Pharmacological activation of SIRT1 by metformin prevented trauma-induced heterotopic ossification through inhibiting macrophage mediated inflammation

Metformin: From Diabetes to Cancer-Unveiling Molecular Mechanisms and Therapeutic Strategies

Metformin, a widely used anti-diabetic drug, has garnered attention for its potential in cancer management, particularly in breast and colorectal cancer. It is established that metformin reduces mitochondrial respiration, but its specific molecular targets within mitochondria vary. Proposed mechanisms include inhibiting mitochondrial respiratory chain Complex I and/or Complex IV, and mitochondrial glycerophosphate dehydrogenase, among others. These actions lead to cellular energy deficits, redox state changes, and several molecular changes that reduce hyperglycemia in type 2 diabetic patients. Clinical evidence supports metformin's role in cancer prevention in type 2 diabetes mellitus patients. Moreover, in these patients with breast and colorectal cancer, metformin consumption leads to an improvement in survival outcomes and prognosis. The synergistic effects of metformin with chemotherapy and immunotherapy highlights its potential as an adjunctive therapy for breast and colorectal cancer. However, nuanced findings underscore the need for further research and stratification by molecular subtype, particularly for breast cancer. This comprehensive review integrates metformin-related findings from epidemiological, clinical, and preclinical studies in breast and colorectal cancer. Here, we discuss current research addressed to define metformin's bioavailability and efficacy, exploring novel metformin-based compounds and drug delivery systems, including derivatives targeting mitochondria, combination therapies, and novel nanoformulations, showing enhanced anticancer effects.

Role of the NF-kB signalling pathway in heterotopic ossification: biological and therapeutic significance

Heterotopic ossification (HO) is a pathological process in which ectopic bone develops in soft tissues within the skeletal system. Endochondral ossification can be divided into the following types of acquired and inherited ossification: traumatic HO (tHO) and fibrodysplasia ossificans progressiva (FOP). Nuclear transcription factor kappa B (NF-κB) signalling is essential during HO. NF-κB signalling can drive initial inflammation through interactions with the NOD-like receptor protein 3 (NLRP3) inflammasome, Sirtuin 1 (SIRT1) and AMP-activated protein kinase (AMPK). In the chondrogenesis stage, NF-κB signalling can promote chondrogenesis through interactions with mechanistic target of rapamycin (mTOR), phosphatidylinositol-3-kinase (PI3K)/AKT (protein kinase B, PKB) and other molecules, including R-spondin 2 (Rspo2) and SRY-box 9 (Sox9). NF-κB expression can modulate osteoblast differentiation by upregulating secreted protein acidic and rich in cysteine (SPARC) and interacting with mTOR signalling, bone morphogenetic protein (BMP) signalling or integrin-mediated signalling under stretch stimulation in the final osteogenic stage. In FOP, mutated ACVR1-induced NF-κB signalling exacerbates inflammation in macrophages and can promote chondrogenesis and osteogenesis in mesenchymal stem cells (MSCs) through interactions with smad signalling and mTOR signalling. This review summarizes the molecular mechanism of NF-κB signalling during HO and highlights potential therapeutics for treating HO.

Pristimerin suppresses AIM2 inflammasome by modulating AIM2-PYCARD/ASC stability via selective autophagy to alleviate tendinopathy

