Cap-independent translation of GPLD1 enhances markers of brain health in long-lived mutant and drug-treated mice

Lifespan effects in male UM-HET3 mice treated with sodium thiosulfate, 16-hydroxyestriol, and late-start canagliflozin

Genetically heterogeneous UM-HET3 mice born in 2020 were used to test possible lifespan effects of alpha-ketoglutarate (AKG), 2,4-dinitrophenol (DNP), hydralazine (HYD), nebivolol (NEBI), 16α-hydroxyestriol (OH_Est), and sodium thiosulfate (THIO), and to evaluate the effects of canagliflozin (Cana) when started at 16 months of age. OH_Est produced a 15% increase (p = 0.0001) in median lifespan in males but led to a significant (7%) decline in female lifespan. Cana, started at 16 months, also led to a significant increase (14%, p = 0.004) in males and a significant decline (6%, p = 0.03) in females. Cana given to mice at 6 months led, as in our previous study, to an increase in male lifespan without any change in female lifespan, suggesting that this agent may lead to female-specific late-life harm. We found that blood levels of Cana were approximately 20-fold higher in aged females than in young males, suggesting a possible mechanism for the sex-specific disparities in its effects. NEBI was also found to produce a female-specific decline (4%, p = 0.03) in lifespan. None of the other tested drugs provided a lifespan benefit in either sex. These data bring to 7 the list of ITP-tested drugs that induce at least a 10% lifespan increase in one or both sexes, add a fourth drug with demonstrated mid-life benefits on lifespan, and provide a testable hypothesis that might explain the sexual dimorphism in lifespan effects of the SGLT2 inhibitor Cana.

Exercise activates interferon response of the liver via Gpld1 to enhance antiviral innate immunity

Healthy behavioral patterns could modulate organ functions to enhance the body's immunity. However, how exercise regulates antiviral innate immunity remains elusive. Here, we found that exercise promotes type I interferon (IFN-I) production in the liver and enhances IFN-I immune activity of the body. Despite the possibility that many exercise-induced factors could affect IFN-I production, we identified Gpld1 as a crucial molecule, and the liver as the major organ to promote IFN-I production after exercise. Exercise largely loses the efficiency to induce IFN-I in Gpld1-/- mice. Further studies demonstrated that exercise-produced 3-hydroxybutanoic acid (3-HB) critically induces Gpld1 expression in the liver. Gpld1 blocks the PP2A-IRF3 interaction, thus enhancing IRF3 activation and IFN-I production, and eventually improving the body's antiviral ability. This study reveals that exercise improves antiviral innate immunity by linking the liver metabolism to systemic IFN-I activity and uncovers an unknown function of liver cells in innate immunity.

Proteomic changes induced by longevity-promoting interventions in mice

Using mouse models and high-throughput proteomics, we conducted an in-depth analysis of the proteome changes induced in response to seven interventions known to increase mouse lifespan. This included two genetic mutations, a growth hormone receptor knockout (GHRKO mice) and a mutation in the Pit-1 locus (Snell dwarf mice), four drug treatments (rapamycin, acarbose, canagliflozin, and 17α-estradiol), and caloric restriction. Each of the interventions studied induced variable changes in the concentrations of proteins across liver, kidney, and gastrocnemius muscle tissue samples, with the strongest responses in the liver and limited concordance in protein responses across tissues. To the extent that these interventions promote longevity through common biological mechanisms, we anticipated that proteins associated with longevity could be identified by characterizing shared responses across all or multiple interventions. Many of the proteome alterations induced by each intervention were distinct, potentially implicating a variety of biological pathways as being related to lifespan extension. While we found no protein that was affected similarly by every intervention, we identified a set of proteins that responded to multiple interventions. These proteins were functionally diverse but tended to be involved in peroxisomal oxidation and metabolism of fatty acids. These results provide candidate proteins and biological mechanisms related to enhancing longevity that can inform research on therapeutic approaches to promote healthy aging.

