Genetic modulation of apoptotic pathways fails to alter disease course in tripeptidyl-peptidase 1 deficient mice

Pre-clinical Mouse Models of Neurodegenerative Lysosomal Storage Diseases

There are over 50 lysosomal hydrolase deficiencies, many of which cause neurodegeneration, cognitive decline and death. In recent years, a number of broad innovative therapies have been proposed and investigated for lysosomal storage diseases (LSDs), such as enzyme replacement, substrate reduction, pharmacologic chaperones, stem cell transplantation, and various forms of gene therapy. Murine models that accurately reflect the phenotypes observed in human LSDs are critical for the development, assessment and implementation of novel translational therapies. The goal of this review is to summarize the neurodegenerative murine LSD models available that recapitulate human disease, and the pre-clinical studies previously conducted. We also describe some limitations and difficulties in working with mouse models of neurodegenerative LSDs.

Chronic Enzyme Replacement to the Brain of a Late Infantile Neuronal Ceroid Lipofuscinosis Mouse Has Differential Effects on Phenotypes of Disease

Late infantile neuronal ceroid lipofuscinosis (LINCL) is a fatal inherited neurodegenerative disease caused by loss of lysosomal protease tripeptidyl peptidase 1 (TPP1). We have investigated the effects of chronic intrathecal (IT) administration using enzyme replacement therapy (ERT) to the brain of an LINCL mouse model, in which locomotor function declines dramatically prior to early death. Median lifespan was significantly extended from 126 days to >259 days when chronic IT treatment was initiated before the onset of disease. While treated animals lived longer and showed little sign of locomotor dysfunction as measured by stride length, some or all (depending on regimen) still died prematurely. One explanation is that cerebrospinal fluid (CSF)-mediated delivery may not deliver TPP1 to all brain regions. Morphological studies support this, showing delivery of TPP1 to ventral, but not deeper and dorsal regions. When IT treatment is initiated in severely affected LINCL mice, lifespan was extended modestly in most but dramatically extended in approximately one-third of the cohort. Treatment improved locomotor function in these severely compromised animals after it had declined to the point at which animals normally die. This indicates that some pathology in LINCL is reversible and does not simply reflect neuronal death.

Cell biology of the NCL proteins: What they do and don't do

The fatal, primarily childhood neurodegenerative disorders, neuronal ceroid lipofuscinoses (NCLs), are currently associated with mutations in 13 genes. The protein products of these genes (CLN1 to CLN14) differ in their function and their intracellular localization. NCL-associated proteins have been localized mostly in lysosomes (CLN1, CLN2, CLN3, CLN5, CLN7, CLN10, CLN12 and CLN13) but also in the Endoplasmic Reticulum (CLN6 and CLN8), or in the cytosol associated to vesicular membranes (CLN4 and CLN14). Some of them such as CLN1 (palmitoyl protein thioesterase 1), CLN2 (tripeptidyl-peptidase 1), CLN5, CLN10 (cathepsin D), and CLN13 (cathepsin F), are lysosomal soluble proteins; others like CLN3, CLN7, and CLN12, have been proposed to be lysosomal transmembrane proteins. In this review, we give our views and attempt to summarize the proposed and confirmed functions of each NCL protein and describe and discuss research results published since the last review on NCL proteins. This article is part of a Special Issue entitled: "Current Research on the Neuronal Ceroid Lipofuscinoses (Batten Disease)".

Mouse models of neuronal ceroid lipofuscinoses: useful pre-clinical tools to delineate disease pathophysiology and validate therapeutics

