Elevated alpha-synuclein attenuates phagocytosis in SNCA triplication human iPSC-derived neuron:microglia co-cultures

Synucleinopathies such as Parkinsons disease (PD) are characterized by pathologic production, aggregation, and cell-to-cell transmission of -synuclein (-syn) protein that results in impaired cellular function. While neurons of the substantia nigra pars compacta express high levels of -synuclein and are highly vulnerable to its aberrant expression or conformation, brain-resident macrophages (microglia) are also sensitive to abnormal -synuclein, with recent reports indicating that elevated levels impair phagocytic ability in vivo and in vitro. To explore the impact of elevated -syn on microglial function we employed a co-culture model containing iPSC-derived neurons and microglia-like cells. iPSCs from healthy control donors and a Parkinsons donor with an allelic triplication of the SNCA gene locus were differentiated into neurons and microglia-like cells. In monoculture, neurons and microglia generated from the SNCA triplication donor expressed higher levels of SNCA transcript and protein. Neurons were found to have significantly greater expression of SNCA compared to microglia, regardless of donor genotype. Co-cultures of neurons and microglia revealed that microglia cultured with SNCA triplication neurons displayed reduction in phagocytosis of fluorescent E. coli, irrespective of microglia donor genotype. SNCA mRNA and protein expression could be reduced with treatment with an antisense oligonucleotide (ASO) targeting SNCA. ASO treatment partially rescued microglia phagocytosis in SNCA triplication co-cultures and in co-cultures containing SNCA triplication neurons and healthy control microglia. Our results complement and extend previous findings of impaired microglial function in the presence of elevated -synuclein in a novel patient-derived co-culture model that utilizes more disease-relevant conditions rather than the relaying on the addition of exogenous -synuclein.