Role of tumor-associated macrophages in the progression of hepatocellular carcinoma

Recent studies have shown that the tumor microenvironment plays an important role in cancer progression. Tumor-associated macrophages (TAMs), in particular, have been found to be associated with tumor progression. Macrophages have multiple biological roles, including antigen presentation, target cell cytotoxicity, removal of foreign bodies, tissue remodeling, regulation of inflammation, induction of immunity, thrombosis, and endocytosis. Recent immunological studies have identified two distinct states of polarized macrophage activation: the classically activated (M1) and the alternatively activated (M2) macrophage phenotypes. Bacterial moieties such as lipopolysaccharides and the Th1 cytokine interferon-γ polarize macrophages toward the M1 phenotype. The M2 polarization was discovered as a response to the Th2 cytokine interleukin-4. In general, M2 macrophages exert immunoregulatory activity, participate in polarized Th2 responses, and aid tumor progression. TAMs have recently been found to play an important role in hepatocellular carcinoma (HCC) progression. Based on the properties of TAMs, obtained from pathological examination of resected specimens, we have identified new therapeutic approaches, involving the targeting of TAMs with adjuvant therapy after hepatic resection for HCC. This review discusses the roles of TAM in HCC progression and the possibility of new therapies targeting TAMs.     

Macrophages Undergo M1‐to‐M2 Transition in Adipose Tissue Regeneration in a Rat Tissue Engineering Model

Macrophages are involved in the full processes of tissue healing or regeneration and play an important role in the regeneration of a variety of tissues. Although recent evidence suggests the role of different macrophage phenotypes in adipose tissue expansion, metabolism, and remodeling, the spectrum of macrophage phenotype in the adipose tissue engineering field remains unknown. The present study established a rat model of adipose tissue regeneration using a tissue engineering chamber. Macrophage phenotypes were assessed during the regenerative process in the model. Neo‐adipose tissue was generated 6 weeks after implantation. Macrophages were obvious in the chamber constructs 3 days after implantation, peaked at day 7, and significantly decreased thereafter. At day 3, macrophages were predominantly M1 macrophages (CCR7+), and there were few M2 macrophages (CD206+). At day 7, the percentage of M2 macrophages significantly increased and remained stable at day 14. M2 macrophages became the predominant macrophage population at 42 days. Enzyme‐linked immunosorbent assay demonstrated transition of cytokines from pro‐inflammatory to anti‐inflammatory, which was consistent with the transition of macrophage phenotype from M1 to M2. These results showed distinct transition of macrophage phenotypes from a pro‐inflammatory M1 phenotype to an anti‐inflammatory M2 in adipose tissue regeneration in our tissue engineering model. This study provides new insight into macrophage phenotype transition in the regeneration of adipose tissue.     

Inflammation in tendinopathy

Pain and functional limitation are frequent in symptomatic tendinopathy. The essential lesion of tendinopathy is a failed healing response. Understanding the cellular and molecular mechanisms involved in a failed healing response during the early stages of pathogenesis of tendinopathy would help to develop new and effective treatments. The role of inflammation in the development of tendon pathologies has been revived during the last few years, in particular during the first phases of tendinopathies, when “early tendinopathy” may not be clinically evident. This review outlines the possible molecular events that occur in the first phases of tendinopathy onset, stressing the role of pro-inflammatory cytokines, proteolytic enzymes, growth factors and healing genes in the development of tendon disorders.     

The clinical dynamic changes of macrophage phenotype and function in different stages of human wound healing and hypertrophic scar formation

The pathogenesis of hypertrophic scar (HS) is still poorly understood. Macrophages, especially the polarisation of that to M1 or M2, play a pivotal role in control of the degree of scar formation. Profiling of macrophage phenotypes in human specimens during long‐term period of wound healing and HS formation may provide valuable clinical evidence for understanding the pathology of human scars. Human wound and HS specimens were collected, the macrophage phenotype was identified by immunofluorescence, and biomarkers and cytokines associated with M1 and M2 macrophages were detected by RT‐PCR. The correlation between the macrophage phenotype and HS characteristics was analysed by linear regression analyses. We found excessive and persistent infiltration by M1 macrophages around the blood vessels in the superficial layer of the dermis at early wound tissues, whereas M2 macrophages predominated in later wound tissues and the proliferative phase of HS and were scattered throughout the dermis. The density of M1 macrophages was positively correlated with mRNA expression levels of tumour necrosis factor‐alpha (TNF‐α) and IL‐6. The density of M2 macrophages was positively correlated with ARG1 and negatively correlated with the duration of HS. The sequential infiltration by M1 macrophage and M2 macrophages in human wound and HS tissues was confirmed.     

