NF-κB inhibition reveals a novel role for HGF during skeletal muscle repair

Distinct human stem cell subpopulations drive adipogenesis and fibrosis in musculoskeletal injury

Fibroadipogenic progenitors (FAPs) maintain healthy skeletal muscle in homeostasis but drive muscle degeneration in chronic injuries by promoting adipogenesis and fibrosis. To uncover how these stem cells switch from a pro-regenerative to pro-degenerative role we perform single-cell mRNA sequencing of human FAPs from healthy and injured human muscles across a spectrum of injury, focusing on rotator cuff tears. We identify multiple subpopulations with progenitor, adipogenic, or fibrogenic gene signatures. We utilize full spectrum flow cytometry to identify distinct FAP subpopulations based on highly multiplexed protein expression. Injury severity increases adipogenic commitment of FAP subpopulations and is driven by the downregulation of DLK1. Treatment of FAPs both in vitro and in vivo with DLK1 reduces adipogenesis and fatty infiltration, suggesting that during injury, reduced DLK1 within a subpopulation of FAPs may drive degeneration. This work highlights how stem cells perform varied functions depending on tissue context, by dynamically regulating subpopulation fate commitment, which can be targeted improve patient outcomes after injury.

Exploring the role of growth factors as potential regulators in psoriatic plaque formation

Psoriasis is a chronic inflammatory skin disease in which growth activity is more prominent than inflammatory activity at the centre of lesional skin (CE skin). This growth activity is partly influenced by growth factors (GFs) that play an important role in cell growth and inflammation during the plaque development. In this study, we identified potential GFs in CE skin and predicted their regulatory functions and biological activity in mediating transcripts in the plaques. Samples of uninvolved skin (UN skin) and CE skin were biopsied from patients with psoriasis vulgaris for RNA-sequencing analysis in order to identify differentially expressed genes (DEGs). Our finding revealed that epidermal growth factor (EGF), fibroblast growth factor (FGF), platelet-derived growth factor (PDGF) and hepatocyte growth factor (HGF) signalling were enriched by CE/UN skin-derived DEGs. Additionally, several EGFR ligands, namely EGF, heparin-binding EGF like growth factor (HB-EGF), amphiregulin (AREG) and transforming growth factor (TGF)-α, as well as TGF-β1, TGF-β2, vascular endothelial growth factor-A, FGFs, PDGF-B and HGF, were predicted to be GF regulators. The regulatory pattern and biological activity of these GF regulators on mediating the CE/UN skin-derived DEGs was demonstrated. This study provides a novel hypothesis regarding the overall regulatory function of GFs, which appear to modulate the expression of the transcripts involved in inflammation and growth in the CE skin. In addition, some GFs may exert anti-inflammatory effects. Further investigations on the mechanisms underlying this regulation may contribute to a deeper understanding of psoriasis and the identification of potential therapeutic targets for patients with psoriasis.

Does β-Hydroxy-β-Methylbutyrate Have Any Potential to Support the Treatment of Duchenne Muscular Dystrophy in Humans and Animals?

Skeletal muscle is the protein reservoir of our body and an important regulator of glucose and lipid homeostasis. The dystrophin gene is the largest gene and has a key role in skeletal muscle construction and function. Mutations in the dystrophin gene cause Duchenne and Becker muscular dystrophy in humans, mice, dogs, and cats. Duchenne muscular dystrophy (DMD) is an X-linked neuromuscular condition causing progressive muscle weakness and premature death. β-hydroxy β-methylbutyrate (HMB) prevents deleterious muscle responses under pathological conditions, including tumor and chronic steroid therapy-related muscle losses. The use of HMB as a dietary supplement allows for increasing lean weight gain; has a positive immunostimulatory effect; is associated with decreased mortality; and attenuates sarcopenia in elderly animals and individuals. This study aimed to identify some genes, metabolic pathways, and biological processes which are common for DMD and HMB based on existing literature and then discuss the consequences of that interaction.

Mechanism of arterial injury exacerbated by hyperhomocysteinemia in spontaneously hypertensive rats

Hypertension associated with hyperhomocysteinemia (HHcy) accounts for 75% of hypertension in China. HHcy plays a synergistic role with hypertension in vascular injury and significantly increases the incidence of cardiovascular and cerebrovascular diseases. The present study aimed to explore the molecular mechanism of HHcy-induced arterial injury in hypertension. Spontaneously hypertensive rats (SHR) were injected intraperitoneally with DL-homocysteine (Hcy) to construct the model of hypertension associated with HHcy (HHcy + SHR). Biological network was employed to identify the material basis of arterial injury in hypertension associated with HHcy. The prediction molecules in oxidative stress and inflammation pathways were experimentally verified by quantitative real-time polymerase chain reaction (qRT-PCR) and western blot (WB) analysis. The HHcy + SHR group significantly increased oxidative stress pathway molecules: nicotinamide adenine dinucleotide phosphate oxidase (Nox); inflammatory pathway molecules: vascular adhesion protein-1 (VAP-1), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-a); as well as inflammatory pathway regulatory factors: nuclear factor-κ-gene binding (NF-κB) p65 and protein kinase B (Akt1). Among them, IL-6 was also significantly increased in the HHcy group. Both oxidative stress and inflammation contributed to the arterial injury of hypertension associated with HHcy, and inflammation mechanism might play a leading role in HHcy aggravating arterial injury, at least partially through the Akt1/NF-κB p65/IL-6 signaling pathway.

The Efficacy of HGF/VEGF Gene Therapy for Limb Ischemia in Mice with Impaired Glucose Tolerance: Shift from Angiogenesis to Axonal Growth and Oxidative Potential in Skeletal Muscle

BACKGROUND

Combined non-viral gene therapy (GT) of ischemia and cardiovascular disease is a promising tool for potential clinical translation. In previous studies our group has developed combined gene therapy by vascular endothelial growth factor 165 (VEGF165) + hepatocyte growth factor (HGF). Our recent works have demonstrated that a bicistronic pDNA that carries both human HGF and VEGF165 coding sequences has a potential for clinical application in peripheral artery disease (PAD). The present study aimed to test HGF/VEGF combined plasmid efficacy in ischemic skeletal muscle comorbid with predominant complications of PAD-impaired glucose tolerance and type 2 diabetes mellitus (T2DM).

