Irisin reduces amyloid-ß by inducing the release of neprilysin from astrocytes following downregulation of ERK-STAT3 signaling.

A pathological hallmark of Alzheimer's disease (AD) is the deposition of amyloid-ß (Aß) protein in the brain. Physical exercise has been shown to reduce Aß burden in various AD mouse models, but the underlying mechanisms have not been elucidated. Irisin, an exercise-induced hormone, is the secreted form of fibronectin type-III-domain-containing 5 (FNDC5). Here, using a three-dimensional (3D) cell culture model of AD, we show that irisin significantly reduces Aß pathology by increasing astrocytic release of the Aß-degrading enzyme neprilysin (NEP). This is mediated by downregulation of ERK-STAT3 signaling. Finally, we show that integrin αV/ß5 acts as the irisin receptor on astrocytes required for irisin-induced release of astrocytic NEP, leading to clearance of Aß. Our findings reveal for the first time a cellular and molecular mechanism by which exercise-induced irisin attenuates Aß pathology, suggesting a new target pathway for therapies aimed at the prevention and treatment of AD.

Amelioration of pathologic α-synuclein-induced Parkinson's disease by irisin.

Physical activity provides clinical benefit in Parkinson's disease (PD). Irisin is an exercise-induced polypeptide secreted by skeletal muscle that crosses the blood-brain barrier and mediates certain effects of exercise. Here, we show that irisin prevents pathologic α-synuclein (α-syn)-induced neurodegeneration in the α-syn preformed fibril (PFF) mouse model of sporadic PD. Intravenous delivery of irisin via viral vectors following the stereotaxic intrastriatal injection of α-syn PFF cause a reduction in the formation of pathologic α-syn and prevented the loss of dopamine neurons and lowering of striatal dopamine. Irisin also substantially reduced the α-syn PFF-induced motor deficits as assessed behaviorally by the pole and grip strength test. Recombinant sustained irisin treatment of primary cortical neurons attenuated α-syn PFF toxicity by reducing the formation of phosphorylated serine 129 of α-syn and neuronal cell death. Tandem mass spectrometry and biochemical analysis revealed that irisin reduced pathologic α-syn by enhancing endolysosomal degradation of pathologic α-syn. Our findings highlight the potential for therapeutic disease modification of irisin in PD.

Exercise-induced CITED4 expression is necessary for regional remodeling of cardiac microstructural tissue helicity.

Both exercise-induced molecular mechanisms and physiological cardiac remodeling have been previously studied on a whole heart level. However, the regional microstructural tissue effects of these molecular mechanisms in the heart have yet to be spatially linked and further elucidated. We show in exercised mice that the expression of CITED4, a transcriptional co-regulator necessary for cardioprotection, is regionally heterogenous in the heart with preferential significant increases in the lateral wall compared with sedentary mice. Concordantly in this same region, the heart's local microstructural tissue helicity is also selectively increased in exercised mice. Quantification of CITED4 expression and microstructural tissue helicity reveals a significant correlation across both sedentary and exercise mouse cohorts. Furthermore, genetic deletion of CITED4 in the heart prohibits regional exercise-induced microstructural helicity remodeling. Taken together, CITED4 expression is necessary for exercise-induced regional remodeling of the heart's microstructural helicity revealing how a key molecular regulator of cardiac remodeling manifests into downstream local tissue-level changes.

Exercise hormone irisin is a critical regulator of cognitive function.

Identifying secreted mediators that drive the cognitive benefits of exercise holds great promise for the treatment of cognitive decline in ageing or Alzheimer's disease (AD). Here, we show that irisin, the cleaved and circulating form of the exercise-induced membrane protein FNDC5, is sufficient to confer the benefits of exercise on cognitive function. Genetic deletion of Fndc5/irisin (global Fndc5 knock-out (KO) mice; F5KO) impairs cognitive function in exercise, ageing and AD. Diminished pattern separation in F5KO mice can be rescued by delivering irisin directly into the dentate gyrus, suggesting that irisin is the active moiety. In F5KO mice, adult-born neurons in the dentate gyrus are morphologically, transcriptionally and functionally abnormal. Importantly, elevation of circulating irisin levels by peripheral delivery of irisin via adeno-associated viral overexpression in the liver results in enrichment of central irisin and is sufficient to improve both the cognitive deficit and neuropathology in AD mouse models. Irisin is a crucial regulator of the cognitive benefits of exercise and is a potential therapeutic agent for treating cognitive disorders including AD.

