Myeloid Immune Cells CARrying a New Weapon Against Cancer

Chimeric antigen receptor (CAR) engineering for T cells and natural killer cells (NK) are now under clinical evaluation for the treatment of hematologic cancers. Although encouraging clinical results have been reported for hematologic diseases, pre-clinical studies in solid tumors have failed to prove the same effectiveness. Thus, there is a growing interest of the scientific community to find other immune cell candidate to express CAR for the treatment of solid tumors and other diseases. Mononuclear phagocytes may be the most adapted group of cells with potential to overcome the dense barrier imposed by solid tumors. In addition, intrinsic features of these cells, such as migration, phagocytic capability, release of soluble factors and adaptive immunity activation, could be further explored along with gene therapy approaches. Here, we discuss the elements that constitute the tumor microenvironment, the features and advantages of these cell subtypes and the latest studies using CAR-myeloid immune cells in solid tumor models.

The dual effect of acetate on microglial TNF-α production

INTRODUCTION

Short-Chain Fatty Acids (SCFA) are products of intestinal microbial metabolism that can reach the brain and alter microglia in health and disease contexts. However, data are conflicting on the effect of acetate, the most abundant SCFA in the blood, in these cells.

OBJECTIVE

The authors aimed to investigate acetate as a modulator of the inflammatory response in microglia stimulated with LPS.

METHOD

The authors used an immortalized cell line, C8-B4, and primary cells for in vitro treatments with acetate and LPS. Cell viability was analyzed by MTT, cytokine by RT-PCR, ELISA, and flow cytometry. The authors also performed in vivo and in silico analyses to study the role of acetate and the TNF-α contribution to the development of Experimental Autoimmune Encephalomyelitis (EAE).

RESULTS

Acetate co-administered with LPS was able to exacerbate the production of pro-inflammatory cytokines at gene and protein levels in cell lines and primary culture of microglia. However, the same effects were not observed when acetate was administered alone or as pretreatment, prior to the LPS stimulus. Additionally, pharmacological inhibition of histone deacetylase concomitantly with acetate and LPS led to decreased TNF-α production. In silico analysis showed a crucial role of the TNF-α pathway in EAE development. Moreover, acetate administration in vivo during the initial phase of EAE led to a better disease outcome and reduced TNF-α production.

CONCLUSION

Treatment with acetate was able to promote the production of TNF-α in a concomitant LPS stimulus of microglia. However, the immune modulation of microglia by acetate pretreatment may be a component in the generation of future therapies for neurodegenerative diseases.

Distinct macrophage phenotypes and redox environment during the fin fold regenerative process in zebrafish

In contrast to mammals, zebrafish (Danio rerio) has the ability to regenerate injured sites such as different tissues present in the fin. It is known that cells of the innate immune system play essential roles in regeneration; however, some aspects of the molecular mechanisms by which these cells orchestrate regeneration remain unknown. This study aimed to evaluate the infiltration dynamics of neutrophils and macrophages in the regenerative process of fin fold in regard to the influence of the redox environment and oxidative pathways. Fin fold amputation was performed on transgenic larvae for macrophage-expressed gene 1 (mpeg1), lysozyme (lyz), myeloperoxidase (mpo) and tumour necrosis factor alpha (TNFα) at 3 days post-fertilization, followed by confocal microscopy imaging and measurement of the activities of oxidant and antioxidant enzymes. We observed initially an increase in the number of neutrophils (lyz:DsRed+/mpx:GFP+) and then macrophages (mpeg1+) in the injury site followed by a decrease in neutrophils at 7 days post-amputation (dpa). Moreover, macrophages switch from a pro-inflammatory to an anti-inflammatory profile throughout the process, while the activity of superoxide dismutase (SOD) increased at 1 dpa and catalase (CAT) at 5 dpa. Higher levels of lipid peroxidation were also detected during regeneration. Despite oxidative stress, there is, therefore, an antioxidant response throughout the regeneration of the caudal fin. The present work can contribute to future studies on the development of cell therapies, achieving greater effectiveness in the treatment of diseases related to the formation of fibrotic tissue.