METHODS

Male C57BL mice were housed on low-fat (LFD) or high-fat diet (HFD) for 10 weeks and metabolic parameters including FBG level, ITT, and GTT were evaluated. Hindlimb ischemia induction and plasmid administration were performed at 10 weeks with 3 weeks for post-surgical follow-up. Limb blood flow was assessed by laser Doppler scanning at 7, 14, and 21 days after ischemia induction. The necrotic area of m.tibialis anterior, macrophage infiltration, angio- and neuritogenesis were evaluated in tissue sections. The mitochondrial status of skeletal muscle (total mitochondria content, ETC proteins content) was assessed by Western blotting of muscle lysates.

RESULTS

At 10 weeks, the HFD group demonstrated impaired glucose tolerance in comparison with the LFD group. HGF/VEGF plasmid injection aggravated glucose intolerance in HFD conditions. Blood flow recovery was not changed by HGF/VEGF plasmid injection either in LFD or HFD conditions. GT in LFD, but not in HFD conditions, enlarged the necrotic area and CD68+ cells infiltration. However, HGF/VEGF plasmid enhanced neuritogenesis and enlarged NF200+ area on muscle sections. In HFD conditions, HGF/VEGF plasmid injection significantly increased mitochondria content and ETC proteins content.

CONCLUSIONS

The current study demonstrated a significant role of dietary conditions in pre-clinical testing of non-viral GT drugs. HGF/VEGF combined plasmid demonstrated a novel aspect of potential participation in ischemic skeletal muscle regeneration, through regulation of innervation and bioenergetics of muscle. The obtained results made HGF/VEGF combined plasmid a very promising tool for PAD therapy in impaired glucose tolerance conditions.

The protective mechanism of folic acid on hyperhomocysteinemia-related arterial injury in spontaneously hypertensive rats: Folic acid against arterial inflammation

BACKGROUND

Hypertension associated with hyperhomocysteinemia (HHcy) is correlated with a high risk of vascular diseases. Studies found that folic acid (FA) supplementation can reduce the risk of cardiovascular and cerebrovascular events. The aim of the present study was to explore the potential mechanisms of FA attenuating HHcy-related arterial injury in spontaneously hypertensive rats (SHRs).

METHODS

24 SHRs were randomized into the control group, the HHcy group, and the HHcy + FA group (8 per group). The SHRs in the HHcy group and the HHcy + FA group were given DL-Hcy intraperitoneally to mimic hypertension associated with HHcy. The SHRs in the HHcy + FA group were given FA by gavage to mimic an FA-fortified diet. The histopathology and immunohistochemistry of rat aorta and carotid artery were analyzed, and the relative expression levels of immune/inflammation and oxidative stress molecules in arterial tissue were detected by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot.

RESULTS

FA significantly reduced the expression levels of nuclear factor-κ-gene binding (NF-κB) p65/Rela and interleukin-6 (IL-6) in rat arterial tissues, as well as the levels of plasma HHcy and serum malondialdehyde (MDA) in hypertension associated with HHcy rats (p < 0.05). At the same time, FA significantly increased the serum superoxide dismutase (SOD) level in hypertension associated with HHcy rats, and even the SOD level of the HHcy + FA group was higher than that of the control group (p < 0.05). However, HHcy induced the opposite results of the above indicators in SHRs compared with the control group (p < 0.05).

CONCLUSIONS

The arterial protection mechanisms of FA are related to reducing the concentration of HHcy to eliminate the tissue toxicity of HHcy, inhibiting NF-κBp65/Rela/IL-6 pathway molecules to regulate inflammatory response, and promoting the potential anti-oxidative stress pathway molecules to reduce oxidative stress level.

Human placental mesenchymal stromal cell therapy restores the cytokine efflux and insulin signaling in the skeletal muscle of obesity-induced type 2 diabetes rat model

Obesity poses a significant risk factor for the onset of metabolic syndrome with allied complications, wherein mesenchymal stem cell therapy is seen as a promising treatment for obesity-induced metabolic syndrome. In the present study, we aim to explore the beneficial effects of the human placental mesenchymal stromal cells (P-MSCs) on obesity-associated insulin resistance (IR) including inflammation. To understand this, we have analyzed the peripheral blood glucose, serum insulin levels by ELISA, and the glucose uptake capacity of skeletal muscle by a 2-NBDG assay using flow cytometry in WNIN/GR-Ob rats treated with and without P-MSCs. Also, we have studied insulin signaling and cytokine profile in the skeletal muscle by western blotting, dot blotting, and Multiplex-ELISA techniques. The skeletal muscle of WNIN/GR-Ob rats demonstrates dysregulation of cytokines, altered glucose uptake vis-a-vis insulin signaling. However, P-MSCs' treatment was effective in WNIN/GR-Ob rats as compared to its control, to restore HOMA-IR, re-establishes dysregulated cytokines and PI3K-Akt pathway in addition to enhanced Glut4 expression and glucose uptake studied in skeletal muscle. Overall, our data advocate the beneficial effects of P-MSCs to ameliorate inflammatory milieu, improve insulin sensitivity, and normalize glucose homeostasis underlining the Ob-T2D conditions, and we attribute for immunomodulatory, paracrine, autocrine, and multipotent functions of P-MSCs.

Effect of Chinese herbal medicines on the overall survival of patients with muscular dystrophies in Taiwan

ETHNOPHARMACOLOGICAL RELEVANCE

Muscular dystrophies are a rare, severe, and genetically inherited group of disorders characterized by progressive loss of muscle fibers, leading to muscle weakness. The current treatment plan for muscular dystrophies includes the use of steroids to slow muscle deterioration by dampening the inflammatory response.

AIM OF THE STUDY

Chinese herbal medicine (CHM) has been offered as an adjunctive therapy in Taiwan's medical healthcare plan, making it possible to track CHM usage in patients with muscular dystrophic disease. Therefore, we explored the long-term effects of CHM use on the overall mortality of patients with muscular dystrophies.

MATERIALS AND METHODS

A total of 581 patients with muscular dystrophies were identified from the database of Registry for Catastrophic Illness Patients in Taiwan. Among them, 80 and 201 patients were CHM users and non-CHM users, respectively. Student's t-test, chi-squared test, Cox proportional hazard model, and Kaplan-Meier curve (log-rank test) were used for evaluation. Association rules and network analyses were performed to explore the combination of CHMs used in muscular dystrophies.

