Ethylnitrosourea-induced gliomas: a song in the attic?

It is essential to seek the underlying molecular mechanisms of glioma development, and critical to discover interventions that reduce the incidence and attenuate the growth of gliomas using a well-established in vivo experimental model because glioma is clinically one of the most difficult malignant tumors to treat. Ethylnitrosourea (ENU)-induced glioma in the rat has been extensively utilized as an experimental brain tumor model since the mid-1960s, however, the scientific value of ENU-induced glioma has been underappreciated mainly due to the recent development of transgenic mouse glioma models. Because of the pathophysiological characteristics, which are similar to the high grade human malignant gliomas, ENU-induced glioma is an excellent in vivo model to: a) examine the cell origin, development, and pathophysiology of gliomas; b) investigate anti-tumor effects of calorie restriction (CR) and its underlying mechanisms; and c) discover new preventive and/or therapeutic interventions of glioma. Further exploration of genetic changes during initiation, malignant transformation of glial cells, and progression of glioma as well as CR's anti-tumor effects on cellular processes using cutting edge technology, e.g., spatial transcriptomics, could provide more insight and a deeper understanding of the pathophysiology of gliomas.

Local senolysis in aged mice only partially replicates the benefits of systemic senolysis

Clearance of senescent cells (SnCs) can prevent several age-related pathologies, including bone loss. However, the local versus systemic roles of SnCs in mediating tissue dysfunction remain unclear. Thus, we developed a mouse model (p16-LOX-ATTAC) that allowed for inducible SnC elimination (senolysis) in a cell-specific manner and compared the effects of local versus systemic senolysis during aging using bone as a prototype tissue. Specific removal of Sn osteocytes prevented age-related bone loss at the spine, but not the femur, by improving bone formation without affecting osteoclasts or marrow adipocytes. By contrast, systemic senolysis prevented bone loss at the spine and femur and not only improved bone formation, but also reduced osteoclast and marrow adipocyte numbers. Transplantation of SnCs into the peritoneal cavity of young mice caused bone loss and also induced senescence in distant host osteocytes. Collectively, our findings provide proof-of-concept evidence that local senolysis has health benefits in the context of aging, but, importantly, that local senolysis only partially replicates the benefits of systemic senolysis. Furthermore, we establish that SnCs, through their senescence-associated secretory phenotype (SASP), lead to senescence in distant cells. Therefore, our study indicates that optimizing senolytic drugs may require systemic instead of local SnC targeting to extend healthy aging.

Abstract 4230: Transcriptomic evaluation of exercise-induced suppression of prostate cancer aggressiveness

Previous studies from our laboratory have showed that aerobic exercise significantly reduced the number of aggressive poorly differentiated tumors in the transgenic adenocarcinoma of the mouse prostate (TRAMP) model. Despite these encouraging data the underlying mechanism of how exercise reduces tumor aggressiveness remains undefined. We aimed to fill this scientific gap by utilizing a transcriptomics approach to identify potential mechanisms by which aerobic exercise suppresses prostate tumor aggressiveness.

Methods: Twelve TRAMP mice, 8-10 weeks of age, were equally randomized to exercise or control group. Mice in the exercise group were singularly housed in cages with running wheels for 12 weeks. Mice in the control group maintained normal group housing and activity conditions for 12 weeks. At euthanasia, prostate tumors were excised, weighed and processed for immunohistochemistry and transcriptome analysis. Two independent pathologists, blinded to the interventions, performed histological analysis of the genitourinary mass. Outputs of sequencing data were assessed for quality and accuracy. Counts for all known mRNA, differential expression, and heatmap were prepared. Differential expression was filtered to identify genes that had a ≥2-fold change with an adjusted p<0.05. Gene ontology and pathway analyses was performed to reveal selective pathways activated.

Results: No significant difference in genitourinary mass, body mass or tumor free body mass was found between groups. Pathology revealed majority of the tissue from the control group exhibited moderate to poorly differentiated tumors (3/6). On the other hand, none of the animals in the exercise intervention group showed such pathology. Four out of five showed well differentiated tumors including prostatic intraepithelial neoplasia (PIN) lesions in one animal. Transcriptomic analysis coupled with gene set enrichment identified pathways associated with triglyceride catabolic process, lipid homeostasis, lipid metabolic process, triglyceride metabolic process to be most impacted. Differentially expressed genes of interest include haptoglobin (HP) and hormone sensitive lipoprotein lipase (Lipe) were significantly lower in the exercise group.

Conclusion: Our preliminary findings provide novel evidence suggesting that exercise suppresses prostate tumor aggressiveness, in part, through transcriptomic modulation and altered cellular pathways associated with intratumoral energy metabolism. This project was supported by the National Center Institute designated Mays Cancer Center at UT Health San Antonio.

Citation Format: Darpan I. Patel, Paul Rivas, Yidong Chen, Zhao Lai, Robert L. Reddick, Yuji Ikeno, Rita Ghosh, A. Pratap Kumar. Transcriptomic evaluation of exercise-induced suppression of prostate cancer aggressiveness. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4230.

A new gene set identifies senescent cells and predicts senescence-associated pathways across tissues

Although cellular senescence drives multiple age-related co-morbidities through the senescence-associated secretory phenotype, in vivo senescent cell identification remains challenging. Here, we generate a gene set (SenMayo) and validate its enrichment in bone biopsies from two aged human cohorts. We further demonstrate reductions in SenMayo in bone following genetic clearance of senescent cells in mice and in adipose tissue from humans following pharmacological senescent cell clearance. We next use SenMayo to identify senescent hematopoietic or mesenchymal cells at the single cell level from human and murine bone marrow/bone scRNA-seq data. Thus, SenMayo identifies senescent cells across tissues and species with high fidelity. Using this senescence panel, we are able to characterize senescent cells at the single cell level and identify key intercellular signaling pathways. SenMayo also represents a potentially clinically applicable panel for monitoring senescent cell burden with aging and other conditions as well as in studies of senolytic drugs.

Targeted clearance of p21- but not p16-positive senescent cells prevents radiation-induced osteoporosis and increased marrow adiposity

Cellular senescence, which is a major cause of tissue dysfunction with aging and multiple other conditions, is known to be triggered by p16Ink4a or p21Cip1 , but the relative contributions of each pathway toward inducing senescence are unclear. Here, we directly addressed this issue by first developing and validating a p21-ATTAC mouse with the p21Cip1 promoter driving a "suicide" transgene encoding an inducible caspase-8 which, upon induction, selectively kills p21Cip1 -expressing senescent cells. Next, we used the p21-ATTAC mouse and the established p16-INK-ATTAC mouse to directly compare the contributions of p21Cip1 versus p16Ink4a in driving cellular senescence in a condition where a tissue phenotype (bone loss and increased marrow adiposity) is clearly driven by cellular senescence-specifically, radiation-induced osteoporosis. Using RNA in situ hybridization, we confirmed the reduction in radiation-induced p21Cip1 - or p16Ink4a -driven transcripts following senescent cell clearance in both models. However, only clearance of p21Cip1 +, but not p16Ink4a +, senescent cells prevented both radiation-induced osteoporosis and increased marrow adiposity. Reduction in senescent cells with dysfunctional telomeres following clearance of p21Cip1 +, but not p16Ink4a +, senescent cells also reduced several of the radiation-induced pro-inflammatory senescence-associated secretory phenotype factors. Thus, by directly comparing senescent cell clearance using two parallel genetic models, we demonstrate that radiation-induced osteoporosis is driven predominantly by p21Cip1 - rather than p16Ink4a -mediated cellular senescence. Further, this approach can be used to dissect the contributions of these pathways in other senescence-associated conditions, including aging across tissues.

