Screening of pure synthetic coating substrates for induced pluripotent stem cells and iPSC-derived neuroepithelial progenitors with short peptide based integrin array

Expansion and differentiation of human neural stem cells on synthesized integrin binding peptide surfaces

The extracellular matrix plays a crucial role in the growth of human neural stem cells (hNSCs) by forming a stem cell niche, bothin vitroandin vivo. The demand for defined synthetic substrates has been increasing recently in stem cell research, reflecting the requirements for precise functions and safety concerns in potential clinical approaches. In this study, we tested the adhesion and expansion of one of the most representative hNSC lines, the ReNcell VM Human Neural Progenitor Cell Line, in a pure-synthesized short peptide-basedin vitroniche using a previously established integrin-binding peptide array. Spontaneous cell differentiation was then induced using two differentin vitroapproaches to further confirm the multipotent features of cells treated with the peptides. Twelve different integrin-binding peptides were capable of supporting hNSC adhesion and expansion at varied proliferation rates. In the ReNcell medium-based differentiation approach, cells detached in almost all peptide-based groups, except integrinα5β1 binding peptide. In an altered differentiation process induced by retinoic acid containing neural differentiation medium, cell adhesion was retained in all 12 peptide groups. These peptides also appeared to have varied effects on the differentiation potential of hNSCs towards neurons and astrocytes. Our findings provide abundant options for the development ofin vitroneural stem cell niches and will help develop promising tools for disease modeling and future stem cell therapies for neurological diseases.

Generation of induced pluripotent stem cells from rat fibroblasts and optimization of its differentiation into mature functional neurons

BACKGROUND

Induced pluripotent stem cells (iPSCs) derived neural stem cells (NSCs) provide a potential for autologous neural transplantation therapy following neurological insults. Thus far, in preclinical studies the donor iPSCs-NSCs are mostly of human or mouse origin with concerns centering around graft rejection when applied to rat brain injury models. For better survival and integration of transplanted cells in the injured brain in rat models, use of rat-iPSC-NSCs and in combination with biomaterials is of advantageous. Herein, we report a detailed method in generating rat iPSCs with improved reprogramming efficiency and differentiation into neurons.

NEW METHOD

Rat fibroblasts were reprogrammed into iPSCs with polybrene and EF1α-STEMCCA-LoxP lentivirus vector. Pluripotency characterization, differentiation into neuronal linage cells were assessed with RT-qPCR, Western blotting, immunostaining and patch-clamp methods. Cells were cultured in a custom-designed integrin array system as well as in a hydrogel-based 3D condition.

RESULTS

We describe a thorough method for the generation of rat-iPSC-NSCs, and identify integrin αvβ8 as a substrate for the optimal growth of rat-iPSC-NSCs. Furthermore, with hydrogel as the supporting biomaterial in the 3-D culture, when combined with integrin αvβ8 binding peptide, it forms a conducive environment for optimal growth and differentiation of iPSC-NSCs into mature neurons.

COMPARISON WITH EXISTING METHODS

Published studies about rat-iPSC-NSCs are rare. This study provides a detailed protocol for the generation of rat iPSC-NSCs and optimal growth conditions for neuronal differentiation. Our method is useable for studies to assess the utility of rat iPSC-NSCs for neural transplantation in rat brain injury models.

Integrin binding peptides facilitate growth and interconnected vascular-like network formation of rat primary cortical vascular endothelial cells in vitro

