CSF1R inhibitor PLX5622 and environmental enrichment additively improve metabolic outcomes in middle-aged female mice

Colony Stimulating Factor-1 Receptor: An emerging target for neuroinflammation PET imaging and AD therapy

Although neuroinflammation is a significant pathogenic feature of many neurologic disorders, its precise function in-vivo is still not completely known. PET imaging enables the longitudinal examination, quantification, and tracking of different neuroinflammation biomarkers in living subjects. Particularly, PET imaging of Microglia, specialised dynamic immune cells crucial for maintaining brain homeostasis in central nervous system (CNS), is crucial for staging the neuroinflammation. Colony Stimulating Factor- 1 Receptor (CSF-1R) PET imaging is a novel method for the quantification of neuroinflammation. CSF-1R is mainly expressed on microglia, and neurodegenerative disorders greatly up-regulate its expression. The present review primarily focuses on the development, pros and cons of all the CSF-1R PET tracers reported for neuroinflammation imaging. Apart from neuroinflammation imaging, CSF-1R inhibitors are also reported for the therapy of neurodegenerative diseases such as Alzheimer's disease (AD). AD is a prevalent, advancing, and fatal neurodegenerative condition that have the characteristic feature of persistent neuroinflammation and primarily affects the elderly. The aetiology of AD is profoundly influenced by amyloid-beta (Aβ) plaques, intracellular neurofibrillary tangles, and microglial dysfunction. Increasing evidence suggests that CSF-1R inhibitors (CSF-1Ri) can be helpful in preclinical models of neurodegenerative diseases. This review article also summarises the most recent developments of CSF-1Ri-based therapy for AD.

Role of NLRP3 Inflammasome in Post-Spinal-Cord-Injury Anxiety and Depression: Molecular Mechanisms and Therapeutic Implications

The majority of research on the long-term effects of spinal cord injury (SCI) has primarily focused on neuropathic pain (NP), psychological issues, and sensorimotor impairments. Among SCI patients, mood disorders, such as anxiety and depression, have been extensively studied. It has been found that chronic stress and NP have negative consequences and reduce the quality of life for individuals living with SCI. Our review examined both human and experimental evidence to explore the connection between mood changes following SCI and inflammatory pathways, with a specific focus on NLRP3 inflammasome signaling. We observed increased proinflammatory factors in the blood, as well as in the brain and spinal cord tissues of SCI models. The NLRP3 inflammasome plays a crucial role in various diseases by controlling the release of proinflammatory molecules like interleukin 1β (IL-1β) and IL-18. Dysregulation of the NLRP3 inflammasome in key brain regions associated with pain processing, such as the prefrontal cortex and hippocampus, contributes to the development of mood disorders following SCI. In this review, we summarized recent research on the expression and regulation of components related to NLRP3 inflammasome signaling in mood disorders following SCI. Finally, we discussed potential therapeutic approaches that target the NLRP3 inflammasome and regulate proinflammatory cytokines as a way to treat mood disorders following SCI.

Environmental Enrichment Improves Motor Function and Muscle Transcriptome of Aged Mice

Aging results in the progressive decline of muscle strength. Interventions to maintain muscle strength may mitigate the age-related loss of physical function, thus maximizing health span. The work on environmental enrichment (EE), an experimental paradigm recapitulating aspects of an active lifestyle, has revealed EE-induced metabolic benefits mediated by a brain-fat axis across the lifespan of mice. EE initiated at 18-month of age shows a trend toward an increased mean lifespan. While previous work described EE's influences on the aging dynamics of several central-peripheral processes, its influence on muscle remained understudied. Here, the impact of EE is investigated on motor function, neuromuscular physiology, and the skeletal muscle transcriptome. EE is initiated in 20-month-old mice for a five-month period. EE mice exhibit greater relative lean mass that is associated with improved mobility and hindlimb grip strength. Transcriptomic profiling of muscle tissue reveals an EE-associated enrichment of gene expression within several metabolic pathways related to oxidative phosphorylation and the TCA cycle. Many mitochondrial-related genes-several of which participate in the electron transport chain-are upregulated. Stress-responsive signaling pathways are downregulated because of EE. The results suggest that EE improves motor function-possibly through preservation of mitochondrial function-even late in life.

