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Thesis Format

Alternative Format

Degree

Master of Science

Program

Pathology and Laboratory Medicine

Supervisor

Rupar, Tony

Abstract

Metachromatic leukodystrophy (MLD) is an inherited lysosomal storage disease caused by deficient arylsulfatase A (ARSA) activity, resulting in intra-lysosomal accumulation of sulfatide. Sulfatide is integral for proper maintenance of myelin in the central and peripheral nervous systems. This study characterized mitochondrial morphology, cytokine secretion and phagocytic activity in Schwann and mesenchymal cells isolated from ARSA-/- mice. Cells were treated with different, increasing concentrations of sulfatide for a period of 24 hours. ARSA-/- cells presented with persistent, increased fragmented mitochondrial structures suggestive of prolonged mitochondrial fission. Sulfatide treatments increased secretion of pro-inflammatory cytokines TNF-α and IL-1β in ARSA-/- cells. No differences were noted in the cellular phagocytic capacities following sulfatide treatment. These findings suggest that mitochondrial function is impacted. Further characterization of in vivo mitochondrial function in MLD tissues can provide a clearer pathological picture.

Summary for Lay Audience

Metachromatic leukodystrophy (MLD) is a rare, fatal nervous system disease that mainly affects children. At 1 year of age, children develop difficulties with walking, speech, mental abilities, and vision. MLD is caused by the loss of an enzyme, known as arylsulfatase A (ARSA) that functions in the recycling centers of the cell (known as lysosomes). ARSA breaks down sulfatide, an important lipid that has a role in the development and function of white matter (an insulating tissue that allows nerve signals to travel throughout the body) in the brain and peripheral nerves. In MLD, new sulfatide is constantly made despite the accumulation of sulfatide due to the absence of ARSA. Numerous efforts at correcting this disease have had varied success and only impacted brain-associated symptoms. Destruction of peripheral nerves continued in patients suggesting that sulfatide accumulation has different consequences across tissue and cell types.

Research in diseases like MLD has shown improper lysosomal accumulation causes other cellular organelles to function inappropriately. The collective dysfunction in multiple cellular components is thought to contribute to eventual cell death. Some components examined include mitochondria (cellular energy-producing centers) and immune responses to stress such as cytokine secretion (ability of the cell to release signaling molecules to recruit outside help) and phagocytosis (process used to engulf and degrade abnormal and/or foreign particles). We harvested Schwann and mesenchymal stromal cells from mice that lack ARSA to characterize the impact of sulfatide on cells outside the brain. Cells were treated with increasing amounts of sulfatide, over 24 hours. Unlike healthy cells, MLD cells displayed mitochondria that were small and fragmented. Persistence of fragmented mitochondria for 24 hours is suggestive of irregularities in mitochondrial function. We also noticed that MLD cells release cytokines TNF-α and IL-1β when exposed to sulfatide. We saw no change in the phagocytic ability in sulfatide treated cells. Taken together, these results suggest that mitochondrial function in MLD cells is impacted by sulfatide-induced stress. Going forward, deciphering details of different mechanisms involved in this increased cellular sensitivity as it relates to slower, more progressive accumulation of sulfatide can help us design more effective therapies.

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