Characterizing the Electron Transport Chain: Structural Approach

The mitochondrial respiratory chain which carries out the oxidative phosphorylation (OXPHOS) consists of five multi-subunit protein complexes. Emerging evidences suggest that the supercomplexes which further consist of multiple respiratory complexes play important role in regulating OXPHOS function. Dysfunction of the respiratory chain and its regulation has been implicated in various human diseases including neurodegenerative diseases and muscular disorders. Many mouse models have been established which exhibit mitochondrial defects in brain and muscles. Protocols presented here aim to help to analyze the structures of mitochondrial respiratory chain which include the preparation of the tissue samples, isolation of mitochondrial membrane proteins, and analysis of their respiratory complexes by Blue Native Polyacrylamide Gel Electrophoresis (BN-PAGE) in particular.

Characterizing the Electron Transport Chain: Functional Approach Using Extracellular Flux Analyzer on Mouse Tissue Samples

The Seahorse Extracellular Flux Analyzer enables the high-throughput characterization of oxidative phosphorylation capacity based on the electron transport chain organization and regulation with relatively small amount of material. This development over the traditional polarographic Clark-type electrode approaches make it possible to analyze the respiratory features of mitochondria isolated from tissue samples of particular animal models. Here we provide a description of an optimized approach to carry out multi-well measurement of O₂ consumption, with the Agilent Seahorse XFe96 analyzer on mouse brain and muscles to determine the tissue-specific oxidative phosphorylation properties. Protocols include the preparation of the tissue samples, isolation of mitochondria, and analysis of their function; in particular, the preparation and optimization of the reagents and samples.

Growth hormone receptor gene disruption in mature-adult mice improves male insulin sensitivity and extends female lifespan

Studies in multiple species indicate that reducing growth hormone (GH) action enhances healthy lifespan. In fact, GH receptor knockout (GHRKO) mice hold the Methuselah prize for the world's longest-lived laboratory mouse. We previously demonstrated that GHR ablation starting at puberty (1.5 months), improved insulin sensitivity and female lifespan but results in markedly reduced body size. In this study, we investigated the effects of GHR disruption in mature-adult mice at 6 months old (6mGHRKO). These mice exhibited GH resistance (reduced IGF-1 and elevated GH serum levels), increased body adiposity, reduced lean mass, and minimal effects on body length. Importantly, 6mGHRKO males have enhanced insulin sensitivity and reduced neoplasms while females exhibited increased median and maximal lifespan. Furthermore, fasting glucose and oxidative damage was reduced in females compared to males irrespective of Ghr deletion. Overall, disrupted GH action in adult mice resulted in sexual dimorphic effects suggesting that GH reduction at older ages may have gerotherapeutic effects.

San Antonio Nathan Shock Center: your one-stop shop for aging research

With evolving cores, enrichment and training programs, and supported research projects, the San Antonio (SA) Nathan Shock Center has for 26 years provided critical support to investigators locally, nationally, and abroad. With its existing and growing intellectual capital, the SA Nathan Shock Center provides to local and external investigators an enhanced platform to conduct horizontally integrated (lifespan, healthspan, pathology, pharmacology) transformative research in the biology of aging, and serves as a springboard for advanced educational and training activities in aging research. The SA Nathan Shock Center consists of six cores: Administrative/Program Enrichment Core, Research Development Core, Aging Animal Models and Longevity Assessment Core, Pathology Core, Analytical Pharmacology and Drug Evaluation Core, and Integrated Physiology of Aging Core. The overarching goal of the SA Nathan Shock Center is to advance knowledge in the basic biology of aging and to identify molecular and cellular mechanisms that will facilitate the development of pharmacologic interventions and other strategies to extend healthy lifespan. In pursuit of this goal, we provide an innovative "one-stop shop" venue to accelerate transformative research in the biology of aging through our integrated research cores. Moreover, we aim to foster and promote career development of early-stage investigators in aging biology through our research development programs, to serve as a resource and partner to investigators from other Shock Centers, and to disseminate scientific knowledge and enhanced awareness about aging research. Overall, the SA Nathan Shock Center aims to be a leader in research that advances our understanding of the biology of aging and development of approaches to improve longevity and healthy aging.

Chloride channel accessory 1 integrates chloride channel activity and mTORC1 in aging-related kidney injury

The mechanism of kidney injury in aging are not well understood. In order to identify hitherto unknown pathways of aging‐related kidney injury, we performed RNA‐Seq on kidney extracts of young and aged mice. Expression of chloride (Cl) channel accessory 1 (CLCA1) mRNA and protein was increased in the kidneys of aged mice. Immunostaining showed a marked increase in CLCLA1 expression in the proximal tubules of the kidney from aged mice. Increased kidney CLCA1 gene expression also correlated with aging in marmosets and in a human cohort. In aging mice, increased renal cortical CLCA1 content was associated with hydrogen sulfide (H₂S) deficiency, which was ameliorated by administering sodium hydrosulfide (NaHS), a source of H₂S. In order to study whether increased CLCA1 expression leads to injury phenotype and the mechanisms involved, stable transfection of proximal tubule epithelial cells overexpressing human CLCA1 (hCLCA1) was performed. Overexpression of hCLCA1 augmented Cl⁻ current via the Ca⁺⁺‐dependent Cl⁻ channel TMEM16A (anoctamin‐1) by patch‐clamp studies. hCLCA1 overexpression also increased the expression of fibronectin, a matrix protein, and induced the senescence‐associated secretory phenotype (SASP). Mechanistic studies underlying these changes showed that hCLCA1 overexpression leads to inhibition of AMPK activity and stimulation of mTORC1 as cellular signaling determinants of injury. Both TMEM16A inhibitor and NaHS reversed these signaling events and prevented changes in fibronectin and SASP. We conclude that CLCA1‐TMEM16A‐Cl⁻ current pathway is a novel mediator of kidney injury in aging that is regulated by endogenous H₂S.

The implications of mitochondria in doxorubicin treatment of cancer in the context of traditional and modern medicine

Doxorubicin (DOX) is an antibiotic anthracycline extensively used in the treatment of different malignancies, such as breast cancer, lymphomas and leukemias. The cardiotoxicity induced by DOX is one of the most important pathophysiological events that limit its clinical application. Accumulating evidence highlights mitochondria as a central role in this process. Modulation of mitochondrial functions as therapeutic strategy for DOX-induced cardiotoxicity has thus attracted much attention. In particular, emerging studies investigated the potential of natural mitochondria-targeting compounds from Traditional Chinese Medicine (TCM) as adjunct or alternative treatment for DOX-induced toxicity. This review summarizes studies about the mechanisms of DOX-induced cardiotoxicity, evidencing the importance of mitochondria and presenting TCM treatment alternatives for DOX-induced cardiomyopathy.

Thioredoxin - a magic bullet or a double-edged sword for mammalian aging?

After the discovery of thioredoxin as a reductant for many important enzymes in the early 1960s, biological roles of thioredoxin in pathophysiology have been examined using various species and experimental models, e.g., yeast, invertebrates, rodents, and humans. A large number of studies demonstrated that thioredoxin plays an essential role to maintain a reduced cellular environment and possesses many beneficial effects by maintaining cellular/organ functions and against diseases. However, an important question that remains to be answered is whether thioredoxin could attenuate aging by reducing oxidative damage and changing cellular redox state, which alters redox-sensitive signaling pathways. To address this important question, we have been conducting aging studies with transgenic and knockout mice, and transgenic rats to examine whether the upregulation or downregulation of thioredoxin alters lifespan and age-related pathology. Aging studies conducted by our laboratory and others revealed that the roles of thioredoxin on pathophysiology seem to be more complex than our initial expectations as a potential magic bullet to solve the issues with age. Recent studies indicate that thioredoxin could have both beneficial and potentially deleterious effects on aging and age-related diseases. To critically evaluate the biological effects of thioredoxin on aging and age-related diseases, studies require further consideration to assess additional factors, e.g. levels of thioredoxin in different cellular compartments, different effects in each cell/tissue/organ, physiological aging vs. pathology, and/or at different life stages.

