Kilpatrick, BS; (2015) Connecting Ca2+ Stores and Parkinson Disease. Doctoral thesis , UCL (University College London).

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Abstract

Accumulating evidence implicates lysosomes as mobilisable stores of Ca2+, but their relationship to the better-characterised endoplasmic reticulum (ER) Ca2+ store and significance for disease remains unclear. Here I show that the rapid osmotic permeabilisation of lysosomes evokes prolonged, spatiotemporally complex Ca2+ signals in primary cultured human fibroblasts. These Ca2+ signals comprised an initial response that correlated with lysosomal disruption and secondary long-lasting spatially heterogeneous Ca2+ oscillations that required ER-localised inositol trisphosphate receptors. Pharmacological and molecular inhibition of the trafficking protein Rab7 supressed lysosome induced Ca2+ oscillations. A synthetic agonist, of the endolysosomal ion channel TRPML, also evoked ER-dependent complex Ca2+ signals. Thus, like the Ca2+ messenger NAADP, direct mobilisation of lysosomal Ca2+ stores is sufficient to evoke ER-dependent Ca2+ signals through a mechanism that maybe Rab7-dependent. I also identify Ca2+ defects in fibroblasts from Gaucher disease (GD) and Parkinson disease (PD) patients with mutations in the gene (GBA1) encoding the lysosomal enzyme glucocerebrosidase. ER Ca2+ levels were increased in younger (but not older) patients and associated with enhanced responses to the ryanodine receptor modulator, cyclic ADP-ribose. ER Ca2+ signalling was unaffected by molecular or chemical inhibition of glucocerebrosidase, implicating mis-folded enzyme in pathology. Conversely, lysosomal Ca2+ signals were reduced in GD and PD and associated with disrupted lysosome morphology. Therefore, remodelling of ER-lysosomal Ca2+ stores by pathogenic GBA1 might predispose to PD. Finally, I identify lysosomal morphology defects in fibroblasts from PD patients with a common mutation in the enzyme LRRK2. These defects were reversed by silencing the endolysosomal ion channel, TPC2. Lysosomal pathology was recapitulated in SH-SY5Y cells overexpressing mutant LRRK2 and by an environmental toxin linked to PD. Ca2+ dependent regulation of lysosomal morphology may thus contribute in PD pathology. In summary, Ca2+ stores are functionally connected and their compromised homeostasis might connect to PD pathology. Abstract

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