The Role of Autophagy in M2 Polarization of Macrophages Induced by Micro/Nano Topography

All Roads Lead to Rome: Comparing Nanoparticle- and Small Molecule-Driven Cell Autophagy

Autophagy, vital for removing cellular waste, is triggered differently by small molecules and nanoparticles. Small molecules, like rapamycin, non-selectively activate autophagy by inhibiting the mTOR pathway, which is essential for cell regulation. This can clear damaged components but may cause cytotoxicity with prolonged use. Nanoparticles, however, induce autophagy, often causing oxidative stress, through broader cellular interactions and can lead to a targeted form known as "xenophagy." Their impact varies with their properties but can be harnessed therapeutically. In this review, the autophagy induced by nanoparticles is explored and small molecules across four dimensions: the mechanisms behind autophagy induction, the outcomes of such induction, the toxicological effects on cellular autophagy, and the therapeutic potential of employing autophagy triggered by nanoparticles or small molecules. Although small molecules and nanoparticles each induce autophagy through different pathways and lead to diverse effects, both represent invaluable tools in cell biology, nanomedicine, and drug discovery, offering unique insights and therapeutic opportunities.

The role of autophagy in odontogenesis, dental implant surgery, periapical and periodontal diseases

Autophagy is a cellular process that is evolutionarily conserved, involving the sequestration of damaged organelles and proteins into autophagic vesicles, which subsequently fuse with lysosomes for degradation. Autophagy controls the development of many diseases by influencing apoptosis, inflammation, the immune response and different cellular processes. Autophagy plays a significant role in the aetiology of disorders associated with dentistry. Autophagy controls odontogenesis. Furthermore, it is implicated in the pathophysiology of pulpitis and periapical disorders. It enhances the survival, penetration and colonization of periodontal pathogenic bacteria into the host periodontal tissues and facilitates their escape from host defences. Autophagy plays a crucial role in mitigating exaggerated inflammatory reactions within the host's system during instances of infection and inflammation. Autophagy also plays a role in the relationship between periodontal disease and systemic diseases. Autophagy promotes wound healing and may enhance implant osseointegration. This study reviews autophagy's dento-alveolar effects, focusing on its role in odontogenesis, periapical diseases, periodontal diseases and dental implant surgery, providing valuable insights for dentists on tooth development and dental applications. A thorough examination of autophagy has the potential to discover novel and efficacious treatment targets within the field of dentistry.

The M2 Macrophages Derived Migrasomes From the Surface of Titania Nanotubes Array as a New Concept for Enhancing Osteogenesis

As newly discovered substrate anchored extracellular vesicles, migrasomes (Migs) may bring a new opportunity for manipulating target cells bioactivities. In this study, the M2 macrophages derived Migs are obtained by titania nanotubes surface (NTs). Due to the benefits of nanostructuring, the NTs surface is not only able to induce RAW264.7 for M2 polarization but also to generate more Migs formation, which can be internalized by following seeded mesenchymal stem cells (MSCs). Then, the NTs surface induced Migs are collected by density-gradient centrifugation for MSCs treatment. As indicated by immunofluorescence staining, alkaline phosphatase activity, and alizarin red staining, the osteogenic differentiation capacity of MSCs is significantly enhanced by Migs treatment, in line with the dosage. By RNA-sequence analysis, the enhancement of osteogenic differentiation is correlated with PI3K-AKT pathway activation that may originate from the M2 polarization state of donor cells. Finally, the Migs are coated onto Ti surface for therapeutic application. Both the in vitro and in vivo analysis reveal that the Migs coated Ti implant shows significant enhancement of osteogenesis. In conclusion, this study suggests that the nanosurface may be a favorable platform for Migs production, which may bring a new concept for tissue regeneration.

The dual role of autophagy in the regulation of cancer treatment

As a catabolic process, autophagy through lysosomes degrades defective and damaged cellular materials to support homeostasis in stressful conditions. Therefore, autophagy dysregulation is associated with the induction of several human pathologies, including cancer. Although the role of autophagy in cancer progression has been extensively studied, many issues need to be addressed. The available evidence suggest that autophagy shows both cytoprotective and cytotoxic mechanisms. This dual role of autophagy in cancer has supplied a renewed interest in the development of novel and effective cancer therapies. Considering this, a deeper understanding of the molecular mechanisms of autophagy in cancer treatment is crucial. This article provides a summary of the recent advances regarding the dual and different mechanisms of autophagy-mediated therapeutic efficacy in cancer.

