Platelet hyaluronidase-2: an enzyme that translocates to the surface upon activation to function in extracellular matrix degradation

Abstract

• Platelet HYAL2 is stored in a-granules and upon activation it becomes surface expressed where it functions to degrade extracellular matrix.• Platelets from IBD patients contain lower HYAL2 protein and activity than those from non-IBD controls.Following injury, platelets rapidly interact with the exposed extracellular matrix (ECM) of the vessel wall and the surrounding tissues. Hyaluronan (HA) is a major glycosaminoglycan component of the ECM and plays a significant role in regulating inflammation. We have recently reported that human platelets degrade HA from the surfaces of activated endothelial cells into fragments capable of inducing immune responses by monocytes. We also showed that human platelets contain the enzyme hyaluronidase-2 (HYAL2), one of two major hyaluronidases that digest HA in somatic tissues. The deposition of HA increases in inflamed tissues in several inflammatory diseases, including inflammatory bowel disease (IBD). We therefore wanted to define the mechanism by which platelets degrade HA in the inflamed tissues. In this study, we show that human platelets degrade the proinflammatory matrix HA through the activity of HYAL2 and that platelet activation causes the immediate translocation of HYAL2 from a distinct population of a-granules to platelet surfaces where it exerts its catalytic activity. Finally, we show that patients with IBD have lower platelet HYAL2 levels and activity than healthy controls. (Blood. 2015; 125(9):1460-1469 Introduction Hyaluronan (HA) is a ubiquitous glycosaminoglycan and a major component of the extracellular matrix (ECM), and it has a crucial role in regulating inflammation.1 HA is produced by the HA synthase enzymes (HAS1-3) and is composed of repeating disaccharides of D-glucuronic acid and N-acetylglucosamine. Not only can HA be synthesized and released, but it can also form a voluminous pericellular coat that surrounds cells. The HA coat is either anchored to the cell surface through binding to specific cell-surface receptors, such as CD44, or it can be retained at the cell surface by sustained transmembrane interactions with its synthases.2 Interestingly, a growing body of literature suggests that different sizes of HA exert a wide spectrum of functions.3 Under normal conditions in tissues, HA is present in its high molecular weight (HMWHA) form (1 to 10 3 10 6 Da). HMWHA functions as a structural hydrating polymer and is also known to be antiinflammatory, 4 protecting from T-cellmediated liver injury and bleomycin-mediated lung injury in mice. 5,6 HMWHA also promotes the suppressive effects of regulatory CD4 1 CD251 T cells. 7Increased HA deposition has also been reported in many inflammatory diseases including inflammatory bowel disease (IBD), arthritis, and asthma. [8][9][10] Importantly, degradation of HA results in HA fragments that function as damage-associated molecular patterns. 11Fragmented HA contributes to wound healing, angiogenesis, and inflammation and is capable of signaling cellular responses through specific receptors. 12 For example, HA ...

Intracellular Trafficking, Localization, and Mobilization of Platelet-Borne Thiol Isomerases

“…This is consistent with the reported lack of overlap between PDI and lysosomes 50 or hyaluronidase-2 in human platelets, where the latter enzyme has been localized to α-granules via IFM and subcellular fractionation. 51 The thiol isomerase compartment appears to surround the P-selectin matrix (Figure 2B) and to be contained by the outer cell membrane (Figure 2C), a pattern that holds in GPS human and mouse Nbeal2 -/- platelets where α-granule cargo is absent (Figure 2C). The observation that α-granule cargo-deficient platelets have normal levels of thiol isomerases (Figure 2D,E) further supports the independence of their trafficking from granule cargo.…”

Experimental cerebral malaria is associated with profound loss of both glycan and protein components of the endothelial glycocalyx

“…Glycocalyx shedding may thus reduce both the amount of AT3 (6) and the synergy between AT3 and HS, which will increase thrombin activity (43) that may lead to further endothelial damage. Thrombin activates endothelial cells and induces heparanase and hyaluronidase secretion from platelets (44)(45)(46) that are sequestered in the brain during CM (47,48). This action may explain why AT3 treatment could prevent glycocalyx shedding in our model even though it does not directly inhibit glycosidases.…”

Hyaluronan as a therapeutic target in human diseases

“…However, a recent study showed that patients with IBD had lower platelet HYAL2 levels and activity than healthy controls [246]. Platelet activation caused the translocation of HYAL2 from α-granules to platelet surfaces where it exerts its catalytic activity [246]. …”