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eNeuro. 2017 Aug 18;4(4). pii: ENEURO.0100-17.2017. doi: 10.1523/ENEURO.0100-17.2017. eCollection 2017 Jul-Aug.

Intracellular Proteolysis of Progranulin Generates Stable, Lysosomal Granulins that Are Haploinsufficient in Patients with Frontotemporal Dementia Caused by GRN Mutations.

Author information

1
Department of Pharmacology, Emory University School of Medicine, Atlanta, GA 30322.
2
Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322.
3
Center for Neurodegenerative Disease, Emory University School of Medicine, Atlanta, GA 30322.
4
Department of Neurology, Emory University School of Medicine, Atlanta, GA 30322.

Abstract

Homozygous or heterozygous mutations in the GRN gene, encoding progranulin (PGRN), cause neuronal ceroid lipofuscinosis (NCL) or frontotemporal dementia (FTD), respectively. NCL and FTD are characterized by lysosome dysfunction and neurodegeneration, indicating PGRN is important for lysosome homeostasis in the brain. PGRN is trafficked to the lysosome where its functional role is unknown. PGRN can be cleaved into seven 6-kDa proteins called granulins (GRNs); however, little is known about how GRNs are produced or if levels of GRNs are altered in FTD-GRN mutation carriers. Here, we report the identification and characterization of antibodies that reliably detect several human GRNs by immunoblot and immunocytochemistry. Using these tools, we find that endogenous GRNs are present within multiple cell lines and are constitutively produced. Further, extracellular PGRN is endocytosed and rapidly processed into stable GRNs within lysosomes. Processing of PGRN into GRNs is conserved between humans and mice and is modulated by sortilin expression and mediated by cysteine proteases (i.e. cathpesin L). Induced lysosome dysfunction caused by alkalizing agents or increased expression of transmembrane protein 106B (TMEM106B) inhibit processing of PGRN into GRNs. Finally, we find that multiple GRNs are haploinsufficient in primary fibroblasts and cortical brain tissue from FTD-GRN patients. Taken together, our findings raise the interesting possibility that GRNs carry out critical lysosomal functions and that loss of GRNs should be explored as an initiating factor in lysosomal dysfunction and neurodegeneration caused by GRN mutations.

KEYWORDS:

Alzheimer's disease; Parkinson's disease; amyotophic lateral sclerosis; autophagy; cathepsin L; frontotemporal dementia; granulins; lysosomal storage disease; neurodegeneration; neuroinflammation; neuronal ceroid lipofuscinosis; progranulin

PMID:
28828399
PMCID:
PMC5562298
DOI:
10.1523/ENEURO.0100-17.2017
[Indexed for MEDLINE]
Free PMC Article

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