bims-meprid Biomed News
on Metabolic-dependent epigenetic reprogramming in differentiation and disease
Issue of 2021‒01‒24
five papers selected by
Alessandro Carrer
Veneto Institute of Molecular Medicine

  1. Nat Metab. 2021 Jan;3(1): 75-89
      NADPH has long been recognized as a key cofactor for antioxidant defence and reductive biosynthesis. Here we report a metabolism-independent function of NADPH in modulating epigenetic status and transcription. We find that the reduction of cellular NADPH levels, achieved by silencing malic enzyme or glucose-6-phosphate dehydrogenase, impairs global histone acetylation and transcription in both adipocytes and tumour cells. These effects can be reversed by supplementation with exogenous NADPH or by inhibition of histone deacetylase 3 (HDAC3). Mechanistically, NADPH directly interacts with HDAC3 and interrupts the association between HDAC3 and its co-activator nuclear receptor corepressor 2 (Ncor2; SMRT) or Ncor1, thereby impairing HDAC3 activation. Interestingly, NADPH and the inositol tetraphosphate molecule Ins(1,4,5,6)P4 appear to bind to the same domains on HDAC3, with NADPH having a higher affinity towards HDAC3 than Ins(1,4,5,6)P4. Thus, while Ins(1,4,5,6)P4 promotes formation of the HDAC3-Ncor complex, NADPH inhibits it. Collectively, our findings uncover a previously unidentified and metabolism-independent role of NADPH in controlling epigenetic change and gene expression by acting as an endogenous inhibitor of HDAC3.
  2. Mol Metab. 2021 Jan 13. pii: S2212-8778(21)00005-3. [Epub ahead of print] 101165
      BACKGROUND: The abundance of energy metabolites is intimately interconnected with the activity of chromatin modifying enzymes in order to guarantee the finely tuned modulation of gene expression in response to cellular energetic status. Metabolism-induced epigenetic gene regulation is a key molecular axis for the maintenance of cellular homeostasis and its deregulation is associated with several pathological conditions. Nicotinamide N-methyltransferase (NNMT) is a metabolic enzyme that catalyzes the methylation of nicotinamide (NAM) using the universal methyl donor S-adenosyl methionine (SAM), directly linking one-carbon metabolism with a cell's methylation balance and nicotinamide adenine dinucleotide (NAD+) levels. NNMT expression and activity are regulated in a tissue-specific-manner and the protein can act either physiologically or pathologically depending on its distribution. While in the liver NNMT exerts a beneficial effect by regulating lipid parameters, in adipose tissue its expression correlates with obesity and insulin resistance. NNMT upregulation has been observed in a variety of cancers, and increased NNMT expression has been associated with tumor progression, metastasis and worse clinical outcomes. Accordingly, NNMT represents an appealing druggable target for metabolic disorders as well as oncological and other disease where the protein is improperly activated.SCOPE OF REVIEW: This review examines emerging findings concerning the complex NNMT regulatory network and the role of NNMT in both NAD metabolism and cell methylation balance. We extensively describe recent findings concerning the physiological and pathological regulation of NNMT with a specific focus on the function of NNMT in obesity, insulin resistance and other associated metabolic disorders along with its well-accepted role as a cancer-associated metabolic enzyme. Advances in strategies targeting NNMT pathways are also reported, together with current limitations of NNMT inhibitor drugs in clinical use.
    MAJOR CONCLUSIONS: NNMT is emerging as a key point of intersection between cellular metabolism and epigenetic gene regulation and growing evidence supports its central role in several pathologies. The use of molecules that target NNMT represents a current pharmaceutical challenge for the treatment of several metabolic-related disease as well as in cancer.
