Processing of progranulin into granulins involves multiple lysosomal proteases and is affected in frontotemporal lobar degeneration
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 show increased PGRN processing to granulin F and an increased activity of AEP, in a region-specific manner.
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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Due to technical limitations, tables 1-2 are only available as downloads in the supplemental files section.
Table 1. PGRN cleavage by lysosomal proteases in vitro
Summary of whether the enzymes tested could cleave progranulin (PGRN) or not along with the potential compartment it may cleave PGRN depending on the pH it processed progranulin in vitro. En, endosomes; Ly, lysosomes; Ex, extracellular.
Table 2. Clinical Information for control and FTLD-TDP-Pgrn subjects
Clinical information for the control and FTLD-TDP-Pgrn subjects. PMI, post-mortem interval; IOC, inferior occipital cortex; MFG, middle frontal gyrus.
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Table 1. PGRN cleavage by lysosomal proteases in vitro Summary of whether the enzymes tested could cleave progranulin (PGRN) or not along with the potential compartment it may cleave PGRN depending on the pH it processed progranulin in vitro. En, endosomes; Ly, lysosomes; Ex, extracellular. Table 2. Clinical Information for control and FTLD-TDP-Pgrn subjects Clinical information for the control and FTLD-TDP-Pgrn subjects. PMI, post-mortem interval; IOC, inferior occipital cortex; MFG, middle frontal gyrus.
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On 16 Jul, 2020
Processing of progranulin into granulins involves multiple lysosomal proteases and is affected in frontotemporal lobar degeneration
Posted 29 Dec, 2020
On 29 Dec, 2020
Received 22 Dec, 2020
Received 21 Dec, 2020
Received 21 Dec, 2020
On 15 Dec, 2020
On 13 Dec, 2020
On 13 Dec, 2020
Invitations sent on 13 Dec, 2020
On 13 Dec, 2020
Received 13 Dec, 2020
On 11 Dec, 2020
On 11 Dec, 2020
On 11 Dec, 2020
On 14 Oct, 2020
Received 12 Oct, 2020
Received 29 Sep, 2020
On 28 Sep, 2020
Received 27 Sep, 2020
On 22 Sep, 2020
On 21 Sep, 2020
Received 20 Sep, 2020
On 16 Sep, 2020
Received 04 Aug, 2020
Invitations sent on 31 Jul, 2020
On 31 Jul, 2020
On 23 Jul, 2020
On 22 Jul, 2020
On 22 Jul, 2020
On 18 Jul, 2020
On 17 Jul, 2020
On 17 Jul, 2020
On 16 Jul, 2020
On 16 Jul, 2020
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 show increased PGRN processing to granulin F and an increased activity of AEP, in a region-specific manner.
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.
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Due to technical limitations, tables 1-2 are only available as downloads in the supplemental files section.
Table 1. PGRN cleavage by lysosomal proteases in vitro
Summary of whether the enzymes tested could cleave progranulin (PGRN) or not along with the potential compartment it may cleave PGRN depending on the pH it processed progranulin in vitro. En, endosomes; Ly, lysosomes; Ex, extracellular.
Table 2. Clinical Information for control and FTLD-TDP-Pgrn subjects
Clinical information for the control and FTLD-TDP-Pgrn subjects. PMI, post-mortem interval; IOC, inferior occipital cortex; MFG, middle frontal gyrus.