Characterization of Uranyl (UO22+) Ion Binding to Amyloid Beta (Aβ) Peptides: Effects on Aβ Structure and Aggregation

Uranium (U) is naturally present in ambient air, water, and soil, and depleted uranium (DU) is released into the environment via industrial and military activities. While the radiological damage from U is rather well understood, less is known about the chemical damage mechanisms, which dominate in DU. Heavy metal exposure is associated with numerous health conditions, including Alzheimer's disease (AD), the most prevalent age-related cause of dementia. The pathological hallmark of AD is the deposition of amyloid plaques, consisting mainly of amyloid-β (Aβ) peptides aggregated into amyloid fibrils in the brain. However, the toxic species in AD are likely oligomeric Aβ aggregates. Exposure to heavy metals such as Cd, Hg, Mn, and Pb is known to increase Aβ production, and these metals bind to Aβ peptides and modulate their aggregation. The possible effects of U in AD pathology have been sparsely studied. Here, we use biophysical techniques to study in vitro interactions between Aβ peptides and uranyl ions, UO22+, of DU. We show for the first time that uranyl ions bind to Aβ peptides with affinities in the micromolar range, induce structural changes in Aβ monomers and oligomers, and inhibit Aβ fibrillization. This suggests a possible link between AD and U exposure, which could be further explored by cell, animal, and epidemiological studies. General toxic mechanisms of uranyl ions could be modulation of protein folding, misfolding, and aggregation.

PepFect14 mediates the delivery of mRNA into human primary keratinocytes and in vivo

mRNA-based vaccines and candidate therapeutics have great potential in various medical fields. For the delivery of mRNA into target cells and tissues, lipid formulations are often employed. However, this approach could cause the activation of immune responses, making it unsuitable for the treatment of inflammatory conditions. Therefore, alternative delivery systems are highly demanded. In this study, we evaluated the transport efficiency and characteristics of cell-penetrating peptide PepFect14 (PF14) and mRNA nanoparticles in the presence of different additives. Our results show that all PF14-mRNA formulations entered cultured cells, while calcium chloride enhanced the transport and production of the encoded protein in HeLa and HaCaT cell lines, and polysorbate 80 did so in primary human keratinocytes. All formulations had similar physical properties and did not remarkably affect cell viability. By selectively blocking endocytosis pathways, we show that PF14-mRNA nanoparticles primarily entered HeLa cells via macropinocytosis and HaCaT cells via both macropinocytosis and clathrin-mediated endocytosis, while none of the blockers significantly affected the delivery into primary keratinocytes. Finally, subcutaneous injection of PF14-mRNA nanoparticles before inducing mouse irritant contact dermatitis resulted in the expression of a reporter protein without provoking harmful immune responses in the skin. Together, our findings suggest that PF14-mRNA nanoparticles have the potential for developing mRNA-based therapeutics for treating inflammatory skin conditions.

Divalent Metal Ions Boost Effect of Nucleic Acids Delivered by Cell-Penetrating Peptides

Cell-penetrating peptides (CPPs) are promising tools for the transfection of various substances, including nucleic acids, into cells. The aim of the current work was to search for novel safe and effective approaches for enhancing transfection efficiency of nanoparticles formed from CPP and splice-correcting oligonucleotide (SCO) without increasing the concentration of peptide. We analyzed the effect of inclusion of calcium and magnesium ions into nanoparticles on CPP-mediated transfection in cell culture. We also studied the mechanism of such transfection as well as its efficiency, applicability in case of different cell lines, nucleic acid types and peptides, and possible limitations. We discovered a strong positive effect of these ions on transfection efficiency of SCO, that translated to enhanced synthesis of functional reporter protein. We observed significant changes in intracellular distribution and trafficking of nanoparticles formed by the addition of the ions, without increasing cytotoxicity. We propose a novel strategy for preparing CPP-oligonucleotide nanoparticles with enhanced efficiency and, thus, higher therapeutic potential. Our discovery may be translated to primary cell cultures and, possibly, in vivo studies, with the aim of increasing CPP-mediated transfection efficiency and the likelihood of using CPPs in clinics.

Dual role of the miR-146 family in rhinovirus-induced airway inflammation and allergic asthma exacerbation

Rhinovirus (RV) infections are associated with asthma exacerbations. MicroRNA-146a and microRNA-146b (miR-146a/b) are anti-inflammatory miRNAs that suppress signaling through the nuclear factor kappa B (NF-κB) pathway and inhibit pro-inflammatory chemokine production in primary human bronchial epithelial cells (HBECs). In the current study, we aimed to explore whether miR-146a/b could regulate cellular responses to RVs in HBECs and airways during RV-induced asthma exacerbation. We demonstrated that expression of miR-146a/b and pro-inflammatory chemokines was increased in HBECs and mouse airways during RV infection. However, transfection with cell-penetrating peptide (CPP)-miR-146a nanocomplexes before infection with RV significantly reduced the expression of the pro-inflammatory chemokines CCL5, IL-8 and CXCL1, increased interferon-λ production, and attenuated infection with the green fluorescent protein (GFP)-expressing RV-A16 in HBECs. Concordantly, compared to wild-type (wt) mice, Mir146a/b-/- mice exhibited more severe airway neutrophilia and increased T helper (Th)1 and Th17 cell infiltration in response to RV-A1b infection and a stronger Th17 response with a less prominent Th2 response in house dust mite extract (HDM)-induced allergic airway inflammation and RV-induced exacerbation models. Interestingly, intranasal administration of CPP-miR-146a nanocomplexes reduced HDM-induced allergic airway inflammation without a significant effect on the Th2/Th1/Th17 balance in wild-type mice. In conclusion, the overexpression of miR-146a has a strong anti-inflammatory effect on RV infection in HBECs and a mouse model of allergic airway inflammation, while a lack of miR-146a/b leads to attenuated type 2 cell responses in mouse models of allergic airway inflammation and RV-induced exacerbation of allergic airway inflammation. Furthermore, our data indicate that the application of CPP-miR-146a nanocomplexes has therapeutic potential for targeting airway inflammation.

