Linking endo-lysosomal pH, sterol, and trafficking to neurodegenerative disease

Although endo-lysosomal abnormalities have been recognized as a pathognomonic feature of Alzheimer's disease, the lack of druggable targets has hampered the translation from bench to bedside. This article provides an overview of the insights gained from yeast research with a focus on understudied luminal acidification mechanisms and their major impact on disease progression. The yeast-to-human discovery and validation strategy identified a "druggable" triad featuring luminal pH, sterol content, and trafficking that (dys)regulate reciprocally. Endosomal Na+/H+ exchangers (eNHE), discovered in yeast and later described in mammals, provide independent support for this pathogenic model. The brain is often the most severely affected organ in patients with eNHE mutations, and a subset is causally linked to progressive and severe neurodegeneration, demonstrating that neurons heavily rely on fine-tuning of endosomal pH. We present recent advances on the role of eNHE in ageing related neurodegenerative diseases, which has implications for pathogenesis and therapy. Future studies should unravel the broader landscape of endo-lysosomal pH in neurodegenerative diseases. Given that pharmacologic correction of luminal hyperacidification defect completely ameliorates endo-lysosomal deficits in eNHE deletion yeast, there is compelling reason to believe that efforts to target endo-lysosomal acid-base homeostasis will eventually lead to novel therapeutic approaches for neurodegenerative diseases.