Conversations with Lipid Leaders: Dr. Fumio Sakane

Posted on July 01, 2021

Fumio Sakane

Tell us a little bit about yourself (current role, background, family, etc.)

I am currently a professor (since 2009) in the Department of Chemistry in Chiba University Graduate School of Science, Chiba, Japan. I was born and grew up in Hokkaido Island (a new world in Japan resembling America in the world) where is rich in nature. In 1987, I gained PhD from Hokkaido University (Laboratory of Hygienic Chemistry (Biochemistry), Graduate School of Pharmaceutical Sciences). After a postdoctoral fellow at Hokkaido University, I worked as Assistant Professor/Associate Professor in Department of Biochemistry, Sapporo Medical University (Professor Kanoh’s Lab) from 1988 to 2009. In addition, I worked as a visiting fellow in the University of Utah (Professor Prescott’s Lab) in 1997–2000. Because I am busy, I cannot take my partner anywhere for sightseeing, hot springs etc.. However, she who is soft and gentle understands my job.

What do you consider the largest breakthrough in lipid research in the last few years?

This question is very difficult to answer. There are many breakthroughs in lipid research in recent years. As for me, recent progresses in mass spectrometric analyses on lipids including imaging mass microscope are impressive.

Did you always envision yourself becoming a scientist? If not, what did you want to be when you grew up? Who influenced you to become a scientist?

Yes. When I was a primary school child, I liked to catch and watch fishes and insects. Moreover, I read an encyclopedia and many biological picture books. So, I felt the mystery of life and wanted to know its molecular mechanisms. Since then, I had been always and vaguely envisioning myself becoming a scientist. In my opinion, no one influenced me to become a scientist.

How did you identify that diacylglycerol kinases/lipid-metabolizing enzymes was what you wanted to study most? What is the significance of understanding these enzymes and controlling their activity?

In my doctoral thesis, I reported that a superoxide anion-generating enzyme needs lipids (e.g. phosphatidylcholine (PC)) for maximum activity. Thus, I began to be interested in “lipid” as a research target and thus selected Professor Kanoh’s Lab, which was performing lipid research. When I went to the Lab, he had already purified diacylglycerol kinase (DGK) (later designated as DGKa), which phosphorylates diacylglycerol (DG) to produce phosphatidic acid (PA), from pig thymus. Then, for the first time, I cDNA-cloned the DGKa gene in 1989. I next identified several DGK isozymes (finally ten isozymes were found by us and other groups). In those days, Professor Kanoh (and most researchers) thought that DGK isozymes are just scavengers/converters of excess DG during phospholipid biogenesis and the PI turnover (the PI(4,5)P2 pathway). Therefore, he (and most researchers) did not think that DGKs are very interesting research targets. However, I have been believing that DGKs play various important roles in signal transduction in cells. There were several reasons: (1) Ten isozymes have distinct regulatory domains. I thought that If DGK is just a scavenger of excess DG, only one or a few DGK isozymes without regulatory domains are needed. (2) As for the PI turnover, only DGKe selectively phosphorylates PI-turnover-derived DG (arachidonic acid (20:4)-containing DG) in vitro. In contrast, other nine DGK isozymes fail to show such selectivity, suggesting that they have broad physiological functions that are not bound by the PI turnover and potential for expansion looking toward the future. (3) The DGK catalytic reaction is an energy (ATP)-consuming process. If just a scavenger is needed, DG lipase, a non-energy consuming enzyme, would be selected by life. I considered that PA produced in exchanged for ATP likely has physiologically important roles. (4) There are many PA species that have two fatty acids with various chain lengths and degrees of unsaturation. In contrast, phosphoinositide are different in phosphorylation numbers and positions of inositol, which are far from fatty acid moieties. I speculated that PA-binding proteins can access to fatty acid moieties because the hydrophilic head of PA is small. Therefore, it is possible that, among phospholipids, differences in fatty acid moieties of PA molecules most strongly affect affinities of their binding proteins. Thus, PA can be a good model to address physiological significance of fatty acid compositions in phospholipids. (5) DG is considerably hydrophobic and has no charge. In contrast, PA has phosphate group, which is compact and negatively (2–) charged. Therefore, DG–PA conversion likely produces greater physicochemical changes in biomembranes and their proximity than those of PI(4)P–PI(4,5)P2 transition by PI(4)P 5-kinase and PC–PA conversion by phospholipase D. I thought that the dynamic change caused by the DGK-dependent DG–PA conversion would be physiologically important.

