Skeletal Muscle Fibrosis Research Articles

Reduced mitochondrial translation prevents diet-induced metabolic dysfunction but not inflammation.

The contribution of dysregulated mitochondrial gene expression and consequent imbalance in biogenesis is not well understood in metabolic disorders such as insulin resistance and obesity. The ribosomal RNA maturation protein PTCD1 is essential for mitochondrial protein synthesis and its reduction causes adult-onset obesity and liver steatosis. We used haploinsufficient Ptcd1 mice fed normal or high fat diets to understand how changes in mitochondrial biogenesis can lead to metabolic dysfunction. We show that Akt-stimulated reduction in lipid content and upregulation of mitochondrial biogenesis effectively protected mice with reduced mitochondrial protein synthesis from excessive weight gain on a high fat diet, resulting in improved glucose and insulin tolerance and reduced lipid accumulation in the liver. However, inflammation of the white adipose tissue and early signs of fibrosis in skeletal muscle, as a consequence of reduced protein synthesis, were exacerbated with the high fat diet. We identify that reduced mitochondrial protein synthesis and OXPHOS biogenesis can be recovered in a tissue-specific manner via Akt-mediated increase in insulin sensitivity and transcriptional activation of the mitochondrial stress response.

Influence of Platelet Rich Plasma on the Skeletal Muscle Fibrosis after Limb Lengthening in Mice

Category:Basic Sciences/BiologicsIntroduction/Purpose:Skeletal muscle fibrosis induced by the increase of collagen occurs after limb lengthening which is also called distraction osteogenesis. Although there are studies about influence of platelet rich plasma (PRP) on tissues healing process, its effectiveness is still controversial. The aim of this study was to examine whether PRP decreased the skeletal muscle fibrosis induced by limb lengthening.Methods:Tibial osteotomy was done to 8-week-old wild type mice. Tibia was lengthened at a rate of 0.42 mm/day during 2 weeks, launching 1 week after tibial osteotomy. Just after lengthening completed (3 weeks after tibial osteotomy), PRP was injected into the gastrocnemius muscle (PRP group). As a sham group, phosphate buffered saline (PBS) was injected into the gastrocnemius muscle (non-PRP group). The gastrocnemius (GC) muscles were taken and analyzed at 4, 6, 8 and 10 weeks after tibial osteotomy.Results:The fibrotic area of the GC muscles in the both groups increased at 4 weeks after tibial osteotomy in histological analysis (Figure). Then, it gradually decreased at 6, 8, and 10 weeks after tibial osteotomy. There were no significant differences between the both groups at 6, 8, and 10 weeks after tibial osteotomy. Hydroxyproline, which was a major constituent of collagen, increased in the non-PRP and PRP groups by limb lengthening as well. However, significant changes were not found between the both groups at all any points.Conclusion:At first, we anticipated that PRP should reduce the skeletal muscle fibrosis after limb lengthening significantly. But our results implied that PRP did not decrease the skeletal muscle fibrosis induced by limb lengthening.

Fast repetitive stretch suppresses denervation-induced muscle fibrosis.

We aimed to examine the influence of different speeds of stretching on denervation-induced skeletal muscle fibrosis. Stretching was passively applied to rat plantaris muscle denervated by sciatic nerve excision in three different cycles of 0.5, 3, or 12 cycles/min, for 20 min/d for 2 weeks. Gene analysis results showed greater expression of fibrosis-related factors with fast stretching compared with non-stretched muscle. Laser Doppler blood flow analysis indicated reduced intramuscular blood flow during stretching. Histological analysis demonstrated fibrotic area decreases in 12 cycles/min stretched muscle compared with non-stretched muscle. Slower stretching induced greater mRNA expression of collagen and fibroblasts and greater decrement of blood flow. Histologically, faster stretching suppressed fibrosis. These results suggest that fast repetitive stretching of denervated muscle might suppress processes of muscle fibrosis.

