The glucose metabolic reprogramming in hepatitis B virus infection and hepatitis B virus associated diseases

Hepatitis B virus (HBV) infection is closely related to viral hepatitis, liver cirrhosis, and hepatocellular carcinoma. HBV infection can reprogram metabolism processes of the host cells including glucose metabolism. The aberrant glucose metabolism may aid in viral infection and immune escape and may contribute to liver associated pathology. In this review, we discussed the interplay between HBV infection and glucose metabolism, which may provide new insights into HBV infection and pathology, novel intervention targets for HBV‐related diseases.


Introduction
Hepatitis B virus (HBV) is the most prevalent hepatitis-causing virus.Chronic HBV infection is closely linked to liver cirrhosis and hepatocellular carcinoma (HCC).The World Health Organization reports that in 2019, there were an estimated 1.5 million new instances of chronic HBV infection, and 820 000 patients died from it. 1However, only 10% of patients had a diagnosis and 2% received appropriate treatment.HBV infection accounted for 54.5% of new HCC cases. 2 In China, the ratio of seropositive HBV infection in HCC was 84.4% according to an epidemiological study in 2022. 3Although the vaccination and some antiviral treatments are effective in reducing the numbers of HBV infection, there are still 87 million HBV carriers in China, accounting for about one-third of the world. 4Therefore, it is still in urgent need to have an overall understanding of HBV infection-related pathological processes and developing novel treatment strategies.
HBV is a member of hepadnaviridae family with a partial double-stranded DNA.It has four overlapping open reading frames in its genome, encoding five main kinds of proteins including HBV core antigen (HBcAg), E antigen (HBeAg), polymerase, x protein (HBx), and surface antigen (HBsAg).Among them, HBsAg consists of three kinds of glycoproteins with different molecular weights: small (S), medium (M), and large (L) HBs. 5,6Sodium taurocholate cotransporting polypeptide is the known receptor for the entry of HBV, which is highly expressed on hepatocytes. 7Upon penetrating the cells, the HBV genome enters the nucleus and the covalently closed circular DNA (cccDNA) is synthesized, which provides the template for replication.The transcription products include the pregenomic RNA, which is packaged into nucleocapsids together with reverse transcriptase where the partial double-stranded DNA is synthesized. 8Due to the presence of cccDNA, HBV infection is hard to be completely cleared, and persistent chronic infection is a common phenomenon. 9uring the battle between the virus and the host, HBV may remold the host environment for viral replication. 10Glucose is the main carbon and energy source for the host and the virus. 11][14] Glucose metabolism includes glucose catabolism and anabolism.Glucose catabolism encompasses glycolysis, tricarboxylic acid cycle, and pentose phosphate pathway (PPP).Glycolysis and tricarboxylic acid cycle are the primary sources of ATP, 15 whereas PPP provides pentose for nucleotide synthesis.PPP also helps to synthesize nicotinamide adenine dinucleotide phosphate, protecting cells from oxidative damage. 16As well, glucose anabolism is active in the body.Gluconeogenesis could be roughly regarded as a reverse process of glycolysis, which is important to stabilize the level of blood glucose. 17Glycogen is a storage form of glucose.Glucose and hepatic glycogen could interconvert in different demand of energy. 18Recent studies have highlighted that reprogramming of glucose metabolism due to HBV infection is closely associated with persistent HBV infection, as well as pathological damage to the liver caused by HBV infection.In this review, we discussed the crosstalk between HBV infection and glucose metabolism and the association with hepatic diseases.

Hepatitis B virus infection reprograms the glucose metabolism
HBV proteins may interact with the key proteins or enzymes in glucose metabolism to interfere with the host glucose metabolism processes.The altered metabolism products may benefit HBV replication and immune escape.HBV is able to hijack cell metabolism of the host, especially the "Warburg effect." 19,20"Warburg effect" is also named as aerobic glycolysis, primarily observed in cancers.It refers to enhanced glucose uptake and lactate secretion even in the presence of enough oxygen for oxidative phosphorylation (OXPHOS). 21Warburg effect may aid in the early expansion of viruses.
The glucose metabolism reprogrammed by HBV is divided into two strategies.First, manipulating the key enzymes in the metabolic process of the host cells to help viral replication.Second, interfering with different phases of immune responses such as virus recognition, antigen intaking, and effector cell response.By interfering with these important biological processes, it exacerbates HBV infection, the development of chronic viral infection, inflammation, liver fibrosis, and even liver cancer.In Table 1, we summarized the recent advancement of the crosstalk between HBV infection and glucose metabolism.