Macroautophagy/autophagy plays an important role in regulating cellular homeostasis and influences the pathogenesis of degenerative diseases. Tendinopathy is characterized by tendon degeneration and inflammation. However, little is known about the role of selective autophagy in tendinopathy. Here, we find that pristimerin (PM), a quinone methide triterpenoid, is more effective in treating tendinopathy than the first-line drug indomethacin. PM inhibits the AIM2 inflammasome and alleviates inflammation during tendinopathy by promoting the autophagic degradation of AIM2 through a PYCARD/ASC-dependent manner. A mechanistic study shows that PM enhances the K63-linked ubiquitin chains of PYCARD/ASC at K158/161, which serves as a recognition signal for SQSTM1/p62-mediated autophagic degradation of the AIM2-PYCARD/ASC complex. We further identify that PM binds the Cys53 site of deubiquitinase USP50 through the Michael-acceptor and blocks the binding of USP50 to PYCARD/ASC, thereby reducing USP50-mediated cleavage of K63-linked ubiquitin chains of PYCARD/ASC. Finally, PM treatment in vivo generates an effect comparable to inflammasome deficiency in alleviating tendinopathy. Taken together, these findings demonstrate that PM alleviates the progression of tendinopathy by modulating AIM2-PYCARD/ASC stability via SQSTM1/p62-mediated selective autophagic degradation, thus providing a promising autophagy-based therapeutic for tendinopathy.Abbreviations: 3-MA: 3-methyladenine; AIM2: absent in melanoma 2; AT: Achilles tenotomy; ATP: adenosine triphosphate; BMDMs: bone marrow-derived macrophages; CHX: cycloheximide; Col3a1: collagen, type III, alpha 1; CQ: chloroquine; Cys: cysteine; DARTS: drug affinity responsive target stability; DTT: dithiothreitol; DUB: deubiquitinase; gDNA: genomic DNA; GSH: glutathione; His: histidine; IL1B/IL-1β: interleukin 1 beta; IND: indomethacin; IP: immunoprecipitation; LPS: lipopolysaccharide; MMP: mitochondrial membrane potential; NLRP3: NLR family, pyrin domain containing 3; PM: pristimerin; PYCARD/ASC: PYD and CARD domain containing; SN: supernatants; SOX9: SRY (sex determining region Y)-box 9; SQSTM1: sequestosome 1; Tgfb: transforming growth factor, beta; TIMP3: tissue inhibitor of metalloproteinase 3; TNMD: tenomodulin; TRAF6: TNF receptor-associated factor 6; Ub: ubiquitin; USP50: ubiquitin specific peptidase 50; WCL: whole cell lysates.

SENP1-mediated SUMOylation of SIRT1 affects glioma development through the NF-κB pathway

Gliomas are the most common primary brain tumors in adults. Although they exist in different malignant stages, most gliomas are clinically challenging because of their infiltrative growth patterns and inherent relapse tendency with increased malignancy. Epigenetic alterations have been suggested to be an important factor for glioma genesis. Using mRNA probe hybridization, we identified SUMO-specific protease 1 (SENP1) as the most significantly upregulated SUMOylation regulator in glioma. Moreover, SENP1 was overexpressed in gliomas and predicted poor prognoses. Depletion of SENP1 reduced glioma cell activity, cycle arrest, and increased apoptotic activity. Mechanistically, SENP1 inhibited the protein expression of sirtuin 1 (SIRT1) through de-SUMOylation, and SIRT1 inhibited the activity of nuclear factor kappaB (NF-κB) by deacetylation. Rescue experiments revealed that downregulation of SIRT1 reversed the inhibitory effect of sh-SENP1 on glioma cell malignant phenotype, while downregulation of NF-κB reversed the activating effect of sh-SIRT1 on glioma cell malignant phenotype. Thus, SENP1-mediated de-SUMOylation of SIRT1 might be therapeutically important in gliomas.

Interleukin-17A Promotes Proliferation and Osteogenic Differentiation of Human Ligamentum Flavum Cells Through Regulation of β-Catenin Signaling

STUDY DESIGN

A basic experimental study.

OBJECTIVE

To elucidate the role and mechanism of interleukin (IL)-17A in thoracic ossification of the ligamentum flavum (TOLF).

SUMMARY OF BACKGROUND DATA

TOLF is characterized by the replacement of the thoracic ligamentum flavum with ossified tissue and is one of the leading causes of thoracic spinal stenosis. IL-17A is an important member of the IL-17 family that has received widespread attention for its key contributions to the regulation of bone metabolism and heterotopic ossification. However, it is unclear whether IL-17A is involved in TOLF.

