Up-regulation of Metabotropic glutamate receptor 3 (mGluR3) in rat fibrosis and cirrhosis model of persistent hypoxic condition

Glutamate is the major excitatory neurotransmitter in the central nervous system, and evidence for peripheral glutamatergic fibers in mammals is still lacking. However, glutamate receptors have been identified in peripheral organs, including taste buds, myenteric plexus, and pancreatic islet cell. Protection against anoxic damage could also be explained by mechanisms mediated by postsynaptic mGluR2 or mGluR3, such as the inhibition of membrane excitability resulting from a reduction of cAMP formation by a G-protein-dependent modulation of ion channels. In addition, activation of mGluR3 present in glial cells may contribute to neuroprotection by enhancing the production of death. Thus, mGluR2/3 behaves potentially as a major defensive mechanism anoxia-tolerant species. There are a few reports for the regional pattern of hypoxic damage, which was inversely related to the expression of mGluR2/3. The aim of this study was to characterize the expression of mGluR3 in hypoxic liver in experimental model of rat liver. Proteomic analysis of protein extracts from CCl₄-induced cirrhotic liver revealed the presence of the mGluR3. The presence of mGluR3 in the cirrhotic liver was confirmed by immunohistochemical analysis. There were a number of macrophages expressing mGluR3 mainly in the fibrous septa. After 2 weeks recovery, however, most of mGluR3 positive macrophages disappeared with collagen fibers. These results demonstrate that mGluR3 involved in the liver in response to persistent hypoxic status such as fibrotic/cirrhotic condition, and suggest that the expression of mGluR3 may be a key role functional metabolism and viability in the liver by interacting with the glutamate receptors in vivo.