Mice that lack the angiogenesis inhibitor, thrombospondin 2, mount an altered foreign body reaction characterized by increased vascularity

Harnessing IL-10 induced anti-inflammatory response in maturing macrophages in presence of electrospun dexamethasone-loaded PLLA scaffold

The ultimate goal of tissue engineering is to repair and regenerate damaged tissue or organ. Achieving this goal requires blood vessel networks to supply oxygen and nutrients to new forming tissues. Macrophages are part of the immune system whose behavior plays a significant role in angiogenesis and blood vessel formation. On the other hand, macrophages are versatile cells that change their behavior in response to environmental stimuli. Given that implantation of a biomaterial is followed by inflammation; therefore, we reasoned that this inflammatory condition in tissue spaces modulates the final phenotype of macrophages. Also, we hypothesized that anti-inflammatory glucocorticoid dexamethasone improves modulating macrophages behavior. To check these concepts, we investigated the macrophages that had matured in an inflammatory media. Furthermore, we examined macrophages' behavior after maturation on a dexamethasone-containing scaffold and analyzed how the behavioral change of maturing macrophages stimulates other macrophages in the same environment. In this study, the expression of pro-inflammatory markers TNFa and NFκB1 along with pro-healing markers IL-10 and CD163 were investigated to study the behavior of macrophages. Our results showed that macrophages that were matured in the inflammatory media in vitro increase expression of IL-10, which in turn decreased the expression of pro-inflammatory markers TNFa and NFκB in maturing macrophages. Also, macrophages that were matured on dexamethasone-containing scaffolds decreased the expression of IL-10, TNFa, and NFκB and increase the expression of CD163 compared to the control group. Moreover, the modulation of anti-inflammatory response in maturing macrophages on dexamethasone-containing scaffold resulted in increased expression of TNFa and CD163 by other macrophages in the same media. The results obtained in this study, proposing strategies to improve healing through controlling the behavior of maturing macrophages and present a promising perspective for inflammation control using tissue engineering scaffolds.

The foreign body response: emerging cell types and considerations for targeted therapeutics

The foreign body response (FBR) remains a clinical challenge in the field of biomaterials due to its ability to elicit a chronic and sustained immune response. Modulating the immune response to materials is a modern paradigm in tissue engineering to enhance repair while limiting fibrous encapsulation and implant isolation. Though the classical mediators of the FBR are well-characterized, recent studies highlight that our understanding of the cell types that shape the FBR may be incomplete. In this review, we discuss the emerging role of T cells, stromal-immune cell interactions, and senescent cells in the biomaterial response, particularly to synthetic materials. We emphasize future studies that will deepen the field's understanding of these cell types in the FBR, with the goal of identifying therapeutic targets that will improve implant integration. Finally, we briefly review several considerations that may influence our understanding of the FBR in humans, including rodent models, aging, gut microbiota, and sex differences. A better understanding of the heterogeneous host cell response during the FBR can enable the design and development of immunomodulatory materials that favor healing.

Molecular mechanisms of Thrombospondin-2 modulates tumor vasculogenic mimicry by PI3K/AKT/mTOR signaling pathway

Vasculogenic mimicry (VM) differs from the classical tumor angiogenesis model. VM does not depend on endothelial cells; instead, highly aggressive tumor cells mimic endothelial cells to form a vascular-like channel structure. VM mediated by tumor cells is significantly and positively associated with a poor prognosis and low survival rates in patients with highly aggressive cancer. In the treatment of highly aggressive malignancies, the presence of VM is considered an important reason for the unsatisfactory clinical efficacy of anti-tumor-angiogenesis therapy (e.g., therapy targeting vascular endothelial growth factor A). Many targeted therapeutic drugs based on traditional tumor blood vessels have been used clinically. Although some progress has been made in certain tumors, problems such as drug resistance have restricted the expected therapeutic effects. Thrombospondin 2 (THBS2) is one of the most important genes associated with angiogenesis, and this gene exerts angiogenesis-related functions through the PI3K/AKT signaling pathway. Although the PI3K/AKT/mTOR signaling pathway is closely related to the progression of VM, the mechanism by which the promising biomarker THBS2 participates in and regulates tumor VM by activating the PI3K/AKT/mTOR signaling pathway is unclear. In this review, we analyze the monomer structure and biological activity of THBS2, the structure and potential synthesis mechanisms of VM, and the complex mechanisms between THBS2, the PI3K/AKT/mTOR signaling pathway, and VM.

Matricellular proteins in cutaneous wound healing

Cutaneous wound healing is a complex process that encompasses alterations in all aspects of the skin including the extracellular matrix (ECM). ECM consist of large structural proteins such as collagens and elastin as well as smaller proteins with mainly regulative properties called matricellular proteins. Matricellular proteins bind to structural proteins and their functions include but are not limited to interaction with cell surface receptors, cytokines, or protease and evoking a cellular response. The signaling initiated by matricellular proteins modulates differentiation and proliferation of cells having an impact on the tissue regeneration. In this review we give an overview of the matricellular proteins that have been found to be involved in cutaneous wound healing and summarize the information known to date about their functions in this process.

Designing electrospun fiber platforms for efficient delivery of genetic material and genome editing tools

Electrospun fibers are versatile biomaterial platforms with great potential to support regeneration. Electrospun fiber characteristics such as fiber diameter, degree of alignment, rate of degradation, and surface chemistry enable the creation of unique, tunable scaffolds for various drug or gene delivery applications. The delivery of genetic material and genome editing tools via viral and non-viral vectors are approaches to control cellular protein production. However, immunogenicity, off-target effects, and low delivery efficiencies slow the progression of gene delivery strategies to clinical settings. The delivery of genetic material from electrospun fibers overcomes such limitations by allowing for localized, tunable delivery of genetic material. However, the process of electrospinning is harsh, and care must be taken to retain genetic material bioactivity. This review presents an up-to-date summary of strategies to incorporate genetic material onto or within electrospun fiber platforms to improve delivery efficiency and enhance the regenerative potential of electrospun fibers for various tissue engineering applications.

Fibrin polymer on the surface of biomaterial implants drives the foreign body reaction

Implantation of biomaterials and medical devices in the body triggers the foreign body reaction (FBR) which is characterized by macrophage fusion at the implant surface leading to the formation of foreign body giant cells and the development of the fibrous capsule enveloping the implant. While adhesion of macrophages to the surface is an essential step in macrophage fusion and implanted biomaterials are known to rapidly acquire a layer of host proteins, a biological substrate that is responsible for this process in vivo is unknown. Here we show that mice with genetically imposed fibrinogen deficiency display a dramatic reduction of macrophage fusion on biomaterials implanted intraperitoneally and subcutaneously and are protected from the formation of the fibrin-containing fibrous capsule. Furthermore, macrophage fusion on biomaterials implanted in Fib^AEK mice that express a mutated form of fibrinogen incapable of thrombin-mediated polymerization was strongly reduced. Despite the lack of fibrin, the capsule was formed in Fib^AEK mice, although it had a different composition and distinct mechanical properties than that in wild-type mice. Specifically, while mononuclear α-SMA-expressing macrophages embedded in the capsule of both strains of mice secreted collagen, the amount of collagen and its density in the tissue of Fib^AEK mice was reduced. These data identify fibrin polymer as a key biological substrate driving the development of the FBR.

