Lipid Phosphate Phosphatase-3 Research Articles

Lipid phosphate phosphatase 3 maintains NO-mediated flow-mediated dilatation in human adipose resistance arterioles.

Microvascular dysfunction predicts adverse cardiovascular events despite absence of large vessel disease. A shift in the mediator of flow-mediated dilatation (FMD) from nitric oxide (NO) to mitochondrial-derived hydrogen peroxide (H2 O2 ) occurs in arterioles from patients with coronary artery disease (CAD). The underlying mechanisms governing this shift are not completely defined. Lipid phosphate phosphatase 3 (LPP3) is a transmembrane protein that dephosphorylates lysophosphatidic acid, a bioactive lipid, causing a receptor-mediated increase in reactive oxygen species. A single nucleotide loss-of-function polymorphism in the gene coding for LPP3 (rs17114036) is associated with elevated risk for CAD, independent of traditional risk factors. LPP3 is suppressed by miR-92a, which is elevated in the circulation of patients with CAD. Repression of LPP3 increases vascular inflammation and atherosclerosis in animal models. We investigated the role of LPP3 and miR-92a as a mechanism for microvascular dysfunction in CAD. We hypothesized that modulation of LPP3 is critically involved in the disease-associated shift in mediator of FMD. LPP3 protein expression was reduced in left ventricle tissue from CAD relative to non-CAD patients (P=0.004), with mRNA expression unchanged (P=0.96). Reducing LPP3 expression (non-CAD) caused a shift from NO to H2 O2 (% maximal dilatation: Control 78.1±11.4% vs. Peg-Cat 30.0±11.2%; P<0.0001). miR-92a is elevated in CAD arterioles (fold change: 1.9±0.01 P=0.04), while inhibition of miR-92a restored NO-mediated FMD (CAD), and enhancing miR-92a expression (non-CAD) elicited H2 O2 -mediated dilatation (P<0.0001). Our data suggests LPP3 is crucial in the disease-associated switch in the mediator of FMD. KEY POINTS: Lipid phosphate phosphatase 3 (LPP3) expression is reduced in heart tissuepatients with coronary artery disease (CAD). Loss of LPP3 in CAD is associated with an increase in the LPP3 inhibitor, miR-92a. Inhibition of LPP3 in the microvasculature of healthy patients mimics the CAD flow-mediated dilatation (FMD) phenotype. Inhibition of miR-92a restores nitric oxide-mediated FMD in the microvasculature of CAD patients.

Lipid phosphate phosphatase‐3 dysfunction exaggerates neointimal hyperplasia following diabetic vascular injury

IntroductionDiabetes mellitus is a major risk factor for cardiovascular diseases and promotes neointimal hyperplasia characterized by occlusive disorders such as atherosclerosis and stenosis, caused by excessive proliferation and migration of vascular smooth muscle cells (VSMCs) following endovascular interventions such as balloon angioplasty and stent placement. Lipid phosphate phosphatase‐3 (LPP3) is an enzyme that regulates the availability of lysophosphatidic acid (LPA) and has been reported to play a significant role in vascular genesis, cellular permeability, tumor progression, vascular remodeling, and myocardial infarction. However, the functional role and mechanism of LPP3 in diabetic neointimal hyperplasia is unclear. LPP3 dysfunction may lead to LPA accumulation at the vascular injury site, leading to vascular inflammation, proliferation, and migration, causing restenosis. Recently, the Receptor for Advanced Glycation End product (RAGE) has been presented as a potential receptor for LPA leading to downstream signaling in vascular smooth muscle cells (VSMCs).MethodsIn this study, we used a streptozocin‐induced diabetes mice model. We made SM‐22 specific LPP3 knock‐out mice and performed endothelial denudation surgery in the carotid artery to induce neointima hyperplasia to tease out the role of LPP3 in restenosis. We isolated aortic VSMCs from LPP3 floxed and LPP3 knock‐out mice and cultured them under normal or high glucose media. The immunoblotting was performed and probed with antibodies for total extracellular signal‐regulated kinase (ERK) and phosphorylated‐ERK. The cell proliferation and migration assay was performed using the Electric Cell substrate Impedance Sensing (ECIS) with or without LPP3 in VSMC under normal or high glucose conditions. Data are mean ± SEM; P‐values were determined by Student t‐test or one‐way ANOVA with Tukey's post‐hoc tests.ResultWe observed a significant increase in proliferation (P&lt;0.01) and exaggerated migration (p&lt;0.01) of VSMC that lack LPP3 under the hyperglycemic condition in real‐time using ECIS. These effects are at least partially a consequence of decreased lysophosphatidic acid hydrolysis due to lack of LPP3 activity. Furthermore, VSMC that lack LPP3 showed increased phospho‐ERK expression (P&lt;0.01) under hyperglycemic conditions. The diabetic LPP3 knock‐out mice exhibited exaggerated neo‐intimal areas after the carotid injury compared to LPP3 floxed mice.ConclusionThese findings implicate that LPP3 plays a vital role as a negative regulator of smooth muscle phenotypic modulation. We speculate that changes in LPP3 expression control the development of neo‐intima by limiting smooth muscle cell proliferation, migration, and vascular inflammation in diabetic restenosis.

