Development of an Optical System for Strain Drop Measurement of Osteosarcoma Cells on Substrates with Different Stiffness.

Adherent cells perceive mechanical feedback from the underlying matrix and convert it into biochemical signals through a process known as mechanotransduction. The response to changes in the microenvironment relies on the cell's mechanical properties, including elasticity, which was recently identified as a biomarker for various diseases. Here, we propose the design, development, and characterization of a new system for the measurement of adherent cells' strain drop, a parameter correlated with cells' elasticity. To consider the interplay between adherent cells and the host extracellular matrix, cell stretching was combined with adhesion on substrates with different stiffnesses. The technique is based on the linear stretching of silicone chambers, high-speed image acquisition, and feedback for image centering. The system was characterized in terms of the strain homogeneity, impact of collagen coating, centering capability, and sensitivity. Subsequently, it was employed to measure the strain drop of two osteosarcoma cell lines, low-aggressive osteoblast-like SaOS-2 and high-aggressive 143B, cultured on two different substrates to recall the stiffness of the bone and lung extracellular matrices. Results demonstrated good substrate homogeneity, a negligible effect of the collagen coating, and an accurate image centering. Finally, the experimental results showed an average strain drop that was lower in the 143B cells in comparison with the SaOS-2 cells in all the tested conditions.

Modelling three-dimensional cancer-associated cachexia and therapy: The molecular basis and therapeutic potential of interleukin-6 transignalling blockade.

BACKGROUND: Causes and mechanisms underlying cancer cachexia are not fully understood, and currently, no therapeutic approaches are available to completely reverse the cachectic phenotype. Interleukin-6 (IL-6) has been extensively described as a key factor in skeletal muscle physiopathology, exerting opposite roles through different signalling pathways. METHODS: We employed a three-dimensional ex vivo muscle engineered tissue (X-MET) to model cancer-associated cachexia and to study the effectiveness of selective inhibition of IL-6 transignalling in counteracting the cachectic phenotype. Conditioned medium (CM) derived from C26 adenocarcinoma cells was used as a source of soluble factors contributing to the establishment of cancer cachexia in the X-MET model. A dose of 1.2 ng/mL of glycoprotein-130 fused chimaera (gp130Fc) was added to cachectic culture medium to neutralize IL-6 transignalling. RESULTS: C26-conditioned medium induced a cachectic-like phenotype in the X-MET, leading to a decline of muscle mass (-60%; P < 0.001), a reduction in myosin expression (-92.4%; P < 0.005) and a reduction of the contraction frequency spectrum (-94%). C26-conditioned medium contains elevated amounts of IL-6 (8.61 ± 4.09 pg/mL) and IL6R (56.85 ± 10.96 pg/mL). These released factors activated the signal transducer and activator of transcription 3 (STAT3) signalling in the C26_CM X-MET system (phosphorylated STAT3/TOTAL +54.6%; P < 0.005), which in turn promote an enhancement of Il-6 (+69.2%; P < 0.05) and Il6r (+43%; P < 0.05) gene expression, suggesting the induction of a feed-forward loop. The selective neutralization of IL-6 transignalling, by gp130Fc, in C26_CM X-MET prevented the hyperactivation of STAT3 (-55.8%; P < 0.005), countered the reduction of cross-sectional area (+28.2%; P < 0.05) and reduced the expression of proteolytic factors including muscle ring finger-1 (-88%; P < 0.005) and ATROGIN1 (-92%; P < 0.05), thus preserving the robustness and increasing the contractile force (+20%) of the three-dimensional muscle system. Interestingly, the selective inhibition of IL-6 transignalling modulated gene regulatory networks involved in myogenesis and apoptosis, normalizing the expression of pro-apoptotic miRNAs, including miR-31 (-53.2%; P < 0.05) and miR-34c (-65%; P < 0.005), and resulting in the reduction of apoptotic pathways highlighted by the sensible reduction of cleaved caspase 3 (-92.5%; P < 0.005) in gp130Fc-treated C26_CM X-MET. CONCLUSIONS: IL-6 transignalling appeared as a promising target to counter cancer cachexia-related alterations. The X-MET model has proven to be a reliable drug-screening tool to identify novel therapeutic approaches and to test them in preclinical studies, significantly reducing the use of animal models.

Determination of a Measurement Procedure for the Study of Cells' Dielectric Properties through Descriptive Statistic.

