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

Abstract

Asymmetric dimethylarginine (ADMA) is catalyzed by the enzyme dimethylarginine dimethylaminohydrolase (DDAH) in humans, and the role for ADMA has been associated with hepatic fibrogenesis. Transforming growth factor‑β (TGF‑β) has been shown to mediate the myofibroblastic transformation of quiescent hepatic stellate cells (HSCs), a pivotal step in liver fibrogenesis. However, the underlying molecular mechanisms are not well understood. Accumulation of ADMA due to low activity of DDAH has been reported to be associated with liver damage and hepatic fibrosis. In this study, the role of the DDAH/ADMA pathway in the TGF‑β1‑induced HSC activation was assessed. Freshly harvested primary HSCs from rat liver were used in this study. It was demonstrated that TGF‑β1 treatment significantly suppressed the DDAH protein expression and activity, and increased levels of ADMA in the culture medium of rat primary HSCs. Notably, the TGF‑β1‑mediated effects on DDAH/ADMA were significantly abrogated by the p38 mitogen activated protein kinase specific inhibitor, SB203580. Furthermore, it was demonstrated that excessive ADMA led to an increase in the number of TGF‑β1‑positive HSCs and induced the expression of α‑smooth muscle actin and collagen type I in rat primary HSCs. In addition, rat primary HSCs exposed to excessive ADMA showed a significant increase in the expressions of α‑SMA and collagen type I. Finally, it was revealed that ADMA treatment promoted the proliferation of rat primary HSCs. In conclusion, the results obtained from the study suggest a potentially novel role for the ADMA/DDAH1 signaling pathway in TGF‑β1‑induced HSC activation, and along with the studies of others, suppression of the ADMA/DDAH1 pathway may be an alterative approach for the treatment of liver fibrosis.

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

“…Previous studies have demonstrated that hyperglycemia in diabetic patients stimulates HSC activation and proliferation, and contributes to the development of hepatic fibrosis (37,38). EMT is an indispensable mechanism in embryogenesis, development and tissue remodeling, that contributes to the progression of organ fibrosis and cancer (39).…”

A multicentric consortium study demonstrates that dimethylarginine dimethylaminohydrolase 2 is not a dimethylarginine dimethylaminohydrolase

“…Our data are consistent with previous observations in bovine aortic endothelial cells, in which knockdown of DDAH2, in contrast to knockdown of DDAH1, did not affect total DDAH activity 53 . As acknowledged in the introduction section of this manuscript, the results of previous cell culture studies investigating the effect of DDAH2 expression modulation on ADMA metabolism are contradictory; however, an advantage of our studies and the experiments in bovine aortic endothelial cells performed by Pope and colleagues is that we measured DDAH activity in cell lysates using a highly sensitive and reliable stable isotope-based method, whereas most of the prior cell culture studies simply measured ADMA concentrations in culture medium or cell lysates 31 , 54 , 55 . Our results, however, contradict the previous observation that DDAH2 overexpression increased total DDAH activity in microvascular endothelial cells, where DDAH activity was also measured by an isotope-based method 56 .…”

Curcumin attenuates endothelial cell fibrosis through inhibiting endothelial–interstitial transformation

“…Abnormal EndMT refers to the process in which endothelial cells gradually lose their original morphology, phenotype and function and obtain the morphology, phenotype and function of mesenchymal cells such as fibroblasts or myofibroblasts. [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] The expression of VE-cadherin, a specific marker of endothelial cells, is gradually weakened or lost, and the myofibroblast-specific marker α-SMA is expressed instead. 35 Studies have shown that many regulatory factors are involved in the EndMT, of which TGF-β1 is considered to be the most potent factor in the EndMT and myocardial fibrosis.…”

“…Studies have found that increased expression of DDAH inhibits matrix metalloproteinase-9 (MMP9), ADMA, epidermal growth factor receptor (EGFR) and extracellular regulated protein kinases (ERK) signalling pathways, while TGF-β1 inhibits the expression and activity of DDAH, thereby inducing ADMA. 23,24 In addition, studies have shown that TGF-β1 significantly inhibits the expression and activity of nuclear factor erythroid-2-related factor 2 (NRF-2), which is a potential therapeutic target for liver fibrosis. 25 Curcumin (Cur) is a polyphenolic substance that is naturally extracted from the rhizome of turmeric plants and has antifibrotic, anti-inflammatory, antioxidant and hypolipidaemic effects.…”