Tristetraprolin overexpression drives hematopoietic changes in young and middle-aged mice generating dominant mitigating effects on induced inflammation in murine models.

Tristetraprolin (TTP), encoded by Zfp36 in mice, is one of the best-characterized tandem zinc-finger mRNA binding proteins involved in mRNA deadenylation and decay. TTPΔARE mice lack an AU-rich motif in the 3'-untranslated regions of TTP mRNA, leading to increased TTP mRNA stability and more TTP protein, resulting in elevated mRNA decay rates of TTP targets. We examined the effect of TTP overexpression on the hematopoietic system in both young and middle-aged mice using TTPΔARE mice and found alterations in blood cell frequencies, with loss of platelets and B220 cells and gains of eosinophils and T cells. TTPΔARE mice also have skewed primitive populations in the bone marrow, with increases in myeloid-biased hematopoietic stem cells (HSCs) but decreases in granulocyte/macrophage-biased multipotent progenitors (MPP3) in both young and middle-aged mice. Changes in the primitive cells' frequencies were associated with transcriptional alterations in the TTP overexpression cells specific to age as well as cell type. Regardless of age, there was a consistent elevation of transcripts regulated by TNFα and TGFß signaling pathways in both the stem and multipotent progenitor populations. HSCs with TTP overexpression had decreased reconstitution potential in murine transplants but generated hematopoietic environments that mitigated the inflammatory response to the collagen antibody-induced arthritis (CAIA) challenge, which models rheumatoid arthritis and other autoimmune disorders. This dampening of the inflammatory response was even present when there was only a small frequency of TTP overexpressing cells present in the middle-aged mice. We provide an analysis of the early hematopoietic compartments with elevated TTP expression in both young and middle-aged mice which inhibits the reconstitution potential of the HSCs but generates a hematopoietic system that provides dominant repression of induced inflammation.

Boosting NAD ameliorates hematopoietic impairment linked to short telomeres in vivo.

Short telomeres are a defining feature of telomere biology disorders (TBDs), including dyskeratosis congenita (DC), for which there is no effective general cure. Patients with TBDs often experience bone marrow failure. NAD, an essential metabolic coenzyme, is decreased in models of DC. Herein, using telomerase reverse transcriptase null (Tert-/-) mice with critically short telomeres, we investigated the effect of NAD supplementation with the NAD precursor, nicotinamide riboside (NR), on features of health span disrupted by telomere impairment. Our results revealed that NR ameliorated body weight loss in Tert-/- mice and improved telomere integrity and telomere dysfunction-induced systemic inflammation. NR supplementation also mitigated myeloid skewing of Tert-/- hematopoietic stem cells. Furthermore, NR alleviated villous atrophy and inflammation in the small intestine of Tert-/- transplant recipient mice. Altogether, our findings support NAD intervention as a potential therapeutic strategy to enhance aspects of health span compromised by telomere attrition.

Male rat leukocyte population dynamics predict a window for intervention in aging.

Many age-associated changes in the human hematopoietic system have been reproduced in murine models; however, such changes have not been as robustly explored in rats despite the fact these larger rodents are more physiologically similar to humans. We examined peripheral blood of male F344 rats ranging from 3 to 27 months of age and found significant age-associated changes with distinct leukocyte population shifts. We report CD25+ CD4+ population frequency is a strong predictor of healthy aging, generate a model using blood parameters, and find rats with blood profiles that diverge from chronologic age indicate debility; thus, assessments of blood composition may be useful for non-lethal disease profiling or as a surrogate measure for efficacy of aging interventions. Importantly, blood parameters and DNA methylation alterations, defined distinct juncture points during aging, supporting a non-linear aging process. Our results suggest these inflection points are important considerations for aging interventions. Overall, we present rat blood aging metrics that can serve as a resource to evaluate health and the effects of interventions in a model system physiologically more reflective of humans.

