Acod1/itaconate activates Nrf2 in pulmonary microvascular endothelial cells to protect against the obesity-induced pulmonary microvascular endotheliopathy.

BACKGROUND: Obesity is the main risk factor leading to the development of various respiratory diseases, such as asthma and pulmonary hypertension. Pulmonary microvascular endothelial cells (PMVECs) play a significant role in the development of lung diseases. Aconitate decarboxylase 1 (Acod1) mediates the production of itaconate, and Acod1/itaconate axis has been reported to play a protective role in multiple diseases. However, the roles of Acod1/itaconate axis in the PMVECs of obese mice are still unclear. METHODS: mRNA-seq was performed to identify the differentially expressed genes (DEGs) between high-fat diet (HFD)-induced PMVECs and chow-fed PMVECs in mice (|log2 fold change| ≥ 1, p ≤ 0.05). Free fatty acid (FFA) was used to induce cell injury, inflammation and mitochondrial oxidative stress in mouse PMVECs after transfection with the Acod1 overexpressed plasmid or 4-Octyl Itaconate (4-OI) administration. In addition, we investigated whether the nuclear factor erythroid 2-like 2 (Nrf2) pathway was involved in the effects of Acod1/itaconate in FFA-induced PMVECs. RESULTS: Down-regulated Acod1 was identified in HFD mouse PMVECs by mRNA-seq. Acod1 expression was also reduced in FFA-treated PMVECs. Acod1 overexpression inhibited cell injury, inflammation and mitochondrial oxidative stress induced by FFA in mouse PMVECs. 4-OI administration showed the consistent results in FFA-treated mouse PMVECs. Moreover, silencing Nrf2 reversed the effects of Acod1 overexpression and 4-OI administration in FFA-treated PMVECs, indicating that Nrf2 activation was required for the protective effects of Acod1/itaconate. CONCLUSION: Our results demonstrated that Acod1/Itaconate axis might protect mouse PMVECs from FFA-induced injury, inflammation and mitochondrial oxidative stress via activating Nrf2 pathway. It was meaningful for the treatment of obesity-caused pulmonary microvascular endotheliopathy.

4-Octyl itaconate alleviates renal ischemia reperfusion injury by ameliorating endoplasmic reticulum stress via Nrf2 pathway.

Renal ischemia-reperfusion injury (IRI) is a common clinical complication of multiple severe diseases. Owing to its high mortality and the lack of effective treatment, renal IRI is still an intractable problem for clinicians. Itaconate, which is a metabolite of cis-aconitate, can exert anti-inflammatory and antioxidant roles in many diseases. As a derivative of itaconate with high cell membrane permeability, 4-octyl itaconate (4-OI) could provide a protective effect for various diseases. However, the role of 4-OI in renal IRI is still unclear. Herein, we examined whether 4-OI afforded kidney protection through attenuating endoplasmic reticulum stress (ERS) via nuclear factor erythroid-2-related factor 2 (Nrf2) pathway. To observe the effects of 4-OI on alleviating renal pathologic injury, improving renal dysfunction, decreasing inflammatory cytokines, and reducing oxidative stress, we utilized C57BL/6J mice with bilateral renal pedicle clamped and HK-2 cells with hypoxia/reoxygenation (H/R) exposure in our study. In addition, through western blot assay, we found 4-OI ameliorated renal IRI-induced ERS, and activated Nrf2 pathway. Moreover, Nrf2-knockout (KO) mice and Nrf2 knockdown HK-2 cells were used to validate the role of Nrf2 signaling pathway in 4-OI-mediated alleviation of ERS caused by renal IRI. We demonstrated that 4-OI relieved renal injury and suppressed ERS in wild-type mice, while the therapeutic role was not shown in Nrf2-KO mice. Similarly, 4-OI could exert cytoprotective effect and inhibit ERS in HK-2 cells after H/R, but not in Nrf2 knockdown cells. Our in vivo and in vitro studies revealed that 4-OI protected renal IRI through attenuating ERS via Nrf2 pathway.

4-Octyl itaconate reduces influenza A replication by targeting the nuclear export protein CRM1.

IMPORTANCE: Itaconate derivates, as well as the naturally produced metabolite, have been proposed as antivirals against influenza virus. Here, the mechanism behind the antiviral effects of exogenous 4-octyl itaconate (4-OI), a derivative of itaconate, against the influenza A virus replication is demonstrated. The data indicate that 4-OI targets the cysteine at position 528 of the CRM1 protein, resulting in inhibition of the nuclear export of viral ribonucleoprotein complexes in a similar manner as previously described for other selective inhibitors of nuclear export. These results postulate a mechanism not observed before for this immuno-metabolite derivative. This knowledge is helpful for the development of derivatives of 4-OI as potential antiviral and anti-inflammatory therapeutics.

4-Octyl itaconate restricts STING activation by blocking its palmitoylation.