Lipid phosphate phosphatase 3 in smooth muscle cells regulates angiotensin II-induced abdominal aortic aneurysm formation

Genetic variants that regulate lipid phosphate phosphatase 3 (LPP3) expression are risk factors for the development of atherosclerotic cardiovascular disease. LPP3 is dynamically upregulated in the context of vascular inflammation with particularly heightened expression in smooth muscle cells (SMC), however, the impact of LPP3 on vascular pathology is not fully understood. We investigated the role of LPP3 and lysophospholipid signaling in a well-defined model of pathologic aortic injury and observed Angiotensin II (Ang II) increases expression of PLPP3 in SMCs through nuclear factor kappa B (NF-κB) signaling Plpp3 global reduction (Plpp3+/−) or SMC-specific deletion (SM22-Δ) protects hyperlipidemic mice from AngII-mediated aneurysm formation. LPP3 expression regulates SMC differentiation state and lowering LPP3 levels promotes a fibroblast-like phenotype. Decreased inactivation of bioactive lysophosphatidic acid (LPA) in settings of LPP3 deficiency may underlie these phenotypes because deletion of LPA receptor 4 in mice promotes early aortic dilation and rupture in response to AngII. LPP3 expression and LPA signaling influence SMC and vessel wall responses that are important for aortic dissection and aneurysm formation. These findings could have important implications for therapeutics targeting LPA metabolism and signaling in ongoing clinical trials.

Downregulation of Lipid Phosphate Phosphatase 3 Correlates With Tumor-Infiltrating Immune Cells in Oral Cancer.

BackgroundSphingosine-1-phosphate (S1P) is a potent oncogenic lipid. Intracellular levels of S1P are tightly regulated by eight S1P-metabolizing enzymes. S1P synthesis is catalyzed by two sphingosine kinases, i.e., sphingosine kinase 1 (SphK1) and sphingosine kinase 2 (SphK2). Five lipid phosphatases (two S1P phosphatases and lipid phosphate phosphatases (LPPs) 1, 2, and 3) reversibly convert S1P back to sphingosine. Previously, we have determined the mRNA expression profile of eight S1P-metabolizing enzymes in tumor tissues and adjacent normal tissues from oral squamous cell carcinoma (OSCC) patients. Except for SphK1, the role of S1P-metabolizing enzymes in OSCC has been poorly studied.MethodsWe have determined the protein expression of four S1P-metabolizing enzymes (SphK1, SphK2, sphingosine-1-phosphate phosphatase 1 (SGPP1), and lipid phosphate phosphatase 3 (LPP3)) by immunohistochemistry (IHC) in tumor tissues of 46 OSCC patients. Six subjects with non-dysplastic oral mucosa were also included in the study. The immunoreactivity score (IRS) was calculated for each protein in every subject. Further, we determined the associations of expression of S1P-metabolizing enzymes with clinicopathological features of OSCC patients.ResultsWe demonstrate the low IRS for SphK2 and LPP3 in OSCC tumors. Importantly, expression of SphK2 and LPP3 was downregulated in malignant epithelial cells compared to non-malignant mucosa. Further, LPP3 expression negatively correlated with tumor‑node‑metastasis (TNM) staging of patients (r = −0.307, p = 0.043). Importantly, expression of LPP3 in tumors was found to be an independent predictor of perinodal extension (b = −0.440, p = 0.009), lymphovascular invasion (b = −0.614, p < 0.001), lymph node ratio (b = 0.336, p = 0.039), and TNM staging (b = −0.364, p = 0.030).ConclusionTaken together, our data show that expression of SphK2 and LPP3 is decreased compared to normal mucosa. Thus, the S1P signaling pathway could represent a potential therapeutic target.