Recapitulation of anti-aging phenotypes by global overexpression of PTEN in mice

The PTEN gene negatively regulates the oncogenic PI3K-AKT pathway by encoding a lipid and protein phosphatase that dephosphorylates lipid phosphatidylinositol-3,4,5-triphosphate (PIP3) resulting in the inhibition of PI3K and downstream inhibition of AKT. Overexpression of PTEN in mice leads to a longer lifespan compared to control littermates, although the mechanism is unknown. Here, we provide evidence that young adult PTENOE mice exhibit many characteristics shared by other slow-aging mouse models, including those with mutations that affect GH/IGF1 pathways, calorie-restricted mice, and mice treated with anti-aging drugs. PTENOE white adipose tissue (WAT) has increased UCP1, a protein linked to increased thermogenesis. WAT of PTENOE mice also shows a change in polarization of fat-associated macrophages, with elevated levels of arginase 1 (Arg1, characteristic of M2 macrophages) and decreased production of inducible nitric oxide synthase (iNOS, characteristic of M1 macrophages). Muscle and hippocampus showed increased expression of the myokine FNDC5, and higher levels of its cleavage product irisin in plasma, which has been linked to increased conversion of WAT to more thermogenic beige/brown adipose tissue. PTENOE mice also have an increase, in plasma and liver, of GPLD1, which is known to improve cognition in mice. Hippocampus of the PTENOE mice has elevation of both BDNF and DCX, indices of brain resilience and neurogenesis. These changes in fat, macrophages, liver, muscle, hippocampus, and plasma may be considered "aging rate indicators" in that they seem to be consistently changed across many of the long-lived mouse models and may help to extend lifespan by delaying many forms of late-life illness. Our new findings show that PTENOE mice can be added to the group of long-lived mice that share this multi-tissue suite of biochemical characteristics.

Exercise mimetics: a novel strategy to combat neuroinflammation and Alzheimer's disease

Neuroinflammation is a pathological hallmark of Alzheimer's disease (AD), characterized by the stimulation of resident immune cells of the brain and the penetration of peripheral immune cells. These inflammatory processes facilitate the deposition of amyloid-beta (Aβ) plaques and the abnormal hyperphosphorylation of tau protein. Managing neuroinflammation to restore immune homeostasis and decrease neuronal damage is a therapeutic approach for AD. One way to achieve this is through exercise, which can improve brain function and protect against neuroinflammation, oxidative stress, and synaptic dysfunction in AD models. The neuroprotective impact of exercise is regulated by various molecular factors that can be activated in the same way as exercise by the administration of their mimetics. Recent evidence has proven some exercise mimetics effective in alleviating neuroinflammation and AD, and, additionally, they are a helpful alternative option for patients who are unable to perform regular physical exercise to manage neurodegenerative disorders. This review focuses on the current state of knowledge on exercise mimetics, including their efficacy, regulatory mechanisms, progress, challenges, limitations, and future guidance for their application in AD therapy.

Four anti-aging drugs and calorie-restricted diet produce parallel effects in fat, brain, muscle, macrophages, and plasma of young mice

Average and maximal lifespan can be increased in mice, in one or both sexes, by four drugs: rapamycin, acarbose, 17a-estradiol, and canagliflozin. We show here that these four drugs, as well as a calorie-restricted diet, can induce a common set of changes in fat, macrophages, plasma, muscle, and brain when evaluated in young adults at 12 months of age. These shared traits include an increase in uncoupling protein UCP1 in brown fat and in subcutaneous and intra-abdominal white fat, a decline in proinflammatory M1 macrophages and corresponding increase in anti-inflammatory M2 macrophages, an increase in muscle fibronectin type III domain containing 5 (FNDC5) and its cleavage product irisin, and higher levels of doublecortin (DCX) and brain-derived neurotrophic factor (BDNF) in brain. Each of these proteins is thought to play a role in one or more age-related diseases, including metabolic, inflammatory, and neurodegenerative diseases. We have previously shown that the same suite of changes is seen in each of four varieties of slow-aging single-gene mutant mice. We propose that these changes may be a part of a shared common pathway that is seen in slow-aging mice whether the delayed aging is due to a mutation, a low-calorie diet, or a drug.

The role of GPLD1 in chronic diseases

Glycosylphosphatidylinositol-specific phospholipase D (GPLD1) is a specific enzyme for glycosylphosphatidylinositol (GPI) anchors, thereby exerting its biological functions by cleaving membrane-associated GPI molecules. GPLD1 is abundant in serum, with a concentration of approximately 5-10 µg/mL. Previous studies have demonstrated that GPLD1 plays a crucial role in the pathogenesis of numerous chronic diseases including disorders of lipid and glucose metabolism, cancer, and neurological disorders. In the present study, we reviewed the structure, functions, and localization of GPLD1 in chronic diseases, as well as exercise-mediated regulation of GPLD1, thus providing a theoretical support to develop GPLD1 as a new therapeutic target for chronic diseases.

