Level of Expression of the NonmutantFerrochelataseAllele is a Determinant of Biochemical Phenotype in a Mouse Model of Erythropoietic Protoporphyria

Joseph Bloomer,Dongquan Chen,Yongming Wang

doi:10.4137/grsb.s636

Joseph Bloomer, Dongquan Chen + Show 1 more

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https://doi.org/10.4137/grsb.s636

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Abstract

Ferrochelatase (FECH) activity is decreased in erythropoietic protoporphyria (EPP), causing increased production and excretion of protoporphyrin. This study examined whether the level of expression of the nonmutant FECH allele is a determinant of phenotype in a mouse model of EPP that carries a heterozygous deletion of exon 10 in FECH. Two mice strains that had a two-fold difference in FECH mRNA levels in bone marrow and liver (low expressing C3H/HeJ and high expressing CBA/J) were used to establish congenic strains containing the mutation. Erythrocyte protoporphyrin levels in C3H/HeJ heterozygous mice were significantly higher than in their wildtype littermates, whereas levels in CBA/J heterozygous mice did not differ significantly from their wildtype littermates. Biliary excretion of protoporphyrin was also significantly higher in C3H/HeJ heterozygous mice. The levels of normal FECH mRNA in bone marrow measured by real time PCR were 138 +/- 30 copies per ug total RNA in C3H/HeJ +/- mice, 320 +/- 59 in C3H/HeJ +/+ mice and 634 +/- 38 in CBA/J +/+ mice. Levels in liver tissue of the mice differed significantly in the same pattern. Thus, the level of expression of the nonmutant FECH allele is a determinant of phenotype in a mouse model of EPP as has been demonstrated in human EPP.

Highlights

Erythropoietic protoporphyria (EPP) is a genetic disorder of porphyrin metabolism in humans that was first described in 1961 by Magness and co-workers when they reported a man with lifelong sensitivity to sunlight and increased protoporphyrin levels in erythrocytes and feces (Magness et al 1961)
The levels of normal FECH mRNA in bone marrow and liver of wildtype C3H/HeJ mice were approximately 50% of those in CBA/J wildtype mice (Table 3), which agreed well with the relative levels estimated by relative quantitative PCR (Table 1)
The lowest levels of normal FECH mRNA were found in C3H/HeJ heterozygous mice, in which bone marrow and liver levels were

Summary

Introduction

Erythropoietic protoporphyria (EPP) is a genetic disorder of porphyrin metabolism in humans that was first described in 1961 by Magness and co-workers when they reported a man with lifelong sensitivity to sunlight and increased protoporphyrin levels in erythrocytes and feces (Magness et al 1961). Some patients develop hepatobiliary disease due to protoporphyrin induced damage to liver structure and function (Doss and Frank, 1989). This may progress to liver failure and necessitate liver transplantation (McGuire et al 2005). All heme forming tissues may potentially contribute to the excess formation of protoporphyrin in EPP, with the bone marrow being the major source (Poh-Fitzpatrick, 1985). The functional human FECH enzyme is a homodimer that contains two NO sensitive and coordinated 2Fe-2S clusters (Wu et al 2001). There is a single transcript with 2 polyadenylation sites in erythroid and non-erythroid cells, indicating there is only one FECH gene in heme forming tissues (Taketani et al 1992)

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