Our blood contains many types of white blood cells, which play important roles in defending the body against infections and other threats to our health. The number of these cells changes with age, and this in turn contributes to many other alterations that happen in the body as we get older. For example, the immune system generally gets weaker at fighting infections and preventing other cells from developing into cancer. On top of that, the white blood cells themselves can become cancerous, resulting in several types of blood cancer that are more likely to happen in older people. Many previous studies have examined how the number of white blood cells changes with age in humans and mice. However, our understanding of this process in rats is still poor, despite the fact that the way the human body works has more in common with the rat body than the mouse body. Here, Yanai, Dunn et al. have studied samples of blood from rats between three to 27 months old. The experiments found that it is possible to accurately predict the age of healthy rats by measuring the frequency of populations of white blood cells, especially a certain type known as CD25+ CD4+ cells. If the animals had any form of illness, their predicted age deviated from their actual age. Furthermore, while some changes in the blood were gradual and continuous, others displayed distinct shifts when the rats reached specific ages. In the future, these findings may be used as a tool to help researchers diagnose illnesses in rats before the animals develop symptoms, or to more easily establish if a treatment is having a positive effect on the rats' health. The work of Yanai, Dunn et al. also provides new insights into aging that could potentially aid the design of new screening methods to predict cancer and intervene using a model system that is more similar to humans.

NAD+ augmentation with nicotinamide riboside improves lymphoid potential of Atm-/- and old mice HSCs.

NAD+ supplementation has significant benefits in compromised settings, acting largely through improved mitochondrial function and DNA repair. Elevating NAD+ to physiological levels has been shown to improve the function of some adult stem cells, with implications that these changes will lead to sustained improvement of the tissue or system. Here, we examined the effect of elevating NAD+ levels in models with reduced hematopoietic stem cell (HSC) potential, ATM-deficient and aged WT mice, and showed that supplementation of nicotinamide riboside (NR), a NAD+ precursor, improved lymphoid lineage potential during supplementation. In aged mice, this improved lymphoid potential was maintained in competitive transplants and was associated with transcriptional repression of myeloid gene signatures in stem and lineage-committed progenitor cells after NR treatment. However, the altered transcriptional priming of the stem cells toward lymphoid lineages was not sustained in the aged mice after NR removal. These data characterize significant alterations to the lineage potential of functionally compromised HSCs after short-term exposure to NR treatment.

Proliferation: Driver of HSC aging phenotypes?

The decline of stem cell performance with age is a potential paramount mechanism of aging. Hematopoietic stem cells (HSCs) are perhaps the most studied and best characterized tissue-specific somatic stem cells. As such, HSCs offer an excellent research model of how aging affects stem cell performance, and vice versa. Studies from recent years have elucidated major aging phenotypes of HSCs including a decline in reconstitution potential, altered differentiation predisposition, an increase in number, accumulation of DNA damage/mutations and several others. However, what drives these changes, and exactly how they translate to pathology is poorly understood. Recent studies point to proliferative stress of HSCs as a potential driver of their aging and the resulting pathologies. Here we discuss the recent discoveries and suggest the context in which aging phenotypes could be driven, and the relevant mechanisms by which HSCs could be affected.

Differential decrease in soluble and DNA-bound telomerase in senescent human fibroblasts.

The role of telomere shortening in the induction of replicative cellular senescence (CS) is well known and as a result, the involvement of telomerase and in particular its catalytic subunit, the telomerase reverse transcriptase (TERT) in CS has also been investigated. However, the majority of studies were conducted on cells that generally express high levels of TERT (cancer and immortalized cells) while the role of telomerase in CS in normal cells has been investigated to a much lesser extent. In particular, it was reported that active TERT is expressed in early passages of cultured human keratinocytes but rapidly diminished towards entry to CS, without telomere shortening. With the putative importance of TERT/telomerase in CS and the aging process in mind, we investigated the expression of TERT and telomerase activity in primary cultures of adult human dermal fibroblasts (HDFs) in the in vitro model of replicative CS. We found that (i) HDFs expressed active TERT; (ii) TERT protein levels and telomerase activity were markedly decreased in senescent HDFs; and (iii) the reduction of TERT in the soluble fraction was more pronounced than in the DNA-bound one. The results suggest the importance of the non-canonical (telomere-unrelated) functions of TERT in cellular senescence.