Sensing soluble uric acid by Naip1-Nlrp3 platform

Uric acid (UA), a product of purine nucleotide degradation able to initiate an immune response, represents a breakpoint in the evolutionary history of humans, when uricase, the enzyme required for UA cleavage, was lost. Despite being inert in human cells, UA in its soluble form (sUA) can increase the level of interleukin-1β (IL-1β) in murine macrophages. We, therefore, hypothesized that the recognition of sUA is achieved by the Naip1-Nlrp3 inflammasome platform. Through structural modelling predictions and transcriptome and functional analyses, we found that murine Naip1 expression in human macrophages induces IL-1β expression, fatty acid production and an inflammation-related response upon sUA stimulation, a process reversed by the pharmacological and genetic inhibition of Nlrp3. Moreover, molecular interaction experiments showed that Naip1 directly recognizes sUA. Accordingly, Naip may be the sUA receptor lost through the human evolutionary process, and a better understanding of its recognition may lead to novel anti-hyperuricaemia therapies.

The role of uric acid in inflammasome-mediated kidney injury

PURPOSE OF REVIEW

Uric acid is produced after purine nucleotide degradation, upon xanthine oxidase catalytic action. In the evolutionary process, humans lost uricase, an enzyme that converts uric acid into allantoin, resulting in increased serum uric acid levels that may vary according to dietary ingestion, pathological conditions, and other factors. Despite the controversy over the inflammatory role of uric acid in its soluble form, crystals of uric acid are able to activate the NLRP3 inflammasome in different tissues. Uric acid, therefore, triggers hyperuricemic-related disease such as gout, metabolic syndrome, and kidney injuries. The present review provides an overview on the role of uric acid in the inflammasome-mediated kidney damage.

RECENT FINDINGS

Hyperuricemia is present in 20-35% of patients with chronic kidney disease. However, whether this increased circulating uric acid is a risk factor or just a biomarker of renal and cardiovascular injuries has become a topic of intense discussion. Despite these conflicting views, several studies support the idea that hyperuricemia is indeed a cause of progression of kidney disease, with a putative role for soluble uric acid in activating renal NLRP3 inflammasome, in reprograming renal and immune cell metabolism and, therefore, in promoting kidney inflammation/injury.

SUMMARY

Therapies aiming to decrease uric acid levels prevent renal NLRP3 inflammasome activation and exert renoprotective effects in experimental kidney diseases. However, further clinical studies are needed to investigate whether reduced circulating uric acid can also inhibit the inflammasome and be beneficial in human conditions.

The Role of NLRP3 Inflammasome Activation in the Epithelial to Mesenchymal Transition Process During the Fibrosis

Fibrosis is considered a complex form of tissue damage commonly present in the end stage of many diseases. It is also related to a high percentage of death, whose predominant characteristics are an excessive and abnormal deposition of fibroblasts and myofibroblasts -derived extracellular matrix (ECM) components. Epithelial-to-mesenchymal transition (EMT), a process in which epithelial cells gradually change to mesenchymal ones, is a major contributor in the pathogenesis of fibrosis. The key mediator of EMT is a multifunctional cytokine called transforming growth factor-β (TGF-β) that acts as the main inducer of the ECM assembly and remodeling through the phosphorylation of Smad2/3, which ultimately forms a complex with Smad4 and translocates into the nucleus. On the other hand, the bone morphogenic protein-7 (BMP-7), a member of the TGF family, reverses EMT by directly counteracting TGF-β induced Smad-dependent cell signaling. NLRP3 (NACHT, LRR, and PYD domains-containing protein 3), in turn, acts as cytosolic sensors of microbial and self-derived molecules and forms an immune complex called inflammasome in the context of inflammatory commitments. NLRP3 inflammasome assembly is triggered by extracellular ATP, reactive oxygen species (ROS), potassium efflux, calcium misbalance, and lysosome disruption. Due to its involvement in multiple diseases, NLRP3 has become one of the most studied pattern-recognition receptors (PRRs). Nevertheless, the role of NLRP3 in fibrosis development has not been completely elucidated. In this review, we described the relation of the previously mentioned fibrosis pathway with the NLRP3 inflammasome complex formation, especially EMT-related pathways. For now, it is suggested that the EMT happens independently from the oligomerization of the whole inflammasome complex, requiring just the presence of the NLRP3 receptor and the ASC protein to trigger the EMT events, and we will present different pieces of research that give controversial point of views.

