TSC1 controls IL-1β expression in macrophages via mTORC1-dependent C/EBPβ pathway

The tuberous sclerosis complex 1 (TSC1) is a tumor suppressor that inhibits the mammalian target of rapamycin (mTOR), which serves as a key regulator of inflammatory responses after bacterial stimulation in monocytes, macrophages, and primary dendritic cells. Previous studies have shown that TSC1 knockout (KO) macrophages produced increased inflammatory responses including tumor necrosis factor-alpha (TNF-alpha) and IL-12 to pro-inflammatory stimuli, but whether and how TSC1 regulates pro-IL-1 beta expression remains unclear. Here using a mouse model in which myeloid lineage-specific deletion of TSC1 leads to constitutive mTORC1 activation, we found that TSC1 deficiency resulted in impaired expression of pro-IL-1 beta in macrophages following lipopolysaccharide stimulation. Such decreased pro-IL-1 beta expression in TSC1 KO macrophages was rescued by reducing mTORC1 activity with rapamycin or deletion of mTOR. Rictor deficiency has no detectable effect on pro-IL-1 beta synthesis, suggesting that TSC1 positively controls pro-IL-1 beta expression through mTORC1 pathway. Moreover, mechanism studies suggest that mTORC1-mediated downregulation of the CCAAT enhancer-binding protein (C/EBP beta) critically contributes to the defective pro-IL-1 beta expression. Overall, these findings highlight a critical role of TSC1 in regulating innate immunity by control of the mTOR1-C/EBP beta pathway.