MATERIALS AND METHODS

Cell counting kit-8 assay and 5-ethynyl-2'-deoxyuridine staining were performed to assess the proliferation of ligamentum flavum cells (LFCs). Alkaline phosphatase activity assay, Alizarin red staining, and protein level expression of osteogenic-related genes were used to evaluate the osteogenic differentiation potential of LFCs. The effect of IL-17A on the proliferation and osteogenic differentiation of LFCs was further assessed after silencing β-catenin by transfection with small interfering RNA. In addition, the possible source of IL-17A was further demonstrated by coculture assays of T helper 17 (Th17) cells with LFCs. Student t test was used for comparisons between groups, and the one-way analysis of variance, followed by the Tukey post hoc test, was used for comparison of more than two groups.

RESULTS

IL-17A was elevated in TOLF tissue compared with normal ligamentum flavum. IL-17A stimulation promoted the proliferation and osteogenic differentiation of LFCs derived from patients with TOLF. We found that IL-17A promoted the proliferation and osteogenic differentiation of LFCs by regulating the β-catenin signaling. Coculture of Th17 cells with LFCs enhanced β-catenin signaling-mediated proliferation and osteogenic differentiation of LFCs. However, these effects were markedly attenuated after the neutralization of IL-17A.

CONCLUSIONS

This is the first work we are aware of to highlight the importance of IL-17A in TOLF. IL-17A secreted by Th17 cells in the ligamentum flavum may be involved in the ossification of the microenvironment by regulating β-catenin signaling to promote the proliferation and osteogenic differentiation of LFCs.

The physiological phenomenon and regulation of macrophage polarization in diabetic wound

Macrophages play a crucial role in regulating wound healing, as they undergo a transition from the proinflammatory M1 phenotype to the proliferative M2 phenotype, ultimately contributing to a favorable outcome. However, in hyperglycemic and hyper-reactive oxygen species environments, the polarization of macrophages becomes dysregulated, hindering the transition from the inflammatory to proliferative phase and consequently delaying the wound healing process. Consequently, regulating macrophage polarization is often regarded as a potential target for the treatment of diabetic wounds. The role of macrophages in wound healing and the changes in macrophages in diabetic conditions were discussed in this review. After that, we provide a discussion of recent therapeutic strategies for diabetic wounds that utilize macrophage polarization. Furthermore, this review also provides a comprehensive summary of the efficacious treatment strategies aimed at enhancing diabetic wound healing through the regulation of macrophage polarization. By encompassing a thorough understanding of the fundamental principles and their practical implementation, the advancement of treatment strategies for diabetic wounds can be further facilitated.

Association Between Tranexamic Acid Use and Heterotopic Ossification Prevalence After Elbow Trauma Surgery: A Propensity-Score-Matched Cohort Study

BACKGROUND

Heterotopic ossification (HO) is a common complication of elbow trauma that can affect limb mobility. Inflammation is an initiating factor for HO formation. Tranexamic acid (TXA) can reduce the inflammatory response after orthopaedic surgery. However, evidence regarding the effectiveness of TXA use for HO prevention after elbow trauma surgery is lacking.

METHODS

This retrospective observational propensity-score-matched (PSM) cohort study was conducted from July 1, 2019, to June 30, 2021, at the National Orthopedics Clinical Medical Center, Shanghai, People's Republic of China. A total of 640 patients who underwent surgery following elbow trauma were evaluated. The present study excluded patients with an age of <18 years; those with a history of elbow fracture; those with a central nervous system injury, spinal cord injury, burn injury, or destructive injury; and those who had been lost to follow-up. After 1:1 matching on the basis of sex, age, dominant arm, injury type, open injury, comminuted fracture, ipsilateral trauma, time from injury to surgery, and nonsteroidal anti-inflammatory drug use, the TXA group and the no-TXA group comprised 241 patients each.

