Reversing PAI-1 deficiency in blood using mRNA lipid nanoparticles

Plasminogen activator inhibitor-1 (PAI-1) deficiency is a rare disorder that causes moderate to severe bleeding and cardiac fibrosis, caused by mutation in the <i>SERPINE-1</i> gene and no detectable circulating PAI-1 protein. There are currently no therapies that can effectively replace PAI-1 because the protein has a short half-life. An alternative approach to using recombinant protein is to endogenously increase circulating PAI-1 levels using mRNA therapy. Delivering mRNA encoding PAI-1 to the liver, a major site of PAI-1 synthesis, using lipid nanoparticles (mPAI-1) is a potential approach to increase circulating PAI-1 protein. Here, we developed mPAI-1, which induced expression of PAI-1 <i>in vivo</i> upon intravenous administration. In both wild-type (WT) mice and PAI-1 knockout mice, mPAI-1 induced supraphysiological circulating PAI-1 and inhibited fibrinolysis when measured <i>ex vivo</i>. In WT mice, plasma PAI-1 levels increased in a dose-dependent manner between 0.1 and 1 mg of mRNA per kg of body weight, peaking at 6 h post-injection and returning to baseline by 48 h. There was consistent production of PAI-1 after repeat dosing of mPAI-1 in the same mice. Expression of PAI-1 using mRNA-based approaches has the potential to be a preventive therapy for bleeding and cardiac fibrosis for PAI-1-deficient patients.