LC3-associated phagocytosis and its potential neuroinflammatory role in Parkinson’s Disease

Abstract

Parkinson’s disease (PD) is a neurodegenerative movement disorder characterised by the
progressive loss of dopaminergic neurons (vmDANs) in the ventral midbrain. Post-mortem
studies have determined that neuroinflammation- orchestrated by glial cells (astrocytes,
microglia)- accompanies PD and that chronic glial reactivity in a pro-inflammatory
environment is a key contributing factor. LC3-associated phagocytosis (LAP) directs
phagocytic cargo to degradative lysosomes using selective components of the autophagy
machinery, and is dependent on the actions of Rubicon. LAP dampens macrophages
inflammation via suppression of pro-inflammatory cytokines (e.g IL-6, IL-1β, CXCL10), with
Rubicon depletion concomitantly causing elevated inflammation. Whilst there is emerging
evidence that glia use LAP to remove axon debris in models of CNS injury, its potential
involvement in neuroinflammatory PD (patho)physiology has not been explored. The current
study used vmDANs, ventral midbrain astrocytes (vmAstros) and midbrain conditioned
microglia (vmMicroglia) derived from human induced pluripotent stem cells to model
neuronal debris clearance and the inflammatory response in PD. As proof of concept, we
showed that vmAstros and vmMicroglia phagocytosed zymosan into LC3+ve LAPosomes.
Additionally, when vmAstros were activated to a pro-inflammatory phenotype characteristic
of PD, the rate of canonical phagocytosis was not influenced by vmAstro reactive status;
however, the number of LC3+ve LAPosomes after LAP induction with zymosan significantly
decreased. This suggests our inflammatory vmAstros were LAP-deficient which could have
important implications to local midbrain pathology. vmDAN fragments were also employed
as physiologically relevant phagocytic cargo to monitor the LAP response in our PD-like
model. However, no pro- or anti-inflammatory response was detected in wild-type or
Rubicon-deficient vmAstros challenged with vmDAN corpses. These results indicate several
amendments to our in vitro model of human neuroinflammation are required to fully
characterise the protective roles of LAP and the consequence of LAP-deficiency in the
ventral midbrain and in the context of PD.

Date of Award	23 Jan 2024
Original language	English
Awarding Institution	University of Bristol
Supervisor	Jon D Lane (Supervisor) & Catherine Nobes (Supervisor)