CSF1R inhibition with PLX5622 affects multiple immune cell compartments and induces tissue-specific metabolic effects in lean mice

AIMS/HYPOTHESIS

Colony stimulating factor 1 (CSF1) promotes the proliferation, differentiation and survival of macrophages, which have been implicated in both beneficial and detrimental effects on glucose metabolism. However, the physiological role of CSF1 signalling in glucose homeostasis and the potential therapeutic implications of modulating this pathway are not known. We aimed to study the composition of tissue macrophages (and other immune cells) following CSF1 receptor (CSF1R) inhibition and elucidate the metabolic consequences of CSF1R inhibition.

METHODS

We assessed immune cell populations in various organs by flow cytometry, and tissue-specific metabolic effects by hyperinsulinaemic-euglycaemic clamps and insulin secretion assays in mice fed a chow diet containing PLX5622 (a CSF1R inhibitor) or a control diet.

RESULTS

CSF1R inhibition depleted macrophages in multiple tissues while simultaneously increasing eosinophils and group 2 innate lymphoid cells. These immunological changes were consistent across different organs and were sex independent and reversible after cessation of the PLX5622. CSF1R inhibition improved hepatic insulin sensitivity but concomitantly impaired insulin secretion. In healthy islets, we found a high frequency of IL-1β+ islet macrophages. Their depletion by CSF1R inhibition led to downregulation of macrophage-related pathways and mediators of cytokine activity, including Nlrp3, suggesting IL-1β as a candidate insulin secretagogue. Partial restoration of physiological insulin secretion was achieved by injecting recombinant IL-1β prior to glucose stimulation in mice lacking macrophages.

CONCLUSIONS/INTERPRETATION

Macrophages and macrophage-derived factors, such as IL-1β, play an important role in physiological insulin secretion. A better understanding of the tissue-specific effects of CSF1R inhibition on immune cells and glucose homeostasis is crucial for the development of targeted immune-modulatory treatments in metabolic disease.

DATA AVAILABILITY

The RNA-Seq dataset is available in the Gene Expression Omnibus (GEO) under the accession number GSE189434 ( http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE189434 ).

Diesel Exhaust Particle (DEP)-induced glucose intolerance is driven by an intestinal innate immune response and NLRP3 activation in mice

BACKGROUND

We previously found that air pollution particles reaching the gastrointestinal tract elicit gut inflammation as shown by up-regulated gene expression of pro-inflammatory cytokines and monocyte/macrophage markers. This inflammatory response was associated with beta-cell dysfunction and glucose intolerance. So far, it remains unclear whether gut inflammatory changes upon oral air pollution exposure are causally linked to the development of diabetes. Hence, our aim was to assess the role of immune cells in mediating glucose intolerance instigated by orally administered air pollutants.

METHODS

To assess immune-mediated mechanisms underlying air pollution-induced glucose intolerance, we administered diesel exhaust particles (DEP; NIST 1650b, 12 µg five days/week) or phosphate-buffered saline (PBS) via gavage for up to 10 months to wild-type mice and mice with genetic or pharmacological depletion of innate or adaptive immune cells. We performed unbiased RNA-sequencing of intestinal macrophages to elucidate signaling pathways that could be pharmacologically targeted and applied an in vitro approach to confirm these pathways.

RESULTS

Oral exposure to air pollution particles induced an interferon and inflammatory signature in colon macrophages together with a decrease of CCR2^- anti-inflammatory/resident macrophages. Depletion of macrophages, NLRP3 or IL-1β protected mice from air pollution-induced glucose intolerance. On the contrary, Rag2-/- mice lacking adaptive immune cells developed pronounced gut inflammation and glucose intolerance upon oral DEP exposure.

CONCLUSION

In mice, oral exposure to air pollution particles triggers an immune-mediated response in intestinal macrophages that contributes to the development of a diabetes-like phenotype. These findings point towards new pharmacologic targets in diabetes instigated by air pollution particles.

