An anti-inflammatory role for leukemia inhibitory factor receptor signaling in regenerating skeletal muscle

Benfotiamine improves dystrophic pathology and exercise capacity in mdx mice by reducing inflammation and fibrosis

Duchenne Muscular Dystrophy (DMD) is a progressive and fatal neuromuscular disease. Cycles of myofibre degeneration and regeneration are hallmarks of the disease where immune cells infiltrate to repair damaged skeletal muscle. Benfotiamine is a lipid soluble precursor to thiamine, shown clinically to reduce inflammation in diabetic related complications. We assessed whether benfotiamine administration could reduce inflammation related dystrophic pathology. Benfotiamine (10 mg/kg/day) was fed to male mdx mice (n = 7) for 15 weeks from 4 weeks of age. Treated mice had an increased growth weight (5-7 weeks) and myofibre size at treatment completion. Markers of dystrophic pathology (area of damaged necrotic tissue, central nuclei) were reduced in benfotiamine mdx quadriceps. Grip strength was increased and improved exercise capacity was found in mdx treated with benfotiamine for 12 weeks, before being placed into individual cages and allowed access to an exercise wheel for 3 weeks. Global gene expression profiling (RNAseq) in the gastrocnemius revealed benfotiamine regulated signalling pathways relevant to dystrophic pathology (Inflammatory Response, Myogenesis) and fibrotic gene markers (Col1a1, Col1a2, Col4a5, Col5a2, Col6a2, Col6a2, Col6a3, Lum) towards wildtype levels. In addition, we observed a reduction in gene expression of inflammatory gene markers in the quadriceps (Emr1, Cd163, Cd4, Cd8, Ifng). Overall, these data suggest that benfotiamine reduces dystrophic pathology by acting on inflammatory and fibrotic gene markers and signalling pathways. Given benfotiamine's excellent safety profile and current clinical use, it could be used in combination with glucocorticoids to treat DMD patients.

Nicotinamide N-methyltransferase inhibition mimics and boosts exercise-mediated improvements in muscle function in aged mice

Human hallmarks of sarcopenia include muscle weakness and a blunted response to exercise. Nicotinamide N-methyltransferase inhibitors (NNMTis) increase strength and promote the regenerative capacity of aged muscle, thus offering a promising treatment for sarcopenia. Since human hallmarks of sarcopenia are recapitulated in aged (24-month-old) mice, we treated mice from 22 to 24 months of age with NNMTi, intensive exercise, or a combination of both, and compared skeletal muscle adaptations, including grip strength, longitudinal running capacity, plantarflexor peak torque, fatigue, and muscle mass, fiber type, cross-sectional area, and intramyocellular lipid (IMCL) content. Exhaustive proteome and metabolome analyses were completed to identify the molecular mechanisms underlying the measured changes in skeletal muscle pathophysiology. Remarkably, NNMTi-treated aged sedentary mice showed ~ 40% greater grip strength than sedentary controls, while aged exercised mice only showed a 20% increase relative to controls. Importantly, the grip strength improvements resulting from NNMTi treatment and exercise were additive, with NNMTi-treated exercised mice developing a 60% increase in grip strength relative to sedentary controls. NNMTi treatment also promoted quantifiable improvements in IMCL content and, in combination with exercise, significantly increased gastrocnemius fiber CSA. Detailed skeletal muscle proteome and metabolome analyses revealed unique molecular mechanisms associated with NNMTi treatment and distinct molecular mechanisms and cellular processes arising from a combination of NNMTi and exercise relative to those given a single intervention. These studies suggest that NNMTi-based drugs, either alone or combined with exercise, will be beneficial in treating sarcopenia and a wide range of age-related myopathies.

IL-4, IL-13 and IFN-γ -induced genes in highly purified human neutrophils

Interleukin (IL)-4 and IL-13 are related cytokines with well-known specific roles in type 2 immune response. However, their effects on neutrophils are not completely understood. For this, we studied human primary neutrophil responses to IL-4 and IL-13. Neutrophils are dose-dependently responsive to both IL-4 and IL-13 as indicated by signal transducer and activator of transcription 6 (STAT6) phosphorylation upon stimulation, with IL-4 being more potent inducer of STAT6. IL-4-, IL-13- and Interferon (IFN)-γ-stimulated gene expression in highly purified human neutrophils induced both overlapping and unique gene expression in highly purified human neutrophils. IL-4 and IL-13 specifically regulate several immune-related genes, including IL-10, tumor necrosis factor (TNF) and leukemia inhibitory factor (LIF), while type1 immune response-related IFN-γ induced gene expression related for example, to intracellular infections. In analysis of neutrophil metabolic responses, oxygen independent glycolysis was specifically regulated by IL-4, but not by IL-13 or IFN-γ, suggesting specific role for type I IL-4 receptor in this process. Our results provide a comprehensive analysis of IL-4, IL-13 and IFN-γ -induced gene expression in neutrophils while also addressing cytokine-mediated metabolic changes in neutrophils.

Leukemia inhibitory factor, a double-edged sword with therapeutic implications in human diseases

Leukemia inhibitory factor (LIF) is a pleiotropic cytokine of the interleukin-6 (IL-6) superfamily. LIF was initially discovered as a factor to induce the differentiation of myeloid leukemia cells and thus inhibit their proliferation. Subsequent studies have highlighted the multi-functions of LIF under a wide variety of physiological and pathological conditions in a highly cell-, tissue-, and context-dependent manner. Emerging evidence has demonstrated that LIF plays an essential role in the stem cell niche, where it maintains the homeostasis and regeneration of multiple somatic tissues, including intestine, neuron, and muscle. Further, LIF exerts a crucial regulatory role in immunity and functions as a protective factor against many immunopathological diseases, such as infection, inflammatory bowel disease (IBD), and graft-verse-host disease (GVHD). It is worth noting that while LIF displays a tumor-suppressive function in leukemia, recent studies have highlighted the oncogenic role of LIF in many types of solid tumors, further demonstrating the complexities and context-dependent effects of LIF. In this review, we summarize the recent insights into the roles and mechanisms of LIF in stem cell homeostasis and regeneration, immunity, and cancer, and discuss the potential therapeutic options for human diseases by modulating LIF levels and functions.

