Glycocalyx in Endotoxemia and Sepsis

Along with the recognition of a crucial role played by endothelial dysfunction secondarily igniting cardiovascular, pulmonary, and renal complications, investigational focus has extended toward endothelial glycocalyx. This delicate coating of cells, including the vascular endothelium, regulates permeability, leukocyte traffic, nitric oxide production, and coagulation, and harbors diverse growth and survival factors. In this brief overview, we discuss the metabolic signatures of sepsis as they relate to the loss of glycocalyx integrity and highlight the contribution of several proteases, heparanase, and hyaluronidase to the shedding of glycocalyx. Clinical manifestations of glycocalyx degradation in unraveling acute respiratory distress syndrome and the cardiovascular, microcirculatory, and renal complications of sepsis are concisely presented. Finally, we list therapeutic strategies for preventing the degradation of, and for restoration of, the glycocalyx. Along with the recognition of a crucial role played by endothelial dysfunction secondarily igniting cardiovascular, pulmonary, and renal complications, investigational focus has extended toward endothelial glycocalyx. This delicate coating of cells, including the vascular endothelium, regulates permeability, leukocyte traffic, nitric oxide production, and coagulation, and harbors diverse growth and survival factors. In this brief overview, we discuss the metabolic signatures of sepsis as they relate to the loss of glycocalyx integrity and highlight the contribution of several proteases, heparanase, and hyaluronidase to the shedding of glycocalyx. Clinical manifestations of glycocalyx degradation in unraveling acute respiratory distress syndrome and the cardiovascular, microcirculatory, and renal complications of sepsis are concisely presented. Finally, we list therapeutic strategies for preventing the degradation of, and for restoration of, the glycocalyx. Sepsis is an ominous clinical manifestation of a severe generalized infection leading to systemic multiorgan sequelae such as hypotension, acute respiratory distress syndrome, renal failure, and lactic acidosis, among others. It afflicts >750,000 people each year in the United States alone and has a mortality rate of 28% to 50%. One of the key molecular causes of gram-negative septicemia is a component of the outer membrane of gram-negative bacteria, lipopolysaccharide (LPS). It binds with high affinity to LPS-binding glycoproteins and activates Toll-like receptor (TLR)-4 and co-receptor CD14 expressed on monocytes/macrophages and endothelial cells to induce the secretion of proinflammatory cytokines.1Aird W. The role of the endothelium in severe sepsis and multiorgan dysfunction syndrome.Blood. 2003; 101: 3765-3777Crossref PubMed Scopus (901) Google Scholar This is, however, not the only and, perhaps, not the main pathogenic mechanism of LPS. Recent clinical trials of TLR4 inhibitors have not produced an expected amelioration of severe sepsis.2Rice T.W. Wheeler A.P. Bernard G.R. Vincent J.L. Angus D.C. Aikawa N. Demeyer I. Sainati S. Amlot N. Cao C. Ii M. Matsuda H. Mouri K. Cohen J. A randomized, double-blind, placebo-controlled trial of TAK-242 for the treatment of severe sepsis.Crit Care Med. 2010; 38: 1685-1694Crossref PubMed Scopus (331) Google Scholar,3Laterre P.F. Francois B. LaRosa S.P. Angus D.C. Mira J.P. Wittebole X. Dugernier T. Perrotin D. Tidswell M. Jauregui L. Krell K. Pachl J. Takahashi T. Peckelsen C. Cordasco E. Chang C.S. Oeyen S. Aikawa N. Maruyama T. Schein R. Kalil A.C. Van Nuffelen M. Lynn M. Rossignol D.P. Gogate J. Roberts M.B. Wheeler J.L. Vincent J.L. 