Project description:The ubiquitous redox coenzyme nicotinamide adenine dinucleotide (NAD) acts as a non-canonical cap structure on prokaryotic and eukaryotic ribonucleic acids. Here we find that in budding yeast, NAD-RNAs are abundant (>1400 species), short (<170 nt), and mostly correspond to mRNA 5'-ends. The modification percentage is low (<5%). NAD is incorporated during the initiation step by RNA polymerase II, which uses distinct promoters with a YAAG motif for this purpose. Most NAD-RNAs are 3'-truncated. At least three decapping enzymes, Rai1, Dxo1, and Npy1, guard against NAD-RNA at different cellular locations, targeting overlapping transcript populations. NAD-mRNAs do not support translation in vitro. Our work indicates that in budding yeast, most of the NAD incorporation into RNA seems to be accidental and undesirable to the cell, which has evolved a diverse surveillance machinery to prematurely terminate, decap and reject NAD-RNAs.
Project description:A progressive loss of protein homeostasis is characteristic of aging and a driver of neurodegeneration. To investigate this process quantitatively, we characterized proteome dynamics during brain aging in the short-lived vertebrate Nothobranchius furzeri combining transcriptomics and proteomics. We detected a progressive reduction in the correlation between protein and mRNA mainly due to post-transcriptional mechanisms that account for over 40% of the age-regulated proteins. These changes cause a progressive loss of stoichiometry in several protein complexes, including ribosomes, which show impaired assembly and are enriched in protein aggregates in old brains. Mechanistically, we show that reduction of proteasome activity is an early event during brain aging and is sufficient to induce proteomic signatures of aging and loss of stoichiometry in vivo. Using longitudinal transcriptomic data, we show that the magnitude of early life decline in proteasome levels is the major risk factor for mortality. Our work defines causative events in the aging process that can be targeted to prevent loss of protein homeostasis and delay the onset of age-related neurodegeneration.
Project description:Mass spectrometry-based whole proteome analysis of parental and RFX7 knock-out U2OS cells treated with 10 µM Nutlin-3a or DMSO solvent control. Ten biological replicates were used.
Project description:Many proteins undergo glycosylation in the endoplasmic reticulum (ER) and the Golgi apparatus. Altered glycosylation can manifest in serious, sometimes fatal malfunctions. We recently showed that mutations in the cytoplasmic protein GDP-mannose pyrophosphorylase A (GMPPA) cause a syndrome characterized by alacrima, achalasia, mental retardation and myopathic alterations. GMPPA acts as feedback inhibitor of GDP-mannose pyrophosphorylase B (GMPPB), which provides GDP-mannose as a substrate for protein glycosylation. Loss of GMPPA enhances incorporation of mannose into glycochains of various proteins, including α-dystroglycan (α-DG), a protein that links the extracellular matrix with the cytoskeleton. Here, we show that loss of GMPPA affects the functionality of the Golgi apparatus using different approaches. First, we show a fragmentation of the Golgi apparatus in skeletal muscle fibers and in neurons of GMPPA KO mice. A major reorganization is also evident by mass spectrometry of KO tissues with a regulation of several ER- and Golgi-resident proteins. We further show that loss of GMPPA increases the retention of α-DG in the ER. Notably, mannose supplementation can mimic changes in ER and Golgi structure and function in WT cells. In summary, our data underline the importance of a balanced mannose homeostasis for structure and function of the secretory pathway.
Project description:Reveal a specific set of proteins important to maintain centromere integrity, through quantitative PICh (Proteomics of Isolated Chromatin). Centromeric chromatin was pulled down through RNA probes annealing specifically to a 300bp-long conserved centromeric sequence.
Project description:Anabolic activities such as ribosome biogenesis and protein synthesis are linked to aging. Ribosomal RNA (rRNA) synthesis is the limiting step of ribosome biogenesis, thus dictating the number of ribosomes in cells and, consequently, the capacity for mRNA translation. Knockdown of the rRNA synthesis repressor, NCL-1, accelerated aging, whereas knocking down the transcription initiation factor C36E8.1 promoted longevity. This suggested that rRNA synthesis has a negative correlation with lifespan. To investigate the metabolic changes upon manipulation of rRNA synthesis the proteome of NCL-1 KD and C36E8.1 KD were analyzed at young, middle, and old age (AD2, AD6, AD12).
Project description:Heart failure is one of the leading causes of death in an ageing population. Hallmarks are cardiac hypertrophy, fibrosis and inflammation. The molecular mechanisms, however, are poorly understood. Glycosylation is one of the most common posttranslational modifications of proteins, which can have important consequences for protein folding, function and turnover. We hypothesized that changes in glycoprotein abundance and glycosylation patterns may contribute to cardiac aging. Western Blot analysis suggests increased protein mannosylation in the aging heart. Glycoprotein pull-downs from heart lysates of young (3 months) and old (2 years) mice in combination with quantitative mass spectrometry support widespread alterations of the glycoproteome in aged hearts.
Project description:Specific autoantibodies against the NMDA-receptor (NMDAR) GluN1 subunit cause severe and debilitating NMDAR-encephalitis. Autoantibodies induce prototypic disease symptoms resembling schizophrenia, including psychosis and cognitive dysfunction. Using a mouse passive transfer model applying human monoclonal anti-GluN1-autoantibodies, we observed CA1 pyramidal neuron hypoexcitability, reduced AMPA-receptor (AMPAR) signaling, and faster synaptic inhibition resulting in disrupted excitatory-inhibitory balance. Functional alterations were supported by widespread remodeling of the hippocampal proteome, including changes in glutamatergic and GABAergic neurotransmission. At the network level, anti-GluN1-autoantibodies amplified gamma oscillations and disrupted theta-gamma coupling. A data-informed network model revealed that lower AMPAR strength and faster GABAA-receptor current kinetics chiefly account for these abnormal oscillations. As predicted by our model and evidenced experimentally, positive allosteric modulation of AMPARs alleviated aberrant gamma activity and thus reinforced the causative effects of the excitatory-inhibitory imbalance. Collectively, NMDAR-hypofunction-induced aberrant synaptic, cellular, and network dynamics provide new mechanistic insights into disease symptoms in NMDAR-encephalitis and schizophrenia.
Project description:Hematopoietic stem cell transplantation (HSCT) is successfully applied since the late 1950s, however, its efficacy still needs to be improved. A promising strategy is to transplant high numbers of pluripotent hematopoietic stem cells (HSCs). Therefore, an advanced ex vivo culture system is needed that supports the proliferation and maintains the pluripotency of HSC to override possible limitations in cell numbers gained from donors. To model the natural HSC niche in vitro and thus, to amplify high numbers of undifferentiated HSCs, we used an optimized HSC cell culture medium in combination with artificial 3D bone marrow-like scaffolds made of polydimethylsiloxane (PDMS). After 14 days in vitro (DIV) cell culture, we performed transcriptome and proteome analysis of the whole cell populations. Ingenuity pathway analysis (IPA) indicated that our 3D PDMS cell culture scaffolds activated interleukin, SREBP, mTOR and FOXO signaling pathways as well as the HSC metabolism, which we confirmed by ELISA, Western blot and metabolic flux analysis. These molecular signaling pathways and HSC metabolism are well known to promote the expansion HSCs and are involved in their pluripotency maintenance. After selection and enrichment of immature CD34-positive/CD38-negative HSCs using FACS sorting, we could confirm our findings by another proteome analysis followed by IPA. Thus, we could show that our 3D bone marrow-like PDMS scaffolds activate key molecular signaling pathways to amplify the numbers of undifferentiated HSC efficiently ex vivo.