Cellular proliferative capacity and life span in small and large dogs

Factors related to longevity and mortality of dogs in Italy

Besides its translational value, an improved understanding of dog longevity and mortality is necessary to guide health management decisions, breed selection, and improve dog welfare. In order to analyse the lifespan of dogs in Italy, identify the most common causes of death, and evaluate possible risk factors, anonymised medical records were collected from 9 veterinary teaching hospitals and 2 public health institutions. Data regarding breed, sex, neuter status, age, diagnosis, and mechanism of death were retrieved. Cause of death (COD) was classified by pathophysiologic process (PP) and organ system (OS). Of the 4957 dogs that died between 2004 and 2020 included in the study, 2920 (59.0%) were purebred, 2293 (46.2%) were female, 3005 (60.6%) were intact, 2883 (58.2%) were euthanised. Overall median longevity was 10.0 years. Median longevity was significantly longer for crossbreds, females, neutered dogs, and small-sized breeds. The breeds with the highest median age at death were the Yorkshire terrier, English cocker spaniel, West Highland white terrier, Italian volpino, and Shih Tzu, whilst the American bulldog, English bulldog, American pit bull terrier, Bernese mountain dog and the Maremma and the Abruzzes sheepdog had the lowest median age at death. The most frequent COD by PP was neoplasia (34.0%), which occurred more frequently in large breeds, namely German shepherd, Labrador retriever and Boxer. Degenerative diseases mostly affected small-sized dogs like Miniature pinscher and Dachshund. Regarding the OS involved, diseases of the renal/urinary system were most frequently responsible for COD (15.0%), prevalently degenerative and inflammatory/infectious. Substantial variation in median longevity according to causes of death by PP and OS was observed. These data are relevant for breeders, veterinary practitioners, and owners, to assist breed selection, facilitate early diagnosis, guide choice when purchasing a purebred dog and making health management decisions, and ultimately improve dog welfare.

Longevity of companion dog breeds: those at risk from early death

The companion dog is one of the most phenotypically diverse species. Variability between breeds extends not only to morphology and aspects of behaviour, but also to longevity. Despite this fact, little research has been devoted to assessing variation in life expectancy between breeds or evaluating the potential for phylogenetic characterisation of longevity. Using a dataset of 584,734 unique dogs located within the UK, including 284,734 deceased, we present variation in longevity estimates within the following: parental lineage (purebred = 1 breed, crossbred ≥ 2 breeds), breed (n = 155), body size (large, medium, small), sex (male, female) and cephalic index (brachycephalic, mesocephalic, dolichocephalic). Survival estimates were then partitioned amongst phylogenetic clades: providing evidence that canine evolutionary history (via domestication and associated artificial selection) is associated with breed lifespan. This information provides evidence to inform discussions regarding pedigree health, whilst helping current/prospective owners, breeders, policy makers, funding bodies and welfare organisations improve decision making regarding canine welfare.

Neuronal mTORC1 inhibition promotes longevity without suppressing anabolic growth and reproduction in C. elegans

mTORC1 (mechanistic target of rapamycin complex 1) is a metabolic sensor that promotes growth when nutrients are abundant. Ubiquitous inhibition of mTORC1 extends lifespan in multiple organisms but also disrupts several anabolic processes resulting in stunted growth, slowed development, reduced fertility, and disrupted metabolism. However, it is unclear if these pleiotropic effects of mTORC1 inhibition can be uncoupled from longevity. Here, we utilize the auxin-inducible degradation (AID) system to restrict mTORC1 inhibition to C. elegans neurons. We find that neuron-specific degradation of RAGA-1, an upstream activator of mTORC1, or LET-363, the ortholog of mammalian mTOR, is sufficient to extend lifespan in C. elegans. Unlike raga-1 loss of function genetic mutations or somatic AID of RAGA-1, neuronal AID of RAGA-1 robustly extends lifespan without impairing body size, developmental rate, brood size, or neuronal function. Moreover, while degradation of RAGA-1 in all somatic tissues alters the expression of thousands of genes, demonstrating the widespread effects of mTORC1 inhibition, degradation of RAGA-1 in neurons only results in around 200 differentially expressed genes with a specific enrichment in metabolism and stress response. Notably, our work demonstrates that targeting mTORC1 specifically in the nervous system in C. elegans uncouples longevity from growth and reproductive impairments, and that many canonical effects of low mTORC1 activity are not required to promote healthy aging. These data challenge previously held ideas about the mechanisms of mTORC1 lifespan extension and underscore the potential of promoting longevity by neuron-specific mTORC1 modulation.

The effect of age on the induction dose of propofol for general anesthesia in dogs

OBJECTIVE

In people, the dose of propofol (DOP) required for procedural sedation and anesthesia decreases significantly with age. The objective of this study was to determine if the DOP required to perform endotracheal intubation decreases with age in dogs.

STUDY DESIGN

Retrospective case series.

ANIMALS

1397 dogs.

METHODS

Data from dogs anesthetized at referral center (2017-2020) were analyzed with three multivariate linear regression models with backward elimination using a combination of either absolute age, physiologic age, or life expectancy (ratio between age at the time of anesthetic event and expected age of death for each breed obtained from previous literature) as well as other factors as independent variables, and DOP as the dependent variable. The DOP for each quartile of life expectancy (<25%, 25-50%, 50-75%, 75-100%, >100%) was compared using one-way ANOVA. Significance was set at alpha = 0.025.

RESULTS

Mean age was 7.2 ± 4.1 years, life expectancy 59.8 ± 33%, weight 19 ± 14 kg, and DOP 3.76 ± 1.8 mg kg-1. Among age models, only life expectancy was a predictor of DOP (-0.37 mg kg-1; P = 0.013) but of minimal clinical importance. The DOP by life age expectancy quartile was 3.9 ± 2.3, 3.8 ± 1.8, 3.6 ± 1.8, 3.7 ± 1.7, and 3.4 ± 1.6 mg kg-1, respectively (P = 0.20). Yorkshire Terrier, Chihuahua, Maltese, mixed breed dogs under 10 kg, and Shih Tzu required higher DOP. Status of neutered male, ASA E, and Boxer, Labrador and Golden Retriever breeds decreased DOP, along with certain premedication drugs.

