Domain V Research Articles

Atomistic characterization of β2-glycoprotein I domain V interaction with anionic membranes

BackgroundInteraction of β2-glycoprotein I (β2GPI) with anionic membranes is crucial in antiphospholipid syndrome (APS), implicating the role of its membrane-binding domain, domain V (DV). The mechanism of DV binding to anionic lipids is not fully understood. ObjectivesThis study aimed to elucidate the molecular details of β2GPI DV binding to anionic membranes. MethodsWe utilized molecular dynamics simulations to investigate the structural basis of anionic lipid recognition by DV. To corroborate the membrane-binding mode identified in the highly mobile membrane mimetic simulations, we conducted additional simulations using a full membrane model. ResultsThe study identified critical regions in DV, namely the lysine-rich loop and the hydrophobic loop, which are essential for membrane association via electrostatic and hydrophobic interactions, respectively. A novel lysine pair contributing to membrane binding was also discovered, providing new insights into β2GPI’s membrane interaction. Simulations revealed 2 distinct binding modes of DV to the membrane, with mode 1 characterized by the insertion of the hydrophobic loop into the lipid bilayer, suggesting a dominant mechanism for membrane association. This interaction is pivotal for the pathogenesis of APS, as it facilitates the recognition of β2GPI by antiphospholipid antibodies. ConclusionThe study advances our understanding of the molecular interactions between β2GPI’s DV and anionic membranes, which are crucial for APS pathogenesis. It highlights the importance of specific regions in DV for membrane binding and reveals a predominant binding mode. These findings have significant implications for APS diagnostics and therapeutics, offering a deeper insight into the molecular basis of the syndrome.

An allosteric redox switch in domain V of β2-glycoprotein I controls membrane binding and anti-domain I autoantibody recognition

β2-glycoprotein I (β2GPI) is an abundant multidomain plasma protein that plays various roles in the clotting and complement cascades. It is also the main target of antiphospholipid antibodies (aPL) in the acquired coagulopathy known as antiphospholipid syndrome (APS). Previous studies have shown that β2GPI adopts two interconvertible biochemical conformations, oxidized and reduced, depending on the integrity of the disulfide bonds. However, the precise contribution of the disulfide bonds to β2GPI structure and function is unknown. Here, we substituted cysteine residues with serine to investigate how the disulfide bonds C32-C60 in domain I (DI) and C288-C326 in domain V (DV) regulate β2GPI's structure and function. Results of our biophysical and biochemical studies support the hypothesis that the C32-C60 disulfide bond plays a structural role, whereas the disulfide bond C288-C326 is allosteric. We demonstrate that absence of the C288-C326 bond, unlike absence of the C32-C60 bond, diminishes membrane binding without affecting the thermodynamic stability and overall structure of the protein, which remains elongated in solution. We also document that, while absence of the C32-C60 bond directly impairs recognition of β2GPI by pathogenic anti-DI antibodies, absence of the C288-C326 disulfide bond is sufficient to abolish complex formation in the presence of anionic phospholipids. We conclude that the disulfide bond C288-C326 operates as a molecular switch capable of regulating β2GPI's physiological functions in a redox-dependent manner. We propose that in APS patients with anti-DI antibodies, selective rupture of the C288-C326 disulfide bond may be a valid strategy to lower the pathogenic potential of aPL.

Abstract P755: Perlecan Lg3 is Neuroprotective and Functionally Restorative in Experimental Ischemic Stroke

