Interleukin-1α deficiency attenuates endoplasmic reticulum stress-induced liver damage and CHOP expression in mice

ER stress promotes liver fat accumulation and induction of inflammatory cytokines, which contribute to the development of steatohepatitis. Unresolved ER stress upregulates the pro-apoptotic CHOP. IL-1α is localized to the nucleus in apoptotic cells, but is released when these cells become necrotic and induce sterile inflammation. We investigated whether IL-1α is involved in ER stress-induced apoptosis and steatohepatitis.

We employed WT and IL-1α-deficient mice to study the role of IL-1α in ER stress-induced steatohepatitis.

Liver CHOP mRNA was induced in a time dependent fashion in the atherogenic diet-induced steatohepatitis model, and was twofold lower in IL-1α deficient compared to WT mice. In the ER stress-driven steatohepatitis model, IL-1α deficiency decreased the elevation in serum ALT levels, the number of apoptotic cells (measured as caspase-3-positive hepatocytes), and the expression of IL-1β, IL-6, TNFα, and CHOP, with no effect on the degree of fatty liver formation. IL-1α was upregulated in ER-stressed-macrophages and the protein was localized to the nucleus. IL-1β mRNA and CHOP mRNA and protein levels were lower in ER-stressed-macrophages from IL-1α deficient compared to WT mice. ER stress induced the expression of IL-1α and IL-1β also in mouse primary hepatocytes. Recombinant IL-1α treatment in hepatocytes did not affect CHOP expression but upregulated both IL-1α and IL-1β mRNA levels.

We show that IL-1α is upregulated in response to ER stress and IL-1α deficiency reduces ER stress-induced CHOP expression, apoptosis and steatohepatitis. As a dual function cytokine, IL-1α may contribute to the induction of CHOP intracellularly, while IL-1α released from necrotic cells accelerates steatohepatitis via induction of inflammatory cytokines by neighboring cells.