Modified middle cerebral artery occlusion model provides detailed intraoperative cerebral blood flow registration and improves neurobehavioral evaluation.

BACKGROUND: Middle cerebral artery occlusion (MCAO) with 1 -h ischemia followed by reperfusion is a widely used stroke model in rodents that has significant limitations such as high mortality and severe neurological deficit hampering comprehensive neurobehavioral evaluation. The goal of this study was to establish a mouse model of 30-minute MCAO followed by 48 h of reperfusion and compare it with 1 -h MCAO followed by 24 h of reperfusion. NEW METHOD: Here we propose a modified MCAO model that is favorable for both neurobehavioral and infarct volume evaluation. The model includes shorter ischemic time (30 min) of MCAO followed by 48 h of reperfusion and use of standardized intraoperative partial and total reperfusion, which allows for the detailed evaluation of initial and total reperfusion by means of the monitoring of CBF by LDF. RESULTS AND COMPARISON WITH EXISTING METHOD: Intraoperative CBF parameters and infarct volume (1-h MCAO at 24 h: 69 ±â€¯9; 30-minute MCAO at 48 h: 65 ±â€¯14 mm3) did not significantly differ between groups. Neurological deficit was less severe in 30-minute MCAO group where mice also had significantly longer ambulatory distance and time, lower resting time, and higher vertical count on the OPF. The latency to fall in the rotarod test was significantly higher in 30-minute MCAO group. The mortality was higher after 1 -h MCAO. CONCLUSIONS: 30-minute MCAO followed by 48 h of reperfusion causes intraoperative ischemia, reperfusion and infarct volume comparable with 1 -h MCAO followed by 24 h of reperfusion but results in lower mortality with milder neurological deficit allowing for more extensive neurobehavioral evaluation.

Treadmill Exercise During Cerebral Hypoperfusion Has Only Limited Effects on Cognitive Function in Middle-Aged Subcortical Ischemic Vascular Dementia Mice.

Clinical and basic research suggests that exercise is a safe behavioral intervention and is effective for improving cognitive function in cerebrovascular diseases, including subcortical ischemic vascular dementia (SIVD). However, most of the basic research uses young animals to assess the effects of exercise, although SIVD is an age-related disease. In this study, therefore, we used middle-aged mice to examine how treadmill exercise changes the cognitive function of SIVD mice. As a mouse model of SIVD, prolonged cerebral hypoperfusion was induced in 8-month-old male C57BL/6J mice by bilateral common carotid artery stenosis. A week later, the mice were randomly divided into two groups: a group that received 6-week treadmill exercise and a sedentary group for observation. After subjecting the mice to multiple behavioral tests (Y-maze, novel object recognition, and Morris water maze tests), the treadmill exercise training was shown to only be effective in ameliorating cognitive decline in the Y-maze test. We previously demonstrated that the same regimen of treadmill exercise was effective in young hypoperfused-SIVD mice for all three cognitive tests. Therefore, our study may indicate that treadmill exercise during cerebral hypoperfusion has only limited effects on cognitive function in aging populations.

Diffusion tensor-MRI detects exercise-induced neuroplasticity in the hippocampal microstructure in mice.

BACKGROUND: Despite considerable research on exercise-induced neuroplasticity in the brain, a major ongoing challenge in translating findings from animal studies to humans is that clinical and preclinical settings employ very different techniques. OBJECTIVE: Here we aim to bridge this divide by using diffusion tensor imaging MRI (DTI), an advanced imaging technique commonly applied in human studies, in a longitudinal exercise study with mice. METHODS: Wild-type mice were exercised using voluntary free-wheel running, and MRI scans were at baseline and after four weeks and nine weeks of running. RESULTS: Both hippocampal volume and fractional anisotropy, a surrogate for microstructural directionality, significantly increased with exercise. In addition, exercise levels correlated with effect size. Histological analysis showed more PDGFRα+ oligodendrocyte precursor cells in the corpus callosum of running mice. CONCLUSIONS: These results provide compelling in vivo support for the concept that similar adaptive changes occur in the brains of mice and humans in response to exercise.

