A knock-in mouse model of congenital erythropoietic porphyria

Abstract

Congenital erythropoietic porphyria (CEP) is a recessive autosomal disorder characterized by a deficiency in uroporphyrinogen III synthase (UROS), the fourth enzyme of the heme biosynthetic pathway. The severity of the disease, the lack of specific treatment except for allogeneic bone marrow transplantation, and the knowledge of the molecular lesions are strong arguments for gene therapy. An animal model of CEP has been designed to evaluate the feasibility of retroviral gene transfer in hematopoietic stem cells. We have previously demonstrated that the knockout of the Uros gene is lethal in mice (Uros(del) model). This work describes the achievement of a knock-in model, which reproduces a mutation of the UROS gene responsible for a severe UROS deficiency in humans (P248Q missense mutant). Homozygous mice display erythrodontia, moderate photosensitivity, hepatosplenomegaly, and hemolytic anemia. Uroporphyrin (99% type I isomer) accumulates in urine. Total porphyrins are increased in erythrocytes and feces, while Uros enzymatic activity is below 1% of the normal level in the different tissues analyzed. These pathological findings closely mimic the CEP disease in humans and demonstrate that the Uros(mut248) mouse represents a suitable model of the human disease for pathophysiological, pharmaceutical, and therapeutic purposes.

Therapeutic potential of proteasome inhibitors in congenital erythropoietic porphyria

“…Uroporphyrin I accumulation is a hallmark of the disease and leads to the spontaneous fluorescence of RBCs (i.e., fluorocytes), which can be monitored by flow cytometry analysis (15). We observed a progressive decrease in porphyrin accumulation in peripheral RBCs after serial bortezomib injections, as demonstrated by the decreased fluorocyte count over time (Fig.…”

“…CEP mice demonstrated a typical hemolytic anemia characterized by decreased hemoglobin, hematocrit, and RBC count and significant spleen enlargement (Table S1) (15). The administration of bortezomib during a 9-wk period did not induce hematotoxicity, as indicated by blood cell counts.…”

“…We next investigated whether bortezomib delivery can affect porphyrin accumulation and rescue the skin phenotype in CEP mice in vivo (15). We began by performing a dose-response analysis of proteasome inhibition after bortezomib injection into WT congenic BalbC/J mice.…”

“…We previously generated a knock-in CEP mouse model by introducing the P248Q mutation to embryonic stem cells using homologous recombination, and used this animal model to demonstrate the feasibility of gene therapy in CEP (4,15). As a proof of concept, we then evaluated the therapeutic potential of proteasomal inhibition in CEP mice chronically treated with bortezomib (Velcade; PS-341).…”

Succès de la thérapie génique d’un modèle murin de porphyrie érythropoïétique congénitale

“…Un modèle murin knock-in de PEC (uros mut248 ) reproduisant une mutation faux-sens observée dans la maladie humaine, a été obtenu dans notre laboratoire [8]. Les souris homozygotes uros mut248/mut248 présentent les lésions de photosensibilité observées dans les formes modérées de la maladie humaine.…”