Role of Glucocorticoids on Rat Brain Metallothionein-I and-III Response to Stress

Abstract

The metallothionein (MT) gene family consists of four members (MT-I through -IV) that are tightly regulated during development. Whereas MT-I and MT-II are widely expressed isoforms, MT-III has been found to be mainly expressed in the central nervous system in adult animals, and is the only isoform that inhibits survival and neurite formation of cortical neurons in vitro. A number of models of brain injury have been shown to affect MT-III mRNA levels, which has been suggested to be related to the putative neurotrophic role of this protein. However, a stress response will presumably be associated to the brain injury which could, in turn, drive MT-III regulation. In the present report the effect of a classical stress model, immobilization stress, on brain MT regulation has been studied in rats. MT-I+II protein levels were measured by radioimmunoassay in up to eight brain areas and, as expected, it was found that stress increased selectively MT-I+II levels. Adrenalectomy (ADX) had a general decreasing effect on basal MT-I+II levels; however, ADX blunted the MT-I+II response to stress in cerebellum and presumably in frontal cortex and medulla plus pons but not in the hypothalamus. MT-I mRNA measurements were in accordance with the MT-I+II protein levels in the brain areas studied. In contrast to MT-I mRNA, MT-III mRNA levels of brain cortex tended to decrease during stress, although this effect was not statistically significant. ADX also tended to decrease basal MT-III mRNA levels. Northern blot assays of pooled mRNAs suggested similar differential regulation of these two brain MT isoforms in the cerebellum. These results indicate that glucocorticoids mediate brain MT-I+II response to stress in some but not all brain areas, that a role of these hormones is likely also for MT-III, and that the regulation of MT isoforms differs substantially in the brain.

Metallothionein: the multipurpose protein

“…It has been proposed that MT-3 has a different function in the brain to that of MT-1 and -2. Supporting this viewpoint are the observations that (i) MT-3 is poorly induced and appears to be regulated differently [254,256], (ii) its expression pattern is different, being predominantly found in the hippocampal neurones which sequester Zn in synaptic vesicles and (iii) it is the only MT isoform that has neuroinhibitory activity, first demonstrated by its inhibition of survival and neuritic sprouting of rat cortical neurones in culture [251]. At physiological pH, MT-3, which contains a six-amino-acid (three glutamates) insertion at position 55, is more acidic than other MT isoforms.…”

“…MT-3 is associated predominantly with neurones and the choroid plexus epithelium, whereas MT-1 and -2 are found mainly in astrocytes [255]. MT-1 and -2 genes are coordinately expressed and together respond to a variety of inducers, including metals, oxidants, hormones and cytokines [254,256]. The nature of these inducers and the relative abundance of MT-1 and -2 in astrocytes, which are intricately linked with neurones, suggest that these isoforms function chiefly to protect the brain from oxidative intermediates which arise during stress, infection or inflammation.…”

Antiserum specific for the intact isoform-3 of metallothionein

“…The isoforms, MT3 and MT1, respond differently to zinc deprivation of cells in culture with only MT1 being down-regulated in these cells [7]. Transcriptional regulation of MT3 levels is differentially regulated compared to MT1 and MT2 [8][9][10][11]. These data suggest that MT3 is not involved in metal ion homeostasis, as the MT1 and MT2 isoforms seem to be.…”

Metallothioneins I/II Expression in Rat Strains with Genetically Different Susceptibility to Experimental Autoimmune Encephalomyelitis

“…3C, 4C), i.e. in the brain areas that are usually involved in the response to stress [44]. However, it should be emphasized that GCs in the brain often exert different - even opposed - effects depending on the concentration of GCs and duration of exposure, on the type of implicated cells in affected brain areas (microglia, astroglia or neurons), as well as on the type of receptors for GCs (mineraloreceptors vs. glucoreceptors) [reviewed in [39]].…”