HT, TY and TS participated in the design of the study and the writing of the manuscript. overexpressing the human Swedish mutant APP (APPswe) and the mutant human PS1, which TIAM1 lacks exon 9 (PS1dE9). Therefore, the data on X11-family protein function in transgenic human APP metabolism em in vivo /em are inconsistent. Results To confirm the conversation of X11L with human APP ectopically expressed in mouse brain, we examined the amyloidogenic metabolism of human APP in two lines of human APP transgenic mice generated to also lack X11L. In agreement with previous reports from our lab as well as others, we found that the amyloidogenic metabolism of human APP increased in the absence of X11L. Conclusion X11L appears to aid in the suppression of amyloidogenic processing of human APP in brain em in vivo /em , as has been demonstrated by previous studies using several human APP transgenic lines with various genetic backgrounds. X11L appears to (-)-Gallocatechin gallate regulate human APP in a manner similar to that seen in endogenous mouse APP metabolism. Background X11 proteins (X11s) comprise a family of three adaptor proteins in mammals: X11 (X11/X11/Mint1), X11-like (X11L/X11/Mint2) and X11-like 2 (X11L2/X11/Mint3) [1]. These molecules are evolutionally conserved in em D. melanogaster /em [2,3] and em C. elegans /em [4]. In mammals, X11 and X11L are expressed predominantly in neurons, while X11L2 is usually expressed ubiquitously [reviewed in ref. [5]]. X11s associate with the cytoplasmic domain name of amyloid -protein precursor (APP) and suppress APP metabolism, including amyloid -protein (A) generation [1,6,7], which is usually widely believed to be the major cause of Alzheimer’s disease (AD) pathogenesis [8]. APP is usually subjected to (-)-Gallocatechin gallate option cleavages by a combination of – and -secretases or – and -secretases. (-)-Gallocatechin gallate Primary cleavage of APP by -secretase is usually amyloidolytic and generates a C-terminal fragment, CTF, which includes the C-terminal half of the A sequence, whereas cleavage by -secretase is usually amyloidogenic and generates CTF, which includes an intact A sequence. Both CTF and CTF are further cleaved by -secretase in the lipid bilayer, resulting in the secretion of the amyloidolytic p3 fragment from CTF and the neurotoxic A from CTF [9]. The association of X11s with APP is usually mediated by conversation between the phosphotyrosine interaction domain name (PTB) of X11s and the 681-GYENPTY-687 motif of APP. This association has been shown to greatly suppress the amyloidogenic metabolism of APP in the brain em in vivo /em . Specifically, the production of amyloidogenic CTF, but not amyloidolytic CTF, derived from endogenous mouse APP was found to be enhanced, and accumulation of mouse A was found to be increased, in the brains of X11-knockout, X11L-knockout, (-)-Gallocatechin gallate and X11 plus X11L double-gene knockout mice [10-12]. Recent evidence indicates that the majority of both – and -secretases are located in cholesterol- and sphingolipid-rich detergent-resistant membrane domains (DRM domains or lipid rafts) as active forms [13,14]. DRMs in the brains of mice lacking X11 and X11L are rich in mature APP ( em N- /em and em O- /em glycosylated form), the substrate to secretases, and the amyloidogenic metabolite CTF [11]. These observations suggest that X11 (-)-Gallocatechin gallate and X11L function to form a complex with APP that then remains outside of the DRMs. In this way, they regulate amyloidogenic cleavage of APP through suppression. This suppressive inhibition of human APP amyloidogenic metabolism by X11 and X11L was also confirmed in the brains of X11- or X11L-Tg mice expressing human Swedish mutant APP (APPswe/Tg2576) [15,16] (Table ?(Table1).1). On the other hand, a controversial report analyzing human APP metabolism in the brains of mice lacking X11s found that the amyloidogenic metabolism of APPswe was suppressed in the brains of mice lacking X11 proteins and constitutively expressing the active PS1 mutant PS1dE9 [17] (Table ?(Table1).1). In this study, we investigated whether the amyloidogenic metabolism of human APP, as well as endogenous mouse APP, is usually facilitated in murine brains lacking X11L. We focused on X11L, rather than X11, because it is usually more widely distributed and because it suppresses APP metabolism more strongly [10,11]. Our data showed increased amyloidogenic metabolism in two transgenic mouse lines expressing relatively higher (APP23) and lower (APP-ibl) levels of human APPswe in the absence of X11L, indicating that X11L functions to suppress APP amyloidogenic metabolism in brain em in vivo /em . Table 1 Effect.
