Quasi-Periodic Substructure in the Microvessel Endothelial Glycocalyx: A Possible Explanation for Molecular Filtering?

Squire, John M.; Chew, Michael; Nneji, Gwen A.; Neal, Chris; Barry, John; Michel, C. C.

doi:10.1006/jsbi.2002.4441

Cited by 245 publications

(304 citation statements)

References 26 publications

(41 reference statements)

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“…However, this value seems too small to agree with the experimental evidence that tracers of 6 nm diameter can pass through canaliculi (15). On the other hand, an alternative structure of endothelial glycocalyx was proposed recently by Squire et al (39) and Weinbaum et al (40), where, instead of extended side chains, spherical clusters (radius of 5-6 nm) are attached to core proteins such that the clusters repeat every 20 nm in all three dimensions. This structure was found to allow for albumin exclusion, to better explain transendothelial permeability data, and to transmit fluid shear stresses to the actin cytoskeleton (39,40).…”

Section: Discussionmentioning

confidence: 96%

“…Although the detailed structure of the pericellular matrix surrounding osteocytes is unknown, fiber matrix theory can be applied to the current data to predict the molecular sieving properties of the pericellular matrix as previously used in analyzing the structural features of the endothelial glycocalyx (16,39,40). Assuming that the osteocytic pericellular matrix is an ordered structure, like the endothelial glycocalyx, diffusion of a solute of radius a through this fibrous matrix relative to its free diffusion in aqueous solution will depend on fiber volume fraction (v f ), fiber radius (r f ), and solute radius (a).…”

Section: Discussionmentioning

confidence: 99%

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In situ measurement of solute transport in the bone lacunar-canalicular system

Wang

Han

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

183

212

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Solute transport through the bone lacunar-canalicular system is believed to be essential for osteocyte survival and function but has proved difficult to measure. We report an approach that permits direct measurement of real-time solute movement in intact bones. By using fluorescence recovery after photobleaching, the movement of a vitally injected fluorescent dye (sodium fluorescein) among individual osteocytic lacunae was visualized in situ beneath the periosteal surface of mouse cortical bone at depths up to 50 m with laser scanning confocal microscopy. Transport was analyzed by using a two-compartment mathematical model of solute diffusion that accounted for the characteristic anatomical features of the lacunar-canalicular system. The diffusion coefficient of fluorescein (376 Da) was determined to be 3.3 ؎ 0.6 ؋ 10 ؊6 cm 2 ͞sec, which is 62% of its diffusion coefficient in water and is similar to diffusion coefficients measured for comparably sized molecules in cartilage. The diffusion of fluorescein in bone is also consistent with the presence of an osteocyte pericellular matrix whose structure resembles that proposed for the endothelial glycocalyx diffusion coefficient ͉ fiber matrix theory ͉ fluorescence recovery after photobleaching ͉ osteocyte ͉ confocal microscopy

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Section: Discussionmentioning

confidence: 96%

Section: Discussionmentioning

confidence: 99%

In situ measurement of solute transport in the bone lacunar-canalicular system

Wang

Han

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

183

212

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“…The polygonal nature of the ACW was first reported in optical tweezer experiments (30). Recent freeze-fracture EMs by Squire et al (13) in regions close to the plasmalemma have revealed a highly ordered hexagonal lattice with a characteristic spacing of 100 nm between junctional nodes (Inset). Schematic diagrams show adaptation steps for confluent ECs predicted by the bumper-car model for intact (B) and compromised (C) EG in response to fluid shear stress; see text for detailed discussion.…”

Section: Discussionmentioning

confidence: 99%

“…Squire et al (13) showed that the ultrastructural organization of the EG was quasiperiodic, anchored to a geodesic-like scaffold of hexagonally arranged filamentous actin (F-actin) filaments forming an actin cortical web (ACW) (14) just beneath the plasmalemma. A fundamental question addressed in ref.…”

mentioning

confidence: 99%

The role of the glycocalyx in reorganization of the actin cytoskeleton under fluid shear stress: A “bumper-car” model

