A purine metabolic checkpoint that prevents autoimmunity and autoinflammation.

Still's disease, the paradigm of autoinflammation-cum-autoimmunity, predisposes for a cytokine storm with excessive T lymphocyte activation upon viral infection. Loss of function of the purine nucleoside enzyme FAMIN is the sole known cause for monogenic Still's disease. Here we discovered that a FAMIN-enabled purine metabolon in dendritic cells (DCs) restrains CD4+ and CD8+ T cell priming. DCs with absent FAMIN activity prime for enhanced antigen-specific cytotoxicity, IFNγ secretion, and T cell expansion, resulting in excessive influenza A virus-specific responses. Enhanced priming is already manifest with hypomorphic FAMIN-I254V, for which ∼6% of mankind is homozygous. FAMIN controls membrane trafficking and restrains antigen presentation in an NADH/NAD+-dependent manner by balancing flux through adenine-guanine nucleotide interconversion cycles. FAMIN additionally converts hypoxanthine into inosine, which DCs release to dampen T cell activation. Compromised FAMIN consequently enhances immunosurveillance of syngeneic tumors. FAMIN is a biochemical checkpoint that protects against excessive antiviral T cell responses, autoimmunity, and autoinflammation.

FAMIN Is a Multifunctional Purine Enzyme Enabling the Purine Nucleotide Cycle.

Mutations in FAMIN cause arthritis and inflammatory bowel disease in early childhood, and a common genetic variant increases the risk for Crohn's disease and leprosy. We developed an unbiased liquid chromatography-mass spectrometry screen for enzymatic activity of this orphan protein. We report that FAMIN phosphorolytically cleaves adenosine into adenine and ribose-1-phosphate. Such activity was considered absent from eukaryotic metabolism. FAMIN and its prokaryotic orthologs additionally have adenosine deaminase, purine nucleoside phosphorylase, and S-methyl-5'-thioadenosine phosphorylase activity, hence, combine activities of the namesake enzymes of central purine metabolism. FAMIN enables in macrophages a purine nucleotide cycle (PNC) between adenosine and inosine monophosphate and adenylosuccinate, which consumes aspartate and releases fumarate in a manner involving fatty acid oxidation and ATP-citrate lyase activity. This macrophage PNC synchronizes mitochondrial activity with glycolysis by balancing electron transfer to mitochondria, thereby supporting glycolytic activity and promoting oxidative phosphorylation and mitochondrial H+ and phosphate recycling.

Interleukin-1 Receptor Antagonist Decreases Hypothalamic Oxidative Stress During Experimental Sepsis.

In our previous work, we demonstrated that the intracerebroventricular (i.c.v.) injection of an interleukin-1 receptor antagonist (IL-1ra) prevented the impairment in vasopressin secretion and increased survival rate in septic rats. Additionally, we saw a reduction in nitric oxide (NO) levels in cerebroventricular spinal fluid (CSF), suggesting that the IL-1ra prevents apoptosis that seems to occur in vasopressinergic neurons. Here, we investigated the effect of IL-1ra pre-treatment on the sepsis-induced increase in oxidative stress markers in the hypothalamus of rats. The animals were pre-treated by an i.c.v. injection of IL-1ra (9 nmol) or vehicle (0.01 M PBS) before being subjected to cecal ligation and puncture (CLP) or left as control (sham-operation or naive). After 4, 6, and 24 h, the animals were decapitated (n = 9/group) and the brain removed for hypothalamic tissue collection. Transcript and protein levels of IL-1, inducible nitric oxide synthase (iNOS), caspase-3, and hypoxia-inducible factor 1-alpha (HIF-1α) were measured by quantitative polymerase chain reaction (qPCR) and western blot, respectively. Hypothalamic mRNA levels of all these genes were significantly (P < 0.005) increased at 4, 6, and 24 h CLP, as compared to sham-operated animals. IL-1ra pre-treatment in these CLP animals significantly decreased IL-1 gene expression at all time points and also of iNOS, caspase-3, and HIF-1α at 24 h when compared to vehicle-treated CLP animals. The effect of the pre-treatment on protein expression was most clearly seen for IL-1ß and iNOS at 24 h. Our results showed that blocking the IL-1-IL-1r signaling pathway by central administration of an IL-1ra decreases hypothalamic oxidative stress markers during sepsis.