Role of DDAH/ADMA pathway in TGF-β1-mediated activation of hepatic stellate cells

The Power of Plasticity-Metabolic Regulation of Hepatic Stellate Cells

Hepatic stellate cells (HSCs) are resident non-parenchymal liver pericytes whose plasticity enables them to regulate a remarkable range of physiologic and pathologic responses. To support their functions in health and disease, HSCs engage pathways regulating carbohydrate, mitochondrial, lipid, and retinoid homeostasis. In chronic liver injury, HSCs drive hepatic fibrosis and are implicated in inflammation and cancer. To do so, the cells activate, or transdifferentiate, from a quiescent state into proliferative, motile myofibroblasts that secrete extracellular matrix, which demands rapid adaptation to meet a heightened energy need. Adaptations include reprogramming of central carbon metabolism, enhanced mitochondrial number and activity, endoplasmic reticulum stress, and liberation of free fatty acids through autophagy-dependent hydrolysis of retinyl esters that are stored in cytoplasmic droplets. As an archetype for pericytes in other tissues, recognition of the HSC's metabolic drivers and vulnerabilities offer the potential to target these pathways therapeutically to enhance parenchymal growth and modulate repair.

Curcumin attenuates endothelial cell fibrosis through inhibiting endothelial-interstitial transformation

Curcumin (Cur) has various pharmacological activities, including anti-inflammatory, antiapoptotic and anticancer effects. However, there is no report on the effect of Cur on endothelial cell fibrosis. This study was designed to investigate the effect and mechanism of Cur on endothelial cell fibrosis. An endothelial cell fibrosis model was established by using transforming growth factor (TGF) induction. Proliferation assays, qRT-PCR, western blotting and immunostaining were performed to investigate the effects and mechanism of Cur on endothelial cell fibrosis. We found that in human umbilical vein endothelial cells (HUVECs), TGF-β1 treatment significantly decreased the expression of nuclear factor erythroid-2-related factor 2 (NRF-2), dimethylarginine dimethylaminohydrolase-1 (DDAH1), and VE-cadherin, the secretion of cellular nitric oxide (NO) and the activity of nitrous oxide synthase (NOS), while asymmetric dimethylarginine (ADMA) and the release of inflammatory factors were elevated. Immunofluorescence showed decreased CD31 and increased α-smooth muscle actin (α-SMA). Overexpression of NRF-2 significantly attenuated the effects of TGF-β1, while downregulation of DDAH1 potently counteracted the effect of NRF-2. In addition, ADMA treatment resulted in similar results to those of TGF-β1, and Cur significantly attenuated the effect of TGF-β1, accompanied by increased VE-cadherin, DDAH1 and NRF-2 and decreased matrix metalloproteinase-9 (MMP-9) and extracellular regulated protein kinases 1/2 (ERK1/2) phosphorylation. The NRF-2 inhibitor ML385 had the opposite effect as that of Cur. These results demonstrated that Cur inhibits TGF-β1-induced endothelial-to-mesenchymal transition (EndMT) by stimulating DDAH1 expression via the NRF-2 pathway, thus attenuating endothelial cell fibrosis.

TGF-β1 signaling activates hepatic stellate cells through Notch pathway

Hepatic stellate cells (HSCs), as the most important stromal cells in the liver microenvironment, play crucial roles in hepatic fibrosis, hepatocellular carcinoma, liver regeneration and fetal liver development after transdifferentiating into myofibroblasts (MFs). Transforming growth factor β1 (TGF-β1), as an important polyergic cytokine, is involved in HSCs activation process. However, the specific mechanisms of HSCs transdifferentiation process are not clearly demonstrated. Here we added exogenous recombinant TGF-β1 protein and transforming growth factor β receptor 1 (TGF-βR1) inhibitor SB431542 into mouse HSCs to detect the detailed impact of TGF-β1 signaling on HSCs activation. TGF-β1 signaling significantly increased phosphorylated (P)-Smad2/3 level and promoted Smad2/3 translocation from the cytoplasm to the nucleus, which also caused transdifferentiation of HSCs into MFs. Importantly, TGF-β1 signaling also resulted in high expression of Notch pathway markers Notch1, Jagged1, Hes1 in HSCs. In contrast, expression of those above markers in mouse HSCs were obviously decreased after hampering TGF-β1 signaling via TGF-βR1 inhibitor SB431542. To further examine the effect of Notch pathway on HSCs activation process, TGF-β1-stimulated HSCs and control HSCs were treated with or without LY450139, a specific inhibitor of Notch pathway. LY450139 evidently decreased the expression of Notch1 and MFs marker α-smooth muscle actin (α-SMA) expression in HSCs. These above results may provide a novel insight that TGF-β1 signaling controls HSCs activation process through regulating the expression of Notch pathway markers.

High glucose promotes hepatic fibrosis via miR‑32/MTA3‑mediated epithelial‑to‑mesenchymal transition

Hepatic fibrosis is characterized by the aberrant production and deposition of extracellular matrix (ECM) proteins. Growing evidence indicates that the epithelial‑mesenchymal transition serves a crucial role in the progression of liver fibrogenesis. Although a subset of microRNAs (miRNAs or miRs) has recently been identified as essential regulators of the EMT gene expression, studies of the EMT in hyperglycemic‑induced liver fibrosis are limited. In the current study, it was observed that high glucose‑treated AML12 cells occurred EMT process, and miR‑32 expression was markedly increased in the liver tissue of streptozotocin‑induced diabetic rats and in high glucose‑treated AML12 cells. Additionally, the contribution of the EMT to liver fibrosis by targeting metastasis‑associated gene 3 (MTA3) under hyperglycemic conditions was suppressed by AMO‑32. The results indicated that miR‑32 and MTA3 may be considered as novel drug targets in the prevention and treatment of liver fibrosis under hyperglycemic conditions. These finding improves the understanding of the progression of liver fibrogenesis.