Protective action of ultrasound-guided electrolysis technique on the muscle damage induced by notexin in rats

It is known that exercise can be one of the causes of muscular damage. In recent times, physiotherapists and medical professionals have been employing USGET techniques to stimulate muscle recovery to improve its performance after the injury. We pretend to analyse if the Ultrasound-guided electrolysis (USGET) technique could reduce muscle damage, inflammation, and pain in the present study. Female Wistar rats were assigned to one of three different groups: control (C), notexin (NOT) and notexin with USGET (electrolysis at 6mA) (NOT+USGET). We used the USGT technique, based on electrical stimulation with a continuous current of 4 pulses at an intensity of 6 mA for 5 seconds, conveyed to the muscle. The response was tested with motor function tests. In these tests, we could observe an increase in time and foot faults when crossing a beam in the NOT group compared to C group rats. On the other hand, a significant decrease in both variables was detected in the NOT+USGET compared to the NOT group. Muscle power was measured with a grip strength test, obtaining far better performances in NOT+USGET rats when compared to NOT rats. Moreover, the USGET technique prevented the increase of pro-inflammatory proteins IL-6 and chemokines CCL3 (Chemokine (C-C motif) ligand 3), CCL4 (Chemokine (C-C motif) ligand 4), and CCL5 (Chemokine (C-C motif) ligand 5) with their receptor CCR5 (C-C chemokine receptor type 5), induced by notexin in the quadriceps. At the same time, the study evidenced a decrease in both CCR8 (C-C chemokine receptor type 5,) and NF-ᴋB (nuclear factor- ᴋB) expressions after USGET treatment. On the other hand, we obtained evidence that demonstrated anti-inflammatory properties of the USGET technique, thus being the increase in IL-10 (Interleukin 10) and IL-13 (Interleukin 13) in the NOT+USGET group compared to the NOT group. Furthermore, when applying NSGET after damage, an increase in anti-inflammatory mediators and reduction of pro-inflammatory mediators, which, overall, promoted muscle regeneration, was observed. These results support the idea that the NSGET technique improves muscle recovery after toxic damages, which would justify its employment.

Exerkines in health, resilience and disease

The health benefits of exercise are well-recognized and are observed across multiple organ systems. These beneficial effects enhance overall resilience, healthspan and longevity. The molecular mechanisms that underlie the beneficial effects of exercise, however, remain poorly understood. Since the discovery in 2000 that muscle contraction releases IL-6, the number of exercise-associated signalling molecules that have been identified has multiplied. Exerkines are defined as signalling moieties released in response to acute and/or chronic exercise, which exert their effects through endocrine, paracrine and/or autocrine pathways. A multitude of organs, cells and tissues release these factors, including skeletal muscle (myokines), the heart (cardiokines), liver (hepatokines), white adipose tissue (adipokines), brown adipose tissue (baptokines) and neurons (neurokines). Exerkines have potential roles in improving cardiovascular, metabolic, immune and neurological health. As such, exerkines have potential for the treatment of cardiovascular disease, type 2 diabetes mellitus and obesity, and possibly in the facilitation of healthy ageing. This Review summarizes the importance and current state of exerkine research, prevailing challenges and future directions.

Growth Factors Do Not Improve Muscle Function in Young or Adult mdx Mice

Muscular dystrophies constitute a broad group of genetic disorders leading to muscle wasting. We have previously demonstrated that treating a muscular atrophy mouse model with growth factors resulted in increased muscle mass. In the present study, we treated the Duchenne mouse model mdx for 12 weeks with myogenic growth factors peri- and post-onset of muscular degeneration to explore the effects in the oxidative muscle soleus and the glycolytic muscle extensor digitorum longus (EDL). We found no overall beneficial effect in the peri-onset group at the conclusion of the study. In the post-onset group, the functional improvement by means of electrophysiological examinations ex vivo was mostly confined to the soleus. EDL benefitted from the treatment on a molecular level but did not improve functionally. Histopathology revealed signs of inflammation at the end of treatment. In conclusion, the growth factor cocktail failed to improve the mdx on a functional level.

Myeloid cell-mediated targeting of LIF to dystrophic muscle causes transient increases in muscle fiber lesions by disrupting the recruitment and dispersion of macrophages in muscle

Leukemia inhibitory factor (LIF) can influence development by increasing cell proliferation and inhibiting differentiation. Because of its potency for expanding stem cell populations, delivery of exogenous LIF to diseased tissue could have therapeutic value. However, systemic elevations of LIF can have negative, off-target effects. We tested whether inflammatory cells expressing a LIF transgene under control of a leukocyte-specific, CD11b promoter provide a strategy to target LIF to sites of damage in the mdx mouse model of Duchenne muscular dystrophy, leading to increased numbers of muscle stem cells and improved muscle regeneration. However, transgene expression in inflammatory cells did not increase muscle growth or increase numbers of stem cells required for regeneration. Instead, transgene expression disrupted the normal dispersion of macrophages in dystrophic muscles, leading to transient increases in muscle damage in foci where macrophages were highly concentrated during early stages of pathology. The defect in inflammatory cell dispersion reflected impaired chemotaxis of macrophages to C-C motif chemokine ligand-2 and local increases of LIF production that produced large aggregations of cytolytic macrophages. Transgene expression also induced a shift in macrophage phenotype away from a CD206+, M2-biased phenotype that supports regeneration. However, at later stages of the disease when macrophage numbers declined, they dispersed in the muscle, leading to reductions in muscle fiber damage, compared to non-transgenic mdx mice. Together, the findings show that macrophage-mediated delivery of transgenic LIF exerts differential effects on macrophage dispersion and muscle damage depending on the stage of dystrophic pathology.

Exercise plasma boosts memory and dampens brain inflammation via clusterin

Physical exercise is generally beneficial to all aspects of human and animal health, slowing cognitive ageing and neurodegeneration¹. The cognitive benefits of physical exercise are tied to an increased plasticity and reduced inflammation within the hippocampus^2-4, yet little is known about the factors and mechanisms that mediate these effects. Here we show that 'runner plasma', collected from voluntarily running mice and infused into sedentary mice, reduces baseline neuroinflammatory gene expression and experimentally induced brain inflammation. Plasma proteomic analysis revealed a concerted increase in complement cascade inhibitors including clusterin (CLU). Intravenously injected CLU binds to brain endothelial cells and reduces neuroinflammatory gene expression in a mouse model of acute brain inflammation and a mouse model of Alzheimer's disease. Patients with cognitive impairment who participated in structured exercise for 6 months had higher plasma levels of CLU. These findings demonstrate the existence of anti-inflammatory exercise factors that are transferrable, target the cerebrovasculature and benefit the brain, and are present in humans who engage in exercise.

