Lactate-Dependent Regulation of Immune Responses by Dendritic Cells and Macrophages

The role of glycolysis and lactate in the induction of tumor-associated macrophages immunosuppressive phenotype

Growing evidence highlights that glycolysis and tumor-derived lactate could skew tumor-associated macrophages (TAMs) toward an immunosuppressive phenotype. However, the updated research has not been systematically summarized yet. TAMs are educated by the tumor microenvironment (TME) and exert immunosuppressive functions and tumorigenic effects via multiple biological processes. It is well known that lactate generated by aerobic glycolysis is significantly accumulated in TME and promotes tumor progression in solid tumors. Moreover, some recent research demonstrated that glycolysis is activated in TAMs to support M2-like polarization, which is absolutely in contrast with the metabolic profile of M2 macrophages in inflammation. Notably, lactate produced by high levels of glycolysis is not only a metabolic by-product but also an oncometabolite. TAMs could access the biological information delivered by lactate and further enhance protumor functions such as immunosuppression and angiogenesis. Here, we outline the connection between glycolysis and TAM phenotype to elucidate the metabolic characteristics of TAMs. Further, insights into the specific molecular mechanisms of lactate-induced TAM polarization and potential therapeutic targets are summarized. We sought to discuss the reciprocal interaction between tumor cells and TAMs mediated by lactate, which will lay a foundation for the research aiming to elucidate the complex functions of TAMs.

Lactate Neuroprotection against Transient Ischemic Brain Injury in Mice Appears Independent of HCAR1 Activation

Lactate can protect against damage caused by acute brain injuries both in rodents and in human patients. Besides its role as a metabolic support and alleged preferred neuronal fuel in stressful situations, an additional signaling mechanism mediated by the hydroxycarboxylic acid receptor 1 (HCAR1) was proposed to account for lactate’s beneficial effects. However, the administration of HCAR1 agonists to mice subjected to middle cerebral artery occlusion (MCAO) at reperfusion did not appear to exert any relevant protective effect. To further evaluate the involvement of HCAR1 in the protection against ischemic damage, we looked at the effect of HCAR1 absence. We subjected wild-type and HCAR1 KO mice to transient MCAO followed by treatment with either vehicle or lactate. In the absence of HCAR1, the ischemic damage inflicted by MCAO was less pronounced, with smaller lesions and a better behavioral outcome than in wild-type mice. The lower susceptibility of HCAR1 KO mice to ischemic injury suggests that lactate-mediated protection is not achieved or enhanced by HCAR1 activation, but rather attributable to its metabolic effects or related to other signaling pathways. Additionally, in light of these results, we would disregard HCAR1 activation as an interesting therapeutic strategy for stroke patients.

Targeting the Tumor Microenvironment: A Close Up of Tumor-Associated Macrophages and Neutrophils

The importance of the tumor microenvironment (TME) in dynamically regulating cancer progression and influencing the therapeutic outcome is widely accepted and appreciated. Several therapeutic strategies to modify or modulate the TME, like angiogenesis or immune checkpoint inhibitors, showed clinical efficacy and received approval from regulatory authorities. Within recent decades, new promising strategies targeting myeloid cells have been implemented in preclinical cancer models. The predominance of specific cell phenotypes in the TME has been attributed to pro- or anti-tumoral. Hence, their modulation can, in turn, alter the responses to standard-of-care treatments, making them more or less effective. Here, we summarize and discuss the current knowledge and the correlated challenges about the tumor-associated macrophages and neutrophils targeting strategies, current treatments, and future developments.

Role of Lactate in Inflammatory Processes: Friend or Foe

During an inflammatory process, shift in the cellular metabolism associated with an increase in extracellular acidification are well-known features. This pH drop in the inflamed tissue is largely attributed to the presence of lactate by an increase in glycolysis. In recent years, evidence has accumulated describing the role of lactate in inflammatory processes; however, there are differences as to whether lactate can currently be considered a pro- or anti-inflammatory mediator. Herein, we review these recent advances on the pleiotropic effects of lactate on the inflammatory process. Taken together, the evidence suggests that lactate could exert differential effects depending on the metabolic status, cell type in which the effects of lactate are studied, and the pathological process analyzed. Additionally, various targets, including post-translational modifications, G-protein coupled receptor and transcription factor activation such as NF-κB and HIF-1, allow lactate to modulate signaling pathways that control the expression of cytokines, chemokines, adhesion molecules, and several enzymes associated with immune response and metabolism. Altogether, this would explain its varied effects on inflammatory processes beyond its well-known role as a waste product of metabolism.

