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 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 paralogues 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 synchronises mitochondrial activity with glycolysis by balancing electron transfer to mitochondria, thereby supporting glycolytic activity and promoting oxidative phosphorylation and mitochondrial H+ and phosphate recycling.Includes ERC. Wellcome Trust and MRC

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 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 paralogues 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 synchronises mitochondrial activity with glycolysis by balancing electron transfer to mitochondria, thereby supporting glycolytic activity and promoting oxidative phosphorylation and mitochondrial H+ and phosphate recycling.Includes ERC. Wellcome Trust and MRC

FAMIN in dendritic cells biochemically restrains T cell priming

FAMIN is a purine nucleoside enzyme that was first identified in genome-wide association studies (GWAS) as increasing risk for Crohn’s disease (CD). Defects in the enzyme that result in loss of catalytic activity are the only known monogenic cause of Still’s disease, a severe autoinflammatory condition that predisposes for the risk of developing macrophage activation syndrome (MAS). MAS can be triggered by common viral infections and result in hyperactivation of T lymphocytes. The work presented in this thesis builds on the discovery that FAMIN-sufficient mice are protected against influenza A infection, with dendritic cell (DC)- dependent excessive activation of CD8+ T cell responses in their FAMIN-deficient counterparts. Loss of FAMIN activity in DCs was shown to result in increased priming of both CD4+ and CD8+ T cells both in vitro and in vivo, resulting in enhanced antigen-specific cytotoxicity, IFNg secretion, and T cell expansion. Here, we discovered that FAMIN controls the pace of membrane trafficking and DC antigen processing to restrain T cell priming via a cytosolic NADH/ NAD+-dependent mechanism. We describe wide-reaching metabolic defects resulting from loss of FAMIN activity, including in the core pathways of glycolysis and TCA cycle activity, as well as upstream changes in glucose, fatty acid and amino acid metabolism. Notably, depressed rates of glycolysis and oxidative phosphorylation DCs lacking FAMIN function were not responsible for increased T cell priming capacity. Instead, we find that FAMIN balances flux through adenine-guanine nucleotide interconversion cycles to maintain the cytosolic NADH/ NAD+ ratio. We found that FAMIN additionally regulates T cell priming by DCs directly through the enzyme’s purine nucleoside phosphorylase (PNP) activity, converting exogenous hypoxanthine to inosine that acts on the T cell adenosine 2A receptor (A2AR). In summary, FAMIN is a multifunctional purine nucleoside enzyme enabling flux through purine interconversion pathways highly integrated with cytoplasmic and mitochondrial metabolism. In DCs, FAMIN acts as a biochemical checkpoint to restrain T cell priming and prevent autoimmunity and autoinflammation

Medical and cardio-vascular emergency department visits during the COVID-19 pandemic in 2020: is there a collateral damage? A retrospective routine data analysis

Background In this retrospective routine data analysis, we investigate the number of emergency department (ED) consultations during the COVID-19 pandemic of 2020 in Germany compared to the previous year with a special focus on numbers of myocardial infarction and acute heart failure. Methods Aggregated case numbers for the two consecutive years 2019 and 2020 were obtained from 24 university hospitals and 9 non-university hospitals in Germany and assessed by age, gender, triage scores, disposition, care level and by ICD-10 codes including the tracer diagnoses myocardial infarction (I21) and heart failure (I50). Results A total of 2,216,627 ED consultations were analyzed, of which 1,178,470 occurred in 2019 and 1,038,157 in 2020. The median deviation in case numbers between 2019 and 2020 was - 14% [CI (- 11)-(- 16)]. After a marked drop in all cases in the first COVID-19 wave in spring 2020, case numbers normalized during the summer Thereafter starting in calendar week 39 case numbers constantly declined until the end of the year 2020. The decline in case numbers predominantly concerned younger [- 16%; CI (- 13)-(- 19)], less urgent [- 18%; CI (- 12)-(- 22)] and non-admitted cases [- 17%; CI (- 13)-(- 20)] in particular during the second wave. During the entire observation period admissions for chest pain [- 13%; CI (- 21)-2], myocardial infarction [- 2%; CI (- 9)-11] and heart failure [- 2%; CI (- 10)-6] were less affected and remained comparable to the previous year. Conclusions ED visits were noticeably reduced during both SARS-CoV-2 pandemic waves in Germany but cardiovascular diagnoses were less affected and no refractory increase was noted. However, long-term effects cannot be ruled out and need to be analysed in future studies. [GRAPHICS]