Anti-GPVI nanobody blocks collagen- and atherosclerotic plaque-induced GPVI clustering, signaling, and thrombus formation

BACKGROUND

The collagen receptor glycoprotein VI (GPVI) is an attractive antiplatelet target due to its critical role in thrombosis but minor involvement in hemostasis.

OBJECTIVE

To investigate GPVI receptor involvement in platelet activation by collagen-I and atherosclerotic plaque using novel blocking and non-blocking anti-GPVI nanobodies (Nbs).

METHODS

Nb effects on GPVI-mediated signaling and function were assessed by western blot and whole blood thrombus formation under flow. GPVI clustering was visualized in thrombi using fluorescently labeled Nb28.

RESULTS

Under arterial shear, inhibitory Nb2 blocks thrombus formation and platelet activation on collagen and plaque, but only reduces adhesion on plaque. In contrast, adhesion on collagen, but not plaque, is decreased by blocking integrin α2β1. Adhesion on plaque is maintained despite inhibition of integrins αvβ3, α5β1, α6β1, and αIIbβ3. Only combined αIIbβ3 and α2β1 blockade inhibits adhesion and thrombus formation to the same extent as Nb2 alone. Nb2 prevents GPVI signaling, with loss of Syk, Lat, and PLCɣ2 phosphorylation, especially to plaque stimulation. Non-blocking fluorescently labeled Nb28 reveals distinct GPVI distribution patterns on collagen and plaque, with GPVI clustering clearly apparent on collagen fibers and less frequent on plaque. Clustering on collagen fibers is lost in the presence of Nb2.

CONCLUSIONS

This work emphasizes the critical difference in GPVI-mediated platelet activation by plaque and collagen; it highlights the importance of GPVI clustering for downstream signaling and thrombus formation. Labeled Nb28 is a novel tool for providing mechanistic insight into this process and the data suggest Nb2 warrants further investigation as a potential anti-thrombotic agent.

Rhesus rotavirus receptor-binding site affects high mobility group box 1 release, altering the pathogenesis of experimental biliary atresia

Biliary atresia (BA) is a neonatal inflammatory cholangiopathy that requires surgical intervention by Kasai portoenterostomy to restore biliary drainage. Even with successful portoenterostomy, most patients diagnosed with BA progress to end-stage liver disease, necessitating a liver transplantation for survival. In the murine model of BA, rhesus rotavirus (RRV) infection of neonatal mice induces an inflammatory obstructive cholangiopathy that parallels human BA. The model is triggered by RRV viral protein (VP)4 binding to cholangiocyte cell-surface proteins. High mobility group box 1 (HMGB1) protein is a danger-associated molecular pattern that when released extracellularly moderates innate and adaptive immune response. In this study, we investigated how mutations in three RRV VP4-binding sites, RRVVP4-K187R (sialic acid-binding site), RRVVP4-D308A (integrin α2β1-binding site), and RRVVP4-R446G (heat shock cognate 70 [Hsc70]-binding site), affects infection, HMGB1 release, and the murine model of BA. Newborn pups injected with RRVVP4-K187R and RRVVP4-D308A developed an obstruction within the extrahepatic bile duct similar to wild-type RRV, while those infected with RRVVP4-R446G remained patent. Infection with RRVVP4-R446G induced a lower level of HMGB1 release from cholangiocytes and in the serum of infected pups. RRV infection of HeLa cells lacking Hsc70 resulted in no HMGB1 release, while transfection with wild-type Hsc70 into HeLa Hsc70-deficient cells reestablished HMGB1 release, indicating a mechanistic role for Hsc70 in its release. Conclusion: Binding to Hsc70 contributes to HMGB1 release; therefore, Hsc70 potentially serves as a therapeutic target for BA.