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Inflammatory caspases are innate immune receptors for intracellular LPS.Nature. 2014; 514: 187-192Crossref PubMed Scopus (47) Google Scholar The incidence of sepsis is on a rise, while the mortality rate maintains the level of about 30%.6Huet O. Chin-Dusting J. Septic shock: desperately seeking treatment.Clin Sci. 2014; 128: 31-39Crossref Scopus (36) Google Scholar With the conceptual shift from the idea of a “disproportionate”7Hawiger I. Veach R. Zienkiewicz J. New paradigms in sepsis: from prevention to protection of failing microcirculation.J Thromb Haemost. 2015; 13: 1743-1756Crossref PubMed Scopus (78) Google Scholar,pp.1743 cytokine response to infection in septic shock to that of a “severe endothelial dysfunction syndrome in response to intravascular and extravascular infection”7Hawiger I. Veach R. Zienkiewicz J. New paradigms in sepsis: from prevention to protection of failing microcirculation.J Thromb Haemost. 2015; 13: 1743-1756Crossref PubMed Scopus (78) Google Scholar,pp.1743 came the emphasis on the crucial role of impaired microcirculation to vital organs as the leading mechanism of sepsis and septic shock. Considering the systemic nature of septicemia, vascular endothelium represents the front line of exposure to bacterial endotoxins. Endothelial dysfunction and impaired microcirculation develop in the course of sepsis and determine its severity and duration8Morrison D. Ulevitch R. The effect of bacterial endotoxins on host mediation systems: a review.Am J Pathol. 1978; 93: 526-617PubMed Google Scholar,9Becker B. Chappell D. Jacob M. Endothelial glycocalyx and coronary vascular permeability: the fringe benefit.Basic Res Cardiol. 2010; 105: 687-701Crossref PubMed Scopus (184) Google Scholar This role of microcirculation and microvascular endothelium in the pathogenesis of septic multiorgan failure has been known for decades,1Aird W. The role of the endothelium in severe sepsis and multiorgan dysfunction syndrome.Blood. 2003; 101: 3765-3777Crossref PubMed Scopus (901) Google Scholar,10Schmidt E. Yang Y. Janssen W. Gandjeva A. Perez M.J. Barthel L. Zemans R.L. Bowman J.C. Koyanagi D.E. Yunt Z.X. Smith L.P. Cheng S.S. Overdier K.H. Thompson K.R. Geraci M.W. Douglas I.S. Pearse D.B. Tuder R.M. The pulmonary endothelial glycocalyx regulates neutrophil adhesion and lung injury during experimental sepsis.Nat Med. 2012; 18: 1217-1223Crossref PubMed Scopus (504) Google Scholar, 11Annecke T. Fischer J. Hartmann H. Tschoep J. Rehm M. Conzen P. Sommerhoff C.P. Becker B.F. Shedding of the coronary endothelial glycocalyx: effects of hypoxia/reoxygenation vs ischemia/reperfusion.Br J Anaesth. 2011; 107: 679-686Abstract Full Text Full Text PDF PubMed Scopus (73) Google Scholar, 12Mulivor A. Lipowsky H. Inflammation and ischemia-induced shedding of venular glycocalyx.Am J Physiol Heart Circ Physiol. 2004; 286: H1672-H1680Crossref PubMed Scopus (284) Google Scholar but recent studies have implicated endothelial glycocalyx (EG) in at least some manifestations of endothelial dysfunction in sepsis.10Schmidt E. Yang Y. Janssen W. Gandjeva A. Perez M.J. Barthel L. Zemans R.L. Bowman J.C. Koyanagi D.E. Yunt Z.X. Smith L.P. Cheng S.S. Overdier K.H. Thompson K.R. Geraci M.W. Douglas I.S. Pearse D.B. Tuder R.M. The pulmonary endothelial glycocalyx regulates neutrophil adhesion and lung injury during experimental sepsis.Nat Med. 2012; 18: 1217-1223Crossref PubMed Scopus (504) Google Scholar, 11Annecke T. Fischer J. Hartmann H. Tschoep J. Rehm M. Conzen P. Sommerhoff C.P. Becker B.F. Shedding of the coronary endothelial glycocalyx: effects of hypoxia/reoxygenation vs ischemia/reperfusion.Br J Anaesth. 