RESULTS

In the PSM population, the prevalence of HO was 8.71% in the TXA group and 16.18% in the no-TXA group (with rates of 2.07% and 5.80% for clinically important HO, respectively). Logistic regression analyses showed that TXA use was associated with a lower rate of HO (odds ratio [OR], 0.49; 95% CI, 0.28 to 0.86; p = 0.014) than no TXA use, as well as with a lower rate of clinically important HO (OR, 0.34; 95% CI, 0.11 to 0.91; p = 0.044). None of the baseline covariates significantly affected the relationship between TXA use and HO rate (p > 0.05 for all). Sensitivity analyses supported these findings.

CONCLUSIONS

TXA prophylaxis may be an appropriate method for the prevention of HO following elbow trauma.

LEVEL OF EVIDENCE

Therapeutic Level III . See Instructions for Authors for a complete description of levels of evidence.

Ethyl caffeate inhibits macrophage polarization via SIRT1/NF-κB to attenuate traumatic heterotopic ossification in mice

Heterotopic ossification (HO) denotes the presence of mature bone tissue in soft tissues or around joints. Inflammation is a key driver of traumatic HO, and macrophages play an important role in this process. Ethyl caffeate (ECF), a critical active compound found in Petunia, exerts significant anti-inflammatory effects. Herein, we established a mouse model of HO by transection of the Achilles tendon and back burn and found abundant macrophage infiltration in the early stage of HO, which decreased with time. In vitro and in vivo experiments indicated that ECF inhibited macrophage polarization, and mechanistic studies showed that it inhibited the SIRT1/NF-κB signalling pathway, thereby suppressing the release of downstream inflammatory cytokines. ECF reduced HO in mice, and its effect was comparable to indomethacin (INDO). In vitro studies revealed that ECF did not directly affect the mineralization of mesenchymal stem cells (MSCs) or osteogenic differentiation but inhibited these processes by reducing the level of inflammatory cytokines in the conditioned medium (CM). Thus, M1 macrophages may play a crucial role in the pathogenesis of HO, and ECF is a prospective candidate for the prevention of trauma-induced HO. DATA AVAILABILITY: Data will be made available on request.

STING contributes to trauma-induced heterotopic ossification through NLRP3-dependent macrophage pyroptosis

Trauma-induced heterotopic ossification (HO) is featured by aberrant bone formation at extra-skeletal site. STING is a master adaptor protein linking cellular damage to immune responses, while its role in HO remains elusive. A murine burn/tenotomy model was used to mimic trauma-induced HO in vivo. We demonstrated elevated STING expression in macrophages in inflammatory stage after burn/tenotomy, and STING inhibition significantly alleviated HO formation. Activated NLRP3-dependent macrophage pyroptosis was also found in inflammatory stage after burn/tenotomy. Either STING or NLRP3 suppression reduced mature HO by weakening macrophage pyroptotic inflammation, while protective effects of STING were abolished by NLRP3 overexpression. Further, in vitro, we also found a prominent STING level in pyroptotic BMDMs. STING suppression relieved macrophage pyroptotic inflammation, while abolished by NLRP3 overexpression. Our results reveal that STING poses regulatory effects on trauma-induced HO formation, via modulating NLRP3-dependent macrophage pyroptosis. Targeting STING-NLRP3 axis represents an attractive approach for trauma-induced HO prevention.

Pathogenesis of acquired heterotopic ossification: Risk factors, cellular mechanisms, and therapeutic implications

Heterotopic ossification (HO), including hereditary and acquired HO, is the formation of extraskeletal bone in skeletal muscle and surrounding soft tissues. Acquired HO is often caused by range of motion, explosion injury, nerve injury or burns. Severe HO can lead to pain and limited joint activity, affecting functional rehabilitation and quality of life. Increasing evidence shows that inflammatory processes and mesenchymal stem cells (MSCs) can drive HO. However, explicit knowledge about the specific mechanisms that result in HO and related cell precursors is still limited. Moreover, there are no effective methods to prevent or reduce HO formation. In this review, we provide an update of known risk factors and relevant cellular origins for HO. In particular, we focus on the underlying mechanisms of MSCs in acquired HO, which follow the osteogenic program. We also discuss the latest therapeutic value and implications for acquired HO. Our review highlights the current gaps in knowledge regarding the pathogenesis of acquired HO and identifies potential targets for the prevention and treatment of HO.