ATX‐LPP3 axis mediated LPA regulation following myocardial injury

The bioactive lysophosphatidic acid (LPA) plays a well-known role in atherosclerotic disease, whereas its role in myocardial function remains virtually unexplored. Following acute myocardial infarction, serum LPA concentration rises by six-fold over control human subjects, suggesting LPA may contribute to the pathogenesis of myocardial infarction. LPA production involves hydrolysis of lysophosphatidylcholine by the secreted enzyme autotaxin, whereas lipid phosphate phosphatase-3 (LPP3) catalyzes LPA dephosphorylation to generate lipid products that are not receptor active. We present the first evidence that cardiac ischemia/reperfusion (I/R) injury enhances myocardial autotaxin levels and decreases myocardial LPP3 expression, and this is associated with increased serum LPA levels. Upon reperfusion, reactive oxygen species production arises as a burst of superoxide from mitochondria following I/R injury. The redox-sensitive transcription factor NFAT has been shown to bind to the autotaxin promoter and induce its expression. Therefore, we looked at the autotaxin and LPP3 regulation in mice following I/R injury in the myocardium. After 1h ligation followed by 3h reperfusion in the myocardium, we observed a 3 fold increase in the autotaxin protein levels, whereas LPP3 protein levels were significantly downregulated as observed through Western blot analysis in these myocardial ischemic tissues. Autotaxin and miR-92a mRNA expression levels were significantly upregulated, whereas KLF2 and LPP3 mRNA expressions were significantly downregulated following I/R injury at 24 hours. Western blot analysis showed a 3 fold increase autotaxin protein levels and immunohistochemistry of human infarct tissues at 24 hours showed disruption of the sarcomere with decreased LPP3 staining. We found that I/R injury transactivates miR-92a, and inhibit KLF2, an upstream activator of LPP3. Taken together, our in vivo data, from the myocardial I/R injury and human infarct tissues, suggest that regulation of autotaxin and LPP3 activity might cause the rise in serum LPA levels as reported with acute myocardial infarct patients.

Abstract 16007: Myeloid-specific Deletion in Lipid Phosphate Phosphatase3 (plpp3) Increases Cardiac Inflammation

Introduction and Hypothesis: Acute myocardial infarction (AMI) is the leading cause of morbidity and mortality worldwide. The innate immune response plays a major role in cardiac remodeling after AMI. Lysophosphatidic acid (LPA), produced by autotaxin (ATX) and degraded by Lipid phosphate phosphatase 3 (LPP3), regulates monocytosis and promotes inflammation. However, the role of LPP3 in post-AMI inflammation is not understood. Here, we investigated the possible role of Myeloid-specific Plpp3 KO mice in cardiac and systemic inflammation and resulting in adverse cardiac remodeling post-MI. Methods and Results: To generate mice with Myeloid-specific Plpp3 deletion , female Plpp3 fl/fl mice were crossed to male Plpp3 mice expressing Cre recombinase under the control of the LysM promoter to generate lysm-plpp3. mice. These mice and their littermate control underwent MI or sham surgery. Inflammatory cell content was assessed using flow cytometry and immunohistochemistry. Cardiac function and scar size were assessed by echocardiography and Mason Trichrome staining, respectively. Increased number of Ly6C hi monocytes (CD45 + /Ly6C/G hi /CD115 hi ) and pro-inflammatory macrophages (CD45 + /F4-80 + /CD11b + ) (CD45 + /F4-80 + /CD86 + ), in cardiac tissue of Cre+LysM mice was observed compared to Cre-fl/fl littermate controls during peak post-MI inflammation, as assessed by flow cytometry ( Fig.1A-C ). This increase in inflammatory cells and inflammation may be the consequence of the significant increase in bone marrow and spleen progenitor cell count and proliferation. Moreover, Cre+LysM mice cardiac functional recovery was also reduced significantly ( Fig. 1D-F ) as assessed by echocardiography. Conclusion: Myeloid-specific Plpp3 deletion increases the deleterious effects of inflammation on the ischemic myocardium and ATX/ LPA signaling could represent a novel therapeutic target for future clinical studies of coronary heart diseases.

Autotaxin inhibition reduces cardiac inflammation and mitigates adverse cardiac remodeling after myocardial infarction

ObjectiveAcute myocardial infarction (AMI) initiates pathological inflammation which aggravates tissue damage and causes heart failure. Lysophosphatidic acid (LPA), produced by autotaxin (ATX), promotes inflammation and the development of atherosclerosis. The role of ATX/LPA signaling nexus in cardiac inflammation and resulting adverse cardiac remodeling is poorly understood. Approach and resultsWe assessed autotaxin activity and LPA levels in relation to cardiac and systemic inflammation in AMI patients and C57BL/6 (WT) mice. Human and murine peripheral blood and cardiac tissue samples showed elevated levels of ATX activity, LPA, and inflammatory cells following AMI and there was strong correlation between LPA levels and circulating inflammatory cells. In a gain of function model, lipid phosphate phosphatase-3 (LPP3) specific inducible knock out (Mx1-Plpp3Δ) showed higher systemic and cardiac inflammation after AMI compared to littermate controls (Mx1-Plpp3fl/fl); and a corresponding increase in bone marrow progenitor cell count and proliferation. Moreover, in Mx1- Plpp3Δ mice, cardiac functional recovery was reduced with corresponding increases in adverse cardiac remodeling and scar size (as assessed by echocardiography and Masson's Trichrome staining). To examine the effect of ATX/LPA nexus inhibition, we treated WT mice with the specific pharmacological inhibitor, PF8380, twice a day for 7 days post AMI. Inhibition of the ATX/LPA signaling nexus resulted in significant reduction in post-AMI inflammatory response, leading to favorable cardiac functional recovery, reduced scar size and enhanced angiogenesis. ConclusionATX/LPA signaling nexus plays an important role in modulating inflammation after AMI and targeting this mechanism represents a novel therapeutic target for patients presenting with acute myocardial injury.