Neovascularization and angiogenesis in the brain are important physiological processes for normal brain development and repair/regeneration following insults. Integrins are cell surface adhesion receptors mediating important function of cells such as survival, growth and development during tissue organization, differentiation and organogenesis. In this study, we used an integrin-binding array platform to identify the important types of integrins and their binding peptides that facilitate adhesion, growth, development, and vascular-like network formation of rat primary brain microvascular endothelial cells. Brain microvascular endothelial cells were isolated from rat brain on post-natal day 7. Cells were cultured in a custom-designed integrin array system containing short synthetic peptides binding to 16 types of integrins commonly expressed on cells in vertebrates. After 7 days of culture, the brain microvascular endothelial cells were processed for immunostaining with markers for endothelial cells including von Willibrand factor and platelet endothelial cell adhesion molecule. 5-Bromo-2'-dexoyuridine was added to the culture at 48 hours prior to fixation to assess cell proliferation. Among 16 integrins tested, we found that α5β1, αvβ5 and αvβ8 greatly promoted proliferation of endothelial cells in culture. To investigate the effect of integrin-binding peptides in promoting neovascularization and angiogenesis, the binding peptides to the above three types of integrins were immobilized to our custom-designed hydrogel in three-dimensional (3D) culture of brain microvascular endothelial cells with the addition of vascular endothelial growth factor. Following a 7-day 3D culture, the culture was fixed and processed for double labeling of phalloidin with von Willibrand factor or platelet endothelial cell adhesion molecule and assessed under confocal microscopy. In the 3D culture in hydrogels conjugated with the integrin-binding peptide, brain microvascular endothelial cells formed interconnected vascular-like network with clearly discernable lumens, which is reminiscent of brain microvascular network in vivo. With the novel integrin-binding array system, we identified the specific types of integrins on brain microvascular endothelial cells that mediate cell adhesion and growth followed by functionalizing a 3D hydrogel culture system using the binding peptides that specifically bind to the identified integrins, leading to robust growth and lumenized microvascular-like network formation of brain microvascular endothelial cells in 3D culture. This technology can be used for in vitro and in vivo vascularization of transplants or brain lesions to promote brain tissue regeneration following neurological insults.

Cell-binding peptides on the material surface guide stem cell fate of adhesion, proliferation and differentiation

Human cells, especially stem cells, need to communicate and interact with extracellular matrix (ECM) proteins, which not only serve as structural components but also guide and support cell fate and properties such as cell adhesion, proliferation, survival and differentiation. The binding of the cells with ECM proteins or ECM-derived peptides via cell adhesion receptors such as integrins activates several signaling pathways that determine the cell fate, morphological change, proliferation and differentiation. The development of synthetic ECM protein-derived peptides that mimic the biological and biochemical functions of natural ECM proteins will benefit academic and clinical application. Peptides derived from or inspired by specific ECM proteins can act as agonists of each ECM protein receptor. Given that most ECM proteins function in cell adhesion via integrin receptors, many peptides have been developed that bind to specific integrin receptors. In this review, we discuss the peptide sequence, immobilization design, reaction method, and functions of several ECM protein-derived peptides. Various peptide sequences derived from mainly ECM proteins, which are used for coating or grafting on dishes, scaffolds, hydrogels, implants or nanofibers, have been developed to improve the adhesion, proliferation or differentiation of stem cells and to culture differentiated cells. This review article will help to inform the optimal choice of ECM protein-derived peptides for the development of scaffolds, implants, hydrogels, nanofibers and 2D cell culture dishes to regulate the proliferation and direct the differentiation of stem cells into specific lineages.

Design of chemically defined synthetic substrate surfaces for the in vitro maintenance of human pluripotent stem cells: A review

Human pluripotent stem cells (hPSCs) have the potential of long-term self-renewal and differentiation into nearly all cell types in vitro. Prior to the downstream applications, the design of chemically defined synthetic substrates for the large-scale proliferation of quality-controlled hPSCs is critical. Although great achievements have been made, Matrigel and recombinant proteins are still widely used in the fundamental research and clinical applications. Therefore, much effort is still needed to improve the performance of synthetic substrates in the culture of hPSCs, realizing their commercial applications. In this review, we summarized the design of reported synthetic substrates and especially their limitations in terms of cell culture. Moreover, much attention was paid to the development of promising peptide displaying surfaces. Besides, the biophysical regulation of synthetic substrate surfaces as well as the three-dimensional culture systems were described.

