Recombinant Domain V of Human Perlecan Is a Bioactive Vascular Proteoglycan

Biofunctionalization of electrospun silk scaffolds with perlecan for vascular tissue engineering

Electrospun silk fibroin scaffolds have garnered significant interest in vascular tissue engineering due to their biocompatibility, mechanical strength, and tunable degradation. However, their lack of intrinsic cell-binding domains limits endothelialization, a critical factor for vascular graft success. This study explores the biofunctionalization of electrospun silk scaffolds with recombinant perlecan domain V (rDV) using plasma immersion ion implantation (PIII) treatment, a surface modification method enabling robust covalent immobilization without the use of reagents. The biofunctionalized scaffolds enhanced endothelial cell adhesion, proliferation, and retention under physiological flow conditions while inhibiting smooth muscle cell proliferation. Additionally, the functionalized scaffolds demonstrated angiogenic potential in vivo. These findings underscore the potential of rDV-functionalized silk scaffolds as a promising candidate for small-diameter vascular grafts, addressing key challenges of endothelialization and vascular cell modulation in clinical applications.

Tuning Recombinant Perlecan Domain V to Regulate Angiogenic Growth Factors and Enhance Endothelialization of Electrospun Silk Vascular Grafts

Synthetic vascular grafts are used to bypass significant arterial blockage when native blood vessels are unsuitable, yet their propensity to fail due to poor blood compatibility and progressive graft stenosis remains an intractable challenge. Perlecan is the major heparan sulfate (HS) proteoglycan in the blood vessel wall with an inherent ability to regulate vascular cell activities associated with these major graft failure modes. Here the ability of the engineered form of perlecan domain V (rDV) to bind angiogenic growth factors is tuned and endothelial cell proliferation via the composition of its glycosaminoglycan (GAG) chain is supported. It is shown that the HS on rDV supports angiogenic growth factor signaling, including fibroblast growth factor (FGF) 2 and vascular endothelial growth factor (VEGF)165, while both HS and chondroitin sulfate on rDV are involved in VEGF189 signaling. It is also shown that physisorption of rDV on emerging electrospun silk fibroin vascular grafts promotes endothelialization and patency in a murine arterial interposition model, compared to the silk grafts alone. Together, this study demonstrates the potential of rDV as a tunable, angiogenic biomaterial coating that both potentiates growth factors and regulates endothelial cells.

Diverse and multifunctional roles for perlecan (HSPG2) in repair of the intervertebral disc

Perlecan is a widely distributed, modular, and multifunctional heparan sulfate proteoglycan, which facilitates cellular communication with the extracellular environment to promote tissue development, tissue homeostasis, and optimization of biomechanical tissue functions. Perlecan-mediated osmotic mechanotransduction serves to regulate the metabolic activity of cells in tissues subjected to tension, compression, or shear. Perlecan interacts with a vast array of extracellular matrix (ECM) proteins through which it stabilizes tissues and regulates the proliferation or differentiation of resident cell populations. Here we examine the roles of the HS-proteoglycan perlecan in the normal and destabilized intervertebral disc. The intervertebral disc cell has evolved to survive in a hostile weight bearing, acidic, low oxygen tension, and low nutrition environment, and perlecan provides cytoprotection, shields disc cells from excessive compressive forces, and sequesters a range of growth factors in the disc cell environment where they aid in cellular survival, proliferation, and differentiation. The cells in mechanically destabilized connective tissues attempt to re-establish optimal tissue composition and tissue functional properties by changing the properties of their ECM, in the process of chondroid metaplasia. We explore the possibility that perlecan assists in these cell-mediated tissue remodeling responses by regulating disc cell anabolism. Perlecan's mechano-osmotic transductive property may be of potential therapeutic application.

Biomimetic strategies for the deputization of proteoglycan functions

Proteoglycans (PGs), which have glycosaminoglycan chains attached to their protein cores, are essential for maintaining the morphology and function of healthy body tissues. Extracellular PGs perform various functions, classified into the following four categories: i) the modulation of tissue mechanical properties; ii) the regulation and protection of the extracellular matrix; iii) protein sequestration; and iv) the regulation of cell signaling. The depletion of PGs may significantly impair tissue function, encompassing compromised mechanical characteristics and unregulated inflammatory responses. Since PGs play critical roles in the function of healthy tissues and their synthesis is complex, the development of PG mimetic molecules that recapitulate PG functions for tissue engineering and therapeutic applications has attracted the interest of researchers for more than 20 years. These approaches have ranged from semisynthetic graft copolymers to recombinant PG domains produced by cells that have undergone genetic modifications. This review discusses some essential extracellular PG functions and approaches to mimicking these functions.