Pathophysiological basis and promise of experimental therapies for Gulf War Illness, a chronic neuropsychiatric syndrome in veterans

This article describes the pathophysiology and potential treatments for Gulf War Illness (GWI), which is a chronic neuropsychiatric illness linked to a combination of chemical exposures experienced by service personnel during the first Gulf War in 1991. However, there is currently no effective treatment for veterans with GWI. The article focuses on the current status and efficacy of existing therapeutic interventions in preclinical models of GWI, as well as potential perspectives of promising therapies. GWI stems from changes in brain and peripheral systems in veterans, leading to neurocognitive deficits, as well as physiological and psychological effects resulting from multifaceted changes such as neuroinflammation, oxidative stress, and neuronal damage. Aging not only renders veterans more susceptible to GWI symptoms, but also attenuates their immune capabilities and response to therapies. A variety of experimental models are being used to investigate the pathophysiology and develop therapies that have the ability to alleviate devastating symptoms. Over two dozen therapeutic interventions targeting neuroinflammation, mitochondrial dysfunction, neuronal injury, and neurogenesis are being tested, including agents such as curcumin, curcumin nanoparticles, monosodium luminol, melatonin, resveratrol, fluoxetine, rolipram, oleoylethanolamide, ketamine, levetiracetam, nicotinamide riboside, minocycline, pyridazine derivatives, and neurosteroids. Preclinical outcomes show that some agents have promise, including curcumin, resveratrol, and ketamine, which are being tested in clinical trials in GWI veterans. Neuroprotectants and other compounds such as monosodium luminol, melatonin, levetiracetam, oleoylethanolamide, and nicotinamide riboside appear promising for future clinical trials. Neurosteroids have been shown to have neuroprotective and disease-modifying properties, which makes them a promising medicine for GWI. Therefore, accelerated clinical studies are urgently needed to evaluate and launch an effective therapy for veterans displaying GWI.

Social isolation exacerbates diet-induced obesity and peripheral inflammation in young male mice under thermoneutrality

Social isolation (SI) is associated with an increased risk of mortality and various chronic diseases-including obesity-in humans. Murine studies probing SI metabolic outcomes remain inconsistent, due in part to a lack of consideration for housing temperature. Such experiments typically occur at room temperature, subjecting mice to chronic cold stress. Single housing prevents social thermoregulation, further exacerbating cold stress and obscuring psychosocial influences on metabolism at room temperature. In this study, C57BL/6 and BALB/c male mice were group- and single-housed under thermoneutral conditions to determine whether SI affects the development of high-fat diet-induced obesity. We report SI promotes weight gain, increases food intake, increases adiposity, worsens glycemic control, reduces insulin signaling, exacerbates systemic and adipose inflammatory responses, and induces a molecular signature within the hypothalamus. This study establishes a murine model that recapitulates the SI-induced propensity for obesity, which may further our understanding of SI's influence on health and disease.

The effectiveness of anti-inflammatory agents in reducing chemotherapy-induced cognitive impairment in preclinical models - A systematic review

Chemotherapy-induced cognitive impairment (CICI) is a debilitating condition resulting from chemotherapy administration for cancer treatment. CICI is characterised by various cognitive impairments, including issues with learning, memory, and concentration, impacting quality of life. Several neural mechanisms are proposed to drive CICI, including inflammation, therefore, anti-inflammatory agents could ameliorate such impairments. Research is still in the preclinical stage; however, the efficacy of anti-inflammatories to reduce CICI in animal models is unknown. Therefore, a systematic review was conducted, with searches performed in PubMed, Scopus, Embase, PsycInfo and Cochrane Library. A total of 64 studies were included, and of the 50 agents identified, 41 (82%) reduced CICI. Interestingly, while non-traditional anti-inflammatory agents and natural compounds reduced impairment, the traditional agents were unsuccessful. Such results must be taken with caution due to the heterogeneity observed in terms of methods employed. Nevertheless, preliminary evidence suggests anti-inflammatory agents could be beneficial for treating CICI, although it may be critical to think beyond the use of traditional anti-inflammatories when considering which specific compounds to prioritise in development.

What microglia depletion approaches tell us about the role of microglia on synaptic function and behavior

Microglia are dynamic cells, constantly surveying their surroundings and interacting with neurons and synapses. Indeed, a wealth of knowledge has revealed a critical role of microglia in modulating synaptic transmission and plasticity in the developing brain. In the past decade, novel pharmacological and genetic strategies have allowed the acute removal of microglia, opening the possibility to explore and understand the role of microglia also in the adult brain. In this review, we summarized and discussed the contribution of microglia depletion strategies to the current understanding of the role of microglia on synaptic function, learning and memory, and behavior both in physiological and pathological conditions. We first described the available microglia depletion methods highlighting their main strengths and weaknesses. We then reviewed the impact of microglia depletion on structural and functional synaptic plasticity. Next, we focused our analysis on the effects of microglia depletion on behavior, including general locomotor activity, sensory perception, motor function, sociability, learning and memory both in healthy animals and animal models of disease. Finally, we integrated the findings from the reviewed studies and discussed the emerging roles of microglia on the maintenance of synaptic function, learning, memory strength and forgetfulness, and the implications of microglia depletion in models of brain disease.

