Competitive Reverse Transcriptase–Polymerase Chain Reaction Shows That Dietary Zinc Supplementation in Humans Increases Monocyte Metallothionein mRNA Levels1–3

Northern blotting, in situ hybridization, and oligodeoxyribonucleotide excess solution hybridization were used to quantitate metallothionein-I (MT-I) and MT-II mRNAs in mouse testes. Testes from sexually mature adults contained high levels of both MT mRNAs (approximately 10-fold higher than those in control adult liver). Testicular MT mRNA levels were age dependent, being low the first 2 weeks after birth and increasing slowly thereafter to maximal levels in the adult (by 9 weeks after birth). In the adult testis, in situ hybridization indicated that only cells within the adluminal compartment (germ cells) of the seminiferous tubules contain high levels of MT mRNA. The appearance of cells containing elevated levels of MT mRNA during development was delayed from the onset of spermatogenesis. In situ hybridization suggested that MT mRNA accumulates after the initial differentiation of primary spermatocytes and is maintained in spermatids. Pachytene spermatocytes (PSC) and round spermatids (RTD) isolated from adult testes contained both MT-I and MT-II mRNAs in levels equivalent to those found in zinc-treated hepatocytes, whereas very low levels of MT mRNA were detected in isolated Sertoli cells (ST). In situ hybridization suggested that MT mRNA was present at only basal levels in interstitial, spermatogonial, and mature sperm cells at all developmental stages examined. Northern blot and in situ hybridization to sulfated glycoprotein-2 (SGP-2) mRNA, a ST-specific transcript, showed that SGP-2 mRNA is high in the testis of 1-week-old mice and decreases gradually to a lower level in the adult. In situ detection of this mRNA was consistent with the location of ST in the testis. SGP-2 mRNA was abundant in ST and rare in PSC and RTD preparations. Analysis of pulse-labeled proteins from isolated PSC and RTD indicated that these cells actively synthesize MT-I and MT-II. The high levels of MT mRNA in adult testes were not increased substantially after systemic injection of cadmium, zinc, or bacterial lipopolysaccharide. In marked contrast, these treatments led to dramatically increased levels of hepatic and ovarian MT mRNA. This study establishes that the MT genes are actively expressed in a developmentally regulated fashion in the male germ cells of the mouse. This suggests a role for MT in the process of spermatogenesis.

Metallothionein gene expression under different time in testicular Sertoli and spermatogenic cells of rats treated with cadmium

Metallothionein Expression Is Increased in Monocytes and Erythrocytes of Young Men during Zinc Supplementation , ,

The effects of aging and acupuncture on brain MT1 and MT3 mRNA levels in senescence-accelerated mice (SAMP10) and accelerated senescence resistant mice (SAMR1) were analyzed by Northern blot analysis. Both MT1 and MT3 mRNA levels in SAMR1 were increased significantly from birth to month 4 and decreased gradually thereafter. In SAMP10, the MT3 mRNA level followed the same pattern as in SAMR1 before month 4, then decreased from month 4 to 6, but was over-expressed and exceeded the previous level at month 8. The MT1 mRNA expression in SAMP10 showed a zigzag pattern. Of two groups of SAMP10 mice treated with acupuncture, the xingnao group (PC6 and Du26 as acupoints) and the zibuganshen group (BL18 and BL23 as acupoints), both showed a higher MT1 mRNA level and a lower MT3 mRNA level than the age-matched control group. Meanwhile, in both of the acupuncture groups, the ratios of MT3 to MT1 were down-regulated to the normal range. Overall, these results suggested that over-expression of MT3 mRNA and the increase in MT3 to MT1 ratios in SAMP10 were correlated with aging, and could be an important physiological and pathological event in the aging process. Acupuncture altered the expression levels of MT1 and MT3 mRNA and differences between the effects of the two stimulated acupoints were seen. Therefore, maintenance of the balance between MTs mRNA expression and correct MTs concentrations is crucial for brain-endocrine-immune response and normal aging. Acupuncture could improve zinc ion bioavailability, by maintaining the balance between MT1 and MT3 mRNA expression levels and might explain one of the mechanisms by which acupuncture treatments defer aging and treat some age-related neurodegenerative diseases.