Functions of Thrombospondin-1 in the Tumor Microenvironment

The identification of thrombospondin-1 as an angiogenesis inhibitor in 1990 prompted interest in its role in cancer biology and potential as a therapeutic target. Decreased thrombospondin-1 mRNA and protein expression are associated with progression in several cancers, while expression by nonmalignant cells in the tumor microenvironment and circulating levels in cancer patients can be elevated. THBS1 is not a tumor suppressor gene, but the regulation of its expression in malignant cells by oncogenes and tumor suppressor genes mediates some of their effects on carcinogenesis, tumor progression, and metastasis. In addition to regulating angiogenesis and perfusion of the tumor vasculature, thrombospondin-1 limits antitumor immunity by CD47-dependent regulation of innate and adaptive immune cells. Conversely, thrombospondin-1 is a component of particles released by immune cells that mediate tumor cell killing. Thrombospondin-1 differentially regulates the sensitivity of malignant and nonmalignant cells to genotoxic stress caused by radiotherapy and chemotherapy. The diverse activities of thrombospondin-1 to regulate autophagy, senescence, stem cell maintenance, extracellular vesicle function, and metabolic responses to ischemic and genotoxic stress are mediated by several cell surface receptors and by regulating the functions of several secreted proteins. This review highlights progress in understanding thrombospondin-1 functions in cancer and the challenges that remain in harnessing its therapeutic potential.

Role of thrombospondin‑1 and thrombospondin‑2 in cardiovascular diseases (Review)

Thrombospondin (TSP)-1 and TSP-2 are matricellular proteins in the extracellular matrix (ECM), which serve a significant role in the pathological processes of various cardiovascular diseases (CVDs). The multiple effects of TSP-1 and TSP-2 are due to their ability to interact with various ligands, such as structural components of the ECM, cytokines, cellular receptors, growth factors, proteases and other stromal cell proteins. TSP-1 and TSP-2 regulate the structure and activity of the aforementioned ligands by interacting directly or indirectly with them, thereby regulating the activity of different types of cells in response to environmental stimuli. The pathological processes of numerous CVDs are associated with the degradation and remodeling of ECM components, and with cell migration, dysfunction and apoptosis, which may be regulated by TSP-1 and TSP-2 through different mechanisms. Therefore, investigating the role of TSP-1 and TSP-2 in different CVDs and the potential signaling pathways they are associated with may provide a new perspective on potential therapies for the treatment of CVDs. In the present review, the current understanding of the roles TSP-1 and TSP-2 serve in various CVDs were summarized. In addition, the interacting ligands and the potential pathways associated with these thrombospondins in CVDs are also discussed.

TSP1 and TSP2 deficiencies affect LOX protein distribution in the femoral diaphysis and pro-peptide removal in marrow-derived mesenchymal stem cells in vitro

Thrombospondin-1 and 2 have each been implicated in collagen fibrillogenesis. We addressed the possibility that deficits in lysyl oxidase (LOX) contribute to the extracellular matrix (ECM) phenotype of TSP-deficient bone. We examined detergent insoluble (mature cross-linked) and soluble (newly secreted) ECM fractions prepared from diaphyseal cortical bone. Detergent-insoluble hydroxyproline content, an indicator of cross-linked collagen content and LOX function, was reduced in female TSP-deficient bones. In male diaphyses, only TSP2 deficiency affected insoluble hydroxyproline content. Western blot suggested that removal of the LOX-pro-peptide (LOPP), an indication of LOX activation, was not affected by TSP status. Instead, the distribution of pro-LOX and mature LOX between immature and mature ECM was altered by TSP-status. LOX was also examined in primary marrow-derived mesenchymal stem cells (MSC) treated with ascorbate. Relative LOPP levels were elevated compared to WT in MSC conditioned medium from female TSP-deficient mice. When cells were serum starved to limit LOX pro-peptide removal, pro-LOX levels were elevated in TSP2-/- cells compared to wild-type. This phenotype was associated with a transient increase in BMP1 levels in TSP2-/- conditioned medium. TSP2 was detected in bone tissue and osteoblast cell culture. TSP1 was only detected in insoluble ECM prepared from WT diaphyseal bone samples. Our data suggest that the trimeric thrombospondins contribute to bone matrix quality by regulating the distribution of pro and mature LOX between newly secreted, immature ECM and mature, cross-linked ECM.

Thrombospondin-4 increases with the severity of peripheral arterial disease and is associated with diabetes

Thrombospondin-4 (TSP-4) is an extracellular matrix protein of the vessel wall. Despite bench evidence, its significance in the clinical setting of atherosclerosis is missing. TSP-4 (ng/ml) was measured in 365 PAD patientsusing a commercially available ELISA. PAD was diagnosed by the ankle–brachial index (ABI) and clinically graded using the Fontaine classification. TSP-4 levels were significantly higher in Fontaine II vs. Fontaine I (4.78 ± 0. 42, 4.69 ± 0.42, p = 0.043). TSP-4 significantly correlated with ABI (r = − 0.141, p = 0.023, n = 259) after the exclusion of mediasclerotic patients. Binary logistic regression analysis for Fontaine I vs. II showed an OR of 1.70 (1.02–2.82) in a multivariable model adjusted for traditional risk factors. Interestingly, TSP-4 levels were higher in patients with type 2 diabetes mellitus or prediabetes (DGT) compared with normal glucose tolerance (NGT) (4.76 ± 0.42 vs. 4.66 ± 0.41, p = 0.035). ANOVA for PAD and diabetes subgroups showed a linear increase with disease burden with the highest difference between Fontaine I-NGT and Fontaine II-DGT (4.59 ± 0.40, 4.79 ± 0.43, p = 0.015). TSP-4 levels increased with PAD severity and showed a former unknown association with diabetes. Thus, TSP-4 could be a novel marker of atherosclerotic activity, especially in the major subgroup of patients with concomitant diabetes.

Cancer-derived exosomal miR-221-3p promotes angiogenesis by targeting THBS2 in cervical squamous cell carcinoma

AIMS

Recently, cancer-derived exosomes were shown to have pro-metastasis function in cancer, but the mechanism remains unclear. Angiogenesis is essential for tumor progression and is a great promising therapeutic target for advanced cervical cancer. Here, we investigated the role of cervical cancer cell-secreted exosomal miR-221-3p in tumor angiogenesis.

METHODS AND RESULTS

miR-221-3p was found to be closely correlated with microvascular density in cervical squamous cell carcinoma (CSCC) by evaluating the microvascular density with immunohistochemistry and miR-221-3p expression with in situ hybridization in clinical specimens. Using the groups of CSCC cell lines (SiHa and C33A) with miR-221-3p overexpression and silencing, the CSCC exosomes were characterized by electron microscopy, western blotting, and fluorescence microscopy. The enrichment of miR-221-3p in CSCC exosomes and its transfer into human umbilical vein endothelial cells (HUVECs) were confirmed by qRT-PCR. CSCC exosomal miR-221-3p promoted angiogenesis in vitro in Matrigel tube formation assay, spheroid sprouting assay, migration assay, and wound healing assay. Then, exosome intratumoral injection indicated that CSCC exosomal miR-221-3p promoted tumor growth in vivo. Thrombospondin-2 (THBS2) was bioinformatically predicted to be a direct target of miR-221-3p, and this was verified by using the in vitro and in vivo experiments described above. Additionally, overexpression of THBS2 in HUVECs rescued the angiogenic function of miR-221-3p.

CONCLUSIONS

Our results suggest that CSCC exosomes transport miR-221-3p from cancer cells to vessel endothelial cells and promote angiogenesis by downregulating THBS2. Therefore, CSCC-derived exosomal miR-221-3p could be a possible novel diagnostic biomarker and therapeutic target for CSCC progression.