Glomerular basement membrane deposition of collagen α1(III) in Alport glomeruli by mesangial filopodia injures podocytes via aberrant signaling through DDR1 and integrin α2β1

In Alport mice, activation of the endothelin A receptor (ETA R) in mesangial cells results in sub-endothelial invasion of glomerular capillaries by mesangial filopodia. Filopodia deposit mesangial matrix in the glomerular basement membrane (GBM), including laminin 211 which activates NF-κB, resulting in induction of inflammatory cytokines. Herein we show that collagen α1(III) is also deposited in the GBM. Collagen α1(III) localized to the mesangium in wild-type mice and was found in both the mesangium and the GBM in Alport mice. We show that collagen α1(III) activates discoidin domain receptor family, member 1 (DDR1) receptors both in vitro and in vivo. To elucidate whether collagen α1(III) might cause podocyte injury, cultured murine Alport podocytes were overlaid with recombinant collagen α1(III), or not, for 24 h and RNA was analyzed by RNA sequencing (RNA-seq). These same cells were subjected to siRNA knockdown for integrin α2 or DDR1 and the RNA was analyzed by RNA-seq. Results were validated in vivo using RNA-seq from RNA isolated from wild-type and Alport mouse glomeruli. Numerous genes associated with podocyte injury were up- or down-regulated in both Alport glomeruli and cultured podocytes treated with collagen α1(III), 18 of which have been associated previously with podocyte injury or glomerulonephritis. The data indicate α2β1 integrin/DDR1 co-receptor signaling as the dominant regulatory mechanism. This may explain earlier studies where deletion of either DDR1 or α2β1 integrin in Alport mice ameliorates renal pathology. © 2022 Boys Town National Research Hospital. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

[Prostate stem cells: an update]

Stem cells are characterized by self-renewing, multipotent differentiation, and high proliferation and receiving more and more attention for their roles in the development and management of various diseases. There are epithelial stem cells and mesenchymal stem cells in the prostate. The markers of the epithelial stem cells include cytokeratin, stem cell antigen-1, and integrins alpha2beta1, CD49f, CD133, CD117, and CD44. The markers of the mesenchymal stem cells include CD30, CD44, CD133, neuron-specific enolase, and vascular endothelial growth factor receptor-1. Prostate stem cells are involved in the development and treatment of prostatic diseases. This review focuses on the latest progress in the studies of prostate stem cells.

Gene receptor polymorphism as a risk factor for BMD deterioration in adolescent girls with anorexia nervosa

Anorexia nervosa is a serious eating disorder that is associated with decreased bone mineral density and greater lifetime risk for fractures. This case-controlled study, analyzed single nucleotide polymorphisms of genes encoding vitamin D receptor, estrogen receptor alpha (ESR1), collagen type I and calcitonin receptor (CTR). Relationships between genotype and body mass index, cycling status and lumbar spine bone mineral density (LBMD) were determined in 40 adolescent girls with anorexia nervosa and 10 age-matched controls. The distribution of CTR-AluI genotypes differed between groups, but this polymorphism was not associated with LBMD Z-score. Distribution of ESR1-XbaI genotypes did not differ between groups, but the AA genotype was associated with decreased LBMD Z-score (≤-1) (OR = 24.79, 95% CI, 1.01-606.08). Carriers of the A allele were more likely to have decreased LBMD Z-scores compared with carriers of the G allele (OR = 4.12, 95% CI, 1.23-13.85, p = 0.022). In conclusion, our study shows that anorexic patients with wild-type genotype ESR-XbaI receptor are in greater risk for decreased BMD in relation to those with the mutated gene. Prompt recognition of these patients is crucial because early administration of the proper therapeutic treatment may contribute to the prevention of adverse sequelae on bone metabolism.

Microfluidic focal thrombosis model for measuring murine platelet deposition and stability: PAR4 signaling enhances shear-resistance of platelet aggregates

BACKGROUND

Flow chambers allow the ex vivo study of platelet response to defined surfaces at controlled wall shear stresses. However, most assays require 1-10 mL of blood and are poorly suited for murine whole blood experiments.

OBJECTIVE

To measure murine platelet deposition and stability in response to focal zones of prothrombotic stimuli using 100 microL of whole blood and controlled flow exposure.