Characterization of Peptide-Oligonucleotide Complexes Using Electron Microscopy, Dynamic Light Scattering, and Protease Resistance Assay

Cationic peptides designed for cellular delivery of nucleic acid molecules form noncovalent nanocomplexes with negatively charged oligonucleotides (ON). The electrostatically associated complexes are further compacted by hydrophobic interactions yielding nanoparticles (NP) of homogeneous shape and size that are efficiently taken up by cells. The shape and size of NP often correlate with the biological activity of delivered ON inside cells; and the stability and accessibility of NP in biological fluids govern its circulation in organism and the cellular uptake. Therefore, here we provide protocols for characterizing the shape and size and surface charge of peptide/ON NP by negative staining transmission electron microscopy (TEM) and dynamic light scattering (DLS) respectively, and analysis of NP stability against proteolytic degradation.

Deciphering the internalization mechanism of WRAP:siRNA nanoparticles

Gene silencing mediated by double-stranded small interfering RNA (siRNA) has been widely investigated as a potential therapeutic approach for a variety of diseases and, indeed, the first therapeutic siRNA was approved by the FDA in 2018. As an alternative to the traditional delivery systems for nucleic acids, peptide-based nanoparticles (PBNs) have been applied successfully for siRNA delivery. Recently, we have developed amphipathic cell-penetrating peptides (CPPs), called WRAP allowing a rapid and efficient siRNA delivery into several cell lines at low doses (20 to 50 nM). In this study, using a highly specific gene silencing system, we aimed to elucidate the cellular uptake mechanism of WRAP:siRNA nanoparticles by combining biophysical, biological, confocal and electron microscopy approaches. We demonstrated that WRAP:siRNA complexes remain fully active in the presence of chemical inhibitors of different endosomal pathways suggesting a direct cell membrane translocation mechanism. Leakage studies on lipid vesicles indicated membrane destabilization properties of the nanoparticles and this was supported by the measurement of WRAP:siRNA internalization in dynamin triple-KO cells. However, we also observed some evidences for an endocytosis-dependent cellular internalization. Indeed, nanoparticles co-localized with transferrin, siRNA silencing was inhibited by the scavenger receptor A inhibitor Poly I and nanoparticles encapsulated in vesicles were observed by electron microscopy in U87 cells. In conclusion, we demonstrate here that the efficiency of WRAP:siRNA nanoparticles is mainly based on the use of multiple internalization mechanisms including direct translocation as well as endocytosis-dependent pathways.

Targeted gene silencing in human embryonic stem cells using cell-penetrating peptide PepFect 14

Background

Human embryonic stem (hES) cells serve as an invaluable tool for research and future medicine, but their transfection often leads to unwanted side effects as the method itself may induce differentiation. On the other hand, RNA interference (RNAi)-based targeted gene silencing is a quick, cost-effective, and easy-to-perform method to address questions regarding the function of genes, especially when hypomorphic knockdowns are needed. Therefore, effective transfection method with minimal side effects is essential for applying RNAi to hES cells. Here, we report a highly promising approach for targeted gene silencing in hES cells with siRNA complexed with cell-penetrating peptide PepFect 14 (PF14). This strategy provides researchers with efficient tool for unraveling the functions of genes or addressing the differentiation of pluripotent stem cells.

Methods

We present a method for delivery of siRNA into hES cells with cell-penetrating peptide PF14. Accordingly, hES cells were transfected in ROCK inhibitor containing medium for 24 h right after EDTA passaging as small cell clumps. Fluorescently labeled siRNA and siRNAs targeting OCT4 or beta-2-microglobulin (B2M) mRNA sequences were used to evaluate the efficiency of transfection and silencing. Analyses were performed at various time points by flow cytometry, RT-qPCR, and immunofluorescence microscopy.

Results

Effective downregulation of OCT4 in 70% of treated hES cells at protein level was achieved, along with 90% reduction at mRNA level in bulk population of cells. The applicability of this low-cost and easy-to-perform method was confirmed by inducing silencing of another target not associated with hES cell pluripotency (B2M). Furthermore, we discovered that downregulation of OCT4 induces neuroectodermal differentiation accompanied by reduced expression of B2M during early stage of this lineage.

Conclusions

The results demonstrate PF14 as a promising tool for studying gene function and regulatory networks in hES cells by using RNAi.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1144-x) contains supplementary material, which is available to authorized users.

Enhancement of siRNA transfection by the optimization of fatty acid length and histidine content in the CPP

Depending on the pH, polyhistidines in the CPP influence interactions in CPP/siRNA nanoparticles by switching from hydrophobic to charged.

The role of integrin β1 in the heterogeneity of human embryonic stem cells culture

The maintenance of the pluripotency of human embryonic stem (hES) cells requires special conditions for culturing. These conditions include specific growth factors containing media and extracellular matrix (ECM) or an appropriate substrate for adhesion. Interactions between the cells and ECM are mediated by integrins, which interact with the components of ECM in active conformation. This study focused on the characterisation of the role of integrin β1 in the adhesion, migration and differentiation of hES cells. Blocking integrin β1 abolished the adhesion of hES cells, decreasing their survival and pluripotency. This effect was in part rescued by the inhibition of RhoA signalling with Y-27632. The presence of Y-27632 increased the migration of hES cells and supported their differentiation into embryoid bodies. The differences in integrin β1 recycling in the phosphorylation of the myosin light chain and in the localisation of TSC2 were observed between the hES cells growing as a single-cell culture and in a colony. The hES cells at the centre and borders of the colony were found to have differences in their morphology, migration and signalling network activity. We concluded that the availability of integrin β1 was essential for the contraction, migration and differentiation ability of hES cells.

Summary: The interaction between integrin β1 and the extracellular matrix differs at the centre of the colony and at the periphery, and is crucial for the survival of embryonic stem cells.

