Research reportLate onset neurodegeneration in the Cln3−/− mouse model of juvenile neuronal ceroid lipofuscinosis is preceded by low level glial activation
Introduction
The neuronal ceroid lipofuscinoses (NCLs) are a heterogeneous group of at least eight progressive neurodegenerative storage disorders, with onset ranging from infancy to adulthood [9], [21]. These autosomal recessive disorders result from mutations in one of the six different ‘CLN’ genes cloned to date [14], [21]. However, the precise mechanisms by which these mutations result in the devastating effects of these disorders are poorly understood and the therapeutic outlook for affected individuals is uniformly bleak. Juvenile NCL (JNCL) is the result of mutations in the Cln3 gene that codes for a transmembrane protein whose precise function remains unknown [35]. JNCL typically presents first with visual failure between 5 and 7 years of age, followed by progressively more frequent seizures, loss of motor skills, profound cognitive impairment and an early death [14], [21].
Very little detailed quantitative information exists about which parts of the brain are affected in JNCL and until now, these studies have been largely restricted to autopsy material [3], [4], [5], [37]. However, the recent development of Cln3 null mutant mice (Cln3−/−) provides an opportunity to investigate the progressive pathogenesis of the disease [24], [27]. Preliminary analysis of these mice on a mixed strain background revealed characteristic accumulation of autofluorescent storage material and selective pathological changes in populations of GABAergic interneurons [26], a phenotype consistent with mice that model other forms of NCL [2], [9], [10], [25], [27].
In addition to widespread neuronal loss, pronounced gliosis has been described in human NCL autopsy material [3], [4], [18], [19], [20], [36], [37]. Similar reactive changes are evident in mouse models of NCL [2], [9], [10], [17], [25], [27], but very little is known about the relative timing of these events. In contrast, there is an emerging picture of early glial and inflammatory responses that precede acute neurodegeneration in mouse models of other storage disorders [22], [28], [39], prompting us to investigate whether similar events occur in JNCL.
To begin exploring these issues we have undertaken a detailed morphological characterization of Cln3−/− mice and examined the timing and progression of glial activation compared with the onset of neuronal loss. In this study, we report that presymptomatic Cln3−/− mice exhibit significant upregulation of astrocytic and microglial markers at 5 months of age, that is well in advance of the widespread loss of hippocampal interneurons.
Section snippets
Animals
Cln3−/− mice inbred on a 129S6/SvEv background and control (+/+) littermates resulting from heterozygous crosses were used in this study. Appropriately aged animals were perfused as described below and fixed brains shipped to the Pediatric Storage Disorders Laboratory (PSDL), Institute of Psychiatry for histological analysis. All perfusion procedures were carried out in accordance with the NIH Guide for the Care and Use of Laboratory Animals (NIH Publications No. 80-23) and the animal care
Late onset regional atrophy in 129S6/SvEv inbred Cln3−/−
To screen for progressive neurodegenerative changes in 129S6/SvEv inbred Cln3−/− we carried out a stereological survey of regional volume at 5 and 14 months of age. Cln3−/− mice already show significant intracellular accumulation of storage material by 5 months of age [26], a progressive phenotype that is apparent as early as 21 days of age (Mitchison, personal communication). The Cavalieri method [16] was used to obtain unbiased estimates of the volume of the cortical mantle, striatum,
Discussion
This study represents the first detailed neuropathological characterization of 129S6/SvEv inbred Cln3−/− mice. Our data revealed a neurodegenerative phenotype that resembles models of other forms of NCL, including the selective loss of interneuron populations. However, this neurodegenerative phenotype of Cln3−/− had a relatively late onset and was preceded by subtle changes in glial cell populations that are distinct from those seen in other lysosomal storage disorders. These findings raise the
Acknowlegdements
We would like to thank Dr. Robert Nussbaum for his continued support, Stephen Shemilt and Noreen Alexander for their expert advice and the other members of the PSDL for their valuable contributions; Timothy Curran, Andrew Serour, Alfredo Ramirez and David Bernard for skilled technical assistance and Dr. Alison Barnwell for constructive comments on the manuscript. These studies were supported by National Institutes of Health (NIH) grants NS41930 (JDC), NS40580 (DAP), NS44310 (DAP, JDC), UK Royal
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