CONCLUSIONS AND CLINICAL RELEVANCE

In contrast to what is observed in people, an age cut-off predictive of DOP does not exist. Percentage of elapsed life expectancy along with other factors such as breed, premedication drug, emergency procedure, and reproductive status significantly alter DOP. In older dogs, the dose of propofol can be adjusted based on their elapsed life expectancy.

CD4+/CD8+ Ratio and Growth Differentiation Factor 8 Levels in Peripheral Blood of Large Canine Males Are Useful Parameters to Build an Age Prediction Model

Purpose

To build an age prediction model, we measured CD4+ and CD8+ cells, and humoral components in canine peripheral blood.

Materials and Methods

Large Belgian Malinois (BGM) and German Shepherd Dog (GSD) breeds (n=27), aged from 1 to 12 years, were used for this study. Peripheral bloods were obtained by venepuncture, then plasma and peripheral blood mononuclear cells (PBMCs) were separated immediately. Six myokines, including interleukin (IL)-6, IL-8, IL-15, leukemia inhibitory factor (LIF), growth differentiation factor 8 (GDF8), and GDF11 were measured from plasma and CD4+/CD8+ T-lymphocytes ratio were measured from PBMC. These parameters were then tested with age prediction models to find the best fit model.

Results

We found that the T-lymphocyte ratio (CD4+/CD8+) was significantly correlated with age (r=0.46, p=0.016). Among the six myokines, only GDF8 showed a significant correlation with age (r=0.52, p=0.005). Interestingly, these two markers showed better correlations in male dogs than females, and BGM breed than GSD. Using these two age biomarkers, we could obtain the best fit in a quadratic linear mixed model (r=0.77, p=3×10^-6).

Conclusions

Age prediction is a challenging task because of complication with biological age. Our quadratic linear mixed model using CD4+/CD8+ ratio and GDF8 level showed a meaningful age prediction.

Heritability and genetic variance estimation of Osteosarcoma (OSA) in Irish Wolfhound, using deep pedigree information

Background

Osteosarcoma (OSA) is a devastating disease that is common in the Irish Wolfhound breed. The aim of this study was to use a pedigree-based approach to determine the heritability of OSA in the Irish Wolfhound using data from a large publically available database.

Results

The pedigree used for this study included 5110 pure-bred Irish Wolfhounds, including 332 dogs diagnosed with OSA and 360 control dogs; dogs were considered controls if they lived over 10 years of age and were not reported to have developed OSA. The estimated heritability of OSA in the Irish Wolfhound was 0.65.

Conclusion

The results of this study indicate that OSA in the Irish Wolfhound is highly heritable, and support the need for future research investigating associated genetic mutations.

Osteosarcoma is a devastating condition that is prevalent in the Irish Wolfhound breed. In this study, our aim was to estimate heritability of osteosarcoma in the Irish Wolfhound breed. We undertook a pedigree-based analysis to estimate heritability of osteosarcoma in the Irish Wolfhound. The pedigree used included 5110 pure-bred Irish Wolfhounds, including 332 dogs diagnosed with osteosarcoma and 360 control dogs. We considered dogs to be controls if they were over 10 years of age and were not reported to have developed osteosarcoma. This study found the heritability estimate of osteosarcoma in the Irish Wolfhound to be 0.65. This score means that osteosarcoma in this breed is: 1) highly heritable and 2) a complex trait, which means that both environmental and genetic factors influence disease risk. Overall, our results provide support for further investigation into the genetic variants involved in the development of osteosarcoma in Irish Wolfhounds.

Age-specific variations in hematological and biochemical parameters in middle- and large-sized of dogs

Aging triggers cellular and molecular alterations, including genomic instability and organ dysfunction, which increases the risk of disease in mammals. Recently, due to the markedly growing number of aging dogs in the world, as much as 49% in total number of pet dogs, it is necessary to improve and maintain their quality of life by understanding of the biological effects of aging. Therefore, the aim of this study was to determine specific biomarkers in aging dogs as a means of defining a set of hematological/biochemical biomarkers that influence the aging process. Blood samples were collected from younger (1-3 years) and older (7-10 years) dogs of middle/large size. The hematological/biochemistry analysis was performed to evaluate parameters significantly associated with age. Enzyme-linked immunosorbent assay was used to target growth hormone (GH)/insulin growth factor-1 (IGF-1), one of the main regulators of the aging process. Declining levels of total protein and increased levels of glucose in young dogs was observed regardless of their body size. Notably, a significantly high concentration of GH and IGF-1 in the younger dogs compared to the older dogs was found in middle/large-sized dogs. GH and IGF-1 were also found at significantly high levels in large-sized dogs compared to middle-sized dogs, suggesting a similar trend to that of elderly humans. Consequently, glucose, total protein, GH, and IGF-1 were identified as potential biomarkers for regulating the aging process in large/middle-sized dogs. These findings provide an invaluable insight into the mechanism of aging for the field of aging research.

Estimating the life expectancy of companion dogs in Japan using pet cemetery data

The life expectancy provides valuable information about population health. The life expectancies were evaluated in 12,039 dogs which were buried or cremated during January 2012 to March 2015. The data of dogs were collected at the eight animal cemeteries in Tokyo. The overall life expectancy of dogs was 13.7 (95% confidence interval (CI): 13.7-13.8) years. The probability of death was high in the first year of life, lowest in the fourth year, and increased exponentially after four years of age like Gompertz curve in semilog graph. The life expectancy of companion dogs in Tokyo has increased 1.67 fold from 8.6 years to 13.7 years over the past three decades. Canine crossbreed life expectancy (15.1 years, 95% CI 14.9-15.3) was significantly greater than pure breed life expectancy (13.6 years, 95%CI 13.5-13.7, P-value <0.001). The life expectancy for male and for female dogs were 13.6 (95% CI: 13.5-13.7) and 13.5 (95% CI: 13.4-13.6) years, respectively, with no significant difference (P=0.097). In terms of the median age of death and life expectancy for major breeds, Shiba had the highest median age of death (15.7 years), life expectancy (15.5 years) and French Bulldog had the lowest median age of death (10.2 years), life expectancy (10.2 years). When considering life expectancy alone, these results suggest that the health of companion dogs in Japan has significantly improved over the past 30 years.

