Actin polymerization stabilizes α4β1 integrin anchors that mediate monocyte adhesion

Leukocytes arrested on inflamed endothelium via integrins are subjected to force imparted by flowing blood. How leukocytes respond to this force and resist detachment is poorly understood. Live-cell imaging with Lifeact-transfected U937 cells revealed that force triggers actin polymerization at upstream α4β1 integrin adhesion sites and the adjacent cortical cytoskeleton. Scanning electron microscopy revealed that this culminates in the formation of structures that anchor monocyte adhesion. Inhibition of actin polymerization resulted in cell deformation, displacement, and detachment. Transfection of dominant-negative constructs and inhibition of function or expression revealed key signaling steps required for upstream actin polymerization and adhesion stabilization. These included activation of Rap1, phosphoinositide 3-kinase γ isoform, and Rac but not Cdc42. Thus, rapid signaling and structural adaptations enable leukocytes to stabilize adhesion and resist detachment forces

Leukocyte Structural Adaptations in Response to Hemodynamic Forces: Tension Transmitted Through VLA-4 Activates Upstream Rap1, PI3K, and Rac-Dependent Actin Polymerization

During inflammation, leukocytes modulate α4β1(VLA-4) integrin avidity in order to rapidly stabilize nascent adhesive contacts to VCAM-1-expressing endothelial cells and resist detachment forces imparted by the flowing blood. Linkage to the actin cytoskeleton is critical for integrin function, yet the exact role of the actin cytoskeleton in leukocyte adhesion stabilization under conditions of fluid flow remains poorly understood. We modeled leukocyte (U937 cell, mouse lymphocyte and human monocyte) arrest and adhesion stabilization through the use of a parallel plate flow chamber and visualized cells by phase contrast or fluorescent confocal microscopy. Live cell imaging with Lifeact-transfected U937 cells revealed that mechanical forces imparted by fluid flow induced formation of upstream tension-bearing anchors attached to the VCAM-1-coated surface. Scanning electron microscopy confirmed that flow-induced mechanical force culminates in the formation of structures that anchor monocyte adhesion. These structures are critical for adhesion stabilization, since disruption of actin polymerization dramatically inhibited VLA-4-dependent resistance to detachment, but did not affect VLA-4 expression, affinity modulation, and clustering or constitutive linkage to F-actin. Transfection of dominant-negative constructs and inhibition of kinase function or expression revealed key signaling steps required for upstream actin polymerization and adhesion stabilization. Rap1 was shown to be critical for resistance to flow-induced detachment and accumulated in its GTP form at the sites of anchor formation. A key mediator of force-induced Rac activation and actin polymerization is PI3K. Live cell imaging revealed accumulation of PIP3 within tension-bearing anchors and blockade of PI3K or deficiency of PI3Kγ isoform reproduced the adhesion defect produced by inhibition of actin polymerization. Thus, rapid signaling and structural adaptations enable leukocytes to stabilize adhesion and resist detachment forces; these included activation of Rap1, phosphoinositide 3-kinase γ-isoform and Rac, but not Cdc42.Ph

Alternating Involvement of Bilateral Oculomotor Nerves in Recurrent Ophthalmoplegic Cranial Neuropathy

Recurrent ophthalmoplegic cranial neuropathy (ROCN), formerly ophthalmoplegic migraine, is a rare disorder of episodic unilateral headache with reversible paresis of ipsilateral cranial nerves III, IV, and/or VI. Almost exclusively, laterality is consistent between recurrences(1). We report a case of alternating laterality of headache and oculomotor paresis between ROCN episodes

Fulminant Sequential Optic Neuropathies Secondary to Hemophagocytic Lymphohistiocytosis

Hemophagocytic Lymphohistiocytosis (HLH) is a rare disorder characterized by immune overactivation.1 Control of inflammation may be challenging and is necessary to prevent morbidity and mortality.2 We present a case of sequential optic neuropathies as a manifestation of HLH

Thrombophlebitis-Mediated Polycranial Neuropathy Secondary to Herpes Zoster Ophthalmicus

Herpes zoster ophthalmicus (HZO) accounts for 10-20% of cases of varicella zoster virus (VZV) reactivation.1 Neuro-ophthalmic manifestations include cranial nerve (CN) involvement, but the underlying mechanism is not always known.2 We present a case of polycranial neuropathy and thrombophlebitis in the setting of HZO. We propose that a venous vasculitis may mediate some HZOrelated cranial neuropathies

A Curious Case of Arteritis: Infectious, Inflammatory or Both

Takayasu arteritis is a large-vessel vasculitis affecting the aorta and its primary branches resulting in fibrosis and stenosis. The ocular manifestations of Takyasu's arteritis include arteriovenous irregularities, ocular ischemic syndrome, and reduced perfusion of the retina and choroid. Takayasu's arteritis rarely manifests in the eye as a first presentation

Changes in Scleral Thickness Following Repeated Anti-vascular Endothelial Growth Factor Injections

Purpose: This cross-sectional study aimed to compare changes in scleral thickness between eyes injected with repeated anti-vascular endothelial growth factor (anti-VEGF) drugs and fellow injection naive eyes using optical coherence tomography (OCT). Methods: A total of 79 patients treated with three intravitreal anti-VEGF injections in one eye versus no injections in the fellow eye were included. Anterior segment- OCT measured scleral thickness in the inferotemporal quadrant 4 mm away from the limbus. Results: Injected eyes had a mean scleral thickness of 588 ± 95 μm versus 618 ± 85 μm in fellow naïve eyes (P < 0.001). Comparing injected eyes to fellow naïve eyes stratified by injection number showed a mean scleral thickness of 585 ± 93 μm versus 615 ± 83 μm in eyes with 3–10 injections (n = 32, P = 0.042); 606 ± 90 μm versus 636 ± 79 μm in eyes with 11–20 injections (n = 24, P = 0.017); and 573 ± 104 μm versus 604 ± 93 μm in eyes with >20 injections (n = 23, P = 0.041). There was no significant correlation between injection number and scleral thickness change (r = –0.07, P = 0.26). When stratified by indication, subjects with retinal vein occlusions showed a statistically significant difference in scleral thickness between injected and fellow naïve eyes (535 ± 94 μm and 598 ± 101 μm, respectively, P = 0.001). Conclusion: Compared to injection naive eyes, multiple intravitreal injections at the repeated scleral quadrant results in scleral thinning. Consideration of multiple injection sites should be considered to avoid these changes