T. gondii infection induces IL-1R dependent chronic cachexia and perivascular fibrosis in the liver and skeletal muscle

Cachexia is a progressive muscle wasting disease that contributes to death in a wide range of chronic diseases. Currently, the cachexia field lacks animal models that recapitulate the long-term kinetics of clinical disease, which would provide insight into the pathophysiology of chronic cachexia and a tool to test therapeutics for disease reversal. Toxoplasma gondii (T. gondii) is a protozoan parasite that uses conserved mechanisms to infect rodents and human hosts. Infection is lifelong and has been associated with chronic weight loss and muscle atrophy in mice. We have recently shown that T. gondii-induced muscle atrophy meets the clinical definition of cachexia. Here, the longevity of the T. gondii-induced chronic cachexia model revealed that cachectic mice develop perivascular fibrosis in major metabolic organs, including the adipose tissue, skeletal muscle, and liver by 9 weeks post-infection. Development of cachexia, as well as liver and skeletal muscle fibrosis, is dependent on intact signaling through the type I IL-1R receptor. IL-1α is sufficient to activate cultured fibroblasts and primary hepatic stellate cells (myofibroblast precursors in the liver) in vitro, and IL-1α is elevated in the sera and liver of cachectic, suggesting a mechanism by which chronic IL-1R signaling could be leading to cachexia-associated fibrosis.

Hydrogen Sulfide Alleviates Skeletal Muscle Fibrosis via Attenuating Inflammation and Oxidative Stress.

The purpose of this study was to investigate the effect of exogenous hydrogen sulfide (H2S) treatment on skeletal muscle contusion. We established a skeletal muscle contusion model (S group) and an H2S treated of skeletal muscle contusion model (H2S group). Gastrocnemius muscles (GMs) were collected at day 1, day 5, day 10, and day 15 after injury, and comprehensive morphological and genetic analyses was conducted. H2S treatment reduced M1 macrophage (CD68), profibrotic cytokines (TGF-β), pro-inflammatory cytokines (TNF-α, IFN-γ, IL-1β, and IL-6), chemokines (CCL2, CCR2, CCL3, CCL5, CXCL12, and CXCR4), matrix metalloproteinases (MMP-1, MMP-2, MMP-9, and MMP-14) and oxidative stress factor (gp91phox) expression levels, improved M2 macrophage (CD206) level. Thus, exogenous H2S treatment reduced inflammation and oxidative stress, attenuated skeletal muscle fibrosis, and partly improved skeletal muscle injury.

O3-020 Ultrasound analysis of skeletal muscle fibrosis in patients with systemic fibrosis

O3-020 Ultrasound analysis of skeletal muscle fibrosis in patients with systemic fibrosis

Angiotensin-II drives human satellite cells toward hypertrophy and myofibroblast trans- differentiation by two independent pathways: A basis to support the use of renin angiotensin system blockers in skeletal muscle wasting and fibrosis

Angiotensin-II drives human satellite cells toward hypertrophy and myofibroblast trans- differentiation by two independent pathways: A basis to support the use of renin angiotensin system blockers in skeletal muscle wasting and fibrosis

Anti-Fibrotic Effect of Human Wharton's Jelly-Derived Mesenchymal Stem Cells on Skeletal Muscle Cells, Mediated by Secretion of MMP-1.

Extracellular matrix (ECM) components play an important role in maintaining skeletal muscle function, but excessive accumulation of ECM components interferes with skeletal muscle regeneration after injury, eventually inducing fibrosis. Increased oxidative stress level caused by dystrophin deficiency is a key factor in fibrosis in Duchenne muscular dystrophy (DMD) patients. Mesenchymal stem cells (MSCs) are considered a promising therapeutic agent for various diseases involving fibrosis. In particular, the paracrine factors secreted by MSCs play an important role in the therapeutic effects of MSCs. In this study, we investigated the effects of MSCs on skeletal muscle fibrosis. In 2–5-month-old mdx mice intravenously injected with 1 × 105 Wharton’s jelly (WJ)-derived MSCs (WJ-MSCs), fibrosis intensity and accumulation of calcium/necrotic fibers were significantly decreased. To elucidate the mechanism of this effect, we verified the effect of WJ-MSCs in a hydrogen peroxide-induced fibrosis myotubes model. In addition, we demonstrated that matrix metalloproteinase-1 (MMP-1), a paracrine factor, is critical for this anti-fibrotic effect of WJ-MSCs. These findings demonstrate that WJ-MSCs exert anti-fibrotic effects against skeletal muscle fibrosis, primarily via MMP-1, indicating a novel target for the treatment of muscle diseases, such as DMD.