Cellular metabolism and oxidative stress as a possible determinant for longevity in small breed and large breed dogs

Among species, larger animals tend to live longer than smaller ones, however, the opposite seems to be true for dogs-smaller dogs tend to live significantly longer than larger dogs across all breeds. We were interested in the mechanism that may allow for small breeds to age more slowly compared with large breeds in the context of cellular metabolism and oxidative stress. Primary dermal fibroblasts from small and large breed dogs were grown in culture. We measured basal oxygen consumption (OCR), proton leak, and glycolysis using a Seahorse XF96 oxygen flux analyzer. Additionally, we measured rates of reactive species (RS) production, reduced glutathione (GSH) content, mitochondrial content, lipid peroxidation (LPO) damage and DNA (8-OHdg) damage. Our data suggests that as dogs of both size classes age, proton leak is significantly higher in older dogs, regardless of size class. We found that all aspects of glycolysis were significantly higher in larger breeds compared with smaller breeds. We found significant differences between age classes in GSH concentration, and a negative correlation between DNA damage in puppies and mean breed lifespan. Interestingly, RS production showed no differences across size and age class. Thus, large breed dogs may have higher glycolytic rates, and DNA damage, suggesting a potential mechanism for their decreased lifespan compared with small breed dogs.

Factors Informing Outcomes for Older Cats and Dogs in Animal Shelters

Simple Summary

Historically, older cats and dogs have been particularly at-risk for euthanasia in animal shelters due to their lower perceived appeal for adoption. This study found that the condition at intake had the greatest impact on the outcomes of older cats and dogs. Additionally, the application of specialized veterinary care, such as orthopedic surgery or chronic disease maintenance, is discussed as factors that inform higher rates of live outcomes for these senior companion animals. These findings demonstrate that if shelters integrate practices that address the specific needs of ageing companion animals, the live outcomes for this population can increase.

Abstract

With advances in veterinary medicine that can increase the lifespan of cats and dogs and the effectiveness of spay/neuter programs in reducing the juvenile population of pets, animal shelters are experiencing an increasing population of older companion animals in their care. The purpose of this study was to assess the factors that inform the outcomes of these older cats and dogs. The sample consisted of 124 cats and 122 dogs that were over the age of 84 months (seven years) who were taken into a shelter over a one-year period. To assess the impact of condition at intake on the outcome for the senior animals, a multinomial logistic regression was performed. These findings indicate that preventative programming that can address the reasons these older animals are surrendered, as well as advancements in specialized medical or behavioral programs for ageing companion animals, may support an increase in live outcomes for older cats and dogs in shelters. Further study is needed to evaluate how the quality of life of older animals is impacted by remaining in the care of shelters rather than being euthanized.

An epigenetic aging clock for dogs and wolves

Several articles describe highly accurate age estimation methods based on human DNA-methylation data. It is not yet known whether similar epigenetic aging clocks can be developed based on blood methylation data from canids. Using Reduced Representation Bisulfite Sequencing, we assessed blood DNA-methylation data from 46 domesticated dogs (Canis familiaris) and 62 wild gray wolves (C. lupus). By regressing chronological dog age on the resulting CpGs, we defined highly accurate multivariate age estimators for dogs (based on 41 CpGs), wolves (67 CpGs), and both combined (115 CpGs). Age related DNA methylation changes in canids implicate similar gene ontology categories as those observed in humans suggesting an evolutionarily conserved mechanism underlying age-related DNA methylation in mammals.

Aging and Veterinary Care of Cats, Dogs, and Horses through the Records of Three University Veterinary Hospitals

The present article examines over 63,000 medical records belonging to the Veterinary Hospitals of the Universities of Bologna, Torino, and Padova, all in Northern Italy, and relative to dogs (approximately 50,000), cats (approximately 12,000), and companion horses (slightly less than 1,000). The animals of the three species were divided into age classes and categorized per sex into males, females, and neutered individuals. The mean age at visit and the effects of age classes and category (analyzed via ANOVA) are presented and discussed. The data indicate that many animals are presented to the hospitals either in the early phases of their life (presumably for vaccination and, in cats and dogs, gonadectomy) or in the advanced age (over 10 years in dogs, over 15 years in cats, and over 17 years in horses). The records of very old individuals of the three species are also reported. On the whole, the results suggest that a growing population of mature to old domestic carnivores or companion horses reaches ages that were considered exceptional only a few years ago. The data also testify an evolution in the animal–owner relationship and a renewed respect for the value of life in companion domestic mammals.

Life expectancy and causes of death in Bernese mountain dogs in Switzerland

BACKGROUND

New regulations by the Swiss Federal Food Safety and Veterinary Office provide for the monitoring of breed health by Swiss breeding clubs. In collaboration with the Swiss Bernese Mountain Dog Club, the purpose of this study was to investigate the causes of death in purebred dogs registered by the club and born in 2001 and 2002.

RESULTS

Of a total of 1290 Bernese mountain dogs (BMDs) born in 2001 and 2002 in Switzerland, data was collected from owners and veterinarians using a questionnaire designed for this study from 389 dogs (30.2 %). By the end of the study, 381/389 dogs (97.9 %) had died. The median life expectancy of all dogs was 8.4 years (IQR, 6.9-9.7). Female dogs had a significantly longer median survival (8.8 years; IQR, 7.1-10.3) than male dogs (7.7 years; IQR, 6.6-9.3) (P < 0.00). The cause of death was unknown in 89/381 dogs (23.4 %). For the remaining dogs, the most frequent causes of death were neoplasia (222/381, 58.3 %), degenerative joint disease (16/381, 4.2 %), spinal disorders (13/381, 3.4 %), renal injury (12/381, 3.1 %), and gastric or mesenteric volvulus (7/381, 1.8 %). However, large numbers of dogs were diagnosed with neoplasia without histopathologic or cytologic confirmation. Dogs with neoplasms had a shorter median survival than dogs with other disorders. The shortest median survival (6.8 years) was found for dogs with renal injury.