This paper presents a measurement procedure for analyzing the dielectric properties of cells using descriptive statistics. The study focuses on four cancer cell lines (MDA-MB-231 and MCF-7 breast cancer, SaOS-2, and 143B osteosarcoma) and DMEM culture medium, utilizing the Lorentzian fit model of the return-loss function. The measurements are performed using a circular patch resonator with a 40 mm diameter, powered by a miniVNA operating in the frequency range of 1 MHz to 3 GHz. Eight specimens are prepared for each group to ensure reliability, and the return loss is recorded ten times for each specimen. Various statistical parameters are calculated and evaluated, including the average value, standard deviation, coefficient of variation, and relative error between the average and the first values. The results demonstrate that one single acquisition highly represents the entire set of ten data points, especially for the resonant frequency, with an accuracy error lower than 0.05%. These findings have significant implications for the methodological approach to detecting cells' dielectric properties, as they substantially reduce time and preserve the specimens without compromising the accuracy of the experimental results.

Remodeled eX vivo muscle engineered tissue improves heart function after chronic myocardial ischemia.

The adult heart displays poor reparative capacities after injury. Cell transplantation and tissue engineering approaches have emerged as possible therapeutic options. Several stem cell populations have been largely used to treat the infarcted myocardium. Nevertheless, transplanted cells displayed limited ability to establish functional connections with the host cardiomyocytes. In this study, we provide a new experimental tool, named 3D eX vivo muscle engineered tissue (X-MET), to define the contribution of mechanical stimuli in triggering functional remodeling and to rescue cardiac ischemia. We revealed that mechanical stimuli trigger a functional remodeling of the 3D skeletal muscle system toward a cardiac muscle-like structure. This was supported by molecular and functional analyses, demonstrating that remodeled X-MET expresses relevant markers of functional cardiomyocytes, compared to unstimulated and to 2D- skeletal muscle culture system. Interestingly, transplanted remodeled X-MET preserved heart function in a murine model of chronic myocardial ischemia and increased survival of transplanted injured mice. X-MET implantation resulted in repression of pro-inflammatory cytokines, induction of anti-inflammatory cytokines, and reduction in collagen deposition. Altogether, our findings indicate that biomechanical stimulation induced a cardiac functional remodeling of X-MET, which showed promising seminal results as a therapeutic product for the development of novel strategies for regenerative medicine.

A Novel Microwave Resonant Sensor for Measuring Cancer Cell Line Aggressiveness.

The measurement of biological tissues' dielectric properties plays a crucial role in determining the state of health, and recent studies have reported microwave biosensing to be an innovative method with great potential in this field. Research has been conducted from the tissue level to the cellular level but, to date, cellular adhesion has never been considered. In addition, conventional systems for diagnosing tumor aggressiveness, such as a biopsy, are rather expensive and invasive. Here, we propose a novel microwave approach for biosensing adherent cancer cells with different malignancy degrees. A circular patch resonator was designed adjusting its structure to a standard Petri dish and a network analyzer was employed. Then, the resonator was realized and used to test two groups of different cancer cell lines, based on various tumor types and aggressiveness: low- and high-aggressive osteosarcoma cell lines (SaOS-2 and 143B, respectively), and low- and high-aggressive breast cancer cell lines (MCF-7 and MDA-MB-231, respectively). The experimental results showed that the sensitivity of the sensor was high, in particular when measuring the resonant frequency. Finally, the sensor showed a good ability to distinguish low-metastatic and high-metastatic cells, paving the way to the development of more complex measurement systems for noninvasive tissue diagnosis.

Sustained Systemic Levels of IL-6 Impinge Early Muscle Growth and Induce Muscle Atrophy and Wasting in Adulthood.

IL-6 is a pleiotropic cytokine that can exert different and opposite effects. The muscle-induced and transient expression of IL-6 can act in an autocrine or paracrine manner, stimulating anabolic pathways associated with muscle growth, myogenesis, and with regulation of energy metabolism. In contrast, under pathologic conditions, including muscular dystrophy, cancer associated cachexia, aging, chronic inflammatory diseases, and other pathologies, the plasma levels of IL-6 significantly increase, promoting muscle wasting. Nevertheless, the specific physio-pathological role exerted by IL-6 in the maintenance of differentiated phenotype remains to be addressed. The purpose of this study was to define the role of increased plasma levels of IL-6 on muscle homeostasis and the mechanisms contributing to muscle loss. Here, we reported that increased plasma levels of IL-6 promote alteration in muscle growth at early stage of postnatal life and induce muscle wasting by triggering a shift of the slow-twitch fibers toward a more sensitive fast fiber phenotype. These findings unveil a role for IL-6 as a potential biomarker of stunted growth and skeletal muscle wasting.