Arginine-Rich Cell-Penetrating Peptides Require Nucleolin and Cholesterol-Poor Subdomains for Translocation across Membranes

Proficient transport vectors called cell-penetrating peptides (CPPs) internalize into eukaryotic cells mostly via endocytic pathways and facilitate the uptake of various cargo molecules attached to them. However, some CPPs are able to induce disturbances in the plasma membrane and translocate through it seemingly in an energy-independent manner. For understanding this phenomenon, giant plasma membrane vesicles (GPMVs) derived from the cells are a beneficial model system, since GPMVs have a complex membrane composition comparable to the cells yet lack cellular energy-dependent mechanisms. We investigated the translocation of arginine-rich CPPs into GPMVs with different membrane compositions. Our results demonstrate that lower cholesterol content favors accumulation of nona-arginine and, additionally, sequestration of cholesterol increases the uptake of the CPPs in vesicles with higher cholesterol packing density. Furthermore, the proteins on the surface of vesicles are essential for the uptake of arginine-rich CPPs: downregulation of nucleolin decreases the accumulation and digestion of proteins on the membrane suppresses translocation even more efficiently.

Targeted deletion of RIC8A in mouse neural precursor cells interferes with the development of the brain, eyes, and muscles

Autosomal recessive disorders such as Fukuyama congenital muscular dystrophy, Walker-Warburg syndrome, and the muscle-eye-brain disease are characterized by defects in the development of patient's brain, eyes, and skeletal muscles. These syndromes are accompanied by brain malformations like type II lissencephaly in the cerebral cortex with characteristic overmigrations of neurons through the breaches of the pial basement membrane. The signaling pathways activated by laminin receptors, dystroglycan and integrins, control the integrity of the basement membrane, and their malfunctioning may underlie the pathologies found in the rise of defects reminiscent of these syndromes. Similar defects in corticogenesis and neuromuscular disorders were found in mice when RIC8A was specifically removed from neural precursor cells. RIC8A regulates a subset of G-protein α subunits and in several model organisms, it has been reported to participate in the control of cell division, signaling, and migration. Here, we studied the role of RIC8A in the development of the brain, muscles, and eyes of the neural precursor-specific conditional Ric8a knockout mice. The absence of RIC8A severely affected the attachment and positioning of radial glial processes, Cajal-Retzius' cells, and the arachnoid trabeculae, and these mice displayed additional defects in the lens, skeletal muscles, and heart development. All the discovered defects might be linked to aberrancies in cell adhesion and migration, suggesting that RIC8A has a crucial role in the regulation of cell-extracellular matrix interactions and that its removal leads to the phenotype characteristic to type II lissencephaly-associated diseases. © 2018 Wiley Periodicals, Inc. Develop Neurobiol 78: 374-390, 2018.

Formulation of Stable and Homogeneous Cell-Penetrating Peptide NF55 Nanoparticles for Efficient Gene Delivery In Vivo

Although advances in genomics and experimental gene therapy have opened new possibilities for treating otherwise incurable diseases, the transduction of nucleic acids into the cells and delivery in vivo remain challenging. The high molecular weight and anionic nature of nucleic acids require their packing into nanoparticles for the delivery. The efficacy of nanoparticle drugs necessitates the high bioactivity of constituents, but their distribution in organisms is mostly governed by the physical properties of nanoparticles, and therefore, generation of stable particles with strictly defined characteristics is highly essential. Using previously designed efficient cell-penetrating peptide NF55, we searched for strategies enabling control over the nanoparticle formation and properties to further improve transfection efficacy. The size of the NF55/pDNA nanoparticles correlates with the concentration of its constituents at the beginning of assembly, but characteristics of nanoparticles measured by DLS do not reliably predict the applicability of particles in in vivo studies. We introduce a new formulation approach called cryo-concentration, where we acquired stable and homogeneous nanoparticles for administration in vivo. The cryo-concentrated NF55/pDNA nanoparticles exhibit several advantages over standard formulation: They have long shelf-life and do not aggregate after reconstitution, have excellent stability against enzymatic degradation, and show significantly higher bioactivity in vivo.

Role of autophagy in cell-penetrating peptide transfection model

Cell-penetrating peptides (CPPs) uptake mechanism is still in need of more clarification to have a better understanding of their action in the mediation of oligonucleotide transfection. In this study, the effect on early events (1 h treatment) in transfection by PepFect14 (PF14), with or without oligonucleotide cargo on gene expression, in HeLa cells, have been investigated. The RNA expression profile was characterized by RNA sequencing and confirmed by qPCR analysis. The gene regulations were then related to the biological processes by the study of signaling pathways that showed the induction of autophagy-related genes in early transfection. A ligand library interfering with the detected intracellular pathways showed concentration-dependent effects on the transfection efficiency of splice correction oligonucleotide complexed with PepFect14, proving that the autophagy process is induced upon the uptake of complexes. Finally, the autophagy induction and colocalization with autophagosomes have been confirmed by confocal microscopy and transmission electron microscopy. We conclude that autophagy, an inherent cellular response process, is triggered by the cellular uptake of CPP-based transfection system. This finding opens novel possibilities to use autophagy modifiers in future gene therapy.

