Effect of semax and its C-terminal fragment Pro-Gly-Pro on the expression of VEGF family genes and their receptors in experimental focal ischemia of the rat brain

Insight into Glyproline Peptides' Activity through the Modulation of the Inflammatory and Neurosignaling Genetic Response Following Cerebral Ischemia-Reperfusion

Glyprolines are Gly-Pro (GP)- or Pro-Gly (PG)-containing biogenic peptides. These peptides can act as neutrophil chemoattractants, or atheroprotective, anticoagulant, and neuroprotective agents. The Pro-Gly-Pro (PGP) tripeptide is an active factor of resistance to the biodegradation of peptide drugs. The synthetic Semax peptide, which includes Met-Glu-His-Phe (MEHF) fragments of adrenocorticotropic hormone and the C-terminal tripeptide PGP, serves as a neuroprotective drug for the treatment of ischemic stroke. Previously, we revealed that Semax mostly prevented the disruption of the gene expression pattern 24 h after a transient middle cerebral artery occlusion (tMCAO) in a rat brain model. The genes of this pattern were grouped into an inflammatory cluster (IC) and a neurotransmitter cluster (NC). Here, using real-time RT-PCR, the effect of other PGP-containing peptides, PGP and Pro-Gly-Pro-Leu (PGPL), on the expression of a number of genes in the IC and NC was studied 24 h after tMCAO. Both the PGP and PGPL peptides showed Semax-unlike effects, predominantly without changing gene expression 24 h after tMCAO. Moreover, there were IC genes (iL1b, iL6, and Socs3) for PGP, as well as IC (iL6, Ccl3, Socs3, and Fos) and NC genes (Cplx2, Neurod6, and Ptk2b) for PGPL, that significantly changed in expression levels after peptide administration compared to Semax treatment under tMCAO conditions. Furthermore, gene enrichment analysis was carried out, and a regulatory gene network was constructed. Thus, the spectra of the common and unique effects of the PGP, PGPL, and Semax peptides under ischemia-reperfusion were distinguished.

Peptide Regulation of Gene Expression: A Systematic Review

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.

Neuroprotective Effects of Peptides in the Brain: Transcriptome Approach

The importance of studying the action mechanisms of drugs based on natural regulatory peptides is commonly recognized. Particular attention is paid to the peptide drugs that contribute to the restoration of brain functions after acute cerebrovascular accidents (stroke), which for many years continues to be one of the main problems and threats to human health. However, molecular genetic changes in the brain in response to ischemia, as well as the mechanisms of protective effects of peptides, have not been sufficiently studied. This limits the use of neuroprotective peptides and makes it difficult to develop new, more efficient drugs with targeted action on brain functions. Transcriptome analysis is a promising approach for studying the mechanisms of the damaging effects of cerebral ischemia and neuroprotective action of peptide drugs. Beside investigating the role of mRNAs in protein synthesis, the development of new neuroprotection strategies requires studying the involvement of regulatory RNAs in ischemia. Of greatest interest are microRNAs (miRNAs) and circular RNAs (circRNAs), which are expressed predominantly in the brain. CircRNAs can interact with miRNAs and diminish their activity, thereby inhibiting miRNA-mediated repression of mRNAs. It has become apparent that analysis of the circRNA/miRNA/mRNA system is essential for deciphering the mechanisms of brain damage and repair. Here, we present the results of studies on the ischemia-induced changes in the activity of genes and peptide-mediated alterations in the transcriptome profiles in experimental ischemia and formulate the basic principles of peptide regulation in the ischemia-induced damage.

