Increased Expression of Lysosomal Enzyme NAGLU Improves Health in Flies
Lysosomes are the destination for excess and damaged proteins and structures in the cell. A lysosome is a membrane-wrapped collection of enzymes capable of breaking down near everything it encounters into the raw materials a cell uses to manufacture new molecular machinery. Lysosomal function is known to decline with age, and improved lysosomal function might be expected to improve long-term health prospects. Here, researchers look at one specific lysosomal enzyme that is known to exhibit higher levels in human centenarians, and find that it improves health in flies. There is extension of life, but the effect size is so small, a few percentage points, that it shouldn't be taken seriously.
To identify new factors that promote longevity and healthy aging, we studied Drosophila CG13397, an ortholog of the human NAGLU gene, a lysosomal enzyme overexpressed in centenarians. We found that the overexpression of CG13397 (dNAGLU) ubiquitously, or tissue specifically, in the nervous system or fat body could extend fly life span. It also extended the life span of flies overexpressing human Aβ42, in a Drosophila Alzheimer's disease (AD) model.
To investigate whether dNAGLU could influence health span, we analyzed the effect of its overexpression on AD flies and found that it improved the climbing ability and stress resistance, including desiccation and hunger, suggesting that dNAGLU improved fly healthspan. We found that the deposition of Aβ42 in the mushroom body, which is the fly central nervous system, was reduced, and the lysosomal activity in the intestine was increased in dNAGLU over-expressing flies.
When NAGLU was overexpressed in human U251-APP cells, which expresses a mutant form of the Aβ-precursor protein (APP), these cells exhibited stronger lysosomal activity and and enhanced expression of lysosomal pathway genes. The concentration of Aβ42 was reduced, and the growth arrest caused by APP expression was reversed, suggesting that NAGLU could play a wider role beyond its catalytic activity to enhance lysosomal activity.
These results also suggest that NAGLU overexpression could be explored to promote healthy aging and to prevent the onset of neurodegenerative diseases, including AD.