👤 Julia M Assini

Elevated levels of lipoprotein(a) (Lp[a]) are a causal risk factor for atherosclerotic cardiovascular disease. Similarities between the apolipoprotein(a) (apo[a]) component of Lp(a) and plasminogen suggest that antifibrinolytic properties may account for the pathological effects of Lp(a). However, the antifibrinolytic effects of apo(a) do not appear to be retained by the complete Lp(a) particle. We evaluated the effects of Lp(a), apo(a), and various apo(a) variants on clot formation and lysis times, thrombin generation, plasminogen activation, and fibrin architectures in ex vivo plasma clots. We also constructed predictive protein models to gain insight into the apo(a)-plasminogen interaction. Apo(a) strongly inhibited fibrinolysis, an effect dependent on the presence of the apo(a) protease domain and mediated by Lys216 in this domain. Modeling of apo(a) suggests that Lys216 is blocked from binding to plasminogen in the Lp(a) particle by the presence of the apoB-containing lipoprotein. Lp(a) and apo(a) shortened plasma clot formation times, and accounting for this revealed a small but significant prolongation of fibrinolysis by Lp(a). The procoagulant effects involved the development of lysis-resistant clot architectures and were mediated through the strong lysine-binding site in apo(a) kringle IV type 10. In addition, Lp(a) (but not apo[a]) accelerated thrombin generation. The strong antifibrinolytic effects of apo(a) do not appear to be retained in the complete Lp(a) particle. However, Lp(a) and apo(a) displayed procoagulant effects, in part dependent on the kringle 4-like lysine-binding site. Further analysis is required to determine whether these reported procoagulant effects of Lp(a) impact thrombosis in vivo. Show less

Lipoprotein(a) (Lp(a)) is a genetically determined causal risk factor for cardiovascular disease, with approximately 20% of the population exhibiting elevated levels. While there are promising drugs in development, there are currently no approved therapies specifically designed to lower Lp(a) levels. For high-risk individuals with extreme levels of Lp(a), liver-directed genome editing could be an effective one-time solution. Genome editing approaches such as CRISPR and TALENs can reduce Lp(a) in LPA-transgenic mouse models, but they frequently induce large and potentially harmful genomic deletions. Here, we report the first application of TadA-derived cytosine base editing (CBE), delivered via helper-dependent adenovirus (HDAdV) and adeno-associated virus (AAV) vectors, to introduce premature stop codons into LPA. This strategy produced robust and durable lowering of circulating apolipoprotein(a) (apo(a)) in LPA-transgenic mice. Using SMRT-seq with single-molecule unique molecular identifiers, we quantified deletion events and found that CBE did not induce large deletions when targeting a single LPA site and produced only a small fraction (<4%) of large deletions when editing across multiple sites. In contrast, CRISPR-Cas9 cutting of LPA resulted primarily in large deletions. These findings demonstrate that CBE enables sustained reduction of circulating apolipoprotein(a) in an LPA-transgenic mouse model while largely preserving genomic integrity. Show less