Elucidation of GlcNAc-binding properties of type III intermediate filament proteins, using GlcNAc-bearing polymers

N-acetylglucosamine-bearing polymers mimicking O-GlcNAc-modified proteins elicit anti-fibrotic activities in myofibroblasts and activated stellate cells

O-linked β-N-acetylglucosamine (O-GlcNAc)-modified proteins are post-translationally modified with GlcNAc conjugated to serine and threonine residues. This modification is associated with various physiological functions such as serine and threonine phosphorylation and Notch signaling. Here, we demonstrated that O-GlcNAc-modified proteins leaked from dead cells and GlcNAc-bearing polymers mimicking the multivalent GlcNAc moiety of these proteins induced anti-fibrotic activities, such as the suppression of α-smooth muscle actin and collagen and the induction of matrix metalloprotease 1 in myofibroblasts. We have previously reported that O-GlcNAc-modified proteins and GlcNAc-bearing polymers could interact with cell surface vimentin and desmin. In the current study, it was demonstrated that a multivalent GlcNAc moiety structure of these molecules activated PI3K/Akt and p38MAPK pathway and elicited these anti-fibrotic activities in myofibroblasts by interacting with cell surface vimentin. Since the interaction of O-GlcNAc-modified proteins with desmin was observed in the fibrotic liver of carbon tetrachloride-treated mice via an in situ proximity ligation assay, it was assumed that the activated stellate cells could bind to the O-GlcNAc-modified proteins from the damaged hepatocytes. In addition, the administration of anti-O-GlcNAc antibody to inhibit the interaction exacerbated liver fibrosis in the mice. Moreover, administration of the GlcNAc-bearing polymers into carbon tetrachloride-treated mice could ameliorate liver fibrosis. Thus, O-GlcNAc-modified proteins leaked from dead cells can interact with myofibroblasts and activated stellate cells and function as fibrosis suppressors. Moreover, we anticipate that GlcNAc-bearing polymers mimicking O-GlcNAc-modified proteins will be applied as novel therapeutic tools for fibrosis.

Curcumin Prevents the Glycation of Tricarboxylic Acid Cycle and Cell Respiration Proteins in the Heart of Mice Fed with a High-Fructose Diet

BACKGROUND

A high fructose diet (HFD) induces protein glycation. The latter is related to a higher risk of cardiovascular disease. Curcumin is a natural pleiotropic compound that may possess antiglycant properties.

OBJECTIVE

To analyze the effect of curcumin on the content of glycated proteins in the hearts of 6-week-old mice fed with a HFD for 15 weeks.

METHODS

Mice were allocated in four groups (n = 6/group): a control group that received a standard diet (CT); a group that received 30% w/v fructose in water (F); a group that received 0.75% w/w curcumin supplemented in food (C); a group that received 30% w/v fructose in water and 0.75% w/w curcumin supplemented in food (F+C). The content of glycated proteins in the heart was determined by Western Blot (whereas the spots were detected by 2D-PAGE) using anti-AGE and anti-CML antibodies. A densitometric analysis was performed using the ImageLab software. Glycated proteins were identified by MALDI-TOF-MS, and an ontological analysis was performed in terms of biological processes and molecular function based on the STRING and DAVID databases.

RESULTS

Fourteen glycated protein spots were detected, two of them with anti-AGE and the other 12 with anti-CML. In total, eleven glycated proteins were identified, out of which three had decreased glycation levels due to curcumin exposure. The identified proteins participate in processes such as cellular respiration, oxidative phosphorylation, lipid metabolism, carbohydrate metabolism, the tricarboxylic acid cycle (TAC), and the organization of intermediate filaments.

CONCLUSIONS

Curcumin decreased the fructose-induced glycation level of the ACO2, NDUFS7, and DLAT proteins.

MicroSPECT Imaging-Guided Treatment of Idiopathic Pulmonary Fibrosis in Mice with a Vimentin-Targeting 99mTc-Labeled N-Acetylglucosamine-Polyethyleneimine

