Dorit Farfara

Neuroprotective and neurotoxic properties of glial cells in the pathogenesis of Alzheimer's disease

•  Introduction •  Innate immune response in the AD brain ‐  Microglia ‐  Astrocyte •  Glial cells mediate the peripheral immune response in AD ‐  Glial cell interaction with endothelial cells ‐  Glial cell interaction with T cells •  Glial cell activation as a therapeutic target in AD •  Conclusion

Inhibition of Glycogen Synthase Kinase-3 Ameliorates β-Amyloid Pathology and Restores Lysosomal Acidification and Mammalian Target of Rapamycin Activity in the Alzheimer Disease Mouse Model: IN VIVO AND IN VITRO STUDIES*

Background: The mechanisms behind the contribution of GSK-3 to Alzheimer disease pathogenesis remain elusive. Results: A GSK-3 inhibitor reduced Aβ pathology and ameliorated cognitive decline in an Alzheimer disease mouse model. GSK-3 impairs lysosomal acidification and impacts mTOR activity. Conclusion: Inhibition of GSK-3 reverses Alzheimer disease pathogenesis via restoration of lysosomal acidification and reactivation of mTOR. Significance: We identified novel mechanisms linking GSK-3 with Aβ pathology. Accumulation of β-amyloid (Aβ) deposits is a primary pathological feature of Alzheimer disease that is correlated with neurotoxicity and cognitive decline. The role of glycogen synthase kinase-3 (GSK-3) in Alzheimer disease pathogenesis has been debated. To study the role of GSK-3 in Aβ pathology, we used 5XFAD mice co-expressing mutated amyloid precursor protein and presenilin-1 that develop massive cerebral Aβ loads. Both GSK-3 isozymes (α/β) were hyperactive in this model. Nasal treatment of 5XFAD mice with a novel substrate competitive GSK-3 inhibitor, L803-mts, reduced Aβ deposits and ameliorated cognitive deficits. Analyses of 5XFAD hemi-brain samples indicated that L803-mts restored the activity of mammalian target of rapamycin (mTOR) and inhibited autophagy. Lysosomal acidification was impaired in the 5XFAD brains as indicated by reduced cathepsin D activity and decreased N-glycoyslation of the vacuolar ATPase subunit V0a1, a modification required for lysosomal acidification. Treatment with L803-mts restored lysosomal acidification in 5XFAD brains. Studies in SH-SY5Y cells confirmed that GSK-3α and GSK-3β impair lysosomal acidification and that treatment with L803-mts enhanced the acidic lysosomal pool as demonstrated in LysoTracker Red-stained cells. Furthermore, L803-mts restored impaired lysosomal acidification caused by dysfunctional presenilin-1. We provide evidence that mTOR is a target activated by GSK-3 but inhibited by impaired lysosomal acidification and elevation in amyloid precursor protein/Aβ loads. Taken together, our data indicate that GSK-3 is a player in Aβ pathology. Inhibition of GSK-3 restores lysosomal acidification that in turn enables clearance of Aβ burdens and reactivation of mTOR. These changes facilitate amelioration in cognitive function.

Orally administrated cinnamon extract reduces β-amyloid oligomerization and corrects cognitive impairment in Alzheimer's disease animal models.

An increasing body of evidence indicates that accumulation of soluble oligomeric assemblies of β-amyloid polypeptide (Aβ) play a key role in Alzheimers disease (AD) pathology. Specifically, 56 kDa oligomeric species were shown to be correlated with impaired cognitive function in AD model mice. Several reports have documented the inhibition of Aβ plaque formation by compounds from natural sources. Yet, evidence for the ability of common edible elements to modulate Aβ oligomerization remains an unmet challenge. Here we identify a natural substance, based on cinnamon extract (CEppt), which markedly inhibits the formation of toxic Aβ oligomers and prevents the toxicity of Aβ on neuronal PC12 cells. When administered to an AD fly model, CEppt rectified their reduced longevity, fully recovered their locomotion defects and totally abolished tetrameric species of Aβ in their brain. Furthermore, oral administration of CEppt to an aggressive AD transgenic mice model led to marked decrease in 56 kDa Aβ oligomers, reduction of plaques and improvement in cognitive behavior. Our results present a novel prophylactic approach for inhibition of toxic oligomeric Aβ species formation in AD through the utilization of a compound that is currently in use in human diet.

Toll-Like Receptors Expression and Signaling in Glia Cells in Neuro-Amyloidogenic Diseases: Towards Future Therapeutic Application

Toll-like receptors (TLRs) are known to be expressed by innate immune response cells and to play a critical role in their activation against foreign pathogens. It was recently suggested that TLRs have an important role in the crosstalk between neurons and glial cells in the central nervous system (CNS). TLR signaling was reported to be associated with a yin-yang effect in the CNS. While TLR signaling was linked to neurogenesis, it was also found to be involved in the pathogenesis of neurodegenerative diseases. This paper will focus on TLR signaling in glial cells in neurodegenerative diseases such as Alzheimers disease, prion diseases, amyotrophic lateral sclerosis, and Parkinsons disease. Understanding the pattern of TLR signaling in the glial cells may lead to the identification of new targets for therapeutic application.

