Irisin: A bridge between exercise and neurological diseases

Exercise plasma improves traumatic brain injury outcomes in mice

Traumatic brain injury (TBI) is associated with pain and cognitive impairment although exercise may improve some adverse outcomes. We hypothesized that transfer of plasma derived from exercised mice would improve outcomes related to pain and memory after TBI. These studies used a concussive murine model of mild TBI. Plasma from sedentary or exercised mice was administered to TBI mice beginning 3 days after injuries. Mechanical nociceptive sensitization and descending control of nociception (DCN) were assessed. Object recognition memory and Y-maze were used to assess working memory. In addition, the spinal expression of Pdyn, Bdnf, Cxcl1 and Cxcl2 was measured 7 and 28 days after injuries. Levels of several candidate mediators of the exercise effects were measured in the transferred plasma. Mechanical allodynia following TBI recovered more quickly and DCN responses were partially preserved in animals receiving exercise plasma. Working memory was preserved in the same mice. The upregulation of spinal pain genes Pdyn and Bdnf was reduced by exercise plasma. Finally, exercise was associated with substantially higher plasma levels of TIMP2 and irisin. The present study suggests that developing therapies based on the administration of exercise plasma or its components may help reduce pain and cognitive loss after TBI.

Role and Functions of Irisin: A Perspective on Recent Developments and Neurodegenerative Diseases

Irisin is a peptide derived from fibronectin type III domain-containing protein 5 (FNDC5) and is primarily produced by muscle fibers under the regulation of peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) during exercise. Irisin has been the subject of extensive research due to its potential as a metabolic regulator and its antioxidant properties. Notably, it has been associated with protective actions within the brain. Despite growing interest, many questions remain regarding the molecular mechanisms underlying its effects. This review summarizes recent findings on irisin, highlighting its pleiotropic functions and the biological processes and molecular cascades involved in its action, with a particular focus on the central nervous system. Irisin plays a crucial role in neuron survival, differentiation, growth, and development, while also promoting mitochondrial homeostasis, regulating apoptosis, and facilitating autophagy-processes essential for normal neuronal function. Emerging evidence suggests that irisin may improve conditions associated with non-communicable neurological diseases, including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, frontotemporal dementia, and multiple sclerosis. Given its diverse benefits, irisin holds promise as a novel therapeutic agent for preventing and treating neurological diseases.

Exosomal irisin from FNDC5-engineered BMSCs improves ischemic stroke via inhibiting YAP/EGR1/ACSL4-mediated ferroptosis

BACKGROUND

BMSCs-derived exosomes play an important role in ischemic stroke. Irisin and its precursor fibronectin type III domain-containing protein 5 (FNDC5) are implicated in neuroprotective effect. We aimed to clarify the role of exosomal irisin from FNDC5-overexpressed BMSCs in ischemic stroke.

METHODS

Oxygen-glucose deprivation and reoxygenation (OGD/R) neuronal cells (HT-22 and Neuro-2a cells) model and middle cerebral artery occlusion (MCAO) mice model were established. Exosomes were isolated from FNDC5-overexpressed BMSCs (BMSCs-FNDC5-exos). Cell viability was estimated with CCK-8. Fe2+, lactate dehydrogenase (LDH), glutathione (GSH) and malondialdehyde (MDA) were determined with commercial kits. Moreover, lipid reactive oxygen species (ROS) was analyzed using flow cytometry. Neurological dysfunction, infarct volume and mitochondria injury were estimated with modified neurological severity score (mNSS), TTC staining and transmission electron microscopy (TEM). Chromatin immunoprecipitation and dual luciferase assay were applied to verify the molecular interactions. Western blot, RT-qPCR and ELISA were performed for the detection of related genes and proteins.