Systemic Delivery of Folate-PEG siRNA Lipopolyplexes with Enhanced Intracellular Stability for In Vivo Gene Silencing in Leukemia

Protection of small interfering RNA (siRNA) against degradation and targeted delivery across the plasma and endosomal membranes to the final site of RNA interference (RNAi) are major aims for the development of siRNA therapeutics. Targeting for folate receptor (FR)-expressing tumors, we optimized siRNA polyplexes by coformulating a folate-PEG-oligoaminoamide (for surface shielding and targeting) with one of three lipo-oligoaminoamides (optionally tyrosine-modified, for optimizing stability and size) to generate ∼100 nm targeted lipopolyplexes (TLPs), which self-stabilize by cysteine disulfide cross-links. To better understand parameters for improved tumor-directed gene silencing, we analyzed intracellular distribution and siRNA release kinetics. FR-mediated endocytosis and endosomal escape of TLPs was confirmed by immuno-TEM. We monitored colocalization of TLPs with endosomes and lysosomes, and onset of siRNA release by time-lapse confocal microscopy; analyzed intracellular stability by FRET using double-labeled siRNA; and correlated results with knockdown of eGFPLuc protein and EG5 mRNA expression. The most potent formulation, TLP1, containing lipopolyplex-stabilizing tyrosine trimers, was found to unpack siRNA in sustained manner with up to 5-fold higher intracellular siRNA stability after 4 h compared to other TLPs. Unexpectedly, data indicated that intracellular siRNA stability instead of an early endosomal exit dominate as a deciding factor for silencing efficiency of TLPs. After i.v. administration in a subcutaneous leukemia mouse model, TLP1 exhibited ligand-dependent tumoral siRNA retention, resulting in 65% EG5 gene silencing at mRNA level without detectable adverse effects. In sum, tyrosine-modified TLP1 conveys superior protection of siRNA for an effective tumor-targeted delivery and RNAi in vivo.

RIC8A is essential for the organisation of actin cytoskeleton and cell-matrix interaction

RIC8A functions as a chaperone and guanine nucleotide exchange factor for a subset of G protein α subunits. Multiple G protein subunits mediate various signalling events that regulate cell adhesion and migration and the involvement of RIC8A in some of these processes has been demonstrated. We have previously shown that the deficiency of RIC8A causes a failure in mouse gastrulation and neurogenesis - major events in embryogenesis that rely on proper association of cells with the extracellular matrix (ECM) and involve active cell migration. To elaborate on these findings, we used Ric8a^-/- mouse embryonic stem cells and Ric8a-deficient mouse embryonic fibroblasts, and found that RIC8A plays an important role in the organisation and remodelling of actin cytoskeleton and cell-ECM association. Ric8a-deficient cells were able to attach to different ECM components, but were unable to spread correctly, and did not form stress fibres or focal adhesion complexes. We also found that the presence of RIC8A is necessary for the activation of β1 integrins and integrin-mediated cell migration.

Saturated Fatty Acid Analogues of Cell-Penetrating Peptide PepFect14: Role of Fatty Acid Modification in Complexation and Delivery of Splice-Correcting Oligonucleotides

Modifying cell-penetrating peptides (CPPs) with fatty acids has long been used to improve peptide-mediated nucleic acid delivery. In this study we have revisited this phenomenon with a systematic approach where we developed a structure-activity relationship to describe the role of the acyl chain length in the transfection process. For that we took a well-studied CPP, PepFect14, as the basis and varied its N-terminal acyl chain length from 2 to 22 carbons. To evaluate the delivery efficiency, the peptides were noncovalently complexed with a splice-correcting oligonucleotide (SCO) and tested in HeLa pLuc705 reporter cell line. Our results demonstrate that biological splice-correction activity emerges from acyl chain of 12 carbons and increases linearly with each additional carbon. To assess the underlying factors regarding how the transfection efficacy of these complexes is dependent on hydrophobicity, we used an array of different methods. For the functionally active peptides (C12-22) there was no apparent difference in their physicochemical properties, including complex formation efficiency, hydrodynamic size, and zeta potential. Moreover, membrane activity studies with peptides and their complexes with SCOs confirmed that the toxicity of the complexes at higher molar ratios is mainly caused by the free fraction of the peptide which is not incorporated into the peptide/oligonucleotide complexes. Finally, we show that the increase in splice-correcting activity correlates with the ability of the complexes to associate with the cells. Collectively these studies lay the ground work for how to design highly efficient CPPs and how to optimize their oligonucleotide complexes for lowest toxicity without losing efficiency.

Optimization of in vivo DNA delivery with NickFect peptide vectors

As the field of gene therapy progresses, an increasingly urgent need has arisen for efficient and non-toxic vectors for the in vivo delivery of nucleic acids. Cell-penetrating peptides (CPP) are very efficient transfection reagents in vitro, however, their application in vivo needs improvement. To enhance in vivo transfection we designed various CPPs based on previous knowledge of internalization studies and physiochemical properties of NickFect (NF) nanoparticles. We show that increment of the helicity of these Transportan10 analogues improves the transfection efficiency. We rationally design by modifying the net charge and the helicity of the CPP a novel amphipathic α-helical peptide NF55 for in vivo application. NF55 condenses DNA into stable nanoparticles that are resistant to protease degradation, promotes endosomal escape, and transfects the majority of cells in a large cell population. We demonstrate that NF55 mediates DNA delivery in vivo with gene induction efficiency that is comparable to commercial transfection reagents. In addition to gene induction in healthy mice, NF55/DNA nanoparticles showed promising tumor transfection in various mouse tumor models, including an intracranial glioblastoma model. The efficiency of NF55 to convey DNA specifically into tumor tissue increased even further after coupling a PEG2000 to the peptide via a disulphide-bond. Furthermore, a solid formulation of NF55/DNA displayed an excellent stability profile without additives or special storage conditions. Together, its high transfection efficacy and stability profile make NF55 an excellent vector for the delivery of DNA in vivo.

Pre-administration of PepFect6-microRNA-146a nanocomplexes inhibits inflammatory responses in keratinocytes and in a mouse model of irritant contact dermatitis

The skin is a difficult to access tissue for efficient delivery of large and/or charged macromolecules, including therapeutic DNA and RNA oligonucleotides. Cell-penetrating peptide PepFect6 (PF6) has been shown to be suitable transport vehicle for siRNAs in cell culture and systemically in vivo in mice. MiR-146a is known as anti-inflammatory miRNA that inhibits multiple factors from the nuclear factor (NF)-κB pathway in various cell types, including keratinocytes. In this study, PF6 was shown to form unimodal nanocomplexes with miR-146a mimic that entered into human primary keratinocytes, where miR-146a inhibited the expression of its direct targets from the NF-κB pathway and the genes known to be activated by NF-κB, C-C motif ligand (CCL)5 and interleukin (IL)-8. The transfection of miR-146a mimic with PF6 was more efficient in sub-confluent keratinocyte cultures, affected keratinocyte proliferation less and had similar effect on cell viability when compared with a lipid based agent. Subcutaneous pre-administration of PF6-miR-146a nanocomplexes attenuated ear-swelling and reduced the expression of pro-inflammatory cytokines and chemokines IL-6, CCL11, CCL24 and C-X-C motif ligand 1 (CXCL1) in a mouse model of irritant contact dermatitis. Our data demonstrates that PF6-miR-146a nanoparticles might have potential in the development of therapeutics to target inflammatory skin diseases.

