Efferocytosis by Paneth cells within the intestine

Identification and Characterization of Multiple Paneth Cell Types in the Mouse Small Intestine

The small intestinal crypts harbor secretory Paneth cells (PCs) which express bactericidal peptides that are crucial for maintaining intestinal homeostasis. Considering the diverse environmental conditions throughout the course of the small intestine, multiple subtypes of PCs are expected to exist. We applied single-cell RNA-sequencing of PCs combined with deep bulk RNA-sequencing on PC populations of different small intestinal locations and discovered several expression-based PC clusters. Some of these are discrete and resemble tuft cell-like PCs, goblet cell (GC)-like PCs, PCs expressing stem cell markers, and atypical PCs. Other clusters are less discrete but appear to be derived from different locations along the intestinal tract and have environment-dictated functions such as food digestion and antimicrobial peptide production. A comprehensive spatial analysis using Resolve Bioscience was conducted, leading to the identification of different PC's transcriptomic identities along the different compartments of the intestine, but not between PCs in the crypts themselves.

Therapeutic implication of targeting mitochondrial drugs designed for efferocytosis dysfunction

Efferocytosis refers to the process by which phagocytes remove apoptotic cells and related apoptotic products. It is essential for the growth and development of the body, the repair of damaged or inflamed tissues, and the balance of the immune system. Damaged efferocytosis will cause a variety of chronic inflammation and immune system diseases. Many studies show that efferocytosis is a process mediated by mitochondria. Mitochondrial metabolism, mitochondrial dynamics, and communication between mitochondria and other organelles can all affect phagocytes' clearance of apoptotic cells. Therefore, targeting mitochondria to modulate phagocyte efferocytosis is an anticipated strategy to prevent and treat chronic inflammatory diseases and autoimmune diseases. In this review, we introduced the mechanism of efferocytosis and the pivoted role of mitochondria in efferocytosis. In addition, we focused on the therapeutic implication of drugs targeting mitochondria in diseases related to efferocytosis dysfunction.

Integrated meta-omics reveals the regulatory landscape involved in lipid metabolism between pig breeds

BACKGROUND

Domesticated pigs serve as an ideal animal model for biomedical research and also provide the majority of meat for human consumption in China. Porcine intramuscular fat content associates with human health and diseases and is essential in pork quality. The molecular mechanisms controlling lipid metabolism and intramuscular fat accretion across tissues in pigs, and how these changes in response to pig breeds, remain largely unknown.

RESULTS

We surveyed the tissue-resident cell types of the porcine jejunum, colon, liver, and longissimus dorsi muscle between Lantang and Landrace breeds by single-cell RNA sequencing. Combining lipidomics and metagenomics approaches, we also characterized gene signatures and determined key discriminating markers of lipid digestibility, absorption, conversion, and deposition across tissues in two pig breeds. In Landrace, lean-meat swine mainly exhibited breed-specific advantages in lipid absorption and oxidation for energy supply in small and large intestinal epitheliums, nascent high-density lipoprotein synthesis for reverse cholesterol transport in enterocytes and hepatocytes, bile acid formation, and secretion for fat emulsification in hepatocytes, as well as intestinal-microbiota gene expression involved in lipid accumulation product. In Lantang, obese-meat swine showed a higher synthesis capacity of chylomicrons responsible for high serum triacylglycerol levels in small intestinal epitheliums, the predominant characteristics of lipid absorption in muscle tissue, and greater intramuscular adipcytogenesis potentials from muscular fibro-adipogenic progenitor subpopulation.

CONCLUSIONS

The findings enhanced our understanding of the cellular biology of lipid metabolism and opened new avenues to improve animal production and human diseases. Video Abstract.

