Immunometabolism: an overview and therapeutic prospects in autoimmune diseases

Metabolism is a critical immune regulator under physiologic and pathologic conditions. Culminating evidence has disentangled the contribution of distinct metabolic pathways, namely glucolysis, pentose phosphate, fatty acid oxidation, glutaminolysis, Krebs cycle and oxidative phosphorylation, in modulating innate and adaptive immune cells based on their activation/differentiation state. Metabolic aberrations and changes in the intracellular levels of specific metabolites are linked to the inflammatory phenotype of immune cells implicated in autoimmune disorders such as systemic lupus erythematosus, rheumatoid arthritis, multiple sclerosis and diabetes. Notably, targeting metabolism such as the mTOR by rapamycin, hexokinase by 2-deoxy-D-glucose, AMP-activated protein kinase by metformin, may be used to ameliorate autoimmune inflammation. Accordingly, research in immunometabolism is expected to offer novel opportunities for monitoring and treating immune-mediated diseases.

Long non-coding RNA SeT and miR-155 regulate the Tnfα gene allelic expression profile

It is becoming increasingly appreciated that the non-coding genome may have a great impact on the regulation of chromatin structure and gene expression. The innate immune response can be mediated upon lipopolysaccharide stimulation of macrophages which leads to immediate transcriptional activation of early responsive genes including tumor necrosis factor alpha (Tnfα). The functional role of non-coding RNAs, such as lncRNAs and microRNAs, on the transcriptional activation of proinflammatory genes and the subsequent regulation of the innate immune response is still lacking mechanistic insights. In this study we wanted to unravel the functional role of the lncRNA SeT, which is encoded from the murine Tnfα gene locus, and miR-155 on the transcriptional regulation of the Tnfα gene. We utilized genetically modified mice harboring either a deletion of the SeT promoter elements or the mature miR-155 and studied the response of macrophages to lipopolysaccharide (LPS) stimulation. We found that decreased expression of the lncRNA SeT in murine primary macrophages resulted in increased mortality of mice challenged with LPS, which was corroborated by increased Tnfα steady state mRNA levels and a higher frequency of biallelically expressing macrophages. On the contrary, miR-155 deletion resulted in reduced Tnfα mRNA levels supported by a lower frequency of biallelically expressing macrophages upon stimulation with LPS. In both cases, in the absence of either lncRNA SeT or miR-155 we observed a deregulation of the Tnfα allele homologous pairing, previously shown to regulate the switch from mono- to bi-allelic gene expression. Although lncRNA SeT was not found to be a direct target of miR-155 its stability was increased upon miR-155 deletion. This study suggests a role of the non-coding genome in mediating Tnfα mRNA dosage control based on the regulation of homologous pairing of gene alleles and their subsequent biallelic expression.

Asymptomatic Bacteriuria in Patients with Type 2 Diabetes Mellitus

Objectives: Asymptomatic bacteriuria (ASB) is a common finding in patients with diabetes. Moreover, patients with diabetes and ASB have a greater risk for symptomatic urinary tract infections and associated severe complications. The aim of this study was to estimate the prevalence of ASB, as well as to identify independent risk factors and related pathogens associated with ASB in female and male patients with type 2 diabetes mellitus (T2D). Methods: This prospective case-control study was performed at the University hospital, and the Venezeleion General Hospital, Heraklion, Greece between 2012 and 2019. All patients with T2D attending the diabetes and hypertension outpatient clinics at both hospitals were enrolled, and data regarding their medical history and clinical and laboratory profiles were recorded. Asymptomatic patients with positive urine cultures were assigned as cases while those with negative urine cultures were designated as controls. Results: A total of 437 adult patients of which 61% were female and 39% were male patients with a mean age of 70.5 ± 9.6 years, were enrolled. The prevalence of ASB was 20.1%, in total. ASB was noted in 27% of female participants and 9.4% of male participants. Higher glycated hemoglobin (OR = 3.921, 95%CI: 1.521−10.109, p < 0.001) and urinary tract infection within the previous year (OR = 13.254, 95%CI: 2.245−78.241, p < 0.001) were independently positively associated with ASB, while higher levels of vitamin B12 were independently negatively associated with ASB (OR = 0.994 per ng/mL, 95%CI: 0.989−0.999, p < 0.001). Conclusions: Development of ASB was associated with specific factors, some of which may be modifiable. Interestingly, high B12 was found to be negatively associated with ASB.