Thioredoxin overexpression in mitochondria showed minimum effects on aging and age-related diseases in male C57BL/6 mice

Objective:

In this study, the effects of overexpression of thioredoxin 2 (Trx2) on aging and age-related diseases were examined using Trx2 transgenic mice [Tg(TXN2]^+/0]. Because our previous studies demonstrated that thioredoxin (Trx) overexpression in the cytosol (Trx1) did not extend maximum lifespan, this study was conducted to test if increased Trx2 expression in mitochondria shows beneficial effects on aging and age-related pathology.

Methods:

Trx2 transgenic mice were generated using a fragment of the human genome containing the TXN2 gene. Effects of Trx2 overexpression on survival, age-related pathology, oxidative stress, and redox-sensitive signaling pathways were examined in male Tg(TXN2)^+/0 mice.

Results:

Trx2 levels were significantly higher (approximately 1.6- to 5-fold) in all of the tissues we examined in Tg(TXN2)^+/0 mice compared to wild-type (WT) littermates, and the expression levels were maintained during aging (up to 22-24 months old). Trx2 overexpression did not alter the levels of Trx1, glutaredoxin, glutathione, or other major antioxidant enzymes. Overexpression of Trx2 was associated with reduced reactive oxygen species (ROS) production from mitochondria and lower isoprostane levels compared to WT mice. When we conducted the survival study, male Tg(TXN2)^+/0 mice showed a slight extension (approximately 8-9%] of mean, median, and 10th percentile lifespans; however, the survival curve was not significantly different from WT mice. Cross-sectional pathological analysis (22-24 months old) showed that Tg(TXN2)^+/0 mice had a slightly higher severity of lymphoma; however, tumor burden, disease burden, and severity of glomerulonephritis and inflammation were similar to WT mice. Trx2 overexpression was also associated with higher c-Jun and c-Fos levels; however, mTOR activity and levels of NFκB p65 and p50 were similar to WT littermates.

Conclusions:

Our findings suggest that the increased levels of Trx2 in mitochondria over the lifespan in Tg(TXN2)^+/0 mice showed a slight life-extending effect, reduced ROS production from mitochondria and oxidative damage to lipids, but showed no significant effects on aging and age-related diseases.

Development of a Geropathology Grading Platform for nonhuman primates

A geropathology grading platform (GGP) for assessing age-related lesions has been established and validated for in inbred strain of mice. Because nonhuman primates (NHPs) share significant similarities in aging and spontaneous chronic diseases with humans, they provide excellent translational value for correlating histopathology with biological and pathological events associated with increasing age. Descriptive age-associated pathology has been described for rhesus macaques and marmosets, but a grading platform similar to the mouse GGP does not exist. The value of these NHP models is enhanced by considerable historical data from clinical, bio-behavioral, and social domains that align with health span in these animals. Successful adaptation of the mouse GGP for NHPs will include 1) expanding the range of organs examined; 2) standardizing necropsy collection, tissue trimming, and descriptive lesion terminology; 3) expanding beyond rhesus macaques and marmosets to include other commonly used NHPs in research; and 4) creating a national resource for age-related pathology to complement the extensive in-life datasets. Adaptation of the GGP to include translational models other than mice will be crucial to advance geropathology designed to enhance aging research.

Thioredoxin and aging: What have we learned from the survival studies?

Our laboratory has conducted the first systematic survival studies to examine the biological effects of the antioxidant protein thioredoxin (Trx) on aging and age-related pathology. Our studies with C57BL/6 mice overexpressing Trx1 [Tg(act-TRX1)^+/0 and Tg(TXN)^+/0) demonstrated a slight extension in early lifespan compared to wild-type (WT) mice; however, no significant effects were observed in the later part of life. Overexpression of Trx2 in male C57BL/6 mice [Tg(TXN2)^+/0] demonstrated a slightly extended lifespan compared to WT mice. The pathology results from two lines of Trx1 transgenic mice showed a slightly higher incidence of age-related neoplastic diseases compared to WT mice, and a slight increase in the severity of lymphoma, a major neoplastic disease, was observed in Trx2 transgenic mice. Together these studies indicate that Trx overexpression in one compartment of the cell (cytosol or mitochondria alone) has marginal beneficial effects on lifespan. On the other hand, down-regulation of Trx in either the cytosol (Trx1KO) or mitochondria (Trx2KO) showed no significant changes in lifespan compared to WT mice, despite several changes in pathophysiology of these knockout mice. When we examined the synergetic effects of overexpressing Trx1 and Trx2, TXNTg x TXN2Tg mice showed a significantly shorter lifespan with accelerated cancer development compared to WT mice. These results suggest that synergetic effects of Trx overexpression in both the cytosol and mitochondria on aging are deleterious and the development of age-related cancer is accelerated. On the other hand, we have recently found that down-regulation of Trx in both the cytosol and mitochondria in Trx1KO x Trx2KO mice has beneficial effects on aging. The results generated from our lab along with our ongoing study using Trx1KO x Trx2KO mice could elucidate the key pathways (i.e., apoptosis and autophagy) that prevent accumulation of damaged cells and genomic instability leading to reduced cancer formation.

Obesity-Induced Cellular Senescence Drives Anxiety and Impairs Neurogenesis

Cellular senescence entails a stable cell-cycle arrest and a pro-inflammatory secretory phenotype, which contributes to aging and age-related diseases. Obesity is associated with increased senescent cell burden and neuropsychiatric disorders, including anxiety and depression. To investigate the role of senescence in obesity-related neuropsychiatric dysfunction, we used the INK-ATTAC mouse model, from which p16Ink4a-expressing senescent cells can be eliminated, and senolytic drugs dasatinib and quercetin. We found that obesity results in the accumulation of senescent glial cells in proximity to the lateral ventricle, a region in which adult neurogenesis occurs. Furthermore, senescent glial cells exhibit excessive fat deposits, a phenotype we termed "accumulation of lipids in senescence." Clearing senescent cells from high fat-fed or leptin receptor-deficient obese mice restored neurogenesis and alleviated anxiety-related behavior. Our study provides proof-of-concept evidence that senescent cells are major contributors to obesity-induced anxiety and that senolytics are a potential new therapeutic avenue for treating neuropsychiatric disorders.

