Inhibition of p38 mitogen-activated protein kinase signaling reduces fibrosis and lipid accumulation after rotator cuff repair

Fat infiltration in skeletal muscle: Influential triggers and regulatory mechanism

Fat infiltration in skeletal muscle (also known as myosteatosis) is now recognized as a distinct disease from sarcopenia and is directly related to declining muscle capacity. Hence, understanding the origins and regulatory mechanisms of fat infiltration is vital for maintaining skeletal muscle development and improving human health. In this article, we summarized the triggering factors such as aging, metabolic diseases and metabolic syndromes, nonmetabolic diseases, and muscle injury that all induce fat infiltration in skeletal muscle. We discussed recent advances on the cellular origins of fat infiltration and found several cell types including myogenic cells and non-myogenic cells that contribute to myosteatosis. Furthermore, we reviewed the molecular regulatory mechanism, detection methods, and intervention strategies of fat infiltration in skeletal muscle. Based on the current findings, our review will provide new insight into regulating function and lipid metabolism of skeletal muscle and treating muscle-related diseases.

Interventions used to mitigate muscle fatty degeneration following the repair of massive rotator cuff tears. A systematic review of animal studies

BACKGROUND

Muscle fatty degeneration following rotator cuff tears has been unequivocally associated with poorer functional outcomes and increased risk for retear following rotator cuff repair. Promising results have emerged from animal studies, with the implementation of various interventions for biologic inhibition of this fatty muscle degeneration. The lack of high quality randomized human evidence on this topic, increases the impact of pooled results from animal literature. The aim of the present study was to systematically review the available published literature for animal studies evaluating the ability of several interventions used to mitigate muscle fatty degeneration following the repair of massive rotator cuff tears.

PATIENTS AND METHODS

A comprehensive search was conducted on Pubmed, Scopus and Google Scholar, covering the period from conception until 16th April 2022. Datasets were stratified based on the type of intervention performed. SYRCLE risk of bias instrument was implemented for quality assessment of the included studies.

RESULTS

Rotator cuff repair augmentation with Adipose derived stem cells (ADSC's), Mesenchymal stem cells (MSC's) and Nandrolone was effective against fatty infiltration, but less effective against muscle atrophy. More beneficial effect was shown by the utilization of Beige adipose tissue - Fibroadipogenic progenitors (BAT-FAP) stimulation, using either Amibregon or BAT-FAPs transplantation. Both provided good results in mitigating muscle atrophy, fatty infiltration and fibrosis.

DISCUSSION

ADSC's, MSC's, Nandrolone and BAT-FAP stimulation may have a role in mitigating muscle fatty degeneration following rotator cuff tears. Large scale human studies are required to further elucidate their role in the clinical setting.

LEVEL OF EVIDENCE

V; systematic review of pre-clinical studies.

Effect of PARP-1 Inhibition on Rotator Cuff Healing: A Feasibility Study Using Veliparib in a Rat Model of Acute Rotator Cuff Repair

BACKGROUND

PARP-1 (poly[ADP-ribose]) was shown to influence the inflammatory response after rotator cuff tear, leading to fibrosis, muscular atrophy, and fatty infiltration in mouse rotator cuff degeneration. So far, it is not known how PARP-1 influences enthesis healing after rotator cuff tear repair.

HYPOTHESIS/PURPOSE

This study aimed to examine the feasibility of oral PARP-1 inhibition and investigate its influence on rat supraspinatus enthesis and muscle healing after rotator cuff repair. The hypothesis was that oral PARP-1 inhibition would improve enthesis healing after acute rotator cuff repair in a rat model.

STUDY DESIGN

Controlled laboratory study.

METHODS

In 24 Sprague-Dawley rats, the supraspinatus tendon was sharply detached and immediately repaired with a single transosseous suture. The rats were randomly allocated into 2 groups, with the rats in the inhibitor group receiving veliparib with a target dose of 12.5 mg/kg/d via drinking water during the postoperative recovery period. The animals were sacrificed 8 weeks after surgery. For the analysis, macroscopic, biomechanical, and histologic methods were used.

RESULTS

Oral veliparib was safe for the rats, with no adverse effects observed. In total, the inhibitor group had a significantly better histologic grading of the enthesis with less scar tissue formation. The macroscopic cross-sectional area of the supraspinatus muscles was 10.5% higher (P = .034) in the inhibitor group, which was in agreement with an 8.7% higher microscopic muscle fiber diameter on histologic sections (P < .0001). There were no statistically significant differences in the biomechanical properties between the groups.

CONCLUSION

This study is the first to investigate the influence of PARP-1 inhibition on healing enthesis. On the basis of these findings, we conclude that oral veliparib, which was previously shown to inhibit PARP-1 effectively, is safe to apply and has beneficial effects on morphologic enthesis healing and muscle fiber size.

CLINICAL RELEVANCE

Modulating the inflammatory response through PARP-1 inhibition during the postoperative healing period is a promising approach to improve enthesis healing and reduce rotator cuff retearing. With substances already approved by the Food and Drug Administration, PARP-1 inhibition bears high potential for future translation into clinical application.