AB0013 THE COHESIN COMPLEX PROTEIN SMC1A IS A PUTATIVE REGULATOR OF SEX-BIASED INFLAMMATORY RESPONSES IN SYSTEMIC LUPUS ERYTHEMATOSUS

Background

A strong female predisposition is characteristic of Systemic Lupus Erythematosus (SLE), with female-to-male ratio ranging from 7:1 to 15:1. The molecular basis of this gender bias remains incompletely understood. In a previous whole-blood RNA profiling study, we identified genes with differential expression in SLE males versus females but not in their healthy counterparts. Among these genes, the cohesin complex protein SMC1A (Structural Maintenance of Chromosomes 1A) displayed the highest statistical significance [1].

Objectives

To (a) determine the immune cell type that displays the strongest gender-biased SMC1A expression in SLE versus healthy individuals, and (b) elucidate the role of SMC1A in regulating immune/inflammatory responses in the context of SLE.

Methods

Multiple immune cell types (CD19+ B cells, CD4+ T cells, CD14+ monocytes, neutrophils) were purified from peripheral blood specimens of SLE and healthy individuals, followed by Taqman PCR and Western blot to measure SMC1A mRNA and protein levels, respectively. The genome-binding properties of SMC1A were assayed by chromatin immunoprecipitation (ChIP)-sequencing in monocytes cultured under lupus-inducing conditions (lupus-like monocytes) [2]. To recapitulate the female/male difference in SMC1A expression, ex vivo cultured lupus-like monocytes were transfected with si-SMC1A (to downregulate SMC1A) versus si-control reagent, followed by genome-wide transcriptome analysis by RNA-sequencing.

Results

Among the various tested immune cell types, CD14+ monocytes best recapitulated the initial whole blood RNA-seq findings, demonstrating significantly decreased SMC1A mRNA and protein expression in male versus female SLE patients but not in their healthy counterparts. In blood monocytes cultured under lupus-inducing conditions and tested by ChIP-sequencing, SMC1A binding was increased on enhancers and promoters of genes associated with inflammation (including type I/II interferon and other inflammatory cytokines) and cell migration. In accordance, lupus-like monocytes with lowered SMC1A expression (i.e., male-like) displayed significantly reduced expression of inflammatory genes like IL6, GBP5, ADA and IL1A, as compared to monocytes with unaffected SMC1A (i.e., female-like). Furthermore, IL6 mRNA synthesis was significantly enhanced in female versus male monocytes cultured under lupus-inducing conditions.

Conclusion

SMC1A may transcriptionally regulate genes associated with the inflammatory response of monocytes. Our findings of gender-biased SMC1A levels in SLE monocytes raise the hypothesis that differential SMC1A expression and function might contribute to the disease gender bias and/or sexual dimorphism.

References

[1]Panousis NI, et al. Ann Rheum Dis. 2019 Aug;78(8):1079-1089.

[2]Park SH, et al. Nat Immunol. 2017 Oct;18(10):1104-1116.

Acknowledgements

The current work is funded by the Hellenic Foundation for Research & Innovation (HFRI). This research is co-financed by Greece and the European Union (European Social Fund- ESF) through the Operational Programme «Human Resources Development, Education and Lifelong Learning» in the context of the project “Strengthening Human Resources Research Potential via Doctorate Research” (MIS-5000432), implemented by the State Scholarships Foundation (IΚΥ)

Disclosure of Interests

None declared

POS0404 IFNα-MEDIATED METABOLIC REPROGRAMMING IN HUMAN SLE MONOCYTES INVOLVES PERTURBATIONS IN GLYCOLYTIC AND LIPID METABOLISM TO REGULATE PROINFLAMMATORY MARKERS AND CYTOKINES

Background

Systemic Lupus Erythematosus (SLE) is a prototype interferonopathy characterized by multiple organ damage1. Metabolomic analyses of patient-derived sera indicate distinct metabolic pertubations in oxidative and lipid metabolism2,3. Among innate effectors, monocytes (Mo) are implicated in SLE pathogenesis and also display a perturbed metabolic phenotype4.

Objectives

Based on previous data indicating a prominent IFNα-gene signature in SLE monocytes even during disease remission5, we herein sought to delineate the metabolic repercussion of IFNα signaling contributing to SLE autoimmunity.

