Abnormally increased surface expression of AMPA receptors in the cerebellum, cortex and striatum of Cln3(-/-) mice

Mutations in the CLN3 gene cause a fatal neurodegenerative disorder, juvenile CLN3 disease. Exploring the cause of the motor coordination deficit in the Cln3(-/-) mouse model of the disease we have previously found that attenuation of AMPA receptor activity in 1-month-old Cln3(-/-) mice significantly improves their motor coordination [20]. To elucidate the mechanism of the abnormally increased AMPA receptor function in Cln3(-/-) mice, we examined the surface expression of AMPA receptors using surface cross-linking in brain slices from 1-month-old wild type (WT) and Cln3(-/-) mice. In surface cross-linked brain samples, Western blotting for AMPA receptor subunits revealed significantly increased surface levels of GluA1 and GluA2 in the cerebellum, and of GluA2 in the cortex and striatum of Cln3(-/-) mice as compared to WT mice. Expression levels of the GluA4 subunit were similar in the cerebellum of WT and Cln3(-/-) mice. While intracellular GluA1 levels in the WT and Cln3(-/-) cerebellum or cortex were similar, the intracellular expression of GluA1 in the Cln3(-/-) striatum was decreased to 56% of the WT level. Our results show a prominent increase in AMPA receptor surface expression in the brain of Cln3(-/-) mice and suggest that CLN3 is involved in the regulation of AMPA receptor surface expression.

A novel mutation af Cln3 associated with delayed-classic juvenile ceroid lipofuscinois and autophagic vacuolar myopathy

Juvenile neuronal-ceroid-lipofuscinosis (JNCL) is a lysosomal storage disease caused by mutations in CLN3. The most frequent mutation is a 1.02-kb deletion that, when homozygous, causes the classical clinical presentation. Patients harboring mutations different than the major deletion show a marked clinical heterogeneity, including protracted disease course with possible involvement of extraneuronal tissues. Cardiac involvement is relatively rare in JNCL and it is usually due to myocardial storage of ceroid-lipofuscinin. Only recently, histopathological findings of autophagic vacuolar myopathy (AVM) were detected in JNCL patients with severe cardiomyopathy. We describe a 35-year-old male showing a delayed-classic JNCL with visual loss in childhood and neurological manifestations only appearing in adult life. He had an unusual CLN3 genotype with an unreported deletion (p.Ala349_Leu350del) and the known p.His315Glnfs*67 mutation. Autophagic vacuolar myopathy was shown by muscle biopsy. At clinical follow-up, moderately increased CPK levels were detected whereas periodic cardiac assessments have been normal to date. Adult neurologists should be aware of protracted JNCL as cause of progressive neurological decline in adults. The occurrence of autophagic vacuolar myopathy necessitates periodic cardiac surveillance, which is not usually an issue in classic JNCL due to early neurological death.

Unbiased Cell-based Screening in a Neuronal Cell Model of Batten Disease Highlights an Interaction between Ca2+ Homeostasis, Autophagy, and CLN3 Protein Function

Abnormal accumulation of undigested macromolecules, often disease-specific, is a major feature of lysosomal and neurodegenerative disease and is frequently attributed to defective autophagy. The mechanistic underpinnings of the autophagy defects are the subject of intense research, which is aided by genetic disease models. To gain an improved understanding of the pathways regulating defective autophagy specifically in juvenile neuronal ceroid lipofuscinosis (JNCL or Batten disease), a neurodegenerative disease of childhood, we developed and piloted a GFP-microtubule-associated protein 1 light chain 3 (GFP-LC3) screening assay to identify, in an unbiased fashion, genotype-sensitive small molecule autophagy modifiers, employing a JNCL neuronal cell model bearing the most common disease mutation in CLN3. Thapsigargin, a sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) Ca(2+) pump inhibitor, reproducibly displayed significantly more activity in the mouse JNCL cells, an effect that was also observed in human-induced pluripotent stem cell-derived JNCL neural progenitor cells. The mechanism of thapsigargin sensitivity was Ca(2+)-mediated, and autophagosome accumulation in JNCL cells could be reversed by Ca(2+) chelation. Interrogation of intracellular Ca(2+) handling highlighted alterations in endoplasmic reticulum, mitochondrial, and lysosomal Ca(2+) pools and in store-operated Ca(2+) uptake in JNCL cells. These results further support an important role for the CLN3 protein in intracellular Ca(2+) handling and in autophagic pathway flux and establish a powerful new platform for therapeutic screening.

The Batten disease gene CLN3 confers resistance to endoplasmic reticulum stress induced by tunicamycin

Mutations in CLN3 gene cause juvenile neuronal ceroid lipofuscinosis (JNCL or Batten disease), an early-onset neurodegenerative disorder that is characterized by the accumulation of ceroid lipofuscin within lysosomes. The function of the CLN3 protein remains unclear and is presumed to be related to Endoplasmic reticulum (ER) stress. To investigate the function of CLN3 in the ER stress signaling pathway, we measured proliferation and apoptosis in cells transfected with normal and mutant CLN3 after treatment with the ER stress inducer tunicamycin (TM). We found that overexpression of CLN3 was sufficient in conferring increased resistance to ER stress. Wild-type CLN3 protected cells from TM-induced apoptosis and increased cell proliferation. Overexpression of wild-type CLN3 enhanced expression of the ER chaperone protein, glucose-regulated protein 78 (GRP78), and reduced expression of the proapoptotic protein CCAAT/-enhancer-binding protein homologous protein (CHOP). In contrast, overexpression of mutant CLN3 or siRNA knockdown of CLN3 produced the opposite effect. Together, our data suggest that the lack of CLN3 function in cells leads to a failure of management in the response to ER stress and this may be the key deficit in JNCL that causes neuronal degeneration.