Epigenetic Changes in Bone Marrow Progenitor Cells Influence the Inflammatory Phenotype and Alter Wound Healing in Type 2 Diabetes

Classically activated (M1) macrophages are known to play a role in the development of chronic inflammation associated with impaired wound healing in type 2 diabetes (T2D); however, the mechanism responsible for the dominant proinflammatory (M1) macrophage phenotype in T2D wounds is unknown. Since epigenetic enzymes can direct macrophage phenotypes, we assessed the role of histone methylation in bone marrow (BM) stem/progenitor cells in the programming of macrophages toward a proinflammatory phenotype. We have found that a repressive histone methylation mark, H3K27me3, is decreased at the promoter of the IL-12 gene in BM progenitors and this epigenetic signature is passed down to wound macrophages in a murine model of glucose intolerance (diet-induced obese). These epigenetically “preprogrammed” macrophages result in poised macrophages in peripheral tissue and negatively impact wound repair. We found that in diabetic conditions the H3K27 demethylase Jmjd3 drives IL-12 production in macrophages and that IL-12 production can be modulated by inhibiting Jmjd3. Using human T2D tissue and murine models, we have identified a previously unrecognized mechanism by which macrophages are programmed toward a proinflammatory phenotype, establishing a pattern of unrestrained inflammation associated with nonhealing wounds. Hence, histone demethylase inhibitor–based therapy may represent a novel treatment option for diabetic wounds.     

Macrophages in renal disease

Macrophages have heterogeneous phenotypes as they exercise their twofold role in the development and recovery of renal diseases. Some subpopulations of macrophages (M1) have a pathogenic function in renal inflammation, making them a logical target for elimination. Alternatively, M2 macrophage subpopulations resolve inflammation and repair injury, making them a potential therapeutic tool against renal injury. Here, we summarize recent findings regarding macrophage plasticity, and the various strategies for targeting or utilizing macrophages to treat renal disease. We highlight, in particular, the potential of renoprotective M2 macrophages to resolve inflammation and repair the kidney.     

Effects of Type II Diabetes Mellitus on Tendon Homeostasis and Healing

Over 300,000 tendon repairs are performed annually in the United States to repair damage to tendons as a result of either acute trauma or chronic tendinopathy. Individuals with type II diabetes mellitus (T2DM) are four times more likely to experience tendinopathy, and up to five times more likely to experience a tendon tear or rupture than non-diabetics. As nearly 10% of the US population is diabetic, with an additional 33% pre-diabetic, this is a particularly problematic health care challenge. Tendon healing in general is challenging and often unsatisfactory due to the formation of mechanically inferior scar-tissue rather than regeneration of native tendon structure. In T2DM tendons, there is evidence of an amplified scar tissue response, which may be associated with the increased the risk of rupture or impaired restoration of range of motion. Despite the dramatic effect of T2DM on tendon function and outcomes following injury, there are few therapies available to promote improved healing in these patients. Several recent studies have enhanced our understanding of the pro-inflammatory environment of T2DM healing and have assessed potential treatment approaches to mitigate pathological progression in pre-clinical models of diabetic tendinopathy. This review discusses the current state of knowledge of diabetic tendon healing from molecular to mechanical disruptions and identifies promising approaches and critical knowledge gaps as the field moves toward identification of novel therapeutic strategies to maintain or restore tendon function in diabetic patients. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:13–22, 2020     

Macrophages: A review of their role in wound healing and their therapeutic use

Macrophages are mononuclear phagocytes established during embryogenesis and derived from the yolk sac or the fetal liver but also recruited from the blood and bone marrow under proliferative inflammatory conditions (such as tissue repair). Most importantly, they take on distinct phenotypes and functions crucial to healing upon localization in the wound. The objective of this review is to summarize recent findings in regard to the cellular mechanisms of macrophages and chronic wounds. Advances in the potential use of macrophage therapy have arisen based, in part, on the fact that early recruitment of macrophages is critical to wound healing. Higher quality evidence is needed to support the use of macrophage therapy for chronic wound types, as is a better understanding of the signaling related to macrophage polarization, activation of macrophages, and their effect of mechanisms of repair. An evaluation of the currently available research on mechanism of action may lead to a better understanding of the signaling processes of the many macrophage phenotypes, as well as their roles and outcomes in wound healing, which could then guide the development and eventual widespread use of macrophage therapies.     