RESULTS

Compared to non-CHM users, there were more female patients, more comorbidities, including chronic pulmonary disease and peptic ulcer disease in the CHM user group. Patients with prednisolone usage exhibited a lower risk of overall mortality than those who did not, after adjusting for age, sex, use of CHM, and comorbidities. CHM users showed a lower risk of overall mortality after adjusting for age, sex, prednisolone use, and comorbidities. The cumulative incidence of the overall survival was significantly higher in CHM users. Association rule and network analysis showed that one main CHM cluster was commonly used to treat patients with muscular dystrophies in Taiwan. The cluster includes Yin-Qiao-San, Ban-Xia-Bai-Zhu-Tian-Ma-Tang, Zhi-Ke (Citrus aurantium L.), Yu-Xing-Cao (Houttuynia cordata Thunb.), Che-Qian-Zi (Plantago asiatica L.), and Da-Huang (Rheum palmatum L.).

CONCLUSIONS

Our data suggest that adjunctive therapy with CHM may help to reduce the overall mortality among patients with muscular dystrophies. The identification of the CHM cluster allows us to narrow down the key active compounds and may enable future therapeutic developments and clinical trial designs to improve overall survival in these patients.

Folate Reverses NF-κB p65/Rela/IL-6 Level Induced by Hyperhomocysteinemia in Spontaneously Hypertensive Rats

Hyperhomocysteinemia (HHcy) is derived from the abnormal metabolism of homocysteine (Hcy) and is related to metabolic-related diseases. In addition, HHcy combined with hypertension increases the risk of cardiovascular diseases (CVD). However, the mechanism of HHcy aggravating hypertensive arterial damage and the efficacy of folate (FA) as a beneficial supplement have not been fully elucidated. In this study, we established a rat HHcy model and a hypertension combined with HHcy model. Rat tail artery blood pressure (BP), plasma Hcy, serum superoxide dismutase (SOD), and malondialdehyde (MDA) were measured. Rat thoracic aorta was for pathological analysis after 12 weeks of the experiment. The relative expression levels of oxidative stress and immune/inflammation in rat arterial tissues were detected by quantitative real-time polymerase chain reaction (qRT-PCR) and western blotting. The results demonstrated that the relative expression levels of oxidative stress and immune/inflammation were the highest in the hypertension combined with HHcy group, followed by the hypertension group. Compared with the hypertension group, the hypertension combined with HHcy group up-regulated the expression levels of interleukin-6 (IL-6) and nuclear factor-κ-gene binding (NF-κB) p65/Rela, but not NADPH oxidase (Nox). Furthermore, folate inhibited the expression of IL-6 and NF-κB p65/Rela, reduced the levels of MDA and HHcy, but significantly increased the SOD level. In conclusion, HHcy synergistically aggravated the arterial damage factor of hypertension through immune/inflammatory response. However, folate demonstrated anti-inflammatory properties and reversed the NF-κB p65/Rela/IL-6 level induced by HHcy in hypertensive rats.

Combined gene therapy via VEGF and mini-dystrophin synergistically improves pathologies in temporalis muscle of dystrophin/utrophin double knockout mice

Duchenne muscular dystrophy (DMD) is a severe X-linked inherited muscular disorder characterized by the loss of dystrophin. We have previously shown that monogene therapy using the mini-dystrophin gene improves muscle function in DMD. However, chronic inflammation plays an important role in progressive muscle degeneration in DMD as well. Vascular endothelial growth factor (VEGF) has been used to enhance muscle vasculature, reduce local inflammation and improve DMD muscle function. Temporalis muscles are the key skeletal muscles for mastication and loss of their function negatively affects DMD patient quality of life by reducing nutritional intake, but little is known about the pathology and treatment of the temporalis muscle in DMD. In this work, we tested the hypothesis that the combined delivery of the human mini-dystrophin and human VEGF genes to the temporalis muscles using separate recombinant adeno-associated viral (rAAV) vectors will synergistically improve muscle function and pathology in adult male dystrophin/utrophin double-knockout (mdx/utrn+/-) mice. The experimental mice were divided into four groups including: dystrophin + VEGF combined, dystrophin only, VEGF only and PBS control. After 2 months, gene expression and histological analysis of the temporalis muscles showed a synergistic improvement in temporalis muscle pathology and function coincident with increased restoration of dystrophin-associated protein complexes and nNOS in the dystrophin + VEGF combined group. We also observed significantly reduced inflammatory cell infiltration, central nucleation, and fibrosis in the dystrophin + VEGF combined group. We have demonstrated the efficacy of combined rAAV-mediated dystrophin and VEGF treatment of temporalis muscles in a DMD mouse model.

Muscle Precursor Cells Enhance Functional Muscle Recovery and Show Synergistic Effects With Postinjury Treadmill Exercise in a Muscle Injury Model in Rats

BACKGROUND

Skeletal muscle injuries represent a major concern in sports medicine. Cell therapy has emerged as a promising therapeutic strategy for muscle injuries, although the preclinical data are still inconclusive and the potential clinical use of cell therapy has not yet been established.

PURPOSE

To evaluate the effects of muscle precursor cells (MPCs) on muscle healing in a small animal model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 27 rats were used in the study. MPCs were isolated from rat (n = 3) medial gastrocnemius muscles and expanded in primary culture. Skeletal muscle injury was induced in 24 rats, and the animals were assigned to 3 groups. At 36 hours after injury, animals received treatment based on a single ultrasound-guided MPC (10⁵ cells) injection (Cells group) or MPC injection in combination with 2 weeks of daily exercise training (Cells+Exercise group). Animals receiving intramuscular vehicle injection were used as controls (Vehicle group). Muscle force was determined 2 weeks after muscle injury, and muscles were collected for histological and immunofluorescence evaluation.