Circulating Procollagen Type III N-Terminal Peptide and Physical Function in Adults from the Long Life Family Study.

Circulating levels of procollagen type III N-terminal peptide (P3NP) may reflect increased fibrosis of skeletal muscle and other tissues with aging. Herein, we tested if P3NP was associated with baseline and 7-year change in physical function. Participants (n = 400) were from the Long Life Family Study, a study of exceptional familial longevity. Plasma P3NP concentration was measured using a sandwich enzyme-linked immunosorbent assay (inter-assay coefficient of variation <5.5%). At baseline and 7-year follow-up visits, physical function was measured using the Short Physical Performance Battery (SPPB score 0-12), which consists of gait speed, balance, and chair-rise tests. Grip strength was measured using a handheld dynamometer. The association between log-transformed P3NP and physical function was examined using generalized estimating equations adjusted for familial relatedness, age, sex, height, weight, lifestyle characteristics, liver function, kidney function, lung function, and chronic disease prevalence. Participants were aged 73.1 ± 15.2 years (range: 39-104), 54% female, had body mass index of 26.6 ± 4.3 kg/m2, and gait speeds of 1.0 ± 0.3 m/s. One standard deviation higher log-transformed P3NP was related to worse baseline SPPB score (β = -0.9points), gait speed (β = -0.05m/s), chair-rises per-second (β = -0.46chair-rises/10 seconds), and grip strength (β = -2.0kg; all p < .001). Higher P3NP was also associated with greater declines in gait speed (β = -1.41, p < .001) and transitioning to being unable to perform chair-rises (β = 0.41, p < .001) after 7 years. Plasma P3NP may be a strong, novel biomarker of current and future physical function. Future research is needed to extend our findings to other cohorts and determine mechanisms underlying these associations.

Biologics for Skeletal Muscle Healing: The Role of Senescence and Platelet-Based Treatment Modalities

Skeletal muscle is a highly interactive connective tissue that makes up a large portion of an adult's body mass. Muscles are integrated with tendons as well as other specialized structures to support physiologic and homeostatic functions. In the state of injury, muscles have the ability to innately repair themselves through various phases of tightly regulated healing that can result in fibrotic tissue development. However, during aging, these homeostatic processes are disrupted leading to sarcopenia and reduced muscle regeneration capacity. Several cell-based therapies and biologic therapies have been investigated to regenerate skeletal muscle tissue and reduce fibrosis following injury or during aging. These include platelet-rich plasma (PRP) and an acellular portion of blood known as platelet-poor plasma (PPP). However, current clinical practice recommendations for the utilization of different PRP preparations vs PPP are unclear. Recent efforts have strove to improve the understanding of the role of senescent cells and profiles in the presence of early to late stage skeletal muscle injury and fibrosis, yet targeted interventions to remove senescent cells and attenuate the secretory environment to improve muscle regeneration are still forthcoming. Therefore, the purpose of this article is to review the basic principles of skeletal muscle repair, the role of senescence in attenuated muscle regeneration, and discuss current standards and literature supporting PRP and PPP treatment for skeletal muscle repair. This review concludes with future directions to improve biologic therapies and ongoing initiatives to customize PRP and PPP preparations using Food and Drug Administration-approved medications.

Characterization Of Muscle Inflammation Susceptibility: A Potential Prognostic Factor For Optimal Post-surgical Rehabilitation