Glucose metabolic reprogramming benefits hepatitis B virus replication
HBV infection alters cellular metabolic processes, including glucose metabolism.In turn, reprogramming of glucose metabolism may facilitate HBV replication.Pyruvate kinase M2 (PKM2) is the last rate-limiting enzyme in glycolysis, and it has two forms: inactive dimer or active tetramer. 33HBsAg interacts with PKM2 by its c-terminal and facilitates the dimerization of PKM2, leading to enhanced aerobic glycolysis. 12Additionally, normal PKM2 activity could repress the expression of HBV proteins.PKM2 agonists TEPP-46 or DASA-58 surprisingly diminishes the growth of immortalized hepatocytes induced by LHBs, which indicates PKM2 agonists are one kind of promising treatment for restraint of HBV infection. 12icroRNA-130a (miR-130a) is reported to be upregulated in occult HBV infection patients' sera. 34It is able to inhibit the formation of cccDNA possibly by adjusting glucose metabolism. 22iR-130a targets pyruvate kinase in liver and red blood cell (PKLR) in the 30 untranslated region and decreases PKLR expression.Pyruvate, as the product of PKLR, is identified as a key molecule that could promote HBV replication.Thus, miR-130a negatively modulates HBV replication by decreasing PKLR expression.Another group obtains similar results that miR-130a directly targets peroxisome proliferator-activated receptor-γ coactivator 1α (PGC1α) and peroxisome proliferator-activated receptor γ (PPARγ) and exerts negative regulation. 25Moreover, in miR-130a expressing cells, the glycolysis is upregulated, and gluconeogenesis is downregulated.And in this report, the expression of miR-130a is downregulated upon HBV infection, 25 which contradicts with the clinical study mentioned above. 34This controversy may be due to different phases of infection.This clinical research showed a significant increase of miR-130a only in occult infection, when the virus is still at a disadvantage.The two reports present different expression patterns of miR-130a after HBV infection.However, they agree in part on the finding that miR-130 regulates the expression of key enzymes in glucose metabolism, which in turn affects HBV replication.Hexosamine biosynthetic pathway (HBP) is a bypass of glucose metabolism.About 2-5% intracellular glucose fluxes into HBP and produces uridine diphosphate-N-acetylglucosamine (UDP-GlcNAc), which could participate in the GlcNAcylation of many proteins by targeting threonine and serine. 35,36It has been proved to be associated with tumor and metabolic diseases. 37,38This pathway is also linked with HBV infection.HBV could induce the expression of GFAT1, the rate-limiting enzyme of HBP, and UDP-GlcNAc increases in the meantime.In turn, the upregulated HBP could promote the replication of HBV and the expression of HBsAg. 32However, another research reveals that the upregulated HBP could also increase antiviral innate immune of the host by GlcNAcylation of SAMHD1, which enhances ability of SAMHD1 to restrict viral DNA synthesis. 39

