Richard M. Mortensen

Itaconate has emerged as a critical immunoregulatory metabolite. Here, we examined the therapeutic potential of itaconate in atherosclerosis. We found that both itaconate and the enzyme that synthesizes it, aconitate decarboxylase 1 (Acod1, also known as immune-responsive gene 1 [IRG1]), are upregulated during atherogenesis in mice. Deletion of Acod1 in myeloid cells exacerbated inflammation and atherosclerosis in vivo and resulted in an elevated frequency of a specific subset of M1-polarized proinflammatory macrophages in the atherosclerotic aorta. Importantly, Acod1 levels were inversely correlated with clinical occlusion in atherosclerotic human aorta specimens. Treating mice with the itaconate derivative 4-octyl itaconate attenuated inflammation and atherosclerosis induced by high cholesterol. Mechanistically, we found that the antioxidant transcription factor, nuclear factor erythroid 2–related factor 2 (Nrf2), was required for itaconate to suppress macrophage activation induced by oxidized lipids in vitro and to decrease atherosclerotic lesion areas in vivo. Overall, our work shows that itaconate suppresses atherogenesis by inducing Nrf2-dependent inhibition of proinflammatory responses in macrophages. Activation of the itaconate pathway may represent an important approach to treat atherosclerosis.

Preservation quality of donor hearts is a key determinant of transplant success. Preservation duration beyond 4 hours is associated with primary graft dysfunction (PGD). Given transport time constraints, geographical limitations exist for donor-recipient matching, leading to donor heart underutilization. Here, we showed that metabolic reprogramming through up-regulation of the enzyme immune response gene 1 (IRG1) and its product itaconate improved heart function after prolonged preservation. Irg1 transcript induction was achieved by adding the histone deacetylase (HDAC) inhibitor valproic acid (VPA) to a histidine-tryptophan-ketoglutarate solution used for donor heart preservation. VPA increased acetylated H3K27 occupancy at the IRG1 enhancer and IRG1 transcript expression in human donor hearts. IRG1 converts aconitate to itaconate, which has both anti-inflammatory and antioxidant properties. Accordingly, our studies showed that Irg1 transcript up-regulation by VPA treatment increased nuclear translocation of nuclear factor erythroid 2–related factor 2 (Nrf2) in mice, which was accompanied by increased antioxidant protein expression [hemeoxygenase 1 (HO1) and superoxide dismutase 1 (SOD1)]. Deletion of Irg1 in mice (Irg1 ^−/− ) negated the antioxidant and cardioprotective effects of VPA. Consistent with itaconate’s ability to inhibit succinate dehydrogenase, VPA treatment of human hearts increased itaconate availability and reduced succinate accumulation during preservation. VPA similarly increased IRG1 expression in pig donor hearts and improved its function in an ex vivo cardiac perfusion system both at the clinical 4-hour preservation threshold and at 10 hours. These results suggest that augmentation of cardioprotective immune-metabolomic pathways may be a promising therapeutic strategy for improving donor heart function in transplantation.

Objective: The intersection between immunology and metabolism contributes to the pathogenesis of obesity‐associated metabolic diseases as well as molecular control of inflammatory responses. The metabolite itaconate and the cell‐permeable derivatives have robust anti‐inflammatory effects; therefore, it is hypothesized that cis‐aconitate decarboxylase (Acod1)‐produced itaconate has a protective, anti‐inflammatory effect during diet‐induced obesity and metabolic disease.Methods: Wild‐type and Acod1^−/− mice were subjected to diet‐induced obesity. Glucose metabolism was analyzed by glucose tolerance tests, insulin tolerance tests, and indirect calorimetry. Gene expression and transcriptome analysis was performed using quantitative reverse transcription‐polymerase chain reaction (qRT‐PCR) and RNA sequencing.Results: Wild‐type and Acod1^−/− mice on high‐fat diet had equivalent weight gain, but Acod1^−/− mice had impaired glucose metabolism. Insulin tolerance tests and glucose tolerance tests after 12 weeks on high‐fat diet revealed significantly higher blood glucose levels in Acod1^−/− mice. This was associated with significant enrichment of inflammatory gene sets and a reduction in genes related to adipogenesis and fatty acid metabolism. Analysis of naive Acod1^−/− mice showed a significant increase in fat deposition at 3 and 6 months of age and obesity and insulin resistance by 12 months.Conclusions: The data show that Acod1 has an important role in the regulation of glucose homeostasis and obesity under normal and high‐fat diet conditions.

