Macrophage Glucose Metabolism Reprogramming and Cardiovascular Complications of Diabetes

Review Article

J Immun Res. 2022; 8(1): 1047.

Macrophage Glucose Metabolism Reprogramming and Cardiovascular Complications of Diabetes

He Yuqi¹, Chen Cong¹, Haitao X¹* and Jingsong C²*

1Department of Laboratory Medicine, The First Affiliated Hospital, University of South China, China

2Department of Endocrinology and Metabolism, The First Affiliated Hospital, Institute of Clinical Medicine, University of South China, China

*Corresponding author: Cao Jingsong, Xie Haitao, Institute of Clinical Medicine, The First Affiliated Hospital of University of South China, Hengyang City, 421000, Hunan Province, China

Received: July 18, 2022; Accepted: August 17, 2022; Published: August 24, 2022

Abstract

Macrophages are the main participants in the pathogenesis of many chronic inflammatory and autoimmune diseases, including diabetes, and cardiovascular complications mediated by abnormal activation of macrophages caused by various reasons are the main causes of morbidity and death in patients with diabetes. Different environmental stimuli can easily lead to glucose metabolism reprogramming in macrophages, resulting in a series of changes in metabolization-related enzymes, metabolites and metabolic pathways. Glucose metabolism reprogramming is closely related to M1 polarization and M2 polarization of macrophages, for example, M1 macrophages tend to anaerobic glycolysis while M2 macrophages tend to aerobic metabolism, and different polarization of macrophages is closely related to various diseases. Therefore, this paper reviews the mechanism and inducing factors of reprogramming of glucose metabolic pathways, as well as the effect of these pathways on macrophage polarization, so as to provide services for clinical research and treatment of the occurrence and development of cardiovascular complications in the context of chronic inflammation of diabetes.

Keywords: Glucose metabolism reprogramming; Macrophage polarization; Diabetes; Cardiovascular complications

Introduction

Diabetes is a group of chronic metabolic diseases worldwide characterized by chronic hyperglycemia, which easily induces the activation of the immune system and leads to chronic inflammation, eventually leading to a series of serious cardiovascular diseases and other complications [1,2]. The World Health Organization predicts diabetes as the seventh leading cause of death in the world by 2035 [3], and the International Diabetes Federation estimates that the number of people diagnosed with T2DM worldwide will rise to 640 million by 2040 [4,5]. Among diabetes-related deaths, cardiovascular complications are a major contributing factor. Among diabetes-related deaths, cardiovascular complications are a major contributing factor. Therefore, the study of diabetes and its main complications cardiovascular complications is of far-reaching significance for its clinical treatment [6,7]. However, at present, there is no cure for this type of disease, so in-depth research on diabetes treatment is very important to the development of diabetes patients and medical services around the world [8]. Macrophages are a very important class of innate immune cells, widely found in various tissues and organs of the body. They have major functions such as phagocytosis, chemotaxis, regulating of inflammation, and clearing pathogenic microorganisms; they are usually divided into classically activated M1 type and alternative activated M2 type [9-11]. Studies have shown that metabolic reprogramming is a core component of macrophage plasticity and polarization [12], and changes in glucose metabolism pathways can support macrophage polarization into different subtypes, contributing to their immune homeostasis and immune system in vivo. It plays an important function in the inflammatory response [13]. Normally, the metabolism of M1 macrophage is biased towards glycolysis, while M2 macrophage metabolism is biased towards the oxidative phosphorylation pathway to obtain its required adenosine triphosphate [14,15]. Therefore, this article reviews the related research on macrophage polarization with glucose metabolism as an entry point, and provides a systematic and comprehensive understanding of the related research on the involvement of macrophage glucose metabolism reprogramming in the complications of diabetes and cardiovascular disease.

Mechanisms of Glucose Metabolism Reprogramming

Restriction Enzymes Related To Glucose Metabolism

Glucose metabolism is a complex and systematic regulation process, mainly including glycolysis, oxidative phosphorylation, and pentose phosphate pathway. The process of glucose catabolism and energy production requires the participation of a variety of enzymes, and this review mentions some of the enzymes that play the main role. For example, the activity changes of hexokinase, 6-phosphate kinase-1, pyruvate kinase, glucose-6-phosphate dehydrogenase and glyceraldehyde 3-phosphate dehydrogenase exerts different regulatory effects on glucose metabolism.

Hexokinase (HK) has 4 isoforms, of which HK2 is considered to be the prototypical inducible isoform of HK family members because it can be up-regulated by various environmental factors and signaling pathways [16,17]. Studies have proved that 2-Deoxygenation-DGlucose (2-DG) is a glycolytic inhibitor targeting HK2, which can significantly reduce the ATP concentration of M1 macrophages, and effectively inhibit the aerobic glycolytic activity of macrophage [18,19]; promotes oxidative phosphorylation, induce macrophage polarization to M2, and thus produce serial metabolic effects such as glucose metabolism reprogramming [20,21].

