Targeting Gα13-integrin interaction ameliorates systemic inflammation

Systemic inflammation as manifested in sepsis is an excessive, life-threatening inflammatory response to severe bacterial or viral infection or extensive injury. It is also a thrombo-inflammatory condition associated with vascular leakage/hemorrhage and thrombosis that is not effectively treated by current anti-inflammatory or anti-thrombotic drugs. Here, we show that MB2mP6 peptide nanoparticles, targeting the Gα13-mediated integrin "outside-in" signaling in leukocytes and platelets, inhibited both inflammation and thrombosis without causing hemorrhage/vascular leakage. MB2mP6 improved mouse survival when infused immediately or hours after onset of severe sepsis. Furthermore, platelet Gα13 knockout inhibited septic thrombosis whereas leukocyte Gα13 knockout diminished septic inflammation, each moderately improving survival. Dual platelet/leukocyte Gα13 knockout inhibited septic thrombosis and inflammation, further improving survival similar to MB2mP6. These results demonstrate that inflammation and thrombosis independently contribute to poor outcomes and exacerbate each other in systemic inflammation, and reveal a concept of dual anti-inflammatory/anti-thrombotic therapy without exacerbating vascular leakage.

Shear and Integrin Outside-In Signaling Activate NADPH-Oxidase 2 to Promote Platelet Activation

[Figure: see text].

HIV-1 capsids mimic a microtubule regulator to coordinate early stages of infection

While the microtubule end-binding protein, EB1 facilitates early stages of HIV-1 infection, how it does so remains unclear. Here, we show that beyond its effects on microtubule acetylation, EB1 also indirectly contributes to infection by delivering the plus-end tracking protein (+TIP), cytoplasmic linker protein 170 (CLIP170) to the cell periphery. CLIP170 bound to intact HIV-1 cores or in vitro assembled capsid-nucleocapsid complexes, while EB1 did not. Moreover, unlike EB1 and several other +TIPs, CLIP170 enhanced infection independently of effects on microtubule acetylation. Capsid mutants and imaging revealed that CLIP170 bound HIV-1 cores in a manner distinct from currently known capsid cofactors, influenced by pentamer composition or curvature. Structural analyses revealed an EB-like +TIP-binding motif within the capsid major homology region (MHR) that binds SxIP motifs found in several +TIPs, and variability across this MHR sequence correlated with the extent to which different retroviruses engage CLIP170 to facilitate infection. Our findings provide mechanistic insights into the complex roles of +TIPs in mediating early stages of retroviral infection, and reveal divergent capsid-based EB1 mimicry across retroviral species.

High-loading Gα13-binding EXE peptide nanoparticles prevent thrombosis and protect mice from cardiac ischemia/reperfusion injury

Inefficient delivery is a major obstacle to the development of peptide-based drugs targeting the intracellular compartment. We recently showed that selectively inhibiting integrin outside-in signaling using a peptide (mP6) derived from the Gα13-binding ExE motif within the integrin β3 cytoplasmic domain had antithrombotic effects. Here, we engineered lipid-stabilized, high-loading peptide nanoparticles (HLPN), in which a redesigned ExE peptide (M3mP6) constituted up to 70% of the total nanoparticle molarity, allowing efficient in vivo delivery. We observed that M3mP6 HLPN inhibited occlusive thrombosis more potently than a clopidogrel/aspirin combination without adverse effects on hemostasis in rodents. Furthermore, M3mP6 HLPN synergized with P2Y12 receptor inhibitors or the clopidogrel/aspirin combination in preventing thrombosis, without exacerbating hemorrhage. M3mP6 HLPN also inhibited intravascular coagulation more potently than the P2Y12 inhibitor cangrelor. Postischemia injection of M3mP6 HLPN protected the heart from myocardial ischemia-reperfusion injury in a mouse model. This study demonstrates an efficient in vivo peptide delivery strategy for a therapeutic that not only efficaciously prevented thrombosis with minimal bleeding risk but also protected from myocardial ischemia-reperfusion injury in mice.

