Tissue iron is negatively correlated with TERC or TERT mRNA expression: A heterochronic parabiosis study in mice

Abstract

To test the hypothesis that iron accumulation in tissues with age is a key harmful factor for the development of aging, we established heterochronic parabiosis-pairings and investigated changes in serum iron, the expression of major iron transport proteins and iron contents, as well as telomerase reverse transcriptase (TERT), telomerase RNA component (TERC), and telomere length in the liver, kidney and heart of Y-O(O) (old pairing with young), Y-O(Y) (young pairing with old), O-O (pairings between two old) and Y-Y (pairings between two young) mice. We demonstrated that the reduced serum iron, increased iron and reduced expression of TERT and TERC in the tissues of aged mice are reversible by exposure to a younger mouse's circulation. All of these measurements in young mice are reversible by exposure to an older mouse's circulation. Correlation analysis showed that tissue iron is negatively correlated with TERT and TERC expression in the liver, kidney and heart of parabiotic mice. These findings provide new evidence for the key role of iron in aging and also imply the existence of rejuvenating factors in young serum with an anti-ageing role that act by reversing the impaired activity of iron metabolism in old mice.

Keywords: heterochronic parabiosis; iron homeostasis; liver, kidney and heart of mice; telomere and telomerase; young and old mice.

Figure 1

(A-F) Serum iron and other relevant indices in young and old mice. Serum iron (A), Tf saturation (B), UIBC (C), TIBC (D) and the contents of Tf, Ft-H, Ft-L, CP (E and F) were measured or calculated (Tf saturation and TIBC) in young (Y: 2-3 months) and old (O: 18-20 months) mice using commercial kits or western blot analysis as described in Methods and Materials. Data are presented as means ± SD (n=3). *p<0.05, **p<0.01 and ***p<0.001 vs. the control. (G-L) The contents of iron and the expression of iron metabolism proteins in the liver, kidney and heart of young and old mice. The contents of iron in the liver (G), kidney (H) and heart (I); the expression of TfR1, Fpn1, Ft-H, Ft-L and CP proteins in the liver (J and M), kidney (K and N) and heart (L and O) were determined in young (Y: 2-3 months) and old mice (O: 18-20 months) using western blot analysis or the methods described in Methods and Materials. Data are presented as means ± SEM (n=5). *p<0.05, **p<0.01 and ***p<0.001 vs. the control.

Figure 2

The effects of heterochronic parabiosis on serum iron and other relevant indices in mice. Serum iron (A), Tf saturation (B), UIBC (C), TIBC (D), and the contents of Tf, Ft-H, Ft-L, CP (E-H) were measured or calculated (Tf saturation and TIBC) in Y-Y (pairings between two young mice - isochronic parabiont), Y-O(Y) (young pairing with old – heterochronic parabiont), O-O (parings between two old - isochronic parabiont) and Y-O(O) (old pairing with young - heterochronic parabiont) mice using commercial kits or western blot analysis as described in Methods and Materials. Data are presented as means ± SEM (n=4). *p<0.05 and ** p<0.01 vs. the control.

Figure 3

The effects of heterochronic parabiosis on the contents of iron and the expression of iron metabolism proteins in the liver of mice. The contents of iron (A), and the expression of TfR1, Fpn1, Ft-H, Ft-L and CP proteins (B – E) in the liver were determined in Y-Y, Y-O(Y), O-O and Y-O(O) mice using western blot analysis or the methods described previously. Data are presented as means ± SEM (n=3). *p<0.05 and **p<0.01 vs. the control.

Figure 4

The effects of heterochronic parabiosis on the contents of iron and the expression of iron metabolism proteins in the kidney of mice. The contents of iron (A), and TfR1, Fpn1, Ft-H, Ft-L and CP proteins (B – E) in the kidney were determined in Y-Y, Y-O(Y), O-O and Y-O(O) mice using western blot analysis or the methods described previously. Data are presented as means ± SEM (n=4). *p<0.05 and **p<0.01 vs. the control.

Figure 5

The effects of heterochronic parabiosis on the contents of iron and the expression of iron metabolism proteins in the heart of mice. The contents of iron (A), and the expression of TfR1, Fpn1, Ft-H, Ft-L and CP proteins (B – E) in the heart were determined in Y-Y, Y-O(Y), O-O and Y-O(O) mice using western blot analysis or the methods described previously. Data are presented as means ± SEM (n=4). *p<0.05 and **p<0.01 vs. the control.

Figure 6

The effects of heterochronic parabiosis on the length of the telomere and the expression of TERC or TERT mRNA in mice. The telomere length in the liver (A), kidney (B) and heart (C) and the expression of TERC (D, F and H) or TERT mRNA (E, G and I) in the liver (D and E), kidney (F and G) and heart (H and I) were determined in Y-Y, Y-O(Y), O-O and Y-O(O) mice using real-time PCR as described in Methods and Materials. Data are presented as means ± SEM (n=3). *p<0.05 and **p<0.01 vs. the control.

Figure 7

Correlation analysis of the relationship between the contents of tissue iron and the expression of TERC or TERT mRNA in heterochronic parabiotic mice. Correlation analysis of the content of iron and the expression of TERC or TERT mRNA in the liver (A and B), kidney (C and D) and heart (E and F) of heterochronic parabiotic mice was conducted by plotting the values for the relevant pairs against one another as described previously. Tissue iron contents were found to be negatively correlated with TERC or TERT mRNA expression in all-three organs examined.