Cellular and Molecular Mechanisms Activated by a Left Ventricular Assist Device

Left ventricular assist devices (LVADs) represent the final treatment for patients with end-stage heart failure (HF) not eligible for transplantation. Although LVAD design has been further improved in the last decade, their use is associated with different complications. Specifically, inflammation, fibrosis, bleeding events, right ventricular failure, and aortic valve regurgitation may occur. In addition, reverse remodeling is associated with substantial cellular and molecular changes of the failing myocardium during LVAD support with positive effects on patients’ health. All these processes also lead to the identification of biomarkers identifying LVAD patients as having an augmented risk of developing associated adverse events, thus highlighting the possibility of identifying new therapeutic targets. Additionally, it has been reported that LVAD complications could cause or exacerbate a state of malnutrition, suggesting that, with an adjustment in nutrition, the general health of these patients could be improved

Irisin injected mice display increased tibial cortical mineral density and polar moment of inertia

It has been recently reported that, after physical activity, the skeletal muscle releases Irisin, the newly identified myokine able of driving transition of white adipocytes into brown [1]. This result supported the role of skeletal muscle as endocrine organ, suggesting that it could target other tissues besides adipose tissue. In our previous work, we demonstrated that conditioned media collected from primary myoblasts of exercised mice were able to increase OB differentiation and this effect was Irisinmediated [2]. Here we show that Irisin has positive effect on cortical mineral density and geometry in vivo. Young male mice were injected with r-Irisin and cortical bone adaptation was analyzed by micro-CT at tibial midshaft. Our results show that cortical tissue mineral density is significantly increased in Irisin-injected mice compared to vehicle-injected littermates (+7.15%; p<0.01). Furthermore, this higher density of calcium hydroxyapatite at cortical site is accompanied by increase in periosteal circumference (+7.5%; p<0.03) and polar moment of Inertia (pMOI +19,21%; p<0,01). A greater pMOI indicates stronger resistance of a long bone to torsion and, together with higher bone mineral density, suggests higher protection against fracture. The effect of Irisin is fully comparable to the effect of physical activity that is widely accepted method for increasing bone mineral density and bone size in healthy populations. In view of further proving the involvement of Irisin in bone metabolism, we validate its direct effect on osteoblasts in vitro. Phosphorylation of the MAP kinase ERK and the expression of Atf4 were significantly increased after Irisin treatment, as well as ALP and pro-Collagen I mRNA expression. Our data highlight a novel link in muscle-fat-bone axis demonstrating that Irisin targets bone tissue directly, driving positive effects on cortical mineral density and geometry in vivo. These findings would expand the research of exercise-mimetic drugs that might be widely used to treat osteoporotic patients who are suffering from immobilization and cannot perform physical activity

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

The effect of Irisin on bone cells in vivo and in vitro

REVIEW ARTICLE| JANUARY 15 2021 The effect of Irisin on bone cells in vivo and in vitro Cinzia Buccoliero; Angela Oranger; Graziana Colaianni; Patrizia Pignataro; Roberta Zerlotin; Roberto Lovero; Mariella Errede; Maria Grano Crossmark: Check for Updates Biochem Soc Trans (2021) BST20200978. https://doi.org/10.1042/BST20200978 Article history Share Icon Share Cite Icon Cite Get Permissions The myokine Irisin, produced during physical exercise, has an anabolic effect on bone, both in vitro and in vivo. Very recently, using a controlled in vitro 3D cell model to mimic the bone microenvironment aboard the International Space Station, it has been shown that Irisin treatment in microgravity prevents the down-regulation of the transcription factors Atf4, Runx2 and Osterix, as well as Collagen I and Osteoprotegerin proteins, crucial for osteoblast differentiation in physiologic conditions. Irisin action has also been investigated in human subjects, in which it correlates with bone health status, supporting its physiological importance also in human bone, both in healthy subjects and in patients suffering from diseases related to bone metabolism, such as hyperparathyroidism and type 1 diabetes. Low levels of circulating Irisin have been found in post-menopausal women affected by hyperparathyroidism. Furthermore, Irisin is positively correlated with bone strength in athletes and bone mineral density in football players. Moreover, in healthy children, Irisin is positively associated with bone mineral status and in children with type 1 diabetes, Irisin is positively correlated with improved glycemic control and skeletal health. In this review, we will focus on recent findings about Irisin action on microgravity induced bone loss and on osteocyte activity and survival through its αV/β5 integrin receptor

AQP4ex is crucial for the anchoring of AQP4 at the astrocyte end-feet and for neuromyelitis optica antibody binding