Extension of longevity and reduction of inflammation is ovarian-dependent, but germ cell-independent in post-reproductive female mice

Cardiovascular disease, rare in premenopausal women, increases sharply at menopause and is typically accompanied by chronic inflammation. Previous work in our laboratory demonstrated that replacing senescent ovaries in post-reproductive mice with young, actively cycling ovaries restored many health benefits, including decreased cardiomyopathy and restoration of immune function. Our objective here was to determine if depletion of germ cells from young transplanted ovaries would alter the ovarian-dependent extension of life and health span. Sixty-day-old germ cell-depleted and germ cell-containing ovaries were transplanted to post-reproductive, 17-month-old mice. Mean life span for female CBA/J mice is approximately 644 days. Mice that received germ cell-containing ovaries lived 798 days (maximum = 815 days). Mice that received germ cell-depleted ovaries lived 880 days (maximum = 1046 days), 29% further past the time of surgery than mice that received germ cell-containing ovaries. The severity of inflammation was reduced in all mice that received young ovaries, whether germ cell-containing or germ cell-depleted. Aging-associated inflammatory cytokine changes were reversed in post-reproductive mice by 4 months of new-ovary exposure. In summary, germ cell depletion enhanced the longevity-extending effects of the young, transplanted ovaries and, as with germ cell-containing ovaries, decreased the severity of inflammation, but did so independent of germ cells. Based on these observations, we propose that gonadal somatic cells are programed to preserve the somatic health of the organism with the intent of facilitating future germline transmission. As reproductive potential decreases or is lost, the incentive to preserve the somatic health of the organism is lost as well.

Daily Fasting Improves Health and Survival in Male Mice Independent of Diet Composition and Calories

The importance of dietary composition and feeding patterns in aging remains largely unexplored, but was implicated recently in two prominent nonhuman primate studies. Here, we directly compare in mice the two diets used in the primate studies focusing on three paradigms: ad libitum (AL), 30% calorie restriction (CR), and single-meal feeding (MF), which accounts for differences in energy density and caloric intake consumed by the AL mice. MF and CR regimes enhanced longevity regardless of diet composition, which alone had no significant impact within feeding regimens. Like CR animals, MF mice ate quickly, imposing periods of extended daily fasting on themselves that produced significant improvements in morbidity and mortality compared with AL. These health and survival benefits conferred by periods of extended daily fasting, independent of dietary composition, have major implications for human health and clinical applicability.

Continuous overexpression of thioredoxin 1 enhances cancer development and does not extend maximum lifespan in male C57BL/6 mice

We examined the effects of continuous overexpression of thioredoxin (Trx) 1 on aging in Trx1 transgenic mice [Tg(TXN)^+/0]. This study was conducted to test whether increased thioredoxin expression over the lifespan in mice would alter aging and age-related pathology because our previous study demonstrated that Tg(act-TXN)^+/0 mice had no significant maximum life extension, possibly due to the use of actin as a promoter, which may have resulted in loss of Trx1 overexpression during aging. To test this hypothesis, we generated new Trx1 transgenic mice using a fragment of the human genome containing the TXN gene with an endogenous promoter to ensure continuous overexpression of Trx1 throughout the lifespan. Universal overexpression of Trx1 was observed, and Trx1 overexpression was maintained during aging (up to 22–24 months old) in the Tg(TXN)^+/0 mice. The levels of Trx1 are significantly higher (approximately 4 to 31 fold) in all of the tissues examined in the Tg(TXN)^+/0 mice compared to the wild-type (WT) littermates. The overexpression of Trx1 did not cause any changes in the levels of Trx2, glutaredoxin, glutathione, or other major antioxidant enzymes. The survival study demonstrated that male Tg(TXN)^+/0 mice slightly extended the earlier part of the lifespan compared to WT littermates, but no significant life extension was observed over the lifespan. The cross-sectional pathological analysis (22–25 months old) showed that Tg(TXN)^+/0 mice had a significantly higher severity of lymphoma and more tumor burden than WT mice, which was associated with the suppression of the apoptosis signal-regulating kinase 1 (ASK1) pathway. Our findings suggest that the increased levels of Trx1 over the lifespan in Tg(TXN)^+/0 mice showed some beneficial effects (slight extension of lifespan) in the earlier part of life but had no significant effects on median or maximum lifespans, and increased Trx1 levels enhanced tumor development in old mice.

Senolytics improve physical function and increase lifespan in old age

Physical function declines in old age, portending disability, increased health expenditures, and mortality. Cellular senescence, leading to tissue dysfunction, may contribute to these consequences of aging, but whether senescence can directly drive age-related pathology and be therapeutically targeted is still unclear. Here we demonstrate that transplanting relatively small numbers of senescent cells into young mice is sufficient to cause persistent physical dysfunction, as well as to spread cellular senescence to host tissues. Transplanting even fewer senescent cells had the same effect in older recipients and was accompanied by reduced survival, indicating the potency of senescent cells in shortening health- and lifespan. The senolytic cocktail, dasatinib plus quercetin, which causes selective elimination of senescent cells, decreased the number of naturally occurring senescent cells and their secretion of frailty-related proinflammatory cytokines in explants of human adipose tissue. Moreover, intermittent oral administration of senolytics to both senescent cell-transplanted young mice and naturally aged mice alleviated physical dysfunction and increased post-treatment survival by 36% while reducing mortality hazard to 65%. Our study provides proof-of-concept evidence that senescent cells can cause physical dysfunction and decreased survival even in young mice, while senolytics can enhance remaining health- and lifespan in old mice.

A new role for oxidative stress in aging: The accelerated aging phenotype in Sod1-/- mice is correlated to increased cellular senescence

In contrast to other mouse models that are deficient in antioxidant enzymes, mice null for Cu/Zn-superoxide dismutase (Sod1^−/− mice) show a major decrease in lifespan and several accelerated aging phenotypes. The goal of this study was to determine if cell senescence might be a contributing factor in the accelerated aging phenotype observed in the Sod1^−/− mice. We focused on kidney because it is a tissue that has been shown to a significant increase in senescent cells with age. The Sod1^−/− mice are characterized by high levels of DNA oxidation in the kidney, which is attenuated by DR. The kidney of the Sod1^−/− mice also have higher levels of double strand DNA breaks than wild type (WT) mice. Expression (mRNA and protein) of p16 and p21, two of the markers of cellular senescence, which increased with age, are increased significantly in the kidney of Sod1^−/− mice as is β-gal staining cells. In addition, the senescence associated secretory phenotype was also increased significantly in the kidney of Sod1^−/− mice compared to WT mice as measured by the expression of transcripts for IL-6 and IL-1β. Dietary restriction of the Sod1^−/− mice attenuated the increase in DNA damage, cellular senescence, and expression of IL-6 and IL-1β. Interestingly, the Sod1^−/− mice showed higher levels of circulating cytokines than WT mice, suggesting that the accelerated aging phenotype shown by the Sod1^−/− mice could result from increased inflammation arising from an accelerated accumulation of senescent cells. Based on our data with Sod1^−/− mice, we propose that various bouts of increased oxidative stress over the lifespan of an animal leads to the accumulation of senescent cells. The accumulation of senescent cells in turn leads to increased inflammation, which plays a major role in the loss of function and increased pathology that are hallmark features of aging.

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Sod1^−/− mice have high levels of oxidative damage and DNA double strand breaks.

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Sod1^−/− mice show increased cellular senescence, e.g., p16, p21 and β-gal+ cells.

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Sod1^−/− mice showed an increase in the senescence associated secretory phenotype.

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Dietary restriction attenuated cellular senescence and inflammation in Sod1^−/− mice.

Effects of Sex, Strain, and Energy Intake on Hallmarks of Aging in Mice

Calorie restriction (CR) is the most robust non-genetic intervention to delay aging. However, there are a number of emerging experimental variables that alter CR responses. We investigated the role of sex, strain, and level of CR on health and survival in mice. CR did not always correlate with lifespan extension, although it consistently improved health across strains and sexes. Transcriptional and metabolomics changes driven by CR in liver indicated anaplerotic filling of the Krebs cycle together with fatty acid fueling of mitochondria. CR prevented age-associated decline in the liver proteostasis network while increasing mitochondrial number, preserving mitochondrial ultrastructure and function with age. Abrogation of mitochondrial function negated life-prolonging effects of CR in yeast and worms. Our data illustrate the complexity of CR in the context of aging, with a clear separation of outcomes related to health and survival, highlighting complexities of translation of CR into human interventions.

