Molecular Neurodegeneration (Aug 2021)

Processing of progranulin into granulins involves multiple lysosomal proteases and is affected in frontotemporal lobar degeneration

  • Swetha Mohan,
  • Paul J. Sampognaro,
  • Andrea R. Argouarch,
  • Jason C. Maynard,
  • Mackenzie Welch,
  • Anand Patwardhan,
  • Emma C. Courtney,
  • Jiasheng Zhang,
  • Amanda Mason,
  • Kathy H. Li,
  • Eric J. Huang,
  • William W. Seeley,
  • Bruce L. Miller,
  • Alma Burlingame,
  • Mathew P. Jacobson,
  • Aimee W. Kao

DOI
https://doi.org/10.1186/s13024-021-00472-1
Journal volume & issue
Vol. 16, no. 1
pp. 1 – 18

Abstract

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Abstract Background Progranulin loss-of-function mutations are linked to frontotemporal lobar degeneration with TDP-43 positive inclusions (FTLD-TDP-Pgrn). Progranulin (PGRN) is an intracellular and secreted pro-protein that is proteolytically cleaved into individual granulin peptides, which are increasingly thought to contribute to FTLD-TDP-Pgrn disease pathophysiology. Intracellular PGRN is processed into granulins in the endo-lysosomal compartments. Therefore, to better understand the conversion of intracellular PGRN into granulins, we systematically tested the ability of different classes of endo-lysosomal proteases to process PGRN at a range of pH setpoints. Results In vitro cleavage assays identified multiple enzymes that can process human PGRN into multi- and single-granulin fragments in a pH-dependent manner. We confirmed the role of cathepsin B and cathepsin L in PGRN processing and showed that these and several previously unidentified lysosomal proteases (cathepsins E, G, K, S and V) are able to process PGRN in distinctive, pH-dependent manners. In addition, we have demonstrated a new role for asparagine endopeptidase (AEP) in processing PGRN, with AEP having the unique ability to liberate granulin F from the pro-protein. Brain tissue from individuals with FTLD-TDP-Pgrn showed increased PGRN processing to granulin F and increased AEP activity in degenerating brain regions but not in regions unaffected by disease. Conclusions This study demonstrates that multiple lysosomal proteases may work in concert to liberate multi-granulin fragments and granulins. It also implicates both AEP and granulin F in the neurobiology of FTLD-TDP-Pgrn. Modulating progranulin cleavage and granulin production may represent therapeutic strategies for FTLD-Pgrn and other progranulin-related diseases.

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