Pompe disease (PD) is a rare genetic disorder stemming from mutations inactivating the gene encoding acid maltase (GAA), the enzyme responsible for glycogen breakdown within lysosomes. Due to the impairment in these organelles function, PD has been the first described lysosomal storage disease, affecting 1 in 40,000 live births. GAA deficiency leads to pathological glycogen accumulation in several tissues; in the infantile form, this triggers a severe cardiomyopathy that can be successfully reverted by enzyme replacing therapy (ERT). Moreover, both infantile and late onset (LOPD) forms exhibit a severe, ERT resistant and progressive skeletal muscle wasting and weakness that force patients to wheelchairs and mechanical ventilation; to date, respiratory failure is still the main cause of death in LOPD patients even if in treatment.
Studies clarifying the pathogenic cascade guided the optimization of available therapies and the development of next-generation ERT; however, no systematic assessment of lysosomal signaling abnormalities during PD progression has been made due to major technical challenges in the isolation and characterization of functional organelles.
For this reason, we developed an innovative in vivo system crossing GAA KO mice with LysoTag carriers and exploited this model to optimize a robust and reliable protocol for rapid lysosomes immunopurification starting from skeletal muscles, diaphragm and heart.Thanks to this innovative methodology, we captured highly resolved lysosomal signaling events; remarkably, LysoIP proteomics revealed the enrichment of all ten glycolytic enzymes in muscular lysosomal fraction of healthy mice, leading us to hypothesize the existence of glycolysis microdomains on lysosomal surface. To clarify the contribution of this phenomenon to PD pathogenesis, we investigated GAA knockout muscles and found that glucosidase deficient lysosomes exhibit a significantly reduced content of mature lytic enzymes, suggesting that the lack of lysosomal resident glycolysis could impair fundamental cellular processes such as lysosomal function and/or vesicle trafficking in a progressive and tissue dependent manner.
Despite further investigations are needed to mechanistically clarify this evidence, our findings identified a neglected but novel and fundamental cellular phenomenon originating on lysosomal surface that could be a significant breakthrough to bridge fundamental gaps in the comprehension of GAA deficiency pathogenesis.