Domesticating the foreign body response: Recent advances and applications

The foreign body response is an immunological process that leads to the rejection of implanted devices and presents a fundamental challenge to their performance, durability, and therapeutic utility. Recent advances in materials development and device design are now providing strategies to overcome this immune-mediated reaction. Here, we briefly review our current mechanistic understanding of the foreign body response and highlight new anti-FBR technologies from this decade that have been applied successfully in biomedical applications relevant to implants, devices, and cell-based therapies. Further development of these important technologies promises to enable new therapies, diagnostics, and revolutionize the management of patient care for many intractable diseases.

Melatonin promotes Cashmere goat (Capra hircus) secondary hair follicle growth: a view from integrated analysis of long non-coding and coding RNAs

The role of melatonin in promoting the yield of Cashmere goat wool has been demonstrated for decades though there remains a lack of knowledge regarding melatonin mediated hair follicle growth. Recent studies have demonstrated that long non-coding RNAs (lncRNAs) are widely transcribed in the genome and play ubiquitous roles in regulating biological processes. However, the role of lncRNAs in regulating melatonin mediated hair follicle growth remains unclear. In this study, we established an in vitro Cashmere goat secondary hair follicle culture system, and demonstrated that 500 ng/L melatonin exposure promoted hair follicle fiber growth. Based on long intergenic RNA sequencing, we demonstrated that melatonin promoted hair follicle elongation via regulating genes involved in focal adhesion and extracellular matrix receptor pathways and further cis predicting of lncRNAs targeted genes indicated that melatonin mediated lncRNAs mainly targeted vascular smooth muscle contraction and signaling pathways regulating the pluripotency of stem cells. We proposed that melatonin exposure not only perturbed key signals secreted from hair follicle stem cells to regulate hair follicle development, but also mediated lncRNAs mainly targeted to pathways involved in the microvascular system and extracellular matrix, which constitute the highly orchestrated microenvironment for hair follicle stem cell. Taken together, our findings here provide a profound view of lncRNAs in regulating Cashmere goat hair follicle circadian rhythms and broaden our knowledge on melatonin mediated hair follicle morphological changes.

Decellularized materials derived from TSP2-KO mice promote enhanced neovascularization and integration in diabetic wounds

Decellularized biologic scaffolds are gaining popularity over synthetic biomaterials as naturally derived materials capable of promoting improved healing. Nevertheless, the most widely used biologic material - acellular dermal matrix (ADM) - exhibits slow repopulation and remodeling, which prevents integration. Additionally, engineering control of these materials is limited because they require a natural source for their production. In the current report, we demonstrate the feasibility of using genetically engineered animals to create decellularized biologic scaffolds with favorable extracellular matrix (ECM) properties. Specifically, we utilized skin from thrombospondin (TSP)-2 KO mice to derive various decellularized products. Scanning electron microscopy and mechanical testing showed that TSP-2 KO ADM exhibited an altered structure and a reduction in elastic modulus and ultimate tensile strength, respectively. When a powdered form of KO ADM was implanted subcutaneously, it was able to promote enhanced vascularization over WT. Additionally, when implanted subcutaneously, intact slabs of KO ADM were populated by higher number of host cells when compared to WT. In vitro studies confirmed the promigratory properties of KO ADM. Specifically, degradation products released by pepsin digestion of KO ADM induced greater cell migration than WT. Moreover, cell-derived ECM from TSP-2 null fibroblasts was more permissive to fibroblast migration. Finally, ADMs were implanted in a diabetic wound model to examine their ability to accelerate wound healing. KO ADM exhibited enhanced remodeling and vascular maturation, indicative of efficient integration. Overall, we demonstrate that genetic manipulation enables engineered ECM-based materials with increased regenerative potential.

Alternative transcription of a shorter, non-anti-angiogenic thrombospondin-2 variant in cancer-associated blood vessels

Thrombospondin-2 (TSP2) is an anti-angiogenic matricellular protein that inhibits tumor growth and angiogenesis. Tumor-associated blood vascular endothelial cells (BECs) were isolated from human invasive bladder cancers and from matched normal bladder tissue by immuno-laser capture microdissection. Exon expression profiling analyses revealed a particularly high expression of a short TSP2 transcript containing only the last 9 (3′) exons of the full-length TSP2 transcript. Using 5′ and 3′ RACE (rapid amplification of cDNA ends) and Sanger sequencing, we confirmed the existence of the shorter transcript of TSP2 (sTSP2) and determined its sequence which completely lacked the anti-angiogenic thrombospondin type 1 repeats domain. The largest open reading frame predicted within the transcript comprises 209 amino acids and matches almost completely the C-terminal lectin domain of full-length TSP2. We produced recombinant sTSP2 and found that unlike the full-length TSP2, sTSP2 did not inhibit vascular endothelial growth factor-A-induced proliferation of cultured human BECs, but in contrast when combined with TSP2 blocked the inhibitory effects of TSP2 on BEC proliferation. In vivo studies with stably transfected A431 squamous cell carcinoma cells revealed that full-length TSP2, but not sTSP2, inhibited tumor growth and angiogenesis. This study reveals that the transcriptional program of tumor stromal cells can change to transcribe a new version of an endogenous angiogenesis inhibitor that has lost its anti-angiogenic activity.

Multicompartment Drug Release System for Dynamic Modulation of Tissue Responses

Pharmacological modulation of responses to injury is complicated by the need to deliver multiple drugs with spatiotemporal resolution. Here, a novel controlled delivery system containing three separate compartments with each releasing its contents over different timescales is fabricated. Core-shell electrospun fibers create two of the compartments in the system, while electrosprayed spheres create the third. Utility is demonstrated by targeting the foreign body response to implants because it is a dynamic process resulting in implant failure. Sequential delivery of a drug targeting nuclear factor-κB (NF-κB) and an antifibrotic is characterized in in vitro experiments. Specifically, macrophage fusion and p65 nuclear translocation in the presence of releasate or with macrophages cultured on the surfaces of the constructs are evaluated. In addition, releasate from pirfenidone scaffolds is shown to reduce transforming growth factor-β (TGF-β)-induced pSMAD3 nuclear localization in fibroblasts. In vivo, drug eluting constructs successfully mitigate macrophage fusion at one week and fibrotic encapsulation in a dose-dependent manner at four weeks, demonstrating effective release of both drugs over different timescales. Future studies can employ this system to improve and prolong implant lifetimes, or load it with other drugs to modulate other dynamic processes.

A Role for CD154, the CD40 Ligand, in Granulomatous Inflammation

Granulomatous inflammation is a distinctive form of chronic inflammation in which predominant cells include macrophages, epithelioid cells, and multinucleated giant cells. Mechanisms regulating granulomatous inflammation remain ill-understood. CD154, the ligand of CD40, is a key mediator of inflammation. CD154 confers a proinflammatory phenotype to macrophages and controls several macrophagic functions. Here, we studied the contribution of CD154 in a mouse model of toxic liver injury with carbon tetrachloride and a model of absorbable suture graft. In both models, granulomas are triggered in response to endogenous persistent liver calcified necrotic lesions or by grafted sutures. CD154-deficient mice showed delayed clearance of carbon tetrachloride-induced liver calcified necrotic lesions and impaired progression of suture-induced granuloma. In vitro, CD154 stimulated phagocytosis of opsonized erythrocytes by macrophages, suggesting a potential mechanism for the altered granulomatous inflammation in CD154KO mice. These results suggest that CD154 may contribute to the natural history of granulomatous inflammation.