Prospects of magnetically based approaches addressing inflammation in tendon tissues

Tendon afflictions constitute a significant share of musculoskeletal diseases and represent a primary cause of incapacity worldwide. Unresolved/chronic inflammatory states have been associated with the onset and progression of tendon disorders, contributing to undesirable immune stimulation and detrimental tissue effects. Thus, targeting persistent inflammatory events could assist important developments to solve pathophysiological processes and innovative therapeutics to address impaired healing and accomplish complete tendon regeneration. This review overviews the impact of inflammation and inflammatory mediators in tendon niches, unveiling the importance of tendon cell populations and their signature features, and the influence of microenvironmental factors on inflamed and injured tendons. The demand for non-invasive instructive strategies to manage persistent inflammatory mediators, guide inflammatory pathways, and modulate cellular responses will also be approached by exploring the role of pulsed electromagnetic field (PEMF). PEMF alone or combined with more sophisticated systems triggered by magnetic fields will be considered in the design of successful therapies to control inflammation in tendinopathic conditions.

Lysyl oxidase-like 2 inhibitor rescues D-galactose-induced skeletal muscle fibrosis

Aging-related sarcopenia is currently the most common sarcopenia. The main manifestations are skeletal muscle atrophy, replacement of muscle fibers with fat and fibrous tissue. Excessive fibrosis can impair muscle regeneration and function. Lysyl oxidase-like 2 (LOXL2) has previously been reported to be involved in the development of various tissue fibrosis. Here, we investigated the effects of LOXL2 inhibitor on D-galactose (D-gal)-induced skeletal muscle fibroblast cells and mice. Our molecular and physiological studies show that treatment with LOXL2 inhibitor can alleviate senescence, fibrosis, and increased production of reactive oxygen species in fibroblasts caused by D-gal. These effects are related to the inhibition of the TGF-β1/p38 MAPK pathway. Furthermore, in vivo, mice treatment with LOXL2 inhibitor reduced D-gal-induced skeletal muscle fibrosis, partially enhanced skeletal muscle mass and strength and reduced redox balance disorder. Taken together, these data indicate the possibility of using LOXL2 inhibitors to prevent aging-related sarcopenia, especially with significant fibrosis.

BMP-2 Induced Signaling Pathways and Phenotypes: Comparisons Between Senescent and Non-senescent Bone Marrow Mesenchymal Stem Cells

The use of BMP-2 in orthopedic surgery is limited by uncertainty surrounding its effects on the differentiation of mesenchymal stem cells (MSCs) and how this is affected by cellular aging. This study compared the effects of recombinant human BMP-2 (rhBMP-2) on osteogenic and adipogenic differentiation between senescent and non-senescent MSCs. Senescent and non-senescent MSCs were cultured in osteogenic and adipogenic differentiation medium containing various concentrations of rhBMP-2. The phenotypes of these cells were compared by performing a calcium assay, adipogenesis assay, staining, real-time PCR, western blotting, and microarray analysis. rhBMP-2 induced osteogenic differentiation to a lesser extent (P < 0.001 and P = 0.005 for alkaline phosphatase activity and Ca²⁺ release) in senescent MSCs regardless of dose-dependent increase in both cells. However, the induction of adipogenic differentiation by rhBMP-2 was comparable between them. There was no difference between these two groups of cells in the adipogenesis assay (P = 0.279) and their expression levels of PPARγ were similar. Several genes such as CHRDL1, NOG, SMAD1, SMAD7, and FST encoding transcription factors were proposed to underlie the different responses of senescent and non-senescent MSCs to rhBMP-2 in microarray analyses. Furthermore, inflammatory, adipogenic, or cell death-related signaling pathways such as NF-kB or p38-MAPK pathways were upregulated by BMP-2 in senescent MSCs, whereas bone forming signaling pathways involving BMP, SMAD, and TGF- ß were upregulated in non-senescent MSCs as expected. This phenomenon explains bone forming dominance by non-senescent MSCs and possible frequent complications such as seroma, osteolysis, or neuritis in senescent MSCs during BMP-2 use in orthopedic surgery.

Supraspinatus muscle architecture and physiology in a rabbit model of tenotomy and repair

