Origins of Beta Amyloid Differ Between Vascular Amyloid Deposition and Parenchymal Amyloid Plaques in the Spinal Cord of a Mouse Model of Alzheimer's Disease

Cerebral amyloid angiopathy (CAA) refers to pathological changes occurring in cerebral blood vessels caused by deposition of beta amyloid (A beta) protein. However, the mechanisms involved in the origin of A beta for the formation of CAA and its link to parenchymal amyloid depositions remained to be unraveled. Here, we found CAA and parenchymal plaques distributed separately instead of mingling with each other in the spinal cord of TgCRND8 mice. Parenchymal plaques predominantly located in the dorsal horn whereas CAA distributed in the ventral horn. We further found that the ratio of A beta 40/A beta 42 was significantly higher in the ventral than that in the dorsal by ELISA assay, suggesting that origin of A beta forming parenchymal plaques may be different from that of CAA in the spinal cord. This hypothesis was further demonstrated by the surgical methods which indicated eliminating parenchymal plaques did not alter CAA in the affected spinal cord. We also examined the ratio of A beta 40/A beta 42 in the cerebral spinal fluid (CSF) in order to identify the origin of the CAA formation, and found the A beta 40/A beta 42 ratio was similar to that of CAA formation in the ventral horn. We further demonstrated that CSF tracer distributed along ventral horn vessels, in exactly the same pattern as A beta deposition in CAA in ventral part of spinal cord. These findings verified the concept that CSF influx may act as a constant source for delivering A beta, and contribute to the growth of paraarterial deposits in CAA. Taken together, the results of the present study highlight the important role of the A beta 40/A beta 42 ratio in determining vascular versus parenchymal amyloid deposition. Unlike parenchymal plaques, A beta of CAA comes from CSF; thus, manipulation of CSF A beta could represent a novel strategy to treat CAA.