Inflammation-like changes in the urothelium of Lifr-deficient mice and LIFR-haploinsufficient humans with urinary tract anomalies

Congenital anomalies of the kidney and urinary tract (CAKUT) are the most common cause of end-stage kidney disease in children. While the genetic aberrations underlying CAKUT pathogenesis are increasingly being elucidated, their consequences on a cellular and molecular level commonly remain unclear. Recently, we reported rare heterozygous deleterious LIFR variants in 3.3% of CAKUT patients, including a novel de novo frameshift variant, identified by whole-exome sequencing, in a patient with severe bilateral CAKUT. We also demonstrated CAKUT phenotypes in Lifr-/- and Lifr+/- mice, including a narrowed ureteric lumen due to muscular hypertrophy and a thickened urothelium. Here, we show that both in the ureter and bladder of Lifr-/- and Lifr+/- embryos, differentiation of the three urothelial cell types (basal, intermediate and superficial cells) occurs normally but that the turnover of superficial cells is elevated due to increased proliferation, enhanced differentiation from their progenitor cells (intermediate cells) and, importantly, shedding into the ureteric lumen. Microarray-based analysis of genome-wide transcriptional changes in Lifr-/- versus Lifr+/+ ureters identified gene networks associated with an antimicrobial inflammatory response. Finally, in a reverse phenotyping effort, significantly more superficial cells were detected in the urine of CAKUT patients with versus without LIFR variants indicating conserved LIFR-dependent urinary tract changes in the murine and human context. Our data suggest that LIFR signaling is required in the epithelium of the urinary tract to suppress an antimicrobial response under homeostatic conditions and that genetically induced inflammation-like changes underlie CAKUT pathogenesis in Lifr deficiency and LIFR haploinsufficiency.

Leukemia inhibitory factor regulates the activation of inflammatory signals in macrophages and trophoblast cells

The pleiotropic cytokine leukemia inhibitory factor (LIF) is a key gestational factor known to establish dynamic cellular and molecular cross talk at the feto-maternal interface. Previously, we described the regulatory role of the LIF-trophoblast-IL10 axis in the process of macrophage deactivation in response to pro-inflammatory cytokines. However, the direct regulatory effects of LIF in macrophage and trophoblast cell function remains elusive. In this study, we aimed to examine whether and how LIF regulates the behavior of macrophages and trophoblast cells in response to pro-inflammatory stress factors. We found that LIF modulated the activating effects of interferon-gamma (IFNγ) and granulocyte-macrophage colony-stimulating factor (GM-CSF) in macrophages and trophoblast cells by reducing the phosphorylation levels of signal transducer and activator of transcription-1 (Stat1) and -5 (Stat5). Cell activation with IFNγ inhibited cell invasion and migration but this immobilizing effect was abrogated when macrophages and trophoblast cells were deactivated with LIF; macrophage cell motility restitution could in part be explained by the positive effects of LIF in Stat3 activation and matrix metalloproteinase 9 (MMP-9) expression. Pharmacological inhibition of Stat1 and Stat3 indicated that IFNγ-induced Stat1 activation mediated macrophage motility inhibition, and that cell motility in IFNγ-activated macrophages is restored via LIF-induced Stat3 activation and Stat1 inhibition. Moreover, IFNγ-induced TNFα gene expression was also abrogated by LIF through Stat1 inhibition and Stat3 activation. Finally, we have found that cell invasion of trophoblast cells is inhibited when they were cocultured with GM-CSF-differentiated, IFNγ-stimulated macrophages. This effect, however, was inhibited when macrophages were exposed to LIF. Overall, this in vitro study reveals for the first time the anti-inflammatory and pro-gestational activities of LIF by acting directly on macrophages and trophoblast cells.

Targeting a therapeutic LIF transgene to muscle via the immune system ameliorates muscular dystrophy

Many potentially therapeutic molecules have been identified for treating Duchenne muscular dystrophy. However, targeting those molecules only to sites of active pathology is an obstacle to their clinical use. Because dystrophic muscles become extensively inflamed, we tested whether expressing a therapeutic transgene in leukocyte progenitors that invade muscle would provide selective, timely delivery to diseased muscle. We designed a transgene in which leukemia inhibitory factor (LIF) is under control of a leukocyte-specific promoter and transplanted transgenic cells into dystrophic mice. Transplantation diminishes pathology, reduces Th2 cytokines in muscle and biases macrophages away from a CD163+/CD206+ phenotype that promotes fibrosis. Transgenic cells also abrogate TGFβ signaling, reduce fibro/adipogenic progenitor cells and reduce fibrogenesis of muscle cells. These findings indicate that leukocytes expressing a LIF transgene reduce fibrosis by suppressing type 2 immunity and highlight a novel application by which immune cells can be genetically modified as potential therapeutics to treat muscle disease.

Leukemia inhibitory factor promotes the regeneration of rat uterine horns with full-thickness injury

Severe uterine injuries may lead to infertility or pregnancy complications. There is a lack of effective methods to restore the structure and function of seriously injured uteri. Leukemia inhibitory factor (LIF), which plays a crucial role in blastocyst implantation, promotes the process of regeneration after injury in several different tissues. In this study, we explored the effect of LIF on the regeneration of rat uterine horns following full-thickness injury. One hundred and twenty four female Sprague-Dawley rats were assigned to three groups, including a sham-operated group (n = 34 uterine horns), a PBS/collagen group (n = 90 uterine horns), and a LIF/collagen group (n = 124 uterine horns). The regenerated uterine horns were collected at 1, 2, 4, 8, or 12 weeks after the surgery. The results showed that LIF/collagen scaffolds increased the number of endometrial cells and neovascularization 2 weeks after uterine full-thickness defect in excision sites (p < 0.001 vs PBS/collagen). Eight weeks after the surgery, the number of endometrial glands was dramatically higher in the LIF/collagen scaffolds group (35.2 ± 4.1/field) than in the PBS/collagen scaffolds (15.1 ± 1.4/field). The percentage of a-smooth muscle actin (a-SMA)-positive areas in the LIF/collagen scaffolds (88.8% ± 9.8%) was also significantly higher than that in the PBS/collagen group (52.9% ± 3.7%). Moreover, LIF improved the pregnancy rate and fetus number. We also found that LIF inhibited the infiltration of inflammatory cells and down-regulated the pro-inflammatory cytokine IL-12 expression while up-regulating the anti-inflammatory cytokine IL-10 expression in the injured part of the uterine horns. Our results indicate that LIF promotes regeneration of the uterus after injury, and this is at least partially due to its immunomodulatory properties. In addition, it is worth to explore further the possibility for LIF/collagen to be an alternative therapeutic approach for uterine damage in the clinic in near future.