Naringenin facilitates M2 macrophage polarization after myocardial ischemia-reperfusion by promoting nuclear translocation of transcription factor EB and inhibiting the NLRP3 inflammasome pathway

Myocardial ischemia-reperfusion injury (MIRI) remains an unsolved puzzle in medical circles. Naringenin (NAR) is a flavonoid with cardioprotective potential. The purpose of this article was to discuss the protective mechanism of NAR in MIRI by regulating macrophage polarization. The MIRI mouse model was established and perfused with NAR before surgery. In the in vitro experiment, macrophages RAW264.7 were treated with lipopolysaccharide to induce M1 polarization after pretreatment with NAR. Rescue experiments were carried out to validate the functions of transcription factor EB (TFEB), the NLR pyrin domain containing 3 (NLRP3) inflammasome, and autophagy in macrophage polarization. NAR reduced histopathological injury and infarction of myocardial tissues in MIRI mice, inhibited M1 polarization and promoted M2 polarization of macrophages, diminished levels of pro-inflammatory factors, and augmented levels of anti-inflammatory factors. NAR facilitated TFEB nuclear translocation and inhibited the NLRP3 inflammasome pathway. Silencing TFEB or Nigericin partly nullified the effect of NAR on macrophage polarization. NAR increased autophagosome formation, autophagy flux, and autophagy level. Autophagy inhibitor 3-methyladenine partly invalidated the inhibition of NAR on the NLRP3 inflammasome pathway. In animal experiments, NAR protected MIRI mice through the TFEB-autophagy-NLRP3 inflammasome pathway. Collectively, NAR inhibited NLRP3 inflammasome activation and facilitated M2 macrophage polarization by stimulating TFEB nuclear translocation, thus protecting against MIRI.

Macrophage polarization in bone implant repair: A review

Macrophages (MΦ) are highly adaptable and functionally polarized cells that play a crucial role in various physiological and pathological processes. Typically, MΦ differentiate into two distinct subsets: the proinflammatory (M1) and anti-inflammatory (M2) phenotypes. Due to their potent immunomodulatory and anti-inflammatory properties, MΦ have garnered significant attention in recent decades. In the context of bone implant repair, the immunomodulatory function of MΦ is of paramount importance. Depending on their polarization phenotype, MΦ can exert varying effects on osteogenesis, angiogenesis, and the inflammatory response around the implant. This paper provides an overview of the immunomodulatory and inflammatory effects of MΦ polarization in the repair of bone implants.

Dietary lactate supplementation can alleviate DSS-induced colitis in piglets

Colitis is a common and complex intestinal inflammatory disease in which lactate, a metabolite of anaerobic glycolysis, plays a crucial role. Our study aimed to investigate the alleviated effect of lactate in colitis, and to provide a nutritional measure to alleviate colitis injury. The variations in colonic lactate in piglets with DSS-induced colitis were investigated in Experiment 1 (Exp.1). Thirty weaned pigs were allotted into three groups and sampled at different stages of DSS-induced colitis (days 0, 5, and 7). The colonic level of lactate and interleukin 10 (IL-10) was significantly decreased on day 5 when compared to day 0. Colonic lactate, IL-10, and G protein receptor 81 (GPR81) levels were significantly increased on day 7 when compared to day 5. Sixty weaned piglets were assigned to control (basal diet), DSS (basal diet with DSS gavage), or lactate (2% lactate supplementation diet with DSS gavage) groups to investigate the effects of lactate on DSS-induced colitis in Experiment 2 (Exp.2). Lactate reduced the disease activity index (DAI), DSS-induced impairment of colonic structure in response to the critical inflammatory cytokines interleukin 1β (IL-1β) and interleukin 18 (IL-18) when compared with the DSS group. Furthermore, GPR-81 levels, colonic M2 macrophages, and IL-10 levels, the colonic antioxidant capacity, colonic butyrate levels were increased, and eventually improved growth performance post-colitis. The results of this study show that lactate was decreased at the peak of colitis, accumulated in subsidized colitis. Furthermore, dietary lactate supplementation helped to alleviate DSS-induced colitis injury.

