A Mouse Model of Classical Late-Infantile Neuronal Ceroid Lipofuscinosis Based on Targeted Disruption of the CLN2 Gene Results in a Loss of Tripeptidyl-Peptidase I Activity and Progressive Neurodegeneration

Abstract

Mutations in the CLN2 gene, which encodes a lysosomal serine protease, tripeptidyl-peptidase I (TPP I), result in an autosomal recessive neurodegenerative disease of children, classical late-infantile neuronal ceroid lipofuscinosis (cLINCL). cLINCL is inevitably fatal, and there currently exists no cure or effective treatment. In this report, we provide the characterization of the first CLN2-targeted mouse model for cLINCL. CLN2-targeted mice were fertile and apparently healthy at birth despite an absence of detectable TPP I activity. At ϳ7 weeks of age, neurological deficiencies became evident with the onset of a tremor that became progressively more severe and was eventually accompanied by ataxia. Lifespan of the affected mice was greatly reduced (median survival, 138 d), and extensive neuronal pathology was observed including a prominent accumulation of cytoplasmic storage material within the lysosomal-endosomal compartment, a loss of cerebellar Purkinje cells, and widespread axonal degeneration. The CLN2-targeted mouse therefore recapitulates much of the pathology and clinical features of cLINCL and represents an animal model that should provide clues to the normal cellular function of TPP I and the pathogenic processes that underlie neuronal death in its absence. In addition, the CLN2-targeted mouse also represents a valuable model for the evaluation of different therapeutic strategies.

Determination of the Substrate Specificity of Tripeptidyl-peptidase I Using Combinatorial Peptide Libraries and Development of Improved Fluorogenic Substrates

“…The procedure for measurement of TPP I activity at different pH values was described previously (13). CLN2(Ϫ/Ϫ) mouse specimens were from the gene-targeted model described previously (35).…”

Gene transfer of human acid sphingomyelinase corrects neuropathology and motor deficits in a mouse model of Niemann-Pick type A disease

“…Section 5 contained the cerebellum (i.e., injection site) and brainstem. The right hemisphere was used to quantify brain SPM levels (19) and the left hemisphere was used to determine hASM levels (18).…”

“…Each mouse was tested by accelerating and rocking rotarod for motor function on the Smartrod (AccuScan) using an established protocol (19). Mice that received unilateral injection of AAV-hASM were tested at 7 weeks after treatment (14 weeks of age), whereas mice that received bilateral injections were tested 14 weeks after treatment (20 weeks of age).…”

AAV2-mediated CLN2 gene transfer to rodent and non-human primate brain results in long-term TPP-I expression compatible with therapy for LINCL

“…The recent characterization of a CLN2-deficient mouse, 24 which displays a similar pathology as LINCL in humans will also allow the potential therapeutic benefit of intracranial gene transfer to be assessed more rigorously. There is currently favorable short-term safety data related to the intracranial transfer of AAV2 CU hCLN2 in human patients based upon the growing clinical experience of AAV2-mediated gene transfer to the brain for the treatment of Canavan and Parkinson's diseases.…”

“…The CNS manifestations of LINCL are diffuse, and thus successful gene therapy will need to provide TPP-I activity over as broad a volume of the brain as possible. 1,2 Second, the absence of an experimental animal model for the disease until very recently 24 required that the detection of gene transfer-mediated TPP-I expression is above the background corresponding to normal expression in a naive animal. However, the target level for therapy is only 5% of the endogenous level and the various detection methods for TPP-I are not sensitive enough to detect this amount above the background.…”