Regulation of expression and role of peroxisome proliferator-activated receptors (PPARs) in luminal epithelial and stromal cells of the porcine endometrium

Peroxisome proliferator-activated receptors (PPARs) are members of the nuclear receptor family of ligand-dependent transcription factors. PPARs are important regulators of glucose and fatty acid metabolism, apoptosis, angiogenesis, cell proliferation and differentiation, and immune response. Their possible role in the female reproductive tract was demonstrated. In the present study, cultured luminal epithelial (LE) and stromal (ST) cells of the porcine endometrium were used to examine (1) the effect of conceptus exposed medium (CEM) on mRNA and protein expression and DNA binding activity of PPARA, PPARD, and PPARG isoforms, and (2) the effect of PPARA, PPARD, and PPARG agonists on the expression of selected genes, apoptosis, and cell proliferation. The addition of CEM stimulated PPARA expression and DNA binding activity of this isoform in LE and ST cells (P < 0.05). Increased expression of PPARD mRNA in the presence of CEM was detected in ST cells (P < 0.05), while the concentration of PPARG transcripts decreased in response to CEM in both cell types (P < 0.05). LE and ST cells of the pig endometrium possess PPARA, PPARD, and PPARG proteins, with clear nuclear staining visible predominately in ST cells. In LE cells, activation of PPARG with 15-deoxy-Δ12,14-prostaglandin(PG)J2 down-regulated the expression of genes encoding amino acid transporter 1 (SLC38A1), leukemia inhibitory factor (LIF) and enzymes involved in PG synthesis (P < 0.05). In ST cells, activation of PPARD isoform with both agonists used (L-165,041 and cPGI2) and PPARG isoform with 15-deoxy-Δ12,14-PGJ2 increased vascular endothelial growth factor A (VEGFA) mRNA expression (P < 0.05). Moreover, GW9578 (PPARA agonist) and 15-deoxy-Δ12,14-PGJ2 stimulated glucose transporter 1 (SLC2A1) gene expression in ST cells. 15-deoxy-Δ12,14-PGJ2 was also effective in up-regulation of the ratio of BAX/BCL2 mRNA expression and active caspase-3 concentration in ST cells (P < 0.05). Finally, GW9578 stimulated LE and ST cell proliferation, while rosiglitazone (PPARG agonist) increased the number of viable ST but not LE cells. In conclusion, this study demonstrated that conceptus products differentially modulate PPARs expression and activity in the porcine endometrium. Activation of PPARs may in turn affect nutrient transport, PG synthesis, angiogenesis, apoptosis, or cell proliferation in this tissue. Therefore, PPAR isoforms seem to play an important role in development and function of the porcine uterus.

Applications and potential mechanisms of herbal medicines for rheumatoid arthritis treatment: a systematic review

In this review, we systematically discuss the role of traditional Chinese medicine (TCM) in rheumatoid arthritis (RA) disease treatment. TCM classifies the subtypes of RA through its own theoretical method, which is beneficial for more accurate diagnosis and treatment with Chinese herbal medicines (CHMs) that are more suitable for different syndromes. TCM mainly uses a flexible combination of CHMs to play an important role in RA treatment. The main components of these extracts can be subdivided into alkaloids, flavonoids, triterpenes, saponins and other compounds. Using a platform of transgenic and induced arthritis models, we explore the potential mechanisms of TCM against RA with the help of omics analysis techniques and methods. These mechanisms are mainly CHM and its extracts can inhibit RA patients and experimental animal models, including synovitis, vascular proliferation and bone injury; this involves many biological signal exchange targets and pathways. In conclusion, the role of TCM in RA treatment mainly involves reducing the expression and secretion of pro-inflammatory factors, thus decreasing the degree of abnormal immune response.

In this review, we systematically discuss the role of traditional Chinese medicine (TCM) in rheumatoid arthritis (RA) disease treatment.

Leukemia inhibitory factor promotes extracellular matrix synthesis in degenerative nucleus pulposus cells via MAPK-ERK1/2 signaling pathway

Extracellular matrix (ECM) anabolism and catabolism imbalance is key feature of chondrocyte and intervertebral disc nucleus pulposus (NP) cell degeneration. The role of LIF as a multifunctional cytokine in the ECM metabolism of chondrocytes is controversial, but no relevant research in the ECM metabolism of NP cells. This study aimed to explore the biofunction and related mechanisms of LIF in the degenerative NP cells. We obtained an increase in the expression of LIF in the human degenerated NP specimens. The addition of recombinant human leukemia inhibitory factor (rhLIF) to the degenerated NP cells cultured in vitro was found to stimulate the synthesis of ECM, and rhLIF could activate the ERK1/2 signaling pathway. However, coculture with PD98059, a signal inhibitor of ERK1/2, blocked the effect of rhLIF on the synthesis of ECM. To furtherly clarify the role of LIF, we carried out animal experiments and found that rhLIF treatment could successfully delay the degree of degeneration of the intervertebral disc in a rabbit model; but with the addition of PD98059, the function of rhLIF for degeneration protection disappeared. In summary, this study demonstrates that LIF plays a role in promoting ECM synthesis in the degenerated NP cells as a protective role in intervertebral disc degeneration (IDD), which is related to the activation of ERK1/2 signaling pathway.

Knockdown of a disintegrin A metalloprotease 12 (ADAM12) during adipogenesis reduces cell numbers, delays differentiation, and increases lipid accumulation in 3T3-L1 cells

Mouse models have shown that a disintegrin A metalloprotease 12 (ADAM12) is implicated during adipogenesis; the molecular pathways are not well understood. Stealth RNA interference was used to knock down ADAM12 in 3T3-L1 cells. Using gene profiling and metabolic enzymatic markers, we have identified signaling pathways ADAM12 impacts upon during proliferation, differentiation, and maturation of adipocytes. ADAM12 reduced cell numbers in proliferating preadipocytes, delayed differentiation of preadipocytes to adipocytes, and increased lipid accumulation in mature adipocytes. The pathway most affected by ADAM12 knockdown was regulation of insulin-like growth factor (IGF) activity by insulin-like growth factor binding proteins (IGFBPs); ADAM12 is known to cleave IGFBP3 and IGFBP5. The IGF/mTOR signaling pathway was down-regulated, supporting a role for ADAM12 in the IGFBP/IGF/mTOR-growth pathway. PPARγ signaling was also down-regulated by ADAM12 knockdown. Gene ontology (GO) analysis revealed that the extracellular matrix was the cellular compartment most impacted. Filtering for matrisome genes, connective tissue growth factor (Ctgf) was up-regulated. CTGF and IGBP3 can interact with PPARγ to hinder its regulation. Increased expression of these molecules could have influenced PPARγ signaling reducing differentiation and an imbalance of lipids. We believe ADAM12 regulates cell proliferation of preadipocytes through IGFBP/IGF/mTOR signaling and delays differentiation through altered PPAR signaling to cause an imbalance of lipids within mature adipocytes.