Cellular Senescence Markers p16INK4a and p21CIP1/WAF Are Predictors of Hodgkin Lymphoma Outcome.

PURPOSE: There is evidence that Hodgkin Reed-Sternberg (HRS) cells in classical Hodgkin lymphoma (cHL) could display some molecular and morphologic markers of cellular senescence (CS). We hypothesized that CS mechanisms may have potential prognostic relevance in cHL and investigated whether the expression of the well-established CS biomarkers p21(CIP1/WAF1) and p16(INK4a) by HRS cells might be predictive of the probability of event-free survival (EFS). EXPERIMENTAL DESIGN: The study analyzed a retrospective cohort of 147 patients and the results were validated on a cohort of 91 patients independently diagnosed and treated in a different institution. p16(INK4a) and p21(CIP1/WAF1) were categorized as dichotomous variables (< or ≥ 30% of HRS cells at diagnosis) and evaluated in univariate and multivariate analysis. RESULTS: Both molecules were independent prognostic factors. A positive staining of one of the two molecules in more than 30% HRS cells predicted a better EFS (P < 0.01). p16(INK4a)/p21(CIP1/WAF1) together as a unique categorical variable (both <30%, either <30%, both ≥ 30%) sorted out three prognostic groups with better, intermediate, or worse outcome either overall or within I-II, bulky and advanced stages. The presence or the lack of the robust expression of p21(CIP1/WAF1) and/or p16(INK4a) defined the prognosis in our series. CONCLUSIONS: These findings point to (i) the relevance of CS-related mechanisms in cHL, and to (ii) the prognostic value of a simple, reproducible, and low-cost immunohistochemical evaluation of p16(INK4a) and p21(CIP1/WAF1) expression.

Wound healing and longevity: lessons from long-lived αMUPA mice.

Does the longevity phenotype offer an advantage in wound healing (WH)? In an attempt to answer this question, we explored skin wound healing in the long-lived transgenic αMUPA mice, a unique model of genetically extended life span. These mice spontaneously eat less, preserve their body mass, are more resistant to spontaneous and induced tumorigenesis and live longer, thus greatly mimicking the effects of caloric restriction (CR). We found that αMUPA mice showed a much slower age-related decline in the rate of WH than their wild-type counterparts (FVB/N). After full closure of the wound, gene expression in the skin of old αMUPA mice returned close to basal levels. In contrast, old FVB/N mice still exhibited significant upregulation of genes associated with growth-promoting pathways, apoptosis and cell-cell/cell-extra cellular matrix interaction, indicating an ongoing tissue remodeling or an inability to properly shut down the repair process. It appears that the CR-like longevity phenotype is associated with more balanced and efficient WH mechanisms in old age, which could ensure a long-term survival advantage.

Uncovering the geroprotective potential of medicinal plants from the Judea region of Israel.

Plants growing in the Judea region are widely used in traditional medicine. This phytogeographic zone stands out in its climatic conditions and biodiversity. Consequently, both endemic and widely distributed Mediterranean plants growing in the area have unique chemotypes characterized by accumulation of relatively high levels of phytosteroids. Our comprehensive analysis revealed that many of the plants growing in the Judea region may hold a geroprotective potential. With this in mind, we undertook a wide screen of dozens of candidate herbal extracts for their cell protective, wound-healing, anti-inflammatory, and anti-cancer activities. The results obtained thus far have clearly shown that the extracts tested (1) protect normal human fibroblasts from genotoxic stress (prevent DNA double-strand beaks, increase cell survival and reduce the number of cells undergoing cellular senescence), (2) decrease secretion of pro-inflammatory cytokines, (3) promote wound healing, and (4) exert more pronounced cytotoxicity toward cancer cells.

The role of DNA damage and repair in aging through the prism of Koch-like criteria.