HIF-1α represses the expression of the angiogenesis inhibitor thrombospondin-2

Thrombospondin-2 (TSP2) is a potent inhibitor of angiogenesis whose expression is dynamically regulated following injury. In the present study, it is shown that HIF-1α represses TSP2 transcription. Specifically, in vitro studies demonstrate that the prolyl hydroxylase inhibitor DMOG or hypoxia decrease TSP2 expression in fibroblasts. This effect is shown to be via a transcriptional mechanism as hypoxia does not alter TSP2 mRNA stability and this effect requires the TSP2 promoter. In addition, the documented repressive effect of nitric oxide (NO) on TSP2 is shown to be non-canonical and involves stabilization of hypoxia inducible factor-1a (HIF-1α). The regulation of TSP2 by hypoxia is supported by the in vivo observation that TSP2 has spatiotemporal expression distinct from regions of hypoxia in gastrocnemius muscle following murine hindlimb ischemia (HLI). A role for TSP2 regulation by HIF-1α is supported by the dysregulation of TSP2 expression in SM22α-cre HIF-1α KO mice following HLI. Indeed, there is a reduction in blood flow recovery in the SM22a-cre HIF-1α KO mice compared to littermate controls following HLI surgery, associated with impaired recovery and increased TSP2 levels. Moreover, SM22α-cre HIF-1α KO smooth muscle cells mice have increased TSP2 mRNA levels that persist in hypoxia. These findings identify a novel, ischemia-induced pro-angiogenic mechanism involving the transcriptional repression of TSP2 by HIF-1α.

Thrombospondins: A Role in Cardiovascular Disease

Thrombospondins (TSPs) represent extracellular matrix (ECM) proteins belonging to the TSP family that comprises five members. All TSPs have a complex multidomain structure that permits the interaction with various partners including other ECM proteins, cytokines, receptors, growth factors, etc. Among TSPs, TSP1, TSP2, and TSP4 are the most studied and functionally tested. TSP1 possesses anti-angiogenic activity and is able to activate transforming growth factor (TGF)-β, a potent profibrotic and anti-inflammatory factor. Both TSP2 and TSP4 are implicated in the control of ECM composition in hypertrophic hearts. TSP1, TSP2, and TSP4 also influence cardiac remodeling by affecting collagen production, activity of matrix metalloproteinases and TGF-β signaling, myofibroblast differentiation, cardiomyocyte apoptosis, and stretch-mediated enhancement of myocardial contraction. The development and evaluation of TSP-deficient animal models provided an option to assess the contribution of TSPs to cardiovascular pathology such as (myocardial infarction) MI, cardiac hypertrophy, heart failure, atherosclerosis, and aortic valve stenosis. Targeting of TSPs has a significant therapeutic value for treatment of cardiovascular disease. The activation of cardiac TSP signaling in stress and pressure overload may be therefore beneficial.

Inadequate Processing of Decellularized Dermal Matrix Reduces Cell Viability In Vitro and Increases Apoptosis and Acute Inflammation In Vivo

Decellularized tissue scaffolds are commonly used in the clinic because they can be used as substitutes for more traditional biomaterials, while imparting additional physiological effects. Nevertheless, reports of complications associated with their use are widespread and poorly understood. This study probes possible causes of these complications by examining cell viability and apoptosis in response to eluents from decellularized dermis. Using multiple sources of decellularized dermis, this study shows that typical decellularized scaffolds (prepared with commonly used laboratory techniques, as well as purchased from commercial sources) contain soluble components that are cytotoxic and that these components can be removed by extensive washes in cell culture media. In addition, this study demonstrates that these observed in vitro phenotypes correlate with increased apoptosis and acute inflammation when implanted subcutaneously in mice.

Tendon development and musculoskeletal assembly: emerging roles for the extracellular matrix

Tendons and ligaments are extracellular matrix (ECM)-rich structures that interconnect muscles and bones. Recent work has shown how tendon fibroblasts (tenocytes) interact with muscles via the ECM to establish connectivity and strengthen attachments under tension. Similarly, ECM-dependent interactions between tenocytes and cartilage/bone ensure that tendon-bone attachments form with the appropriate strength for the force required. Recent studies have also established a close lineal relationship between tenocytes and skeletal progenitors, highlighting the fact that defects in signals modulated by the ECM can alter the balance between these fates, as occurs in calcifying tendinopathies associated with aging. The dynamic fine-tuning of tendon ECM composition and assembly thus gives rise to the remarkable characteristics of this unique tissue type. Here, we provide an overview of the functions of the ECM in tendon formation and maturation that attempts to integrate findings from developmental genetics with those of matrix biology.

Extracellular matrix-based biomaterial scaffolds and the host response

Extracellular matrix (ECM) collectively represents a class of naturally derived proteinaceous biomaterials purified from harvested organs and tissues with increasing scientific focus and utility in tissue engineering and repair. This interest stems predominantly from the largely unproven concept that processed ECM biomaterials as natural tissue-derived matrices better integrate with host tissue than purely synthetic biomaterials. Nearly every tissue type has been decellularized and processed for re-use as tissue-derived ECM protein implants and scaffolds. To date, however, little consensus exists for defining ECM compositions or sources that best constitute decellularized biomaterials that might better heal, integrate with host tissues and avoid the foreign body response (FBR). Metrics used to assess ECM performance in biomaterial implants are arbitrary and contextually specific by convention. Few comparisons for in vivo host responses to ECM implants from different sources are published. This review discusses current ECM-derived biomaterials characterization methods including relationships between ECM material compositions from different sources, properties and host tissue response as implants. Relevant preclinical in vivo models are compared along with their associated advantages and limitations, and the current state of various metrics used to define material integration and biocompatibility are discussed. Commonly applied applications of these ECM-derived biomaterials as stand-alone implanted matrices and devices are compared with respect to host tissue responses.

Matricellular proteins in drug delivery: Therapeutic targets, active agents, and therapeutic localization

Extracellular matrix is composed of a complex array of molecules that together provide structural and functional support to cells. These properties are mainly mediated by the activity of collagenous and elastic fibers, proteoglycans, and proteins such as fibronectin and laminin. ECM composition is tissue-specific and could include matricellular proteins whose primary role is to modulate cell-matrix interactions. In adults, matricellular proteins are primarily expressed during injury, inflammation and disease. Particularly, they are closely associated with the progression and prognosis of cardiovascular and fibrotic diseases, and cancer. This review aims to provide an overview of the potential use of matricellular proteins in drug delivery including the generation of therapeutic agents based on the properties and structures of these proteins as well as their utility as biomarkers for specific diseases.

Biomaterials as carrier, barrier and reactor for cell-based regenerative medicine

Cell therapy has achieved tremendous success in regenerative medicine in the past several decades. However, challenges such as cell loss, death and immune-rejection after transplantation still persist. Biomaterials have been designed as carriers to deliver cells to desirable region for local tissue regeneration; as barriers to protect transplanted cells from host immune attack; or as reactors to stimulate host cell recruitment, homing and differentiation. With the assistance of biomaterials, improvement in treatment efficiency has been demonstrated in numerous animal models of degenerative diseases compared with routine free cell-based therapy. Emerging clinical applications of biomaterial assisted cell therapies further highlight their great promise in regenerative therapy and even cure for complex diseases, which have been failed to realize by conventional therapeutic approaches.

Biomedical implant capsule formation: lessons learned and the road ahead

Clinicians and investigators have been implanting biomedical devices into patients and experimental animals for centuries. There is a characteristic complex inflammatory response to the presence of the biomedical device with diverse cell signaling, followed by migration of fibroblasts to the implant surface and the eventual walling off of the implant in a collagen capsule. If the device is to interact with the surrounding tissues, the collagen envelope will eventually incapacitate the device or myofibroblasts can cause capsular contracture with resulting distortion, migration, or firmness. This review analyzes the various tactics used in the past to modify or control capsule formation with suggestions for future investigative approaches.

