acetylation. Recent studies have shown that cancer cells upregulate acetyl-CoA synthetase 2 (ACSS2), an enzyme that converts acetate to acetyl-CoA, in response to stresses such as low nutrient availability and hypoxia. Stressed cancer cells use ACSS2 as a means to exploit acetate as an alternative nutrient source. Genetic depletion of ACSS2 in tumors inhibits the growth of a wide variety of cancers. However, there are no studies on the use of an ACSS2 inhibitor to block tumor growth. In this study, we synthesized a small-molecule inhibitor that acts as a transition-state mimetic to block ACSS2 activity in vitro and in vivo. Pharmacologic inhibition of ACSS2 as a single agent impaired breast tumor growth. Collectively, our findings suggest that targeting ACSS2 may be an effective therapeutic approach for the treatment of patients with breast cancer. SIGNIFICANCE: These findings suggest that targeting acetate metabolism through ACSS2 inhibitors has the potential to safely and effectively treat a wide range of patients with cancer.
Assuntos
Acetato-CoA Ligase/antagonistas & inibidores , Antineoplásicos/farmacologia , Neoplasias de Mama Triplo Negativas/tratamento farmacológico , Acetato-CoA Ligase/genética , Acetato-CoA Ligase/metabolismo , Animais , Antineoplásicos/química , Linhagem Celular Tumoral , Ensaios de Seleção de Medicamentos Antitumorais/métodos , Estabilidade de Medicamentos , Inibidores Enzimáticos/química , Inibidores Enzimáticos/farmacologia , Ácidos Graxos/metabolismo , Feminino , Regulação Neoplásica da Expressão Gênica/efeitos dos fármacos , Células HEK293 , Humanos , Camundongos Endogâmicos , Simulação de Acoplamento Molecular , Terapia de Alvo Molecular/métodos , Neoplasias de Mama Triplo Negativas/metabolismo , Neoplasias de Mama Triplo Negativas/patologia , Ensaios Antitumorais Modelo de XenoenxertoRESUMO
Brain metastasis, the most lethal form of melanoma and carcinoma, is the consequence of favorable interactions between the invading cancer cells and the brain cells. Peroxisome proliferator-activated receptor γ (PPARγ) has ambiguous functions in cancer development, and its relevance in advanced brain metastasis remains unclear. Here, we demonstrate that astrocytes, the unique brain glial cells, activate PPARγ in brain metastatic cancer cells. PPARγ activation enhances cell proliferation and metastatic outgrowth in the brain. Mechanistically, astrocytes have a high content of polyunsaturated fatty acids that act as "donors" of PPARγ activators to the invading cancer cells. In clinical samples, PPARγ signaling is significantly higher in brain metastatic lesions. Notably, systemic administration of PPARγ antagonists significantly reduces brain metastatic burden in vivo. Our study clarifies a prometastatic role for PPARγ signaling in cancer metastasis in the lipid-rich brain microenvironment and argues for the use of PPARγ blockade to treat brain metastasis. SIGNIFICANCE: Brain-tropic cancer cells take advantage of the lipid-rich brain microenvironment to facilitate their proliferation by activating PPARγ signaling. This protumor effect of PPARγ in advanced brain metastases is in contrast to its antitumor function in carcinogenesis and early metastatic steps, indicating that PPARγ has diverse functions at different stages of cancer development.This article is highlighted in the In This Issue feature, p. 1631.
Assuntos
Astrócitos/metabolismo , Neoplasias Encefálicas/patologia , Neoplasias Encefálicas/secundário , Ácidos Graxos Insaturados/metabolismo , PPAR gama/genética , Animais , Astrócitos/citologia , Astrócitos/patologia , Neoplasias Encefálicas/genética , Neoplasias Encefálicas/metabolismo , Linhagem Celular Tumoral , Movimento Celular , Proliferação de Células , Perfilação da Expressão Gênica , Humanos , Camundongos , Transplante de Neoplasias , Transdução de SinaisRESUMO
We report a novel strategy to enzymatically release affinity-selected cells, such as circulating tumor cells (CTCs), from surfaces with high efficiency (â¼90%) while maintaining cell viability (>85%). The strategy utilizes single-stranded DNAs that link a capture antibody to the surfaces of a CTC selection device. The DNA linkers contain a uracil residue that can be cleaved.