Irisin Levels in Cerebrospinal Fluid Correlate with Biomarkers and Clinical Dementia Scores in Alzheimer Disease.

OBJECTIVE: Irisin, released by muscles during exercise, was recently identified as a neuroprotective factor in mouse models of Alzheimer disease (AD). In a cohort of AD patients, we studied cerebrospinal fluid (CSF) and plasma irisin levels, sex interactions, and correlations with disease biomarkers. METHODS: Correlations between CSF and plasma irisin levels and AD biomarkers (amyloid ß 1-42, hyperphosphorylated tau, and total tau [t-tau]) and Clinical Dementia Rating Scale Sum of Boxes (CDR-SOB) were analyzed in a cohort of patients with Alzheimer dementia (n = 82), mild cognitive impairment (n = 44), and subjective memory complaint (n = 20) biologically characterized according to the recent amyloid/tau/neurodegeneration classification. RESULTS: CSF irisin was reduced in Alzheimer dementia patients (p < 0.0001), with lower levels in female patients. Moreover, CSF irisin correlated positively with Aß42 in both female (r = 0.379, p < 0.001) and male (r = 0.262, p < 0.05) patients, and negatively with CDR-SOB (r = -0.234, p < 0.05) only in female patients. A negative trend was also observed between CSF irisin and t-tau levels in all patients (r = -0.144, p = 0.082) and in the female subgroup (r = -0.189, p = 0.084). INTERPRETATION: The results highlight the relationship between irisin and biomarkers of AD pathology, especially in females. Our findings also offer perspectives toward the use of irisin as a marker of the AD continuum. ANN NEUROL 2024;96:61-73.

Impact of 10-day bed rest on serum levels of irisin and markers of musculoskeletal metabolism.

The bed rest (BR) is a ground-based model to simulate microgravity mimicking skeletal-muscle alterations as in spaceflight. Molecular coupling between bone and muscle might be involved in physiological and pathological conditions. Thus, the new myokine irisin and bone-muscle turnover markers have been studied during and after 10 days of BR. Ten young male individuals were subjected to 10 days of horizontal BR. Serum concentrations of irisin, myostatin, sclerostin, and haptoglobin were assessed, and muscle tissue gene expression on vastus lateralis biopsies was determined. During 10-days BR, we observed no significant fluctuation levels of irisin, myostatin, and sclerostin. Two days after BR (R+2), irisin serum levels significantly decreased while myostatin, sclerostin, and haptoglobin were significantly increased compared with BR0. Gene expression of myokines, inflammatory molecules, transcription factors, and markers of muscle atrophy and senescence on muscle biopsies were not altered, suggesting that muscle metabolism of young, healthy subjects is able to adapt to the hypomobility condition during 10-day BR. However, when subjects were divided according to irisin serum levels at BR9, muscle ring finger-1 mRNA expression was significantly lower in subjects with higher irisin serum levels, suggesting that this myokine may prevent the triggering of muscle atrophy. Moreover, the negative correlation between p21 mRNA and irisin at BR9 indicated a possible inhibitory effect of the myokine on the senescence marker. In conclusion, irisin could be a prognostic marker of hypomobility-induced muscle atrophy, and its serum levels could protect against muscle deterioration by preventing and/or delaying the expression of atrophy and senescence cellular markers.

Vitamin D Increases Irisin Serum Levels and the Expression of Its Precursor in Skeletal Muscle.

