Volume 88, Nº 12 (2023)

GABA and glutamate are the most abundant neurotransmitters in the CNS and play a pivotal part in synaptic stability/plasticity. Glutamate and GABA homeostasis is important for healthy aging and reducing the risk of various neurological diseases, while long-term imbalance can contribute to the development of neurodegenerative disorders, including Alzheimer’s disease (AD). Its normalization discussed as a promising strategy for the prevention and/or treatment of AD, however, data on changes in the GABAergic and glutamatergic systems in with age, as well as in the dynamics of AD development, are limited. It is not clear whether the imbalance of the excitatory/inhibitory systems is a cause or a consequence of the development of the disease. Here we analyzed age-related alterations of the expression of glutamate, GABA, and enzymes that synthesize them (glutaminase, glutamine synthetase, GABA-T, and GAD67), transporters (GLAST, GLT-1, and GAT1), and relevant receptors (GluA1, NMDAR1, NMDA2B, and GABAAr1) in the whole hippocampus of Wistar rats and of senescence-accelerated OXYS rats, a model of the most common (> 95%) sporadic AD. Our results suggest that there is a decline of glutamate and GABA signaling with aging in the hippocampus of the both rat strains. However, we have not identified significant changes or compensatory enhancements in this system in the hippocampus of OXYS rats during development of neurodegenerative processes that are characteristic of AD.

Despite the variety of manifestations of aging, there are some common features and underlying mechanisms. In particular, mitochondria appears to be one of the most vulnerable systems in both metazoa and fungi. In this review, we discuss how mitochondrial dysfunction is related to replicative aging in the simplest eukaryotic model, the baker’s yeast Saccharomyces cerevisiae. We discuss a chain of events that starts from asymmetric inheritance of mitochondria by mother and daughter cells. With age, yeast mother cells start to experience a decrease in mitochondrial transmembrane potential and, consequently, a decrease in mitochondrial protein import efficiency. This induces mitochondrial protein precursors accumulation in the cytoplasm, the loss of mitochondrial DNA, and at the later stages - cell death. Interestingly, yeast strains without mitochondrial DNA can have both increased and increased lifespan compared to their counterparts with mtDNA. The direction of the effect depends on their ability to activate compensatory mechanisms preventing or mitigating negative consequences of mitochondrial dysfunction. The central role of mitochondria in yeast aging and death indicates that it is one of the most complex and, therefore, deregulation-prone systems in eukaryotic cells.

Selective degradation of cellular proteins by the ubiquitin -proteasome system is one of the key regulatory mechanisms in eukaryotic cells. Accumulating data indicate that the ubiquitin - proteasome system is involved in the regulation of fundamental processes in mammalian stem cells, including proliferation, differentiation, cell migration, aging and programmed cell death. Regulation can be carried out either by proteolytic degradation of key transcription factors and signaling pathway proteins, or by posttranslational modifications of target proteins with ubiquitin or other ubiquitin-like modifiers. Studies of the molecular mechanisms of proteostasis maintenance in stem cells are of great importance for the development of new therapeutic approaches aimed at the treatment of autoimmune and neurodegenerative diseases, cancer and other socially significant pathologies. This review covers current data on the function of the ubiquitin-proteasome system in stem cells.

Genome stability is critical for normal functioning of cells and depends on accuracy of DNA replication, chromosome segregation, and DNA repair. Cellular defense mechanisms against DNA damage are important for preventing the development of cancer and aging. The E3 ubiquitin ligase RNF168 of the RING superfamily is an essential component of the complex responsible for the ubiquitination of H2A/H2A.X histones near DNA double-strand breaks, which is a key step in attracting repair factors to the injury site. In this study, we unequivocally showed that RNF168 does not have ability to directly distinguish the architecture of polyubiquitin chains, except for tropism of its two ubiquitin-binding domains UDM1/2 to K63 ubiquitin chains. Analysis of the intracellular chromatosomal environment of full-length RNF168 and its domains by ligand-induced bioluminescence resonance energy transfer (BRET) revealed that the C-terminal part of UDM1 is associated with K63 ubiquitin chains; RING and the N-terminal part of UDM2 are sterically close to K63- and K48- ubiquitin chains, while the C-terminal part of UDM1 is colocalized with all possible ubiquitin variants. Our observations together with the available structural data suggest that the C-terminal part of UDM1 binds K63 polyubiquitin chains on linker histone H1; RING and the N-terminal part of UDM2 are located in the central part of the nucleosome and sterically close to H1 and K48-ubiquitinated alternative substrates of RNF168, such as JMJD2A/B demethylases, while the C-terminal part of UDM1 is in the region of an activated ubiquitin residue associated with E2 ubiquitin ligase, engaged by RNF168.

