Composition and activity of the proteasome in human iPSC-derived neuronal model of early-stage sporadic Alzheimer's disease.

Introduction: The proteasome is a critical cellular degradative machinery impaired in late-stage Alzheimer's disease (AD). However, the status and activity of the proteasome in early-stage sporadic AD (sAD) is unknown. Methods: A cellular model of human early-stage sAD was generated from sAD patient iPSC-derived cortical neurons by dual-SMAD inhibition. The iPSCs, neuroprogenitors, and cortical neurons were validated by the expressions of key markers. The level of total intraneuronal Aβ was measured by ELISA. Composition and native proteolytic activities of the proteasome in control and sAD cortical neurons were measured using complementary fluorogenic probes. Results: Control and sAD patients iPSCs expressed pluripotent markers OCT4, NANOG, and SSEA4 which induced into neuroprogenitors expressing NESTIN and PAX6. The neuroprogenitors terminally differentiated into cortical neurons expressing neuronal markers MAP2 and TUJ1, and cortical layer marker TBR1. The level of intraneuronal Aβ in the sAD cortical neurons was significantly higher compared to control. Control and sAD cortical neurons expressed native 30S, 26S, and 20S proteasome assemblies with the sAD cortical neurons displaying higher 20S assemblies. Increased active 20S assemblies was associated with higher β1, β2, and β5 proteolytic sites activities. Discussion: The significant elevation in the proteolytic activities of the β1, β2, and β5 subunits of 20S proteasome in sAD cortical neurons suggests that this may be a possible compensatory response to elevated intraneuronal Aβ.