Glucose metabolic reprogramming mediates hepatitis B virus immune escape
Immune escape is a common phenomenon in both infectious diseases and tumors.HBV also has the ability to mediate immune escape from both innate and adaptive immune systems by targeting a variety of immune molecules and immune cells. 40Recently, glucose metabolism is also involved in HBV escape.
Innate immunity.Type I interferons (IFN-I) are antiviral cytokines produced by histocytes and immune cells, which perform many functions during innate immunity. 41HBV infection affects intracellular glucose metabolic pathways during glycolytic metabolism by converting pyruvate to lactate in lactate dehydrogenase dependent manner to inhibit the expression of interferon and thus mediates immune escape.During HBV infection, the association between AKT and hexokinase 2 (HK2) is enhanced and they are activated by phosphorylation.Activated HK2 forms a ternary complex with voltage-dependent anion channels and mitochondrial antiviral signaling on the outer mitochondrial membrane, which in turn reduces mitochondrial antiviral signaling binding to RIG-I and inhibits type I IFN expression. 24acrophages are important innate immune cells and antigen-presenting cells, which have the ability to phagocytose, present antigens, and modulate the immune response.The activated macrophages have a strong effect on inhibiting production of HBV proteins. 27Notably, the macrophages activated by HBV have enhanced OXPHOS, along with decreased IL-1β secretion. 27nd IL-1β is reported as an inhibitor of PPARα and FOXO3, both of which increase HBV RNA levels. 27This could be a strategy for HBV to bypass local innate immunity.
Furthermore, neutrophil dysfunction is detected in HBV-related acute-on-chronic liver failure patients.The circulating neutrophils of these patients have different phenotypes, along with enhanced phagocytosis and high formation of neutrophil extracellular traps (NETs). 42These neutrophils have active glucose intake and express more glucose transporter 1 (GLUT1), because producing NETs needs the involvement of glucose metabolism. 43The increased NET formation may compensate for the impaired phagocytosis to fight secondary bacterial infection. 42aptive immunity.The relationship between HBV-specific T or B cells and glucose metabolism is also reported.A study compared the metabolic change of HBV-specific T cells and CMV specific T cells in chronic infection. 28GLUT1 and programmed cell death protein 1 (PD-1) is upregulated, which may be associated with the hypoxic environment of the liver.OXPHOS of HBV-specific CD8 + T cells is impaired under galactose culture condition, suggesting that they rely on glycolysis for energy supply.Whether this property is also present in other chronic infections requires additional experimental evidence.
Metabolic changes also occur in B cells.It has been verified that normally HBV could active mTOR pathway of B cell and promote its glycolysis. 44But a comparative clinical study showed decreased glycolysis and OXPHOS in patients with decompensated HBV-related liver cirrhosis (HBV D-LC) patients. 26It may be due to reduced glucose uptake, impaired mitochondrial function, or weak activation of the AKT-mTOR pathway.

