Glycocalyx

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Glycocalyx
TEM micrograph of a B. subtilis bacterium, with the hair-like glycocalyx visible surrounding the cell membrane (scale bar = 200 nm)
Identifiers
MeSHD019276
THH1.00.01.1.00002
FMA66838
Anatomical terms of microanatomy

The glycocalyx (pl.: glycocalyces or glycocalyxes), also known as the pericellular matrix and sometime cell coat, is a

epithelial cells, and other cells. It was described in a review article in 1970.[1]

Animal

plasma membranes. This viscous coating is the glycocalyx that consists of several carbohydrate moieties of membrane glycolipids and glycoproteins, which serve as backbone molecules for support. Generally, the carbohydrate portion of the glycolipids found on the surface of plasma membranes helps these molecules contribute to cell–cell recognition, communication, and intercellular adhesion.[2]

The glycocalyx is a type of identifier that the body uses to distinguish between its own healthy cells and transplanted tissues, diseased cells, or invading organisms. Included in the glycocalyx are cell-adhesion molecules that enable cells to adhere to each other and guide the movement of cells during embryonic development.

capillaries.[4]

The term was initially applied to the polysaccharide matrix coating epithelial cells, but its functions have been discovered to go well beyond that.

In vascular endothelial tissue

The glycocalyx is located on the

thrombocyte
adherence, since its principal role in the vasculature is to maintain plasma and vessel-wall homeostasis. These enzymes and proteins include:

The enzymes and proteins listed above serve to reinforce the glycocalyx barrier against vascular and other diseases. Another main function of the glycocalyx within the vascular endothelium is that it shields the vascular walls from direct exposure to blood flow, while serving as a vascular permeability barrier.

interstitial fluid from capillaries into the interstitial space.[7]

The glycocalyx, which is located on the

endothelial cells, is composed of a negatively charged network of proteoglycans, glycoproteins, and glycolipids.[8] Along the luminal surface of the vascular glycocalyx exists an empty layer that excludes red blood cells.[9]

Disruption and disease

Because the glycocalyx is so prominent throughout the cardiovascular system, disruption to this structure has detrimental effects that can cause disease. Certain stimuli that cause

atherothrombosis. In microvasculature, dysfunction of the glycocalyx leads to internal fluid imbalance, and potentially edema. In arterial vascular tissue, glycocalyx disruption causes inflammation and atherothrombosis.[10]

Experiments have been performed to test precisely how the glycocalyx can be altered or damaged. One particular study used an isolated perfused heart model designed to facilitate detection of the state of the vascular barrier portion, and sought to cause insult-induced shedding of the glycocalyx to ascertain the cause-and-effect relationship between glycocalyx shedding and vascular permeability.

tumor necrosis factor-alpha. Whatever the stimulus is, however, shedding of the glycocalyx leads to a drastic[clarification needed] increase in vascular permeability. Vascular walls being permeable is disadvantageous, since that would enable passage of some macromolecules or other harmful antigens.[11]

Other sources of damage to the endothelial glycocalyx have been observed in several pathological conditions such as inflammation,[12] hyperglycemia,[13] ischemia-reperfusion,[14] viral infections[15] and sepsis.[16]

Some key components of the glycocalyx such as syndecans, heparan sulphate, chondroitin sulphate and hyaluronan can be shed of the endothelial layer by enzymes. Hyaluronidase, hepararanse/heparinase, matrix and membrane-type matrix metalloproteases, thrombin, plasmin and elastase are some examples of enzymes that can induce shedding of the glycocalyx and these sheddases can therefor contribute to degradation of the glycocalyx layer in several pathological conditions.[17] Research shows that plasma hyaluronidase activity is decreased in experimental as well as in clinical septic shock and is therefore not considered to be a sheddase in sepsis.[18] Concomitant, the endogenous plasma inhibition of hyaluronidase is increased and could serve as a protection against glycocalyx shedding.

Fluid shear stress is also a potential problem if the glycocalyx is degraded for any reason. This type of frictional stress is caused by the movement of viscous fluid (i.e. blood) along the lumen boundary. Another similar experiment was carried out to determine what kinds of stimuli cause fluid shear stress. The initial measurement was taken with intravital microscopy, which showed a slow-moving plasma layer, the glycocalyx, of 1 μm thick. Light dye damaged the glycocalyx minimally, but that small change increased capillary hematocrit. Thus, fluorescence light microscopy should not be used to study the glycocalyx because that particular method uses a dye. The glycocalyx can also be reduced in thickness when treated with oxidized LDL.[19] These stimuli, along with many other factors, can cause damage to the delicate glycocalyx. These studies are evidence that the glycocalyx plays a crucial role in cardiovascular system health.