CONCLUSIONS

Findings of this study confirm a high prevalence of neoplasia and associated low life expectancy in BMDs. The results underline a need for more widespread precise diagnostics and further research on malignant tumours in this breed to improve overall breed health.

The Companion Dog as a Model for the Longevity Dividend

The companion dog is the most phenotypically diverse species on the planet. This enormous variability between breeds extends not only to morphology and behavior but also to longevity and the disorders that affect dogs. There are remarkable overlaps and similarities between the human and canine species. Dogs closely share our human environment, including its many risk factors, and the veterinary infrastructure to manage health in dogs is second only to the medical infrastructure for humans. Distinct breed-based health profiles, along with their well-developed health record system and high overlap with the human environment, make the companion dog an exceptional model to improve understanding of the physiological, social, and economic impacts of the longevity dividend (LD). In this review, we describe what is already known about age-specific patterns of morbidity and mortality in companion dogs, and then explore whether this existing evidence supports the LD. We also discuss some potential limitations to using dogs as models of aging, including the fact that many dogs are euthanized before they have lived out their natural life span. Overall, we conclude that the companion dog offers high potential as a model system that will enable deeper research into the LD than is otherwise possible.

Dogslife: A cohort study of Labrador Retrievers in the UK

Studies of animals that visit primary and secondary veterinary centres dominate companion animal epidemiology. Dogslife is a research initiative that collects data directly from owners about the health and lifestyle of Kennel Club (KC) registered Labrador Retrievers (LR) in the UK. The ultimate aim is to seek associations between canine lifestyle and health. A selection of data from Dogslife regarding the height, weight and lifestyle of 4307 LR up to four years of age is reported here. The majority of the dogs were household pets, living with at least one other pet, in families or households with more than one adult. The dogs typically ate diets of dried food and daily meal frequency decreased as the dogs aged. Working dogs spent more time exercising than pets, and dogs in Wales and Scotland were exercised more than their counterparts in England. Dogs in households with children spent less time exercising than dogs in other types of households. There was considerable variation in height and weight measurements indicative of a highly heterogeneous population. The average male height at the shoulders was 2-3cm taller than the UK breed standard. Dog weights continued to increase between one and four years of age. Those with chocolate coloured coats were heavier than their yellow and black counterparts. Greater dog weight was also associated with dogs whose owners reported restricting their dog's exercise due to where they lived. These findings highlight the utility of wide public engagement in the collation of phenotypic measures, providing a unique insight into the physical development and lifestyle of a cohort of LRs. In combination with concurrently collected data on the health of the cohort, phenotypic data from the Dogslife Project will contribute to understanding the relationship between dog lifestyle and health.

A current life table and causes of death for insured dogs in Japan

The life expectancies and causes of death were evaluated in 299,555 dogs insured in Japan between 1 April 2010 and 31 March 2011, of which 4169 dogs died during this period. The overall life expectancy of dogs was 13.7 years. The probability of death was high in the first year of life, lowest in the second and third years, and increased exponentially after 3 years of age. The life expectancy was 13.8 years in the <5 kg body weight group, 14.2 years in the 5-10 kg body weight group, 13.6 years in the 10-20 kg body weight group, 12.5 years in the 20-40 kg body weight group and 10.6 years in the ≥40 kg body weight group. As body weight increases, life expectancy tended to decrease except in the <5 kg body weight group. The probability of death increased as dogs got older for most potential causes of death. Neoplasia resulted in the highest probability of death, especially in the large and giant breed groups. Cardiovascular system disorders were the second major cause of death and the toy group had a probability of death significantly higher than the other breed groups at age 12+.

How Much Should We Weigh for a Long and Healthy Life Span? The Need to Reconcile Caloric Restriction versus Longevity with Body Mass Index versus Mortality Data

Total caloric restriction (CR) without malnutrition is a well-established experimental approach to extend life span in laboratory animals. Although CR in humans is capable of shifting several endocrinological parameters, it is not clear where the minimum inflection point of the U-shaped curve linking body mass index (BMI) with all-cause mortality lies. The exact trend of this curve, when used for planning preventive strategies for public health is of extreme importance. Normal BMI ranges from 18.5 to 24.9; many epidemiological studies show an inverse relationship between mortality and BMI inside the normal BMI range. Other studies show that the lowest mortality in the entire range of BMI is obtained in the overweight range (25-29.9). Reconciling the extension of life span in laboratory animals by experimental CR with the BMI-mortality curve of human epidemiology is not trivial. In fact, one interpretation is that the CR data are identifying a known: "excess fat is deleterious for health"; although a second interpretation may be that: "additional leanness from a normal body weight may add health and life span delaying the process of aging." This short review hope to start a discussion aimed at finding the widest consensus on which weight range should be considered the "healthiest" for our species, contributing in this way to the picture of what is the correct life style for a long and healthy life span.

Reproductive capability is associated with lifespan and cause of death in companion dogs

Reproduction is a risky affair; a lifespan cost of maintaining reproductive capability, and of reproduction itself, has been demonstrated in a wide range of animal species. However, little is understood about the mechanisms underlying this relationship. Most cost-of-reproduction studies simply ask how reproduction influences age at death, but are blind to the subjects' actual causes of death. Lifespan is a composite variable of myriad causes of death and it has not been clear whether the consequences of reproduction or of reproductive capability influence all causes of death equally. To address this gap in understanding, we compared causes of death among over 40,000 sterilized and reproductively intact domestic dogs, Canis lupus familiaris. We found that sterilization was strongly associated with an increase in lifespan, and while it decreased risk of death from some causes, such as infectious disease, it actually increased risk of death from others, such as cancer. These findings suggest that to understand how reproduction affects lifespan, a shift in research focus is needed. Beyond the impact of reproduction on when individuals die, we must investigate its impact on why individuals die, and subsequently must identify the mechanisms by which these causes of death are influenced by the physiology associated with reproductive capability. Such an approach may also clarify the effects of reproduction on lifespan in people.