Glucose metabolic reprogramming exacerbates liver diseases
The pathology from hepatitis to cirrhosis and HCC is step-by-step and can hardly be reversed without intervention.The basic changes of this process are composed of liver tissue destruction, hepatocyte regeneration, fibrous tissue padding, and tumorigenesis.HBV infection as the main inducement works in almost every step and glucose metabolism acts as an assistor. 45,46irstly, HBV infection reduces the ability of hepatocytes to repair damage by regulating insulin receptor expression.Low expression of insulin receptor in HBV-infected hepatocytes diminishes compensatory regeneration of the liver and increases susceptibility to liver disease. 29Secondly, chronic HBV infection is closely associated with HCC development.HBV induced glucose reprogramming may be involved in this process.
HBx is encoded by the smallest open reading frame in the HBV genome and consists of 154 amino acids.HBx localizes in both the nucleus and cytoplasm.HBx in the nucleus is thought to be a weak transactivator that regulates many viral and cellular promoters. 47HBx has been reported to be closely linked with hepatocarcinogenesis, [48][49][50] which is also related to gluconeogenesis, PPP, and aerobic glycolytic processes.Firstly, HBx can induce high expression of inducible nitric oxide synthase/nitric oxide system, and the latter can boost hepatocyte gluconeogenesis by enhancing expression of glucose-6-phosphatase and phosphoenolpyruvate carboxykinase. 14Secondly, HBx interrupts the Keap1-Nrf2 pathway to make Nrf2 entering nucleus to promote glucose-6-phosphate dehydrogenase (G6PD) transcription and then increases PPP process. 132][53] Besides, overexpression of HBx promotes cancer stemness and enhances intracellular BNIP3L-dependent mitochondrial autophagy and glycolytic metabolism.The glycolysis genes are upregulated, whereas OXPHOS associated genes are downregulated. 31n addition to HBx, other HBV proteins are also reported to be involved in HBV glucose metabolism.HBV pre-S2 mutant could activate mTOR/yin yang 1/myelocytomatosis oncogene pathway to enhance GLUT1 expression, upregulating aerobic glycolysis. 54HBs upregulates the expression of adenylyl cyclase 1 and then activate cAMP/PKA/CREB pathway to increase gluconeogenesis enzymes expression. 30HBc overexpression can upregulate many key enzymes in glucose metabolism including aldolase C (ALDOC), phosphoglycerate kinase 1 (PGK1), and phosphoenolpyruvate carboxykinase (PEPCK). 55INPP1, a gene in glycolytic bypass pathway, is involved in the development of HCC.MINPP1 is downregulated in HBV positive HCC by miRNA-30b-5p.Further studies demonstrate that mRNA-30b-5p-MINPP1 axis promotes the conversion from glucose to 2,3-bisphosphoglycerate and lactate, then promoting HCC tumorigenesis. 56e potential treatments targeting glucose metabolism in hepatitis B virus-related diseases As summarized earlier, aberrant glucose metabolism raised by HBV infection is a common phenomenon.Therefore, developing novel treatments targeting glucose metabolism are promising strategies to treat HBV-related disorders.
Curcumin, a natural drug derived from turmeric, has antiinflammatory, antioxidant, and antitumor activities. 57It can adjust PGC1α and disrupt the reprogramming pathway that promotes gluconeogenesis in HBV infection. 58It is worth mentioning in particular that curcumin also works as a Nrf2 activator in viral infection, 59 and activated Nrf2 is the accomplice of HBV to manipulate PPP pathway in host cells. 13It is not well understood about the exact roles of Nrf2 with different conditions in HBV infection.One possibility is that Nrf2 activation in HBV infection is sustained and excessive, while curcumin-induced activation is transient and physiological. 60he mTOR pathway is an essential bridge connecting HBV and glucose metabolism as mentioned earlier.Sirolimus is an mTOR inhibitor, and its inhibitory effect is enhanced by metformin in a clinical study. 61One hundred and thirty-three HBV-related HCC patients were recruited after liver transplantation. 61They were divided into four groups receiving sirolimus treatment plus metformin, sirolimus alone, and other immunosuppressant treatment in patients with or without concomitant diabetes mellitus.Survival was found to be significantly longer in the combined treatment group, while there was no significant difference in the other three groups.This combination therapy was also used in a mouse model of HCC, and there was a significant reduction in tumor volume. 61e authors did not provide the mechanism of synergism or test for changes in cellular glucose metabolism.But the mTOR pathway is known to be highly correlated with glycolysis, and metformin also affects gluconeogenesis, glucose uptake, and AMPK activation. 62n addition to metformin, canagliflozin as a novel antidiabetic agent that inhibits the sodium-glucose cotransporter has been reported to counteract HCC development by blocking glucose uptake and promoting β-catenin degradation. 63Similar results were also revealed in chronic HBV infection with type 2 diabetes patients. 64

Conclusion and perspective
Here, we discussed the link between HBV infection and glucose metabolism.Similar to other viruses, HBV alters metabolism to provide a favorable intracellular environment for survival and replication.In order to ensure that it has enough nutrients necessary for survival, it employed a variety of strategies to promote aerobic glycolysis 12,23 and PPP 13 so that gluconeogenesis and GLUT1 can raise the glucose reserve. 14,25,55Notably, lactate, a "waste product" of aerobic glycolysis, is used by HBV and other viruses to inhibit the innate immune response. 24,65][28] Until now, interferon and nucleotide analogs are the two main drugs used to treat HBV infection.There are no clinical trials on the addition of glucose metabolism modifying drugs during HBV treatment.However, promising applications have been demonstrated in cellular and animal experiments.Glucose metabolism has become a non-negligible driving force in HBV infection and related disease processes, and future more in-depth and detailed studies in this area will have important theoretical and applied implications for the pathogenesis of HBV infection and even other viral infection-related diseases.

Table 1
Crosstalk between HBV infection and glucose metabolism HBV could induce the expression of GFAT1 and UDP-GlcNAc to promote its replication.Li et al.