Methods

Using transcriptomic data, we compared the enriched metabolic categories of IFNα(+) and IFNα(-) SLE-Mo6. In order to compare metabolic perturbations pertaining to SLE, we performed transcriptomic Gene Set Enrichment Analysis (GSEA)7 from in vitro cultured IFNα-activated Mo. We supplemented the analysis with selective ex vivo biochemical inhibition of the metabolic pathways arising from the GSEA and evaluated the effect on inflammatory markers of healthy IFNα-Mo.

Results

We found a statistically significant enrichment of transcripts associated with glycolytic metabolism and lipid biosynthetic and catabolic processes in both IFNα(+)-SLE Mo and healthy IFNα-Mo, but not in IFNα(-)-SLE Mo, which in turn resembled healthy-Mo. Additionally, transcripts associated with cholesterol biosynthetic processes such PMVK, SQLE, LSS, DHCR7, and LDLR, MVK, FFT1 were significantly upregulated in IFNα(+)-SLE Mo and healthy IFNα-Mo respectively. In accordance, blockade of either glycolysis with the use of 2-DG hexokinase inhibitor, or mevalonic acid synthesis with the use of fluvastatin, attenuated proinflammatory cytokine secretion (IL6, CXCL10) associated with IFN-response in both IFNα(+)-SLE Mo and healthy IFNα-Mo.

Conclusion

Our results link IFNα mediated metabolic shifts in Mo with corresponding metabolic perturbations found in SLE patient-Mo. Pending further confirmation with targeted metabolomics, these data further rationalize the use of IFN blockade and also suggest the potential use of specific metabolites as novel therapeutic targets in SLE.

References

[1]Crampton, S. P., Morawski, P. A. & Bolland, S. Linking susceptibility genes and pathogenesis mechanisms using mouse models of systemic lupus erythematosus. Dis. Model. Mech. 9, 1033–1046 (2014).

[2]Yan, B. et al. Serum metabolomic profiling in patients with systemic lupus erythematosus by GC/MS. Mod. Rheumatol. 26, 914–922 (2016).

[3]Gkirtzimanaki, K. et al. IFNα impairs autophagic degradation of mtDNA promoting autoreactivity of SLE monocytes in a STING-dependent fashion. Cell Rep. 25, 921-933.e5 (2018).

[4]Huang, N. & Perl, A. Metabolism as a target for modulation in autoimmune diseases. Trends Immunol. 39, 562–576 (2018).

[5]Panousis, N. I. et al. Combined genetic and transcriptome analysis of patients with SLE : distinct, targetable signatures for susceptibility and severity. Ann. Rheum. Dis. 78, 1079–1089 (2019).

[6]El-Sherbiny, Y. M. et al. A novel two-score system for interferon status segregates autoimmune diseases and correlates with clinical features. Sci. Rep. 8, 5793 (2018).

[7]Subramanian, A. et al. Gene set enrichment analysis: A knowledge-based approach for interpreting genome-wide expression profiles. Proc. Natl. Acad. Sci. 102, 15545–15550 (2005).

Disclosure of Interests

None declared.

Deciphering the Molecular Mechanism of Flares in Patients with Systemic Lupus Erythematosus through Single-Cell Transcriptome Analysis of the Peripheral Blood

A remarkable, yet poorly explained feature of Systemic Lupus Erythematosus (SLE) is the propensity to flare following a preceding period of disease inactivity. The clinical burden of lupus flares is substantial since they often tend to involve multiple or major organs, and carry a near two-fold increased risk for accrual of irreversible organ damage. The cellular and molecular mechanisms underlying the progression of SLE from inactive to active state remain ill-defined. Application of novel sequencing technologies together with cellular immunology assays, have illustrated the important role of multiple types of both innate and adaptive cells and associated pathways. We have previously described significant differences in the blood transcriptome of SLE patients at active versus inactive disease, and we have also defined genome regions (domains) with co-ordinated expression of genes implicated in the disease. In the present study, we aim to decipher the cellular and molecular basis of SLE exacerbations by utilising novel single-cell sequencing approaches, which allow us to characterise the transcriptional and epigenetic landscapes of thousands of cells in the peripheral blood of patients. The significance of the study lies in the detailed characterisation of the molecular and regulatory program of immune cell subpopulations that underlie progression from inactive to active SLE. Accordingly, our results may be exploited to identify biomarkers for disease monitoring and novel therapeutic targets.