Idiopathic pulmonary fibrosis (IPF) is a progressive fibrotic disease with poor prognosis. Evidence has shown that vimentin is a key regulator of lung fibrogenesis. ^99mTc-labeled N-acetylglucosamine-polyethyleneimine (NAG-PEI), a vimentin-targeting radiotracer, was used for the early diagnosis of IPF, and NAG-PEI was also used as a therapeutic small interfering RNA (siRNA) delivery vector for the treatment of IPF in this study. Single-photon emission-computed tomography (SPECT) imaging of bleomycin (BM)- and silica-induced IPF mice with ^99mTc-labeled NAG-PEI was performed to visualize pulmonary fibrosis and monitor the treatment efficiency of siRNA-loaded NAG-PEI, lipopolysaccharide (LPS, a tolerogenic adjuvant), or zymosan (ZYM, an immunostimulant). The lung uptakes of ^99mTc-NAG-PEI in the BM- and silica-induced IPF mice were clearly and directly correlated with IPF progression. The lung uptake of ^99mTc-NAG-PEI in the NAG-PEI/TGF-β1-siRNA treatment group or LPS treatment group was evidently lower than that in the control group, while the lung uptake of ^99mTc-NAG-PEI was significantly higher in the ZYM treatment group compared to that in the control group. These results demonstrate that NAG-PEI is a potent MicroSPECT imaging-guided theranostic platform for IPF diagnosis and therapy.

Interactions of N-acetyl-D-glucosamine-conjugated silk fibroin with lectins, cytoskeletal proteins and cardiomyocytes

We have reported that cytoskeletal proteins such as desmin and vimentin are expressed on the surface of muscle, mesenchymal and cancer cells, and possess N-acetyl-β-D-glucosamine (β-GlcNAc) residue-binding properties. As cell-recognizable β-GlcNAc residue-bearing biopolymer, we prepared glycoconjugates (SF-GlcNAc) composed of silk fibroin (SF) and monosaccharide N-acetyl-D-glucosamine (GlcNAc) by chemical modification using cyanuric chloride. The covalent immobilization of GlcNAc into SF was assessed by ¹H-NMR measurements. The ¹H-NMR spectrum of SF-GlcNAc conjugates showed new peaks attributed to the methyl protons of the N-acetyl group in GlcNAc, and the integration of these peaks revealed that the GlcNAc content in the conjugates was 9 wt%. The existence of β-GlcNAc residues in SF-GlcNAc was examined by the criteria using lectins such as wheat germ agglutinin (WGA). Addition of WGA to SF-GlcNAc solution caused an increase in the turbidity of the solution due to lectin-mediated aggregation. Solid-phase lectin binding assay based on the biotin-avidin interaction showed that biotinylated succinylated WGA bound more strongly onto SF-GlcNAc conjugate-coated wells compared to SF-coated well. Following the establishment of the existence of β-GlcNAc residues in SF-GlcNAc, the interaction of SF-GlcNAc with desmin was examined by enzyme-linked immunosorbent assay using anti-desmin antibody. The stronger binding of desmin was observed for SF-GlcNAc conjugate-coated wells compared to SF-coated wells. The use of SF-GlcNAc conjugates as a substrate for culturing desmin-expressing human cardiac myocytes demonstrated an increase in the numbers of attached cells and proliferating cells on the conjugate-coated wells compared to SF-coated wells. These results suggest that the immobilization of monosaccharide GlcNAc is a useful method for the versatile functionalization of SF as an application in tissue engineering.

Development of a Gene Delivery System of Oligonucleotides for Fibroses by Targeting Cell-Surface Vimentin-Expressing Cells with N-Acetylglucosamine-Bearing Polymer-Conjugated Polyethyleneimine

Targeting myofibroblasts and activated stellate cells in lesion sites of fibrotic tissues is an important approach to treat fibroses. Herein, we focused on targeting the cytoskeletal proteins vimentin, which are reportedly highly expressed on the surface of these cells and have N-acetylglucosamine (GlcNAc)-binding activity. A GlcNAc-bearing polymer synthesized via radical polymerization with a reversible addition-fragmentation chain transfer reagent has been previously found to interact with cell-surface vimentin-expressing cells. We designed a GlcNAc-bearing polymer-conjugated polyethyleneimine (PEI), as the gene carrier to target cell-surface vimentin-expressing cells and specifically deliver nuclear factor-κB decoy oligonucleotides (ODNs) and heat shock protein 47 (HSP47)-small interfering RNA (siRNA) to normal human dermal fibroblasts (NHDFs) that express cell-surface vimentin. The results showed that the expression of tumor necrosis factor-α in lipopolysaccharide-stimulated NHDFs and HSP47 in transforming growth factor-β1-stimulated NHDFs was suppressed by cellular uptake of the GlcNAc-bearing polymer-conjugated PEI/nuclear factor (NF)-κB decoy ODNs and HSP47-siRNA complexes through cell-surface vimentin, respectively. These findings suggest that the effective and specific delivery of ODNs and siRNA for cell-surface vimentin-expressing cells such as myofibroblasts and activated stellate cells can be achieved using GlcNAc-bearing polymer-conjugated PEI. This therapeutic approach could prove advantageous to prevent the promotion of various fibroses.