Zbtb7a induction in alveolar macrophages is implicated in anti-HLA-mediated lung allograft rejection

Chronic rejection significantly limits long-term success of solid organ transplantation. De novo donor-specific antibodies (DSAs) to mismatched donor human leukocyte antigen after human lung transplantation predispose lung grafts to chronic rejection. We sought to delineate mediators and mechanisms of DSA pathogenesis and to define early inflammatory events that trigger chronic rejection in lung transplant recipients and obliterative airway disease, a correlate of human chronic rejection, in mouse. Induction of transcription factor zinc finger and BTB domain containing protein 7a (Zbtb7a) was an early response critical in the DSA-induced chronic rejection. A cohort of human lung transplant recipients who developed DSA and chronic rejection demonstrated greater Zbtb7a expression long before clinical diagnosis of chronic rejection compared to nonrejecting lung transplant recipients with stable pulmonary function. Expression of DSA-induced Zbtb7a was restricted to alveolar macrophages (AMs), and selective disruption of Zbtb7a in AMs resulted in less bronchiolar occlusion, low immune responses to lung-restricted self-antigens, and high protection from chronic rejection in mice. Additionally, in an allogeneic cell transfer protocol, antigen presentation by AMs was Zbtb7a-dependent where AMs deficient in Zbtb7a failed to induce antibody and T cell responses. Collectively, we demonstrate that AMs play an essential role in antibody-induced pathogenesis of chronic rejection by regulating early inflammation and lung-restricted humoral and cellular autoimmunity.

Synovial tissue quantitative proteomics analysis reveals paeoniflorin decreases LIFR and ASPN proteins in experimental rheumatoid arthritis

Background

Rheumatoid arthritis (RA) is a common worldwide public health problem, which causes a chronic, systemic inflammatory disorder of synovial joints. Paeoniflorin (PA) has achieved positive results to some extent for the treatment of RA.

Purpose

This study aimed to reveal the potential druggable targets of PA in an experimental RA model using quantitative proteomics analysis.

Study design and methods

Thirty Sprague-Dawley rats were randomly divided into a normal group, model group and PA group. PA (1 mg/kg) was used to treat collagen-induced arthritis (CIA) rats for 42 days. We used isobaric tags for relative and absolute quantitation-based quantitative proteomics to analyze the synovial tissue of rats. Ingenuity pathway analysis (IPA) software was applied to process the data. The proteins that were targeted via IPA software were verified by Western blots.

Results

We found that PA caused 86 differentially expressed proteins (≥1.2-fold or ≤0.84-fold) compared with the CIA group. Of these varied proteins, 20 significantly changed (p<0.05) proteins referred to 41 CIA-relative top pathways after IPA pathway analysis. Thirteen of the PA-regulated pathways were anchored, which intervened in 24 biological functions. Next, network analysis revealed that leukemia inhibitory factor receptor (LIFR) and asporin (ASPN), which participate in two significant networks, contributed the most to the efficacy of PA treatment. Additionally, Western blots confirmed the aforementioned druggable targets of PA for the treatment of RA.

Conclusion

The results reveal that PA may treat RA by decreasing two key proteins, LIFR and ASPN. Our research helps to identify potential agents for RA treatment.

A neuro-immune, neuro-oxidative and neuro-nitrosative model of prenatal and postpartum depression

A large body of evidence indicates that major affective disorders are accompanied by activated neuro-immune, neuro-oxidative and neuro-nitrosative stress (IO&NS) pathways. Postpartum depression is predicted by end of term prenatal depressive symptoms whilst a lifetime history of mood disorders appears to increase the risk for both prenatal and postpartum depression. This review provides a critical appraisal of available evidence linking IO&NS pathways to prenatal and postpartum depression. The electronic databases Google Scholar, PubMed and Scopus were sources for this narrative review focusing on keywords, including perinatal depression, (auto)immune, inflammation, oxidative, nitric oxide, nitrosative, tryptophan catabolites (TRYCATs), kynurenine, leaky gut and microbiome. Prenatal depressive symptoms are associated with exaggerated pregnancy-specific changes in IO&NS pathways, including increased C-reactive protein, advanced oxidation protein products and nitric oxide metabolites, lowered antioxidant levels, such as zinc, as well as lowered regulatory IgM-mediated autoimmune responses. The latter pathways coupled with lowered levels of endogenous anti-inflammatory compounds, including ω3 polyunsaturated fatty acids, may also underpin the pathophysiology of postpartum depression. Although increased bacterial translocation, lipid peroxidation and TRYCAT pathway activation play a role in mood disorders, similar changes do not appear to be relevant in perinatal depression. Some IO&NS biomarker characteristics of mood disorders are found in prenatal depression indicating that these pathways partly contribute to the association of a lifetime history of mood disorders and perinatal depression. However, available evidence suggests that some IO&NS pathways differ significantly between perinatal depression and mood disorders in general. This review provides a new IO&NS model of prenatal and postpartum depression.

Interval exercise training increases LIF expression and prevents myocardial infarction-induced skeletal muscle atrophy in rats

AIMS

Myocardial infarction (MI) is commonly associated with body weight loss and skeletal muscle atrophy. Studies have shown that exercise training could give beneficial effects on skeletal muscle growth. Leukemia inhibitory factor (LIF) is a key regulator of muscle growth and regeneration. The aim of this study was to investigate the effects of interval exercise training (IET) on the expression of LIF and the MI-induced skeletal muscle atrophy.

MAIN METHODS

Male Sprague-Dawley rats were used to establish the MI model by ligation of the left anterior descending coronary artery. Infarcted Rats were divided into two groups: sedentary MI group (MI) and MI with interval exercise group (ME), and compared to sham-operated group (Sham). Exercise-trained animals were subjected to eight weeks of IET. Cardiac function, collagen volume fraction, expression of LIF and its receptor LIFR, myofiber size, apoptosis and proliferation in gastrocnemius muscle were analyzed.

KEY FINDINGS

IET increased heart functional performance and was accompanied with reversing cardiac pathological remodeling. Moreover, IET increased the expression of LIF and LIFR, activated signal transducer and activator of transcription (STAT3), reduced apoptosis and promoted proliferation in gastrocnemius muscle compared with the MI group. In addition, there was a significant negative correlation between skeletal muscle atrophy and LIF expression which was stimulated by IET in infarcted rats.