Glycosaminoglycans are required for translocation of amphipathic cell-penetrating peptides across membranes

Cell-penetrating peptides (CPPs) are considered as one of the most promising tools to mediate the cellular delivery of various biologically active compounds that are otherwise cell impermeable. CPPs can internalize into cells via two different pathways - endocytosis and direct translocation across the plasma membrane. In both cases, the initial step of internalization requires interactions between CPPs and different plasma membrane components. Despite the extensive research, it is not yet fully understood, which of these cell surface molecules mediate the direct translocation of CPPs across the plasma- and endosomal membrane. In the present study we used giant plasma membrane vesicles (GPMVs) as a model membrane system to elucidate the specific molecular mechanisms behind the internalization and the role of cell surface glycosaminoglycans (GAGs) in the translocation of four well-known CPPs, classified as cationic (nona-arginine, Tat peptide) and amphipathic (transportan and TP10). We demonstrate here that GAGs facilitate the translocation of amphipathic CPPs, but not the internalization of cationic CPPs; and that the uptake is not mediated by a specific GAG class, but rather the overall amount of these polysaccharides is crucial for the internalization of amphipathic peptides.

Characteristics of Cell-Penetrating Peptide/Nucleic Acid Nanoparticles

Nucleic acids are highly promising candidates for the treatment of various genetic diseases. However, due to the large size and negative charge, nucleic acids are not efficiently taken up by cells, and thus, their clinical potential remains limited so far. Therefore, various delivery vehicles have been designed to assist the cellular uptake of nucleic acids. Among these, cell-penetrating peptides (CPPs) have gained increasing popularity as efficient and nontoxic delivery vectors. CPPs can be coupled to nucleic acids either by covalent or noncovalent association. Noncovalent coupling, which is based on the formation of nanoparticle-like nanocomplexes (NP), has received much attention in recent years, and the number of studies employing the strategy is explosively increasing due to the high therapeutic potential. However, the properties of CPP/nucleic acid NPs have not been characterized in sufficient detail yet. We performed a comprehensive analysis of the size and morphology of nucleic acid nanoparticles with novel transfection peptides, PepFects (PFs) and NickFects (NFs), using negative staining transmission electron microscopy (TEM). In addition, we examined whether the attachment of fluorescence or (nano)gold label to nucleic acid affects the nanocomplex formation or its morphology. We demonstrated that transportan-10-based new generation CPPs from PF and NF families condense nucleic acids to NPs of homogeneous size and shape. The size and shape of assembled nanoparticles depend on the type of the complexed nucleic acid and the sequence of the used peptide, whereas the label on the nucleic acid does not influence the gross characteristics of formed NPs.

Cell-penetrating peptide secures an efficient endosomal escape of an intact cargo upon a brief photo-induction

Since their discovery, cell-penetrating peptides (CPPs) have provided a novel, efficient, and non-invasive mode of transport for various (bioactive) cargos into cells. Despite the ever-growing number of successful implications of the CPP-mediated delivery, issues concerning their intracellular trafficking, significant targeting to degradative organelles, and limited endosomal escape are still hindering their widespread use. To overcome these obstacles, we have utilized a potent photo-induction technique with a fluorescently labeled protein cargo attached to an efficient CPP, TP10. In this study we have determined some key requirements behind this induced escape (e.g., dependence on peptide-to-cargo ratio, time and cargo), and have semi-quantitatively assessed the characteristics of the endosomes that become leaky upon this treatment. Furthermore, we provide evidence that the photo-released cargo remains intact and functional. Altogether, we can conclude that the photo-induced endosomes are specific large complexes-condensed non-acidic vesicles, where the released cargo remains in its native intact form. The latter was confirmed with tubulin as the cargo, which upon photo-induction was incorporated into microtubules. Because of this, we propose that combining the CPP-mediated delivery with photo-activation technique could provide a simple method for overcoming major limitations faced today and serve as a basis for enhanced delivery efficiency and a subsequent elevated cellular response of different bioactive cargo molecules.

Ablation of RIC8A function in mouse neurons leads to a severe neuromuscular phenotype and postnatal death

Resistance to inhibitors of cholinesterase 8 (RIC8) is a guanine nucleotide exchange factor required for the intracellular regulation of G protein signalling. RIC8 activates different Gα subunits via non-canonical pathway, thereby amplifying and prolonging the G protein mediated signal. In order to circumvent the embryonic lethality associated with the absence of RIC8A and to study its role in the nervous system, we constructed Ric8a conditional knockout mice using Cre/loxP technology. Introduction of a synapsin I promoter driven Cre transgenic mouse strain (SynCre) into the floxed Ric8a (Ric8a (F/F) ) background ablated RIC8A function in most differentiated neuron populations. Mutant SynCre (+/-) Ric8 (lacZ/F) mice were born at expected Mendelian ratio, but they died in early postnatal age (P4-P6). The mutants exhibited major developmental defects, like growth retardation and muscular weakness, impaired coordination and balance, muscular spasms and abnormal heart beat. Histological analysis revealed that the deficiency of RIC8A in neurons caused skeletal muscle atrophy and heart muscle hypoplasia, in addition, the sinoatrial node was misplaced and its size reduced. However, we did not observe gross morphological changes in brains of SynCre (+/-) Ric8a (lacZ/F) mutants. Our results demonstrate that in mice the activity of RIC8A in neurons is essential for survival and its deficiency causes a severe neuromuscular phenotype.