RESULTS

Red fluorescence-labeled MPCs were successfully transplanted in the site of the injury by ultrasound-guided injection and were localized in the injured area after 2 weeks. Transplanted MPCs participated in the formation of regenerating muscle fibers as corroborated by the co-localization of red fluorescence with developmental myosin heavy chain (dMHC)-positive myofibers by immunofluorescence analysis. A strong beneficial effect on muscle force recovery was detected in the Cells and Cells+Exercise groups (102.6% ± 4.0% and 101.5% ± 8.5% of maximum tetanus force of the injured vs healthy contralateral muscle, respectively) compared with the Vehicle group (78.2% ± 5.1%). Both Cells and Cells+Exercise treatments stimulated the growth of newly formed regenerating muscles fibers, as determined by the increase in myofiber cross-sectional area (612.3 ± 21.4 µm² and 686.0 ± 11.6 µm², respectively) compared with the Vehicle group (247.5 ± 10.7 µm²), which was accompanied by a significant reduction of intramuscular fibrosis in Cells and Cells+Exercise treated animals (24.2% ± 1.3% and 26.0% ± 1.9% of collagen type I deposition, respectively) with respect to control animals (40.9% ± 4.1% in the Vehicle group). MPC treatment induced a robust acceleration of the muscle healing process as demonstrated by the decreased number of dMHC-positive regenerating myofibers (enhanced replacement of developmental myosin isoform by mature myosin isoforms) (4.3% ± 2.6% and 4.1% ± 1.5% in the Cells and Cells+Exercise groups, respectively) compared with the Vehicle group (14.8% ± 13.9%).

CONCLUSION

Single intramuscular administration of MPCs improved histological outcome and force recovery of the injured skeletal muscle in a rat injury model that imitates sports-related muscle injuries. Cell therapy showed a synergistic effect when combined with an early active rehabilitation protocol in rats, which suggests that a combination of treatments can generate novel therapeutic strategies for the treatment of human skeletal muscle injuries.

CLINICAL RELEVANCE

Our study demonstrates the strong beneficial effect of MPC transplant and the synergistic effect when the cell therapy is combined with an early active rehabilitation protocol for muscle recovery in rats; this finding opens new avenues for the development of effective therapeutic strategies for muscle healing and clinical trials in athletes undergoing MPC transplant and rehabilitation protocols.

Overfeeding and Substrate Availability, But Not Age or BMI, Alter Human Satellite Cell Function

Satellite cells (SC) aid skeletal muscle growth and regeneration. SC-mediated skeletal muscle repair can both be influenced by and exacerbate several diseases linked to a fatty diet, obesity, and aging. The purpose of this study was to evaluate the effects of different lifestyle factors on SC function, including body mass index (BMI), age, and high-fat overfeeding. For this study, SCs were isolated from the vastus lateralis of sedentary young (18–30 years) and sedentary older (60–80 years) men with varying BMIs (18–32 kg/m²), as well as young sedentary men before and after four weeks of overfeeding (OVF) (55% fat/ + 1000 kcal, n = 4). The isolated SCs were then treated in vitro with a control (5 mM glucose, 10% fetal bovine serum (FBS)) or a high substrate growth media (HSM) (10% FBS, 25 mM glucose, and 400 μM 2:1 oleate–palmitate). Cells were assessed on their ability to proliferate, differentiate, and fuel substrate oxidation after differentiation. The effect of HSM was measured as the percentage difference between SCs exposed to HSM compared to control media. In vitro SC function was not affected by donor age. OVF reduced SC proliferation rates (–19% p < 0.05) but did not influence differentiation. Cellular proliferation in response to HSM was correlated to the donor’s body mass index (BMI) (r² = 0.6121, p < 0.01). When exposed to HSM, SCs from normal weight (BMI 18–25 kg/m²) participants exhibited reduced proliferation and fusion rates with increased fatty-acid oxidation (p < 0.05), while SCs from participants with higher BMIs (BMI 25–32 kg/m²) demonstrated enhanced proliferation in HSM. HSM reduced proliferation and fusion (p < 0.05) in SCs isolated from subjects before OVF, whereas HSM exposure accelerated proliferation and fusion in SCs collected following OVF. These results indicated that diet has a greater influence on SC function than age and BMI. Though age and BMI do not influence in vitro SC function when grown in controlled conditions, both factors influenced the response of SCs to substrate challenges, indicating age and BMI may mediate responses to diet.

Effects of ASC Application on Endplate Regeneration Upon Glycerol-Induced Muscle Damage

Amongst other approaches, adipose-derived stromal cells (ASCs) have recently been tested with respect to their regenerative capacity for treatment of neuromuscular disorders. While beneficial effects of ASCs on muscle recovery were observed previously, their impact on regeneration of neuromuscular junctions (NMJs) is unclear. Here, we used a murine glycerol damage model to study disruption and regeneration of NMJs and to evaluate the effects of systemic application of ASCs on muscle and NMJ recovery. In mice that were not treated with ASCs, a differential response of NMJ pre- and post-synapses to glycerol-induced damage was observed. While post-synapses were still present in regions that were necrotic and lacking actin and dystrophin, pre-synapses disappeared soon in those affected areas. Partial regeneration of NMJs occurred within 11 days after damage. ASC treatment slightly enhanced NMJ recovery and reduced the loss of presynaptic sites, but also led to a late phase of muscle necrosis and fibrosis. In summary, the results suggest a differential sensitivity of NMJ pre- and post-synapses to glycerol-induced muscle damage and that the use of ASC for the treatment of neuromuscular disorders needs further careful evaluation.

Tumor progression locus 2 (TPL2) in tumor-promoting Inflammation, Tumorigenesis and Tumor Immunity

Over the years, tumor progression locus 2 (TPL2) has been identified as an essential modulator of immune responses that conveys inflammatory signals to downstream effectors, subsequently modulating the generation and function of inflammatory cells. TPL2 is also differentially expressed and activated in several cancers, where it is associated with increased inflammation, malignant transformation, angiogenesis, metastasis, poor prognosis and therapy resistance. However, the relationship between TPL2-driven inflammation, tumorigenesis and tumor immunity has not been addressed. Here, we reconcile the function of TPL2-driven inflammation to oncogenic functions such as inflammation, proliferation, apoptosis resistance, angiogenesis, metastasis, immunosuppression and immune evasion. We also address the controversies reported on TPL2 function in tumor-promoting inflammation and tumorigenesis, and highlight the potential role of the TPL2 adaptor function in regulating the mechanisms leading to pro-tumorigenic inflammation and tumor progression. We discuss the therapeutic implications and limitations of targeting TPL2 for cancer treatment. The ideas presented here provide some new insight into cancer pathophysiology that might contribute to the development of more integrative and specific anti-inflammatory and anti-cancer therapeutics.