SIGNIFICANCE

IET reverses MI-induced cardiac dysfunction and skeletal muscle atrophy. In addition, IET up-regulates the expression of muscle LIF/LIFR and activates the STAT3.

Genetic biomarkers in non-contact muscle injuries in elite soccer players

PURPOSE

Damage to skeletal muscle necessitates regeneration to maintain proper muscle form and function. Interindividual differences in injury severity, recovery time, and injury rate could be explained by the presence of single nucleotide polymorphisms (SNPs) in genes involved in the reparation and regeneration of connective tissue . We wished to identify new genetic biomarkers that could help to prevent or minimize the risk of non-contact muscle injuries and are associated with a predisposition to developing muscle injuries.

METHODS

Using allelic discrimination techniques, we analysed 12 SNPs in selected genes from the genomic DNA of 74 elite soccer players.

RESULTS

SNPs in the hepatocyte growth factor (HGF) gene showed evidence of a statistically significant association with injury incidence, severity, and recovery time. SNPs in the SOX15 gene showed evidence of a statistically significant association with injury incidence. SNPs in the GEFT and LIF genes showed evidence of a statistically significant association with recovery time.

CONCLUSIONS

Genetic profile could explain why some elite soccer players are predisposed to suffer more injuries than others and why they need more time to recover from a particular injury. SNPs in HGF genes have an important role as biomarkers of biological processes fragility within muscle injuries related to injury rate, severity, and long recovery time.

Receptor for advanced glycation end-products and World Trade Center particulate induced lung function loss: A case-cohort study and murine model of acute particulate exposure

World Trade Center-particulate matter(WTC-PM) exposure and metabolic-risk are associated with WTC-Lung Injury(WTC-LI). The receptor for advanced glycation end-products (RAGE) is most highly expressed in the lung, mediates metabolic risk, and single-nucleotide polymorphisms at the AGER-locus predict forced expiratory volume(FEV). Our objectives were to test the hypotheses that RAGE is a biomarker of WTC-LI in the FDNY-cohort and that loss of RAGE in a murine model would protect against acute PM-induced lung disease. We know from previous work that early intense exposure at the time of the WTC collapse was most predictive of WTC-LI therefore we utilized a murine model of intense acute PM-exposure to determine if loss of RAGE is protective and to identify signaling/cytokine intermediates. This study builds on a continuing effort to identify serum biomarkers that predict the development of WTC-LI. A case-cohort design was used to analyze a focused cohort of male never-smokers with normal pre-9/11 lung function. Odds of developing WTC-LI increased by 1.2, 1.8 and 1.0 in firefighters with soluble RAGE (sRAGE)≥97pg/mL, CRP≥2.4mg/L, and MMP-9≤397ng/mL, respectively, assessed in a multivariate logistic regression model (ROCAUC of 0.72). Wild type(WT) and RAGE-deficient(Ager-/-) mice were exposed to PM or PBS-control by oropharyngeal aspiration. Lung function, airway hyperreactivity, bronchoalveolar lavage, histology, transcription factors and plasma/BAL cytokines were quantified. WT-PM mice had decreased FEV and compliance, and increased airway resistance and methacholine reactivity after 24-hours. Decreased IFN-γ and increased LPA were observed in WT-PM mice; similar findings have been reported for firefighters who eventually develop WTC-LI. In the murine model, lack of RAGE was protective from loss of lung function and airway hyperreactivity and was associated with modulation of MAP kinases. We conclude that in a multivariate adjusted model increased sRAGE is associated with WTC-LI. In our murine model, absence of RAGE mitigated acute deleterious effects of PM and may be a biologically plausible mediator of PM-related lung disease.

Impact of β-hydroxy β-methylbutyrate (HMB) on age-related functional deficits in mice

β-Hydroxy β-methylbutyrate (HMB) is a metabolite of the essential amino acid leucine. Recent studies demonstrate a decline in plasma HMB concentrations in humans across the lifespan, and HMB supplementation may be able to preserve muscle mass and strength in older adults. However, the impact of HMB supplementation on hippocampal neurogenesis and cognition remains largely unexplored. The purpose of this study was to simultaneously evaluate the impact of HMB on muscle strength, neurogenesis and cognition in young and aged mice. In addition, we evaluated the influence of HMB on muscle-resident mesenchymal stem/stromal cell (Sca-1⁺CD45^-; mMSC) function to address these cells potential to regulate physiological outcomes. Three month-old (n=20) and 24 month-old (n=18) female C57BL/6 mice were provided with either Ca-HMB or Ca-Lactate in a sucrose solution twice per day for 5.5weeks at a dose of 450mg/kg body weight. Significant decreases in relative peak and mean force, balance, and neurogenesis were observed in aged mice compared to young (age main effects, p≤0.05). Short-term HMB supplementation did not alter activity, balance, neurogenesis, or cognitive function in young or aged mice, yet HMB preserved relative peak force in aged mice. mMSC gene expression was significantly reduced with age, but HMB supplementation was able to recover expression of select growth factors known to stimulate muscle repair (HGF, LIF). Overall, our findings demonstrate that while short-term HMB supplementation does not appear to affect neurogenesis or cognitive function in young or aged mice, HMB may maintain muscle strength in aged mice in a manner dependent on mMSC function.

Regulation of myokine expression: Role of exercise and cellular stress

Exercise training is well known to improve physical fitness and to combat chronic diseases and aging related disorders. Part of this is thought to be mediated by myokines, muscle derived secretory proteins (mainly cytokines) that elicit auto/paracrine but also endocrine effects on organs such as liver, adipose tissue, and bone. Today, several hundred potential myokines have been identified most of them not exclusive to muscle cells. Strenuous exercise is associated with increased production of free radicals and reactive oxidant species (ROS) as well as endoplasmic reticulum (ER)-stress which at an excessive level can lead to muscle damage and cell death. On the other hand, transient elevations in oxidative and ER-stress are thought to be necessary for adaptive improvements by regular exercise through a hormesis action termed mitohormesis since mitochondria are essential for the generation of energy and tightly connected to ER- and oxidative stress. Exercise induced myokines have been identified by various in vivo and in vitro approaches and accumulating evidence suggests that ROS and ER-stress linked pathways are involved in myokine induction. For example, interleukin (IL)-6, the prototypic exercise myokine is also induced by oxidative and ER-stress. Exercise induced expression of some myokines such as irisin and meteorin-like is linked to the transcription factor PGC-1α and apparently not related to ER-stress whereas typical ER-stress induced cytokines such as FGF-21 and GDF-15 are not exercise myokines under normal physiological conditions. Recent technological advances have led to the identification of numerous potential new myokines but for most of them regulation by oxidative and ER-stress still needs to be unraveled.