New generation of efficient peptide-based vectors, NickFects, for the delivery of nucleic acids

Harnessing of a branched structure is a novel approach in the design of cell-penetrating peptides and it has provided highly efficient transfection reagents for intracellular delivery of nucleic acids. The new stearylated TP10 analogs, NickFects, condense plasmid DNA, splice correcting oligonucleotides and short interfering RNAs into stable nanoparticles with a size of 62-160nm. Such nanoparticles have a negative surface charge (-11 to -18mV) in serum containing medium and enable highly efficient gene expression, splice correction and gene silencing. One of the novel peptides, NickFect51 is capable of transfecting plasmid DNA into a large variety of cell lines, including refractory suspension and primary cells and in several cases exceeds the transfection level of commercially available reagent Lipofectamine™ 2000 without any cytotoxic side effects. Additionally we demonstrate the advantages of NickFect51 in a protein production system, QMCF technology, for expression and production of recombinant proteins in hardly transfectable suspension cells.

PepFect14 peptide vector for efficient gene delivery in cell cultures

The successful applicability of gene therapy approaches will heavily rely on the development of efficient and safe nonviral gene delivery vectors, for example, cell-penetrating peptides (CPPs). CPPs can condense oligonucleotides and plasmid DNA (pDNA) into nanoparticles, thus allowing the transfection of genetic material into cells. However, despite few promising attempts, CPP-mediated pDNA delivery has been relatively inefficient due to the unfavorable nanoparticle characteristics or the nanoparticle entrapment to endocytic compartments. In many cases, both of these drawbacks could be alleviated by modifying CPPs with a stearic acid residue, as demonstrated in the delivery of both the pDNA and the short oligonucleotides. In this study, PepFect14 (PF14) peptide, previously used for the transport of shorter oligonucleotides, is demonstrated to be suited also for the delivery of pDNA. It is shown that PF14 forms stable nanoparticles with pDNA with a negative surface charge and size of around 130-170 nm. These nanoparticles facilitate efficient gene delivery and expression in a variety of regular adherent cell lines and also in difficult-to-transfect primary cells. Uptake studies indicate that PF14/pDNA nanoparticles are utilizing class A scavenger receptors (SCARA) and caveolae-mediated endocytosis as the main route for cellular internalization. Conclusively, PF14 is an efficient nonviral vector for gene delivery.

Cell-penetrating peptides split into two groups based on modulation of intracellular calcium concentration

Cell-penetrating peptides (CPPs) promote the uptake of different cargo molecules, e.g. therapeutic compounds, making the harnessing of CPPs a promising strategy for drug design and delivery. However, the internalization mechanisms of CPPs are still under discussion, and it is not clear how cells compensate the disturbances induced by peptides in the plasma membrane. In this study, we demonstrate that the uptake of various CPPs enhances the intracellular Ca(2+) levels in Jurkat and HeLa cells. The elevated Ca(2+) concentration in turn triggers plasma membrane blebbing, lysosomal exocytosis, and membrane repair response. Our results indicate that CPPs split into two major classes: (i) amphipathic CPPs that modulate the plasma membrane integrity inducing influx of Ca(2+) and activating downstream responses starting from low concentrations; (ii) non-amphipathic CPPs that do not evoke changes at relevant concentrations. Triggering of the membrane repair response may help cells to replace distorted plasma membrane regions and cells can recover from the influx of Ca(2+) if its level is not drastically elevated.

Cell-penetrating peptides as versatile vehicles for oligonucleotide delivery

Short regulatory oligonucleotides (ONs) have a great therapeutic potential for the modulation of gene expression due to their high specificity and low toxicity. The major obstacles for in vivo clinical applications of ONs are the poor permeability of plasma membrane to nucleic acids and the sensitivity of ONs to enzymatic degradation. Hence, various delivery vehicles have been developed to ensure the transduction of ONs into cells. Among these, the cell-penetrating peptides (CPPs) have gained quickly broadening popularity as promising nonviral transmembrane delivery vectors. For coupling of nucleic acids to CPPs, two distinct strategies may be applied-covalent and noncovalent. The majority of earlier studies have used covalent coupling of CPPs to ONs. However, the number of studies demonstrating very high therapeutic potential of noncovalent complexes of ONs with novel CPP-based delivery vehicles is explosively increasing. In this review, the recent developments in the application of CPP-mediated oligonucleotide delivery by noncovalent strategy will be discussed.

Scavenger receptor-mediated uptake of cell-penetrating peptide nanocomplexes with oligonucleotides

Cell-penetrating peptides (CPPs) are short cationic peptides that penetrate cells by interacting with the negatively charged plasma membrane; however, the detailed uptake mechanism is not clear. In contrary to the conventional mode of action of CPPs, we show here that a CPP, PepFect14 (PF14), forms negatively charged nanocomplexes with oligonucleotides and their uptake is mediated by class-A scavenger receptors (SCARAs). Specific inhibitory ligands of SCARAs, such as fucoidin, polyinosinic acid, and dextran sulfate, totally inhibit the activity of PF14-oligonucleotide nanocomplexes in the HeLa pLuc705 splice-correction cell model, while nonspecific, chemically related molecules do not. Furthermore, RNA interference (RNAi) knockdown of SCARA subtypes (SCARA3 and SCARA5) that are expressed in this cell line led to a significant reduction of the activity to <50%. In line with this, immunostaining shows prevalent colocalization of the nanocomplexes with the receptors, and electron microscopy images show no binding or internalization of the nanocomplexes in the presence of the inhibitory ligands. Interestingly, naked oligonucleotides also colocalize with SCARAs when used at high concentrations. These results demonstrate the involvement of SCARA3 and SCARA5 in the uptake of PF14-oligonucleotide nanocomplexes and suggest for the first time that some CPP-based systems function through scavenger receptors, which could yield novel possibilities to understand and improve the transfection by CPPs.