MET receptor in oncology: From biomarker to therapeutic target

First discovered in the 1984, the MET receptor tyrosine kinase (RTK) and its ligand hepatocyte growth factor or HGF (also known as scatter factor or SF) are implicated as key players in tumor cell migration, proliferation, and invasion in a variety of cancers. This pathway also plays a key role during embryogenesis in the development of muscular and nervous structures. High expression of the MET receptor has been shown to correlate with poor prognosis and resistance to therapy. MET exon 14 splicing variants, initially identified by us in lung cancer, is actionable through various tyrosine kinase inhibitors (TKIs). For this reason, this pathway is of interest as a therapeutic target. In this chapter we will be discussing the history of MET, the genetics of this RTK, and give some background on the receptor biology. Furthermore, we will discuss directed therapeutics, mechanisms of resistance, and the future of MET as a therapeutic target.

Canonical NF-κB signaling regulates satellite stem cell homeostasis and function during regenerative myogenesis

Skeletal muscle regeneration in adults is attributed to the presence of satellite stem cells that proliferate, differentiate, and eventually fuse with injured myofibers. However, the signaling mechanisms that regulate satellite cell homeostasis and function remain less understood. While IKKβ-mediated canonical NF-κB signaling has been implicated in the regulation of myogenesis and skeletal muscle mass, its role in the regulation of satellite cell function during muscle regeneration has not been fully elucidated. Here, we report that canonical NF-κB signaling is induced in skeletal muscle upon injury. Satellite cell-specific inducible ablation of IKKβ attenuates skeletal muscle regeneration in adult mice. Targeted ablation of IKKβ also reduces the number of satellite cells in injured skeletal muscle of adult mice, potentially through inhibiting their proliferation and survival. We also demonstrate that the inhibition of specific components of the canonical NF-κB pathway causes precocious differentiation of cultured satellite cells both ex vivo and in vitro. Finally, our results highlight that the constitutive activation of canonical NF-κB signaling in satellite cells also attenuates skeletal muscle regeneration following injury in adult mice. Collectively, our study demonstrates that the proper regulation of canonical NF-κB signaling is important for the regeneration of adult skeletal muscle.

Impaired Regeneration in Dystrophic Muscle-New Target for Therapy

Muscle stem cells (MuSCs), known as satellite cells (SCs) have an incredible ability to regenerate, which enables the maintenance and growth of muscle tissue. In response to damaging stimuli, SCs are activated, proliferate, differentiate, and fuse to repair or generate a new muscle fiber. However, dystrophic muscles are characterized by poor muscle regeneration along with chronic inflammation and fibrosis. Indications for SC involvement in muscular dystrophy pathologies are accumulating, but their contribution to muscle pathophysiology is not precisely understood. In congenital muscular dystrophy type 1A (LAMA2-CMD), mutations in Lama2 gene cause either complete or partial absence in laminin-211 protein. Laminin-211 functions as a link between muscle extracellular matrix (ECM) and two adhesion systems in the sarcolemma; one is the well-known dystrophin-glycoprotein complex (DGC), and the second is the integrin complex. Because of its protein interactions and location, laminin-211 has a crucial role in muscle function and survival by maintaining sarcolemma integrity. In addition, laminin-211 is expressed in SCs and suggested to have a role in SC proliferation and differentiation. Downstream to the primary defect in laminin-211, several secondary genes and pathways accelerate disease mechanism, while at the same time there are unsuccessful attempts to regenerate as compensation for the dystrophic process. Lately, next-generation sequencing platforms have advanced our knowledge about the secondary events occurring in various diseases, elucidate the pathophysiology, and characterize new essential targets for development of new treatment strategies. This review will mainly focus on SC contribution to impaired regeneration in muscular dystrophies and specifically new findings suggesting SC involvement in LAMA2-CMD pathology.

EGFR-TKI resistance promotes immune escape in lung cancer via increased PD-L1 expression

BACKGROUND

The ATLANTIC trial reported that higher PD-L1 expression in tumors was involved in a higher objective response in patients with EGFR⁺/ALK⁺ non-small cell lung cancer (NSCLC), indicating the possibility of anti-PD-1/PD-L1 therapy as a third-line (or later) treatment for advanced NSCLC. Therefore, the determination of status and regulatory mechanisms of PD-L1 in EGFR mutant NSCLC before and after acquired EGFR-TKIs resistance are meaningful.

METHODS

The correlation among PD-L1, c-MET, and HGF was analyzed based on TCGA datasheets and paired NSCLC specimens before and after acquired EGFR-TKI resistance. EGFR-TKI resistant NSCLC cells with three well-known mechanisms, c-MET amplification, hepatocyte growth factor (HGF), and EGFR-T790M, were investigated to determinate PD-L1 expression status and immune escape ability. PD-L1-deleted EGFR-TKIs sensitive and resistant cells were used to evaluate the immune escape ability of tumors in mice xenograft models.

RESULTS

Positive correlations were found among PD-L1, c-MET, and HGF, based on TCGA datasheets and paired NSCLC specimens. Moreover, the above three resistant mechanisms increased PD-L1 expression and attenuated activation and cytotoxicity of lymphocytes in vitro and in vivo, and downregulation of PD-L1 partially restored the cytotoxicity of lymphocytes. Both MAPK and PI3K pathways were involved in the three types of resistance mechanism-induced PD-L1 overexpression, whereas the NF-kappa B pathway was only involved in T790M-induced PD-L1 expression.

CONCLUSIONS

HGF, MET-amplification, and EGFR-T790M upregulate PD-L1 expression in NSCLC and promote the immune escape of tumor cells through different mechanisms.

Impact of co-blocking the costimulatory signals on immune-related genes after high-risk rabbit corneal allograft using 2nd-generation DNA sequencing technology

The aim of this study was to evaluate the impact and mechanism of co-blocking of costimulatory signals CD28-B7-CD40-CD40L during immune allograft rejection. Forty-eight recipient rabbits were prepared as a high-risk corneal allograft model. After surgery, the animals were randomly divided into: control group, MR1 group, anti-B7 group, and co-blocking group (n=12, each group). Subconjunctival injection was first performed on the allograft surgery day until post-surgery day five. Four weeks later, or when immune rejection occurred, the cornea was sampled to detect and analyze the gene spectrum. The survival time in the co-blocking group was significantly longer than that in the other three groups (p < 0.05). Gene expression analysis revealed that the expression of genes associated with immune rejection, interleukin (IL)-1α, IL-1β, intercellular cell adhesion molecule-1, and IL-2 was down-regulated in the co-blocking group, while IL-10 was up-regulated, but the changes in nuclear factor-κB and interferon-γ were not significant. In conclusion, the co-blocking of costimulatory signals can significantly reduce genes that promote corneal allograft rejection. The inhibition of corneal allograft rejection gene expression was significantly enhanced. These gene expression results can explain the conclusion of previous work at the genetic level.