Scara1 deficiency impairs clearance of soluble amyloid-β by mononuclear phagocytes and accelerates Alzheimer’s-like disease progression

In Alzheimer’s disease soluble amyloid beta (sAβ) causes synaptic dysfunction and neuronal loss. Receptors involved in clearance of sAβ are not known. Here we use shRNA screening and identify the scavenger receptor Scara1 as a receptor for sAβ expressed on myeloid cells. To determine the role of Scara1 in clearance of sAβ in vivo, we cross Scara1 null mice with PS1-APP mice, a mouse model of Alzheimer’s disease and generate PS1-APP- Scara1-deficient mice. Scara1 deficiency markedly accelerates Aβ accumulation leading to increased mortality. In contrast, pharmacological upregulation of Scara1 expression on mononuclear phagocytes increases Aβ clearance. This approach is a potential treatment strategy for Alzheimer’s disease.

γ-Secretase component presenilin is important for microglia β-amyloid clearance.

The cleavage of amyloid precursor protein by γ‐secretase is an important aspect of the pathogenesis of Alzheimers disease. γ‐Secretase also cleaves other membrane proteins (eg, Notch), which control cell development and homeostasis. Presenilin 1 and 2 are considered important determinants of the γ‐secretase catalytic site. Our aim was to investigate whether γ‐secretase can be important for microglial phagocytosis of Alzheimers disease β‐amyloid.

Nasal vaccination with troponin reduces troponin specific T-cell responses and improves heart function in myocardial ischemia–reperfusion injury

Myocardial ischemia with subsequent reperfusion (MI/R) can lead to significant myocardial damage. Ischemia initiates inflammation at the blood-microvascular endothelial cell interface and contributes significantly to both acute injury and repair of the damaged tissue. We have found that MI/R injury in mice is associated with a cellular immune response to troponin. Myocardial cells exclusively synthesize troponin and release the troponin into the bloodstream following injury. Mucosally administered proteins induce T cells that secrete anti-inflammatory cytokines such as IL-10 and transforming growth factor beta at the anatomical site where the protein localizes. We found that nasal administration of the three subunits of troponin (C, I and T isoforms), given prior to or 1 h following MI/R, decreased infarct size by 40% measured 24 h later. At 1.5 months following MI/R, there was a 50% reduction in infarct size and improvement in cardiac function as measured by echocardiography. Protection was associated with a reduction of cellular immunity to troponin. Immunohistochemistry demonstrated increased IL-10 and reduced IFN-gamma in the area surrounding the ischemic infarct following nasal troponin. Adoptive transfer of CD4+ T cells to mice from nasally troponin-treated mice 1 h after the MI/R decreased infarct size by 72%, whereas CD4+ T cells from IL-10-/- mice or nasally BSA-treated mice had no effect. Our results demonstrate that IL-10-secreting CD4+ T cells induced by nasal troponin reduce injury following MI/R. Modulation of cardiac inflammation by nasal troponin provides a novel treatment to decrease myocardial damage and enhance recovery after myocardial ischemia.

Naphthoquinone-tyrptophan reduces neurotoxic Aβ*56 levels and improves cognition in Alzheimer's disease animal model.

An increasing body of evidence indicates a role for oligomers of the amyloid-β peptide (Aβ) in the neurotoxicity of this peptide and the pathology of Alzheimers disease (AD). Several neurotoxic oligomeric forms of Aβ have been noted ranging from the larger Amyloid β-Derived Diffusible Ligands (ADDLs) to smaller trimers and dimers of Aβ. More recently a dodecameric form of Aβ with a 56 kDa molecular weight, denoted Aβ*56, was shown to cause memory impairment in AD model mice. Here, we present for the first time a potential therapeutic strategy for AD that targets the early stages in the formation of neurotoxic Aβ*56 oligomers using a modified quinone-Tryptophan small molecule N-(3-chloro-1,4-dihydro-1,4-dioxo-2-naphthalenyl)-L-Tryptophan (Cl-NQTrp). Using NMR spectroscopy we show that this compound binds the aromatic recognition core of Aβ and prevents the formation of oligomers. We assessed the effect of Cl-NQTrp in vivo in transgenic flies expressing Aβ(1-42) in their nervous system. When these flies were fed with Cl-NQTrp a marked alleviation of their Aβ-engendered reduced life span and defective locomotion was observed. Finally, intraperitoneal injection of Cl-NQTrp into an aggressive AD mouse model reduced the level of the Aβ*56 species in their brain and reversed their cognitive defects. Further experiments should assess whether this is a direct effect of the drug in the brain or an indirect peripheral effect. This is the first demonstration that targeted reduction of Aβ*56 results in amelioration of AD symptoms. This second generation of tryptophan-modified naphthoquinones could therefore serve as potent disease modifying therapeutic for AD.