Altered Central Nervous System Cytokine-Growth Factor Expression Profiles and Angiogenesis in Metallothionein-I+II Deficient Mice

Abstract

Summary:To study the importance of metallothionein-I and -II (MT-I+II) for brain inflammation and regeneration, the authors examined normal and MT-I+II knock-out (MT-KO) mice subjected to a cortical freeze injury. Normal mice showed profound neurodegeneration, inflammation, and gliosis around the injury, which was repaired by 20 days postlesion (dpl). However, in MT-KO mice the lesion-associated inflammation was still present as late as 90 dpl. Scanning electron microscopy demonstrated that the number of capillaries was lower, and ultrastructural preservation of the lesioned parenchyma was poorer in MT-KO mice, suggesting an altered angiogenesis. To gain insight into the mechanisms involved, a number of cytokines and growth factors were evaluated. The number of cells expressing the proinflammatory cytokines IL-1␤, IL-6, and TNF-␣ was higher in MT-KO mice than in normal mice, which was confirmed by RNase protection analysis, whereas the number of cells expressing the growth factors bFGF, TGF␤1, VEGF, and NT-3 was lower. Increased expression of proinflammatory cytokines could be involved in the sustained recruitment of CD-14+ and CD-34+ inflammatory cells and their altered functions observed in MT-KO mice. Decreases in trophic factors bFGF, TGF␤1, and VEGF could mediate the decreased angiogenesis and regeneration observed in MT-KO mice after the freeze lesion. A role for MT-I+II in angiogenesis was also observed in transgenic mice expressing IL-6 under the control of the promoter of glial fibrillary acidic protein gene (GFAP-IL6 mice) because MT-I+II deficiency dramatically decreased the IL-6-induced angiogenesis of the GFAP-IL6 mice. In situ hybridization analysis indicated that the MT-III expression was not altered by MT-I+II deficiency. These results suggest that the MT-I+II isoforms have major regulatory functions in the brain inflammatory response to injury, especially in the angiogenesis process. Key Words: MT-I+II-MT-IIIInflammation-Angiogenesis-Regeneration-Cytokines.Metallothioneins are a family of cysteine-rich, ubiquitous intracellular proteins. In the central nervous system (CNS), MT-I+II are expressed coordinately and are increased in macrophages/microglia and astrocytes during various inflammatory and pathologic conditions, including human neurodegenerative disorders, experimentally induced brain injury, epileptic seizures, brain ischemia, astroglial cell death, metal exposure, stress, and myelin deficiency

Metallothionein rescues hypoxia-inducible factor-1 transcriptional activity in cardiomyocytes under diabetic conditions

“…Our finding in the present study indicates MT plays an important role in VEGF expression in the heart under diabetic conditions through restoration of HIF-1α transcriptional activity. This finding is in an agreement with a previous observation that MT plays a major regulatory role in the angiogenesis process [15].…”

“…MT also plays important roles in other biological functions, such as anti-oxidation. Some studies have shown that the absence of MT results in a reduction of the expression of several angiogenic factors in mice, such as vascular endothelial growth factor (VEGF) [15]. Down-regulation of VEGF in the heart is associated with the increased risk of cardiovascular morbidity and mortality in patients with diabetes [16].…”

Overexpression of metallothioneins, stem cell niches and field cancerization in experimental gliomagenesis

“…(MTOEC) in our findings is clearly different because (a) it is highly and specifically restricted to the subpial area of the spinal cord, at the same location of putative target cell in the ENU carcinogenesis model 6 and (b) the staining pattern of the affected cells is far more intense, affecting both cytoplasm and nucleus, than the eventual findings in positive cells of control animals or in the inflammatory stimulated MT expression, as reported in the literature 10 . The MTOEC herein described are similar to the previously described MTOEC that spread in the colon and liver of mouse treated with a single dose of carcinogen 5,11 .…”

“…It is known that MT is involved in the regulation of the functions of endothelial cells, as well as in their protection against cytotoxic agents 18 . MT knock-out (MT-KO) mice presented dramatically decreased IL-6-induced angiogenesis caused by cortical freeze injury, suggesting that the MT have major regulatory functions in the angiogenesis process 10 . Interestingly, recent data suggest that stem cells of glioblastoma are situated in close proximity to endothelial cells and seem to be dependent on cues from aberrant vascular niches that mimic the normal neural stem cell niche, facilitating communication between these cell types, what may influence the stem cell regulation 19,20 .…”

Metallothioneins and brain injury: What transgenic mice tell us

“…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.…”