Aging amplifies multiple phenotypic defects in mice with zinc transporter Zip14 (Slc39a14) deletion

Abstract

Inflammation and zinc dyshomeostasis are two common hallmarks of aging. A major zinc transporter ZIP14 (slc39a14) is upregulated by proinflammatory stimuli, e.g. interleukin-6. We have evaluated the influence of age on the Zip14 KO phenotype using wild-type (WT) and Zip14 knockout (KO) mice. Aging produced a major increase in serum IL-6 concentrations that was dramatically augmented in the Zip14 KO mice. In keeping with enhanced serum IL-6 concentrations, aging produced tissue-specific increases in zinc concentration of skeletal muscle and white adipose tissue. Metabolic endotoxemia produced by Zip14 ablation is maintained in aged KO mice. Muscle non-heme iron (NHI) was increased in aged WT mice but not in aged Zip14 KO mice demonstrating NHI uptake by muscle is ZIP14-dependent and increases with age. NF-κB and STAT3 activation was greater in aged mice, but was tissue specific and inversely related to tissue zinc. Micro-CT analysis revealed that Zip14 KO mice had markedly reduced trabecular bone that was greatly amplified with aging. These results demonstrate that the inflammation-responsive zinc transporter ZIP14 has phenotypic effects that are amplified with aging.

Keywords: Bone; Growth; Inflammation; Interleukin-6; Sarcopenia; Signaling pathways.

Fig. 1

Influence of aging and Zip14 ablation using young and aged WT and Zip14 KO mice on (A) body weight, (B) serum endotoxin, (C) serum IL-6, (D) splenic IL-6 mRNA and (E) inflammatory pathways in spleen, muscle and liver. (A)-(D) values are mean ± SE, n=4 per group. P< values are shown.

Fig. 2

Influence of aging and Zip14 ablation using young and aged WT and Zip14 KO mice on (A) serum zinc concentration, (B) splenic zinc concentration, (C) muscle and liver zinc concentrations, (D) muscle and liver non-heme iron (NHI) concentrations. Values are mean ± SE, n=4 per group. P< values are shown.

Fig. 3

Influence of aging and Zip14 ablation using young and aged WT and Zip14 KO mice on (A) muscle and liver ZIP14 using western blots normalized to tubulin, (B) spleen, muscle and liver ZIP8 using western blots normalized to tubulin (C) MT1 mRNA in muscle and spleen. Values are mean ± SE, n=4 per group.

Fig. 4

Cortical bone microstructure of midshaft femur of young and aged WT and Zip14 KO mice measured using micro-CT. (A) Representative 3D reconstructions of femur cross sections. (B) Estimates of cortical bone volume/total volume (BV/TV), bone surface/bone volume (BS/BV) and cortical thickness (TbTh). Values are mean ± SE, n=4 per group.

Fig. 5

Trabecular bone microstructure of distal femur of young and aged WT and Zip14 KO mice measured using micro-CT. (A) Representative 3D reconstructions of trabecular architecture of the femur. (B) Estimates of trabecular bone volume/total volume (BV/TV), connectivity density (ConnD), trabecular thickness mgHA/cm³ (TbTh) and bone mineral density (BMD). Values are mean ± SE, n=4 per group.

Fig. 6

Summary of changes associated with aging and those associated with ablation of Zip14. Increased circulating IL-6 is a signature of aging that is augmented with ZIP14 ablation. Aging increases muscle zinc and non-heme iron and decreases bone mineral density. These are influenced with ablation of ZIP14. Metabolic endotoxemia is a signature of ZIP14 ablation, but is not changed in aging.