Attenuation of rapid inflammasome activation in post-myocardial infarction monocytes is potentially mediated by TNFAIP3
Authors: Giral H , Franke V , Moobed M , Hartung J , Kraenkel N , Seppelt C , Meteva D , Haghikia A , Akalin A , Landmesser U , Kratzer A 
Published: November 2023

Abstract

Background
Inflammation is a protective response triggered not only upon pathogen insults but also- in sterile injury as happening during hypoxic episodes in acute myocardial infarction (AMI). Monocytes are among the first responder immune cells playing an important role in inflammation induction but also in its timely resolution. Understanding the mechanisms governing this two-sided modulation can help to uncover novel therapeutic approaches.
Inflammasomes are crucial gatekeepers of the immune response, but their maladaptive activation associates with inflammatory pathologies. Besides canonical activation, monocytes can trigger non-transcriptional or rapid inflammasome activation. In this project, we defined rapid inflammasome activation (by simultaneous TLR priming and ATP stimulation) in the context of AMI and examined its regulation.

Methods
Human blood was collected in EDTA tubes according to ethical standards and upon consent of the included patients. The three main monocyte subpopulations, defined as classical, intermediate and non-classical were sorted on a FACS Aria II based on the expression of the surface markers CD14 and CD16. We measured caspase-1 (CASP1) activity in monocyte subpopulations with FLICA Assay and quantified interleukin-1β and interleukin-18 release via ELISA. RNA and protein levels of inflammasome associated genes were determined by real-time PCR and Western blotting. We also measured hsTnT in plasma of AMI patients with ELISA.

Results
Circulating monocytes from AMI patients, especially the classical subpopulation, displayed strong attenuation of CASP1 activity but not total since inflammasome inhibition (MCC950) reduced CASP1 activation further. Rapid activation of NLRP3 induced acute IL18 release, mostly in classical monocytes of healthy subjects. IL18 release was also reduced in monocytes obtained from AMI patients compared to healthy. Blood circulating monocytes seemed to be primed by DAMPs released from the ischemic lesion. This induced transcriptional reprogramming inducing upregulation of TNFa induced protein 3 (TNFAIP3) and IRAKM, two early response genes, although at different time scales. TNFAIP3 protein levels positively associated with cardiac injury measured via hsTnT levels in plasma. We also observed upregulation of TNFAIP3-AS in AMI patients, which is the lncRNA antisense in the TNFAIP3 loci.

Conclusion and Future Approaches
Circulating monocytes in AMI present a phenotype with attenuated inflammasome activation and IL18 release. TNFAIP3 expression correlates with cardiac injury (hsTnT) and acts as a potential modulator of inflammasome activity in a protective mechanism against hyper-activation of systemic inflammation . In the future we aim to define the mechanisms of TNFAIP3 and its splicing isoforms in the attenuation of inflammasome activation as well as the function of TNFAIP3 antisense in the regulation of this response.