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

The Role of Blood-Derived Factors in Protection and Regeneration of Aged Tissues

Tissue regeneration substantially relies on the functionality of tissue-resident endogenous adult stem cell populations. However, during aging, a progressive decline in organ function and regenerative capacities impedes endogenous repair processes. Especially the adult human heart is considered as an organ with generally low regenerative capacities. Interestingly, beneficial effects of systemic factors carried by young blood have been described in diverse organs including the heart, brain and skeletal muscle of the murine system. Thus, the interest in young blood or blood components as potential therapeutic agents to target age-associated malignancies led to a wide range of preclinical and clinical research. However, the translation of promising results from the murine to the human system remains difficult. Likewise, the establishment of adequate cellular models could help to study the effects of human blood plasma on the regeneration of human tissues and particularly the heart. Facing this challenge, this review describes the current knowledge of blood plasma-mediated protection and regeneration of aging tissues. The current status of preclinical and clinical research examining blood borne factors that act in stem cell-based tissue maintenance and regeneration is summarized. Further, examples of cellular model systems for a more detailed examination of selected regulatory pathways are presented.

Evaluation of the effect of age of the younger mice on the rejuvenation of the older mice by heterochronic parabiosis

Heterochronic parabiosis is used to study the systemic effects of aging and involves surgically connecting two animals of different ages such that they have common blood circulation. Although this technique has been prevalent for a long time, there is no scientific consensus on the age of the animals that should be used. We hypothesized that the younger the animal, the greater would be its rejuvenating effect. Hence, to test this hypothesis, we created parabiosis of 67-week-old mice with younger mice of different ages (4-week-old and 8-week-old). We evaluated the changes in appearance and the expression IL-1A, IL-6, and Cdkn2a (p16) in the liver, kidney, brain, and skin. These cytokines belong to the senescence-associated secretory phenotype (SASP) factors, and are indicators of aging. Although we did not find any significant changes in the appearance of the mice, we found statistically significant differences in some SASP factors between the liver of the 4-week-old and 8-week-old pairs. However, overall, compared to the 8-week-old mice, the 4-week-old does not exert a significantly higher rejuvenation effect on the older mice. Hence, we concluded that the rejuvenation of older mice during heterochronic parabiosis might not be affected by the exact age of the younger mice.

Insights into the Molecular Basis of Genome Stability and Pristine Proteostasis in Naked Mole-Rats

The naked mole-rat (Heterocephalus glaber) is the longest-lived rodent, with a maximal reported lifespan of 37 years. In addition to its long lifespan - which is much greater than predicted based on its small body size (longevity quotient of ~4.2) - naked mole-rats are also remarkably healthy well into old age. This is reflected in a striking resistance to tumorigenesis and minimal declines in cardiovascular, neurological and reproductive function in older animals. Over the past two decades, researchers have been investigating the molecular mechanisms regulating the extended life- and health- span of this animal, and since the sequencing and assembly of the naked mole-rat genome in 2011, progress has been rapid. Here, we summarize findings from published studies exploring the unique molecular biology of the naked mole-rat, with a focus on mechanisms and pathways contributing to genome stability and maintenance of proteostasis during aging. We also present new data from our laboratory relevant to the topic and discuss our findings in the context of the published literature.

Vitamin D Rescues Pancreatic β Cell Dysfunction due to Iron Overload via Elevation of the Vitamin D Receptor and Maintenance of Ca2+ Homeostasis

SCOPE

Accumulating evidence indicates that micronutrients are related to metabolic diseases. However, comparatively less attention has been devoted to their influence on each other during the development of metabolic diseases. To investigate the underlying mechanisms, the effects of iron and vitamin D on pancreatic β cell functions are examined.

METHODS AND RESULTS

Iron overload is induced in INS-1 rat insulinoma pancreatic β cells and it is found that iron overload dramatically reduce expression of the vitamin D receptor (VDR). Iron overload-induced β cell dysfunction is rescued by 1,25-dihydroxyvitamin D3 (1,25(OH)2 D3 ) cotreatment via restoration of VDR level and the consequent maintenance of Ca2+ homeostasis. Iron accumulation is also observed in the islets of 22-month-old C57BL/6 mice fed with a chow diet (1000 IU vitamin D3 per kg). In contrast, islet iron accumulation and hyperinsulinemia are ameliorated in mice fed with a vitamin D3 -supplemented diet (20 000 IU kg-1 ).

CONCLUSION

The authors show that functional failure of β cells due to iron accumulation is rescued by 1,25(OH)2 D3 , and iron overload significantly reduces VDR levels in β cells. These results suggest that iron and vitamin D inversely influence pancreatic β cell function.

Sex-Specific Negative Association between Iron Intake and Cellular Aging Markers: Mediation Models Involving TNFα

Background

Given that the dysregulation of iron homeostasis leads to genomic instability, iron has been linked to cellular aging. However, epidemiological research on dietary iron intake and cellular aging markers is scarce. The aim of this study was to explore the relationship between dietary iron intake and cellular aging markers and to investigate whether tumor necrosis factor-α (TNFα) mediated this relationship.

Methods

We conducted a cross-sectional analysis with a total of 467 subjects. Detailed dietary data were obtained using 24 h food recalls. Peripheral blood leukocyte telomere length (LTL) and mitochondrial DNA copy number (mtDNAcn) were assessed using real-time PCR assay. The association between dietary iron intake and cellular aging markers and TNFα and superoxide dismutase (SOD) was analyzed by Pearson correlation analysis and regression models adjusted by covariates. Simple mediation models were generated to examine whether TNFα mediated the association between iron intake and cellular aging markers using PROCESS macro Version 3.3.

Results

The study population contained more women than men, but their basic demographic and metabolic characteristics did not differ. After adjusting for age, LTL was the same for men and women, while mtDNAcn was lower in men. Multiple linear regression adjusted for confounding factors found that iron intake was negatively associated with LTL only in women and negatively associated with mtDNAcn only in men. Moreover, iron intake was positively associated with TNFα in both women and men but positively associated with SOD only in men. Path modeling showed that TNFα significantly mediated the indirect detrimental effect of iron intake on LTL only in women; in men, mediation of the indirect effect of iron intake on mtDNAcn by TNFα did not reach significance.

Conclusions

The study found sex-specific negative associations between dietary iron intake and cellular aging markers in that iron intake had deleterious effects on LTL attrition in women and mtDNAcn in men; only the former was partly mediated by TNFα. Consequently, when dietary iron intake and iron supplementation is recommended, the effects of iron imbalance on genomic stability and cellular aging markers must be considered.