SHMT2 Promotes Liver Regeneration Through Glycine-activated Akt/mTOR Pathway

P53/miR-34a/SIRT1 positive feedback loop regulates the termination of liver regeneration

BACKGROUND

The capacity of the liver to restore its architecture and function assures good prognoses of patients who suffer serious hepatic injury, cancer resection, or living donor liver transplantation. Only a few studies have shed light on the mechanisms involved in the termination stage of LR. Here, we attempt to further verify the role of the p53/miR-34a/SIRT1 positive feedback loop in the termination of liver regeneration and its possible relationship with liver cancer.

METHOD

We performed partial hepatectomy (PH) in mice transfected with adenovirus (Ade) overexpressing P53 and adenovirus-associated virus (AAV) overexpressing miR-34a. LR was analyzed by liver weight/body weight, serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels and cell proliferation, and the related cellular signals were investigated. Bile acid (BA) levels during LR were analyzed by metabolomics of bile acids.

RESULTS

We found that the P53/miR-34a/SIRT1 positive feedback loop was activated in the late phase of LR. Overexpression of P53 or miR-34a terminated LR early and enhanced P53/miR-34a/SIRT1 positive feedback loop expression and its proapoptotic effect. T-β-MCA increased gradually during LR and peaked at 7 days after PH. T-β-MCA inhibited cell proliferation and promoted cell apoptosis via facilitating the P53/miR-34a/SIRT1 positive feedback loop during LR by suppressing FXR/SHP. The P53/miR-34a/SIRT1 positive feedback loop was abolished in HCC patients with P53 mutations.

CONCLUSIONS

The P53/miR-34a/SIRT1 positive feedback loop plays an important role in the termination of LR. Our findings showed the molecular and metabolic mechanisms of LR termination and provide a potential therapeutic alternative for treating P53-wild-type HCC patients.

Charged multivesicular body protein 2B ameliorates biliary injury in the liver from donation after cardiac death rats via autophagy with air-oxygenated normothermic machine perfusion

Normothermic machine perfusion (NMP) could provide a curative treatment to reduce biliary injury in donation after cardiac death (DCD) donor livers; however, the underlying mechanisms remain poorly understood. In a rat model, our study compared air-oxygenated NMP to hyperoxygenated NMP and found that air-oxygenated NMP improved DCD functional recovery. Here, we found that the charged multivesicular body protein 2B (CHMP2B) expression was substantially elevated in the intrahepatic biliary duct endothelium of the cold-preserved rat DCD liver after air-oxygenated NMP or in biliary endothelial cells under hypoxia/physoxia. CHMP2B knockout (CHMP2B^-/-) rat livers showed increased biliary injury after air-oxygenated NMP, indicated by decreased bile production and bilirubin level, elevated biliary levels of lactate dehydrogenase and gamma-glutamyl transferase. Mechanically, we demonstrated that CHMP2B was transcriptionally regulated by Kruppel-like transcription factor 6 (KLF6) and alleviated biliary injury through decreasing autophagy. Collectively, our results suggested that air-oxygenated NMP regulates CHMP2B expression through the KLF6, which reduces biliary injury by inhibiting autophagy. Targeting the KLF6-CHMP2B autophagy axis may provide a solution to reducing biliary injury in DCD livers undergoing NMP.

Serine hydroxymethyltransferase 2 knockdown induces apoptosis in ccRCC by causing lysosomal membrane permeabilization via metabolic reprogramming

Serine hydroxymethyltransferase 2 (SHMT2) plays an important role in converting serine to glycine and supplying carbon to one-carbon metabolism to sustain cancer cell proliferation. However, the expression, function, and underlying mechanisms of SHMT2 in clear cell renal cell carcinoma (ccRCC) remain largely unknown. In this study, we demonstrated that SHMT2 was upregulated in ccRCC tissues compared with controls and associated with patient survival. SHMT2 knockdown inhibited proliferation, migration, and invasion in ccRCC cells. Overexpression of SHMT2 promoted tumor progression. Mechanistically, SHMT2 depletion disrupted one-carbon metabolism, increased reactive oxygen species (ROS) levels, and decreased ATP levels via metabolic reprogramming, which destroyed cell homeostasis. The SHMT2 knockdown-induced stress activated autophagy. A mass of autophagosomes fused with lysosomes, resulting in lysosomal membrane permeabilization (LMP) and leakage of lysosomal contents into the cytoplasm, which eventually led to apoptosis. Our work reveals that SHMT2 functions as an oncogenic gene to promote ccRCC progression. SHMT2 depletion induces apoptosis by causing LMP through excessive activation of the autophagy-lysosome pathway via metabolic reprogramming.