Measures of Healthspan as Indices of Aging in Mice-A Recommendation

Over the past decade, a large number of discoveries have shown that interventions (genetic, pharmacological, and nutritional) increase the lifespan of invertebrates and laboratory rodents. Therefore, the possibility of developing antiaging interventions for humans has gone from a dream to a reality. However, it has also become apparent that we need more information than just lifespan to evaluate the translational potential of any proposed antiaging intervention to humans. Information is needed on how an intervention alters the "healthspan" of an animal, that is, how the physiological functions that change with age are altered. In this report, we describe the utility and the limitations of assays in mice currently available for measuring a wide range of physiological functions that potentially impact quality of life. We encourage investigators and reviewers alike to expect at minimum an overall assessment of health in several domains across several ages before an intervention is labeled as "increasing healthspan." In addition, it is important that investigators indicate any tests in which the treated group did worse or did not differ statistically from controls because overall health is a complex phenotype, and no intervention discovered to date improves every aspect of health. Finally, we strongly recommend that functional measurements be performed in both males and females so that sex differences in the rate of functional decline in different domains are taken into consideration.

The Vital Role of Pathology in Improving Reproducibility and Translational Relevance of Aging Studies in Rodents

Pathology is a discipline of medicine that adds great benefit to aging studies of rodents by integrating in vivo, biochemical, and molecular data. It is not possible to diagnose systemic illness, comorbidities, and proximate causes of death in aging studies without the morphologic context provided by histopathology. To date, many rodent aging studies do not utilize end points supported by systematic necropsy and histopathology, which leaves studies incomplete, contradictory, and difficult to interpret. As in traditional toxicity studies, if the effect of a drug, dietary treatment, or altered gene expression on aging is to be studied, systematic pathology analysis must be included to determine the causes of age-related illness, moribundity, and death. In this Commentary, the authors discuss the factors that should be considered in the design of aging studies in mice, with the inclusion of robust pathology practices modified after those developed by toxicologic and discovery research pathologists. Investigators in the field of aging must consider the use of histopathology in their rodent aging studies in this era of integrative and preclinical geriatric science (geroscience).

IGF-1 Regulates Vertebral Bone Aging Through Sex-Specific and Time-Dependent Mechanisms

Advanced aging is associated with increased risk of bone fracture, especially within the vertebrae, which exhibit significant reductions in trabecular bone structure. Aging is also associated with a reduction in circulating levels of insulin-like growth factor (IGF-1). Studies have suggested that the reduction in IGF-1 compromises healthspan, whereas others report that loss of IGF-1 is beneficial because it increases healthspan and lifespan. To date, the effect of decreases in circulating IGF-1 on vertebral bone aging has not been thoroughly investigated. Here, we delineate the consequences of a loss of circulating IGF-1 on vertebral bone aging in male and female Igf(f/f) mice. IGF-1 was reduced at multiple specific time points during the mouse lifespan: early in postnatal development (crossing albumin-cyclic recombinase [Cre] mice with Igf(f/f) mice); and in early adulthood and in late adulthood using hepatic-specific viral vectors (AAV8-TBG-Cre). Vertebrae bone structure was analyzed at 27 months of age using micro-computed tomography (μCT) and quantitative bone histomorphometry. Consistent with previous studies, both male and female mice exhibited age-related reductions in vertebral bone structure. In male mice, reduction of circulating IGF-1 induced at any age did not diminish vertebral bone loss. Interestingly, early-life loss of IGF-1 in females resulted in a 67% increase in vertebral bone volume fraction, as well as increased connectivity density and increased trabecular number. The maintenance of bone structure in the early-life IGF-1-deficient females was associated with increased osteoblast surface and an increased ratio of osteoprotegerin/receptor-activator of NF-κB-ligand (RANKL) levels in circulation. Within 3 months of a loss of IGF-1, there was a 2.2-fold increase in insulin receptor expression within the vertebral bones of our female mice, suggesting that local signaling may compensate for the loss of circulating IGF-1. Together, these data suggest the age-related loss of vertebral bone density in females can be reduced by modifying circulating IGF-1 levels early in life.

Significant life extension by ten percent dietary restriction

Although it is well documented that dietary restriction (DR) increases the life span of rodents and other animals, this increase is observed at relatively high levels of DR, in which rodents are typically fed 40% less than that consumed by rodents fed ad libitum. It is generally assumed that lower levels of DR will have a lesser impact on life span; however, there are very little published data on the effect of low levels of DR on life span. In this study, we show that 10% DR increased life span to almost the same extent as 40% DR. While both 10% and 40% DR resulted in similar changes in non-neoplastic lesions, 10% DR had no significant effect on the incidence of neoplasia (except for pituitary adenoma), and 40% DR resulted in a significant reduction (40%) in neoplasia. These data clearly demonstrate that the life span of F344 rats does not increase linearly with the level of DR; rather, even a low level of DR can substantially affect life span. This rodent study has important translational implications because it suggests that a modest reduction in calories might have significant health benefits for humans.

Rapamycin Increases Mortality in db/db Mice, a Mouse Model of Type 2 Diabetes

We examined the effect of rapamycin on the life span of a mouse model of type 2 diabetes, db/db mice. At 4 months of age, male and female C57BLKSJ-lepr (db/db) mice (db/db) were placed on either a control diet, lacking rapamycin or a diet containing rapamycin and maintained on these diets over their life span. Rapamycin was found to reduce the life span of the db/db mice. The median survival of male db/db mice fed the control and rapamycin diets was 349 and 302 days, respectively, and the median survival of female db/db mice fed the control and rapamycin diets was 487 and 411 days, respectively. Adjusting for gender differences, rapamycin increased the mortality risk 1.7-fold in both male and female db/db mice. End-of-life pathological data showed that suppurative inflammation was the main cause of death in the db/db mice, which is enhanced slightly by rapamycin treatment.

The Geropathology Research Network: An Interdisciplinary Approach for Integrating Pathology Into Research on Aging

Geropathology is the study of aging and age-related lesions and diseases in the form of whole necropsies/autopsies, surgical biopsies, histology, and molecular biomarkers. It encompasses multiple subspecialties of geriatrics, anatomic pathology, molecular pathology, clinical pathology, and gerontology. In order to increase the consistency and scope of communication in the histologic and molecular pathology assessment of tissues from preclinical and clinical aging studies, a Geropathology Research Network has been established consisting of pathologists and scientists with expertise in the comparative pathology of aging, the design of aging research studies, biostatistical methods for analysis of aging data, and bioinformatics for compiling and annotating large sets of data generated from aging studies. The network provides an environment to promote learning and exchange of scientific information and ideas for the aging research community through a series of symposia, the development of uniform ways of integrating pathology into aging studies, and the statistical analysis of pathology data. The efforts of the network are ultimately expected to lead to a refined set of sentinel biomarkers of molecular and anatomic pathology that could be incorporated into preclinical and clinical aging intervention studies to increase the relevance and productivity of these types of investigations.

