Regulatory T cells suppress muscle inflammation and injury in muscular dystrophy

Fragile Treg cells: Traitors in immune homeostasis?

Regulatory T (Treg) cells play a key role in maintaining immune tolerance and tissue homeostasis. However, in some disease microenvironments, Treg cells exhibit fragility, which manifests as preserved FoxP3 expression accompanied by inflammation and loss of immunosuppression. Fragile Treg cells are formatively, phenotypically and functionally diverse in various diseases, further complicating the role of Treg cells in the immunotherapeutic response and offering novel targets for disease treatment by modulating specific Treg subsets. In this review, we summarize findings on fragile Treg cells to provide a framework for characterizing the formation and role of fragile Treg cells in different diseases, and we discuss how this information may guide the development of more specific Treg-targeted immunotherapies.

ASM is a therapeutic target in dermatomyositis by regulating the differentiation of naive CD4 + T cells into Th17 and Treg subsets

BACKGROUND

This study aims to investigate the involvement of acid sphingomyelinase (ASM) in the pathology of dermatomyositis (DM), making it a potential therapeutic target for DM.

METHODS

Patients with DM and healthy controls (HCs) were included to assess the serum level and activity of ASM, and to explore the associations between ASM and clinical indicators. Subsequently, a myositis mouse model was established using ASM gene knockout and wild-type mice to study the significant role of ASM in the pathology and to assess the treatment effect of amitriptyline, an ASM inhibitor. Additionally, we investigated the potential treatment mechanism by targeting ASM both in vivo and in vitro.

RESULTS

A total of 58 DM patients along with 30 HCs were included. The ASM levels were found to be significantly higher in DM patients compared to HCs, with median (quartile) values of 2.63 (1.80-4.94) ng/mL and 1.64 (1.47-1.96) ng/mL respectively. The activity of ASM in the serum of DM patients was significantly higher than that in HCs. Furthermore, the serum levels of ASM showed correlations with disease activity and muscle enzyme levels. Knockout of ASM or treatment with amitriptyline improved the severity of the disease, rebalanced the CD4 T cell subsets Th17 and Treg, and reduced the production of their secreted cytokines. Subsequent investigations revealed that targeting ASM could regulate the expression of relevant transcription factors and key regulatory proteins.

CONCLUSION

ASM is involved in the pathology of DM by regulating the differentiation of naive CD4 + T cells and can be a potential treatment target.

Immunological regulation of skeletal muscle adaptation to exercise

Exercise has long been acknowledged for its powerful disease-preventing, health-promoting effects. However, the cellular and molecular mechanisms responsible for the beneficial effects of exercise are not fully understood. Inflammation is a component of the stress response to exercise. Recent work has revealed that such inflammation is not merely a symptom of exertion; rather, it is a key regulator of exercise adaptations, particularly in skeletal muscle. The purpose of this piece is to provide a conceptual framework that we hope will integrate exercise immunology with exercise physiology, muscle biology, and cellular immunology. We start with an overview of early studies in the field of exercise immunology, followed by an exploration of the importance of stromal cells and immunocytes in the maintenance of muscle homeostasis based on studies of experimental muscle injury. Subsequently, we discuss recent advances in our understanding of the functions and physiological relevance of the immune system in exercised muscle. Finally, we highlight a potential immunological basis for the benefits of exercise in musculoskeletal diseases and aging.

Treg-tissue cell interactions in repair and regeneration

Regulatory T (Treg) cells are classically known for their critical immunosuppressive functions that support peripheral tolerance. More recent work has demonstrated that Treg cells produce pro-repair mediators independent of their immunosuppressive function, a process that is critical to repair and regeneration in response to numerous tissue insults. These factors act on resident parenchymal and structural cells to initiate repair in a tissue-specific context. This review examines interactions between Treg cells and tissue-resident non-immune cells-in the context of tissue repair, fibrosis, and cancer-and discusses areas for future exploration.

The muscle regeneration marker FOXP3 is associated with muscle injury in Duchenne muscular dystrophy

BACKGROUND

In Duchenne muscular dystrophy (DMD), the immune system cells (ISC) synthesize molecules to regulate inflammation, a process needed to regenerate muscle. The relationship between those molecules and the muscle injury is unknown. Monocytes belonging to ISC are regulated by omega-3 fatty acids (ω-3 LCPUFAs) in DMD, but whether those fatty acids influence other ISC like T-cells is unknown.

OBJECTIVE

We analyzed the expression of the muscle regeneration markers (FOXP3 and AREG) in circulating leukocytes of DMD patients with different lower limb muscle functions and whether ω-3 LCPUFAs regulate the expression of those markers, and the populations of circulating T-cells, their intracellular cytokines, and disease progression (CD69 and CD49d) markers.

METHODS

This placebo-controlled, double-blind, randomized study was conducted in DMD boys supplemented with ω-3 LCPUFAs (n = 18) or placebo (sunflower oil, n = 13) for six months. FOXP3 and AREG mRNA expression in leukocytes, immunophenotyping of T-cell populations, CD49d and CD69 markers, and intracellular cytokines in blood samples were analyzed at baseline and months 1, 2, 3, and 6 of supplementation.

RESULTS

Patients with assisted ambulation expressed higher (P = 0.015) FOXP3 mRNA levels than ambulatory patients. The FOXP3 mRNA expression correlated (Rho = -0.526, P = 0.03) with the Vignos scale score at month six of supplementation with ω-3 LCPUFAs. CD49d + CD8 + T-cells population was lower (P = 0.037) in the ω -3 LCPUFAs group than placebo at month six of supplementation.

CONCLUSION

FOXP3 is highly expressed in circulating leukocytes of DMD patients with the worst muscle function. Omega-3 LCPUFAs might modulate the synthesis of the adhesion marker CD49d + CD8 + T-cells, but their plausible impact on FOXP3 needs more research.

Niche-specific control of tissue function by regulatory T cells-Current challenges and perspectives for targeting metabolic disease

Tissue regulatory T cells (Tregs) exert pivotal functions in both immune and metabolic regulation, maintaining local tissue homeostasis, integrity, and function. Accordingly, Tregs play a crucial role in controlling obesity-induced inflammation and supporting efficient muscle function and repair. Depending on the tissue context, Tregs are characterized by unique transcriptomes, growth, and survival factors and T cell receptor (TCR) repertoires. This functional specialization offers the potential to selectively target context-specific Treg populations, tailoring therapeutic strategies to specific niches, thereby minimizing potential side effects. Here, we discuss challenges and perspectives for niche-specific Treg targeting, which holds promise for highly efficient and precise medical interventions to combat metabolic disease.

Beyond FOXP3: a 20-year journey unravelling human regulatory T-cell heterogeneity

The initial idea of a distinct group of T-cells responsible for suppressing immune responses was first postulated half a century ago. However, it is only in the last three decades that we have identified what we now term regulatory T-cells (Tregs), and subsequently elucidated and crystallized our understanding of them. Human Tregs have emerged as essential to immune tolerance and the prevention of autoimmune diseases and are typically contemporaneously characterized by their CD3+CD4+CD25high CD127lowFOXP3+ phenotype. It is important to note that FOXP3+ Tregs exhibit substantial diversity in their origin, phenotypic characteristics, and function. Identifying reliable markers is crucial to the accurate identification, quantification, and assessment of Tregs in health and disease, as well as the enrichment and expansion of viable cells for adoptive cell therapy. In our comprehensive review, we address the contributions of various markers identified in the last two decades since the master transcriptional factor FOXP3 was identified in establishing and enriching purity, lineage stability, tissue homing and suppressive proficiency in CD4+ Tregs. Additionally, our review delves into recent breakthroughs in innovative Treg-based therapies, underscoring the significance of distinct markers in their therapeutic utilization. Understanding Treg subsets holds the key to effectively harnessing human Tregs for immunotherapeutic approaches.

