Extracellular Prolyl Oligopeptidase Derived from Activated Microglia is a Potential Neuroprotection Target

Abstract

Prolyl oligopeptidase (PREP) is an abundant peptidase in the brain and periphery, but its physiological functions are still largely unknown. Recent findings point to a role for PREP in inflammatory processes. This study assessed the cellular and extracellular PREP activities in cultures of mouse primary cortical neurons, microglial cells and astrocytes, and immortalized microglial BV‐2 cells under neuroinflammatory conditions induced by lipopolysaccharide (LPS) and interferon gamma (IFNγ). Furthermore, we evaluated the neuroprotective effect of a specific PREP inhibitor, KYP‐2047, in a neuroinflammation model based on a coculture of primary cortical neurons and activated BV‐2 cells. The inflammatory insult reduced intracellular and increased extracellular PREP activity specifically in microglial cells, suggesting that activated microglia excretes active PREP. A targeted proteomics approach revealed up‐regulation in PREP protein levels in BV‐2 cell growth medium but down‐regulation in crude membrane‐bound PREP after LPS+IFNγ. In the coculture of BV‐2 cells and primary neurons, an increase in extracellular PREP activity was also detected after inflammation. KYP‐2047 (10 μmol/L) significantly protected neurons against microglial toxicity and reduced the levels of the pro‐inflammatory cytokine tumour necrosis factor alpha. In conclusion, these data point to an extracellular role for microglial PREP in the inflammatory process. Inhibition of PREP during neuroinflammation is a potential target for neuroprotection. Thus, PREP inhibitors may offer a novel therapeutic approach for the treatment of neurodegenerative disorders with an inflammatory component including Parkinson's and Alzheimer's diseases.