The alpha v beta 3 integrin "vitronectin receptor"

RGD-coated polymeric microbubbles promote ultrasound-mediated drug delivery in an inflamed endothelium-pericyte co-culture model of the blood-brain barrier

Drug delivery to central nervous pathologies is compromised by the blood-brain barrier (BBB). A clinically explored strategy to promote drug delivery across the BBB is sonopermeation, which relies on the combined use of ultrasound (US) and microbubbles (MB) to induce temporally and spatially controlled opening of the BBB. We developed an advanced in vitro BBB model to study the impact of sonopermeation on the delivery of the prototypic polymeric drug carrier pHPMA as a larger molecule and the small molecule antiviral drug ribavirin. This was done under standard and under inflammatory conditions, employing both untargeted and RGD peptide-coated MB. The BBB model is based on human cerebral capillary endothelial cells and human placental pericytes, which are co-cultivated in transwell inserts and which present with proper transendothelial electrical resistance (TEER). Sonopermeation induced a significant decrease in TEER values and facilitated the trans-BBB delivery of fluorescently labeled pHPMA (Atto488-pHPMA). To study drug delivery under inflamed endothelial conditions, which are typical for e.g. tumors, neurodegenerative diseases and CNS infections, tumor necrosis factor (TNF) was employed to induce inflammation in the BBB model. RGD-coated MB bound to and permeabilized the inflamed endothelium-pericyte co-culture model, and potently improved Atto488-pHPMA and ribavirin delivery. Taken together, our work combines in vitro BBB bioengineering with MB-mediated drug delivery enhancement, thereby providing a framework for future studies on optimization of US-mediated drug delivery to the brain.

The protective role of GATA6+ pericardial macrophages in pericardial inflammation

Prior research has suggested that GATA6+ pericardial macrophages may traffic to the myocardium to prevent interstitial fibrosis after myocardial infarction (MI), while subsequent literature claims that they do not. We demonstrate that GATA6+ pericardial macrophages are critical for preventing IL-33 induced pericarditis and attenuate trafficking of inflammatory monocytes and granulocytes to the pericardial cavity after MI. However, absence of GATA6+ macrophages did not affect myocardial inflammation due to MI or coxsackievirus-B3 induced myocarditis, or late-stage cardiac fibrosis and cardiac function post MI. GATA6+ macrophages are significantly less transcriptionally active following stimulation in vitro compared to bone marrow-derived macrophages and do not induce upregulation of inflammatory markers in fibroblasts. This suggests that GATA6+ pericardial macrophages attenuate inflammation through their interactions with surrounding cells. We therefore conclude that GATA6+ pericardial macrophages are critical in modulating pericardial inflammation, but do not play a significant role in controlling myocardial inflammation or fibrosis.

Acetyl-NPKY of integrin-β1 binds KINDLIN2 to control endothelial cell proliferation and junctional integrity

Integrin-dependent crosstalk between cell-matrix adhesions and cell-cell junctions is critical for controlling endothelial permeability and proliferation in cancer and inflammatory diseases but remains poorly understood. Here, we investigated how acetylation of the distal NPKY-motif of Integrin-β1 influences endothelial cell physiology and barrier function. Expression of an acetylation-mimetic β1-K794Q-GFP mutant led to the accumulation of immature cell-matrix adhesions accompanied by a transcriptomic reprograming of endothelial cells, involving genes associated with cell adhesion, proliferation, polarity, and barrier function. β1-K794Q-GFP induced constitutive MAPK signaling, junctional impairment, proliferation, and reduced contact inhibition at confluence. Structural analysis of Integrin-β1 interaction with KINDLIN2, biochemical pulldown assay, and binding energy determination by using molecular dynamics simulation showed that acetylation of K794 and the K794Q-mutant increased KINDLIN2 binding affinity to the Integrin-β1. Thus, enhanced recruitment of KINDLIN2 to Lysine-acetylated Integrin-β1 and resulting modulation of barrier function, offers new therapeutic possibilities for controlling vascular permeability and disease conditions.

Integrating integrins with the hallmarks of cancer

Epithelial cells adhere to a specialized extracellular matrix called the basement membrane which allows them to polarize and form epithelial tissues. The extracellular matrix provides essential physical scaffolding and biochemical and biophysical cues required for tissue morphogenesis, differentiation, function, and homeostasis. Epithelial cell adhesion to the extracellular matrix (i.e., basement membrane) plays a critical role in organizing epithelial tissues, separating the epithelial cells from the stroma. Epithelial cell detachment from the basement membrane classically results in death, though detachment or invasion through the basement membrane represents a critical step in carcinogenesis. Epithelial cells bind to the extracellular matrix via specialized matrix receptors, including integrins. Integrins are transmembrane receptors that form a mechanical linkage between the extracellular matrix and the intracellular cytoskeleton and are required for anchorage-dependent cellular functions such as proliferation, migration, and invasion. The role of integrins in the development, growth, and dissemination of multiple types of carcinomas has been investigated by numerous methodologies, which has led to great complexity. To organize this vast array of information, we have utilized the "Hallmarks of Cancer" from Hanahan and Weinberg as a convenient framework to discuss the role of integrins in the pathogenesis of cancers. This review explores this biology and how its complexity has impacted the development of integrin-targeted anti-cancer therapeutics.

Acidity-Triggered "Sticky Spotlight": CCK2R-Targeted TME-Sensitive NIR Fluorescent Probes for Tumor Imaging In Vivo

Cancer which causes high mortality globally threatens public health seriously. There is an urgent need to develop tumor-specific near-infrared (NIR) imaging agents to achieve precise diagnosis and guide effective treatment. In recent years, imaging probes that respond to acidic environments such as endosomes, lysosomes, or acidic tumor microenvironments (TMEs) are being developed. However, because of their nonspecific internalization by both normal and tumor cells, resulting in a poor signal-to-noise ratio in diagnosis, these pH-sensitive probes fail to be applied to in vivo tumor imaging. To address this issue, a cholecystokinin-2 receptor (CCK2R)-targeted TME-sensitive NIR fluorescent probe R2SM was synthesized by coupling pH-sensitive heptamethine cyanine with a CCK2R ligand, minigastrin analogue 11 (MG11) for in vivo imaging, in which MG11 would target overexpressed CCK2Rs in gastrointestinal stromal tumors (GISTs). Cell uptake assay demonstrated that R2SM exhibited a high affinity for CCK2R, leading to receptor-mediated internalization and making probes finally accumulated in the lysosomes of tumor cells, which suggested in the tumor tissues, the probes were distributed in the extracellular acidic TME and intracellular lysosomes. With a pKa of 6.83, R2SM can be activated at the acidic TME (pH = 6.5-6.8) and lysosomes (pH = 4.5-5.0), exhibiting an apparent pH-dependent behavior and generating more intense fluorescence in these acidic environments. In vivo imaging showed that coupling of MG11 with a pH-sensitive NIR probe facilitated the accumulation of probe and enhanced the fluorescence in CCK2R-overexpressed HT-29 tumor cells. A high signal was observed in the tumor region within 0.5 h postinjection, indicating its potential application in intraoperative imaging. Fluorescence imaging of R2SM exhibited higher tumor-to-liver and tumor-to-kidney ratios (2.1:1 and 2.3:1, respectively), compared separately with the probes that are lipophilic, pH-insensitive, or MG11-free. In vitro and in vivo studies demonstrated that the synergistic effect of tumor targeting with pH sensitivity plays a vital role in the high signal-to-noise ratio of the NIR imaging probe. Moreover, different kinds of tumor-targeting vectors could be conjugated simultaneously with the NIR dye, which would further improve the receptor affinity and targeting efficiency.

Deep Flow Cytometry Unveils Distinct Immune Cell Subsets in Inducible T Cell Co-Stimulator Ligand (ICOSL)- and ICOS-Knockout Mice during Experimental Autoimmune Encephalomyelitis

The inducible T cell co-stimulator ligand (ICOSL), expressed by antigen presenting cells, binds to the inducible T cell co-stimulator (ICOS) on activated T cells. Improper function of the ICOS/ICOSL pathway has been implicated in several autoimmune diseases, including multiple sclerosis (MS). Previous studies showed that ICOS-knockout (KO) mice exhibit severe experimental autoimmune encephalomyelitis (EAE), the animal model of MS, but data on ICOSL deficiency are not available. In our study, we explored the impact of both ICOS and ICOSL deficiencies on MOG35-55 -induced EAE and its associated immune cell dynamics by employing ICOSL-KO and ICOS-KO mice with a C57BL/6J background. During EAE resolution, MOG-driven cytokine levels and the immunophenotype of splenocytes were evaluated by ELISA and multiparametric flow cytometry, respectively. We found that both KO mice exhibited an overlapping and more severe EAE compared to C57BL/6J mice, corroborated by a reduction in memory/regulatory T cell subsets and interleukin (IL-)17 levels. It is noteworthy that an unsupervised analysis showed that ICOSL deficiency modifies the immune response in an original way, by affecting T central and effector memory (TCM, TEM), long-lived CD4+ TEM cells, and macrophages, compared to ICOS-KO and C57BL/6J mice, suggesting a role for other binding partners to ICOSL in EAE development, which deserves further study.