Biomaterials containing extracellular matrix molecules as biomimetic next-generation vascular grafts

The performance of synthetic biomaterial vascular grafts for the bypass of stenotic and dysfunctional blood vessels remains an intractable challenge in small-diameter applications. The functionalization of biomaterials with extracellular matrix (ECM) molecules is a promising approach because these molecules can regulate multiple biological processes in vascular tissues. In this review, we critically examine emerging approaches to ECM-containing vascular graft biomaterials and explore opportunities for future research and development toward clinical use.

Comparison of protein quantification methods for protein encapsulation with ZIF-8 metal-organic frameworks

The use of metal-organic frameworks (MOFs) as delivery systems for biologically functional macromolecules has been explored widely in recent years due to their ability to protect their payload from a wide range of harsh conditions. Given the wide usage and diversity of potential applications, optimising the encapsulation efficiency by MOFs for different biological is of particular importance. Here, several protein quantitation methods and report were compared on the accuracy, practicality, limitations, and sensitivity of these methods to assess the encapsulation efficiency of zeolitic imidazolate frameworks (ZIF)-8 MOFs for two common biologicals commonly used in nanomedicine, bovine serum albumin (BSA), and the enzyme catalase (CAT). Using these methods, ZIF-8 encapsulation of BSA and CAT was confirmed to enrich for high molecular weight and glycosylated protein forms. However, contrary to most reports, a high degree of variance was observed across all methods assessed, with fluorometric quantitation providing the most consistent results with the lowest background and greatest dynamic range. While bicinchoninic acid (BCA) assay has showed greater detection range than the Bradford (Coomassie) assay, BCA and Bradford assays were found to be susceptible to background from the organic "MOF" linker 2-methylimidazole, reducing their overall sensitivity. Finally, while very sensitive and useful for assessing protein quality SDS-PAGE is also susceptible to confounding artifacts and background. Given the increasing use of enzyme delivery using MOFs, and the diversity of potential uses in biomedicine, identifying a rapid and efficient method of assessing biomolecule encapsulation is key to their wider acceptance.

Engineered short forms of perlecan enhance angiogenesis by potentiating growth factor signalling

Growth factors are key molecules involved in angiogenesis, a process critical for tissue repair and regeneration. Despite the potential of growth factor delivery to stimulate angiogenesis, limited clinical success has been achieved with this approach. Growth factors interact with the extracellular matrix (ECM), and particularly heparan sulphate (HS), to bind and potentiate their signalling. Here we show that engineered short forms of perlecan, the major HS proteoglycan of the vascular ECM, bind and signal angiogenic growth factors, including fibroblast growth factor 2 and vascular endothelial growth factor-A. We also show that engineered short forms of perlecan delivered in porous chitosan biomaterial scaffolds promote angiogenesis in a rat full thickness dermal wound model, with the fusion of perlecan domains I and V leading to superior vascularisation compared to native endothelial perlecan or chitosan scaffolds alone. Together, this study demonstrates the potential of engineered short forms of perlecan delivered in chitosan scaffolds as next generation angiogenic therapies which exert biological activity via the potentiation of growth factors.

