Macrophage Involvement in Aging-Associated Skeletal Muscle Regeneration

Bazi Bushen mitigates age-related muscular atrophy by alleviating cellular senescence of skeletal muscle

Background and aim

Muscular atrophy is one of the most common age-related conditions characterized by the deterioration of skeletal muscle structures and impaired functions. It is associated with cellular senescence and chronic inflammation, which impair the function of muscle stem cells. Bazi Bushen (BZBS) is a patent compound Chinese medicine that has been shown to have anti-aging effects in various animal models. In this study, we investigated the effects and mechanisms of BZBS on muscular atrophy in naturally aged mice.

Experimental procedure

A muscular atrophy model of naturally aged mice (18 months) was employed with administration of BZBS (2 g/kg/d, 1 g/kg/d) and nicotinamide mononucleotide (NMN, 200 mg/kg/d). After six months of drug administration, muscle weight loss, muscle function and muscle histopathology were measured to evaluate the therapeutic effect of BZBS. The expression of cellular senescence, inflammatory and satellite cell-related factors were used to assess the effects of BZBS in inhibiting cellular senescence, reducing inflammation and improving muscle atrophy.

Results and conclusion

Compared with age matched natural aging mice, we found that BZBS improved muscle strength, mass, and morphology by reducing senescent cells, inflammatory cytokines, and intermyofiber fibrosis in aged muscle tissues. We also found that BZBS prevented the reduction of Pax7 positive stem cells and stimulated the activation and differentiation into myocytes. Our results suggest that BZBS might be a promising intervention in senile muscular atrophy.

A comprehensive single-cell RNA transcriptomic analysis identifies a unique SPP1+ macrophages subgroup in aging skeletal muscle

Senescence of skeletal muscle (SkM) has been a primary contributor to senior weakness and disability in recent years. The gradually declining SkM function associated with senescence has recently been connected to an imbalance between damage and repair. Macrophages (Mac) are involved in SkM aging, and different macrophage subgroups hold different biological functions. Through comprehensive single-cell transcriptomic analysis, we first compared the metabolic pathways and biological functions of different types of cells in young (Y) and old (O) mice SkM. Strikingly, the Mac population in mice SkM was also explored, and we identified a unique Mac subgroup in O SkM characterized by highly expressed SPP1 with strong senescence and adipogenesis features. Further work was carried out on the metabolic and biological processes for these Mac subgroups. Besides, we verified that the proportion of the SPP1+ Mac was increased significantly in the quadriceps tissues of O mice, and the senotherapeutic drug combination dasatinib + quercetin (D + Q) could dramatically reduce its proportion. Our study provides novel insight into the potential role of SPP1+ Mac in SkM, which may serve as a senotherapeutic target in SkM aging.

Macrophage plasticity: signaling pathways, tissue repair, and regeneration

Macrophages are versatile immune cells with remarkable plasticity, enabling them to adapt to diverse tissue microenvironments and perform various functions. Traditionally categorized into classically activated (M1) and alternatively activated (M2) phenotypes, recent advances have revealed a spectrum of macrophage activation states that extend beyond this dichotomy. The complex interplay of signaling pathways, transcriptional regulators, and epigenetic modifications orchestrates macrophage polarization, allowing them to respond to various stimuli dynamically. Here, we provide a comprehensive overview of the signaling cascades governing macrophage plasticity, focusing on the roles of Toll-like receptors, signal transducer and activator of transcription proteins, nuclear receptors, and microRNAs. We also discuss the emerging concepts of macrophage metabolic reprogramming and trained immunity, contributing to their functional adaptability. Macrophage plasticity plays a pivotal role in tissue repair and regeneration, with macrophages coordinating inflammation, angiogenesis, and matrix remodeling to restore tissue homeostasis. By harnessing the potential of macrophage plasticity, novel therapeutic strategies targeting macrophage polarization could be developed for various diseases, including chronic wounds, fibrotic disorders, and inflammatory conditions. Ultimately, a deeper understanding of the molecular mechanisms underpinning macrophage plasticity will pave the way for innovative regenerative medicine and tissue engineering approaches.

Characterizing the skeletal muscle immune microenvironment for sarcopenia: insights from transcriptome analysis and histological validation

Background

Sarcopenia is a condition characterized by the age-related loss of skeletal muscle mass and function. The pathogenesis of the disease is influenced by chronic low-grade inflammation. However, the specific changes in the immune landscape changes of sarcopenic muscle are not yet fully understood.

Methods

To gain insights into the immune cell composition and interactions, we combined single-nucleus RNA sequencing data, bulk RNA sequencing dataset, and comprehensive bioinformatic analyses on the skeletal muscle samples from young, aged, and sarcopenic individuals. Histological staining was then performed on skeletal muscles to validate the distribution of immune cells in clinical samples.