BACKGROUND: Many individuals with end-stage osteoarthritis undergo elective total hip/knee arthroplasty (THA/TKA) to relieve pain and improve mobility and quality of life. However, ~35% suffer long-term mobility impairment following surgery. Previously, we have shown this may be in part due to muscle inflammation susceptibility (MuIS(+)), an overt pro-inflammatory state localized to skeletal muscle surrounding the diseased joint, found in some but not all TKA/THA patients. PURPOSE: We are interrogating the hypotheses that a) MuIS(+/-) status will result in a differential perioperative expression profile that may partially explain low functional outcomes, and b) resistance training rehabilitation will more effectively overcome MuIS(+) status than usual care for effective recovery post-surgery. METHODS: Muscle samples were leveraged from our ongoing two-site, randomized, controlled trial (N=84). Participants were dichotomized to MuIS status (+/-) based on surgical (SX) muscle gene expression of Fn14 which drives pro-inflammatory signaling via NFκB. MuIS(+/-) samples were probed for pro-inflammatory gene and protein expression targets, and indices of skeletal muscle function. Preliminary perioperative comparisons were made using two-tailed T-tests; alpha P≤0.05. RESULTS: 84 participants (29M/55F; 62±8yrs; BMI 30.7±5.4kg/m2) undergoing THA/TKA were assessed. Thus far, 37 have been clustered as MuIS(+) (n=14, ~4-fold greater Fn14 mRNA) or MuIS(-) (n=23). SX thigh muscle mass (TMM), quadriceps power and torque were lower (P<0.05) than the contralateral limb (CTR). Additionally, skeletal muscle fibrosis and type II cross-sectional area were greater in the SX leg and MuIS(+) respectively (P<0.05). Tumor necrosis factor-α receptor and IL-6 trended higher in MuIS(+) (P>0.05). Phosphorylated (P)-RPS6 was lower in the SX leg and P-4E-BP1 was significantly lower in MuIS(+) (P>0.05). CONCLUSIONS: Preliminary results suggest patients undergoing TKA/THA exhibit more inflammation on the SX limb, accompanied by lower TMM, torque and power. MuIS(+) leads to greater inflammation and blunted anabolic signaling, highlighting the profound impact of muscle inflammation and emphasizing the potential value in perioperative MuIS assessment to inform optimal post-surgical care. Grant: R01HD084124

The effect of 6 weeks moderate intensity endurance training on skeletal muscle fibrosis in diabetic rats

Background: Diabetes leads to both structural and functional dysfunction in the tissues and causes problems such as fibrosis. The purpose of this study was to investigate the effect of 6 weeks moderate intensity endurance training on skeletal muscle fibrosis in diabetic rats. Methods: Twenty eight adult male wistar rats in the weight range of 200-250gr, randomly assigned to four equal groups: diabetes and training, diabetes control, healthy and training, healthy control. After twelve hours of food deprivation, intraperitoneal injection of Streptozotocin solution method was used. Two weeks after STZ injection, the moderate intensity endurance training protocol was performed for six weeks. Twenty four hours after the last training session, soleus and EDL muscles were dissected. Mason’s trichrome staining method was used for analysis of fibrosis. Results: Compared with the healthy control group, diabetes caused a significant increase in fibrosis in soleus muscle (P=0.002) and extensor digitorum longus muscle (P=0.048). Also, endurance training resulted in significant reduction of fibrosis in soleus muscle in the Diabetes and training group compared to the diabetes control group (P=0.043), but endurance training did not have a significant effect on fibrosis of the extensor digitorum longus muscle (P=0.341). The exercise also significantly reduced blood glucose levels in the diabetic group compared to the control group. Conclusion: It seems that moderate intensity endurance training could inhibit from muscle fibrosis caused by diabetes. So, it is suggested that moderate intensity endurance training could be used as a non-pharmacotherapy intervention for inhibition of fibrosis in diabetic patient’s muscles.

Reduce Muscle Fibrosis through Exercise via NRG1/ErbB2 Modification in Diabetic Rats.

Diabetic myopathy refers to the manifestations in the skeletal muscle as a result of altered glucose homeostasis which reflects as fibrosis. Since physical exercise has been indicated a protective strategy for improving glucose metabolism in skeletal muscle, we tested a hypothesis under which the endurance exercise training could reverse the produced skeletal muscle fibrosis by diabetes. Eight-week-old male Wistar rats were randomly assigned into four groups including healthy control (HC), healthy trained (HT), diabetic control (DC), and diabetic trained (DT) groups. Diabetes was induced by a single intraperitoneal injection of streptozotocin (STZ; 45 mg/kg). Rats in the HT and DT groups carried out an exercise program on a motorized treadmill for five days a week over six weeks. Skeletal muscle levels of NRG1and ErbB2 were measured by the Western blot method. Exercise training decreased blood glucose levels in the DT group. Induction of diabetes increased skeletal muscle fibrosis in both the fast extensor digitorum longus (EDL) and slow soleus muscles, while endurance training modified it in diabetic trained rats. Moreover, muscle NRG1and ErbB2 levels were increased in diabetic rats, while training modified muscle NRG1and ErbB2 levels in diabetic trained rats. Our study provides novel evidence that endurance training could modify skeletal muscle fibrosis through NRG1/ErbB2 modification in STZ-induced diabetic rats.