METHODS

Microfluidic methods were used for patterning acid-soluble collagen in 100 microm x 100 microm patches and creating flow channels with a volume of 150 nL. Within 1 min of collection into PPACK and fluorescent anti-mouse CD41 mAb, whole blood from normal mice or from mice deficient in the integrin alpha(2) subunit was perfused for 5 min over the patterned collagen. Platelet accumulation was measured at venous and arterial wall shear rates. After 5 min, thrombus stability was measured with a 'shear step-up' to 8000 s(-1).

RESULTS

Wild-type murine platelets adhered and aggregated on collagen in a biphasic shear-dependent manner with increased deposition from 100 to 400 s(-1), but decreased deposition at 1000 s(-1). Adhesion to patterned collagen was severely diminished for platelets lacking a functional alpha(2)beta(1) integrin. Those integrin alpha(2)-deficient platelets that did adhere were removed from the surface when challenged to shear step-up. PAR4 agonist (AYPGKF) treatment of the thrombus at 5 min enhanced aggregate stability during the shear step-up.

CONCLUSIONS

PAR4 signaling enhances aggregate stability by mechanisms independent of other thrombin-dependent pathways such as fibrin formation.

Type I collagen receptor (alpha 2 beta 1) signaling promotes the growth of human prostate cancer cells within the bone

The most frequent site of prostate cancer metastasis is the bone. Adhesion to bone-specific factors may facilitate the selective metastasis of prostate cancer to the skeleton. Therefore, we tested whether prostate cancer bone metastasis is mediated by binding to type I collagen, the most abundant bone protein. We observed that only bone metastatic prostate cancer cells bound collagen I, whereas cells that form only visceral metastases failed to bind collagen. To confirm the relationship between collagen adhesion and bone metastatic potential, a collagen-binding variant of human LNCaP prostate cancer cells was derived through serial passage on type I collagen (LNCaP(col)). Fluorescence-activated cell sorting analysis showed that LNCaP(col) cells express increased levels of the integrin collagen I receptor alpha(2)beta(1) compared with LNCaP cells. Antibodies to the alpha(2)beta(1) complex inhibited LNCaP(col) binding to collagen, confirming that integrins mediated the attachment. Correspondingly, LNCaP(col) cells displayed enhanced chemotactic migration toward collagen I compared with LNCaP cells, an activity that could be blocked with alpha(2)beta(1) antibodies. To directly test the role of alpha(2)beta(1)-dependent collagen binding in bone metastasis, LNCaP and LNCaP(col) cells were injected into the tibia of nude mice. After 9 weeks, 7 of 13 (53%) mice injected with LNCaP(col) developed bone tumors, whereas 0 of 8 mice injected with LNCaP cells had evidence of boney lesions. LNCaP(col) cells were found to express increased levels of the metastasis-promoting RhoC GTPase compared with parental LNCaP. We conclude that collagen I attachment mediated by alpha(2)beta(1) initiates motility programs through RhoC and suggest a mechanism for prostate cancer metastasis to the bone.

Increase in platelet non-integrin type I collagen receptor in patients with systemic sclerosis

Microvascular injury is one of the major pathogenetic processes involved in systemic sclerosis (SSc). Interaction of the platelet types I and III collagen receptors with their respective ligand in the exposed subendothelial stroma as a result of ongoing microvascular injury in SSc patients results in platelet activation and aggregation with the release of mediators, which contribute to vascular damage and inflammation. We have found that there is a twofold increase in radiolabeled type I collagen binding to washed platelets from patients with SSc compared to platelets obtained from normal volunteers. Western blot analyses showed that the non-integrin platelet type I collagen receptor protein (65 kDa) is increased dramatically in lysates of platelet from patients with SSc. However, the integrin (alpha(2)beta(1)) and other non-integrin receptors such as glycoprotein VI, glycoprotein IV, and the platelet receptor for type III collagen remain unchanged. In addition, platelet lysates from rheumatic disease controls (rheumatoid arthritis, osteoarthritis, gout, and systemic lupus erythematosus) do not show any significant increases. There is no nitrotyrosylation on 65 kDa in patients with SSc compared to controls, suggesting this might also contribute to binding of CI to the 65-kDa CIR. These results suggest that there is a specific increase in the number of platelet type I collagen receptors in SSc patient's platelets. In addition, the activity of nitric oxide synthase is decreased in patients' platelet lysates compared to controls. The increase in platelet expression of the 65-kDa non-integrin platelet type I collagen receptor may explain the enhanced aggregation of platelets from patients with SSc to CI in vitro and microvascular thrombosis in the disease in vivo.

