Identification and characterization of synthetic chondroitin-4-sulfate binding peptides in neuronal functions

Effects of local and systemic treatment with human natural killer-1 mimetic peptide (HNK-1) after ventral root avulsion and reimplantation in mice

Background

Spinal ventral root injuries generate significant motoneuron degeneration, which hinders full functional recovery. The poor prognosis of functional recovery can be attributed to the use or combination of different therapeutic approaches. Several molecules have been screened as potential treatments in combination with surgical reimplantation of the avulsed roots, the gold standard approach for such injuries. Among the studied molecules, human natural killer-1 (HNK-1) stands out as it is related to the stimulation of motor axon outgrowth. Therefore, we aimed to comparatively investigate the effects of local administration of an HNK-1 mimetic peptide (mp-HNK-1) and systemic treatment with ursolic acid (UA), another HNK-1 mimetic, after ventral root avulsion and reimplantation with heterologous fibrin biopolymer (HFB).

Methods

Female mice of the isogenic strain C57BL/6JUnib were divided into five experimental groups: Avulsion, Reimplantation, mp-HNK-1 (in situ), and UA (systemic treatment). Mice were evaluated 2 and 12 weeks after surgery. Functional assessment was performed every four days using the Catwalk platform. Neuronal survival was analyzed by cytochemistry, and glial reactions and synaptic coverage were evaluated by immunofluorescence.

Results

Treatment with UA elicited long-term neuroprotection, accompanied by a decrease in microglial reactions, and reactive astrogliosis. The neuroprotective effects of UA were preceded by increased glutamatergic and GABAergic inputs in the ventral spinal cord two weeks after injury. However, a single application of mp-HNK-1 had no significant effects. Functional analysis showed that UA treatment led to an improvement in motor and sensory recovery.

Conclusion

Overall, the results indicate that UA is neuroprotective, acting on glial cells and synaptic maintenance, and the combination of these findings led to a better functional recovery.

In vitro assessment of protamine toxicity with neural cells, its therapeutic potential to counter chondroitin sulfate mediated neuron inhibition, and its effects on reactive astrocytes

Multiple therapies have been studied to ameliorate the neuroinhibitory cues present after traumatic injury to the central nervous system. Two previous in vitro studies have demonstrated the efficacy of the FDA-approved cardiovascular therapeutic, protamine (PRM), to overcome neuroinhibitory cues presented by chondroitin sulfates; however, the effect of a wide range of PRM concentrations on neuronal and glial cells has not been evaluated. In this study, we investigate the therapeutic efficacy of PRM with primary cortical neurons, hippocampal neurons, mixed glial cultures, and astrocyte cultures. We show the threshold for PRM toxicity to be at or above 10 μg/ml depending on the cell population, that 10 μg/ml PRM enables neurons to overcome the inhibitory cues presented by chondroitin sulfate type A, and that soluble PRM allows neurons to more effectively overcome inhibition compared to a PRM coating. We also assessed changes in gene expression of reactive astrocytes with soluble PRM and determined that PRM does not increase their neurotoxic phenotype and that PRM may reduce brevican production and serpin transcription in cortical and spinal cord astrocytes. This is the first study to thoroughly assess the toxicity threshold of PRM with neural cells and study astrocyte response after acute exposure to PRM in vitro.

CHST11-modified chondroitin 4-sulfate as a potential therapeutic target for glioblastoma

Aberrant chondroitin sulfate (CS) accumulation in glioblastoma (GBM) tissue has been documented, but the role of excessive CS in GBM progression and whether it can be a druggable target are largely unknown. The aim of this study is to clarify the biological functions of CHST11 in GBM cells, and evaluate therapeutic effects of blocking CHST11-derived chondroitin 4-sulfate (C4S). We investigated the expression of CHST11 in glioma tissue by immunohistochemistry, and analyzed CHST11 associated genes using public RNA sequencing datasets. The effects of CHST11 on aggressive cell behaviors have been studied in vitro and in vivo. We demonstrated that CHST11 is frequently overexpressed in GBM tissue, promoting GBM cell mobility and modulating C4S on GBM cells. We further discovered that CSPG4 is positively correlated with CHST11, and CSPG4 involved in CHST11-mediated cell invasiveness. In addition, GBM patients with high expression of CHST11 and CSPG4 have a significantly shorter survival time. We examined the effects of treating C4S-specific binding peptide (C4Sp) as a therapeutic agent in vitro and in vivo. C4Sp treatment attenuated GBM cell invasiveness and, notably, improved survival rate of orthotopic glioma cell transplant mice. Our results propose a possible mechanism of CHST11 in regulating GBM malignancy and highlight a novel strategy for targeting aberrant chondroitin sulfate in GBM cells.