The role of SHMT2 in modulating lipid metabolism in hepatocytes via glycine-mediated mTOR activation

Serine hydroxymethyltransferase 2 (SHMT2) converts serine into glycine in the mitochondrial matrix, transferring a methyl group to tetrahydrofolate. SHMT2 plays an important role in the maintenance of one-carbon metabolism. Previously, we found a negative correlation between the serine concentration and the progression of fatty liver disease (FLD). However, little is known about the role of SHMT2 in hepatic lipid metabolism. We established SHMT2 knockdown (KD) mouse primary hepatocytes using RNA interference to investigate the role of SHMT2 in lipid metabolism. SHMT2 KD hepatocytes showed decreased lipid accumulation with reduced glycine levels compared to the scramble cells, which was restored upon reintroducing SHMT2. SHMT2 KD hepatocytes showed downregulation of the mTOR/PPARɣ pathway with decreased gene expression related to lipogenesis and fatty acid uptake. Pharmacological activation of mTOR or PPARɣ overexpression blocked the inhibitory effect of SHMT2 KD on lipid accumulation. We also showed that glycine activated mTOR/PPARɣ signaling and identified glycine as a mediator of SHMT2-responsive lipid accumulation in hepatocytes. In conclusion, silencing SHMT2 in hepatocytes ameliorates lipid accumulation via the glycine-mediated mTOR/PPARɣ pathway. Our findings underscore the possibility of SHMT2 as a therapeutic target of FLD.

Induction of serine hydroxymethyltransferase 2 promotes tumorigenesis and metastasis in neuroblastoma

High-risk neuroblastoma (NB) remains an extremely difficult subgroup to cure and is associated with MYCN amplification. Serine hydroxymethyltransferase 2 (SHMT2) regulates serine metabolism in a myc-dependent manner; it is upregulated in several cancers and is associated with tumor aggressiveness. Akt-2, an important regulator of MYCN via the PI3K/Akt pathway, induces metastatic potential in NB. The association between SHMT2 and PI3K/Akt in hepatocyte regeneration has been well established but its mechanistic interaction in cancer has yet to be clearly elucidated. Herein, we evaluated the exact role of SHMT2 on the PI3K/Akt pathway, in addition to NB tumorigenesis and metastatic potential in vitro. SHMT2 gene expression and overall survival (OS) were assessed. Two human NB cell lines were examined. SHMT2 silencing and overexpression were performed. The downstream effects were analyzed with immunoblotting, RT-qPCR and functional assays were performed. We found SHMT2 gene expression is associated with decreased OS and MYCN amplification. SHMT2 protein and mRNA expression are increased in MYCN-amplified cells. SHMT2 expression has a direct interaction with Akt-2 and MYCN. Induction of SHMT2 increased cellular proliferation, colony formation and cellular migration and SHMT2 expression was increased in metastatic NB cells. We conclude that SHMT2 regulates N-Myc via phosphorylation of Akt-2 and plays an important role in NB tumorigenesis by contributing to cell growth, migration, colony formation and metastasis in vitro.

Glycinergic Signaling in Macrophages and Its Application in Macrophage-Associated Diseases

Accumulating evidences support that amino acids direct the fate decision of immune cells. Glycine is a simple structural amino acid acting as an inhibitory neurotransmitter. Besides, glycine receptors as well as glycine transporters are found in macrophages, indicating that glycine alters the functions of macrophages besides as an inhibitory neurotransmitter. Mechanistically, glycine shapes macrophage polarization via cellular signaling pathways (e.g., NF-κB, NRF2, and Akt) and microRNAs. Moreover, glycine has beneficial effects in preventing and/or treating macrophage-associated diseases such as colitis, NAFLD and ischemia-reperfusion injury. Collectively, this review highlights the conceivable role of glycinergic signaling for macrophage polarization and indicates the potential application of glycine supplementation as an adjuvant therapy in macrophage-associated diseases.

Roles of Mitochondrial Serine Hydroxymethyltransferase 2 (SHMT2) in Human Carcinogenesis

In the last few years, cellular metabolic reprogramming has been acknowledged as a hallmark of human cancer and evaluated for its crucial role in supporting the proliferation and survival of human cancer cells. In a variety of human tumours, including hepatocellular carcinoma (HCC), breast cancer and non-small-cell lung cancer (NSCLC), a large amount of carbon is reused in serine/glycine biosynthesis, accompanied by higher expression of the key glycine synthetic enzyme mitochondrial serine hydroxymethyltransferase 2 (SHMT2). This enzyme can convert serine into glycine and a tetrahydrofolate-bound one-carbon unit, ultimately supporting thymidine synthesis and purine synthesis and promoting tumour growth. In tumour samples, elevated expression of SHMT2 was found to be associated with poor prognosis. In this review, the pivotal roles of SHMT2 in human carcinogenesis are described, highlighting the underlying regulatory mechanisms through promotion of tumour progression. In conclusion, SHMT2 may serve as a prognostic marker and a target for anticancer therapies.