HGF Reduces Disease Severity and Inflammation by Attenuating the NF-κB Signaling in a Rat Model of Pulmonary Artery Hypertension

The purpose of the present study was to investigate the anti-inflammatory effect of hepatocyte growth factor (HGF) on pulmonary artery hypertension (PAH) in a rat model and underlying mechanisms. Wistar rats were treated with monocrotaline intravenously to induce PAH and then treated with vehicle or HGF for 2 weeks, respectively. The mean pulmonary artery pressure (mPAP), the index of right heart ventricular hypertrophy (RHVI), pathological changes, and inflammation in the lungs of individual rats were measured. The levels of serum inflammatory interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), intercellular adhesion molecule-1 (ICAM-1), and high mobility group protein B1 (HMGB1) and the relative levels of IκBα and NF-κB p65 expression in the lungs of individual rats were determined by methods of enzyme-linked immunosorbent assay (ELISA) and Western blot. The levels of mPAP and RVHI in the HGF group were significantly lower than that in the PAH group (P < 0.05), but remained significantly higher than that of the control group (P < 0.05). Similar patterns of inflammatory scores and the levels of serum IL-6, TNF-α, ICAM-1, and HMGB1 were detected among the different groups of rats. Furthermore, the relative levels of IκBα expression in the lungs of the HGF group of rats were significantly higher than that in the control group, which were significantly higher than that in the PAH group. In contrast, the relative levels of NF-kB p65 expression in the HGF group were significantly lower than that in the PAH group (P < 0.05). HGF treatment significantly mitigated the severity of PAH and inhibited inflammation by attenuating the NF-kB signaling in the lungs of PAH rats.

Nuclear factor-kappa B influences early phase of compensatory lung growth after pneumonectomy in mice

Background

Compensatory lung growth (CLG) is a well-established lung regeneration model. However, the sequential mechanisms, including unknown molecular triggers or regulators, remain unclear. Nuclear factor- kappa B (NF-κB) is known to be essential for inflammation and tissue regeneration; therefore, we investigated the role of NF-κB in CLG.

Methods

C57BL/6 J mice underwent either a left pneumonectomy or a thoracotomy (n = 77). Gene microarray analysis was performed to detect genes that were upregulated at 12 h after pneumonectomy. NF-κB protein expression was examined by immunohistochemistry and Western blot. To investigate the influence of NF-κB on CLG, either an NF-κB inhibitor SN50 or saline was administered following pneumonectomy and the degree of CLG was evaluated in each group by measuring the lung dry weight index (LDWI) and the mean linear intercept.

Results

Gene microarray analysis identified 11 genes that were significantly but transiently increased at 12 h after pneumonectomy. Among the 11 genes, NF-κB was selected based on its reported functions. Western blot analysis showed that NF-κB protein expression after pneumonectomy was significantly higher at 12 h compared to 48 h. Additionally, NF-κB protein expression at 12 h after pneumonectomy was significantly higher than at both 12 and 48 h after thoracotomy (p < 0.029 for all). NF-κB protein expression, evaluated through immunohistochemistry, was expressed mainly in type 2 alveolar epithelial cells and was significant increased 12 h after pneumonectomy compared to 48 h after pneumonectomy and both 12 and 48 h after thoracotomy (p < 0.001 for all). SN50 administration following pneumonectomy induced a significant decrease in NF-κB expression (p = 0.004) and LDWI compared to the vehicle administration (p = 0.009).

Conclusions

This is the first report demonstrating that NF-κB signaling may play a key role in CLG. Given its pathway is crucial in tissue regeneration of various organs, NF-κB may shed light on identification of molecular triggers or clinically usable key regulators of CLG.

Implantation of healthy matrix-embedded endothelial cells rescues dysfunctional endothelium and ischaemic tissue in liver engraftment

OBJECTIVE

Liver transplantation is limited by ischaemic injury which promotes endothelial cell and hepatocyte dysfunction and eventually organ failure. We sought to understand how endothelial state determines liver recovery after hepatectomy and engraftment.

DESIGN

Matrix-embedded endothelial cells (MEECs) with retained healthy phenotype or control acellular matrices were implanted in direct contact with the remaining median lobe of donor mice undergoing partial hepatectomy (70%), or in the interface between the remaining median lobe and an autograft or isograft from the left lobe in hepatectomised recipient mice. Hepatic vascular architecture, DNA fragmentation and apoptosis in the median lobe and grafts, serum markers of liver damage and phenotype of macrophage and lymphocyte subsets in the liver after engraftment were analysed 7 days post-op.

RESULTS

Healthy MEECs create a functional vascular splice in donor and recipient liver after 70% hepatectomy in mouse protecting these livers from ischaemic injury, hepatic congestion and inflammation. Macrophages recruited adjacent to the vascular nodes into the implants switched to an anti-inflammatory and regenerative profile M2. MEECs improved liver function and the rate of liver regeneration and prevented apoptosis in donor liver lobes, autologous grafts and syngeneic engraftment.

CONCLUSIONS

Implants with healthy endothelial cells rescue liver donor and recipient endothelium and parenchyma from ischaemic injury after major hepatectomy and engraftment. This study highlights endothelial-hepatocyte crosstalk in hepatic repair and provides a promising new approach to improve regenerative medicine outcomes and liver transplantation.

Inhibition of NF-κB improves the stress resistance and myogenic differentiation of MDSPCs isolated from naturally aged mice

A decline in the regenerative capacity of adult stem cells with aging is well documented. As a result of this decline, the efficacy of autologous stem cell therapies is likely to decline with increasing donor age. In these cases, strategies to restore the function of aged stem cells would have clinical utility. Globally, the transcription factor NF-κB is up-regulated in aged tissues. Given the negative role that NF-κB plays in myogenesis, we investigated whether the age-related decline in the function of muscle-derived stem/progenitor cells (MDSPCs) could be improved by inhibition of NF-κB. Herein, we demonstrate that pharmacologic or genetic inhibition of NF-κB activation increases myogenic differentiation and improves resistance to oxidative stress. Our results suggest that MDSPC “aging” may be reversible, and that pharmacologic targeting of pathways such as NF-κB may enhance the efficacy of cell-based therapies.