Thi

Tarbell

Weinbaum

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

279

308

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We propose a conceptual model for the cytoskeletal organization of endothelial cells (ECs) based on a major dichotomy in structure and function at basal and apical aspects of the cells. Intracellular distributions of filamentous actin (F-actin), vinculin, paxillin, ZO-1, and Cx43 were analyzed from confocal micrographs of rat fat-pad ECs after 5 h of shear stress. With intact glycocalyx, there was severe disruption of the dense peripheral actin bands (DPABs) and migration of vinculin to cell borders under a uniform shear stress (10.5 dyne͞cm 2 ; 1 dyne ‫؍‬ 10 N). This behavior was augmented in corner flow regions of the flow chamber where high shear stress gradients were present. In striking contrast, no such reorganization was observed if the glycocalyx was compromised. These results are explained in terms of a ''bumper-car'' model, in which the actin cortical web and DPAB are only loosely connected to basal attachment sites, allowing for two distinct cellular signaling pathways in response to fluid shear stress, one transmitted by glycocalyx core proteins as a torque that acts on the actin cortical web (ACW) and DPAB, and the other emanating from focal adhesions and stress fibers at the basal and apical membranes of the cell. mechanotransduction ͉ actin cortical web ͉ dense peripheral actin band H emodynamic shearing stresses on endothelial cells (ECs) are widely recognized as playing a vital role in the regulation of vessel wall remodeling, cellular signaling, mass transport, red and white cell interaction, and atherogenesis (1-3). The possible roles of the endothelial glycocalyx (EG) in this regulation as a molecular sieve, as a barrier and modulator of interactions between blood cells and ECs, and as a mechanotransducer of fluid shear stress have been studied more recently (4-7). Relatively little is known about the specific proteins in the EG, although hyaluronan, chondroitin, and heparan sulfate play a significant role in its assembly (8, 9). In the early 1990s, investigators first observed that the shear-induced dilation of small arteries was abolished when sialic acids were removed from the EG by neuraminidase (10). Florian et al. (11) recently verified the presence of heparan sulfate proteoglycan (HSPG) in the glycocalyx of cultured bovine aortic ECs and demonstrated that partial removal of HSPG with heparinase completely blocked shear-induced NO release. A puzzling and still not understood consequence of EG degradation was the observation that shear-induced NO production was greatly inhibited without apparent effect on shear-dependent vasodilation due to prostaglandin I 2 release (12). Squire et al. (13) showed that the ultrastructural organization of the EG was quasiperiodic, anchored to a geodesic-like scaffold of hexagonally arranged filamentous actin (F-actin) filaments forming an actin cortical web (ACW) (14) just beneath the plasmalemma. A fundamental question addressed in ref. 7 is how fluid shear stresses acting at the surface of the EG are transmitted to this ACW if there is essentially ...

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“…Within the canaliculi, a pericellular fiber matrix is believed to keep the osteocyte processes in position, connecting them to the canalicular wall [25,27] and preventing them from collapsing [28]. The fiber matrix spacing is believed to be approximately 7-8 nm, similar to the surface glycocalyx on endothelial cells, and the fiber matrix has been proposed to work as a sieve, allowing only molecules smaller than the pore diameter to pass through [3,21,25]. Lastly, the smallest bone porosity is the collagen-apatite porosity associated with the space between the collagen fibers and the crystallites of mineral apatite.…”

Section: Introductionmentioning

confidence: 99%

Mapping bone interstitial fluid movement: Displacement of ferritin tracer during histological processing

Ciani¹,

Doty²,

Fritton³

2005

Bone

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Bone interstitial fluid flow is thought to play a fundamental role in the mechanical stimulation of bone cells, either via shear stresses or cytoskeletal deformations. Recent evidence indicates that osteocytes are surrounded by a fiber matrix that may be involved in the mechanotransduction of external stimuli as well as in nutrient exchange. In our previous tracer studies designed to map how different-sized molecules travel through the bone porosities, we found that injected ferritin was confined to blood vessels and did not pass into the mineralized matrix. However, other investigators have shown that ferritin forms halo-shaped labeling that enters the mineralized matrix around blood vessels. This labeling is widely used to explain normal interstitial fluid movement in bone; in particular, it is said to demonstrate bulk centrifugal interstitial fluid movement away from a highly pressurized vascular porosity. In addition, appositional ferritin fronts are said to demonstrate centrifugal interstitial fluid movement from the medullary canal to the periosteal surface. The purpose of this study was to investigate the conflicting ferritin labeling results by evaluating the role of different histological processes in the formation of ferritin "halos." Ferritin was injected into the rat vasculature and allowed to circulate for 5 min. Samples obtained from tibiae were reacted for different times with Perl's reagent and then were either paraffin-embedded or sectioned with a cryostat. Halo-like labeling surrounding vascular pores was found in all groups, ranging from 1.2-3.9% for the samples treated with the shortest histological processes (unembedded, frozen sections) to 5.6-15% for the samples treated with the longest histological processes (paraffin-embedded sections). These results indicate that different histological processing methods are able to create ferritin "halos," with some processing methods allowing more redistribution of the ferritin tracer than others. Based on these results and the fact that "halo" labeling has not been found with any other tracer, as we seek to further delineate the movement of interstitial fluid and the role it plays in bone mechanotransduction, we believe that ferritin "halo" labeling should not be used to demonstrate physiological bone interstitial fluid flow.

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Quasi-Periodic Substructure in the Microvessel Endothelial Glycocalyx: A Possible Explanation for Molecular Filtering?

Cited by 245 publications

References 26 publications

In situ measurement of solute transport in the bone lacunar-canalicular system

In situ measurement of solute transport in the bone lacunar-canalicular system

The role of the glycocalyx in reorganization of the actin cytoskeleton under fluid shear stress: A “bumper-car” model

Mapping bone interstitial fluid movement: Displacement of ferritin tracer during histological processing

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