title: Abnormal mannose-6-phosphate receptor trafficking impairs recombinant alpha-glucosidase uptake in Pompe disease fibroblasts.
abstract: BACKGROUND
  Pompe disease (PD) is a metabolic myopathy caused by alpha-glucosidase (GAA) deficiency and characterized by generalized glycogen storage. Heterogeneous GAA gene mutations result in wide phenotypic variability, ranging from the severe classic infantile presentation to the milder intermediate and late-onset forms. Enzyme replacement therapy (ERT) with recombinant human GAA (rhGAA), the only treatment available for PD, intriguingly shows variable efficacy in different PD patients. To investigate the mechanisms underlying the variable response to ERT, we studied cell morphology of PD fibroblasts, the distribution and trafficking of the cation-independent mannose-6-phosphate receptor (CI-MPR) that mediates rhGAA uptake, and rhGAA uptake itself.
  
  
  RESULTS
  We observed abnormalities of cell morphology in PD cells. Electron microscopy analysis showed accumulation of multivesicular bodies and expansion of the Golgi apparatus, and immunolocalization and western blot analysis of LC3 showed activation of autophagy. Immunofluorescence analysis showed abnormal intracellular distribution of CI-MPR in PD fibroblasts, increased co-localization with LC3 and reduced availability of the receptor at the plasma membrane. The recycling of CI-MPR from the plasma membrane to the trans-Golgi network was also impaired. All these abnormalities were more prominent in severe and intermediate PD fibroblasts, correlating with disease severity. In severe and intermediate PD cells rhGAA uptake and processing were less efficient and correction of GAA activity was reduced.
  
  
  CONCLUSIONS
  These results indicate a role for disrupted CI-MPR trafficking in the variable response to ERT in PD and have implications for ERT efficacy and optimization of treatment protocols.
authors.affiliation: Telethon Institute of Genetics and Medicine, Via Castellino, 80131 Naples, Italy. parenti@tigem.it.
authors.forename: Monica
authors.initials: M
authors.lastname: Cardone
authors.forename: Caterina
authors.initials: C
authors.lastname: Porto
authors.forename: Antonietta
authors.initials: A
authors.lastname: Tarallo
authors.forename: Mariella
authors.initials: M
authors.lastname: Vicinanza
authors.forename: Barbara
authors.initials: B
authors.lastname: Rossi
authors.forename: Elena
authors.initials: E
authors.lastname: Polishchuk
authors.forename: Francesca
authors.initials: F
authors.lastname: Donaudy
authors.forename: Generoso
authors.initials: G
authors.lastname: Andria
authors.forename: Maria Antonietta
authors.initials: MA
authors.lastname: De Matteis
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Parenti