Irisin is a myokine synthesized by skeletal muscle, which performs key actions on whole-body metabolism. Previous studies have hypothesized a relationship between irisin and vitamin D, but the pathway has not been thoroughly investigated. The purpose of the study was to evaluate whether vitamin D supplementation affected irisin serum levels in a cohort of 19 postmenopausal women with primary hyperparathyroidism (PHPT) treated with cholecalciferol for six months. In parallel, to understand the possible link between vitamin D and irisin, we analyzed the expression of the irisin precursor, Fndc5, in the C2C12 myoblast cell line treated with a biologically active form of vitamin D, 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3). Our results demonstrate that vitamin D supplementation resulted in a significant increase in irisin serum levels (p = 0.031) in PHPT patients. In vitro, we show that vitamin D treatment on myoblasts enhanced Fndc5 mRNA after 48 h (p = 0.013), while it increased mRNAs of sirtuin 1 (Sirt1) (p = 0.041) and peroxisome proliferator-activated receptor γ coactivator 1α (Pgc1α) (p = 0.017) over a shorter time course. Overall, our data suggest that vitamin-D-induced modulation of Fndc5/irisin occurs through up-regulation of Sirt1, which together with Pgc1α, is an important regulator of numerous metabolic processes in skeletal muscle.

Irisin Protects against Loss of Trabecular Bone Mass and Strength in Adult Ovariectomized Mice by Stimulating Osteoblast Activity.

Irisin is a peptide secreted by skeletal muscle that plays a major role in bone metabolism. Experiments in mouse models have shown that administration of recombinant irisin prevents disuse-induced bone loss. In this study, we aimed to evaluate the effects of irisin treatment for the prevention of bone loss in the ovariectomized (Ovx) mouse, the animal model commonly used to investigate osteoporosis caused by estrogen deficiency. Micro-Ct analysis conducted on Sham mice (Sham-veh) and Ovx mice treated with vehicle (Ovx-veh) or recombinant irisin (Ovx-irisn) showed bone volume fraction (BV/TV) decreases in femurs (Ovx-veh 1.39± 0.71 vs. Sham-veh 2.84 ± 1.23; p = 0.02) and tibia at both proximal condyles (Ovx-veh 1.97 ± 0.68 vs. Sham-veh 3.48 ± 1.26; p = 0.03) and the subchondral plate (Ovx-veh 6.33 ± 0.36 vs. Sham-veh 8.18 ± 0.41; p = 0.01), which were prevented by treatment with a weekly dose of irisin for 4 weeks. Moreover, histological analysis of trabecular bone showed that irisin increased the number of active osteoblasts per bone perimeter (Ovx-irisin 32.3 ± 3.9 vs. Ovx-veh 23.5 ± 3.6; p = 0.01), while decreasing osteoclasts (Ovx-irisin 7.6 ± 2.4 vs. Ovx-veh 12.9 ± 3.04; p = 0.05). The possible mechanism by which irisin enhances osteoblast activity in Ovx mice is upregulation of the transcription factor Atf4, one of the key markers of osteoblast differentiation, and osteoprotegerin, thereby inhibiting osteoclast formation.

Short-Term Irisin Treatment Enhanced Neurotrophin Expression Differently in the Hippocampus and the Prefrontal Cortex of Young Mice.

As a result of physical exercise, muscle releases multiple exerkines, such as "irisin", which is thought to induce pro-cognitive and antidepressant effects. We recently demonstrated in young healthy mice the mitigation of depressive behaviors induced by consecutive 5 day irisin administration. To understand which molecular mechanisms might be involved in such effect, we here studied, in a group of mice previously submitted to a behavioral test of depression, the gene expression of neurotrophins and cytokines in the hippocampus and prefrontal cortex (PFC), two brain areas frequently investigated in the depression pathogenesis. We found significantly increased mRNA levels of nerve growth factor (NGF) and fibroblast growth factor 2 (FGF-2) in the hippocampus and brain-derived growth factor (BDNF) in the PFC. We did not detect a difference in the mRNA levels of interleukin 6 (IL-6) and IL-1ß in both brain regions. Except for BDNF in the PFC, two-way ANOVA analysis did not reveal sex differences in the expression of the tested genes. Overall, our data evidenced a site-specific cerebral modulation of neurotrophins induced by irisin treatment in the hippocampus and the PFC, contributing to the search for new antidepressant treatments targeted at single depressive events with short-term protocols.

Once-Daily Subcutaneous Irisin Administration Mitigates Depression- and Anxiety-like Behavior in Young Mice.

