In sporadic Alzheimer's disease (AD), impaired A␤ removal contributes to elevated extracellular A␤ levels that drive amyloid plaque pathogenesis. Extracellular proteolysis, export across the blood-brain barrier, and cellular uptake facilitate physiologic A␤ clearance. Astrocytes can take up and degrade A␤, but it remains unclear whether this function is insufficient in AD or can be enhanced to accelerate A␤ removal. Additionally, age-related dysfunction of lysosomes, the major degradative organelles wherein A␤ localizes after uptake, has been implicated in amyloid plaque pathogenesis. We tested the hypothesis that enhancing lysosomal function in astrocytes with transcription factor EB (TFEB), a master regulator of lysosome biogenesis, would promote A␤ uptake and catabolism and attenuate plaque pathogenesis. Exogenous TFEB localized to the nucleus with transcriptional induction of lysosomal biogenesis and function in vitro. This resulted in significantly accelerated uptake of exogenously applied A␤42, with increased localization to and degradation within lysosomes in C17.2 cells and primary astrocytes, indicating that TFEB is sufficient to coordinately enhance uptake, trafficking, and degradation of A␤. Stereotactic injection of adeno-associated viral particles carrying TFEB driven by a glial fibrillary acidic protein promoter was used to achieve astrocyte-specific expression in the hippocampus of APP/PS1 transgenic mice. Exogenous TFEB localized to astrocyte nuclei and enhanced lysosome function, resulting in reduced A␤ levels and shortened half-life in the brain interstitial fluid and reduced amyloid plaque load in the hippocampus compared with control virus-injected mice. Therefore, activation of TFEB in astrocytes is an effective strategy to restore adequate A␤ removal and counter amyloid plaque pathogenesis in AD.

In AD, an imbalance between A␤ production and removal drives elevated brain A␤ levels and eventual amyloid plaque deposition. APP undergoes nonamyloidogenic processing via ␣-cleavage at the plasma membrane, amyloidogenic ␤-and ␥-cleavage within endosomes to generate A␤, or lysosomal degradation in neurons. Considering multiple reports implicating impaired lysosome function as a driver of increased amyloidogenic processing of APP, we explored the efficacy of targeting transcription factor EB (TFEB), a master regulator of lysosomal pathways, to reduce A␤ levels. CMV promoter-driven TFEB, transduced via stereotactic hippocampal injections of adenoassociated virus particles in APP/PS1 mice, localized primarily to neuronal nuclei and upregulated lysosome biogenesis. This resulted in reduction of APP protein, the ␣ and ␤ C-terminal APP fragments (CTFs), and in the steady-state A␤ levels in the brain interstitial fluid. In aged mice, total A␤ levels and amyloid plaque load were selectively reduced in the TFEB-transduced hippocampi. TFEB transfection in N2a cells stably expressing APP695, stimulated lysosome biogenesis, reduced steady-state levels of APP and ␣-and ␤-CTFs, and attenuated A␤ generation by accelerating flux through the endosome-lysosome pathway. Cycloheximide chase assays revealed a shortening of APP half-life with exogenous TFEB expression, which was prevented by concomitant inhibition of lysosomal acidification. These data indicate that TFEB enhances flux through lysosomal degradative pathways to induce APP degradation and reduce A␤ generation. Activation of TFEB in neurons is an effective strategy to attenuate A␤ generation and attenuate amyloid plaque deposition in AD.

Background and Purpose Cerebral Amyloid Angiopathy (CAA) is a common cause of recurrent intracerebral hemorrhage (ICH) in the elderly. Previous studies have shown that CAA induces inflammation and expression of matrix metalloproteinase-2 and -9 (gelatinases) in amyloid-laden vessels. Here, we inhibited both using minocycline in CAA mouse models to determine if spontaneous ICH could be reduced. Methods Tg2576 (n=16) and 5×FAD/ApoE4 knock-in mice (n=16), aged to 17 and 12 months, respectively, were treated with minocycline (50 mg/kg, i.p.) or saline every other day for two months. Brains were extracted and stained with X-34 (to quantify amyloid), Perl’s blue (to quantify hemorrhage), and immunostained to examined Aβ load, gliosis (GFAP, Iba-1), and vascular markers of blood-brain-barrier integrity (ZO-1 and collagen IV). Brain extracts were used to quantify mRNA for a variety of inflammatory genes. Results Minocycline treatment significantly reduced hemorrhage frequency in the brains of Tg2576 and 5×FAD/ApoE4 mice relative to the saline-treated mice, without affecting CAA load. Gliosis (GFAP and Iba-1 immunostaining), gelatinase activity, and expression of a variety of inflammatory genes (MMP-9, Nox4, CD45, S-100b, Iba-1) were also significantly reduced. Higher levels of microvascular tight junction and basal lamina proteins were found in the brains of minocycline-treated Tg2576 mice relative to saline-treated controls. Conclusions Minocycline reduced gliosis, inflammatory gene expression, gelatinase activity, and spontaneous hemorrhage in two different mouse models of CAA, supporting the importance of MMP-related and inflammatory pathways in ICH pathogenesis. As an FDA-approved drug, minocycline might be considered for clinical trials to test efficacy in preventing CAA-related ICH.