In green photosynthetic bacteria, light absorption occurs in bacteriochlorophyll (BChl) c/d/e oligomers, which are located in chlorosomes - unique structures created by nature to collect the energy of very weak light fluxes. Using coherent femtosecond spectroscopy at cryogenic temperature, we detected and studied low-frequency vibrational motions of BChl c oligomers in the chlorosomes of the green bacteria Chloroflexus (Cfx.) aurantiacus. The objects of the study were chlorosomes isolated from bacterial cultures grown under different light intensity. It was found that the Fourier spectrum of low-frequency coherent oscillations in the Q_y band of BChl c oligomers depends on the light intensity used for the growth of bacteria. It turned out that the number of low-frequency vibrational modes of chlorosomes increases as the illumination under which they were cultivated decreases. Also, the frequency range within which these modes are observed expands, and the frequencies of most modes change. Theoretical modeling of the obtained data and analysis of the literature led to the conclusion that the structural basis of Cfx. aurantiacus chlorosomes are short linear chains of BChl c combined into more complex structures. An increase in the length of these chains in chlorosomes grown under weaker light leads to the observed changes in the spectrum of vibrations of BChl c oligomers. This increase is an effective mechanism for the adaptation of bacteria to changing external conditions.

Resistance of tumor cells to retinoic acid (RA), a promising therapeutic agent, is the major factor limiting the use of RA in clinical practice. The mechanisms of RA resistance are still poorly understood. Cellular Retinoic Acid Binding Proteins, CRABP1 and CRABP2, are essential mediators of RA signaling, but the role of the two CRABP homologs in regulating cellular sensitivity to RA has not been well studied. In addition, the effects of CRABP1 and CRABP2 on cell proliferation have not been compared. Here, using a broad panel of breast cancer cell lines with different levels of RA sensitivity/resistance, we show for the first time that in RA-sensitive cells, CRABP1 expression is restricted by methylation and protein levels are highly variable. In moderately RA-resistant lines, a high level of CRABP1 is observed both at the mRNA and protein levels, unchanged by inhibition of DNA methylation. The maximally resistant cell lines are characterized by complete repression of CRABP1 implemented at transcriptional and posttranscriptional levels, and exogenous expression of each of CRABP homologs has no effect on the studied characteristics. CRABP1 and CRABP2 proteins have opposing effects on proliferation and sensitivity to RA. Specifically, in initially RA-sensitive cells CRABP1 stimulates and CRABP2 reduces proliferation and resistance to RA, while in more resistant cells the role of each homolog in both of these indications is reversed. Overall, we have shown for the first time that CRABP proteins exert different effects on the growth and sensitivity to RA of breast cancer cells (stimulation, suppression, or no effect) depending on the baseline level of RA-sensitivity, with the effects of CRABP1 and CRABP2 homologs on the studied properties always being opposite.

The neuropeptide nocistatin (NS) is expressed by cells of the nervous system and neutrophils as part of a precursor protein and can undergo limited proteolysis through stepwise degradation. Previously, it was shown that rat NS (rNS) is able to activate acid-sensing ion channels (ASIC), but this effect correlated with the acidic nature of NS. In this work, we investigated the change in the properties of rNS during its degradation by a comparison of rNS and its two synthesized fragments. We estimated their activity on rat ASIC3 channels expressed in X. laevis oocytes, and the effects in pain tests on mice. We have shown that rNS combines the properties of both positive and negative modulators of ASIC3, which is expressed in the ability to lower the channel’s steady-state desensitization in the pH range 6.8-7.0 and the reduction of the channel’s response to stimuli in the 6.0-6.9 pH range. A shortened analogue (rNSΔ21) (21 amino acid residues (aa) from the N-terminus) retained the effect of the ASIC3 positive modulator only, while the C-terminal pentapeptide (rNSΔ30) retained the ability of the ASIC3 negative modulator only. This tendency was confirmed in animal tests, where rNS and rNSΔ21 induced pain related behavior, but rNSΔ30 showed an analgesic effect. Thus, we have shown the change of the rNS action mode during stepwise degradation, from an algesic molecule through a pain-enhancer to a pain-relief wherefore the final pentapeptide can even be considered as a promising starting point for further drug development.