Propagation Capacity of Phage Display Peptide Libraries Is Affected by the Length and Conformation of Displayed Peptide

The larger size and diversity of phage display peptide libraries enhance the probability of finding clinically valuable ligands. A simple way of increasing the throughput of selection is to mix multiple peptide libraries with different characteristics of displayed peptides and use it as biopanning input. In phage display, the peptide is genetically coupled with a biological entity (the phage), and the representation of peptides in the selection system is dependent on the propagation capacity of phages. Little is known about how the characteristics of displayed peptides affect the propagation capacity of the pooled library. In this work, next-generation sequencing (NGS) was used to investigate the amplification capacity of three widely used commercial phage display peptide libraries (Ph.D.™-7, Ph.D.™-12, and Ph.D.™-C7C from New England Biolabs). The three libraries were pooled and subjected to competitive propagation, and the proportion of each library in the pool was quantitated at two time points during propagation. The results of the inter-library competitive propagation assay led to the conclusion that the propagation capacity of phage libraries on a population level is decreased with increasing length and cyclic conformation of displayed peptides. Moreover, the enrichment factor (EF) analysis of the phage population revealed a higher propagation capacity of the Ph.D.^TM-7 library. Our findings provide evidence for the contribution of the length and structural conformation of displayed peptides to the unequal propagation rates of phage display libraries and suggest that it is important to take peptide characteristics into account once pooling multiple combinatorial libraries for phage display selection through biopanning.

Targeting Chondroitin Sulphate Synthase 1 (Chsy1) Promotes Axon Growth Following Neurorrhaphy by Suppressing Versican Accumulation

Versican is a chondroitin sulfate proteoglycan (CSPG), which deposits in perineurium as a physical barrier and prevents the growth of axons out of the fascial boundary. Several studies have indicated that the chondroitin sulfate (CS) chains on versican have several possible functions beyond the physical barrier, including the ability to stabilize versican core protein in the extracellular matrix. As chondroitin sulfate synthase 1 (Chsy1) is a crucial enzyme for CS elongation, we hypothesized that in vivo knockdown of Chsy1 at peripheral nerve lesion site may decrease CS and versican accumulation, and result in accelerating neurite regeneration. In the present study, end-to-side neurorrhaphy (ESN) in Wistar rats was used as an in vivo model of peripheral nerve injury to evaluate nerve regeneration after surgical intervention. The distribution and expression of versican and Chsy1 in regenerating axons after ESN was studied using confocal microscopy and western blotting. Chsy1 was silenced at the nerve lesion (surgical) site using in vivo siRNA transfection. The results indicated that Chsy1 was successfully silenced in nerve tissue, and its downregulation was associated with functional recovery of compound muscle action potential. Silencing of Chsy1 also decreased the accumulation of versican core protein, suggesting that transient treating of Chsy1-siRNA may be an alternative and an effective strategy to promote injured peripheral nerve regeneration.