IGF1R levels in the brain negatively correlate with longevity in 16 rodent species

The insulin/insulin-like growth factor signaling (IIS) pathway is a major conserved regulator of aging. Nematode, fruit fly and mouse mutants with reduced IIS signaling exhibit extended lifespan. These mutants are often dwarfs leading to the idea that small body mass correlates with longevity within species. However, when different species are compared, larger animals are typically longer-lived. Hence, the role of IIS in the evolution of life history traits remains unresolved. Here we used comparative approach to test whether IGF1R signaling changes in response to selection on lifespan or body mass and whether specific tissues are involved. The IGF1R levels in the heart, lungs, kidneys, and brains of sixteen rodent species with highly diverse lifespans and body masses were measured via immunoblot after epitope conservation analysis. We report that IGF1R levels display strong negative correlation with maximum lifespan only in brain tissue and no significant correlations with body mass for any organ. The brain-IGF1R and lifespan correlation holds when phylogenetic non-independence of data-points is taken into account. These results suggest that modulation of IGF1R signaling in nervous tissue, but not in the peripheral tissues, is an important factor in the evolution of longevity in mammals.

The size-life span trade-off decomposed: why large dogs die young

Large body size is one of the best predictors of long life span across species of mammals. In marked contrast, there is considerable evidence that, within species, larger individuals are actually shorter lived. This apparent cost of larger size is especially evident in the domestic dog, where artificial selection has led to breeds that vary in body size by almost two orders of magnitude and in average life expectancy by a factor of two. Survival costs of large size might be paid at different stages of the life cycle: a higher early mortality, an early onset of senescence, an elevated baseline mortality, or an increased rate of aging. After fitting different mortality hazard models to death data from 74 breeds of dogs, we describe the relationship between size and several mortality components. We did not find a clear correlation between body size and the onset of senescence. The baseline hazard is slightly higher in large dogs, but the driving force behind the trade-off between size and life span is apparently a strong positive relationship between size and aging rate. We conclude that large dogs die young mainly because they age quickly.

Genes against aging

Individual mutations in mice can slow aging: They extend life span by retarding a wide range of harmful, age-dependent changes in multiple cells and tissues. Evolutionary changes-by definition, changes in DNA sequence-can lead to even more dramatic postponement of age-dependent deterioration. Genetic variation within a species, for example among breeds of dogs, can also lead to major changes in aging rate, although there is not yet any strong evidence for similar genetic variation that modulates aging in rodents or humans. This essay compares different strategies for using genetic information to clarify questions in biogerontology, suggesting an emphasis on genes that can retard multiple forms of age-dependent dysfunction in parallel.

Myxomatous mitral valve disease in dogs: does size matter?

Myxomatous mitral valve disease (MMVD) is the most commonly diagnosed cardiovascular disease in the dog accounting for more than 70% of all cardiovascular disease in dogs. As are most canine diseases with genetic underpinnings, risk of MMVD is greatly increased in a subset of breeds. What is uncommon is that the vast majority of the breeds at elevated risk for MMVD are small or toy breeds with average adult weights under 9 kg. These breeds appear to have little in common other than their diminutive size. In the following review we propose a number of mechanisms by which relatively unrelated small breeds may have developed a predisposition for chronic valvular disorders. Although factors such as age are key in the expression of MMVD, taking a comprehensive look at the commonalities, as well as the differences, between the susceptible breeds may assist in finding the causal variants responsible for MMVD and translating them to improved treatments for both dogs and humans.

Height and survival at older ages among men born in an inland village in Sardinia (Italy), 1866-2006

This study investigated the relationship between individual height and survival at older ages among conscripts born between 1866 and 1915 in an inland village of Sardinia, Italy. Individual age at death was related to military height measurement at age 20. Differential longevity of conscripts at older ages was investigated through the comparison of age-specific mortality rates and life expectancy estimates. Results indicated that short conscripts (<161.1 cm) generally had higher survival rates than their tall peers (≥ 161.1 cm). At 70 years of age, tall peers were expected to live two years less than short conscripts. Biological mechanisms were examined in relation to the greater longevity of shorter people.

Biodemography of exceptional longevity: early-life and mid-life predictors of human longevity

This study explores the effects of early-life and middle-life conditions on exceptional longevity using two matched case-control studies. The first study compares 198 validated centenarians born in the United States between 1890 and 1893 to their shorter-lived siblings. Family histories of centenarians were reconstructed and exceptional longevity validated using early U.S. censuses, the Social Security Administration Death Master File, state death indexes, online genealogies, and other supplementary data resources. Siblings born to young mothers (aged less than 25 years) had significantly higher chances of living to 100 compared to siblings born to older mothers (odds ratio = 2.03, 95% CI = 1.33-3.11, p = .001). Paternal age and birth order were not associated with exceptional longevity. The second study explores whether people living to 100 years and beyond differ in physical characteristics at a young age from their shorter-lived peers. A random representative sample of 240 men who were born in 1887 and survived to age 100 was selected from the U.S. Social Security Administration database and linked to U.S. World War I civil draft registration cards collected in 1917 when these men were 30 years old. These validated centenarians were then compared to randomly selected controls who were matched by calendar year of birth, race, and place of draft registration in 1917. Results showed a negative association between "stout" body build (being in the heaviest 15 percent of the population) and survival to age 100. Having the occupation of "farmer" and a large number of children (4 or more) at age 30 increased the chances of exceptional longevity. The results of both studies demonstrate that matched case-control design is a useful approach in exploring effects of early-life conditions and middle-life characteristics on exceptional longevity.

Preservation of femoral bone thickness in middle age predicts survival in genetically heterogeneous mice

To see whether age-related changes in bone could predict subsequent lifespan, we measured multiple aspects of femur size and shape at 4, 15, and 24 months of age in genetically heterogeneous mice. Mice whose cortical bone became thicker from 4 to 15 months, associated with preservation of the endosteal perimeter, survived longer than mice whose endosteal cavity expanded, at the expense of cortical bone, over this age range. Femur size at age 4 months was also associated with a difference in life expectancy: mice with larger bones (measured by length, cortical thickness, or periosteal perimeter) had shorter lifespans. Femur length, midlife change in cortical bone thickness, and midlife values of CD8 T memory cells each added significant power for longevity prediction. Mice in the upper half of the population for each of these three endpoints lived, on average, 103 days (12%) longer than mice with the opposite characteristics. Thus, measures of young adult bone dimensions, changes as a result of bone remodeling in middle age, and immunological maturation provide partially independent indices of aging processes that together help to determine lifespan in genetically heterogeneous mice.

