OC 26.1 - A novel rat model of spontaneous thrombotic thrombocytopenia Purpura Reveals a Critical Role of ADAMTS13 in Fetal Health

Background: Thrombotic thrombocytopenia purpura (TTP) is characterized by severe thrombocytopenia and microangiopathic hemolytic anemia with various degrees of organ injury. Therapeutic options are still limited.

Aims: To establish a rat model of TTP for testing triggering factors and novel therapeutics.

Methods: CRISPR/Cas9 (Fig. 1), Cattle-FRETS71 assay, complete blood cell count, urea nitrogen/creatinine, LDH, VWF antigen, and VWF multimer assays, as well as histology were performed.

Results: One mutant carrying a 13-bp deletion was predicted to generate a premature stop codon in Adamts13 transcript. We demonstrated that mean plamsa activity in wild type (WT), heterozygous (Adamts13+/-), and homozygous (Adamts13-/-) rats was 67.7%, 48.3%, and 2.5% (p < 0.0001), respectively (Fig. 2A). Adamts13-/- rats develop severe spontaneous thrombocytopenia with the mean platelet count in WT, Adamts13+/-, and Adamts13-/- rats 474.1x10^9/L, 511.8 x10^9/L, and 135.4x10^9/L (p < 0.0001), respectively (Fig. 2B). Plasma from Adamts13-/- rats showed a statistically significant increase in high molecular weight VWF multimers (p < 0.05) (Fig. 2C/D). Plasma levels of urea nitrogen (Fig. 2E), creatinine, and LDH were elevated in Adamts13-/- rats compared with those in the WT controls. More interestingly, Adamts13-/- rats had a significantly smaller litter size when bred with the Adamts13-/- rats (p < 0.05), compared to that bred with the WT rats (Fig. 2F), suggesting that severe plasma Adamts13 deficiency in both maternal and fetal circulation may be detrimental for fetal survival.

Conclusion(s): We have successsfully established and fully characterized a novel rat model of TTP. Adamts13-/- rats develop spontenous and severe thrombocytopenia with evidence of organ injury and potentially fetal death. This new rat model may provide an invaluable tool for further investigating a potential genetic and environmental trigger of TTP and testing various novel therapeutics for acute TTP. The model may also be used to investigate how pregnancy may affect the onset and progression of TTP.