RESULTS

YAP, EGR1 and ACSL4 were increased in OGD/R-subjected cells. Irisin from BMSCs-FNDC5-exos elevated cell viability and suppressed ferroptosis. EGR1 transcriptionally upregulated ACSL4 and promoted OGD/R-induced ferroptosis. Additionally, YAP transcriptionally upregulated EGR1 and promoted OGD/R-induced ferroptosis. EGR1 or YAP overexpression could reverse the effects of BMSCs-FNDC5-exos. EGR1 silencing or BMSCs-FNDC5-exos overturned the facilitated ferroptosis induced by YAP overexpression, meanwhile, EGR1 silencing further enhanced the effect elicited by BMSCs-FNDC5-exos. BMSCs-FNDC5-exos reduced cerebral infarction, improved neurological impairment, inhibited ferroptosis, downregulated YAP, EGR1, ACSL4 and up-regulated irisin in MCAO mice.

CONCLUSION

Exosomal irisin from FNDC5-overexpressed BMSCs improves ischemic stroke via inhibiting YAP/EGR1/ACSL4-mediated ferroptosis, which shed light on discovering new strategy against ischemic stroke.

The role of irisin in exercise-induced muscle and metabolic health: a narrative review

Irisin, a myokine released during physical exercise, has emerged as a key mediator of muscle health and metabolic regulation. This review synthesizes current evidence on how aerobic exercise stimulates irisin release and its subsequent effects, including enhanced muscle mass, strength, and recovery. Additionally, irisin promotes the browning of white adipose tissue, improving fat metabolism and glucose regulation. These adaptations position irisin as a promising therapeutic target for preventing metabolic disorders and optimizing exercise protocols. By exploring human studies and mechanistic insights, this review underscores irisin's potential to address global health challenges, such as obesity and type 2 diabetes, while advancing strategies for personalized exercise interventions.

Evolutionary Insights into Irisin/FNDC5: Roles in Aging and Disease from Drosophila to Mammals

The Irisin/FNDC5 protein family has emerged as a pivotal link between exercise and the prevention of age-associated diseases. Irisin is highly expressed during exercise from skeletal and cardiac muscle cells, playing a critical role in mediating systemic health benefits through its actions on various tissues. However, Irisin levels decline with age, correlating with a heightened incidence of diseases such as muscle weakness, cardiovascular disorders, and neurodegeneration. Notably, the administration of Irisin has shown significant potential in both preventing and treating these conditions. Recently, an Irisin/FNDC5 homolog was identified in an invertebrate Drosophila model, providing valuable insights into its conserved role in exercise physiology. Importantly, Irisin/FNDC5 has been demonstrated to regulate autophagy-a process essential for clearing excessive nutrients, toxic aggregates, and dysfunctional organelles-in both flies and mammals. Dysregulated autophagy is often implicated in age-related diseases, highlighting its relevance to Irisin/FNDC5's functions. These findings deepen our understanding of Irisin/FNDC5's roles and its potential as a therapeutic target for mitigating aging-related health decline. Further studies are needed to elucidate the precise mechanisms by which Irisin regulates autophagy and its broader impact on physiological aging and related diseases.

Irisin in thyroid diseases

Irisin, a hormone-like adipo-myokine, has garnered considerable attention in recent years for its potential impact in metabolic diseases. Its physiological effects are similar to those of thyroid hormones, prompting numerous investigations into potential correlations and interactions between irisin and thyroid function through various in vitro and animal experiments. However, existing studies suggest that the relationship between irisin and thyroid diseases is highly complex and multifaceted. In this paper, we have summarized the research results on serum irisin and thyroid function, providing an overview of advancements and constraints in current research on irisin and thyroid hormones. The aim is to offer insights and directions for future clinical trials in this field.

Targeting AMPK with Irisin: Implications for metabolic disorders, cardiovascular health, and inflammatory conditions - A systematic review

