Evidence of a novel mechanism for partial γ-secretase inhibition induced paradoxical increase in secreted amyloid β protein

Eliza Barnwell, Vasudevaraju Padmaraju, Robert Baranello, Javier Pacheco-Quinto, Craig Crosson, Zsolt Ablonczy, Elizabeth Eckman, Christopher B. Eckman, Viswanathan Ramakrishnan, Nigel H. Greig, Miguel Pappolla, Kumar Sambamurti

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

BACE1 (β-secretase) and a-secretase cleave the Alzheimer's amyloid β protein (Aβ) precursor (APP) to C-terminal fragments of 99 aa (CTFβ) and 83 aa (CTFα), respectively, which are further cleaved by γ-secretase to eventually secrete Aβ and Aα (a.k.a. P3) that terminate predominantly at residues 40 and 42. A number of c-secretase inhibitors (GSIs), such as N-[N-(3,5- Difluorophenacetyl-L-alanyl)]-S- phenylglycine t-butyl ester (DAPT), have been developed with the goal of reducing Aβ to treat Alzheimer's disease (AD). Although most studies show that DAPT inhibits Aβ in a dose-dependent manner several studies have also detected a biphasic effect with an unexpected increase at low doses of DAPT in cell cultures, animal models and clinical trials. In this article, we confirm the increase in Aβ40 and Aβ42 in SH-SY5Y human neuroblastoma cells treated with low doses of DAPT and identify one of the mechanisms for this paradox. We studied the pathway by first demonstrating that stimulation of Aβ, a product of γ-secretase, was accompanied by a parallel increase of its substrate CTFβ, thereby demonstrating that the inhibitor was not anomalously stimulating enzyme activity at low levels. Secondly, we have demonstrated that inhibition of an Aβ degrading activity, endothelin converting enzyme (ECE), yielded more Aβ, but abolished the DAPT-induced stimulation. Finally, we have demonstrated that Aα, which is generated in the secretory pathway before endocytosis, is not subject to the DAPT-mediated stimulation. We therefore conclude that impairment of γ-secretase can paradoxically increase Aβ by transiently skirting Aβ degradation in the endosome. This study adds to the growing body of literature suggesting that preserving γ-secretase activity, rather than inhibiting it, is important for prevention of neurodegeneration.

Original languageEnglish (US)
Article numbere91531
JournalPLoS One
Volume9
Issue number3
DOIs
StatePublished - Mar 21 2014

Fingerprint

Amyloidogenic Proteins
Amyloid Precursor Protein Secretases
amyloid
dosage
endosomes
endothelins
proteins
endocytosis
Alzheimer disease
clinical trials
cell culture
animal models
esters
Animal cell culture
enzyme activity
degradation
Serum Amyloid A Protein
enzymes
Amyloid beta-Protein Precursor
Secretory Pathway

ASJC Scopus subject areas

  • Agricultural and Biological Sciences(all)
  • Biochemistry, Genetics and Molecular Biology(all)
  • Medicine(all)

Cite this

Barnwell, E., Padmaraju, V., Baranello, R., Pacheco-Quinto, J., Crosson, C., Ablonczy, Z., ... Sambamurti, K. (2014). Evidence of a novel mechanism for partial γ-secretase inhibition induced paradoxical increase in secreted amyloid β protein. PLoS One, 9(3), [e91531]. https://doi.org/10.1371/journal.pone.0091531

Evidence of a novel mechanism for partial γ-secretase inhibition induced paradoxical increase in secreted amyloid β protein. / Barnwell, Eliza; Padmaraju, Vasudevaraju; Baranello, Robert; Pacheco-Quinto, Javier; Crosson, Craig; Ablonczy, Zsolt; Eckman, Elizabeth; Eckman, Christopher B.; Ramakrishnan, Viswanathan; Greig, Nigel H.; Pappolla, Miguel; Sambamurti, Kumar.

In: PLoS One, Vol. 9, No. 3, e91531, 21.03.2014.