Hijacking homeostasis: Regulation of the tumor microenvironment by apoptosis

Cancers are genetically driven, rogue tissues which generate dysfunctional, obdurate organs by hijacking normal, homeostatic programs. Apoptosis is an evolutionarily conserved regulated cell death program and a profoundly important homeostatic mechanism that is common (alongside tumor cell proliferation) in actively growing cancers, as well as in tumors responding to cytotoxic anti-cancer therapies. Although well known for its cell-autonomous tumor-suppressive qualities, apoptosis harbors pro-oncogenic properties which are deployed through non-cell-autonomous mechanisms and which generally remain poorly defined. Here, the roles of apoptosis in tumor biology are reviewed, with particular focus on the secreted and fragmentation products of apoptotic tumor cells and their effects on tumor-associated macrophages, key supportive cells in the aberrant homeostasis of the tumor microenvironment. Historical aspects of cell loss in tumor growth kinetics are considered and the impact (and potential impact) on tumor growth of apoptotic-cell clearance (efferocytosis) as well as released soluble and extracellular vesicle-associated factors are discussed from the perspectives of inflammation, tissue repair, and regeneration programs. An "apoptosis-centric" view is proposed in which dying tumor cells provide an important platform for intricate intercellular communication networks in growing cancers. The perspective has implications for future research and for improving cancer diagnosis and therapy.

Paneth cells protect intestinal stem cell niche to alleviate deoxynivalenol-induced intestinal injury

Deoxynivalenol (DON) is a common toxin in grains and feeds, and DON exposure triggers severe small intestinal injury and inflammation, which harms the health of humans and livestock. DON treatment leads to a decrease in Paneth cells, whereas the role of Paneth cells in DON-induced intestinal injury is poorly understood. We utilized dithizone (40 mg/kg) to keep murine Paneth cell number at a low level. The results showed that dithizone-mediated long-term disruption of Paneth cells aggravated intestinal injury, intestinal stem cell (ISC) loss, and microbiota disorder in DON (2 mg/kg)-treated mice. Unexpectedly, the number of goblet cells and proliferative cells was boosted in mice treated with dithizone and DON. After dithizone and DON treatments, the Firmicutes/Bacteroidetes (F/B) ratio was reduced, and the increased abundance of Dubosiella and the decreased abundance of Lactobacillus were observed in mice. The functional recovery of Paneth cells by lysozyme (200 U/day) supplementation improved intestinal injury and ISC loss in mice after DON challenge. In addition, lysozyme also promoted the growth and ISC activity of intestinal organoids. Taken together, these results demonstrate the protective role of Paneth cells in DON-induced intestinal injury. Our study raises a novel target, Paneth cell, for the treatment of DON exposure.

Paneth cells in farm animals: current status and future direction

A healthy intestine plays an important role in the growth and development of farm animals. In small intestine, Paneth cells are well known for their regulation of intestinal microbiota and intestinal stem cells (ISCs). Although there has been a lot of studies and reviews on human and murine Paneth cells under intestinal homeostasis or disorders, little is known about Paneth cells in farm animals. Most farm animals possess Paneth cells in their small intestine, as identified by various staining methods, and Paneth cells of various livestock species exhibit noticeable differences in cell shape, granule number, and intestinal distribution. Paneth cells in farm animals and their antimicrobial peptides (AMPs) are susceptible to multiple factors such as dietary nutrients and intestinal infection. Thus, the comprehensive understanding of Paneth cells in different livestock species will contribute to the improvement of intestinal health. This review first summarizes the current status of Paneth cells in pig, cattle, sheep, horse, chicken and rabbit, and points out future directions for the investigation of Paneth cells in the reviewed animals.