The expression of metallothionein genes (MT-I and MT-II) was shown to be enhanced within 2 h of addition of 2.5-5 mM sodium butyrate to cultures of teratocarcinoma cells. Both undifferentiated stem cells (F9 and OC15) and differentiated cells (PSA5E and OC15 END) reacted similarly to butyrate by increased accumulation of MT mRNAs. As expected, all of the teratocarcinoma cells that were tested also responded to Zn2+ and Cd2+ by 5- to 10-fold increases in MT mRNA accumulation within 2-24 h of metal addition to the culture media. Surprisingly, MT genes in cells pretreated with butyrate were hypersensitive to metal induction, and this was demonstrated by accumulated transcript levels and by synthesis of MT protein. The maximal metal response was obtained by exposure of cells to butyrate for around 5-8 h together with 10 microM heavy metals. Metal additions to culture media over a range of concentrations and times only induced half the levels of MT mRNA that were achieved by butyrate plus metals. Butyrate enhanced the rate of accumulation of MT mRNA in response to metals, increased the sensitivity of the MT gene to metals, and protected cells from toxic effects of high concentrations of metals. The butyrate and metal ion responses were selective in that no accumulation of c-myc, c-fms, HSP-70, or AFP mRNA was detected. However, c-fos mRNA accumulated in cells exposed to toxic concentrations of metals (50 microM and higher) and this was also potentiated by butyrate treatment. These results suggest that butyrate alters the chromatin conformation of both the MT-I and MT-II genes leading to an accentuated transcriptional response to metals.

Effect of molybdenum on the acute toxicity of mercuric chloride. IV. Effect of molybdenum on mercury-mediated metallothionein mRNA induction

In Vivo Expression of Metallothionein in Rat Alveolar Macrophages and Type II Epithelial Cells Following Repeated Cadmium Aerosol Exposures

White adipose tissue (WAT) has been examined to determine whether the gene encoding metallothionein (MT), a low-molecular-weight stress response protein, is expressed in the tissue and whether MT may be a secretory product of adipocytes. The MT-1 gene was expressed in epididymal WAT, with MT-1 mRNA levels being similar in lean and obese (ob/ob) mice. MT-1 mRNA was found in each of the main adipose tissue sites (epididymal, perirenal, omental, subcutaneous), and there was no major difference between depots. Separation of adipocytes from the stromal-vascular fraction of WAT indicated that the MT gene (MT-1 and MT-2) was expressed in adipocytes themselves. Treatment of mice with zinc had no effect on MT-1 mRNA levels in WAT, despite strong induction of MT-1 expression in the liver. MT-1 gene expression in WAT was also unaltered by fasting or norepinephrine. However, administration of a beta(3)-adrenoceptor agonist, BRL-35153A, led to a significant increase in MT-1 mRNA. On differentiation of fibroblastic preadipocytes to adipocytes in primary culture, MT was detected in the medium, suggesting that the protein may be secreted from WAT. It is concluded that WAT may be a significant site of MT production; within adipocytes, MT could play an antioxidant role in protecting fatty acids from damage.

Metallothionein mRNA in Monocytes and Peripheral Blood Mononuclear Cells and in Cells from Dried Blood Spots Increases after Zinc Supplementation of Men

Metallothionein gene expression in peripheral lymphocytes and renal dysfunction in a population environmentally exposed to cadmium

In the nematode Caenorhabditis elegans, dauer formation, stress resistance, and longevity are determined in part by DAF-2 (insulin receptor-like protein), AGE-1 (phosphatidylinositol-3-OH kinase catalytic subunit), and DAF-16 (forkhead transcription factor). Mutations in daf-2 and age-1 result in increased resistance to heat, oxidants, and UV. We have discovered that daf-2 and age-1 mutations result in increased Cd and Cu ion resistance in a 24 h toxicity assay. Lethal concentration (LC50) values for Cd and Cu ions in daf-2 and age-1 mutants were significantly (P<0.001) higher than in wild-type nematodes. However, LC50 values in daf-16;age-1 mutants were not significantly different, implying that metal resistance is influenced by a DAF-16-related function. As metallothionein (MT) proteins play a major role in metal detoxification, we examined the expression of MT genes both under noninducing conditions and after exposure to sublethal and acute heavy metal stress. MT1 mRNA levels were significantly (P<0.05) higher in daf-2 mutants compared to age-1 mutants and wild-type C. elegans under basal conditions. After 10 mM Cd treatment, induction of MT1 and MT2 mRNA was three- and twofold higher, respectively, in daf-2 mutant worms than in wild-type. However, a sublethal concentration of Cd (0.1 mM) resulted in even higher (three- to sevenfold) levels of both MT mRNAs in all strains. Cu did not induce MT1 or MT2 mRNAs. These results are consistent with a model in which the insulin-signaling pathway determines life span through regulation of stress protein genes