Bioactive nanofibers enable the identification of thrombospondin 2 as a key player in enamel regeneration

Tissue regeneration and development involves highly synchronized signals both between cells and with the extracellular environment. Biomaterials can be tuned to mimic specific biological signals and control cell response(s). As a result, these materials can be used as tools to elucidate cell signaling pathways and candidate molecules involved with cellular processes. In this work, we explore enamel-forming cells, ameloblasts, which have a limited regenerative capacity. By exposing undifferentiated cells to a self-assembling matrix bearing RGDS epitopes, we elicited a regenerative signal at will that subsequently led to the identification of thrombospondin 2 (TSP2), an extracellular matrix protein that has not been previously recognized as a key player in enamel development and regeneration. Targeted disruption of the thrombospondin 2 gene (Thbs2) resulted in enamel formation with a disordered architecture that was highly susceptible to wear compared to their wild-type counterparts. To test the regenerative capacity, we injected the bioactive matrix into the enamel organ and discovered that the enamel organic epithelial cells in TSP-null mice failed to polarize on the surface of the artificial matrix, greatly reducing integrin β1 and Notch1 expression levels, which represent signaling pathways known to be associated with TSP2. These results suggest TSP2 plays an important role in regulating cell-matrix interactions during enamel formation. Exploiting the signaling pathways activated by biomaterials can provide insight into native signaling mechanisms crucial for tooth development and cell-based strategies for enamel regeneration.

Thrombospondin-2 Expression During Retinal Vascular Development and Neovascularization

PURPOSE

To determine thrombospondin-2 (TSP2) expression and its impact on postnatal retinal vascular development and retinal neovascularization.

METHODS

The TSP2-deficient (TSP2(-/-)) mice and a line of TSP2 reporter mice were used to assess the expression of TSP2 during postnatal retinal vascular development and neovascularization. The postnatal retinal vascularization was evaluated using immunostaining of wholemount retinas prepared at different postnatal days by collagen IV staining and/or TSP2 promoter driven green fluorescent protein (GFP) expression. The organization of astrocytes was evaluated by glial fibrillary acidic protein (GFAP) staining. Retinal vascular densities were determined using trypsin digestion preparation of wholemount retinas at 3- and 6-weeks of age. Retinal neovascularization was assessed during the oxygen-induced ischemic retinopathy (OIR). Choroidal neovascularization (CNV) was assessed using laser-induced CNV.

RESULTS

Using the TSP2-GFP reporter mice, we observed significant expression of TSP2 mRNA in retinas of postnatal day 5 (P5) mice, which increased by P7 and remained high up to P42. Similar results were observed in retinal wholemount preparations, and western blotting for GFP with the highest level of GFP was observed at P21. In contrast to high level of mRNA at P42, the GFP fluorescence or protein level was dramatically downregulated. The primary retinal vasculature developed at a faster rate in TSP2(-/-) mice compared with TSP2(+/+) mice up to P5. However, the developing retinal vasculature in TSP2(+/+) mice caught up with that of TSP2(-/-) mice after P7. No significant differences in retinal vascular density were observed at 3- or 6-weeks of age. TSP2(-/-) mice also exhibited a similar sensitivity to the hyperoxia-mediated vessel obliteration and similar level of neovascularization during OIR as TSP2(+/+) mice. Lack of TSP2 expression minimally affected laser-induced CNV compared with TSP2(+/+) mice.

CONCLUSIONS

Lack of TSP2 expression was associated with enhanced retinal vascularization during early postnatal days but not at late postnatal times, and minimally affected retinal and CNV. However, the utility of TSP2 as a potential therapeutic target for inhibition of ocular neovascularization awaits further investigation.

Molecular Characterization of Macrophage-Biomaterial Interactions

Implantation of biomaterials in vascularized tissues elicits the sequential engagement of molecular and cellular elements that constitute the foreign body response. Initial events include the non-specific adsorption of proteins to the biomaterial surface that render it adhesive for cells such as neutrophils and macrophages. The latter undergo unique activation and in some cases undergo cell-cell fusion to form foreign body giant cells that contribute to implant damage and fibrotic encapsulation. In this review, we discuss the molecular events that contribute to macrophage activation and fusion with a focus on the role of the inflammasome, signaling pathways such as JAK/STAT and NF-κB, and the putative involvement of micro RNAs in the regulation of these processes.

Up-regulation of thrombospondin-2 in Akt1-null mice contributes to compromised tissue repair due to abnormalities in fibroblast function

Vascular remodeling is essential for tissue repair and is regulated by multiple factors, including thrombospondin-2 (TSP2) and hypoxia/VEGF-induced activation of Akt. In contrast to TSP2 knock-out (KO) mice, Akt1 KO mice have elevated TSP2 expression and delayed tissue repair. To investigate the contribution of increased TSP2 to Akt1 KO mice phenotypes, we generated Akt1/TSP2 double KO (DKO) mice. Full-thickness excisional wounds in DKO mice healed at an accelerated rate when compared with Akt1 KO mice. Isolated dermal Akt1 KO fibroblasts expressed increased TSP2 and displayed altered morphology and defects in migration and adhesion. These defects were rescued in DKO fibroblasts or after TSP2 knockdown. Conversely, the addition of exogenous TSP2 to WT cells induced cell morphology and migration rates that were similar to those of Akt1 KO cells. Akt1 KO fibroblasts displayed reduced adhesion to fibronectin with manganese stimulation when compared with WT and DKO cells, revealing an Akt1-dependent role for TSP2 in regulating integrin-mediated adhesions; however, this effect was not due to changes in β1 integrin surface expression or activation. Consistent with these results, Akt1 KO fibroblasts displayed reduced Rac1 activation that was dependent upon expression of TSP2 and could be rescued by a constitutively active Rac mutant. Our observations show that repression of TSP2 expression is a critical aspect of Akt1 function in tissue repair.

Revisiting the matricellular concept

The concept of a matricellular protein was first proposed by Paul Bornstein in the mid-1990s to account for the non-lethal phenotypes of mice with inactivated genes encoding thrombospondin-1, tenascin-C, or SPARC. It was also recognized that these extracellular matrix proteins were primarily counter or de-adhesive. This review reappraises the matricellular concept after nearly two decades of continuous investigation. The expanded matricellular family as well as the diverse and often unexpected functions, cellular location, and interacting partners/receptors of matricellular proteins are considered. Development of therapeutic strategies that target matricellular proteins are discussed in the context of pathology and regenerative medicine.

Delineation of candidate genes responsible for structural brain abnormalities in patients with terminal deletions of chromosome 6q27

Patients with terminal deletions of chromosome 6q present with structural brain abnormalities including agenesis of corpus callosum, hydrocephalus, periventricular nodular heterotopia, and cerebellar malformations. The 6q27 region harbors genes that are important for the normal development of brain and delineation of a critical deletion region for structural brain abnormalities may lead to a better genotype-phenotype correlation. We conducted a detailed clinical and molecular characterization of seven unrelated patients with deletions involving chromosome 6q27. All patients had structural brain abnormalities. Using array comparative genomic hybridization, we mapped the size, extent, and genomic content of these deletions. The smallest region of overlap spans 1.7 Mb and contains DLL1, THBS2, PHF10, and C6orf70 (ERMARD) that are plausible candidates for the causation of structural brain abnormalities. Our study reiterates the importance of 6q27 region in normal development of brain and helps identify putative genes in causation of structural brain anomalies.

