Progranulin is Neurotrophic In Vivo and Protects against a Mutant TDP-43 Induced Axonopathy

Angela S Laird,Mieke Timmers,Ludo Van Den Bosch,Wim Robberecht,Philip Van Damme,Louis De Muynck,Annelies Van Hoecke,Mel B Feany

doi:10.1371/journal.pone.0013368

Abstract

Mislocalization, aberrant processing and aggregation of TAR DNA-binding protein 43 (TDP-43) is found in the neurons affected by two related diseases, amyotrophic lateral sclerosis (ALS) and frontotemporal lobe dementia (FTLD). These TDP-43 abnormalities are seen when TDP-43 is mutated, such as in familial ALS, but also in FTLD, caused by null mutations in the progranulin gene. They are also found in many patients with sporadic ALS and FTLD, conditions in which only wild type TDP-43 is present. The common pathological hallmarks and symptomatic cross over between the two diseases suggest that TDP-43 and progranulin may be mechanistically linked. In this study we aimed to address this link by establishing whether overexpression of mutant TDP-43 or knock-down of progranulin in zebrafish embryos results in motor neuron phenotypes and whether human progranulin is neuroprotective against such phenotypes. Mutant TDP-43 (A315T mutation) induced a motor axonopathy characterized by short axonal outgrowth and aberrant branching, similar, but more severe, than that induced by mutant SOD1. Knockdown of the two zebrafish progranulin genes, grna and grnb, produced a substantial decrease in axonal length, with knockdown of grna alone producing a greater decrease in axonal length than grnb. Progranulin overexpression rescued the axonopathy induced by progranulin knockdown. Interestingly, progranulin also rescued the mutant TDP-43 induced axonopathy, whilst it failed to affect the mutant SOD1-induced phenotype. TDP-43 was found to be nuclear in all conditions described. The findings described here demonstrate that progranulin is neuroprotective in vivo and may have therapeutic potential for at least some forms of motor neuron degeneration.

Highlights

The biological role of progranulin (PGRN) is incompletely understood
The axonal shortening induced by grna knockdown was rescued by coexpression of human PGRN mRNA (Figure 2A), indicating that the effect was caused by PGRN deficiency
Real time PCR, following reverse transcription of RNA extracted from 24 hours post fertilization zebrafish embryos injected with PGRN mRNA (250ng/ml), confirmed the presence of human PGRN mRNA following injection (Figure 2B)

Summary

Introduction

The biological role of progranulin (PGRN) is incompletely understood. It has been reported to be involved in development, tumor growth, wound healing and inflammation, but its role in the nervous system remains to be elucidated [1,2,3,4]. Null mutations in the PGRN gene are responsible for about a third of hereditary FTLD, which itself represents about 40% of all FTLD, the second most common form of dementia in patients under 65 years of age [6,7,8]. These mutations produce progranulin haplo-insufficiency, evident by decreased PGRN levels in the cerebrospinal fluid and serum of patients with FTLD caused by PGRN mutations [5,9,10]. Similar TDP-43 containing inclusions are seen in the majority of patients with sporadic FTLD [13]

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Conclusion