Alcohol Induced Oxidative Stress in neonatal Cardio myocytes

Alcohol Induced Oxidative Stress in neonatal Cardio myocytes

Coronary Artery Disease Risk-Associated Plpp3 Gene and Its Product Lipid Phosphate Phosphatase 3 Regulate Experimental Atherosclerosis.

Genome-wide association studies identified novel loci in PLPP3(phospholipid phosphatase 3) that associate with coronary artery disease risk independently of traditional risk factors. PLPP3 encodes LPP3 (lipid phosphate phosphatase 3), a cell-surface enzyme that can regulate the availability of bioactive lysophopsholipids including lysophosphatidic acid (LPA). The protective allele of PLPP3 increases LPP3 expression during cell exposure to oxidized lipids, however, the role of LPP3 in atherosclerosis remains unclear. Approach and Results: In this study, we sought to validate LPP3 as a determinate of the development of atherosclerosis. In experimental models of atherosclerosis, LPP3 is upregulated and co-localizes with endothelial, smooth muscle cell, and CD68-positive cell markers. Global post-natal reductions in Plpp3 expression in mice substantially increase atherosclerosis, plaque-associated LPA, and inflammation. Although LPP3 expression increases during ox-LDL (oxidized low-density lipoprotein)-induced phenotypic modulation of bone marrow-derived macrophages, myeloid Plpp3 does not appear to regulate lesion formation. Rather, smooth muscle cell LPP3 expression is a critical regulator of atherosclerosis and LPA content in lesions. Moreover, mice with inherited deficiency in LPA receptor signaling are protected from experimental atherosclerosis. Our results identify a novel lipid signaling pathway that regulates inflammation in the context of atherosclerosis and is not related to traditional risk factors. Pharmacological targeting of bioactive LPP3 substrates, including LPA, may offer an orthogonal approach to lipid-lowering drugs for mitigation of coronary artery disease risk.

Regulation of PLPP3 gene expression by NF-κB family transcription factors

Lipid phosphate phosphatase 3 (LPP3), encoded by the PLPP3 gene, is an integral membrane enzyme that dephosphorylates phosphate esters of glycero- and sphingophospholipids. Cell surface LPP3 can terminate the signaling actions of bioactive lysophosphatidic acid (LPA) and sphingosine 1 phosphate, which likely explains its role in developmental angiogenesis, vascular injury responses, and cell migration. Heritable variants in the final intron PLPP3 associate with interindividual variability in coronary artery disease risk that may result from disruption of enhancer sequences that normally act in cis to increase expression of the gene. However, the mechanisms regulating PLPP3 expression are not well understood. We show that the human PLPP3 promoter contains three functional NF-κB response elements. All of these are required for maximal induction of PLPP3 promoter activity in reporter assays. The identified sequences recruit RelA and RelB components of the NF-κB transcription complex to chromatin, and these transcription factors bind to the identified target sequences in two different cell types. LPA promotes binding of Rel family transcription factors to the PLPP3 promoter and increases PLPP3 gene expression through mechanisms that are attenuated by an NF-κB inhibitor, LPA receptor antagonists, and inhibitors of phosphoinositide 3 kinase. These findings indicate that up-regulation of PLPP3 during inflammation and atherosclerosis results from canonical activation of the NF-κB signaling cascade to increase PLPP3 expression through nuclear import and binding of RelA and RelB transcription factors to the PLPP3 promoter and suggest a mechanism by which the LPP3 substrate, LPA, can regulate PLPP3 expression.

Abstract 290: Lpp3 Deficiency Impairs Mitochondrial Function And Enhances Myocardial Lpa Mediated Signaling