To study the responses of digestive system of the freshwater crab Sinopotamon henanense to the exposure with cadmium (Cd), crabs were acutely exposed to 7.25, 14.50, and 29.00 mg/l Cd for 96 h and subchronically exposed to 0.725, 1.450, and 2.900 mg/l for 21 days. Cd bioaccumulation in the hepatopancreas and digestive tract (esophagus and intestine) was examined. Furthermore, histopathological alterations of the esophagus, midgut, hindgut, and hepatopancreas were assessed in animals from the 29.0 and 2.90 mg/l Cd treatment groups, and expression of metallothionein messenger RNA (MT mRNA) in the hepatopancreas and intestine was measured in all treatment groups. The results showed difference in the middle and high concentrations between acute and subchronic treatment groups. Cd content in digestive tract after acute 14.5 and 29.0 mg/l Cd exposure was significantly higher than that at subchronic 1.45 and 2.90 mg/l exposure, but Cd levels in hepatopancreas were not significantly different under the same condition. Acute exposure to Cd induced greater morphological damage than subchronic exposure: large areas of epithelial cells were necrotic in hepatopancreas and midgut, which detached from the basal lamina. Vacuolated muscle cells were observed in the hindgut of animals from the acute exposure group, but the changes of esophageal morphology were not obvious after acute or subchronic treatments. The expression of MT mRNA increased with increasing Cd concentration, and MT mRNA level in acute exposure groups was significantly lower when compared to the subchronic exposure groups. Higher Cd content and lower MT mRNA expression in the acutely exposed groups may be responsible for more severe damage of digestive system in these exposure groups.

BackgroundMetallothionein (MT) is a small, cysteine-rich, metal-binding protein that plays an important role in protecting against toxicity of heavy metal and chemicals. This study was aimed to define diurnal and sex variation of MT in mice.MethodsAdult mice were maintained in light- and temperature-controlled facilities for 2 weeks with light on at 8:00 and light off at 20:00. The blood, liver, and kidneys were collected every 4 h during the 24 h period. Total RNA was isolated, purified, and subjected to real-time RT-PCR analysis and MT protein was determined by western blot and the Cd/hemoglobin assay.ResultsThe diurnal variations in mRNA levels of MT-1 and MT-2in liver were dramatic, up to a 40-foldpeak/trough ratio. MT mRNA levels in kidneys and blood also showed diurnal variation, up to 5-fold peak/trough ratio. The diurnal variation of MT mRNAs resembled the clock gene albumin site D-binding protein (Dbp), and was anti-phase to the clock gene Brain and Muscle ARNT-like Protein 1 (Bmal1) in liver and kidneys. The peaks of MT mRNA levels were higher in females than in males. Hepatic MT protein followed a similar pattern, with about a 3-fold difference.ConclusionMT mRNA levels and protein showed diurnal- and sex-variation in liver, kidney, and blood of mice, which could impact the body defense against toxic stimuli.

Mechanisms of regulation of rat hepatic metallothionein-I and metallothionein-II levels following administration of zinc

Seedlings of 10 Arabidopsis ecotypes were compared with respect to copper tolerance, expression of two metallothionein genes (MT1 and MT2), and nonprotein thiol levels. MT1 was uniformly expressed in all treatments, and MT2 was copper inducible in all 10 ecotypes. MT1 and MT2 mRNA levels were compared with various growth parameters for the 10 ecotypes in the presence of 40 microM Cu2+. The best correlation (R = 0.99) was obtained between MT2 mRNA and the rate of root extension. MT2 mRNA levels also paralleled the recovery phase following inhibition by copper. Induction of MT2 mRNA was initiated at copper concentrations below the threshold for growth inhibition. In cross-induction experiments, Ag+, Cd2+, Zn2+, Ni2+, and heat shock all induced significant levels of MT2 gene expression, whereas Al3+ and salicylic acid did not. The correlation between copper tolerance and nonprotein thiol levels in the 10 ecotypes was not statistically significant. However, 2 ecotypes, Ws and Enkheim, previously shown to exhibit an acclimation response, had the highest levels of nonprotein thiols. We conclude that MT2 gene expression may be the primary determinant of ecotypic differences in the copper tolerance of nonpretreated Arabidopsis seedlings.