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 Ca²⁺ activity, as both Aβ_1-40-induced VSMC hypercontractility and increased Ca²⁺ influx are inhibited by pharmacological HSPG depletion. Moreover, chelation of extracellular Ca²⁺ 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.