Inhibition of colony stimulating factor-1 receptor (CSF-1R) as a potential therapeutic strategy for neurodegenerative diseases: opportunities and challenges

Microglia are specialized dynamic immune cells in the central nervous system (CNS) that plays a crucial role in brain homeostasis and in disease states. Persistent neuroinflammation is considered a hallmark of many neurodegenerative diseases, including Alzheimer’s disease (AD), Parkinson's disease (PD), Huntington’s disease (HD), amyotrophic lateral sclerosis (ALS) and primary progressive multiple sclerosis (MS). Colony stimulating factor 1-receptor (CSF-1R) is predominantly expressed on microglia and its expression is significantly increased in neurodegenerative diseases. Cumulative findings have indicated that CSF-1R inhibitors can have beneficial effects in preclinical neurodegenerative disease models. Research using CSF-1R inhibitors has now been extended into non-human primates and humans. This review article summarizes the most recent advances using CSF-1R inhibitors in different neurodegenerative conditions including AD, PD, HD, ALS and MS. Potential challenges for translating these findings into clinical practice are presented.

Hypothalamic inflammation in metabolic disorders and aging

The hypothalamus is a critical brain region for the regulation of energy homeostasis. Over the years, studies on energy metabolism primarily focused on the neuronal component of the hypothalamus. Studies have recently uncovered the vital role of glial cells as an additional player in energy balance regulation. However, their inflammatory activation under metabolic stress condition contributes to various metabolic diseases. The recruitment of monocytes and macrophages in the hypothalamus helps sustain such inflammation and worsens the disease state. Neurons were found to actively participate in hypothalamic inflammatory response by transmitting signals to the surrounding non-neuronal cells. This activation of different cell types in the hypothalamus leads to chronic, low-grade inflammation, impairing energy balance and contributing to defective feeding habits, thermogenesis, and insulin and leptin signaling, eventually leading to metabolic disorders (i.e., diabetes, obesity, and hypertension). The hypothalamus is also responsible for the causation of systemic aging under metabolic stress. A better understanding of the multiple factors contributing to hypothalamic inflammation, the role of the different hypothalamic cells, and their crosstalks may help identify new therapeutic targets. In this review, we focus on the role of glial cells in establishing a cause-effect relationship between hypothalamic inflammation and the development of metabolic diseases. We also cover the role of other cell types and discuss the possibilities and challenges of targeting hypothalamic inflammation as a valid therapeutic approach.

Treatment With the CSF1R Antagonist GW2580, Sensitizes Microglia to Reactive Oxygen Species

Microglia activation and proliferation are hallmarks of many neurodegenerative disorders and may contribute to disease pathogenesis. Neurons actively regulate microglia survival and function, in part by secreting the microglia mitogen interleukin (IL)-34. Both IL-34 and colony stimulating factor (CSF)-1 bind colony stimulating factor receptor (CSFR)1 expressed on microglia. Systemic treatment with central nervous system (CNS) penetrant, CSFR1 antagonists, results in microglia death in a dose dependent matter, while others, such as GW2580, suppress activation during disease states without altering viability. However, it is not known how treatment with non-penetrant CSF1R antagonists, such as GW2580, affect the normal physiology of microglia. To determine how GW2580 affects microglia function, C57BL/6J mice were orally gavaged with vehicle or GW2580 (80mg/kg/d) for 8 days. Body weights and burrowing behavior were measured throughout the experiment. The effects of GW2580 on circulating leukocyte populations, brain microglia morphology, and the transcriptome of magnetically isolated adult brain microglia were determined. Body weights, burrowing behavior, and circulating leukocytes were not affected by treatment. Analysis of Iba-1 stained brain microglia indicated that GW2580 treatment altered morphology, but not cell number. Analysis of RNA-sequencing data indicated that genes related to reactive oxygen species (ROS) regulation and survival were suppressed by treatment. Treatment of primary microglia cultures with GW2580 resulted in a dose-dependent reduction in viability only when the cells were concurrently treated with LPS, an inducer of ROS. Pre-treatment with the ROS inhibitor, YCG063, blocked treatment induced reductions in viability. Finally, GW2580 sensitized microglia to hydrogen peroxide induced cell death. Together, these data suggest that partial CSF1R antagonism may render microglia more susceptible to reactive oxygen and nitrogen species.

