Immunosenescence and macrophages: From basics to therapeutics

Elevated CD47 Expression Impairs Elimination of Photoaged Fibroblasts by Macrophages and Serves as a Potential Biomarker for Photoaging

BACKGROUND

CD47 could negatively regulate macrophage-mediated phagocytosis and contribute to senescent cells accumulation in aging. However, it remains unknown whether CD47 is overexpressed in photoaged skin and involved in photoaging pathogenesis.

AIMS

To investigate the expression, clinical significance, and mechanism of CD47 in photoaging.

METHODS

Sun-exposed (n = 10) and sun-protected (n = 10) skin samples were collected from elderly subjects and stained for CD47, and its association with collagen and elastin content and p16 expression was subsequently analyzed. A cellular photoaging model was then established to examine CD47 expression in photoaged fibroblasts. Furthermore, the influence of photoaged fibroblasts on macrophage-mediated phagocytosis and elimination was assessed by constructing a co-culture system. SiRNA was applied to block the CD47/SIRPα axis to determine its role in this process. Finally, the activation of the CD47/SIRPα axis was evaluated in skin samples.

RESULTS

We showed the increased dermal CD47 expression in sun-exposed aged skin, which was closely correlated with the reduced collagen content and enhanced elastin accumulation and dermal p16 expression. Next, elevated CD47 was detected in both sun-exposed aged skin-derived fibroblasts and photoaged ones. We discovered that photoaged fibroblasts impaired the phagocytotic function of co-cultured macrophages via CD47/SIRPα axis, and blocking the CD47/SIRPα axis could improve their elimination. Moreover, the CD47/SIRPα axis was found to be activated in the sun-exposed aged skin.

CONCLUSIONS

The present study demonstrated for the first time that CD47 was highly expressed and involved in mediating photoaged fibroblasts accumulation, providing important evidence for CD47 as a potential biomarker and therapeutic target for photoaging.

Molecular mechanism of macrophage polarization regulating the cell senescence of nucleus pulposus during intervertebral disc degeneration

In orthopedics, intervertebral disc degeneration (IVDD) is a prevalent chronic condition whose cellular molecular processes are yet unclear. The objective of this research was to uncover the molecular causes of aging and identify the immunological microenvironmental alterations and immune cell infiltration in IVDD. IVDD gene datasets were obtained using GeneCards, and gene expression profiles were chosen from the Gene Expression Synthesis database (GSE244889). The Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) databases were used to examine biological processes. The analysis of immune cell infiltration was done using CIBERSORT. To shed light on the variations in cell types among intervertebral discs with varying degrees of degeneration, single-cell analysis was carried out. Lastly, it was confirmed in vitro that important proteins and genes were expressed. At first, 10 hub genes and 58 intersecting genes were found. Major biological processes include the inflammatory response, chemokine-mediated signaling pathways, and immune response. The three main signaling mechanisms in IVDD are HIF, apoptosis, and cellular senescence. Macrophages M0, M1, M2, T cells, CD4 memory resting, NK cells, T cells regulatory (Tregs), and T cells were all markedly infiltrated in IVDD patients. According to in vitro validation, the IVDD model group had higher levels of proteins linked to the immunological microenvironment. In conclusion, immune cell infiltration-particularly macrophage infiltration, which stimulates the release of inflammatory factors that cause the inflammatory response and cellular senescence in NPCs-is linked to the primary molecular mechanisms underlying the pathogenesis of IVDD. Our research may also help direct future investigations into the senescence signaling pathway in IVDD.

Exercise intensity and training alter the innate immune cell type and chromosomal origins of circulating cell-free DNA in humans

