Mahnoor Zia

Introduction: Alzheimer’s Disease (AD) is a neurodegenerative disease associated with a progressive memory loss and cognitive disabilities. Neurodegenerative process starts decades before symptoms appear. AD brains have shown two main pathological hallmarks: extracellular accumulation of amyloid-beta (Aβ) plaques and intracellular accumulation of hyperphosphorylated Tau (neurofibrillary tangles, NFT). These pathologies are secondary to mechanical disturbances in cellular clearance, mitochondrial functioning, and oxidative processes. This project focuses on a describing an autophagy mechanism that is downregulated in AD brains and leads to NFTs. Autophagy adapter protein NDP-52 and transcription activator Nrf-2 are the two main intermediates of the pathway. Sulforaphane, an organosulfur compound obtained from cruciferous vegetables, is a Nrf-2 activator. Methods: The cell cultures used in the studies consisted of mice and human cortical cells. X-ray crystallography and NMR on human NDP-52 elucidated its structural and functional domains (1). Nrf-2’s binding sequences on DNA were determined from DNA databases (ENCODE and JASPER)(2). Protein quantification for NDP-52 and Nrf-2 was by western blot and qRT-PCR methods (1,2,3). Phosphorylated Tau was analyzed in tissue samples using immunoblotting and fluorescence antibody assays4. Results: Structural analysis of NDP-52 showed a C-terminal binding domain for ubiquitin and myosin VI, and a separate SIKCH domain for GFP-Tau (1,4). Primary cortical neurons of mice treated with Nrf-2 activator resulted increased NDP-52 mRNA, where as the control showed a reduction in NDP-52 mRNA (4). Nrf-2 was found to be down- regulated in autopsied AD brains (3). Hippocampal tissue obtained from Nrf-2 (-/-) mice showed accumulation of more phosphorylated Tau than tissue samples from Nrf-2 (WT). Methylation specific PCR of mouse neuroblastoma cells treated with sulforaphane showed a decrease in Nrf-2 promoter methylation (3). Furthermore, Western Blot analysis of Nrf2 protein in the nucleus vs. cytoplasm of sulforaphane treated cells had increased level of Nrf2 in the nucleus, while the cytoplasmic protein level remains constant (3). Conclusions: Intracellular Tau tangles have been associated with neurodegeneration and cognitive decline seen in patients with AD. These aggregates are often found in autophagosomes, with halted autophagy. NDP-52 with its binding domain for myosin IV, ubiquitin and phosphorylated Tau is involved in autophagosome maturation. NDP-52 is transcriptionally upregulated by Nrf-2. Therefore, a reduction in Nrf-2, as seen in AD brains, will severely downregulate degradation of phosphorylated Tau by the mechanisms mediated by NDP52. Sulforaphane, can be used to upregulate the process. Consequently, consumption of cruciferous vegetables may be useful in upregulating cellular clearance of NFTs.

1. Xie X, Li F, Wang Y, et al. Molecular basis of ubiquitin recognition by the autophagy receptor CALCOCO2. Autophagy. 2015;11(10):1775-1789.
2. Pajares M, Moreno N, et al. Transcription factor NFE2L2/NRF2 is a regulator of macroautophagy genes. Autophagy. 2016; 12 (10); 1902-1916.
3. Zhao F, Zhang J, Chang N. Epigenetic Modification of Nrf-2 by sulforaphane increases the antioxidative and anti-inflammatory capacity in a cellular model of Alzheimer’sDisease. European Journal of Pharmacology.2018; 824(10); 1-10.
4. Jo C, Gundemir S. Nrf-2 Reduces Levels of Phosphorylated Tau Protein by inducing Autophagy Adaptor protein NDP 52. Nature Communications. 2014; 5 (3496); 1-13.