Amylin and pramlintide modulate γ-secretase level and APP processing in lipid rafts

Abstract

A major characteristic of Alzheimer's disease (AD) is the accumulation of misfolded amyloid-β (Aβ) peptide. Several studies linked AD with type 2 diabetes due to similarities between Aβ and human amylin. This study investigates the effect of amylin and pramlintide on Aβ pathogenesis and the predisposing molecular mechanism(s) behind the observed effects in TgSwDI mouse, a cerebral amyloid angiopathy (CAA) and AD model. Our findings showed that thirty days of intraperitoneal injection with amylin or pramlintide increased Aβ burden in mice brains. Mechanistic studies revealed both peptides altered the amyloidogenic pathway and increased Aβ production by modulating amyloid precursor protein (App) and γ-secretase levels in lipid rafts. in addition, both peptides increased levels of B4GALNT1 enzyme and GM1 ganglioside, and only pramlintide increased the level of GM2 ganglioside. Increased levels of GM1 and GM2 gangliosides play an important role in regulating amyloidogenic pathway proteins in lipid rafts. increased brain Aβ burden by amylin and pramlintide was associated with synaptic loss, apoptosis, and microglia activation. In conclusion, our findings showed amylin or pramlintide increase Aβ levels and related pathology in tgSwDi mice brains, and suggest that increased amylin levels or the therapeutic use of pramlintide could increase the risk of AD.Alzheimer's disease (AD) is a complex neurodegenerative disorder characterized by multiple dysregulated neurobiological networks and cellular functions, neuronal death, and memory loss 1 . The major hallmarks for AD include amyloid-β (Aβ) deposits and neurofibrillary tangles of hyper-phosphorylated tau protein 1,2 . Aβ is produced from the amyloid-β precursor protein (APP), which, after synthesis, traffics to the Golgi apparatus and eventually to plasma membrane 3 . The majority of plasma membrane bound APP is rapidly endocytosed 3 , while approximately 10% of the total APP is processed in the plasma membrane by α-secretase to release soluble APP-α (sAPP-α) 4 . Alternatively, APP can be processed by β-site APP cleaving enzyme 1 (BACE1) in plasma membrane, trans-Golgi, and early endosomes to produce soluble APP-β (sAPP-β) and β-C-terminal fragments (β-CTF), followed by subsequent proteolytic cleavage of β-CTF by γ-secretase to release Aβ 4 . Besides Aβ production, another contributing factor to Aβ accumulation in AD is the failure to clear Aβ from the brain 5 , and across the blood-brain barrier (BBB) 6 .The accumulation of Aβ due to decreased clearance or increased production leads to multiple dysregulated cellular functions including synaptic loss and neuroinflammation 7,8 . Aβ initiates synaptic loss by down-regulating synaptic markers in AD including the pre-synaptic marker SNAP-25 and synapsin I and post-synaptic marker PSD-95 9 . Moreover, the accumulation of Aβ in the brain parenchyma of AD patients is associated with strong inflammatory processes and glial cells activation 7 .Mounting evidence supports the localization of APP, BACE1 and each of the four core subu...

Genetic Depletion of Amylin/Calcitonin Receptors Improves Memory and Learning in Transgenic Alzheimer’s Disease Mouse Models

“…The amylin receptor, a class B GPCR, is viewed as a plausible therapeutic target for AD based upon observations that modulation of this receptor by either synthetic amylin analogs or amylin antagonists confers improvement in spatial memory and learning [ 6 – 8 , 16 , 17 ]. In order to resolve the dichotomy of whether it is activation or blockade of the amylin receptor that holds promise as a therapeutic strategy, we used a genetic approach consisting of a deletion within one copy of an endogenous chromosomal locus.…”

High-Speed Atomic Force Microscopy Reveals the Structural Dynamics of the Amyloid-β and Amylin Aggregation Pathways

“…High-speed AFM (HS-AFM) enabled the kinetic measurement of the structural dynamics of biological molecular processes [79][80][81][82][83][84] including amyloid aggregation [93,[108][109][110][111][112][113][114][115][116]. Here, we show that HS-AFM links structural and dynamics studies, reviewing recent HS-AFM studies and including our findings for Aβ42 [93] and amylin [116], which is associated with not only type II diabetes but also AD [117][118][119][120][121][122][123].…”

“…Amylin crosses the blood-brain barrier (BBB) [157][158][159], and its aggregate deposition is found in the brains of type II diabetes patients with AD [121]. The mechanisms underlying the pathological [122,123] and suppressive [117][118][119][120] effects of amylin to AD remain controversial [160].…”

Genetic Depletion of Amylin/Calcitonin Receptors Improves Memory and Learning in Transgenic Alzheimer’s Disease Mouse Models.

“…A robust in uence of altered AMY/CTR signaling upon Aβ-directed pathogenesis is supported by improvements in memory and pathology scored in two independent lines of APP695 transgenic mice that have both different genetic backgrounds and different tempos of AD-related changes (13,14). Moreover, a recent study revealed that amylin and its synthetic analog, pramlintide, when administered to AD mice, result in increased Aβ production via upregulation of APP and its processing enzyme, γ-secretase (17).…”

“…The amylin receptor, a class B GPCR, is viewed as a plausible therapeutic target for AD based upon observations that modulation of this receptor by either synthetic amylin analogs or amylin antagonists, confers improvement in spatial memory and learning (6,7,8,16,17). In order to resolve the dichotomy of whether it is activation or blockade of the amylin receptor that holds promise as a therapeutic strategy, we used a genetic approach consisting of a deletion within one copy of an endogenous chromosomal locus.…”