Elsevier

Neurobiology of Disease

Volume 45, Issue 1, January 2012, Pages 395-408
Neurobiology of Disease

Core features of frontotemporal dementia recapitulated in progranulin knockout mice

https://doi.org/10.1016/j.nbd.2011.08.029Get rights and content

Abstract

Frontotemporal dementia (FTD) is typified by behavioral and cognitive changes manifested as altered social comportment and impaired memory performance. To investigate the neurodegenerative consequences of progranulin gene (GRN) mutations, which cause an inherited form of FTD, we used previously generated progranulin knockout mice (Grn−/−). Specifically, we characterized two cohorts of early and later middle-aged wild type and knockout mice using a battery of tests to assess neurological integrity and behavioral phenotypes analogous to FTD. The Grn−/− mice exhibited reduced social engagement and learning and memory deficits. Immunohistochemical approaches were used to demonstrate the presence of lesions characteristic of frontotemporal lobar degeneration (FTLD) with GRN mutation including ubiquitination, microgliosis, and reactive astrocytosis, the pathological substrate of FTD. Importantly, Grn−/− mice also have decreased overall survival compared to Grn+/+ mice. These data suggest that the Grn−/− mouse reproduces some core features of FTD with respect to behavior, pathology, and survival. This murine model may serve as a valuable in vivo model of FTLD with GRN mutation through which molecular mechanisms underlying the disease can be further dissected.

Highlights

► Characterization of a progranulin knockout mouse model of frontotemporal dementia. ► The mice exhibit reduced social engagement and learning and memory deficits. ► Pathology includes ubiquitination, microgliosis, and reactive astrocytosis. ► Progranulin knockout mice have decreased overall survival compared to wild type. ► These mice reflect key aspects of FTD in terms of behavior, pathology, and survival.

Introduction

Frontotemporal dementia (FTD) represents 5–20% of all dementia cases and is the second most frequent dementia in people under the age of 65 years (Neary et al., 1998). Frontotemporal lobar degeneration (FTLD), the pathology causing FTD, is heterogeneous. Three FTD phenotypes are recognized: behavioral variant FTD (bvFTD), primary progressive aphasia (PPA) and semantic dementia (SD); these are initially characterized by changes in behavior, personality, and language with dementia and parkinsonism appearing late in the disease (McKhann et al., 2001). Behavioral changes include altered social comportment, lack of motivation, withdrawal, and apathy. Memory deficits are manifested by impaired social learning and memory performance. Dominantly inherited FTD comprises 5–10% of all FTD cases, with mutations in the progranulin gene (GRN) accounting for 53% of familial FTD (http://www.molgen.ua.ac.be/FTDMutations). Mutations in the progranulin gene co-segregate with affected individuals in these kindreds and have also been identified in cases of sporadic FTD (Baker et al., 2006, Behrens et al., 2007, Cruts et al., 2006, Gass et al., 2006, Mesulam et al., 2007, Mukherjee et al., 2006). The pathology of FTLD with GRN mutation is characterized by focal atrophy of the frontal and temporal lobes and the striatum is frequently affected. Microscopy reveals the signature lesions of all FTLD entities: neuronal loss, gliosis, and ubiquitin-immunoreactive neuronal inclusions in affected areas. The pathological protein of the ubiquitinated inclusions in FTLD with GRN mutation has been identified as the TAR DNA-binding protein of 43 kDa (TDP-43) and TDP-43-positive aggregates are found at four sites: neuronal cytoplasmic inclusions (NCI), neuronal intranuclear inclusions (NII), dystrophic neurites (DN), and glial cytoplasmic inclusions (GCI) that are negative for tau, α-synuclein, β-amyloid and FUS (Cairns et al., 2007, Mackenzie et al., 2010).