Microdamage accumulation changes according to animal mass: an intraspecies investigation

The fatigue life of a structure is also influenced by its size. Statistically, a bone from a large animal is expected to bear a higher risk of stress fracture if compared to the same bone from a small animal of the same species. This is not documented in the dog, where individuals can have a 40 times difference in body mass. We investigated the effect of body size on cortical bone microdamage accumulation, cortical microstructural organization (porosity, osteon area, and osteocyte lacunar density), and turnover in dogs with a wide body mass range. The aim was to understand and mathematically model how the bone tissue copes with the microdamage accumulation linked to body mass increase. Calcified transverse cortical sections of 18 canine radii of remarkably different size were examined by means of a standard bulk-staining technique and histomorphometric standard algorithms. Relationships between the investigated histomorphometric variables age, sex and mass were analyzed by general linear multivariate models and exponential equations. Type and location of microdamage and bone turnover were not influenced by body mass. Gender did not influence any parameter. Age influenced bone turnover and activation frequency. Microcrack density was influenced by bone mass. Bones had a similar microstructural organization within the same species regardless of the subject's dimension. Microdamage accumulation is inversely related to bone mass, whereas bone turnover is mass-invariant. We theorize a mass-related change in the bone fracture toughness targeted to reach an optimal unique dimensionless curve for fatigue life.

Mortality in north american dogs from 1984 to 2004: an investigation into age-, size-, and breed-related causes of death

BACKGROUND

Anecdotal beliefs and limited research suggest variable patterns of mortality in age, size, and breed cohorts of dogs. Detailed knowledge of mortality patterns would facilitate development of tailored health-maintenance practices and contribute to the understanding of the genetic basis of disease.

HYPOTHESIS/OBJECTIVES

To describe breed-specific causes of death in all instances of canine mortality recorded in the Veterinary Medical Database (VMDB)(a) between 1984 and 2004. We hypothesized that causes of death, categorized by organ system (OS) or pathophysiologic process (PP), would segregate by age, body mass, and breed.

ANIMALS

74,556 dogs from the VMDB for which death was the outcome of the recorded hospital visit.

METHODS

Retrospective study. Causes of death from abstracted VMDB medical records were categorized by OS and PP and analyzed by age, breed, and breed-standard mass of dog.

RESULTS

Causes of death, categorized by OS or PP, segregated by age, breed, and breed-standard mass. Young dogs died more commonly of gastrointestinal and infectious causes whereas older dogs died of neurologic and neoplastic causes. Increasing age was associated with an increasing risk of death because of cardiovascular, endocrine, and urogenital causes, but not because of hematopoietic or musculoskeletal causes. Dogs of larger breeds died more commonly of musculoskeletal and gastrointestinal causes whereas dogs of smaller breeds died more commonly of endocrine causes.

CONCLUSIONS AND CLINICAL IMPORTANCE

Not all causes of death contribute equally to mortality within age, size, or breed cohorts. Documented patterns now provide multiple targets for clinical research and intervention.

Litter size at birth in purebred dogs--a retrospective study of 224 breeds

Despite the long history of purebred dogs and the large number of existing breeds, few studies of canine litter size based upon a large number of breeds exist. Previous studies are either old or include only one or a few selected breeds. The aim of this large-scale retrospective study was to estimate the mean litter size in a large population of purebred dogs and to describe some factors that might influence the litter size. A total of 10,810 litters of 224 breeds registered in the Norwegian Kennel Club from 2006 to 2007 were included in the study. The overall mean litter size at birth was 5.4 (± 0.025). A generalized linear mixed model with a random intercept for breed revealed that the litter size was significantly influenced by the size of the breed, the method of mating and the age of the bitch. A significant interaction between breed size and age was detected, in that the expected number of puppies born decreased more for older bitches of large breeds. Mean litter size increased with breed size, from 3.5 (± 0.04) puppies in miniature breeds to 7.1 (± 0.13) puppies in giant breeds. No effect on litter size was found for the season of birth or the parity of the bitch. The large number of breeds and the detail of the registered information on the litters in this study are unique. In conclusion, the size of the breed, the age of the bitch and the method of mating were found to influence litter size in purebred dogs when controlling for breed, with the size of the breed as the strongest determinant.

Role of the GH/IGF-1 axis in lifespan and healthspan: lessons from animal models

Animal models are fundamentally important in our quest to understand the genetic, epigenetic, and environmental factors that contribute to human aging. In comparison to humans, relatively short-lived mammals are useful models as they allow for rapid assessment of both genetic manipulation and environmental intervention as related to longevity. These models also allow for the study of clinically relevant pathologies as a function of aging. Data associated with more distant species offers additional insight and critical consideration of the basic physiological processes and molecular mechanisms that influence lifespan. Consistently, two interventions, caloric restriction and repression of the growth hormone (GH)/insulin-like growth factor-1/insulin axis, have been shown to increase lifespan in both invertebrates and vertebrate animal model systems. Caloric restriction (CR) is a nutrition intervention that robustly extends lifespan whether it is started early or later in life. Likewise, genes involved in the GH/IGF-1 signaling pathways can lengthen lifespan in vertebrates and invertebrates, implying evolutionary conservation of the molecular mechanisms. Specifically, insulin and insulin-like growth factor-1 (IGF-1)-like signaling and its downstream intracellular signaling molecules have been shown to be associated with lifespan in fruit flies and nematodes. More recently, mammalian models with reduced growth hormone (GH) and/or IGF-1 signaling have also been shown to have extended lifespans as compared to control siblings. Importantly, this research has also shown that these genetic alterations can keep the animals healthy and disease-free for longer periods and can alleviate specific age-related pathologies similar to what is observed for CR individuals. Thus, these mutations may not only extend lifespan but may also improve healthspan, the general health and quality of life of an organism as it ages. In this review, we will provide an overview of how the manipulation of the GH/IGF axis influences lifespan, highlight the invertebrate and vertebrate animal models with altered lifespan due to modifications to the GH/IGF-1 signaling cascade or homologous pathways, and discuss the basic phenotypic characteristics and healthspan of these models.