The bioactive lysophosphatidic acid (LPA) plays a well-known role in atherosclerotic disease, whereas, its role in myocardial function remains virtually unexplored. Following acute myocardial infarction, serum LPA concentration rises by six-fold over control human subjects, suggesting LPA may contribute to the pathogenesis of myocardial infarction. LPA production involves hydrolysis of lysophosphatidylcholine by the secreted enzyme autotaxin, whereas lipid phosphate phosphatase-3 (LPP3) catalyzes LPA dephosphorylation to generate lipid products that are not receptor active. We present the first evidence that cardiac ischemia/reperfusion (I/R) injury enhances myocardial autotaxin levels and decreases myocardial LPP3 expression, and this is associated with increased serum LPA levels. Upon reperfusion, reactive oxygen species production arises as a burst of superoxide from mitochondria following I/R injury. The redox-sensitive transcription factor NFAT has been shown to bind to the autotaxin promoter and induce its expression. Therefore, we looked at the autotaxin and LPP3 regulation in mice following I/R injury in the myocardium. After 1h ligation followed by 3h reperfusion in the myocardium, we observed a 3-fold increase in the autotaxin protein levels, whereas LPP3 protein levels were significantly downregulated as observed through Western blot analysis in these myocardial ischemic tissues. Autotaxin and miR-92a mRNA expression levels were significantly upregulated, whereas KLF2 and LPP3 mRNA expressions were significantly downregulated following I/R injury at 24 hours. Western blot analysis showed a 3-fold increase autotaxin protein levels and immunohistochemistry of human infarct tissues at 24 hours showed disruption of the sarcomere with decreased LPP3 staining. We found that I/R injury transactivates miR-92a, and inhibit KLF2, an upstream activator of LPP3. Taken together, us in vivo data, from the myocardial I/R injury and human infarct tissues, suggest that regulation of autotaxin and LPP3 activity might cause the rise in serum LPA levels as reported with acute myocardial infarct patients

Doxorubicin in myocardial lysophosphatidic acid signaling

Generation of reactive oxygen species has been implicated in the toxicity of nearly 50% of the current FDA approved cancer therapeutic drugs. Mitochondrial respiration is a major source of reactive oxygen species production and that the presence of the mitochondrial antioxidant enzyme, manganese superoxide dismutase, is essential for the survival of all aerobic life. Our studies of animals using the prototype redox‐active anticancer drug, doxorubicin, indicate that overexpression of manganese superoxide dismutase protects the heart against doxorubicin‐induced cardiac injury and reduction of manganese superoxide dismutase by heterozygous knockout mice increases cardiac injury after exposure to doxorubicin. While the bioactive glycerophospholipid lysophosphatidic acid rises by seven‐fold over control subjects, suggesting lysophosphatidic acid may contribute to the doxorubicin‐induced cardiac toxicity. Lysophosphatidic acid production involves hydrolysis of lysophosphatidylcholine by the secreted enzyme autotaxin, whereas lipid phosphate phosphatase‐3 (LPP3) catalyzes lysophosphatidic acid dephosphorylation to generate lipid products that are not receptor active. In this application, we present the first evidence that doxorubicin‐induced cardiac injury enhances myocardial autotaxin levels and decreases myocardial LPP3 expression, and this is associated with increased serum lysophosphatidic acid levels. Reactive oxygen species production arises as a burst of superoxide from mitochondria following doxorubicin‐induced cardiac injury. The redox‐sensitive transcription factor NFAT (a nuclear factor of activated T‐cells) has been shown to bind to the autotaxin promoter and induce its expression. Similarly, oxidant stress may deplete LPP3 levels in the context of cardiac injury through reduced LPP3 expression or enhanced LPP3 degradation. Thus, we hypothesize that doxorubicin‐induced cardiac injury alters autotaxin and LPP3 expression through mitochondrial superoxide production to drive lysophosphatidic acid signaling and cardiomyocyte dysfunction. The following interrelated specific aims are designed to provide step‐wise and in‐depth studies in vitro, in vivo, and in experimental therapeutics settings. Specific aim 1 will assess the role of myocardial superoxide production in autotaxin expression and lysophosphatidic acid production in doxorubicin‐induced cardiac injury. Specific aim 2 will determine the role of mitochondrial superoxide production in LPP3 depletion and lysophosphatidic acid regulation in doxorubicin‐induced cardiac injury. We could identify whether modulation of cellular versus mitochondrial antioxidant status confers a differential protective effect in doxorubicin‐induced cardiac injury models.Support or Funding InformationAAA‐ FGAP Fellow grant funded by the American Association of Anatomists.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

201 - Oxidative stress mediated myocardial lysophosphatidic acid signaling

The bioactive lysophosphatidic acid (LPA) plays a well-known role in atherosclerotic disease, whereas, its role in myocardial function remains virtually unexplored. Following acute myocardial infarction, serum LPA concentration rises by six-fold over control human subjects, suggesting LPA may contribute to the pathogenesis of myocardial infarction. LPA production involves hydrolysis of lysophosphatidylcholine by the secreted enzyme autotaxin, whereas lipid phosphate phosphatase-3 (LPP3) catalyzes LPA dephosphorylation to generate lipid products that are not receptor active. We present the first evidence that cardiac ischemia/reperfusion (I/R) injury enhances myocardial autotaxin levels and decreases myocardial LPP3 expression, and this is associated with increased serum LPA levels. Upon reperfusion, reactive oxygen species production arises as a burst of superoxide from mitochondria following I/R injury. The redox-sensitive transcription factor NFAT has been shown to bind to the autotaxin promoter and induce its expression. Therefore, we looked at the autotaxin and LPP3 regulation in mice following I/R injury in the myocardium. After 1h ligation followed by 3h reperfusion in the myocardium, we observed a 3 fold increase in the autotaxin protein levels, whereas LPP3 protein levels were significantly downregulated as observed through Western blot analysis in these myocardial ischemic tissues. Autotaxin and miR-92a mRNA expression levels were significantly upregulated, whereas KLF2 and LPP3 mRNA expressions were significantly downregulated following I/R injury at 24 hours. Western blot analysis showed a 3 fold increase autotaxin protein levels and immunohistochemistry of human infarct tissues at 24 hours showed disruption of the sarcomere with decreased LPP3 staining. We found that I/R injury transactivates miR-92a, and inhibit KLF2, an upstream activator of LPP3. Taken together, our in vivo data, from the myocardial I/R injury and human infarct tissues, suggest that regulation of autotaxin and LPP3 activity might cause the rise in serum LPA levels as reported with acute myocardial infarct patients