Regulatory T cells in dominant immunologic tolerance

Regulatory T cells expressing the transcription factor forkhead box protein 3 mediate peripheral immune tolerance both to self-antigens and to the commensal flora. Their defective function due to inborn errors of immunity or acquired insults is associated with a broad range of autoimmune and immune dysregulatory diseases. Although their function in suppressing autoimmunity and enforcing commensalism is established, a broader role for regulatory T cells in tissue repair and metabolic regulation has emerged, enabled by unique programs of tissue adaptability and specialization. In this review, we focus on the myriad roles played by regulatory T cells in immunologic tolerance and host homeostasis and the potential to harness these cells in novel therapeutic approaches to human diseases.

Regulatory T cells shield muscle mitochondria from interferon-γ-mediated damage to promote the beneficial effects of exercise

Exercise enhances physical performance and reduces the risk of many disorders such as cardiovascular disease, type 2 diabetes, dementia, and cancer. Exercise characteristically incites an inflammatory response, notably in skeletal muscles. Although some effector mechanisms have been identified, regulatory elements activated in response to exercise remain obscure. Here, we have addressed the roles of Foxp3+CD4+ regulatory T cells (Tregs) in the healthful activities of exercise via immunologic, transcriptomic, histologic, metabolic, and biochemical analyses of acute and chronic exercise models in mice. Exercise rapidly induced expansion of the muscle Treg compartment, thereby guarding against overexuberant production of interferon-γ and consequent metabolic disruptions, particularly mitochondrial aberrancies. The performance-enhancing effects of exercise training were dampened in the absence of Tregs. Thus, exercise is a natural Treg booster with therapeutic potential in disease and aging contexts.

Single-cell profiling of muscle-infiltrating T cells in idiopathic inflammatory myopathies

Idiopathic inflammatory myopathies (IIM) are rare autoimmune systemic diseases characterized by muscle weakness and the presence of muscle-infiltrating T cells. IIM represent a clinical challenge due to heterogeneity of symptoms and variability of response to immunosuppressive treatment. Here, we performed in-depth single-cell sequencing on muscle-infiltrating T cells and peripheral blood memory T cells in six patients with recently diagnosed IIM. We identified tissue resident memory T-cell (TRM ) signatures including the expression of HOBIT, XCL1 and CXCR6 in the muscle biopsies of all patients with IIM. Clonally expanded T-cell clones were mainly found among cytotoxic and TRM implying their role in the disease pathogenesis. Finally, identical expanded T-cell clones persisting at follow-up in the muscle tissue of two patients suggest their involvement in disease chronicity. Our study reveals a muscle tissue resident memory T-cell signature in patients with IIM and a transcriptomic map to identify novel therapeutic targets in IIM.

"IL-2 immunotherapy for targeting regulatory T cells in autoimmunity"

FOXP3+ regulatory T cells (Treg) are indispensable for immune homoeostasis and for the prevention of autoimmune diseases. Interleukin-2 (IL-2) signalling is critical in all aspects of Treg biology. Consequences of defective IL-2 signalling are insufficient numbers or dysfunction of Treg and hence autoimmune disorders in human and mouse. The restoration and maintenance of immune homoeostasis remain central therapeutic aims in the field of autoimmunity. Historically, broadly immunosuppressive drugs with serious side-effects have been used for the treatment of autoimmune diseases or prevention of organ-transplant rejection. More recently, ex vivo expanded or in vivo stimulated Treg have been shown to induce effective tolerance in clinical trials supporting the clinical benefit of targeting natural immunosuppressive mechanisms. Given the central role of exogenous IL-2 in Treg homoeostasis, a new and promising focus in drug development are IL-2-based approaches for in vivo targeted expansion of Treg or for enhancement of their suppressive activity. In this review, we summarise the role of IL-2 in Treg biology and consequences of dysfunctional IL-2 signalling pathways. We then examine evidence of efficacy of IL-2-based biological drugs targeting Treg with specific focus on therapeutic candidates in clinical trials and discuss their limitations.

Contribution of αβ T cells to macrophage polarization and MSC recruitment and proliferation on titanium implants

Physiochemical cues like topography and wettability can impact the inflammatory response and tissue integration after biomaterial implantation. T cells are essential for immunomodulation of innate immune cells and play an important role in the host response to biomaterial implantation. This study aimed to understand how CD4+ and CD8+ T cell subsets, members of the αβ T cell family, polarize in response to smooth, rough, or rough-hydrophilic titanium (Ti) implants and whether their presence modulates immune cell crosstalk and mesenchymal stem cell (MSC) recruitment following biomaterial implantation. Post-implantation in mice, we found that CD4+ and CD8+ T cell subsets polarized differentially in response to modified Ti surfaces. Additionally, mice lacking αβ T cells had significantly more pro-inflammatory macrophages, fewer anti-inflammatory macrophages, and reduced MSC recruitment in response to modified Ti post-implantation than αβ T cell -competent mice. Our results demonstrate that T cell activation plays a significant role during the inflammatory response to implanted biomaterials, contributing to macrophage polarization and MSC recruitment and proliferation, and the absence of αβ T cells compromises new bone formation at the implantation site. STATEMENT OF SIGNIFICANCE: T cells are essential for immunomodulation and play an important role in the host response to biomaterial implantation. Our results demonstrate that T cells actively participate during the inflammatory response to implanted biomaterials, controlling macrophage phenotype and recruitment of MSCs to the implantation site.

The Role of Supporting Cell Populations in Satellite Cell Mediated Muscle Repair

Skeletal muscle has a high capacity to repair and remodel in response to damage, largely through the action of resident muscle stem cells, termed satellite cells. Satellite cells are required for the proper repair of skeletal muscle through a process known as myogenesis. Recent investigations have observed relationships between satellite cells and other cell types and structures within the muscle microenvironment. These findings suggest that the crosstalk between inflammatory cells, fibrogenic cells, bone-marrow-derived cells, satellite cells, and the vasculature is essential for the restoration of muscle homeostasis. This review will discuss the influence of the cells and structures within the muscle microenvironment on satellite cell function and muscle repair.

