Disease correction by AAV-mediated gene therapy in a new mouse model of mucopolysaccharidosis type IIID

Abstract

Gene therapy is a promising therapeutic alternative for Lysosomal Storage Disorders (LSD), as it is not necessary to correct the genetic defect in all cells of an organ to achieve therapeutically significant levels of enzyme in body fluids, from which non-transduced cells can uptake the protein correcting their enzymatic deficiency. Animal models are instrumental in the development of new treatments for LSD. Here we report the generation of the first mouse model of the LSD Muccopolysaccharidosis Type IIID (MPSIIID), also known as Sanfilippo syndrome type D. This autosomic recessive, heparan sulphate storage disease is caused by deficiency in N-acetylglucosamine 6-sulfatase (GNS). Mice deficient in GNS showed lysosomal storage pathology and loss of lysosomal homeostasis in the CNS and peripheral tissues, chronic widespread neuroinflammation, reduced locomotor and exploratory activity and shortened lifespan, a phenotype that closely resembled human MPSIIID. Moreover, treatment of the GNS-deficient animals with GNS-encoding adeno-associated viral (AAV) vectors of serotype 9 delivered to the cerebrospinal fluid completely corrected pathological storage, improved lysosomal functionality in the CNS and somatic tissues, resolved neuroinflammation, restored normal behaviour and extended lifespan of treated mice. Hence, this work represents the first step towards the development of a treatment for MPSIIID.

Molecular Bases of Neurodegeneration and Cognitive Decline, the Major Burden of Sanfilippo Disease

“…The same areas also showed extensive astrocytosis revealed by staining with antibodies against GFAP [76]. Astrogliosis and microgliosis have also been described in mouse models of other subtypes of MPS III [67][68][69]73,74,[77][78][79][80][81][82]95].…”

“…Similar symptoms were detected when the mice were cross-bred to a congenic C57Bl/6 genetic background [64], as well as in a knockout MPS IIIB mouse [65], and a knockout model of MPS IIIC [66], though the age at which this became apparent varied. All mouse models showed storage of GAGs in the CNS as well as in peripheral organs such as the liver, kidney and spleen [63][64][65][66][67][68][69]. Motor deficits such as gait abnormalities, reduced grip strength or decreased performance in the rocking rotarod test were found in models of MPS IIIA [64,67,70] and MPS IIIB [71], mainly in older mice, recapitulating the human disease.…”

“…Several mouse models developed hepatosplenomegaly as the disease progressed [63,67,68]. Most mouse models had a lifespan of approximately 7-12 months [63][64][65][66], but some lived longer; a mouse model of MPS IIID survived to a median age of 16 months [69] and a gene-targeted model of MPS IIIC survived to a median age of 21 months [68]. It is possible, however, that incomplete gene targeting resulting in higher residual HGSNAT and GNS levels could explain the mild phenotype observed in the latter studies.…”

Pre-clinical Mouse Models of Neurodegenerative Lysosomal Storage Diseases

“…A Gns (−/−) mouse was generated exhibiting similar symptomology to the human disease, such as widespread neuroinflammation, reduced locomotion, and a decrease in lifespan. AAVmediated GT of GNS to the cerebrospinal fluid in this mouse model ameliorated disease pathology, resolving lysosomal storage, neuroinflammation and behavioral phenotypes (Roca et al, 2017).…”

How close are we to therapies for Sanfilippo disease?

“…This, however, raises questions about safety of the treatment. Finally, very recent work has demonstrated the first attempt to test gene therapy in the novel animal model of MPS IIID (Roca et al 2017 ). Following administration of the AAV9-derived vector bearing the GNS gene to the cerebrospinal fluid of MPS IIID mice, particularly encouraging results were obtained, including normalization of GAG storage, reduction of neuro-inflammation, and correction of behavior.…”