The Achilles' heel of senescent cells: from transcriptome to senolytic drugs

The healthspan of mice is enhanced by killing senescent cells using a transgenic suicide gene. Achieving the same using small molecules would have a tremendous impact on quality of life and the burden of age-related chronic diseases. Here, we describe the rationale for identification and validation of a new class of drugs termed senolytics, which selectively kill senescent cells. By transcript analysis, we discovered increased expression of pro-survival networks in senescent cells, consistent with their established resistance to apoptosis. Using siRNA to silence expression of key nodes of this network, including ephrins (EFNB1 or 3), PI3Kδ, p21, BCL-xL, or plasminogen-activated inhibitor-2, killed senescent cells, but not proliferating or quiescent, differentiated cells. Drugs targeting these same factors selectively killed senescent cells. Dasatinib eliminated senescent human fat cell progenitors, while quercetin was more effective against senescent human endothelial cells and mouse BM-MSCs. The combination of dasatinib and quercetin was effective in eliminating senescent MEFs. In vivo, this combination reduced senescent cell burden in chronologically aged, radiation-exposed, and progeroid Ercc1^−/Δ mice. In old mice, cardiac function and carotid vascular reactivity were improved 5 days after a single dose. Following irradiation of one limb in mice, a single dose led to improved exercise capacity for at least 7 months following drug treatment. Periodic drug administration extended healthspan in Ercc1^−/Δ mice, delaying age-related symptoms and pathology, osteoporosis, and loss of intervertebral disk proteoglycans. These results demonstrate the feasibility of selectively ablating senescent cells and the efficacy of senolytics for alleviating symptoms of frailty and extending healthspan.

Removal of growth hormone receptor (GHR) in muscle of male mice replicates some of the health benefits seen in global GHR-/- mice

Global disruption of the GH receptor in mice (GHR-/-) produces a large and reproducible extension in lifespan. Since lack of GH action in muscle resulting in improved glucose homeostasis is potentially a mechanism by which GHR-/- mice are long-lived, and since no information on muscle-specific GHR disruption in females is available, we generated and characterized a line of muscle-specific GHR disrupted (MuGHRKO) mice. As expected, male MuGHRKO mice had improved fasting blood glucose, insulin, c-peptide, and glucose tolerance. In contrast, female MuGHRKO mice exhibited normal glucose, insulin, and glucose tolerance. Body weight was mildly but significantly altered in opposite directions in males (decreased) and females (increased) compared to controls. Grip strength and treadmill endurance were unchanged with advanced age in both sexes, suggesting that the direct action of GH on muscle has minimal effect on age-related musculoskeletal frailty. Longevity was unchanged in both sexes at Ohio University and significantly increased for males at University of Michigan. These data suggest that removal of GHR in muscle of male MuGHRKO mice replicates some of the health benefits seen in global GHR-/- mice including improvements to glucose homeostasis and smaller body weight in males, which may explain the trends observed in lifespan.

Altered metabolism and resistance to obesity in long-lived mice producing reduced levels of IGF-I

The extension of lifespan due to reduced insulin-like growth factor 1 (IGF-I) signaling in mice has been proposed to be mediated through alterations in metabolism. Previously, we showed that mice homozygous for an insertion in the Igf1 allele have reduced levels of IGF-I, are smaller, and have an extension of maximum lifespan. Here, we tested whether this specific reduction of IGF-I alters glucose metabolism both on normal rodent chow and in response to high-fat feeding. We found that female IGF-I-deficient mice were lean on a standard rodent diet but paradoxically displayed an insulin-resistant phenotype. However, these mice gained significantly less weight than normal controls when placed on a high-fat diet. In control animals, insulin response was significantly impaired by high-fat feeding, whereas IGF-I-deficient mice showed a much smaller shift in insulin response after high-fat feeding. Gluconeogenesis was also elevated in the IGF-I-deficient mice relative to controls on both normal and high-fat diet. An analysis of metabolism and respiratory quotient over 24 h indicated that the IGF-I-deficient mice preferentially utilized fatty acids as an energy source when placed on a high-fat diet. These results indicate that reduction in the circulating and tissue IGF-I levels can produce a metabolic phenotype in female mice that increases peripheral insulin resistance but renders animals resistant to the deleterious effects of high-fat feeding.

Reduced expression of MYC increases longevity and enhances healthspan

MYC is a highly pleiotropic transcription factor whose deregulation promotes cancer. In contrast, we find that Myc haploinsufficient (Myc(+/-)) mice exhibit increased lifespan. They show resistance to several age-associated pathologies, including osteoporosis, cardiac fibrosis, and immunosenescence. They also appear to be more active, with a higher metabolic rate and healthier lipid metabolism. Transcriptomic analysis reveals a gene expression signature enriched for metabolic and immune processes. The ancestral role of MYC as a regulator of ribosome biogenesis is reflected in reduced protein translation, which is inversely correlated with longevity. We also observe changes in nutrient and energy sensing pathways, including reduced serum IGF-1, increased AMPK activity, and decreased AKT, TOR, and S6K activities. In contrast to observations in other longevity models, Myc(+/-) mice do not show improvements in stress management pathways. Our findings indicate that MYC activity has a significant impact on longevity and multiple aspects of mammalian healthspan.

Reductions in serum IGF-1 during aging impair health span

In lower or simple species, such as worms and flies, disruption of the insulin-like growth factor (IGF)-1 and the insulin signaling pathways has been shown to increase lifespan. In rodents, however, growth hormone (GH) regulates IGF-1 levels in serum and tissues and can modulate lifespan via/or independent of IGF-1. Rodent models, where the GH/IGF-1 axis was ablated congenitally, show increased lifespan. However, in contrast to rodents where serum IGF-1 levels are high throughout life, in humans, serum IGF-1 peaks during puberty and declines thereafter during aging. Thus, animal models with congenital disruption of the GH/IGF-1 axis are unable to clearly distinguish between developmental and age-related effects of GH/IGF-1 on health. To overcome this caveat, we developed an inducible liver IGF-1-deficient (iLID) mouse that allows temporal control of serum IGF-1. Deletion of liver Igf -1 gene at one year of age reduced serum IGF-1 by 70% and dramatically impaired health span of the iLID mice. Reductions in serum IGF-1 were coupled with increased GH levels and increased basal STAT5B phosphorylation in livers of iLID mice. These changes were associated with increased liver weight, increased liver inflammation, increased oxidative stress in liver and muscle, and increased incidence of hepatic tumors. Lastly, despite elevations in serum GH, low levels of serum IGF-1 from 1 year of age compromised skeletal integrity and accelerated bone loss. We conclude that an intact GH/IGF-1 axis is essential to maintain health span and that elevated GH, even late in life, associates with increased pathology.

Rapamycin extends life span of Rb1+/- mice by inhibiting neuroendocrine tumors

Chronic treatment of mice with an enterically released formulation of rapamycin (eRapa) extends median and maximum life span, partly by attenuating cancer. The mechanistic basis of this response is not known. To gain a better understanding of these in vivo effects, we used a defined preclinical model of neuroendocrine cancer, Rb1^+/− mice. Previous results showed that diet restriction (DR) had minimal or no effect on the lifespan of Rb1^+/− mice, suggesting that the beneficial response to DR is dependent on pRb1. Since long-term eRapa treatment may at least partially mimic chronic DR in lifespan extension, we predicted that it would have a minimal effect in Rb1^+/− mice. Beginning at 9 weeks of age until death, we fed Rb1^+/− mice a diet without or with eRapa at 14 mg/kg food, which results in an approximate dose of 2.24 mg/kg body weight per day, and yielded rapamycin blood levels of about 4 ng/ml. Surprisingly, we found that eRapa dramatically extended life span of both female and male Rb1^+/− mice, and slowed the appearance and growth of pituitary and decreased the incidence of thyroid tumors commonly observed in these mice. In this model, eRapa appears to act differently than DR, suggesting diverse mechanisms of action on survival and anti-tumor effects. In particular the beneficial effects of rapamycin did not depend on the dose of Rb1.