Nanotopographical cues for regulation of macrophages and osteoclasts: emerging opportunities for osseointegration

Nanotopographical cues of bone implant surface has direct influences on various cell types during the establishment of osseointegration, a prerequisite of implant bear-loading. Given the important roles of monocyte/macrophage lineage cells in bone regeneration and remodeling, the regulation of nanotopographies on macrophages and osteoclasts has arisen considerable attentions recently. However, compared to osteoblastic cells, how nanotopographies regulate macrophages and osteoclasts has not been properly summarized. In this review, the roles and interactions of macrophages, osteoclasts and osteoblasts at different stages of bone healing is firstly presented. Then, the diversity and preparation methods of nanotopographies are summarized. Special attentions are paid to the regulation characterizations of nanotopographies on macrophages polarization and osteoclast differentiation, as well as the focal adhesion-cytoskeleton mediated mechanism. Finally, an outlook is indicated of coordinating nanotopographies, macrophages and osteoclasts to achieve better osseointegration. These comprehensive discussions may not only help to guide the optimization of bone implant surface nanostructures, but also provide an enlightenment to the osteoimmune response to external implant.

Autophagic reprogramming of bone marrow–derived macrophages

Macro-autophagy is a highly conserved catabolic process among eukaryotes affecting macrophages. This work studies the genetic regulatory network involving the interplay between autophagy and macrophage polarization (activation). Autophagy-related genes (Atgs) and differentially expressed genes (DEGs) of macrophage polarization (M1–M2) were predicted, and their regulatory networks constructed. Naïve (M0) mouse bone marrow–derived monocytes were differentiated into M1 and M2a. Validation of the targets of Smad1, LC3A and LC3B, Atg16L1, Atg7, IL-6, CD68, Arg-1, and Vamp7 was performed in vitro. Immunophenotyping by flow cytometry revealed three macrophage phenotypes: M0 (IL-6 + /CD68 +), M1 (IL-6 + /CD68 + /Arg-1 +), and M2a (CD68 + /Arg-1). Confocal microscopy revealed increased autophagy in both M1 and M2a and a significant increase in the pre-autophagosomes size and number. Bafilomycin A increased the expression of CD68 and Arg-1 in all cell lineages. In conclusion, our approach predicted the protein targets mediating the interplay between autophagy and macrophage polarization. We suggest that autophagy reprograms macrophage polarization via CD68, arginase 1, Atg16L1-1, and Atg16L1-3. The current findings provide a foundation for the future use of macrophages in immunotherapy of different autoimmune disorders.

In Situ Growth of Tunable Gold Nanoparticles by Titania Nanotubes Templated Electrodeposition for Improving Osteogenesis through Modulating Macrophages Polarization

Driving macrophages M2 polarization has attracted growing attention for improving osteogenesis. Here, the in situ growth of tunable gold nanoparticles (AuNPs) on titania nanotubes (TiNTs) array was realized by electrodeposition, with the guidance of TiNTs. The fabricated Au layer showed excellent biocompatibility with different osteoimmune effects. Briefly, the Au deposition on 5 and 10 V anodized TiNTs surface could induce RAW264.7 cells to M2 polarization, whereas the Au deposition on 20 V anodized TiNTs surface showed M1 polarization, as indicated by various markers determination through immunofluorescence staining, qPCR, Western blot, and ELISA. Furthermore, the osteogenic differentiation of MC3T3-E1 was significantly enhanced by the macrophages conditioned medium from the Au@10VNTs surface. The in vivo tests also confirmed denser and thicker new trabecula bone formation and more M2 macrophages infiltration both on and adjacent to the Au@10VNTs implant surface. In mechanism, the cytokine array analysis of macrophages conditioned medium from the Au@10VNTs surface revealed the upregulation of pro-healing cytokines such as IL-10 and VEGF and downregulation of pro-inflammatory cytokines such as IL-1β and MCSF. In addition, the NF-κB pathway was significantly inhibited. In conclusion, the electrodeposition of a Au layer guided by TiNTs is a promising strategy for reducing postoperative inflammatory reactions and improving osseointegration through modulating macrophages polarization.

