Inflammatory stimulus enhances synaptic material uptake by adult APP microglia in a microfluidic neuron-microglia co-culture model.

Microglia play a critical role in synapse remodeling and neuroinflammation, both of which are dysregulated in Alzheimer’s disease (AD). However, most in vitro models rely on neonatal or immortalized microglia, limiting their relevance to adult pathophysiological context. Here, we present a compartmentalized microfluidic co-culture platform that enables spatially controlled interactions between primary cortical neurons and adult microglia from wild-type (WT) and APP-transgenic mice. This system allows precise functional analysis of microglia–synapse interactions under defined inflammatory conditions. Upon lipopolysaccharide (LPS) stimulation, APP microglia exhibited exaggerated morphological responses, elevated IL-1β secretion, and selectively increased uptake of synaptic material. In contrast, internalization of non-specific substrates such as pHrodo™ Zymosan remained unchanged, suggesting substrate-specific microglial responses. Blocking the complement receptor CD11b abolished the LPS-induced increase in synaptic uptake, confirming the role of complement-dependent pathways. Transcriptomic profiling revealed robust inflammatory responses in both genotypes, with genotype-dependent differences in proinflammatory gene expression, consistent with a primed immune phenotype. Importantly, increased synaptic uptake occurred without measurable loss of global synaptic connectivity, highlighting the ability of the system to detect microglial functional changes. This model captures genotype-dependent microglial reactivity under inflammatory stimulus and provides a physiologically relevant, tractable in vitro platform for dissecting microglial contributions to synaptic vulnerability under inflammatory conditions relevant to neurodegenerative diseases.