Altered biometal homeostasis is associated with CLN6 mRNA loss in mouse neuronal ceroid lipofuscinosis

Abstract

SummaryNeuronal ceroid lipofuscinoses, the most common fatal childhood neurodegenerative illnesses, share many features with more prevalent neurodegenerative diseases. Neuronal ceroid lipofuscinoses are caused by mutations in CLN genes. CLN6 encodes a transmembrane endoplasmic reticulum protein with no known function. We characterized the behavioural phenotype of spontaneous mutant mice modeling CLN6 disease, and demonstrate progressive motor and visual decline and reduced lifespan in these mice, consistent with symptoms observed in neuronal ceroid lipofuscinosis patients. Alterations to biometal homeostasis are known to play a critical role in pathology in Alzheimer's, Parkinson's, Huntington's and motor neuron diseases. We have previously shown accumulation of the biometals, zinc, copper, manganese and cobalt, in CLN6 Merino and South Hampshire sheep at the age of symptom onset. Here we determine the physiological and disease-associated expression of CLN6, demonstrating regional CLN6 transcript loss, and concurrent accumulation of the same biometals in the CNS and the heart of presymptomatic CLN6 mice. Furthermore, increased expression of the ER/Golgi-localized cation transporter protein, Zip7, was detected in cerebellar Purkinje cells and whole brain fractions. Purkinje cells not only control motor function, an early symptomatic change in the CLN6 mice, but also display prominent neuropathological changes in mouse models and patients with different forms of neuronal ceroid lipofuscinoses. Whole brain fractionation analysis revealed biometal accumulation in fractions expressing markers for ER, Golgi, endosomes and lysosomes of CLN6 brains. These data are consistent with a link between CLN6 expression and biometal homeostasis in CLN6 disease, and provide further support for altered cation transporter regulation as a key factor in neurodegeneration.

Oral Treatment with CuII(atsm) Increases Mutant SOD1 In Vivo but Protects Motor Neurons and Improves the Phenotype of a Transgenic Mouse Model of Amyotrophic Lateral Sclerosis

“…Early studies showed that higher levels of expressed mutant SOD1 correlate with more rapid onset and progression of disease symptoms in the ALS model mice (Gurney et al, 1994;Wong et al, 1995;Dal Canto and Gurney, 1997). This correlation is substantiated by delayed symptoms in ALS mice due to decreased mutant SOD1 levels (Ralph et al, 2005;Urushitani et al, 2007;Henriques et al, 2010).…”

“…Underscoring this, transgenic mice overexpressing mutant SOD1 develop an ALS-like phenotype that is proportional to the expression level of the mutant SOD1. Higher levels of mutant SOD1 cause earlier disease onset, more severe disease symptoms, and more rapid disease progression (Gurney et al, 1994;Wong et al, 1995;Henriques et al, 2010). However, despite the clear link between motor neuron death and disease symptoms in SOD1-associated forms of ALS, the fundamental basis of SOD1 toxicity in ALS is not fully understood.…”

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

“…In particular, Zn 2ϩ homeostasis is a major focus of current research in other forms of NCL and NCL-Parkinsonism overlap disorders, caused by CLN6 mutation and ATP13A2 mutation, respectively (52)(53)(54). In CLN6 disease models, a major disturbance in intracellular Zn 2ϩ regulation and Ca 2ϩ regulation have been identified (55,56). To date, there is no compelling evidence that CLN3 itself functions as an ion transporter, but this possibility cannot yet be ruled out.…”

Compartmentalized zinc deficiency and toxicities caused by ZnT and Zip gene over expression result in specific phenotypes in Drosophila

“…Lysosomes have been shown to act as a zinc sink, ameliorating toxicity by absorbing excess zinc from the cytosol (Kukic et al, 2013). This process requires lysosome acidification and subsequent exocytosis (Kukic et al, 2014) and can lower toxic cytosolic zinc concentrations in disease states such as neuronal ceroid lipofuscinoses (NCLs, Kanninen et al, 2013) and breast cancer (Lopez et al, 2011). Drosophila CATSUP is the homologue of human Zip7 which has been shown to release zinc from the ER and Golgi (Huang et al, 2005, Taylor et al, 2004.…”