Exercising regularly promotes health, but these benefits are complicated by acute inflammation induced by exercise. A potential source of inflammation is cell-free DNA (cfDNA), yet the cellular origins, molecular causes, and immune system interactions of exercise-induced cfDNA are unclear. To study these, 10 healthy individuals were randomized to a 12-wk exercise program of either high-intensity tactical training (HITT) or traditional moderate-intensity training (TRAD). Blood plasma was collected pre- and postexercise at weeks 0 and 12 and after 4 wk of detraining upon program completion. Whole-genome enzymatic methylation sequencing (EM-seq) with cell-type proportion deconvolution was applied to cfDNA obtained from the 50 plasma samples and paired to concentration measurements for 90 circulating cytokines. Acute exercise increased the release of cfDNA from neutrophils, dendritic cells (DCs), and macrophages proportional to exercise intensity. Exercise training reduced cfDNA released in HITT participants but not TRAD and from DCs and macrophages but not neutrophils. For most participants, training lowered mitochondrial cfDNA at rest, even after detraining. Using a sequencing analysis approach we developed, we concluded that rapid ETosis, a process of cell death where cells release DNA extracellular traps, was the likely source of cfDNA, demonstrated by enrichment of nuclear DNA. Further, several cytokines were induced by acute exercise, such as IL-6, IL-10, and IL-16, and training attenuated the induction of only IL-6 and IL-17F. Cytokine levels were not associated with cfDNA induction, suggesting that these cytokines are not the main cause of exercise-induced cfDNA. Overall, exercise intensity and training modulated cfDNA release and cytokine responses, contributing to the anti-inflammatory effects of regular exercise.

Choroidal macrophages in homeostasis, aging and age-related macular degeneration

With increasing age, the optimal functioning of the choroid is essential for efficient removal of waste products formed from photoreceptor renewal. A decline in regulatory elements of the immune system, termed immunosenescence, and the failure of para-inflammation to restore tissue homeostasis can result in the progression of healthy aging to sight-threatening inflammation of the choroid. Macrophages are uniquely situated between the innate and adaptive immune systems, with a high capacity for phagocytosis, recognition of complement components, as well as antigen presentation. In this review, we provide an overview of macrophages and their properties in the healthy choroid and cover the impact of aging, immunosenescence and inflammaging on the function of choroidal macrophages. We will discuss the impact of age on macrophage phenotype and behaviour in the pathophysiology of age-related macular degeneration.

Histone lactylation in macrophage biology and disease: from plasticity regulation to therapeutic implications

Epigenetic modifications have been identified as critical molecular determinants influencing macrophage plasticity and heterogeneity. Among these, histone lactylation is a recently discovered epigenetic modification. Research examining the effects of histone lactylation on macrophage activation and polarization has grown substantially in recent years. Evidence increasingly suggests that lactate-mediated changes in histone lactylation levels within macrophages can modulate gene transcription, thereby contributing to the pathogenesis of various diseases. This review provides a comprehensive analysis of the role of histone lactylation in macrophage activation, exploring its discovery, effects, and association with macrophage diversity and phenotypic variability. Moreover, it highlights the impact of alterations in macrophage histone lactylation in diverse pathological contexts, such as inflammation, tumorigenesis, neurological disorders, and other complex conditions, and demonstrates the therapeutic potential of drugs targeting these epigenetic modifications. This mechanistic understanding provides insights into the underlying disease mechanisms and opens new avenues for therapeutic intervention.

Hyperglycemia causes differential change in macrophage population in the lacrimal gland, conjunctiva and cornea

Background

Due to its location, the ocular surface is exposed to environmental microbes. Innate immune cells including macrophages are first line defense against infections. In vitro exposure to high glucose as well as diabetes-associated hyperglycemia has been shown to affect innate immune cell function and population. The present study was designed to examine the effect of diabetes-associated hyperglycemia on the lacrimal gland, conjunctiva and cornea macrophage population, phenotypic changes and cytokines/chemokines.

Methods

Mouse model of Streptozotocin-induced diabetes was used to induce hyperglycemia. Immunostaining for CD11b and F4/80 was performed to stain macrophages in whole mount cornea, conjunctiva and 50 µm lacrimal gland sections. Flowcytometry was performed on single cell suspension to identify macrophage phenotypes and activation using CD11b, F4/80, CD80, CD206 and MHCII staining. Real time PCR was performed to quantify gene expression for macrophage-associated cytokines (IL-1β, TNF-α, IFN-γ) and chemokine (CCL2).