Mice producing reduced levels of insulin-like growth factor type 1 display an increase in maximum, but not mean, life span

Reduced signaling through the IGF type 1 (IGF-1) receptor increases life span in multiple invertebrate organisms. Studies on mammalian longevity suggest that reducing levels of IGF-1 may also increase life span. However, the data are conflicting and complicated by the physiology of the mammalian neuroendocrine system. We have performed life-span analysis on mice homozygous for an insertion in the Igf1 gene. These mice produce reduced levels of IGF-1 and display a phenotype consistent with a significant decrease in IGF-1. Life-span analysis was carried out at three independent locations. Although the life-span data varied between sites, the maximum life span of the IGF-1-deficient mice was significantly increased and age-specific mortality rates were reduced in the IGF-1-deficient mice; however, mean life span did not differ except at one site, where mean life span was increased in female IGF-1-deficient animals. Early life mortality was noted in one cohort of IGF-1-deficient mice. The results are consistent with a significant role for IGF-1 in the modulation of life span but contrast with the published life-span data for the hypopituitary Ames and Snell dwarf mice and growth hormone receptor null mice, indicating that a reduction in IGF-1 alone is insufficient to increase both mean and maximal life span in mice.

Dietary restriction attenuates the accelerated aging phenotype of Sod1(-/-) mice

Dietary restriction is a powerful aging intervention that extends the life span of diverse biological species ranging from yeast to invertebrates to mammals, and it has been argued that the antiaging action of dietary restriction occurs through reduced oxidative stress/damage. Using Sod1(-/-) mice, which have previously been shown to have increased levels of oxidative stress associated with a shorter life span and a high incidence of neoplasia, we were able to test directly the ability of dietary restriction to reverse an aging phenotype due to increased oxidative stress/damage. We found that dietary restriction increased the life span of Sod1(-/-) mice 30%, returning it to that of wild-type, control mice fed ad libitum. Oxidative damage in Sod1(-/-) mice was markedly reduced by dietary restriction, as indicated by a reduction in liver and brain F2-isoprostanes, a marker of lipid peroxidation. Analysis of end of life pathology showed that dietary restriction significantly reduced the overall incidence of pathological lesions in the Sod1(-/-) mice fed the dietary-restricted diet compared to Sod1(-/-) mice fed ad libitum, including the incidence of lymphoma (27 vs 5%) and overall liver pathology. In addition to reduced incidence of overall and liver-specific pathology, the burden and severity of both neoplastic and nonneoplastic lesions was also significantly reduced in the Sod1(-/-) mice fed the dietary-restricted diet. These data demonstrate that dietary restriction can significantly attenuate the accelerated aging phenotype observed in Sod1(-/-) mice that arises from increased oxidative stress/damage.

Do Ames dwarf and calorie-restricted mice share common effects on age-related pathology?

Since 1996, aging studies using several strains of long-lived mutant mice have been conducted. Among these studies, Ames dwarf mice have been extensively examined to seek clues regarding the role of the growth hormone/insulin-like growth factor-1 axis in the aging process. Interestingly, these projects demonstrate that Ames dwarf mice have physiological characteristics that are similar to those seen with calorie restriction, which has been the most effective experimental manipulation capable of extending lifespan in various species. However, this introduces the question of whether Ames dwarf and calorie-restricted (CR) mice have an extended lifespan through common or independent pathways. To answer this question, we compared the disease profiles of Ames dwarf mice to their normal siblings fed either ad libitum (AL) or a CR diet. Our findings show that the changes in age-related diseases between AL-fed Ames dwarf mice and CR wild-type siblings were similar but not identical. Moreover, the effects of CR on age-related pathology showed similarities and differences between Ames dwarf mice and their normal siblings, indicating that calorie restriction and Ames dwarf mice exhibit their anti-aging effects through both independent and common mechanisms.

Rapamycin extends life and health in C57BL/6 mice

Target of rapamycin inhibition by rapamycin feeding has previously been shown to extend life in genetically heterogeneous mice. To examine whether it similarly affected mouse health, we fed encapsulated rapamycin or a control diet to C57BL/6Nia mice of both sexes starting at 19 months of age. We performed a range of health assessments 6 and 12 months later. Rapamycin feeding significantly reduced mTOR activity in most but not all tissues. It also reduced total and resting metabolic rate during the light (inactive) phase of the light:dark cycle in females only but had no effect on spontaneous activity or metabolism during the dark (active) phase of either sex. Males only had less fragmented sleep when fed rapamycin, whereas stride length and rotarod performance were improved in both sexes. Survival was also improved by this late-life rapamycin feeding, and some pathological lesions were delayed. We found no adverse health consequences associated with rapamycin treatment.

Pathology is a critical aspect of preclinical aging studies

Experimental design for mouse aging studies has historically involved lifespan, but it is now clear that survival data without pathology data limit the information that can be obtained on aging animals. This limitation becomes more serious when interventions of any sort are implemented. Pathology gives an insight into the health of an animal by revealing lesions not readily observable in the live animal. As such, it is a snapshot of disease conditions at the time of death. Therefore, a long-term goal is to establish pathology information as an essential component of studies involving health span and lifespan of aging animals. Given that pathology assessment is essential to help define the progression of lesions associated with aging, the real challenge is including it in aging studies because there is currently a lack of specialized expertise and resources. An increase in the level and scope of pathology assessment of tissues from old mice involved in aging studies is needed. A focus on the correlation of pathology data with longitudinal and cross-sectional lifespan data and health span physiology data can be established by enhancing standard histologic assessment of lesions observed in tissues from old mice. An environment for the development and integration of pathology data into aging studies of mice is needed to encourage more pathologists and other scientists to specialize in pathology of aging, and establish relevant standards to compare with other species including humans. Such results will have an important positive impact on aging studies because of the significant empowerment on data analyses and interpretation.

Decreased insulin sensitivity and increased oxidative damage in wasting adipose tissue depots of wild-type mice

Unintentional weight loss (wasting) in the elderly is a major health concern as it leads to increased mortality. Several studies have focused on muscle loss, but little is known about the mechanisms giving rise to loss of fat mass at old ages. To investigate potential mechanisms, white adipose tissue (WAT) characteristics and proteomic profiles were compared between adult (10-12-month-old) and aged (22-24-month-old) wild-type mice. Four individual WAT depots were analyzed to account for possible depot-specific differences. Proteomic profiles of WAT depots, along with body weights and compositions, plasma levels of insulin, leptin and adiponectin, insulin tolerance, adipocyte sizes, and products of oxidative damage in each WAT depot were determined. We found that lean mass remained constant while fat mass and insulin tolerance were decreased in old age, as were adipocyte sizes in the WAT depots. Proteomic results showed increased levels of enolase, pyruvate dehydrogenase E1β, NAD(+)-dependent isocitrate dehydrogenase α, and ATP synthase subunit β, and decreased levels of carbonic anhydrase 3 in WAT of aged mice. These data suggest increased aerobic glucose oxidation in wasting WAT, consistent with decreased insulin signaling. Also, Cu/Zn superoxide dismutase and two chaperones were increased in aged WAT depots, indicating higher stress resistance. In agreement, lipid peroxidation (HNE-His adducts) increased in old age, although protein oxidation (carbonyl groups) showed no increase. In conclusion, features of wasting WAT were similar in the four depots, including decreased adipocyte sizes and alterations in protein expression profiles that indicated decreased insulin sensitivity and increased lipid peroxidation.