Increased Circulating Levels of Interleukin-6 Affect the Redox Balance in Skeletal Muscle.

The extent of oxidative stress and chronic inflammation are closely related events which coexist in a muscle environment under pathologic conditions. It has been generally accepted that the inflammatory cells, as well as myofibers, are sources of reactive species which are, in turn, able to amplify the activation of proinflammatory pathways. However, the precise mechanism underlining the physiopathologic interplay between ROS generation and inflammatory response has to be fully clarified. Thus, the identification of key molecular players in the interconnected pathogenic network between the two processes might help to design more specific therapeutic approaches for degenerative diseases. Here, we investigated whether elevated circulating levels of the proinflammatory cytokine Interleukin-6 (IL-6) are sufficient to perturb the physiologic redox balance in skeletal muscle, independently of tissue damage and inflammatory response. We observed that the overexpression of circulating IL-6 enhances the generation and accumulation of free radicals in the diaphragm muscle of adult NSE/IL-6 mice, by deregulating redox-associated molecular circuits and impinging the nuclear factor erythroid 2-related factor 2- (Nrf2-) mediated antioxidant response. Our findings are coherent with a model in which uncontrolled levels of IL-6 in the bloodstream can influence the local redox homeostasis, inducing the establishment of prooxidative conditions in skeletal muscle tissue.

Src nuclear localization and its prognostic relevance in human osteosarcoma.

Osteosarcoma is the most common malignant bone tumor in children and young adults. The identification of proteins which exhibit different subcellular localization in low- versus high-risk osteosarcoma can be instrumental to obtain prognostic information and to develop innovative therapeutic strategies. Beside the well-characterized membrane and cytoplasmic localization of Src protein, this study evaluated the prognostic relevance of its so-far unknown nuclear compartmentalization. We analyzed the subcellular distribution of total and activated (pY418) Src in a tissue microarray including 60 osteosarcoma samples. Immunohistochemical analyses revealed a variable pattern of Src expression and localization, ranging from negative to high-stained nuclei combined with a substantial cytoplasmic staining for total and activated forms. The analysis of Kaplan-Meier survival curves in relationship to the diverse permutations of cytoplasmic and nuclear staining suggested a correlation between Src subcellular localization and the overall survival (OS) of osteosarcoma patients. In order to explain this different subcellular localization, normal osteoblasts and three osteosarcoma cell lines were used to investigate the molecular mechanism. Once confirmed a variable Src localization also in these cell lines, we demonstrated a correlation between the N-myristoyltransferase enzymes expression and activity and the Src nuclear content. In conclusion, these results described a so-far unknown Src nuclear localization in osteosarcoma cells, suggesting that the combined detection of nuclear and cytoplasmic Src levels can be used as a prognostic marker for osteosarcoma patient survival. A correlation between the N-myristoyltransferase enzymes and the Src subcellular localization was described as well.

The mitochondrial metabolic reprogramming agent trimetazidine as an 'exercise mimetic' in cachectic C26-bearing mice.

BACKGROUND: Cancer cachexia is characterized by muscle depletion and exercise intolerance caused by an imbalance between protein synthesis and degradation and by impaired myogenesis. Myofibre metabolic efficiency is crucial so as to assure optimal muscle function. Some drugs are able to reprogram cell metabolism and, in some cases, to enhance metabolic efficiency. Based on these premises, we chose to investigate the ability of the metabolic modulator trimetazidine (TMZ) to counteract skeletal muscle dysfunctions and wasting occurring in cancer cachexia. METHODS: For this purpose, we used mice bearing the C26 colon carcinoma as a model of cancer cachexia. Mice received 5 mg/kg TMZ (i.p.) once a day for 12 consecutive days. A forelimb grip strength test was performed and tibialis anterior, and gastrocnemius muscles were excised for analysis. Ex vivo measurement of skeletal muscle contractile properties was also performed. RESULTS: Our data showed that TMZ induces some effects typically achieved through exercise, among which is grip strength increase, an enhanced fast-to slow myofibre phenotype shift, reduced glycaemia, PGC1α up-regulation, oxidative metabolism, and mitochondrial biogenesis. TMZ also partially restores the myofibre cross-sectional area in C26-bearing mice, while modulation of autophagy and apoptosis were excluded as mediators of TMZ effects. CONCLUSIONS: In conclusion, our data show that TMZ acts like an 'exercise mimetic' and is able to enhance some mechanisms of adaptation to stress in cancer cachexia. This makes the modulation of the metabolism, and in particular TMZ, a suitable candidate for a therapeutic rehabilitative protocol design, particularly considering that TMZ has already been approved for clinical use.

