Broad segmental progeroid changes in short-lived Ercc1(-/Δ7) mice

Abstract

Genome maintenance is considered a prime longevity assurance mechanism as apparent from many progeroid human syndromes that are caused by genome maintenance defects. The ERCC1 protein is involved in three genome maintenance systems: nucleotide excision repair, interstrand cross-link repair, and homologous recombination. Here we describe in-life and post-mortem observations for a hypomorphic Ercc1 variant, Ercc1(-/Δ7), which is hemizygous for a single truncated Ercc1 allele, encoding a protein lacking the last seven amino acids. Ercc1(-/Δ7) mice were much smaller and median life span was markedly reduced compared to wild-type siblings: 20 and 118 weeks, respectively. Multiple signs and symptoms of aging were found to occur at an accelerated rate in the Ercc1(-/Δ7) mice as compared to wild-type controls, including a decline in weight of both whole body and various organs, numerous histopathological lesions, and immune parameters. Together they define a segmental progeroid phenotype of the Ercc1(-/Δ7) mouse model.

Keywords: C57BL/6; Ercc1; FVB; aging; body weight; cross sectional; genome maintenance; immunosenescense; life span; mouse; organ weight; pathology.

Fig. 1

Life span (A) and mean body weight (B) curves of Ercc1 ^−/Δ7 and Ercc1 ^+/+ sibling control mice of the life span cohorts. Mice entered the study at weaning age (3 weeks); deaths before weaning age are not depicted (see text). Ercc1 ^−/Δ7 males: blue (n=31); Ercc1 ^−/Δ7 females: green (n=29); Ercc1 ^+/+ males: red (n=50); and Ercc1 ^+/+ females: orange (n=51).

Fig. 2

Mean total body weights and mean absolute and relative organ weights of Ercc1 ^−/Δ7 and Ercc1 ^+/+ sibling control mice of the cross-sectional cohorts (filled symbols and lines) and grouped moribund mice of the life span cohorts, termed ‘end-of-life’ (open symbols). The relative organ weights are expressed as a percentage of the total body weights. The position on the y-axis (age) for the ‘end-of-life’ data is arbitrary to keep it distinct from the cross-sectional data points in the graph layout; mean ages (±SD) in weeks of the end-of-life groups are: Ercc1 ^−/Δ7 males: 19.6±2.6; Ercc1 ^−/Δ7 females: 21.0±4.9; Ercc1 ^+/+ males: 123±22; and Ercc1 ^+/+ females: 116±20 weeks. The means of the cross-sectional data are based on 4–16 animals or tissues per group; the means of the end-of-life groups are based on 19–40 animals or tissues per group. The error bars represent standard deviations of the means. Ercc1 ^−/Δ7 males: blue diamonds; Ercc1 ^−/Δ7 females: green dots; Ercc1 ^+/+ males: red triangles; and Ercc1 ^+/+ females: orange inverted triangles.

Fig. 3

Mean pathology scores of liver and kidney observations at cross-sectional age groups in Ercc1 ^−/Δ7 and Ercc1 ^+/+ mice. A: kidney anisokayosis, B: kidney tubular degeneration, C: liver anisokaryosis, D: liver intranuclear inclusions, and E: liver lipofuscin. Means are based on 5–31 organs per genotype and age group (males and females combined). The bars indicate the 95% confidence intervals. Ercc1 ^−/Δ7: blue dots; Ercc1 ^+/+: red triangles. F: Calculated age to reach lipofuscin pathology score for male and female Ercc1 ^−/Δ7 and Ercc1 ^+/+ mice. Modeled by PROAST, with exponential model 2: y=a exp(bx) as selected model, based on a total of 115 observations. Age at score 1 could not be calculated. Ercc1 ^−/Δ7 males: blue diamonds; Ercc1 ^−/Δ7 females: green dots; Ercc1 ^+/+ males: red triangles; and Ercc1 ^+/+ females: orange inverted triangles.

Fig. 4

Examples of histopathology in aging male Ercc1 ^+/+ and Ercc1 ^−/Δ7 mice. Liver of Ercc1 ^+/+, 110 weeks (A). Marked scattered anisokaryosis and karyomegaly (larger nuclei); note general absence of nuclear inclusions. Compare to liver of 19 weeks old Ercc1 ^−/Δ7 mutant (B): marked anisokaryosis and marked intranuclear cytoplasmic inclusions/invaginations. Kidney of 110 weeks old Ercc1 ^+/+ mouse shows rare karyomegaly (C) compared to 19 weeks old Ercc1 ^−/Δ7 mutant (D). Bone marrow fatty infiltration and atrophy is present in 120 weeks old Ercc1 ^+/+ (E) but even more pronounced in Ercc1 ^−/Δ7 mutant at 20 weeks (F).

Fig. 5

Lymphocyte subset distributions in Ercc1 ^−/Δ7 and Ercc1 ^+/+ mice at cross-sectional age groups. A: T-cell distribution in the thymus as ratios of immature, stage II cells over mature stage III cells. B: Percentage of natural killer cells among CD45 positive splenocytes. C: Ratio of naïve over memory CD4 positive T-cells in spleen. D: Ratio of naïve over memory CD8 positive T-cells in spleen. All symbols display means of n=5, except in graph A at 96 weeks, which represent a single individual value for each sex (see text for details). The error bars indicate standard deviations. Ercc1 ^−/Δ7 males: blue diamonds; Ercc1 ^−/Δ7 females: green dots; Ercc1 ^+/+ males: red triangles; and Ercc1 ^+/+ females: orange inverted triangles.