Bruch's-Mimetic Nanofibrous Membranes Functionalized with the Integrin-Binding Peptides as a Promising Approach for Human Retinal Pigment Epithelium Cell Transplantation

BACKGROUND

This study aimed to develop an ultrathin nanofibrous membrane able to, firstly, mimic the natural fibrous architecture of human Bruch's membrane (BM) and, secondly, promote survival of retinal pigment epithelial (RPE) cells after surface functionalization of fibrous membranes.

METHODS

Integrin-binding peptides (IBPs) that specifically interact with appropriate adhesion receptors on RPEs were immobilized on Bruch's-mimetic membranes to promote coverage of RPEs. Surface morphologies, Fourier-transform infrared spectroscopy spectra, contact angle analysis, Alamar Blue assay, live/dead assay, immunofluorescence staining, and scanning electron microscopy were used to evaluate the outcome.

RESULTS

Results showed that coated membranes maintained the original morphology of nanofibers. After coating with IBPs, the water contact angle of the membrane surfaces varied from 92.38 ± 0.67 degrees to 20.16 ± 0.81 degrees. RPE cells seeded on IBP-coated membranes showed the highest viability at all time points (Day 1, p < 0.05; Day 3, p < 0.01; Days 7 and 14, p < 0.001). The proliferation rate of RPE cells on uncoated poly(ε-caprolactone) (PCL) membranes was significantly lower than that of IBP-coated membranes (p < 0.001). SEM images showed a well-organized hexa/polygonal monolayer of RPE cells on IBP-coated membranes. RPE cells proliferated rapidly, contacted, and became confluent. RPE cells formed a tight adhesion with nanofibers under high-magnification SEM. Our findings confirmed that the IBP-coated PCL membrane improved the attachment, proliferation, and viability of RPE cells. In addition, in this study, we used serum-free culture for RPE cells and short IBPs without immunogenicity to prevent graft rejection and immunogenicity during transplantation.

CONCLUSIONS

These results indicated that the biomimic BM-IBP-RPE nanofibrous graft might be a new, practicable approach to increase the success rate of RPE cell transplantation.

An integrin-binding array platform identifies αvβ8 and α5β1 integrins on rat primary cortical neurons to support their survival and growth

BACKGROUND

Integrins are the major cell adhesion receptors expressed in almost all cell types connecting the extracellular matrix with cell cytoskeletons and transducing bi-directional signals across cell membranes. In the central nervous system (CNS), integrins are pivotal for CNS cell migration, differentiation, neurite outgrowth and synaptogenesis in both physiological and pathological conditions. Here we studied the effect of different integrin biding peptides for growth and development of primary cortical neurons in vitro.

NEW METHOD

Rat primary cortical neurons were cultured in an integrin-binding array platform, which contains immobilized varying short synthetic peptides that bind to 16 individual types of integrin on a 48-well cell culture plate. After cultured for 7 days, cells were fixed and processed for immunostaining with neuronal markers. The overall neuronal growth and neurite outgrowths were quantified.

RESULTS

We found that binding peptides for integrin α_vβ₈, α₅β₁ and α₃β₁ particularly the former two provided superior condition for neuronal growth, survival and maturation. Moreover, optimal neurite outgrowth was observed when neurons were cultured in 3-dimension using injectable hydrogel along with binding peptide for α_vβ₈ or α₅β₁ integrins.

COMPARISON WITH EXISTING METHOD

For primary neuronal culture, poly-D-lysine coating is conventional method to support cell attachment. Our study has demonstrated that selected integrin binding peptides provide greater support for the growth of cultured primary neurons.

CONCLUSION

These data suggest that integrin α_vβ₈ and α₅β₁ are conducive for survival, growth and maturation of primary cortical neurons. This information could be utilized in designing combinational biomaterial and cell-based therapy for neural regeneration following brain injury.