Skeletal muscle myopenia in mice model of bile duct ligation and carbon tetrachloride-induced liver cirrhosis.

Skeletal muscle myopathy is universal in cirrhotic patients, however, little is known about the main mechanisms involved. The study aims to investigate skeletal muscle morphological, histological, and functional modifications in experimental models of cirrhosis and the principal molecular pathways responsible for skeletal muscle myopathy. Cirrhosis was induced by bile duct ligation (BDL) and carbon tetrachloride (CCl4) administration in mice. Control animals (CTR) underwent bile duct exposure or vehicle administration only. At sacrifice, peripheral muscles were dissected and weighed. Contractile properties of extensor digitorum longus (EDL) were studied in vitro. Muscle samples were used for histological and molecular analysis. Quadriceps muscle histology revealed a significant reduction in cross-sectional area of muscle and muscle fibers in cirrhotic mice with respect to CTR. Kinetic properties of EDL in both BDL and CCl4 were reduced with respect to CTR; BDL mice also showed a reduction in muscle force and a decrease in the resistance to fatigue. Increase in myostatin expression associated with a decrease in AKT-mTOR expressions was observed in BDL mice, together with an increase in LC3 protein levels. Upregulation of the proinflammatory citochines TNF-a and IL6 and an increased expression of NF-kB and MuRF-1 were observed in CCl4 mice. In conclusion, skeletal muscle myopenia was present in experimental models of BDL and CCl4-induced cirrhosis. Moreover, reduction in protein synthesis and activation of protein degradation were the main mechanisms responsible for myopenia in BDL mice, while activation of ubiquitin-pathway through inflammatory cytokines seems to be the main potential mechanism involved in CCl4 mice.

Aerobic Exercise and Pharmacological Treatments Counteract Cachexia by Modulating Autophagy in Colon Cancer.

Recent studies have correlated physical activity with a better prognosis in cachectic patients, although the underlying mechanisms are not yet understood. In order to identify the pathways involved in the physical activity-mediated rescue of skeletal muscle mass and function, we investigated the effects of voluntary exercise on cachexia in colon carcinoma (C26)-bearing mice. Voluntary exercise prevented loss of muscle mass and function, ultimately increasing survival of C26-bearing mice. We found that the autophagic flux is overloaded in skeletal muscle of both colon carcinoma murine models and patients, but not in running C26-bearing mice, thus suggesting that exercise may release the autophagic flux and ultimately rescue muscle homeostasis. Treatment of C26-bearing mice with either AICAR or rapamycin, two drugs that trigger the autophagic flux, also rescued muscle mass and prevented atrogene induction. Similar effects were reproduced on myotubes in vitro, which displayed atrophy following exposure to C26-conditioned medium, a phenomenon that was rescued by AICAR or rapamycin treatment and relies on autophagosome-lysosome fusion (inhibited by chloroquine). Since AICAR, rapamycin and exercise equally affect the autophagic system and counteract cachexia, we believe autophagy-triggering drugs may be exploited to treat cachexia in conditions in which exercise cannot be prescribed.

Increased levels of interleukin-6 exacerbate the dystrophic phenotype in mdx mice.

Duchenne muscular dystrophy (DMD) is characterized by progressive lethal muscle degeneration and chronic inflammatory response. The mdx mouse strain has served as the animal model for human DMD. However, while DMD patients undergo extensive necrosis, the affected muscles of adult mdx mice rapidly regenerates and regains structural and functional integrity. The basis for the mild effects observed in mice compared with the lethal consequences in humans remains unknown. In this study, we provide evidence that interleukin-6 (IL-6) is causally linked to the pathogenesis of muscular dystrophy. We report that forced expression of IL-6, in the adult mdx mice, recapitulates the severe phenotypic characteristics of DMD in humans. Increased levels of IL-6 exacerbate the dystrophic muscle phenotype, sustaining inflammatory response and repeated cycles of muscle degeneration and regeneration, leading to exhaustion of satellite cells. The mdx/IL6 mouse closely approximates the human disease and more faithfully recapitulates the disease progression in humans. This study promises to significantly advance our understanding of the pathogenic mechanisms that lead to DMD.