Aspergillus-Derived Cellulase Preparation Exhibits Prebiotic-like Effects on Gut Microbiota in Rats

Aspergillus-derived cellulase, which is involved in the production of Aspergillus-fermented foods, has been employed in the food and animal feed industries. However, the effect of dietary Aspergillus cellulase on health is poorly understood. Previously, we discovered that supplemental Aspergillus-derived protease and lipase preparations had substantial bifidogenic effects on rats fed a high-fat diet. Therefore, this study reports on the effects of a 0.1% dietary Aspergillus-derived cellulase preparation (CEL) on the gut microbiota of rats fed a high-fat diet. Gene sequencing analysis of 16S rRNA revealed that CEL treatment markedly affected the microbiota profiles of the cecal contents (p < 0.05). Notably, CEL markedly increased the relative abundance (RA) of typical probiotics, such as Bifidobacterium and Lactobacillus, at the genus level (28- and 5-fold, respectively, p < 0.05). Similarly, at the family level, CEL treatment significantly increased the RA of Bifidobacteriaceae and Lactobacillaceae (p < 0.05). Furthermore, CEL increased the RA of other genera, such as Collinsella and Enterococcus, but decreased the RA of Oscillospira, Dorea and Coprobacillus (p < 0.05). The effects on these genera are similar to those reported for typical prebiotic oligosaccharides. Overall, this study demonstrates the prebiotic-like effects of dietary CEL by significantly increasing Bifidobacterium and Lactobacillus abundance.

Immune effects of PI3K/Akt/HIF-1α-regulated glycolysis in polymorphonuclear neutrophils during sepsis

Background

Effective removal of pathogenic bacteria is key to improving the prognosis of sepsis. Polymorphonuclear neutrophils (PMNs) are the most important components of innate cellular immunity and play vital roles in clearing pathogenic bacteria. However, the metabolic characteristics and immunomodulatory pathways of PMNs during sepsis have not been investigated. In the present study, we explored the immune metabolism characteristics of PMNs and the mechanism by which neutrophilic glycolysis is regulated during sepsis.

Methods

Metabolomics analysis was performed on PMNs isolated from 14 septic patients, 26 patients with acute appendicitis, and 19 healthy volunteers. Transcriptome analysis was performed on the PMNs isolated from the healthy volunteers and the patients with sepsis to assess glycolysis and investigate its mechanism. Lipopolysaccharide (LPS) was used to stimulate the neutrophils isolated from the healthy volunteers at different time intervals to build an LPS-tolerant model. Chemotaxis, phagocytosis, lactate production, oxygen consumption rate (OCR), and extracellular acidification rate (ECAR) were evaluated.

Results

Transcriptomics showed significant changes in glycolysis and the mTOR/HIF-1α signaling pathway during sepsis. Metabolomics revealed that the Warburg effect was significantly altered in the patients with sepsis. We discovered that glycolysis regulated PMNs’ chemotaxis and phagocytosis functions during sepsis. Lactate dehydrogenase A (LDHA) downregulation was a key factor in the inhibition of glycolysis in PMNs. This study confirmed that the PI3K/Akt-HIF-1α pathway was involved in the LDHA expression level and also influenced PMNs’ chemotaxis and phagocytosis functions.

Conclusions

The inhibition of glycolysis contributed to neutrophil immunosuppression during sepsis and might be controlled by PI3K/Akt-HIF-1α pathway-mediated LDHA downregulation. Our study provides a scientific theoretical basis for the management and treatment of patients with sepsis and promotes to identify therapeutic target for the improvement of immune function in sepsis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13054-022-03893-6.

Phosphatases of regenerating liver are key regulators of metabolism in cancer cells - role of Serine/Glycine metabolism

PURPOSE OF REVIEW

Phosphatases of regenerating liver (PRL) are dual-specificity phosphatases and comprise three members, PRL-1, -2 and -3. Despite the importance of PRLs as oncoproteins, there is no consensus function for this family of phosphatases. In the current review paper, we summarize recent findings on the role of PRLs in metabolic regulation.