2011; 107: 679-686Abstract Full Text Full Text PDF PubMed Scopus (73) Google Scholar, 12Mulivor A. Lipowsky H. Inflammation and ischemia-induced shedding of venular glycocalyx.Am J Physiol Heart Circ Physiol. 2004; 286: H1672-H1680Crossref PubMed Scopus (284) Google Scholar, 13Zullo J. Fan J. Azar T. Yen W. Zeng M. Chen J. Ratliff B.B. Song J. Tarbell J.M. Goligorsky M.S. Fu B.M. Exocytosis of endothelial lysosome-related organelles hair-triggers a patchy loss of glycocalyx at the onset of sepsis.Am J Pathol. 2016; 186: 248-258Abstract Full Text Full Text PDF PubMed Scopus (29) Google Scholar We and others have shown that preventive strategies for reducing the degradation of EG result in improved survival in mice with polymicrobial sepsis.10Schmidt E. Yang Y. Janssen W. Gandjeva A. Perez M.J. Barthel L. Zemans R.L. Bowman J.C. Koyanagi D.E. Yunt Z.X. Smith L.P. Cheng S.S. Overdier K.H. Thompson K.R. Geraci M.W. Douglas I.S. Pearse D.B. Tuder R.M. The pulmonary endothelial glycocalyx regulates neutrophil adhesion and lung injury during experimental sepsis.Nat Med. 2012; 18: 1217-1223Crossref PubMed Scopus (504) Google Scholar,13Zullo J. Fan J. Azar T. Yen W. Zeng M. Chen J. Ratliff B.B. Song J. Tarbell J.M. Goligorsky M.S. Fu B.M. Exocytosis of endothelial lysosome-related organelles hair-triggers a patchy loss of glycocalyx at the onset of sepsis.Am J Pathol. 2016; 186: 248-258Abstract Full Text Full Text PDF PubMed Scopus (29) Google Scholar,14Song J.W. Zullo J.A. Liveris D. Dragovich M. Zhang X.F. Goligorsky M.S. Therapeutic restoration of endothelial glycocalyx in sepsis.J Pharmacol Exp Ther. 2017; 361: 115-121Crossref PubMed Scopus (62) Google Scholar The global loss of EG in polymicrobial sepsis has been documented by Song et al14Song J.W. Zullo J.A. Liveris D. Dragovich M. Zhang X.F. Goligorsky M.S. Therapeutic restoration of endothelial glycocalyx in sepsis.J Pharmacol Exp Ther. 2017; 361: 115-121Crossref PubMed Scopus (62) Google Scholar using dilution technique with two fluorophores, glycocalyx-penetrating and -nonpenetrating probes. All of these studies have prompted the present focus on EG in sepsis. EG covers most of the vascular luminal surface. Two-photon laser scanning microscopy of murine carotid arteries labeled with fluorescent wheat germ agglutinin and visualized in areas prone and not prone to develop atherosclerotic plaques showed labeling of >90% of the surface in nonprone areas of the common carotid artery, with only 73% of the surface area in atherogenesis-prone internal carotid arteries15Reitsma S. oude Egbrink M. Vink H. van den Berg B. Pasos V. Engels W. Slaaf D. van Zandvoort M. Endothelial glycocalyx structure in the internal carotid artery: a two-photon laser scanning microscopy study.J Vasc Res. 2011; 48: 297-306Crossref PubMed Scopus (52) Google Scholar and the thickness of glycocalyx reaching 2.3 to 2.5 μm. These findings are in part supported by the results obtained using high-resolution confocal microscopy and labeling of glycocalyx with antibodies against heparan sulfate (HS),16Yen W. Cai B. Zeng M. Tarbell J. Fu B. Quantification of the endothelial surface glycocalyx on rat and mouse blood vessels.Microvasc Res. 2012; 83: 337-346Crossref PubMed Scopus (65) Google Scholar which revealed the thickness of glycocalyx varying between 0.9 and 1.5 μm. Of note, in this study the access to the glycocalyx for ex vivo perfused wheat germ agglutinin–fluorescein isothiocyanate, which binds to sialic acid and N-acetylglucosaminyl residues, was impeded, and labeling required prior perfusion of an air