Cell divisions and mammalian aging: integrative biology insights from genes that regulate longevity

Despite recent progress in the identification of genes that regulate longevity, aging remains a mysterious process. One influential hypothesis is the idea that the potential for cell division and replacement are important factors in aging. In this work, we review and discuss this perspective in the context of interventions in mammals that appear to accelerate or retard aging. Rather than focus on molecular mechanisms, we interpret results from an integrative biology perspective of how gene products affect cellular functions, which in turn impact on tissues and organisms. We review evidence suggesting that mutations that give rise to features resembling premature aging tend to be associated with cellular phenotypes such as increased apoptosis or premature replicative senescence. In contrast, many interventions in mice that extend lifespan and might delay aging, including caloric restriction, tend to either hinder apoptosis or result in smaller animals and thus may be the product of fewer cell divisions. Therefore, it appears plausible that changes in the number of times that cells, and particularly stem cells, divide during an organism's lifespan influence longevity and aging. We discuss possible mechanisms related to this hypothesis and propose experimental paradigms.

Life and death: metabolic rate, membrane composition, and life span of animals

Maximum life span differences among animal species exceed life span variation achieved by experimental manipulation by orders of magnitude. The differences in the characteristic maximum life span of species was initially proposed to be due to variation in mass-specific rate of metabolism. This is called the rate-of-living theory of aging and lies at the base of the oxidative-stress theory of aging, currently the most generally accepted explanation of aging. However, the rate-of-living theory of aging while helpful is not completely adequate in explaining the maximum life span. Recently, it has been discovered that the fatty acid composition of cell membranes varies systematically between species, and this underlies the variation in their metabolic rate. When combined with the fact that 1) the products of lipid peroxidation are powerful reactive molecular species, and 2) that fatty acids differ dramatically in their susceptibility to peroxidation, membrane fatty acid composition provides a mechanistic explanation of the variation in maximum life span among animal species. When the connection between metabolic rate and life span was first proposed a century ago, it was not known that membrane composition varies between species. Many of the exceptions to the rate-of-living theory appear explicable when the particular membrane fatty acid composition is considered for each case. Here we review the links between metabolic rate and maximum life span of mammals and birds as well as the linking role of membrane fatty acid composition in determining the maximum life span. The more limited information for ectothermic animals and treatments that extend life span (e.g., caloric restriction) are also reviewed.

Statistical analysis regarding the effects of height and weight on life span of the domestic dog

This study was undertaken to determine the association between life spans and breed size in the dog, based upon data derived from the pet population. Seventy-seven American Kennel Club breeds were analyzed with data collected for more than 700 dogs. Multiple linear regression analysis was carried out with longevity as the dependent variable and height or weight as the independent variable. A negative correlation was observed between height and longevity (r=-0.603, p<0.05), and between weight and longevity (r=-0.679, p<0.05). Weight was the significant predictor of life span (p<0.001), revealing that breeds smaller by weight generally live longer than heavier breeds. These data form the ground work for investigations of aging utilizing the dog as a model and provide owners with a quantitative method for predicting lifespan of dog breeds, thereby aiding in pet selection.

Mouse (Mus musculus) stocks derived from tropical islands: new models for genetic analysis of life-history traits

Founder effects, together with access to unoccupied ecological niches, may allow rodent populations on isolated islands to evolve constellations of life‐history traits that distinguish them from their mainland relatives, for example in body size, litter size, and longevity. In particular, low intrinsic mortality risks on islands with reduced predator numbers and not subject to harsh winter climates may in principle support the development of stocks with extended longevity. Conversely, the conditions under which laboratory rodents are typically bred are thought to select for genotypes that produce large, rapidly maturing races with high early reproductive rates but diminished longevity. To test these ideas, and to generate new mouse stocks suitable for genetic and molecular analysis of the processes that time life‐history events, we have developed specific pathogen‐free stocks from mice trapped from three distinct populations: the U.S. mainland (Idaho) and the tropical Pacific islands Majuro and Pohnpei. Mice from all three locations were found to be shorter and lighter, to have smaller litters, and to have higher faecal corticosterone levels than mice of a genetically heterogeneous stock derived from four common laboratory inbred strains. Among the wild‐derived stocks, mice from Pohnpei and Majuro were significantly lighter and shorter than Idaho‐derived animals, even in populations kept from birth under identical housing conditions. Litter size and reproductive success rates did not differ significantly among the three wild‐derived stocks. Although further work will be needed to see if, as predicted, the wild‐derived stocks differ from one another and from laboratory mice in longevity, these stocks provide useful tools for genetic dissection of factors that regulate body size and reproductive success.

Diverse aging rates in metazoans: targets for functional genomics

Aging, or senescence, has typically been measured by demographic analysis, which has its merits but is blind to key aspects of functional development and deterioration. If one uses demographic analyses, however, the approach providing most insight is the analysis of age-specific mortality. The continuing increase in DNA sequencing power combined with emerging computational techniques will allow in the near future detailed investigation of mechanisms of aging in diverse species beyond the typical laboratory bestiary. A comparative approach of this sort needs to consider, in addition to simple longevity, the effects of phylogeny and body size on the species in question. Insight may be gained from the study of species exhibiting accelerated aging relative to more "typical" species. These naturally short-lived species, such as several small shrews and marsupials, avoid the worry inherent in "accelerated aging" genotypes of common models, which is that they are only short-lived because of some idiosyncratic pathology unrelated to general aging. A case of special interest that has yet to be seriously investigated is the domestic dog, in which selective breeding has produced phenotypes within the same species that age at two-fold different rates. Exceptionally long-lived species offer exceptional opportunities to discover whether there are few or many ways to create long-lived organisms. Slow-aging species with the most to offer include bats and naked mole-rats. Perhaps no fundamental question in biology is more intriguing that why and how nature has produced such a dazzling array of aging rates. The development of functional genetics over the next several decades promises to lead us toward an answer.