Direct translocation as major cellular uptake for CADY self-assembling peptide-based nanoparticles

Cell penetrating peptides constitute a potent approach to overcome the limitations of in vivo siRNA delivery. We recently proposed a peptide-based nanoparticle system, CADY, for efficient delivery of siRNA into numerous cell lines. CADY is a secondary amphipathic peptide that forms stable complexes with siRNA thereby improving both their cellular uptake and biological response. With the aim of understanding the cellular uptake mechanism of CADY:siRNA complexes, we have combined biochemical, confocal and electron microscopy approaches. In the present work, we provide evidence that the major route for CADY:siRNA cellular uptake involves direct translocation through the membrane but not the endosomal pathway. We have demonstrated that CADY:siRNA complexes do not colocalize with most endosomal markers and remain fully active in the presence of inhibitors of the endosomal pathway. Moreover, neither electrostatic interactions with cell surface heparan sulphates nor membrane potential are essential for CADY:siRNA cell entry. In contrast, we have shown that CADY:siRNA complexes clearly induce a transient cell membrane permeabilization, which is rapidly restored by cell membrane fluidity. Therefore, we propose that direct translocation is the major gate for cell entry of CADY:siRNA complexes. Membrane perturbation and uptake are driven mainly by the ability of CADY to interact with phospholipids within the cell membrane, followed by rapid localization of the complex in the cytoplasm, without affecting cell integrity or viability.

Nucleotide exchange factor RIC-8 is indispensable in mammalian early development

The guanine nucleotide exchange factor RIC-8 is a conserved protein essential for the asymmetric division in the early embryogenesis in different organisms. The function of RIC-8 in mammalian development is not characterized so far. In this study we map the expression of RIC-8 during the early development of mouse. To elucidate the RIC-8 function we used Ric-8(-/-) mutant embryos. The Ric-8(-/-) embryos reach the gastrulation stage but do not develop further and die at E6.5-E8.5. We characterized the Ric-8(-/-) embryonic phenotype by morphological and marker gene analyses. The gastrulation is initiated in Ric-8(-/-) embryos but their growth is retarded, epiblast and mesoderm disorganized. Additionally, the basement membrane is defective, amnion folding and the formation of allantois are interfered, also the cavitation. Furthermore, the orientation of the Ric-8(-/-) embryo in the uterus was abnormal. Our study reveals that the activity of RIC-8 protein is irreplaceable for the correct gastrulation of mouse embryo.

Insight into cell-entry mechanisms of CPPs by electron microscopy

Despite the quickly widening application of cell-penetrating peptides (CPP) for the cellular delivery of various macromolecules, the cell entry mechanisms of these peptides have remained elusive so far. The basic features of the translocation of CPPs into cells have been mapped by fluorescence microscopy and activity-based assays revealing that endocytotic mechanisms are mainly responsible for the uptake at physiological temperature. However, the high concentration of CPP or the lowering of the incubation temperature below 10°C (re)activates a nonvesicular cell entry mode. The fluorescence microscopy can hardly provide detailed information about the interaction of CPP molecules with the extracellular structures, the induced changes in the morphology of the plasma membrane, etc. Therefore, application of electron microscopy could help to shed light on the nature of nonvesicular uptake mechanism. Transmission electron microscopy (TEM) has been a valuable tool for the morphological characterization of biological material at high resolution. It can provide useful information at the ultrastructural level about the interaction and arrangement of CPPs on the cell surface, the entrapment in cellular organelles and the translocation to the cytoplasm. In this chapter, we present a method for the tagging of CPPs covalently with a 1.4 nm gold cluster and provide a flat-embedding protocol for the mapping of Nanogold™-labeled CPPs in cultured cells by TEM. This method enables to retain the cell monolayers in their in situ orientation. The Nanogold™ tag is putatively not interfering with the uptake of CPPs and enables the production of specimens with excellent morphology and good contrast.

Mapping of protein transduction pathways with fluorescent microscopy

The number of various cargo delivered into cells by CPPs demonstrates the effective transport abilities of these short-peptidic sequences. Over the years of research, the translocation process of CPP-cargo complexes has been mapped to being of mostly endocytic nature, however, there is still no consensus on which of the endocytic routes is prevalent and to which extent the interplay between different modes of endocytosis is taking place. The intracellular trafficking of CPPs attached to a cargo molecule is even less understood. Therefore, the internalization and the subsequent intracellular targeting of complexes need clarification in order to define cellular destinations and improve the targeting of the cargo molecule to specific cellular compartments depending on the cargo attached to the transporting vector. This chapter focuses on describing the methods for visualizing the CPP-protein complexes in relation to different endocytic markers, for example transferrin (marker for clathrin-mediated endocytosis) and cholera toxin (ambiguous marker for clathrin-, caveolin-, and flotillin-mediated, but also clathrin- and caveolin-independent endocytosis) to determine the role of the respective pathways during entry to cells, and to different intracellular targets, for instance the lysosomal organelles or the Golgi apparatus. Additionally, antibody staining of respective endocytic vesicles following the internalization of CPP-protein complexes will be discussed.

Retro-inversion of certain cell-penetrating peptides causes severe cellular toxicity

Cell-penetrating peptides (CPPs) are a promising group of delivery vectors for various therapeutic agents but their application is often hampered by poor stability in the presence of serum. Different strategies to improve peptide stability have been exploited, one of them being "retro-inversion" (RI) of natural peptides. With this approach the stability of CPPs has been increased, thereby making them more efficient transporters. Several RI-CPPs were here assessed and compared to the corresponding parent peptides in different cell-lines. Surprisingly, treatment of cells with these peptides induced trypsin insensitivity and rapid severe toxicity in contrast to L-peptides. This was measured as reduced metabolic activity and condensed cell nuclei, in parity with the apoptosis inducing agent staurosporine. Furthermore, effects on mitochondrial network, focal adhesions, actin cytoskeleton and caspase-3 activation were analyzed and adverse effects were evident at 20 μM peptide concentration within 4 h while parent L-peptides had negligible effects. To our knowledge this is the first time RI peptides are reported to cause cellular toxicity, displayed by decreased metabolic activity, morphological changes and induction of apoptosis. Considering the wide range of research areas that involves the use of RI-peptides, this finding is of major importance and needs to be taken under consideration in applications of RI-peptides.

