Abstract
Juvenile Neuronal Ceroid Lipofuscinosis (JNCL) is a lysosomal storage disease caused by an autosomal recessive mutation in CLN3 that leads to vision loss, progressive cognitive and motor decline, and premature death. Morphological evidence of astrocyte activation occurs early in the disease process and coincides with regions where neuronal loss eventually ensues. However, the consequences of CLN3 mutation on astrocyte function remain relatively ill-defined. Astrocytes play a critical role in CNS homeostasis, in part, by their ability to regulate the extracellular milieu via the formation of extensive syncytial networks coupled by gap junction (GJ) channels. In contrast, unopposed hemichannels (HCs) have been implicated in CNS pathology by allowing the non-discriminant passage of molecules between the intracellular and extracellular milieus. Here we examined acute brain slices from CLN3 mutant mice (CLN3Δex7/8) to determine whether CLN3 loss alters the balance of GJ and HC activity. CLN3Δex7/8 mice displayed transient increases in astrocyte HC opening at postnatal day 30 in numerous brain regions, compared to wild type (WT) animals; however, HC activity steadily decreased at postnatal days 60 and 90 in CLN3Δex7/8 astrocytes to reach levels lower than WT cells. This suggested a progressive decline in astrocyte function, which was supported by significant reductions in glutamine synthetase, GLAST, and connexin expression in CLN3Δex7/8 mice compared to WT animals. Based on the early increase in astrocyte HC activity, CLN3Δex7/8 mice were treated with the novel carbenoxolone derivative INI-0602 to inhibit HCs. Administration of INI-0602 for a one month period significantly reduced lysosomal ceroid inclusions in the brains of CLN3Δex7/8 mice compared to WT animals, which coincided with significant increases in astrocyte GJ communication and normalization of astrocyte resting membrane potential to WT levels. Collectively, these findings suggest that alterations in astrocyte communication may impact the progression of JNCL and could offer a potential therapeutic target.
Highlights
Juvenile Neuronal Ceroid Lipofuscinosis (JNCL), or Juvenile Batten Disease, is an autosomal recessively inherited lysosomal storage disorder caused by mutations in the CLN3 gene [1]
Since the fluorescent dyes ethidium bromide (EtBr) and sulforhodamine 101 (SR101), which are commonly used for assessing HC activity and astrocyte identification, respectively [41,48], have overlapping wavelengths, we examined a panel of fluorescent molecules that could be used for astrocyte detection with excitation/emission properties distinct from EtBr
Reactive astrocytes are a hallmark of JNCL in both the human brain and associated mouse models [8,20], yet little information is available regarding the biological impact of astrocytes on disease pathogenesis
Summary
Juvenile Neuronal Ceroid Lipofuscinosis (JNCL), or Juvenile Batten Disease, is an autosomal recessively inherited lysosomal storage disorder caused by mutations in the CLN3 gene [1]. Similar inclusions can occur in the aged brain, commonly referred to as lipofuscin, which can be detected in Alzheimer’s or Parkinson’s disease patients [11,12,13,14] This suggests the possibility of common underlying pathologies between these neurodegenerative disorders, and JNCL presents within the first decade of life, it is notable that these children progress to develop Parkinson-like symptoms that coincide with neuronal loss in the substantia nigra [15]. Evidence is emerging suggesting conserved autophagy and mitochondrial abnormalities associated with NCLs and adult-onset neurodegenerative diseases [16,17] This suggests that studies investigating mechanisms of CNS dysfunction during
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