Chronic rotator cuff tears can cause severe functional deficits. Addressing the chronic fatty and fibrotic muscle changes is of high clinical interest; however, the architectural and physiological consequences of chronic tear and repair are poorly characterized. We present a detailed architectural and physiological analysis of chronic tear and repair (both over 8 and 16 wk) compared with age-matched control rabbit supraspinatus (SSP) muscles. Using female New Zealand White Rabbits (n = 30, n = 6/group) under 2% isoflurane anesthesia, the SSP was surgically isolated and maximum isometric force was measured at four to six muscle lengths. Architectural analysis was performed, and maximum isometric stress was computed. Whole muscle length-tension curves were generated using architectural measurements to compare experimental physiology to theoretical predictions. Architectural measures are consistent with persistent radial and longitudinal atrophy over time in tenotomy that fails to recover after repair. Maximum isometric force was significantly decreased after 16 wk tenotomy and not significantly improved after repair. Peak isometric force reported here are greater than prior reports of rabbit SSP force after tenotomy. Peak stress was not significantly different between groups and consistent with prior literature of SSP stress. Muscle strain during contraction was significantly decreased after 8 wk of tenotomy and repair, indicating effects of tear and repair on muscle function. The experimental length-tension data were overlaid with predicted curves for each experimental group (generated from structural data), exposing the altered structure-function relationship for tenotomy and repair over time. Data presented here contribute to understanding the physiological implications of disease and repair in the rotator cuff.NEW & NOTEWORTHY We utilize an established method to measure the length-tension relationship for the rabbit supraspinatus in normal, torn, and repaired muscles. We then perform architectural analysis to evaluate structural changes after tear and repair. Although peak isometric force is lower in the tear and repair groups, there are no differences in peak stresses across groups. These findings indicate persistent structural changes (both radial and longitudinal atrophy) and physiological deficiencies (decreased peak force and uncoupling structure-function relationship) after tenotomy that do not significantly recover after repair.

Human tendon-derived cell sheets created by magnetic force-based tissue engineering hold tenogenic and immunomodulatory potential

Cell sheet technology and magnetic based tissue engineering hold the potential to become instrumental in developing magnetically responsive living tissues analogues that can be potentially used both for modeling and therapeutical purposes. Cell sheet constructions more closely recreate physiological niches, through the preservation of contiguous cells and cell-ECM interactions, which assist the cellular guidance in regenerative processes. We herein propose to use magnetically assisted cell sheets (magCSs) constructed with human tendon-derived cells (hTDCs) and magnetic nanoparticles to study inflammation activity upon magCSs exposure to IL-1β, anticipating its added value for tendon disease modeling. Our results show that IL-1β induces an inflammatory profile in magCSs, supporting its in vitro use to enlighten inflammation mediated events in tendon cells. Moreover, the response of magCSs to IL-1β is modulated by pulsed electromagnetic field (PEMF) stimulation, favoring the expression of anti-inflammatory genes, which seems to be associated to MAPK(ERK1/2) pathway. The anti-inflammatory response to PEMF together with the immunomodulatory potential of magCSs opens new perspectives for their applicability on tendon regeneration that goes beyond advanced cell based modeling. STATEMENT OF SIGNIFICANCE: The combination of cell sheets and magnetic-based technologies holds promise as instrumental bio-instructive tools both for tendon disease modelling and for the development of magnetically responsive living tendon substitutes. We have previously shown that remote actuation of a pulsed electromagnetic field (PEMF) modulated the inflammatory response of IL-1β-treated human tendon-derived cell (hTDCs) monolayers. As magnetic cell sheets (magCSs) technologies enable improved cellular organization and matrix deposition, these constructions could better recapitulate tendon niches. In this work, we aimed to apply magCSs technologies to study hTDCs responses in inflammatory environments. Overall results show that PEMF-stimulated-magCSs hold evidence for immunomodulatory properties and to become a living tendon model envisioning tendon regenerative therapies.

Enhanced Tendon-to-Bone Healing via IKKβ Inhibition in a Rat Rotator Cuff Model

BACKGROUND

More than 450,000 rotator cuff repairs are performed annually, yet healing of tendon to bone often fails. This failure is rooted in the fibrovascular healing response, which does not regenerate the native attachment site. Better healing outcomes may be achieved by targeting inflammation during the early period after repair. Rather than broad inhibition of inflammation, which may impair healing, the current study utilized a molecularly targeted approach to suppress IKKβ, shutting down only the inflammatory arm of the nuclear factor κB (NF-κB) signaling pathway.

PURPOSE

To evaluate the therapeutic potential of IKKβ inhibition in a clinically relevant model of rat rotator cuff repair.

STUDY DESIGN

Controlled laboratory study.

METHODS

After validating the efficacy of the IKKβ inhibitor in vitro, it was administered orally once a day for 7 days after surgery in a rat rotator cuff repair model. The effect of treatment on reducing inflammation and improving repair quality was evaluated after 3 days and 2, 4, and 8 weeks of healing, using gene expression, biomechanics, bone morphometry, and histology.

RESULTS

Inhibition of IKKβ attenuated cytokine and chemokine production in vitro, demonstrating the potential for this inhibitor to reduce inflammation in vivo. Oral treatment with IKKβ inhibitor reduced NF-κB target gene expression by up to 80% compared with a nontreated group at day 3, with a subset of these genes suppressed through 14 days. Furthermore, the IKKβ inhibitor led to enhanced tenogenesis and extracellular matrix production, as demonstrated by gene expression and histological analyses. At 4 weeks, inhibitor treatment led to increased toughness, no effects on failure load and strength, and decreases in stiffness and modulus when compared with vehicle control. At 8 weeks, IKKβ inhibitor treatment led to increased toughness, failure load, and strength compared with control animals. IKKβ inhibitor treatment prevented the bone loss near the tendon attachment that occurred in repairs in control.