Identifying dysregulated immune cell subsets following volumetric muscle loss with pseudo-time trajectories

Volumetric muscle loss (VML) results in permanent functional deficits and remains a substantial regenerative medicine challenge. A coordinated immune response is crucial for timely myofiber regeneration, however the immune response following VML has yet to be fully characterized. Here, we leveraged dimensionality reduction and pseudo-time analysis techniques to elucidate the cellular players underlying a functional or pathological outcome as a result of subcritical injury or critical VML in the murine quadriceps, respectively. We found that critical VML resulted in a sustained presence of M2-like and CD206hiLy6Chi 'hybrid' macrophages whereas subcritical defects resolved these populations. Notably, the retained M2-like macrophages from critical VML injuries presented with aberrant cytokine production which may contribute to fibrogenesis, as indicated by their co-localization with fibroadipogenic progenitors (FAPs) in areas of collagen deposition within the defect. Furthermore, several T cell subpopulations were significantly elevated in critical VML compared to subcritical injuries. These results demonstrate a dysregulated immune response in critical VML that is unable to fully resolve the chronic inflammatory state and transition to a pro-regenerative microenvironment within the first week after injury. These data provide important insights into potential therapeutic strategies which could reduce the immune cell burden and pro-fibrotic signaling characteristic of VML.

Immunomodulation for Tissue Repair and Regeneration

Various immune cells participate in repair and regeneration following tissue injury or damage, orchestrating tissue inflammation and regeneration processes. A deeper understanding of the immune system's involvement in tissue repair and regeneration is critical for the development of successful reparatory and regenerative strategies. Here we review recent technologies that facilitate cell-based and biomaterial-based modulation of the immune systems for tissue repair and regeneration. First, we summarize the roles of various types of immune cells in tissue repair. Second, we review the principle, examples, and limitations of regulatory T (Treg) cell-based therapy, a representative cell-based immunotherapy. Finally, we discuss biomaterial-based immunotherapy strategies that aim to modulate immune cells using various biomaterials for tissue repair and regeneration.

The Role of P2X7 Purinoceptors in the Pathogenesis and Treatment of Muscular Dystrophies

Muscular dystrophies are inherited neuromuscular diseases, resulting in progressive disability and often affecting life expectancy. The most severe, common types are Duchenne muscular dystrophy (DMD) and Limb-girdle sarcoglycanopathy, which cause advancing muscle weakness and wasting. These diseases share a common pathomechanism where, due to the loss of the anchoring dystrophin (DMD, dystrophinopathy) or due to mutations in sarcoglycan-encoding genes (LGMDR3 to LGMDR6), the α-sarcoglycan ecto-ATPase activity is lost. This disturbs important purinergic signaling: An acute muscle injury causes the release of large quantities of ATP, which acts as a damage-associated molecular pattern (DAMP). DAMPs trigger inflammation that clears dead tissues and initiates regeneration that eventually restores normal muscle function. However, in DMD and LGMD, the loss of ecto-ATPase activity, that normally curtails this extracellular ATP (eATP)-evoked stimulation, causes exceedingly high eATP levels. Thus, in dystrophic muscles, the acute inflammation becomes chronic and damaging. The very high eATP over-activates P2X7 purinoceptors, not only maintaining the inflammation but also tuning the potentially compensatory P2X7 up-regulation in dystrophic muscle cells into a cell-damaging mechanism exacerbating the pathology. Thus, the P2X7 receptor in dystrophic muscles is a specific therapeutic target. Accordingly, the P2X7 blockade alleviated dystrophic damage in mouse models of dystrophinopathy and sarcoglycanopathy. Therefore, the existing P2X7 blockers should be considered for the treatment of these highly debilitating diseases. This review aims to present the current understanding of the eATP-P2X7 purinoceptor axis in the pathogenesis and treatment of muscular dystrophies.

The P2X7 purinoceptor in pathogenesis and treatment of dystrophino- and sarcoglycanopathies

Dystrophinopathy and sarcoglycanopathies are incurable diseases caused by mutations in the genes encoding dystrophin or members of the dystrophin associated protein complex (DAPC). Restoration of the missing dystrophin or sarcoglycans via genetic approaches is complicated by the downsides of personalised medicines and immune responses against re-expressed proteins. Thus, the targeting of disease mechanisms downstream from the mutant protein has a strong translational potential. Acute muscle damage causes release of large quantities of ATP, which activates P2X7 purinoceptors, resulting in inflammation that clears dead tissues and triggers regeneration. However, in dystrophic muscles, loss of α-sarcoglycan ecto-ATPase activity further elevates extracellular ATP (eATP) levels, exacerbating the pathology. Moreover, seemingly compensatory P2X7 upregulation in dystrophic muscle cells, combined with high eATP leads to further damage. Accordingly, P2X7 blockade alleviated dystrophic damage in mouse models of both dystrophinopathy and sarcoglycanopathy. Existing P2X7 blockers could be re-purposed for the treatment of these highly debilitating diseases.

Tregs dysfunction aggravates postoperative cognitive impairment in aged mice

OBJECTIVES

Enhanced neuroinflammation is an important mechanism underlying perioperative neurocognitive disorders. Regulatory T cells (Tregs) play a crucial role in regulating systemic immune responses. The present study was aimed to investigate the participation of Tregs in the development of postoperative cognitive dysfunction (POCD).

METHODS

Surgery-associated neurocognitive disorder was induced in 18-month-old mice subjected to internal fixation of tibial fracture. Morris water maze was used to examine mice cognitive function. Splenic Tregs were collected for RNA sequencing and flow cytometry. Levels of inflammatory factors in the circulation and hippocampus were measured by enzyme-linked immunosorbent assay. Protein presences of tight junction proteins were detected by immunofluorescence.

RESULTS

Surgery of internal fixation of tibial fracture induced cognitive impairment in aged mice, accompanied by elevated plasma levels of inflammatory factors and increased circulating Tregs. Transfusion of Tregs from young mice partially restored the structure of the blood-brain barrier and alleviated POCD in aged mice. Compared with young Tregs, differentially expressed genes in aged Tregs were enriched in tumor necrosis factor (TNF) signaling pathway and cytokine-cytokine receptor interaction. Flow cytometry revealed that aged Tregs had blunted functions under basal and stimulated conditions. Blockade of the CD25 epitope protected the blood-brain barrier structure, reduced TNF-α levels in the hippocampus, and improved surgery-associated cognition in aged mice.

CONCLUSIONS

Blocking peripheral regulatory T cells improves surgery-induced cognitive function in aged mice. Therefore, aged Tregs play an essential role in the occurrence of POCD.

The potential for Treg-enhancing therapies in tissue, in particular skeletal muscle, regeneration

Foxp3+CD4+ regulatory T cells (Tregs) are famous for their role in maintaining immunological tolerance. With their distinct transcriptomes, growth-factor dependencies and T-cell receptor (TCR) repertoires, Tregs in nonlymphoid tissues, termed "tissue-Tregs," also perform a variety of functions to help assure tissue homeostasis. For example, they are important for tissue repair and regeneration after various types of injury, both acute and chronic. They exert this influence by controlling both the inflammatory tenor and the dynamics of the parenchymal progenitor-cell pool in injured tissues, thereby promoting efficient repair and limiting fibrosis. Thus, tissue-Tregs are seemingly attractive targets for immunotherapy in the context of tissue regeneration, offering several advantages over existing therapies. Using skeletal muscle as a model system, we discuss the existing literature on Tregs' role in tissue regeneration in acute and chronic injuries, and various approaches for their therapeutic modulation in such contexts, including exercise as a natural Treg modulator.

