Methylthioninium chloride (methylene blue) induces autophagy and attenuates tauopathy in vitro and in vivo

Abstract

aldehyde phosphatase dehydrogenase; GSK-3, glycogen synthase kinase 3; GFP, green fluorescent protein; Hsc, heat shock cognate; Hsp, heat shock protein; IGF, insulin-like growth factor; IRS, insulin receptor substrate; MB, methylene blue; LC, liquid chromatography; MS, mass spectroscopy; mTOR, mammalian target of rapamycin; PI3, phosphoinositide 3-kinase; PBS, phosphate buffered saline; p70, p70S6 kinase; pp70, phosphorylated p70S6 kinase; RFP, red fluorescent protein; shRNA, short hairpin RNA More than 30 neurodegenerative diseases including Alzheimer disease (AD), frontotemporal lobe dementia (FTD), and some forms of Parkinson disease (PD) are characterized by the accumulation of an aggregated form of the microtubulebinding protein tau in neurites and as intracellular lesions called neurofibrillary tangles. Diseases with abnormal tau as part of the pathology are collectively known as the tauopathies. Methylthioninium chloride, also known as methylene blue (MB), has been shown to reduce tau levels in vitro and in vivo and several different mechanisms of action have been proposed. Herein we demonstrate that autophagy is a novel mechanism by which MB can reduce tau levels. Incubation with nanomolar concentrations of MB was sufficient to significantly reduce levels of tau both in organotypic brain slice cultures from a mouse model of FTD, and in cell models. Concomitantly, MB treatment altered the levels of LC3-II, cathepsin D, BECN1, and p62 suggesting that it was a potent inducer of autophagy. Further analysis of the signaling pathways induced by MB suggested a mode of action similar to rapamycin. Results were recapitulated in a transgenic mouse model of tauopathy administered MB orally at three different doses for two weeks. These data support the use of this drug as a therapeutic agent in neurodegenerative diseases.

Methylene Blue Modulates β-Secretase, Reverses Cerebral Amyloidosis, and Improves Cognition in Transgenic Mice

“…Although these reports apparently contradict earlier in vitro studies showing that MB can inhibit Tau aggregation (67,68), there have been accumulating positive reports using Tau transgenic mice and other systems (e.g. primary neuronal or organotypic slice cultures) that confirm the original observations (70,71). Given this apparent effect of MB on Tau, the compound's use as an AD therapeutic has been evaluated.…”

Methylene Blue Reduces Acute Cerebral Ischemic Injury via the Induction of Mitophagy

“…To identify the potential mechanism by which MB inhibited necrosis, we focused on the effect of MB on mitochondrial structure and function after stroke, considering that the mitochondrion is an important target of MB (50). The observation and scoring of the mitochondrial ultrastructure indicated that the mitochondrial structure was seriously disrupted after stroke, but that MB dramatically ameliorated the disintegration of the mitochondrial structure.…”

Synthesis and Initial Evaluation of YM-08, a Blood-Brain Barrier Permeable Derivative of the Heat Shock Protein 70 (Hsp70) Inhibitor MKT-077, Which Reduces Tau Levels

“…7,11 In cellular models, inhibitors of the ATPase activity of Hsp70 have been shown to favor tau turnover and "re-set" its homeostasis. 12 Moreover, first-generation Hsp70 inhibitors, such as methylene blue (MB), improve learning and memory in mouse models of tauopathy, 13,14 suggesting that this strategy holds promise for the eventual treatment of AD and other tauopathies.…”