Proliferation of Multiple Cell Types in the Skeletal Muscle Tissue Elicited by Acute p21 Suppression.

Although in the last decades the molecular underpinnings of the cell cycle have been unraveled, the acquired knowledge has been rarely translated into practical applications. Here, we investigate the feasibility and safety of triggering proliferation in vivo by temporary suppression of the cyclin-dependent kinase inhibitor, p21. Adeno-associated virus (AAV)-mediated, acute knockdown of p21 in intact skeletal muscles elicited proliferation of multiple, otherwise quiescent cell types, notably including satellite cells. Compared with controls, p21-suppressed muscles exhibited a striking two- to threefold expansion in cellularity and increased fiber numbers by 10 days post-transduction, with no detectable inflammation. These changes partially persisted for at least 60 days, indicating that the muscles had undergone lasting modifications. Furthermore, morphological hyperplasia was accompanied by 20% increases in maximum strength and resistance to fatigue. To assess the safety of transiently suppressing p21, cells subjected to p21 knockdown in vitro were analyzed for γ-H2AX accumulation, DNA fragmentation, cytogenetic abnormalities, ploidy, and mutations. Moreover, the differentiation competence of p21-suppressed myoblasts was investigated. These assays confirmed that transient suppression of p21 causes no genetic damage and does not impair differentiation. Our results establish the basis for further exploring the manipulation of the cell cycle as a strategy in regenerative medicine.

Molecular, cellular and physiological characterization of the cancer cachexia-inducing C26 colon carcinoma in mouse.

BACKGROUND: The majority of cancer patients experience dramatic weight loss, due to cachexia and consisting of skeletal muscle and fat tissue wasting. Cachexia is a negative prognostic factor, interferes with therapy and worsens the patients' quality of life by affecting muscle function. Mice bearing ectopically-implanted C26 colon carcinoma are widely used as an experimental model of cancer cachexia. As part of the search for novel clinical and basic research applications for this experimental model, we characterized novel cellular and molecular features of C26-bearing mice. METHODS: A fragment of C26 tumor was subcutaneously grafted in isogenic BALB/c mice. The mass growth and proliferation rate of the tumor were analyzed. Histological and cytofluorometric analyses were used to assess cell death, ploidy and differentiation of the tumor cells. The main features of skeletal muscle atrophy, which were highlighted by immunohistochemical and electron microscopy analyses, correlated with biochemical alterations. Muscle force and resistance to fatigue were measured and analyzed as major functional deficits of the cachectic musculature. RESULTS: We found that the C26 tumor, ectopically implanted in mice, is an undifferentiated carcinoma, which should be referred to as such and not as adenocarcinoma, a common misconception. The C26 tumor displays aneuploidy and histological features typical of transformed cells, incorporates BrdU and induces severe weight loss in the host, which is largely caused by muscle wasting. The latter appears to be due to proteasome-mediated protein degradation, which disrupts the sarcomeric structure and muscle fiber-extracellular matrix interactions. A pivotal functional deficit of cachectic muscle consists in increased fatigability, while the reported loss of tetanic force is not statistically significant following normalization for decreased muscle fiber size. CONCLUSIONS: We conclude, on the basis of the definition of cachexia, that ectopically-implanted C26 carcinoma represents a well standardized experimental model for research on cancer cachexia. We wish to point out that scientists using the C26 model to study cancer and those using the same model to study cachexia may be unaware of each other's works because they use different keywords; we present strategies to eliminate this gap and discuss the benefits of such an exchange of knowledge.

Flavocoxid counteracts muscle necrosis and improves functional properties in mdx mice: a comparison study with methylprednisolone.

Muscle degeneration in dystrophic muscle is exacerbated by the endogenous inflammatory response and increased oxidative stress. A key role is played by nuclear factor(NF)-kappaB. We showed that NF-kappaB inhibition through compounds with also antioxidant properties has beneficial effects in mdx mice, the murine model of Duchenne muscular dystrophy (DMD), but these drugs are not available for clinical studies. We evaluated whether flavocoxid, a mixed flavonoid extract with anti-inflammatory, antioxidant and NF-kappaB inhibiting properties, has beneficial effects in mdx mice in comparison with methylprednisolone, the gold standard treatment for DMD patients. Five-week-old mdx mice were treated for 5 weeks with flavocoxid, methylprednisolone or vehicle. The evaluation of in vivo and ex vivo functional properties and morphological parameters was performed. Serum samples were assayed for oxidative stress markers, creatine-kinase (CK) and leukotriene B-4. Cyclooxygenase-2 (COX-2), 5-lipoxygenase (5-LOX), tumor necrosis factor-alpha, p-38, JNK1 expression was evaluated in muscle by western blot analysis. NF-kappaB binding activity was investigated by electrophoresis mobility shift assay. The administration of flavocoxid: (1) ameliorated functional properties in vivo and ex vivo; (2) reduced CK; (3) reduced the expression of oxidative stress markers and of inflammatory mediators; (4) inhibited NF-kappaB and mitogen-activated protein kinases (MAPKs) signal pathways; (5) reduced muscle necrosis and enhanced regeneration. Our results highlight the detrimental effects of oxidative stress and NF-kappaB, MAPKs and COX/5-LOX pathways in the dystrophic process and show that flavocoxid is more effective in mdx mice than methylprednisolone.