Surface Biofunctionalization of Silk Biomaterials Using Dityrosine Cross-Linking

Biofunctionalization of silk biomaterial surfaces with extracellular matrix (ECM) molecules, cell binding peptides, or growth factors is important in a range of applications, including tissue engineering and development of implantable medical devices. Passive adsorption is the most common way to immobilize molecules of interest on preformed silk biomaterials but can lead to random molecular orientations and displacement from the surface, limiting their applications. Herein, we developed techniques for covalent immobilization of biomolecules using enzyme- or photoinitiated formation of dityrosine bonds between the molecule of interest and silk. Using recombinantly expressed domain V of the human basement membrane proteoglycan perlecan (rDV) as a model molecule, we demonstrated that rDV can be covalently immobilized via dityrosine cross-linking without the need to modify rDV or silk biomaterials. Dityrosine-based immobilization resulted in a different molecular orientation to passively absorbed rDV with less C- and N-terminal region exposure on the surface. Dityrosine-based immobilization supported functional rDV immobilization where immobilized rDV supported endothelial cell adhesion, spreading, migration, and proliferation. These results demonstrate the utility of dityrosine-based cross-linking in covalent immobilization of tyrosine-containing molecules on silk biomaterials in the absence of chemical modification, adding a simple and accessible technique to the silk biofunctionalization toolbox.

Perlecan, A Multi-Functional, Cell-Instructive, Matrix-Stabilizing Proteoglycan With Roles in Tissue Development Has Relevance to Connective Tissue Repair and Regeneration

This review highlights the multifunctional properties of perlecan (HSPG2) and its potential roles in repair biology. Perlecan is ubiquitous, occurring in vascular, cartilaginous, adipose, lymphoreticular, bone and bone marrow stroma and in neural tissues. Perlecan has roles in angiogenesis, tissue development and extracellular matrix stabilization in mature weight bearing and tensional tissues. Perlecan contributes to mechanosensory properties in cartilage through pericellular interactions with fibrillin-1, type IV, V, VI and XI collagen and elastin. Perlecan domain I - FGF, PDGF, VEGF and BMP interactions promote embryonic cellular proliferation, differentiation, and tissue development. Perlecan domain II, an LDLR-like domain interacts with lipids, Wnt and Hedgehog morphogens. Perlecan domain III binds FGF-7 and 18 and has roles in the secretion of perlecan. Perlecan domain IV, an immunoglobulin repeat domain, has cell attachment and matrix stabilizing properties. Perlecan domain V promotes tissue repair through interactions with VEGF, VEGF-R2 and α2β1 integrin. Perlecan domain-V LG1-LG2 and LG3 fragments antagonize these interactions. Perlecan domain V promotes reconstitution of the blood brain barrier damaged by ischemic stroke and is neurogenic and neuroprotective. Perlecan-VEGF-VEGFR2, perlecan-FGF-2 and perlecan-PDGF interactions promote angiogenesis and wound healing. Perlecan domain I, III and V interactions with platelet factor-4 and megakaryocyte and platelet inhibitory receptor promote adhesion of cells to implants and scaffolds in vascular repair. Perlecan localizes acetylcholinesterase in the neuromuscular junction and is of functional significance in neuromuscular control. Perlecan mutation leads to Schwartz-Jampel Syndrome, functional impairment of the biomechanical properties of the intervertebral disc, variable levels of chondroplasia and myotonia. A greater understanding of the functional working of the neuromuscular junction may be insightful in therapeutic approaches in the treatment of neuromuscular disorders. Tissue engineering of salivary glands has been undertaken using bioactive peptides (TWSKV) derived from perlecan domain IV. Perlecan TWSKV peptide induces differentiation of salivary gland cells into self-assembling acini-like structures that express salivary gland biomarkers and secrete α-amylase. Perlecan also promotes chondroprogenitor stem cell maturation and development of pluripotent migratory stem cell lineages, which participate in diarthrodial joint formation, and early cartilage development. Recent studies have also shown that perlecan is prominently expressed during repair of adult human articular cartilage. Perlecan also has roles in endochondral ossification and bone development. Perlecan domain I hydrogels been used in tissue engineering to establish heparin binding growth factor gradients that promote cell migration and cartilage repair. Perlecan domain I collagen I fibril scaffolds have also been used as an FGF-2 delivery system for tissue repair. With the availability of recombinant perlecan domains, the development of other tissue repair strategies should emerge in the near future. Perlecan co-localization with vascular elastin in the intima, acts as a blood shear-flow endothelial sensor that regulates blood volume and pressure and has a similar role to perlecan in canalicular fluid, regulating bone development and remodeling. This complements perlecan's roles in growth plate cartilage and in endochondral ossification to form the appendicular and axial skeleton. Perlecan is thus a ubiquitous, multifunctional, and pleomorphic molecule of considerable biological importance. A greater understanding of its diverse biological roles and functional repertoires during tissue development, growth and disease will yield valuable insights into how this impressive proteoglycan could be utilized successfully in repair biology.