Radiosynthesis of Stable 198Au-Nanoparticles by Neutron Activation of αvβ3-Specific AuNPs for Therapy of Tumor Angiogenesis

This paper reports on the development of stable tumor-specific gold nanoparticles (AuNPs) activated by neutron irradiation as a therapeutic option for the treatment of cancer with high tumor angiogenesis. The AuNPs were designed with different mono- or dithiol-ligands and decorated with different amounts of Arg-Gly-Asp (RGD) peptides as a tumor-targeting vector for αvβ3 integrin, which is overexpressed in tissues with high tumor angiogenesis. The AuNPs were evaluated for avidity in vitro and showed favorable properties with respect to tumor cell accumulation. Furthermore, the therapeutic properties of the [198Au]AuNPs were evaluated in vitro on U87MG cells in terms of cell survival, suggesting that these [198Au]AuNPs are a useful basis for future therapeutic concepts.

ECM proteins and cationic polymers coating promote dedifferentiation of patient-derived mature adipocytes to stem cells

Reprogramming of mature adipocytes is an attractive research area due to the plasticity of these cells. Mature adipocytes can be reprogrammed in vitro, transforming them into dedifferentiated fat cells (DFATs), which are considered a new type of stem cell, and thereby have a high potential for use in tissue engineering and regenerative medicine. However, there are still no reports or findings on in vitro controlling the dedifferentiation. Although ceiling culture performed in related studies is a relatively simple method, its yield is low and does not allow manipulation of mature adipocytes to increase or decrease the dedifferentiation. In this study, to understand the role of physicochemical surface effects on the dedifferentiation of patient-derived mature adipocytes, the surfaces of cell culture flasks were coated with extracellular matrix, basement membrane proteins, and cationic/anionic polymers. Extracellular matrix such as fibronectin and collagen type I, and basement membrane proteins such as collagen type IV and laminin strongly promoted dedifferentiation of mature adipocytes, with laminin showing the highest effect with a DFAT ratio of 2.98 (±0.84). Interestingly, cationic polymers also showed a high dedifferentiation effect, but anionic polymers did not, and poly(diallyl dimethylammonium chloride) showed the highest DFAT ratio of 2.27 (±2.8) among the cationic polymers. Protein assay results revealed that serum proteins were strongly adsorbed on the surfaces of the cationic polymer coating, including inducing high mature adipocyte adhesion. This study demonstrates for the first time the possibility of regulating the transformation of mature adipocytes to DFAT stem cells by controlling the physicochemical properties of the surface of conventional cell culture flasks.

Cilengitide inhibits osteoclast adhesion through blocking the αvβ3-mediated FAK/Src signaling pathway

The remodeling of actin cytoskeleton of osteoclasts on the bone matrix is essential for osteoclastic resorption activity. A specific regulator of the osteoclast cytoskeleton, integrin αvβ3, is known to provide a key role in the degradation of mineralized bone matrixes. Cilengitide is a potent inhibitor of integrins and is capable of affecting αvβ3 receptors, and has anti-tumor and anti-angiogenic and apoptosis-inducing effects. However, its function on osteoclasts is not fully understood. Here, the cilengitide role on nuclear factor κB ligand-receptor activator (RANKL)-induced osteoclasts was explored. Cells were cultured with varying concentrations of cilengitide (0,0.002,0.2 and 20 μM) for 7 days, followed by detected via Cell Counting Kit-8, staining for tartrate resistant acid phosphatase (TRAP), F-actin ring formation, bone resorption assays, adhesion assays, immunoblotting assays, and real-time fluorescent quantitative PCR. Results demonstrated that cilengitide effectively restrained the functionality and formation of osteoclasts in a concentration-dependent manner, without causing any cytotoxic effects. Mechanistically, cilengitide inhibited osteoclast-relevant genes expression; meanwhile, cilengitide downregulated the expression of key signaling molecules associated with the osteoclast cytoskeleton, including focal adhesion kinase (FAK), integrin αvβ3 and c-Src. Therefore, this results have confirmed that cilengitide regulates osteoclast activity by blocking the integrin αvβ3 signal pathway resulting in diminished adhesion and bone resorption of osteoclasts.

Gene expression profile of placentomes and clinical parameters in the cows with retained placenta

BACKGROUND

Retained placenta (RP) is a prevalent disorder in cattle with many health-related and economic costs for the farm owners. Its etiology has not been clarified yet and there is no definite therapy for this disorder. In this study we conducted RNA-seq, hematologic and histologic experiments to survey the causes of RP development.

METHODS

Blood samples were collected from 4 RP and 3 healthy cows during periparturtion period for hematological assessments followed by placentome sampling within 30 min after parturition. Cows were grouped as RP and control in case the placenta was retained or otherwise expelled, respectively. Total RNA was extracted from placentome samples followed by RNA-sequencing.

RESULTS

We showed 240 differentially expressed genes (DEGs) between the RP and control groups. Enrichment analyzes indicated immune system and lipid metabolism as prominent over- and under-represented pathways in RP cows, respectively. Hormonal assessments showed that estradiol-17β (E2) was lower and cortisol tended to be higher in RP cows compared to controls at the day of parturition. Furthermore, histologic experiment showed that villi-crypt junctions remain tighter in RP cows compared to controls and the crypts layer seemed thicker in the placentome of RP cows. Complete blood cell (CBC) parameters were not significantly different between the two groups.

CONCLUSION

Overall, DEGs derived from expression profiling and these genes contributed to enrichment of immune and lipid metabolism pathways. We suggested that E2 could be involved in development of RP and the concentrations of P4 and CBC counts periparturition might not be a determining factor.

Effective treatment of intractable diseases using nanoparticles to interfere with vascular supply and angiogenic process

Angiogenesis is a vital biological process involving blood vessels forming from pre-existing vascular systems. This process contributes to various physiological activities, including embryonic development, hair growth, ovulation, menstruation, and the repair and regeneration of damaged tissue. On the other hand, it is essential in treating a wide range of pathological diseases, such as cardiovascular and ischemic diseases, rheumatoid arthritis, malignancies, ophthalmic and retinal diseases, and other chronic conditions. These diseases and disorders are frequently treated by regulating angiogenesis by utilizing a variety of pro-angiogenic or anti-angiogenic agents or molecules by stimulating or suppressing this complicated process, respectively. Nevertheless, many traditional angiogenic therapy techniques suffer from a lack of ability to achieve the intended therapeutic impact because of various constraints. These disadvantages include limited bioavailability, drug resistance, fast elimination, increased price, nonspecificity, and adverse effects. As a result, it is an excellent time for developing various pro- and anti-angiogenic substances that might circumvent the abovementioned restrictions, followed by their efficient use in treating disorders associated with angiogenesis. In recent years, significant progress has been made in different fields of medicine and biology, including therapeutic angiogenesis. Around the world, a multitude of research groups investigated several inorganic or organic nanoparticles (NPs) that had the potential to effectively modify the angiogenesis processes by either enhancing or suppressing the process. Many studies into the processes behind NP-mediated angiogenesis are well described. In this article, we also cover the application of NPs to encourage tissue vascularization as well as their angiogenic and anti-angiogenic effects in the treatment of several disorders, including bone regeneration, peripheral vascular disease, diabetic retinopathy, ischemic stroke, rheumatoid arthritis, post-ischemic cardiovascular injury, age-related macular degeneration, diabetic retinopathy, gene delivery-based angiogenic therapy, protein delivery-based angiogenic therapy, stem cell angiogenic therapy, and diabetic retinopathy, cancer that may benefit from the behavior of the nanostructures in the vascular system throughout the body. In addition, the accompanying difficulties and potential future applications of NPs in treating angiogenesis-related diseases and antiangiogenic therapies are discussed.