Major depression is one of the most common psychiatric disorders worldwide, usually associated with anxiety. The multi-etiological nature of depression has increased the search for new antidepressant molecules, including irisin, for which, in a previous study, we tested its effect in young mice when administered intraperitoneally in a long-term intermittent manner. Here, we evaluated the effect of subcutaneous short-term irisin administration (100 µg/Kg/day/5 days) in male and female mice subjected to behavioral paradigms: Tail Suspension Test (TST), Forced Swim Test (FST), Elevated Plus Maze (EPM), and Y Maze (YM). Moreover, a qRT-PCR assay was performed to analyze the impact of irisin treatment on Pgc-1α/FNDC5 expression in the brain. A significant reduction in immobility time in TST and FST was observed in irisin-treated mice. Furthermore, irisin treatment significantly increased the number of entries and time spent in open arms, demonstrating its anxiolytic effect. Memory-enhancing effects were not reported in YM. Interestingly, no gender differences were observed in all behavioral tests. Overall, these results suggest that short-term subcutaneous irisin administration can exert an antidepressant and anxiolytic role, probably due to the activation of the Pgc-1α/FNDC5 system in the brain. Further investigation could lead to the identification of irisin as a new agent for the treatment of psychiatric disorders.

Irisin and Secondary Osteoporosis in Humans.

Irisin is a peptide secreted by skeletal muscle following exercise that plays an important role in bone metabolism. Numerous experiments in vitro and in mouse models have shown that the administration of recombinant irisin promotes osteogenesis, protects osteocytes from dexamethasone-induced apoptosis, prevents disuse-induced loss of bone and muscle mass, and accelerates fracture healing. Although some aspects still need to be elucidated, such as the dose- and frequency-dependent effects of irisin in cell cultures and mouse models, ample clinical evidence is emerging to support its physiological relevance on bone in humans. A reduction in serum irisin levels, associated with an increased risk of osteoporosis and bone fractures, was observed in postmenopausal women and in both men and women during aging, Recently, cohort studies of subjects with secondary osteoporosis showed that these patients have lower circulating levels of irisin, suggesting that this myokine could be a novel marker to monitor bone quality in this disease. Although there are still few studies, this review discusses the emerging data that are highlighting the involvement of irisin in some diseases that cause secondary osteoporosis.

Antidepressant Effect of Intermittent Long-Term Systemic Administration of Irisin in Mice.

Depression is a psychiatric disorder increasingly diffused worldwide. Evidence suggests that irisin, a myokine secreted by contracting muscle, mediates beneficial effects on several targets, including the brain. Here, the potential antidepressant properties of long-term intermittent systemic irisin administration (100 µg/kg/weekly for 1 month) were evaluated in mice by the Tail Suspension Test (TST), Forced Swim Test (FST), and Open Field Test (OFT). Furthermore, to deepen the molecular pathways underlying irisin treatment, the expression of irisin precursor, neurotrophic/growth factors, and cytokines was analyzed. Irisin treatment significantly decreased the immobility time in the TST and FST, suggesting an antidepressant effect. Additionally, irisin seemed to display an anxiolytic-like effect increasing the time spent in the OFT arena center. These findings were probably due to the modulation of endogenous brain factors as the gene expression of some neurotrophins, such as brain-derived neurotrophic factor (BDNF) and insulin-like growth factor (IGF-1), was upregulated only in irisin-treated mouse brain. Moreover, irisin modulated the expression of some cytokines (IL-1ß, IL-4, IL-6, and IL-10). To the best of our knowledge, this is the first study demonstrating that the irisin antidepressant effect may be observed even with a systemic administration in mice. This could pave the way toward intriguing preclinical research in humans.

The Novel Role of PGC1α in Bone Metabolism.

Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) is a protein that promotes transcription of numerous genes, particularly those responsible for the regulation of mitochondrial biogenesis. Evidence for a key role of PGC1α in bone metabolism is very recent. In vivo studies showed that PGC1α deletion negatively affects cortical thickness, trabecular organization and resistance to flexion, resulting in increased risk of fracture. Furthermore, in a mouse model of bone disease, PGC1α activation stimulates osteoblastic gene expression and inhibits atrogene transcription. PGC1α overexpression positively affects the activity of Sirtuin 3, a mitochondrial nicotinammide adenina dinucleotide (NAD)-dependent deacetylase, on osteoblastic differentiation. In vitro, PGC1α overexpression prevents the reduction of mitochondrial density, membrane potential and alkaline phosphatase activity caused by Sirtuin 3 knockdown in osteoblasts. Moreover, PGC1α influences the commitment of skeletal stem cells towards an osteogenic lineage, while negatively affects marrow adipose tissue accumulation. In this review, we will focus on recent findings about PGC1α action on bone metabolism, in vivo and in vitro, and in pathologies that cause bone loss, such as osteoporosis and type 2 diabetes.

FNDC5/Irisin System in Neuroinflammation and Neurodegenerative Diseases: Update and Novel Perspective.

Irisin, the circulating peptide originating from fibronectin type III domain-containing protein 5 (FNDC5), is mainly expressed by muscle fibers under peroxisome proliferator-activated receptor gamma coactivator 1-alpha PGC1α control during exercise. In addition to several beneficial effects on health, physical activity positively affects nervous system functioning, particularly the hippocampus, resulting in amelioration of cognition impairments. Recently, FNDC5/irisin detection in hippocampal neurons and the presence of irisin in the cerebrospinal fluid opened a new intriguing chapter in irisin history. Interestingly, in the hippocampus of mice, exercise increases FNDC5 levels and upregulates brain-derived neurotrophic factor (BDNF) expression. BDNF, displaying neuroprotection and anti-inflammatory effects, is mainly produced by microglia and astrocytes. In this review, we discuss how these glial cells can morphologically and functionally switch during neuroinflammation by modulating the expression of a plethora of neuroprotective or neurotoxic factors. We also focus on studies investigating the irisin role in neurodegenerative diseases (ND). The emerging involvement of irisin as a mediator of the multiple positive effects of exercise on the brain needs further studies to better deepen this issue and the potential use in therapeutic approaches for neuroinflammation and ND.

Systemic Administration of Recombinant Irisin Accelerates Fracture Healing in Mice.

To date, pharmacological strategies designed to accelerate bone fracture healing are lacking. We subjected 8-week-old C57BL/6 male mice to closed, transverse, mid-diaphyseal tibial fractures and treated them with intraperitoneal injection of a vehicle or r-irisin (100 µg/kg/weekly) immediately following fracture for 10 days or 28 days. Histological analysis of the cartilaginous callus at 10 days showed a threefold increase in Collagen Type X (p = 0.0012) and a reduced content of proteoglycans (40%; p = 0.0018). Osteoclast count within the callus showed a 2.4-fold increase compared with untreated mice (p = 0.026), indicating a more advanced stage of endochondral ossification of the callus during the early stage of fracture repair. Further evidence that irisin induced the transition of cartilage callus into bony callus was provided by a twofold reduction in the expression of SOX9 (p = 0.0058) and a 2.2-fold increase in RUNX2 (p = 0.0137). Twenty-eight days post-fracture, microCT analyses showed that total callus volume and bone volume were increased by 68% (p = 0.0003) and 67% (p = 0.0093), respectively, and bone mineral content was 74% higher (p = 0.0012) in irisin-treated mice than in controls. Our findings suggest that irisin promotes bone formation in the bony callus and accelerates the fracture repair process, suggesting a possible use as a novel pharmacologic modulator of fracture healing.

Iron Overload Mimicking Conditions Skews Bone Marrow Dendritic Cells Differentiation into MHCIIlowCD11c+CD11b+F4/80+ Cells.