Abstract Brain water homeostasis is essential for the appropriate control of neuronal activity. Furthermore, the encasement of the central nervous system (CNS) by a hard structure, greatly limits its tolerance for the volume changes occurring with acute brain edema, which quickly leads to severe damage or death. The recent discovery of the extended isoform of AQP4 (AQP4ex), generated by translational readthrough, revealed a potential new mechanism of water transport regulation and polarization at the blood-brain-barrier level. In the present study we used CRISPR/Cas9 technology to generate an AQP4ex−/− mouse model and evaluate the effect on the overall AQP4 expression, polarization, supramolecular organization in orthogonal arrays of particles (OAPs) and neuromyelitis optica (NMO-IgG) autoantibodies binding. AQP4ex removal did not cause a decrease in total AQP4 protein expression but completely suppressed the specific location of AQP4 at the astrocyte endfeet. Without AQP4ex, AQP4 was mislocalized and α-syntrophin expression, the selective partner for AQP4 localization, was partially altered. The supramolecular organization of AQP4 in OAPs was subtly altered. Indeed, the absence of AQP4ex reduced the size of AQP4-OAPs but the number of AQP4-OAP pools remained largely the same. More importantly, AQP4ex resulted critical for the binding of pathogenic human NMO-IgG autoantibodies to the brain. Indeed, the absence of AQP4ex completely abolished the binding of NMO-IgG at the perivascular astrocyte endfeet. This study provides the first direct evidence in vivo on the specific role of AQP4ex in AQP4 perivascular OAPs assembly and confinement and reveals AQP4ex as new and important player in neuromyelitis optica

The effects of bone pâté on human osteoblasts cell cultures

The aim of the present study was to evaluate the effect of bone pate on human osteoblast differentiation by measuring cell viability, alkaline phosphatase activity and expression of the transcription factors and of the major components of the extracellular matrix. Although bone paté has been used in ear surgery for many years and when placed in contact with mastoid and external auditory canal bone become viable, the cellular mechanisms that lead to its osteointegration have never been described. Bone paté taken from four patients subjected to mastoidectomy and affected by middle ear and mastoid cholesteatoma was placed in contact with osteoblast-like cell cultures. Four experimental conditions were obtained: cell cultures treated with bone patè, with bone paté mixed with fibrin glue, with fibrin glue and untreated. After 24 h, the viability of the cells was evaluated; after 1 week, alkaline phosphatase activity and the expression of transcription factors and bone matrix proteins were assessed by quantitative polymerase chain reaction. After 24 h osteoblasts showed increased viability when treated with bone paté (19 % increase) and bone pate mixed with fibrin glue (34 % increase). After 1 week, the number of alkaline phosphatase positive cells increased by 97 and 94 % in cultures treated with bone paté alone and bone pate mixed with fibrin glue. Treatment with bone patè upregulated transcription factors and components of the extracellular matrix. The present data show that bone paté has a high osteoinductive potential on human osteoblasts, enhancing their activity

Supramolecular aggregation of aquaporin-4 is different in muscle and brain: correlation with tissue susceptibility in neuromyelitis optica

Neuromyelitis optica (NMO) is an autoimmune demyelinating disease of the central nervous system (CNS) caused by autoantibodies (NMO-IgG) against the water channel aquaporin-4 (AQP4). Though AQP4 is also expressed outside the CNS, for example in skeletal muscle, patients with NMO generally do not show clinical/diagnostic evidence of skeletal muscle damage. Here, we have evaluated whether AQP4 supramolecular organization is at the basis of the different tissue susceptibility. Using immunofluorescence we found that while the sera of our cohort of patients with NMO gave typical perivascular staining in the CNS, they were largely negative in the skeletal muscle. This conclusion was obtained using human, rat and mouse skeletal muscle including the AQP4-KO mouse. A biochemical analysis using a new size exclusion chromatography approach for AQP4 suprastructure fractionation revealed substantial differences in supramolecular AQP4 assemblies and isoform abundance between brain and skeletal muscle matching a lower binding affinity of NMO-IgG to muscle compared to the brain. Super-resolution microscopy analysis with g-STED revealed different AQP4 organization in native tissues, while in the brain perivascular astrocyte endfoot membrane AQP4 was mainly organized in large interconnected and raft-like clusters, in the sarcolemma of fast-twitch fibres AQP4 aggregates often appeared as small, relatively isolated linear entities. In conclusion, our results provide evidence that AQP4 supramolecular structure is different in brain and skeletal muscle, which is likely to result in different tissues susceptibility to the NMO disease

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

Irisin Modulates Inflammatory, Angiogenic, and Osteogenic Factors during Fracture Healing

Bone fractures are a widespread clinical event due to accidental falls and trauma or bone fragility; they also occur in association with various diseases and are common with aging. In the search for new therapeutic strategies, a crucial link between irisin and bone fractures has recently emerged. To explore this issue, we subjected 8-week-old C57BL/6 male mice to tibial fracture, and then we treated them with intra-peritoneal injection of r-Irisin (100 µg/kg/weekly) or vehicle as control. At day 10 post fracture, histological analysis showed a significant reduced expression of inflammatory cytokines as tumor necrosis factor-alpha (TNFα) (p = 0.004) and macrophage inflammatory protein-alpha (MIP-1α) (p = 0.015) in the cartilaginous callus of irisin-treated mice compared to controls, supporting irisin’s anti-inflammatory role. We also found increased expressions of the pro-angiogenic molecule vascular endothelial growth factor (VEGF) (p = 0.002) and the metalloproteinase MMP-13 (p = 0.0006) in the irisin-treated mice compared to the vehicle ones, suggesting a myokine involvement in angiogenesis and cartilage matrix degradation processes. Moreover, the bone morphogenetic protein (BMP2) expression was also upregulated (p = 0.002). Taken together, our findings suggest that irisin can contribute to fracture repair by reducing inflammation and promoting vessel invasion, matrix degradation, and bone formation, supporting its possible role as a novel molecule for fracture treatment