Metallothioneins Are Upregulated in Symptomatic Mice with Astrocyte-Targeted Expression of Tumor Necrosis Factor-α

Abstract

Transgenic mice expressing TNF-␣ under the regulatory control of the GFAP gene promoter (GFAP-TNF␣ mice) exhibit a unique, late-onset chronic-progressive neurological disorder with meningoencephalomyelitis, neurodegeneration, and demyelination with paralysis. Here we show that the metallothionein-I ؉ II (MT-I ؉ II) isoforms were dramatically upregulated in the brain of symptomatic but not presymptomatic GFAP-TNF␣ mice despite TNF-␣ expression being present in both cases. In situ hybridization analysis for MT-I RNA and radioimmunoassay results for MT-I ؉ II protein revealed that the induction was observed in the cerebellum but not in other brain areas. Increased MT-I RNA levels occurred in the Purkinje and granular neuronal layers of the cerebellum but also in the molecular layer. Reactive astrocytes, activated rod-like microglia, and macrophages, but not the infiltrating lymphocytes, were identified as the cellular sources of the MT-I ؉ II proteins. In situ hybridization for MT-III RNA revealed a modest increase in the white matter of the cerebellum, which was confirmed by immunocytochemistry. MT-III immunoreactivity was present in cells which were mainly round or amoeboid monocytes/macrophages. The pattern of expression of the different MT isoforms in the GFAP-TNF␣ mice differed substantially from that described previously in GFAP-IL6 mice, demonstrating unique effects associated with the expression of each cytokine. The results suggest that the MT expression in the CNS reflects the inflammatory response and associated damage rather than a direct role of the TNF-␣ in their regulation and support a major role of these proteins during CNS injury.

Metallothioneins are multipurpose neuroprotectants during brain pathology

“…During CNS inflammation, major MT‐I + II regulatory factors are proinflammatory cytokines and especially interleukin (IL)‐6 [1]. Accordingly, IL‐6, IL‐3, tumor necrosis factor (TNF)‐α, macrophage‐colony stimulating factor (M‐CSF), and interferons increase brain MT‐I + II expression in a cytokine‐specific manner as demonstrated by using transgenic mice with cytokine overexpression [48–51] or cytokine deficiency [29,52–55].…”

Metallothioneins and brain injury: What transgenic mice tell us

“…Studies of in situ hybridization (21, 24-28) and immunohistochemistry (19,21,(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38), have demonstrated that MT-1&2 expression occurs throughout the brain and spinal cord, and that the principal cellular source is the astrocyte, particularly following injury. Significant MT-1&2 expression is also found in ependymal cells, epithelial cells of the choroid plexus, meningeal cells of the pia mater and endothelial cells of blood vessels, while neurons appear to express very low levels.…”

“…Although in most cases no thorough cell identification has been established by robust methods such as double labeling or use of the MT-3 KO mice as controls, in the normal brain it appears that the MT-3 mRNA signal is more consistent with neuronal than with glial cells, with astrocyte MT-3 upregulation eventually occurring following injury (26,27,36,53,(56)(57)(58)(59)(60)(61)(62)(63)(64)(65)(66)(67)(68). In contrast to the MT-3 messenger, the MT-3 protein has been shown to be present mainly in astrocytes by a number of studies (36,40,65,66,(69)(70)(71)(72)(73)(74). Other reports, however, show MT-3 protein presence basically in neurons (63,64,(75)(76)(77).…”

Differential role of tumor necrosis factor receptors in mouse brain inflammatory responses in cryolesion brain injury

“…Several CNS pathologies involve inflammatory mediators, including stroke, brain trauma, seizures, ischemia (Olanow, 1993;Yankner, 1996;Price et al, 1998;Penkowa et al, 1999Penkowa et al, , 2000aCarrasco et al, 2000), and neurodegenerative disorders such as Alzheimer's and Parkinson's diseases (for review see Campbell, 1998;Culpan et al, 2003;Ethell and Buhler, 2003;McGeer and McGeer, 2003;Eissner et al, 2004). Inflammation may be a protective mechanism that isolates the injured area, destroys affected cells, and repairs the extracellular matrix; however, chronic presence of inflammatory mediators may be followed by increased oxidative stress and cell death (for review see Muñoz-Fernandez and Fresno, 1998;Hicks et al, 1999;Shohami et al, 1999;Sayer et al, 2002;Rothwell, 2003).…”