Project Summary:
Glycogen metabolism is impaired in >20 individual rare genetic diseases. Several of these diseases are
caused by the formation of insoluble glycogen, which deposits in polyglucosan bodies (PBs). Without
treatment currently available, PB accumulation causes pathology in liver, muscle, heart, and/or brain tissue.
The mechanisms underlying the prevention of pathogenic insoluble glycogen are poorly understood. The PI’s
work with established mouse models of polyglucosan body diseases links both glycogen phosphate and
branching directly to glycogen solubility and imply a functional interdependence of phosphate and branching.
The objective of this proposal is to identify how phosphate covalently linked to glycogen and glycogen
branching impacts glycogen solubility in health and disease, and whether genetic modulation of each factor
can decrease pathogenic PB accumulation in vivo. Utilizing novel in vitro and in vivo approaches, the
proposed work will test the central hypothesis that glycogen phosphorylation and glycogen branching 1) are
interrelated cellular processes that affect the solubility of glycogen, and 2) that when genetically manipulated
can improve the physiological functionality of glycogen.
Aim 1 characterizes the impact of glycogen phosphate, branching, and associated proteome on the
precipitation risk of soluble glycogen in mouse models with insoluble glycogen accumulation. Analyses and
experimental manipulation of these parameters will provide a mechanistic explanation for the structural
changes in soluble glycogen that lead to glycogen insolubility. Aim 2 focuses on the impact and regulation of
phosphorylation during glycogen synthesis, to interrogate glycogen phosphate as part of a GBE1-regulated
protection mechanism of the cell to prevent glycogen insolubility. Aim3 determines the potential of enhanced
branching in the prevention of insoluble glycogen. The impact of branching on glycogen precipitation risk will
be characterized, and a new therapeutic approach for polyglucosan body diseases will be provided. This
proposal uses established mouse models with PB-triggered pathology. In addition, two new mouse lines were
generated, to separately modulate glycogen phosphate and branching in vivo. Combined with state-of-the-art
glycogen biochemistry and proteomics, these new tools provide a unique opportunity to tease apart the
interrelations of glycogen phosphate and branching and their effects on glycogen solubility. The proposed
work can (1) shift the paradigm of glycogen phosphate being detrimental for glycogen solubility to phosphate
as a protection mechanism from glycogen insolubility, (2) reveal regulatory connections between glycogen
branching and phosphorylation, as well as (3) lead to the discovery of unknown glycogen kinases. It will (4) lay
the ground work for new therapeutic approaches for polyglucosan body diseases and (5) provide a better
grasp of vital cellular processes related to glycogen metabolism with implications for several rare diseases.