bubble, allegedly improving the access of the fluoroprobe to its targets in the glycocalyx. As mentioned above, EG is an early victim of endotoxemia; so is the function of endothelial cells.17Levi M. van der Poll T. Endothelial injury in sepsis.Intensive Care Med. 2013; 39: 1839-1842Crossref PubMed Scopus (51) Google Scholar The question is: Are those two events related? We proposed the concept of a vicious circle–type relationship between endothelial dysfunction and the loss of glycocalyx. This concept, stemming from a score of previous studies,8Morrison D. Ulevitch R. The effect of bacterial endotoxins on host mediation systems: a review.Am J Pathol. 1978; 93: 526-617PubMed Google Scholar has been formulated to explain the tight association between the two conditions and to emphasize the need for therapeutic interventions targeting both, as summarized by Zhang et al.18Zhang X. Sun D. Song J. Zullo J. Lipphardt M. Cohen-Gould L. Goligorsky M.S. Endothelial cell dysfunction and glycocalyx – a vicious circle.Matrix Biol. 2018; 71–72: 421-431Crossref PubMed Scopus (86) Google Scholar Endothelial cell dysfunction—as characterized by reduced nitric oxide (NO) bioavailability, enhanced production of reactive oxygen species, activation of sheddases, and impaired exocytosis of lysosome-related organelles (Lysosome-Related Organelles)—triggers degradation of EG, which, in turn, leads to defective shear stress–induced activation of endothelial NO synthase and further decline in NO bioavailability, shedding of components of glycocalyx endowed with proinflammatory properties, and loss of glycocalyx-bound growth and survival factors, thus fueling the vicious circle. In general, sepsis is characterized as a catabolic state of degradation of proteins, lipids, and carbohydrates.19Wyngene L. Wandewalle J. Libert C. Reprogramming of basic metabolic pathways in microbial sepsis: therapeutic targets at last?.EMBO Mol Med. 2018; 10: e8712PubMed Google Scholar Remarkably, recent advanced metabolic gene expression systems analysis of LPS-induced endothelial dysfunction revealed an increase in glycan production (together with fatty acid metabolism) to accompany glycocalyx loss in endothelial cells exposed to LPS and an increase in their permeability by 60%.20McGarrity S. Anuforo O. Halldorsson H. Bergmann A. Halldorsson S. Palsson S. Henriksen H. Johansson P. Rolfsson O. Metabolic systems analysis of LPS-induced endothelial dysfunction applied to septic patient stratification.Sci Rep. 2018; 8: 6811Crossref PubMed Scopus (22) Google Scholar Confirmation of these in vitro findings in patients with sepsis showed that upregulation of glycan synthesis was among the worst-affected areas of metabolism, being most deranged in nonsurvivors. The data are consistent with a view of compensatory induction of synthesis of structural components of glycocalyx, among others, upon application of glycocalyx-degrading stressors such as LPS, thus suggesting a tight feedback control mechanism coupling its synthesis and degradation. The fact that the degradation of glycocalyx in sepsis prevails over increased synthesis of at least one of its components strongly favors its enhanced enzymatic degradation. It is carried out by sheddases, a disintegrin and metalloproteinases (ADAMs), matrix metalloproteinase (MMPs), heparanase-1, and hyaluronidases (Figure 1). ADAMs show sequence similarity, yet ADAM10 is expressed constitutively, while ADAM17 is inducible, as it is converted into an active form upon cell stimulation.21Mishra H. Ma J. Walcheck B. Ectodomain shedding by ADAM17: its role in neutrophil recruitment and the impairment of this process during sepsis.Front Cell Infect Microbiol. 