Train your T cells: How skeletal muscles and T cells keep each other fit during aging

Frailty and a failing immune system lead to significant morbidities in the final years of life and bring along a significant burden on healthcare systems. The good news is that regular exercise provides an effective countermeasure for losing muscle tissue when we age while supporting proper immune system functioning. For a long time, it was assumed that exercise-induced immune responses are predominantly mediated by myeloid cells, but it has become evident that they receive important help from T lymphocytes. Skeletal muscles and T cells interact, not only in muscle pathology but also during exercise. In this review article, we provide an overview of the most important aspects of T cell senescence and discuss how these are modulated by exercise. In addition, we describe how T cells are involved in muscle regeneration and growth. A better understanding of the complex interactions between myocytes and T cells throughout all stages of life provides important insights needed to design strategies that effectively combat the wave of age-related diseases the world is currently faced with.

The Bi-directional Relationship Between Sleep and Inflammation in Muscular Dystrophies: A Narrative Review

Muscular dystrophies vary in presentation and severity, but are associated with profound disability in many people. Although characterised by muscle weakness and wasting, there is also a very high prevalence of sleep problems and disorders which have significant impacts on quality of life in these individuals. There are no curative therapies for muscular dystrophies, with the only options for patients being supportive therapies to aid with symptoms. Therefore, there is an urgent need for new therapeutic targets and a greater understanding of pathogenesis. Inflammation and altered immunity are factors which have prominent roles in some muscular dystrophies and emerging roles in others such as type 1 myotonic dystrophy, signifying a link to pathogenesis. Interestingly, there is also a strong link between inflammation/immunity and sleep. In this review, we will explore this link in the context of muscular dystrophies and how it may influence potential therapeutic targets and interventions.

Spatial compartmentalization of signaling imparts source-specific functions on secreted factors

Efficient regeneration requires multiple cell types acting in coordination. To better understand the intercellular networks involved and how they change when regeneration fails, we profile the transcriptome of hematopoietic, stromal, myogenic, and endothelial cells over 14 days following acute muscle damage. We generate a time-resolved computational model of interactions and identify VEGFA-driven endothelial engagement as a key differentiating feature in models of successful and failed regeneration. In addition, the analysis highlights that the majority of secreted signals, including VEGFA, are simultaneously produced by multiple cell types. To test whether the cellular source of a factor determines its function, we delete VEGFA from two cell types residing in close proximity: stromal and myogenic progenitors. By comparing responses to different types of damage, we find that myogenic and stromal VEGFA have distinct functions in regeneration. This suggests that spatial compartmentalization of signaling plays a key role in intercellular communication networks.

Regulatory T-cell stability and functional plasticity in health and disease

FOXP3-expressing regulatory T cells (T_reg ) are indispensable for immune homeostasis and tolerance, and in addition tissue-resident T_reg have been found to perform noncanonical, tissue-specific functions. For optimal tolerogenic function during inflammatory disease, T_reg are equipped with mechanisms that assure lineage stability. T_reg lineage stability is closely linked to the installation and maintenance of a lineage-specific epigenetic landscape, specifically a T_reg -specific DNA demethylation pattern. At the same time, for local and directed immune regulation T_reg must possess a level of functional plasticity that requires them to partially acquire T helper cell (T_H ) transcriptional programs-then referred to as T_H -like T_reg . Unleashing T_H programs in T_reg , however, is not without risk and may threaten the epigenetic stability of T_reg with consequently pathogenic ex-T_reg contributing to (auto-) inflammatory conditions. Here, we review how the T_reg -stabilizing epigenetic landscape is installed and maintained, and further discuss the development, necessity and lineage instability risks of T_H 1-, T_H 2-, T_H 17-like T_reg and follicular T_reg .

AMP-activated protein kinase inhibition in fibro-adipogenic progenitors impairs muscle regeneration and increases fibrosis

BACKGROUND

Following muscle injury, fibro-adipogenic progenitors (FAPs) are rapidly activated and undergo apoptosis at the resolution stage, which is required for proper muscle regeneration. When excessive FAPs remain, it contributes to fibrotic and fatty infiltration, impairing muscle recovery. Mechanisms controlling FAP apoptosis remain poorly defined. We hypothesized that AMP-activated protein kinase (AMPK) in FAPs mediates their apoptosis during the muscle regeneration.

METHODS

To test, AMPKα1^fl/fl PDGFRα^Cre mice were used to knock out AMPKα1 in FAPs. Following AMPKα1 knockout, the mice were injected with phosphate-buffered saline or glycerol to induce muscle injury. Tibialis anterior muscle and FAPs were collected at 3, 7 and 14 days post-injury (dpi) for further analysis.

RESULTS

We found that AMPKα1 deletion in FAPs enhanced p65 translocation to the nuclei by 110% (n = 3; P < 0.01). AMPKα1 knockout group had a higher gene expression of MMP-9 (matrix metalloproteinase-9) by 470% (n = 3; P < 0.05) and protein level by 39% (n = 3; P < 0.05). Loss of AMPKα1 up-regulated the active TGF-β1 (transforming growth factor-β1) levels by 21% (n = 3; P < 0.05). TGF-β promoted apoptotic resistance, because AMPKα1-deficient group had 36% lower cleaved Caspase 3 (cCAS3) content (n = 3; P < 0.05). Fibrotic differentiation of FAPs was promoted, with increased collagen protein level by 54% (n = 3; P < 0.05). Moreover, obesity decreased phosphorylation of AMPK by 54% (n = 3; P < 0.05), which decreased cCAS3 in FAPs by 44% (n = 3; P < 0.05) and elevated collagen accumulation (52%; n = 3; P < 0.05) during muscle regeneration.

CONCLUSIONS

These data suggest that AMPK is a key mediator of FAPs apoptosis, and its inhibition due to obesity results in fibrosis of regenerated muscle.

Nano-Immunomodulation: A New Strategy for Skeletal Muscle Diseases and Aging?

The skeletal muscle has a very remarkable ability to regenerate upon injury under physiological conditions; however, this regenerative capacity is strongly diminished in physio-pathological conditions, such as those present in diseased or aged muscles. Many muscular dystrophies (MDs) are characterized by aberrant inflammation due to the deregulation of both the lymphoid and myeloid cell populations and the production of pro-inflammatory cytokines. Pathological inflammation is also observed in old muscles due to a systemic change in the immune system, known as "inflammaging". Immunomodulation represents, therefore, a promising therapeutic opportunity for different skeletal muscle conditions. However, the use of immunomodulatory drugs in the clinics presents several caveats, including their low stability in vivo, the need for high doses to obtain therapeutically relevant effects, and the presence of strong side effects. Within this context, the emerging field of nanomedicine provides the powerful tools needed to control the immune response. Nano-scale materials are currently being explored as biocarriers to release immunomodulatory agents in the damaged tissues, allowing therapeutic doses with limited off-target effects. In addition, the intrinsic immunomodulatory properties of some nanomaterials offer further opportunities for intervention that still need to be systematically explored. Here we exhaustively review the state-of-the-art regarding the use of nano-sized materials to modulate the aberrant immune response that characterizes some physio-pathological muscle conditions, such as MDs or sarcopenia (the age-dependent loss of muscle mass). Based on our learnings from cancer and immune tolerance induction, we also discuss further opportunities, challenges, and limitations of the emerging field of nano-immunomodulation.