Abstract 541: LPP3 Deficiency Impairs Mitochondrial Function and Enhances Myocardial LPA Mediated Signaling

The enzyme autotaxin is responsible for the conversion of lysophosphatidylcholine to lysophosphatidic acid (LPA), and the enzyme lipid phosphate phosphatase 3 (LPP3) is responsible for the degradation of LPA. Recently, we have shown that LPP3 plays a prominent role in the heart compared to other isoforms of LPP(Redox Biol. 2018 Apr;14:261-271). LPP3 is localized on the Mitochondria-Associated Endoplasmic Reticulum Membranes (MEM), and changes in the activity of LPP3 in the MEM play a critical role in the transport of essential membranous lipids. Mitochondrial membranous lipids regulated by the MEM are necessary for the mitochondria to survive, as they are not produced in the mitochondria. Lack of LPP3 decreased both diacylglycerols (P &lt; 0.001) and phosphatidylglycerol (P &lt; 0.001) in the membrane fractions as assessed by mass spectrometry(MS/MS). Lpp3 Δ myocardium showed distorted intercalated disc with damaged mitochondria with disorganized cristae and amorphous matrix densities as compared to lpp3 fl in transmission electron microscopy. Lack of LPP3 resulted in deteriorating cardiac function. To further understand the mitochondrial regulation mediated by LPP3, we studied the effect of LPA on mitochondrial respiration under different conditions using the Seahorse XF24 analyzer to measure the oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) in cardiomyocytes. Our results show that the exposure to LPA significantly decreased OCR (P &lt; 0.001) and increased ECAR (P &lt; 0.001). The addition of autotaxin inhibitors PF8380 had a reverse effect on OCR and ECAR. The increase in OCR and reduction in ECAR was even more pronounced after blocking of LPA signaling using Brp-LPA receptor blocker (P &lt; 0.001). Our real-time observation studies on mitochondrial oxidative phosphorylation status revealed mitochondrial dysfunction with increased production of superoxide (a normal byproduct of oxidative phosphorylation that is formed at increased rates when the electron transport chain is defective) in the cardiomyocytes that lack LPP3. The re-expression of LPP3 mitigated oxidative stress. This study is crucial for the understanding of the importance of LPP3 in the preservation of both cardiac and mitochondrial function.

Cardiac-specific inactivation of LPP3 in mice leads to myocardial dysfunction and heart failure

Lipid Phosphate phosphatase 3 (LPP3), encoded by the Plpp3 gene, is an enzyme that dephosphorylates the bioactive lipid mediator lysophosphatidic acid (LPA). To study the role of LPP3 in the myocardium, we generated a cardiac specific Plpp3 deficient mouse strain. Although these mice were viable at birth in contrast to global Plpp3 knockout mice, they showed increased mortality ~ 8 months. LPP3 deficient mice had enlarged hearts with reduced left ventricular performance as seen by echocardiography. Cardiac specific Plpp3 deficient mice had longer ventricular effective refractory periods compared to their Plpp3 littermates. We observed that lack of Lpp3 enhanced cardiomyocyte hypertrophy based on analysis of cell surface area. We found that lack of Lpp3 signaling was mediated through the activation of Rho and phospho-ERK pathways. There are increased levels of fetal genes Natriuretic Peptide A and B (Nppa and Nppb) expression indicating myocardial dysfunction. These mice also demonstrate mitochondrial dysfunction as evidenced by a significant decrease (P < 0.001) in the basal oxygen consumption rate, mitochondrial ATP production, and spare respiratory capacity as measured through mitochondrial bioenergetics. Histology and transmission electron microscopy of these hearts showed disrupted sarcomere organization and intercalated disc, with a prominent disruption of the cristae and vacuole formation in the mitochondria. Our findings suggest that LPA/LPP3-signaling nexus plays an important role in normal function of cardiomyocytes.