Role of β-adrenergic receptors in regulation of hepatic fat accumulation during aging

Excessive fat accumulation in liver (hepatic steatosis) predisposes to hepatic functional and structural impairment and overall metabolic risk. Previous studies noted an association between hepatic steatosis and age in humans and rodents. However, the mechanisms leading to age-associated hepatic fat accumulation remain unknown. Earlier work from our group showed that β-adrenergic receptor (β-AR) levels and β-AR-stimulated adenylyl cyclase activity increase in rat liver during aging. Here we investigated whether age-associated increases in β-AR signaling play a role in augmenting hepatic lipid accumulation. We demonstrate an increase in hepatic lipid content during senescence and a significant correlation between hepatic fat content and stimulation of adenylyl cyclase activity by the β-AR agonist isoproterenol in rat liver. Isoproterenol administration to young and old rodents in vivo increased hepatic lipid accumulation. Furthermore, in vitro overexpression of β1- and β2-AR subtypes in hepatocytes from young rodents increased cellular lipid content, whereas inhibition of β-ARs by receptor subtype-specific inhibitors reduced lipid levels in hepatocytes from senescent animals. Isoproterenol-induced hepatic lipid accumulation in vivo was prevented by the β-AR nonselective blocker propranolol, suggesting a novel therapeutic effect of this class of drugs in hepatic steatosis. Acipimox, which inhibits adipose tissue lipolysis, did not alter isoproterenol-mediated hepatic fat accumulation; thus β-AR responsive hepatic lipid accumulation does not appear to be related primarily to altered lipolysis. These findings suggest that augmented hepatic β-AR signaling during aging may increase lipid accumulation in liver and advocate a possible role for β-adrenergic blockers in preventing or retarding the development of hepatic steatosis.

Reduction of glucose intolerance with high fat feeding is associated with anti-inflammatory effects of thioredoxin 1 overexpression in mice

Aging is associated with reduced ability to maintain normal glucose homeostasis. It has been suggested that an age-associated increase in chronic pro-inflammatory state could drive this reduction in glucoregulatory function. Thioredoxins (Trx) are oxido-reductase enzymes that play an important role in the regulation of oxidative stress and inflammation. In this study, we tested whether overexpression of Trx1 in mice [Tg(TRX1)^+/0] could protect from glucose metabolism dysfunction caused by high fat diet feeding. Body weight and fat mass gains with high fat feeding were similar in Tg(TRX1)^+/0 and wild-type mice; however, high fat diet induced glucose intolerance was reduced in Tg(TRX1)^+/0 mice relative to wild-type mice. In addition, expression of the pro-inflammatory cytokine TNF-α was reduced in adipose tissue of Tg(TRX1)^+/0 mice compared to wild-type mice. These findings suggest that activation of thioredoxins may be a potential therapeutic target for maintenance of glucose metabolism with obesity or aging.

Does reduced IGF-1R signaling in Igf1r+/- mice alter aging?

Mutations in insulin/IGF-1 signaling pathway have been shown to lead to increased longevity in various invertebrate models. Therefore, the effect of the haplo- insufficiency of the IGF-1 receptor (Igf1r^+/−) on longevity/aging was evaluated in C57Bl/6 mice using rigorous criteria where lifespan and end-of-life pathology were measured under optimal husbandry conditions using large sample sizes. Igf1r^+/− mice exhibited reductions in IGF-1 receptor levels and the activation of Akt by IGF-1, with no compensatory increases in serum IGF-1 or tissue IGF-1 mRNA levels, indicating that the Igf1r^+/− mice show reduced IGF-1 signaling. Aged male, but not female Igf1r^+/− mice were glucose intolerant, and both genders developed insulin resistance as they aged. Female, but not male Igf1r^+/− mice survived longer than wild type mice after lethal paraquat and diquat exposure, and female Igf1r^+/− mice also exhibited less diquat-induced liver damage. However, no significant difference between the lifespans of the male Igf1r^+/− and wild type mice was observed; and the mean lifespan of the Igf1r^+/− females was increased only slightly (less than 5%) compared to wild type mice. A comprehensive pathological analysis showed no significant difference in end-of-life pathological lesions between the Igf1r^+/− and wild type mice. These data show that the Igf1r^+/− mouse is not a model of increased longevity and delayed aging as predicted by invertebrate models with mutations in the insulin/IGF-1 signaling pathway.

Thioredoxin 1 overexpression extends mainly the earlier part of life span in mice

We examined the effects of increased levels of thioredoxin 1 (Trx1) on resistance to oxidative stress and aging in transgenic mice overexpressing Trx1 [Tg(TRX1)(+/0)]. The Tg(TRX1)(+/0) mice showed significantly higher Trx1 protein levels in all the tissues examined compared with the wild-type littermates. Oxidative damage to proteins and levels of lipid peroxidation were significantly lower in the livers of Tg(TRX1)(+/0) mice compared with wild-type littermates. The survival study demonstrated that male Tg(TRX1)(+/0) mice significantly extended the earlier part of life span compared with wild-type littermates, but no significant life extension was observed in females. Neither male nor female Tg(TRX1)(+/0) mice showed changes in maximum life span. Our findings suggested that the increased levels of Trx1 in the Tg(TRX1)(+/0) mice were correlated to increased resistance to oxidative stress, which could be beneficial in the earlier part of life span but not the maximum life span in the C57BL/6 mice.

The anti-tumor effects of calorie restriction are correlated with reduced oxidative stress in ENU-induced gliomas

The anti-tumor effects of calorie restriction (CR) and the possible underlying mechanisms were investigated using ethylnitrosourea (ENU)-induced glioma in rats. ENU was given transplacentally at gestational day 15, and male offspring were used in this experiment. The brain from 4-, 6-, and 8-month-old rats fed either ad libitum (AL) or calorie-restricted diets (40% restriction of total calories compared to AL rats) was studied. Tumor burden was assessed by comparing the number and size of gliomas present in sections of the brain. Immunohistochemical analysis was used to document lipid peroxidation [4-hydroxy-2-nonenal (HNE) and malondialdehyde (MDA)], protein oxidation (nitrotyrosine), glycation and AGE formation [methylglyoxal (MG) and carboxymethyllysine (CML)], cell proliferation activity [proliferating cell nuclear antigen (PCNA)], cell death [single-stranded DNA (ssDNA)], presence of thioredoxin 1 (Trx1), and presence of heme oxygenase-1 (HO-1) associated with the development of gliomas. The results showed that the number of gliomas did not change with age in the AL groups; however, the average size of the gliomas was significantly larger in the 8-month-old group compared to that of the younger groups. Immunopositivity was observed mainly in tumor cells and reactive astrocytes in all histological types of ENU-induced glioma. Immunopositive areas for HNE, MDA, nitrotyrosine, MG, CML, HO-1, and Trx1 increased with the growth of gliomas. The CR group showed both reduced number and size of gliomas, and tumors exhibited less accumulation of oxidative damage, decreased formation of glycated end products, and a decreased presence of HO-1 and Trx1 compared to the AL group. Furthermore, gliomas of the CR group showed less PCNA positive and more ssDNA positive cells, which are correlated to the retarded growth of tumors. Interestingly, we also discovered that the anti-tumor effects of CR were associated with decreased hypoxia-inducible factor-1α (HIF-1α) levels in normal brain tissue. Our results are very exciting because they not only demonstrate the anti-tumor effects of CR in gliomas, but also indicate the possible underlying mechanisms, i.e. anti-tumor effects of CR observed in this investigation are associated with reduced accumulation of oxidative damage, decreased formation of glycated end products, decreased presence of HO-1 and Trx1, reduced cell proliferation and increased apoptosis, and decreased levels of HIF-1α.