Interstitial Cell Remodeling Promotes Aberrant Adipogenesis in Dystrophic Muscles

Fibrosis and fat replacement in skeletal muscle are major complications that lead to a loss of mobility in chronic muscle disorders, such as muscular dystrophy. However, the invivo properties of adipogenic stem and precursor cells remain unclear, mainly due to the high cell heterogeneity in skeletal muscles. Here, we use single-cell RNA sequencing to decomplexify interstitial cell populations in healthy and dystrophic skeletal muscles. We identify an interstitial CD142-positive cell population in mice and humans that is responsible for the inhibition of adipogenesis through GDF10 secretion. Furthermore, we show that the interstitial cell composition is completely altered in muscular dystrophy, with a near absence of CD142-positive cells. The identification of these adipo-regulatory cells in the skeletal muscle aids our understanding of the aberrant fat deposition in muscular dystrophy, paving the way for treatments that could counteract degeneration in patients with muscular dystrophy.

Angiotensin-converting-enzyme inhibitor prevents skeletal muscle fibrosis in myocardial infarction mice

BackgroundTransforming growth factor beta (TGF-β)-Smad2/3 is the major signaling pathway of fibrosis, which is characterized by the excessive production and accumulation of extracellular matrix (ECM) components, including collagen. Although the ECM is an essential component of skeletal muscle, fibrosis may be harmful to muscle function. On the other hand, our previous studies have shown that levels of angiotensin II, which acts upstream of TGF-β-Smad2/3 signaling, is increased in mice with myocardial infarction (MI). In this study, we found higher skeletal muscle fibrosis in MI mice compared with control mice, and we investigated the mechanisms involved therein. Moreover, we administered an inhibitor based on the above mechanism and investigated its preventive effects on skeletal muscle fibrosis.MethodsMale C57BL/6 J mice with MI were created, and sham-operated mice were used as controls. The time course of skeletal muscle fibrosis post-MI was analyzed by picrosirius-red staining (days 1, 3, 7, and 14). Mice were then divided into 3 groups: sham + vehicle (Sham + Veh), MI + Veh, and MI + lisinopril (an angiotensin-converting enzyme [ACE] inhibitor, 20 mg/kg body weight/day in drinking water; MI + Lis). Lis or Veh was administered from immediately after the surgery to 14 days postsurgery.ResultsSkeletal muscle fibrosis was significantly increased in MI mice compared with sham mice from 3 to 14 days postsurgery. Although mortality was lower in the MI + Lis mice than the MI + Veh mice, there was no difference in cardiac function between the 2 groups at 14 days. Skeletal muscle fibrosis and hydroxyproline (a key marker of collagen content) were significantly increased in MI + Veh mice compared with the Sham + Veh mice. Consistent with these results, protein expression of TGF-β and phosphorylated Smad2/3 in the skeletal muscle during the early time points after surgery (days 1–7 postsurgery) and blood angiotensin II at 14 days postsurgery was increased in MI mice compared with sham mice. These impairments were improved in MI + Lis mice, without any effects on spontaneous physical activity, muscle strength, muscle weight, and blood pressure.ConclusionsACE inhibitor administration prevents increased skeletal muscle fibrosis during the early phase after MI. Our findings indicate a new therapeutic target for ameliorating skeletal muscle abnormalities in heart diseases.

Tuning Macrophage Phenotype to Mitigate Skeletal Muscle Fibrosis.