CONCLUSION

Pharmacological inhibition of IKKβ successfully suppressed excessive inflammation and enhanced tendon-to-bone healing after rotator cuff repair in a rat model.

CLINICAL RELEVANCE

The NF-κB pathway is a promising target for enhancing outcomes after rotator cuff repair.

Artemisinin and artemisinin derivatives as anti-fibrotic therapeutics

Fibrosis is a pathological reparative process that can occur in most organs and is responsible for nearly half of deaths in the developed world. Despite considerable research, few therapies have proven effective and been approved clinically for treatment of fibrosis. Artemisinin compounds are best known as antimalarial therapeutics, but they also demonstrate antiparasitic, antibacterial, anticancer, and anti-fibrotic effects. Here we summarize literature describing anti-fibrotic effects of artemisinin compounds in in vivo and in vitro models of tissue fibrosis, and we describe the likely mechanisms by which artemisinin compounds appear to inhibit cellular and tissue processes that lead to fibrosis. To consider alternative routes of administration of artemisinin for treatment of internal organ fibrosis, we also discuss the potential for more direct oral delivery of Artemisia plant material to enhance bioavailability and efficacy of artemisinin compared to administration of purified artemisinin drugs at comparable doses. It is our hope that greater understanding of the broad anti-fibrotic effects of artemisinin drugs will enable and promote their use as therapeutics for treatment of fibrotic diseases.

Regeneration of Damaged Tendon-Bone Junctions (Entheses)-TAK1 as a Potential Node Factor

Musculoskeletal dysfunctions are highly prevalent due to increasing life expectancy. Consequently, novel solutions to optimize treatment of patients are required. The current major research focus is to develop innovative concepts for single tissues. However, interest is also emerging to generate applications for tissue transitions where highly divergent properties need to work together, as in bone-cartilage or bone-tendon transitions. Finding medical solutions for dysfunctions of such tissue transitions presents an added challenge, both in research and in clinics. This review aims to provide an overview of the anatomical structure of healthy adult entheses and their development during embryogenesis. Subsequently, important scientific progress in restoration of damaged entheses is presented. With respect to enthesis dysfunction, the review further focuses on inflammation. Although molecular, cellular and tissue mechanisms during inflammation are well understood, tissue regeneration in context of inflammation still presents an unmet clinical need and goes along with unresolved biological questions. Furthermore, this review gives particular attention to the potential role of a signaling mediator protein, transforming growth factor beta-activated kinase-1 (TAK1), which is at the node of regenerative and inflammatory signaling and is one example for a less regarded aspect and potential important link between tissue regeneration and inflammation.

The MRL/MpJ Mouse Strain Is Not Protected From Muscle Atrophy and Weakness After Rotator Cuff Tear

Chronic rotator cuff tears are a common source of shoulder pain and disability. Patients with rotator cuff tears often have substantial weakness, fibrosis, and fat accumulation, which limit successful surgical repair and postoperative rehabilitation. The Murphy Roths Large (MRL) strain of mice have demonstrated superior healing and protection against pathological changes in several disease and injury conditions. We tested the hypothesis that, compared with the commonly used C57Bl/6 (B6) strain, MRL mice would have less muscle fiber atrophy and fat accumulation, and be protected against the loss in force production that occurs after cuff tear. Adult male B6 and MRL mice were subjected to a rotator cuff tear, and changes in muscle fiber contractility and histology were measured. RNA sequencing and shotgun metabolomics and lipidomics were also performed. The muscles were harvested one month after tear. B6 and MRL mice had a 40% reduction in relative muscle force production after rotator cuff tear. RNA sequencing identified an increase in fibrosis-associated genes and a reduction in mitochondrial metabolism genes. The markers of glycolytic metabolism increased in B6 mice, while MRL mice appeared to increase amino acid metabolism after tear. There was an accumulation of lipid after injury, although there was a divergent response between B6 and MRL mice in the types of lipid species that accrued. There were strain-specific differences between the transcriptome, metabolome, and lipidome of B6 and MRL mice, but these differences did not protect MRL mice from weakness and pathological changes after rotator cuff tear. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:811-822, 2020.