Nanoparticle targeting of mechanically modulated glycocalyx

The mechanical properties and forces in the extracellular environment surrounding alveolar epithelial cells have the potential to modulate their behavior. Particularly, breathing applies 3-dimensional cyclic stretches to the cells, while the stiffness of the interstitium changes in disease states, such as fibrosis and cancer. A platform was developed that effectively imitates the active forces in the alveolus, while allowing one to control the interstitium matrix stiffnesses to mimic fibrotic lung tumor microenvironments. Alveolar epithelial cancer cells were cultured on these platforms and changes in the glycocalyx expression were evaluated. A complex combination of stiffness and dynamic forces altered heparan sulfate and chondroitin sulfate proteoglycan expressions. Consequently, we designed liposomal nanoparticles (LNPs) modified with peptides that can target heparan sulphate and chondroitin sulfates of cell surface glycocalyx. Cellular uptake of these modified nanoparticles increased in stiffer conditions depending on the stretch state. Namely, chondroitin sulfate A targeting improved uptake efficiency in cells experiencing dynamic stretches, while cells seeded on static stiff interstitium preferentially took up heparan sulfate targeting LNPs. These results demonstrate the critical role that mechanical stiffness and stretching play in the alveolus and the importance of including these properties in nanotherapeutic design for cancer treatment.

Chondroitin 6-sulfate-binding peptides improve recovery in spinal cord-injured mice

The role of glycosaminoglycan sulfation patterns, particularly in regard to scar formation and inhibition of neuritogenesis, has been mainly studied in cell culture with a focus on chondroitin 4-sulfate. In this study, we investigated chondroitin 6-sulfate (C6S) and found that it also inhibits neurite outgrowth of mouse cerebellar granule neurons in vitro. To examine whether the inhibitory activity of C6S could be neutralized, seven previously characterized high-affinity C6S-binding peptides were tested, among which three peptides neutralized the inhibitory functions of C6S. We further investigated these peptides in a mouse model of spinal cord injury, since upregulation of C6S expression in the glial scar following injury has been associated with reduced axonal regrowth and functional recovery. We here subjected mice to severe compression injury at thoracic levels T7-T9, immediately followed by inserting gelfoam patches soaked in C6S-binding peptides or in a control peptide. Application of C6S-binding peptides led to functional recovery after injury and prevented fibrotic glial scar formation, as seen by decreased activation of astrocytes and microglia/macrophages. Decreased expression of several lecticans and deposition of fibronectin at the site of injury were also observed. Application of C6S-binding peptides led to axonal regrowth and inhibited the C6S-mediated activation of RhoA/ROCK and decrease of PI3K-Akt-mTOR signaling pathways. Taken together, these results indicate that treatment with C6S-binding peptides improves functional recovery in a mouse model of spinal cord injury.

Autosomal recessive variants in TUBGCP2 alter the γ-tubulin ring complex leading to neurodevelopmental disease

Microtubules help building the cytoskeleton of neurons and other cells. Several components of the gamma-tubulin (γ-tubulin) complex have been previously reported in human neurodevelopmental diseases. We describe two siblings from a consanguineous Turkish family with dysmorphic features, developmental delay, brain malformation, and epilepsy carrying a homozygous mutation (p.Glu311Lys) in TUBGCP2 encoding the γ-tubulin complex 2 (GCP2) protein. This variant is predicted to disrupt the electrostatic interaction of GCP2 with GCP3. In primary fibroblasts carrying the variant, we observed a faint delocalization of γ-tubulin during the cell cycle but normal GCP2 protein levels. Through mass spectrometry, we observed dysregulation of multiple proteins involved in the assembly and organization of the cytoskeleton and the extracellular matrix, controlling cellular adhesion and of proteins crucial for neuronal homeostasis including axon guidance. In summary, our functional and proteomic studies link TUBGCP2 and the γ-tubulin complex to the development of the central nervous system in humans.

Neural glycomics: the sweet side of nervous system functions

The success of investigations on the structure and function of the genome (genomics) has been paralleled by an equally awesome progress in the analysis of protein structure and function (proteomics). We propose that the investigation of carbohydrate structures that go beyond a cell's metabolism is a rapidly developing frontier in our expanding knowledge on the structure and function of carbohydrates (glycomics). No other functional system appears to be suited as well as the nervous system to study the functions of glycans, which had been originally characterized outside the nervous system. In this review, we describe the multiple studies on the functions of LewisX, the human natural killer cell antigen-1 (HNK-1), as well as oligomannosidic and sialic (neuraminic) acids. We attempt to show the sophistication of these structures in ontogenetic development, synaptic function and plasticity, and recovery from trauma, with a view on neurodegeneration and possibilities to ameliorate deterioration. In view of clinical applications, we emphasize the need for glycomimetic small organic compounds which surpass the usefulness of natural glycans in that they are metabolically more stable, more parsimonious to synthesize or isolate, and more advantageous for therapy, since many of them pass the blood brain barrier and are drug-approved for treatments other than those in the nervous system, thus allowing a more ready access for application in neurological diseases. We describe the isolation of such mimetic compounds using not only Western NIH, but also traditional Chinese medical libraries. With this review, we hope to deepen the interests in this exciting field.

