Genome-wide analysis reveals mechanisms modulating autophagy in normal brain aging and in Alzheimer's disease

Abstract

Dysregulation of autophagy, a cellular catabolic mechanism essential for degradation of misfolded proteins, has been implicated in multiple neurodegenerative diseases. However, the mechanisms that lead to the autophagy dysfunction are still not clear. Based on the results of a genome-wide screen, we show that reactive oxygen species (ROS) serve as common mediators upstream of the activation of the type III PI3 kinase, which is critical for the initiation of autophagy. Furthermore, ROS play an essential function in the induction of the type III PI3 kinase and autophagy in response to amyloid β peptide, the main pathogenic mediator of Alzheimer's disease (AD). However, lysosomal blockage also caused by Aβ is independent of ROS. In addition, we demonstrate that autophagy is transcriptionally down-regulated during normal aging in the human brain. Strikingly, in contrast to normal aging, we observe transcriptional upregulation of autophagy in the brains of AD patients, suggesting that there might be a compensatory regulation of autophagy. Interestingly, we show that an AD drug and an AD drug candidate have inhibitory effects on autophagy, raising the possibility that decreasing input into the lysosomal system may help to reduce cellular stress in AD. Finally, we provide a list of candidate drug targets that can be used to safely modulate levels of autophagy without causing cell death.reactive oxygen species | type III PI3 kinase | neurodegeneration | signaling | transcriptional regulation A utophagy, a lysosome-dependent catabolic process mediating turnover of cellular components, plays an important role in regulating cellular homeostasis in the nervous system (1). Even in the absence of any other risk factors, autophagy deficiency in the CNS has been shown to lead to the accumulation of protein aggregates and progressive neurodegeneration (2). Thus, autophagy has been established as an important mechanism mediating degradation of misfolded proteins in the CNS. Because accumulation of misfolded proteins is a common feature in multiple human neurodegenerative diseases, activation of autophagy has been proposed as a strategy for combating neurodegeneration (3). However, little is currently known about how defects in autophagy might be involved in specific neurodegenerative diseases. Furthermore, as induction of autophagy is frequently associated with cell death, it remains a challenge to identify molecular targets whose inhibition can specifically activate autophagy without compromising cell viability.Pathological evidence supports the involvement of autophagy dysfunction in neurodegenerative diseases in humans. In Alzheimer's disease (AD), one of the earliest pathological changes include accumulation of autophagic vesicles (AVs) specifically within damaged neuritic processes and synaptic terminals (4). This phenotype is also observed in AD animal models and in cellbased models upon exposure to amyloid β peptide (Aβ). However, the mechanisms leading to the accumulation of AVs and the causal relationship to neurodegener...

Autophagy controls mesenchymal stem cell properties and senescence during bone aging

“…Here, we demonstrated that autophagy levels of aged BMMSCs were decreased compared with young BMMSCs. Numerous studies have indicated that with aging, autophagy decreases in different kinds of tissue such as kidney and brain (Kume et al., 2010; Lipinski et al., 2010). There are also studies revealing that autophagy is activated during aging in cells such as fibroblasts (Demirovic, Nizard, & Rattan, 2015) as in aged BMMSCs (Zheng et al., 2014).…”

AMPK activation protects cells from oxidative stress‐induced senescence via autophagic flux restoration and intracellular NAD + elevation

“…Dysfunctional autophagy has been observed in aging and age‐related diseases (Levine & Kroemer, 2008; Lipinski et al ., 2010). Autophagy is a homeostatic cellular recycling mechanism responsible for degrading injured or dysfunctional cellular organelles and proteins in all living cells (Mizushima et al ., 2010).…”

Evidence that a mitochondrial death spiral underlies antagonistic pleiotropy

“…Indeed, inhibiting autophagy confers cellular deficits related to aging (Blagosklonny, 2010; Rubinsztein et al ., 2011). Furthermore, autophagy declines during normal aging in Drosophila muscle (Demontis & Perrimon, 2010), mouse lung (Shirakabe et al ., 2016), and human brain (Lipinski et al ., 2010), and the mitochondrial autophagy (mitophagy) inducer PINK1 is transcriptionally downregulated during aging in mouse lung (Sosulski et al ., 2015). It was previously proposed that IIS pathway activity is deleterious to old organisms via inhibition of autophagy (Blagosklonny, 2010; Gems & de la Guardia, 2012).…”

“…Autophagy declines during normal aging in Drosophila muscle (Demontis & Perrimon, 2010), rat liver (Del Roso et al ., 2003); mouse lung (Shirakabe et al ., 2016), and human brain (Keller et al ., 2004; Lipinski et al ., 2010). Finally, the mitophagy inducer PINK1 is transcriptionally downregulated during aging in mouse lung (Sosulski et al ., 2015).…”