Hippocampal volumes in juvenile neuronal ceroid lipofuscinosis: a longitudinal magnetic resonance imaging study

BACKGROUND

Juvenile neuronal ceroid lipofuscinosis is an inherited, autosomal recessive, progressive, neurodegenerative disorder of childhood. It belongs to the lysosomal storage diseases, which manifest with loss of vision, seizures, and loss of cognitive and motor functions, and lead to premature death. Imaging studies have shown cerebral and cerebellar atrophy, yet no previous studies evaluating particularly hippocampal atrophy have been published. This study evaluates the hippocampal volumes in adolescent juvenile neuronal ceroid lipofuscinosis patients in a controlled 5-year follow-up magnetic resonance imaging study.

METHODS

Hippocampal volumes of eight patients (three female, five male) and 10 healthy age- and sex-matched control subjects were measured from two repeated magnetic resonance imaging examinations. Three male patients did not have controls and were excluded from the statistics. In the patient group, the first examination was performed at the mean age of 12.2 years and the second examination at the mean age of 17.3 years. In the control group, the mean ages at the time of examinations were 12.5 years and 19.3 years.

RESULTS

Progressive hippocampal atrophy was found in the patient group. The mean total hippocampal volume decreased by 0.85 cm³ during the 5-year follow-up in the patient group, which corresponds to a 3.3% annual rate of volume loss. The whole brain volume decreased by 2.9% per year. The observed annual rate of hippocampal atrophy also exceeded the previously reported 2.4% annual loss of total gray matter volume in juvenile neuronal ceroid lipofuscinosis patients.

CONCLUSIONS

These data suggest that progressive hippocampal atrophy is one of the characteristic features of brain atrophy in juvenile neuronal ceroid lipofuscinosis in adolescence.

A novel c.1135_1138delCTGT mutation in CLN3 leads to juvenile neuronal ceroid lipofuscinosis

Neuronal ceroid lipofuscinosis is the most common childhood neurodegenerative disorder in the world, with an incidence of 1 in 100,000 live births. More than 400 mutations in at least 14 different genes are linked to multiple clinical variants. These progressive genetic disorders primarily manifest in the central nervous system due to an extensive loss of neurons, primarily in the cerebral and cerebellar cortices. Juvenile neuronal ceroid lipofuscinosis is the most common form and is primarily due to mutations in CLN3, which encodes a protein of unknown function. The most common such mutation in CLN3 is a 1.02-kb deletion that results in a frameshift and subsequent premature termination codon. Here we describe a patient with juvenile neuronal ceroid lipofuscinosis who has a novel c.1135_1138delCTGT mutation in CLN3. This deletion induces a frameshift and premature termination codon in CLN3 messenger ribonucleic acid that is likely recognized by nonsense-mediated decay and degraded, subsequently leading to decreased CLN3 protein abundance.

Microglia in juvenile neuronal ceroid lipofuscinosis are primed toward a pro-inflammatory phenotype

Juvenile neuronal ceroid lipofuscinosis (JNCL) is a lysosomal storage disease caused by an autosomal recessive mutation in CLN3. Regions of microglial activation precede and predict areas of neuronal loss in JNCL; however, the functional role of activated microglia remains to be defined. The inflammasome is a key molecular pathway for activating pro-IL-1β in microglia, and IL-1β is elevated in the brains of JNCL patients and can induce neuronal cell death. Here, we utilized primary microglia isolated from CLN3(Δex7/8) mutant and wild-type (WT) mice to examine the impact of CLN3 mutation on microglial activation and inflammasome function. Treatment with neuronal lysates and ceramide, a lipid intermediate elevated in the JNCL brain, led to inflammasome activation and IL-1β release in CLN3(Δex7/8) microglia but not WT cells, as well as increased expression of additional pro-inflammatory mediators. Similar effects were observed following either TNF-α or IL-1β treatment, suggesting that CLN3(Δex7/8) microglia exist in primed state and hyper-respond to several inflammatory stimuli compared to WT cells. CLN3(Δex7/8) microglia displayed constitutive caspase-1 activity that when blocked led to increased glutamate release that coincided with hemichannel opening. Conditioned medium from activated CLN3(Δex7/8) or WT microglia induced significant cell death in CLN3(Δex7/8) but not WT neurons, demonstrating that intrinsically diseased CLN3(Δex7/8) neurons are less equipped to withstand cytotoxic insults generated by activated microglia. Collectively, aberrant microglial activation may contribute to the pathological chain of events leading to neurodegeneration during later stages of JNCL.