Peroxisomes are key regulators of cellular and metabolic homeostasis. These organelles play important roles in redox metabolism, the oxidation of very-long-chain fatty acids (VLCFAs), and the biosynthesis of ether phospholipids. Given the essential role of peroxisomes in cellular homeostasis, peroxisomal dysfunction has been linked to various pathological conditions, tissue functional decline, and aging. In the past few decades, a variety of cellular signaling and metabolic changes have been reported to be associated with defective peroxisomes, suggesting that many cellular processes and functions depend on peroxisomes. Peroxisomes communicate with other subcellular organelles, such as the nucleus, mitochondria, endoplasmic reticulum (ER), and lysosomes. These inter-organelle communications are highly linked to the key mechanisms by which cells surveil defective peroxisomes and mount adaptive responses to protect them from damages. In this review, we highlight the major cellular changes that accompany peroxisomal dysfunction and peroxisomal inter-organelle communication through membrane contact sites, metabolic signaling, and retrograde signaling. We also discuss the age-related decline of peroxisomal protein import and its role in animal aging and age-related diseases. Unlike other organelle stress response pathways, such as the unfolded protein response (UPR) in the ER and mitochondria, the cellular signaling pathways that mediate stress responses to malfunctioning peroxisomes have not been systematically studied and investigated. Here, we coin these signaling pathways as “peroxisomal stress response pathways”. Understanding peroxisomal stress response pathways and how peroxisomes communicate with other organelles are important and emerging areas of peroxisome research.

Aims: Airway mucosa is constantly exposed to various airborne microbes, and epithelial host defense requires a robust innate immunity. Recently, it has been suggested that NADPH oxidase (NOX) isozymes serve functional roles in toll-like receptor (TLR)-mediated innate immune responses. However, the molecular mechanism between TLR and NOX-mediated reactive oxygen species (ROS) production in human airway mucosa has been poorly understood. Results: Here, we show that flagellin-induced ROS generation is dependent on dual oxidase 2 (DUOX2) activation, which is regulated by [Ca²⁺]_i mobilization in primary normal human nasal epithelial (NHNE) cells. Interestingly, we observed that silencing of DUOX2 expression in NHNE cells and nasal epithelium of Duox2 knockout mice failed to trigger mucin and MIP-2α production upon challenging flagellin. Innovation: Our observation in this study reveals that flagellin-induced hydrogen peroxide (H₂O₂) generation is critical for TLR5-dependent innate immune responses, including IL-8 production and MUC5AC expression in the nasal epithelium. Furthermore, DUOX2-mediated H₂O₂ generation activated by the flagellin-TLR5 axis might serve as a novel therapeutic target for infectious inflammation diseases in the airway tract. Conclusion: Taken together, we propose that DUOX2 plays pivotal roles in TLR5-dependent inflammatory response of nasal airway epithelium. Antioxid. Redox Signal. 16, 57–70.

Aims NADPH oxidase (Nox) isozymes that generate intracellular reactive oxygen species (ROS) and Toll-like receptor 2 (TLR2), an inflammatory mediator, are both involved in the development of atherosclerotic lesions. To identify the molecular connection between TLR2 and Nox isozymes in vascular remodelling, we analysed generation of ROS and pro-inflammatory cytokines in aortic smooth muscle cells from Nox1-deficient mice in response to the synthetic triacylated lipoprotein Pam3CSK, a TLR2 agonist. Methods and results We showed that TLR2 signalling stimulates progression of the pro-inflammatory phenotype in mouse aortic smooth muscle cells (MASMCs) through activation of Nox1. We demonstrated the interaction of TLR2 with Nox1 using yeast two-hybrid and co-immunoprecipitation assays. MASMCs from Nox1-deficient mice failed to generate of ROS in response to Pam3CSK4, indicating that Nox1 is essential for TLR2-dependent production of ROS. We also found that Pam3CSK4 stimulated migration of MASMCs from wild-type mice in a Transwell system, but MASMCs from Nox1-deficient mice failed to show this response. Wild-type MASMCs produced matrix metalloprotease 2 in response to Pam3CSK4, whereas Nox1-deficient MASMCs failed to generate this protease. Moreover, stimulation of MASMCs with Pam3CSK4 resulted in increased expression of the pro-inflammatory cytokine macrophage inflammatory protein 2 in a Nox1-dependent manner, leading to enhanced monocyte-endothelial cell adhesion and trans-endothelial migration of U937 cells. Conclusion These data suggest that Nox1 plays an important role in TLR2-mediated intracellular H2O2 generation, activation of matrix metalloprotease 2, and secretion of pro-inflammatory cytokines, which in turn stimulate MASMC migration and vascular remodelling.