Sunitinib induced hepatotoxicity in L02 cells via ROS-MAPKs signaling pathway

Sunitinib is a multi-targeted tyrosine kinase inhibitor with remarkable anticancer activity, while hepatotoxicity is a potentially fatal adverse effect of its administration. The aim of this study was to elucidate the mechanism of hepatotoxicity induced by Sunitinib and the protective effect of glycyrrhetinic acid (GA). Sunitinib significantly reduced the survival of human normal hepatocytes (L02 cells), induced the increase of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH). Chloroquine (CQ) and Z-VAD-FMK were applied to clarify the cell death patterns induced by Sunitinib. Sunitinib significantly induced L02 cells death by triggering apoptosis and autophagy acted as a self-defense mechanism to promote survival. Sunitinib exposure caused excessive ROS generation which activated mitogen-activated protein kinases (MAPKs) signaling. Mechanistically, SP600125 (JNK inhibitor) and SB203580 (p38 inhibitor) respectively blocked apoptosis and autophagy induced by Sunitinib. And inhibition of ROS by NAC pretreatment ameliorated the effect of Sunitinib on MAPKs phosphorylation. GA alleviated Sunitinib-induced cell damage by inhibiting apoptosis and autophagy. These results suggested ROS/MAPKs signaling pathway was responsible for Sunitinib-induced hepatotoxicity and GA could be a preventive strategy to alleviate liver injury caused by Sunitinib.

Resveratrol promotes osteogenesis and angiogenesis through mediating immunology of senescent macrophages

Orthopedic implants have been used clinically to restore the functions of the compromised bone tissues, but there is still a relatively high risk of failure for elderly people. A critical reason is pro-inflammatory immune microenvironment created by senescent macrophages with homeostasis imbalance impairs osteogenesis and angiogenesis, two major processes involved in implant osseointegration. The present work proposes to use resveratrol as an autophagy inducing agent to upregulate the autophagy level of senescent macrophages to restore homeostasis, consequently generating a favorable immune microenvironment. The results show 0.1-1 µM of resveratrol can induce autophagy of senescent macrophages, promote cell viability and proliferation, reduce intracellular reactive oxygen species (ROS) level, and polarize the cells to pro-healing M2 phenotype. The immune microenvironment created by senescent macrophages upon resveratrol stimulation can promote osteogenesis and angiogenesis, as manifested by upregulated proliferation, alkaline phosphatase activity, type I collagen secretion, and extracellular matrix mineralization of senescent osteoblasts as well as nitric oxide production, migration, and in vitro angiogenesis of senescent endothelial cells. In addition, resveratrol-loaded silk fibroin coatings can be fabricated on titanium surface through electrophoretic co-deposition and the coatings show beneficial effects on the functions of senescent macrophages. Our results suggest resveratrol can be used as surface additive of titanium implants to promote osseointegration of elderly people though regulating immunology of senescent macrophages.

The role of nanopores constructed on micropitted titanium surface on immune responses of macrophages and the potential mechanisms

Delayed transition of pro-inflammatory M1 to pro-healing M2 of macrophages (MΦs) on implant surface is one of the most important reasons accounting for poor osseointegration. The present work proposes to...

Micro/nano topography of selective laser melting titanium inhibits osteoclastogenesis via mediation of macrophage polarization