RECENT FINDINGS

Reprogramming of cellular metabolism is a cancer hallmark. Glucose is the major source of energy in cells. Glucose metabolism occurs through the glycolysis and can continue through the pathways such as serine synthesis pathway or the tricarboxylic acid cycle (TCA). Magnesium (Mg2+), the second most abundant cation in cells, plays an essential role in energy production by acting as a cofactor for most enzymes involved in glycolysis and in TCA. Recent findings have shown that the PRL family has a role in metabolic reprogramming mediated by (1) Mg2+ homeostasis, (2) shifting the energy source preference to glucose consumption and fueling serine/glycine pathway and (3) regulating PI3 kinase/Mammalian target of rapamycin complex. Both the phosphatase and nonphosphatase activity of PRLs appear to be important for its oncogenic role.

SUMMARY

The PRL family contributes to the metabolic plasticity of cancer cells and, thereby, allows cancer cells to meet the high metabolic demands required for cell proliferation.

PDAC as an Immune Evasive Disease: Can 3D Model Systems Aid to Tackle This Clinical Problem?

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive cancer with a high mortality rate. The presence of a dense desmoplastic stroma rich in fibroblasts, extracellular matrix, and immune cells plays a critical role in disease progression, therapy response and is a distinguishing feature of PDAC. PDAC is currently treated with a combination of surgery, chemotherapy and radiation therapy in selected cases which results in long-term survival only in a small percentage of patients. Cancer therapies that incorporate immunotherapy-based techniques have become increasingly common in recent years. While such a strategy has been shown to be effective for immunogenic, “hot” tumors like melanoma and lung cancer, thus far PDAC patients display poor responses to this therapeutic approach. Various factors, such as low tumor mutational burden, increased infiltration of immunosuppressive cells, like MDSCs and Treg cells promote tolerance and immune deviation, further aggravating adaptive immunity in PDAC. In this review we will elaborate on the ability of PDAC tumors to evade immune detection. We will also discuss various 3D model system that can be used as a platform in preclinical research to investigate rational combinations of immunotherapy with chemotherapy or targeted therapy, to prime the immune microenvironment to enhance antitumor activity.

Supplemental Aspergillus Lipase and Protease Preparations Display Powerful Bifidogenic Effects and Modulate the Gut Microbiota Community of Rats

Aspergillus-derived protease and lipase, which are involved in the production of Aspergillus-fermented foods, are consumed as digestive enzyme supplements. A marked bifidogenic effect of supplemental Aspergillus protease preparation (AP) in rats fed with a high-fat diet was identified. This study was conducted to examine whether the consumption of Aspergillus-derived lipase exerts similar bifidogenic effect. Rats were fed diets supplemented with either an Aspergillus-derived lipase preparation (AL) or AP at 0.1% for two weeks. 16S rRNA gene sequencing analysis indicated that supplemental AL and AP markedly influenced cecal microbial community. At the phylum level, treatment with AL and AP resulted in a lower relative abundance of Firmicutes and Bacteroidetes, but a higher relative abundance of Actinobacteria and Proteobacteria than the control rats (p < 0.05). At the genus level, AL and AP remarkedly elevated the relative abundances of Bifidobacterium, Collinsella, and Enterococcus, but significantly reduced those of Oscillospira, Dorea, and Coprobacillus (p < 0.05). These modulations were similar to those reported by several studies with typical prebiotic oligosaccharides. Notably, the bifidogenic effect of AL was much greater than that of AP. Our results show that the two different Aspergillus-derived preparations, AL and AP, have strong bifidogenic effects and can change the microbiota’s composition.

Metabolite G-Protein Coupled Receptors in Cardio-Metabolic Diseases

G protein-coupled receptors (GPCRs) have originally been described as a family of receptors activated by hormones, neurotransmitters, and other mediators. However, in recent years GPCRs have shown to bind endogenous metabolites, which serve functions other than as signaling mediators. These receptors respond to fatty acids, mono- and disaccharides, amino acids, or various intermediates and products of metabolism, including ketone bodies, lactate, succinate, or bile acids. Given that many of these metabolic processes are dysregulated under pathological conditions, including diabetes, dyslipidemia, and obesity, receptors of endogenous metabolites have also been recognized as potential drug targets to prevent and/or treat metabolic and cardiovascular diseases. This review describes G protein-coupled receptors activated by endogenous metabolites and summarizes their physiological, pathophysiological, and potential pharmacological roles.