Gene Expression Patterns and Functional Characterization of CD36 in Normal Hematopoietic Cells

Metabolic reprogramming is a hallmark of cancer development and progression. Lipid metabolism is among the most deregulated metabolic pathways in cancer contributing to cell survival and invasion. The fatty acid translocase CD36 has attracted attention in cancer research in recent years due to its role in fatty acid transport as a scavenger receptor. We have recently reported that upregulated APOC2 cooperates with CD36 contributing to leukemia growth by promoting the LYN-ERK signaling mediated metabolic activities of acute myeloid leukemia (AML) cells. Consistently, the knockdown of CD36 or treatment with anti-CD36 antibody reduced the leukemia progression and promoted the overall survival of AML xenograft mice. CD36 is also present on various types of normal cells, including monocytes, macrophages, endothelial cells, adipocytes, and platelets and contribute to their normal functions. Thus, whether targeting CD36 in normal hematopoietic cells poses any toxicity warrants investigation to bring the therapeutic strategy of targeting CD36 in AML to maturity. Here, we leveraged public data to assess the expression patterns of CD36 in normal hematopoietic cells. We found that CD36 expression is several folds higher in dendritic cells, monocytes, and NK cells compared with B cells, eosinophils, neutrophils, and T cells (ANOVA P < 0.001). To investigate the role of Cd36 in normal hematopoietic cells, we carried out gain- and loss-of-function approaches in murine normal hematopoietic primary cells. We engineered a tet-on inducible shRNA lentiviral plasmid targeting two different sequences of the mouse Cd36. In both healthy mouse primary spleen and bone marrow cells, the two pairs of shRNAs reduced the Cd36 mRNA levels compared with scramble control group (~70-90% reduction in mRNA expression). We also engineered two different lentivirus ectopic expression plasmid to overexpress murine Cd36 (PLVX-Cd36 virus and PCDH-Cd36). Lentiviral transduction of both spleen and bone marrow mouse cells confirmed by microscopy visualization of GFP-expressing cells showed several folds increase in Cd36 expression for both plasmids measured by qPCR and western blot. We assessed the effect of Cd36 knockdown on the expansion of spleen and bone marrow hematopoietic cells over five days of cell culture. Relative to the 1 ^st day of cell count, there was no significant decrease in the mean bone marrow cell and spleen count between the two pair of shRNA compared with scramble control group at day 3 and day 5 post doxycycline treatment (P > 0.05). Cells in the different groups showed about 2 folds expansion on day 5 relative to day 1. Our preliminary data suggest that Cd36 knockdown has limited impact on the survival of normal hematopoietic cells. In vivo experiments assessing the effect of Cd36 gain and loss of function on the engraftment of normal hematopoietic cells in mice are ongoing to further establish the functional impact of Cd36 manipulation on normal hematopoietic cells. Altogether, our studies will demonstrate whether CD36 is dispensable for the survival of normal hematopoietic cells and thus may potentially present a viable therapeutic approach in AML.