Matricellular proteins and biomaterials

Biomaterials are essential to modern medicine as components of reconstructive implants, implantable sensors, and vehicles for localized drug delivery. Advances in biomaterials have led to progression from simply making implants that are nontoxic to making implants that are specifically designed to elicit particular functions within the host. The interaction of implants and the extracellular matrix during the foreign body response is a growing area of concern for the field of biomaterials, because it can lead to implant failure. Expression of matricellular proteins is modulated during the foreign body response and these proteins interact with biomaterials. The design of biomaterials to specifically alter the levels of matricellular proteins surrounding implants provides a new avenue for the design and fabrication of biomimetic biomaterials.

Thrombospondin-2 overexpression in the skin of transgenic mice reduces the susceptibility to chemically induced multistep skin carcinogenesis

BACKGROUND

We have previously reported stromal upregulation of the endogenous angiogenesis inhibitor thrombospondin-2 (TSP-2) during multistep carcinogenesis, and we found accelerated and enhanced skin angiogenesis and carcinogenesis in TSP-2 deficient mice.

GOALS

To investigate whether enhanced levels of TSP-2 might protect from skin cancer development.

METHODS

We established transgenic mice with targeted overexpression of TSP-2 in the skin and subjected hemizygous TSP-2 transgenic mice and their wild-type littermates to a chemical skin carcinogenesis regimen.

RESULTS

TSP-2 transgenic mice showed a significantly delayed onset of tumor formation compared to wild-type mice, whereas the ratio of malignant conversion to squamous cell carcinomas was comparable in both genotypes. Computer-assisted morphometric analysis of blood vessels revealed pronounced tumor angiogenesis already in the early stages of carcinogenesis in wild type mice. TSP-2 overexpression significantly reduced tumor blood vessel density in transgenic mice but had no overt effect on LYVE-1 positive lymphatic vessels. The percentage of desmin surrounded, mature tumor-associated blood vessels and the degree of epithelial differentiation remained unaffected. The antiangiogenic effect of transgenic TSP-2 was accompanied by a significantly increased number of apoptotic tumor cells in transgenic mice.

CONCLUSION

Our results demonstrate that enhanced levels of TSP-2 in the skin result in reduced susceptibility to chemically-induced skin carcinogenesis and identify TSP-2 as a new target for the prevention of skin cancer.

Thrombospondin-2 and extracellular matrix assembly

BACKGROUND

Numerous proteins and small leucine-rich proteoglycans (SLRPs) make up the composition of the extracellular matrix (ECM). Assembly of individual fibrillar components in the ECM, such as collagen, elastin, and fibronectin, is understood at the molecular level. In contrast, the incorporation of non-fibrillar components and their functions in the ECM are not fully understood.

SCOPE OF REVIEW

This review will focus on the role of the matricellular protein thrombospondin (TSP) 2 in ECM assembly. Based on findings in TSP2-null mice and in vitro studies, we describe the participation of TSP2 in ECM assembly, cell-ECM interactions, and modulation of the levels of matrix metalloproteinases (MMPs).

MAJOR CONCLUSIONS

Evidence summarized in this review suggests that TSP2 can influence collagen fibrillogenesis without being an integral component of fibrils. Altered ECM assembly and excessive breakdown of ECM can have both positive and negative consequences including increased angiogenesis during tissue repair and compromised cardiac tissue integrity, respectively.

GENERAL SIGNIFICANCE

Proper ECM assembly is critical for maintaining cell functions and providing structural support. Lack of TSP2 is associated with increased angiogenesis, in part, due to altered endothelial cell-ECM interactions. Therefore, minor changes in ECM composition can have profound effects on cell and tissue function. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

Gene silencing in human aortic smooth muscle cells induced by PEI-siRNA complexes released from dip-coated electrospun poly(ethylene terephthalate) grafts

An excessive tissue response to prosthetic arterial graft material leads to intimal hyperplasia (IH), the leading cause of late graft failure. Seroma and abnormal capsule formation may also occur after prosthetic material implantation. The matricellular protein Thrombospondin-2 (TSP-2) has shown to be upregulated in response to biomaterial implantation. This study evaluates the uptake and release of small interfering RNA (siRNA) from unmodified and surface functionalized electrospun PET graft materials. ePET graft materials were synthesized using electrospinning technology. Subsets of the ePET materials were then chemically modified to create surface functional groups. Unmodified and surface-modified ePET grafts were dip-coated in siRNAs alone or siRNAs complexed with transfection reagents polyethyleneimine (PEI) or Lipofectamine RNAiMax. Further, control and TSP-2 siRNA-PEI complex treated ePET samples were placed onto a confluent layer of human aortic smooth muscle cells (AoSMCs). Complexation of all siRNAs with PEI led to a significant increase in adsorption to unmodified ePET. TSP-2 siRNA-PEI released from unmodified-ePET silenced TSP-2 in AoSMC. Regardless of the siRNA-PEI complex evaluated, AoSMC migrated into the ePET. siRNA-PEI complexes delivered to AoSMC from dip-coated ePET can result in gene knockdown. This methodology for siRNA delivery may improve the tissue response to vascular and other prosthetics.

Long-term gene therapy with thrombospondin 2 inhibits TGF-β activation, inflammation and angiogenesis in chronic allograft nephropathy

We recently identified Thrombospondin-2 (TSP-2) as a regulator of matrix remodelling and inflammation in experimental kidney disease by using TSP-2 null mice and successfully proved TSP-2 overexpression as a therapeutic concept in a short term glomerulonephritis model in the rat. In this current study, we investigated if long-term TSP-2 overexpression is also capable to ameliorate the progression of chronic kidney disease in the setting of the chronic allograft nephropathy F344-Lewis model in the rat. Two weeks after renal transplantation, two rat thigh muscles were transfected once only with either a TSP-2 overexpressing plasmid (n = 8) or a luciferase-expressing plasmid as control (n = 8). Rats were monitored for renal function, histological changes and gene expression in the graft for up to 30 weeks after transplantation. Unexpectedly, only in the TSP-2 treated group 2 rats died before the end of the experiment and renal function tended to be worsened in the TSP-2 group compared to the luciferase-treated controls. In addition, glomerular sclerosis and tubular interstitial injury as well as cortical fibronectin deposition was significantly increased in the TSP-2 treated kidneys despite reduced TGF-β activation and marked anti-inflammatory (macrophages, T-cells and B-cells) effects in this group. Long-term TSP-2 therapy impaired repair of renal endothelium, as demonstrated by significant higher glomerular and peritubular endothelial rarefaction and reduced endothelial cell proliferation in the transplanted kidneys from TSP-2 treated rats compared to controls. This TSP-2 effect was associated with decreased levels of renal VEGF but not VEGF1 receptor. In conclusion, despite its anti-inflammatory and TGF-β activation blocking effects, TSP-2 gene therapy did not ameliorate but rather worsened experimental chronic allograft nephropathy most likely via its anti-angiogenic properties on the renal microvasculature.

Angiogenesis and scar formation in healing wounds

PURPOSE OF REVIEW

One well described feature of wound healing is the ingrowth of new capillaries or angiogenesis. At its peak, the capillary content in healing wounds may reach three or more times that of normal uninjured tissue. This new vasculature is required to restore oxygenation and allow the growth of new tissue to fill the wound space. This review examines the assumption that a capillary content in excess of normal density is essential for adequate healing.

RECENT FINDINGS

The regulation of wound angiogenesis has been demonstrated to involve both proangiogenic and antiangiogenic stimuli, with the level of capillary growth reliant upon both sets of factors. Several studies now show that normal skin wounds heal adequately even when the angiogenic response is artificially reduced. In normal skin, a reduction of capillary growth to a level consistent with normal tissue does not affect wound closure and may even lead to highly favorable long term healing outcomes.

SUMMARY

The angiogenic response in normal wounds may exceed what is needed for optimal repair.

