This article is available online at http://www.jlr.org Overweight and obesity are global health issues affecting 1.6 billion individuals worldwide ( 1 ). One potential strategy for reducing adiposity is consumption of conjugated linoleic acid (CLA), a group of conjugated octadecadienoic acid isomers derived from linoleic acid, a fatty acid (FA) that contains 18 carbons and 2 double bonds in the cis confi guration at the 9 th and 12 th carbons (i.e., cis -9, cis -12 octadecadienoic acid) ( 2 ). CLA is found in ruminant meats and dairy products, as microbes in the gastrointestinal tract of ruminant animals convert linoleic acid into different isoforms of CLA through biohydrogenation ( 2 ). This process changes the position and confi guration of the double bonds, resulting in a single bond between the two double bonds. The major isomers produced include cis -9, trans -11 (c9,t11) and trans -10, cis -12 (t10,c12) CLA. Food sources of CLA contain ‫ف‬ 80% c9,t11 CLA and 10% t10,c12 CLA, and the remaining 10% is composed of other isomers ( 2 ). CLA is also produced chemically from linoleic acid for inclusion in supplements and fortifi ed foods, yielding a composition containing ‫ف‬ 40% c9,t11 CLA, ‫ف‬ 40% t10,c12 CLA isomers, and the remaining 20% other isomers ( 2 ).Abstract Diacylglycerol kinases (DGK) convert diacylglycerol to phosphatidic acid, which has been reported to stimulate calcium release from the endoplasmic reticulum. Based on our published data showing that trans -10, cis -12 conjugated linoleic acid (t10,c12 CLA)-mediated intracellular calcium accumulation is linked to infl ammation and insulin resistance, we hypothesized that inhibiting DGKs with R59022 would prevent t10,c12 CLA-mediated infl ammatory signaling and insulin resistance in human adipocytes. Consistent with our hypothesis, R59022 attenuated t10,c12 CLA-mediated i ) increased gene expression and protein secretion of interleukin (IL)-8, IL-6, and monocyte chemoattractant protein-1 (MCP-1); ii ) increased activation of extracellular signal-related kinase (ERK), cJun-NH2-terminal kinase (JNK), and cJun; iii ) increased intracellular calcium levels; iv ) suppressed mRNA or protein levels of peroxisome proliferator activated receptor ␥ , adiponectin, and insulin-dependent glucose transporter 4; and v ) decreased fatty acid and glucose uptake and triglyceride content. DGK was targeted for investigation based on our fi ndings that i ) DGK was highly expressed in primary human adipocytes and timedependently induced by t10,c12 CLA and that ii ) t10,c12 CLA-induced DGK expression was dose-dependently decreased with R59022. Small interfering RNA (siRNA) targeting DGK decreased t10,c12 CLA-induced DGK , IL-8, and MCP-1 gene expression, as well as activation of JNK and cJun. Taken together, these data suggest that DGKs mediate, in part, t10,c12 CLA-induced infl ammatory signaling in primary human adipocytes.