[Expression of platelet collagen receptor-glycoprotein VI fragment in E. coli and its biological activities]

This study was aimed to further investigate the function of platelet collagen receptor-glycoprotein VI and to screen its specific inhibitor. The extracellular domain of platelet glycoprotein VI (GPVI) in E. coli was expressed by recombinant technology, the extracellular domain cDNA of GPVI was amplified from pBluescript KS(-)-GPVI plasmid by PCR. Proved by sequencing, the expression vector pET-20b(+)-GPVI was constructed, which was then transformed into E. coli (BL21(DE3)pLysS) and induced by IPTG. The recombinant GPVI was purified on Ni-NTA resin column and renatured in PBS containing GSH and GSSG. The anti-penta His McAb and anti-GPVI polyclonal antibody were used to identify the recombinant GPVI in Western blotting. Collagen binding test was conducted to investigate the biological activity of recombinant GPVI. The results showed that the recombinant GPVI was expressed in E. coli and successfully purified, which was confirmed to be similar to the native GPVI in Western blotting. The recombinant GPVI can bind the type I collagen in dose-dependent manner. In conclusion, the recombinant GPVI can be achieved in E. coli and restore its native characteristics after renaturation.

α2β1integrin-specific collagen-mimetic surfaces supporting osteoblastic differentiation

The interactions of osteoblasts with their surrounding extracellular matrix (ECM) are essential for skeletal development, homeostasis, and maintenance of the mature osteoblastic phenotype. Integrins are the principal transducers of ECM signals that regulate this process of osteoblast commitment and differentiation. Several studies indicate that the alpha(2)beta(1) integrin interaction with type I collagen is a crucial signal for the induction of osteoblastic differentiation and matrix mineralization. Integrin alpha(2)beta(1) recognizes the Gly-Phe-Hyp-Gly-Glu-Arg (GFOGER) motif in residues 502-507 of the alpha(1)[I] chain of type I collagen. This study demonstrates that an alpha(2)beta(1) integrin-specific GFOGER peptide triggers the activation of focal adhesion kinase and alkaline phosphatase in MC3T3-E1 murine immature osteoblast-like cells, two events that have been implicated in the osteoblastic differentiation pathway. These GFOGER-peptide surfaces also support the expression of multiple osteoblast-specific genes, including osteocalcin and bone sialoprotein, and induce matrix mineralization in a manner similar to type I collagen. This triple-helical peptide represents a promising surface modification strategy for the design of collagen-mimetic bioadhesive surfaces that support osteoblastic differentiation.

Laminin 5 deposition regulates keratinocyte polarization and persistent migration

Repair of wounded epidermis requires both keratinocyte migration and deposition of laminin 5 over exposed dermal collagen. To understand the coupling between leading cell migration and laminin 5 deposition, we developed a novel migration assay using time-lapse microscopy. We demonstrate that in migrating, human keratinocytes the deposition of laminin 5 promoted 'processive migration', characterized by stable cell polarization that was tightly coupled to persistent, linear migration in the absence of a chemotactic gradient. Processive migration required deposition of laminin 5, which was restricted to the rear of the polar cell. Integrin alpha 3 beta 1 interacted with these laminin 5 deposits at contact sites that did not require actin-dependent cross-linking. Further, we show that the migrating cells switched adhesion by integrin alpha 2 beta 1 on collagen at the front of the cell to integrin alpha 3 beta 1 on exogenous laminin 5 at the rear of the cell. Along with this switch of integrin usage was the removal of collagen from sites under the cell that precisely correlated with deposition of laminin 5. Processive migration was blocked with suppressors of microtubule dynamics (nocodazole and taxol) or rottlerin, a PKC-delta inhibitor. These drugs were also shown to block deposition of laminin 5 but, surprisingly, constitutive secretion was unimpaired, suggesting deposition was a regulated event. Thus, at the front of the cell, the leading lamellipodium was stabilized through integrin interactions in focal complexes with the exogenous substratum. However, at the rear of the cell, stable cell polarization and linear migration was promoted by laminin 5 deposits and integrin alpha 3 beta 1.