An updated review of the immunological mechanisms of keloid scars

Keloid is a type of disfiguring pathological scarring unique to human skin. The disorder is characterized by excessive collagen deposition. Immune cell infiltration is a hallmark of both normal and pathological tissue repair. However, the immunopathological mechanisms of keloid remain unclear. Recent studies have uncovered the pivotal role of both innate and adaptive immunity in modulating the aberrant behavior of keloid fibroblasts. Several novel therapeutics attempting to restore regulation of the immune microenvironment have shown variable efficacy. We review the current understanding of keloid immunopathogenesis and highlight the potential roles of immune pathway-specific therapeutics.

Soluble interleukin 2 receptor is risk for sarcopenia in Men with high fracture risk

Background & aims

Sarcopenia is an age-related disease that increases the risk of falls and fractures in older adults. However, there is no blood biochemical marker to help to predict or diagnose sarcopenia in clinical practice. Soluble interleukin 2 receptor (sIL-2R) was reported to be associated with muscle satellite cell dysfunction which played an important role in the pathogenesis of sarcopenia. Thereby, we aimed to explore the association between serum sIL-2R and sarcopenia in older adults at high risk of fractures.

Methods

A total of 429 hospitalized older adults (age ≥55 years) were enrolled in this cross-sectional study (mean age ​= ​66.62 ​± ​6.59 years; 62.7% female). Logistic regression analysis was performed to assess the association of sIL-2R with sarcopenia, muscle mass, muscle strength, and physical performance, respectively. The optimal models for the diagnosis of sarcopenia and low hand grip strength (HGS) were established by multivariable binary logistic regression analysis with backward selection, and further were evaluated for the diagnostic values by receiver operating characteristic (ROC) curve.

Results

Higher sIL-2R levels were found in sarcopenia than no-sarcopenia group in male (median 421 U/mL (interquartile range [IQR] 217 U/mL) vs median 362 U/mL (IQR 157 U/mL); n ​= ​77 vs 83; p ​< ​0.01). Compared to the lowest sIL-2R tertile, the highest tertile of sIL-2R was independently associated with the risk of low HGS (odds ratio [OR] 4.608, 95% confidence interval [CI] 1.673–12.695) and the risk of sarcopenia (OR 3.306, 95% CI 1.496–7.302) in men. ROC curves revealed that the Area Under the Curve (AUC) of the optimal models for diagnosing sarcopenia and low HGS was 0.752 and 0.846.

Conclusion

Our results suggest that serum sIL-2R is the independent risk factor for sarcopenia and low muscle strength only in men. sIL-2R may be developed to be a biochemical marker for sarcopenia and low muscle strength diagnoses in older men at high risk of fractures, but more prospective studies are needed to prove it.

The translational potential of this article

Our results showed that the highest tertile of sIL-2R was independent of low risk of HGS and sarcopenia in men, compared to the lowest tertile. As the population ages, sIL-2R may become a potential diagnostic tool for predicting low HGS and sarcopenia among men at high risk of fractures.

Histological Methods to Assess Skeletal Muscle Degeneration and Regeneration in Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a progressive disease caused by the loss of function of the protein dystrophin. This protein contributes to the stabilisation of striated cells during contraction, as it anchors the cytoskeleton with components of the extracellular matrix through the dystrophin-associated protein complex (DAPC). Moreover, absence of the functional protein affects the expression and function of proteins within the DAPC, leading to molecular events responsible for myofibre damage, muscle weakening, disability and, eventually, premature death. Presently, there is no cure for DMD, but different treatments help manage some of the symptoms. Advances in genetic and exon-skipping therapies are the most promising intervention, the safety and efficiency of which are tested in animal models. In addition to in vivo functional tests, ex vivo molecular evaluation aids assess to what extent the therapy has contributed to the regenerative process. In this regard, the later advances in microscopy and image acquisition systems and the current expansion of antibodies for immunohistological evaluation together with the development of different spectrum fluorescent dyes have made histology a crucial tool. Nevertheless, the complexity of the molecular events that take place in dystrophic muscles, together with the rise of a multitude of markers for each of the phases of the process, makes the histological assessment a challenging task. Therefore, here, we summarise and explain the rationale behind different histological techniques used in the literature to assess degeneration and regeneration in the field of dystrophinopathies, focusing especially on those related to DMD.

Regulatory T cells-centered regulatory networks of skeletal muscle inflammation and regeneration

As the understanding of skeletal muscle inflammation is increasingly clarified, the role of Treg cells in the treatment of skeletal muscle diseases has attracted more attention in recent years. A consensus has been reached that the regulation of Treg cells is the key to completing the switch of inflammation and repair of skeletal muscle, whose presence directly determine the repairing quality of the injured skeletal muscle. However, the functioning process of Treg cells remains unreported, thereby making it necessary to summarize the current role of Treg cells in skeletal muscle. In this review, the characteristics, origins, and cellular kinetics of these Treg cells are firstly described; Then, the relationship between Treg cells and muscle satellite cells (MuSCs), conventional T cells (Tconv) is discussed (the former is involved in the entire repair and regeneration process, while the latter matters considerably in causing most skeletal muscle autoimmune diseases); Next, focus is placed on the control of Treg cells on the phenotypic switch of macrophages, which is the key to the switch of inflammation; Finally, factors regulating the functional process of Treg cells are analyzed, and a regulatory network centered on Treg cells is summarized. The present study summarizes the cell-mediated interactions in skeletal muscle repair over the past decade, and elucidates the central role of regulatory T cells in this process, so that other researchers can more quickly and comprehensively understand the development and direction of this very field. It is believed that the hereby proposed viewpoints and problems can provide fresh visions for the latecomers.

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

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

The inflammatory response, a mixed blessing for muscle homeostasis and plasticity

Skeletal muscle makes up almost half the body weight of heathy individuals and is involved in several vital functions, including breathing, thermogenesis, metabolism, and locomotion. Skeletal muscle exhibits enormous plasticity with its capacity to adapt to stimuli such as changes in mechanical loading, nutritional interventions, or environmental factors (oxidative stress, inflammation, and endocrine changes). Satellite cells and timely recruited inflammatory cells are key actors in muscle homeostasis, injury, and repair processes. Conversely, uncontrolled recruitment of inflammatory cells or chronic inflammatory processes leads to muscle atrophy, fibrosis and, ultimately, impairment of muscle function. Muscle atrophy and loss of function are reported to occur either in physiological situations such as aging, cast immobilization, and prolonged bed rest, as well as in many pathological situations, including cancers, muscular dystrophies, and several other chronic illnesses. In this review, we highlight recent discoveries with respect to the molecular mechanisms leading to muscle atrophy caused by modified mechanical loading, aging, and diseases. We also summarize current perspectives suggesting that the inflammatory process in muscle homeostasis and repair is a double-edged sword. Lastly, we review recent therapeutic approaches for treating muscle wasting disorders, with a focus on the RANK/RANKL/OPG pathway and its involvement in muscle inflammation, protection and regeneration processes.

