Structurally abnormal collagen fibrils in abdominal aortic aneurysm resist platelet adhesion

Abstract

Background: Platelet adhesion to the subendothelial collagen fibrils is one of the first steps in hemostasis. Understanding how structural perturbations in the collagen fibril affect platelet adhesion can provide novel insights into disruption of hemostasis in various diseases. We have recently identified the presence of abnormal collagen fibrils with compromised D-periodic banding in the extracellular matrix remodeling present in abdominal aortic aneurysms (AAA).Objective: In this study, we employed multimodal microscopy approaches to characterize how collagen fibril structure impacts platelet adhesion in clinical AAA tissues.Methods: Ultrastructural atomic force microscopy (AFM) analysis was performed on tissue sections after staining with fluorescently labeled collagen hybridizing peptide (CHP) to recognize degraded collagen. Second harmonic generation (SHG) microscopy was used on CHP-stained sections to identify regions of intact versus degraded collagen. Finally, platelet adhesion was identified via SHG and indirect immunofluorescence on the same tissue sections. Results:Our results indicate that ultrastructural features characterizing collagen fibril abnormalities coincide with CHP staining. SHG signal was absent from CHP-positive regions. Additionally, platelet binding was primarily localized to regions with SHG signal. Abnormal collagen fibrils present in AAA (in SHG negative regions) were thus found to inhibit platelet adhesion compared to normal fibrils. Conclusions:Our investigations reveal how the collagen fibril structure in the vessel wall can serve as another regulator of platelet-collagen adhesion. These results can be broadly applied to understand the role of collagen fibril structure in regulating thrombosis or bleeding disorders.

The Chemistry and Biology of Collagen Hybridization

“…Besides, mechanical damages to connective tissues can also render the collagen triple-helix in a denatured state. Our understanding of the biological significance of collagen denaturation in disease and injury is still in its infancy, although evidence for the presence and disease-correlation of denatured collagen is emerging from dozens of recent studies − enabled by the CHP-collagen hybridization (Table ).…”

The Detrimental Role of Intraluminal Thrombus Outweighs Protective Advantage in Abdominal Aortic Aneurysm Pathogenesis: The Implications for the Anti-Platelet Therapy

“…However, whether platelet transfusion can be used as a therapy for the repair of rAAA is still controversial [ 71 ]. Jones et al reported that platelet adhesion is mainly restricted to areas composed of normal collagen fibers instead of the abnormal ones [ 72 ]. The collagen fibril structure is likely to be normal in the early (compared to advanced) stage of AAA, which may explain why in one report, diminished platelet adhesiveness in AAA remained abnormal even after transfusion of normal blood [ 73 ].…”