5-methoxytryptophan protects against toll-like receptor 2 mediated renal tissue inflammation and fibrosis in a murine unilateral ureteral obstruction model.

Introduction: 5-methoxytryptophan (5-MTP) is an anti-inflammatory metabolite. Several recent reports indicate that 5-MTP protects against post-injury tissue fibrosis. It was unclear how 5-MTP controls tissue fibrosis. We postulated that 5-MTP attenuates renal interstitial fibrosis by blocking toll-like receptor 2 (TLR2) and transforming growth factor β (TGFβ) signaling pathways.

Methods: The effect of 5-MTP on renal fibrosis was evaluated by pretreatment of wild-type UUO mice with intraperitoneal administration of 5-MTP. To determine whether 5-MTP attenuates fibrosis by inhibiting TLR2 and TGFβ signaling pathways, we evaluated the effect of 5-MTP on TLR2-induced fibroblast phenotypic switch in NRK-49F fibroblasts and TLR2 and TGFβ signaling pathways in human proximal tubular epithelial cells (HPTEC) and RAW264.7 macrophages stimulated with Pam3CSK4 (Pam3) or TGFβ1.

Results: UUO-induced renal fibrosis was abrogated in tlr2-/- mice consistent with a crucial role of TLR2 in UUO-induced renal fibrosis. UUO-induced macrophage infiltration and pro-fibrotic cytokine production in renal tissues were suppressed by tlr2 knockout. 5-MTP attenuated renal tissue fibrosis accompanied by reduction of macrophage infiltration and IL-6 and TGFβ levels. 5-MTP inhibits TLR2 upregulation and blocks TLR2-MyD88-TRAF6 signaling pathway in macrophages. Furthermore, 5-MTP blocked Pam3- and TGFβ1-induced phenotypic switch of NRK-49F to myofibroblasts and inhibited Pam3- and TGFβ1-induced signaling pathways in HPTECs and RAW264.7 cells.

Conclusion: 5-MTP effectively protects against UUO-induced renal interstitial fibrosis by blocking TLR2 and TGFβ signaling pathways.