Integrin regulation by tissue factor promotes cancer stemness and metastatic dissemination in breast cancer

Tissue Factor (TF) is the initiator of blood coagulation but also functions as a signal transduction receptor. TF expression in breast cancer is associated with higher tumor grade, metastasis and poor survival. The role of TF signaling on the early phases of metastasis has never been addressed. Here, we show an association between TF expression and metastasis as well as cancer stemness in 574 breast cancer patients. In preclinical models, blockade of TF signaling inhibited metastasis tenfold independent of primary tumor growth. TF blockade caused a reduction in epithelial-to-mesenchymal-transition, cancer stemness and expression of the pro-metastatic markers Slug and SOX9 in several breast cancer cell lines and in ex vivo cultured tumor cells. Mechanistically, TF forms a complex with β1-integrin leading to inactivation of β1-integrin. Inhibition of TF signaling induces a shift in TF-binding from α3β1-integrin to α6β4 and dictates FAK recruitment, leading to reduced epithelial-to-mesenchymal-transition and tumor cell differentiation. In conclusion, TF signaling inhibition leads to reduced pro-metastatic transcriptional programs, and a subsequent integrin β1 and β4-dependent reduction in metastasic dissemination.

The recombinant disintegrin, jarastatin, inhibits platelet adhesion and endothelial cell migration

Integrins are transmembrane heterodimeric glycoproteins, present in most cell types that act as mechanoreceptors, connecting extracellular matrix proteins to the cytoskeleton of the cell, mediating several physiological and pathological processes. The disintegrins are peptides capable of modulating the activity of integrins, such as αIIbβ3, responsible for the platelet aggregation and αvβ3, related to angiogenesis. The aim of this study was to produce the recombinant disintegrin jarastatin (rJast), to evaluate its secondary structure and biological activity. rJast was expressed in the yeast Komagataella phaffii (earlier Pichia pastoris) purified using molecular exclusion chromatography and the internal sequence and molecular mass were confirmed by mass spectrometry. The yield was approximately 40 mg/L of culture. rJast inhibited platelet aggregation induced by 2-4 μM ADP, 10 nM thrombin, and 1 μg/mL collagen (IC₅₀ of 244.8 nM, 166.3 nM and 223.5 nM, respectively). It also blocked the adhesion of platelets to collagen under continuous flow in approximately 60% when used 1 μM. We also evaluated the effect of rJast on HMEC-1 cells. rJast significantly inhibited the adhesion of these cells to vitronectin, as well as cell migration (IC₅₀ 1.77 μM) without changing the viability. Conclusions: rJast was successfully expressed with activity in human platelets aggregation identical to the native molecule. Also, rJast inhibits adhesion and migration of endothelial cells. Thus, being relevant for the development of anti-thrombotic and anti-angiogenic drugs.

Involvement of phosphatidylserine receptors in the skeletal muscle regeneration: therapeutic implications

Sarcopenia is a progressive loss of muscle mass and strength with a risk of adverse outcomes such as disability, poor quality of life, and death. Increasing evidence indicates that diminished ability of the muscle to activate satellite cell-dependent regeneration is one of the factors that might contribute to its development. Skeletal muscle regeneration following myogenic cell death results from the proliferation and differentiation of myogenic stem cells, called satellite cells, located beneath the basal lamina of the muscle fibres. Satellite cell differentiation is not a satellite cell-autonomous process but depends on signals provided by the surrounding cells. Infiltrating macrophages play a key role in the process partly by clearing the necrotic cell debris, partly by producing cytokines and growth factors that guide myogenesis. At the beginning of the muscle regeneration process, macrophages are pro-inflammatory, and the cytokines produced by them trigger the proliferation and differentiation of satellite cells. Following the uptake of dead cells, however, a transcriptionally regulated phenotypic change (macrophage polarization) is induced in them resulting in their transformation into healing macrophages that guide resolution of inflammation, completion of myoblast differentiation, myoblast fusion and growth, and return to homeostasis. Impaired efferocytosis results in delayed cell death clearance, delayed macrophage polarization, prolonged inflammation, and impaired muscle regeneration. Thus, proper efferocytosis by macrophages is a determining factor during muscle repair. Here we review that both efferocytosis and myogenesis are dependent on the cell surface phosphatidylserine (PS), and surprisingly, these two processes share a number of common PS receptors and signalling pathways. Based on these findings, we propose that stimulating the function of PS receptors for facilitating muscle repair following injury could be a successful approach, as it would enhance efferocytosis and myogenesis simultaneously. Because increasing evidence indicates a pathophysiological role of impaired efferocytosis in the development of chronic inflammatory conditions, as well as in impaired muscle regeneration both contributing to the development of sarcopenia, improving efferocytosis should be considered also in its management. Again applying or combining those treatments that target PS receptors would be expected to be the most effective, because they would also promote myogenesis. A potential PS receptor-triggering candidate molecule is milk fat globule-EGF-factor 8 (MFG-E8), which not only stimulates PS-dependent efferocytosis and myoblast fusion but also promotes extracellular signal-regulated kinase (ERK) and Akt activation-mediated cell proliferation and cell cycle progression in myoblasts.

Expression of αV integrin and its potential partners in bull reproductive tissues, germ cells and spermatozoa

Integrins are transmembrane receptors expressed in all nucleated mammalian cells, critically involved in cell-matrix adhesion and cell-cell interactions that modulate many signalling cascades. It is assumed that integrins also provide essential functions of the reproductive system. In this study, we describe the detailed localization and distribution of αV integrin in the plasma membrane of bull sperm head and tail. Integrin αV was observed in the area of forming acrosome in developing sperm since the stage of round spermatids and persists in the acrosome during epididymal maturation and ejaculation till the acrosomal exocytosis. We detected CD9 and CD81 tetraspanins as the potential partners of αV integrin. Their similar staining pattern in testicular tissue suggested the involvement of these molecules in the tetraspanin web of "testisomes". Moreover, the complex of αV with β1 and β3 integrin subunits cannot be excluded at least in sperm. The presented findings contribute to understanding the mutual action of integrins and tetraspanins during sperm development and maturation.

Paxillin: A Hub for Mechano-Transduction from the β3 Integrin-Talin-Kindlin Axis

Focal adhesions are specialized integrin-dependent adhesion complexes, which ensure cell anchoring to the extracellular matrix. Focal adhesions also function as mechano-signaling platforms by perceiving and integrating diverse physical and (bio)chemical cues of their microenvironment, and by transducing them into intracellular signaling for the control of cell behavior. The fundamental biological mechanism of creating intracellular signaling in response to changes in tensional forces appears to be tightly linked to paxillin recruitment and binding to focal adhesions. Interestingly, the tension-dependent nature of the paxillin binding to adhesions, combined with its scaffolding function, suggests a major role of this protein in integrating multiple signals from the microenvironment, and accordingly activating diverse molecular responses. This minireview offers an overview of the molecular bases of the mechano-sensitivity and mechano-signaling capacity of core focal adhesion proteins, and highlights the role of paxillin as a key component of the mechano-transducing machinery based on the interaction of cells to substrates activating the β3 integrin-talin1-kindlin.

Preliminary Clinical Application of RGD-Containing Peptides as PET Radiotracers for Imaging Tumors

Angiogenesis is a common feature of many physiological processes and pathological conditions. RGD-containing peptides can strongly bind to integrin αvβ3 expressed on endothelial cells in neovessels and several tumor cells with high specificity, making them promising molecular agents for imaging angiogenesis. Although studies of RGD-containing peptides combined with radionuclides, namely, 18F, 64Cu, and 68Ga for positron emission tomography (PET) imaging have shown high spatial resolution and accurate quantification of tracer uptake, only a few of these radiotracers have been successfully translated into clinical use. This review summarizes the RGD-based tracers in terms of accumulation in tumors and adjacent tissues, and comparison with traditional 18F-fluorodeoxyglucose (FDG) imaging. The value of RGD-based tracers for diagnosis, differential diagnosis, tumor subvolume delineation, and therapeutic response prediction is mainly discussed. Very low RGD accumulation, in contrast to high FDG metabolism, was found in normal brain tissue, indicating that RGD-based imaging provides an excellent tumor-to-background ratio for improved brain tumor imaging. However, the intensity of the RGD-based tracers is much higher than FDG in normal liver tissue, which could lead to underestimation of primary or metastatic lesions in liver. In multiple studies, RGD-based imaging successfully realized the diagnosis and differential diagnosis of solid tumors and also the prediction of chemoradiotherapy response, providing complementary rather than similar information relative to FDG imaging. Of most interest, baseline RGD uptake values can not only be used to predict the tumor efficacy of antiangiogenic therapy, but also to monitor the occurrence of adverse events in normal organs. This unique dual predictive value in antiangiogenic therapy may be better than that of FDG-based imaging.

Nuclear Molecular Imaging of Cardiac Remodeling after Myocardial Infarction

The role of molecular imaging technologies in detecting, evaluating, and monitoring cardiovascular disease and their treatment is expanding rapidly. Gradually replacing the conventional anatomical or physiological approaches, molecular imaging strategies using biologically targeted markers provide unique insight into pathobiological processes at molecular and cellular levels and allow for cardiovascular disease evaluation and individualized therapy. This review paper will discuss currently available and developing molecular-based single-photon emission computed tomography (SPECT) and positron emission tomography (PET) imaging strategies to evaluate post-infarction cardiac remodeling. These approaches include potential targeted methods of evaluating critical biological processes, such as inflammation, angiogenesis, and scar formation.