Differential gene expression by Osterix knockdown in mouse chondrogenic ATDC5 cells

Osterix (Osx) is a transcription factor required for osteoblast differentiation during intramembranous and endochondral ossification. Recently, several reports have described novel functions of Osx in chondrocyte differentiation. In an in vitro study, in which the effects of Osx gene silencing were examined in mouse chondrogenic ATDC5 cells, chondrocyte marker genes were found to be expressionally downregulated and chondrocyte differentiation reduced. On the other hand, in vivo studies based on chondrocyte-specific Osx knockouts demonstrated impaired endochondral bone formation with delayed chondrocyte differentiation and reduced cartilage matrix ossification. However, little is known about the mechanism or targets of Osx involved in the control of chondrocyte differentiation. Here, we attempted to high-density of Affymetrix GeneChip microarray to investigate global gene expression profile changes caused by Osx knockdown in ATDC5 chondrocytes. The mRNA expressions of 112 genes were significantly modified by Osx knockdown: 68 genes were upregulated and 44 genes downregulated. Functional categories of gene expression classified by gene ontology demonstrated that genes related to cell adhesion, development, and signal transduction were highly affected by Osx knockdown. The expressions of differential genes, such as Sfrp2, Sema3a, Nox4, Rgs4, Zfp521, Has2, Sox6, Scn2a1, Sirpa, and Thbs2, were validated by quantitative real-time PCR. This study shows that expression profiling can be used to identify genes that are transcriptionally modified following Osx knockdown and to reveal the molecular mechanism of chondrocyte differentiation regulated by Osx.

Surface treatments for microfluidic biocompatibility

Microfluidic systems allow small volumes of liquids to be manipulated, either by being passed through channels or moved around as liquid droplets. Such systems have been developed to separate, purify, analyze, and deliver molecules to reaction zones. Although volumes are small, reaction rates, catalysis, mixing, and heat transfer can be high, enabling the accurate sensing of tiny quantities of agents and the synthesis of novel products. The incorporation of multiple components, such as pumps, valves, mixers, and heaters, onto a single microfluidic platform has brought about the field of lab-on-a-chip devices or micro total analysis systems (μTAS). Although used in the research laboratory for numerous years, few of these devices have made it into the commercial market, due to their complexity of fabrication and limited choice of material. As the dimensions of these systems become smaller, interfacial interactions begin to dominate in terms of device performance. Appropriate selection of bulk materials, or the application of surface coatings, can allow control over surface properties, such as the adsorption of (bio)molecules. Here we review current microfluidic technology in terms of biocompatibility issues, examining the use of modification strategies to improve device longevity and performance.

Lack of thrombospondin-2 reduces fibrosis and increases vascularity around cardiac cell grafts

BACKGROUND

Fibrosis around cardiac cell injections represents an obstacle to graft integration in cell-based cardiac repair. Thrombospondin-2 (TSP-2) is a pro-fibrotic, anti-angiogenic matricellular protein and an attractive target for therapeutic knockdown to improve cardiac graft integration and survival.

METHODS

We used a TSP-2 knockout (KO) mouse in conjunction with a fetal murine cardiomyocyte grafting model to evaluate the effects of a lack of TSP-2 on fibrosis, vascular density, and graft size in the heart.

RESULTS

Two weeks after grafting in the uninjured heart, fibrosis area was reduced 4.5-fold in TSP-2 KO mice, and the thickness of the peri-graft scar capsule was reduced sevenfold compared to wild-type (WT). Endothelial cell density in the peri-graft region increased 2.5-fold in the absence of TSP-2, and cardiomyocyte graft size increased by 46% in TSP-2 KO hearts.

CONCLUSIONS

TSP-2 is a key regulator of fibrosis and angiogenesis following cell grafting in the heart, and its absence promotes better graft integration, vascularization, and survival.

SUMMARY

Fibrosis around cardiac cell injections impairs graft integration in cell-based cardiac repair. TSP-2 is a pro-fibrotic, anti-angiogenic matricellular protein. Using a TSP-2-knockout mouse model and cardiac cell transplantation, we found significantly reduced fibrosis and increased endothelial cell density in the peri-graft region. Thus, TSP-2 is an attractive target for therapeutic knockdown to improve cardiac graft integration and survival.

Cultured primary macrophage activation by lipopolysaccharide depends on adsorbed protein composition and substrate surface chemistry

Recent efforts show that significantly reducing implant-adsorbed proteins does not avoid the foreign body response. Fluorinated surfaces are commonly used to passivate cell-mediated inflammatory responses to implanted materials but adsorb host proteins and facilitate the attachment and proliferation of macrophages. This study considers in vitro macrophage activation to fluorinated TeflonAF(®) compared to tissue-culture polystyrene using pre-adsorbed proteins (fibrinogen, BSA, collagen and elastin). Primary macrophage cultures adhere on all pre-adsorbed protein surfaces in a protein concentration-dependent manner and activate to the same extent after 72 h, regardless of surface chemistry. However, macrophages alter their cultured adherent morphology depending on which protein is pre-adsorbed to these surfaces. Macrophages cultured on TeflonAF(®) on all pre-adsorbed proteins produced overall higher levels of the pro-inflammatory cytokines - TNF-α, IL-6, IL-1β or MCP-1 - than those cultured on tissue-culture polystyrene and those cultured in serum-free media. However, at 72 h, macrophages adherent on BSA or fibrinogen pre-adsorbed surfaces failed to exhibit increased amounts of TNF-a, IL-6 or IL-1/S on either TeflonAF(®) or TCPS, as well as MCP-1 on TCPS, in the presence of activating lipopolysaccharide. Different cell responses to pre-adsorbed proteins reflect substrate-specific regulation of macrophage cytokine secretion, indicative of LPS tolerance distinct from secondary macrophage cultures, and also distinct from macrophages adherent to surfaces in the absence of proteins. This result has bearing on connecting macrophage adhesion via adsorbed proteins on (fluorinated) biomaterials, and their resulting chronic activation that yields the FBR and possibly reduces effective macrophage clearance of microbes around implanted materials.

Functionalization of deproteinized bovine bone with a coating-incorporated depot of BMP-2 renders the material efficiently osteoinductive and suppresses foreign-body reactivity

The repair of critical-sized bony defects remains a challenge in the fields of implantology, maxillofacial surgery and orthopaedics. As an alternative bone-defect filler to autologous bone grafts, deproteinized bovine bone (DBB) is highly osteoconductive and clinically now widely used. However, this product suffers from the disadvantage of not being intrinsically osteoinductive. In the present study, this property was conferred by coating DBB with a layer of calcium phosphate into which bone morphogenetic protein 2 (BMP-2) was incorporated. Granules of DBB bearing a coating-incorporated depot of BMP-2--together with the appropriate controls (DBB bearing a coating but no BMP-2; uncoated DBB bearing adsorbed BMP-2; uncoated DBB bearing no BMP-2)--were implanted subcutaneously in rats. Five weeks later, the implants were withdrawn for a histomorphometric analysis of the volume densities of (i) bone, (ii) bone marrow, (iii) foreign-body giant cells and (iv) fibrous capsular tissue. Parameters (i) and (ii) were highest, whilst parameters (iii) and (iv) were lowest in association with DBB bearing a coating-incorporated depot of BMP-2. Hence, this mode of functionalization not only confers DBB with the property of osteoinductivity but also improves its biocompatibility--thus dually enhancing its clinical potential in the repair of bony defects.