Colony stimulating factors in the nervous system

Although traditionally seen as regulators of hematopoiesis, colony-stimulating factors (CSFs) have emerged as important players in the nervous system, both in health and disease. This review summarizes the cellular sources, patterns of expression and physiological roles of the macrophage (CSF-1, IL-34), granulocyte-macrophage (GM-CSF) and granulocyte (G-CSF) colony stimulating factors within the nervous system, with a particular focus on their actions on microglia. CSF-1 and IL-34, via the CSF-1R, are required for the development, proliferation and maintenance of essentially all CNS microglia in a temporal and regional specific manner. In contrast, in steady state, GM-CSF and G-CSF are mainly involved in regulation of microglial function. The alterations in expression of these growth factors and their receptors, that have been reported in several neurological diseases, are described and the outcomes of their therapeutic targeting in mouse models and humans are discussed.

Enhancing Effects of Environmental Enrichment on the Functions of Natural Killer Cells in Mice

The environment of an organism can convey a powerful influence over its biology. Environmental enrichment (EE), as a eustress model, has been used extensively in neuroscience to study neurogenesis and brain plasticity. EE has also been used as an intervention for the treatment and prevention of neurological and psychiatric disorders with limited clinical application. By contrast, the effects of EE on the immune system are relatively less investigated. Recently, accumulating evidence has demonstrated that EE can robustly impact immune function. In this review, we summarize the major components of EE, the impact of EE on natural killer (NK) cells, EE's immunoprotective roles in cancer, and the underlying mechanisms of EE-induced NK cell regulation. Moreover, we discuss opportunities for translational application based on insights from animal research of EE-induced NK cell regulation.

The Impact of Obesity on Microglial Function: Immune, Metabolic and Endocrine Perspectives

Increased life expectancy in combination with modern life style and high prevalence of obesity are important risk factors for development of neurodegenerative diseases. Neuroinflammation is a feature of neurodegenerative diseases, and microglia, the innate immune cells of the brain, are central players in it. The present review discusses the effects of obesity, chronic peripheral inflammation and obesity-associated metabolic and endocrine perturbations, including insulin resistance, dyslipidemia and increased glucocorticoid levels, on microglial function.

Enrichment Protocol for Rat Models

An environmental enrichment (EE) cage consisting of a broad living area and various stimulators triggers social, cognitive, and physical activities. EE has been utilized in a wide range of neurological and non-neurological studies. However, the details of the environmental enrichment protocol were not well described in these studies. This has resulted in uncertainty and inconsistency in methodology, which may thus fail to replicate environmental enrichment effects, influencing the study outcome. Here we describe the basic guidelines and present an easy-to-follow protocol for environmental enrichment in rat models. © 2021 Wiley Periodicals LLC. Basic Protocol: Environmental enrichment housing.

Hypothalamic Microglial Heterogeneity and Signature under High Fat Diet-Induced Inflammation

Under high-fat feeding, the hypothalamus atypically undergoes pro-inflammatory signaling activation. Recent data from transcriptomic analysis of microglia from rodents and humans has allowed the identification of several microglial subpopulations throughout the brain. Numerous studies have clarified the roles of these cells in hypothalamic inflammation, but how each microglial subset plays its functions upon inflammatory stimuli remains unexplored. Fortunately, these data unveiling microglial heterogeneity have triggered the development of novel experimental models for studying the roles and characteristics of each microglial subtype. In this review, we explore microglial heterogeneity in the hypothalamus and their crosstalk with astrocytes under high fat diet-induced inflammation. We present novel currently available ex vivo and in vivo experimental models that can be useful when designing a new research project in this field of study. Last, we examine the transcriptomic data already published to identify how the hypothalamic microglial signature changes upon short-term and prolonged high-fat feeding.