Despite promising advancements, ischemic stroke remains a leading cause of death and disability. We previously determined that human recombinant ~85-kDa C-terminal protein fragment of the vascular basement membrane proteoglycan perlecan termed domain V (DV) is neuroprotective, pro-angiogenic, neurogenic and functionally restorative when administered after experimental stroke (transient and permanent middle cerebral artery occlusion -MCAO) in mice and rats. As previous studies suggest, the 23-kDa subdomain of DV called laminin globular domain 3 (LG3) may confer most of DV’s biological activity and is more amenable to production, we tested whether human recombinant perlecan DV LG3 (also termed “DV LG3 ”) might be neuroprotective and functionally restorative in the transient MCAO (intraluminal filament model). Methods: Fifty male mice (C57BL/6J, 10-12 weeks old, 24–30 g) underwent MCAO for 60 min and were survived for seven days. At reperfusion mice were randomly allocated to one of three treatment groups and immediately received either human recombinant DV treatment (positive control, n=16 2 mg/kg, i.p.), LG3 (n=19 6 mg/kg, i.p.), or equivalent volume of PBS vehicle (n=15) ; and again on post-MCAO days 2 and 4. The DV:LG3 dose ratio was selected based on a preliminary in vivo dose evaluation study of therapeutic equivalence. Functional outcome measures (grip strength and grid-hang tests) were determined at baseline and on post-MCAO days 1, 3 and 7. Body weight was measured daily as per welfare. To determine infarct size on post-MCAO day 7, whole brain samples were harvested, sectioned and stained with 2,3,5- Triphenyltetrazolium chloride. The induction of MCAO, DV, DV LG3 or PBS treatments, functional tests and analyses were performed, blindly, by different individuals. While DV treatment significantly reduced mean infarct volume as expected (p<0.022, compared to PBS control group), DV LG3 further reduced infarct volumes (p<0.0001), weight loss (p<0.0002) and improved functional outcome measures (p<0.01) compared to PBS group. Our findings show that human recombinant DV LG3 is neuroprotective and functionally restorative, may be even more effective than DV, and is worthy of more study as a readily producible therapy for ischemic stroke.

Characterization of Beta-2-Glycoprotein I Domain V interaction with Plasma Membrane

Beta-2-Glycoprotein I (β2GPI), also known as apolipoprotein H, is a 48kDa protein which circulates in blood at a high concentration [0.2 mg/ml]. β2GPI is the main target of autoantibodies in antiphospholipid syndrome (APS) which results in thrombosis and/or recurrent miscarriage. Therefore, investigating membrane binding mechanism of β2GPI is important to elucidate how this protein become immunogenic upon binding to plasma membrane and to help target specific drug development for APS. It is known that β2GPI binds to anionic phospholipids in the plasma membrane via its positively charged domain V (DV) but the mechanism of binding is still elusive. in this study, we performed multiple 500-ns molecular dynamics simulations of β2GPI-DV in the presence of membranes containing PC and PS in varying compositions employing the HMMM (highly mobile membrane mimetic) model. We observed stable membrane binding in eight out of ten replicas. Our results show that in seven out of eight replicas, β2GPI-DV interacts with the membrane via its flexible loop (311-317) which insert into the membrane below the PO4 level. interestingly, in one replica we observe insertion of the loop carrying three lysine residues, a mode which closely corresponds to an alternative binding mode reported previously. The orientation of membrane-bound states was characterized by measuring the tilt angle between the protein and the membrane. After insertion of the flexible loop, β2GPI-DV held an average tilt angle of 92 with respect to the membrane normal. This study establishes the significance of the flexible loop for membrane binding of β2GPI which could lead to a more rational approach in drug design for treatment of APS.

The J-elongated conformation of β2-glycoprotein I predominates in solution: implications for our understanding of antiphospholipid syndrome

β2-Glycoprotein I (β2GPI) is an abundant plasma protein displaying phospholipid-binding properties. Because it binds phospholipids, it is a target of antiphospholipid antibodies (aPLs) in antiphospholipid syndrome (APS), a life-threatening autoimmune thrombotic disease. Indeed, aPLs prefer membrane-bound β2GPI to that in solution. β2GPI exists in two almost equally populated redox states: oxidized, in which all the disulfide bonds are formed, and reduced, in which one or more disulfide bonds are broken. Furthermore, β2GPI can adopt multiple conformations (i.e. J-elongated, S-twisted, and O-circular). While strong evidence indicates that the J-form is the structure bound to aPLs, which conformation exists and predominates in solution remains controversial, and so is the conformational pathway leading to the bound state. Here, we report that human recombinant β2GPI purified under native conditions is oxidized. Moreover, under physiological pH and salt concentrations, this oxidized form adopts a J-elongated, flexible conformation, not circular or twisted, in which the N-terminal domain I (DI) and the C-terminal domain V (DV) are exposed to the solvent. Consistent with this model, binding kinetics and mutagenesis experiments revealed that in solution the J-form interacts with negatively charged liposomes and with MBB2, a monoclonal anti-DI antibody that recapitulates most of the features of pathogenic aPLs. We conclude that the preferential binding of aPLs to phospholipid-bound β2GPI arises from the ability of its preexisting J-form to accumulate on the membranes, thereby offering an ideal environment for aPL binding. We propose that targeting the J-form of β2GPI provides a strategy to block pathogenic aPLs in APS.