Novel Insights into the Protective Properties of ACTH(4-7)PGP (Semax) Peptide at the Transcriptome Level Following Cerebral Ischaemia-Reperfusion in Rats

Cerebral ischaemia is the most common cause of impaired brain function. Biologically active peptides represent potential drugs for reducing the damage that occurs after ischaemia. The synthetic melanocortin derivative, ACTH_(4-7)PGP (Semax), has been used successfully in the treatment of patients with severe impairment of cerebral blood circulation. However, its molecular mechanisms of action within the brain are not yet fully understood. Previously, we used the transient middle cerebral artery occlusion (tMCAO) model to study the damaging effects of ischaemia-reperfusion on the brain transcriptome in rats. Here, using RNA-Seq analysis, we investigated the protective properties of the Semax peptide at the transcriptome level under tMCAO conditions. We have identified 394 differentially expressed genes (DEGs) (>1.5-fold change) in the brains of rats at 24 h after tMCAO treated with Semax relative to saline. Following tMCAO, we found that Semax suppressed the expression of genes related to inflammatory processes and activated the expression of genes related to neurotransmission. In contrast, ischaemia-reperfusion alone activated the expression of inflammation-related genes and suppressed the expression of neurotransmission-related genes. Therefore, the neuroprotective action of Semax may be associated with a compensation of mRNA expression patterns that are disrupted during ischaemia-reperfusion conditions.

Proline-containing peptides-New insight and implications: A Review

The family of regulatory proline-containing peptides (PCPs), also known as glyprolines, exhibit significant biological activity. The group of glyprolines includes Gly-Pro (GP), Pro-Gly-Pro (PGP), cyclic Gly-Pro (cGP), as well as PGP derivatives, for example, N-acetylated PGP (N-a-PGP) and N-methylated PGP (N-m-PGP). PCPs are engaged in various biological processes including the proinflammatory neutrophil chemoattraction in lung diseases, inflammatory bowel diseases or ischemic stroke. Glyprolines have been also postulated to play an important role as atheroprotective and anticoagulant agents, exhibit neuroprotective effects in Parkinson's disease, as well as regulate insulin-like growth factor (IGF) homeostasis. It was also noticed that PCPs inhibit proliferation and migration of keratinocytes in wound healing, protection of the gastric mucosa and stimulation of its regeneration. The regulatory glyprolines are derived from endogenous and exogenous sources. Most PCPs are derived from collagen or diet protein degradation. Recently, great interest is concentrated on short proline-rich oligopeptides derived from IGF-1 degradation. The mechanism of PCPs biological activity is not fully explained. It involves receptor-mediated mechanisms, for example, N-a-PGP acts as CXCR1/2 receptor ligand, whereas cGP regulates IGF-1 bioavailability by modifying the IGF-1 binding to the IGF-1 binding protein-3. PGP has been observed to interact with collagen-specific receptors. The data suggest a promising role of PGP as a target of various diseases therapy. This review is focused on the effect of PCPs on metabolic processes in different tissues and the molecular mechanism of their action as an approach to pharmacotherapy of PCPs-dependent diseases.

An integrated approach to study the molecular aspects of regulatory peptides biological mechanism

An integrated methodological approach to study the molecular aspects of short regulatory neuropeptides biological mechanism is proposed. The complex research is based on radioligand-receptor method of analysis and covers such points of peptides molecular activity as: specific binding of peptides to brain cells plasmatic membranes, formation of tissue specific synacton, influence of peptides (as allosteric modulators) on functionality of different neuroreceptors as well as delayed in time effects of peptides on receptor-binding activity of well-known neuroreceptor systems. Radiolabeled ligands in such complex study are the one of the best and precision instruments to uncover the molecular mechanism of multiple and multitarget biological effects of regulatory peptides. In this issue we used heptapeptide Semax as a model regulatory peptide, [³ H]Ach and [³ H]GABA as an effector molecules, and the rat model of stress-induced memory and behavior impairment as a morbid state. We showed the ability of Semax to modulate in a dose-dependent manner [³ H]Ach and [³ H]GABA specific binding to some of its corresponding receptors as well as to affect the number of [³ H]GABA specific binding places on rat neurons plasmatic membranes after complex stress exposure.