Analysis of Chondroitin/Dermatan Sulphate Disaccharides Using High-Performance Liquid Chromatography

Chondroitin sulphates belong to a group of naturally occurring glycosaminoglycans and play a role in many physiological processes including ageing and the effects of various diseases. Research into chondroitin sulphates has found that the most important analytes are 4- and 6-sulphated disaccharides. We developed an HPLC method for the separation and quantification of underivatized chondroitin/dermatan sulphates—unsaturated disaccharides (4- and 6-sulphated disaccharides). This method is based on the separation of disaccharides by amido as well as amino columns under acidic conditions. These columns enabled the successful separation of 4- and 6-sulphated disaccharides using 50 (amido column) and 25 mmol/L (amino column) phosphate buffer, pH 4.25 (detection at 230 nm), at retention times of less than 10 min. The limit of quantification was 0.5 μg/mL. The applicability of this method was demonstrated through analysis of unsaturated disaccharides produced from the enzymatic digestion of chondroitin/dermatan sulphates of the solubilized extracellular matrix produced from porcine urinary bladder and human umbilical cord.

Role of Chondroitin Sulfation Following Spinal Cord Injury

Traumatic spinal cord injury produces long-term neurological damage, and presents a significant public health problem with nearly 18,000 new cases per year in the U.S. The injury results in both acute and chronic changes in the spinal cord, ultimately resulting in the production of a glial scar, consisting of multiple cells including fibroblasts, macrophages, microglia, and reactive astrocytes. Within the scar, there is an accumulation of extracellular matrix (ECM) molecules—primarily tenascins and chondroitin sulfate proteoglycans (CSPGs)—which are considered to be inhibitory to axonal regeneration. In this review article, we discuss the role of CSPGs in the injury response, especially how sulfated glycosaminoglycan (GAG) chains act to inhibit plasticity and regeneration. This includes how sulfation of GAG chains influences their biological activity and interactions with potential receptors. Comprehending the role of CSPGs in the inhibitory properties of the glial scar provides critical knowledge in the much-needed production of new therapies.

A mimetic peptide of α2,6-sialyllactose promotes neuritogenesis

Oxidative stress contributes to the pathogenesis of neurodegenerative diseases. With the aim to find reagents that reduce oxidative stress, a phage display library was screened for peptides mimicking α2,6-sialyllactose (6'-SL), which is known to beneficially influence neural functions. Using Sambucus nigra lectin, which specifically binds to 6'-SL, we screened a phage display library and found a peptide comprising identical sequences of 12 amino acids. Mimetic peptide, reverse peptide and scrambled peptide were tested for inhibition of 6'-SL binding to the lectin. Indeed, lectin binding to 6'-SL was inhibited by the most frequently identified mimetic peptide, but not by the reverse or scrambled peptides, showing that this peptide mimics 6'-SL. Functionally, mimetic peptide, but not the reverse or scrambled peptides, increased viability and expression of neural cell adhesion molecule L1 in SK-N-SH human neuroblastoma cells, and promoted survival and neurite outgrowth of cultured mouse cerebellar granule neurons challenged by H₂O₂-induced oxidative stress. The combined results indicate that the 6'-SL mimetic peptide promotes neuronal survival and neuritogenesis, thus raising hopes for the treatment of neurodegenerative diseases. This study was approved by the Medical Ethics Committee of Shantou University Medical College, China (approval No. SUMC 2014-004) on February 20, 2014.

