Reactive oxygen species (ROS), a by-product of aerobic life, are highly reactive molecules with unpaired electrons. The excess of ROS leads to oxidative stress, instigating the peroxidation of polyunsaturated fatty acids (PUFA) in the lipid membrane through a free radical chain reaction and the formation of the most bioactive aldehyde, known as 4-hydroxynonenal (4-HNE). 4-HNE functions as a signaling molecule and toxic product and acts mainly by forming covalent adducts with nucleophilic functional groups in proteins, nucleic acids, and lipids. The mitochondria have been implicated as a site for 4-HNE generation and adduction. Several studies clarified how 4-HNE affects the mitochondria’s functions, including bioenergetics, calcium homeostasis, and mitochondrial dynamics. Our research group has shown that 4-HNE activates mitochondria apoptosis-inducing factor (AIFM2) translocation and facilitates apoptosis in mice and human heart tissue during anti-cancer treatment. Recently, we demonstrated that a deficiency of SOD2 in the conditional-specific cardiac knockout mouse increases ROS, and subsequent production of 4-HNE inside mitochondria leads to the adduction of several mitochondrial respiratory chain complex proteins. Moreover, we highlighted the physiological functions of HNE and discussed their relevance in human pathophysiology and current discoveries concerning 4-HNE effects on mitochondria.

Autotaxin (ATX) is an extracellular secretory enzyme (lysophospholipase D) that catalyzes the hydrolysis of lysophosphatidyl choline to lysophosphatidic acid (LPA). The ATX–LPA axis is a well-known pathological mediator of liver fibrosis, metastasis in cancer, pulmonary fibrosis, atherosclerosis, and neurodegenerative diseases. Additionally, it is believed that LPA may cause vascular permeability. In ischemic stroke, vascular permeability leading to hemorrhagic transformation is a major limitation for therapies and an obstacle to stroke management. Therefore, in this study, we generated an endothelial-specific ATX deletion in mice (ERT2 ATX−/−) to observe stroke outcomes in a mouse stroke model to analyze the role of endothelial ATX. The AR2 probe and Evans Blue staining were used to perform the ATX activity and vascular permeability assays, respectively. Laser speckle imaging was used to observe the cerebral blood flow following stroke. In this study, we observed that stroke outcomes were alleviated with the endothelial deletion of ATX. Permeability and infarct volume were reduced in ERT2 ATX−/− mice compared to ischemia–reperfusion (I/R)-only mice. In addition, the cerebral blood flow was retained in ERT2 ATX−/− compared to I/R mice. The outcomes in the stroke model are alleviated due to the limited LPA concentration, reduced ATX concentration, and ATX activity in ERT2 ATX−/− mice. This study suggests that endothelial-specific ATX leads to increased LPA in the brain vasculature following ischemic–reperfusion and ultimately disrupts vascular permeability, resulting in adverse stroke outcomes.

Neointimal hyperplasia is characterized by a loss of the contractile phenotype of vascular smooth muscle cells (VSMCs). Our group has recently shown that VSMC proliferation and migration are mediated by lysophosphatidic acid (LPA) during restenosis, but the role of autotaxin (ATX; lysophospholipase D), which produces LPA, remains unclear. Endothelial denudation of the mouse carotid artery was performed to induce neointimal hyperplasia, and the extent of damage caused by the ATX-LPA axis was assessed in VSMCs. We observed the upregulation of ATX activity (p < 0.0002) in the injured carotid artery using an AR2 probe fluorescence assay. Further, the tissue carotid LPA levels were elevated 2.7-fold in carotid vessels, augmenting neointimal hyperplasia. We used an electrical cell–substrate impedance sensor (ECIS) to measure VSMC proliferation and migration. Treatment with an ATX inhibitor (PF8380) or LPA receptor inhibitor (Ki16425) attenuated VSMC proliferation (extracellular signal-regulated kinases) activity and migration in response to recombinant ATX. Indeed, PF8380 treatment rescued the aggravated post-wire injury neointima formation of carotid arteries. The upregulation of ATX following vessel injury leads to LPA production in VSMCs, favoring restenosis. Our observations suggest that inhibition of the ATX-LPA axis could be therapeutically targeted in restenosis to minimize VSMC phenotypic modulation and inflammation after vascular injury.

Lysophosphatidic acid (LPA), a multifunctional endogenous phospholipid, plays a vital role in cellular homeostasis and the malignant behavior of cancer cells through G-protein-coupled receptors. However, the role of LPA in β-catenin-mediated gastric cancer is unknown. Here, we have noted the high expression of LPAR2 in human gastric cancer tissues, and that LPA treatment significantly increased the proliferation, migration, and invasion of human gastric cancer cells. Results from our biochemical experiments showed that an LPA exposure increased the expression of β-catenin and its nuclear localization, increased the phosphorylation of glycogen synthase kinase 3β (GSK-3β), decreased the expression of Axin2, and increased the expression of the target genes of the β-catenin signaling pathway. The LPA2 receptor (LPAR2) antagonist significantly reduced the LPA-induced nuclear localization of β-catenin, the primary signaling event. The knockdown of LPAR2 in the gastric cancer cell lines robustly reduced the LPA-induced β-catenin activity. An LPA exposure increased the ATP production by both oxidative phosphorylation and glycolysis, and this effect was abrogated with the addition of an LPAR2 antagonist and XAV393, which stabilizes the Axin and inhibits the β-catenin signaling pathway. Based on our findings, the possibility that LPA contributes to gastric cancer initiation and progression through the β-catenin signaling pathway as well as by the dysregulation of the energy metabolism via the LPAR2 receptor and Axin2, respectively, provides a novel insight into the mechanism of and possible therapeutic targets of gastric cancer.

Myocardial ischemia-reperfusion injury (I/R) causes damage to cardiomyocytes through oxidative stress and apoptosis. We investigated the cardioprotective effects of MnTnBuOE-2-PyP5+ (BMX-001), a superoxide dismutase mimic, in an in vitro model of I/R injury in H9c2 cardiomyocytes. We found that BMX-001 protected against hypoxia/reoxygenation (H/R)-induced oxidative stress, as evident by a significant reduction in intracellular and mitochondrial superoxide levels. BMX-001 pre-treatment also reduced H/R-induced cardiomyocyte apoptosis, as marked by a reduction in TUNEL-positive cells. We further demonstrated that BMX-001 pre-treatment significantly improved mitochondrial function, particularly O2 consumption, in mouse adult cardiomyocytes subjected to H/R. BMX-001 treatment also attenuated cardiolipin peroxidation, 4-hydroxynonenal (4-HNE) level, and 4-HNE adducted proteins following H/R injury. Finally, the pre-treatment with BMX-001 improved cell viability and lactate dehydrogenase (LDH) activity in H9c2 cells following H/R injury. Our findings suggest that BMX-001 has therapeutic potential as a cardioprotective agent against oxidative stress-induced H/R damage in H9c2 cardiomyocytes.