Browsing by Author "Mammadov, Busra"

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Open Access
Cooperative effect of heparan sulfate and laminin mimetic peptide nanofibers on the promotion of neurite outgrowth
(Elsevier, 2012) Mammadov, Busra; Mammadov, Rashad; Güler, Mustafa O.; Tekinay, Ayse B.
Extracellular matrix contains an abundant variety of signals that are received by cell surface receptors contributing to cell fate, via regulation of cellular activities such as proliferation, migration and differentiation. Cues from extracellular matrix can be used for the development of materials to direct cells into their desired fate. Neural extracellular matrix (ECM) is rich in axonal growth inducer proteins, and by mimicking these permissive elements in the cellular environment, neural differentiation as well as neurite outgrowth can be induced. In this paper, we used a synthetic peptide nanofiber system that can mimic not only the activity of laminin, an axonal growth-promoting constituent of the neural ECM, but also the activity of heparan sulfate proteoglycans in order to induce neuritogenesis. Heparan sulfate mimetic groups that were utilized in our system have an affinity to growth factors and induce the neuroregenerative effect of laminin mimetic peptide nanofibers. The self-assembled peptide nanofibers with heparan sulfate mimetic and laminin-derived epitopes significantly promoted neurite outgrowth by PC-12 cells. In addition, these scaffolds were even effective in the presence of chondroitin sulfate proteoglycans (CSPGs), which are the major inhibitory components of the central nervous system. In the presence of these nanofibers, cells could overcome CSPG inhibitory effect and extend neurites on peptide nanofiber scaffolds. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
Open Access
Extracellular matrix mimetic peptide scaffolds for neural stem cell culture and differentiation
(Humana Press, 2014) Mammadov, Busra; Güler, Mustafa O.; Tekinay, Ayşe B.
Self-assembled peptide nanofibers form three-dimensional networks that are quite similar to fibrous extracellular matrix (ECM) in their physical structure. By incorporating short peptide sequences derived from ECM proteins, these nanofibers provide bioactive platforms for cell culture studies. This protocol provides information about preparation and characterization of self-assembled peptide nanofiber scaffolds, culturing of neural stem cells (NSCs) on these scaffolds, and analysis of cell behavior. As cell behavior analyses, viability and proliferation of NSCs as well as investigation of differentiation by immunocytochemistry, qRT-PCR, western blot, and morphological analysis on ECM mimetic peptide nanofiber scaffolds are described.
Open Access
Growth factor binding on heparin mimetic peptide nanofibers
(American Chemical Society, 2012) Mammadov, Rashad; Mammadov, Busra; Güler, Mustafa O.; Tekinay, Ayşe B.
Immobilization of growth factors in scaffolds is important for controlling their dose and bioactivity for regenerative medicine applications. Although numerous covalent and noncovalent immobilization strategies have been proposed, better growth factor loading and dose control inside the scaffold is necessary. Nature of the binding site on the growth factor interacting with scaffold is critical for preserving and achieving maximal growth factor functionality, which has been a relatively less emphasized issue in previous studies. We recently reported heparin mimetic peptide nanofibers, which mimic chemistry of heparan sulfates. Heparin mimetic nanofibers were shown to bind to vascular endothelial growth factor (VEGF) and direct endothelial cells to angiogenesis. Here, we further investigated interactions between heparin mimetic peptide nanofibers and growth factors. We tested bioactivity of the nanofiber bound growth factors in order to understand the potential use of these peptide nanofiber scaffolds as analogues of heparan sulfates. We observed that heparin mimetic peptide nanofibers demonstrate better binding profiles to VEGF, hepatocyte growth factor (HGF), and fibroblast growth factor-2 (FGF-2) than control peptide nanofibers. We also identified that the heparin-binding domain of VEGF is critical for its interaction with these nanofibers. However, the heparin-binding site is not indispensable for binding of all growth factors to nanofibers. We also showed that binding of growth factors to nanofibers does not cause any loss in bioactivity through in vitro cell culture assays with PC-12 cells. These results reveal that heparin mimetic peptide nanofibers can effectively mimic heparan sulfates in extracellular matrix and provide an optimal milieu for spatial presentation of important growth factors. These properties make peptide nanofiber scaffolds promising materials for regenerative medicine applications through efficient and precisely controlled growth factor delivery. © 2012 American Chemical Society.