Anti‐inflammatory effects of haptoglobin on LPS‐stimulated macrophages: Role of HMGB1 signaling and implications in chronic wound healing

Nonhealing wounds possess elevated numbers of pro‐inflammatory M1 macrophages, which fail to transition to anti‐inflammatory M2 phenotypes that promote healing. Hemoglobin (Hb) and haptoglobin (Hp) proteins, when complexed (Hb‐Hp), can elicit M2‐like macrophages through the heme oxygenase‐1 (HO‐1) pathway. Despite the fact that nonhealing wounds are chronically inflamed, previous studies have focused on non‐inflammatory systems, and do not thoroughly compare the effects of complexed vs individual proteins. We aimed to investigate the effect of Hb/Hp treatments on macrophage phenotype in an inflammatory, lipopolysaccharide (LPS)‐stimulated environment, similar to chronic wounds. Human M1 macrophages were cultured in vitro and stimulated with LPS. Concurrently, Hp, Hb, or Hb‐Hp complexes were delivered. The next day, 27 proteins related to inflammation were measured in the supernatants. Hp treatment decreased a majority of inflammatory factors, Hb increased many, and Hb‐Hp had intermediate trends, indicating that Hp attenuated overall inflammation to the greatest extent. From this data, Ingenuity Pathway Analysis software identified high motility group box 1 (HMGB1) as a key canonical pathway—strongly down‐regulated from Hp, strongly up‐regulated from Hb, and slightly activated from Hb‐Hp. HMGB1 measurements in macrophage supernatants confirmed this trend. In vivo results in diabetic mice with biopsy punch wounds demonstrated accelerated wound closure with Hp treatment, and delayed wound closure with Hb treatment. This work specifically studied Hb/Hp effects on macrophages in a highly inflammatory environment relevant to chronic wound healing. Results show that Hp—and not Hb‐Hp, which is known to be superior in noninflammatory conditions—reduces inflammation in LPS‐stimulated macrophages, and HMGB1 signaling is also implicated. Overall, Hp treatment on M1 macrophages in vitro reduced the inflammatory secretion profile, and also exhibited benefits in in silico and in vivo wound‐healing models.     

Diabetes‐impaired wound healing and altered macrophage activation: A possible pathophysiologic correlation

Macrophages play a critical role in wound healing and can be activated to two distinctive phenotypes in vitro: classical macrophage activation (caM) and alternative macrophage activation (aaM). This study investigated whether the impaired cutaneous repair observed in streptozotocin‐induced diabetic rats was associated with altered macrophage activation. Our results show that macrophage activation phenotypes could be observed in wound healing through double immunostaining. The caM macrophages appeared in the initial stage of wound healing, followed by aaM macrophages, which predominated in normal wounds. However, through examining markers associated with activation by immunoblotting and real‐time polymerase chain reaction (PCR), diabetic wounds demonstrated insufficient caM in the early stage but excessive aaM in the later proliferative phase. Moreover, the macrophage activation markers were correlated with the instructive T helper cell type 1 (Th1)/Th2 cytokines in both groups. It was indicated that changed macrophage activation might contribute to impaired healing in diabetes wounds, and that strategies for reverting this abnormal activation could be useful for enhancing the wound healing process.     

