Immune surveillance of cellular homeostasis by NOD1/2 via sensing cytosolic sphingosine-1-phosphate (S1P)

Chronic inflammation is associated with disruption of cellular homeostasis, yet the underlying mechanisms remain elusive1. Nucleotide-binding oligomerization domain-containing protein 1/2 (NOD1/2) are intracellular pathogen recognition receptors that activate innate immune responses via sensing bacterial peptidoglycans2-4. We demonstrate that NOD1/2 sense not only microbe-specific molecular patterns but also perturbation of cell homeostasis, and thereby cause inflammation. Host generation of sphingosine-1-phosphate (S1P) via the hydrolysis pathway is essential for NOD1/2 signaling upon such stress. Cytosolic delivery of S1P activates NOD1/2 dependent NF-κB activation and inflammation. Finally, we demonstrate that S1P directly binds to and activates NOD1/2. In sum, we describe a hitherto unknown role of NOD1/2 by revealing that they initiate innate immune responses by surveillance of cellular homeostasis through sensing of cytosolic S1P. Our findings provide a novel link between host cytosolic S1P and NOD1/2 mediated immune activation upon perturbation of cellular homeostasis and thus form the basis for future intervention strategies targeting the S1P-NOD1/2 axis. Microarray experiments were performed as single-color hybridizations according the recommendation of Agilent Technologies. Quality control and quantification of total RNA amount was assessed using an Agilent 2100 bioanalyzer (Agilent Technologies), an AATI Fragment Analyzer (Advanced Analytical) and a NanoDrop 1000 spectrophotometer (Kisker).