Stem cells tightly regulate dead cell clearance to maintain tissue fitness

Macrophages and dendritic cells have long been appreciated for their ability to migrate to and engulf dying cells and debris, including some of the billions of cells that are naturally eliminated from our body daily. However, a substantial number of these dying cells are cleared by 'non-professional phagocytes', local epithelial cells that are critical to organismal fitness. How non-professional phagocytes sense and digest nearby apoptotic corpses while still performing their normal tissue functions is unclear. Here, we explore the molecular mechanisms underlying their multifunctionality. Exploiting the cyclical bouts of tissue regeneration and degeneration during the hair cycle, we show that stem cells can transiently become non-professional phagocytes when confronted with dying cells. Adoption of this phagocytic state requires both local lipids produced by apoptotic corpses to activate RXRα, and tissue-specific retinoids for RARγ activation. This dual factor dependency enables tight regulation of the genes requisite to activate phagocytic apoptotic clearance. The tunable phagocytic program we describe here offers an effective mechanism to offset phagocytic duties against the primary stem cell function of replenishing differentiated cells to preserve tissue integrity during homeostasis. Our findings have broad implications for other non-motile stem or progenitor cells which experience cell death in an immune-privileged niche.

Function of stem cells in radiation-induced damage

PURPOSE

The aim of this review is to discuss previous studies on the function of stem cells in radiation-induced damage, and the factors affecting these processes, in the hope of improving our understanding of the different stem cells and the communication networks surrounding them. This is essential for the development of effective stem cell-based therapies to regenerate or replace normal tissues damaged by radiation.

CONCLUSION

In salivary glands, senescence-associated cytokines and inflammation-associated cells have a greater effect on stem cells. In the intestinal glands, Paneth cells strongly affect stem cell-mediated tissue regeneration after radiation treatment. In the pancreas, β-cells as well as protein C receptor positive (Procr) cells are expected to be key cells in the treatment of diabetes. In the bone marrow, a variety of cytokines such as CXC-chemokine ligand 12 (CXCL12) and stem cell factor (SCF), contribute to the functional recovery of hematopoietic stem cells after irradiation.

Multifaceted involvements of Paneth cells in various diseases within intestine and systemically

Serving as the guardians of small intestine, Paneth cells (PCs) play an important role in intestinal homeostasis maintenance. Although PCs uniquely exist in intestine under homeostasis, the dysfunction of PCs is involved in various diseases not only in intestine but also in extraintestinal organs, suggesting the systemic importance of PCs. The mechanisms under the participation of PCs in these diseases are multiple as well. The involvements of PCs are mostly characterized by limiting intestinal bacterial translocation in necrotizing enterocolitis, liver disease, acute pancreatitis and graft-vs-host disease. Risk genes in PCs render intestine susceptible to Crohn’s disease. In intestinal infection, different pathogens induce varied responses in PCs, and toll-like receptor ligands on bacterial surface trigger the degranulation of PCs. The increased level of bile acid dramatically impairs PCs in obesity. PCs can inhibit virus entry and promote intestinal regeneration to alleviate COVID-19. On the contrary, abundant IL-17A in PCs aggravates multi-organ injury in ischemia/reperfusion. The pro-angiogenic effect of PCs aggravates the severity of portal hypertension. Therapeutic strategies targeting PCs mainly include PC protection, PC-derived inflammatory cytokine elimination, and substituting AMP treatment. In this review, we discuss the influence and importance of Paneth cells in both intestinal and extraintestinal diseases as reported so far, as well as the potential therapeutic strategies targeting PCs.