Engineering IL-2 for immunotherapy of autoimmunity and cancer

Preclinical studies of the T cell growth factor activity of IL-2 resulted in this cytokine becoming the first immunotherapy to be approved nearly 30 years ago by the US Food and Drug Administration for the treatment of cancer. Since then, we have learnt the important role of IL-2 in regulating tolerance through regulatory T cells (Treg cells) besides promoting immunity through its action on effector T cells and memory T cells. Another pivotal event in the history of IL-2 research was solving the crystal structure of IL-2 bound to its tripartite receptor, which spurred the development of cell type-selective engineered IL-2 products. These new IL-2 analogues target Treg cells to counteract the dysregulated immune system in the context of autoimmunity and inflammatory disorders or target effector T cells, memory T cells and natural killer cells to enhance their antitumour responses. IL-2 biologics have proven to be effective in preclinical studies and clinical assessment of some is now underway. These studies will soon reveal whether engineered IL-2 biologics are truly capable of harnessing the IL-2-IL-2 receptor pathway as effective monotherapies or combination therapies for autoimmunity and cancer.

Boosting regulatory T cell function for the treatment of autoimmune diseases – That’s only half the battle!

Regulatory T cells (Treg) represent a subset of specialized T cells that are essential for the regulation of immune responses and maintenance of peripheral tolerance. Once activated, Treg exert powerful immunosuppressive properties, for example by inhibiting T cell-mediated immune responses against self-antigens, thereby protecting our body from autoimmunity. Autoimmune diseases such as multiple sclerosis, rheumatoid arthritis or systemic lupus erythematosus, exhibit an immunological imbalance mainly characterized by a reduced frequency and impaired function of Treg. In addition, there has been increasing evidence that – besides Treg dysfunction – immunoregulatory mechanisms fail to control autoreactive T cells due to a reduced responsiveness of T effector cells (Teff) for the suppressive properties of Treg, a process termed Treg resistance. In order to efficiently treat autoimmune diseases and thus fully induce immunological tolerance, a combined therapy aimed at both enhancing Treg function and restoring Teff responsiveness could most likely be beneficial. This review provides an overview of immunomodulating drugs that are currently used to treat various autoimmune diseases in the clinic and have been shown to increase Treg frequency as well as Teff sensitivity to Treg-mediated suppression. Furthermore, we discuss strategies on how to boost Treg activity and function, and their potential use in the treatment of autoimmunity. Finally, we present a humanized mouse model for the preclinical testing of Treg-activating substances in vivo.

Regulatory T cells in skeletal muscle repair and regeneration: recent insights

Skeletal muscle repair and regeneration after injury is a multi-stage process, involving a dynamic inflammatory microenvironment consisting of a complex network formed by the interaction of immune cells and their secreted cytokines. The homeostasis of the inflammatory microenvironment determines whether skeletal muscle repair tissues will ultimately form scar tissue or regenerative tissue. Regulatory T cells (Tregs) regulate homeostasis within the immune system and self-immune tolerance, and play a crucial role in skeletal muscle repair and regeneration. Dysregulated Tregs function leads to abnormal repair. In this review, we discuss the role and mechanisms of Tregs in skeletal muscle repair and regeneration after injury and provide new strategies for Treg immunotherapy in skeletal muscle diseases.

Implications of regulatory T cells in non-lymphoid tissue physiology and pathophysiology

Treg cells have been initially described as gatekeepers for the control of autoimmunity, as they can actively suppress the activity of other immune cells. However, their role goes beyond this as Treg cells further control immune responses during infections and tumor development. Furthermore, Treg cells can acquire additional properties for e.g., the control of tissue homeostasis. This is instructed by a specific differentiation program and the acquisition of effector properties unique to Treg cells in non-lymphoid tissues. These tissue Treg cells can further adapt to their tissue environment and acquire distinct functional properties through specific transcription factors activated by a combination of tissue derived factors, including tissue-specific antigens and cytokines. In this review, we will focus on recent findings extending our current understanding of the role and differentiation of these tissue Treg cells. As such we will highlight the importance of tissue Treg cells for tissue maintenance, regeneration, and repair in adipose tissue, muscle, CNS, liver, kidney, reproductive organs, and the lung.

Metabolic reprogramming of skeletal muscle by resident macrophages points to CSF1R inhibitors as muscular dystrophy therapeutics

The role of tissue-resident macrophages during tissue regeneration or fibrosis is not well understood, mainly due to the lack of a specific marker for their identification. Here, we identified three populations of skeletal muscle-resident myelomonocytic cells: a population of macrophages positive for lymphatic vessel endothelial receptor 1 (LYVE1) and T cell membrane protein 4 (TIM4 or TIMD4), a population of LYVE1^-TIM4^- macrophages, and a population of cells likely representing dendritic cells that were positive for CD11C and major histocompatibility complex class II (MHCII). Using a combination of parabiosis and lineage-tracing experiments, we found that, at steady state, TIM4^- macrophages were replenished from the blood, whereas TIM4⁺ macrophages locally self-renewed [self-renewing resident macrophages (SRRMs)]. We further showed that Timd4 could be reliably used to distinguish SRRMs from damage-induced infiltrating macrophages. Using a colony-stimulating factor 1 receptor (CSF1R) inhibition/withdrawal approach to specifically deplete SRRMs, we found that SRRMs provided a nonredundant function in clearing damage-induced apoptotic cells early after extensive acute injury. In contrast, in chronic mild injury as seen in a mouse model of Duchenne muscular dystrophy, depletion of both TIM4^-- and TIM4⁺-resident macrophage populations through long-term CSF1R inhibition changed muscle fiber composition from damage-sensitive glycolytic fibers toward damage-resistant glycolytic-oxidative fibers, thereby protecting muscle against contraction-induced injury both ex vivo and in vivo. This work reveals a previously unidentified role for resident macrophages in modulating tissue metabolism and may have therapeutic potential given the ongoing clinical testing of CSF1R inhibitors.

Role of Regulatory T Cells in Skeletal Muscle Regeneration: A Systematic Review

Muscle injuries are frequent in individuals with genetic myopathies and in athletes. Skeletal muscle regeneration depends on the activation and differentiation of satellite cells present in the basal lamina of muscle fibers. The skeletal muscle environment is critical for repair, metabolic and homeostatic function. Regulatory T cells (Treg) residing within skeletal muscle comprise a distinct and special cell population that modifies the inflammatory environment by secreting cytokines and amphiregulin, an epidermal growth factor receptor (EGFR) ligand that acts directly upon satellite cells, promoting tissue regeneration. This systematic review summarizes the current knowledge regarding the role of Treg in muscle repair and discusses their therapeutic potential in skeletal muscle injuries. A bibliographic search was carried out using the terms Treg and muscle regeneration and repair, covering all articles up to April 2021 indexed in the PubMed and EMBASE databases. The search included only published original research in human and experimental animal models, with further data analysis based on the PICO methodology, following PRISMA definitions and Cochrane guidelines.

Identification of Auxiliary Biomarkers and Description of the Immune Microenvironmental Characteristics in Duchenne Muscular Dystrophy by Bioinformatical Analysis and Experiment

Background

Duchenne muscular dystrophy (DMD) is a genetic muscle disorder characterized by progressive muscle wasting associated with persistent inflammation. In this study, we aimed to identify auxiliary biomarkers and further characterize the immune microenvironment in DMD.

Methods

Differentially expressed genes (DEGs) were identified between DMD and normal muscle tissues based on Gene Expression Omnibus (GEO) datasets. Bioinformatical analysis was used to screen and identify potential diagnostic signatures of DMD which were further validated by real-time quantitative reverse transcription PCR (RT-qPCR). We also performed single-sample gene-set enrichment analysis (ssGSEA) to characterize the proportion of tissue-infiltrating immune cells to determine the inflammatory state of DMD.

