Facilitated replacement of Kupffer cells expressing a paraoxonase-1 transgene is essential for ameliorating atherosclerosis in mice

Resident macrophages (i.e., Kupffer cells) are derived from hematopoietic stem cells (HSCs) and are primarily responsible for the removal from plasma of oxidized forms of low-density lipoprotein (LDL). The therapeutic potential of Kupffer cell expression of a transgene encoding paraoxonase-1 (PON1), whose plasma activity correlates with the protection from atherosclerosis, was examined in mice rendered atherosclerosis-susceptible through genetic deletion of the LDL receptor. Mice having their bone marrow engrafted with HSCs expressing the PON1 transgene (PON1-Tg) driven by a macrophage-specific promoter were injected i.v. with saline (vehicle only) or with gadolinium chloride (GdCl(3)), an agent that rapidly causes Kupffer cell apoptosis. One month later, GdCl(3)-facilitated Kupffer cell apoptosis increased the hepatic expression of transgenic PON1 mRNA by 9-fold. After 12 weeks of being fed a cholesterol-enriched atherogenic diet, mice injected with GdCl(3) exhibited 50% reductions in both aortic sinus atherosclerotic lesions (P < 0.0097) and surface lesions of the abdominal aorta (P < 0.006). In contrast, mice receiving HSCs expressing the PON1-Tg but not treated with GdCl(3) showed no protection from atherosclerosis. In addition, mice engrafted with HSCs not expressing the PON1-Tg but injected with GdCl(3) also showed no protection from atherosclerosis. These findings, showing that GdCl(3)-enhanced hepatic expression of the PON1-Tg is essential for reducing atherosclerosis, indicate that Kupffer cells play an important role in atherogenesis. GdCl(3)-facilated replacement of Kupffer cells may enhance the efficacy of other HSC-based gene therapies.