Myeloid cells are critical to the development of fibrosis following muscle injury; however, the mechanism of their role in fibrosis formation remains unclear. In this study, we demonstrate that myeloid cell-derived TGF-β1 signaling is increased in a profibrotic ischemia reperfusion and cardiotoxin muscle injury model. We found that myeloid-specific deletion of Tgfb1 abrogates the fibrotic response in this injury model and reduces fibro/adipogenic progenitor cell proliferation while simultaneously enhancing muscle regeneration, which is abrogated by adaptive transfer of normal macrophages. Similarly, a murine TGFBRII-Fc ligand trap administered after injury significantly reduced muscle fibrosis and improved muscle regeneration. This study ultimately demonstrates that infiltrating myeloid cell TGF-β1 is responsible for the development of traumatic muscle fibrosis, and its blockade offers a promising therapeutic target for preventing muscle fibrosis after ischemic injury.

Determining Resistance to Protein Turnover in Aged Skeletal Muscle Collagen Using a Novel Stable Isotope Timecourse Approach

BACKGROUNDAged skeletal muscle presents with an accumulation of extracellular matrix (ECM) proteins, including collagen, that are stiffer and fibrotic (i.e., unresolvable and resistant to turnover) which alters the cellular microenvironment leading to reduced muscle function. A limitation of current assessments of protein turnover using a single timepoint is that they do not account for how much of a protein pool is actively turning over. In addition, defining the proportion of the protein pool actively turning over also informs on how much of the same pool is fibrotic. Thus, determining aging muscle changes in both collagen protein synthesis and the collagen protein pool actively turning over is vital for a more comprehensive understanding of fibrosis in aged skeletal muscle ECM.PURPOSETo test the hypothesis that with age the fraction of collagen proteins actively turning over would decrease, indicating an increase in fibrotic collagen, and that the fraction of the protein pool turning over would be inverse to the amount of collagen cross‐linking and overall protein oxidative damage.METHODSYoung adult (6 mo.) and old (23 mo.) female C57BL/6 mice were labeled with the stable isotope deuterium oxide (D2O) for 4, 15, 30, 45, or 60 days (n=3–5/timepoint). Gastrocnemius muscles were analyzed for collagen protein synthesis (k 1/day) and the plateau (P) value for fraction new as a novel indicator of the protein pool capable of turning over (with 1.0 equal to 100% of the total pool turning over). Collagen cross‐linking was assessed using a pepsin digestion collagen solubility and hydroxyproline assay and Western Blotting for lysyl oxidase (LOX, catalyzes collagen cross‐links), while muscle protein carbonylation was assessed as a marker of oxidative damage.RESULTSCollagen protein synthesis and collagen plateau fraction new were significantly (p &lt; 0.05) lower in old compared to young (0.011±0.002 vs 0.027±0.003 k 1/day and 0.141±0.015 vs 0.280±0.051 P, respectively). The lower collagen turnover in old compared to young muscle was paralleled by higher total LOX expression (20183±600 vs 16333±435 arbitrary density units, respectively), lower pepsin soluble collagen (15.1±1.28 vs 37.4±5.96 ng/mg muscle, respectively), higher pepsin insoluble (285±17.5 vs 201±16.4 ng/mg muscle, respectively) and total collagen (303±19.8 vs 237±18.4 ng/mg muscle, respectively), and unchanged protein carbonylation (0.083±0.002 vs 0.083±0.008 arbitrary density units, respectively).CONCLUSIONSThe pool of collagen proteins actively turning over was significantly reduced in aged compared to young muscle, indicating that a greater proportion of the collagen proteins in aged muscle were fibrotic. The reduced proportion of collagen turning over was associated with increased markers of collagen cross‐linking, but not overall protein oxidative damage. Further research is warranted to identify which individual ECM proteins become fibrotic with aging to develop therapeutics to rescue muscle function.Support or Funding InformationThis research was supported by NIA Training Grant T32AG052363.

Glycans Meet Sphingolipids: Structure-Based Design of Glycan Containing Analogues of a Sphingosine Kinase Inhibitor

Sphingosine 1-phosphate (S1P) is a bioactive lipid mediator associated with diverse homeostatic and signaling roles. Enhanced biosynthesis of S1P, mediated by the sphingosine kinase isozymes (SK1 and SK2), is implicated in several pathophysiological conditions and diseases, including skeletal muscle fibrosis, inflammation, multiple sclerosis, and cancer. Therefore, therapeutic approaches that control S1P production have focused on the development of SK1/2 inhibitors. In this framework, we designed a series of natural monosaccharide-based compounds to enhance anchoring of the known SK1 inhibitor PF-543 at the polar head of the J-shaped substrate-binding channel. Herein, we describe the structure-based design and synthesis of new glycan-containing PF-543 analogues and we demonstrate their efficiency in a TGFβ1-induced pro-fibrotic assay.

