Aggrecan protects against plaque accumulation and is essential for proper microglial responses to plaques.

Alzheimer's disease (AD) is a neurodegenerative disease characterized by amyloid plaques and neurofibrillary tangles. Recent evidence implicates extracellular matrix (ECM) dysfunction in disease pathogenesis, including extensive loss of perineuronal nets (PNNs). PNNs are neuron-ensheathing condensed ECM structures composed of chondroitin sulfate proteoglycans, including the main constituent aggrecan (ACAN). To explore the role of PNNs in AD, we utilize the 5xFAD model and genetically target Acan in Nestin-expressing cells, resulting in loss of ACAN and ablation of the PNN structure. In 5xFAD mice, ACAN cKO results in increased plaque deposition, reduced plaque sphericity, and impaired microglia-plaque association. Single-cell spatial transcriptomics identifies an enhanced disease-associated microglia (DAM) phenotype in 5xFAD ACAN cKO mice, which is accompanied by decreased dystrophic neurite formation. Collectively, our data suggest that PNNs may play a crucial role in mediating the microglial response to plaques.