The thrombospondins

Thrombospondins are evolutionarily conserved, calcium-binding glycoproteins that undergo transient or longer-term interactions with other extracellular matrix components. They share properties with other matrix molecules, cytokines, adaptor proteins, and chaperones, modulate the organization of collagen fibrils, and bind and localize an array of growth factors or proteases. At cell surfaces, interactions with an array of receptors activate cell-dependent signaling and phenotypic outcomes. Through these dynamic, pleiotropic, and context-dependent pathways, mammalian thrombospondins contribute to wound healing and angiogenesis, vessel wall biology, connective tissue organization, and synaptogenesis. We overview the domain organization and structure of thrombospondins, key features of their evolution, and their cell biology. We discuss their roles in vivo, associations with human disease, and ongoing translational applications. In many respects, we are only beginning to appreciate the important roles of these proteins in physiology and pathology.

Endothelial nitric oxide synthase controls the expression of the angiogenesis inhibitor thrombospondin 2

Injury- and ischemia-induced angiogenesis is critical for tissue repair and requires nitric oxide (NO) derived from endothelial nitric oxide synthase (eNOS). We present evidence that NO induces angiogenesis by modulating the level of the angiogenesis inhibitor thrombospondin 2 (TSP2). TSP2 levels were higher than WT in eNOS KO tissues in hind-limb ischemia and cutaneous wounds. In vitro studies confirmed that NO represses TSP2 promoter activity. Moreover, double-eNOS/TSP2 KO mice were generated and found to rescue the phenotype of eNOS KO mice. Studies in mice with knock-in constitutively active or inactive eNOS on the Akt-1 KO background showed that eNOS activity correlates with TSP2 levels. Our observations of NO-mediated regulation of angiogenesis via the suppression of TSP2 expression provide a description of improved eNOS KO phenotype by means other than restoring NO signaling.

Absence of thrombospondin-2 increases cardiomyocyte damage and matrix disruption in doxorubicin-induced cardiomyopathy

Clinical use of the antineoplastic agent doxorubicin (DOX) is limited by its cardiomyocyte toxicity. Attempts to decrease cardiomyocyte injury showed promising results in vitro, but failed to reduce the adverse effects of DOX in vivo, suggesting that other mechanisms contribute to its cardiotoxicity as well. Evidence that DOX also induces cardiac injury by compromising extracellular matrix integrity is lacking. The matricellular protein thrombospondin-2 (TSP-2) is known for its matrix-preserving function, and for modulating cellular function. Here, we investigated whether TSP-2 modulates the process of doxorubicin-induced cardiomyopathy (DOX-CMP). TSP-2-knockout (TSP-2-KO) and wild-type (WT) mice were treated with DOX (2 mg/kg/week) for 12 weeks to induce DOX-CMP. Mortality was significantly increased in TSP-2-KO compared to WT mice. Surviving DOX-treated TSP-2-KO mice had depressed cardiac function compared to WT animals, accompanied by increased cardiomyocyte apoptosis and matrix damage. Enhanced myocyte damage in the absence of TSP-2 was associated with impaired activation of the Akt signaling pathway in TSP-2-KO compared to WT. The absence of TSP-2, in vivo and in vitro, reduced Akt activation both under non-treated conditions and after DOX. Importantly, inhibition of Akt phosphorylation in cardiomyocytes significantly reduced TSP-2 expression, unveiling a unique feedback loop between Akt and TSP-2. Finally, enhanced matrix disruption in DOX-treated TSP-2-KO hearts went along with increased matrix metalloproteinase-2 levels. Taken together, this study is the first to provide evidence for the implication of the matrix element TSP-2 in protecting against DOX-induced cardiac injury and dysfunction.

Cervical softening during pregnancy: regulated changes in collagen cross-linking and composition of matricellular proteins in the mouse

A greater understanding of the parturition process is essential in the prevention of preterm birth, which occurs in 12.7% of infants born in the United States annually. Cervical remodeling is a critical component of this process. Beginning early in pregnancy, remodeling requires cumulative, progressive changes in the cervical extracellular matrix (ECM) that result in reorganization of collagen fibril structure with a gradual loss of tensile strength. In the current study, we undertook a detailed biochemical analysis of factors in the cervix that modulate collagen structure during early mouse pregnancy, including expression of proteins involved in processing of procollagen, assembly of collagen fibrils, cross-link formation, and deposition of collagen in the ECM. Changes in these factors correlated with changes in the types of collagen cross-links formed and packing of collagen fibrils as measured by electron microscopy. Early in pregnancy there is a decline in expression of two matricellular proteins, thrombospondin 2 and tenascin C, as well as a decline in expression of lysyl hydroxylase, which is involved in cross-link formation. These changes are accompanied by a decline in both HP and LP cross-links by gestation Days 12 and 14, respectively, as well as a progressive increase in collagen fibril diameter. In contrast, collagen abundance remains constant over the course of pregnancy. We conclude that early changes in tensile strength during cervical softening result in part from changes in the number and type of collagen cross-links and are associated with a decline in expression of two matricellular proteins thrombospondin 2 and tenascin C.

Biomimetic coatings for bone tissue engineering of critical-sized defects

The repair of critical-sized bone defects is still challenging in the fields of implantology, maxillofacial surgery and orthopaedics. Current therapies such as autografts and allografts are associated with various limitations. Cytokine-based bone tissue engineering has been attracting increasing attention. Bone-inducing agents have been locally injected to stimulate the native bone-formation activity, but without much success. The reason is that these drugs must be delivered slowly and at a low concentration to be effective. This then mimics the natural method of cytokine release. For this purpose, a suitable vehicle was developed, the so-called biomimetic coating, which can be deposited on metal implants as well as on biomaterials. Materials that are currently used to fill bony defects cannot by themselves trigger bone formation. Therefore, biological functionalization of such materials by the biomimetic method resulted in a novel biomimetic coating onto different biomaterials. Bone morphogenetic protein 2 (BMP-2)-incorporated biomimetic coating can be a solution for a large bone defect repair in the fields of dental implantology, maxillofacial surgery and orthopaedics. Here, we review the performance of the biomimetic coating both in vitro and in vivo.

Profiles of carbohydrate ligands associated with adsorbed proteins on self-assembled monolayers of defined chemistries

Conserved protein-carbohydrate-lipid pathogen-associated molecular patterns (PAMPs) interact with cells of the innate immune system to mediate antigen recognition and internalization and activation of immune cells. We examined if analogous "biomaterial-associated molecular patterns" composed of proteins, specifically their carbohydrate modifications, existed on biomaterials, which can play a role in mediating the innate immune response to biomaterials. To probe for these carbohydrates in the adsorbed protein layer, as directed by the underlying biomaterial chemistry, self-assembled monolayers (SAMs) presenting -CH(3), -OH, -COOH, or -NH(2) were preincubated with serum/plasma, and the presence of carbohydrate ligands of C-type lectin receptors (CLRs) was investigated using lectin probes in an enzyme-linked lectin assay (ELLA). Presentation of CLR ligands was detected on control tissue culture polystyrene (TCPS). Absorbances of mannose or N-acetylglucosamine increased with decreasing incubating serum concentration, whereas absorbances of sialylated epitopes or fucose remained unchanged. Absorbances of alpha-galactose or N-acetylgalactosamine decreased with decreasing incubating serum concentration; beta-galactose was undetectable. Among SAM endgroups, preincubation with 10% serum resulted in differential presentation of CLR ligands: higher alpha-galactose on COOH SAMs than NH(2) or CH(3) SAMs, highest complex mannose on NH(2) SAMs, and higher complex mannose on OH SAMs than CH(3) SAMs. Least sialylated groups were detected on CH(3) SAMs. In summary, biomaterial chemistry may regulate protein adsorption and hence unique presentation of associated carbohydrates. The ultimate goal is to identify the effects of protein glycosylations associated with biomaterials in stimulating innate immune responses.