Macrophages and the kidney

PURPOSE OF REVIEW: Macrophage infiltration is a hallmark of all forms of inflammatory and non-inflammatory renal injury. However, the classical view of macrophages as cells that cause injury has been superseded with evidence of their heterogeneous role, i.e. with involvement in all stages of the inflammatory process including tissue repair and healing. This review summarizes the major advances in macrophage biology achieved in the last year, highlighting the different activation states, how these are regulated, and their relevance in renal disease. RECENT FINDINGS: New concepts have emerged concerning the factors controlling monocyte recruitment into inflamed tissue and their subsequent differentiation into activated macrophages. There is now compelling evidence for the heterogeneity of macrophages in clinical disease, i.e. they appear to be able to both promote and downregulate inflammation. An increased understanding of the factors regulating the expression of pro-inflammatory or reparative characteristics by macrophages is establishing how their function can be manipulated to attenuate renal inflammation in experimental models. SUMMARY: An understanding of the role of macrophages at different time-points in renal inflammation, and the development of techniques for modulating macrophage activation in vivo, will provide a powerful method for exploiting the reparative attributes of these cells in clinical settings, restoring regulation to the inflammatory process and promoting healing.     

Renal microenvironments and macrophage phenotypes determine progression or resolution of renal inflammation and fibrosis

Chronic kidney disease involves renal inflammation, interstitial fibrosis, and tubular and vascular atrophy. Macrophages seem to foster all of these histomorphological abnormalities, but their specific contributions remain controversial. Recruited monocytes differentiate into different tissue macrophage phenotypes, but current classifications are largely based on in vitro studies that do not adequately mirror tissue environments in vivo. To overcome this limitation, we propose to classify tissue macrophages according to their predominant roles in the phases of wound healing tissue environments, that is, inflammation, epithelial healing, mesenchymal healing, and fibrolysis. In this review, we discuss the evidence on respective macrophage phenotypes in renal pathology. This view sheds light on several aspects of renal remodeling in kidney disease: (1) renal infection or cell necrosis induces proinflammatory 'M1' macrophages that exacerbate renal cell damage, (2) uptake of apoptotic cells induces anti-inflammatory 'M2c/suppressor' macrophages that promote epithelial and vascular repair, (3) insufficient vascular and epithelial healing despite abundant growth factor secretion promotes profibrotic 'M2a/wound healing' macrophages that accelerate fibrogenesis, and (4) theoretically, fibrolytic macrophages should exist and await investigation.     

Expression of chondro‐osteogenic BMPs in ossified failed tendon healing model of tendinopathy

Chondrocytes phenotype/markers were expressed in clinical samples of tendinopathy and calcifying tendinopathy. This study examined the spatial‐temporal expression of chondro‐osteogenic Bone Morphogenetic Proteins (BMPs), which might contribute to ectopic chondro‐osteogenesis and failed healing process in tendinopathy. Collagenase was injected into patellar tendon of rats to induce ossified failed tendon healing. At week 2, 4, 8, 12, and 16, the patella tendon was harvested for immunohistochemical staining and analysis of BMP‐2/4/7. BMP‐4/7 showed similar expression patterns, which was different from BMP‐2. The expression of BMP‐2 in the tendon matrix increased at week 2 and was reduced to nearly undetectable level afterwards except at the chondro‐ossification sites. However, the expression of BMP‐4/7 in the healing tendon fibroblast‐like cells and matrix increased at week 2, reduced at week 4 and 8 and increased again at week 12 and 16, consistent with transient healing at week 8 in this animal model. There was increasing strong expression of BMP‐4/7 in the chondrocyte‐like cells in the un‐ossified and ossified areas from week 8–16. BMP‐4/7, besides BMP‐2, might also contribute to ectopic chondro‐osteogenesis and failed healing in tendon injuries. BMP‐4/7, but not BMP‐2, might be involved in regulating late events in ossified failed tendon healing. © 2010 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29:816–821     

Blocking Interleukin-1β Induces a Healing-Associated Wound Macrophage Phenotype and Improves Healing in Type 2 Diabetes