In bacteria and nature

The glycocalyx exists in bacteria as either a capsule or a slime layer. Item 6 points at the glycocalyx. The difference between a capsule and a slime layer is that in a capsule polysaccharides are firmly attached to the cell wall, while in a slime layer, the glycoproteins are loosely attached to the cell wall.

A glycocalyx, literally meaning "sugar coat" (glykys = sweet, kalyx = husk), is a network of

bacteria, which classifies it as a universal surface component of a bacterial cell, found just outside the bacterial cell wall. A distinct, gelatinous glycocalyx is called a capsule, whereas an irregular, diffuse layer is called a slime layer. This coat is extremely hydrated and stains with ruthenium red
.

Bacteria growing in natural ecosystems, such as in soil, bovine intestines, or the human urinary tract, are surrounded by some sort of glycocalyx-enclosed

prokaryotes
, or other bacteria which can fuse their glycocalices to envelop the colony).

In the digestive tract

A glycocalyx can also be found on the apical portion of

plasma membrane of epithelial absorptive cells. It provides additional surface for adsorption and includes enzymes
secreted by the absorptive cells that are essential for the final steps of digestion of proteins and sugars.

Other generalized functions

References

  1. ISBN 9780123643292
    .
  2. ^ McKinley, M. & V.D. O’Loughlin. Human Anatomy. McGraw-Hill, 2012. 3rd ed. p. 30-31.
  3. ^ Saladin, Kenneth. "Anatomy & Physiology: The unity of form and function." McGraw Hill. 5th Edition. 2010. p. 94-95
  4. ^ Reitsma, Sietze. "The endothelial glycocalyx: composition, functions, and visualization." European Journal of Physiology. 2007. Vol. 454. Num. 3. p. 345-359
  5. PMID 21474821
    .
  6. ^ Van de Berg, Bernard M., Max Nieuwdorp, Erik S.G. Stroes, Hans Vink. "Glycocalyx and endothelial (dys) function: from mice to men." Pharmacological Reports, 2006, 57: 75-80.
  7. ^ Drake-Holland, Angela & Mark Noble. "The Important New Drug Target in Cardiovascular Medicine – the Vascular Glycocalyx." Cardiovascular & Hematological Disorders-Drug Targets, 2009, 9, p. 118-123
  8. ^ Van de Berg, Bernard M., Max Nieuwdorp, Erik S.G. Stroes, Hans Vink. Glycocalyx and endothelial (dys) function: from mice to men. Pharmacological Reports, 2006, 57: 75-80.
  9. PMID 17256154
    .
  10. ^ Drake-Holland, Angela & Mark Noble. "The Important New Drug Target in Cardiovascular Medicine – the Vascular Glycocalyx." Cardiovascular & Hematological Disorders-Drug Targets, 2009, 9, p. 118–123
  11. ^ Annecke, T., et al. "Shedding of the coronary endothelial glycocalyx: effects of hypoxia/reoxygenation vs ischaemia/reperfusion." British Journal of Anaesthesia, 2011. 107 (5): 679–86
  12. S2CID 86646327
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  13. PMID 16024521
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  14. PMID 14704229
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  15. PMID 25778676
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  16. PMID 19560161
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  17. PMID 25778676
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  18. PMID 34632531
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  19. ^ Gouverneur, Mirella. Dissertation. "Fluid shear stress directly stimulates synthesis of the endothelial glycocalyx : perturbations by hyperglycemia." 2006. University of Amsterdam. p. 115–153
  20. ^ Costerton & Irvin. Bacterial Glycocalyx in Nature and Disease. Annual Reviews Microbiology, 1981. Vol. 35: p. 299-324
  21. ^ Near-Wall {micro}-PIV Reveals a Hydrodynamically Relevant Endothelial Surface Layer in Venules In Vivo - Smith et al. 85 (1): 637 - Biophysical Journal Archived 2008-12-03 at the Wayback Machine
  22. PMID 10465522
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External links
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