Today, it has been established that DGK isozymes are involved in a variety of signal transduction pathways and physiological functions, and that their disfunctions lead to pathogenesis of many diseases including cancer, type 2 diabetes, bipolar disorder, obsessive-compulsive disorder. Therefore, DGKs have become very attractive research targets.

Recently, your group discovered a novel diacylglycerol/phosphatidic acid signaling pathway together with diacylglycerol kinase. This pathway was proven to be independent of the PI(4,5)P2 pathway. What could be the future significance of identifying this novel pathway?

Liquid chromatography-mass spectrometry (LC-MS) is a powerful tool for lipid research. However, PA was difficult to quantitate with high reproducibility and accuracy under the general LC conditions because of ion suppression caused by other major phospholipids, PC and sphingomyelin. Consequently, we optimized LC mobile phases to segregate PA from major phospholipids. Then, we detected the PA molecular species generated by different DGK isozymes in cells and organs and revealed that various PA species (e.g. 16:0/16:0-, 16:0/16:1-, 16:0/18:1-, 18:1/20:2-, and 18:0/22:6-PA) other than 18:0/20:4-PA, which is exclusively derived from the PI turnover, were produced by DGK isozymes. Notably, these results support a new view that DGK isozymes, except for DGKe, utilize DG species derived from pathways independent of the PI turnover.

Recently, we proposed the alternative DG metabolic pathway “Phosphatidylethanolamine (PE)/PI/PC/PA –> sphingomyelin synthase-related protein (SMSr) –> DG –> DGKd –> PA”. This pathway metabolizes palmitic acid (16:0)- and/or palmitoleic acid (16:1)-containing glycerolipids, but not arachidonic acid (20:4)-containing glycerolipids. Therefore, this new pathway is likely independent of the PI turnover, although the substrate of DGK is generally thought to be derived from the PI-dependent pathway like a dogma. Interestingly, we found the previously unrecognized enzyme activities of mammalian SMSr (ceramide phosphoethanolamine synthase), novel PA phosphatase, PI-phospholipase C (PLC), PE-PLC and PC-PLC activities, i.e. multi-glycerophospholipid PLC hydrolase, which hydrolyses these phospholipids to produce DG in the absence of ceramide. Because SMSr provides only 16:0- and/or 16:1-containing DG species, other DG-supply enzymes for DGK isozymes would exist in addition to SMSr.

It is possible that diverse PA molecular species are generated by several novel DG/PA pathways, which link to distinct DGK isozymes. However, PA molecular species-selective binding proteins have not ever been eagerly searched for. Thus, we speculate that there are unidentified PA molecular species-selective binding proteins, and are searching for them. Indeed, several 16:0/16:0-PA-, 18:0/22:6-PA- and 18:1/18:1-PA-selective binding proteins have been identified by us. Probably, there are more PA molecular species-selective binding proteins.

Taken together, novel DG/PA signaling pathways probably make the wide networks consist of distinct DG-supply enzymes, distinct DG–PA converting enzymes (DGK isozymes), distinct PA molecular species and distinct PA molecular species-selective binding proteins. The networks would play critical roles in a variety of cell events. I keenly want to reveal the entire picture of the novel pathways/networks, which may cover wider ranges of biological processes than the PI turnover.

What are your hobbies? What do you like to do outside of the lab?

My research work consists of my job (50%) and primary hobby (50%). My second hobby is cycling. I go cycling 15–20 km (one way) to coasts, riversides, forests, hills etc. every weekend to see good sights and to address my lack of exercise due to long desk work.

What was your favorite and least favorite course in school? What was the hardest course for you while you were in school?

My favorite courses in school were mathematics, physical education (gym) and art. I hated calligraphy, which forced to trace typical examples.

Do you have a favorite Avanti product or category of products? Maybe a product that you’ve found most helpful in your research?

A wide variety of DG and PA molecular species (and other phospholipid molecular species) containing different fatty acid moieties are very helpful in my research.

We would like to thank Dr. Fumio Sakane for taking time to catch up with us!

Click HERE to learn even more about his exciting research!