Iron overload is an undesired effect of frequent blood transfusions or genetic diseases. Myelodysplastic syndrome (MDS) patients become transfusion dependent, but due to the combination of ineffective haematopoiesis and repeated blood transfusions they are often subject to iron overload. In this study, we demonstrate that iron-overload mimicking condition alters bone marrow progenitor differentiation towards dendritic cells (DCs). Cells cultured in iron-enriched culture medium for seven days fail to differentiate into conventional CD11c+MHCIIhi DCs and fail to efficiently respond to LPS (Lipopolysaccharides). Cells appear smaller than control DCs but vital and able to perform FITC-dextran (Fluorescein isothiocyanate-dextran) endocytosis. At molecular level, cells cultured in iron-enriched conditions show increased ARG1 and PU.1, and decreased IRF8 expression.

Winnie-APCMin/+ Mice: A Spontaneous Model of Colitis-Associated Colorectal Cancer Combining Genetics and Inflammation.

(1) Background: Colorectal cancer (CRC) is among the best examples of the relationship between inflammation and increased cancer risk. (2) Methods: To examine the effects of spontaneous low-grade chronic inflammation on the pathogenesis of CRC, we developed a new murine model of colitis-associated cancer (CAC) by crossing Mucin 2 mutated mice (Winnie) with ApcMin/+ mice. (3) Results: The resulting Winnie-ApcMin/+ model combines an inflammatory background with a genetic predisposition to small intestinal polyposis. Winnie-ApcMin/+ mice show an early occurrence of inflammatory signs and dysplastic lesions in the distal colon with a specific molecular signature. (4) Conclusion: The Winnie-ApcMin/+ model is a perfect model to demonstrate that chronic inflammation represents a crucial risk factor for the onset and progression of tumoral lesions in individuals genetically predisposed to CRC.

Synovium-derived stromal cell-induced osteoclastogenesis: a potential osteoarthritis trigger.

Purpose: To shed light on the idea that mesenchymal stem/stromal cells (MSCs) recruited in synovium (SM) (i.e. Synovium-Derived Stromal Cells, SDSCs) could be involved in Osteoarthritis (OA) pathophysiology. Attention was also paid to a further stromal cell type with a peculiar ultrastructure called telocytes (TCs), whose role is far from clarified. Methods: In the present in vitro study, we compared SDSCs isolated from healthy and OA subjects in terms of phenotype, morphology and differentiation potential as well as in their capability to activate normal Peripheral Blood Mononuclear Cells (PBMCs). Histological, immunohistochemical and ultrastructural analyses were integrated by qRT-PCR and functional resorbing assays. Results: Our data demonstrated that both SDSC populations stimulated the formation of osteoclasts from PBMCs: the osteoclast-like cells generated by healthy-SDSCs via transwell co-cultures were inactive, while OA-derived SDSCs have a much greater effectiveness. Moreover, the presence of TCs was more evident in cultures obtained from OA subjects and suggests a possible involvement of these cells in OA. Conclusions: Osteoclastogenic differentiation capability of PBMCs from OA subjects, also induced by B synoviocytes has been already documented. Here we hypothesized that SDSCs, generally considered for their regenerative potential in cartilage lesions, have also a role in the onset/maintenance of OA. Clinical relevance: Our observations may represent an interesting opportunity for the development of a holistic approach for OA treatment, that considers the multifaceted capability of MSCs in relation to the environment.

Quercetin Exposure Suppresses the Inflammatory Pathway in Intestinal Organoids from Winnie Mice.

Inflammatory bowel diseases (IBDs) are chronic and relapsing immune disorders that result, or possibly originate, from epithelial barrier defects. Intestinal organoids are a new reliable tool to investigate epithelial response in models of chronic inflammation. We produced organoids from the ulcerative colitis murine model Winnie to explore if the chronic inflammatory features observed in the parental intestine were preserved by the organoids. Furthermore, we investigated if quercetin administration to in vitro cultured organoids could suppress LPS-induced inflammation in wild-type organoids (WT-organoids) and spontaneous inflammation in ulcerative colitis organoids (UC-organoids). Our data demonstrate that small intestinal organoids obtained from Winnie mice retain the chronic intestinal inflammatory features characteristic of the parental tissue. Quercetin administration was able to suppress inflammation both in UC-organoids and in LPS-treated WT-organoids. Altogether, our data demonstrate that UC-organoids are a reliable experimental system for investigating chronic intestinal inflammation and pharmacological responses.

