Abstract 5336: Establishment and characterization of a novel inducible Apoc2 knockout mouse model to study the roles of Apoc2 in normal hematopoiesis

Abstract Apolipoprotein C2 (Apoc2) is upregulated in acute myeloid leukemia and presents a viable therapeutic target. Whether this gene plays a role in normal hematopoiesis remains unknown. To investigate the impact of targeting Apoc2 on normal hematopoiesis, we established and characterized an inducible Apoc2 knockout mouse model. Homozygous floxed Apoc2 mice (Apoc2fl/fl) were obtained from the NIH (Dr. Remaley’s lab) and were crossed with homozygous R26-CreERT2 mice. After three generations, Gt(ROSA)26SorCre/Cre, Apoc2fl/fl mice were generated and confirmed by genotyping. Male (M) and female (F) mice were injected with tamoxifen (TAM: 20mg/mL dissolved in corn oil) intraperitoneally (75mg/kg per day for 5 days) to induce Apoc2 knockout (Apoc2-KO). The control wild type (WT) group included Gt(ROSA)26Sorwt/wt, Apoc2fl/fl mice, and CD45.2+ WT mice injected with TAM, or Gt(ROSA)26SorCre/Cre, Apoc2fl/fl mice injected with corn oil.No obvious abnormal phenotypes were observed in Apoc2-KO mice. The average increase of body weight 3 weeks post TAM or corn oil injections of 5-week-old Gt(ROSA)26SorCre/Cre, Apoc2fl/fl siblings was not statistically significantly different (Apoc2-KO (n = 2M + 2F) vs WT (n = 2M + 2F) = 2.450g vs 2.125g, P = 0.63). Analyses of Apoc2-KO (n = 5M + 3F) and WT (n = 4M + 2F showed no significant difference in livers and spleens weight when normalized to mice age. The percentage of knockdown in liver (99.96%), spleen (77.32%), bone marrow (BM, 83.56%) and blood (82.02%) was confirmed by qPCR. In-vitro cell expansion was performed in the presence of thrombopoietin and stem cell factor for BM cells and IL-2 and PHA for T cells. Apoc2-KO BM cells exhibited similar in vitro expansion to that of control mice (Apoc2-KO vs WT: Day 10/Day 6: 1.22 fold vs 1.57 fold; Day 10/Day 1: 57.26% vs 72.34%; P > 0.05; and Cell Trace assay: mean fluorescence intensity (MFI) of Day 9 normalized to Day1: Apoc2-KO vs WT = 0.37 vs 0.39; P > 0.05). Also, the colony forming ability was not significantly different between Apoc2-KO and WT BM cells (Apoc2-KO vs WT = 79.09 units vs 81.47 units, P = 0.62). In-vitro T cell expansions of splenocytes were not significantly different between Apoc2-KO and WT mice (Apoc2-KO vs WT: Day 10/Day 4: 1.73 fold vs 1.83 fold; Cell Trace: mean MFI of Day 9 normalized to Day1: Apoc2-KO vs WT = 0.6208 vs 0.7088; P > 0.05). Hematology analysis assessing white blood cell count, red blood cell count, hemoglobin count, neutrophil, lymphocytes, showed no significant difference between the groups.Here we report the first inducible Apoc2 knockout mouse model and demonstrated that Apoc2 knockout has limited impact on normal hematopoietic cells in mice. On-going research using this model will assess the impact of Apoc2 knockout on ageing related phenotypes and leukemia progression. Citation Format: Xiaochen Zhang, Ritu Chandwani, Mateusz Pospiech, Yiting Meng, Kanaka Dhuri, Bhakti Thakker, Atham Ali, Shephali M. Kadam, Yu-Chun Wei, Houda Alachkar. Establishment and characterization of a novel inducible Apoc2 knockout mouse model to study the roles of Apoc2 in normal hematopoiesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5336.