Accumulation of tau has been implicated in various neurodegenerative diseases termed tauopathies. Tau is a microtubule-associated protein but is also actively released into the extracellular fluids including brain interstitial fluid and cerebrospinal fluid (CSF). However, it remains elusive whether clearance of extracellular tau impacts tau-associated neurodegeneration. Here, we show that aquaporin-4 (AQP4), a major driver of the glymphatic clearance system, facilitates the elimination of extracellular tau from the brain to CSF and subsequently to deep cervical lymph nodes. Strikingly, deletion of AQP4 not only elevated tau in CSF but also markedly exacerbated phosphorylated tau deposition and the associated neurodegeneration in the brains of transgenic mice expressing P301S mutant tau. The current study identified the clearance pathway of extracellular tau in the central nervous system, suggesting that glymphatic clearance of extracellular tau is a novel regulatory mechanism whose impairment contributes to tau aggregation and neurodegeneration.

An ER transmembrane protein, vesicle-associated membrane protein-associated protein B (VAPB), binds to several organelle-resident membrane proteins to mediate ER-organelle tethering. Mutation in amyotrophic lateral sclerosis (ALS) induces protein misfolding and aggregation, leading to ER disorganization. Gain or loss of function is suggested for VAPB mutation, however comprehensive study focusing on VAPB-ER domain has yet been performed. We here conducted proteomic characterization of the ER containing VAPB and its ALS-linked P56S mutant. For this purpose, we first optimized the proteomics of different ER domains immuno-isolated from cultured cells, and identified ER sheet- and tubule-specific proteomes. By using these as references, we found that VAPB-ER proteome had intermediate ER domain properties but its tubular property was specifically decreased by its mutation. Biochemical, immunofluorescence and proximity ligation assays suggested this was mediated by delocalization of VAPB from ER tubules. The VAPB-ER proteomics further suggested reduced incorporation of multiple proteins located in different organelles, which was confirmed by proximity ligation assay. Taken together, our proteomics-based approach indicates altered ER domain properties and impaired ER-organelle tethering by VAPB mutation.

Obesity is associated with proliferation and differentiation of adipose-derived stem cells (ADSCs) into mature adipocytes. Nutritional stimuli induce ADSCs proliferation and differentiation, and this process is well established because master regulators of adipogenic differentiation, C/EBPalpha and PPARgamma were identified. However, under normal condition, molecular mechanisms to maintain stemness of ADSCs are largely unknown. To identify genes essential for the maintenance, microarray analysis was performed on murine ADSCs and 4-day cultured ADSCs (preadipocytes). Among the 223 up-regulated transcriptional factor genes in ADSCs, we focused on nuclear receptor 4a (Nr4a) family, which play diverse roles including metabolic processes. Nr4a-overexpressed preadipocytes showed reduced accumulation of lipid droplet and decreased expressions of C/EBPalpha and PPARgamma. ChIP analysis confirmed that Nr4a directly bound to C/EBPalpha and PPARgamma promotor. Nr4a family is induced by multiple signals including cyclic AMP in a cell type-specific manner. Application of a cAMP analogue to ADSCs induced Nr4a expressions and decreased expressions of PPARgamma. These data suggested that Nr4a inhibited ADSCs differentiation in a cAMP-dependent manner.