The intracellular localisation of ATP13A2 and its possible role in cholesterol and manganese transport

2017-02-22T23:15:52Z (GMT) by Chan, Jianxiong
The pathogenesis of neurodegenerative diseases remains to be fully elucidated and abnormal accumulations of specific metals and macromolecules such as lipid is known to be a factor contributing to it. Recent discovery of loss-of- function mutations in the ATP13A2 gene, which encodes a novel P-type ATPase, has been linked to causing familial Parkinson’s disease. Although the substrate for ATP13A2 is still unclear, it has been reported that expression of ATP13A2 in a Parkinson’s disease model rescues dopaminergic neuron loss caused by α-synuclein over-expression, and also protect yeast from Manganese (Mn) toxicity. On the other hand, Atp13a2 knockout mouse studies showed accumulation of lipofuscin deposits, which may be a result of damaged mitochondria or lysosomes, in these mice. Consistent with that, preliminary experiments from our laboratory showed that an isoform of ATP13A2, interacts with the cholesterol-binding protein NPC2. This present study focuses on gaining more insight on the intracellular localisation of the ATP13A2 and demonstrates its effects on lipids and metals in vivo and in vitro. Chapter 3 demonstrates for the first time that endogenous ATP13A2 is localised in organelles involving in endocytic and exocytotic pathways. It was observed that they are predominantly found in various organelles involved in cholesterol and Mn trafficking. This includes the lysosomes, golgi apparatus, the ER, and mitochondria. Chapter 4 provides a first insight into ATP13A2 functions at an in vivo level using Atp13a2 knockout mice. Findings from this study showed that Atp13a2 knockoutmice had higher level of apoptosis in the cortical regions of the brain. It was also suggested that Atp13a2 can affect intracellular cholesterol and Mn levels in the brain. Similar effects of Atp13a2 on lipid and Mn were also observed in Chapter 5 where its effects on lipid and Mn were examined in greater detail with cell culture. Results indicate that ATP13A2 may facilitate the movement of free cholesterol out of organelles into the cytoplasm and the movement of Mn into mitochondria. In summary, this thesis reveals a possibility that ATP13A2 functions as a transporter for both Mn and cholesterol between organelles involving endocytic and exocytotic pathways. By contributing to the maintenance of correct intracellular distribution and homeostasis of cholesterol and Mn, ATP13A2 could potentially prevent the development of certain neurological disorders.