Histidine kinase NME1 and NME2 are involved in TGF-β1-induced HSC activation and CCl4-induced liver fibrosis.

Histidine phosphorylation (pHis) was first reported in 1962. There are few studies on pHis because of the thermal and acidic instability of pHis and the lack of specific methods to detect it. pHis has two isomers of 1-phosphate histidine (1-pHis) and 3-phosphate histidine (3-pHis). pHis antibodies have been developed recently and have promoted research in this field. In this study, we established a CCl4-induced liver fibrosis model in C57 mice and a TGF-β1-induced HSC activation model in LX-2 cells, to study the role of histidine phosphorylation. The expression of histidine kinases NME1 and NME2 was increased, histidine phosphatase PGAM5 and PHPT1 was unchanged, and 1-pHis and 3-pHis were increased in the in vivo and in vitro models. The expression of LHPP was decreased in the in vivo model but not in the in vitro model. To further study the role of NME1, NME2, and histidine phosphorylation in HSC activation, we silenced NME1 or NME2 and administered TGF-β1 in LX-2 cells. The results showed silencing NME1 or NME2 decreased TGF-β1-induced pHis levels and the expression of α-SMA and COL1A1, indicating the activation of HSC was suppressed. Then, we found the inhibitory effect on HSC activation is due to reduced phosphorylation of Smad2 and Smad3. In summary, our studies indicate that NME1 and NME2 are involved in TGF-β1-induced HSC activation and CCl4-induced liver fibrosis, which may be mediated by histidine phosphorylation.