Hereditary cataract of the Nakano mouse: Involvement of a hypomorphic mutation in the coproporphyrinogen oxidase gene

BALB.NCT-Cpox is a unique mouse model of hereditary coproporphyria

In humans, mutations in the coproporphyrinogen oxidase (CPOX) gene can result in hereditary coproporphyria (HCP), characterized by high levels of coproporphyrin excretion in the urine and feces, as well as acute neurovisceral and chronic cutaneous manifestations. Appropriate animal models for comprehending the precise pathogenesis mechanism of HCP have not been reported that show similarities in terms of gene mutation, reduced CPOX activity, excess coproporphyrin accumulation, and clinical symptoms. As previously discovered, the BALB.NCT-Cpox ^nct mouse carries a hypomorphic mutation in the Cpox gene. Due to the mutation, BALB.NCT-Cpox ^nct had a drastic increase in coproporphyrin in the blood and liver persistently from a young age. In this study, we found that BALB.NCT-Cpox ^nct mice manifested HCP symptoms. Similar to HCP patients, BALB.NCT-Cpox ^nct excreted an excessive amount of coproporphyrin and porphyrin precursors in the urine and displayed neuromuscular symptoms, such as a lack of grip strength and impaired motor coordination. Male BALB.NCT-Cpox ^nct had nonalcoholic steatohepatitis (NASH)-like liver pathology and sclerodermatous skin pathology. A portion of male mice had liver tumors as well, whereas female BALB.NCT-Cpox ^nct lacked these hepatic and cutaneous pathologies. In addition, we discovered that BALB.NCT-Cpox ^nct exhibited microcytic anemia. These results indicate that BALB.NCT-Cpox ^nct mice serve as the suitable animal model to help gain insight into the pathogenesis and therapy of HCP.

Effects of Dexamethasone on DNA Synthesis in Lens Epithelial Cells are Dependent on Cell Type and Growth Factor

PURPOSE

To determine the factors that influence the ability of dexamethasone (dex) to inhibit or stimulate the growth of lens epithelial cells.

METHOD

Different growth factors with or without dex (10^-6 M) were added to quiescent cultures of two clones of Nakano mouse lens epithelial cells (NK11) in serum-free medium. DNA synthesis was then measured after 8 to 12 hours by the incorporation of tritiated thymidine.

RESULTS

Dex was found to both stimulate and inhibit mitogen-induced ³H-thymidine incorporation into the DNA of cultured mouse lens epithelial cells. Enhancement or repression by dex was found to depend on the growth factor used to stimulate the quiescent cell. EGF and insulin were consistently inhibited with dex. Basic fibroblast growth factor (bFGF) and retinoblastoma-derived growth factor (RbDGF) were both enhanced and inhibited by dex, depending on the growth factor concentration and the cell clone used for the experiment. Additionally, RbDGF protects against the dex inhibition of insulin stimulation, but not the inhibition of EGF stimulation. Progesterone, an inhibitor of the activation of the glucocorticoid receptor, blocks the dex inhibitory effect on the EGF and insulin stimulation of DNA synthesis.The ability of progesterone to affect the dex inhibition is consistent with the dex receptor modulating DNA synthesis. The dex effect on DNA synthesis, either stimulatory or inhibitory, was still seen if dex was added as late as 10 hours after the growth factor.

CONCLUSIONS

The study demonstrated that dex reduces the overall growth and activity of lens epithelial cells in vitro. This result provides insight into the risk of developing posterior subcapsular cataracts (PSC) in patients on oral glucocorticoid therapy. Understanding the basic mechanisms by which steroids mediate lens cell growth may provide the ability to more accurately predict who will develop PSC. The present studies show the difference in the effect of dex from lens cell to lens cell, but, more importantly, suggest a pattern of dependent variables that might prove useful in such predictions.

Polygenic control of the wavy coat of the NCT mouse: involvement of an intracisternal A particle insertional mutation of the protease, serine 53 (Prss53) gene, and a modifier gene

The Nakano cataract mouse (NCT) manifests a wavy coat for their first hair as a genetic trait. In this study, we explored the molecular genetic basis of the wavy coat. We revealed by crossing experiments that the wavy coat is controlled by a major gene on chromosome 7 of NCT, homozygosity of which is a prerequisite for developing the wavy coat, and by a gene on chromosome 9 with a minor effect to reinforce the manifestation of the trait. In humans, a polymorphism of the protease, serine 53 (PRSS53) gene on the homologous chromosome is known to be associated with curly scalp hair. We then investigated the Prss53 gene and discovered that NCT has an insertion of an intracisternal A particle element in the first intron of the gene. Nevertheless, the expression of the Prss53 is not altered in the NCT skin both in transcript and protein levels. Subsequently, we created C57BL/6J-Prss53^em1 knockout mice and found that these mice manifest vague wavy coats. A portion of backcross and intercross mice between the C57BL/6J-Prss53^em1 and NCT manifested intense or vague wavy coats. These findings demonstrate the polygenic nature of the wavy coat of NCT and Prss53 knockout mice and highlight the similarity of the trait to the curly hair of humans associated with the PRSS53 alteration.

