Contact System and Alzheimer's Disease: Mechanism and Therapeutic Potential

PROJECT SUMMARY Alzheimer's disease (AD) is a complex, multifactorial disease that leads to profound neurodegeneration, cognitive decline, and eventually death. There is strong evidence that the Alzheimer's beta-amyloid peptide (Aβ) is an important driver of the disease. However, the mechanisms by which Aβ is toxic are not defined. There is increasing evidence that inflammation and vascular abnormalities contribute to AD pathology. One pathway that links these two processes is the plasma contact system. We have found that this system can be initiated by Aβ and is activated in AD plasma from human patients and mouse models. Furthermore, inhibition of the contact system in AD mice improves their pathology and cognition. We propose to further define how the contact system and its components, specifically high molecular weight kininogen (HK) and coagulation factor XII (FXII), contribute to AD pathophysiology. We have found that Aβ protofibrils are the most effective Aβ species to activate the contact system. Aβ protofibrils are also the main target of lecanemab, the promising new FDA-approved antibody therapy for AD patients. We will investigate how lecanemab might interfere with the contact system to generate its beneficial effects in humans and determine if both lecanemab and a contact system inhibitor could have a synergistic effect on AD pathology. We will also study the structural interaction between Aβ protofibrils, HK, and FXII to determine mechanistically how Aβ causes contact system dysfunction in AD. Finally, we will explore the potential of an anti-HK antibody as a new therapeutic avenue for AD.