Evaluating Glycosaminoglycan Composition at the Blood-Brain Barrier

Cerebral amyloid angiopathy (CAA) is the most common vascular comorbidity in Alzheimer’s disease (AD), and evidence suggest poor perivascular clearance of amyloid beta (Ab) as a major contributor to the onset and progression of these dementing disorders. An important, yet understudied facet of Ab clearance in CAA is the alteration of the extracellular matrix glycan composition on the brain endothelial cell (BEC). Chondroitin sulfate (CS) glycosaminoglycans line the BEC matrix with anionic chains of repeating disaccharide units, which can be differentially sulfated to effect brain cell function through unique protein-glycan interactions on the cell surface. Using our innovative liquid chromatography tandem mass spectrometry (LC-MSMS) method, we report CS hypersulfation in human brain tissue from AD patients, compared to non-demented controls. While changes in brain CS sulfation have been strongly associated with AD clinicopathology, CS sulfation as a mechanism of Ab accumulation on BECs in CAA has not yet been evaluated. Our understanding of CS sulfation at the cellular level is limited to non-specific histochemical approaches and sensitivity restraints. Emerging LC-MSMS technologies now provide us with the sensitivity to quantify CS sulfation on the human BEC. For the first time, LC-MSMS will identify CS sulfation patterns on BECs isolated from human cortical tissue with confirmed CAA pathology. Reducing CS sulfo groups on BECs with CS sulfation inhibitors will elucidate CS sulfation as a novel mechanism of perivascular Ab accumulation. Whereas changes in CS composition have been strongly correlated to Ab accumulation within the extracellular spaces of the brain, we predict that physiochemical interactions between Ab and CS sulfation patterns on BECs promotes CAA clinicopathology. We show that human BECs exhibit a unique CS sulfation pattern compared to their corresponding brain partitions (p < 0.05), and human BECs from AD individuals demonstrate CS hypersulfation, compared to non-demented controls (p < 0.05). Moreover, the enzymatic removal of CS sulfo groups diminishes Ab binding on human BECs (p < 0.05). We hypothesize that CS hypersulfation augments perivascular Ab accumulation and contributes, in part, to the onset and progression of the CAA pathogenesis. To test our hypothesis, we will 1) Identify CS sulfation patterns on BECs from humans with CAA, 2) Evaluate the CAA phenotype in rTg-DI rats treated with CS sulfation inhibitors. We expect that CS hypersulfation on BECs from humans and rats with CAA will strongly associate with levels of perivascular Ab accumulation. We predict that CS sulfation inhibition will improve cognition and reduce perivascular Ab accumulation in rats with CAA. If fully successful, this research would illuminate vascular CS sulfation as a targetable mechanism for treating the onset and progression of the CAA pathogenesis.