RAGE signaling in liver progenitor cells affects fibrosis upon liver injury

Persistent liver injury results in abundant cell death and activation of liver progenitor cells (LPCs). The receptor for advanced glycation end products (RAGE) signaling axis is often associated with chronic inflammation-associated tissue damage and plays an essential role in modulating the tumor microenvironment. It functions as a key regulator in LPC activation mediated by damage-associated molecular pattern (DAMP) molecules, such as HMGB1 and S100 proteins that are released by immune and necrotic cells.

In this study, we aim to delineate the functional role and underlying mechanism of RAGE activity in LPC activation in response to inflammation-associated liver injury. R26TomHnf1β-CreER transgenic mice were crossed with RAGE flox/flox (RAGEfl/fl) mice to generate tamoxifen-inducible LPC-specific RAGE knockout mice (RAGEΔLPC). They were exposed to a choline-deficient ethionine-supplemented (CDE) diet for three weeks to induce liver damage. Although RageWT and RageΔLPC mice showed comparable levels of liver injury, inflammation and steatosis upon CDE treatment, ablation of RAGE in LPCs strongly impairs LPC expanding and migratory capacities, which are accompanied by reduction of bridging fibrosis, suggesting that RAGE signaling in LPCs is a mediator of liver fibrosis.

Primary LPCs were isolated from CDE-treated Ragefl/fl C57BL/6 mouse and cultured in vitro. A Rage knockout cell line was established by transient transfection of a Cre recombinase-carrying plasmid. LPCs were stimulated with supernatants from necrotic hepatocytes (necrotic medium) followed by RNA-Seq to identify downstream targets of RAGE-dependent pathways. Stress response, inflammatory and pro-fibrotic pathways, such as TNF, ErbB, TGF-Beta and NF-kB pathways were induced in LPCs upon treatment with necrotic medium. Most interestingly, Hippo signaling, PI3K-Akt signaling and leukocyte transepithelial migration-associated pathways were found to be RAGE-dependent. Moreover, clusters of stem cell renewal-related genes, such as EpCam, Nf2, Bmp4 and Notch1 were deregulated upon ablation of RAGE. Consistent with the RNA-seq results, we demonstrated that ablation of Rage attenuates LPCs organoid-forming ability.

Our recent results implied that RAGE regulates stemness properties of LPCs and is required for LPCs activation in supporting fibrogenesis. Taken together, our data provide a potential mechanistic insight on the role of RAGE in LPCs in association with fibrosis upon chronic liver injury.