Neuroferritinopathies are rare genetic diseases caused by mutations in the C−terminal domain of ferritin L−chain (FTL). They have an autosomic dominant transmission, likely due to the dominant negative effect of the mutations, and are associated with abnormal iron accumulation in the brain. Thus, they belong to a group of disorders named Neurodegeneration with Brain Iron Accumulation (NBIA). The causative mutations consist in 1 or 2−nucleotide insertions in the 3’ end of the coding region which cause frame shifts and modify the last 7−18 amino acids of FTL. The modifications of the C−terminus do not inhibit assembly into the 20−mer cage, but strongly alter the structure of the hydrophobic channels, shell permeability and capacity to iron store in the mineral core. To study the biological effects of the mutations we produced transgenic mice which express the mutant FTL498InsTC under the PGK promoter. The transgene was strongly expressed in all the tissues analyzed. Its concentration increased steadily up to 12 months in the liver and even more so in the brain, and this was accompanied by an upregulation of the endogenous H and L ferritins, which occurred earlier in the liver than in the brain. Liver iron concentration was not affected by transgene expression, but the ferritin−bound iron, detected by Perl’s staining of the PAGEs, decreased in the transgenic mice. The expression of the mutant ferritin did not seem to alter systemic iron homeostasis, however, oxyblot analyses showed that the brains of the transgenic mice presented signs of enhanced protein oxidation. Immunohistochemical analysis demonstrated transgene expression, and in the brain it seemed to be localized mainly in neurons; in particular the staining intensity increased with age, in agreement with the biochemical data. More interestingly, the mice showed the formation of ferritin/iron nuclear granules both in the liver and in the brain, which are an hallmark of the disease. Initial approaches to modify body iron loading consisted in repeated phlebotomies: that strongly reduced liver iron concentration, but had no effect on the number and size of the iron granules in the brain and liver. Other approaches to modify iron levels in the liver and brain are under study. In conclusion, the mice expressing the pathogenic FTL498InsTC mutant have morphological alterations that recapitulate the human disease, and can be used to test new therapies to reduce the brain iron accumulation, which is an hallmark of the disease.

Characterization of mice expressing the pathogenic L ferritin mutant (FTL-498insTC) causing hereditary Ferritinopathy

F. Maccarinelli;B. Buffoli;D. Finazzi;V. Porrini;P. Ruzzenenti;L. F. Rodella;P. Arosio
2011-01-01

Abstract

Neuroferritinopathies are rare genetic diseases caused by mutations in the C−terminal domain of ferritin L−chain (FTL). They have an autosomic dominant transmission, likely due to the dominant negative effect of the mutations, and are associated with abnormal iron accumulation in the brain. Thus, they belong to a group of disorders named Neurodegeneration with Brain Iron Accumulation (NBIA). The causative mutations consist in 1 or 2−nucleotide insertions in the 3’ end of the coding region which cause frame shifts and modify the last 7−18 amino acids of FTL. The modifications of the C−terminus do not inhibit assembly into the 20−mer cage, but strongly alter the structure of the hydrophobic channels, shell permeability and capacity to iron store in the mineral core. To study the biological effects of the mutations we produced transgenic mice which express the mutant FTL498InsTC under the PGK promoter. The transgene was strongly expressed in all the tissues analyzed. Its concentration increased steadily up to 12 months in the liver and even more so in the brain, and this was accompanied by an upregulation of the endogenous H and L ferritins, which occurred earlier in the liver than in the brain. Liver iron concentration was not affected by transgene expression, but the ferritin−bound iron, detected by Perl’s staining of the PAGEs, decreased in the transgenic mice. The expression of the mutant ferritin did not seem to alter systemic iron homeostasis, however, oxyblot analyses showed that the brains of the transgenic mice presented signs of enhanced protein oxidation. Immunohistochemical analysis demonstrated transgene expression, and in the brain it seemed to be localized mainly in neurons; in particular the staining intensity increased with age, in agreement with the biochemical data. More interestingly, the mice showed the formation of ferritin/iron nuclear granules both in the liver and in the brain, which are an hallmark of the disease. Initial approaches to modify body iron loading consisted in repeated phlebotomies: that strongly reduced liver iron concentration, but had no effect on the number and size of the iron granules in the brain and liver. Other approaches to modify iron levels in the liver and brain are under study. In conclusion, the mice expressing the pathogenic FTL498InsTC mutant have morphological alterations that recapitulate the human disease, and can be used to test new therapies to reduce the brain iron accumulation, which is an hallmark of the disease.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11379/500896
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