Synthetic calpain activator boosts neuronal excitability without extra Ca2+

Enhancing Cell Penetration Efficiency of Cyclic Oligoarginines Using Rigid Scaffolds

Delivering therapeutic agents into cells has always been a major challenge. In recent years, cyclization emerged as a tool for designing CPPs to increase their internalization and stability. Cyclic ring(s) can protect the peptide from enzymatic degradation, so cyclic peptides remain intact. Therefore they can be good carrier molecules. In this work, the preparation and investigation of efficient cyclic CPPs are described. Different oligoarginines were designed to conjugate with rigid aromatic scaffolds or form disulfide bonds. The reaction between the scaffolds and the peptides forms stable thioether bonds, constraining the peptide into a cyclic structure. The constructs presented very efficient internalization on cancerous cell lines. Our peptides use more than one endocytic pathway for cellular uptake. In this way, short peptides, which can compete with the penetration of well-known CPPs such as octaarginine (Arg₈), may be synthesized through cyclization.

Peptide Based Inhibitors of Protein Binding to the Mitogen-Activated Protein Kinase Docking Groove

Mitogen-activated protein kinases (MAPK) are important regulatory units in cells and they take part in the regulation of many cellular functions such as cell division, differentiation or apoptosis. All MAPKs have a shallow docking groove that interacts with linear binding motifs of their substrate proteins and their regulatory proteins such as kinases, phosphatases, scaffolds. Inhibition of these protein–protein interactions may reduce or abolish the activity of the targeted kinase. Based on the wide range of their biological activity, this kind of inhibition can be useful in the treatment of many disorders like tumors, inflammation or undesired cell apoptosis. In this study a linear binding motif from the RHDF1 protein—a 15 amino acids long peptide—was selected for optimization to increase its cellular uptake but retaining its low micromolar binding affinity. First, we synthesized an octaarginine conjugate that showed efficient cellular uptake. Next, we set out to reduce the size of this construct. We were able to decrease the length of the original peptide, and to increase its cellular uptake with specific chemical modifications. These new constructs bound better to ERK2 and p38 kinases than the original peptide and they showed markedly increased cellular uptake. The new octaarginine conjugate and one of the minimized bicyclic derivatives could inhibit the phosphorylation of intracellular ERK or p38. However, the modulation of MAPK phosphorylation levels by these cell-penetrating peptides were complex, despite that in biochemical assays they all inhibited MAPK-substrate binding as well as phosphorylation. The optimized peptides depending on the applied concentration caused an expected decrease, but also some unexpected increase in MAPK phosphorylation patterns in the cell. This possibly reflects the complexity of MAPK docking groove mediated protein–protein interactions including bone fide MAPK clients such activator kinases, deactivating phosphatases or regulatory scaffolds. Thus, our findings with optimized cell-penetrating “inhibitory” peptides highlight the opportunities but also the pitfalls of docking peptide based MAPK activity regulation and call for a better quantitative understanding of MAPK mediated protein–protein interactions in cells.

Effect of Endothelin-1 on the Excitability of Rat Cortical and Hippocampal Slices In Vitro

Endothelin-1 (ET-1) is a neuroactive protein produced in most brain cell types and participates in regulation of cerebral blood flow and blood pressure. In addition to its vascular effects, ET-1 affects synaptic and nonsynaptic neuronal and glial functions. Direct application of ET-1 to the hippocampus of immature rats results in cerebral ischemia, acute seizures, and epileptogenesis. Here, we investigated whether ET-1 itself modifies the excitability of hippocampal and cortical circuitry and whether acute seizures observed in vivo are due to nonvascular actions of ET-1. We used acute hippocampal and cortical slices that were preincubated with ET-1 (20 µM) for electrophysiological recordings. None of the slices preincubated with ET-1 exhibited spontaneous epileptic activity. The slope of the stimulus intensity-evoked response (input-output) curve and shape of the evoked response did not differ between ET-1-pretreated and control groups, suggesting no changes in excitability after ET-1 treatment. The threshold for eliciting an evoked response was not significantly increased in either hippocampal or cortical regions when pretreated with ET-1. Our data suggest that acute seizures after intrahippocampal application of ET-1 in rats are likely caused by ischemia rather than by a direct action of ET-1 on brain tissue.