Citrate synthase (CS), the rate-limiting enzyme in the tricarboxylic acid (TCA) cycle catalyzes the first step of the cycle, namely, the condensation of oxaloacetate and acetyl-CoA to produce citrate. The expression and enzymatic activity of CS are altered in cancers, but posttranslational modification (PTM) of CS and its regulation in tumorigenesis remain largely obscure. SIRT5 belongs to the nicotinamide adenine dinucleotide (NAD)+-dependent deacetylase sirtuin family and plays vital roles in multiple biological processes via modulating various substrates. Here, we show that SIRT5 interacts with CS and that SIRT5 desuccinylates CS at the evolutionarily conserved residues K393 and K395. Moreover, hypersuccinylation of CS at K393 and K395 dramatically reduces its enzymatic activity and suppresses colon cancer cell proliferation and migration. These results provide experimental evidence in support of a potential therapeutic approach for colon cancer.
In animal models, prolonged exposure (2 h) to high-level noise causes an irreparable damage to the synapses between the inner hair cells and auditory nerve fibers within the cochlea. Nevertheless, this injury does not necessarily alter the hearing threshold. Similar findings have been observed as part of typical aging in animals. This type of cochlear synaptopathy, popularly called “hidden hearing loss,” has been a significant issue in neuroscience research and clinical audiology scientists. The results obtained in different investigations are inconclusive in their diagnosis and suggest new strategies for both prognosis and treatment of cochlear synaptopathy. Here we review the major physiological findings regarding cochlear synaptopathy in animals and humans and discuss mathematical models. We also analyze the potential impact of these results on clinical practice and therapeutic options.
Glycosylation is a very frequent post-translational modification in proteins, and the initiation of O-N-acetylgalactosamine (O-GalNAc) glycosylation has been recently described on relevant nuclear proteins. Here we evaluated the nuclear incorporation of a second sugar residue in the biosynthesis pathway of O-GalNAc glycans to yield the terminal core 1 glycan (C1G, Galβ3GalNAcαSer/Thr). Using confocal microscopy, enzymatic assay, affinity chromatography, and mass spectrometry, we analyzed intact cells, purified nuclei and soluble nucleoplasms to identify the essential factors for C1G biosynthesis in the cell nucleus. The enzyme C1GalT1 responsible for C1G synthesis was detected inside the nucleus, while catalytic activity of C1Gal-transferase was present in nucleoplasm and purified nuclei. In addition, C1G were detected in the nucleus inside of intact cells, and nuclear proteins exposing C1G were also identified. These evidences represent the first demonstration of core 1 O-GalNAc glycosylation of proteins in the human cell nucleus. These findings reveal a novel post-translational modification on nuclear proteins, with relevant repercussion in epigenetic and chemical biology areas.
The ketogenic diet (KD) is characterized by a diet ratio of 4:1 fat to non-fat energy sources. For decades KD has been successfully used to control seizures in epilepsy patients. Investigations into its mechanism of action suggest that it may have an effect on the metabolic, nervous, immune, and digestive systems. In this review, we postulate that KD may also improve depressive symptoms – for that, we highlight the similarities between depression and epilepsy, describe the extent to which body systems involved in both conditions are affected by the KD, and ultimately hypothesize how KD could improve MDD outcomes. Research into animal models and human patients have reported that KD can increase mitochondrial biogenesis and increase cellular resistance to oxidative stress both at the mitochondrial and genetic levels. Its effect on neurotransmitters alters cell-to-cell communication in the brain and may decrease hyperexcitability by increasing Gamma Aminobutyric Acid (GABA) and decreasing excitatory neurotransmitter levels. Its anti-inflammatory effects are mediated by decreasing chemo- and cytokine levels, including TNF-alpha and IL-1 levels. Finally, KD can alter gut microbiota (GM). Certain strains of microbiota predominate in major depressive disorder (MDD) when compared to healthy individuals. Recent evidence points to Bacteroidetes as a potential treatment predictor as it seems to increase in KD treatment responders for epilepsy. Each of these observations contributes to the presumed modulatory effects of KD on mood and supports its potential role as antidepressant.