Shear-induced integrin signaling in platelet phosphatidylserine exposure, microvesicle release, and coagulation

It is currently unclear why agonist-stimulated platelets require shear force to efficiently externalize the procoagulant phospholipid phosphatidylserine (PS) and release PS-exposed microvesicles (MVs). We reveal that integrin outside-in signaling is an important mechanism for this requirement. PS exposure and MV release were inhibited in β3-/- platelets or by integrin antagonists. The impaired MV release and PS exposure in β3-/- platelets were rescued by expression of wild-type β3 but not a Gα13 binding-deficient β3 mutant (E733EE to AAA), which blocks outside-in signaling but not ligand binding. Inhibition of Gα13 or Src also diminished agonist/shear-dependent PS exposure and MV release, further indicating a role for integrin outside-in signaling. PS exposure in activated platelets was induced by application of pulling force via an integrin ligand, which was abolished by inhibiting Gα13-integrin interaction, suggesting that Gα13-dependent transmission of mechanical signals by integrins induces PS exposure. Inhibition of Gα13 delayed coagulation in vitro. Furthermore, inhibition or platelet-specific knockout of Gα13 diminished laser-induced intravascular fibrin formation in arterioles in vivo. Thus, β3 integrins serve as a shear sensor activating the Gα13-dependent outside-in signaling pathway to facilitate platelet procoagulant function. Pharmacological targeting of Gα13-integrin interaction prevents occlusive thrombosis in vivo by inhibiting both coagulation and platelet thrombus formation.

Differential Roles of the NADPH-Oxidase 1 and 2 in Platelet Activation and Thrombosis

OBJECTIVE

Reactive oxygen species (ROS) are known to regulate platelet activation; however, the mechanisms of ROS production during platelet activation remain unclear. Platelets express different isoforms of nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) oxidases (NOXs). Here, we investigated the role of NOX1 and NOX2 in ROS generation and platelet activation using NOX1 and NOX2 knockout mice.

APPROACH AND RESULTS

NOX1(-/Y) platelets showed selective defects in G-protein-coupled receptor-mediated platelet activation induced by thrombin and thromboxane A2 analog U46619, but were not affected in platelet activation induced by collagen-related peptide, a glycoprotein VI agonist. In contrast, NOX2(-/-) platelets showed potent inhibition of collagen-related peptide-induced platelet activation, and also showed partial inhibition of thrombin-induced platelet activation. Consistently, production of ROS was inhibited in NOX1(-/Y) platelets stimulated with thrombin, but not collagen-related peptide, whereas NOX2(-/-) platelets showed reduced ROS generation induced by collagen-related peptide or thrombin. Reduced ROS generation in NOX1/2-deficient platelets is associated with impaired activation of Syk and phospholipase Cγ2, but minimally affected mitogen-activated protein kinase pathways. Interestingly, laser-induced arterial thrombosis was impaired but the bleeding time was not affected in NOX2(-/-) mice. Wild-type thrombocytopenic mice injected with NOX2(-/-) platelets also showed defective arterial thrombosis, suggesting an important role for platelet NOX2 in thrombosis in vivo but not hemostasis.

CONCLUSIONS

NOX1 and NOX2 play differential roles in different platelet activation pathways and in thrombosis. ROS generated by these enzymes promotes platelet activation via the Syk/phospholipase Cγ2/calcium signaling pathway.

The role of Rac1 in glycoprotein Ib-IX-mediated signal transduction and integrin activation

OBJECTIVE

The platelet receptor for von Willebrand factor, the glycoprotein Ib-IX (GPIb-IX) complex, mediates platelet adhesion at sites of vascular injury and transmits signals leading to platelet activation. von Willebrand factor/GPIb-IX interaction sequentially activates the Src family kinase Lyn (SFK), phosphoinositide 3-kinase (PI3K), and Akt, leading to activation of integrin α(IIb)β(3) and integrin-dependent stable platelet adhesion and aggregation. It remains unclear how Lyn activates the PI3K/Akt pathway after ligand binding to GPIb-IX.

