Alterations in presenilin 1 processing by amyloid-beta peptide in the rat retina

In-Depth Proteomic Analysis of the Porcine Retina by Use of a four Step Differential Extraction Bottom up LC MS Platform

The eye of the house swine (Sus scrofa domestica Linnaeus, 1758) represents a promising model for the study of human eye diseases encircling neurodegenerative retina disorders that go along with proteomic changes. To provide an in-depth view into the "normal" (untreated & healthy) porcine retina proteome as an important reference, a proteomic strategy has been developed encircling stepwise/differential extraction, LC MS and peptide de novo sequencing. Accordingly, pooled porcine retina homogenates were processed by stepwise DDM, CHAPS, ASB14 and ACN/TFA extraction. Retinal proteins were fractionated by 1D-SDS PAGE and further analyzed by LC ESI MS following database and de novo sequencing related protein identification and functional analyses. In summary, >2000 retinal proteins (FDR < 1 %) could be identified by use of the highly reproducible and selective extraction procedure. Moreover, an identification surplus of 36 % comparing initial one step extraction to the four step method could be documented. Despite most proteins were identified in the DDM and CHAPS fraction, all extraction steps contributed exclusive proteins with nucleus proteins enriched in the final ACN/TFA fraction. Additionally, for the first time new non-annotated de novo peptides could be documented for the porcine retina. The generated porcine retina proteome reference map contributes importantly to the understanding of the pig eye proteome and the developed workflow has strong translational potential considering retina studies of various species.

Differential effects of amyloid-β peptide aggregation status on in vivo retinal neurotoxicity

The present study examined the relationship between amyloid beta (Aβ)-peptide aggregation state and neurotoxicity in vivo using the rat retinal-vitreal model. Following single unilateral intravitreal injection of either soluble Aβ1-42 or Aβ1-42 preaggregated for different periods, retinal pathology was evaluated at 24 hours, 48 hours, and 1-month postinjection. Injection of either soluble Aβ (sAβ) or preaggregated Aβ induced a rapid reduction in immunoreactivity (IR) for synaptophysin, suggesting that direct contact with neurons is not necessary to disrupt synapses. Acute neuronal ionic and metabolic dysfunction was demonstrated by widespread loss of IR to the calcium buffering protein parvalbumin (PV) and protein gene product 9.5, a component of the ubiquitin-proteosome system. Injection of sAβ appeared to have a more rapid impact on PV than the preaggregated treatments, producing a marked reduction in PV cell diameters at 48 hours, an effect that was only observed for preaggregated Aβ after 1-month survival. Extending the preaggregation period from 4 to 8 days to obtain highly fibrillar Aβ species significantly increased the loss of choline acteyltransferase IR, but had no effect on PV-IR. These findings prompt the conclusion that Aβ assembly state has a significant impact on in vivo neurotoxicity by triggering distinct molecular changes within the cell.

Differential effects of interleukin-1beta and S100B on amyloid precursor protein in rat retinal neurons

Purpose:

Interleukin-1β (IL-1β) and S100B calcium binding protein B (S100B) have been implicated in the pathogenesis of Alzheimer’s disease. Both are present in and around senile plaques and have been shown to increase levels of amyloid precursor protein (APP) mRNA in vitro. However, it is not known how either of these substances affects APP in vivo.

Methods:

We have studied the effects of IL-1β and S100B on the expression and processing of APP using a retinal-vitreal model. We have also investigated the effect of amyloid beta peptide (Aβ) on APP in the same system and the regulation of S100B production by Aβ and IL-1β from retinal glial cells.

Results:

Retinal ganglion cells constitutively express APP. However, after intravitreal injection of IL-1β or Aβ there was a marked reduction in APP levels as detected by Western blotting and IL-1β produced a decrease in APP immunoreactivity (IR). Nissl staining showed that the integrity of the injected retinas was unchanged after injection. Two days after S100B injection, there was a small reduction in APP-IR but this was accompanied by the appearance of some intensely stained large ganglion cells and there was some up-regulation in APP holoprotein levels on Western blot. Seven days post-S100B injection, these large, highly stained cells had increased in number throughout the retina. Injection of Aβ and IL-1β also caused an increase in S100B production within the retinal Müller glial cells.

Conclusion:

These results support the hypothesis that S100B (a glial-derived neurotrophic factor) and IL-1β (a pro-inflammatory cytokine) can modulate the expression and processing of APP in vivo and so may contribute to the progression of Alzheimer’s disease.

Acute and chronic effects of intravitreally injected beta-amyloid on the neurotransmitter system in the retina

The potential cytotoxic effect of aggregated Abeta(1-42) to neurons that express classical neurotransmitters, including acetylcholine, gamma-amino butyric acid, catecholamines and serotonin was assessed. The cholinergic system has been the central focus of the therapeutic drug strategies in amyloid-depositing pathologies such as Alzheimer's disease. Aggregated Abeta(1-42) has a multisystem cytotoxic effect causing non-specific reduction in immunoreactivity, dysfunction, or loss of retinal nerve cells. The extent of this was investigated using immunocytochemistry, TUNEL staining for apoptosis, and measurement of cell density as well as retinal surface area. There was a differential acute and/or chronic effect of Abeta on choline acetyltransferase, gamma-aminobutyric acid and 5-tryptamine hydroxylase systems, observed with the increasing time course of 6h to 5 months, and a bilateral/systemic effect. In contrast, the overall pattern of catecholaminergic system, as revealed by tyrosine hydroxylase immunoreactivity of the retina, appears to have remained relatively unaffected by Abeta (however this may reflect neuronal loss due to reduction in the retinal surface). This is the first in vivo evidence in a CNS model to show that not only all major neurotransmitter systems are differentially affected by Abeta aggregates but the effect may vary from one transmitter system to another under the same experimental conditions in situ and in a dose- and time-dependent manner.