The 6-Phosphate Kinase-1 (PFK) is activated by its strongest allosteric activator, fructose-2, 6-diphosphatase 3 (PFKFB3), which then promotes the glycolytic pathway [22,23]. There are PFK1 and PFK2, and PFK2 has L-PFK2 (liver) and U-PFK (universal) forms, in which L-PFK2 causes PFKFB3 degradation, and U-PFK shows high phosphokinase activity and catalyzes the production of more PFKFB3, so glycolysis pathway enhanced sugars cause metabolic reprogramming [24,25]. In M1 macrophages, U-PKF is induced by pro-inflammatory stimulators and growth factors, and down regulation of U-PFK2 expression suppresses the activity of M1 macrophages [26,27]. Because PFK2 can regulate the properties of glycolytic metabolism under various physiological conditions, it plays a clinical therapeutic role as a therapeutic target of glucose metabolism [28].

Pyruvate Kinase (PK) consists of four isoenzymes, commonly PK1 and PK2. At present, muscle-type PKM can be widely studied as a protein kinase of various transcription factors in the nucleus [29]. In the process of macrophage polarization, inhibition of PKM2 activity leads to the formation of dimer of PKM2 and its interaction with HIF-1α, which in turn up-regulates the expression of HIF-1α related glucose metabolism enzyme genes, thereby enhancing the activity of glycolytic metabolism enzyme and inducing the development of glucose metabolism reprogramming [30]. PKM2 can not only regulate gene expression in the nucleus, but also attach to the outer mitochondrial membrane, leading to mitochondrial dysfunction by disrupting the balance of fission and fusion, resulting in abnormal oxidative phosphorylation metabolic pathways [31,32].

Glucose-6-Phosphate Dehydrogenase (G6PD) is a key enzyme in the Pentose Phosphate Pathway (PPP), which promotes intracellular oxidative stress and pro-inflammatory cytokine expression by activating p38 mitogen-activated protein kinase (p38MAPK) and nuclear factor NF-KB signaling pathway. Inhibition of G6PD expression with chemical inhibitors or small interfering RNA can significantly reduce p38MAPK and NF-KB signals, and downregulate the expression of inflammatory factors such as IL-1β and IL-6 [33,34]. Thus, playing a role in regulating the reprogramming of glucose metabolism, and regulating its activity can provide a clinical approach for related treatment.

In addition to the above-mentioned key enzymes of glucose catabolism, other enzymes involved also play important roles in the differentiation, activation and glucose metabolism reprogramming of macrophages. Understanding the role of glucose metabolismrelated enzyme formation or regulated metabolic network in the physiological function of macrophages will facilitate the further study of the molecular mechanism of macrophage polarization and glucose metabolism reprogramming.

Molecular Mechanisms of Glucose Metabolism Reprogramming

PI3K/Akt - mTOR - HIF1-α Signal Enhances Glycolysis

Phosphatidylinositol Kinase (PI3K)/ protein kinase B(Akt) signaling can promote the expression of Glucose Transporter (GLUT) and protein translocation to improve glucose uptake and metabolism [35]. Target rapamycin (mTOR) is a downstream effector of the PI3K/Akt pathway that regulates cell proliferation, growth, survival, and metabolic activity by integrating various signals, including energy, growth factors nutrition and stress [36,37]. It has been demonstrated that activation of pi3K-Akt-MTOR pathway increases HIF-1A synthesis and upregulates HIF-1 regulatory gene mRNA level, while HIF1-α directly activates glycoly-related enzymes to stimulate glycolysis [38,39]. Such as glucose transporters 1 and 3 (GLUT1, GLUT3), HK1 and 2, GAPDH, phosphoglycerate kinase (PGK1), PKM2, Lactate Dehydrogenase (LDHA) and Pyruvate Dehydrogenase Kinase (PDK), etc [40,44]. In addition, enhanced HIF-1 not only blocks TCA cycle and oxidative phosphorylation in mitochondria, but also plays an important role in macrophage migration by promoting the expression of LDHA and PDK migration [45,46], improves cell utilization of acetyl-CoA (CoA) and inhibiting pyruvate dehydrogenase activity to enhance glycolysis [47]. Therefore, regulating mTOR activity to explore the mechanism and effect of aerobic glycolysis is an important strategy to study glucose metabolism reprogramming in macrophages.

NF-KB-CARKL-Enhances Pentose Phosphate Pathway

Nuclear transcription factor (NF-κB) is involved in regulating apoptosis and stress response, and its inactivation or overactivation can lead to abnormal changes in metabolic balance [48,49]. Carbohydrate Kinase-Like Protein (CARKL) is an important factor in the production of setoheptose-7-phosphate (S7P), the intermediate of pentose phosphate pathway [50,51]. LPS can inhibit the expression of CARKL through the NF-κB pathway and up-regulate the PPP pathway, which weakens the restrictive effect on TNF-α and pentose phosphate pathways, thereby promoting the polarization of M1 macrophages [52]. CARKL is expressed at a high level in M2 macrophages, indicating that the metabolic level of the PPP pathway is higher than that of M1. These results suggest that CARKL is an important regulatory factor regulating the balance of glucose reprogramming intermediates in macrophages and may be an important target for glucose reprogramming studies in macrophages.