Function and Mechanism of RGD in Bone and Cartilage Tissue Engineering

Bone and cartilage injury is common, tissue engineered scaffolds are potential means to repair. Because most of the scaffold materials used in bone and cartilage tissue engineering are bio-inert, it is necessary to increase the cellular adhesion ability of during tissue engineering reconstruction. The Arginine - Glycine - Aspartic acid (Arg-Gly-Asp, RGD) peptide family is considered as a specific recognition site for the integrin receptors. Integrin receptors are key regulators of cell-cell and cell-extracellular microenvironment communication. Therefore, the RGD polypeptide families are considered as suitable candidates for treatment of a variety of diseases and for the regeneration of various tissues and organs. Many scaffold material for tissue engineering and has been approved by US Food and Drug Administration (FDA) for human using. The application of RGD peptides in bone and cartilage tissue engineering was reported seldom. Only a few reviews have summarized the applications of RGD peptide with alloy, bone cements, and PCL in bone tissue engineering. Herein, we summarize the application progress of RGD in bone and cartilage tissue engineering, discuss the effects of structure, sequence, concentration, mechanical stimulation, physicochemical stimulation, and time stimulation of RGD peptide on cells differentiation, and introduce the mechanism of RGD peptide through integrin in the field of bone and cartilage tissue engineering.

Imaging of peripheral vascular malformations - current concepts and future perspectives

Vascular Malformations belong to the spectrum of orphan diseases and can involve all segments of the vascular tree: arteries, capillaries, and veins, and similarly the lymphatic vasculature. The classification according to the International Society for the Study of Vascular Anomalies (ISSVA) is of major importance to guide proper treatment. Imaging plays a crucial role to classify vascular malformations according to their dominant vessel type, anatomical extension, and flow pattern. Several imaging concepts including color-coded Duplex ultrasound/contrast-enhanced ultrasound (CDUS/CEUS), 4D computed tomography angiography (CTA), magnetic resonance imaging (MRI) including dynamic contrast-enhanced MR-angiography (DCE-MRA), and conventional arterial and venous angiography are established in the current clinical routine. Besides the very heterogenous phenotypes of vascular malformations, molecular and genetic profiling has recently offered an advanced understanding of the pathogenesis and progression of these lesions. As distinct molecular subtypes may be suitable for targeted therapies, capturing certain patterns by means of molecular imaging could enhance non-invasive diagnostics of vascular malformations. This review provides an overview of subtype-specific imaging and established imaging modalities, as well as future perspectives of novel functional and molecular imaging approaches. We highlight recent pioneering imaging studies including thermography, positron emission tomography (PET), and multispectral optoacoustic tomography (MSOT), which have successfully targeted specific biomarkers of vascular malformations.

The effect of endocrine disrupting chemicals on the vitronectin-receptor (integrin αvβ3)-mediated cell adhesion of human umbilical vein endothelial cells

Endocrine disrupting chemicals (EDCs) are associated with cancer development and progression due to their promotion of increased cell invasiveness and metastasis formation. However, the effects of EDCs on cell adhesion mediated through integrins have not been well studied to date. Their actions are implicated by binding sites for hormones on the vitronectin receptor (VTNR; or integrin α_vβ₃), which is involved in tumor angiogenesis and metastasis. VTNR-expressing human umbilical vein endothelial cells (HUVECs) were used to determine the effects of EDCs and endogenous hormones on cell adhesion to vitronectin-coated surfaces, and on VTNR activation. Cell adhesion was significantly increased for bisphenol A, triclocarban, and triclosan (10, 100 nM; p < 0.05), with similar trends for bisphenols AF and S (10, 100 nM; p > 0.05). No changes in cell adhesion were seen for 5α-dihydrotestosterone, 17β-estradiol, triiodothyronine, imatinib and paroxetine. These data indicate that EDC-mediated increases in HUVEC adhesion to vitronectin are not mediated through androgenic, estrogenic, or thyroid activities, nor through activation of VTNR. Although these effects of EDCs on HUVEC adhesion require further investigation of the underlying mechanism(s) of action to define their biological relevance, the low-dose effects and nonmonotonic responses revealed here define the need for further investigation of these EDCs.

Positron Emission Tomography Techniques to Measure Active Inflammation, Fibrosis and Angiogenesis: Potential for Non-invasive Imaging of Hypertensive Heart Failure

Heart failure, which is responsible for a high number of deaths worldwide, can develop due to chronic hypertension. Heart failure can involve and progress through several different pathways, including: fibrosis, inflammation, and angiogenesis. Early and specific detection of changes in the myocardium during the transition to heart failure can be made via the use of molecular imaging techniques, including positron emission tomography (PET). Traditional cardiovascular PET techniques, such as myocardial perfusion imaging and sympathetic innervation imaging, have been established at the clinical level but are often lacking in pathway and target specificity that is important for assessment of heart failure. Therefore, there is a need to identify new PET imaging markers of inflammation, fibrosis and angiogenesis that could aid diagnosis, staging and treatment of hypertensive heart failure. This review will provide an overview of key mechanisms underlying hypertensive heart failure and will present the latest developments in PET probes for detection of cardiovascular inflammation, fibrosis and angiogenesis. Currently, selective PET probes for detection of angiogenesis remain elusive but promising PET probes for specific targeting of inflammation and fibrosis are rapidly progressing into clinical use.

Interaction between Galectin-3 and Integrins Mediates Cell-Matrix Adhesion in Endothelial Cells and Mesenchymal Stem Cells

Galectin-3 (Gal-3) is a β-galactoside-binding protein that influences various cell functions, including cell adhesion. We focused on the role of Gal-3 as an extracellular ligand mediating cell-matrix adhesion. We used human adipose tissue-derived stem cells and human umbilical vein endothelial cells that are promising for vascular tissue engineering. We found that these cells naturally contained Gal-3 on their surface and inside the cells. Moreover, they were able to associate with exogenous Gal-3 added to the culture medium. This association was reduced with a β-galactoside LacdiNAc (GalNAcβ1,4GlcNAc), a selective ligand of Gal-3, which binds to the carbohydrate recognition domain (CRD) in the Gal-3 molecule. This ligand was also able to detach Gal-3 newly associated with cells but not Gal-3 naturally present on cells. In addition, Gal-3 preadsorbed on plastic surfaces acted as an adhesion ligand for both cell types, and the cell adhesion was resistant to blocking with LacdiNAc. This result suggests that the adhesion was mediated by a binding site different from the CRD. The blocking of integrin adhesion receptors on cells with specific antibodies revealed that the cell adhesion to the preadsorbed Gal-3 was mediated, at least partially, by β1 and αV integrins-namely α5β1, αVβ3, and αVβ1 integrins.

Bioactive potential of natural biomaterials: identification, retention and assessment of biological properties

Biomaterials have had an increasingly important role in recent decades, in biomedical device design and the development of tissue engineering solutions for cell delivery, drug delivery, device integration, tissue replacement, and more. There is an increasing trend in tissue engineering to use natural substrates, such as macromolecules native to plants and animals to improve the biocompatibility and biodegradability of delivered materials. At the same time, these materials have favourable mechanical properties and often considered to be biologically inert. More importantly, these macromolecules possess innate functions and properties due to their unique chemical composition and structure, which increase their bioactivity and therapeutic potential in a wide range of applications. While much focus has been on integrating these materials into these devices via a spectrum of cross-linking mechanisms, little attention is drawn to residual bioactivity that is often hampered during isolation, purification, and production processes. Herein, we discuss methods of initial material characterisation to determine innate bioactivity, means of material processing including cross-linking, decellularisation, and purification techniques and finally, a biological assessment of retained bioactivity of a final product. This review aims to address considerations for biomaterials design from natural polymers, through the optimisation and preservation of bioactive components that maximise the inherent bioactive potency of the substrate to promote tissue regeneration.

Angiogenesis-Targeted 68Ga-DOTA-RGD2 PET/CT Imaging: a Potential Theranostic Application in the Case of Chondrosarcoma

Chondrosarcoma is a cartilaginous tumor of mesenchymal origin. The histology and grade of the tumor determine the chances of relapse and survival. These tumors usually respond poorly to chemo-radiotherapy in cases of non-resectable and recurrent disease. ¹⁸F-FDG PET/CT has been used in evaluation of recurrence. However, these tumors show only mild to moderate FDG avidity due to their lower mitotic activity and large acellular matrix. These tumors are known to have a high degree of angiogenesis, especially in those of higher grade. We present a case of a 53-year-old man with grade II chondrosarcoma of the left femur showing only mild avidity on ¹⁸F-FDG PET/CT but showing moderate to intense tracer avidity on ⁶⁸Ga-DOTA-RGD₂ PET/CT. This may enable the use of angiogenesis-targeted positron and beta-emitting radiopharmaceuticals as a potentially new theranostic alternative treatment in cases of refractory metastatic chondrosarcoma.