A novel ENU-induced Cpox mutation causes microcytic hypochromic anemia in mice

Mouse models of red blood cell abnormalities are important for understanding the underlying molecular mechanisms of human erythrocytic diseases. DBA.B6-Mha (Microcytic hypochromic anemia) congenic mice were generated from the cross between N-ethyl-N-nitrosourea (ENU)-mutagenized male C57BL/6J and female DBA/2J mice as part of the RIKEN large-scale ENU mutagenesis project. The mice were established by backcrossing with DBA/2J mice for more than 20 generations. These mice showed autosomal-dominant microcytic hypochromic anemia with decreased mean corpuscular volume (MCV) and mean corpuscular hemoglobin (MCH) levels and increased red blood cell distribution width (RDW) and plasma ferritin levels. Linkage analysis indicated that the Mha locus was located within an interval of approximately 1.95-Mb between D16Nut1 (58.35 Mb) and D16Mit185 (60.30 Mb) on mouse chromosome 16. Mutation analysis revealed that DBA.B6-Mha mice had a point mutation (c.921-2A>G) at the acceptor site of intron 4 in the coproporphyrinogen oxidase (Cpox) gene, a heme-synthesizing gene. RT-PCR revealed that the Cpox mRNA in DBA.B6-Mha mice caused splicing errors. Our results suggest that microcytic hypochromic anemia in DBA.B6-Mha mice is owing to impaired heme synthesis caused by splice mutations in Cpox. Therefore, the DBA.B6-Mha mice may be used to elucidate the molecular mechanisms underlying microcytic hypochromic anemia caused by mutations in Cpox. Although low MCV levels are known to confer malarial resistance to the host, there were no marked changes in the susceptibility of DBA.B6-Mha mice to rodent malarial (Plasmodium yoelii 17XL) infection.

Involvement of increased endoplasmic reticulum stress in the development of cataracts in BALB.NCT-Cpoxnct mice

The BALB.NCT-Cpox^nct is a mutant mouse model for hereditary cataracts. We previously uncovered that the primary cause of the cataracts of BALB.NCT-Cpox^nct is a mutation in the coproporphyrinogen oxidase (Cpox) gene. Because of the mutation, excessive coproporphyrin is accumulated in the BALB.NCT-Cpox^nct lens. In this study, we analyzed the changes in transcriptome and proteins in the lenses of 4- and 12-week-old BALB.NCT-Cpox^nct to further elucidate the molecular etiology of cataracts in this mouse strain. Transcriptome analysis revealed that endoplasmic reticulum (ER) stress was increased in the BALB.NCT-Cpox^nct lens that induced persistent activation of the PERK signaling pathway of the ER stress response. Also, levels of crystallin transcripts and proteins were reduced in the BALB.NCT-Cpox^nct lens. Analysis of proteins disclosed aggregation of crystallins and keratins prior to the manifestation of cataracts in 4-week-old BALB.NCT-Cpox^nct mice. At 12 weeks of age, insoluble crystallins were accumulated in the cataractous BALB.NCT-Cpox^nct lens. Overall, our data suggest the following sequence of events in the BALB.NCT-Cpox^nct lens: accumulated coproporphyrin induces the aggregation of proteins including crystallins. Aggregated proteins increase ER stress that, in turn, leads to the repression of global translation of proteins including crystallins. The decline in the molecular chaperone crystallin aggravates aggregation and insolubilization of proteins. This vicious cycle would eventually lead to cataracts in BALB.NCT-Cpox^nct.

CRISPR-Mediated Induction of Neuron-Enriched Mitochondrial Proteins Boosts Direct Glia-to-Neuron Conversion

Astrocyte-to-neuron conversion is a promising avenue for neuronal replacement therapy. Neurons are particularly dependent on mitochondrial function, but how well mitochondria adapt to the new fate is unknown. Here, we determined the comprehensive mitochondrial proteome of cortical astrocytes and neurons, identifying about 150 significantly enriched mitochondrial proteins for each cell type, including transporters, metabolic enzymes, and cell-type-specific antioxidants. Monitoring their transition during reprogramming revealed late and only partial adaptation to the neuronal identity. Early dCas9-mediated activation of genes encoding mitochondrial proteins significantly improved conversion efficiency, particularly for neuron-enriched but not astrocyte-enriched antioxidant proteins. For example, Sod1 not only improves the survival of the converted neurons but also elicits a faster conversion pace, indicating that mitochondrial proteins act as enablers and drivers in this process. Transcriptional engineering of mitochondrial proteins with other functions improved reprogramming as well, demonstrating a broader role of mitochondrial proteins during fate conversion.