On the importance of fatty acid composition of membranes for aging

The membrane pacemaker theory of aging is an extension of the oxidative stress theory of aging. It emphasises variation in the fatty acid composition of membranes as an important influence on lipid peroxidation and consequently on the rate of aging and determination of lifespan. The products of lipid peroxidation are reactive molecules and thus potent damagers of other cellular molecules. It is suggested that the feedback effects of these peroxidation products on the oxidative stress experienced by cells is an important part of the aging process. The large variation in the chemical susceptibility of individual fatty acids to peroxidation coupled with the known differences in membrane composition between species can explain the different lifespans of species, especially the difference between mammals and birds as well as the body-size-related variation in lifespan within mammals and birds. Lifespan extension by calorie-restriction can also be explained by changes in membrane fatty acid composition which result in membranes more resistant to peroxidation. It is suggested that lifespan extension by reduced insulin/IGF signalling may also be mediated by changes in membrane fatty acid composition.

A new mutation in the timing of autogamy in Paramecium tetraurelia

We have isolated a new type of Paramecium tetraurelia mutant, named rie-2, that has a long immaturity period until autogamy. We previously isolated such an autogamy mutant, designated rie-1. These two mutants had some additional common features such as dependence of the occurrence of autogamy on the temperature, involvement of a single recessive gene, lower fission rate and shorter clonal life span. However, rie-2 was considered a new type mutant distinguishable from rie-1 because of their different natures of temperature sensitivity. First, the temperature at which they resembled the wild-type phenotype was low (19 degrees C) in rie-2, although it was high (32 degrees C) in rie-1. Second, the clonal life span of rie-2 at 25 degrees C was similar to that of the wild-type, but it was extremely shorter at 32 degrees C than at 25 degrees C, although it was similarly shorter at both temperatures in rie-1. Third, the difference of the fission rate between mutant and wild-type was greater at 32 degrees C than at 25 degrees C in rie-2, although it was similar at both temperatures in rie-1. This report shows that a gene mutation to elongate the period until sexual maturation does not necessarily assure the long life span.

Hormone-treated snell dwarf mice regain fertility but remain long lived and disease resistant

Snell dwarf mice have multiple hormonal deficits, but the way in which these deficits postpone aging are still uncertain. In this study, Snell dwarf mice received 11 weeks of growth hormone and thyroxine injections that increased their weight by approximately 45%, although they remained much smaller than controls. The hormone treatment also restored fertility to male dwarf mice. Despite these effects on growth and maturation, the hormone treatments did not diminish life span or lower the resistance of dwarf mice to cataracts and kidney disease. Administration of thyroxine in food throughout adult life did diminish longevity of Snell dwarf mice, although these mice remain longer lived than control animals. These results show that a 45% increase in body size does not impair longevity or disease resistance for dwarf mice of either sex, and that the exceptional longevity of Snell dwarf mice does not, at least for males, depend on prepubertal immaturity.

The genetics of human longevity

Many of the genes that affect aging and longevity in model organisms, such as mice, fruit flies, and worms, have human homologs. This article reviews several genetic pathways that may extend lifespan through effects on aging, rather than through effects on diseases such as atherosclerosis or cancer. These include some of the genes involved in the regulation of DNA repair and nuclear structure, which cause the progeroid syndromes when mutated, as well as those that may affect telomere length, since shorter telomeres have been associated with shorter survival. Other potential longevity genes, such as sirtuins, are involved in regulating the response to cellular stress, including caloric restriction. The best-studied pathway involves insulin and insulin-like growth factor 1 signaling; mutations in homologs of these genes have extended lifespan up to sixfold in model organisms. Other potential candidates include mitochondrial DNA and the genes that regulate the inflammatory response. Despite the challenges in study design and analysis that face investigators in this area, the identification of genetic pathways that regulate longevity may suggest potential targets for therapy.

Juvenile diet restriction and the aging and reproduction of adult Drosophila melanogaster

Mutations of the insulin signal pathway in Drosophila melanogaster produce long-lived adults with many correlated phenotypes. Homozygotes of insulin-like receptor (InR) and insulin-like receptor substrate (chico) delay time to eclosion, reduce body size, decrease reproduction and increase life span. Because these mutations are expressed through all life stages it is unclear when insulin signals must be reduced to increase life span. As a first analysis of this problem in D. melanogaster we have manipulated the larval diet to determine if changes in metabolic regulation at this stage are sufficient to slow aging. We controlled the dietary yeast fed to third instar larvae and studied the size, mortality, fecundity and hormones of the resulting adults, which were fed a normal, yeast-replete diet. Adults from yeast-deprived larvae phenocopied many traits of InR and chico mutants: small body size, delayed eclosion, reduced ovariole number and reduced age-specific fecundity. But unlike constitutive mutants of the insulin/IGF system, adults from yeast-deprived larvae had normal patterns of demographic senescence, and this was accompanied by normal insulin-like peptide and juvenile hormone syntheses. Surprisingly, the normal aging in these adults was also associated with greatly reduced fecundity. Although nutritional conditions of the larvae can affect the subsequent body size and fecundity of adults, these are not sufficient to slow aging.

Exceptional Longevity in Pet Dogs Is Accompanied by Cancer Resistance and Delayed Onset of Major Diseases

To characterize extreme aged pet dogs as a first step in developing an animal model of exceptional longevity, we constructed lifetime medical histories for 345 Rottweiler dogs using information collected from owners and veterinarians. Extreme aged dogs (alive at the 95th percentile age at death for the study population, > or =13.3 years) were compared with a usual longevity group (9-10 years). Exceptional longevity in Rottweiler dogs was accompanied by a significant delay in the onset of major life-threatening diseases; 76% of extreme aged dogs remained free of all major diseases during the first 9 years of life. Only 19% of extreme aged dogs died of cancer versus 82% of dogs with usual longevity (p <.0001). The reduction in cancer mortality in oldest-old pet dogs mimics that seen in human centenarians and provides strong rationale for using this animal model to study comparative mechanisms of cancer resistance in the extreme aged.