Proteoglycans and proteoglycan mimetics for tissue engineering

Proteoglycans play a crucial role in proper tissue morphology and function throughout the body that is defined by a combination of their core protein and the attached glycosaminoglycan chains. Although they serve a myriad of roles, the functions of extracellular proteoglycans can be generally sorted into four categories: modulation of tissue mechanical properties, regulation and protection of the extracellular matrix, sequestering of proteins, and regulation of cell signaling. The loss of proteoglycans can result in significant tissue disfunction, ranging from poor mechanical properties to uncontrolled inflammation. Because of the key roles they play in proper tissue function and due to their complex synthesis, the past two decades have seen significant research into the development of proteoglycan mimetic molecules to recapitulate the function of proteoglycans for therapeutic and tissue engineering applications. These strategies have ranged from semisynthetic graft copolymers to recombinant proteoglycan domains synthesized by genetically engineered cells. In this review, we highlight some of the important functions of extracellular proteoglycans, as well as the strategies developed to recapitulate these functions.

Pentosan Polysulphate (PPS), a Semi-Synthetic Heparinoid DMOAD With Roles in Intervertebral Disc Repair Biology emulating The Stem Cell Instructive and Tissue Reparative Properties of Heparan Sulphate

This review highlights the attributes of pentosan polysulphate (PPS) in the promotion of intervertebral disc (IVD) repair processes. PPS has been classified as a disease modifying osteoarthritic drug (DMOAD) and many studies have demonstrated its positive attributes in the countering of degenerative changes occurring in cartilaginous tissues during the development of osteoarthritis (OA). Degenerative changes in the IVD also involve inflammatory cytokines, degradative proteases and cell signalling pathways similar to those operative in the development of OA in articular cartilage. PPS acts as a heparan sulphate (HS) mimetic to effect its beneficial effects in cartilage. The IVD contains small cell membrane HS-proteoglycans (HSPGs) such as syndecan, and glypican and a large multifunctional HS/chondroitin sulphate (CS) hybrid proteoglycan (HSPG2/perlecan) that have important matrix stabilising properties and sequester, control and present growth factors from the FGF, VEGF, PDGF and BMP families to cellular receptors to promote cell proliferation, differentiation and matrix synthesis. HSPG2 also has chondrogenic properties and stimulates the synthesis of extracellular matrix (ECM) components, expansion of cartilaginous rudiments and has roles in matrix stabilisation and repair. Perlecan is a perinuclear and nuclear proteoglycan in IVD cells with roles in chromatin organisation and control of transcription factor activity, immunolocalises to stem cell niches in cartilage, promotes escape of stem cells from quiescent recycling, differentiation and attainment of pluripotency and migratory properties. These participate in tissue development and morphogenesis, ECM remodelling and repair. PPS also localises in the nucleus of stromal stem cells, promotes development of chondroprogenitor cell lineages, ECM synthesis and repair and discal repair by resident disc cells. The availability of recombinant perlecan and PPS offer new opportunities in repair biology. These multifunctional agents offer welcome new developments in repair strategies for the IVD.

Biomimetic silk biomaterials: Perlecan-functionalized silk fibroin for use in blood-contacting devices

