It has been shown that ACLY is localized
It has been shown that ACLY is localized to not only the cytoplasm but also the nucleus. Nuclear ACLY may supply acetyl-CoA for histone acetylation, leading to global regulation of the gene expression , . We previously reported that AZ2 is also localized to both the cytoplasm and nucleus whereas AZ1 is mainly localized to the cytoplasm . Although we did not confirm the co-localization of AZ2 and ACLY to the nucleus in the present study, AZ2 may have a specific role in regulating nuclear ACLY.
Acknowledgment This work was supported by the MEXT*-Supported Program for the Strategic Research Foundation at Private Universities 2011–2015 (S1101006) and The Jikei University Research Fund for Graduate Students (*Ministry of Education, Culture, Sports, Science and Technology).
Introduction Inflammation is the body’s basic response to a variety of external or internal insults, such as infectious agents, physical injury, hypoxia, or disease processes . Macrophages play a major role in the inflammatory process by detecting these insults and releasing various pro-inflammatory molecules including prostaglandins (PGs), reactive oxygen species (ROS), nitric oxide (NO) and cytokines. These factors promote inflammation by causing vasodilation and recruitment of neutrophils, monocytes and by altering the functionality of many tissues and organs. Depending on the inducer, the inflammatory response has a different physiological purpose and pathological consequences. For instance, during microbial infections one of the most potent macrophage activators is the gram-negative bacterial cell wall component lipopolysaccharide (LPS) which leads to the production of a variety of inflammatory mediators . Here we investigate the role of ATP-citrate lyase (ACLY), a cross-link between glucose metabolism and fatty CVT 10216 receptor synthesis. In the cytoplasm, glucose-derived citrate is transformed, in the presence of ATP, into acetyl-CoA by ACLY , . Acetyl CoA is an essential substrate for cholesterol, isoprenoids and fatty acid synthesis pathways. Acetyl-CoA is also required for acetylation of nuclear histones in mammalian cells . ACLY is most abundantly expressed in liver and white adipose tissue. Additionally, ACLY expression has been reported to be upregulated in many tumors, nonalcoholic fatty liver disease and other pathological conditions . Surprisingly, we find that ACLY expression levels markedly and quickly increase in normal peripheral blood differentiated macrophages as well as in macrophage cell lines activated by exogenous and endogenous inducers. Furthermore, the specific ACLY activity inhibition or gene silencing is sufficient to reduce production of inflammatory mediators. Overall these results indicate a central role for ACLY in inflammation. In light of the evidence presented here, the ability of ACLY to integrate energy metabolism and inflammatory signaling makes it a particularly attractive target in human inflammatory diseases.
Materials and methods
Discussion In activated macrophages, the inflammatory response is characterized by the release of an array of pro-inflammatory mediators, which results in a signal transduction that activates the transcription of numerous pro-inflammatory genes. In these conditions, activated macrophages shift towards an increased glycolysis in concert with the attenuation of oxidative phosphorylation to maintain ATP levels . It is likely that the altered metabolism parallels TCA cycle changes from being a purely catabolic pathway generating ATP to become, at least in part, an anabolic pathway. Recently we found an upregulation of the mitochondrial citrate carrier (CIC) gene expression in LPS-activated macrophages and a reduction of inflammatory mediators when CIC activity was inhibited . To shed light on citrate metabolism and inflammation, the present study investigates the role of ACLY, the enzyme which acts immediately downstream to CIC, in activated macrophages. Very unexpectedly, the observed ACLY gene upregulation is earlier than CIC activation (24h after LPS-stimulation) in macrophages from peripheral blood as well as in macrophage cell lines induced with LPS , even though CIC is essential for citrate export from mitochondria and therefore to provide the substrate for ACLY activity. In light of these observations, it can be assumed that CIC function needs only when the cytosolic citrate is depleted following the quick ACLY activation. This outcome suggests a primary role for cytosolic citrate, substrate of ACLY, which could be a signal molecule in inflammation. Importantly, our data also highlight an early gene upregulation of ACLY in IFNγ and/or TNFα-induced macrophages.