**2.4 Hyalectans**

Hyalectans are hyaluronan- and lectin-binding PGs of the ECM. They all share a tridomain structure, with the central domain carrying the majority of GAG chains (the number of which varies from 3 in brevican up to 100 in aggrecan), and the N- and C-terminal domains making contact with hyaluronan and lectins, respectively (Schaefer & Schaefer, 2010). Strategically positioned around hyaluronan, a principal ECM component, hyalectans regulate matrix assembly, and mediate a plethora of cell-ECM interactions. The group currently counts four members: versican, aggrecan, neurocan, and brevican.

Although the CS/DSPG versican is expressed throughout the body, is known to regulate a multitude of cellular processes, and has been reported to contribute to the progression of several tumor types (Ricciardelli et al., 2009; Theocharis et al., 2010), no specific investigations have been targeted to versican in the liver, except for a single study where versican was detected in activated rat HSCs (Szende et al., 1992). With respect to the liver, even less is known about aggrecan, a CS/KSPG primarily found in cartilage and brain, and the CSPGs brevican and neurocan which have never been observed outside of the central nervous system (Theocharis et al., 2010).

#### **2.5 Secreted PGs: Endocan and PG-100**

Secreted PGs are 'odd one outs' in the new classification of PGs, being neither anchored to the cell surface nor immobilized in the ECM. *Endocan* (Béchard et al., 2001), or endothelial cell-specific molecule-1 (ESM-1), is a soluble PG by default which is secreted by endothelial cells directly into the bloodstream. Production of endocan by endothelial cells is boosted by both inflammatory and pro-angiogenic mediators; endocan, in turn, enhances HGF signaling. Endocan has been shown to be overexpressed in several human tumor types, and elevated serum levels in late-stage cancer patients is regarded as an adverse prognostic factor (Abid et al., 2006; Sarrazin et al., 2006).

as a co-receptor for class 3 semaphorins, soluble signal molecules implicated in axonal guidance and vascular patterning (Adams & Eichmann, 2010). Later, neuropilins have also been identified as accessory receptors of VEGFs. NRP1 affects VEGFR signaling in a way that enhances migration and survival of endothelial cells, modulates vascular permeability,

During development, NRP1 is broadly expressed in the vasculature, preferentially in arteries (Koch et al., 2011). In the adult liver, NRP1 immunostaining positively labels both sinusoidal and portal vessel endothelial cells, but not the hepatocytes (Bergé et al., 2011). When sinusoidal endothelium is subjected to increased shear stress, either *in vitro* or during liver regeneration following partial hepatectomy, NRP1 becomes upregulated in concert with other proangiogenic factors such as VEGF and angiopoetin-1 (Kraizer et al., 2001; Braet et al., 2004). NRP1 is also induced in HSCs upon activation, and has been shown to promote progression of fibrosis by stimulating platelet-derived growth factor- (PDGF-) dependent chemotaxis and TGFβ-mediated matrix deposition of myofibroblasts (Cao et al., 2010).

In HCC, NRP1 expression is seen not only in endothelial cells of tumoral vessels, but – in approx. 50% of cases, and with variable intensity – in tumor hepatocytes, too. The significance of tumor cell NRP1 is unclear, but blocking NRP1-VEGF interaction was shown to inhibit vascular remodeling and growth of primary murine HCC (Bergé et al., 2011).

Hyalectans are hyaluronan- and lectin-binding PGs of the ECM. They all share a tridomain structure, with the central domain carrying the majority of GAG chains (the number of which varies from 3 in brevican up to 100 in aggrecan), and the N- and C-terminal domains making contact with hyaluronan and lectins, respectively (Schaefer & Schaefer, 2010). Strategically positioned around hyaluronan, a principal ECM component, hyalectans regulate matrix assembly, and mediate a plethora of cell-ECM interactions. The group

Although the CS/DSPG versican is expressed throughout the body, is known to regulate a multitude of cellular processes, and has been reported to contribute to the progression of several tumor types (Ricciardelli et al., 2009; Theocharis et al., 2010), no specific investigations have been targeted to versican in the liver, except for a single study where versican was detected in activated rat HSCs (Szende et al., 1992). With respect to the liver, even less is known about aggrecan, a CS/KSPG primarily found in cartilage and brain, and the CSPGs brevican and neurocan which have never been observed outside of the central

Secreted PGs are 'odd one outs' in the new classification of PGs, being neither anchored to the cell surface nor immobilized in the ECM. *Endocan* (Béchard et al., 2001), or endothelial cell-specific molecule-1 (ESM-1), is a soluble PG by default which is secreted by endothelial cells directly into the bloodstream. Production of endocan by endothelial cells is boosted by both inflammatory and pro-angiogenic mediators; endocan, in turn, enhances HGF signaling. Endocan has been shown to be overexpressed in several human tumor types, and elevated serum levels in late-stage cancer patients is regarded as an adverse prognostic

currently counts four members: versican, aggrecan, neurocan, and brevican.

and stimulates angiogenesis (Koch et al., 2011).

**2.4 Hyalectans** 

nervous system (Theocharis et al., 2010).

**2.5 Secreted PGs: Endocan and PG-100** 

factor (Abid et al., 2006; Sarrazin et al., 2006).


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*PG-100* is the PG form of macrophage colony-stimulating factor and, as such, is a 'part-time' PG that may exist in a GAG-less or CS/DS-substituted form, the latter exhibiting less than 1% of cytokine activity compared with the non-PG variant (Schwarz et al., 1990; Partenheimer et al. 1995). PG-100 was first discovered in the conditioned medium of osteosarcoma cells, and later found to be produced by other cell types including endothelia (Nelimarkka et al., 1997). PG-100 was only faintly immunostained in the normal liver, whereas in active fibrosis it was strongly visualized in bile duct epithelia, and thus proposed as a marker of ductular reaction (Högemann et al., 1997). The significance of this elevated expression remains to be clarified.
