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.

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An unbiased LC-MS screen reveals FAMIN as a purine nucleoside enzyme

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FAMIN combines adenosine phosphorylase with ADA-, PNP-, and MTAP-like activities

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FAMIN enables a purine nucleotide cycle (PNC) preventing cytoplasmic acidification

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The FAMIN-dependent PNC balances the glycolysis-mitochondrial redox interface

GPR35 promotes glycolysis, proliferation, and oncogenic signaling by engaging with the sodium potassium pump

The sodium potassium pump (Na/K-ATPase) ensures the electrochemical gradient of a cell through an energy-dependent process that consumes about one-third of regenerated ATP. We report that the G protein-coupled receptor GPR35 interacted with the α chain of Na/K-ATPase and promotes its ion transport and Src signaling activity in a ligand-independent manner. Deletion of Gpr35 increased baseline Ca²⁺ to maximal levels and reduced Src activation and overall metabolic activity in macrophages and intestinal epithelial cells (IECs). In contrast, a common T108M polymorphism in GPR35 was hypermorphic and had the opposite effects to Gpr35 deletion on Src activation and metabolic activity. The T108M polymorphism is associated with ulcerative colitis and primary sclerosing cholangitis, inflammatory diseases with a high cancer risk. GPR35 promoted homeostatic IEC turnover, whereas Gpr35 deletion or inhibition by a selective pepducin prevented inflammation-associated and spontaneous intestinal tumorigenesis in mice. Thus, GPR35 acts as a central signaling and metabolic pacesetter, which reveals an unexpected role of Na/K-ATPase in macrophage and IEC biology.

Recent advances in inflammatory bowel disease: mucosal immune cells in intestinal inflammation

The intestine and its immune system have evolved to meet the extraordinary task of maintaining tolerance to the largest, most complex and diverse microbial commensal habitat, while meticulously attacking and containing even minute numbers of occasionally incoming pathogens. While our understanding is still far from complete, recent studies have provided exciting novel insights into the complex interplay of the many distinct intestinal immune cell types as well as the discovery of entirely new cell subsets. These studies have also revealed how proper development and function of the intestinal immune system is dependent on its specific microbiota, which appears to have evolutionarily co-evolved. Here we review key immune cells that maintain intestinal homeostasis and, conversely, describe how altered function and imbalances may lead to inflammatory bowel disease (IBD). We highlight the latest developments within this field, covering the major players in IBD including intestinal epithelial cells, macrophages, dendritic cells, adaptive immune cells, and the newly discovered innate lymphoid cells, which appear of characteristic importance for immune function at mucosal surfaces. We set these mucosal immune pathways in the functional context of IBD risk genes where such insight is available. Moreover, we frame our discussion of fundamental biological pathways that have been elucidated in model systems in the context of results from clinical trials in IBD that targeted key mediators secreted by these cells, as an attempt of 'functional' appraisal of these pathways in human disease.

Inverse regulation of plasticity-related immediate early genes by calcineurin in hippocampal neurons

In the mammalian hippocampus, changes in the expression of immediate early genes (IEGs) is thought to contribute to long term plastic changes in neurons brought about by learning tasks and high frequency stimulation of synapses. The phosphatase calcineurin has emerged as an important negative regulator of hippocampus-dependent learning and long term potentiation. Here we investigated the possibility that the constraining action of calcineurin on hippocampal plasticity is mediated in part by regulation of gene expression through negative control of transcription factors, such as cAMP-response element (CRE)-binding protein (CREB). We assessed the effect of calcineurin inhibitors on CREB activation by neuronal activity and show that calcineurin activity is in fact required for CREB-mediated gene expression. However, inhibition of calcineurin had disparate effects on the transcriptional induction of CREB-dependent IEGs. We find that the IEG c-fos is unaffected by suppression of calcineurin activity, the plasticity-related genes Egr1/Zif268 and Egr2/Krox-20 are up-regulated, and genes encoding the orphan nuclear hormone receptors Nor1 and Nur77 are down-regulated. We further show that the up-regulation of particular IEGs is probably due to the presence of serum response elements (SREs) in their promoters, because SRE-mediated gene expression is enhanced by calcineurin blockers. Moreover, expression of the c-fos gene, which is unaffected by calcineurin inhibitors, could be down-regulated by mutating the SRE. Conversely, SRE-mediated c-fos induction in the absence of a functional CRE was enhanced by calcineurin inhibitors. Our experiments thus implicate calcineurin as a negative regulator of SRE-dependent neuronal genes.