Perlecan Domain V Increases Amyloid Clearance in Co‐Morbid VCID

IntroductionVascular contributions to cognitive impairment and dementia (VCID) is a broad term that encompasses a spectrum of initial asymptomatic cerebrovascular changes (seen in small vessel disease and cerebral amyloid angiopathy) to the profound symptomatic damage following acute stroke(s). Besides aging, metabolic disorders such as type 2 diabetes complicate our understanding of underlying mechanisms. Cerebrovascular remodeling and angiogenesis may represent early compensatory changes to the reduced blood flow seen in VCID by increasing the proteolytic turnover of the surrounding extracellular matrix. We have demonstrated that one such extracellular matrix protein, perlecan, possesses a C terminal domain V (DV) protein that, upon cleavage from perlecan, greatly enhances brain angiogenesis.ObjectiveWe hypothesize that DV therapy can reduce pathological changes in the cerebrovasculature, an underlying component of VCID.MethodsDV's mechanism and therapeutic potential in facilitating Aβ clearance were examined in an ex vivo model of isolated mouse brain capillaries in normal and high glucose environments. We also determined the cerebrovascular changes in a comorbidity mouse model of VCID (diabetic APP/PS1 knock in (db/AD)) that is associated with hemorrhages, aneurysms, Aβ deposition, cognitive decline and increased mortality.ResultsDV (300 and 600 nM) doubled the transport of fluorescently tagged hAβ1‐42 over 24 hours from the bath (abluminal) to luminal side of the brain capillaries. One of Aβ's known transport proteins, P‐glycoprotein (P‐gp), also increased in total protein expression and in transport activity in the presence of DV. At 3–6 months in db/AD mice, we observed a decrease in BBB proteins (claudin‐5) indicating an altered cerebrovascular function correlating with DV expression increase during the asymptomatic angiogenic stage. At 9–12 months, cognitive changes were associated with altered cerebrovascular protein expression in PECAM, Collagen IV, and DV correlating with the aberrant two‐photon vascular imaging, increased saccular aneurysms, and microhemorrhages.ConclusionThese data show that DV increases cerebrovascular Aβ clearance through P‐gp. Increased DV expression correlates with early cerebrovascular changes induced by angiogenic‐remodeling in a diabetic co‐morbid mouse model of VCID. Lower DV expression is associated with aberrant vasculature that contribute to increased mortality, suggesting that DV ‘replacement therapy’ could represent a novel therapeutic for VCID.Support or Funding InformationNIH RO1 N5089515‐01This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Abstract WP558: Benefits of Perlecan Domain V in Diabetic Co-morbid Models of VCID

Introduction: Vascular contributions to cognitive impairment and dementia (VCID) are a major factor in the overall clinical burden of dementia. Besides aging, metabolic disorders such as type 2 diabetes complicate understanding of underlying mechanisms. Despite the complexity, we hypothesize that pathological changes in cerebrovascular extracellular matrix (ECM) are an underlying component of VCID that can be therapeutically targeted to reduce neurodegeneration and improve outcomes . One such ECM component, the terminal domain V (DV) of perlecan, greatly reduces amyloid toxicity and enhances angiogenic cerebrovascular remodeling. Methods: DV’s mechanism and therapeutic potential in facilitating Aβ clearance were examined in an ex vivo model of isolated mouse brain capillaries in normal and high glucose environments. We also determined the cerebrovascular changes in a comorbidity mouse model of VCID (diabetic APP/PS1 knock in (db/AD)) that is associated with hemorrhages, aneurysms, Aβ deposition, cognitive decline and increased mortality. Results: DV (300 and 600 nM) doubled the transport of fluorescently tagged hAβ1-42 over 24 hours from the bath (abluminal) to luminal side of the brain capillaries. One of Aβ’s known transport proteins, P-glycoprotein (P-gp), also increased in total protein expression and in transport activity in the presence of DV. At 3-6 months in db/AD mice, we observed a decrease in BBB proteins (claudin-5) indicating an altered cerebrovascular function correlating with DV expression increase during the asymptomatic angiogenic stage. At 9-12 months, cognitive changes were associated with altered cerebrovascular protein expression in PECAM, Collagen IV, and DV correlating with the aberrant two-photon vascular imaging, increased saccular aneurysms, and microhemorrhages. Conclusion: These data show that DV increases cerebrovascular Aβ clearance through P-gp. Increased DV expression correlates with early cerebrovascular changes induced by angiogenic-remodeling in a diabetic co-morbid mouse model of VCID. Lower DV expression is associated with aberrant vasculature that contribute to increased mortality, suggesting that DV ‘replacement therapy’ could represent a novel therapeutic for VCID.