Defining the Balance between Regeneration and Pathological Ossification in Skeletal Muscle Following Traumatic Injury

Heterotopic ossification (HO) is characterized by the formation of bone at atypical sites. This type of ectopic bone formation is most prominent in skeletal muscle, most frequently resulting as a consequence of physical trauma and associated with aberrant tissue regeneration. The condition is debilitating, reducing a patient's range of motion and potentially causing severe pathologies resulting from nerve and vascular compression. Despite efforts to understand the pathological processes governing HO, there remains a lack of consensus regarding the micro-environmental conditions conducive to its formation, and attempting to define the balance between muscle regeneration and pathological ossification remains complex. The development of HO is thought to be related to a complex interplay between factors released both locally and systemically in response to trauma. It develops as skeletal muscle undergoes significant repair and regeneration, and is likely to result from the misdirected differentiation of endogenous or systemically derived progenitors in response to biochemical and/or environmental cues. The process can be sequentially delineated by the presence of inflammation, tissue breakdown, adipogenesis, hypoxia, neo-vasculogenesis, chondrogenesis and ossification. However, exactly how each of these stages contributes to the formation of HO is at present not well understood. Our previous review examined the cellular contribution to HO. Therefore, the principal aim of this review will be to comprehensively outline changes in the local tissue micro-environment following trauma, and identify how these changes can alter the balance between skeletal muscle regeneration and ectopic ossification. An understanding of the mechanisms governing this condition is required for the development and advancement of HO prophylaxis and treatment, and may even hold the key to unlocking novel methods for engineering hard tissues.

Muscle-specific microRNA-206 targets multiple components in dystrophic skeletal muscle representing beneficial adaptations

Over the last several years, converging lines of evidence have indicated that miR-206 plays a pivotal role in promoting muscle differentiation and regeneration, thereby potentially impacting positively on the progression of neuromuscular disorders, including Duchenne muscular dystrophy (DMD). Despite several studies showing the regulatory function of miR-206 on target mRNAs in skeletal muscle cells, the effects of overexpression of miR-206 in dystrophic muscles remain to be established. Here, we found that miR-206 overexpression in mdx mouse muscles simultaneously targets multiple mRNAs and proteins implicated in satellite cell differentiation, muscle regeneration, and at the neuromuscular junction. Overexpression of miR-206 also increased the levels of several muscle-specific mRNAs/proteins, while enhancing utrophin A expression at the sarcolemma. Finally, we also observed that the increased expression of miR-206 in dystrophin-deficient mouse muscle decreased the production of proinflammatory cytokines and infiltration of macrophages. Taken together, our results show that miR-206 acts as a pleiotropic regulator that targets multiple key mRNAs and proteins expected to provide beneficial adaptations in dystrophic muscle, thus highlighting its therapeutic potential for DMD.

Anti-inflammatory drugs for Duchenne muscular dystrophy: focus on skeletal muscle-releasing factors

Duchenne muscular dystrophy (DMD), an incurable and a progressive muscle wasting disease, is caused by the absence of dystrophin protein, leading to recurrent muscle fiber damage during contraction. The inflammatory response to fiber damage is a compelling candidate mechanism for disease exacerbation. The only established pharmacological treatment for DMD is corticosteroids to suppress muscle inflammation, however this treatment is limited by its insufficient therapeutic efficacy and considerable side effects. Recent reports show the therapeutic potential of inhibiting or enhancing pro- or anti-inflammatory factors released from DMD skeletal muscles, resulting in significant recovery from muscle atrophy and dysfunction. We discuss and review the recent findings of DMD inflammation and opportunities for drug development targeting specific releasing factors from skeletal muscles. It has been speculated that nonsteroidal anti-inflammatory drugs targeting specific inflammatory factors are more effective and have less side effects for DMD compared with steroidal drugs. For example, calcium channels, reactive oxygen species, and nuclear factor-κB signaling factors are the most promising targets as master regulators of inflammatory response in DMD skeletal muscles. If they are combined with an oligonucleotide-based exon skipping therapy to restore dystrophin expression, the anti-inflammatory drug therapies may address the present therapeutic limitation of low efficiency for DMD.

Muscle injuries and strategies for improving their repair

Satellite cells are tissue resident muscle stem cells required for postnatal skeletal muscle growth and repair through replacement of damaged myofibers. Muscle regeneration is coordinated through different mechanisms, which imply cell-cell and cell-matrix interactions as well as extracellular secreted factors. Cellular dynamics during muscle regeneration are highly complex. Immune, fibrotic, vascular and myogenic cells appear with distinct temporal and spatial kinetics after muscle injury. Three main phases have been identified in the process of muscle regeneration; a destruction phase with the initial inflammatory response, a regeneration phase with activation and proliferation of satellite cells and a remodeling phase with maturation of the regenerated myofibers. Whereas relatively minor muscle injuries, such as strains, heal spontaneously, severe muscle injuries form fibrotic tissue that impairs muscle function and lead to muscle contracture and chronic pain. Current therapeutic approaches have limited effectiveness and optimal strategies for such lesions are not known yet. Various strategies, including growth factors injections, transplantation of muscle stem cells in combination or not with biological scaffolds, anti-fibrotic therapies and mechanical stimulation, may become therapeutic alternatives to improve functional muscle recovery.

Hepatocyte growth factor and alternative splice variants - expression, regulation and implications in osteogenesis and bone health and repair

INTRODUCTION

Bone marrow-derived mesenchymal stem cells (MSCs) can differentiate into multiple cell types, including osteoblasts, chondrocytes, and adipocytes. These pluripotent cells secrete hepatocyte growth factor (HGF), which regulates cell growth, survival, motility, migration, mitogenesis and is important for tissue development/regeneration. HGF has four splice variants, NK1, NK2, NK3, and NK4 which have varying functions and affinities for the HGF receptor, cMET. HGF promotes osteoblastic differentiation of MSCs into bone forming cells, playing a role in bone development, health and repair.

AREAS COVERED

This review will focus on the effects of HGF in osteogenesis, bone repair and bone health, including structural and functional insights into the role of HGF in the body.

EXPERT OPINION

Approximately 6.2 million Americans experience a fracture annually, with 5-10% being mal- or non-union fractures. HGF is important in priming MSCs for osteogenic differentiation in vitro and is currently being studied to assess its role during bone repair in vivo. Due to the high turnover rate of systemic HGF, non-classic modes of HGF-treatment, including naked-plasmid HGF delivery and the use of HGF splice variants (NK1 & NK2) are being studied to find safe and efficacious treatments for bone disorders, such as mal- or non-union fractures.