Treadmill Exercise Suppresses Cognitive Decline and Increases White Matter Oligodendrocyte Precursor Cells in a Mouse Model of Prolonged Cerebral Hypoperfusion.

Clinical evidence suggests that patients with subcortical ischemic vascular dementia (SIVD) perform better at cognitive tests after exercise. However, the underlying mechanism for this effect is largely unknown. Here, we examined how treadmill exercise changes the cognitive function and white matter cellular pathology in a mouse model of SIVD. Prolonged cerebral hypoperfusion was induced in 2-month-old male C57BL/6J mice by bilateral common carotid artery stenosis. A week later, the mice were randomly divided into a group that received 6-week treadmill exercise and a sedentary group for observation. In multiple behavioral tests (Y-maze, novel object recognition, and Morris water maze tests), the treadmill exercise training was shown to ameliorate cognitive decline in the hypoperfused SIVD mice. In addition, immunohistological analyses confirmed that there was a larger population of oligodendrocyte precursor cells in the subventricular zone of exercised versus sedentary mice. Although further investigations are needed to confirm a causal link between these findings, our study establishes a model and cellular foundation for investigating the mechanisms through which exercise preserves cognitive function in SIVD.

A role for FNDC5/Irisin in the beneficial effects of exercise on the brain and in neurodegenerative diseases.

The beneficial effects of exercise on the brain are well known. However, the underlying molecular mechanisms are much less well understood. Interestingly, myokines, hormones secreted by muscle in response to exercise, gained attention as such beneficial mediators. In this review, we will focus on FNDC5 and its secreted form, the newly discovered myokine "irisin". We will discuss their role in the beneficial effects of exercise and its potential application in neurodegenerative disorders.

Are the neuroprotective effects of exercise training systemically mediated?

To date there is no cure available for dementia, and the field calls for novel therapeutic targets. A rapidly growing body of literature suggests that regular endurance training and high cardiorespiratory fitness attenuate cognitive impairment and reduce dementia risk. Such benefits have recently been linked to systemic neurotrophic factors induced by exercise. These circulating biomolecules may cross the blood-brain barrier and potentially protect against neurodegenerative disorders such as Alzheimer's disease. Identifying exercise-induced systemic neurotrophic factors with beneficial effects on the brain may lead to novel molecular targets for maintaining cognitive function and preventing neurodegeneration. Here we review the recent literature on potential systemic mediators of neuroprotection induced by exercise. We focus on the body of translational research in the field, integrating knowledge from the molecular level, animal models, clinical and epidemiological studies. Taken together, the current literature provides initial evidence that exercise-induced, blood-borne biomolecules, such as BDNF and FNDC5/irisin, may be powerful agents mediating the benefits of exercise on cognitive function and may form the basis for new therapeutic strategies to better prevent and treat dementia.

Irisin Mediates Effects on Bone and Fat via αV Integrin Receptors.

Irisin is secreted by muscle, increases with exercise, and mediates certain favorable effects of physical activity. In particular, irisin has been shown to have beneficial effects in adipose tissues, brain, and bone. However, the skeletal response to exercise is less clear, and the receptor for irisin has not been identified. Here we show that irisin binds to proteins of the αV class of integrins, and biophysical studies identify interacting surfaces between irisin and αV/ß5 integrin. Chemical inhibition of the αV integrins blocks signaling and function by irisin in osteocytes and fat cells. Irisin increases both osteocytic survival and production of sclerostin, a local modulator of bone remodeling. Genetic ablation of FNDC5 (or irisin) completely blocks osteocytic osteolysis induced by ovariectomy, preventing bone loss and supporting an important role of irisin in skeletal remodeling. Identification of the irisin receptor should greatly facilitate our understanding of irisin's function in exercise and human health.

Neuroprotective potential of exercise preconditioning in stroke.

Stroke is one of leading causes of mortality and morbidity in the world with limited availability of therapeutic intervention. Exercise has been shown to improve stroke functional outcome in different preclinical and clinical setup. Exercise preconditioning induced neuroprotection in preclinical stroke models is believed to be mediated through its ability to restore brain vasculature and blood brain barrier integrity, promote neurogenesis, and help fight against neuroinflammation and excitotoxicity. In this short review, we will summarize the molecular mechanisms of exercise preconditioning described in preclinical stroke studies. We will also discuss the neuroprotective effects of pre-ischemic exercise.