2017; 7: 138Crossref PubMed Scopus (41) Google Scholar In addition to the well-known conversion of tumor necrosis factor (TNF)-α to the soluble form, ADAM17 cleaves syndecan-4, whereas ADAM10 sheds syndecan-1. Among other ADAM targets are receptors for IL-6, TNF, and cell adhesion molecules ICAM-1, VCAM-1, L-selectin. All of those receptors are expressed by leukocytes and endothelial cells. ADAM17 activity is induced in sepsis, thus resulting in shedding components of leukocyte–endothelial cell tether machinery and facilitating systemic inflammation. This shedding explains the immune paralysis and impaired microbial clearance in patients with sepsis. In contrast to ADAM17, ADAM13 activity is suppressed in sepsis,22Lin J. Chan O. Hsiao H. Wang Y. Hsia S. Chiu C. Decreased ADAM13 activity is associated with disease severity and outcome in pediatric severe sepsis.Medicine (Baltimore). 2016; 95: e3374Crossref PubMed Scopus (26) Google Scholar thus compromising cleavage of von Willebrand factor multimers and predisposing to the development of intravascular platelet aggregation and thrombosis. Members of the ADAMs family and MMPs (a.k.a. matrixins) are zinc-dependent endopeptidases sharing many structure–functional properties, as well as substrates–extracellular matrix proteins and bound to them growth factors (insulin-like growth factor, vascular endothelial growth factor, transforming growth factor β, fibroblast growth factor, and others), cytokines and chemokines. In addition, they can activate TNFα and alter CD44–hyaluronic acid (HA) interaction.23Levin M. Udi Y. Solomonov I. Sagi I. Next generation MMP inhibitors – novel strategies bring new prospects.Biochem Biophys Acta Mol Cell Res. 2017; 1864: 1927-1939Crossref PubMed Scopus (104) Google Scholar MMPs are induced in sepsis, leading to impairment of host defense.24Vanlaere I. Libert C. MMPs as drug targets in infections caused by gram-negative bacteria and septic shock.Clin Microbiol Rev. 2009; 22: 224-239Crossref PubMed Scopus (114) Google Scholar While the search for highly specific and selective inhibitors is proceeding, it is noteworthy that systemic application of MMP inhibitors may have a broad spectrum of untoward effects, potentially limiting their clinical utility. Heparanase gene expression is epigenetically and p53 controlled, but can be stimulated by early growth response 1 transcription factor, reactive oxygen species, and inflammatory cytokines.25Goldberg R. Meirovitz A. Hirshoren N. Bulvik R. Binder A. Rubinstein A. Elkin M. Versatile role of heparanase in inflammation.Matrix Biol. 2013; 32: 234-240Crossref PubMed Scopus (102) Google Scholar Several mutated variants of p53 induce heparanase expression, thus explaining its overexpression in some malignant tumors.26Ilan N. Elkin M. Vlodavsky I. Regulation, function and clinical significance of heparanase in cancer metastasis and angiogenesis.Int J Biochem Cell Biol. 2006; 38: 2018-2039Crossref PubMed Scopus (462) Google Scholar The enzyme is activated in sepsis, with the consequent degradation of HS moieties, further aggravating the loss of glycocalyx components. The pathogenic role of heparinase activation in sepsis-induced respiratory distress has been convincingly demonstrated by Schmidt et al10Schmidt E. Yang Y. Janssen W. Gandjeva A. Perez M.J. Barthel L. Zemans R.L. Bowman J.C. Koyanagi D.E. Yunt Z.X. Smith L.P. Cheng S.S. Overdier K.H. Thompson K.R. Geraci M.W. Douglas I.S. Pearse D.B. Tuder R.M. The pulmonary endothelial glycocalyx regulates neutrophil adhesion and lung injury during experimental sepsis.Nat Med. 2012; 18: 1217-1223Crossref