Peptides are characterized by their wide range of biological activity: they regulate functions of the endocrine, nervous, and immune systems. The mechanism of such action of peptides involves their ability to regulate gene expression and protein synthesis in plants, microorganisms, insects, birds, rodents, primates, and humans. Short peptides, consisting of 2–7 amino acid residues, can penetrate into the nuclei and nucleoli of cells and interact with the nucleosome, the histone proteins, and both single- and double-stranded DNA. DNA–peptide interactions, including sequence recognition in gene promoters, are important for template-directed synthetic reactions, replication, transcription, and reparation. Peptides can regulate the status of DNA methylation, which is an epigenetic mechanism for the activation or repression of genes in both the normal condition, as well as in cases of pathology and senescence. In this context, one can assume that short peptides were evolutionarily among the first signaling molecules that regulated the reactions of template-directed syntheses. This situation enhances the prospects of developing effective and safe immunoregulatory, neuroprotective, antimicrobial, antiviral, and other drugs based on short peptides.

KED and EDR peptides prevent dendritic spines loss in amyloid synaptotoxicity in in vitro model of Alzheimer’s disease (AD). The objective of this paper was to study epigenetic mechanisms of EDR and KED peptides’ neuroprotective effects on neuroplasticity and dendritic spine morphology in an AD mouse model. Daily intraperitoneal administration of the KED peptide in 5xFAD mice from 2 to 4 months of age at a concentration of 400 μg/kg tended to increase neuroplasticity. KED and EDR peptides prevented dendritic spine loss in 5xFAD-M mice. Their action’s possible molecular mechanisms were investigated by molecular modeling and docking of peptides in dsDNA, containing all possible combinations of hexanucleotide sequences. Similar DNA sequences were found in the lowest-energy complexes of the studied peptides with DNA in the classical B-form. EDR peptide has binding sites in the promoter region of CASP3, NES, GAP43, APOE, SOD2, PPARA, PPARG, GDX1 genes. Protein products of these genes are involved in AD pathogenesis. The neuroprotective effect of EDR and KED peptides in AD can be defined by their ability to prevent dendritic spine elimination and neuroplasticity impairments at the molecular epigenetic level.

Epigenetic regulation of gene expression is necessary for maintaining higher-order cognitive functions (learning and memory). The current understanding of the role of epigenetics in the mechanism of Alzheimer’s disease (AD) is focused on DNA methylation, chromatin remodeling, histone modifications, and regulation of non-coding RNAs. The pathogenetic links of this disease are the misfolding and aggregation of tau protein and amyloid peptides, mitochondrial dysfunction, oxidative stress, impaired energy metabolism, destruction of the blood–brain barrier, and neuroinflammation, all of which lead to impaired synaptic plasticity and memory loss. Ultrashort peptides are promising neuroprotective compounds with a broad spectrum of activity and without reported side effects. The main aim of this review is to analyze the possible epigenetic mechanisms of the neuroprotective action of ultrashort peptides in AD. The review highlights the role of short peptides in the AD pathophysiology. We formulate the hypothesis that peptide regulation of gene expression can be mediated by the interaction of short peptides with histone proteins, cis- and transregulatory DNA elements and effector molecules (DNA/RNA-binding proteins and non-coding RNA). The development of therapeutic agents based on ultrashort peptides may offer a promising addition to the multifunctional treatment of AD.

Cognitive impairments are closely related to synaptic loss in Alzheimer’s disease (AD). Functional changes in synaptic contacts are reflected in dendritic spine morphology. Visualization of neurons for morphological studies in vivo is complicated by the fixed brain slice staining or expensive adeno-associated virus injections. We created a transgenic 5xFAD-M line of mice with AD-associated mutations and expressed GFP protein in single neurons of the brain. This mouse model of AD is a useful tool for the simplified visualization of the hippocampal neurons’ morphology in vivo without additional staining manipulations. The progressive elimination of mushroom spines was demonstrated in 5xFAD-M mice between 4 and 5 months of age. Five-month-old 5xFAD-M male and female mice showed change both in the total density and the mushroom spines number compared to sex-matched control. We conclude 5xFAD-M mice can be a useful AD model for studying the mechanisms of synaptic pathology under neurodegenerative conditions and evaluating the effects of potential therapeutic agents on spine morphology as crucial aspect of memory loss in AD.