Abstract WMP117: Perlecan Regulates Pericyte Dynamics in the Repair Process of the Blood-Brain Barrier Against Ischemic Stroke

Introduction: The blood-brain barrier (BBB) breakdown occurs when the integrity of BBB components is lost as a consequence of ischemic stroke. Perlecan, a major heparan sulfate proteoglycan of basement membranes, is expressed by endothelial cells (ECs) and is adjacent to pericytes (PCs), suggesting supportive functions in the BBB. Recent studies highlight the importance of PCs in the process of repairing BBB functions, which are triggered by the upregulation of platelet-derived growth factor receptor β (PDGFRβ). We hypothesized that perlecan may play a protective role in BBB maintenance through the interaction with PCs during the repair process of the BBB disruption. Methods: We induced a 60-minute middle cerebral artery occlusion (MCAO) in adult conditional perlecan -deficient ( Perlecan -/- -Tg) mice in a C57BL/6 background, which express the perlecan transgene only in cartilage to rescue the perinatal lethality of Perlecan -/- mice. Recombinant perlecan C-terminal domain V (DV) was used for in vitro assays. Results: Perlecan -/- -Tg mice exhibited larger infarct volumes and more BBB leakage than the control mice on post-surgery day (PSD) 2 after MCAO. While the control mice showed increased numbers of PDGFRβ-positive PCs around the ischemic lesion on PSD 3, such upregulation was not observed in Perlecan -/- -Tg mice, suggesting that perlecan may participate in PC activation against the BBB breakdown. In wild-type mice, the expression of integrin α5, a potential receptor for perlecan, was upregulated both in PCs and in ECs in the ischemic lesion. In culture, PCs showed attachment activity to DV through integrin α5β1. DV induced well-assembled actin stress fibers and focal adhesions in PCs and promoted the PC migration induced by PDGF-BB. At molecular level, DV enhanced the PDGF-BB-induced phosphorylation of PDGFRβ, in addition to that of SHP-2 and FAK, suggesting that DV enhanced both PDGFRβ and integrin signaling. Conclusions: These results revealed that perlecan regulates the activation of PCs through the cooperative function of PDGFRβ and integrin α5β1, contributing to the repair process of the BBB. Perlecan DV may provide a potential therapeutic effect, based on a new approach from extracellular matrix to the disrupted BBB in ischemic stroke.

Abstract TMP118: Potential Therapeutic Benefits of Perlecan Domain V in Preclinical Vascular Dementia and Cerebral Angiopathy

Vascular contributions to cognitive impairment and dementia (VCID), the second leading cause of dementia behind Alzheimer’s disease (AD), is a broad term that encompasses a spectrum of initial asymptomatic cerebrovascular changes (seen in small vessel disease and cerebral amyloid angiopathy where pathologic Aβ1-42 protein accumulates around brain blood vessels) to the profound symptomatic damage following acute stroke(s). Cerebrovascular remodeling and new blood vessel growth (angiogenesis) may represent early compensatory changes to reduced cerebral blood flow that can initiate VCID. Angiogenesis, in turn, is supported by various growth factors and the proteolytic turnover of surrounding extracellular matrix. We have demonstrated that one such extracellular matrix protein, perlecan (a heparan sulfate proteoglycan), possesses a C terminal domain V (DV) protein that upon cleavage greatly enhances brain angiogenesis. We characterized VCID induced changes in DV expression in the human parietal cortex and a distinct mouse model (diabetic APP/PS1 knock in (db/AD)), that has a gradual cognitive decline by 9 months with microangiopathy, Aβ1-42 deposition, aneurysms, and microhemorrhages. We also utilized an in vitro model of the blood-brain barrier (BBB) to assess the transport of human Aβ1-42 in the presence of DV. In the human parietal cortex, dementia patients had increased expression of DV despite having fewer cells. In db/AD animals (3-6 months), we observed a decrease in BBB proteins (i.e. claudin-5), indicating that altered function correlated with an increase in brain DV expression during the asymptomatic angiogenic stage, which precedes cognitive changes (9-12 months). In vitro, DV doubled the transport of Aβ1-42 into the lumen of cerebral microvessels over 24 hours with increased activity and total protein expression of P-glycoprotein (P-gp), one of Aβ’s known transport proteins. Collectively, these data indicate that early cerebrovascular changes induce angiogenic-remodeling that correlates with increased expression of DV. DV, in turn, may further enhance angiogenesis and increase brain Aβ clearance into the vascular compartment through P-gp, suggesting that DV could represent a novel therapeutic for VCID.