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Mitochondrial proteomes of cortical astrocytes and neurons are distinct

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Astrocyte-enriched mitochondrial proteins are downregulated late in neuronal conversion

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Neuron-enriched mitochondrial proteins are upregulated late in neuronal conversion

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Early induction of neuronal mitochondrial proteins improves neuronal reprogramming

Genetic modifiers of rodent animal models: the role in cataractogenesis

Visual impairment leads to a decrease in quality of life. Cataract is the most commonly observed ocular disease in humans that causes vision disorders. The risk factors associated with cataract development include aging, infections, eye injuries, environmental causes, such as radiation and exposure to ultraviolet rays in sunlight, and genetic mutations. Additionally, several cataract patients display phenotypic heterogeneity, suggesting the role of genetic modifiers in the modulation of severity and onset time of cataractogenesis. However, the genetic modifiers associated with cataract have not been identified in humans yet. In contrast, the identification and mapping of genetic modifiers have been successfully carried out in mice and rats. In this review, we focus on the genetic modifiers of cataract in the rodent models.

Mouse models for microphthalmia, anophthalmia and cataracts

Mouse mutants are a long-lasting, valuable tool to identify genes underlying eye diseases, because the absence of eyes, very small eyes and severely affected, cataractous eyes are easily to detect without major technical equipment. In mice, actually 145 genes or loci are known for anophthalmia, 269 for microphthalmia, and 180 for cataracts. Approximately, 25% of the loci are not yet characterized; however, some of the ancient lines are extinct and not available for future research. The phenotypes of the mutants represent a continuous spectrum either in anophthalmia and microphthalmia, or in microphthalmia and cataracts. On the other side, mouse models are still missing for some genes, which have been identified in human families to be causative for anophthalmia, microphthalmia, or cataracts. Finally, the mouse offers the possibility to genetically test the roles of modifiers and the role of SNPs; these aspects open new avenues for ophthalmogenetics in the mouse.

Heme and erythropoieis: more than a structural role

Erythropoiesis is the biological process that consumes the highest amount of body iron for heme synthesis. Heme synthesis in erythroid cells is finely coordinated with that of alpha (α) and beta (β)-globin, resulting in the production of hemoglobin, a tetramer of 2α- and 2β-globin chains, and heme as the prosthetic group. Heme is not only the structural component of hemoglobin, but it plays multiple regulatory roles during the differentiation of erythroid precursors since it controls its own synthesis and regulates the expression of several erythroid-specific genes. Heme is synthesized in developing erythroid progenitors by the stage of proerythroblast, through a series of eight enzymatic reactions divided between mitochondria and cytosol. Defects of heme synthesis in the erythroid lineage result in sideroblastic anemias, characterized by microcytic anemia associated to mitochondrial iron overload, or in erythropoietic porphyrias, characterized by porphyrin deposition in erythroid cells. Here, we focus on the heme biosynthetic pathway and on human erythroid disorders due to defective heme synthesis. The regulatory role of heme during erythroid differentiation is discussed as well as the heme-mediated regulatory mechanisms that allow the orchestration of the adaptive cell response to heme deficiency.

A nonsense nucleotide substitution in the oculocutaneous albinism II gene underlies the original pink-eyed dilution allele (Oca2(p)) in mice

The original pink-eyed dilution (p) on chromosome 7 is a very old spontaneous mutation in mice. The oculocutaneous albinism II (Oca2) gene has previously been identified as the p gene. Oca2 transcripts have been shown to be absent in the skin of SJL/J mice with the original p mutant allele (Oca2^p); however, the molecular genetic lesion underlying the original Oca2^p allele has never been reported. The NCT mouse (commonly known as Nakano cataract mouse) has a pink-eyed dilution phenotype, which prompted us to undertake a molecular genetic analysis of the Oca2 gene of this strain. Our genetic linkage analysis suggests that the locus for the pink-eyed dilution phenotype of NCT is tightly linked to the Oca2 locus. PCR cloning and nucleotide sequence analysis indicates that the NCT mouse has a nonsense nucleotide substitution at exon 7 of the Oca2 gene. Examination of three mouse strains (NZW/NSlc, SJL/J, and 129X1/SvJJmsSlc) with the original Oca2^p allele revealed the presence of a nonsense nucleotide substitution identical to that in the NCT strain. RT-PCR analysis revealed that the Oca2 transcripts were absent in the skin of NCT mice, suggesting intervention of the nonsense-mediated mRNA decay pathway. Collectively, the data in this study indicate that the nonsense nucleotide substitution in the Oca2 gene underlies the Oca2^p allele. Our data also indicate that the NCT mouse can be used not only as a cataract model, but also as a model for human type II oculocutaneous albinism.