A genome scan in a single pedigree with a high prevalence of multiple sclerosis

BACKGROUND

Multiple sclerosis (MS) is a disease that is widely believed to be autoimmune in nature. Genetic-epidemiological studies implicate susceptibility genes in the pathogenesis of MS, although non-MHC susceptibility linkages have been difficult to confirm. Insight into pathways that are intrinsic to other complex diseases has come from the genetic analysis of large, autosomal-dominant kindreds. Here, we present a genetic study of a large and unique kindred in which MS appears to follow an autosomal-dominant pattern of inheritance, with consistent penetrance in four generations.

METHODS

Eighty-two individuals of this 370-member family were genotyped with 681 microsatellite markers spanning the genome, with an average spacing of 5.3 cM.

RESULTS

Parametric linkage analysis was performed and no significant LOD score (LOD >3.3) was observed. For a rare dominant disease model with reduced penetrance, 99.6% of the genome was excluded at a LOD score <-1 and 96% at a LOD score <-2. The HLA-DRB1 candidate gene was also genotyped by allele-specific methods. In each instance where at least one parent was positive for HLA-DRB1*15, one or more HLA-DRB1*15 alleles were transmitted to the affected offspring (11/11). HLA-DRB1*15 was transmitted equally from both the familial and the married-in parents and therefore this locus does not appear to be an autosomal-dominant acting gene in this family but an important modifier of risk.

CONCLUSIONS

These results further stress the importance of the HLA-DRB1*15-bearing haplotype in determining MS susceptibility. Furthermore, this study highlights the complexity of MS genetics, even in the presence of a single family, seemingly segregating MS as an autosomal-dominant trait.

Multiple sclerosis susceptibility and the X chromosome

Multiple sclerosis (MS) is a chronic autoimmune complex trait with strong evidence for a genetic component. A female gender bias is clear but unexplained and a maternal parent-of-origin effect has been described. X-linked transmission of susceptibility has been previously proposed, based on pedigree, association and linkage studies. We genotyped 726 relative pairs including 552 affected sib-pairs for 22 X-chromosome microsatellite markers and a novel dataset of 195 aunt-uncle/niece-nephew (AUNN) affected pairs for 18 markers. Parent-of-origin effects were explored by dividing AUNN families into likely maternal and paternal trait transmission. For the sib-pair dataset we were able to establish exclusion at a lambda s = 1.9 for all markers using an exclusion threshold of LOD < or = -2. Similarly for the AUNN dataset, we established exclusion at lambdaAV = 1.9. For the combined dataset we estimate exclusion of lambda = 1.6. We did not identify significant linkage in either the sib-pairs or the AUNN dataset nor when datasets were stratified for the presence/absence of the HLA-DRB1*15 allele or for paternal or maternal transmission. This comprehensive scrutiny of the X-chromosome suggests that it is unlikely to harbour an independent susceptibility locus or one which interacts with the HLA. Complex interactions including epigenetic ones, and masking by balanced polymorphisms are mechanisms not excluded by the approach taken.

The role of hereditary spastic paraplegia related genes in multiple sclerosis. A study of disease susceptibility and clinical outcome

Multiple sclerosis (MS) is a common inflammatory disease of the central nervous system unsurpassed for its variability in disease outcome. It has been observed that axonal loss in MS is significant and that irreversible clinical disability relates to such axonal loss. The clinical similarities between Hereditary Spastic Paraplegia (HSP) and progressive MS, along with their analogous profiles of axonal loss in the long tracts, make the genes known to cause HSP biologically relevant candidates for the study of clinical outcome in MS. A cohort of sporadic MS cases and a set of unaffected controls were used to determine the role of HSP genes on MS susceptibility and disease severity. The MS cases were taken from opposite extremes of the putative distribution of long-term outcome using the most stringent clinical criteria to date. Genotyping the two sets of MS patients and controls could not provide any evidence to suggest that genes involved in the pathogenesis of HSP (Paraplegin, NIPA1, KIF5A, HSPD1, Atlastin, Spartin, Spastin, PLP1, L1CAM, Maspardin and BSCL2) play a role in susceptibility to, or modifying the course of, MS, although small effects of these genes cannot be ruled out.

Severe childhood SMA and axonal CMT due to anticodon binding domain mutations in the GARS gene

We screened 100 patients with inherited and sporadic lower motor neuron degeneration and identified three novel missense mutations in the glycyl-tRNA synthetase (GARS) gene. One mutation was in the anticodon binding domain and associated with onset in early childhood and predominant involvement of the lower limbs, thus extending the phenotype associated with GARS mutations.