Improved Isolation of Mesenchymal Stem Cells Based on Interactions between N-Acetylglucosamine-Bearing Polymers and Cell-Surface Vimentin

Mesenchymal stem cells (MSCs) in bone marrow and adipose tissues are expected to be effective tools for regenerative medicine to treat various diseases. To obtain MSCs that possess both high differentiation and tissue regenerative potential, it is necessary to establish an isolation system that does not require long-term culture. It has previously been reported that the cytoskeletal protein vimentin, expressed on the surfaces of multiple cell types, possesses N-acetylglucosamine- (GlcNAc-) binding activity. Therefore, we tried to exploit this interaction to efficiently isolate MSCs from rat bone marrow cells using GlcNAc-bearing polymer-coated dishes. Cells isolated by this method were identified as MSCs because they were CD34-, CD45-, and CD11b/c-negative and CD90-, CD29-, CD44-, CD54-, CD73-, and CD105-positive. Osteoblast, adipocyte, and chondrocyte differentiation was observed in these cells. In total, yields of rat MSCs were threefold to fourfold higher using GlcNAc-bearing polymer-coated dishes than yields using conventional tissue-culture dishes. Interestingly, MSCs isolated with GlcNAc-bearing polymer-coated dishes strongly expressed CD106, whereas those isolated with conventional tissue-culture dishes had low CD106 expression. Moreover, senescence-associated β-galactosidase activity in MSCs from GlcNAc-bearing polymer-coated dishes was lower than that in MSCs from tissue-culture dishes. These results establish an improved isolation method for high-quality MSCs.

Steroidal glycoalkaloids from Solanum nigrum target cytoskeletal proteins: an in silico analysis

Background

Solanum nigrum (black nightshade; S. nigrum), a member of family Solanaceae, has been endowed with a heterogeneous array of secondary metabolites of which the steroidal glycoalkaloids (SGAs) and steroidal saponins (SS) have vast potential to serve as anticancer agents. Since there has been much controversy regarding safety of use of glycoalkaloids as anticancer agents, this area has remained more or less unexplored. Cytoskeletal proteins like actin play an important role in maintaining cell shape, synchronizing cell division, cell motility, etc. and along with their accessory proteins may also serve as important therapeutic targets for potential anticancer candidates. In the present study, glycoalkaloids and saponins from S. nigrum were screened for their interaction and binding affinity to cytoskeletal proteins, using molecular docking.

Methods

Bioactivity score and Prediction of Activity Spectra for Substances (PASS) analysis were performed using softwares Molinspiration and Osiris Data Explorer respectively, to assess the feasibility of selected phytoconstituents as potential drug candidates. The results were compared with two standard reference drugs doxorubicin hydrochloride (anticancer) and tetracycline (antibiotic). Multivariate data obtained were analyzed using principal component analysis (PCA).

Results

Docking analysis revealed that the binding affinities of the phytoconstituents towards the target cytoskeletal proteins decreased in the order coronin>villin>ezrin>vimentin>gelsolin>thymosin>cofilin. Glycoalkaloid solasonine displayed the greatest binding affinity towards the target proteins followed by alpha-solanine whereas amongst the saponins, nigrumnin-I showed maximum binding affinity. PASS Analysis of the selected phytoconstituents revealed 1 to 3 violations of Lipinski’s parameters indicating the need for modification of their structure-activity relationship (SAR) for improvement of their bioactivity and bioavailability. Glycoalkaloids and saponins all had bioactivity scores between −5.0 and 0.0 with respect to various receptor proteins and target enzymes. Solanidine, solasodine and solamargine had positive values of druglikeness which indicated that these compounds have the potential for development into future anticancer drugs. Toxicity potential evaluation revealed that glycoalkaloids and saponins had no toxicity, tumorigenicity or irritant effect(s). SAR analysis revealed that the number, type and location of sugar or the substitution of hydroxyl group on alkaloid backbone had an effect on the activity and that the presence of α-L-rhamnopyranose sugar at C-2 was critical for a compound to exhibit anticancer activity.

Conclusion

The present study revealed some cytoskeletal target(s) for S. nigrum phytoconstituents by docking analysis that have not been previously reported and thus warrant further investigations both in vitro and in vivo.