Alzheimer's disease (AD) is a very common cause of dementia in the elderly. It is characterized by progressive amnesia and accretions of neurofibrillary tangles (NFTs) of neurons and senile plaques in the neuropil. After aging, the inheritance of the apolipoprotein E (ApoE) epsilon 4 (ε4) allele is the greatest risk factor for late-onset AD. The ApoE protein is the translated product of the ApoE gene. This protein undergoes proteolysis, and the resulting fragments colocalize with neurofibrillary tangles and amyloid plaques, and for that matter may be involved in AD onset and/or progression. Previous studies have reported the pathogenic potential of various ApoE fragments in AD pathophysiology. However, the pathways activated by the fragments are not fully understood. In this review, ApoE fragments obtained from post-mortem brains and body fluids, cerebrospinal fluid (CSF) and plasma, are discussed. Additionally, current knowledge about the process of fragmentation is summarized. Finally, the mechanisms by which these fragments are involved in AD pathogenesis and pathophysiology are discussed.
In this review, a series of experiments is presented, in which γ-amino butyric acid (GABA)ergic and glutamatergic effects on dopamine function in the rat nigrostriatal and mesolimbic system was systematically assessed after pharmacological challenge with GABAA receptor (R) and and N-methyl d-aspartate (NMDA)R agonists and antagonists. In these studies, [123I]iodobenzamide binding to the D2/3R was mesured in nucleus accumbens (NAC), caudateputamen (CP), substantia nigra/ventral tegmental area (SN/VTA), frontal (FC), motor (MC) and parietal cortex (PC) as well as anterior (aHIPP) and posterior hippocampus (pHIPP) with small animal SPECT in baseline and after injection of either the GABAAR agonist muscimol (1 mg/kg), the GABAAR antagonist bicuculline (1 mg/kg), the NMDAR agonist d-cycloserine (20 mg/kg) or the NMDAR antagonist amantadine (40 mg/kg). Muscimol reduced D2/3R binding in NAC, CP, SN/VTA, THAL and pHIPP, while, after amantadine, decreases were confined to NAC, CP and THAL. In contrast, d-cycloserine elevated D2/3R binding in NAC, SN/VTA, THAL, frontal cortex, motor cortex, PC, aHIPP and pHIPP, while, after bicuculline, increases were confined to CP and THAL. Taken together, similar actions on regional dopamine levels were exterted by the GABAAR agonist and the NMDAR antagonist on the one side and by the GABAAR antagonist and the NMDAR agonist on the other, with agonistic action, however, affecting more brain regions. Thereby, network analysis suggests different roles of GABAARs and NMDARs in the mediation of nigrostriatal, nigrothalamocortical and mesolimbocortical dopamine function.
Accumulating studies highlight the critical role of long non-coding RNAs (lncRNAs) in the development of various human cancers. Extracellular leucine rich repeat and fibronectin type III domain containing 1-antisense RNA 1 (ELFN1-AS1) was shown to be a newly found lncRNA that abnormally expressed in human tumors. However, till now the specific function of this lncRNA in esophageal cancer (ESCA) remains unknown. In this study, we discovered that higher ELFN1-AS1 expression indicated shorter patient survival in pan-cancer, including ESCA, using online The Cancer Genome Atlas (TCGA) tools. The lncRNA ELFN1-AS1 was significantly up-regulated in ESCA tissues and cell lines when compared with the counterparts. Down-regulation of ELFN1-AS1 restrained cell proliferation, migration, and invasion of ESCA in vitro. In addition, we found that the expression of microRNA-183-3p (miR-183-3p) and ELFN1-AS1 or glutamine-fructose-6-phosphate transaminase 1 (GFPT1) were inversely correlated in ESCA. Both ELFN1-AS1 and GFPT1 are direct targets of miR-183-3p in ESCA. The effects of ELFN1-AS1 knockdown on ESCA progression were partially rescued by inhibition of miR-183-3p or over-expression of GFPT1. In summary, the results of this study suggest that the lncRNA ELFN1-AS1 facilitates the progression of ESCA by acting as a competing endogenous RNA (ceRNA) to promote GFPT1 expression via sponging miR-183-3p.
The molecular and chemical properties of neuronal nitric oxide synthase (nNOS) have made it a key mediator in many physiological functions and signaling transduction. The NOS monomer is inactive, but the dimer form is active. There are three forms of NOS, which are neuronal (nNOS), inducible (iNOS), and endothelial (eNOS) nitric oxide synthase. nNOS regulates nitric oxide (NO) synthesis which is the mechanism used mostly by neurons to produce NO. nNOS expression and activation is regulated by some important signaling proteins, such as cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB), calmodulin (CaM), heat shock protein 90 (HSP90)/HSP70. nNOS-derived NO has been implicated in modulating many physiological functions, such as synaptic plasticity, learning, memory, neurogenesis, etc. In this review, we have summarized recent studies that have characterized structural features, subcellular localization, and factors that regulate nNOS function. Finally, we have discussed the role of nNOS in the developing brain under a wide range of physiological conditions, especially long-term potentiation and depression.