Role of vitronectin-rich protein corona on tumor-specific siRNA delivery and transfection with lipid nanoparticles

Aim: To evaluate the role of vitronectin-enriched protein corona on systemic delivery of siRNA-encapsulated cationic lipid nanoparticles (LNPs) to αvβ3 integrin expressing solid tumors. Materials & methods: 1,2-Dioleoyl-3-trimethylammonium-propane LNPs were formulated, protein corona formed in nude mice serum and its impact on drug delivery were analyzed. Results: 1,2-Dioleoyl-3-trimethylammonium-propane-containing LNP led to enhanced recruitment of vitronectin and showed preferential transfection to αvβ3-expressed cells relative to controls. Upon systemic administration in mice, the LNPs accumulated in the αvβ3-expressing endothelial lining of the tumor blood vessels before reaching tumor cells. Conclusion: These results present an optimized LNP that selectively recruits endogenous proteins in situ to its corona which may lead to enhanced delivery and transfection in tissues of interest.

Modulation of αVβ6 integrin in osteoarthritis-related synovitis and the interaction with VTN(381-397 a.a.) competing for TGF-β1 activation

Osteoarthritis is characterized by structural alteration of joints. Fibrosis of the synovial tissue is often detected and considered one of the main causes of joint stiffness and pain. In our earlier proteomic study, increased levels of vitronectin (VTN) fragment (amino acids 381–397) were observed in the serum of osteoarthritis patients. In this work, the affinity of this fragment for integrins and its putative role in TGF-β1 activation were investigated. A competition study determined the interaction of VTN_{(381–397 a.a.)} with α_Vβ₆ integrin. Subsequently, the presence of α_Vβ₆ integrin was substantiated on primary human fibroblast-like synoviocytes (FLSs) by western blot and flow cytometry. By immunohistochemistry, β₆ was detected in synovial membranes, and its expression showed a correlation with tissue fibrosis. Moreover, β₆ expression was increased under TGF-β1 stimulation; hence, a TGF-β bioassay was applied. We observed that α_Vβ₆ could mediate TGF-β1 bioavailability and that VTN_{(381–397 a.a.)} could prevent TGF-β1 activation by interacting with α_Vβ₆ in human FLSs and increased α-SMA. Finally, we analyzed serum samples from healthy controls and patients with osteoarthritis and other rheumatic diseases by nano-LC/Chip MS–MS, confirming the increased expression of VTN_{(381–397 a.a.)} in osteoarthritis as well as in lupus erythematosus and systemic sclerosis. These findings corroborate our previous observations concerning the overexpression of VTN_{(381–397 a.a.)} in osteoarthritis but also in other rheumatic diseases. This fragment interacts with α_Vβ₆ integrin, a receptor whose expression is increased in FLSs from the osteoarthritic synovial membrane and that can mediate the activation of the TGF-β1 precursor in human FLSs.

Insights into a mechanism underlying the formation of fibrotic tissue within joints in osteoarthritis may also prove relevant to other rheumatological disorders. The general mechanisms underlying fibrosis are reasonably well understood, but it remains unclear what triggers these processes in osteoarthitis. Researchers of the University of Liège in Belgium have uncovered a possible explanation based on experiments with cultured primary synovial fibroblasts from patients. Osteoarthitis is characterized by increased levels of a fragment of the protein vitronectin, and the researchers demonstrated that this in turn binds to a protein called α_Vβ₆, potentially promoting initiation of fibrosis. They also observed elevated levels of the same vitronectin fragment in two other rheumatoid disorders, lupus and systemic sclerosis, and concluded that further research is needed to characterize this protein’s role in inflammation and fibrosis.

Cellular Receptors Involved in KSHV Infection

The process of Kaposi’s Sarcoma Herpes Virus’ (KSHV) entry into target cells is complex and engages several viral glycoproteins which bind to a large range of host cell surface molecules. Receptors for KSHV include heparan sulphate proteoglycans (HSPGs), several integrins and Eph receptors, cystine/glutamate antiporter (xCT) and Dendritic Cell-Specific Intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN). This diverse range of potential binding and entry sites allows KSHV to have a broad cell tropism, and entry into specific cells is dependent on the available receptor repertoire. Several molecules involved in KSHV entry have been well characterized, particularly those postulated to be associated with KSHV-associated pathologies such as Kaposi’s Sarcoma (KS). In this review, KSHV infection of specific cell types pertinent to its pathogenesis will be comprehensively summarized with a focus on the specific cell surface binding and entry receptors KSHV exploits to gain access to a variety of cell types. Gaps in the current literature regarding understanding interactions between KSHV glycoproteins and cellular receptors in virus infection are identified which will lead to the development of virus infection intervention strategies.

Active integrins regulate white adipose tissue insulin sensitivity and brown fat thermogenesis

Objective

Reorganization of the extracellular matrix is a prerequisite for healthy adipose tissue expansion, whereas fibrosis is a key feature of adipose dysfunction and inflammation. However, very little is known about the direct effects of impaired cell–matrix interaction in adipocyte function and insulin sensitivity. The objective of this study was to determine whether integrin activity can regulate insulin sensitivity in adipocytes and thereby systemic metabolism.

Methods

We characterized integrin activity in adipose tissue and its consequences on whole-body metabolism using adipose-selective deletion of β1 integrin (Itgb1^adipo-cre) and Kindlin-2 (Kind2^adipo-cre) in mice.

Results

We demonstrate that integrin signaling regulates white adipocyte insulin action and systemic metabolism. Consequently, loss of adipose integrin activity, similar to loss of adipose insulin receptors, results in a lipodystrophy-like phenotype and systemic insulin resistance. However, brown adipose tissue of Kind2^adipo-cre and Itgb1^adipo-cre mice is chronically hyperactivated and has increased substrate delivery, reduced endothelial basement membrane thickness, and increased endothelial vesicular transport.

Conclusions

Thus, we establish integrin-extracellular matrix interactions as key regulators of white and brown adipose tissue function and whole-body metabolism.

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β1 and β3 integrins interact with insulin signaling to regulate white adipocyte insulin sensitivity and systemic metabolism.

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Impaired integrin activity results in lipodystrophy in the absence of hepatosteatosis.

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β1 integrin activity regulates energy expenditure and vascular permeability in brown adipose tissue.

Upregulation of amplified in breast cancer 1 contributes to pancreatic ductal adenocarcinoma progression and vulnerability to blockage of hedgehog activation

Background: Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive and devastating cancers without effective treatments. Amplified in breast cancer 1 (AIB1) is a member of the steroid receptor coactivator family that mediates the transcriptional activities of nuclear receptors. While AIB1 is associated with the initiation and progression of multiple cancers, the mechanism by which AIB1 contributes to PDAC progression remains unknown. In this study, we aimed to explore the role of AIB1 in the progression of PDAC and elucidate the underlying mechanisms. Methods: The clinical significance and mRNA level of AIB1 in PDAC were studied by database analysis. To demonstrate whether AIB1 mediates the malignant features of PDAC cells, namely, proliferation, migration, invasion, we performed real-time PCR and Western blot analysis, established xenograft models and used in vivo metastasis assay. With insights into the mechanism of AIB1, we performed RNA sequencing (Seq), ChIP-Seq, luciferase reporter assays and pull-down assays. Furthermore, we analyzed the relationship between AIB1 expression and its target expression in PDAC cells and patients and explored whether PDAC cells with high AIB1 levels are sensitive to inhibitors of its target. Results: We found that AIB1 was significantly upregulated in PDAC and associated with its malignancy. Silencing AIB1 impaired hedgehog (Hh) activation by reducing the expression of smoothened (SMO), leading to cell cycle arrest and the inhibition of PDAC cell proliferation. In addition, AIB1, via upregulation of integrin αv (ITGAV) expression, promoted extracellular matrix (ECM) signaling, which played an important role in PDAC progression. Further studies showed that AIB1 preferably bound to AP-1 related elements and served as a coactivator for enhancing the transcriptional activity of MafB, which promoted the expression of SMO and ITGAV. PDAC cells with high AIB1 levels were sensitive to Hh signaling inhibitors, suggesting that blocking Hh activation is an effective treatment against PDAC with high AIB1 expression. Conclusions: These findings reveal that AIB1 is a crucial oncogenic regulator associated with PDAC progression via Hh and ECM signaling and suggest potential therapeutic targets for PDAC treatment.