Protein delivery with transportans is mediated by caveolae rather than flotillin-dependent pathways

Delivery of large bioactive cargoes into cells with the help of cell-penetrating peptides (CPPs) is mostly based on endocytic processes. Here we map the cellular pathways used by transportan and transportan 10 (TP10) for protein transduction in HeLa cells. CPP-mediated cellular delivery is often suggested to be lipid-raft-dependent; therefore, we used flotillin-1, caveolin, Rab5, and PI3P as markers to elucidate the involvement of these particular endosomal pathways in the protein uptake process. Confocal laser scanning and electron microscopy reveal only a negligible overlap of avidin/neutravidin conveyed into cells by transportans with the raft marker flotillin-1 or early endosomal markers Rab5 and PI3P. However, about 20% of protein-CPP complexes colocalize with the caveolar/caveosomal marker caveolin, and down-regulation of caveolin-1 by siRNA treatment leads to the inhibition of the CPP-mediated protein uptake by 30-50%. On the contrary, the lack of flotillin-1 increases rather than decreases the CPP-mediated protein transport. The participation of the caveolin-1-dependent pathway in CPP-mediated protein delivery was also corroborated by using caveolin-1 knockout mouse embryonic fibroblasts.

Separation of the rotational contribution in fluorescence correlation experiments

The theory of fluorescence correlation spectroscopy is reexamined with the aim of separating the contribution of rotational diffusion. Under constant excitation, fluorescence correlation experiments are characterized by three polarizations: one of the incident beam and two of the two photon detectors. A set of experiments of different polarizations is proposed for study. From the results of the experiments the isotropic factor of the fluorescence intensity correlation functions can be determined, which is independent of the rotational motion of the sample molecule. This function can be used to represent each fluorescence intensity correlation function as the product of the isotropic and the rotational factors. The theory is illustrated by an experiment in which rotational diffusion of porcine pancreatic lipase labeled with Texas Red was observed Texas Red is a label that allows precise fluorescence correlation experiments even in the nanosecond time range.

Distribution of CPP-Protein Complexes in Freshly Resected Human Tissue Material

Interest in cell-penetrating peptides (CPPs) as delivery agents has fuelled a large number of studies conducted on cultured cells and in mice. However, only a few studies have been devoted to the behaviour of CPPs in human tissues. Therefore, we performed ex vivo tissue-dipping experiments where we studied the distribution of CPP-protein complexes in samples of freshly harvested human tissue material. We used the carcinoma or hyperplasia-containing specimens of the uterus and the cervix, obtained as surgical waste from nine hysterectomies. Our aim was to evaluate the tissue of preference (epithelial versus muscular/connective tissue, carcinoma versus adjacent histologically normal tissue) for two well-studied CPPs, the transportan and the TAT-peptide. We complexed biotinylated CPPs with avidin--galactosidase (ABG), which enabled us to apply whole-mount X-gal staining as a robust detection method. Our results demonstrate that both peptides enhanced the tissue distribution of ABG. The enhancing effect of the tested CPPs was more obvious in the normal tissue and in some specimens we detected a striking selectivity of CPP-ABG complexes for the normal tissue. This unexpected finding encourages the evaluation of CPPs as local delivery agents in non-malignant situations, for example in the intrauterine gene therapy of benign gynaecological diseases.

Peptide-mediated protein delivery-which pathways are penetrable?

The growing number of reports on the effective cargo delivery by cell-penetrating peptides (CPPs) has extensively widened our knowledge about the mechanisms involved in CPP-mediated delivery. However, the data available on the internalization mode of CPP-cargo complexes are often conflicting and/or equivocal. Moreover, the intracellular trafficking of CPP-cargo complexes is, to date, relatively unexplored resulting in only minimal information about what is really happening to the complexes inside the cell. This review focuses on defining the endocytic pathways engaged in the transduction of CPP-cargo complexes and seeks to determine the extent of different endocytic routes required for effective uptake. In addition, the intracellular pathways utilized during the trafficking and sorting of CPP-cargo complexes as well as the ultimate fate of the complexes inside cells will be discussed.

CPP-protein constructs induce a population of non-acidic vesicles during trafficking through endo-lysosomal pathway

The major limitation in the application of bioactive molecules is their low permeation across plasma membrane. Effective transporters - cell-penetrating peptides (CPPs) - are utilized to enhance uptake of various cargo upon attachment to its sequences. Still, information about relevance of different endocytic routes during CPP-cargo internalization is ambiguous and underlying mechanism(s) of intracellular trafficking is even less understood. We first defined involvement of recycling pathway in trafficking of 3 different CPPs - transportan, oligoarginine and Tat - complexed to avidin-TexasRed in Cos-7 cells in relation to trans-Golgi network spatially constraining recycling endosomes. By confocal microscopy, only a negligible fraction of complexes-containing vesicles were found inside trans-Golgi ring suggesting its marginal role in CPP-mediated delivery. Secondly, we characterized engagement of endo-lysosomal pathway to assess acidity of complexes-containing vesicles. CPPs induced 3 different populations of complexes-containing vesicles which size and proportion depended on CPP, time and concentration. In time, more complexes were targeted to low-pH structures. However, a population of complexes-containing vesicles was observed to retain rather neutral pH. Induction of vesicles with non-acidic pH generated i.e. by caveolin-dependent endocytosis or by CPPs themselves during intracellular trafficking could be the key step in inducement of escape of complexes from endosomal structures, a limiting step in effective cargo delivery by CPPs.