Diabetes is associated with persistent inflammation and defective tissue repair responses. The hypothesis of this study was that interleukin (IL)-1β is part of a proinflammatory positive feedback loop that sustains a persistent proinflammatory wound macrophage phenotype that contributes to impaired healing in diabetes. Macrophages isolated from wounds in diabetic humans and mice exhibited a proinflammatory phenotype, including expression and secretion of IL-1β. The diabetic wound environment appears to be sufficient to induce these inflammatory phenomena because in vitro studies demonstrated that conditioned medium of both mouse and human wounds upregulates expression of proinflammatory genes and downregulates expression of prohealing factors in cultured macrophages. Furthermore, inhibiting the IL-1β pathway using a neutralizing antibody and macrophages from IL-1 receptor knockout mice blocked the conditioned medium–induced upregulation of proinflammatory genes and downregulation of prohealing factors. Importantly, inhibiting the IL-1β pathway in wounds of diabetic mice using a neutralizing antibody induced a switch from proinflammatory to healing-associated macrophage phenotypes, increased levels of wound growth factors, and improved healing of these wounds. Our findings indicate that targeting the IL-1β pathway represents a new therapeutic approach for improving the healing of diabetic wounds.Chronic wounds associated with diabetes, venous insufficiency, or pressure represent a major health problem, with millions of patients afflicted and the associated treatment costing billions of dollars per year (1). Despite the socioeconomic impact of chronic wounds, the underlying causes of impaired healing are not well-understood and effective treatments remain elusive. A common characteristic of these poorly healing wounds is a persistent inflammatory response, with prolonged accumulation of macrophages and elevated levels of proinflammatory cytokines (2–5). Translational research of the dysregulation of inflammation associated with impaired healing in diabetes should provide insight into the development of new therapeutic approaches.During normal wound healing in mice, inflammatory cells such as macrophages promote healing indirectly by killing pathogens and clearing the wound of damaged tissue, but also promote healing directly by producing growth factors that induce angiogenesis, collagen deposition, and wound closure (6–9). In contrast, during impaired healing of diabetic mice, wounds exhibit prolonged accumulation of macrophage associated with elevated levels of proinflammatory cytokines and proteases and reduced levels of various growth factors, all of which mimic chronic wounds in humans (10–12). We recently demonstrated that in wounds of diabetic mice, macrophages exhibit a sustained proinflammatory phenotype with an impaired upregulation of healing-associated factors that is observed in nondiabetic mice as healing progresses (13). However, the underlying causes of the dysregulation of macrophage in diabetic wounds remain to be elucidated.Multiple factors can influence macrophage phenotype and the actual phenotypes expressed in chronic wounds are likely determined by the balance of the proinflammatory and anti-inflammatory stimuli present in the wound environment. The proinflammatory environment observed in diabetic wounds has the potential to sustain a proinflammatory macrophage phenotype, which, in turn, would contribute to sustaining the proinflammatory environment. In fact, hyperglycemia is known to induce expression of interleukin (IL)-1β in a number of different cell types, including macrophages (14–16), and IL-1β, in turn, is known to induce a proinflammatory macrophage phenotype in part by inducing itself (17). Thus, the IL-1β pathway may be part of a positive feedback loop that sustains inflammation in chronic wounds and contributes to impaired healing. However, little is known about the actual role of IL-1β in diabetic wounds.The central hypothesis of this study is that sustained activity of the IL-1β pathway in diabetic wounds contributes to impaired healing of these wounds. The results of this study demonstrate that sustained IL-1β expression in wounds of diabetic humans and mice is associated with a proinflammatory macrophage phenotype, and that inhibiting the IL-1β pathway in wounds of diabetic mice induces the switch from proinflammatory to healing-associated macrophage phenotypes and improves healing of these wounds.     

Autophagy ameliorates Pseudomonas aeruginosa-infected diabetic wounds by regulating the toll-like receptor 4/myeloid differentiation factor 88 pathway