Mitochondrial Function and Oxidative Phosphorylation OXPHOS Pathway

Mitochondria is key sites for regulating cellular glucose metabolism. Infection, stress and other environmental changes can significantly change the structure and function of macrophages’ mitochondria, and mitochondrial damage can promote the generation of Reactive Oxygen Species (ROS) [53,54], not only promote the stable expression of HIF1-protein, but also promote the production of inflammatory cytokines (such as IL-6 and TNF-α) [55,56]. It has been found that Inducible Nitric Oxide (iNOS) and Nitric Oxide (NO) can modify mitochondrial complex I and IV through nitrosylation, break mitochondrial electron transport chain, and inhibit oxidative phosphorylation of cells [57]. Knockdown of iNOS improves LPSinduced impairment of mitochondrial respiratory function in M1 macrophages [58]; and administration of exogenous NO again leads to mitochondrial dysfunction and glucose metabolism reprogramming, and promotes macrophage inflammatory response [59].

In addition, appropriate mitochondrial division and fusion is also key to determining its structural and functional homeostasis. Excessive mitochondrial division leads to mitochondrial electron transfer disorder and impaired oxidative phosphorylation metabolism, while enhanced fusion promotes the tight connection of mitochondrial complexes and oxidative phosphorylation process [60-62]. It can be seen that the structure and function of mitochondria and the stable expression of related enzymes is conducive to maintaining the glucose metabolism balance of cells, and the occurrence of either tilt may lead to metabolic reprogramming.

Inducible Factors of Glucose Metabolic Reprogramming

The reprogramming of macrophage metabolic pathways is not only caused by nutrition or oxygen, but also by various diseases, intestinal flora disorders, and stimulation of glucose metabolites. In addition, changes in virulence factors, pattern recognition receptors, gene changes, and cytokine receptors can also induce the reprogramming of cellular glucose metabolism.

Intestinal Microflora

With the continuous development of microbial research, the study of intestinal flora, the “hidden organ” of human body, has become hotter and hotter, and it has been found that it plays an important role in a variety of diseases, obesity, diabetes and cardiovascular diseases are closely related to gastrointestinal microbial disorders [63-65]. In recent years, more and more studies have found that metabolites play an important role in the microbiome mediated regulation of glucose metabolism in patients with Type 2 Diabetes Mellitus (T2DM) [66]. For example, propionic acid, butyric acid and succinic acid can promote intestinal gluconeogenesis, affect host appetite and insulin secretion, and inhibit liver gluconeogenesis, thus exerting the effect of glucose metabolism regulation and reprogramming [67,68]. Bile acid derivatives and amino acid derivatives can also promote the synthesis and secretion of glucagon-like peptide 1GLP-1, thus causing insulin secretion to regulate blood glucose and glucose metabolism [69,70]. Therefore, regulating the balance of intestinal flora can regulate glucose metabolism in diabetes and may be an important regulator in macrophages glucose metabolic reprogramming.

Itaconic Acid

It has been suggested that itaconic acid is an immunomodulatory anti-inflammatory metabolite that is synthesized by homeotropic aconite in the TCA cycle in macrophages that are activated by a variety of factors, particularly Lipopolysaccharide (LPS), as well as other Toll-like Receptor (TLR) ligands and cytokine [71,72]. Itaconic acid was found to be significantly higher in women with gestational diabetes, and the current preliminary study found that itaconic acid may have the potential to play an important role as a novel biomarker in predicting the subsequent development of early gestational diabetes [73]. The metabolites itaconic acid and its derivatives inhibit M2 polarization by inhibiting JAK1/STAT6 signaling pathway, and inhibit the transcription of some genes related to M2 polarization process, such as Pparg, CD206 and Fizz1. The mitochondrial oxidative phosphorylation pathway of glucose metabolism is also significantly inhibited [74,75]. It was found that itaconic acid inhibits Succinate Dehydrogenase (SDH), whose activity mediates succinate oxidation to regulate the pro-inflammatory IL-1b-HIF-1α axis, regulates ROS release in vitro and in vivo, and has an effect on mitochondrial function and glucose metabolism TCA cycl [76,77]. The researchers found that itaconate can directly bind to protein Keap1 and promote its alkylation, thus inducing Nrf2 expression, and finally inhibiting inflammation by inhibiting IL-1b expression [76,78]. Itaconate obviously promotes the pentose phosphate pathway, leading to a significantly increased NADPH oxidase activity, and regulating the expression of the gene A20 regulated by the NF-B pathway produces more ROS release [79]. Therefore, the accumulation of chaconic acid can promote the reprogramming of glucose metabolism and also play a role in inducing polarization of macrophages.

Citation: Yuqi H, Cong C, Haitao X and Jingsong C. Macrophage Glucose Metabolism Reprogramming and Cardiovascular Complications of Diabetes. J Immun Res. 2022; 8(1): 1047.