Results

Our data demonstrates the diabetes-associated hyperglycemia caused a rapid onset and significant decrease in macrophage population in lacrimal gland, conjunctiva and cornea. The onset of this noted decrease was as early as 7 days after hyperglycemia in lacrimal gland and conjunctiva followed by a notable increase towards recovery only in conjunctiva but not in the lacrimal gland. The cornea tissue showed a steady decline up to the tested time point of 28 days. Further, hyperglycemia did not cause any notable changes in macrophage phenotypes, their activation status or the expression of IL-1β, TNF-α, IFN-γ, CCL2 except in the cornea where an increase in the cytokine levels was noted after 7 days of hyperglycemia.

Conclusion

Our data shows that diabetes-associated hyperglycemia can cause a significant decrease in microphage population with changing their plasticity or activation status in lacrimal gland, conjunctiva and cornea but the kinetics of decrease and recovery show differential pattern specific for each tissue.

Increased hydrogen sulfide turnover serves a cytoprotective role during the development of replicative senescence

The mammalian gasotransmitter hydrogen sulfide (H2S) is produced by enzymes such as cystathionine β-synthase (CBS), cystathionine γ-lyase (CSE), 3-mercaptopyruvate sulfurtransferase (3-MST). Prior studies suggest that H2S may have cytoprotective and anti-aging effects. This project explores the regulation and role of endogenous H2S in a murine model of replicative senescence. H2S and polysulfide levels in RAW 264.7 murine macrophages (control cells: passage 5-10; senescent cells: passage 30-40) were measured using fluorescent probes. The expression of H2S-related enzymes and the activity of senescence marker beta-galactosidase (SA-β-Gal) were also analyzed. CBS, CSE, and 3-MST were inhibited using selective pharmacological inhibitors. Senescence led to a moderate upregulation of CBS and in a significant increase in CSE and 3-MST. H2S degradation enzymes were also elevated in senescence. Inhibition of H2S-producing enzymes reduced H2S levels but increased polysulfides. Inhibition of H2S production during senescence suppressed cell proliferation, and elevated SA-β-Gal and p21 levels. Comparing young and old mice spleens revealed downregulation of CBS and ETHE1 and upregulation of rhodanese and SUOX in older mice. The results demonstrate that increased reactive sulfur turnover occurs in senescent macrophages and that reactive sulfur species support cell proliferation and regulate cellular senescence.

Combined targeting of senescent cells and senescent macrophages: A new idea for integrated treatment of lung cancer

Lung cancer is one of the most common cancers worldwide and a leading cause of cancer-related deaths. Macrophages play a key role in the immune response and the tumour microenvironment. As an important member of the immune system, macrophages have multiple functions, including phagocytosis and clearance of pathogens, modulation of inflammatory responses, and participation in tissue repair and regeneration. In lung cancer, macrophages are considered to be the major cellular component of the tumor-associated inflammatory response and are closely associated with tumorigenesis, progression and metastasis. However, macrophages gradually undergo a senescence process with age and changes in pathological states. Macrophage senescence is an important change in the functional and metabolic state of macrophages and may have a significant impact on lung cancer development. In lung cancer, senescent macrophages interact with other cells in the tumor microenvironment (TME) by secreting senescence-associated secretory phenotype (SASP) factors, which can either promote the proliferation, invasion and metastasis of tumor cells or exert anti-tumor effects through reprogramming or clearance under specific conditions. Therefore, senescent macrophages are considered important potential targets for lung cancer therapy. In this paper, a systematic review of macrophages and their senescence process, and their role in tumors is presented. A variety of inhibitory strategies against senescent macrophages, including enhancing autophagy, inhibiting SASP, reducing DNA damage, and modulating metabolic pathways, were also explored. These strategies are expected to improve lung cancer treatment outcomes by restoring the anti-tumor function of macrophages.

