Abstract Body: Background: The Aryl Hydrocarbon Receptor (AHR) is a ubiquitously expressed transcription factor that regulates the cellular response to external stimuli through the binding of ligands including tryptophan metabolites such as L-Kynurenine (L-Kyn). Alterations in tryptophan metabolic pathways and downregulation of myocardial AHR are associated with cardiac inflammation and fibrosis in experimental heart failure (HF) induced by transverse aortic constriction (TAC). We hypothesized cardiac fibroblast (CFB) AHR and its agonism by L-Kyn prevent the pro-fibrotic and pro-inflammatory activity of CFBs in experimental HF.

Methods and Results: We performed TAC or sham surgery on Ahr -/- mice and WT littermates for 4 weeks and found that Ahr-/- mice showed significantly decreased contractile function measured by echocardiography, and increased collagen deposition in left ventricular histological sections after TAC compared to WT mice. We performed bulk RNA sequencing in sorted CFB (CD31-CD45-MEFSK4+) from Ahr-/- and WT mice. Gene set enrichment analysis showed Ahr -/- CFB had increased expression in pathways for fibroblast activation, chemokine production, and immune cell recruitment.

To investigate the role of L-Kyn agonism of CFB AHR in transformation and contractile function, murine CFB were treated with Transforming Growth Factor β (TGFβ) (100ng/ml) or seeded in collagen discs, in the presence or absence of L-Kyn(100ug/ml). L-Kyn attenuated TGFβ mediated induction of αSMA and collagen 1 protein expression by immunofluorescence and western blot, as well as decreased disc contraction 72h after mechanical activation and release.

The role of AHR agonism by L-Kyn on the pro-inflammatory function of CFB was determined in WT CFB treated with IFNγ (100U/ml) in the presence or absence of L-Kyn. IFNγ induction of chemokines Cxcl9 and Cxcl10, as well as MHC-II surface expression were attenuated by L-Kyn, so was T cell adhesion to CFB in co-culture assays. In contrast, L-Kyn had no effect on the ability of CFB to take up and process antigens, as determined by DQ-Ovalbumin internalization quantified by flow cytometry.

Conclusions: Our results demonstrate that AHR regulates activation and pro-inflammatory signatures in CFB at baseline, and that stimulation of CFB transformation and pro-inflammatory activity is dampened by agonism with L-Kyn. Current studies are aimed at investigating AHR agonism in the context of pressure overload induced HF in CFB reporter mice.