Middle-age abolishes cardioprotection conferred by thioredoxin-1 in mice

Thioredoxin-1 (Trx1) has cardioprotective effects on ischemia/reperfusion (I/R) injury, although its role in ischemic postconditioning (PostC) in middle-aged mice is not understood. This study aimed to evaluate if combining two cardioprotective strategies, such as Trx1 overexpression and PostC, could exert a synergistic effect in reducing infarct size in middle-aged mice. Young or middle-aged wild-type mice (Wt), transgenic mice overexpressing Trx1, and dominant negative (DN-Trx1) mutant of Trx1 mice were used. Mice hearts were subjected to I/R or PostC protocol. Infarct size, hydrogen peroxide (H2O2) production, protein nitration, Trx1 activity, mitochondrial function, and Trx1, pAkt and pGSK3β expression were measured. PostC could not reduce infarct size even in the presence of Trx1 overexpression in middle-aged mice. This finding was accompanied by a lack of Akt and GSK3β phosphorylation, and Trx1 expression (in Wt group). Trx1 activity was diminished and H2O2 production and protein nitration were increased in middle-age. The respiratory control rate dropped after I/R in Wt-Young and PostC restored this value, but not in middle-aged groups. Our results showed that Trx1 plays a key role in the PostC protection mechanism in young but not middle-aged mice, even in the presence of Trx1 overexpression.

NLRP3 mediates atheromatous plaque macrophage proliferation

Background

Macrophage accumulation in atherosclerotic plaques drives disease progression largely dependent on in situ proliferation. We previously reported that systemic cholesterol lowering or reduced modified lipoprotein uptake supress atheromatous plaque macrophage proliferation. In this work we investigate the intracellular mediators of macrophage proliferation.

Methods and results

Macrophages deficient in scavenger receptors CD36 or Msr1 and impaired in cholesterol-rich lipoprotein uptake, proliferated less compared to control macrophages in the same plaque exposed to the same lipid levels in a LDLR-deficient bone marrow irradiation mixed chimera model. Proliferation of plaque macrophages deficient in the intracellular cholesterol sensor LXR was not impaired, however. As modified LDL uptake can activate the NLRP3 inflammasome, we generated mixed bone marrow knockout chimeras for components of the inflammasome. NLRP3 but not Caspase-1 or interleukin-1 receptor deficient macrophages proliferated 35% less compared to NLRP3-expressing macrophages in the same plaque in vivo. These results were confirmed in NLRP3-deficient oxLDL stimulated macrophages in vitro. In line, NLRP3 inhibition of human carotid artery plaque cultures suppressed human plaque macrophage proliferation and reduced inflammasome-dependent IL-1b secretion. However, IL-1b supplementation did not restore local macrophage proliferation in accord with our findings in IL-1 receptor deficient murine plaque macrophages.

Conclusion

We identified a novel role for NLRP3, independent of the canonical Caspase-1–IL-1b inflammasome pathway, in mediating macrophage proliferation in atherosclerotic plaques in mice and men representing a druggable target.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): DFG