Clinacanthus nutans Lindau (C. nutans), commonly known as Sabah Snake Grass in southeast Asia, is widely used in folk medicine due to its analgesic, antiviral, and anti-inflammatory properties. Our recent study provided evidence for the regulation of cytosolic phospholipase A2 (cPLA2) mRNA expression by epigenetic factors (Tan et al. in Mol Neurobiol. doi: 10.1007/s12035-015-9314-z , 2015). This enzyme catalyzes the release of arachidonic acid from glycerophospholipids, and formation of pro-inflammatory eicosanoids or toxic lipid peroxidation products such as 4-hydroxynonenal. In this study, we examined the effects of C. nutans ethanol leaf extracts on epigenetic regulation of cPLA2 mRNA expression in SH-SY5Y human neuroblastoma cells and mouse primary cortical neurons. C. nutans modulated induction of cPLA2 expression in SH-SY5Y cells by histone deacetylase (HDAC) inhibitors, MS-275, MC-1568, and TSA. C. nutans extracts also inhibited histone acetylase (HAT) activity. Levels of cPLA2 mRNA expression were increased in primary cortical neurons subjected to 0.5-h oxygen-glucose deprivation injury (OGD). This increase was significantly inhibited by C. nutans treatment. Treatment of primary neurons with the HDAC inhibitor MS-275 augmented OGD-induced cPLA2 mRNA expression, and this increase was modulated by C. nutans extracts. OGD-stimulated increase in cPLA2 mRNA expression was also reduced by a Tip60 HAT inhibitor, NU9056. In view of a key role of cPLA2 in the production of pro-inflammatory eicosanoids and free radical damage, and the fact that epigenetic effects on genes are often long-lasting, results suggest a role for C. nutans and phytochemicals to inhibit the production of arachidonic acid-derived pro-inflammatory eicosanoids and chronic inflammation, through epigenetic regulation of cPLA2 expression.

Group IVA cytosolic phospholipase A2 (cPLA2 or PLA2G4A) is a key enzyme that contributes to inflammation via the generation of arachidonic acid and eicosanoids. While much is known about regulation of cPLA2 by posttranslational modification such as phosphorylation, little is known about its epigenetic regulation. In this study, treatment with histone deacetylase (HDAC) inhibitors, trichostatin A (TSA), valproic acid, tubacin and the class I HDAC inhibitor, MS-275, were found to increase cPLA2α messenger RNA (mRNA) expression in SH-SY5Y human neuroblastoma cells. Co-treatment of the histone acetyltransferase (HAT) inhibitor, anacardic acid, modulated upregulation of cPLA2α induced by TSA. Specific involvement of class I HDACs and HAT in cPLA2α regulation was further shown, and a Tip60-specific HAT inhibitor, NU9056, modulated the upregulation of cPLA2α induced by MS-275. In addition, co-treatment of with histone methyltransferase (HMT) inhibitor, 5'-deoxy-5'-methylthioadenosine (MTA) suppressed TSA-induced cPLA2α upregulation. The above changes in cPLA2 mRNA expression were reflected at the protein level by Western blots and immunocytochemistry. Chromatin immunoprecipitation (ChIP) showed TSA increased binding of trimethylated H3K4 to the proximal promoter region of the cPLA2α gene. Cell injury after TSA treatment as indicated by lactate dehydrogenase (LDH) release was modulated by anacardic acid, and a role of cPLA2 in mediating TSA-induced injury shown, after co-incubation with the cPLA2 selective inhibitor, arachidonoyl trifluoromethyl ketone (AACOCF3). Together, results indicate epigenetic regulation of cPLA2 and the potential of such regulation for treatment of chronic inflammation.

No abstract