Evidence for a protective role of metallothionein-1 in focal cerebral ischemia

Abstract

Metallothioneins (MTs) are a family of metal binding proteins that have been proposed to participate in a cellular defense against zinc toxicity and free radicals. In the present study, we investigated whether increased expression of MT in MT-1 isoform-overexpressing transgenic mice (MT-TG) affords protection against mild focal cerebral ischemia and reperfusion. Transient focal ischemia was induced in control (wild type) and MT-TG mice by occluding the right middle cerebral artery for 45 min. Upon reperfusion, cerebral edema slowly developed and peaked at 24 hr as shown by T2-weighted MRI. The volume of affected tissue was on the average 42% smaller in MT-TG mice compared with control mice at 6, 9, 24, and 72 hr and 14 days postreperfusion (P < 0.01). In addition, functional studies showed that 3 weeks after reperfusion MT-TG mice showed a significantly better motor performance compared with control mice (P = 0.011). Although cortical baseline levels of MT-1 mRNA were similar in control and MT-TG mice, there was an increase in MT-1 mRNA levels in the ischemic cortex of MT-TG mice to 7.5 times baseline levels compared with an increase to 2.3 times baseline levels in control mice 24 hr after reperfusion. In addition, MT-TG mice showed an increased MT immunoreactivity in astrocytes, vascular endothelial cells, and neurons 24 hr after reperfusion whereas in control mice MT immunoreactivity was restricted mainly to astrocytes and decreased in the infarcted tissue. These results provide evidence that increased expression of MT-1 protects against focal cerebral ischemia and reperfusion.

Metallothioneins and brain injury: What transgenic mice tell us

“…The generation of genetically modified mice (119-121) has undoubtedly demonstrated that these proteins are indeed important in the CNS. Thus, mice overexpressing MT-1 were partially protected against mild focal cerebral ischemia and reperfusion, showing lower infarcts and better functional recovery than the controls (97). In accordance, the opposite was observed in MT-1&2-null mice (98), pointing to an essential role of MT-1&2 in coping with ischemic damage of the brain.…”

“…Thus, significant upregulation of these proteins has been observed in a number of human neurological diseases, including Alzheimer's disease (55,(79)(80)(81)(82)), Pick's disease (79), short-course Creutzfeld-Jakob disease (72), amyotrophic lateral sclerosis (83)(84)(85), and multiple sclerosis (86,87). Experiments carried out in animal models fully demonstrated the response of MT-1&2 to brain damage elicited by inflammatory factors such as lipopolysaccharides (11, 15, 24, 88), stress (62,(89)(90)(91), glutamate analogues (37,51,59,(92)(93)(94)(95), cryogenic injury (28,32,66,71), stroke/ischemia (17, [95][96][97][98], familial amyotrophic lateral sclerosis models (38,67,99,100), multiple sclerosis models (101)(102)(103), and gliotoxins (104)(105)(106).…”

Cellular and Molecular Pathways of Ischemic Neuronal Death

“…The Zn 2+ translocation was observed in degenerating neurons after transient forebrain ischemia (Koh et al, 1996;Suh et al, 2000). This ischemic neuronal death was prevented by the blockade of Zn 2+ translocation with Ca-EDTA, or the overexpression of metallothionein-1, a Zn 2+ -binding protein (van Lookeren et al, 1999). Zn 2+ ions enter into target cells through voltage-gated calcium channels (VGCC), NMDA, or AMPA/kainate glutamate receptors that are permeable to Ca 2+ , Na + /Ca 2+ exchanger, or Zn 2+ transporter (Freund and Reddig, 1994;Koh and Choi, 1994;Sensi et al, 1997;Sensi et al, 1999;Colvin et al, 2000).…”

Rising Zinc: A Significant Cause of Ischemic Neuronal Death in the CA1 Region of Rat Hippocampus

“…One proposed buffering system is that performed by metallothioneins, which are amplified in number in response to Zn 2 + elevation, and thus provide strong buffering capacity for cytosolic Zn 2 + (Maret, 1994). A protective function of the Zn 2 + -binding protein metallothionein in ischemic cell death has been proposed (van Lookeren Campagne et al, 1999). The influx of Ca 2 + and the subsequent triggering of Ca 2 + release from intracellular stores are generally believed to mediate the rapid cellular demise seen in ischemia.…”