Research output: Contribution to journalArticle

Barnwell, E, Padmaraju, V, Baranello, R, Pacheco-Quinto, J, Crosson, C, Ablonczy, Z, Eckman, E, Eckman, CB, Ramakrishnan, V, Greig, NH, Pappolla, M & Sambamurti, K 2014, 'Evidence of a novel mechanism for partial γ-secretase inhibition induced paradoxical increase in secreted amyloid β protein', PLoS One, vol. 9, no. 3, e91531. https://doi.org/10.1371/journal.pone.0091531
Barnwell, Eliza ; Padmaraju, Vasudevaraju ; Baranello, Robert ; Pacheco-Quinto, Javier ; Crosson, Craig ; Ablonczy, Zsolt ; Eckman, Elizabeth ; Eckman, Christopher B. ; Ramakrishnan, Viswanathan ; Greig, Nigel H. ; Pappolla, Miguel ; Sambamurti, Kumar. / Evidence of a novel mechanism for partial γ-secretase inhibition induced paradoxical increase in secreted amyloid β protein. In: PLoS One. 2014 ; Vol. 9, No. 3.
@article{73bb7d74a1754791bfed78b8557f951b,
title = "Evidence of a novel mechanism for partial γ-secretase inhibition induced paradoxical increase in secreted amyloid β protein",
abstract = "BACE1 (β-secretase) and a-secretase cleave the Alzheimer's amyloid β protein (Aβ) precursor (APP) to C-terminal fragments of 99 aa (CTFβ) and 83 aa (CTFα), respectively, which are further cleaved by γ-secretase to eventually secrete Aβ and Aα (a.k.a. P3) that terminate predominantly at residues 40 and 42. A number of c-secretase inhibitors (GSIs), such as N-[N-(3,5- Difluorophenacetyl-L-alanyl)]-S- phenylglycine t-butyl ester (DAPT), have been developed with the goal of reducing Aβ to treat Alzheimer's disease (AD). Although most studies show that DAPT inhibits Aβ in a dose-dependent manner several studies have also detected a biphasic effect with an unexpected increase at low doses of DAPT in cell cultures, animal models and clinical trials. In this article, we confirm the increase in Aβ40 and Aβ42 in SH-SY5Y human neuroblastoma cells treated with low doses of DAPT and identify one of the mechanisms for this paradox. We studied the pathway by first demonstrating that stimulation of Aβ, a product of γ-secretase, was accompanied by a parallel increase of its substrate CTFβ, thereby demonstrating that the inhibitor was not anomalously stimulating enzyme activity at low levels. Secondly, we have demonstrated that inhibition of an Aβ degrading activity, endothelin converting enzyme (ECE), yielded more Aβ, but abolished the DAPT-induced stimulation. Finally, we have demonstrated that Aα, which is generated in the secretory pathway before endocytosis, is not subject to the DAPT-mediated stimulation. We therefore conclude that impairment of γ-secretase can paradoxically increase Aβ by transiently skirting Aβ degradation in the endosome. This study adds to the growing body of literature suggesting that preserving γ-secretase activity, rather than inhibiting it, is important for prevention of neurodegeneration.",
author = "Eliza Barnwell and Vasudevaraju Padmaraju and Robert Baranello and Javier Pacheco-Quinto and Craig Crosson and Zsolt Ablonczy and Elizabeth Eckman and Eckman, {Christopher B.} and Viswanathan Ramakrishnan and Greig, {Nigel H.} and Miguel Pappolla and Kumar Sambamurti",
year = "2014",
month = "3",
day = "21",
doi = "10.1371/journal.pone.0091531",
language = "English (US)",
volume = "9",
journal = "PLoS One",
issn = "1932-6203",
publisher = "Public Library of Science",
number = "3",

}

TY - JOUR

T1 - Evidence of a novel mechanism for partial γ-secretase inhibition induced paradoxical increase in secreted amyloid β protein

AU - Barnwell, Eliza

AU - Padmaraju, Vasudevaraju

AU - Baranello, Robert

AU - Pacheco-Quinto, Javier

AU - Crosson, Craig

AU - Ablonczy, Zsolt

AU - Eckman, Elizabeth

AU - Eckman, Christopher B.

AU - Ramakrishnan, Viswanathan

AU - Greig, Nigel H.