Understanding the Metabolic Profile of Macrophages During the Regenerative Process in Zebrafish

In contrast to mammals, lower vertebrates, including zebrafish (Danio rerio), have the ability to regenerate damaged or lost tissues, such as the caudal fin, which makes them an ideal model for tissue and organ regeneration studies. Since several diseases involve the process of transition between fibrosis and tissue regeneration, it is necessary to attain a better understanding of these processes. It is known that the cells of the immune system, especially macrophages, play essential roles in regeneration by participating in the removal of cellular debris, release of pro- and anti-inflammatory factors, remodeling of components of the extracellular matrix and alteration of oxidative patterns during proliferation and angiogenesis. Immune cells undergo phenotypical and functional alterations throughout the healing process due to growth factors and cytokines that are produced in the tissue microenvironment. However, some aspects of the molecular mechanisms through which macrophages orchestrate the formation and regeneration of the blastema remain unclear. In the present review, we outline how macrophages orchestrate the regenerative process in zebrafish and give special attention to the redox balance in the context of tail regeneration.

Reduced expression of VAChT increases renal fibrosis

Chronic kidney disease (CKD) is associated with several other long-lasting conditions such as diabetes and cardiovascular diseases and it is a significant contributor to mortality worldwide. Obstructive kidney disease is one of the leading causes of CKD in children and may result from a wide variety of pathologic processes. Recent studies have shown that α7 nicotinic acetylcholine receptor (α7 nAChR) activation in the cholinergic anti-inflammatory pathway reduces production of inflammatory mediators and consequently prevents tissue injury and death. Here, we examined the role of endogenous release of acetylcholine on the development of fibrosis in renal tissue using a model of unilateral ureter obstruction (UUO)-induced CKD, in which obstruction promotes inflammation-mediated kidney damages. To interfere with acetylcholine secretion, we used mice in which the vesicular acetylcholine transporter is genetically reduced (VAChT KD(hom) mice). We observed a higher renal damage in VAChT mutant mice when compared to wild type controls, exemplified by higher proteinuria and increased amount of type 1 collagen in the kidney tissue, indicating accentuated fibrogenesis. These results were accompanied by enhanced localized kidney inflammation, with increased TH1/TH17 profile response. Administration of PNU-282987, a selective agonist of α7 nAChR, significantly attenuated kidney injury after UUO in VAChT KD(hom) mice, indicating that the lack of acetylcholine release decrease the action of the cholinergic anti-inflammatory pathway, promoting an up-regulation of pro-inflammatory and pro-fibrotic pathways. These results suggest that physiological activation of the cholinergic anti-inflammatory pathway regulates inflammatory responses in the kidney suggesting a new therapeutic approach for kidney disease.

Early infiltration of p40IL12(+)CCR7(+)CD11b(+) cells is critical for fibrosis development

INTRODUCTION

Macrophages are heterogeneous and thus can be correlated with distinct tissue outcomes after injury. Conflicting data have indicated that the M2-related phenotype directly triggers fibrosis. Conversely, we hypothesize here that the inflammatory milieu provided by early infiltration of pro-inflammatory macrophages dictates tissue scarring after injury.