Decreased NK cell functions in obesity can be reactivated by fat mass reduction.

OBJECTIVE: Natural killer (NK) cells are the first defense against malignant cells, and their functions are severely impaired in individuals with obesity. However, it is not known whether functions can be re-activated after weight loss. The alterations of NK cell functions after fat mass reduction were investigated. METHODS: Thirty-two healthy adults with obesity were divided into control and experimental groups. Participants of the experimental group performed a 3-month program of exercise training and nutrition. Anthropometric, physiological, and metabolic parameters and plasma adipocytokines were determined. Peripheral blood mononuclear cells were analyzed by means of flow cytometry and Western blot assay for various NK cell-specific functional parameters and leptin signaling components. NK cell-mediated cytotoxicity assay with leptin stimulation was performed. RESULTS: Male participants significantly decreased their body fat mass (P < 0.05) and increased physical fitness (P < 0.05). Plasma leptin levels were significantly reduced (P < 0.05) and intracellular interferon gamma (IFN-γ) expression in CD56(dim) NK cells was significantly increased (P < 0.001) 3 months after study end. Stimulation of NK-92 cells with different leptin dosages revealed a significant dose-dependent decrease of specific tumor cell lysis. CONCLUSIONS: The present study demonstrates a reactivation of NK cell functionality after body fat mass reduction in persons with obesity.

Detection and Quantitation of Circulating Human Irisin by Tandem Mass Spectrometry.

Exercise provides many health benefits, including improved metabolism, cardiovascular health, and cognition. We have shown previously that FNDC5, a type I transmembrane protein, and its circulating form, irisin, convey some of these benefits in mice. However, recent reports questioned the existence of circulating human irisin both because human FNDC5 has a non-canonical ATA translation start and because of claims that many human irisin antibodies used in commercial ELISA kits lack required specificity. In this paper we have identified and quantitated human irisin in plasma using mass spectrometry with control peptides enriched with heavy stable isotopes as internal standards. This precise state-of-the-art method shows that human irisin is mainly translated from its non-canonical start codon and circulates at ∼ 3.6 ng/ml in sedentary individuals; this level is increased to ∼ 4.3 ng/ml in individuals undergoing aerobic interval training. These data unequivocally demonstrate that human irisin exists, circulates, and is regulated by exercise.

Altered NK cell function in obese healthy humans.

BACKGROUND: Obesity is associated with an elevated risk for several types of cancer and thus a major health hazard. However, the mechanism between overweight and cancer susceptibility is still elusive. Leptin, mainly produced by adipocytes links food intake and energy expenditure. In addition, recent studies have shown an immunomodulatory impact of leptin on NK cells. The purpose of the present study was to investigate whether leptin stimulation of NK cells from obese humans leads to altered functions as compared to NK cells from lean subjects. On the basis of body mass index 20 healthy individuals were classified in two groups: normal weight (<25 kg/m(2)) and obese (>30 kg/m(2)). Peripheral blood mononuclear cells (PBMC) were isolated from blood samples. We used flow cytometry to assess differences in phenotype and activity markers (CD107a, CD178 and TRAIL) of PBMCs between both groups. Furthermore, we determined after short-term in vitro leptin stimulation the phosphorylation of JAK2, downstream target of the intracellular signaling cascade of the leptin receptor, by Western Blotting and numbers of NK-cell-tumor-cell-conjugates as well as Granzyme(+) and IFN-γ(+) NK cells by flow cytometry. Finally, the proliferative capacity of control and long-term (7 days) leptin-stimulated NK cells was examined. RESULTS: As opposed to similar NK cell counts, the number of CD3(+)CD56(+) cells was significantly lower in obese compared to lean subjects. Human NK cells express the leptin receptor (Ob-R). For further determination of Ob-R, intracellular target proteins of PBMCs were investigated by Western Blotting. Phosphorylation of JAK2 was lower in obese as compared to normal weight subjects. Furthermore, significantly lower levels of TNF-related apoptosis-inducing ligand (TRAIL) as an NK cell functional marker in obese subjects were found. In vitro leptin stimulation resulted in a higher production of interferon-γ in NK cells of normal weight subjects. Interestingly, long-term leptin stimulation had no significant influence on numbers of proliferating NK cells. CONCLUSIONS: NK cells from obese healthy humans show functional deficits and altered responses after in vitro leptin challenge.