Results

We analyzed the transcriptomes of 101,862 single nuclei, revealing a total of 10 major cell types and 6 subclusters of immune cell types within the human skeletal muscle tissues. Notable variations were identified in the immune microenvironment between young and aged skeletal muscle. Among the immune cells from skeletal muscle microenvironment, macrophages constituted the largest fraction. A specific marker gene LYVE1 for skeletal muscle resident macrophages was further identified. Cellular subclasses included four distinct groups of resident macrophages, which play different roles in physiological or non-physiological conditions. Utilizing bulk RNA sequencing data, we observed a significant enrichment of macrophage-rich inflammation in sarcopenia.

Conclusions

Our findings demonstrate age-related changes in the composition and cross-talk of immune cells in human skeletal muscle microenvironment, which contribute to chronic inflammation in aged or sarcopenia muscle. Furthermore, macrophages emerge as a potential therapeutic target, thus advancing our understanding of the pathogenesis of sarcopenia.

A perspective on muscle phenotyping in musculoskeletal research

Musculoskeletal research should synergistically investigate bone and muscle to inform approaches for maintaining mobility and to avoid bone fractures. The relationship between sarcopenia and osteoporosis, integrated in the term 'osteosarcopenia', is underscored by the close association shown between these two conditions in many studies, whereby one entity emerges as a predictor of the other. In a recent workshop of Working Group (WG) 2 of the EU Cooperation in Science and Technology (COST) Action 'Genomics of MusculoSkeletal traits Translational Network' (GEMSTONE) consortium (CA18139), muscle characterization was highlighted as being important, but currently under-recognized in the musculoskeletal field. Here, we summarize the opinions of the Consortium and research questions around translational and clinical musculoskeletal research, discussing muscle phenotyping in human experimental research and in two animal models: zebrafish and mouse.

Bone marrow mesenchymal stem cell-derived exosomes shuttle microRNAs to endometrial stromal fibroblasts that promote tissue proliferation /regeneration/ and inhibit differentiation

BACKGROUND

Human bone marrow-derived stem cells (hBMDSCs) are well characterized mediators of tissue repair and regeneration. An increasing body of evidence indicates that these cells exert their therapeutic effects largely through their paracrine actions rather than clonal expansion and differentiation. Here we studied the role of microRNAs (miRNAs) present in extracellular vesicles (EVs) from hBMDSCs in tissue regeneration and cell differentiation targeting endometrial stromal fibroblasts (eSF).

METHODS

Extracellular vesicles (EVs) are isolated from hBMDSCs, characterized by transmission electron microscopy (TEM) and nanoparticle tracking analysis (NTA) techniques. Extracted total RNA from EVs was subjected to RNA seq analysis. Transfection and decidualization studies were carried out in endometrial stromal fibroblasts (eSF). Gene expression was analyzed by qRTPCR. Unpaired t-test with Welch's correction was used for data analysis between two groups.

RESULTS

We identified several microRNAs (miRNAs) that were highly expressed, including miR-21-5p, miR-100-5p, miR-143-3p and let7. MiR-21 is associated with several signaling pathways involved in tissue regeneration, quiescence, cellular senescence, and fibrosis. Both miR-100-5p and miR-143-3p promoted cell proliferation. MiR-100-5p specifically promoted regenerative processes by upregulating TGF-ß3, VEGFA, MMP7, and HGF. MiR-100-5p blocked differentiation or decidualization as evidenced by morphologic changes and downregulation of decidualization mediators including HOXA10, IGFBP1, PRL, PR-B, and PR.

CONCLUSION

EVs delivered to tissues by hBMDSCs contain specific miRNAs that prevent terminal differentiation and drive repair and regeneration. Delivery of microRNAs is a novel treatment paradigm with the potential to replace BMDSCs in cell-free regenerative therapies.

Program with last minute abstracts of the Padua Days on Muscle and Mobility Medicine, 27 February - 2 March, 2024 (2024Pdm3)

During the 2023 Padua Days on Muscle and Mobility Medicine the 2024 meeting was scheduled from 28 February to 2 March 2024 (2024Pdm3). During autumn 2023 the program was expanded with Scientific Sessions which will take place over five days (in 2024 this includes February 29), starting from the afternoon of 27 February 2024 in the Conference Rooms of the Hotel Petrarca, Thermae of Euganean Hills (Padua), Italy. As per consolidated tradition, the second day will take place in Padua, for the occasion in the Sala San Luca of the Monastery of Santa Giustina in Prato della Valle, Padua, Italy. Confirming the attractiveness of the Padua Days on Muscle and Mobility Medicine, over 100 titles were accepted until 15 December 2023 (many more than expected), forcing the organization of parallel sessions on both 1 and 2 March 2024. The five days will include lectures and oral presentations of scientists and clinicians from Argentina, Austria, Belgium, Brazil, Bulgaria, Canada, Denmark, Egypt, France, Germany, Iceland, Ireland, Italy, Romania, Russia, Slovenia, Switzerland, UK and USA. Only Australia, China, India and Japan are missing from this edition. But we are confident that authors from those countries who publish articles in the PAGEpress: European Journal of Translational Myology (EJTM: 2022 ESCI Clarivate's Impact Factor: 2.2; SCOPUS Cite Score: 3.2) will decide to join us in the coming years. Together with the program established by 31 January 2024, the abstracts will circulate during the meeting only in the electronic version of the EJTM Issue 34 (1) 2024. See you soon in person at the Hotel Petrarca in Montegrotto Terme, Padua, for the inauguration scheduled the afternoon of 27 February 2024 or on-line for free via Zoom. Send us your email address if you are not traditional participants listed in Pdm3 and EJTM address books.