Altered Protein Function Caused by AMD-associated Variant rs704 Links Vitronectin to Disease Pathology

Purpose

Vitronectin, a cell adhesion and spreading factor, is suspected to play a role in the pathogenesis of age-related macular degeneration (AMD), as it is a major component of AMD-specific extracellular deposits (e.g., soft drusen, subretinal drusenoid deposits). The present study addressed the impact of AMD-associated non-synonymous variant rs704 in the vitronectin-encoding gene VTN on vitronectin functionality.

Methods

Effects of rs704 on vitronectin expression and processing were analyzed by semi-quantitative sequencing of VTN transcripts from retinal pigment epithelium (RPE) cells generated from human induced pluripotent stem cells (hiPSCs) and from human neural retina, as well as by western blot analyses on heterologously expressed vitronectin isoforms. Binding of vitronectin isoforms to retinal and endothelial cells was analyzed by western blot. Immunofluorescence staining followed extracellular matrix (ECM) deposition in cultured RPE cells heterologously expressing the vitronectin isoforms. Adhesion of fluorescently labeled RPE or endothelial cells in dependence of recombinant vitronectin or vitronectin-containing ECM was investigated fluorometrically or microscopically. Tube formation and migration assays addressed effects of vitronectin on angiogenesis-related processes.

Results

Variant rs704 affected expression, secretion, and processing but not oligomerization of vitronectin. Cell binding and influence on RPE-mediated ECM deposition differed between AMD-risk-associated and non-AMD-risk-associated protein isoforms. Finally, vitronectin affected adhesion and endothelial tube formation.

Conclusions

The AMD-risk-associated vitronectin isoform exhibits increased expression and altered functionality in cellular processes related to the sub-RPE aspects of AMD pathology. Although further research is required to address the subretinal disease aspects, this initial study supports an involvement of vitronectin in AMD pathogenesis.

Review of Integrin-Targeting Biomaterials in Tissue Engineering

The ability to direct cell behavior has been central to the success of numerous therapeutics to regenerate tissue or facilitate device integration. Biomaterial scientists are challenged to understand and modulate the interactions of biomaterials with biological systems in order to achieve effective tissue repair. One key area of research investigates the use of extracellular matrix-derived ligands to target specific integrin interactions and induce cellular responses, such as increased cell migration, proliferation, and differentiation of mesenchymal stem cells. These integrin-targeting proteins and peptides have been implemented in a variety of different polymeric scaffolds and devices to enhance tissue regeneration and integration. This review first presents an overview of integrin-mediated cellular processes that have been identified in angiogenesis, wound healing, and bone regeneration. Then, research utilizing biomaterials are highlighted with integrin-targeting motifs as a means to direct these cellular processes to enhance tissue regeneration. In addition to providing improved materials for tissue repair and device integration, these innovative biomaterials provide new tools to probe the complex processes of tissue remodeling in order to enhance the rational design of biomaterial scaffolds and guide tissue regeneration strategies.

Functional role of vitronectin in breast cancer

Breast Cancer is the most common form of cancer in women worldwide, impacting nearly 2.1 million women each year. Identification of new biomarkers could be key for early diagnosis and detection. Vitronectin, a glycoprotein that is abundantly found in serum, extracellular matrix, and bone, binds to integrin αvβ3, and promotes cell adhesion and migration. Current studies indicate that patients with amplified vitronectin levels have lower survival rates than patients without amplified vitronectin levels. In this study, we focused on the role of vitronectin in breast cancer survival and its functional role as a non-invasive biomarker for early stage and stage specific breast cancer detection. To confirm that the expression of vitronectin is amplified in breast cancer, a total of 240 serum samples (n = 240), 200 from breast cancer patients and 40 controls were analyzed using the Reverse Phase Protein Array (RPPA) technique. Of the 240 samples, 120 samples were of African American (AA) descent, while the other 120 were of White American (WA) descent. Data indicated that there were some possible racial disparities in vitronectin levels and, differences also seen in the recurrent patient samples. Next, we tried to uncover the underlying mechanism which plays a critical role in vitronectin expression. The cellular data from four different breast cancer cell lines- MCF7, MDA-MB-231, MDA-MB-468, and HCC1599 indicated that the PI3K/AKT axis is modulating the expression of vitronectin. We believe that vitronectin concentration levels are involved and connected to the metastasis of breast cancer in certain patients, specifically based on recurrence or ethnicity, which is detrimental for poor prognosis. Therefore, in this current study we showed that the serum vitronectin levels could be an early marker for the breast cancer survival and we also determine the cellular signaling factors which modulate the expression and concentration of vitronectin.

Enhanced expression of αVβ3 integrin in villus and extravillous trophoblasts of placenta accreta

BACKGROUND

Placenta accreta is one of the most serious complications in obstetrics and gynecology. Villous trophoblasts (VT) and extravillous trophoblasts (EVT) play a central role in normal placentation. Placenta accreta is characterized by abnormal invasion of EVT cells through the uterine layers, due to changes in several parameters, including adhesion proteins. Although αvβ3 integrin is a central adhesion molecule, participating in multiple invasive pathological conditions including cancer, data on placenta accreta are lacking.

OBJECTIVE

To study the expression pattern of αvβ3 integrin in placenta accreta in comparison with normal placentas.

STUDY DESIGN

We collected tissue samples from placentas defined as percreta, the most severe presentation of placenta accreta and from normal control placentas (n = 10 each). The samples underwent protein extractions for analyses of αvβ3 expression by Western blots (WB) and a parallel tissue assessment by immunohistochemistry (IHC).

RESULTS

WB results indicated significantly elevated αvβ3 integrin expression in the percreta samples compared to normal placentas. These elevated levels were mainly contributed by EVT cells, as demonstrated by IHC. αvβ3 integrin demonstrated a classical membranal expression in the VT cells, whereas a uniformly distributed expression was documented in the EVT cells. These patterns of the αvβ3 integrin localization were similar in both accreta and normal placental samples.

CONCLUSIONS

Enhanced αvβ3 integrin expression, mainly in extra villous trophoblasts of placenta percreta, implies for a role of this adhesion molecule in pathological placentation.

Non-oncological applications of RGD-based single-photon emission tomography and positron emission tomography agents

INTRODUCTION

Non-invasive imaging techniques (especially single-photon emission tomography and positron emission tomography) apply several RGD-based imaging ligands developed during a vast number of preclinical and clinical investigations. The RGD (Arg-Gly-Asp) sequence is a binding moiety for a large selection of adhesive extracellular matrix and cell surface proteins. Since the first identification of this sequence as the shortest sequence required for recognition in fibronectin during the 1980s, fundamental research regarding the molecular mechanisms of integrin action have paved the way for development of several pharmaceuticals and radiopharmaceuticals with clinical applications. Ligands recognizing RGD may be developed for use in the monitoring of these interactions (benign or pathological). Although RGD-based molecular imaging has been actively investigated for oncological purposes, their utilization towards non-oncology applications remains relatively under-exploited.

METHODS AND SCOPE

This review highlights the new non-oncologic applications of RGD-based tracers (with the focus on single-photon emission tomography and positron emission tomography). The focus is on the last 10 years of scientific literature (2009-2020). It is proposed that these imaging agents will be used for off-label indications that may provide options for disease monitoring where there are no approved tracers available, for instance Crohn's disease or osteoporosis. Fundamental science investigations have made progress in elucidating the involvement of integrin in various diseases not pertaining to oncology. Furthermore, RGD-based radiopharmaceuticals have been evaluated extensively for safety during clinical evaluations of various natures.

CONCLUSION

Clinical translation of non-oncological applications for RGD-based radiopharmaceuticals and other imaging tracers without going through time-consuming extensive development is therefore highly plausible. Graphical abstract.

Prominent Receptors of Liver Sinusoidal Endothelial Cells in Liver Homeostasis and Disease

Liver sinusoidal endothelial cells (LSECs) are the most abundant non-parenchymal cells lining the sinusoidal capillaries of the hepatic system. LSECs are characterized with numerous fenestrae and lack basement membrane as well as a diaphragm. These unique morphological characteristics of LSECs makes them the most permeable endothelial cells of the mammalian vasculature and aid in regulating flow of macromolecules and small lipid-based structures between sinusoidal blood and parenchymal cells. LSECs have a very high endocytic capacity aided by scavenger receptors (SR), such as SR-A, SR-B (SR-B1 and CD-36), SR-E (Lox-1 and mannose receptors), and SR-H (Stabilins). Other high-affinity receptors for mediating endocytosis include the FcγRIIb, which assist in the antibody-mediated removal of immune complexes. Complemented with intense lysosomal activity, LSECs play a vital role in the uptake and degradation of many blood borne waste macromolecules and small (<280 nm) colloids. Currently, seven Toll-like receptors have been investigated in LSECs, which are involved in the recognition and clearance of pathogen-associated molecular pattern (PAMPs) as well as damage associated molecular pattern (DAMP). Along with other SRs, LSECs play an essential role in maintaining lipid homeostasis with the low-density lipoprotein receptor-related protein-1 (LRP-1), in juxtaposition with hepatocytes. LSECs co-express two surface lectins called L-Specific Intercellular adhesion molecule-3 Grabbing Non-integrin Receptor (L-SIGN) and liver sinusoidal endothelial cell lectin (LSECtin). LSECs also express several adhesion molecules which are involved in the recruitment of leukocytes at the site of inflammation. Here, we review these cell surface receptors as well as other components expressed by LSECs and their functions in the maintenance of liver homeostasis. We further discuss receptor expression and activity and dysregulation associated with the initiation and progression of many liver diseases, such as hepatocellular carcinoma, liver fibrosis, and cirrhosis, alcoholic and non-alcoholic fatty liver diseases and pseudocapillarization with aging.