Differential effects of Ca2+ and cAMP on transcription mediated by MEF2D and cAMP-response element-binding protein in hippocampal neurons

In neurons, the second messengers Ca(2+) and cAMP are mediators of transcriptional responses that are important for the development and function of the nervous system. The pro-survival neuronal transcription factors cAMP-response elementbinding protein (CREB) and myocyte enhancer factor-2 (MEF2) both stimulate gene expression in response to activity-dependent increases in the concentration of intracellular Ca(2+) ions. CREB is also activated by increases in intracellular cAMP. Here we have investigated whether the MEF2 family member MEF2D, similar to CREB, is also activated by cAMP in hippocampal neurons. We have shown that, unlike CREB, MEF2D is not activated by agents that increase intracellular cAMP. Moreover, increases in cAMP inhibit Ca(2+)-activated MEF2D-mediated gene expression. We have also shown that cAMP inhibits Ca(2+)-induced nuclear export of the MEF2 co-repressor HDAC5 and prevents Ca(2+)-stimulated nuclear import of the MEF2 co-activator NFAT3/c4. Our results suggest that cAMP interferes with MEF2D-mediated gene expression at multiple levels by antagonizing the derepression of MEF2D by HDAC5 and by inhibiting recruitment of the co-activator NFAT.

Follow-up investigation of 12 proposed linkage regions in multiple sclerosis

Multiple sclerosis (MS) is an autoimmune disease with overwhelming evidence for genetic determination, and for which a maternal parent-of-origin effect has been reported. As with many complex diseases, multiple suggestive linkage signals have been observed. However, the only unambiguous association and linkage identified to date is with alleles of the human lymphocyte antigen (HLA) class II region. We have now carried out high-density microsatellite genotyping for 12 of the most promising regions (1p, 1q, 2q, 4q, 5p, 9q, 10p, 11p, 12q, 17q, 18p, 19p) from a whole-genome scan in 552 affected sibling pairs. This has been carried out in 194 families containing avuncular pairs. These permit examination of parent-of-origin effects in non-colineal pairs when divided into likely maternal and paternal trait transmission. The results do not confirm any non-major histocompatibility complex linkage in the overall subset nor in the maternal, paternal or HLA-DRB1*1501 subsets. We were able to establish exclusion for a locus with lambda(AV) > or = 1.3 for all the previously suggested regions. These results again raise the possibility that the paradigm of multiple genes of small individual effect used to justify genome searches in MS is incorrect.

A genome-wide screen and linkage mapping for a large pedigree with episodic ataxia

Episodic ataxias are ion channel disorders characterized by attacks of incoordination. The authors performed a genome-wide screen in a large pedigree segregating a novel episodic ataxia and found significant linkage on 1q42 with a multipoint lod score of 3.65. Haplotype analysis and fine mapping yielded a peak 2-point lod score of 4.14 and indicated a 4-cM region on 1q42 that is likely to harbor an episodic ataxia gene.

TCR β polymorphisms and multiple sclerosis

A total of 267 families with two or more siblings with multiple sclerosis (MS) were genotyped with 14 restriction fragment length polymorphisms at the TCR beta locus. A nonparametric linkage analysis of the data showed no evidence for linkage to this locus (mlod=0.11). No significant allelic or haplotype transmissions were observed in the total sample of 565 patients. After stratification for the presence of HLA DRB1*15, an association was observed between the BV25S1*1-BV26S1*1-BV2S1*1 haplotype and MS (P=0.00089). This was not significant upon correction for multiple comparisons. It was also not significant when the haplotype frequency in affected individuals was compared to a normal control sample (P=0.77). Furthermore, the associated haplotype was followed-up in an independent sample of 97 nuclear families with a single DRB1*15-positive child with MS. The BV25S1*1-BV26S1*1-BV2S1*1 haplotype did not show significant evidence for transmission distortion but the same trend was seen (P=0.21). There were no significant associations observed in the DRB1*15-negative patients and no detectable difference was seen in the DRB1*15-positive BV25S1*1-BV26S1*1-BV2S1*1 association when comparing different subgroups based on clinical course of MS. These results show no evidence for linkage and fail to establish an association between MS susceptibility and the TCR beta locus.

Genetic loading in familial migraine with aura

Migraine with aura (MA) arises from a combination of genetic and environmental factors. The sibling risk, age at onset, and aura type were compared in 54 MA probands categorised by family history of MA. Three family types were ascertained each having an MA proband and: (1) an MA parent and MA offspring (three generation; n=15), (2) either an MA parent or an MA offspring (two generation; n=20), and (3) neither an MA parent nor an MA offspring (one generation; n=19). The crude recurrence risk to siblings of probands was 2.7-fold higher in three generation compared with two generation MA families (chi(2)=6.24, p=0.0125) and 4.8-fold higher in three generation compared with one generation MA families (chi(2)=9.95, p<0.002). The mean age at onset decreased with an increase in genetic load. The MA probands from three generation families were significantly younger than probands from the one generation families (F=5.14, p=0.030). MA probands from three generation families were more likely to report more than one type of aura than MA probands from two generation families (chi(2)=4.44, p=0.035). The significant difference in genetic loading and the earlier age at onset in the three generation families add further evidence for a genetic basis for MA and the difference in sibling risks demonstrates that the MA population is heterogeneous.