Modulation of caspase activity regulates skeletal muscle regeneration and function in response to vasopressin and tumor necrosis factor.

Muscle homeostasis involves de novo myogenesis, as observed in conditions of acute or chronic muscle damage. Tumor Necrosis Factor (TNF) triggers skeletal muscle wasting in several pathological conditions and inhibits muscle regeneration. We show that intramuscular treatment with the myogenic factor Arg(8)-vasopressin (AVP) enhanced skeletal muscle regeneration and rescued the inhibitory effects of TNF on muscle regeneration. The functional analysis of regenerating muscle performance following TNF or AVP treatments revealed that these factors exerted opposite effects on muscle function. Principal component analysis showed that TNF and AVP mainly affect muscle tetanic force and fatigue. Importantly, AVP counteracted the effects of TNF on muscle function when delivered in combination with the latter. Muscle regeneration is, at least in part, regulated by caspase activation, and AVP abrogated TNF-dependent caspase activation. The contrasting effects of AVP and TNF in vivo are recapitulated in myogenic cell cultures, which express both PW1, a caspase activator, and Hsp70, a caspase inhibitor. We identified PW1 as a potential Hsp70 partner by screening for proteins interacting with PW1. Hsp70 and PW1 co-immunoprecipitated and co-localized in muscle cells. In vivo Hsp70 protein level was upregulated by AVP, and Hsp70 overexpression counteracted the TNF block of muscle regeneration. Our results show that AVP counteracts the effects of TNF through cross-talk at the Hsp70 level. Therefore, muscle regeneration, both in the absence and in the presence of cytokines may be enhanced by increasing Hsp70 expression.

Long-term benefit of adeno-associated virus/antisense-mediated exon skipping in dystrophic mice.

Many mutations and deletions in the dystrophin gene, responsible for Duchenne muscular dystrophy (DMD), can be corrected at the posttranscriptional level by skipping specific exons. Here we show that long-term benefit can be obtained in the dystrophic mouse model through the use of adeno-associated viral vectors expressing antisense sequences: persistent exon skipping, dystrophin rescue, and functional benefit were observed 74 weeks after a single systemic administration. The therapeutic benefit was sufficient to preserve the muscle integrity of mice up to old age. These results indicate a possible long-term gene therapy treatment of the DMD pathology.

Local expression of IGF-1 accelerates muscle regeneration by rapidly modulating inflammatory cytokines and chemokines.

Muscle regeneration following injury is characterized by myonecrosis accompanied by local inflammation, activation of satellite cells, and repair of injured fibers. The resolution of the inflammatory response is necessary to proceed toward muscle repair, since persistence of inflammation often renders the damaged muscle incapable of sustaining efficient muscle regeneration. Here, we show that local expression of a muscle-restricted insulin-like growth factor (IGF)-1 (mIGF-1) transgene accelerates the regenerative process of injured skeletal muscle, modulating the inflammatory response, and limiting fibrosis. At the molecular level, mIGF-1 expression significantly down-regulated proinflammatory cytokines, such as tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta, and modulated the expression of CC chemokines involved in the recruitment of monocytes/macrophages. Analysis of the underlying molecular mechanisms revealed that mIGF-1 expression modulated key players of inflammatory response, such as macrophage migration inhibitory factor (MIF), high mobility group protein-1 (HMGB1), and transcription NF-kappaB. The rapid restoration of injured mIGF-1 transgenic muscle was also associated with connective tissue remodeling and a rapid recovery of functional properties. By modulating the inflammatory response and reducing fibrosis, supplemental mIGF-1 creates a qualitatively different environment for sustaining more efficient muscle regeneration and repair.