ATX‐LPP3 axis mediated LPA regulation following myocardial injury

Abstract

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.