Abstract 454: Oxidative Stress Mediated Myocardial Lysophosphatidic Acid Signaling

The bioactive lysophosphatidic acid (LPA) plays a well-known role in atherosclerotic disease, whereas, its role in myocardial function remains virtually unexplored. Following acute myocardial infarction, serum LPA concentration rises by six-fold over control human subjects, suggesting LPA may contribute to the pathogenesis of myocardial infarction. LPA production involves hydrolysis of lysophosphatidylcholine by the secreted enzyme autotaxin, whereas lipid phosphate phosphatase-3 (LPP3) catalyzes LPA dephosphorylation to generate lipid products that are not receptor active. We present the first evidence that cardiac ischemia/reperfusion (I/R) injury enhances myocardial autotaxin levels and decreases myocardial LPP3 expression, and this is associated with increased serum LPA levels. Upon reperfusion, reactive oxygen species production arises as a burst of superoxide from mitochondria following I/R injury. The redox-sensitive transcription factor NFAT has been shown to bind to the autotaxin promoter and induce its expression. Therefore, we looked at the autotaxin and LPP3 regulation in mice following I/R injury in the myocardium. After 1h ligation followed by 3h reperfusion in the myocardium, we observed a 3 fold increase in the autotaxin protein levels, whereas LPP3 protein levels were significantly downregulated as observed through Western blot analysis in these myocardial ischemic tissues. Autotaxin and miR-92a mRNA expression levels were significantly upregulated, whereas KLF2 and LPP3 mRNA expressions were significantly downregulated following I/R injury at 24 hours. Western blot analysis showed a 3 fold increase autotaxin protein levels and immunohistochemistry of human infarct tissues at 24 hours showed disruption of the sarcomere with decreased LPP3 staining. We found that I/R injury transactivates miR-92a, and inhibit KLF2, an upstream activator of LPP3. Taken together, our in vivo data, from the myocardial I/R injury and human infarct tissues, suggest that regulation of autotaxin and LPP3 activity might cause the rise in serum LPA levels as reported with acute myocardial infarct patients.

Epigenetic‐Modification of Adult Fibroblast Cells into OCT4+ and VEGFR‐2+ Angiogenic Cells

RationaleThe epigenome of fibroblast cells is plastic. Here, we address the hypothesis that fibroblast cells can be epigenetically modified into blood vessel forming cells.Methods and ResultsHuman adult dermal fibroblast cells (hADFCs) were treated with optimal concentrations of chromatin‐modifying agents 5‐aza‐2′‐deoxycytidine (5‐Aza) and trichostatin A (TSA), thereafter subjected to activation of canonical Wnt signaling. We provide evidence that these epigenetically modified hADFCs increasingly expressed β‐catenin, pluripotency factor octamer‐binding transcription factor‐4 (OCT4, also known as POU5F1), and endothelial cell (EC) marker called vascular endothelial growth factor receptor‐2 (VEGFR‐2) and Lipid Phosphate Phosphatase‐3 (LPP3). Staining and microscopic analysis showed differential localization of β‐catenin and OCT4 proteins in epigenetically modified hADFCs. Accordingly, in a chromatin immunoprecipitation (ChIP) assay, OCT4 bound to the VEGFR‐2/FLK1 promoter. Finally, these modified hADFCs also transduced Wnt signaling. Importantly, on a three‐dimensional (3D) Matrigel, a subset of modified cells formed branching point network‐like structures in VEGF‐dependent manner.SummaryThe epigenome of adult fibroblast cells is amenable to epigenetic modification, and has significant implications for the use of epigenetically modified cells to promote angiogenesis in vivo.Support or Funding InformationStudies were supported by the RO1‐HL079356 and (GRNT25710129) and by the University of Illinois at Chicago Center for Clinical and Translation Science Award (UL1RR029879) to K.K.W. J.B was supported by AHA pre‐doctoral fellowship Mid‐West affiliate (15PRE22760004) and CCTS‐PECTs (1UL1TR002003). The UIC, RRC Core Imaging Facility, at the University of Illinois Chicago.

MicroRNA-184 is a downstream effector of albuminuria driving renal fibrosis in rats with diabetic nephropathy

