. The prolyl isomerase Pin1 regulates amyloid precursor protein processing and amyloid-beta production. Nature. 2006 Mar 23;440(7083):528-34. PubMed.

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  1. Kun Ping Lu’s group and his collaborators have been at the fore of elucidating Pin1’s cellular roles, including, since discovering that tau is a Pin1 target protein, its involvement in neurodegeneration. They accumulated data that depletion of Pin1 in HeLa cells causes apoptosis in HeLa cells, that patterns of AD pathology correlate with regions of lower Pin1 expression in normal human brain, that Pin1 knockout mice suffer neurodegeneration, and that Pin1 can ameliorate p-tau pathology. On the basis of that, they have suggested that a fuller elucidation of Pin1’s involvement in neurodegeneration (and cancer) might lead to new therapeutic strategies.

    Our group has acquired data confirmatory of, and complementary to, that of Lu and his coworkers. We have observed Pin1 deficits in a range of frontotemporal dementias and in aging normal brain neurons and have suggested that this might be a susceptibility factor both in neurodegenerative disease (Thorpe et al., 2004) and in aging-related neurodegeneration (Hashemzadeh-Bonehi et al., 2006).

    In this latest work, Lu and colleagues suggest that deficits of Pin1 would also be deleterious to neurons in respect of Aβ secretion; it binds to p-Thr668 of APP and its overexpression reduces Aβ secretion in cell cultures, whilst knockdown, both in cells and mice, selectively increases secretion of the toxic amyloid species, Aβ42. A concern is that this data is contradictory to the work of others (Akiyama et al., 2005), which is not referred to in this present work. Akiyama et al. also used knockdown mice and several cell lines (different from those used by Lu et al.). I can only presume that differences in genetic background might account for the discrepant data between these two studies; although the source of the Pin1 KO mouse is the same for both groups, it appears that Lu's group maintain their colony in an inbred C57/S129 line, whereas Akiyama’s group maintain a C57/B6 strain. Clear differences have been observed in these strains’ behavioral phenotypes. Additionally, the mouse brain gene expression database shows higher hippocampal GSK3β expression in an S129-derived strain than in a C57/B6 strain. Such strain differences, especially local concentrations of upstream APP kinases, could influence APP processing. Indeed, the elucidation of these differences might add important new insights into the neurodegenerative process.

    While research showing involvements of just one specific protein in molecular neuropathological pathways do not confirm their centrality to a disease, other recent research evidence supports such a view: Pin1 promoter polymorphisms, which result in lowered protein expression, correlate with AD (Segat et al., 2005), and Pin1 is one of a handful of proteins susceptible to oxidation in MCI hippocampus, with the authors suggesting that this may be involved in the progression from MCI to AD (Butterfield et al., 2006). Thus, if the above concern regarding conflicting data is addressed, this new data from Lu’s group could put Pin1 protein potentially at the heart of the ameliorative influences that might slow or halt the key twin molecular neuropathological pathways leading to plaque and tangle formation and thence neuronal cell death in AD.

    For more information, see our research website.

    References:

    . Pin1 promotes production of Alzheimer's amyloid beta from beta-cleaved amyloid precursor protein. Biochem Biophys Res Commun. 2005 Oct 21;336(2):521-9. PubMed.

    . Redox proteomics identification of oxidatively modified hippocampal proteins in mild cognitive impairment: insights into the development of Alzheimer's disease. Neurobiol Dis. 2006 May;22(2):223-32. PubMed.

    . Pin1 protein associates with neuronal lipofuscin: potential consequences in age-related neurodegeneration. Exp Neurol. 2006 Jun;199(2) Epub 2006 Feb 14 PubMed.

    . PIN1 promoter polymorphisms are associated with Alzheimer's disease. Neurobiol Aging. 2007 Jan;28(1):69-74. PubMed.

    . Shortfalls in the peptidyl-prolyl cis-trans isomerase protein Pin1 in neurons are associated with frontotemporal dementias. Neurobiol Dis. 2004 Nov;17(2) PubMed.