The neuronal ceroid lipofuscinoses (NCL, also known as Batten disease) is a devastating neurodegenerative diseases caused by mutations in either soluble enzymes or membrane-associated structural proteins that result in lysosome dysfunction. Different forms of NCL were defined initially by age of onset, affected population and/or type of storage material but collectively represent the most prevalent pediatric hereditary neurovisceral storage disorder. Specific gene mutations are now known for each subclass of NCL in humans that now largely define the disease: cathepsin D (CTSD) for congenital (CLN10 form); palmitoyl protein thioesterase 1 (PPT1) for infantile (CLN1 form); tripeptidyl peptidase 1 (TPP1) for classic late infantile (CLN2 form); variant late infantile-CLN5, CLN6 or CLN8 for variant late infantile forms; and CLN3 for juvenile (CLN3 form). Several mouse models of NCL have been developed, or in some cases exist sporadically, that exhibit mutations producing a progressive neurodegenerative phenotype similar to that observed in human NCL. The study of these mouse models of NCL has dramatically advanced our knowledge of NCL pathophysiology and in some cases has helped delineate the function of proteins mutated in human NCL. In addition, NCL mutant mice have been tested for several different therapeutic approaches and as such they have become important pre-clinical models for validating treatment options. In this review we will assess the current state of mouse models of NCL with regards to their unique pathophysiology and how these mice have helped investigators achieve a better understanding of human NCL disease and therapy.

Parent-reported benefits of flupirtine in juvenile neuronal ceroid lipofuscinosis (Batten disease; CLN3) are not supported by quantitative data

Juvenile neuronal ceroid lipofuscinosis (JNCL; CLN3 disease; Batten disease) is an autosomal recessive neurodegenerative disease of childhood that typically presents at school age with vision loss followed by progressive cognitive decline, motor dysfunction, seizures, and behavior problems. No therapy has been shown to slow the progression of disease in JNCL patients, and all current treatments are symptomatic. Flupirtine has been shown in vitro to reduce apoptosis in CLN3 lymphocytes. Based on that preclinical study, several children with JNCL were given flupirtine by their parents. The purpose of this study was to determine if there was evidence of attenuated disease progression in any JNCL symptom domain. We administered a survey to parents of JNCL children to qualitatively assess flupirtine efficacy. We used the Unified Batten Disease Rating Scale (UBDRS) to determine specific aspects of disease progression and investigated three age-related factors: loss of independent ambulation, loss of intelligible speech, and loss of ability to perform independent activities of daily living. The median scores for the UBDRS physical, behavior, and capability subscales were determined in flupirtine-exposed subjects and compared to age-, sex-, and genotype-matched subjects who had never taken flupirtine. Twenty-one percent of survey responders reported administering flupirtine to their JNCL child, and 56% of these families perceived beneficial changes that they attributed to flupirtine. However, our quantitative, prospectively obtained data did not show any change in JNCL disease progression that could be attributed to flupirtine. This study highlights the need for prospective experimental therapeutic research.

Therapeutic approaches to the challenge of neuronal ceroid lipofuscinoses

The Neuronal Ceroid Lipofuscinoses (NCLs) are lysosomal storage diseases (LSDs) affecting the central nervous system (CNS), with generally recessive inheritance. They are characterized by pathological lipofuscin-like material accumulating in cells. The clinical phenotypes at all onset ages show progressive loss of vision, decreasing cognitive and motor skills, epileptic seizures and premature death, with dementia without visual loss prominent in the rarer adult forms. Eight causal genes, CLN10/CTSD, CLN1/PPT1, CLN2/TPP1, CLN3, CLN5, CLN6, CLN7/MFSD8, CLN8, with more than 265 mutations and 38 polymorphisms (http://www.ucl.ac.uk/ncl) have been described. Other NCL genes are hypothesized, including CLN4 and CLN9; CLCN6, CLCN7 and possibly SGSH are under study. Some therapeutic strategies applied to other LSDs with significant systemic involvement would not be effective in NCLs due to the necessity of passing the blood brain barrier to prevent the neurodegeneration, repair or restore the CNS functionality. There are therapies for the NCLs currently at preclinical stages and under phase 1 trials to establish safety in affected children. These approaches involve enzyme replacement, gene therapy, neural stem cell replacement, immune therapy and other pharmacological approaches. In the next decade, progress in the understanding of the natural history and the biochemical and molecular cascade of events relevant to the pathogenesis of these diseases in humans and animal models will be required to achieve significant therapeutic advances.