CNS Wound Healing Is Severely Depressed in Metallothionein I- and II-Deficient Mice

Abstract

To characterize the physiological role of metallothioneins I and II (MT-I+II) in the brain, we have examined the chronological effects of a freeze injury to the cortex in normal and MT-I+II null mice. In normal mice, microglia/macrophage activation and astrocytosis were observed in the areas surrounding the lesion site, peaking at approximately 1 and 3 d postlesion (dpl), respectively. At 20 dpl, the parenchyma had regenerated. Both brain macrophages and astrocytes surrounding the lesion increased the MT-I+II immunoreactivity, peaking at approximately 3 dpl, and at 20 dpl it was similar to that of unlesioned mice. In situ hybridization analysis indicates that MT-I+II immunoreactivity reflects changes in the messenger levels. In MT-I+II null mice, microglia/macrophages infiltrated the lesion heavily, and at 20 dpl they were still present. Reactive astrocytosis was delayed and persisted at 20 dpl. In contrast to normal mice, at 20 dpl no wound healing had occurred. The rate of apoptosis, as determined by using terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling, was drastically increased in neurons of ipsilateral cortex of the MT-I+II null mice. Our results demonstrate that MT-I+II are essential for a normal wound repair in the CNS, and that their deficiency impairs neuronal survival.

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

“…Early studies suggested that MT-I ϩ II could have significant antioxidant capacity and functions (32,55,63), and recent reports with transgenic mice overexpressing these MT isoforms and with MT-I ϩ II KO mice fully support such roles (22,28,37,39,40,42,43). We have recently shown that the inflammatory response to glial cell death and the wound healing capacity of the CNS is severely impaired in MT-I ϩ II KO mice (49,50), suggesting a major role of these MT isoforms during CNS injury. MT-III was discovered as an inhibitory neuronal growth factor (in vitro) that appeared to be decreased in Alzheimer's disease brains (64); the latter, however, has not been confirmed (2,9,21).…”

“…Taken together, the results suggest that the brain MT-I ϩ II isoforms are induced in conditions of significant injury to the CNS and that this induction could be coupled to the increased oxidative stress produced. Recent results with MT-I ϩ II KO mice (49) give a rationale for such upregulation, demonstrating a significant role of these proteins for CNS wound healing.…”

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.…”

“…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).…”

“…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. Other studies with transgenic mice have equally involved MT-1&2 as important proteins following damage elicited by kainic acid-induced seizures (94), gliotoxins (105, 122), 6-hydroxydopamine (123), amyotrophic lateral sclerosis (38, 100), multiple sclerosis (103,124), traumatic brain injury (28,125,126), and transgenic IL-6-induced neuropathology (127)(128)(129). All of the above are presumably quite different models of brain injury, yet the general impression is that MT-1&2 have similar effects in all cases, namely, decreasing oxidative stress, inflammation and apoptosis in the CNS.…”