Oxidative Stress-Mediated Skeletal Muscle Degeneration: Molecules, Mechanisms, and Therapies

Oxidative stress is a loss of balance between the production of reactive oxygen species during cellular metabolism and the mechanisms that clear these species to maintain cellular redox homeostasis. Increased oxidative stress has been associated with muscular dystrophy, and many studies have proposed mechanisms that bridge these two pathological conditions at the molecular level. In this review, the evidence indicating a causal role of oxidative stress in the pathogenesis of various muscular dystrophies is revisited. In particular, the mediation of cellular redox status in dystrophic muscle by NF-κB pathway, autophagy, telomere shortening, and epigenetic regulation are discussed. Lastly, the current stance of targeting these pathways using antioxidant therapies in preclinical and clinical trials is examined.

IKKβ acts as a tumor suppressor in cancer-associated fibroblasts during intestinal tumorigenesis

Pallangyo et al. report that fibroblast-specific IKKβ deletion in Col1a2Cre-ERT2 mice promotes AOM/DSS-induced intestinal tumorigenesis, suggesting a tumor suppressor role for this kinase. In contrast, a companion study by Koliaraki et al. based on IKKβ deletion in ColVI-expressing intestinal mesenchymal cells suggests a role for IKKβ in promoting intestinal tumorigenesis. The two studies raise the awareness that in the context of tumorigenesis, IKKβ/NF-κB may have distinct functions in different fibroblast subpopulations.

Cancer-associated fibroblasts (CAFs) comprise one of the most important cell types in the tumor microenvironment. A proinflammatory NF-κB gene signature in CAFs has been suggested to promote tumorigenesis in models of pancreatic and mammary skin cancer. Using an autochthonous model of colitis-associated cancer (CAC) and sporadic cancer, we now provide evidence for a tumor-suppressive function of IKKβ/NF-κB in CAFs. Fibroblast-restricted deletion of Ikkβ stimulates intestinal epithelial cell proliferation, suppresses tumor cell death, enhances accumulation of CD4⁺Foxp3⁺ regulatory T cells, and induces angiogenesis, ultimately promoting colonic tumor growth. In Ikkβ-deficient fibroblasts, transcription of negative regulators of TGFβ signaling, including Smad7 and Smurf1, is impaired, causing up-regulation of a TGFβ gene signature and elevated hepatocyte growth factor (HGF) secretion. Overexpression of Smad7 in Ikkβ-deficient fibroblasts prevents HGF secretion, and pharmacological inhibition of Met during the CAC model confirms that enhanced tumor promotion is dependent on HGF–Met signaling in mucosa of Ikkβ-mutant animals. Collectively, these results highlight an unexpected tumor suppressive function of IKKβ/NF-κB in CAFs linked to HGF release and raise potential concerns about the use of IKK inhibitors in colorectal cancer patients.

c-Met as a Target for Personalized Therapy

MET and its ligand HGF are involved in many biological processes, both physiological and pathological, making this signaling pathway an attractive therapeutic target in oncology. Downstream signaling effects are transmitted via mitogen-activated protein kinase (MAPK), PI3K (phosphoinositide 3-kinase protein kinase B)/AKT, signal transducer and activator of transcription proteins (STAT), and nuclear factor-κB. The final output of the terminal effector components of these pathways is activation of cytoplasmic and nuclear processes leading to increases in cell proliferation, survival, mobilization and invasive capacity. In addition to its role as an oncogenic driver, increasing evidence implicates MET as a common mechanism of resistance to targeted therapies including EGFR and VEGFR inhibitors. In the present review, we summarize the current knowledge on the role of the HGF-MET signaling pathway in cancer and its therapeutic targeting (HGF activation inhibitors, HGF inhibitors, MET antagonists and selective/nonselective MET kinase inhibitors). Recent advances in understanding the role of this pathway in the resistance to current anticancer strategies used in lung, kidney and pancreatic cancer are discussed.

c-Met as a Target for Personalized Therapy

MET and its ligand HGF are involved in many biological processes, both physiological and pathological, making this signaling pathway an attractive therapeutic target in oncology. Downstream signaling effects are transmitted via mitogen-activated protein kinase (MAPK), PI3K (phosphoinositide 3-kinase protein kinase B)/AKT, signal transducer and activator of transcription proteins (STAT), and nuclear factor-κB. The final output of the terminal effector components of these pathways is activation of cytoplasmic and nuclear processes leading to increases in cell proliferation, survival, mobilization and invasive capacity. In addition to its role as an oncogenic driver, increasing evidence implicates MET as a common mechanism of resistance to targeted therapies including EGFR and VEGFR inhibitors. In the present review, we summarize the current knowledge on the role of the HGF-MET signaling pathway in cancer and its therapeutic targeting (HGF activation inhibitors, HGF inhibitors, MET antagonists and selective/nonselective MET kinase inhibitors). Recent advances in understanding the role of this pathway in the resistance to current anticancer strategies used in lung, kidney and pancreatic cancer are discussed.

The interplay between inflammation and metabolism in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by extensive synovitis resulting in erosions of articular cartilage and marginal bone that lead to joint destruction. The autoimmune process in RA depends on the activation of immune cells, which use intracellular kinases to respond to external stimuli such as cytokines, immune complexes, and antigens. An intricate cytokine network participates in inflammation and in perpetuation of disease by positive feedback loops promoting systemic disorder. The widespread systemic effects mediated by pro-inflammatory cytokines in RA impact on metabolism and in particular in lymphocyte metabolism. Moreover, RA pathobiology seems to share some common pathways with atherosclerosis, including endothelial dysfunction that is related to underlying chronic inflammation. The extent of the metabolic changes and the types of metabolites seen may be good markers of cytokine-mediated inflammatory processes in RA. Altered metabolic fingerprints may be useful in predicting the development of RA in patients with early arthritis as well as in the evaluation of the treatment response. Evidence supports the role of metabolomic analysis as a novel and nontargeted approach for identifying potential biomarkers and for improving the clinical and therapeutical management of patients with chronic inflammatory diseases. Here, we review the metabolic changes occurring in the pathogenesis of RA as well as the implication of the metabolic features in the treatment response.