From birth to death: The hardworking life of Paneth cell in the small intestine

Paneth cells are a group of unique intestinal epithelial cells, and they play an important role in host-microbiota interactions. At the origin of Paneth cell life, several pathways such as Wnt, Notch, and BMP signaling, affect the differentiation of Paneth cells. After lineage commitment, Paneth cells migrate downward and reside in the base of crypts, and they possess abundant granules in their apical cytoplasm. These granules contain some important substances such as antimicrobial peptides and growth factors. Antimicrobial peptides can regulate the composition of microbiota and defend against mucosal penetration by commensal and pathogenic bacteria to protect the intestinal epithelia. The growth factors derived from Paneth cells contribute to the maintenance of the normal functions of intestinal stem cells. The presence of Paneth cells ensures the sterile environment and clearance of apoptotic cells from crypts to maintain the intestinal homeostasis. At the end of their lives, Paneth cells experience different types of programmed cell death such as apoptosis and necroptosis. During intestinal injury, Paneth cells can acquire stem cell features to restore the intestinal epithelial integrity. In view of the crucial roles of Paneth cells in the intestinal homeostasis, research on Paneth cells has rapidly developed in recent years, and the existing reviews on Paneth cells have mainly focused on their functions of antimicrobial peptide secretion and intestinal stem cell support. This review aims to summarize the approaches to studying Paneth cells and introduce the whole life experience of Paneth cells from birth to death.

Cystathionine gamma-lyase (Cth) induces efferocytosis in macrophages via ERK1/2 to modulate intestinal barrier repair

BACKGROUND

The inflammatory response induced by intestinal ischaemia‒reperfusion injury (I/R) is closely associated with infectious complications and mortality in critically ill patients, and the timely and effective clearance of apoptotic cells is an important part of reducing the inflammatory response. Studies have shown that the efferocytosis by phagocytes plays an important role. Recently, studies using small intestine organoid models showed that macrophage efferocytosis could promote the repair capacity of the intestinal epithelium. However, no studies have reported efferocytosis in the repair of I/R in animal models.

RESULTS

We used an in vivo efferocytosis assay and discovered that macrophage efferocytosis played an indispensable role in repairing and maintaining intestinal barrier function after I/R. In addition, the specific molecular mechanism that induced macrophage efferocytosis was Cth-ERK1/2 dependent. We found that Cth drove macrophage efferocytosis in vivo and in vitro. Overexpression/silencing Cth promoted/inhibited the ERK1/2 pathway, respectively, which in turn affected efferocytosis and mediated intestinal barrier recovery. In addition, we found that the levels of Cth and macrophage efferocytosis were positively correlated with the recovery of intestinal function in clinical patients.

CONCLUSION

Cth can activate the ERK1/2 signalling pathway, induce macrophage efferocytosis, and thus promote intestinal barrier repair. Video Abstract.

Differentiated Epithelial Cells of the Gut

The intestine is a prime example of self-renewal where stem cells give rise to progenitor cells called transit-amplifying cells which differentiate into more specialized cells. There are two intestinal lineages: the absorptive (enterocytes and microfold cells) and the secretory (Paneth cells, enteroendocrine, goblet cells, and tuft cells). Each of these differentiated cell types has a role in creating an "ecosystem" to maintain intestinal homeostasis. Here, we summarize the main roles of each cell type.

Paneth cells as the cornerstones of intestinal and organismal health: a primer

Paneth cells are versatile secretory cells located in the crypts of Lieberkühn of the small intestine. In normal conditions, they function as the cornerstones of intestinal health by preserving homeostasis. They perform this function by providing niche factors to the intestinal stem cell compartment, regulating the composition of the microbiome through the production and secretion of antimicrobial peptides, performing phagocytosis and efferocytosis, taking up heavy metals, and preserving barrier integrity. Disturbances in one or more of these functions can lead to intestinal as well as systemic inflammatory and infectious diseases. This review discusses the multiple functions of Paneth cells, and the mechanisms and consequences of Paneth cell dysfunction. It also provides an overview of the tools available for studying Paneth cells.