PubMed Scopus (504) Google Scholar through the application of heparinase inhibitors and the use of heparanase-deficient mice. Similar observations were made in a model of ischemic acute kidney injury. HA receptors are many and, in addition to CD44, include receptor for HA-mediated motility, lymphatic vessel endothelial receptor 1, HA receptor for endocytosis, and TLR4, thus making HA a potent signaling molecule, with its repertoire being further enriched by the opposing actions of high– and low–molecular-weight species.27Powell J. Horton M. Threat matrix: low-molecular-weight hyaluronan as a danger signal.Immunol Res. 2005; 31: 207-218Crossref PubMed Scopus (112) Google Scholar,28Stern R. Asari A. Sugahara K. Hyaluronan fragments: an information-rich system.Eur J Cell Biol. 2006; 85: 699-715Crossref PubMed Scopus (865) Google Scholar Hyaluronan metabolism is affected in sepsis. Circulating levels of HA and HS are increased fourfold in patients with sepsis,29Nelson A. Berkestedt I. Bodelsson M. Circulating glycosaminoglycan species in septic shock.Acta Anaesthesiol Scand. 2014; 38: 36-43Crossref Scopus (69) Google Scholar being higher in those who did not survive 90 days, but only HA levels were correlated with the severity of kidney and liver functional damage. In a unilateral renal ischemia reperfusion model in rats, HA was risen at day 1, predominantly as a high–molecular-weight species, with later dominance of lower–molecular-weight fragments. This phenomenon is associated with a 35- to 50-fold increase in hyaluronan synthase mRNA transcripts in the outer and inner medullary stripes and continuing elevation of hyaluronan synthase 2 mRNA. In parallel, the activities of hyaluronidases 1 and 2 are repressed during the first 24 hours after ischemia reperfusion.30Decleves A. Caron N. Voisin V. Legrand A. Bouby N. Kultti A. Tammi M. Flamion B. Synthesis and fragmentation of hyaluronan in renal ischemia.Nephrol Dial Transplant. 2012; 27: 3771-3781Crossref PubMed Scopus (24) Google Scholar Lysosome-related organelles trigger EG degradation. Intriguingly, the luminal surface of lysosomes, as well as late endosomes and autophagosomes, is coated with a thin glycoconjugate-rich layer, referred to as lysosomal glycocalyx.31Wilke S. Krausze J. Bussow K. Crystal structure of the conserved domain of the DC lysosomal associated membrane protein: implications for the lysosomal glycocalyx.BMC Biol. 2012; 10: 62Crossref PubMed Scopus (66) Google Scholar This layer, enriched in lysosomal-associated membrane proteins 1 and 2, is believed to protect the limiting membrane from autodigestion by diverse hydrolyses contained inside lysosomes.32Settembre C. Fraldi A. Medina D. Ballabio A. Signals from the lysosome: a control centre for cellular clearance and energy metabolism.Mol Cell Biol. 2013; 14: 283-296Google Scholar Electron microscopy and computational analysis of the crystal structure of a member of lysosomal-associated membrane proteins posit that the thickness of lysosomal glycocalyx approximates 5 to 12 nm.31Wilke S. Krausze J. Bussow K. Crystal structure of the conserved domain of the DC lysosomal associated membrane protein: implications for the lysosomal glycocalyx.BMC Biol. 2012; 10: 62Crossref PubMed Scopus (66) Google Scholar Although it has been suggested that exocytosis of secretory lysosomes may assist in reconstituting plasma membrane glycocalyx, the dimensions of lysosomal glycocalyx are hardly sufficient for this purpose. In fact, we believe that the opposite is occurring under endotoxemic stress.13Zullo J. Fan J. Azar T. Yen W. Zeng M. Chen J. Ratliff B.B. Song J. Tarbell J.M. Goligorsky M.S. Fu B.M. Exocytosis of endothelial lysosome-related organelles hair-triggers a patchy loss of glycocalyx at the onset of sepsis.Am J Pathol. 