Victor GIRARD - Equipe Mollereau

Abstract:

Neurodegenerative disorders are a worldwide leading cause of disability. Several neurodegenerative disorders including Parkinson's disease (PD) are associated with lipid storage dysregulation in the brain. In particular, the storage of lipids in cytoplasmic organelles, called lipid droplets (LDs), has recently emerged as important mechanism of the stress response. Several labs including ours, found that LD accumulation in glia may promote neuronal survival in condition of oxidative stress. Interestingly, in the context of neurodegeneration, neurons can also accumulate LDs. The contribution of neuronal and glial cells LDs to neurodegeneration remains a topic of debate. During my PhD, I investigated the mechanisms and consequences of LD accumulation in neurons and glia in two Drosophila models of PD.

PD is characterized by the accumulation of misfolded alpha-synuclein (aSyn) in neuronal cytoplasmic inclusions. Interestingly, aSyn contains a lipid-binding domain that shares structural similarities with LD-binding proteins such as perilipins and aSyn can bind synthetic LDs in vitro and induces LD accumulation in yeast by a mechanism that remains unclear. I found that expression of aSyn in association with perilipin impairs LD homeostasis leading to accumulation of LDs in Drosophila photoreceptor neurons. Interestingly, I observed that aSyn co-localizes with perilipins on LD surface in both Drosophila photoreceptor neurons and human neuroblastoma cells. I thus proposed that aSyn by associating with perilipins stabilize LDs and by this mean promote LD accumulation. Finally, modulating LD content in photoreceptor impacts aSyn resistance to proteinase K suggesting that LDs are involved in pathological conversion of aSyn.

Glial cells are early sensor of central nervous system injuries that accumulate LDs in response to neuronal stress to protect neurons from damages associated with lipid peroxidation. We found that Split-ends (Spen), an RNA binding protein previously identified as a glial pro-survival factor during development, maintains LD homeostasis in adult glial cell. In addition, expression of Spen was associated with resistance to paraquat-induced neurotoxicity, a pesticide associated with increased risk of PD in human epidemiologic studies. These results suggest that Spen-mediated lipid metabolism functions is important for neuroprotection in PD.

Collectively the results of my thesis provide new evidences for the formation of LDs in both neurons and glial cells and their contribution in the progression of PD pathology.