Brain transcriptome analysis of a CLN2 mouse model as a function of disease progression

Patricia Claudio-Vázquez,Tatiana Gonzalez,Nancy B Schwartz,Wen-Ching Chan,Miriam S Domowicz

doi:10.1186/s12974-021-02302-z

Abstract

BackgroundNeuronal ceroid lipofuscinoses, (NCLs or Batten disease) are a group of inherited, early onset, fatal neurodegenerative diseases associated with mutations in 13 genes. All forms of the disease are characterized by lysosomal accumulation of fluorescent storage material, as well as profound neurodegeneration, but the relationship of the various genes’ function to a single biological process is not obvious. In this study, we used a well-characterized mouse model of classical late infantile NCL (cLINCL) in which the tripeptidyl peptidase 1 (Tpp1) gene is disrupted by gene targeting, resulting in loss of detectable TPP1 activity and leading to progressive neurological phenotypes including ataxia, increased motor deficiency, and early death.MethodsIn order to identify genes and pathways that may contribute to progression of the neurodegenerative process, we analyzed forebrain/midbrain and cerebellar transcriptional differences at 1, 2, 3 and 4 months of age in control and TPP1-deficient mice by global RNA-sequencing.ResultsProgressive neurodegenerative inflammatory responses involving microglia, astrocytes and endothelial cells were observed, accompanied by activation of leukocyte extravasation signals and upregulation of nitric oxide production and reactive oxygen species. Several astrocytic (i.e., Gfap, C4b, Osmr, Serpina3n) and microglial (i.e., Ctss, Itgb2, Itgax, Lyz2) genes were identified as strong markers for assessing disease progression as they showed increased levels of expression in vivo over time. Furthermore, transient increased expression of choroid plexus genes was observed at 2 months in the lateral and fourth ventricle, highlighting an early role for the choroid plexus and cerebrospinal fluid in the disease pathology. Based on these gene expression changes, we concluded that neuroinflammation starts, for the most part, after 2 months in the Tpp1−/− brain and that activation of microglia and astrocytes occur more rapidly in cerebellum than in the rest of the brain; confirming increased severity of inflammation in this region.ConclusionsThese findings have led to a better understanding of cLINCL pathological onset and progression, which may aid in development of future therapeutic treatments for this disease.

Highlights

Neuronal ceroid lipofuscinoses, (NCLs or Batten disease) are a group of inherited, early onset, fatal neu‐ rodegenerative diseases associated with mutations in 13 genes
Global gene changes at different ages Using the classical late infantile NCL (cLINCL) mouse model in which tripeptidyl peptidase 1 (Tpp1) was disrupted by gene targeting, we analyzed the progression of the disease in forebrain/midbrain (F/M) and cerebellum (Cb) by performing
While knowledge is limited of how a neuroinflammation response is initially mounted during neurodegeneration, our findings suggest the choroid plexus (ChPx) is a possible site of origin for the immune surveillance response and/or an initial line of defense by offering increased neuroprotection, at least in NCLs

Summary

Introduction

Neuronal ceroid lipofuscinoses, (NCLs or Batten disease) are a group of inherited, early onset, fatal neu‐ rodegenerative diseases associated with mutations in 13 genes. We used a well-characterized mouse model of classical late infantile NCL (cLINCL) in which the tripeptidyl peptidase 1 (Tpp1) gene is disrupted by gene targeting, resulting in loss of detectable TPP1 activity and leading to progressive neurological phenotypes including ataxia, increased motor deficiency, and early death. NCL incidence is estimated at 2–4 of 100,000 live births [1, 2] and usually is due to autosomal recessive mutations in genes implicated in the lysosomal pathway (13 genes to date) [3, 4] They are classified as lysosomal storage disorders, are pathologically distinguished by unique intracellular fluorescent protein/lipid aggregates consisting of lipofuscin and the different forms are morphologically distinct at the electron microscopy level [3, 5]. These patients, with 5% residual TPP1 activity in fibroblasts, have later disease onset than cLINCL patients (0.4% residual TPP1 activity), develop ataxia and cerebellar atrophy but not blindness or seizures [7]

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