Diabetic foot ulcers (DFUs) are among the most common complications in patients with diabetes and a leading cause of lower extremity amputation. DFUs are exacerbated by prolonged bacterial infection; therefore, there is an urgent need for effective treatments to alleviate the burden associated with this condition. Although autophagy plays a unique role in pathogen phagocytosis and inflammation, its role in diabetic foot infections (DFIs) remains unclear. Pseudomonas aeruginosa (PA) is the most frequently isolated gram-negative bacterium from DFUs. Here, we evaluated the role of autophagy in ameliorating PA infection in wounds in a diabetic rat model and a bone marrow-derived macrophage (BMDM) hyperglycemia model. Both models were pretreated with or without rapamycin (RAPA) and then infected with or without PA. Pretreatment of rats with RAPA significantly enhanced PA phagocytosis, suppressed wound inflammation, reduced the M1:M2 macrophage ratio, and improved wound healing. In vitro investigation of the underlying mechanisms revealed that enhanced autophagy resulted in decreased macrophage secretion of inflammatory factors such as TNF-α, IL-6, and IL-1β but increased that of IL-10 in response to PA infection. Additionally, RAPA treatment significantly enhanced autophagy in macrophages by increasing LC3 and beclin-1 levels, which led to altered macrophage function. Furthermore, RAPA blocked the PA-induced TLR4/MyD88 pathway to regulate macrophage polarisation and inflammatory cytokine production, which was validated by RNA interference and use of the autophagy inhibitor 3-methyladenine (3-MA). These findings suggest enhancing autophagy as a novel therapeutic strategy against PA infection to ultimately improve diabetic wound healing.     

Tendon biomechanics and mechanobiology--a minireview of basic concepts and recent advancements

Due to their unique hierarchical structure and composition, tendons possess characteristic biomechanical properties, including high mechanical strength and viscoelasticity, which enable them to carry and transmit mechanical loads (muscular forces) effectively. Tendons are also mechanoresponsive by adaptively changing their structure and function in response to altered mechanical loading conditions. In general, mechanical loading at physiological levels is beneficial to tendons, but excessive loading or disuse of tendons is detrimental. This mechanoadaptability is due to the cells present in tendons. Tendon fibroblasts (tenocytes) are the dominant tendon cells responsible for tendon homeostasis and repair. Tendon stem cells (TSCs), which were recently discovered, also play a vital role in tendon maintenance and repair by virtue of their ability to self-renew and differentiate into tenocytes. TSCs may also be responsible for chronic tendon injury, or tendinopathy, by undergoing aberrant differentiation into nontenocytes in response to excessive mechanical loading. Thus, it is necessary to devise optimal rehabilitation protocols to enhance tendon healing while reducing scar tissue formation and tendon adhesions. Moreover, along with scaffolds that can mimic tendon matrix environments and platelet-rich plasma, which serves as a source of growth factors, TSCs may be the optimal cell type for enhancing repair of injured tendons.     

Loss of NADPH Oxidase–Derived Superoxide Skews Macrophage Phenotypes to Delay Type 1 Diabetes

Macrophages are early islet-infiltrating cells seen in type 1 diabetes (T1D). While proinflammatory M1 macrophages induce T1D, M2 macrophages have been shown to delay this autoimmune disease in nonobese diabetic (NOD) mice, but the environmental cues that govern macrophage polarization and differentiation remain unresolved. We previously demonstrated the importance of reactive oxygen species (ROS) in T1D, as NOD mice deficient in NADPH oxidase (NOX)-derived superoxide (Ncf1^m1J) were protected against T1D partly because of blunted Toll-like receptor–dependent macrophage responses. We provide evidence that NOX-derived ROS contribute to macrophage differentiation in T1D. During spontaneous diabetes progression, T1D-resistant NOD.Ncf1^m1J islet-resident macrophages displayed a dampened M1 and increased M2 phenotype. The transfer of diabetogenic T cells into NOX-deficient NOD.Rag.Ncf1^m1J recipients resulted in decreased TNF-α⁺ and IL-1β⁺ islet-infiltrating M1 macrophages and a concomitant enhancement in arginase-1⁺ M2 macrophages. Mechanistic analysis of superoxide-deficient bone marrow–derived macrophages revealed a marked diminution in a proinflammatory M1 phenotype due to decreased P-STAT1 (Y701) and interferon regulatory factor 5 compared with NOD mice. We have therefore defined a novel mechanistic link between NOX-derived ROS and macrophage phenotypes, and implicated superoxide as an important factor in macrophage differentiation. Thus, targeting macrophage redox status may represent a promising therapy in halting human T1D.     

Neutrophils and macrophages accumulate sequentially following Achilles tendon injury.

