Macrophage LRRK2 activity regulates gut epithelial homeostasis

ABSTRACT Crohn’s disease (CD) pathogenesis includes gene-environment interactions. GWAS have identified >100 CD susceptibility genes. Among the CD susceptibility genes, LRRK2 is of particular interest. It is associated with autophagy regulation and is also a Parkinson disease (PD) susceptibility gene. The same LRRK2 single nucleotide polymorphisms (SNPs) that increase susceptibility to PD and CD (G2019S, N2081D) result in LRRK2 kinase hyperactivity. This is of clinical relevance, as LRRK2-targeted therapies are being developed for PD. Understanding how LRRK2 hyperactivity contribute to CD pathogenesis will broaden therapeutic options for CD. We find that in the gut, LRRK2 is expressed predominantly in phagocytes (e.g., macrophages) instead of epithelial cells. We also find that in hosts without LRRK2 risk SNPs, LRRK2 kinase can be activated by gene-environment interactions involving autophagy gene SNP (ATG16L1 T300A) and cigarette smoking. We previously showed that such T300A-smoking interaction results in functional defects of small intestinal Paneth cells, an epithelial cell type with innate immune function. We find that CD patients harboring LRRK2 risk SNPs, Lrrk2 G2019S mice, and T300A-smoked mice are all prone to develop Paneth cell defects, and this is driven by macrophage LRRK2 hyperactivity. Our data suggests a key role of macrophage LRRK2 kinase activity in gut inflammation. The critical questions that need to be addressed before translating these findings to clinic include how LRRK2 kinase is activated in hosts without LRRK2 SNPs, and whether additional CD susceptibility genes contribute to macrophage LRRK2 kinase hyperactivity. Our long-term goal is to provide mechanistic insight and therapeutic strategies for CD patients. The central hypothesis is that macrophage LRRK2 kinase activity is critical in epithelial homeostasis. Our rationale is that identification of the mechanism(s) to restore proper macrophage LRRK2 levels will offer new therapeutic opportunities for CD. Our specific aims will test the following hypotheses: (1) autophagy deficiency sensitizes macrophages to increased reactive oxygen species production upon cigarette smoking, which then activates LRRK2 kinase; (2) additional CD susceptibility genes also contribute to LRRK2 kinase activation. This contribution is significant since it will establish LRRK2 kinase as a CD therapeutic target. The proposed research is innovative because we investigate how LRRK2 kinase activity is central to maintaining gut homeostasis, a heretofore-unexamined process. We also use state-of-the- art air-liquid interface culture and spatial transcriptomics to identify molecular and cellular targets that affect macrophage LRRK2 kinase activities. Identifying the mechanisms of how LRRK2 regulates a key disease- relevant phenotype will provide insight into other inflammatory disorders.