Perlecan Domain V Inhibits Amyloid-β Induced Activation of the α2β1 Integrin-Mediated Neurotoxic Signaling Cascade.

Alzheimer's disease (AD) is characterized by neuronal death, neurofibrillary tangles, and senile plaques. Amyloid-beta (Aβ) is the major component of plaques and consists of two prominent isoforms, Aβ40 and Aβ42. As many risk factors for AD are vascular in origin and blood vessel defects in clearing Aβ from the brain are a potential key component of AD pathology, we have focused on the neuron-blood vessel interface, and in particular, the vascular basement membrane, which coats blood vessels and physically separates them from neurons. A prominent component of the vascular basement membrane is the extracellular matrix proteoglycan perlecan. Domain V (DV) is the C-terminal domain and is generated by perlecan proteolysis. DV interacts with the α2 integrin and Aβ is a ligand for both α2β1 and αvβ1. Due to the known interaction of DV with α2β1 and α2β1's requirement for Aβ deposition and neurotoxicity, we hypothesized that DV and/or its C-terminal domain, LG3, might alter neurotoxic signaling pathways by directly blocking or otherwise interfering with α2β1 binding by Aβ. Our study suggests that α2β1 mediates Aβ-induced activation of c-Jun and caspase-3, key components of the neurotoxic pathway, in primary cortical and hippocampal neurons. We further demonstrate that DV and/or LG3 may therapeutically modulate these α2β1 mediated neurotoxic effects suggesting that they or other α2β1 integrin modulators could represent a novel approach to treat AD. Finally, our results suggest different neurotoxicity susceptibilities between cortical and hippocampal neurons to Aβ40 and Aβ42 as further underscored by differing neuroprotective potencies of LG3 in each cell type.

Bioengineering Proteoglycan‐based Matrices For Blood Contacting Applications

Proteoglycans and their glycosaminoglycan chains are functional components of the extracellular matrix that modulate interactions with other extracellular matrix molecules, as well as with cells and growth factors. Perlecan is an abundant proteoglycan in the vascular basement membrane and contains a C‐terminal domain V (DV) with one glycosaminoglycan attachment site and an α2β1 integrin binding site. Perlecan can only be obtained in low abundance from natural sources, thus alternative sources are needed for therapeutic applications. The aim of this research was to bioengineer DV and to incorporate it into biomaterials for blood‐contacting applications.Human DV was expressed in the human embryonic kidney cell line, HEK‐293 and purified by immunoaffinity chromatography and biochemically characterized with respect to protein core, glycosaminoglycan structure and yield. Human primary endothelial cell, smooth muscle cell and platelet adhesion were assessed.DV was produced as two populations decorated with either chondroitin sulfate or heparan sulfate. The level of heparan sulfate substitution was increased by culturing the cells with higher glucose concentrations in the medium while there was no effect on the level of chondroitin sulfate. DV was produced with a yield of 2 mg/L, which is a 2.5 fold increase in the yield of endothelial‐derived perlecan.The proteoglycan forms of DV were effective in promoting endothelial, but not smooth muscle cell or platelet adhesion. In the absence of glycosaminoglycans DV supported the adhesion of endothelial cells and platelets via integrin α2β1. However, while smooth muscle cells adhere to perlecan in the absence of glycosaminoglycan chains, these cells did not adhere to DV in the absence of glycosaminoglycans. This suggests that the proteoglycan forms of DV have potential roles in encouraging endothelialization of materials while inhibiting unwanted activities associated with platelet and smooth muscle cell adhesion. We have shown this to be the case for the full length perlecan when trialed in an ovine vascular graft model.We are currently developing methods to combine DV with various biomaterials including a silk fibroin substrate through various chemical crosslinking methods. Early work in this area suggests that we can fine tune how both the protein and glycosaminoglycan components of DV are presented to maintain the vascular cell‐selective activities of DV.Support or Funding InformationFunding provided by the Australian Research Council

