Molecular structure of heparan sulfate from Spalax. Implications of heparanase and hypoxia

Spalax, a subterranean blind mole rat, is well adapted to live in an extreme hypoxic environment through up-regulated expression of growth factors and enzymes for ensuring sufficient oxygen supply. One of the overexpressed enzymes is heparanase, an endoglucuronidase that selectively cleaves heparan sulfate (HS) and is implicated in angiogenesis. To assess the implications of the heparanase in Spalax, we have characterized the structure of HS isolated from various organs of the animal. The oligosaccharides obtained after deaminative cleavage of HS samples from the tissues show an overall higher sulfation degree, distinct from that of murine tissues. Of particular significance was the appearance of a trisaccharide moiety in the tissues examined, apart of the even numbered oligosaccharide fractions typically found in HS from human and mouse tissues. The formation of this odd-numbered saccharide is a consequence of heparanase action, in agreement with the notion of high expression of the enzyme in this species. Analysis of HS extracted from human embryonic kidney cells (HEK293) after exposure to hypoxic condition revealed a structural change in the distribution of oligosaccharides similar to HS derived from Spalax organs. The alterations are likely due to up-regulated activity of heparanase, as real-time RT-PCR showed a 2-fold increase in heparanase mRNA expression in the hypoxia treated cells. HEK293 cells stably overexpressing Spalax heparanase produced HS sharing similarity with that from the Spalax organs, and exhibited enhanced MAPK activity in comparison with HEK293 cells, indicating a regulation role of the heparanase in the activity of growth factors.