Heparan sulfate proteoglycans mediate Aβ-induced oxidative stress and hypercontractility in cultured vascular smooth muscle cells.

Background: Substantial evidence suggests that amyloid-β (Aβ) species induce oxidative stress and cerebrovascular (CV) dysfunction in Alzheimer's disease (AD), potentially contributing to the progressive dementia of this disease. The upstream molecular pathways governing this process, however, are poorly understood. In this report, we examine the role of heparan sulfate proteoglycans (HSPG) in Aβ-induced vascular smooth muscle cell (VSMC) dysfunction in vitro.

Results: Our results demonstrate that pharmacological depletion of HSPG (by enzymatic degradation with active, but not heat-inactivated, heparinase) in primary human cerebral and transformed rat VSMC mitigates Aβ(1-40⁻) and Aβ(1-42⁻)induced oxidative stress. This inhibitory effect is specific for HSPG depletion and does not occur with pharmacological depletion of other glycosaminoglycan (GAG) family members. We also found that Aβ(1-40) (but not Aβ(1-42)) causes a hypercontractile phenotype in transformed rat cerebral VSMC that likely results from a HSPG-mediated augmentation in intracellular Ca(2+) activity, as both Aβ(1-40⁻)induced VSMC hypercontractility and increased Ca(2+) influx are inhibited by pharmacological HSPG depletion. Moreover, chelation of extracellular Ca(2+) with ethylene glycol tetraacetic acid (EGTA) does not prevent the production of Aβ(1-40⁻) or Aβ(1-42⁻)mediated reactive oxygen species (ROS), suggesting that Aβ-induced ROS and VSMC hypercontractility occur through different molecular pathways.

Conclusions: Taken together, our data indicate that HSPG are critical mediators of Aβ-induced oxidative stress and Aβ(1-40⁻)induced VSMC dysfunction.