Serine hydroxymethyltransferase 2: a novel target for human cancer therapy

Serine and glycine are the primary sources of one-carbon units that are vital for cell proliferation. Their abnormal metabolism is known to be associated with cancer progression. As the key enzyme of serine metabolism, Serine Hydroxymethyltransferase 2 (SHMT2) has been a research hotspot in recent years. SHMT2 is a PLP-dependent tetrameric enzyme that catalyzes the reversible transition from serine to glycine, thus promoting the production of one-carbon units that are indispensable for cell growth and regulation of the redox and epigenetic states of cells. Under a hypoxic environment, SHMT2 can be upregulated and could promote the generation of nicotinamide adenine dinucleotide phosphate (NADPH) and glutathione for maintaining the redox balance. Accumulating evidence confirmed that SHMT2 facilitates cell proliferation and tumor growth and is tightly associated with poor prognosis. In this review, we present insights into the function and research development of SHMT2 and summarize the possible molecular mechanisms of SHMT2 in promoting tumor growth, in the hope that it could provide clues to more effective clinical treatment of cancer.

Overexpression of SHMT2 Predicts a Poor Prognosis and Promotes Tumor Cell Growth in Bladder Cancer

SHMT2 was overexpressed in many tumors, however, the role of SHMT2 in bladder cancer (BLCA) remains unclear. We first analyzed the expression pattern of SHMT2 in BLCA using the TNMplot, Oncomine, the Cancer Genome Atlas (TCGA), and the Gene Expression Omnibus (GEO) databases. Next, the association between SHMT2 expression and overall survival (OS)/disease-free survival (DFS) in BLCA patients were analyzed using TCGA and PrognoScan database. The correlation between SHMT2 expression and clinicopathology was determined using TCGA database. Furthermore, the genes co-expressed with SHMT2 and their underlying molecular function in BLCA were explored based on the Oncomine database, Metascape and gene set enrichment analysis (GSEA). Finally, the effects of SHMT2 on cell proliferation, cell cycle, and apoptosis were assessed using in vitro experiments. As a results, SHMT2 was significantly overexpressed in BLCA tissues and cells compared to normal bladder tissues and cells. A high SHMT2 expression predicts a poor OS of BLCA patients. In addition, SHMT2 expression was higher in patients with a high tumor grade and in those who were older than 60 years. However, the expression of SHMT2 was not correlated with gender, tumor stage, lymph node stage, and distant metastasis stage. Finally, overexpression of SHMT2 promoted BLCA cell proliferation and suppressed apoptosis, the silencing of SHMT2 significantly inhibited BLCA cell proliferation by impairing the cell cycle, and promoting apoptosis. SHMT2 mediates BLCA cells growth by regulating STAT3 signaling. In summary, SHMT2 regulates the proliferation, cell cycle and apoptosis of BLCA cells, and may act as a candidate therapeutic target for BLCA.

[Protective effect of serine methyltransferase against hepatic ischemia-reperfusion injury in mice]

OBJECTIVE

To investigate the protective effect of serine hydroxymethyl transferase 2 (SHMT2) against hepatic ischemia-reperfusion injury in mice.

METHODS

Sixty C57BL/6 mice were divided equally into sham-operated group, saline adeno-associated virus group (AVV-GFP), and adeno-associated virus silencing group (AAV-SHMT2). The adeno-associated virus and normal saline were injected into the tail vein of the mice 2 weeks before establishment of a 70% ischemia-reperfusion model in the liver. qPCR, Western blotting, immunofluorescence and immunohistochemistry were used to detect the changes of AST/ALT concentration, SHMT2, JNK, NF-κB, caspase-3 and downstream inflammatory factors in the mice, and HE staining was used to observe the pathological damage of the liver tissue in each group; the cell apoptosis in the liver was detected using TUNEL assay.

RESULTS

The expression of SHMT2 increased with time after hepatic ischemia-reperfusion and reached the highest level at 24 h (the relative expression was 1.5, P < 0.05). At 24 h after hepatic ischemia-reperfusion, the levels of AST/ALT in AAV-SHMT2 group (588/416 U/L) were significantly higher than those in the control group (416/345 U/L) and the empty vector group (387/321 U/L) (P < 0.05). Compared with those in the control group and the empty vector group, the level of SHMT2 was significantly decreased in AAV-SHMT2 group (with a relative expression of 0.24, P < 0.05), the levels of p-JNK and p-p65 were significantly increased (relative expression of 0.80 and 0.97, respectively, P < 0.05), and the levels TNF-α and IL-1β were consistently elevated (relative expression levels of 1.6 and 1.2, respectively, P < 0.05). No significant differences were found in these parameters between the empty vector group and the control group (P>0.05).

CONCLUSIONS

SHMT2 may alleviate liver cell apoptosis in mice with hepatic ischemia-reperfusion injury by inhibiting the activation of JNK pathway and excessive activation of NF-κB pathway to reduce hepatic damage.