Engineered Three-Dimensional Tumor Models to Study Natural Killer Cell Suppression

A critical hurdle associated with natural killer (NK) cell immunotherapies is inadequate infiltration and function in the solid tumor microenvironment. Well-controlled 3D culture systems could advance our understanding of the role of various biophysical and biochemical cues that impact NK cell migration in solid tumors. The objectives of this study were to establish a biomaterial which (i) supports NK cell migration and (ii) recapitulates features of the in vivo solid tumor microenvironment, to study NK infiltration and function in a 3D system. Using peptide-functionalized poly(ethylene glycol)-based hydrogels, the extent of NK-92 cell migration was observed to be largely dependent on the density of integrin binding sites and the presence of matrix metalloproteinase degradable sites. When lung cancer cells were encapsulated into the hydrogels to create tumor microenvironments, the extent of NK-92 cell migration and functional activity was dependent on the cancer cell type and duration of 3D culture. NK-92 cells showed greater migration into the models consisting of nonmetastatic A549 cells relative to metastatic H1299 cells, and reduced migration in both models when cancer cells were cultured for 7 days versus 1 day. In addition, the production of NK cell-related pro-inflammatory cytokines and chemokines was reduced in H1299 models relative to A549 models. These differences in NK-92 cell migration and cytokine/chemokine production corresponded to differences in the production of various immunomodulatory molecules by the different cancer cells, namely, the H1299 models showed increased stress ligand shedding and immunosuppressive cytokine production, particularly TGF-β. Indeed, inhibition of TGF-β receptor I in NK-92 cells restored their infiltration in H1299 models to levels similar to that in A549 models and increased overall infiltration in both models. Relative to conventional 2D cocultures, NK-92 cell mediated cytotoxicity was reduced in the 3D tumor models, suggesting the hydrogel serves to mimic some features of the biophysical barriers in in vivo tumor microenvironments. This study demonstrates the feasibility of a synthetic hydrogel system for investigating the biophysical and biochemical cues impacting NK cell infiltration and NK cell-cancer cell interactions in the solid tumor microenvironment.

Structure-Activity Relationship of RGD-Containing Cyclic Octapeptide and αvβ3 Integrin Allows for Rapid Identification of a New Peptide Antagonist

The αvβ3 integrin, a receptor for many extracellular matrix proteins with RGD-sequence motif, is involved in multiple physiological processes and highly expressed in tumor cells, therefore making it a target for cancer therapy and tumor imaging. Several RGD-containing cyclic octapeptide (named LXW analogs) were screened as αvβ3 antagonists with dramatically different binding affinity, and their structure–activity relationship (SAR) remains elusive. We performed systematic SAR studies and optimized LXW analogs to improve antagonistic potency. The NMR structure of LXW64 was determined and docked to the integrin. Structural comparison and docking studies suggested that the hydrophobicity and aromaticity of the X7 amino acid are highly important for LXW analogs binding to the integrin, a potential hydrophobic pocket on the integrin surface was proposed to play a role in stabilizing the peptide binding. To develop a cost-efficient and fast screening method, computational docking was performed on LXW analogs and compared with in vitro screening. A consistency within the results of both methods was found, leading to the continuous optimization and testing of LXW mutants via in silico screening. Several new LXW analogs were predicted as the integrin antagonists, one of which—LXZ2—was validated by in vitro examination. Our study provides new insight into the RGD recognition specificity and valuable clues for rational design of novel αvβ3 antagonists.

c-Src controls stability of sprouting blood vessels in the developing retina independently of cell-cell adhesion through focal adhesion assembly

Endothelial cell adhesion is implicated in blood vessel sprout formation, yet how adhesion controls angiogenesis, and whether it occurs via rapid remodeling of adherens junctions or focal adhesion assembly, or both, remains poorly understood. Furthermore, how endothelial cell adhesion is controlled in particular tissues and under different conditions remains unexplored. Here, we have identified an unexpected role for spatiotemporal c-Src activity in sprouting angiogenesis in the retina, which is in contrast to the dominant focus on the role of c-Src in the maintenance of vascular integrity. Thus, mice specifically deficient in endothelial c-Src displayed significantly reduced blood vessel sprouting and loss in actin-rich filopodial protrusions at the vascular front of the developing retina. In contrast to what has been observed during vascular leakage, endothelial cell-cell adhesion was unaffected by loss of c-Src. Instead, decreased angiogenic sprouting was due to loss of focal adhesion assembly and cell-matrix adhesion, resulting in loss of sprout stability. These results demonstrate that c-Src signaling at specified endothelial cell membrane compartments (adherens junctions or focal adhesions) control vascular processes in a tissue- and context-dependent manner.

Cilostazol Mediates Immune Responses and Affects Angiogenesis During the Acute Phase of Hind Limb Ischemia in a Mouse Model

BACKGROUND

Cilostazol is a drug of choice for the treatment of intermittent claudication that also affects innate and adaptive immune cells. The purpose of our study was the evaluation of cilostazol's impact on the immune and angiogenic response in murine models of hind limb ischemia.

METHODS

We used 108 immunodeficient NOD.CB17-Prkdcscid/J mice and 108 wild-type CB17 mice. At day 0 (D0), all animals underwent hind limb ischemia. Half of them in both groups received daily cilostazol starting at D0 and for the next 7 postoperative days, while the rest of them served as controls, receiving vehicle. Interleukin (IL) 2, IL-4, IL-6, IL-10, IL-17A, tumor necrosis factor α (TNF-α), and interferon γ (IFN-γ) serum concentrations were measured by flow cytometry on postsurgery days D1, D3, D5, and D7. On D7, both groups underwent positron emission tomography scan with ⁶⁸Ga-RGD. Mice were euthanatized and gastrocnemius muscles were obtained for histological evaluation.

RESULTS

There was a statistically significant augmentation (P < .05) in IL-4, IL-10, IL-6, and IFN-γ concentrations in treated CB17 animals, while IL-2 was significantly suppressed. Significant difference was detected between the CiBisch and Bisch groups on D1 and D7 (P < .05) in CD31 staining. In treated NOD.CB17 animals, TNF-α, IL-6, and IFN-γ presented significant augmentation, while ⁶⁸Ga-NODAGA-RGDfK uptake and CD31 expression were found significantly lower for both legs in comparison to the control.

CONCLUSION

Cilostazol seems to significantly increase angiogenesis in wild-type animals during the first postoperational week. It also influences immune cells, altering the type of immune response by promoting anti-inflammatory cytokine production in wild-type animals, while it helps toward inflammation regression in immunodeficient animals.

Molecular imaging of bone metastases using tumor-targeted tracers

Bone metastasis is a disastrous manifestation of most malignancies, especially in breast, prostate and lung cancers. Since asymptomatic bone metastases are not uncommon, early detection, precise assessment, and localization of them are very important. Various imaging modalities have been employed in the setting of diagnosis of bone metastasis, from plain radiography and bone scintigraphy to SPECT, SPECT/CT, PET/CT, MRI. However, each modality showed its own limitation providing accurate diagnostic performance. In this regard, various tumor-targeted radiotracers have been introduced for molecular imaging of bone metastases using modern hybrid modalities. In this article we review the strength of different cancer-specific radiopharmaceuticals in the detection of bone metastases. As shown in the literature, among various tumor-targeted tracers, 68Ga DOTA-conjugated-peptides, 68Ga PSMA, 18F DOPA, 18F galacto-RGD integrin, 18F FDG, 11C/18F acetate, 11C/18F choline, 111In octreotide, 123/131I MIBG, 99mTc MIBI, and 201Tl have acceptable capabilities in detecting bone metastases depending on the cancer type. However, different study designs and gold standards among reviewed articles should be taken into consideration.