Hypothalamic gene transfer of BDNF promotes healthy aging

The aging process and age-related diseases all involve metabolic decline and impaired ability to cope with adversity. Environmental enrichment (EE)-a housing environment which recapitulates aspects of active lifestyle-exerts a wide range of health benefits in laboratory rodents. Brain-derived neurotrophic factor (BDNF) in the hypothalamus orchestrates autonomic and neuroendocrine processes, serving as one key brain mediator of EE-induced resistance to obesity, cancer, and autoimmunity. Recombinant adeno-associated virus (AAV)-mediated hypothalamic BDNF gene transfer alleviates obesity, diabetes, and metabolic syndromes in both diet-induced and genetic models. One recent study by our lab demonstrates the efficacy and safety of a built-in autoregulatory system to control transgene BDNF expression, mimicking the body's natural feedback systems in middle-age mice. Twelve-month old mice were treated with autoregulatory BDNF vector and monitored for 7months. BDNF gene transfer prevented age-associated metabolic decline by: reducing adiposity, preventing the decline of brown fat activity, increasing adiponectin while reducing leptin and insulin in circulation, improving glucose tolerance, increasing energy expenditure, alleviating hepatic steatosis, and suppressing inflammatory genes in the hypothalamus and adipose tissues. Furthermore, BDNF treatment reduced anxiety-like and depression-like behaviors. This chapter summarizes this work and discusses potential roles that hypothalamic BDNF might play in promoting healthy aging.

Conditional genetic deletion of CSF1 receptor in microglia ameliorates the physiopathology of Alzheimer's disease

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most common form of dementia in the world. Microglia are the innate immune cells of CNS; their proliferation, activation, and survival in pathologic and healthy brain have previously been shown to be highly dependent on CSF1R.

METHODS

Here, we investigate the impact of such receptor on AD etiology and microglia. We deleted CSF1R using Cre/Lox system; the knockout (KO) is restricted to microglia in the APP/PS1 mouse model. We induced the knockout at 3 months old, before plaque formation, and evaluated both 6- and 8-month-old groups of mice.

RESULTS

Our findings demonstrated that CSF1R KO did not impair microglial survival and proliferation at 6 and 8 months of age in APP cKO compared to their littermate-control groups APPSwe/PS1. We have also shown that cognitive decline is delayed in CSF1R-deleted mice. Ameliorations of AD etiology are associated with a decrease in plaque volume in the cortex and hippocampus area. A compensating system seems to take place following the knockout, since TREM2/β-Catenin and IL-34 expression are significantly increased. Such a compensatory mechanism may promote microglial survival and phagocytosis of Aβ in the brain.

CONCLUSIONS

Our results provide new insights on the role of CSF1R in microglia and how it interacts with the TREM2/β-Catenin and IL-34 system to clear Aβ and ameliorates the physiopathology of AD.

Regulation of aging and cancer by enhanced environmental activation of a hypothalamic-sympathoneural-adipocyte axis

Social and environmental factors impact cancer and energy balance profoundly. Years ago, our lab established the existence of a novel brain-fat interaction we termed the "hypothalamic-sympathoneural-adipocyte (HSA) axis", through which complex environmental stimuli provided by an enriched environment regulate body composition, energy balance, and development of cancer. We have spent a significant portion of the past decade to further characterize the broad health benefits of an enriched environment (for example, leanness, enhanced immune function, and cancer resistance), and to identify mediators in the brain and periphery along the HSA axis. This review summarizes our recent work regarding the interface between endocrinology, immunology, cancer biology, aging, and neuroscience. We will discuss the interplay between these systemic phenomena and how the HSA axis can be targeted for regulation of cancer and aging.

Improvements to Healthspan Through Environmental Enrichment and Lifestyle Interventions: Where Are We Now?

Environmental enrichment (EE) is an experimental paradigm that is used to explore how a complex, stimulating environment can impact overall health. In laboratory animal experiments, EE housing conditions typically include larger-than-standard cages, abundant bedding, running wheels, mazes, toys, and shelters which are rearranged regularly to further increase stimulation. EE has been shown to improve multiple aspects of health, including but not limited to metabolism, learning and cognition, anxiety and depression, and immunocompetence. Recent advances in lifespan have led some researchers to consider aging as a risk factor for disease. As such, there is a pressing need to understand the processes by which healthspan can be increased. The natural and predictable changes during aging can be reversed or decreased through EE and its underlying mechanisms. Here, we review the use of EE in laboratory animals to understand mechanisms involved in aging, and comment on relative areas of strength and weakness in the current literature. We additionally address current efforts toward applying EE-like lifestyle interventions to human health to extend healthspan. Although increasing lifespan is a clear goal of medical research, improving the quality of this added time also deserves significant attention. Despite hurdles in translating experimental results toward clinical application, we argue there is great potential in using features of EE toward improving human healthy life expectancy or healthspan, especially in the context of increased global longevity.