Abstract 163: Delayed Administration of Perlecan Doman V Significantly Increases Neurogenesis and Improves Functional Outcome after Experimental Ischemic Stroke

Stroke, a major cause of significant morbidity and death, has limited therapeutic options. To that end, our goal is to develop novel stroke therapies by exploiting the brain’s own neuroreparative potential. We have discovered that perlecan, a prominent brain extracellular matrix proteoglycan, is proteolyzed into the bioactive protein fragment domain V (DV) after experimental and human ischemic stroke. DV is both neuroprotective and pro-angiogenic. Furthermore, functional outcome can be significantly improved in rodents by administering DV 6-24 hours after experimental transient (distal MCA occlusion) or permanent (photothrombosis) stroke. Here we studied in mechanistic detail whether delayed DV administration (initiated 7 days post-stroke) could increase neurogenesis and improve functional outcome after mouse transient MCA occlusion. Delayed DV administration also served to minimize confounding neuroprotective and angiogenic effects which occur with acute DV therapy. After two doses of DV (post-stroke day 7 and 9), stroked 3-month old male C57BL6 mice had significant functional improvement (rotor rod) compared to vehicle treated stroke controls. Brain immunohistochemistry 21 days after stroke demonstrated that DV treated mice had significantly more cells that were positive for BrdU (a marker of cell division), doublecortin (DCX, a marker for immature neurons), and NeuN (another neuronal marker) in the infarct area. Furthermore, stereotactic brain injection (AP + 0.00, ML - 1.2, DV – 2.5) with alpha 2 integrin (a known neuronal DV receptor) function blocking antibody on post-stroke day 3 inhibited DV’s post-stroke neurogenic effects. These results suggest that delayed DV treatment after experimental stroke increases neurogenesis, increases the number of new neurons that reach stroked brain regions and survive there, and improves functional outcome through an alpha 2 integrin dependent mechanism. Importantly, as we are unaware of any other delayed treatment other than FLAME clinical trial (fluoxetine treatment initiated 5-10 days after stroke) that significantly improves functional outcome after stroke, our data further suggest the promise of DV as an effective stroke therapy.

The potential role of perlecan domain V as novel therapy in vascular dementia.

Vascular dementia (VaD) is the second most common cause of dementia and leads to a decline in cognitive thinking via conditions that lead to blockage or reduced blood flow to the brain. It is a poorly understood disease, and the changes that occur are often linked to other types of dementia such as Alzheimer's disease. To date, there are no approved therapies or drugs to treat the symptoms of VaD, even though there is some evidence of drugs approved for Alzheimer's that might have some benefit in patients diagnosed with VaD. The altered blood flow that precedes VaD may result in compensatory mechanisms, such as angiogenesis, to increase blood flow in the brain. Angiogenesis, the process of new blood vessel formations from pre-existing ones, involves several pro-angiogenic factors such as vascular endothelial growth factor (VEGF) and is regulated by a variety of growth factors from neurons, astrocytes, and pericytes in the brain as well the extracellular matrix (ECM). The ECM highly regulates angiogenesis and other processes in the brain. One such ECM component is the heparan sulfate proteoglycan perlecan and its bioactive region, Domain V (DV). Here we discuss the potential role of DV as a novel therapy to treat VaD.