2016; 186: 248-258Abstract Full Text Full Text PDF PubMed Scopus (29) Google Scholar,33Kuo M.C. Patschan D. Patschan S. Cohen-Gould L. Park H.C. Ni J. Addabbo F. Goligorsky M.S. Ischemia-induced exocytosis of Weibel-Palade bodies mobilizes stem cells.J Am Soc Nephrol. 2008; 19: 2321-2330Crossref PubMed Scopus (47) Google Scholar Exocytosis of lysosome-related organelles is detectable within minutes after the application of the stressor. Notably, lysosomes contain nearly 60 different soluble hydrolases, including sulphatases, peptidases, phosphatases, lipases, and nucleases, which, although active in acidic pH, retain nearly 20% activity at neutral pH and can hydrolyze glycosaminoglycans, sphingolipids, and an array of proteins.34Freeman C. Parish C. Knox K. Blackmore J. Lobov S. King D. Senden T. Stephens R. The accumulation of circulating histones on heparan sulfate in the capillary glycocalyx of the lungs.Biomaterials. 2013; 34: 5670-5676Crossref PubMed Scopus (34) Google Scholar This singular exocytotic event results in the liberation of a multitude of stored components from the Weibel-Palade bodies and secretory lysosomes. Through the use of stochastic optical reconstruction microscopy of cultured cells stained with anti-HS antibodies, Zullo et al13Zullo J. Fan J. Azar T. Yen W. Zeng M. Chen J. Ratliff B.B. Song J. Tarbell J.M. Goligorsky M.S. Fu B.M. Exocytosis of endothelial lysosome-related organelles hair-triggers a patchy loss of glycocalyx at the onset of sepsis.Am J Pathol. 2016; 186: 248-258Abstract Full Text Full Text PDF PubMed Scopus (29) Google Scholar illustrated the appearance of patchy degradation of EG already 10 to 15 minutes after the application of LPS. This phenomenon was associated with the increased levels of cathepsin B in the culture medium, consistent with the export of lysosomal cargo. When the docking of lysosome-related organelles was inhibited with NO donor, the loss of EG was mitigated. In addition to heparanase-mediated and mast cell–mediated sepsis-induced degradation of glycocalyx, these findings provide a yet another pathway of early loss of this structure, as depicted in Figure 1. The proposed role for exocytosed lysosomal cargo in degradation of glycocalyx has multiple broad-ranging biological equivalents, such as osteoclastic bone resorption, platelet induction of coagulation, spermatozoan hydrolysis in fertilization, and the defense of mast cells and eosinophils against parasites, to name a few examples. All of those mechanisms of shedding of glycocalyx are compiled in Figure 1. Pulmonary manifestations of sepsis are perilous. Pulmonary microvasculature is one of the critically damaged targets of sepsis, leading to acute respiratory distress syndrome. A study by Schmidt et al10Schmidt E. Yang Y. Janssen W. Gandjeva A. Perez M.J. Barthel L. Zemans R.L. Bowman J.C. Koyanagi D.E. Yunt Z.X. Smith L.P. Cheng S.S. Overdier K.H. Thompson K.R. Geraci M.W. Douglas I.S. Pearse D.B. Tuder R.M. The pulmonary endothelial glycocalyx regulates neutrophil adhesion and lung injury during experimental sepsis.Nat Med. 2012; 18: 1217-1223Crossref PubMed Scopus (504) Google Scholar implicated the activation of heparanase in degradation of glycocalyx in pulmonary circulatory beds. Based on the pathogenic role of circulating histone proteins in mediating acute lung injury, Freeman et al34Freeman C. Parish C. Knox K. Blackmore J. Lobov S. King D. Senden T. Stephens R. The accumulation of circulating histones on heparan sulfate in the capillary glycocalyx of the lungs.Biomaterials. 