Chemical Methods for N- and O-Sulfation of Small Molecules, Amino Acids and Peptides

Sulfation of the amino acid residues of proteins is a significant post-translational modification, the functions of which are yet to be fully understood. Current sulfation methods are limited mainly to O-tyrosine (sY), which requires negatively charged species around the desired amino acid residue and a specific sulfotransferase enzyme. Alternatively, for solid-phase peptide synthesis, a de novo protected sY is required. Therefore, synthetic routes that go beyond O-sulfation are required. We have developed a novel route to N-sulfamation and can dial-in/out O-sulfation (without S-sulfurothiolation), mimicking the initiation step of the ping-pong sulfation mechanism identified in structural biology. This rapid, low-temperature and non-racemising method is applicable to a range of amines, amides, amino acids, and peptide sequences.

Microarrays for the screening and identification of carbohydrate-binding peptides

The development of carbohydrate-binding ligands is crucial for expanding knowledge on the glycocode and for achieving systematic carbohydrate targeting. Amongst such ligands, carbohydrate-binding peptides (CBPs) are attractive for use in bioanalytical and biomedical systems due to their biochemical and physicochemical properties; moreover, given the biological significance of lectin-carbohydrate interactions, these ligands offer an opportunity to study peptide sequence and binding characteristics to inform on natural target/ligand interactions. Here, a high-throughput microarray screening technique is described for the identification and study of CBPs, with a focus on polysialic acid (PSA), a polysaccharide found on neural stem cells. The chemical and biological uniqueness of PSA suggests that an ability to exclusively target this glycan may promote a number of diagnostic and therapeutic applications. PSA-binding peptides from phage display screening and from epitope mapping of an scFv for oligosialic acid were screened in an optimized microarray format with three ligand density conditions. Hypothesis-driven mutations were additionally applied to select peptides to modulate peptide affinity and selectivity to PSA. Peptide compositional and positional analyses revealed the significance of various residues for PSA binding and suggested the importance of basic residue positioning for PSA recognition. Furthermore, selectivity studies performed directly on microarrays with chondroitin sulfate A (CS-A) demonstrated the value of screening for both affinity and selectivity in the development of CBPs. Thus, the integrated approach described, with attention to design strategy, screening, and peptide characterization, successfully identified novel PSA-binding ligands and offers a platform for the identification and study of additional polysaccharide-binding peptides.

The Rise of Molecules Able To Regenerate the Central Nervous System

Injury to the adult central nervous system (CNS) usually leads to permanent deficits of cognitive, sensory, and/or motor functions. The failure of axonal regeneration in the damaged CNS limits functional recovery. The lack of information concerning the biological mechanism of axonal regeneration and its complexity has delayed the process of drug discovery for many years compared to other drug classes. Starting in the early 2000s, the ability of many molecules to stimulate axonal regrowth was evaluated through automated screening techniques; many hits and some new mechanisms involved in axonal regeneration were identified. In this Perspective, we discuss the rise of the CNS regenerative drugs, the main biological techniques used to test these drug candidates, some of the most important screens performed so far, and the main challenges following the identification of a drug that is able to induce axonal regeneration in vivo.

Novel Peptide-Based Inhibitors for Microtubule Polymerization in Phytophthora capsici

The plant disease Phytophthora blight, caused by the oomycete pathogen Phytophthora capsici, is responsible for major economic losses in pepper production. Microtubules have been an attractive target for many antifungal agents as they are involved in key cellular events such as cell proliferation, signaling, and migration in eukaryotic cells. In order to design a novel biocompatible inhibitor, we screened and identified inhibitory peptides against alpha- and beta-tubulin of P. capsici using a phage display method. The identified peptides displayed a higher binding affinity (nanomolar range) and improved specificity toward P. capsici alpha- and beta-tubulin in comparison to Homo sapiens tubulin as evaluated by fluorometric analysis. One peptide demonstrated the high inhibitory effect on microtubule formation with a nanomolar range of IC₅₀ values, which were much lower than a well-known chemical inhibitor—benomyl (IC₅₀ = 500 µM). Based on these results, this peptide can be employed to further develop promising candidates for novel antifungal agents against Phytophthora blight.