Blood compatible materials are required for the development of therapeutic and diagnostic blood contacting devices as blood-material interactions are a key factor dictating device functionality. In this work, we explored biofunctionalization of silk biomaterials with a recombinantly expressed domain V of the human basement membrane proteoglycan perlecan (rDV) towards the development of blood compatible surfaces. Perlecan and rDV are of interest in vascular device development as they uniquely support endothelial cell, while inhibiting smooth muscle cell and platelet interactions. rDV was covalently immobilized on silk biomaterials using plasma immersion ion implantation (PIII), a new method of immobilizing proteins on silk biomaterials that does not rely on modification of specific amino acids in the silk protein chain, and compared to physisorbed and carbodiimide immobilized rDV. Untreated and treated silk biomaterials were examined for interactions with blood components with varying degrees of complexity, including isolated platelets, platelet rich plasma, blood plasma, and whole blood, both under agitated and flow conditions. rDV-biofunctionalized silk biomaterials were shown to be blood compatible in terms of platelet and whole blood interactions and the PIII treatment was shown to be an effective and efficient means of covalently immobilizing rDV in its bioactive form. These biomimetic silk biomaterials are a promising platform toward development of silk-based blood-contacting devices for therapeutic, diagnostic, and research applications. STATEMENT OF SIGNIFICANCE: Blood compatible materials are required for the development of therapeutic and diagnostic blood contacting devices as blood-material interactions are a key factor dictating device functionality. In this work, we explored biofunctionalization of silk biomaterials with a recombinantly expressed domain V (rDV) of the human basement membrane proteoglycan perlecan towards the development of blood compatible surfaces. Perlecan and rDV are of interest in vascular device development as they uniquely support endothelial cell, while inhibiting smooth muscle cell and platelet interactions. rDV was covalently immobilized on silk biomaterials using plasma immersion ion implantation (PIII), a new method of immobilizing proteins on silk biomaterials that does not rely on modification of specific amino acids in the silk protein chain. These biomimetic silk biomaterials are a promising platform toward development of silk-based blood-contacting devices for therapeutic, diagnostic, and research applications.

Effect of Recombinant Human Perlecan Domain V Tethering Method on Protein Orientation and Blood Contacting Activity on Polyvinyl Chloride

Surface modification of biomaterials is a promising approach to control biofunctionality while retaining the bulk biomaterial properties. Perlecan is the major proteoglycan in the vascular basement membrane that supports low levels of platelet adhesion but not activation. Thus, perlecan is a promising bioactive for blood-contacting applications. This study furthers the mechanistic understanding of platelet interactions with perlecan by establishing that platelets utilize domains III and V of the core protein for adhesion. Polyvinyl chloride (PVC) is functionalized with recombinant human perlecan domain V (rDV) to explore the effect of the tethering method on proteoglycan orientation and bioactivity. Tethering of rDV to PVC is achieved via either physisorption or covalent attachment via plasma immersion ion implantation (PIII) treatment. Both methods of rDV tethering reduce platelet adhesion and activation compared to the pristine PVC, however, the mechanisms are unique for each tethering method. Physisorption of rDV on PVC orientates the molecule to hinder access to the integrin-binding region, which inhibits platelet adhesion. In contrast, PIII treatment orientates rDV to allow access to the integrin-binding region, which is rendered antiadhesive to platelets via the glycosaminoglycan (GAG) chain. These effects demonstrate the potential of rDV biofunctionalization to modulate platelet interactions for blood contacting applications.

Perlecan in Pericellular Mechanosensory Cell-Matrix Communication, Extracellular Matrix Stabilisation and Mechanoregulation of Load-Bearing Connective Tissues

In this study, we review mechanoregulatory roles for perlecan in load-bearing connective tissues. Perlecan facilitates the co-acervation of tropoelastin and assembly of elastic microfibrils in translamellar cross-bridges which, together with fibrillin and elastin stabilise the extracellular matrix of the intervertebral disc annulus fibrosus. Pericellular perlecan interacts with collagen VI and XI to define and stabilize this matrix compartment which has a strategic position facilitating two-way cell-matrix communication between the cell and its wider extracellular matrix. Cues from the extracellular matrix are fed through this pericellular matrix back to the chondrocyte, allowing it to perceive and respond to subtle microenvironmental changes to regulate tissue homeostasis. Thus perlecan plays a key regulatory role in chondrocyte metabolism, and in chondrocyte differentiation. Perlecan acts as a transport proteoglycan carrying poorly soluble, lipid-modified proteins such as the Wnt or Hedgehog families facilitating the establishment of morphogen gradients that drive tissue morphogenesis. Cell surface perlecan on endothelial cells or osteocytes acts as a flow sensor in blood and the lacunar canalicular fluid providing feedback cues to smooth muscle cells regulating vascular tone and blood pressure, and the regulation of bone metabolism by osteocytes highlighting perlecan's multifaceted roles in load-bearing connective tissues.

