Time-Course and Regional Analyses of the Physiopathological Changes Induced after Cerebral Injection of an Amyloid β Fragment in Rats

Abstract

Alzheimer's disease (AD) is a neurodegenerative pathology characterized by the presence of senile plaques and neurofibrillary tangles, accompanied by synaptic and neuronal loss. The major component of senile plaques is an amyloid ␤ protein (A␤) formed by pathological processing of the A␤ precursor protein. We assessed the time-course and regional effects of a single intracerebroventricular injection of aggregated A␤ fragment 25-35 (A␤ 25-35 ) in rats. Using a combined biochemical, behavioral, and morphological approach, we analyzed the peptide effects after 1, 2, and 3 weeks in the hippocampus, cortex, amygdala, and hypothalamus. The scrambled A␤ 25-35 peptide was used as negative control. The aggregated forms of A␤ peptides were first characterized using electron microscopy, infrared spectroscopy, and Congo Red staining. Intracerebroventricular injection of A␤ 25-35 decreased body weight, induced short-and long-term memory impairments, increased endocrine stress, cerebral oxidative and cellular stress, neuroinflammation, and neuroprotective reactions, and modified endogenous amyloid processing, with specific time-course and regional responses. Moreover, A␤ 25-35 , the presence of which was shown in the different brain structures and over 3 weeks, provoked a rapid glial activation, acetylcholine homeostasis perturbation, and hippocampal morphological alterations. Alzheimer's disease (AD) is a chronic neurodegenerative pathology characterized by the presence of senile plaques and neurofibrillary tangles, accompanied by synaptic and neuronal loss in brain areas responsible for learning and memory impairments. 1 The major component of senile plaques is an amyloid ␤ protein (A␤) derived from amyloid precursor protein (APP). Genetic, cell biological, and postmortem studies on AD brain, together with A␤ neurotoxicity findings, gave rise to the amyloid cascade hypothesis to explain A␤-associated neurodegenerative processes. 2 In normal healthy individuals, A␤ peptides are present only in small quantities, as soluble monomers that circulate in cerebrospinal fluid and blood. In AD patients, A␤ peptides, which vary in length from 40 to 43 amino acids, accumulate as insoluble fibrillar deposits. 3 When cultured rat hippocampal neurons are exposed to aggregated A␤ peptides, their neurites adopt a dystrophic appearance and become comparable to those observed surrounding and infiltrating senile plaques. This observation suggested that A␤ is responsible for the neuritic abnormalities in AD pathology. 4 Structure-activity studies revealed that peptides containing the highly hydrophobic 25-35 region formed stable aggregates and mediated neuronal death by necrosis or apoptosis. 5,6,7 The truncated A␤ 25-35 fragment includes extracellular and intramembrane residues that have been reported to represent an active region of A␤. 8

Blockade of Tau Hyperphosphorylation and Aβ1–42 Generation by the Aminotetrahydrofuran Derivative ANAVEX2-73, a Mixed Muscarinic and σ1 Receptor Agonist, in a Nontransgenic Mouse Model of Alzheimer’s Disease

“…It has been repeatedly shown that the i.c.v. injection of Ab [25][26][27][28][29][30][31][32][33][34][35] in rats and mice increases b-secretase activity and Ab levels in the hippocampus and cortex of the animals (Klementiev et al, 2007;Chavant et al, 2010;Zussy et al, 2011). All treatments resulted in a significant blockade of Ab 25-35 -induced increase in Ab 1-42 levels measured by ELISA.…”

“…Moreover, mice overexpressing GSK-3b showed impaired long-term potentiation and memory deficits (Hernandez et al, 2002), which could be attributable to impaired integration of Akt and Wnt signalling onto mammalian target of rapamycin (mTOR) stimulation (Ma et al, 2010(Ma et al, , 2011. Ab peptides also activate directly GSK-3b in vitro and in vivo, although the mechanism remains unclear (Kim et al, 2003;Akiyama et al, 2005;Klementiev et al, 2007;Zussy et al, 2011). Finally, GSK-3b could have a critical role in Ab production (for review, see Cai et al, 2012).…”

“…The toxicity induced after such central injection of the Ab 25-35 fragment in oligomeric form in mice and rats was repeatedly shown to result in neuroinflammation and reactive gliosis, pro-apoptotic caspases activity, oxidative stress, reduction in the number of neurons measured in hippocampal pyramidal cell layers, loss of cholinergic neurons, and memory deficits (Maurice et al, 1996;Delobette et al, 1997;Stepanichev et al, 2003Stepanichev et al, , 2004Stepanichev et al, , 2006Meunier et al, 2006;Klementiev et al, 2007;Chavant et al, 2010;Villard et al, 2009Villard et al, , 2011Zussy et al, 2011). It is at present widely used to detect the neuroprotective potential of new drugs and natural derivatives (Ruan et al, 2010;Kim et al, 2011;Lu et al, 2012;Wang et al, 2012;Yang et al, 2012).…”

“…Interestingly, the Ab 25-35 injection resulted not only in an aggressive amyloid toxicity but also in accumulation of endogenous Ab species and Tau hyperphosphorylation, as observed in AD physiopathology. One week after Ab [25][26][27][28][29][30][31][32][33][34][35] injection, APP and Ab 1-42 levels were increased in the hippocampus and cortex, Ab-expressing cells could be visualized using immunohistochemistry and b-secretase cleavage products, such as the C-terminal fragment C99, could be detected (Klementiev et al, 2007;Chavant et al, 2010;Zussy et al, 2011). Moreover, an increase in Tau phosphorylation on physiological or AD-related pathological epitopes induced by Ab 25-35 injection in mice was reported in several studies (Dudas et al, 2002;Klementiev et al, 2007;Deng et al, 2010).…”

Alzheimer Diseases

“…Pervious experimental studies have shown that Aβ (25-35) induce a wide pattern of central modifications, reminiscent of the human physiopathology, particularly short-and long-term memory deficit, oxidative stress, apoptosis, neuroinflammation, acetylcholine impairment, hippocampus alteration, tau hyperphosphorylation and amyloid burden (10). The deposition of β-amyloid protein in brain is related to learning impairment and cholinergic neuronal degeneration and the β-amyloid protein-treated rats could be used as AD animal models (11).…”