Oligomeric Amyloid-β Internalization of Scavenger Receptor Class A is Mediated by Both SRCR and Collagenous Domains

• Main Authors: Yi-Jen Chen, 陳宜禎
• Other Authors: Huey-Jen Tsay
• Format: Others
• Language: en_US
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/51445807915306358651

碩士 === 國立陽明大學 === 神經科學研究所 === 99 === The accumulation of oligomeric amyloid-β peptide (oAβ) is responsible for synaptic dysfunctions in Alzheimer’s disease (AD). Our previously data indicates that scavenger receptor class A (SR-A) is a prominent receptor for microglial oAβ clearance. However, the oAβ binding domains of SR-A remain unidentified. Here, we showed that SR-A-dependent endocytosis mediated at least half of the oAβ internalization by microglia and macrophage. The overexpression of SR-A in COS-7 cells can internalize oAβ. In contract, the overexpression of scavenger class B, SR-BI or CD36 can not internalize oAβ. Therefore, we constructed and overexpressed deletion and point mutations of SR-A in cysteine-rich domain (SRCR) and collagenous domain in COS-7 cells. The ligand binding and internalization activity were examined by using fluorescent labeled ligands, oAβ and acetylated low density lipoprotein (AcLDL). These constructs didn’t affect SR-A-mediated membrane targeting shown by the immunostaining. Deletion of either SRCR or collagenous domain reduced oAβ internalization to less than 50 % compared with full-length SR-A. Deletion both SRCR and collagenous domain almost abolish oAβ internalization. The mutation of three lysine clusters in collagenous domain remains approximately 50 % of oAβ internalization activity. In the absence of SRCR, the mutation of three lysine clusters in collagenous domain contained less than 10 % of oAβ internalization activity. SR-AI, SR-AII, and SR-AIII are three alternatively splicing forms of SR-A. All of them contain an intact collagenous domain. SR-AI contains exon10- and 11-encoded SRCR domain. SR-AII used exon 9 without cysteine residues. SR-AIII contains only exon 11-encoded SRCR domain. SR-AII was targeted to the membrane, and had 50 % of the oAβ internalization activity compared with SR-AI. However, SR-AIII was targeted to the membrane, but failed to bind oAβ, which supports the importance of SRCR domain in oAβ internalization. Since exon 11-encoded SRCR domain of SR-AIII abolished the oAβ binding of collagenous domain, we hypothesize some motifs of SRCR domain can interacts with the collagenous domain. Both the truncation of half exon 11 (20 amino acids from the C-terminal) and the deletion of segment encoded exon 11 (43 amino acids from the C-terminal) completely blocked the membrane targeting of mutant SR-AI. Taken together, our results show that both SRCR domain and collagenous domain of SR-AI service as oAβ binding domains. Furthermore, SRCR domain is important for the membrane targeting of SR-AI. Our study suggests that SRCR domain and collagenous domain of SR-AI can interact with each other to mediate the oAβ internalization which is critical for microglial oAβ clearance.