Influence of the N-terminus acetylation of Semax, a synthetic analog of ACTH(4-10), on copper(II) and zinc(II) coordination and biological properties

Semax is a heptapeptide (Met-Glu-His-Phe-Pro-Gly-Pro) that encompasses the sequence 4-7 of N-terminal domain of the adrenocorticotropic hormone and a C-terminal Pro-Gly-Pro tripeptide. N-terminal amino group acetylation (Ac-Semax) modulates the chemical and biological properties of parental peptide, modifying the ability of Semax to form complex species with Cu(II) ion. At physiological pH, the main complex species formed by Ac-Semax, [CuLH_-2]^2-, consists in a distorted CuN₃O chromophore with a weak apical interaction of the methionine sulphur. Such a complex differs from the Cu(II)-Semax complex system, which exhibits a CuN₄ chromophore. The reduced ligand field affects the [CuLH_-2]^2- formal redox potential, which is more positive than that of Cu(II)-Semax corresponding species. In the amino-free form, the resulting complex species is redox-stable and unreactive against ascorbic acid, unlike the acetylated form. Semax acetylation did not protect from Cu(II) induced toxicity on a SH-SY5Y neuroblastoma cell line, thus demonstrating the crucial role played by the free NH₂ terminus in the cell protection. Since several brain diseases are associated either to Cu(II) or Zn(II) dyshomeostasis, here we characterized also the complex species formed by Zn(II) with Semax and Ac-Semax. Both peptides were able to form Zn(II) complex species with comparable strength. Confocal microscopy imaging confirmed that peptide group acetylation does not affect the Zn(II) influx in neuroblastoma cells. Moreover, a punctuate distribution of Zn(II) within the cells suggests a preferred subcellular localization that might explain the zinc toxic effect. A future perspective can be the use of Ac-Semax as ionophore in antibody drug conjugates to produce a dysmetallostasis in tumor cells.

Time-dependent variation of pathways and networks in a 24-hour window after cerebral ischemia-reperfusion injury

Background

Cerebral ischemia-reperfusion injury may simultaneously result in functional variation of multiple genes/pathways. However, most prior time-sequence studies on its pathomechanism only focused on a single gene or pathway. Our study aimed to systematically analyze the time-dependent variation in the expression of multiple pathways and networks within 24 h after cerebral ischemia-reperfusion injury.

Results

By uploading 374 ischemia-related genes into the MetaCore software, the variation in the expression of multiple pathways and networks in 3 h, 12 h, and 24 h after cerebral ischemia-reperfusion injury had been analyzed. The conserved TNFR1-signaling pathway, among the top 10 pathways, was consistently enriched in 3 h, 12 h, and 24 h groups. Three overlapping pathways were found between 3 h and 12 h groups; 2 between 12 h and 24 h groups; and 1 between 3 h and 24 h groups. Five, 4, and 6 non-overlapping pathways were observed in 3 h, 12 h, and 24 h groups, respectively. Apart from pathways reported by earlier studies, we identified a novel pathway related to the time-dependent development of cerebral ischemia pathogenesis. The process of apoptosis stimulation by external signals, among the top 10 processes, was consistently enriched in 3 h, 12 h, and 24 h groups; 2, 1, and 2 processes overlapped between 3 h and 12 h groups, 12 h and 24 h groups, and 3 h and 24 h groups, respectively. Four, 5, and 5 non-overlapping processes were found in 3 h, 12 h and 24 h groups, respectively. The presence of apoptotic processes was observed in all the 3 groups; while anti-apoptotic processes only existed in 3 h and 12 h groups. Additionally, according to node degree, network comparison identified 1, 8,and 5 important genes or proteins (e.g. Pyk2, PKC, E2F1, and VEGF-A) in 3 h, 12 h, and 24 h groups, respectively. The Jaccard similarity index revealed a higher level of similarity between 12 h and 24 h groups than that between 3 h and 12 h groups.

Conclusion

Time-dependent treatment can be utilized to reduce apoptosis, which may activate anti-apoptotic pathways within 12 h after cerebral ischemia-reperfusion injury. Pathway and network analyses may help identify novel pathways and genes implicated in disease pathogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12918-015-0152-4) contains supplementary material, which is available to authorized users.