Structural damage and inflammation occur following tendon injury. The purpose of this study was to determine the time course of inflammatory cell accumulation in two animal models of acute tendinopathy. In the first model, rat Achilles tendons were exposed by blunt dissection, injected with collagenase and sacrificed at 1, 3, 7, 14 and 28 days. In the second model, collagenase was injected percutaneously and rats were sacrificed after 1 and 3 days. Sham animals were sacrificed at 1 and 3 days in both models. Neutrophil and ED1 macrophage populations increased by 46- and 18-fold, respectively, after 1 day in surgically exposed Achilles tendons (EAT) injected with collagenase. Neutrophils dropped by 70% while the concentration of ED1 macrophages remained constant at day 3 post-injury. Neutrophils and ED1+ macrophages returned to control values after 7 and 14 days, respectively. ED2+ macrophages showed a tendency to increase at day 28 although no significant difference was observed relative to ambulatory controls. Collagenase injected percutaneously reduced the extent of inflammation compared with operated animals. Thus, injured tendons exhibited a specific sequence of inflammatory cell accumulation which varied in intensity according to the modality used for collagenase injection.     

M2 Macrophage Polarization Mediates Anti-inflammatory Effects of Endothelial Nitric Oxide Signaling

Endothelial nitric oxide (NO) signaling plays a physiological role in limiting obesity-associated insulin resistance and inflammation. This study was undertaken to investigate whether this NO effect involves polarization of macrophages toward an anti-inflammatory M2 phenotype. Mice with transgenic endothelial NO synthase overexpression were protected against high-fat diet (HFD)-induced hepatic inflammation and insulin resistance, and this effect was associated with reduced proinflammatory M1 and increased anti-inflammatory M2 activation of Kupffer cells. In cell culture studies, exposure of macrophages to endothelial NO similarly reduced inflammatory (M1) and increased anti-inflammatory (M2) gene expression. Similar effects were induced by macrophage overexpression of vasodilator-stimulated phosphoprotein (VASP), a key downstream mediator of intracellular NO signaling. Conversely, VASP deficiency induced proinflammatory M1 macrophage activation, and the transplantation of bone marrow from VASP-deficient donor mice into normal recipients caused hepatic inflammation and insulin resistance resembling that induced in normal mice by consumption of an HFD. These data suggest that proinflammatory macrophage M1 activation and macrophage-mediated inflammation are tonically inhibited by NO → VASP signal transduction, and that reduced NO → VASP signaling is involved in the effect of HFD feeding to induce M1 activation of Kupffer cells and associated hepatic inflammation. Our data implicate endothelial NO → VASP signaling as a physiological determinant of macrophage polarization and show that signaling via this pathway is required to prevent hepatic inflammation and insulin resistance.     

The Peripheral Neuronal Phenotype is Important in the Pathogenesis of Painful Human Tendinopathy: A Systematic Review

Background

The pathogenesis of tendinopathy is complex and incompletely understood. Although significant advances have been made in terms of understanding the pathological changes in both the extracellular matrix and the cells involved, relatively little is known about the role of neuronal regulation in tendinopathy. The frequent mismatch between tendon pathology and pain may be explained, in part, by differences in the peripheral neuronal phenotype of patients.

Questions/purposes

The primary purpose of this review was to determine whether evidence exists of changes in the peripheral neuronal phenotype in painful human tendinopathy and, if so, to identify the associated histological and molecular changes. The secondary purpose was to determine if any changes in the peripheral neuronal phenotype reported correlate with pain symptoms.

Methods

We conducted a systematic review of the scientific literature using the PRISMA and Cochrane guidelines. The Medline and Embase databases were searched using specific search criteria. Only studies analyzing the peripheral tissue of patients with the clinical diagnosis of tendinopathy were included. Inclusion was agreed on by two independent researchers on review of abstracts or full text.

Results

Overall in the 27 included studies, there was clear evidence of changes in the peripheral neuronal phenotype in painful human tendinopathy. The excitatory glutaminergic system was significantly upregulated in seven studies, there was a significant increase in sensory neuropeptide expression in four studies, and there were significant changes in the molecular morphology of tenocytes, blood vessels, and nerves. In rotator cuff tendinopathy, substance P has been shown to correlate with pain and the neural density in the subacromial bursa has been shown to correlate with rest pain.

Conclusions

The peripheral neuronal phenotype is an important factor in the pathogenesis of painful human tendinopathy. Further research in this area specifically correlating tissue changes to clinical scores has great potential in further developing our understanding of the disease process.