Open Access
Heparin mimetic peptide nanofibers promote angiogenesis
(Biomacromolecules, 2011) Mammadov, Rashad; Mammadov, Busra; Toksoz, Sıla; Aydin, B.; Yagci, R.; Tekinay, Ayse B.; Güler, Mustafa O.
New blood vessel formation (angiogenesis) is one of the most important processes required for functional tissue formation. Induction of angiogenesis is usually triggered by growth factors released by cells. Glycosaminoglycans (e.g., heparan sulphates) in the extracellular matrix aid in proper functioning of these growth factors. Therefore, exogeneous heparin or growth factors were required for promoting angiogenesis in previous regenerative medicine studies. Here we report for the first time induction of angiogenesis by a synthetic nanofibrous peptide scaffold without the addition of any exogenous growth factors or heparin. We designed and synthesized a self-assembling peptide amphiphile molecule that is functionalized with biologically active groups to mimic heparin. Like heparin, this molecule has the ability to interact with growth factors and effectively enhance their bioactivity. The nanofibers formed by these molecules were shown to form a 3D network mimicking the structural proteins in the extracellular matrix. Because of heparin mimicking capabilities of the peptide nanofibers, angiogenesis was induced without the addition of exogenous growth factors in vitro. Bioactive interactions between the nanofibers and the growth factors enabled robust vascularization in vivo as well. Heparin mimetic peptide nanofibers presented here provide new opportunities for angiogenesis and tissue regeneration by avoiding the use of heparin and exogenous growth factors. The synthetic peptide nanofiber scaffolds enriched with proper chemical functional groups shown in this study can be used to induce various desired physiological responses for tissue regeneration. © 2011 American Chemical Society.
Open Access
Neural differentiation on synthetic scaffold materials
(Royal Society of Chemistry, 2013) Mammadov, Busra; Sever, Melike; Güler, Mustafa O.; Tekinay, Ayşe B.
The potential of stem cells to differentiate into a variety of subgroups of neural cells makes stem cell differentiation and transplantation a promising candidate for neurodegenerative disorder therapies. However, selective differentiation of stem cells to neurons while preventing glial scar formation is a complex process. Mimicking the natural environment of neural tissue is pivotal, thus various synthetic materials have been developed for this purpose. The synthetic scaffolds can direct stem cells into a neural lineage by including extracellular factors that act on cell fate, which are mainly soluble signals, extracellular matrix proteins and physical factors (e.g. elasticity and topography). This article reviews synthetic materials developed for neural regeneration in terms of their extracellular matrix mimicking properties. Functionalization of synthetic materials by addition of bioactive chemical groups and adjustment of physical properties such as topography, electroactivity and elasticity are discussed. © The Royal Society of Chemistry.
Open Access
Tenascin-C mimetic peptide nanofibers direct stem cell differentiation to osteogenic lineage
(American Chemical Society, 2014) Sever, Melike; Mammadov, Busra; Güler, Mustafa O.; Tekinay, Ayşe B.
Extracellular matrix contains various signals for cell surface receptors that regulate cell fate through modulation of cellular activities such as proliferation and differentiation. Cues from extracellular matrix components can be used for development of new materials to control the stem cell fate. In this study, we achieved control of stem cell fate toward osteogenic commitment by using a single extracellular matrix element despite the contradictory effect of mechanical stiffness. For this purpose, we mimicked bone extracellular matrix by incorporating functional sequence of fibronectin type III domain from native tenascin-C on self-assembled peptide nanofibers. When rat mesenchymal stem cells (rMSCs) were cultured on these peptide nanofibers, alkaline phosphatase (ALP) activity and alizarin red staining indicated osteogenic differentiation even in the absence of osteogenic supplements. Moreover, expression levels of osteogenic marker genes were significantly enhanced revealed by quantitative real-time polymerase chain reaction (qRT-PCR), which showed the remarkable bioactive role of this nanofiber system on osteogenic differentiation. Overall, these results showed that tenascin-C mimetic peptides significantly enhanced the attachment, proliferation, and osteogenic differentiation of rMSCs even in the absence of any external bioactive factors and regardless of the suitable stiff mechanical properties normally required for osteogenic differentiation. Thus, these peptide nanofibers provide a promising new platform for bone regeneration. © 2014 American Chemical Society.