Quantitative analysis of the hydrodynamic integrity of the microvascular glycocalyx in healthy and transgenic mice
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Abstract
By 2004, the existence of an endothelial-cell (EC) glycocalyx surface layer , ~0.5 µm in thickness, was well established in capillaries and venules in vivo. Recent research has suggested many roles for the glycocalyx in vascular physiology, while other studies have linked glycocalyx damage to multiple vascular pathologies. In this dissertation, micro-particle image velocimetry and microviscometric analysis are applied in vivo to estimate the glycocalyx thickness under normal physiological conditions, in pathological states, and in genetic knock-out mice.
Since the glycocalyx is likely to have broad implications for EC function, it is necessary to determine the extent to which it is present in arterioles. Results show the existence of a glycocalyx ~0.4 µm thick in arterioles, slightly thinner than that found in venules (p = 0.025). Data obtained throughout the cardiac cycle indicate that glycocalyx thickness does not fluctuate with flow variations arising from cardiac-induced pulsatility.
Heparan sulfate proteoglycans are thought to be major components of glycocalyx.
To test whether syndecan-1 in particular is an essential glycocalyx anchoring protein, experiments were conducted in syndecan-1 deficient (Sdc1-/-) mice. Results indicate that the glycocalyx in Sdc1-/- mice is "'0.1 J-Lm thinner than in wild-type mice (p = 0.03). Increased leukocyte adhesion was also observed in Sdc1-/- mice. Therefore, while syndecan-1 is not a prerequisite for the existence of the glycocalyx, syndecan-1 deficiency may alter glycocalyx composition and function.
Hyperglycemia results in increased generation of reactive oxygen species, which have been shown to degrade glycocalyx. To assess the effects of hyperglycemia on the glycocalyx and the efficacy of treatments aimed at protecting the glycocalyx during hyperglycemia, experiments were performed in acutely and chronically hyperglycemic mice. Chronic hyperglycemia resulted in significant glycocalyx degradation. Treatments aimed at reducing levels of oxidative stress significantly reduced, but did not eliminate, glycocalyx damage.
While these investigations address many fundamental questions regarding the state of the glycocalyx under normal or pathological conditions, its structure, composition, and function still remain largely unknown. The presence of an intact glycocalyx may be critical to vascular health. FUture experiments are warranted to further explore the possible link between glycocalyx damage and vascular pathology.
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Thesis (Ph.D.)--Boston University
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