METHODS AND RESULTS

We first determined that tissue-localized macrophages exhibit a pro-inflammatory phenotype (p40IL12(+)CCR7(+)CD11b(+)) during the early phase of a chronic injury model, in contrast to a pro-resolving phenotype (Arg1(+)IL10(+)CD206(+)CD11b(+)) at a later stage. Then, we evaluated the effects of injecting macrophages differentiated in vitro in the presence of IFNγ + LPS or IL4 + IL13 or non-differentiated macrophages (hereafter, M0) on promoting inflammation and progression of chronic injury in macrophage-depleted mice. In addition to enhancing the expression of pro-inflammatory cytokines, the injection of M (IFNγ + LPS), but not M (IL4 + IL13) or M0, accentuated fibrosis while augmenting levels of anti-inflammatory molecules, increasing collagen deposition and impairing organ function. We observed a similar profile after injection of sorted CCR7(+)CD11b(+) cells and a more pronounced effect of M (IFNγ + LPS) cells originated from Stat6(-/-) mice. The injection of M (IFNγ + LPS) cells was associated with the up-regulation of inflammation- and fibrosis-related proteins (Thbs1, Mmp7, Mmp8, and Mmp13).

CONCLUSIONS

Our results suggest that pro-inflammatory macrophages promote microenvironmental changes that may lead to fibrogenesis by inducing an inflammatory milieu that alters a network of extracellular-related genes, culminating in tissue fibrosis.

Macrophages During the Fibrotic Process: M2 as Friend and Foe

Macrophages play essential activities in homeostasis maintenance during different organism’s conditions. They may be polarized according to various stimuli, which subsequently subdivide them into distinct populations. Macrophages with inflammatory activity function mainly during pathological context, while those with regulatory activity control inflammation and also remodel the repairing process. Here, we propose to review and to present a concise discuss on the role of different components during tissue repair, including those related to innate immune receptors and metabolic modifications. The scar formation is directly related to the degree of inflammation, but also with the appearance of M2 macrophages. In spite of greater numbers of macrophages in the fibrotic phase, regulatory macrophages present some characteristics related to promotion of fibrosis but also with the control of scar formation. These regulatory macrophages present an oxidative metabolism, and differ from the initial inflammatory macrophages, which in turn, present a glycolytic characteristic, which allow regulatory ones to optimize the oxygen consumption and minimizing their ROS production. We will emphasize the difference in macrophage subpopulations and the origin and plasticity of these cells during fibrotic processes.

MyD88 signaling pathway is involved in renal fibrosis by favoring a TH2 immune response and activating alternative M2 macrophages

Inflammation contributes to the pathogenesis of chronic kidney disease (CKD). Molecules released by the inflamed injured tissue can activate toll-like receptors (TLRs), thereby modulating macrophage and CD4(+) T-cell activity. We propose that in renal fibrogenesis, M2 macrophages are recruited and activated in a T helper subset 2 cell (T(H)2)-prone inflammatory milieu in a MyD88-dependent manner. Mice submitted to unilateral ureteral ligation (UUO) demonstrated an increase in macrophage infiltration with collagen deposition after 7 d. Conversely, TLR2, TLR4 and MyD88 knockout (KO) mice had an improved renal function together with diminished T(H)2 cytokine production and decreased fibrosis formation. Moreover, TLR2, TLR4 and MyD88 KO animals exhibited less M2 macrophage infiltration, namely interleukin (IL)-10(+) and CD206(+) CD11b(high) cells, at 7 d after surgery. We evaluated the role of a T(H)2 cytokine in this context, and observed that the absence of IL-4 was associated with better renal function, decreased IL-13 and TGF-β levels, reduced arginase activity and a decrease in fibrosis formation when compared with IL-12 KO and wild-type (WT) animals. Indeed, the better renal outcomes and the decreased fibrosis formation were restricted to the deficiency of IL-4 in the hematopoietic compartment. Finally, macrophage depletion, rather than the absence of T cells, led to reduced lesions of the glomerular filtration barrier and decreased collagen deposition. These results provide evidence that future therapeutic strategies against renal fibrosis should be accompanied by the modulation of the M1:M2 and T(H)1:T(H)2 balance, as T(H)2 and M2 cells are predictive of fibrosis toward mechanisms that are sensed by innate immune response and triggered in a MyD88-dependent pathway.