Aims/hypothesisRenal fibrosis is a common complication of diabetic nephropathy and is a major cause of end-stage renal disease. Despite the suggested link between renal fibrosis and microRNA (miRNA) dysregulation in diabetic nephropathy, the identification of the specific miRNAs involved is still incomplete. The aim of this study was to investigate miRNA profiles in the diabetic kidney and to identify potential downstream targets implicated in renal fibrosis.MethodsmiRNA expression profiling was investigated in the kidneys of 8-month-old Zucker diabetic fatty (ZDF) rats during overt nephropathy. Localisation of the most upregulated miRNA was established by in situ hybridisation. The candidate miRNA target was identified by in silico analysis and its expression documented in the diabetic kidney associated with fibrotic markers. Cultured tubule cells served to assess which of the profibrogenic stimuli acted as a trigger for the overexpressed miRNA, and to investigate underlying epigenetic mechanisms.ResultsIn ZDF rats, miR-184 showed the strongest differential upregulation compared with lean rats (18-fold). Tubular localisation of miR-184 was associated with reduced expression of lipid phosphate phosphatase 3 (LPP3) and collagen accumulation. Transfection of NRK-52E cells with miR-184 mimic reduced LPP3, promoting a profibrotic phenotype. Albumin was a major trigger of miR-184 expression. Anti-miR-184 counteracted albumin-induced LPP3 downregulation and overexpression of plasminogen activator inhibitor-1. In ZDF rats, ACE-inhibitor treatment limited albuminuria and reduced miR-184, with tubular LPP3 preservation and tubulointerstitial fibrosis amelioration. Albumin-induced miR-184 expression in tubule cells was epigenetically regulated through DNA demethylation and histone lysine acetylation and was accompanied by binding of NF-κB p65 subunit to miR-184 promoter.Conclusions/interpretationThese results suggest that miR-184 may act as a downstream effector of albuminuria through LPP3 to promote tubulointerstitial fibrosis, and offer the rationale to investigate whether targeting miR-184 in association with albuminuria-lowering drugs may be a new strategy to achieve fully anti-fibrotic effects in diabetic nephropathy.

Abstract 205: Impact of PLPP3 Gene Deficiency on Lipid Metabolism and Signaling

Genome wide association studies identify heritable variants within the final intron of the PLPP3 gene that associate with coronary artery disease risk. The risk associated alleles of these variants alter activity of an enhancer sequence that acts in cis to upregulate expression of the gene in response to inflammatory and atherogenic stimuli (for example oxidized low density lipoprotein) and may have longer distance effects on expression of other genes. PLPP3 encodes lipid phosphate phosphatase 3 (LPP3) which is an integral membrane enzyme that dephosphorylates lipid phosphate esters. These substrates are bioactive signaling molecules at the cell surface including lysophosphatidic acid (LPA) and sphingosine 1 phosphate (S1P) and intracellular intermediates in pathways of lipid metabolism and signaling, for example ceramide 1 phosphate and phosphatidic acid. PLPP3 is essential for vascular development in mice. We have generated mice with inducible post-natal and tissue specific inactivation of this gene which are viable and exhibit accelerated atherosclerosis on a low density lipoprotein receptor knockout background after feeding atherogenic diets. Analysis using targeted and untargeted approaches using multistage and high resolution mass spectrometry reveal that LPP3 deficiency results in significant differences in levels of some LPP3 substrates and products in cells, tissues and biological fluids from these animals. These observations support the hypothesis that alterations in levels of these LPP3 substrates or their dephosphorylation products account for or contribute to the mechanisms by which alterations in LPP3 expression influence cardiovascular disease risk.

Abstract 467: Lipid Phosphate Phosphatase 3 in Smooth Muscle Cells Suppresses the Development of Atherosclerosis

Lipid phosphate phosphatase3 (LPP3) encoded by the PPAP2B gene, is an integral membrane enzyme that degrades bioactive lysophospholipids including lysophosphatidic acid (LPA), sphingosine-1-phosphate (S1P) and related bioactive lipids. These bioactive lipids regulate a wide variety of cellular functions such as proliferation, apoptosis and differentiation. We suggest that LPP3 hydrolysis of LPA is a critical step in regulating pathophysiological important responses in vascular cells. To test this hypothesis, we generated mice lacking LPP3 by breeding Ppap2B fl / fl mice (fl/fl) animals expressing Cre recombinase under control of the SM22 promoter on the LDLr-/- background. At weaning, littermate SM22-Δ and fl/fl mice were fed Western Diet (WD) for 12 weeks. LPP3 expression in aortic SMCs was reduced (0.139 ± 0.0246 vs 1.0 ± 0; P &lt; 0.001) and LPA content was significantly higher (9.32 ± 4.66 vs 5.66 ± 2.65; P &lt; 0.05) in the aortic arch in SM22-Δ mice compared to control fl/fl mice. SM22-Δ mice demonstrated increased atherosclerotic lesions (18.98 ± 7.11% vs 6.06 ± 4.01%; P &lt; 0.001), measured by en face analysis, of the aorta and significantly higher IL-6 expression (18.83 ± 2.87 vs 3.59 ± 8.92; P &lt; 0.05) in the aortic arch. Sections of aorta at the level of the aortic root indicated that the loss of LPP3 upregulate CD68 and α-SMA staining. These results reveal that LPP3 normally functions to suppress atherosclerosis. LPP3 deficiency increases vascular LPA content, may promote the infiltration of inflammatory cells as macrophages into lesions and smooth muscle cell proliferation to accelerate the development of atherosclerosis.