Transcriptomic Analysis of Cellular Pathways in Healing Flexor Tendons of Plasminogen Activator Inhibitor 1 (PAI-1/Serpine1) Null Mice

Injuries to flexor tendons can be complicated by fibrotic adhesions, which severely impair the function of the hand. Plasminogen activator inhibitor 1 (PAI-1/SERPINE1), a master suppressor of fibrinolysis and protease activity, is associated with adhesions. Here, we used next-generation RNA sequencing (RNA-Seq) to assess genome-wide differences in messenger RNA expression due to PAI-1 deficiency after zone II flexor tendon injury. We used the ingenuity pathway analysis to characterize molecular pathways and biological drivers associated with differentially expressed genes (DEG). Analysis of hundreds of overlapping and DEG in PAI-1 knockout (KO) and wild-type mice (C57Bl/6J) during tendon healing revealed common and distinct biological processes. Pathway analysis identified cell proliferation, survival, and senescence, as well as chronic inflammation as potential drivers of fibrotic healing and adhesions in injured tendons. Importantly, we identified the activation of PTEN signaling and the inhibition of FOXO1-associated biological processes as unique transcriptional signatures of the healing tendon in the PAI-1/Serpine1 KO mice. Further, transcriptomic differences due to the genetic deletion of PAI-1 were mechanistically linked to PI3K/Akt/mTOR, PKC, and MAPK signaling cascades. These transcriptional observations provide novel insights into the biological roles of PAI-1 in tendon healing and could identify therapeutic targets to achieve scar-free regenerative healing of tendons. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:43-58, 2020.

Identify differential gene expressions in fatty infiltration process in rotator cuff

Background

Rotator cuff tears are one of the most frequent upper extremity injuries and lead to pain and disability. Recent studies have implicated fatty infiltration in rotator cuff is a key failure element with the higher re-tear rates and poorer functional prognosis. Therefore, we investigated the differential expression of key genes in each stage of rotator cuff tear.

Methods

A published expression profile was downloaded from the Gene Expression Omnibus database and analyzed using the Linear Models for Microarray Data (LIMMA) package in R language to identify differentially expressed genes (DEGs) in different stages of injured rotator cuff muscles. Gene ontology (GO) functional and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed to annotate the function of the DEGs. Finally, PPI network and module analysis were used to identify hub genes.

Results

A total of 1089 fatty infiltration-related DEGs were identified, including 733 upregulated and 356 downregulated genes, and GO analyses confirmed that fatty infiltration was strongly associated with inflammatory response, aging, response to lipopolysaccharide, and immune response. Significantly enriched KEGG pathways associated with these DEGs included the phagosome, cell adhesion molecules, tuberculosis, and osteoclast differentiation. Further analyses via a PPI network and module analysis identified a total of 259 hub genes. Among these, Tmprss11d, Ptprc, Itgam, Mmp9, Tlr2, Il1b, Il18, Ccl5, Cxcl10, and Ccr7 were the top ten hub genes.

Conclusions

Our findings indicated the potential key genes and pathways involved in fatty degeneration in the development of fatty infiltration and supplied underlying therapeutic targets in the future.

Electronic supplementary material

The online version of this article (10.1186/s13018-019-1182-1) contains supplementary material, which is available to authorized users.

Anterior Cruciate Ligament Tear Promotes Skeletal Muscle Myostatin Expression, Fibrogenic Cell Expansion, and a Decline in Muscle Quality

BACKGROUND

Anterior cruciate ligament (ACL) tears result in significant quadriceps muscle atrophy that is resistant to recovery despite extensive rehabilitation. Recent work suggests an elevated fibrotic burden in the quadriceps muscle after the injury, which may limit recovery. Elucidating the mechanisms and cell types involved in the progression of fibrosis is critical for developing new treatment strategies.

PURPOSE

To identify factors contributing to the elevated fibrotic burden found after the injury.

STUDY DESIGN

Descriptive laboratory study.

METHODS

After an ACL injury, muscle biopsy specimens were obtained from the injured and noninjured vastus lateralis of young adults (n = 14, mean ± SD: 23 ± 4 years). The expression of myostatin, transforming growth factor β, and other regulatory factors was measured, and immunohistochemical analyses were performed to assess turnover of extracellular matrix components.

RESULTS

Injured limb skeletal muscle demonstrated elevated myostatin gene ( P < .005) and protein ( P < .0005) expression, which correlated ( R² = 0.38, P < .05) with fibroblast cell abundance. Immunohistochemical analysis showed that human fibroblasts express the activin type IIB receptor and that isolated primary human muscle-derived fibroblasts increased proliferation after myostatin treatment in vitro ( P < .05). Collagen 1 and fibronectin, primary components of the muscle extracellular matrix, were significantly higher in the injured limb ( P < .05). The abundance of procollagen 1-expressing cells as well as a novel index of collagen remodeling was also elevated in the injured limb ( P < .05).

CONCLUSION

These findings support a role for myostatin in promoting fibrogenic alterations within skeletal muscle after an ACL injury.

CLINICAL RELEVANCE

The current work shows that the cause of muscle quality decline after ACL injury likely involves elevated myostatin expression, and future studies should explore therapeutic inhibition of myostatin to facilitate improvements in muscle recovery and return to sport.