Chimeric efferocytic receptors improve apoptotic cell clearance and alleviate inflammation

Our bodies turn over billions of cells daily via apoptosis and are in turn cleared by phagocytes via the process of "efferocytosis." Defects in efferocytosis are now linked to various inflammatory diseases. Here, we designed a strategy to boost efferocytosis, denoted "chimeric receptor for efferocytosis" (CHEF). We fused a specific signaling domain within the cytoplasmic adapter protein ELMO1 to the extracellular phosphatidylserine recognition domains of the efferocytic receptors BAI1 or TIM4, generating BELMO and TELMO, respectively. CHEF-expressing phagocytes display a striking increase in efferocytosis. In mouse models of inflammation, BELMO expression attenuates colitis, hepatotoxicity, and nephrotoxicity. In mechanistic studies, BELMO increases ER-resident enzymes and chaperones to overcome protein-folding-associated toxicity, which was further validated in a model of ER-stress-induced renal ischemia-reperfusion injury. Finally, TELMO introduction after onset of kidney injury significantly reduced fibrosis. Collectively, these data advance a concept of chimeric efferocytic receptors to boost efferocytosis and dampen inflammation.

Long COVID and the Neuroendocrinology of Microbial Translocation Outside the GI Tract: Some Treatment Strategies

Similar to previous pandemics, COVID-19 has been succeeded by well-documented post-infectious sequelae, including chronic fatigue, cough, shortness of breath, myalgia, and concentration difficulties, which may last 5 to 12 weeks or longer after the acute phase of illness. Both the psychological stress of SARS-CoV-2 infection and being diagnosed with COVID-19 can upregulate cortisol, a stress hormone that disrupts the efferocytosis effectors, macrophages, and natural killer cells, leading to the excessive accumulation of senescent cells and disruption of biological barriers. This has been well-established in cancer patients who often experience unrelenting fatigue as well as gut and blood–brain barrier dysfunction upon treatment with senescence-inducing radiation or chemotherapy. In our previous research from 2020 and 2021, we linked COVID-19 to myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) via angiotensin II upregulation, premature endothelial senescence, intestinal barrier dysfunction, and microbial translocation from the gastrointestinal tract into the systemic circulation. In 2021 and 2022, these hypotheses were validated and SARS-CoV-2-induced cellular senescence as well as microbial translocation were documented in both acute SARS-CoV-2 infection, long COVID, and ME/CFS, connecting intestinal barrier dysfunction to disabling fatigue and specific infectious events. The purpose of this narrative review is to summarize what is currently known about host immune responses to translocated gut microbes and how these responses relate to fatiguing illnesses, including long COVID. To accomplish this goal, we examine the role of intestinal and blood–brain barriers in long COVID and other illnesses typified by chronic fatigue, with a special emphasis on commensal microbes functioning as viral reservoirs. Furthermore, we discuss the role of SARS-CoV-2/Mycoplasma coinfection in dysfunctional efferocytosis, emphasizing some potential novel treatment strategies, including the use of senotherapeutic drugs, HMGB1 inhibitors, Toll-like receptor 4 (TLR4) blockers, and membrane lipid replacement.

Efferocytosis in multisystem diseases (Review)

Efferocytosis, the phagocytosis of apoptotic cells performed by both specialized phagocytes (such as macrophages) and non‑specialized phagocytes (such as epithelial cells), is involved in tissue repair and homeostasis. Effective efferocytosis prevents secondary necrosis, terminates inflammatory responses, promotes self‑tolerance and activates pro‑resolving pathways to maintain homeostasis. When efferocytosis is impaired, apoptotic cells that could not be cleared in time aggregate, resulting in the necrosis of apoptotic cells and release of pro‑inflammatory factors. In addition, defective efferocytosis inhibits the intracellular cholesterol reverse transportation pathways, which may lead to atherosclerosis, lung damage, non‑alcoholic fatty liver disease and neurodegenerative diseases. The uncleared apoptotic cells can also release autoantigens, which can cause autoimmune diseases. Cancer cells escape from phagocytosis via efferocytosis. Therefore, new treatment strategies for diseases related to defective efferocytosis are proposed. This review illustrated the mechanisms of efferocytosis in multisystem diseases and organismal homeostasis and the pathophysiological consequences of defective efferocytosis. Several drugs and treatments available to enhance efferocytosis are also mentioned in the review, serving as new evidence for clinical application.