Specific 3-O-sulfated heparan sulfate domains regulate salivary gland basement membrane metabolism and epithelial differentiation [female]

FGF signaling is essential for salivary gland (SG) development and heparan sulfate (HS) regulation of FGFR function is determined by immense structural diversity of sulfated HS domains. The basement membrane (BM), containing HS proteoglycans, collagens and laminins, separates epithelia from stroma and controls growth factor-matrix cross-talk. 3-O-sulfotransferases generate highly 3-O-sulfated HS domains (3-O-HS) and Hs3st3a1 and Hs3st3b1 are enriched in myoepithelial cells (MECs), which produce BM and are a growth factor signaling hub. To investigate 3-O-HS regulation of MEC function and growth factor signaling, we generated Hs3st3a1;Hs3st3b1 double knockout (DKO) mice. The DKO HS loses specific highly 3-O-sulfated tetrasaccharides, which increases FGF/FGFR-complex binding to HS. During development this leads to increased FGFR-, BM- and MEC-related gene expression. However, in adult DKO SGs the secretory units containing acinar and MECs, have reduced MECs, increased BM and disrupted acinar polarity, resulting in salivary hypofunction. We used defined 3-O-sulfated-HS in FGFR pulldown assays and primary organ cultures to investigate 3-O-HS-dependent mechanisms regulating MEC development. We find that 3-O-HS modulates FGFR signaling to regulate MEC BM synthesis which is critical for secretory unit homeostasis and acinar function. Understanding how sulfated HS regulates development will inform the use of HS mimetics in organ regeneration.