Detecting senescent fate in mesenchymal stem cells: a combined cytofluorimetric and ultrastructural approach.

Senescence can impair the therapeutic potential of stem cells. In this study, senescence-associated morphofunctional changes in periosteum-derived progenitor cells (PDPCs) from old and young individuals were investigated by combining cytofluorimetry, immunohistochemistry, and transmission electron microscopy. Cell cycle analysis demonstrated a large number of G0/G1 phase cells in PDPCs from old subjects and a progressive accumulation of G0/G1 cells during passaging in cultures from young subjects. Cytofluorimetry documented significant changes in light scattering parameters and closely correlated with the ultrastructural features, especially changes in mitochondrial shape and autophagy, which are consistent with the mitochondrial-lysosomal axis theory of ageing. The combined morphological, biofunctional, and ultrastructural approach enhanced the flow cytometric study of PDPC ageing. We speculate that impaired autophagy, documented in replicative senescent and old PDPCs, reflect a switch from quiescence to senescence. Its demonstration in a tissue with limited turnover-like the cambium layer of the periosteum, where reversible quiescence is the normal stem cell state throughout life-adds a new piece to the regenerative medicine jigsaw in an ageing society.

Silver-loaded chitosan coating as an integrated approach to face titanium implant-associated infections: analytical characterization and biological activity.

The present work focuses on the idea to prevent and/or inhibit the colonization of implant surfaces by microbial pathogens responsible for post-operative infections, adjusting antimicrobial properties of the implant surface prior to its insertion. An antibacterial coating based on chitosan and silver was developed by electrodeposition techniques on poly(acrylic acid)-coated titanium substrates. When a silver salt was added during the chitosan deposition step, a stable and scalable silver incorporation was achieved. The physico-chemical composition of the coating was studied by X-ray photoelectron spectroscopy (XPS), while atomic force microscopy in intermittent contact mode (ICAFM) was used to explore the coating morphology. The amount of silver released from the coating up to 21 days was evaluated by inductively coupled plasma mass spectrometry (ICP-MS). The capability of the proposed coating to interact in vitro with the biological environment in terms of compatibility and antibacterial properties was assessed using MG-63 osteoblast-like cell line and S. aureus and P. aeruginosa strains, respectively. These studies revealed that a coating showing a silver surface atomic percentage equal to 0.3% can be effectively used as antibacterial system, while providing good viability of osteoblast-like cells after 7 days. The antibacterial effectiveness of the prepared coating is mainly driven by a contact killing mechanism, although the low concentration of silver released (below 0.1 ppm up to 21 days) is enough to inhibit bacterial growth, advantaging MG-63 cells in the race for the surface.

Evidence Supporting a Paracrine Effect of IGF-1/VEGF on Human Mesenchymal Stromal Cell Commitment.

Healing of skeletal defects is strictly dependent on osteogenesis and efficient vascularization of engineered scaffolds. Insulin-like growth factor-1 (IGF-1) and vascular endothelial growth factor (VEGF) are both involved in these processes. The in vitro administration of IGF-1 in association with VEGF is able to modulate the osteoblastic or endothelial commitment of mesenchymal stromal cells (MSCs) of different origins (e.g. periosteum and skin). In the present study, in order to deepen a possible paracrine effect of IGF-1 and VEGF on periosteum-derived progenitor cells (PDPCs) and skin-derived MSCs (S-MSCs), a Transwell coculture approach was used. We explored the genes involved in endothelial and osteoblastic differentiation, those modulating mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3'-kinase (PI3K)-AKT signaling pathways as well as genes implicated in stemness (i.e. Sox2, Oct4, and Nanog). Periosteal cells, which are typically committed toward osteoblastogenesis, are driven in the direction of endothelial gene expression when influenced by S-MSCs. The latter, once influenced by PDPCs, lose their endothelial commitment and increase the expression of osteoblast-associated genes. PI3K/AKT and MAPK signaling pathways seem to be markedly involved in this behavior. Our results evidence that paracrine signals between MSCs may differently modulate their commitment in a bone microenvironment, opening stimulating viewpoints for skeletal tissue engineering strategies coupling angiogenesis and osteogenesis processes.