Strategies for re-vascularization and promotion of angiogenesis in trauma and disease

The maintenance of a healthy vascular system is essential to ensure the proper function of all organs of the human body. While macrovessels have the main role of blood transportation from the heart to all tissues, microvessels, in particular capillaries, are responsible for maintaining tissues' functionality by providing oxygen, nutrients and waste exchanges. Occlusion of blood vessels due to atherosclerotic plaque accumulation remains the leading cause of mortality across the world. Autologous vein and artery grafts bypassing are the current gold standard surgical procedures to substitute primarily obstructed vascular structures. Ischemic scenarios that condition blood supply in downstream tissues may arise from blockage phenomena, as well as from other disease or events leading to trauma. The (i) great demand for new vascular substitutes, arising from both the limited availability of healthy autologous vessels, as well as the shortcomings associated with small-diameter synthetic vascular grafts, and (ii) the challenging induction of the formation of adequate and stable microvasculature are current driving forces for the growing interest in the development of bioinspired strategies to ensure the proper function of vasculature in all its dimensional scales. Here, a critical review of well-established technologies and recent biotechnological advances to substitute or regenerate the vascular system is provided.

Skin wound healing assisted by angiogenic targeted tissue engineering: A comprehensive review of bioengineered approaches

Skin injuries and in particular, chronic wounds, are one of the major prevalent medical problems, worldwide. Due to the pivotal role of angiogenesis in tissue regeneration, impaired angiogenesis can cause several complications during the wound healing process and skin regeneration. Therefore, induction or promotion of angiogenesis can be considered as a promising approach to accelerate wound healing. This article presents a comprehensive overview of current and emerging angiogenesis induction methods applied in several studies for skin regeneration, which are classified into the cell, growth factor, scaffold, and biological/chemical compound-based strategies. In addition, the advantages and disadvantages of these angiogenic strategies along with related research examples are discussed in order to demonstrate their potential in the treatment of wounds.

A Biomimetic Approach toward Enhancing Angiogenesis: Recombinantly Expressed Domain V of Human Perlecan Is a Bioactive Molecule That Promotes Angiogenesis and Vascularization of Implanted Biomaterials

Angiogenic therapy involving delivery of pro-angiogenic growth factors to stimulate new blood vessel formation in ischemic disease is promising but has seen limited clinical success due to issues associated with the need to deliver supra-physiological growth factor concentrations. Bio-inspired growth factor delivery utilizing the native growth factor signaling roles of the extracellular matrix proteoglycans has the potential to overcome many of the drawbacks of angiogenic therapy. In this study, the potential of the recombinantly expressed domain V (rDV) of human perlecan is investigated as a means of promoting growth factor signaling toward enhanced angiogenesis and vascularization of implanted biomaterials. rDV is found to promote angiogenesis in established in vitro and in vivo angiogenesis assays by potentiating endogenous growth factor signaling via its glycosaminoglycan chains. Further, rDV is found to potentiate fibroblast growth factor 2 (FGF2) signaling at low concentrations that in the absence of rDV are not biologically active. Finally, rDV immobilized on 3D porous silk fibroin biomaterials promotes enhanced vascular ingrowth and integration of the implanted scaffolds with the surrounding tissue. Together, these studies demonstrate the important role of this biologically active perlecan fragment and its potential in the treatment of ischemia in both native and bioengineered tissues.

Heparan Sulfate Proteoglycans in Human Colorectal Cancer

Colorectal cancer is the third most common cancer worldwide, accounting for more than 610,000 mortalities every year. Prognosis of patients is highly dependent on the disease stage at diagnosis. Therefore, it is crucial to investigate molecules involved in colorectal cancer tumorigenesis, with possible use as tumor markers. Heparan sulfate proteoglycans are complex molecules present in the cell membrane and extracellular matrix, which play vital roles in cell adhesion, migration, proliferation, and signaling pathways. In colorectal cancer, the cell surface proteoglycan syndecan-2 is upregulated and increases cell migration. Moreover, expression of syndecan-1 and syndecan-4, generally antitumor molecules, is reduced. Levels of glypicans and perlecan are also altered in colorectal cancer; however, their role in tumor progression is not fully understood. In addition, studies have reported increased heparan sulfate remodeling enzymes, as the endosulfatases. Therefore, heparan sulfate proteoglycans are candidate molecules to clarify colorectal cancer tumorigenesis, as well as important targets to therapy and diagnosis.