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Aging, Metabolism, Stress, Pathogenesis, and Small RNAs in C. elegans Topic Meeting 2012
Enhancing N-glycosylation Through Activation of the Hexosamine
Pathway Improves ER Protein Folding Capacity and Slows Ageing.
Nadia Storm, Martin Denzel, Adam Antebi
Max Planck Institute, Cologne, Germany
Organismal ageing is the progressive loss of cellular homeostasis - including protein
homeostasis, which comprises all processes maintaining a functional proteome. The endoplasmic
reticulum (ER) is the site of protein synthesis for all secreted and membrane proteins, and
the ER protein folding fidelity is closely monitored. Proper ER protein folding depends on
chaperones, and requires N-glycosylation of the nascent peptide chain. Insufficient folding
capacity triggers a stress response pathway, termed the unfolded protein response (UPR). The
UPR signaling pathway is critical for normal C. elegans lifespan and for lifespan extension via
the insulin signaling pathway. We hypothesized that improving ER stress resistance might result
in lifespan extension. To identify novel mutations that improve ER protein folding we carried
out a developmental drug resistance screen. After chemical mutagenesis, we selected for
resistance to tunicamycin, which interferes with ER protein folding by inhibiting N-glycosylation.
Next, we analyzed the lifespan of the tunicamycin resistant mutants. We found that increasing
metabolite flux through the hexosamine pathway (HP) by gain-of-function mutations of the
pathway’s key enzyme, glucosamine-fructose 6-phosphate aminotransferase (gfat-1), results
in ER stress resistance and lifespan extension. The HP provides UDP-N-acetylglucosamine
(UDP-GlcNAc) that is required in the first step of N-glycan synthesis, which is inhibited by
tunicamycin. Tunicamycin resistance resulting from GFAT-1 hyperacitvation could be mimicked
by feeding wild type C. elegans with HP intermediates and was DAF-16/FOXO-independent.
GFAT-1 hyperactivation or exposure to UDP-GlcNAc precursors reduced the expression of
UPR target genes during ER stress, as seen in the gain-of-function mutants, suggesting an
elevated threshold for UPR activation resulting from increased folding capacity. Increased HP
metabolite flux further alleviated pathology in nematode models of proteotoxic stress, such as
polyglutamine expansion, a model for Huntington’s disease. These data, together with GFAT-1’s
high degree of conservation makes the HP a potential target for the treatment of age-related
proteotoxic diseases in humans.
Contact: nstorm@age.mpg.de
Lab: Antebi
26
Session 4