Tryptophan metabolites suppress Wnt pathway and promote adverse limb events in CKD patients.

Chronic kidney disease (CKD) imposes a strong and independent risk for peripheral artery disease (PAD). While solutes retained in CKD patients (uremic solutes) inflict vascular damage, their role in PAD remain elusive. Here, we show that the dietary tryptophan-derived uremic solute including indoxyl sulfate (IS) and Kynurenine (Kyn), at concentrations corresponding to CKD patients suppressed β-catenin in several cell-types including microvascular endothelial cells (EC), inhibiting Wnt activity and proangiogenic Wnt targets in ECs. Mechanistic probing revealed that these uremic solutes downregulated β-catenin, dependent on serine 33 in its degron motif and through Aryl Hydrocarbon Receptor (AHR). Hindlimb ischemia in adenine-induced CKD and IS solute-specific mice models showed diminished β-catenin and VEGF-A in the capillaries and reduced capillary density, which correlated inversely with blood levels of IS and Kyn and AHR activity in ECs. An AHR inhibitor treatment normalized post-ischemic angiogenic response in CKD mice to a non-CKD level. In a prospective cohort of PAD patients, plasma levels of tryptophan metabolites and plasma's AHR-inducing activity in ECs significantly increased the risk of future adverse limb events. This work uncovers tryptophan metabolites-AHR-β-catenin axis as a mediator of microvascular rarefaction in CKD patients and demonstrates its targetability for PAD in CKD models.