  2. In this very interesting paper, Pastorino et al. demonstrate that Pin1 catalyzes the conformational change of the phosphorylated APP cytoplasmic tail. The Pin1-mediated shift in the Thr668-Pro motif from a cis to trans conformation results in selectivity towards α-secretase processing of APP. Overexpression of Pin1 decreases amyloid-β production by 30-40 percent and conversely, the knockout of Pin1 favors β-secretase processing and results in an increase of Aβ42 by 50 percent (which rivals the change seen in FAD mutations in the presenilins).

    How does Pin1 alter Aβ production? It is interesting that a structural change in the intracellular tail of APP alters its extracellular (or endosomal) cleavage. One attractive mechanism by which Pin1 alters APP processing is by affecting APP’s cytoplasmic binding partners. There are several known binding partners of APP that interact with the TPEE motif including X11, Disabled, and Fe65. Of these candidate proteins, only Fe65 is shown to be sensitive to the phosphorylation state of Thr668 (Ando et al., 2001).

    How would Pin1 affect Fe65 binding to APP? Fe65 has been shown to bind less avidly to APP phosphorylated at Thr668 (Ando et al., 2001; Kimberly et al., 2005). Since Pin1 promotes formation of the trans isomer of phospho-Thr668, then it likely diminishes the interaction of Fe65 with APP (although this was not formally demonstrated in the current manuscript). Since Pin1 and Fe65 may represent competing pathways for APP processing, one would expect Fe65 to have the opposite effect of Pin1 on APP. In support of this speculation, Fe65 overexpression results in a fourfold increase in Aβ production (Sabo et al., 1999). Thus Pin1 and Fe65 may represent competing pathways for the proteolytic processing of APP. Pin1 interaction diverts APP away from β-secretase, whereas Fe65 interaction promotes β-secretase activity. However, it is unlikely that this represents the entire story, as overexpression of Fe65 and its family members also results in a less robust twofold increase in the α-secretase-generated α-APPs (Sabo et al., 1999; Guenette et al., 1999).

    While these potential pathways may represent a mechanism for APP proteolytic regulation, it must be remembered that only a fraction of APP is phosphorylated at Thr668 in neurons and brain lysate, and could therefore be subject to Pin1-mediated regulation. Nevertheless, this important work identifies a new chapter in APP biology and may even open new avenues for therapeutics for Alzheimer disease.

    References:

    . hFE65L influences amyloid precursor protein maturation and secretion. J Neurochem. 1999 Sep;73(3):985-93. PubMed.

    . Phosphorylation-dependent regulation of the interaction of amyloid precursor protein with Fe65 affects the production of beta-amyloid. J Biol Chem. 2001 Oct 26;276(43):40353-61. PubMed.

    . Regulation of beta-amyloid secretion by FE65, an amyloid protein precursor-binding protein. J Biol Chem. 1999 Mar 19;274(12):7952-7. PubMed.

    . Physiological regulation of the beta-amyloid precursor protein signaling domain by c-Jun N-terminal kinase JNK3 during neuronal differentiation. J Neurosci. 2005 Jun 8;25(23):5533-43. PubMed.

    . The prolyl isomerase Pin1 regulates amyloid precursor protein processing and amyloid-beta production. Nature. 2006 Mar 23;440(7083):528-34. PubMed.

  3. Pastorino and colleagues demonstrate an interesting direct role for Pin1 in APP processing both in vivo and in vitro. The tie-in to the differential regulation of the interaction based on cell cycle phase in dividing cells is also intriguing. It leads one to wonder whether Pin1 might also have a potential function to protect neurons that may be pushed to entering the cell cycle by disease processes. Another exciting area to be followed up in subsequent studies, which was also mentioned in an above comment, is how the Pin1 interaction and conformational change in the APP intracellular domain which results from it may influence interactions with other C-terminal binding proteins. The functional consequences of the potentially altered interactions on signaling pathways in neurons may yield interesting information on APP’s normal role(s) and how these role(s) may be disrupted by the disease.