Macrophage-Derived TGF-β and VEGF Promote the Progression of Trauma-Induced Heterotopic Ossification

Heterotopic ossification (HO) is a pathological bone formation process caused by musculoskeletal trauma. HO is characterized by aberrant endochondral ossification and angiogenesis. Our previous studies have indicated that macrophage inflammation is involved in traumatic HO formation. In this study, we found that macrophage infiltration and TGF-β signaling activation are presented in human HO. Depletion of macrophages effectively suppressed traumatic HO formation in a HO mice model, and macrophage depletion significantly inhibited the activation of TGF-β/Smad2/3 signaling. In addition, the TGF-β blockade created by a neutralizing antibody impeded ectopic bone formation in vivo. Notably, endochondral ossification and angiogenesis are attenuated following macrophage depletion or TGF-β inhibition. Furthermore, our observations on macrophage polarization revealed that M2 macrophages, rather than M1 macrophages, play a critical role in supporting HO development by enhancing the osteogenic and chondrogenic differentiation of mesenchymal stem cells. Our findings on ectopic bone formation in HO patients and the mice model indicate that M2 macrophages are an important contributor for HO development, and that inhibition of M2 polarization or TGF-β activity may be a potential method of therapy for traumatic HO.

Role of metformin in inflammation

BACKGROUND

Metformin has good anti-hyperglycemic effectiveness, but does not induce hypoglycemia，is very safe, and has become the preferred drug for the treatment of type 2 diabetes. Recently, the other effects of metformin, such as being anti-inflammatory and delaying aging, have also attracted increased attention.

METHODS AND RESULTS

The relevant literatures on pubmed and other websites for reading, classification and sorting, and did not involve any animal experiments.

CONCLUSION

Metformin has anti-inflammatory effects through multiple routes, which provides potential therapeutic targets for certain inflammatory diseases, such as neuroinflammation and rheumatoid arthritis. In addition, inflammation is a key component of tumor occurrence and development ; thus, targeted inflammatory intervention is a significant benefit for both cancer prevention and treatment. Therefore, metformin may have further potential for inflammation-related disease prevention and treatmen. However, the inflammatory mechanism is complex; various molecules are connected and influence each other. For example, metformin significantly inhibits p65 nuclear translocation, but pretreatment with compound C, an AMPK inhibitor, abolishes this effect, and silencing of HMGB1 inhibits NF-κB activation . SIRT1 deacetylates FoxO, increasing its transcriptional activity . mTOR in dendritic cells regulates FoxO1 via AKT. The interactions among various molecules should be further explored to clarify their specific mechanisms and provide more direction for the treatment of inflammatory diseases, as well as cancer.

Salvianolic Acid B Alleviates Limb Ischemia in Mice via Promoting SIRT1/PI3K/AKT Pathway-Mediated M2 Macrophage Polarization

Salvianolic acid B (Sal B) is an effective treatment agent for ischemic disease in China. However, Sal B's effects on peripheral arterial disease (PAD) and its mechanism remains poorly understood. Macrophage polarization plays a crucial role in PAD. Nevertheless, treatment modalities that increase the population of anti-inflammatory (M2) macrophages are limited. This study aimed to explore the protective effects of Sal B on limb perfusion and investigate the mechanism of Sal B-induced macrophage polarization. C57BL/6 male mice (6 weeks) were randomized into control, Model + NS, and Model + Sal B groups (n = 5). Then, we established a hind limb ischemia mouse model to assess the Sal B's role (15 mg/kg/d) in PAD. We quantified the blood perfusion via laser speckle contrast imaging (LSCI) and measured the capillary density and muscle edema with CD31 and H&E staining. The Sal B-induced macrophage polarization was confirmed by qPCR and ELISA. The results showed that the Sal B group exhibited a significant improvement in the blood perfusion, capillary density, muscle edema, and M2 markers gene expressions. Cell migration and tube formation were promoted in the endothelial cells stimulated with a culture supernatant from Sal B-treated macrophages. In contrast, endothelial functions improved by Sal B-treated macrophages were impaired in groups treated with SIRT1 and PI3K inhibitors. These findings provide evidence for Sal B's protective role in PAD and demonstrate the enhancement of macrophage polarization via the SIRT1/PI3K/AKT pathway.

