Knockdown of interleukin-1α does not attenuate LPS-induced production of interleukin-1β in mouse macrophages

IL-1 alpha and IL-1 beta are synthesized as 31 kDa cell-associated precursors following TLR-4 stimulation, but their processing to the mature form and secretion require a second intracellular stimulus. The unique localization of the precursor of IL-1 alpha (pro-IL-1 alpha) to the nucleus suggested a role in transcriptional regulation of inflammatory cytokines. We explored the hypothesis that pro-IL-1 alpha is involved in regulation of IL-1 beta expression following TLR-4 stimulation. IL-1 beta mRNA and protein levels were specifically decreased in macrophages from IL-1 alpha-deficient mice following TLR-1/2, TLR-4 or TLR-9 stimulation, supporting the hypothesis. However, activation of the main upstream regulators of IL-1 beta expression, IRF3, NFU and p38/JNK, were not reduced in macrophages from IL-1 alpha-deficient mice. In order to assess the specific role of IL-1 alpha in macrophages, we generated mice with myeloid cell deficiency of IL-1 alpha (LyzMCre-loxp). Despite over 90% knockdown of IL-1 alpha, TLR-4 stimulated macrophages from LyzMCreloxp mice did not produce lower levels of IL-1 beta compared to IL-1 alpha-loxp-flanked mice. In order to overcome the possibility that effects are caused by the incomplete deficiency of IL-1 alpha, we generated new whole-body IL-1 alpha knockout mice (GeneralCre-IL-1 alpha) and the findings were similar to myeloid cell-deficient IL-1 alpha. Collectively, our findings do not support the previously suggested role of nuclear IL-la in gene regulation of IL-1 beta. Rather, they suggest that IL-1 alpha acts mainly as an alarmin that is sequestered in the nucleus following stimulation with TLR-4. (c) 2015 Elsevier Ltd. All rights reserved.