Blocking CTGF/CCN2 reduces established skeletal muscle fibrosis in a rat model of overuse injury.

Tissue fibrosis is a hallmark of overuse musculoskeletal injuries and contributes to functional declines. We tested whether inhibition of CCN2 (cellular communication network factor 2, previously known as connective tissue growth factor, CTGF) using a specific antibody (termed FG‐3019 or pamrevlumab) reduces established overuse‐induced muscle fibrosis in a clinically relevant rodent model of upper extremity overuse injury. Young adult rats performed a high repetition high force (HRHF) reaching and lever‐pulling task for 18 weeks, after first being shaped for 6 weeks to learn this operant task. Rats were then euthanized (HRHF‐Untreated), or rested and treated for 6 weeks with FG‐3019 (HRHF‐Rest/FG‐3019) or a human IgG as a vehicle control (HRHF‐Rest/IgG). HRHF‐Untreated and HRHF‐Rest/IgG rats had higher muscle levels of several fibrosis‐related proteins (TGFβ1, CCN2, collagen types I and III, and FGF2), and higher muscle numbers of alpha SMA and pERK immunopositive cells, compared to control rats. Each of these fibrogenic changes was restored to control levels by the blocking of CCN2 signaling in HRHF‐Rest/FG‐3019 rats, as were HRHF task‐induced increases in serum CCN2 and pro‐collagen I intact N‐terminal protein. Levels of cleaved CCN3, an antifibrotic protein, were lowered in HRHF‐Untreated and HRHF‐Rest/IgG rats, compared to control rats, yet elevated back to control levels in HRHF‐Rest/FG‐3019 rats. Significant grip strength declines observed in HRHF‐Untreated and HRHF‐Rest/IgG rats, were restored to control levels in HRHF‐Rest/FG‐3019 rats. These results are highly encouraging for use of FG‐3019 for therapeutic treatment of persistent skeletal muscle fibrosis, such as those induced with chronic overuse.

Peripheral arterial disease: the role of extracellular volume measurements in lower limb muscles with MRI.

Peripheral arterial disease (PAD) is characterised by arterial occlusion and fibrosis in the lower extremities. Extracellular volume matrix fraction (ECV) is a biomarker of skeletal muscle fibrosis, but has not been applied to the lower extremities with PAD. This study investigated the clinical feasibility of using ECV for calf muscle fibrosis quantification by comparing normal controls (NC) and PAD patients. From October 2016 to December 2017, we recruited patients with PAD, and patients with head and neck cancer receiving fibular flap as NC group. All participants underwent magnetic resonance imaging (MRI) to determine the ECV of the calves and the differences between the NC and PAD groups. ECV was calculated from T1 values at steady-state equilibrium, defined as the point in time after contrast agent injection when the variance of T1 relaxation time in blood and muscle becomes less than 5%. A total of 46 patients (18 in the NC group and 28 in the PAD group) were recruited. Steady-state equilibrium was reached at 11-12min after contrast agent injection. The NC group had significantly lower mean ECV than the PAD group (12.71% vs. 31.92%, respectively, p < 0.001). In the PAD group, the mean ECV was slightly lower in patients with collateral vessels than in those without (26.58% vs. 34.88%, respectively, p = 0.047). Evaluation of skeletal fibrosis in PAD using ECV is feasible. ECV can help identify PAD patients with collateral vessel formation and lay the foundation for future research in PAD management. • Steady-state equilibrium for ECV measurement of the lower limbs can be reached at around 11-12 min. • Quantification of lower limb muscle fibrosis by measuring ECV is clinically feasible and can be used to differentiate between patients with PAD and histologically proven normal controls. • ECV can differentiate PAD patients with or without visible collateral vessels, further expanding its role in identifying the presence of collateral supply in clinical decision-making.