Upregulation of Alzheimer's Disease Amyloid-ß Protein Precursor in Astrocytes Both in vitro and in vivo.

BACKGROUND: The amyloid cascade hypothesis of Alzheimer's disease (AD) posits that amyloid-ß (Aß) protein accumulation underlies the pathogenesis of the disease by leading to the formation of amyloid plaques, a pathologic hallmark of AD. Aß is a proteolytic product of amyloid-ß protein precursor (AßPP; APP), which is expressed in both neurons and astrocytes. Although considerable evidence shows that astrocytes may play critical roles in the pathogenesis of AD, the longitudinal changes of amyloid plaques in relationship to AßPP expression in astrocytes and cellular consequences are largely unknown. OBJECTIVE: Here, we aimed to investigate astrocyte-related pathological changes of Aß and AßPP using immunohistochemistry and biochemical studies in both animal and cell models. METHODS/RESULTS: We utilized 5XFAD transgenic mice and found age-dependent upregulation of AßPP in astrocytes demonstrated with astrocytic reactive properties, which followed appearance of amyloid plaques in the brain. We also observed that AßPP proteins presented well-defined punctate immuno reactivity in young animals, whereas AßPP staining showed disrupted structures surrounding amyloid plaques in older mice. Moreover, we utilized astrocyte cell models and showed that pretreatment of Aß42 resulted in downstream astrocyte autonomous changes, including up regulation in AßPP and BACE1 levels, as well as prolonged amyloidogenesis that could be reduced by pharmacological inhibition of BACE1. CONCLUSION: Collectively, our results show that age-dependent AßPP up regulation in astrocytes is a key feature in AD, which will not only provide novel insights for understanding AD progression, but also may offer new therapeutic strategies for treating AD.

Soluble Gamma-secretase Modulators Attenuate Alzheimer's ß-amyloid Pathology and Induce Conformational Changes in Presenilin 1.

A central pathogenic event of Alzheimer's disease (AD) is the accumulation of the Aß42 peptide, which is generated from amyloid-ß precursor protein (APP) via cleavages by ß- and γ-secretase. We have developed a class of soluble 2-aminothiazole γ-secretase modulators (SGSMs) that preferentially decreases Aß42 levels. However, the effects of SGSMs in AD animals and cells expressing familial AD mutations, as well as the mechanism of γ-secretase modulation remain largely unknown. Here, a representative of this SGSM scaffold, SGSM-36, was investigated using animals and cells expressing FAD mutations. SGSM-36 preferentially reduced Aß42 levels without affecting either α- and ß-secretase processing of APP nor Notch processing. Furthermore, an allosteric site was identified within the γ-secretase complex that allowed access of SGSM-36 using cell-based, fluorescence lifetime imaging microscopy analysis. Collectively, these studies provide mechanistic insights regarding SGSMs of this class and reinforce their therapeutic potential in AD.

Antibiotic-induced perturbations in gut microbial diversity influences neuro-inflammation and amyloidosis in a murine model of Alzheimer's disease.

Severe amyloidosis and plaque-localized neuro-inflammation are key pathological features of Alzheimer's disease (AD). In addition to astrocyte and microglial reactivity, emerging evidence suggests a role of gut microbiota in regulating innate immunity and influencing brain function. Here, we examine the role of the host microbiome in regulating amyloidosis in the APPSWE/PS1ΔE9 mouse model of AD. We show that prolonged shifts in gut microbial composition and diversity induced by long-term broad-spectrum combinatorial antibiotic treatment regime decreases Aß plaque deposition. We also show that levels of soluble Aß are elevated and that levels of circulating cytokine and chemokine signatures are altered in this setting. Finally, we observe attenuated plaque-localised glial reactivity in these mice and significantly altered microglial morphology. These findings suggest the gut microbiota community diversity can regulate host innate immunity mechanisms that impact Aß amyloidosis.

A molecular neuroanatomical study of the developing human neocortex from 8 to 17 postconceptional weeks revealing the early differentiation of the subplate and subventricular zone.

We have employed immunohistochemistry for multiple markers to investigate the structure and possible function of the different compartments of human cerebral wall from the formation of cortical plate at 8 postconceptional weeks (PCW) to the arrival of thalamocortical afferents at 17 PCW. New observations include the subplate emerging as a discrete differentiated layer by 10 PCW, characterized by synaptophysin and vesicular gamma-aminobutyric acid transporter expression also seen in the marginal zone, suggesting that these compartments may maintain a spontaneously active synaptic network even before the arrival of thalamocortical afferents. The subplate expanded from 13 to 17 PCW, becoming the largest compartment and differentiated further, with NPY neurons located in the outer subplate and KCC2 neurons in the inner subplate. Glutamate decarboxylase and calretinin-positive inhibitory neurons migrated tangentially and radially from 11.5 PCW, appearing in larger numbers toward the rostral pole. The proliferative zones, marked by Ki67 expression, developed a complicated structure by 12.5 PCW reflected in transcription factor expression patterns, including TBR2 confined to the inner subventricular and outer ventricular zones and TBR1 weakly expressed in the subventricular zone (SVZ). PAX6 was extensively expressed in the proliferative zones such that the human outer SVZ contained a large reservoir of PAX6-positive potential progenitor cells.