Irisin-based interventions have gained attention for their potential to modulate the adenosine monophosphate (AMP)-activated protein kinase (AMPK) pathway in various diseases. Physiologically, irisin is a myokine released during physical exercise that exerts anti-inflammatory effects and is a metabolic and cardiometabolic enhancer. On the other hand, AMPK is crucial for maintaining energy balance and metabolic homeostasis. Therefore, individuals presenting low blood levels of irisin and AMPK dysregulation are more predisposed to metabolic disorders and cardiovascular health inflammatory conditions since regulating energy balance and metabolic homeostasis are crucial for preventing or treating these disorders. In light of those mentioned above and considering that no review has addressed the intricate relationships between irisin and AMPK regulation in the realm of metabolic disorders, cardiovascular health, and inflammatory conditions, we comprehensively reviewed studies involving irisin's effects on AMPK signaling in different models and interventions. Our systematic analysis involved in vitro studies, animal models, and their relevant clinical implications of irisin targeting AMPK due to the absence of relevant clinical trials. The outcomes and limitations of the included studies were extensively highlighted. Objectively, irisin improved metabolic disorders by enhancing β-cell function and insulin secretion in diabetes, mitigating myocardial injury in cardiovascular conditions, and reducing inflammation and oxidative stress in various injury models by targeting AMPK. However, the lack of clinical trials limits the generalizability of these findings to human subjects. Future research should focus on translating these findings into clinical applications and exploring the broader implications of irisin-based interventions in human health.

Irisin and neuroinflammation: Challenges and opportunities

Irisin is a myokine that is cleaved from 5-domain type III fibronectin (FNDC5), and is known for its metabolic functions as it stimulates browning of white adipose tissue; similarly, effects on the central nervous system have been described, specifically in neurodevelopmental and neuroprotection processes. The purpose of this review is to describe recent information on the effects of irisin on neuroinflammation to contribute to the knowledge about the mechanisms by which irisin and exercise could generate benefits for some neurological diseases. The review conducted found several studies describing the effect of irisin on pathways such as STAT3, p38, cAMP/PKA/CREB, as well as effects on GFAP protein expression or apoptosis processes in both in vitro and in vivo models; likewise, these pathways are associated with better BDNF expression. Despite increasing information on this topic, it is still necessary to clarify the mechanisms by which irisin has effects on neuroinflammation and this could represent an opportunity to generate more treatments for diseases such as Alzheimer's, Parkinson's or Diabetes Mellitus.

Irisin-regulated lncRNAs and their potential regulatory functions in chondrogenic differentiation of human mesenchymal stem cells

Objective

Dysregulation of chondrogenic differentiation is associated with osteoarthritis (OA). The myokine irisin is beneficial in OA treatment; yet, the underlying mechanism is not fully understood. Long noncoding RNAs (lncRNAs) act as important regulators of chondrocyte differentiation. This study was conducted to address the role of lncRNAs in mediating irisin-induced chondrocyte differentiation.

Methods

We investigated the irisin-regulated lncRNA profile change in human mesenchymal stem cells (MSCs) using published whole transcriptome sequencing data. We predicted their potential targets and competitive endogenous RNA (ceRNA) prediction and analyzed their molecular functions using functional enrichment analysis.

Results

More differentially expressed lncRNAs (DElncRNAs) were observed in irisin-treated samples. The top irisin-induced lncRNAs were associated with OA or chondrogenic differentiation, including XIST, PAX8-AS1, CASC15, LINC01618, and DLX6-AS1. The DEGs co-expressed with DElncRNAs were enriched in skeletal system development, extracellular matrix (ECM) organization, cell adhesion, and inflammation associated pathways. Several lncRNAs likely acted as ceRNAs to regulate downstream mRNAs including ROR2 and SORBS1 in in OA or chondrogenic differentiation.

Conclusions

We demonstrate the global regulation of lncRNAs by irisin during chondrogenic differentiation of human MSCs. Further study is required to characterize the key irisin-regulated lncRNAs in chondrogenic differentiation.

Serum Irisin Levels are Inversely Correlated with Acute Ischaemic Stroke Incidence: Implications for Early Diagnosis in Southern China

Objective

This study aimed to examine the correlation and prognostic value of serum irisin levels in acute ischaemic stroke (AIS) and the subsequent development of hemiplegia.

Methods

This study recruited participants from the Department of Neurology and Rehabilitation Medicine at Shunde Hospital, Southern Medical University. The Fugl-Meyer Assessment was used to assess functional impairment. Serum irisin levels were measured using the enzyme-linked immunosorbent assay method. Multivariate logistic regression was employed to explore the factors related to serum irisin levels and AIS.