Background: During the development of heart failure, a fetal cardiac gene program is reactivated and accelerates pathological cardiac remodeling. We previously reported that a transcriptional repressor, NRSF (neuron restrictive silencer factor), suppresses the fetal cardiac gene program, thereby maintaining cardiac integrity. The underlying molecular mechanisms remain to be determined, however. Methods: We aim to elucidate molecular mechanisms by which NRSF maintains normal cardiac function. We generated cardiac-specific NRSF knockout mice and analyzed cardiac gene expression profiles in those mice and mice cardiac-specifically expressing a dominant-negative NRSF mutant. Results: We found that cardiac expression of Gα _o , an inhibitory G protein encoded in humans by GNAO1 , is transcriptionally regulated by NRSF and is increased in the ventricles of several mouse models of heart failure. Genetic knockdown of Gnao1 ameliorated the cardiac dysfunction and prolonged survival rates in these mouse heart failure models. Conversely, cardiac-specific overexpression of GNAO1 in mice was sufficient to induce cardiac dysfunction. Mechanistically, we observed that increasing Gα _o expression increased surface sarcolemmal L-type Ca ²⁺ channel activity, activated CaMKII (calcium/calmodulin-dependent kinase-II) signaling, and impaired Ca ²⁺ handling in ventricular myocytes, which led to cardiac dysfunction. Conclusions: These findings shed light on a novel function of Gα _o in the regulation of cardiac Ca ²⁺ homeostasis and systolic function and suggest Gα _o may be an effective therapeutic target for the treatment of heart failure.

Objective: Excess dietary fat and sodium (NaCl) are both associated with obesity and metabolic dysfunction. In mice, high NaCl has been shown to block high‐fat (HF) diet–induced weight gain. Here, the impact of an HF/NaCl diet on metabolic function in the absence of obesity was investigated.Methods: Wild‐type mice were administered chow, NaCl (4%), HF, and HF/NaCl diets. Metabolic analysis was performed by measuring fasted blood glucose and insulin levels and by glucose tolerance test and insulin tolerance test.Results: After 10 weeks on diets, male and female mice on the HF diet gained weight, and HF/NaCl mice had significantly reduced weight gain similar to chow‐fed mice. In the absence of obesity, HF/NaCl mice had significantly elevated fasting blood glucose and impaired glucose control during glucose tolerance tests. Both NaCl and HF/NaCl mice had decreased pancreas and β‐cell mass. Administration of NaCl in drinking water did not protect mice from HF‐diet‐induced weight gain and obesity. Further analysis revealed that longer administration of HF/NaCl diets for 20 weeks resulted in significant weight gain and insulin resistance.Conclusions: The data demonstrate that despite early inhibitory effects on fat deposition and weight gain, an HF/NaCl diet does not prevent the metabolic consequences of HF diet consumption.

Background: Hypertension‐induced cardiovascular remodeling is characterized by chronic low‐grade inflammation. Interleukin‐4 receptor α (IL‐4Rα) signaling is importantly involved in cardiovascular remodeling, however, the target cell type(s) is unclear. Here, we investigated the role of myeloid‐specific IL‐4Rα signaling in cardiovascular remodeling induced by angiotensin II and high salt. Methods and Results: Myeloid IL‐4Rα deficiency suppressed both the in vitro and in vivo expression of alternatively activated macrophage markers including Arg1 (arginase 1), Ym1 (chitinase 3‐like 3), and Relmα/Fizz1 (resistin‐like molecule α). After angiotensin II and high salt treatment, myeloid‐specific IL‐4Rα deficiency did not change hypertrophic remodeling within the heart and aorta. However, myeloid IL‐4Rα deficiency resulted in a substantial reduction in fibrosis through the suppression of profibrotic pathways and the enhancement of antifibrotic signaling. Decreased fibrosis was associated with significant preservation of myocardial function in MyIL4RαKO mice and was mediated by attenuated alternative macrophage activation. Conclusions: Myeloid IL‐4Rα signaling is substantially involved in fibrotic cardiovascular remodeling by controlling alternative macrophage activation and regulating fibrosis‐related signaling. Inhibiting myeloid IL‐4Rα signaling may be a potential strategy to prevent hypertensive cardiovascular diseases.

This study showed, for the first time, the role of endogenous IL4Rα signaling in myeloid cells during cardiac remodeling and the underlying mechanisms. We identified myeloid cells are the critical target cell types of IL4Rα signaling during cardiac remodeling post-MI. Deficiency of myeloid IL4Rα signaling causes deteriorated cardiac function post-MI, due to dysregulated inflammation and insufficient fibrotic remodeling. This study sheds light on the potential of activating myeloid-specific IL4Rα signaling to modify remodeling post-MI. This brings hope to patients with MI and diminishes side effects by cell type-specific instead of whole body treatment.