Progranulin is a 593 amino acid precursor protein, which is further processed to 6 kDa active peptides called granulins (Bateman and Bennett, 2009). In the periphery, intact progranulin is a secreted growth factor that causes tumorigenicity when overexpressed and impaired cell growth and proliferation when less abundant (Bateman and Bennett, 2009). Moreover, progranulin and the granulins appear to have opposing effects. Progranulin functions are trophic and anti-inflammatory, whereas the granulins exhibit pro-inflammatory activity (Bateman and Bennett, 2009). However, the physiologic function of progranulin in the CNS or the mechanism by which it leads to neurodegeneration remain open questions. Most progranulin mutations introduce a premature termination codon leading to nonsense-mediated decay with resultant absence of the mutant GRN transcript. This loss of functional GRN implicates a haploinsufficiency mechanism for neurodegeneration (Bateman and Bennett, 2009).

Since the discovery of progranulin mutations in 2006 (Baker et al., 2006, Behrens et al., 2007, Cruts et al., 2006, Gass et al., 2006, Mesulam et al., 2007, Mukherjee et al., 2006), there has been an interest in developing mouse models of progranulin deficiency with the expectation that aspects of the FTD phenotype will be exhibited by the mice. In 2007, the first Grn knockout mice were simply generated by homologous recombination (exons 2–13 removed) and were described by Kayasuga et al. (2007). These Grn knockout mice are born with an expected Mendelian distribution and appear to grow and develop normally. Young 7–11 week old Grn knockout males exhibited enhanced aggressiveness and anxiety (Chiba et al., 2009, Kayasuga et al., 2007). In the current study, we used these mice to investigate the neurodegenerative consequences of GRN mutations. Specifically, we characterized two cohorts of early and later middle-aged wild type (Grn+/+) and knockout (Grn−/−) mice using a battery of tests to assess neurological integrity and behavioral phenotypes analogous to FTD. Furthermore, immunohistochemical approaches were used to ascertain the presence of pathologic lesions characteristic of FTLD. Data presented here suggest that the Grn−/− mouse reproduces some analogous aspects of the FTD behavioral and FTLD pathological phenotypes.

Section snippets

Animals

Progranulin knockout mice (Grn−/−) were previously generated by insertion of the neomycin resistance gene into mouse Grn gene replacing exons 2–13 by homologous recombination (Kayasuga et al., 2007). The colony was expanded and maintained on a C57BL/6 background (Jackson Laboratory, Bar Harbor, ME). Grn−/− and Grn+/+ animals were obtained by mating heterozygote animals. Genomic DNA was obtained by tail biopsy at postnatal day 5 and genotyping was confirmed by polymerase chain reaction assay for

Grn mice breeding, survival, and housing

Grn+/− mice were crossbred to generate Grn+/+, Grn+/−, and Grn−/− at the expected Mendelian distribution of 25, 50, and 25%, respectively. Predicted Mendelian distribution was achieved in the colony. Grn+/+ offspring represented 25% of the pups (n = 38 of 152 pups). Grn+/− offspring represented 49% of the pups (n = 75 of 152 pups). Grn−/− offspring represented 26% of the pups (n = 39 of 152 pups). Differential survival was noted among the genotypes such that Grn+/+ had median survival of 761 days (n = 

Discussion

Our results show that middle-aged and older Grn−/− mice (comparable to the age at onset in FTD (Turnbull et al., 2003)) have a phenotype that qualifies them as a useful model of frontotemporal dementia. Behavioral characteristics of our middle-aged Grn−/− male mice include an absence of elevated aggressiveness in contrast to the presence of hyperaggressiveness reported in juvenile Grn−/− males (Kayasuga et al., 2007). The middle-aged Grn−/− male mice of our colony also exhibited behavioral

Author disclosure information

N. Ghoshal, has participated or is currently participating in clinical trials of antidementia drugs sponsored by: Bristol-Myers Squibb, Elan/Janssen, Eli Lilly, Novartis, Pfizer, and Wyeth; J.T. Dearborn, None; D.F. Wozniak, None; N.J. Cairns, None.

Acknowledgments

We thank Prof. Masugi Nishihara for providing us with the Grn−/− mice, Sara Conyers of the Washington University Animal Behavior Core for assistance with the behavioral testing, Deborah Carter of the Knight ADRC Neuropathology Core Laboratory for histology and immunohistochemistry, and Cathy Roe of the Knight ADRC Biostatistics Core for guidance and supervision of the survival analyses. Support was provided by the National Institute on Aging of the National Institutes of Health: T32-NS007205

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