Results

Serum irisin levels in the AIS group were significantly lower than those in the control group. However, no significant association was observed between serum irisin and stroke severity within the AIS cohort. Multivariate logistic regression analysis revealed an inverse correlation between serum irisin levels and AIS risk, indicating that it serves as a protective factor against AIS. The increase in serum irisin levels (adjusted odds ratio (OR) 0.938, 95% confidence interval [CI]: 0.899-0.977 per 100 pg/mL increment) was associated with a decreased risk of AIS. Analysis of the receiver operating characteristic curve confirmed the diagnostic value of serum irisin for AIS, with the area under the curve being 0.591 (95% CI: 0.522-0.659, p = 0.012).

Conclusion

Serum irisin levels were significantly lower in AIS and were identified as a protective factor, suggesting that serum irisin may have diagnostic value for AIS.

Dementia and Cognitive Decline: A HEALM Approach

Dementia and cognitive decline pose significant global public health challenges, with prevalence expected to rise in the coming decades. Lifestyle medicine offers a promising approach to mitigating cognitive issues through six key interventions: diet, physical activity, restorative sleep, social connections, stress management, and avoiding risky substances. Traditional methods like randomized controlled trials (RCTs) have limitations in capturing the long-term impacts of these interventions. To overcome these challenges, the American College of Lifestyle Medicine (ACLM) and the True Health Initiative (THI) developed the Hierarchies of Evidence Applied to Lifestyle Medicine (HEALM) framework, informed by the Evidence Threshold Pathway Mapping (ETPM) approach. This framework integrates diverse evidence sources to assess intervention effects over time. Applying HEALM, this review evaluates lifestyle factors' impact on dementia and cognitive decline. It finds strong evidence supporting plant-based nutrition, physical activity, restorative sleep, and avoiding risky substances in promoting cognitive health. Social connections may mitigate cognitive decline, while stress management requires further investigation due to inconclusive findings. Integrating these findings into public health strategies could effectively address the growing dementia burden and enhance overall well-being in aging populations, underscoring the need for continued research in cognitive health.

Impact of menopause-associated frailty on traumatic brain injury

Navigating menopause involves traversing a complex terrain of hormonal changes that extend far beyond reproductive consequences. Menopausal transition is characterized by a decrease in estradiol-17β (E2), and the impact of menopause resonates not only in the reproductive system but also through the central nervous system, musculoskeletal, and gastrointestinal domains. As women undergo menopausal transition, they become more susceptible to frailty, amplifying the risk and severity of injuries, including traumatic brain injury (TBI). Menopause triggers a cascade of changes leading to a decline in muscle mass, accompanied by diminished tone and excitability, thereby restricting the availability of irisin, a crucial hormone derived from muscles. Concurrently, bone mass undergoes reduction, culminating in the onset of osteoporosis and altering the dynamics of osteocalcin, a hormone originating from bones. The diminishing levels of E2 during menopause extend their influence on the gut microbiota, resulting in a reduction in the availability of tyrosine, tryptophan, and serotonin metabolites, affecting neurotransmitter synthesis and function. Understanding the interplay between menopause, frailty, E2 decline, and the intricate metabolisms of bone, gut, and muscle is imperative when unraveling the nuances of TBI after menopause. The current review underscores the significance of accounting for menopause-associated frailty in the incidence and consequences of TBI. The review also explores potential mechanisms to enhance gut, bone, and muscle health in menopausal women, aiming to mitigate frailty and improve TBI outcomes.