Aging is characterized by a chronic, low-grade inflammation, which is a major risk factor for cardiovascular diseases. It remains poorly understood whether pro-inflammatory factors released from non-cardiac tissues contribute to the non-autonomous regulation of age-related cardiac dysfunction. Here, we report that age-dependent induction of cytokine unpaired 3 (upd3) in Drosophila oenocytes (hepatocyte-like cells) is the primary non-autonomous mechanism for cardiac aging. We show that upd3 is significantly up-regulated in aged oenocytes. Oenocyte-specific knockdown of upd3 is sufficient to block aging-induced cardiac arrhythmia. We further show that the age-dependent induction of upd3 is triggered by impaired peroxisomal import and elevated JNK signaling in aged oenocytes. We term hormonal factors induced by peroxisome dysfunction as peroxikines. Intriguingly, oenocyte-specific overexpression of Pex5, the key peroxisomal import receptor, blocks age-related upd3 induction and alleviates cardiac arrhythmicity. Thus, our studies identify an important role of hepatocyte-specific peroxisomal import in mediating non-autonomous regulation of cardiac aging.

It is widely accepted that bacterial infection-mediated inflammation facilitates development of atherosclerosis by activating toll-like receptor (TLR) signaling system. We reasoned that NADPH oxidases (Nox), required for TLR-mediated inflammatory response, are involved in atherogenesis. Here, we show that the activation of Nox4 through TLR5 regulates the inflammation of the endothelium and in atherogenesis. Flagellin-induced interaction between the COOH region of Nox4 and the TIR domain of TLR5 led to H₂O₂ generation, which in turn promoted the secretion of pro-inflammatory cytokines including IL-8, as well as the expression of ICAM-1 in human aortic endothelial cells (HAECs). Knockdown of the Nox4 in HAECs resulted in attenuated expressions of IL-8 and ICAM-1 leading to a reduction in the adhesion and trans-endothelial migration of monocytes. Challenge of recombinant FliC (rFliC) to the ApoE KO mice with high-fat diet (HFD) resulted in significantly increased atherosclerotic plaque sizes compared to the saline-injected mice. However, an injection of rFliC into the Nox4ApoE DKO mice with HFDs failed to generate atherosclerotic plaque, suggesting that Nox4 deficiency resulted in significant protections against rFliC-mediated atherogenesis. We conclude that TLR5-dependent Nox4 activation and subsequent H₂O₂ generation play critical roles for the development of atherosclerosis.

De novo lipogenesis is a highly regulated metabolic process, which is known to be activated through transcriptional regulation of lipogenic genes, including fatty acid synthase (FASN). Unexpectedly, we find that the expression of FASN protein remains unchanged during Drosophila larval development from the second to the third instar larval stages (L2 to L3) when lipogenesis is hyperactive. Instead, acetylation of FASN is significantly upregulated in fast-growing larvae. We further show that lysine K813 residue is highly acetylated in developing larvae, and its acetylation is required for elevated FASN activity, body fat accumulation, and normal development. Intriguingly, K813 is autoacetylated by acetyl-CoA (AcCoA) in a dosage-dependent manner independent of acetyltransferases. Mechanistically, the autoacetylation of K813 is mediated by a novel P-loop-like motif (N-xx-G-x-A). Lastly, we find that K813 is deacetylated by Sirt1, which brings FASN activity to baseline level. In summary, this work uncovers a previously unappreciated role of FASN acetylation in developmental lipogenesis and a novel mechanism for protein autoacetylation, through which Drosophila larvae control metabolic homeostasis by linking AcCoA, lysine acetylation, and de novo lipogenesis.