Irisin prevents trabecular bone damage and tumor invasion in a mouse model of multiple myeloma.

Bone disease associated with multiple myeloma (MM) is characterized by osteolytic lesions and pathological fractures, which remain a therapeutic priority despite new drugs improving MM patient survival. Antiresorptive molecules represent the main option for the treatment of MM-associated bone disease (MMBD), whereas osteoanabolic molecules are under investigation. Among these latter, we here focused on the myokine irisin, which is able to enhance bone mass in healthy mice, prevent bone loss in osteoporotic mouse models, and accelerate fracture healing in mice. Therefore, we investigated irisin effect on MMBD in a mouse model of MM induced by intratibial injection of myeloma cells followed by weekly administration of 100 µg/kg of recombinant irisin for 5 wk. By micro-Ct analysis, we demonstrated that irisin improves MM-induced trabecular bone damage by partially preventing the reduction of femur Trabecular Bone Volume/Total Volume (P = .0028), Trabecular Number (P = .0076), Trabecular Fractal Dimension (P = .0044), and increasing Trabecular Separation (P = .0003) in MM mice. In cortical bone, irisin downregulates the expression of Sclerostin, a bone formation inhibitor, and RankL, a pro-osteoclastogenic molecule, while in BM it upregulates Opg, an anti-osteoclastogenic cytokine. We found that in the BM tibia of irisin-treated MM mice, the percentage of MM cells displays a reduction trend, while in the femur it decreases significantly. This is in line with the in vitro reduction of myeloma cell viability after 48 h of irisin stimulation at both 200 and 500 ng/mL and, after 72 h already at 100 ng/mL rec-irisin. These results could be due to irisin ability to downregulate the expression of Notch 3, which is important for cell-to-cell communication in the tumor niche, and Cyclin D1, supporting an inhibitory effect of irisin on MM cell proliferation. Overall, our findings suggest that irisin could be a new promising strategy to counteract MMBD and tumor burden in one shot.

Time-dependent unloading effects on muscle and bone and involvement of FNDC5/irisin axis.

The identification of biomarkers and countermeasures to prevent the adverse effects on the musculoskeletal system caused by the absence of mechanical loading is the main goal of space biomedical research studies. In this study, we analyzed over 4 weeks of unloading, the modulation in the expression of key proteins in Vastus lateralis, Gastrocnemius and cortical bone in parallel with the modulation of irisin serum levels and its precursor FNDC5 in skeletal muscle of hind limb unloaded (HU) mice. Here we report that Atrogin-1 was up-regulated as early as 1- and 2-week of unloading, whereas Murf-1 at 2- and 3-weeks, along with a marked modulation in the expression of myosin heavy chain isoforms during unloading. Since HU mice showed reduced irisin serum levels at 4-weeks, as well as FNDC5 decrease at 3- and 4-weeks, we treated HU mice with recombinant irisin for 4 weeks, showing that unloading-dependent decline of myosin heavy chain isoforms, MyHCIIα and MyHCIIx, and the anti-apoptotic factor Bcl2, were prevented. In parallel, irisin treatment inhibited the increase of the senescence marker p53, and the pro-apoptotic factor Bax. Overall, these results suggest that the myokine irisin could be a possible therapy to counteract the musculoskeletal impairment caused by unloading.