Since the first publication on Somatic Mutation Theory of Aging (Szilárd, 1959), a great volume of knowledge in the field has been accumulated. Here we attempted to organize the evidence "for" and "against" the hypothesized causal role of DNA damage and mutation accumulation in aging in light of four Koch-like criteria. They are based on the assumption that some quantitative relationship between the levels of DNA damage/mutations and aging rate should exist, so that (i) the longer-lived individuals or species would have a lower rate of damage than the shorter-lived, and (ii) the interventions that modulate the level of DNA damage and repair capacity should also modulate the rate of aging and longevity and vice versa. The analysis of how the existing data meets the proposed criteria showed that many gaps should still be filled in order to reach a clear-cut conclusion. As a perspective, it seems that the main emphasis in future studies should be put on the role of DNA damage in stem cell aging.

Molecular links between cellular senescence, longevity and age-related diseases - a systems biology perspective.

The role of cellular senescence (CS) in age-related diseases (ARDs) is a quickly emerging topic in aging research. Our comprehensive data mining revealed over 250 genes tightly associated with CS. Using systems biology tools, we found that CS is closely interconnected with aging, longevity and ARDs, either by sharing common genes and regulators or by protein-protein interactions and eventually by common signaling pathways. The most enriched pathways across CS, ARDs and aging-associated conditions (oxidative stress and chronic inflammation) are growth-promoting pathways and the pathways responsible for cell-extracellular matrix interactions and stress response. Of note, the patterns of evolutionary conservation of CS and cancer genes showed a high degree of similarity, suggesting the co-evolution of these two phenomena. Moreover, cancer genes and microRNAs seem to stand at the crossroad between CS and ARDs. Our analysis also provides the basis for new predictions: the genes common to both cancer and other ARD(s) are highly likely candidates to be involved in CS and vice versa. Altogether, this study shows that there are multiple links between CS, aging, longevity and ARDs, suggesting a common molecular basis for all these conditions. Modulating CS may represent a potential pro-longevity and anti-ARDs therapeutic strategy.

Is rate of skin wound healing associated with aging or longevity phenotype?

Wound healing (WH) is a fundamental biological process. Is it associated with a longevity or aging phenotype? In an attempt to answer this question, we compared the established mouse models with genetically modified life span and also an altered rate of WH in the skin. Our analysis showed that the rate of skin WH in advanced ages (but not in the young animals) may be used as a marker for biological age, i.e., to be indicative of the longevity or aging phenotype. The ability to preserve the rate of skin WH up to an old age appears to be associated with a longevity phenotype, whereas a decline in WH-with an aging phenotype. In the young, this relationship is more complex and might even be inversed. While the aging process is likely to cause wounds to heal slowly, an altered WH rate in younger animals could indicate a different cellular proliferation and/or migration capacity, which is likely to affect other major processes such as the onset and progression of cancer. As a point for future studies on WH and longevity, using only young animals might yield confusing or misleading results, and therefore including older animals in the analysis is encouraged.

Common gene signature of cancer and longevity.

An association between aging/longevity and cancer has long been suggested, yet the evolutionary and molecular links between these complicated traits remain elusive. Here, we analyze the relationship between longevity- and cancer-associated genes/proteins (LAGs/LAPs and CAGs/CAPs, respectively). Specifically, we address the following questions: (1) to what extent the CAGs and LAGs are evolutionary conserved and how they (or their orthologs) are related to each other in diverse species? (2) Could they act in cooperative manner at a protein level via protein-protein interactions (PPIs) and, if so, by forming a PPI network? We found that (i) the common genes (both LAGs and CAGs) show the same remarkable trend from yeast to humans: tumor suppressors are associated with lifespan extension, whereas the oncogenes are associated with reduced lifespan; (ii) LAPs and CAPs have a significantly higher average connectivity than other proteins in the human interactome; and (iii) LAPs and CAPs may act in cooperative manner via numerous direct and indirect PPIs between themselves and eventually by forming a PPI network. Altogether, the results of this study provide strong evidence for the existence of evolutionary and molecular links between longevity and cancer.