AU - Pappolla, Miguel

AU - Sambamurti, Kumar

PY - 2014/3/21

Y1 - 2014/3/21

N2 - BACE1 (β-secretase) and a-secretase cleave the Alzheimer's amyloid β protein (Aβ) precursor (APP) to C-terminal fragments of 99 aa (CTFβ) and 83 aa (CTFα), respectively, which are further cleaved by γ-secretase to eventually secrete Aβ and Aα (a.k.a. P3) that terminate predominantly at residues 40 and 42. A number of c-secretase inhibitors (GSIs), such as N-[N-(3,5- Difluorophenacetyl-L-alanyl)]-S- phenylglycine t-butyl ester (DAPT), have been developed with the goal of reducing Aβ to treat Alzheimer's disease (AD). Although most studies show that DAPT inhibits Aβ in a dose-dependent manner several studies have also detected a biphasic effect with an unexpected increase at low doses of DAPT in cell cultures, animal models and clinical trials. In this article, we confirm the increase in Aβ40 and Aβ42 in SH-SY5Y human neuroblastoma cells treated with low doses of DAPT and identify one of the mechanisms for this paradox. We studied the pathway by first demonstrating that stimulation of Aβ, a product of γ-secretase, was accompanied by a parallel increase of its substrate CTFβ, thereby demonstrating that the inhibitor was not anomalously stimulating enzyme activity at low levels. Secondly, we have demonstrated that inhibition of an Aβ degrading activity, endothelin converting enzyme (ECE), yielded more Aβ, but abolished the DAPT-induced stimulation. Finally, we have demonstrated that Aα, which is generated in the secretory pathway before endocytosis, is not subject to the DAPT-mediated stimulation. We therefore conclude that impairment of γ-secretase can paradoxically increase Aβ by transiently skirting Aβ degradation in the endosome. This study adds to the growing body of literature suggesting that preserving γ-secretase activity, rather than inhibiting it, is important for prevention of neurodegeneration.

AB - BACE1 (β-secretase) and a-secretase cleave the Alzheimer's amyloid β protein (Aβ) precursor (APP) to C-terminal fragments of 99 aa (CTFβ) and 83 aa (CTFα), respectively, which are further cleaved by γ-secretase to eventually secrete Aβ and Aα (a.k.a. P3) that terminate predominantly at residues 40 and 42. A number of c-secretase inhibitors (GSIs), such as N-[N-(3,5- Difluorophenacetyl-L-alanyl)]-S- phenylglycine t-butyl ester (DAPT), have been developed with the goal of reducing Aβ to treat Alzheimer's disease (AD). Although most studies show that DAPT inhibits Aβ in a dose-dependent manner several studies have also detected a biphasic effect with an unexpected increase at low doses of DAPT in cell cultures, animal models and clinical trials. In this article, we confirm the increase in Aβ40 and Aβ42 in SH-SY5Y human neuroblastoma cells treated with low doses of DAPT and identify one of the mechanisms for this paradox. We studied the pathway by first demonstrating that stimulation of Aβ, a product of γ-secretase, was accompanied by a parallel increase of its substrate CTFβ, thereby demonstrating that the inhibitor was not anomalously stimulating enzyme activity at low levels. Secondly, we have demonstrated that inhibition of an Aβ degrading activity, endothelin converting enzyme (ECE), yielded more Aβ, but abolished the DAPT-induced stimulation. Finally, we have demonstrated that Aα, which is generated in the secretory pathway before endocytosis, is not subject to the DAPT-mediated stimulation. We therefore conclude that impairment of γ-secretase can paradoxically increase Aβ by transiently skirting Aβ degradation in the endosome. This study adds to the growing body of literature suggesting that preserving γ-secretase activity, rather than inhibiting it, is important for prevention of neurodegeneration.

UR - http://www.scopus.com/inward/record.url?scp=84899086858&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84899086858&partnerID=8YFLogxK

U2 - 10.1371/journal.pone.0091531

DO - 10.1371/journal.pone.0091531

M3 - Article

VL - 9

JO - PLoS One

JF - PLoS One

SN - 1932-6203

IS - 3

M1 - e91531

ER -