Tolerogenic dendritic cells specific for β2-glycoprotein-I Domain-I, attenuate experimental antiphospholipid syndrome

Tolerogenic dendritic cells (tDCs) have the potential to control the outcome of autoimmunity by modulating the immune response. The aim of this study was to uncover the tolerance efficacy attributed to beta-2-glycoprotein-I (β2GPI) tDCs or β2GPI domain-I (D-I) and domain-V (D-V)-tDCs in mice with antiphospholipid syndrome (APS). tDCs were pulsed with β2GPI or D-I or D-V derivatives. Our results revealed that β2GPI related tDCs phenotype includes CD80high, CD86high CD40high MHC class IIhigh. The miRNA profiling encompass miRNA 23bhigh, miRNA 142-3plow and miRNA 221low. In addition the β2GPI related tDCs showed reduced secretion of IL-1β, IL-12 and IL-23. D-I tDCs treatment was more efficient than β2GPI tDCs in inducing of tolerance in APS mice, manifested by lowered titers of anti- β2GPI antibodies (Abs) and reduced percentage of fetal loss. Tolerance induction was accompanied by poor T cell response to β2GPI, high numbers of CD4 + CD25 + FOXP3 + T-regulatory cells (Treg), reduced levels of IFNγ, IL-17 and increased expression of IL-10 and TGFβ. Tolerance was successfully transferred by Treg cells from the tolerized mice to β2GPI immunized mice. We conclude that predominantly D-I-tDCs and β2GPI tDCs have the potential to attenuate experimental APS by induction of Treg cells, reduction of anti- β2GPI Abs titers and increased expression of anti-inflammatory cytokines. We suggest that β2-GPI-D-I-tDCs may offer a novel approach for developing therapy for APS patients.

Perlecan Domain V Is Neuroprotective and Affords Functional Improvement in a Photothrombotic Stroke Model in Young and Aged Mice

With the failure of so many pre-clinical stroke studies to translate into the clinic, there is a need to find new therapeutics to minimize the extent of cellular damage and aid in functional recovery. Domain V (DV), the c-terminal protein fragment of the vascular basement membrane component, perlecan, was recently shown to afford significant protection in multiple transient middle cerebral artery occlusion stroke models. We sought here to determine whether DV might have similar therapeutic properties in a focal photothrombosis stroke model in both young and aged mice. Young (3-month old) and aged (24-month old) mice underwent photothrombotic stroke to the motor cortex and were then treated with DV or phosphate buffered saline vehicle at different initial time points up to 7days. Stroke volume was analyzed histologically using cresyl violet and functional recovery assessed behaviorally on both the grid-walking and cylinder tasks. In young mice, DV administration resulted in a significant decrease in infarct volume when treatment started 3 or 6h post-stroke. In aged mice, DV administration was only protective when started 3h post-stroke. In addition to a decrease in the area of infarction, DV treatment was effective in significantly decreasing the number of foot-faults on the grid-walking task and improving use of the stroke-affected limb in the cylinder task in both young and aged. Previously, we have shown that DV can alter the expression profile of various astroglial markers. Consistent with our previous finding, treatment groups that showed therapeutic potential in both young and aged mice also showed an elevation in glial fibrillary acidic protein (GFAP) expression in peri-infarct regions. We conclude that DV is neuroprotective and affords significant improvements in functional recovery in both young and aged mice after focal ischemia. These data also highlight a therapeutic time-window shift that is narrower in aged compared with young mice and is associated with an elevation in GFAP expression and heightened astrogliosis.

Perlecan Domain V Induces VEGf Secretion in Brain Endothelial Cells through Integrin α5β1 and ERK-Dependent Signaling Pathways

Perlecan Domain V (DV) promotes brain angiogenesis by inducing VEGF release from brain endothelial cells (BECs) following stroke. In this study, we define the specific mechanism of DV interaction with the α5β1 integrin, identify the downstream signal transduction pathway, and further investigate the functional significance of resultant VEGF release. Interestingly, we found that the LG3 portion of DV, which has been suggested to possess most of DV’s angio-modulatory activity outside of the brain, binds poorly to α5β1 and induces less BEC proliferation compared to full length DV. Additionally, we implicate DV’s DGR sequence as an important element for the interaction of DV with α5β1. Furthermore, we investigated the importance of AKT and ERK signaling in DV-induced VEGF expression and secretion. We show that DV increases the phosphorylation of ERK, which leads to subsequent activation and stabilization of eIF4E and HIF-1α. Inhibition of ERK activity by U0126 suppressed DV-induced expression and secretion of VEGR in BECs. While DV was capable of phosphorylating AKT we show that AKT phosphorylation does not play a role in DV’s induction of VEGF expression or secretion using two separate inhibitors, LY294002 and Akt IV. Lastly, we demonstrate that VEGF activity is critical for DV increases in BEC proliferation, as well as angiogenesis in a BEC-neuronal co-culture system. Collectively, our findings expand our understanding of DV’s mechanism of action on BECs, and further support its potential as a novel stroke therapy.