Peripheral vascular dysfunction and the aging brain

Aging is the greatest non-modifiable risk factor for most diseases, including cardiovascular diseases (CVD), which remain the leading cause of mortality worldwide. Robust evidence indicates that CVD are a strong determinant for reduced brain health and all-cause dementia with advancing age. CVD are also closely linked with peripheral and cerebral vascular dysfunction, common contributors to the development and progression of all types of dementia, that are largely driven by excessive levels of oxidative stress (e.g., reactive oxygen species [ROS]). Emerging evidence suggests that several fundamental aging mechanisms (e.g., "hallmarks" of aging), including chronic low-grade inflammation, mitochondrial dysfunction, cellular senescence and deregulated nutrient sensing contribute to excessive ROS production and are common to both peripheral and cerebral vascular dysfunction. Therefore, targeting these mechanisms to reduce ROS-related oxidative stress and improve peripheral and/or cerebral vascular function may be a promising strategy to reduce dementia risk with aging. Investigating how certain lifestyle strategies (e.g., aerobic exercise and diet modulation) and/or select pharmacological agents (natural and synthetic) intersect with aging "hallmarks" to promote peripheral and/or cerebral vascular health represent a viable option for reducing dementia risk with aging. Therefore, the primary purpose of this review is to explore mechanistic links among peripheral vascular dysfunction, cerebral vascular dysfunction, and reduced brain health with aging. Such insight and assessments of non-invasive measures of peripheral and cerebral vascular health with aging might provide a new approach for assessing dementia risk in older adults.

Handgrip strength is associated with cognitive function in older patients with stage 3-5 chronic kidney disease: results from the NHANES

In this study, we aimed to investigate the association between handgrip strength (HGS) and cognitive performance in stage 3-5 chronic kidney disease (CKD) patients aged ≥ 60 years. This cross-sectional study analyzed data from National Health and Nutrition Examination Survey (NHANES) database 2011-2014. Three tests were used to assess the cognitive performance, including consortium to establish a registry for Alzheimer's disease (CERAD), animal fluency test (AFT), and digit symbol substitution test (DSST). The multivariate linear regression analyses adjusting for confounding factors were utilized to evaluate the association of HGS with cognitive performance. A total of 678 older stage 3-5 CKD patients were included in this study. After adjusting for multiple factors, a higher HGS was positively associated with a higher CERAD-delayed recall and DSST score. In addition, our analysis indicated that HGS probably correlated with better performance of immediate learning ability in male, while working memory, sustained attention, and processing speed in female. HGS may be an important indicator for cognitive deficits in stage 3-5 CKD patients, especially for learning ability and executive function. Further research to explore the sex-specific and domain-specific and possible mechanisms are required.

Topical Cellular/Tissue and Molecular Aspects Regarding Nonpharmacological Interventions in Alzheimer's Disease-A Systematic Review

One of the most complex and challenging developments at the beginning of the third millennium is the alarming increase in demographic aging, mainly-but not exclusively-affecting developed countries. This reality results in one of the harsh medical, social, and economic consequences: the continuously increasing number of people with dementia, including Alzheimer's disease (AD), which accounts for up to 80% of all such types of pathology. Its large and progressive disabling potential, which eventually leads to death, therefore represents an important public health matter, especially because there is no known cure for this disease. Consequently, periodic reappraisals of different therapeutic possibilities are necessary. For this purpose, we conducted this systematic literature review investigating nonpharmacological interventions for AD, including their currently known cellular and molecular action bases. This endeavor was based on the PRISMA method, by which we selected 116 eligible articles published during the last year. Because of the unfortunate lack of effective treatments for AD, it is necessary to enhance efforts toward identifying and improving various therapeutic and rehabilitative approaches, as well as related prophylactic measures.

The efficacy of community-based exercise programs on circulating irisin level, muscle strength, cardiorespiratory endurance, and body composition for ischemic stroke: a randomized controlled trial

Objective

We investigated the changes in circulating irisin levels after community-based exercise and the association of these levels with improvements in muscle strength, cardiorespiratory endurance, and body composition in people with ischemic stroke.

Methods

Twenty participants were randomly assigned to either a control or an exercise group. The community-based exercise program (CEP) consisted of 8 weeks of 1 h sessions for 3 days a week. Irisin levels, muscle strength, cardiorespiratory endurance, and body composition were assessed before and after the intervention.

Results

Significant improvements were observed in the leg and trunk strength, peak oxygen consumption values, and body composition of the exercise group compared with the control group. In addition, circulating irisin levels were observed to have increased in the exercise group, positively correlated with muscle strength and cardiorespiratory endurance.

Conclusion

CEP might be an effective intervention to increase irisin levels and prevent a stroke-related decline in muscle function.