Activation of the Ahr–IL-6 Axis by Kynurenic Acid Promotes Bone Marrow-Derived MSC Expansion

Kynurenic acid (KYNA), a small molecule derived from the tryptophan-kynurenine pathway, can readily diffuse across biological membranes and act as an endogenous ligand for receptors such as the aryl hydrocarbon receptor (Ahr). While KYNA dysregulation is implicated in neurodegenerative disorders, the role of the KYNA-Ahr-IL-6 axis in MSC proliferation and differentiation remains poorly defined. We investigated the impact of KYNA on murine bone marrow-derived MSCs (BM-MSCs) at various concentrations (10-200 μM) and time points (8-48 h). The BM-MSC phenotype was assessed via flow cytometry; proliferation, via cell counting; and the gene expression of <i>Ahr</i>, <i>Cyp1a1</i>, <i>Cyp1b1</i>, and <i>Il-6,</i> via quantitative real-time PCR. Multipotency was evaluated through adipogenic, osteogenic, and chondrogenic differentiation assays with histochemical confirmation. KYNA significantly upregulated Ahr mRNA expression. Among the tested concentrations, 100 μM KYNA induced the highest <i>Ahr</i> expression (~19.1 ± 1.5-fold greater than that of the untreated controls, <i>p</i> < 0.005). Notably, 10 and 50 μM KYNA caused moderate induction, whereas compared with 100 μM KYNA, 200 μM did not further increase expression. In addition, KYN treatment increased <i>Cyp1a1</i>, <i>Cyp1b1</i>, and <i>Il-6</i> expression, with increases of ~64.6 ± 4.5-fold, ~43.6 ± 2.3-fold, and ~41.6 ± 1.2-fold, respectively. Compared with no treatment, 100 µM KYNA enhanced BM-MSC proliferation by 1.210 ± 0.02, 1.189 ± 0.03, and 1.242 ± 0.02-fold across passages P3, P4, and P5, respectively (<i>p</i> < 0.05), without altering Sca-1, CD90, or CD45 expression or impairing trilineage differentiation potential. KYNA may activate the AHR-IL-6 signaling axis to promote BM-MSC expansion. This controlled proliferative effect, without loss of phenotypic or functional integrity, highlights the pharmacological potential of KYNA as a small-molecule modulator for stem cell-based therapies.