islet beta cells in situ express high intracellular levels of HS, correlating
with the expression of the core proteins for the HS proteoglycans (HSPGs) collagen
type XVIII and syndecan-1. Beta cell HS plays a critical role in maintaining beta
cell survival, is lost in vitro during islet isolation and is degraded by
leukocyte-derived Hpse during T1D development in NOD mice (1). Similarly, we have
previously found that HS is highly expressed in normal human islets in situ and
is depleted in T1D islets.
Aims: To investigate the role of HS in human beta cells and to determine the relationship between HS and HSPG core protein expression in human T1D.
Methods: HS, HSPG core protein (collagen type XVIII, syndecan-1) and insulin expression in nPOD specimens of normal and T1D human pancreas were examined by immunohistochemistry. Isolated human islet cells were cultured ± 50 μg/ml unlabelled or FITC-labelled heparin (HS mimetic), examined for FITC-heparin uptake by confocal microscopy and analysed by Sytox green or 7AAD/Newport Green (NG) staining and flow cytometry for beta cell death.
Results: Normal human islets in situ showed strong HS staining which co-localised with collagen type XVIII and syndecan-1 core proteins. T1D pancreases showed weak or little HS staining in residual insulin+ve beta cells but strong staining for collagen type XVIII. 67-82% of isolated human islet cells were FITC-heparin+ve after culture for 1 day and confocal microscopy confirmed the intracellular localisation of FITC-heparin. Treatment with unlabelled heparin for 2-4 days substantially reduced Sytox green+ve islet cell death by 3.9±2.7-fold (n=6). In parallel, a 3.8-fold decrease was observed in NG+ve7AAD+ve human beta cells cultured with heparin for 2 days (n=1).
Conclusions: These findings suggest that loss of beta cell HS which precedes loss of HSPG core proteins in T1D, leads to beta cell death.