Migraine with aura is not linked to the FHM gene CACNA1A or the chromosomal region, 19p13

Two microsatellite markers, tightly linked to CACNA1A, were genotyped in migraine with aura (MA) families to determine if this gene, which underlies the 19p13 linked forms of familial hemiplegic migraine, is also linked to MA. Two-point parametric lod and nonparametric linkage scores did not support linkage. Transmission disequilibrium testing provided no evidence for linkage of MA to CACNA1A. In a large dataset of 64 Canadian MA families, the authors did not find evidence to support an MA susceptibility gene in the region of 19p13.

A multigenerational family with multiple sclerosis

We report a family with 15 individuals affected with multiple sclerosis present in three and possibly four generations. The segregation of multiple sclerosis within this pedigree is consistent with an autosomal dominant mode of inheritance with reduced penetrance. The clinical characteristics of the affected individuals are indistinguishable from those seen in sporadic multiple sclerosis with respect to sex ratio, age at onset, onset symptom, MRI and clinical course. Eleven of 14 cases (78.6%) were positive for the known multiple sclerosis-associated major histocompatibility complex (MHC) Class II HLA DRB1*15 allele. Parametric linkage analysis gave a non-significant LOD score of 0.31 (theta; = 0.33) for the DRB1 gene. However, among 11 affected children with at least one DRB1*15 bearing parent, all 11 out of 11 received at least one copy of this known susceptibility allele. A transmission disequilibrium test analysis was significant for the DRB1*15 allele within this single family; P = 0.0054. The inheritance pattern in this family suggests the presence of a single major locus responsible for multiple sclerosis susceptibility, with DRB1 acting as an important modifier. This family could be an important resource for the identification of a multiple sclerosis susceptibility gene.

An autosomal dominant disorder with episodic ataxia, vertigo, and tinnitus

The authors report an autosomal dominant episodic ataxia that is clinically distinct from the other episodic ataxias. Vestibular ataxia, vertigo, tinnitus, and interictal myokymia are prominent; attacks are diminished by acetazolamide. Linkage analyses of markers flanking the EA1 and EA2 loci demonstrate genetic exclusion from the other autosomal dominant episodic ataxias. The authors suggest EA3 for periodic vestibulocerebellar ataxia and EA4 for the disorder described here.

Ethnic differences in pre-admission levels of physical activity in patients admitted with myocardial infarction

BACKGROUND

Regular exercise is generally considered to reduce the risk of coronary heart disease. Reduced levels of physical activity in Indo-Asians may partly explain why patients from this ethnic group sustain so many heart attacks.

AIM

To investigate ethnic differences in pre-admission levels of physical activity amongst patients admitted with myocardial infarction and triggers for the acute cardiac event.

DESIGN

Cross-sectional study using standard Baecke questionnaire, which provided a semi-quantitative work score, sport score, leisure score and total activity score of general daily activities, with additional questions on activity at the onset of chest pain.

SETTING

Coronary Care Unit, City Centre Teaching Hospital.

PATIENTS AND RESULTS

We studied 100 consecutive patients (76 males, mean age 62.3 years, S.D. 12.5; 74 caucasians, 26 Indo-Asians) admitted with myocardial infarction. Most patients were engaged in sedentary activities, including lying in bed (25%), sitting (19%), watching television (14%) and sleeping (6%), whilst only 21% of patients were engaged in physical activity at chest pain onset; there were, however, no ethnic differences in activity at chest pain onset. There was a diurnal variation in chest pain onset, with the mode between 08:00 and 10:00 h. As the mean age of Indo-Asians was significantly lower than caucasians in the whole group (56.3 vs. 64.4 years; t-test, P < 0.002), the Baecke questionnaire analysis was confined to only male patients aged < 70 years (n = 56). Indo-Asian patients with myocardial infarction were found to have a significantly lower overall physical activity score (3.78 vs. 5.33; P = 0.003), leisure time physical activity (2.43 vs. 2.74; P < 0.05) and sporting score (0.14 vs. 0.82; P < 0.01) when compared to caucasians, despite a similar mean age and body mass index.

CONCLUSION

The majority of myocardial infarction patients were engaged in sedentary activities at chest pain onset. Although there were no differences between caucasians and Indo-Asians in activity at symptom onset, Indo-Asian patients had a significantly lower overall physical activity score, leisure time physical activity and sporting score compared to caucasians. The lower general physical activity amongst Indo-Asians may in part contribute to the high prevalence of ischaemic heart disease amongst this ethnic group.