Reduced mitochondrial lipid oxidation leads to fat accumulation in myosteatosis

Myosteatosis is the pathologic accumulation of lipid that can occur in conjunction with atrophy and fibrosis following skeletal muscle injury. Little is known about the mechanisms by which lipid accumulates in myosteatosis, but many clinical studies have demonstrated that the degree of lipid infiltration negatively correlates with muscle function and regeneration. Our objective was to determine the pathologic changes that result in lipid accumulation in injured muscle fibers. We used a rat model of rotator cuff injury in this study because the rotator cuff muscle group is particularly prone to the development of myosteatosis after injury. Muscles were collected from uninjured controls or 10, 30, or 60 d after injury and analyzed using a combination of muscle fiber contractility assessments, RNA sequencing, and undirected metabolomics, lipidomics, and proteomics, along with bioinformatics techniques to identify potential pathways and cellular processes that are dysregulated after rotator cuff tear. Bioinformatics analyses indicated that mitochondrial function was likely disrupted after injury. Based on these findings and given the role that mitochondria play in lipid metabolism, we then performed targeted biochemical and imaging studies and determined that mitochondrial dysfunction and reduced fatty acid oxidation likely leads to the accumulation of lipid in myosteatosis.-Gumucio, J. P., Qasawa, A. H., Ferrara, P. J., Malik, A. N., Funai, K., McDonagh, B., Mendias, C. L. Reduced mitochondrial lipid oxidation leads to fat accumulation in myosteatosis.

Crosstalk between mitogen-activated protein kinase inhibitors and transforming growth factor-β signaling results in variable activation of human dermal fibroblasts

Fibroblast activation is a key step in the establishment of skin fibrosis induced by acute injury, and it is characterized by the differentiation of plastic resident tissue fibroblasts into contractile, extracellular matrix‑secreting myofibroblasts. As fibroblast activation must be regulated in vivo, fibroblasts receive signals from the surrounding environment that initiate their fibrotic program. Thus, the present study investigated the effects of mitogen‑activated protein kinase (MAPK) signaling pathways on fibroblast activation. It was demonstrated in primary human dermal fibroblasts that small molecule‑mediated inhibition of extracellular signal‑regulated kinase (ERK) and c‑Jun N‑terminal kinase (JNK) potentiated fibroblast activation, and that small molecule‑mediated inhibition of p38 antagonized fibroblast activation. ERK and JNK inhibition cooperatively enhanced fibroblast activation mediated by treatment with exogenous transforming growth factor (TGF)‑β1, and p38 inhibition antagonized ERK inhibitor‑mediated or JNK inhibitor‑mediated fibroblast activation. Transcript analysis demonstrated that ERK and JNK inhibitor‑mediated fibroblast activation was accompanied by distinct changes in the expression of TGF‑β‑associated ligands and receptors, and that p38 inhibitor‑mediated antagonism of fibroblast activation was accompanied by a distinct expression paradigm of TGF‑β‑associated genes, including upregulation of betaglycan. ERK inhibitor‑mediated and JNK inhibitor‑mediated fibroblast activation was partially antagonized by small molecule‑mediated inhibition of TGF‑β receptor (R)1, indicating that these mechanisms of fibroblast activation are partially dependent on TGF‑β/TGF‑βR signaling. These data collectively demonstrate and provide partial explanations of the varied effects and pathway dependencies of MAPK inhibitor‑mediated effects on fibroblast activation.

Protein imbalance in the development of skeletal muscle wasting in tumour-bearing mice

BACKGROUND

Cancer cachexia occurs in approximately 80% of cancer patients and is a key contributor to cancer-related death. The mechanisms controlling development of tumour-induced muscle wasting are not fully elucidated. Specifically, the progression and development of cancer cachexia are underexplored. Therefore, we examined skeletal muscle protein turnover throughout the development of cancer cachexia in tumour-bearing mice.

METHODS

Lewis lung carcinoma (LLC) was injected into the hind flank of C57BL6/J mice at 8 weeks age with tumour allowed to develop for 1, 2, 3, or 4 weeks and compared with PBS injected control. Muscle size was measured by cross-sectional area analysis of haematoxylin and eosin stained tibialis anterior muscle. ² H₂ O was used to assess protein synthesis throughout the development of cancer cachexia. Immunoblot and RT-qPCR were used to measure regulators of protein turnover. TUNEL staining was utilized to measure apoptotic nuclei. LLC conditioned media (LCM) treatment of C2C12 myotubes was used to analyse cancer cachexia in vitro.

RESULTS

Muscle cross-sectional area decreased ~40% 4 weeks following tumour implantation. Myogenic signalling was suppressed in tumour-bearing mice as soon as 1 week following tumour implantation, including lower mRNA contents of Pax7, MyoD, CyclinD1, and Myogenin, when compared with control animals. AchRδ and AchRε mRNA contents were down-regulated by ~50% 3 weeks following tumour implantation. Mixed fractional synthesis rate protein synthesis was ~40% lower in 4 week tumour-bearing mice when compared with PBS controls. Protein ubiquitination was elevated by ~50% 4 weeks after tumour implantation. Moreover, there was an increase in autophagy machinery after 4 weeks of tumour growth. Finally, ERK and p38 MAPK phosphorylations were fourfold and threefold greater than control muscle 4 weeks following tumour implantation, respectively. Inhibition of p38 MAPK, but not ERK MAPK, in vitro partially rescued LCM-induced loss of myotube diameter.