Anti-inflammatory and Tendon-Protective Effects of Adipose Stem Cell-Derived Exosomes with Concomitant Use of Glucocorticoids

Glucocorticoid (GC) injections are commonly used in clinical practice to relieve pain and improve function in patients with multiple shoulder disabilities but cause detrimental effects on rotator cuff tendons. Adipose stem cell-derived exosomes (ASC-Exos) reportedly recover impaired tendon matrix metabolism by maintaining tissue homeostasis. However, it is unclear whether additional treatment with ASC-Exos overrides the detrimental effects of GCs without interfering with their anti-inflammatory effects. Thus, we aimed to investigate the anti-inflammatory effect of ASC-Exos with GCs and protective effect of ASC-Exos against GC-induced detriments. The present study comprised in vitro and in vivo studies. In vitro inflammatory analysis revealed that ASC-Exos exerted a synergic anti-inflammatory effect with GCs by significantly decreasing secretion of proinflammatory cytokines by RAW cells and increasing secretion of anti-inflammatory cytokines. In vitro cytoprotective analysis showed that ASC-Exos overrode GC-induced detrimental effects on tenocytes by significantly improving GC-suppressed cellular proliferation, migration, and transcription of tenocytic matrix molecules and degradative enzyme inhibitors and significantly decreasing GC-induced cell senescence, apoptosis, and transcription of ROS and tenocytic degradative enzymes. In vivo studies revealed that additional ASC-Exo injection restored impairments in histological and biomechanical properties owing to GC administration. Collectively, these results suggest that ASC-Exos exert a stronger anti-inflammatory effect in combination with GCs, overriding their detrimental effects on rotator cuff tendons.

Metformin regulates macrophage polarization via the Shh signaling pathway to improve pulmonary vascular development in bronchopulmonary dysplasia

Metformin has potential anti-inflammatory properties and accelerates wound healing by enhancing vascular development. In this study, we aimed to investigate the effects of metformin on pulmonary vascular development and the underlying mechanism. Newborn mice were subcutaneously injected with metformin from day 2 after exposure to hyperoxia. Pulmonary vascular development, inflammation, and Shh signaling pathway-related protein expression were evaluated by western blotting and immunofluorescence staining. M2 macrophage polarization was measured by flow cytometry. The effect of metformin on macrophage polarization was determined using RAW264.7 macrophages exposed to 90% oxygen in vitro. The role of metformin and purmorphamine on M1 and M2 polarization was observed by flow cytometry. M2 polarization of pulmonary macrophages was inhibited after hyperoxic exposure, and metformin increased the number of M2 macrophages in the lung on postnatal day 14. Metformin upregulated CD31 expression and suppressed inflammation in the lung of mice exposed to hyperoxia on postnatal days 7 and 14. Metformin downregulated the Gli1 expression in macrophages in the lung after exposure to hyperoxia on postnatal day 14. In vitro studies showed that metformin inhibited the Gli1 expression in RAW264.7 macrophages exposed to 90% oxygen, which was reversed after purmorphamine pretreatment. Exposure to 90% oxygen inhibited the polarization of M2 macrophages, whereas metformin increased the number of M2 macrophages. Purmorphamine reversed the effects of metformin on M2 polarization and vascular endothelial growth factor (VEGF) upregulation in RAW264.7 macrophages exposed to hyperoxia. In conclusion, metformin regulates macrophage polarization via the Shh signaling pathway to improve pulmonary vascular development in bronchopulmonary dysplasia.