Metabolic status generally affects embryogenesis and lifespan. agl-1, which encodes the single C. elegans glycogen debranching enzyme, is involved in embryogeneis and lifespan. The hypomorphic allele jc11 and the more severe putative null allele tm4809 are both partially penetrant, cold-sensitive, maternal-effect alleles that result in embryonic arrest at various stages. Hatching 'escaper' animals have shortened lifespans and suppress the longer lifespan of daf-2 mutants at 20 deg C, and overexpression of AGL-1::GFP results in lifespan extension. AGL-1 affects embryogenesis through regulation of the energy sensor AMP-activated kinase (AMPK). AMPK is a heterotrimeric protein with a catalytic a subunit encoded by aak-1 or aak-2, and regulatory subunits b (aakb-1, aakb-2) and g (5 genes). The b subunit functions as a glycogen sensor and in one vertebrate system, the b1 subunit interacts directly with glycogen debranching enzyme. Strong binding of AMPK b1 to glycogen was shown to depend on the branch structure; binding in turn functions to inhibit AMPK activity. Loss of agl-1 function is predicted to result in the formation of a 'limit dextrin' glycogen molecule with digestion stalled at branch points, and well-suited to bind to and inhibit AMPK activity. Supporting this model are the observations that AMPK activity is reduced in agl-1 mutants, overexpression of aak-2 or the aakb-1 glycogen-binding domain suppresses agl-1 phenotypes, and compounds thought to activate AMPK, such as metformin and resveratrol also suppress agl-1 phenotypes. Finally, AGL-1 and the AAKB-1 co-immunoprecipitate from worm extracts, suggesting that AGL-1 and AAKB-1 physically interact to regulate energy metabolism and lifespan via glycogen. Dietary supplement with cornstarch (mixed linear and branched polysaccharides) bypasses agl-1 phenotypes, whereas supplement with pure amylopectin (branched polysaccharides alone) not only fails to bypass, but enhances agl-1 phenotypes. Supplement with various mono or di-saccharides does not suppress agl-1 phenotypes. These findings support the hypothesis that branched carbohydrates generally inhibit AMPK activation. Interestingly, dietary supplement with glucose and glycerol dramatically enhance agl-1 phenotypes, increasing penetrance of the most severe agl-1 phenotypes to nearly 100%, even at permissive temperatures. Glycogen levels are higher in glucose supplemented animals, while AMPK inactivation is not further reduced and enhancement of agl-1 by glucose is not suppressed by AMPK overexpression, suggesting there are AMPK-independent metabolic functions for agl-1. Genetic suppressors of glucose-enhanced agl-1 phenotypes have been identified, and will be presented.

Affiliation:
- Rammelkamp Ctr, Cleveland, OH.