CONCLUSIONS

Our findings work towards understanding the pathophysiological signalling in skeletal muscle in the initial development of cancer cachexia. Shortly following the onset of the tumour-bearing state alterations in myogenic regulatory factors are apparent, suggesting early onset alterations in the capacity for myogenic induction. Cancer cachexia presents with a combination of a loss of protein synthesis and increased markers of protein breakdown, specifically in the ubiquitin-proteasome system. Also, p38 MAPK may be a potential therapeutic target to combat cancer cachexia via a p38-FOX01-atrogene-ubiquitin-proteasome mechanism.

Alterations in tendon microenvironment in response to mechanical load: potential molecular targets for treatment strategies

Rotator cuff (RC) tendons could beinflicted in many ways with an eventual outcome of pain, weakness and disability, which represent a large burden on health care cost. However, optimal healing, either conservatively or with surgical intervention, remains an issue that needs further investigation. Disorders of the RC tendons may result from external factors like trauma, or internal factors through physiologic and metabolic derangement. Most RC tendon disorders may be asymptomatic and may result from an over-activity of the inflicted shoulder and its tendons. Such tendon disorders are poorly diagnosed since patients do not seek medical attention until pain or weakness ensue. Immunological and biochemical events in RC disorders due to mechanical intolerance have not been investigated. Generally, the mechanical load drives normal physiological properties of the tendon. But, mechanical overload/burden exerts stress on tenocytes, and disrupts the tendon microenvironment by triggering a multitude of signaling pathways leading to extracellular matrix remodeling, disorganization, alteration in collagen composition and apoptosis. These events result in weak tendon which is highly susceptible to rupture or tear. In this article, we critically reviewed the intrinsic signaling pathways that are excessively triggered by continuous mechanical load and the counteracting physiological responses and associated derangements. The elucidation of the molecular events underlying mechanical stress-induced symptomatic/asymptomatic tendinopathy could provide information on potential target sites for translational application in the management of rotator cuff disorders.

Fibroblast-Specific Genetic Manipulation of p38 Mitogen-Activated Protein Kinase In Vivo Reveals Its Central Regulatory Role in Fibrosis

BACKGROUND

In the heart, acute injury induces a fibrotic healing response that generates collagen-rich scarring that is at first protective but if inappropriately sustained can worsen heart disease. The fibrotic process is initiated by cytokines, neuroendocrine effectors, and mechanical strain that promote resident fibroblast differentiation into contractile and extracellular matrix-producing myofibroblasts. The mitogen-activated protein kinase p38α (Mapk14 gene) is known to influence the cardiac injury response, but its direct role in orchestrating programmed fibroblast differentiation and fibrosis in vivo is unknown.

METHODS

A conditional Mapk14 allele was used to delete the p38α encoding gene specifically in cardiac fibroblasts or myofibroblasts with 2 different tamoxifen-inducible Cre recombinase-expressing gene-targeted mouse lines. Mice were subjected to ischemic injury or chronic neurohumoral stimulation and monitored for survival, cardiac function, and fibrotic remodeling. Antithetically, mice with fibroblast-specific transgenic overexpression of activated mitogen-activated protein kinase kinase 6, a direct inducer of p38, were generated to investigate whether this pathway can directly drive myofibroblast formation and the cardiac fibrotic response.

RESULTS

In mice, loss of Mapk14 blocked cardiac fibroblast differentiation into myofibroblasts and ensuing fibrosis in response to ischemic injury or chronic neurohumoral stimulation. A similar inhibition of myofibroblast formation and healing was also observed in a dermal wounding model with deletion of Mapk14. Transgenic mice with fibroblast-specific activation of mitogen-activated protein kinase kinase 6-p38 developed interstitial and perivascular fibrosis in the heart, lung, and kidney as a result of enhanced myofibroblast numbers. Mechanistic experiments show that p38 transduces cytokine and mechanical signals into myofibroblast differentiation through the transcription factor serum response factor and the signaling effector calcineurin.

CONCLUSIONS

These findings suggest that signals from diverse modes of injury converge on p38α mitogen-activated protein kinase within the fibroblast to program the fibrotic response and myofibroblast formation in vivo, suggesting a novel therapeutic approach with p38 inhibitors for future clinical application.

Blockade of p38 Mitogen-Activated Protein Kinase Inhibits Murine Sclerodermatous Chronic Graft-versus-Host Disease

