Exploring the role of IL-1, IL-33, and IL-36 signaling in hepatocytes and metabolic liver disease

Background IL-1, IL-33, and IL-36 are members of the IL-1 family of cytokines, which mediate their effects by heterodimeric receptors made up of a cognate receptor subunit (IL-1R1, IL1RL1/ST2, and IL1RL2 resp.) and the IL-1 receptor accessory protein (IL1RAcP). This study aims to elucidate their effect on hepatocytes and in NAFLD.

Methods Human HepG2 cells and primary hepatocytes were exposed to recombinant human IL-1a/b, IL-33 or IL-36a/b/g protein (≤100ng/ml). Different readouts were assessed after 3, 6 or 18h.

Results IL-1a/b efficiently increased basal IL-1R1 and IL-1RAcP expression in HepG2s at 3–18h. By contrast, we were unable to detect mRNA expression of IL-1RL1 and IL-1RL2 in HepG2s by RT-PCR, and IL-33 and IL-36a/b/g stimulation failed to induce expression of their cognate receptors and IL-1RAcP at the indicated time points. Likewise, only IL-1a/b rapidly increased the expression of RELA (NF-kB p65), pro-inflammatory cytokines, and chemokines (TNF-a, TGF-b, IL-6, IL-8, and CCL2) and induced IL-8 release. Remarkably, in contrast to HepG2s, primary hepatocytes showed an increased mRNA expression of TNF-a and IL-8 following IL-1a/b- and IL-36a/b/g-stimulation, albeit IL1RL2 and IL1RAcP remained unaffected with IL-36 treatment. Oleate treatment of HepG2s, which is less cytotoxic than palmitic acid and strongly steatogenic by upregulating especially SREBP-1 signaling, also increased IL-8 and CCL2 mRNA expression and production.

Conclusion In contrast to IL-33, IL-1a/b and IL-36a/b/g appear to mediate pro-inflammatory transcriptional changes in human hepatocytes. These might amplify the severity of liver disease in NAFLD in concert with fatty acids, which utilize similar pro-inflammatory downstream signaling pathways.

Publikationsverlauf

Artikel online veröffentlicht:
26. Januar 2022