Cell-specific paracrine actions of IL-6 family cytokines from bone, marrow and muscle that control bone formation and resorption

Bone renews itself and changes shape throughout life to account for the changing needs of the body; this requires co-ordinated activities of bone resorbing cells (osteoclasts), bone forming cells (osteoblasts) and bone's internal cellular network (osteocytes). This review focuses on paracrine signaling by the IL-6 family of cytokines between bone cells, bone marrow, and skeletal muscle in normal physiology and in pathological states where their levels may be locally or systemically elevated. These functions include the support of osteoclast formation by osteoblast lineage cells in response to interleukin 6 (IL-6), interleukin 11 (IL-11), oncostatin M (OSM) and cardiotrophin 1 (CT-1). In addition it will discuss how bone-resorbing osteoclasts promote osteoblast activity by secreting CT-1, which acts as a "coupling factor" on osteocytes, osteoblasts, and their precursors to promote bone formation. OSM, produced by osteoblast lineage cells and macrophages, stimulates bone formation via osteocytes. IL-6 family cytokines also mediate actions of other bone formation stimuli like parathyroid hormone (PTH) and mechanical loading. CT-1, OSM and LIF suppress marrow adipogenesis by shifting commitment of pluripotent precursors towards osteoblast differentiation. Ciliary neurotrophic factor (CNTF) is released as a myokine from skeletal muscle and suppresses osteoblast differentiation and bone formation on the periosteum (outer bone surface in apposition to muscle). Finally, IL-6 acts directly on marrow-derived osteoclasts to stimulate release of "osteotransmitters" that act through the cortical osteocyte network to stimulate bone formation on the periosteum. Each will be discussed as illustrations of how the extended family of IL-6 cytokines acts within the skeleton in physiology and may be altered in pathological conditions or by targeted therapies.

Osteopontin ablation ameliorates muscular dystrophy by shifting macrophages to a pro-regenerative phenotype

In the degenerative disease Duchenne muscular dystrophy, inflammatory cells enter muscles in response to repetitive muscle damage. Immune factors are required for muscle regeneration, but chronic inflammation creates a profibrotic milieu that exacerbates disease progression. Osteopontin (OPN) is an immunomodulator highly expressed in dystrophic muscles. Ablation of OPN correlates with reduced fibrosis and improved muscle strength as well as reduced natural killer T (NKT) cell counts. Here, we demonstrate that the improved dystrophic phenotype observed with OPN ablation does not result from reductions in NKT cells. OPN ablation skews macrophage polarization toward a pro-regenerative phenotype by reducing M1 and M2a and increasing M2c subsets. These changes are associated with increased expression of pro-regenerative factors insulin-like growth factor 1, leukemia inhibitory factor, and urokinase-type plasminogen activator. Furthermore, altered macrophage polarization correlated with increases in muscle weight and muscle fiber diameter, resulting in long-term improvements in muscle strength and function in mdx mice. These findings suggest that OPN ablation promotes muscle repair via macrophage secretion of pro-myogenic growth factors.

Effects on Proliferation and Differentiation of Human Umbilical Cord-Derived Mesenchymal Stem Cells Engineered to Express Neurotrophic Factors

Mesenchymal stem cells (MSCs) are multipotential cells with capability to form colonies in vitro and differentiate into distinctive end-stage cell types. Although MSCs secrete many cytokines, the efficacy can be improved through combination with neurotrophic factors (NTFs). Moreover, MSCs are excellent opportunities for local delivery of NTFs into injured tissues. The aim of this present study is to evaluate the effects of overexpressing NTFs on proliferation and differentiation of human umbilical cord-derived mesenchymal stem cells (HUMSCs). Overexpressing NTFs had no effect on cell proliferation. Overexpressing NT-3, BDNF, and NGF also had no significant effect on the differentiation of HUMSCs. Overexpressing NTFs all promoted the neurite outgrowth of embryonic chick E9 dorsal root ganglion (DRG). The gene expression profiles of the control and NT-3- and BDNF-modified HUMSCs were compared using RNA sequencing and biological processes and activities were revealed. This study provides novel information about the effects of overexpressing NTFs on HUMSCs and insight into the choice of optimal NTFs for combined cell and gene therapy.

Inflammation during skeletal muscle regeneration and tissue remodeling: application to exercise-induced muscle damage management

Increase in the practice of sport by more and more numerous people in the Western countries is associated with an increase in muscle injuries, and in demand for improving muscle function and acceleration of muscle recovery after damage. Most of the treatments used target inflammation. Indeed, several lines of experimental evidence in animal models that are supported by human studies identify inflammatory cells, and particularly macrophages, as essential players in skeletal muscle regeneration. Macrophages act not only through their immune functions, but also control myogenesis and extracellular matrix remodeling by directly acting on myogenic precursors and fibro-adipogenic precursors. In light of these recent biological advances, the question of early treatment aiming at blunting inflammation after exercise-induced muscle injury is discussed.

Genetic dissection of milk yield traits and mastitis resistance quantitative trait loci on chromosome 20 in dairy cattle

Intense selection to increase milk yield has had negative consequences for mastitis incidence in dairy cattle. Due to low heritability of mastitis resistance and an unfavorable genetic correlation with milk yield, a reduction in mastitis through traditional breeding has been difficult to achieve. Here, we examined quantitative trait loci (QTL) that segregate for clinical mastitis and milk yield on Bos taurus autosome 20 (BTA20) to determine whether both traits are affected by a single polymorphism (pleiotropy) or by multiple closely linked polymorphisms. In the latter but not the former situation, undesirable genetic correlation could potentially be broken by selecting animals that have favorable variants for both traits. First, we performed a within-breed association study using a haplotype-based method in Danish Holstein cattle (HOL). Next, we analyzed Nordic Red dairy cattle (RDC) and Danish Jersey cattle (JER) with the goal of determining whether these QTL identified in Holsteins were segregating across breeds. Genotypes for 12,566 animals (5,966 HOL, 5,458 RDC, and 1,142 JER) were determined by using the Illumina Bovine SNP50 BeadChip (50K; Illumina, San Diego, CA), which identifies 1,568 single nucleotide polymorphisms on BTA20. Data were combined, phased, and clustered into haplotype states, followed by within- and across-breed haplotype-based association analyses using a linear mixed model. Association signals for both clinical mastitis and milk yield peaked in the 26- to 40-Mb region on BTA20 in HOL. Single-variant association analyses were carried out in the QTL region using whole sequence level variants imputed from references of 2,036 HD genotypes (BovineHD BeadChip; Illumina) and 242 whole-genome sequences. The milk QTL were also segregating in RDC and JER on the BTA20-targeted region; however, an indication of differences in the causal factor(s) was observed across breeds. A previously reported F279Y mutation (rs385640152) within the growth hormone receptor gene showed strong association with milk, fat, and protein yields. In HOL, the highest peaks for milk yield and susceptibility to mastitis were separated by over 3.5 Mb (3.8 Mb by haplotype analysis, 3.6 Mb by single nucleotide polymorphism analysis), suggesting separate genetic variants for the traits. Further analysis yielded 2 candidate mutations for the mastitis QTL, at 33,642,072 bp (rs378947583) in an intronic region of the caspase recruitment domain protein 6 gene and 35,969,994 bp (rs133596506) in an intronic region of the leukemia-inhibitory factor receptor gene. These findings suggest that it may be possible to separate these beneficial and detrimental genetic factors through targeted selective breeding.

