A novel mouse model of a patient mucolipidosis II mutation recapitulates disease pathology [Neurobiology]

August 8th, 2014 by Paton, L., Bitoun, E., Kenyon, J., Priestman, D. A., Oliver, P. L., Edwards, B., Platt, F. M., Davies, K. E.

Mucolipidosis II (MLII) is a lysosomal storage disorder caused by loss of N-acetylglucosamine-1-phosphotransferase which tags lysosomal enzymes with a mannose 6-phosphate marker for transport to the lysosome. In MLII the loss of this marker leads to deficiency of multiple enzymes and non-enzymatic proteins in the lysosome leading to the storage of multiple substrates. Here we present a novel mouse model of MLII homozygous for a patient mutation in the GNPTAB gene. Whilst the current gene knock-out mouse model of MLII lacks some of the characteristic features of the human disease, our novel mouse model more fully recapitulates the human pathology showing growth retardation, skeletal and facial abnormalities, increased circulating lysosomal enzymatic activities, intracellular lysosomal storage and reduced life span. Importantly, MLII behavioural deficits are characterized for the first time, including impaired motor function and psychomotor retardation. Histological analysis of the brain revealed progressive neurodegeneration in the cerebellum with severe Purkinje cell loss as the underlying cause of the ataxic gait. In addition, based on the loss of Niemann Pick type C (Npc) 2 protein expression in the brain, the mice were treated with 2-hydroxypropyl-β-cyclodextrin, a drug previously reported to rescue Purkinje cell death in a mouse model of NPC disease. No improvement in brain pathology was observed. This indicates that cerebellar degeneration is not primarily triggered by loss of Npc2 function. This study emphasizes the value of modelling MLII patient mutations to generate clinically relevant mouse mutants to elucidate the pathogenic molecular pathways of MLII and address their amenability to therapy.