Oxidative stress and modification of renal vascular permeability are associated with acute kidney injury during P. berghei ANKA infection

Malaria associated-acute kidney injury (AKI) is associated with 45% of mortality in adult patients hospitalized with severe form of the disease. However, the causes that lead to a framework of malaria-associated AKI are still poorly characterized. Some clinical studies speculate that oxidative stress products, a characteristic of Plasmodium infection, as well as proinflammatory response induced by the parasite are involved in its pathophysiology. Therefore, we aimed to investigate the development of malaria-associated AKI during infection by P. berghei ANKA, with special attention to the role played by the inflammatory response and the involvement of oxidative stress. For that, we took advantage of an experimental model of severe malaria that showed significant changes in the renal pathophysiology to investigate the role of malaria infection in the renal microvascular permeability and tissue injury. Therefore, BALB/c mice were infected with P. berghei ANKA. To assess renal function, creatinine, blood urea nitrogen, and ratio of proteinuria and creatininuria were evaluated. The products of oxidative stress, as well as cytokine profile were quantified in plasma and renal tissue. The change of renal microvascular permeability, tissue hypoxia and cellular apoptosis were also evaluated. Parasite infection resulted in renal dysfunction. Furthermore, we observed increased expression of adhesion molecule, proinflammatory cytokines and products of oxidative stress, associated with a decrease mRNA expression of HO-1 in kidney tissue of infected mice. The measurement of lipoprotein oxidizability also showed a significant increase in plasma of infected animals. Together, our findings support the idea that products of oxidative stress, as well as the immune response against the parasite are crucial to changes in kidney architecture and microvascular endothelial permeability of BALB/c mice infected with P. berghei ANKA.

Pivotal role of Toll-like receptors 2 and 4, its adaptor molecule MyD88, and inflammasome complex in experimental tubule-interstitial nephritis

Tubule-interstitial nephritis (TIN) results in decreased renal function and interstitial inflammation, which ultimately leads to fibrosis. Excessive adenine intake can cause TIN because xanthine dehydrogenase (XDH) can convert this purine into an insoluble compound, which precipitates in the tubuli. Innate immune sensors, such as Toll-like receptors (TLR) and inflammasome complex, play a crucial role in the initiation of inflammation. The aim of this study was to evaluate the roles of TLR-2 and -4, Myd88 and inflammasome complex in an experimental model of TIN. Here, we show that wild-type (WT) mice fed adenine-enriched food exhibited significant renal dysfunction and enhanced cellular infiltration accompanied by collagen deposition. They also presented higher gene and protein expression of pro-inflammatory cytokines. In contrast, TLR-2, -4, MyD88, ASC and Caspase-1 KO mice showed renoprotection associated with expression of inflammatory molecules at levels comparable to controls. Furthermore, treatment of WT animals with allopurinol, an XDH inhibitor, led to reduced levels of uric acid, oxidative stress, collagen deposition and a downregulation of the NF-kB signaling pathway. We concluded that MyD88 signaling and inflammasome participate in the development of TIN. Furthermore, inhibition of XDH seems to be a promising way to therapeutically target the developing inflammatory process.

New roles for innate immune response in acute and chronic kidney injuries

The innate immune system plays an important role as a first response to tissue injury. This first response is carried out via germline-encoded receptors. They can recognize exogenous Pathogen-Associated Molecular Patterns and endogenous Dangers-Associated Molecular Patterns. The Toll-Like Receptor (TLR) family is well-studied, but more recently another family in the cytoplasmic compartment, called nod-like receptor (NLR), was discovered. In addition to being present in inflammatory cells, these receptors are widely distributed in various cell types, including renal tissue, where these receptors have an important role in triggering the inflammatory response during renal diseases. This review summarizes the present data regarding the role of TLRs and NLRs in the course and development of various kidney pathologies.