Objectives Cell death induced by lipid accumulation in the heart may contribute to cardiac complication of obesity and type 2 diabetes, but its mechnisms remain elusidative.
Methods In the present study, we used H9c2 cardiac cell line and metallothione trasgene H9c2 cell line and treated the cells in vitro with palmitate at 62.5nM for 3 to 15 hours. The palmitate was prepared in medium containing 2%(w/v) fatty acid free BSA at the concentration of 2.5nM. Cell death was examined by activation of caspase-3 and-12 as well as CHOP by Western blotting assay, Endoplasmic reticulum (ER) associated molecules including GRP78 and ATF4 was examined for their expression by Western blotting assay and Akt cell survial singnaling was examined by Western blotting. In addition, we also did Western blotting of Akt negtive regulator Drosophila tribbles homologue3(Trib3).
Results Results showed that in wild type H9c2 cardiac cell line, caspase-3 activation was significantly evident at the 3 hours after the exposure to palmitate, no significant change from 6 to 9 hours, but significant increased again from 12 to 15 hours. H9c2 cells exposed to palmitate for 3 hours also showed a significant induction of GRP78 expression and caspase-12 activation without significant changes of other measurements. However, CHOP and ATF4 expression was increase in H9c2 cells exposed to palmitate for 9 to 15 hours, along with an increase in Trib3 expression from 12 to 15 hours. Akt phosphorylation was significantly down-regulated in the H9c2 cells exposed to palmitate in a time-dependent mannor from 6 to 15 hours. In metallothione transgene cardiac cell line, we could not observe palmitate-induced cell death.
Conclusions These results showed that there was a biphasic cell death in the palmitate-treated cardiac cells, reflected by the activation of caspase-3. ER stress-associated cell death was induced at the early phase aroud 3 hours after palmitate treatment, shown by the increase expression of GRP78 and caspase-12 activation while Akt-related cell survial pathway was down-regulated at the late phase around 12 to 15 hours, which maybe related to the up-regulation of Akt ’s negtive regulator Tri3. Metallothione, as an endogenous antioxidant, can protect palmitate-induced cell death. Its mechnism maybe through Trib3-Akt signaling pathway.