BACKGROUND. Alzheimer’s disease (AD) is the most common neurodegenerative disease that causes memory loss predominantly in eldely and senile people [1]. AD is one of the most common causes of death within 5–12 years after the first detected symptoms. Modern drugs approved by the FDA (U.S. Food and Drug Administration) for the AD treatment (memantine, tacrine, rivastigmine, galantamine, donepezil) do not significantly slow down the disease progression [2] and have a wide range of side effects [3]. In view of the lack of effective treatment, the rising global prevalence of AD and significant costs of patient life support, finding effective and safe potential anti-AD drugs is becoming increasingly critical in the context of a global trend towards longer life expectancy. Peptide bioregulators are promising neuroprotectors with low immunogenicity and high physiological activity. In particular, AD therapy may benefit from studying the activity of EDR and KED short peptides obtained by analysis of amino acid composition of extracts isolated from cattle brain and vessels, respectively. AIM. To evaluate the efficacy of short peptides in in vitro and in vivo models of Alzheimer’s disease with a view to developing a drug for the treatment and prevention of this pathology.MATERIALS AND METHODS. A neuronal culture isolated from the brain of newborn wild-type mice, with the addition of synthetic oligopeptides Aβ (the amyloid synaptotoxicity model) was used as the in vitro model of AD. The study groups were as follows: Group 1: control (without Aβ); Group 2: control with the addition of Aβ; Group 3: the addition of Aβ and EDR peptide (200 ng/mL); Group 4: the addition of Aβ and KED peptide (200 ng/mL). Series of neuron microphotographs were obtained using the ThorLabs confocal microscope and ThorLabs software (USA) at the 100-fold magnification (Olympus UPlanSApo) with resolution 1024×1024, which were used for dendritic spine morphology analysis using NeuronStudio software package according to [4]. The transgenic line of 5xFAD-M mice derived by cross-breeding of 5xFAD and Thy1-GFP mice was used as an in vivo model of AD. The experimental groups were as follows: Group 1: control (a line of healthy mice, which received the injections of physiological solution); Group 2: 5xFAD-M line of mice (AD model), which received the injections of physiological solution; Group 3: 5xFAD-M line of mice (AD model), received the injections of EDR peptide; Group 4: 5xFADM line of mice (AD model), received the injections of KED peptide. Short peptides were intraperitoneally injected in mice aged from 3 to 5 months on a daily basis. At the age of 5 months, the animals underwent transcardial perfusion followed by brain extraction; fixed brain slices (40 μm thick) were prepared using a vibratome. Series of neuron microphotographs were obtained using the ThorLabs confocal microscope and ThorLabs software (USA), followed by morphometric analysis of dendritic spines. RESULTS. EDR peptide at the concentration of 200 ng/mL increased the number of the most functional mushroom spines of neurons (by 71%) to normal levels in the primary neuronal culture under amyloid synaptotoxicity conditions (in vitro AD model). KED peptide at the concentration of 200 ng/mL increased the number of mushroom spines by 20% in the AD model. Daily intraperitoneal injection of EDR and KED peptides at a concentration of 400 μg/kg to 5xFAD mice (in vivo AD model) aged from 3 to 5 months contributed to statistically significant increases in mushroom spines in the CA1 area of the hippocampus by 25% and 27%, respectively. These peptides contributed to the increase in the total dendritic density by 13% and 22%, respectively. CONCLUSIONS. The obtained results demonstrate that EDR and KED short peptides have a neuroprotective effect in the AD model, manifested by an improved functional state of neurons. Further research is needed to identify the mechanism of action of short peptides in AD in order to develop a drug for the prevention and treatment of this pathology.

Болезнь Альцгеймера (БА) является наиболее распространённым нейродегенеративным заболеванием, которое сопровождается прогрессирующим когнитивным дефицитом. В настоящем обзоре представлены известные терапевтические стратегии лечения БА, описаны их недостатки и возможные перспективы. В противовес классическому методу разработки терапевтических стратегий, рассмотрена целесообразность комплексного подхода к терапии БА. В качестве многоцелевых агентов с широким спектром действия описаны короткие пептиды Leu–Ile, Glu–Trp, Lys–Glu, Gly–Pro, Glu–Asp–Arg, Lys–Glu–Asp, Met–Glu–His–Phe–Pro– Gly–Pro и другие. Alzheimer’s disease (AD) is the most common neurodegenerative disorder, characterized by progressive cognitive decline. This review discusses current therapeutic strategies for the treatment of Alzheimer’s disease, their limitations, and potential prospects. The feasibility of comprehensive approach for AD therapy is considered in contrast to the classical method in the development of therapeutic strategy. Leu–Ile, Glu–Trp, Lys–Glu, Gly–Pro, Glu–Asp– Arg, Lys-Glu-Asp, Met–Glu–His–Phe–Pro–Gly–Pro short peptides are described as multitarget agents with a wide range of activity.