    Keywords:  Nicotinamide N-methyltransferase; cancer; epigenetics; metabolism; obesity
  3. Mol Neurobiol. 2021 Jan 21.
      In zebrafish, nicotine is known to regulate sensitivity to psychostimulants via epigenetic mechanisms. Little however is known about the regulation of addictive-like behavior by DNA methylation processes. To evaluate the influence of DNA methylation on nicotine-induced conditioned place preference (CPP), zebrafish were exposed to methyl supplementation through oral L-methionine (Met) administration. Met was found to reduce dramatically nicotine-induced CPP as well as behaviors associated with drug reward. The reduction was associated with the upregulation of DNA methyltransferases (DNMT1 and 3) as well as with the downregulation of methyl-cytosine dioxygenase-1 (TET1) and of nicotinic receptor subunits. Met also increased the expression of histone methyltransferases in nicotine-induced CPP groups. It reversed the nicotine-induced reduction in the methylation at α7 and NMDAR1 gene promoters. Treatment with the DNMT inhibitor 5-aza-2'-deoxycytidine (AZA) was found to reverse the effects of Met in structures of the reward pathway. Interestingly, Met did not modify the amount of the phospho-form of CREB (pCREB), a key factor establishing nicotine conditioning, whereas AZA increased pCREB levels. Our data suggest that nicotine-seeking behavior is partially dependent on DNA methylation occurring probably at specific gene loci, such as α7 and NMDAR1 receptor gene promoters. Overall, they suggest that Met should be considered as a potential therapeutic drug to treat nicotine addiction.
    Keywords:  Conditioned place preference; DNA methylation; Epigenetics; Nicotine; Zebrafish
  4. PLoS One. 2021 ;16(1): e0245348
      The ability of butyrate to promote differentiation of cancer cells has important implication for colorectal cancer (CRC) prevention and therapy. In this study, we examined the effect of sodium butyrate (NaBT) on the energy metabolism of colon adenocarcinoma Caco-2 cells coupled with their differentiation. NaBT increased the activity of alkaline phosphatase indicating differentiation of Caco-2 cells. Changes in the expression of pluripotency-associated markers OCT4, NANOG and SOX2 were characterized during the induced differentiation at mRNA level along with the measures that allowed distinguishing the expression of different transcript variants. The functional activity of mitochondria was studied by high-resolution respirometry. Glycolytic pathway and phosphotransfer network were analyzed using enzymatical assays. The treatment of Caco-2 cells with NaBT increased production of ATP by oxidative phosphorylation, enhanced mitochondrial spare respiratory capacity and caused rearrangement of the cellular phosphotransfer networks. The flexibility of phosphotransfer networks depended on the availability of glutamine, but not glucose in the cell growth medium. These changes were accompanied by suppressed cell proliferation and altered gene expression of the main pluripotency-associated transcription factors. This study supports the view that modulating cell metabolism through NaBT can be an effective strategy for treating CRC. Our data indicate a close relationship between the phosphotransfer performance and metabolic plasticity of CRC, which is associated with the cell differentiation state.
  5. Life (Basel). 2021 Jan 19. pii: E69. [Epub ahead of print]11(1):
      The tricarboxylic acid cycle (TCA) is a series of chemical reactions used in aerobic organisms to generate energy via the oxidation of acetylcoenzyme A (CoA) derived from carbohydrates, fatty acids and proteins. In the eukaryotic system, the TCA cycle occurs completely in mitochondria, while the intermediates of the TCA cycle are retained inside mitochondria due to their polarity and hydrophilicity. Under cell stress conditions, mitochondria can become disrupted and release their contents, which act as danger signals in the cytosol. Of note, the TCA cycle intermediates may also leak from dysfunctioning mitochondria and regulate cellular processes. Increasing evidence shows that the metabolites of the TCA cycle are substantially involved in the regulation of immune responses. In this review, we aimed to provide a comprehensive systematic overview of the molecular mechanisms of each TCA cycle intermediate that may play key roles in regulating cellular immunity in cell stress and discuss its implication for immune activation and suppression.
    Keywords:  Krebs cycle; cellular immunity; immunometabolism; tricarboxylic acid cycle