Blockade of platelet GPIIB-IIIA (Integrin alphaII(b)beta(3)) in flowing human blood leads to passivation of prothrombotic surfaces

We examined the impact of platelet activation on platelet adhesion to collagen in flowing human blood. ADP activation of platelets in ex vivo flowing blood resulted in paradoxical inhibition of platelet deposition on collagen. Blockade of fibrinogen binding to platelets by Lamifiban, a competitive antagonist of GPIIb-IIIa (integrin alpha(IIb)beta(3)), reversed this inhibition, leading to a marked increase in integrin alpha(2)beta(1)-dependent platelet adhesion. Analysis of integrin alpha(2)beta(1)-dependent platelet adhesion to collagen indicated that ADP-induced suppression of platelet adhesion is the result of trans-dominant inhibition of integrin alpha(2)beta(1) caused by fibrinogen binding to integrin GPIIb-IIIa. Lamifiban blocked fibrinogen binding, reversing the trans-dominant inhibition of alpha(2)beta(1) dependent adhesion to collagen. The GPIIb-IIIa antagonist resulted in the formation of a non-thrombogenic, passivated surface comprised of an adherent platelet monolayer. This unexpected consequence of blocking fibrinogen binding to GPIIb-IIIa may explain the long-term benefits of short-term GPIIb-IIIa antagonist treatment of Acute Coronary Syndrome patients.

The signal transduction pathway of the nonintegrin receptor of 65 kDa is different from glycoprotein VI

The identity and signal pathways of a platelet nonintegrin receptor for type I collagen, 65 kDa, are not established. In this investigation, we have examined whether there is a difference in the signal transduction pathways between the 65-kDa protein and glycoprotein VI (GP VI). Results from this study show that these two proteins are different based on the following facts. First, the anti-65-kDa antibody does not precipitate GP VI and vice versa. Second, the Fc receptor (FcR) gamma chain which associates with GP VI after exposure to collagen does not associate with the 65-kDa protein. Third, tyrosine phosphorylation of the FcR gamma chain was obtained by Fab fragments of anti-GP VI but not by anti-65 kDa. These results suggest that the signal transduction pathway of the platelet receptors for the 65-kDa protein and GP VI are different.

Platelet aggregation through prothrombinase activation induced by non-aggregant doses of platelet agonists

Activation of the prothrombinase complex, which catalyzes the formation of thrombin from prothrombin, is crucial for the (patho)physiological processes of hemostasis and thrombosis. We here report that washed platelets supplemented with prothrombin can be irreversibly aggregated with otherwise non-aggregant doses of adenosine diphosphate (10 micromol/l), thrombin (0.06 U/ml), or collagen (1 microg/ml). Prothrombinase-catalyzed prothrombin to thrombin conversion most probably supports this aggregation response, since inhibitors of thrombin (hirudin or heparin) and an inhibitor of activated factor X (DX-9065a) impair the response. A certain degree of agonist-induced platelet activation seems to be required for this prothrombin-supported aggregation response, since prothrombin alone does not induce aggregation, and blockade of glycoprotein Ia/IIa with a specific antibody inhibits the platelet aggregation response to collagen and prothrombin. These results may suggest that activation of the prothrombinase complex could be a common step of the platelet response to distinct agonists, which may be achieved at low levels of platelet stimulation.