Selective laser melting (SLM) titanium (Ti) implants have shown good prospects for personalized clinical application, but further research is necessary to develop stabilized long-term properties. Since surface modification has been proven bioactive for osseointegration, conventional Ti surface treatment technologies, including sandblasting/acid-etching (SLA) and sandblasting/alkali-heating (SAH), were applied to construct micro and micro/nano surfaces. The SAH group with netlike nano-structure topography exhibited appropriate surface roughness and high hydrophilicity, and as expected, the osseointegration capacities in vivo of the three groups were in order of SAH > SLA > SLM. Besides, both in vivo and in vitro studies revealed that the SLA- and SAH-treated SLM Ti implants significantly inhibited osteoclast activity of peri-implants. Considering the close associations between osteoclasts and macrophages, the effects of Ti surface topography on macrophage polarization were detected. The results showed that the SLA- and SAH-treated SLM Ti implants, especially the latter, had the capacity to promote macrophage polarization to the M2 phenotype. Moreover, the cell culture supernatants of M2 macrophages and RAW264.7 cells seeded on SLA- and SAH-treated SLM Ti surfaces had an adverse effect on osteoclastogenesis. Collectively, this study demonstrated that micro/nano topographies of SLM Ti implants were effective for osseointegration promotion, and their inhibition of osteoclastogenesis might be attributed to macrophage polarization. Our findings shed some light on clinical application of SLM Ti implants and also prove a specific association between macrophage polarization and osteoclastogenesis.

Classical Dichotomy of Macrophages and Alternative Activation Models Proposed with Technological Progress

Macrophages are important immune cells that participate in the regulation of inflammation in implant dentistry, and their activation/polarization state is considered to be the basis for their functions. The classic dichotomy activation model is commonly accepted, however, due to the discovery of macrophage heterogeneity and more functional and iconic exploration at different technologies; some studies have discovered the shortcomings of the dichotomy model and have put forward the concept of alternative activation models through the application of advanced technologies such as cytometry by time-of-flight (CyTOF), single-cell RNA-seq (scRNA-seq), and hyperspectral image (HSI). These alternative models have great potential to help macrophages divide phenotypes and functional genes.

Control of innate immune response by biomaterial surface topography, energy, and stiffness

As the focus of implantable biomaterials has shifted from bioinert implants to bioactive designs, recent research has highlighted the complex interactions between cell physiologic systems and material properties, particularly physical cues. From the cells known to interact with implanted biomaterials, the response of the immune system has been a critical target of study recently. Here, we review studies characterizing the response of innate immune cells to various material cues, particularly of those at the surface of implanted materials.The innate immune system consists of cell types with various roles in inflammation. Neutrophils and macrophages serve both phagocytic and signaling roles, especially early in the inflammatory phase of biomaterial implantation. These cell types ultimately dictate the outcome of implants as chronic inflammation, fibrosis, or integration. Other cell types like dendritic cells, mast cells, natural killer cells, and innate lymphoid cells may also serve an immunomodulatory role in the biomaterial context. This review highlights recent advances in our understanding of the role of innate immunity in the response to implantable biomaterials as well as key mechanobiological findings in innate immune cells underpinning these advances. STATEMENT OF SIGNIFICANCE: This review highlights recent advances in the understanding of the role of innate immunity in the response to implantable biomaterials, especially in neutrophils and macrophages, as well as key mechanobiological findings in innate immune cells underpinning these advances. Here we discuss how physicochemical properties of biomaterials control innate immune cell behavior.

The response of macrophages and their osteogenic potential modulated by micro/nano-structured Ti surfaces

Current understanding on the interactions between micro/nano-structured Ti surfaces and macrophages is still limited. In this work, TiO₂ nano-structures were introduced onto acid-etched Ti surfaces by alkali-heat treatment, ion exchange and subsequent heat treatment. By adjusting the concentration of NaOH during alkali-heat treatment, nano-flakes, nano-flakes mixed with nano-wires or nano-wires could formed on acid-etched Ti surfaces. The micro- and micro/nano-structured Ti surfaces possessed similar surface chemical and phase compositions. In vitro results indicate that the morphology of macrophages was highly dependent on the morphological features of nano-structures. Nano-flakes and nano-wires were favorable to induce the formation of lamellipodia and filopodia, respectively. Compared to micro-structured Ti surface, micro/nano-structured Ti surfaces polarized macrophages to their M2 phenotype and enhanced the gene expressions of osteogenic growth factors in macrophages. The M2 polarized macrophages promoted the maturation of osteoblasts. Compared to that with nano-flakes or nano-wires, the surface with mixed features of nano-flakes and nano-wires exhibited stronger anti-inflammatory and osteo-immunomodulatory effects. The findings presented in the current work suggest that introducing micro/nano-topographies onto Ti-based implant surfaces is a promising strategy to modulate the inflammatory response and mediate osteogenesis.