N-glycosylation of uterine endometrium determines its receptivity

Glycosylation alters the molecular and functional features of glycoproteins, which is closely related with many physiological processes and diseases. During "window of implantation", uterine endometrium transforms into a receptive status to accept the embryo, thereby establishing successful embryo implantation. In this article, we aimed at investigating the role of N-glycosylation, a major modification type of glycoproteins, in the process of endometrial receptivity establishment. Results found that human uterine endometrial tissues at mid-secretory phase exhibited Lectin PHA-E+L (recognizes the branched N-glycans) positive N-glycans as measured by the Lectin fluorescent staining analysis. By utilizing in vitro implantation model, we found that de-N-glycosylation of human endometrial Ishikawa and RL95-2 cells by tunicamycin (inhibitor of N-glycosylation) and peptide-N-glycosidase F (PNGase F) impaired their receptive ability to human trophoblastic JAR cells. Meanwhile, N-glycosylation of integrin αvβ3 and leukemia inhibitory factor receptor (LIFR) are found to play key roles in regulating the ECM-dependent FAK/Paxillin and LIF-induced STAT3 signaling pathways, respectively, thus affecting the receptive potentials of endometrial cells. Furthermore, in vivo experiments and primary mouse endometrial cells-embryos coculture model further verified that N-glycosylation of mouse endometrial cells contributed to the successful implantation. Our results provide new evidence to show that N-glycosylation of uterine endometrium is essential for maintaining the receptive functions, which gives a better understanding of the glycobiology of implantation.

Comparison of [99mTc]3PRGD2 Imaging and [18F]FDG PET/CT in Breast Cancer and Expression of Integrin αvβ3 in Breast Cancer Vascular Endothelial Cells

PURPOSE

This study aimed to investigate the value of ^99mtechnetium-three polyethylene glycol spacers-arginine-glycine-aspartic acid ([^99mTc]3PRGD₂) imaging in diagnosis and staging of breast cancer compared with 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) imaging, and to explore the expression of integrin α_vβ₃ in tumor vascular endothelial cells.

PROCEDURES

Forty-two women with suspected breast cancer underwent both [^99mTc]3PRGD₂ imaging and [¹⁸F]FDG imaging. Visual analysis was used to assess primary breast lesion, axillary lymph node, and distant metastasis. The tumor-blood (T/B) ratios from [^99mTc]3PRGD₂ imaging and the maximum standardized uptake value (SUVmax) from [¹⁸F]FDG imaging were analyzed for breast lesions. Integrin α_vβ₃ was analyzed through immunohistochemistry.

RESULTS

Forty-five breast lesions were found (malignant, n = 38; benign, n = 7). The sensitivity, specificity, and accuracy of [^99mTc]3PRGD₂ and [¹⁸F]FDG imaging in visual analysis for the breast lesion were 97.4, 87.5, and 95.6 % and 97.4, 71.4, and 93.3 %, respectively (P > 0.05). For semi-quantitative analysis, no significant difference of the area under the curves (AUC) was found in the imaging using the two radiopharmaceuticals (0.880 and 0.955; Z = 0.88, P > 0.05). The sensitivity, specificity, and accuracy for axillary lymph node metastasis with [^99mTc]3PRGD₂ and [¹⁸F]FDG were 78.05, 99.36, and 94.92 % and 85.37, 98.72, and 95.64 %, respectively (P > 0.05). Nine patients with distant metastases were all detected with the two radiopharmaceuticals. The expression of integrin α_vβ₃ was correlated with [^99mTc]3PRGD₂ uptake (r = 0.582, P = 0.001), which were significantly higher in the HER2-positive and stage III-IV patients (P < 0.05).

CONCLUSIONS

The prospective study demonstrated that [^99mTc]3PRGD₂ imaging seems to be valuable for diagnosis of breast cancer and its staging. It may be less sensitive for detecting small lymph node metastatic lesions when compared with [¹⁸F]FDG imaging. Integrin α_vβ₃ in tumor microvessels was associated with the breast cancer subtype and its staging.

Neutrophil extracellular traps promote peritoneal metastasis of colon cancer cells

Cytoreductive surgery is the only curative option for patients with peritoneal carcinomatosis, however, intraperitoneal recurrence rate is high making new ways to prevent cancer recurrence an urgent need. Recent evidence suggests that neutrophils are involved in cancer progression. The purpose of our study was to examine the role of neutrophils in the spread of colon cancer cells in the peritoneal cavity.

The number of metastatic noduli in the peritoneal cavity was quantified in mice injected with murine colon cancer cells (CT-26) intraperitoneally after surgical laparotomy and treated with a neutrophil depleting antibody or DNase I. In addition, peritoneal metastases were harvested from patients with peritoneal carcinomatosis. Scanning and transmission electron microscopy showed extensive neutrophil extracellular trap (NET) formation in peritoneal colon cancer metastases in mice and patients. Neutrophil depletion markedly reduced the number of metastases in laparotomised animals. Administration of DNase I decreased the number of metastatic nodules by 88% in laparotomised animals as well as NET-induced chemokine-dependent colon cancer cell migration and adhesion in vitro. Finally, CT-26 cancer cells were found to express the α_vβ₃ integrin and inhibition of αv integrin abolished NET-induced adhesion of colon cancer cells to vitronectin. Taken together, our data show that NETs play an important role in colon cancer cell metastasis in the peritoneal cavity and regulate colon cancer cell migration and adhesion to extracellular matrix proteins. These novel findings suggest that targeting NETs might be an effective strategy to antagonize intrabdominal recurrences of colon cancer after cytoreductive surgery in patients with peritoneal carcinomatosis.

Efficient synthesis of novel RGD based peptides and the conjugation of the pyrazine moiety to their N-terminus

Novel RGD based peptides (RGDFAKLF and RGDNGRG) were designed and synthesized and were later coupled to the pyrazine moiety at the N-terminus. The IC₅₀ values from the in vitro study of the target peptides using a cell adhesion assay indicated the essential impact of the existence of the pyrazine moiety. Meanwhile, peptide 4 exhibited the best IC₅₀ value.

Effect of fluid dynamics on decellularization efficacy and mechanical properties of blood vessels

Decellularization of blood vessels is a promising approach to generate native biomaterials for replacement of diseased vessels. The decellularization process affects the mechanical properties of the vascular graft and thus can have a negative impact for in vivo functionality. The aim of this study was to determine how detergents under different fluid dynamics affects decellularization efficacy and mechanical properties of the vascular graft. We applied a protocol utilizing 1% TritonX, 1% Tributyl phosphate (TnBP) and DNase on porcine vena cava. The detergents were applied to the vessels under different conditions; static, agitation and perfusion with 3 different perfusion rates (25, 100 and 400 mL/min). The decellularized grafts were analyzed with histological, immunohistochemical and mechanical tests. We found that decellularization efficacy was equal in all groups, however the luminal ultrastructure of the static group showed remnant cell debris and the 400 mL/min perfusion group showed local damage and tearing of the luminal surface. The mechanical stiffness and maximum tensile strength were not influenced by the detergent application method. In conclusion, our results indicate that agitation or low-velocity perfusion with detergents are preferable methods for blood vessel decellularization.

Regulatory actions of 3',5'-cyclic adenosine monophosphate on osteoclast function: possible roles of Epac-mediated signaling

Alterations in cellular levels of the second messenger 3',5'-cyclic adenosine monophosphate ([cAMP]_i ) regulate a wide range of physiologically important cellular signaling processes in numerous cell types. Osteoclasts are terminally differentiated, multinucleated cells specialized for bone resorption. Their systemic regulator, calcitonin, triggers morphometrically and pharmacologically distinct retraction (R) and quiescence (Q) effects on cell-spread area and protrusion-retraction motility, respectively, paralleling its inhibition of bone resorption. Q effects were reproduced by cholera toxin-mediated G_s -protein activation known to increase [cAMP]_i , unaccompanied by the [Ca²⁺ ]_i changes contrastingly associated with R effects. We explore a hypothesis implicating cAMP signaling involving guanine nucleotide-exchange activation of the small GTPase Ras-proximate-1 (Rap1) by exchange proteins directly activated by cAMP (Epac). Rap1 activates integrin clustering, cell adhesion to bone matrix, associated cytoskeletal modifications and signaling processes, and transmembrane transduction functions. Epac activation enhanced, whereas Epac inhibition or shRNA-mediated knockdown compromised, the appearance of markers for osteoclast differentiation and motility following stimulation by receptor activator of nuclear factor kappa-Β ligand (RANKL). Deficiencies in talin and Rap1 compromised in vivo bone resorption, producing osteopetrotic phenotypes in genetically modified murine models. Translational implications of an Epac-Rap1 signaling hypothesis in relationship to N-bisphosphonate actions on prenylation and membrane localization of small GTPases are discussed.