2013; 34: 5670-5676Crossref PubMed Scopus (34) Google Scholar proposed that the high proportion of positively charged amino acids in histones could be involved in their electrostatic accumulation on the polyanionic surface of EG. Using tagged histones, they demonstrated their preferential and avid binding in rabbit lungs, which could be abolished by the administration of competing polycations or by heparanase, thus localizing the binding sites to the HS moieties of endothelial glycocalyx. Moreover, a number of HS analogues also prevented histone accumulation in the lungs by neutralizing circulating histones. Degradation of EG with the subsequent microcirculatory abnormalities explain, at least in part, the development of the ventilation–perfusion mismatch. Morphologic perturbations in pulmonary microvasculature were comprehensively studied by Inagawa et al.35Inagawa R. Okada H. Takemura G. Suzuki K. Takada C. Yano H. Ando Y. Usui T. Hotta Y. Miyazaki N. Tsujimoto A. Zaikokuji R. Matsumoto A. Kawaguchi T. Doi T. Yoshida T. Yoshida S. Kumada K. Ushikoshi H. Toyoda I. Ogura S. Ultrastructural alteration of pulmonary capillary endothelial glycocalyx during endotoxemia.Chest. 2018; 154: 317-325Abstract Full Text Full Text PDF PubMed Scopus (51) Google Scholar In endotoxemic mice, both scanning and transmission electron microscopy of EG, normally appearing as a mosslike structure, showed that it was severely disrupted, peeled away and coagulated, with numerous spherical structures, which were distinct from exosomes and contained elements of EG, appearing within capillary lumens. Cardiomyopathy manifests in left ventricular dilatation, reduced cardiac contractility, and systolic or diastolic dysfunction with reduced response to volume expansion.36Beesley S. Weber G. Sarge T. Nikravan S. Grissom C.K. Lanspa M.J. Shahul S. Brown S.M. Septic cardiomyopathy.Crit Care Med. 2018; 46: 625-634Crossref PubMed Scopus (188) Google Scholar,37Martin L. Derwall M. Al Zoubi S. Zechendorf E. Reuter D. Thiemermann C. Schuerholz T. The septic heart: current understanding of molecular mechanisms and clinical implications.Chest. 2019; 155: 427-437Abstract Full Text Full Text PDF PubMed Scopus (143) Google Scholar TLRs expressed on cardiomyocytes respond to LPS and other pathogen-associated molecular patterns, such as bacterial wall lipoproteins, to activate NF-κb signaling, leading to the formation of proinflammatory cytokines.38Takeuchi O. Akira S. Pattern recognition receptors and inflammation.Cell. 2010; 140: 805-820Abstract Full Text Full Text PDF PubMed Scopus (5739) Google Scholar The resulting activation of sheddases leads to the degradation of glycocalyx and the release of HS fragments acting as highly potent damage-associated molecular patterns. Annecke et al11Annecke T. Fischer J. Hartmann H. Tschoep J. Rehm M. Conzen P. Sommerhoff C.P. Becker B.F. Shedding of the coronary endothelial glycocalyx: effects of hypoxia/reoxygenation vs ischemia/reperfusion.Br J Anaesth. 2011; 107: 679-686Abstract Full Text Full Text PDF PubMed Scopus (73) Google Scholar attribute this step, present in ischemia reperfusion injury, to the activation of mast cells releasing the stored tryptase β, potentially acting as a sheddase. Similar mechanisms may be invoked in the development of cardiorenal syndrome type V—a concomitant cardiac and renal dysfunction secondary to a systemic condition. It afflicts 40% to 60% of patients with sepsis.39Kotecha A. Vallabhajosyula S. Coville H.H. Kashani K. Cardiorenal syndrome in sepsis: a narrative review.J Crit Care. 2018; 43: 122-127Crossref PubMed Scopus (41)