Aging Rate Indicators: Speedometers for Aging Research in Mice

A "biomarker of aging" is conceptualized as an index of how far an individual has moved along the path from youth to old age. In contrast, an aging rate indicator (ARI) represents a measure of speed, rather than distance, that is, a measure of how rapidly the individual is moving toward the phenotypic changes typical of old age. This essay presents and reviews recent data suggesting common characteristics of slow-aging mice, whether the slowed aging is caused by a mutant allele, the calorie restriction diet, or drugs that slow aging and extend mean and maximal lifespan. Some of the candidate ARIs, shared by nine varieties of slow-aging mice, are physiological changes seen in fat, fat-associated macrophages, muscle, liver, brain, and plasma. Others are molecular measurements, reflecting activity of mTORC1, selective mRNA translation, or each of six MAP kinases in two distinct MAPK cascades in liver, muscle, or kidney. Changes in ARIs are notable in young adult mice after 8 months of drug or diet exposure, are detectable in mutant mice at least as early as 4-6 months of age, and persist until at least 18-22 months. Many of the candidate ARIs are thought to play an influential role in cognition, inflammation, exercise responses, and control of metabolic rate, and are thus plausible as modulators of age-related physiological and neurological illnesses. In principle, screening for drugs that induce alterations in ARIs in normal young adult mice might facilitate the search for preventive medicines that can retard aging and late-life illnesses in mice or in human populations.

Blood-to-brain communication in aging and rejuvenation

Aging induces molecular, cellular and functional changes in the adult brain that drive cognitive decline and increase vulnerability to dementia-related neurodegenerative diseases. Leveraging systemic and lifestyle interventions, such as heterochronic parabiosis, administration of 'young blood', exercise and caloric restriction, has challenged prevalent views of brain aging as a rigid process and has demonstrated that aging-associated cognitive and cellular impairments can be restored to more youthful levels. Technological advances in proteomic and transcriptomic analyses have further facilitated investigations into the functional impact of intertissue communication on brain aging and have led to the identification of a growing number of pro-aging and pro-youthful factors in blood. In this review, we discuss blood-to-brain communication from a systems physiology perspective with an emphasis on blood-derived signals as potent drivers of both age-related brain dysfunction and brain rejuvenation.

Recapitulation of anti-aging phenotypes by global, but not by muscle-specific, deletion of PAPP-A in mice

Deletion of pregnancy-associated plasma protein-A (PAPP-A), a protease that cleaves some but not all IGF1 binding proteins, postpones late-life diseases and extends lifespan in mice, but the mechanism of this effect is unknown. Here we show that PAPP-A knockout (PKO) mice display a set of changes, in multiple tissues, that are characteristic of other varieties of slow-aging mice with alterations in GH production or GH responsiveness, including Ames dwarf, Snell dwarf, and GHRKO mice. PKO mice have elevated UCP1 in brown and white adipose tissues (WAT), and a change in fat-associated macrophage subsets that leads to diminished production of inflammatory cytokines. PKO mice also show increased levels of muscle FNDC5 and its cleavage product, the myokine irisin, thought to cause changes in fat cell differentiation. PKO mice have elevated production of hepatic GPLD1 and plasma GPLD1, consistent with their elevation of hippocampal BDNF and DCX, used as indices of neurogenesis. In contrast, disruption of PAPP-A limited to muscle ("muPKO" mice) produces an unexpectedly complex set of changes, in most cases opposite in direction from those seen in PKO mice. These include declines in WAT UCP1, increases in inflammatory macrophages and cytokines in WAT, and a decline in muscle FNDC5 and plasma irisin. muPKO mice do, however, resemble global PKO mice in their elevation of hippocampal BDNF and DCX. The data for the PKO mice support the idea that these changes in fat, macrophages, liver, muscle, plasma, and brain are consistent and biologically significant features of the slow-aging phenotype in mice. The results on the muPKO mice provide a foundation for further investigation of the complex, local, and global circuits by which PAPP-A modulates signals ordinarily controlled by GH and/or IGF1.