Ferroptosis and immunosenescence in colorectal cancer

Colorectal cancer (CRC), ranked as the globe's third leading malignancy. Despite advancements in therapeutic approaches, the mortality rate remains distressingly high for those afflicted with advanced stages of the disease. Ferroptosis is a programmed form of cell death. The ways of ferroptosis mainly include promoting the accumulation of cellular ROS and increasing the level of cellular Labile iron pool (LIP). Immunosenescence is characterized by a gradual deterioration of the immune system's ability to respond to pathogens and maintain surveillance against cancer cells. In CRC, this decline is exacerbated by the tumor microenvironment, which can suppress the immune response and promote tumor progression. This paper reviews the relationship between iron prolapse and immune senescence in colorectal cancer, focusing on the following aspects: firstly, the different pathways that induce iron prolapse in colorectal cancer; secondly, immune-immune senescence in colorectal cancer; and lastly, the interactions between immune senescence and iron prolapse in colorectal cancer, e.g., immune-immune senescent cells often exhibit increased oxidative stress, leading to the accumulation of ROS, and consequently to lipid peroxidation and induction of iron-induced cell death. At the same time, ferroptosis induces immune cell senescence as well as alterations in the immune microenvironment by promoting the death of damaged or diseased cells and leading to the inflammation usually associated with it. In conclusion, by exploring the potential targets of ferroptosis and immune senescence in colorectal cancer therapy, we hope to provide a reference for future research.

Exploring the Interplay between Cellular Senescence, Immunity, and Fibrosing Interstitial Lung Diseases: Challenges and Opportunities

Fibrosing interstitial lung diseases (ILDs) are characterized by the gradual and irreversible accumulation of scar tissue in the lung parenchyma. The role of the immune response in the pathogenesis of pulmonary fibrosis remains unclear. In recent years, substantial advancements have been made in our comprehension of the pathobiology driving fibrosing ILDs, particularly concerning various age-related cellular disturbances and immune mechanisms believed to contribute to an inadequate response to stress and increased susceptibility to lung fibrosis. Emerging studies emphasize cellular senescence as a key mechanism implicated in the pathobiology of age-related diseases, including pulmonary fibrosis. Cellular senescence, marked by antagonistic pleiotropy, and the complex interplay with immunity, are pivotal in comprehending many aspects of lung fibrosis. Here, we review progress in novel concepts in cellular senescence, its association with the dysregulation of the immune response, and the evidence underlining its detrimental role in fibrosing ILDs.

From Genesis to Old Age: Exploring the Immune System One Cell at a Time with Flow Cytometry

The immune system is a highly complex and tightly regulated system that plays a crucial role in protecting the body against external threats, such as pathogens, and internal abnormalities, like cancer cells. It undergoes development during fetal stages and continuously learns from each encounter with pathogens, allowing it to develop immunological memory and provide a wide range of immune protection. Over time, after numerous encounters and years of functioning, the immune system can begin to show signs of erosion, which is commonly named immunosenescence. In this review, we aim to explore how the immune system responds to initial encounters with antigens and how it handles persistent stimulations throughout a person's lifetime. Our understanding of the immune system has greatly benefited from advanced technologies like flow cytometry. In this context, we will discuss the valuable contribution of flow cytometry in enhancing our knowledge of the immune system behavior in aging, with a specific focus on T-cells. Moreover, we will expand our discussion to the flow cytometry-based assessment of extracellular vesicles, a recently discovered communication channel in biology, and their implications for immune system functioning.

IL-4-ever young: Type 2 cytokine signaling in macrophages slows aging

Macrophages activated via the IL-4 receptor possess non-immune functions that support tissue homeostasis, but their specific role in aging is unknown. In this issue of Immunity, Zhou et al. show that IL-4 extends lifespan by inducing DNA repair pathways that protect macrophages from cellular senescence.

Connecting epigenetics and inflammation in vascular senescence: state of the art, biomarkers and senotherapeutics

Vascular diseases pose major health challenges, and understanding their underlying molecular mechanisms is essential to advance therapeutic interventions. Cellular senescence, a hallmark of aging, is a cellular state characterized by cell-cycle arrest, a senescence-associated secretory phenotype macromolecular damage, and metabolic dysregulation. Vascular senescence has been demonstrated to play a key role in different vascular diseases, such as atherosclerosis, peripheral arterial disease, hypertension, stroke, diabetes, chronic venous disease, and venous ulcers. Even though cellular senescence was first described in 1961, significant gaps persist in comprehending the epigenetic mechanisms driving vascular senescence and its subsequent inflammatory response. Through a comprehensive analysis, we aim to elucidate these knowledge gaps by exploring the network of epigenetic alterations that contribute to vascular senescence. In addition, we describe the consequent inflammatory cascades triggered by these epigenetic modifications. Finally, we explore translational applications involving biomarkers of vascular senescence and the emerging field of senotherapy targeting this biological process.