Thermodynamic investigation of the dinucleotide bulge of domain V of group II intron

Group II introns are self‐splicing ribozymes, found in RNA of organelles in fungi, plants, and protists, as well as in bacterial mRNA. Group II introns are composed of six structural domains, which are designated domain I to domain VI. Domain V (DV) is a short stem loop that contains a dinucleotide AC bulge; it is implicated in the catalytic function of the intron, as it is expected to bind the catalytic Mg2+ ion(s). A crystal structure of a group II intron from Oceanobacillus iheyensis shows inner sphere interactions between two Mg2+ ions and the phosphate oxygens of the cytosine of the dinucleotide bulge. In this study, we are examining the role of the dinucleotide sequence on RNA stability along with quantifying the contribution of RNA‐magnesium interactions. Various RNA and DNA constructs of the dinucleotide bulge were designed and thermal denaturation experiments were performed on the wild type and the modified constructs in 1 M KCl and in varying concentrations of Mg2+ ions. Comparative thermodynamic data will be presented on various dinucleotide RNA and DNA constructs and their ion interactions. This work was funded by NSF Grant MCB‐0950582 to NG.

Perlecan and the Blood-Brain Barrier: Beneficial Proteolysis?

The cerebral microvasculature is important for maintaining brain homeostasis. This is achieved via the blood-brain barrier (BBB), composed of endothelial cells with specialized tight junctions, astrocytes, and a basement membrane (BM). Prominent components of the BM extracellular matrix (ECM) include fibronectin, laminin, collagen IV, and perlecan, all of which regulate cellular processes via signal transduction through various cell membrane bound ECM receptors. Expression and proteolysis of these ECM components can be rapidly altered during pathological states of the central nervous system. In particular, proteolysis of perlecan, a heparan sulfate proteoglycan, occurs within hours following ischemia induced by experimental stroke. Proteolysis of ECM components following stroke results in the degradation of the BM and further disruption of the BBB. While it is clear that such proteolysis has negative consequences for the BBB, we propose that it also may lead to generation of ECM protein fragments, including the C-terminal domain V (DV) of perlecan, that potentially have a positive influence on other aspects of CNS health. Indeed, perlecan DV has been shown to be persistently generated after stroke and beneficial as a neuroprotective molecule and promoter of post-stroke brain repair. This mini-review will discuss beneficial roles of perlecan protein fragment generation within the brain during stroke.

Perlecan domain V modulates astrogliosis In vitro and after focal cerebral ischemia through multiple receptors and increased nerve growth factor release

Astrogliosis constitutes part of the central nervous system's physiological response to injury. Considered for decades to be a major challenge for brain repair, recent studies have highlighted it as a promoter of such repair mechanisms. Recently, our group demonstrated the ability of perlecan domain V (DV) to be a novel potential stroke therapy by its neuroprotective effects. However, the potential for DV to modulate astrogliosis has not been investigated. The aim of this study is to better understand the relevance of DV to astrogliosis using both in vitro and in vivo rodent models. Notably, under basal conditions, astrocytes express all three DV receptors described in the literature: integrin α2β1, α5β1, and α-dystroglycan (αDG). DV promoted astrocyte cell adhesion, cell migration as well as astrocyte stellation. Moreover, DV induced nerve growth factor (NGF) secretion through a αDG- and ERK-dependent pathway. In contrast, α2β1 or α5β1 mediated DV antiproliferative effects in astrocytes. NGF production after DV treatment acted as a strong anti-proliferative agent. Another remarkable effect of DV was that it decreased several markers of astrogliosis such as glial fibrillary acidic protein (GFAP), neurocan and phosphacan both in vitro and in vivo, suggesting the role of DV as a potential modulator of postinjury during late astrogliosis, and eventually the onset of glial scarring. Taken together, our study demonstrates the ability of DV to modulate key events of astrogliosis by promoting early astrogliosis and inhibiting glial scar formation, suggesting an additional therapeutic benefit of DV for recovery from stroke. © 2011 Wiley-Liss, Inc.