METHODS AND RESULTS

Using platelet-specific Rac1(-/-) mice and the Rac1 inhibitor NSC23766, we examined the role of Rac1 in GPIb-IX-dependent platelet activation. Rac1(-/-) mouse platelets and NSC23766-treated human platelets were defective in GPIb-dependent stable adhesion to von Willebrand factor under shear stress, integrin activation, thromboxane A(2) synthesis, and platelet aggregation. Interestingly, GPIb-induced activation of Rac1 and the guanine nucleotide exchange factor for Rac1, Vav, was abolished in both Lyn(-/-) and SFK inhibitor-treated platelets but was unaffected by the PI3K inhibitor LY294002, indicating that Lyn mediates activation of Vav and Rac1 independently of PI3K. Furthermore, GPIb-induced activation of Akt was abolished in Rac1-deficient platelets, suggesting that Rac1 is upstream of the PI3K/Akt pathway.

CONCLUSIONS

A Lyn-Vav-Rac1-PI3K-Akt pathway mediates von Willebrand factor-induced activation of integrin α(IIb)β(3) to promote GPIb-IX-dependent platelet activation.

Inside-out, outside-in, and inside-outside-in: G protein signaling in integrin-mediated cell adhesion, spreading, and retraction

The integrin family of cell adhesion receptors mediates bi-directional signaling: 'inside-out' signaling activates the ligand binding function of integrins and 'outside-in' signaling mediates cellular responses induced by ligand binding to integrins leading to cell spreading, retraction, migration, and proliferation. Integrin signaling requires both heterotrimeric G proteins and monomeric small G proteins. This review focuses on recent development in the roles of G proteins in integrin outside-in signaling. The finding of direct interaction between the heterotrimeric G protein subunit Gα13 and integrin β subunits reveals a new mechanism for integrin signaling, and also uncovers a crosstalk between the signaling pathways initiated by G protein-coupled receptors (GPCRs) and integrins. This crosstalk, which may be referred to as 'inside-outside-in' signaling, dynamically regulates contractility and greatly promotes integrin outside-in signaling.

Signaling during platelet adhesion and activation

Upon vascular injury, platelets are activated by adhesion to adhesive proteins, such as von Willebrand factor and collagen, or by soluble platelet agonists, such as ADP, thrombin, and thromboxane A(2). These adhesive proteins and soluble agonists induce signal transduction via their respective receptors. The various receptor-specific platelet activation signaling pathways converge into common signaling events that stimulate platelet shape change and granule secretion and ultimately induce the "inside-out" signaling process leading to activation of the ligand-binding function of integrin α(IIb)β(3). Ligand binding to integrin α(IIb)β(3) mediates platelet adhesion and aggregation and triggers "outside-in" signaling, resulting in platelet spreading, additional granule secretion, stabilization of platelet adhesion and aggregation, and clot retraction. It has become increasingly evident that agonist-induced platelet activation signals also cross talk with integrin outside-in signals to regulate platelet responses. Platelet activation involves a series of rapid positive feedback loops that greatly amplify initial activation signals and enable robust platelet recruitment and thrombus stabilization. Recent studies have provided novel insight into the molecular mechanisms of these processes.

Intelligibility and the acoustic characteristics of speech in amyotrophic lateral sclerosis (ALS)

The purpose of this study was to analyze the changes in specific speech parameters in 14 patients, 7 dysarthric and 7 non-dysarthric, with amyotrophic lateral sclerosis (ALS), over a 6-month period. Measurements of single word intelligibility, F2 formant trajectories (extent, duration and rate) and diadochokinetic rate showed decreased performance in dysarthric patients as compared to non-dysarthric patients at baseline. F2 transition rates of less than 4 Hz/msec were seen only in dysarthric ALS patients. A relationship between the F2 transition rate and single word intelligibility was noted for patients with moderate to high intelligibility, but at lower levels of intelligibility the F2 rate reached a plateau despite continued decline in intelligibility. Our results support the need for frequent evaluation of dysarthric ALS patients to better understand the relationship between intelligibility and the acoustic parameters of speech.