Regulation of Leucine-Rich Repeat Kinase 2 by inflammation and IL-4

Mutations in Leucine-Rich Repeat protein Kinase 2 (LRRK2) are associated with Parkinson’s disease (PD) and Crohn’s disease (CD), but the regulation of LRRK2 during inflammation remains relatively unexplored. Here we developed a flow cytometry-based assay to assess LRRK2 activity in individual cells and created an EGFP-LRRK2-knock-in reporter mouse to analyse cell-specific LRRK2 expression. Using these tools, we catalogued LRRK2 level and activity in splenic and intestinal tissues. Inflammation increased LRRK2 expression and activity in B-cells, immature neutrophils and immature monocytes, but decreased these in dendritic cells and eosinophils. In mature neutrophils, inflammation stimulated LRRK2 activity but reduced EGFP-LRRK2 level. A kinase-activating PD-associated R1441C-LRRK2 mutation exacerbated inflammation-induced activation of LRRK2 specifically in monocytes and macrophages without affecting LRRK2 levels. Finally, we identified IL-4 as a novel factor that upregulated LRRK2 expression and activity in B-cells in vitro , replicating the inflammatory effects observed in vivo . Our findings provide valuable new insights into the regulation of the LRRK2 pathway in immune cells, crucial for understanding LRRK2 and its therapeutic potential in inflammatory diseases such as CD.