Results

In total, 182 downregulated genes and 263 upregulated genes were identified in DMD. C3, SPP1, TMSB10, TYROBP were regarded as adjunct biomarkers and successfully validated by RT-qPCR. The infiltration of macrophages, CD4+, and CD8+ T cells was significantly higher (p < 0.05) in DMD compared with normal muscle tissues, while the infiltration of activated B cells, CD56dim natural killer cells, and type 17 T helper (Th17) cells was lower. In addition, the four biomarkers (C3, SPP1, TMSB10, TYROBP) were strongly associated with immune cells and immune-related pathways in DMD muscle tissues.

Conclusion

Analyses demonstrated C3, SPP1, TMSB10, and TYROBP may serve as biomarkers and enhance our understanding of immune responses in DMD. The infiltration of immune cells into the muscle microenvironment might exert a critical impact on the development and occurrence of DMD.

Boosting the peripheral immune response in the skeletal muscles improved motor function in ALS transgenic mice

Monocyte chemoattractant protein-1 (MCP1) is one of the most powerful pro-inflammatory chemokines. However, its signalling is pivotal in driving injured axon and muscle regeneration.

IL-17A-producing γδT cells promote muscle regeneration in a microbiota-dependent manner

Subsequent to acute injury, skeletal muscle undergoes a stereotypic regenerative process that reestablishes homeostasis. Various types of innate and adaptive immunocytes exert positive or negative influences at specific stages along the course of muscle regeneration. We describe an unanticipated role for γδT cells in promoting healthy tissue recovery after injection of cardiotoxin into murine hindlimb muscle. Within a few days of injury, IL-17A-producing γδT cells displaying primarily Vγ6+ antigen receptors accumulated at the wound site. Punctual ablation experiments showed that these cells boosted early inflammatory events, notably recruitment of neutrophils; fostered the proliferation of muscle stem and progenitor cells; and thereby promoted tissue regeneration. Supplementation of mice harboring low numbers of IL-17A+ γδT cells with recombinant IL-17A largely reversed their inflammatory and reparative defects. Unexpectedly, the accumulation and influences of γδT cells in this experimental context were microbiota dependent, unveiling an orthogonal perspective on the treatment of skeletal muscle pathologies such as catastrophic wounds, wasting, muscular dystrophies, and myositides.

Tissue Resident Foxp3+ Regulatory T Cells: Sentinels and Saboteurs in Health and Disease

Foxp3⁺ regulatory T (Treg) cells are a CD4 T cell subset with unique immune regulatory function that are indispensable in immunity and tolerance. Their indisputable importance has been investigated in numerous disease settings and experimental models. Despite the extensive efforts in determining the cellular and molecular mechanisms operating their functions, our understanding their biology especially in vivo remains limited. There is emerging evidence that Treg cells resident in the non-lymphoid tissues play a central role in regulating tissue homeostasis, inflammation, and repair. Furthermore, tissue-specific properties of those Treg cells that allow them to express tissue specific functions have been explored. In this review, we will discuss the potential mechanisms and key cellular/molecular factors responsible for the homeostasis and functions of tissue resident Treg cells under steady-state and inflammatory conditions.

A Spotlight on T Lymphocytes in Duchenne Muscular Dystrophy—Not Just a Muscle Defect

The lack of dystrophin in Duchenne muscular dystrophy (DMD) results in membrane fragility resulting in contraction-induced muscle damage and subsequent inflammation. The impact of inflammation is profound, resulting in fibrosis of skeletal muscle, the diaphragm and heart, which contributes to muscle weakness, reduced quality of life and premature death. To date, the innate immune system has been the major focus in individuals with DMD, and our understanding of the adaptive immune system, specifically T cells, is limited. Targeting the immune system has been the focus of multiple clinical trials for DMD and is considered a vital step in the development of better treatments. However, we must first have a complete picture of the involvement of the immune systems in dystrophic muscle disease to better understand how inflammation influences disease progression and severity. This review focuses on the role of T cells in DMD, highlighting the importance of looking beyond skeletal muscle when considering how the loss of dystrophin impacts disease progression. Finally, we propose that targeting T cells is a potential novel therapeutic in the treatment of DMD.

The Immune-Centric Revolution in the Diabetic Foot: Monocytes and Lymphocytes Role in Wound Healing and Tissue Regeneration-A Narrative Review

Monocytes and lymphocytes play a key role in physiologic wound healing and might be involved in the impaired mechanisms observed in diabetes. Skin wound macrophages are represented by tissue resident macrophages and infiltrating peripheral blood recruited monocytes which play a leading role during the inflammatory phase of wound repair. The impaired transition of diabetic wound macrophages from pro-inflammatory M1 phenotypes to anti-inflammatory pro-regenerative M2 phenotypes might represent a key issue for impaired diabetic wound healing. This review will focus on the role of immune system cells in normal skin and diabetic wound repair. Furthermore, it will give an insight into therapy able to immuno-modulate wound healing processes toward to a regenerative anti-inflammatory fashion. Different approaches, such as cell therapy, exosome, and dermal substitute able to promote the M1 to M2 switch and able to positively influence healing processes in chronic wounds will be discussed.

Loss of TDP-43 function and rimmed vacuoles persist after T cell depletion in a xenograft model of sporadic inclusion body myositis

Sporadic inclusion body myositis (IBM) is the most common acquired muscle disease in adults over age 50, yet it remains unclear whether the disease is primarily driven by T cell–mediated autoimmunity. IBM muscle biopsies display nuclear clearance and cytoplasmic aggregation of TDP-43 in muscle cells, a pathologic finding observed initially in neurodegenerative diseases, where nuclear loss of TDP-43 in neurons causes aberrant RNA splicing. Here, we show that loss of TDP-43–mediated splicing repression, as determined by inclusion of cryptic exons, occurs in skeletal muscle of subjects with IBM. Of 119 muscle biopsies tested, RT-PCR–mediated detection of cryptic exon inclusion was able to diagnose IBM with 84% sensitivity and 99% specificity. To determine the role of T cells in pathogenesis, we generated a xenograft model by transplanting human IBM muscle into the hindlimb of immunodeficient mice. Xenografts from subjects with IBM displayed robust regeneration of human myofibers and recapitulated both inflammatory and degenerative features of the disease. Myofibers in IBM xenografts showed invasion by human, oligoclonal CD8+ T cells and exhibited MHC-I up-regulation, rimmed vacuoles, mitochondrial pathology, p62-positive inclusions, and nuclear clearance and cytoplasmic aggregation of TDP-43, associated with cryptic exon inclusion. Reduction of human T cells within IBM xenografts by treating mice intraperitoneally with anti-CD3 (OKT3) suppressed MHC-I up-regulation. However, rimmed vacuoles and loss of TDP-43 function persisted. These data suggest that T cell depletion does not alter muscle degenerative pathology in IBM.