Expression of leukemia inhibitory factor in Müller glia cells is regulated by a redox-dependent mRNA stability mechanism

Background

Photoreceptor degeneration is a main hallmark of many blinding diseases making protection of photoreceptors crucial to prevent vision loss. Thus, regulation of endogenous neuroprotective factors may be key for cell survival and attenuation of disease progression. Important neuroprotective factors in the retina include H₂O₂ generated by injured photoreceptors, and leukemia inhibitory factor (LIF) expressed in Müller glia cells in response to photoreceptor damage.

Results

We present evidence that H₂O₂ connects to the LIF response by inducing stabilization of Lif transcripts in Müller cells. This process was independent of active gene transcription and p38 MAPK, but relied on AU-rich elements (AREs), which we identified within the highly conserved Lif 3′UTR. Affinity purification combined with quantitative mass spectrometry identified several proteins that bound to these AREs. Among those, interleukin enhancer binding factor 3 (ILF3) was confirmed to participate in the redox-dependent Lif mRNA stabilization. Additionally we show that KH-type splicing regulatory protein (KHSRP) was crucial for maintaining basal Lif expression levels in non-stressed Müller cells.

Conclusions

Our results suggest that H₂O₂-induced redox signaling increases Lif transcript levels through ILF3 mediated mRNA stabilization. Generation of H₂O₂ by injured photoreceptors may thus enhance stability of Lif mRNA and therefore augment neuroprotective LIF signaling during degenerative conditions in vivo.

Electronic supplementary material

The online version of this article (doi:10.1186/s12915-015-0137-1) contains supplementary material, which is available to authorized users.

The Histochem Cell Biol conspectus: the year 2013 in review

Herein, we provide a brief synopsis of all manuscripts published in Histochem Cell Biol in the year 2013. For ease of reference, we have divided the manuscripts into the following categories: Advances in Methodologies; Molecules in Health and Disease; Organelles, Subcellular Structures and Compartments; Golgi Apparatus; Intermediate Filaments and Cytoskeleton; Connective Tissue and Extracellular Matrix; Autophagy; Stem Cells; Musculoskeletal System; Respiratory and Cardiovascular Systems; Gastrointestinal Tract; Central Nervous System; Peripheral Nervous System; Excretory Glands; Kidney and Urinary Bladder; and Male and Female Reproductive Systems. We hope that the readership will find this annual journal synopsis of value and serve as a quick, categorized reference guide for “state-of-the-art” manuscripts in the areas of histochemistry, immunohistochemistry, and cell biology.

Anti-inflammatory interventions and skeletal muscle injury: benefit or detriment?

Exercise, eccentric contractions, acute trauma, and disease are all causal mechanisms of skeletal muscle injury. After skeletal muscle is injured, it undergoes sequential phases of degeneration, inflammation, regeneration, and fibrosis. Events that occur in response to inflammation trigger regenerative processes. However, since inflammation causes pain, decreases skeletal muscle function, has a negative effect on performance, and contributes to fibrosis, which is one of the leading causes of delayed regeneration, the general practice has been to reduce inflammation. The problem with this approach is that preventing inflammation may hinder recovery. Current treatment options for inflammation are not necessarily effective and, in some cases, they may be unsafe. This review focuses on the question of whether the most beneficial course of treatment should be to block inflammation or if it is sensible to allow inflammatory processes to progress naturally. If blocking inflammation is perceived as a beneficial approach, it is not yet known at what time point during the inflammatory response it is most sensible to interfere. To address these issues, this review evaluates the effects of various anti-inflammatory agents on recovery processes in response to exercise-induced, traumatic, and disease-associated models of skeletal muscle injury. A collective analysis such as this should lay the foundation for future work that systematically manipulates the inflammatory response to most effectively promote regeneration and functional recovery in injured skeletal muscle, while reducing the negative effects of inflammatory processes such as pain and fibrosis.

Hyaluronan synthesis and myogenesis: a requirement for hyaluronan synthesis during myogenic differentiation independent of pericellular matrix formation

Exogenous hyaluronan is known to alter muscle precursor cell proliferation, migration, and differentiation, ultimately inhibiting myogenesis in vitro. The aim of the current study was to investigate the role of endogenous hyaluronan synthesis during myogenesis. In quantitative PCR studies, the genes responsible for synthesizing hyaluronan were found to be differentially regulated during muscle growth, repair, and pathology. Although all Has genes (Has1, Has2, and Has3) were differentially regulated in these models, only Has2 gene expression consistently associated with myogenic differentiation. During myogenic differentiation in vitro, Has2 was the most highly expressed of the synthases and increased after induction of differentiation. To test whether this association between Has2 expression and myogenesis relates to a role for Has2 in myoblast differentiation and fusion, C2C12 myoblasts were depleted of Has2 by siRNA and induced to differentiate. Depletion of Has2 inhibited differentiation and caused a loss of cell-associated hyaluronan and the hyaluronan-dependent pericellular matrix. The inhibition of differentiation caused by loss of hyaluronan was confirmed with the hyaluronan synthesis inhibitor 4-methylumbelliferone. In hyaluronan synthesis-blocked cultures, restoration of the pericellular matrix could be achieved through the addition of exogenous hyaluronan and the proteoglycan versican, but this was not sufficient to restore differentiation to control levels. These data indicate that intrinsic hyaluronan synthesis is necessary for myoblasts to differentiate and form syncytial muscle cells, but the hyaluronan-dependent pericellular matrix is not sufficient to support differentiation alone; additional hyaluronan-dependent cell functions that are yet unknown may be required for myogenic differentiation.