Alzheimer's Amyloid-ß Accelerates Cell Senescence and Suppresses the SIRT1/NRF2 Pathway in Human Microglial Cells.

Microglia play important roles in maintenance of brain homeostasis, while due to some pathological stimuli in aging-related neurodegenerative diseases including Alzheimer's disease, they are malfunctioning. Here, we demonstrated that amyloid-ß (Aß) accelerated cell senescence characterized by the upregulation of p21 and PAI-1 as well as senescence-associated beta-galactosidase (SA-ß-gal) in human microglial cells. Consistently, Aß induced the senescence-associated mitochondrial dysfunctions such as repression of ATP production, oxygen consumption rate (OCR), and mitochondrial membrane potential and enhancement of ROS production. Furthermore, Aß was found to significantly suppress mRNA expression and protein level of Sirtuin-1 (SIRT1), a key regulator of senescence, and inhibit mRNA expression and translocation of NRF2, a critical transcription factor in inflammatory responses, leading to impairment of phagocytosis. Rescue of SIRT1, as expected, could counteract the pathological effects of Aß. In summary, our findings revealed that Aß accelerates human microglial senescence mainly through its suppression of the SIRT1/NRF2 pathway and suggested that genetic and pharmaceutical rescue of SIRT1 may provide a potential alternative treatment.

PL201, a Reported Rhamnoside Against Alzheimer's Disease Pathology, Alleviates Neuroinflammation and Stimulates Nrf2 Signaling.

Neuroinflammation induced by overactivated glia cells is believed to be a major hallmark of Alzheimer's disease (AD) and a hopeful target against AD. A rhamnoside PL201 was previously reported to promote neurogenesis and ameliorate AD, and in this study, we revealed that PL201 also significantly reduced accumulation of the activated microglia and proinflammatory cytokines in APP/PS1 mice. In vitro, PL201 consistently suppressed the microglia induction of proinflammatory cytokines after stimulation with lipopolysaccharides and Aß42. Further mechanistic studies demonstrated that PL201 considerably enhanced the expression level and the nuclear translocation of Nrf2, a key regulator of neuroinflammation. Moreover, PL201 effectively stimulated Nrf2 signaling cascade, including upregulation of HO-1 and downregulation of NF-κB pathway. Thus, our findings indicated the anti-neuroinflammatory effect by PL201 in vivo and suggested that PL201 or the like, with multiple functions such as neurogenesis, mitochondria maintenance, and anti-neuroinflammation, could be a promising candidate in AD treatment.

An analog derived from phenylpropanoids ameliorates Alzheimer's disease-like pathology and protects mitochondrial function.

The abnormal proliferation and neurogenesis of neural progenitor cells (NPCs) is usually associated with the pathophysiology of neurodegenerative disorders such as Alzheimer's disease (AD). Mitochondrial stress is one of the most prominent features of AD and is thought to be involved in the impairment of the neurogenesis and proliferation of NPCs. Thus, restoring mitochondrial function by pharmaceutical intervention may alleviate disease-related defects in neurogenesis and is considered a potential therapeutic strategy for AD. In the present study, we found that the oral administration of PL201A, a designed analog of phenylpropanoids, which are a family of natural products with antiaging effects, promoted the neurogenesis and proliferation of NPCs and ameliorated cognitive impairment in a transgenic mouse model of AD. Furthermore, PL201A attenuated amyloid-ß-induced mitochondrial stress and promoted NPC proliferation in vitro. Further mechanistic studies showed that PL201A restored the activation of AMP-regulated protein kinase-retinoblastoma signaling, which was suppressed by amyloid-ß. Our findings suggest that PL201A may represent a promising regenerative therapeutic agent for cognitive decline in neurodegenerative diseases.

Naringin Dihydrochalcone Ameliorates Cognitive Deficits and Neuropathology in APP/PS1 Transgenic Mice.

Alzheimer's disease (AD) is a multi-factorial neurodegenerative disorder with abnormal accumulation of amyloid-ß (Aß) plaques, neuroinflammation and impaired neurogenesis. Mounting evidences suggest that single-target drugs have limited effects on clinical treatment and alternative or multiple targets are required. In recent decades, natural compounds and their derivatives have gained increasing attention in AD drug discovery due to their inherently enormous chemical and structural diversity. In this study, we demonstrated that naringin dihydrochalcone (NDC), a widely used dietary sweetener with strong antioxidant activity, improved the cognitive function of transgenic AD mice. Pathologically, NDC attenuated Aß deposition in AD mouse brain. Furthermore, NDC reduced periplaque activated microglia and astrocytes, indicating the inhibition of neuroinflammation. It also enhanced neurogenesis as investigated by BrdU/NeuN double labeling. Additionally, the inhibition of Aß level and neuroinflammation by NDC treatment was also observed in an AD cell model or a microglia cell line. Taken together, our study indicated that NDC might be a potential therapeutic agent for the treatment of AD against multiple targets that include Aß pathology, neuroinflammation and neurogenesis.