Engineering of Immune Microenvironment for Enhanced Tissue Remodeling

The capability to restore the structure and function of tissues damaged by fatal diseases and trauma is essential for living organisms. Various tissue engineering approaches have been applied in lesions to enhance tissue regeneration after injuries and diseases in living organisms. However, unforeseen immune reactions by the treatments interfere with successful healing and reduce the therapeutic efficacy of the strategies. The immune system is known to play essential roles in the regulation of the microenvironment and recruitment of cells that directly or indirectly participate in tissue remodeling in defects. Accordingly, regenerative immune engineering has emerged as a novel approach toward efficiently inducing regeneration using engineering techniques that modulate the immune system. It is aimed at providing a favorable immune microenvironment based on the controlled balance between pro-inflammation and anti-inflammation. In this review, we introduce recent developments in immune engineering therapeutics based on various cell types and biomaterials. These developments could potentially overcome the therapeutic limitations of tissue remodeling.

P2X7 Receptor Antagonist Reduces Fibrosis and Inflammation in a Mouse Model of Alpha-Sarcoglycan Muscular Dystrophy

Limb-girdle muscular dystrophy R3, a rare genetic disorder affecting the limb proximal muscles, is caused by mutations in the α-sarcoglycan gene (Sgca) and aggravated by an immune-mediated damage, finely modulated by the extracellular (e)ATP/purinoceptors axis. Currently, no specific drugs are available. The aim of this study was to evaluate the therapeutic effectiveness of a selective P2X7 purinoreceptor antagonist, A438079. Sgca knockout mice were treated with A438079 every two days at 3 mg/Kg for 24 weeks. The P2X7 antagonist improved clinical parameters by ameliorating mice motor function and decreasing serum creatine kinase levels. Histological analysis of muscle morphology indicated a significant reduction of the percentage of central nuclei, of fiber size variability and of the extent of local fibrosis and inflammation. A cytometric characterization of the muscle inflammatory infiltrates showed that A438079 significantly decreased innate immune cells and upregulated the immunosuppressive regulatory T cell subpopulation. In α-sarcoglycan null mice, the selective P2X7 antagonist A438079 has been shown to be effective to counteract the progression of the dystrophic phenotype and to reduce the inflammatory response. P2X7 antagonism via selective inhibitors could be included in the immunosuppressant strategies aimed to dampen the basal immune-mediated damage and to favor a better engraftment of gene-cell therapies.

Human MuStem cells repress T-cell proliferation and cytotoxicity through both paracrine and contact-dependent pathways

Background

Muscular dystrophies (MDs) are inherited diseases in which a dysregulation of the immune response exacerbates disease severity and are characterized by infiltration of various immune cell types leading to muscle inflammation, fiber necrosis and fibrosis. Immunosuppressive properties have been attributed to mesenchymal stem cells (MSCs) that regulate the phenotype and function of different immune cells. However, such properties were poorly considered until now for adult stem cells with myogenic potential and advanced as possible therapeutic candidates for MDs. In the present study, we investigated the immunoregulatory potential of human MuStem (hMuStem) cells, for which we previously demonstrated that they can survive in injured muscle and robustly counteract adverse tissue remodeling.

Methods

The impact of hMuStem cells or their secretome on the proliferative and phenotypic properties of T-cells was explored by co-culture experiments with either peripheral blood mononucleated cells or CD3-sorted T-cells. A comparative study was produced with the bone marrow (BM)-MSCs. The expression profile of immune cell-related markers on hMuStem cells was determined by flow cytometry while their secretory profile was examined by ELISA assays. Finally, the paracrine and cell contact-dependent effects of hMuStem cells on the T-cell-mediated cytotoxic response were analyzed through IFN-γ expression and lysis activity.

Results

Here, we show that hMuStem cells have an immunosuppressive phenotype and can inhibit the proliferation and the cytotoxic response of T-cells as well as promote the generation of regulatory T-cells through direct contact and via soluble factors. These effects are associated, in part, with the production of mediators including heme-oxygenase-1, leukemia inhibitory factor and intracellular cell adhesion molecule-1, all of which are produced at significantly higher levels by hMuStem cells than BM-MSCs. While the production of prostaglandin E2 is involved in the suppression of T-cell proliferation by both hMuStem cells and BM-MSCs, the participation of inducible nitric oxide synthase activity appears to be specific to hMuStem cell-mediated one.

Conclusions

Together, our findings demonstrate that hMuStem cells are potent immunoregulatory cells. Combined with their myogenic potential, the attribution of these properties reinforces the positioning of hMuStem cells as candidate therapeutic agents for the treatment of MDs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02681-3.

The Role of the Inflammatory Response in Mediating Functional Recovery Following Composite Tissue Injuries

Composite tissue injuries (CTI) are common among US Military Service members during combat operations, and carry a high potential of morbidity. Furthermore, CTI are often complicated due to an altered wound healing response, resulting in part from a dysregulation of the innate and adaptive immune responses. Unlike normal wound healing, in CTI, disruptions occur in innate immune responses, altering neutrophil functions, macrophage activation and polarization, further impacting the functions of T regulatory cells. Additionally, the biological underpinnings of these unfavorable wound healing conditions are multifactorial, including various processes, such as: ischemia, hypoxia, low nutrient levels, and altered cell metabolic pathways, among others, all of which are thought to trigger anergy in immune cells and destabilize adaptive immune responses. As a result, impaired wound healing is common in CTI. Herein, we review the altered innate and adaptive immune cells and their metabolic status and responses following CTI, and discuss the role a multi-pronged immunomodulatory approach may play in facilitating improved outcomes for afflicted patients.

Benefits and pathologies associated with the inflammatory response

Adult skeletal muscle regenerates completely after a damage, thanks to the satellite cells, or muscle stem cells (MuSCs), that implement the adult myogenic program. This program is sustained by both robust intrinsic mechanisms and extrinsic cues coming from the close neighborhood of MuSCs during muscle regeneration. Among the various cell types present in the regenerating muscle, immune cells, and particularly macrophages, exert numerous functions and provide sequential transient niches to support the myogenic program. The adequate orchestration of the delivery of these cues ensures efficient muscle regeneration and full functional recovery. The situation is very different in muscular dystrophies where asynchronous and permanent microinjuries occur, triggering contradictory regenerating cues at the same time in a specific area, that lead to chronic inflammation and fibrogenesis. Here we review the beneficial effects that leukocytes, and particularly macrophages, exert on their neighboring cells during skeletal muscle regeneration after an acute injury. Then, the more complicated (and less beneficial) roles of leukocytes during muscular dystrophies are presented. Finally, we discuss how the inflammatory compartment may be a target to improve muscle regeneration in both acute muscle injury and muscle diseases.

Interleukin-2 and regulatory T cells in rheumatic diseases

Failure of regulatory T (T_reg) cells to properly control immune responses leads invariably to autoimmunity and organ damage. Decreased numbers or impaired function of T_reg cells, especially in the context of inflammation, has been documented in many human autoimmune diseases. Restoration of T_reg cell fitness and/or expansion of their numbers using low-dose natural IL-2, the main cytokine driving T_reg cell survival and function, has demonstrated clinical efficacy in early clinical trials. Genetically modified IL-2 with an extended half-life and increased selectivity for T_reg cells is now in clinical development. Administration of IL-2 combined with therapies targeting other pathways involved in the expression of autoimmune diseases should further enhance its therapeutic potential. Ongoing clinical efforts that capitalize on the early clinical success of IL-2 treatment should bring the use of this cytokine to the forefront of biological treatments for autoimmune diseases.