O3-01-06: Evidence of vascular recovery after removal of vascular Aβ by passive immunotherapy in PDAPP mice

Abstract

Background: Cerebral amyloid angiopathy is a common neuropathological feature of Alzheimer’s disease and is characterized by vascular deposition of fibrillar amyloid -protein (VA ). Vascular structural changes are associated with VA deposits, including localized loss of smooth muscle cells (SMC) and changes in extracellular matrix (ECM). Passive immunization with antibodies to the A N-terminus (3D6, aa 1-5) has been shown to effectively reduce amyloid deposition in the vasculature of PDAPP transgenic mice. In the present study we characterized structural changes induced by amyloid on SMC and ECM of PDAPP mouse vessels and assessed the effects of passive immunotherapy. Methods: Mice were immunized weekly for either 3 or 9 months with 1 or 3 mg/Kg of 3D6 antibody. High-resolution, quantitative IHC analyses of vascular components ( -actin for SMC and collagen-IV for ECM) were performed on meningeal vessels from the sagittal sinus, where VA deposition is prominent ( 70% of vessels affected). Microhemorrhage events were monitored by hemosiderin detection or ferritin immunohistochemistry. Results: We found that changes in the vascular wall are invariably associated with VA , and they included both degeneration (decreased thickness) and hyperplasia/hypertrophy (increased thickness) of SMC and ECM. These two contrasting findings were often observed in the same vessel and were not present in wild type animals or PDAPP vessels lacking amyloid. The extreme degrees of thickening and thinning of the SM resulted in a widely variable vascular phenotype in untreated PDAPP mice. Passive immunotherapy restored the pattern of vascular SMC and ECM thicknesses and reduced the phenotypic variability in a doseand time-dependent manner, with the high dose of 3D6 reaching control levels (wild type) at 9 months. Although the incidence of microhemorrhage increased in the 3-month group, it reduced to control levels after 9 months of treatment. Conclusions: Our results suggest that passive immunotherapy allows the recovery of meningeal vessels from amyloid-induced structural changes. Furthermore, the treatment-related increase in microhemorrhage appears to be a transient event that resolves during VA clearance. Mechanisms of repair may be triggered by VA removal, which ultimately lead to recovery from vascular dysfunction. Experiments to assess this possibility are in progress.