Protective Effects of Positive Lysosomal Modulation in Alzheimer's Disease Transgenic Mouse Models

Abstract

Alzheimer's disease (AD) is an age-related neurodegenerative pathology in which defects in proteolytic clearance of amyloid β peptide (Aβ) likely contribute to the progressive nature of the disorder. Lysosomal proteases of the cathepsin family exhibit up-regulation in response to accumulating proteins including Aβ1–42. Here, the lysosomal modulator Z-Phe-Ala-diazomethylketone (PADK) was used to test whether proteolytic activity can be enhanced to reduce the accumulation events in AD mouse models expressing different levels of Aβ pathology. Systemic PADK injections in APPSwInd and APPswe/PS1ΔE9 mice caused 3- to 8-fold increases in cathepsin B protein levels and 3- to 10-fold increases in the enzyme's activity in lysosomal fractions, while neprilysin and insulin-degrading enzyme remained unchanged. Biochemical analyses indicated the modulation predominantly targeted the active mature forms of cathepsin B and markedly changed Rab proteins but not LAMP1, suggesting the involvement of enhanced trafficking. The modulated lysosomal system led to reductions in both Aβ immunostaining as well as Aβx-42 sandwich ELISA measures in APPSwInd mice of 10–11 months. More extensive Aβ deposition in 20-22-month APPswe/PS1ΔE9 mice was also reduced by PADK. Selective ELISAs found that a corresponding production of the less pathogenic Aβ1–38 occurs as Aβ1–42 levels decrease in the mouse models, indicating that PADK treatment leads to Aβ truncation. Associated with Aβ clearance was the elimination of behavioral and synaptic protein deficits evident in the two transgenic models. These findings indicate that pharmacologically-controlled lysosomal modulation reduces Aβ1–42 accumulation, possibly through intracellular truncation that also influences extracellular deposition, and in turn offsets the defects in synaptic composition and cognitive functions. The selective modulation promotes clearance at different levels of Aβ pathology and provides proof-of-principle for small molecule therapeutic development for AD and possibly other protein accumulation disorders.

Role of Cathepsin D in U18666A-induced Neuronal Cell Death

“…Earlier studies reported that cathepsin D can have a survival or apoptotic effect depending on the subcellular localization and activity of the enzyme. If the levels and activity of the enzyme are increased within the lysosomes, it may represent an adaptive response to protect cells against toxic insults (39,43,70,71), whereas an enhanced activity and cytosolic levels of the enzyme can lead to cell death either directly or indirectly via cytochrome c release from mitochondria (6 -8). This phenomenon has been described under in vitro paradigms using a variety of toxic insults (29,44,(73)(74)(75)(76)(77) and in some animal models of neurodegenerative disorders (78 -80).…”

“…Intraperitoneal administration of pepstatin A has been shown to be beneficial for experimental colitis and bone mineralization (101,102), but it needs to be determined whether intracerebroventricular administration of the inhibitor can mitigate NPC pathology. Given the evidence that selective cathepsin B inhibitor can reduce brain A␤ levels/ deposition and improve cognitive behavioral deficits in animal models of Alzheimer disease (72,103), it is likely that the availability of rather selective and potent cathepsin D inhibitors that can cross the blood-brain barrier may provide a new therapeutic opportunity in the treatment of NPC pathology.…”

Positive Lysosomal Modulation As a Unique Strategy to Treat Age-Related Protein Accumulation Diseases

“…28 Cathepsin B has also been implicated in the cleavage of Ab 1-42 into less amyloidogenic species. 20,29 A wide variety of agents are listed in Table 1 that have been found to elicit positive lysosomal modulation. Chloroquine and bafilomycin A1, the latter being an adenosine triphosphatase (ATPase) blocker that also disrupts lysosomal pH, both cause lysosomal stress resulting in hydrolase responses.…”

Promoting Autophagic Clearance: Viable Therapeutic Targets in Alzheimer's Disease

“…Compounds that modulate lysosomal fusion include potential cystatin B and C antagonists [127], lysosomal cathepsin B modulators [212], and GSK-3β inhibitors, such as lithium, valproate, and NP12 [180,181]. Genetic deletion of cystatin B and C has been shown to improve neurological deficits and restore autophagic dysfunction in the TgCRND8 and hAPP-J20 mouse models of AD [127,213].…”

“…Cathepsin B is a lysosomal/endosomal enzyme with neuroprotective properties based on its protease activity, and in particular, its Aβ 1-42 cleavage function [219]. Z-Phe-Aladiazomethylketone, a positive modulator of cathepsin B activity, reduces Aβ levels in 10-11-month-old APP mice with Swedish and Indiana mutations (APP Swe/Ind ) and in 20-22-month-old APP swedish /PS1ΔE9 mice, protects against synaptic degeneration, and mitigates behavioral deficits [212]. Similarly, cathepsin D, another lysosomal/endosomal enzyme, has been implicated in clearance of Lewy bodies in PD [220].…”