dECM restores macrophage immune homeostasis and alleviates iron overload to promote DTPI healing

Due to its highly insidious and rapid progression, deep tissue pressure injury (DTPI) is a clinical challenge. Our previous study found that DTPI may be a skeletal muscle injury dominated by macrophage immune dysfunction due to excessive iron accumulation. Decellularized extracellular matrix (dECM) hydrogel promotes skeletal muscle injury repair. However, its role in polarizing macrophages and regulating iron metabolism in DTPI remains unclear. Here, porcine dECM hydrogel was prepared, and its therapeutic function and mechanism in repairing DTPI were investigated. The stimulus of dECM hydrogel toward RAW264.7 cells resulted in a significantly higher percentage of CD206+ macrophages and notably decreased intracellular divalent iron levels. In mice DTPI model, dECM hydrogel treatment promoted M1 to M2 macrophage conversion, improved iron metabolism and reduced oxidative stress in the early stage of DTPI. In the remodeling phase, the dECM hydrogel remarkably enhanced revascularization and accelerated skeletal muscle repair. Furthermore, the immunomodulation of dECM hydrogels in vivo was mainly involved in the P13k/Akt signaling pathway, as revealed by GO and KEGG pathway analysis, which may ameliorate the iron deposition and promote the healing of DTPI. Our findings indicate that dECM hydrogel is promising in skeletal muscle repair, inflammation resolution and tissue injury healing by effectively restoring macrophage immune homeostasis and normalizing iron metabolism.

The aging tumor metabolic microenvironment

Despite the higher incidence of cancer with increasing age, few preclinical or clinical studies incorporate age. This, coupled with an aging world population, requires that we improve our understanding of how aging affects cancer development, progression, and treatment. One key area will be how the tumor microenvironment (TME) changes with age. Metabolite levels are an essential component of the TME, and they are affected by the metabolic requirements of the cells present and systemic metabolite availability. These factors are affected by aging, causing different TME metabolic states between young and older adults. In this review, we will summarize what is known about how aging impacts the TME metabolic state, and suggest how we can improve our understanding of it.

New insight into the role of macrophages in ovarian function and ovarian aging

Macrophages (MΦs) are the most abundant leukocytes in mammalian ovaries that have heterogeneity and plasticity. A body of evidence has indicated that these cells are important in maintaining ovarian homeostasis and they play critical roles in ovarian physiological events, such as folliculogenesis, ovulation, corpus luteum formation and regression. As females age, ovarian tissue microenvironment is typified by chronic inflammation with exacerbated ovarian fibrosis. In response to specific danger signals within aged ovaries, macrophages polarize into different M1 or M2 phenotypes, and specialize in unique functions to participate in the ovarian aging process. In this review, we will focus on the physiologic roles of MΦs in normal ovarian functions. Furthermore, we will discuss the roles of MΦs in the process of ovarian senescence, as well as the novel techniques applied in this field.

Unsaturated Long-Chain Fatty Acids Activate Resident Macrophages and Stem Cells in a Human Skeletal Muscle Tissue Model

Phenotypically heterogeneous populations of tissue-resident macrophages and stem cells play important roles in the regeneration of the skeletal muscle tissue. Previous studies using animal and cell culture models implied a beneficial effect of fatty acid (FA) species on tissue regeneration. Here, we applied a human experimental model using excised muscle tissues from reconstructive surgeries to study the effects of FAs on resident macrophages and stem cells in the natural environment of human skeletal muscle tissue. Muscle tissue samples from 20 donors were included in this study. The expression of 34 cytokines/chemokines was determined, using multiplex protein analysis. The phenotypes of macrophages and stem cells were determined immunohistochemically. The numbers of CD80+ macrophages correlated with the expression levels of IL-1α, IL-1RA, IL-8, IL-17A, and MCP-1, while the PAX7+ and MyoD+ stem cell counts were positively correlated with the expression level of CXCL12α, a recognized chemoattractant for muscle stem cells. Treatment of additional tissue sections with FAs revealed that CD80+ or MARCO+ macrophages- and PAX7+ or MyoD+ stem cells were simultaneously increased by unsaturated long-chain FAs. Taken together, this is the first experimental demonstration of a coordinated activation of macrophages and stem cells in human skeletal muscle tissue.