Bone marrow transplantation (BMT) of B10.D2 mice into sublethally irradiated BALB/c mice across minor histocompatibility loci is a well-established animal model for human sclerodermatous chronic graft-versus-host disease (Scl-cGVHD) and systemic sclerosis (SSc). The p38 mitogen-activated protein kinase (MAPK) pathway is a key regulator of inflammation and cytokine production. Furthermore, the activation of p38 MAPK plays an important role in collagen production in SSc. We investigated the effects of p38 MAPK inhibitor, VX-702, on Scl-cGVHD mice. VX-702 was orally administered to Scl-cGVHD mice from day 7 to 35 after BMT. We compared skin fibrosis of Scl-cGVHD mice between the VX-702-treated group and control group. Allogeneic BMT increased the phosphorylation of p38 MAPK in the skin. The administration of VX-702 attenuated the skin fibrosis of Scl-cGVHD compared to the control mice. Immunohistochemical staining showed that VX-702 suppressed the infiltration of CD4⁺ T cells, CD8⁺ T cells, and CD11b⁺ cells into the dermis of Scl-cGVHD mice compared to the control mice. VX-702 attenuated the mRNA expression of extracellular matrix and fibrogenic cytokines, such as IL-6 and IL-13, in the skin of Scl-cGVHD mice. In addition, VX-702 directly inhibited collagen production from fibroblasts in vitro. VX-702 was shown to be a promising candidate for use in treating patients with Scl-cGVHD and SSc.

The Rotator Cuff Organ: Integrating Developmental Biology, Tissue Engineering, and Surgical Considerations to Treat Chronic Massive Rotator Cuff Tears

The torn rotator cuff remains a persistent orthopedic challenge, with poor outcomes disproportionately associated with chronic, massive tears. Degenerative changes in the tissues that comprise the rotator cuff organ, including muscle, tendon, and bone, contribute to the poor healing capacity of chronic tears, resulting in poor function and an increased risk for repair failure. Tissue engineering strategies to augment rotator cuff repair have been developed in an effort to improve rotator cuff healing and have focused on three principal aims: (1) immediate mechanical augmentation of the surgical repair, (2) restoration of muscle quality and contractility, and (3) regeneration of native enthesis structure. Work in these areas will be reviewed in sequence, highlighting the relevant pathophysiology, developmental biology, and biomechanics, which must be considered when designing therapeutic applications. While the independent use of these strategies has shown promise, synergistic benefits may emerge from their combined application given the interdependence of the tissues that constitute the rotator cuff organ. Furthermore, controlled mobilization of augmented rotator cuff repairs during postoperative rehabilitation may provide mechanotransductive cues capable of guiding tissue regeneration and restoration of rotator cuff function. Present challenges and future possibilities will be identified, which if realized, may provide solutions to the vexing condition of chronic massive rotator cuff tears.

A HuR/TGF-β1 feedback circuit regulates airway remodeling in airway smooth muscle cells

Background

Asthma is a worldwide health burden with an alarming prevalence. For years, asthma-associated airway injury remains elusive. Transforming growth factor β1 (TGF-β1) is a pleiotropic cytokine that has been shown to be involved in the synthesis of the matrix molecules associated with airway remodeling. Human antigen R (HuR), the member of the Hu RNA-binding protein family, can bind to a subset of short-lived mRNAs in their 3′ untranslated regions (UTR). However, the functional roles and relevant signaling pathways of HuR in airway remodeling have not been well illustrated. Thus, we aim to explore the relationship between HuR and TGF-β1 in platelet derived growth factor(PDGF)-induced airway smooth muscle (ASM) cells and asthmatic animal.

Methods

Cultured human ASM cells were stimulated by PDGF for 0, 6, 12 and 24 h. Western blotting, RT-PCR and immunofluoresence were used to detect the expression of HuR, TGF-β1, α-smooth muscle actins (α-SMA) and collagen type I (Col-I). Then knockdown of HuR, flow cytomerty was used to detect the morphological change and western blotting for functionally change of ASM cells. Furthermore, the interference of TGF-β1 and exogenous TGF-β1 were implemented to testify the influence on HuR. A murine OVA-driven allergic model based on sensitization and challenge was developed. The inflammatory response was measured by bronchoalveolar lavage fluid (BALF), airway damage was analyzed by hematoxylin and eosin staining, airway remodeling was assessed by sirius red staining and periodic acid-schiff staining, the expression level of HuR, TGF-β1 and α-SMA were measured by RT-PCR, western blotting and immunohistochemistry.

Results

Here, we found that PDGF elevated HuR expression both at mRNA and protein level in cultured ASM cells at a time-dependent manner, which was simultaneously accompanied by the enhanced expression of TGF-β1, α-SMA and Col-I. Further study revealed that the knockdown of HuR significantly increased the apoptosis of ASM cells and dampened TGF-β1, Col-I and α-SMA expression. However, interfering TGF-β1 with siRNA or extra addition of TGF-β1, HuR could restore its production as well as Col-I. Compared with normal mice stimulating with PBS, OVA-induced mice owned high amount of inflammatory cells, such as eosinophils, lymphocytes and neutrophils except macrophages. HE staining showed accumulation of inflammatory cells surrounding bronchiole and sirius red staining distinguished collagen type I and III deposition around the bronchiole. Higher abundance of HuR, TGF-β1 and α-SMA were verified in OVA-induced mice than PBS-induced mice by RT-PCR, western blotting and immunohistochemistry.

Conclusions

A HuR/TGF-β1 feedback circuit was established to regulate airway remodeling in vivo and in vitro and targeting this feedback has considerable potential for the intervention of asthma.