The cyclic guanosine monophosphate adenosine monophosphate synthase (cGAS)-stimulator of interferon genes (STING) axis plays a vital role in defending foreign pathogens and maintaining immune homeostasis. While substantial advances have been made in understanding the metabolic changes that occur during macrophage activation, little is known about how these metabolic changes affect the cGAS-STING axis. In this study, we identify that 4-octyl itaconate (4-OI), a derivative of itaconate, inhibits the activation of cGAS-STING. Furthermore, we show that 4-OI inhibits cGAS-STING-related antiviral immune responses and autoimmune inflammation. However, we find that endogenous itaconate does not affect cGAS-STING activation, indicating that 4-OI and itaconate function differently. Mechanistically, we find that 4-OI directly alkylates STING at Cys91, blocking STING palmitoylation and oligomerization. The alkylation of STING by 4-OI represents another type of post-translational modifications (PTMs) of STING. Our findings reveal a mechanism by which cGAS-STING function is regulated through 4-OI alkylation and provide insights into the crosstalk between different kinds of PTMs.

Macrophage scavenger receptor A1 antagonizes abdominal aortic aneurysm via upregulating IRG1.

AIMS: Abdominal aortic aneurysm (AAA) is a common, usually asymptomatic disease with high mortality and limited therapeutic options. Extensive extracellular matrix (ECM) fragmentation and transmural inflammation act as major pathological processes of AAA. However, the underlying regulatory mechanisms remain incompletely understood. Herein, we aimed to investigate the role of scavenger receptor A1 (SR-A1), a key pattern recognition receptor modulating macrophage activity, in pathogenesis of AAA. METHODS AND RESULTS: The AAA model was generated by administration of angiotensin II (Ang II) into apolipoprotein E knockout mice or peri-arterial application of calcium phosphate in C57BJ/6L mice. We found that SR-A1 was markedly down-regulated in the macrophages isolated from murine AAA aortas. Global or myeloid-specific ablation of SR-A1 aggravated vascular inflammation, loss of vascular smooth muscle cells and degradation of the extracellular matrix. These effects of SR-A1 deficiency on AAA development were mediated by suppressed immunoresponsive gene 1 (IRG1) and increased inflammatory response in macrophages. Mechanically, binding of SR-A1 with Lyn led to STAT3 phosphorylation and translocation into the nucleus, in which STAT3 promoted IRG1 transcription through directly binding to its promoter. Restoration of macrophage SR-A1 in SR-A1-deficient mice by bone marrow transplantation or administration of 4-octyl itaconate, the derivate of IRG1 product itaconate, could relieve murine AAA. CONCLUSION: Our study reveals a protective effect of macrophage SR-A1-STAT3-IRG1 axis against aortic aneurysm formation via inhibiting inflammation.

4-octyl itaconate as a metabolite derivative inhibits inflammation via alkylation of STING.

The Krebs cycle-derived metabolite itaconate, whose production is catalyzed by immune response gene 1 (IRG1), has potential to link immunity and metabolism in activated macrophages through alkylation or competitive inhibition of target proteins. In support of this, our previous study demonstrated that the stimulator of interferon genes (STING) signaling platform functions as a hub in macrophage immunity and has a profound impact on the prognosis of sepsis. Interestingly, we find that itaconate, an endogenous immunomodulator, can significantly inhibit the activation of STING signaling. Moreover, 4-octyl itaconate (4-OI), which is a permeable itaconate derivative, can alkylate cysteine sites 65, 71, 88, and 147 of STING, thereby inhibiting its phosphorylation. Furthermore, itaconate and 4-OI inhibit the production of inflammatory factors in sepsis models. Our results broaden the knowledge on the role of the IRG1-itaconate axis in immunomodulation and highlight itaconate and its derivatives as potential therapeutic agents in sepsis.

Itaconate derivative 4-OI inhibits PRRSV proliferation and associated inflammatory response.

Itaconate, a metabolite of the tricarboxylic acid (TCA) cycle produced by immunoresponsive gene 1 (IRG1) via catalyzation of cis-aconitate, plays important roles in metabolism and immunity. Porcine reproductive and respiratory syndrome virus (PRRSV) is an Arterivirus that has devastated the swine industry worldwide for over 30 years. Here, we found that 4-octyl itaconate (4-OI), a cell-permeable itaconate derivative, dose-dependently inhibited PRRSV proliferation by interfering with viral attachment, replication, and release. Furthermore, 4-OI suppressed the PRRSV-induced inflammatory response by enhancing nuclear factor erythroid 2-related factor 2 (Nrf2) signaling. Interestingly, PRRSV infection caused a reduction in itaconate abundance and simultaneously led to an accumulation of cis-aconitate, the upstream metabolite of itaconate, and both of these effects were accomplished by downregulating IRG1 expression. Taken together, these results demonstrate that 4-OI not only inhibits PRRSV replication but also suppresses PRRSV-induced inflammatory responses, indicating that 4-OI is a promising drug candidate for combating PRRSV.