Downregulation of metallothionein-2 contributes to oxaliplatin-induced neuropathic pain

Background

We previously reported a correlation between small doses of oxaliplatin penetrating onto the spinal cord and acute pain after chemotherapy. Here, we propose that MT2 within the spinal dorsal horns participates in the development of oxaliplatin-induced neuropathic pain and may be a pharmacological target for the prevention and treatment of chemotherapy-induced peripheral neuropathy (CIPN).

Methods

The rat model of CIPN was established by 5 consecutive injections of oxaliplatin (0.4 mg/100 g/day). Genetic restoration of neuron-specific metallothionein-2 was implemented 21 days before oxaliplatin treatment, and also, genetic inhibition by metallothionein-2 siRNA was performed. Mechanical allodynia and locomotor activity were assayed. Cell-specific expression of metallothionein-2, the mRNA levels of pro-inflammatory cytokines, nuclear translocation of NF-κB, the protein levels of expression of IκB-α, and interaction between IκB-α and P65 were evaluated in the spinal dorsal horns. Also, in vitro interaction of sequentially deleted IκB-α promoter with metallothionein-2 was used to assess the signal transduction mechanism.

Results

We found that oxaliplatin induced downregulation of metallothionein-2 in rat spinal cord neurons. By contrast, genetic restoration of metallothionein-2 in the spinal dorsal horn neuron blocked and reversed neuropathic pain in oxaliplatin-treated rats of both sexes, whereas genetic inhibition of metallothionein-2 triggered neuropathic pain in normal rats. Overall locomotor activity was not impaired after the genetic alterations of metallothionein-2. At the molecular level, metallothionein-2 modulated oxaliplatin-induced neuroinflammation, activation of NF-κB, and inactive transcriptional expression of IκB-α promoter, and these processes could be blocked by genetic restoration of metallothionein-2 in the spinal dorsal horn neurons.

Conclusions

Metallothionein-2 is a potential target for the prevention and treatment of CIPN. A reduction of NF-κB activation and inflammatory responses by enhancing the transcription of IκB-α promoter is proposed in the mechanism.

Metallothionein-2: An emerging target in inflammatory diseases and cancers

Metallothionein-2 (MT-2) was originally discovered as a mediator of zinc homeostasis and cadmium detoxification. However, MT-2 has recently received increased attention because altered expression of MT-2 is closely related to various diseases such as asthma and cancers. Several pharmacological strategies have been developed to inhibit or modify MT-2, revealing its potential as drug target in diseases. Therefore, a better understanding of the mechanisms of MT-2 action is warranted to improve drug development for potential clinical applications. In this review, we highlight recent advances in determining the protein structure, regulation, binding partners, and new functions of MT-2 in inflammatory diseases and cancers.

Metallothionein-2 is associated with the amelioration of asthmatic pulmonary function by acupuncture through protein phosphorylation

BACKGROUND

Acupuncture has long been used for asthma treatment but the underlying mechanism remains unclear. Previous study showed that metallothionein-2 (MT-2) was significantly decreased in asthmatic lung tissue. However, the relationship between acupuncture treatment and MT-2 expression during asthma is still unknown, and the detailed effect analysis of MT-2 on phosphorylation in airway smooth muscle cells (ASMCs) is also unclear.

METHODS

The acupuncture effect on pulmonary resistance (RL) was investigated in a rat model of asthma, and the mRNA and protein levels of MT-2 in lung tissue were detected. Primary ASMCs were isolated and treated with MT-2 recombinant protein to study the MT-2 effects on ASMC relaxation. A Phospho Explorer antibody microarray was applied to detect protein phosphorylation changes associated with MT-2-induced ASMC relaxation. Bioinformatic analysis were performed with PANTHER database, DAVID and STRING. Phosphorylation changes in key proteins were confirmed by Western blot.

RESULTS

Acupuncture significantly reduced RL at 2-5 min (P < 0.05 vs asthma) in asthmatic rats. Acupuncture continued to increase MT-2 mRNA expression in lung tissue for up to 14 days (P < 0.05 vs asthma). The MT-2 protein expression was significantly decreased in the asthmatic rats (P < 0.05 vs control), while MT-2 protein expression was significantly increased in the asthmatic model group treated with acupuncture (P < 0.05 vs asthma). Primary ASMCs were successfully isolated and recombinant MT-2 protein (100, 200, 400 ng/ml) significantly relaxed ASMCs (P < 0.05 vs control). MT-2 induced phosphorylation changes in 51 proteins. Phosphorylation of 14 proteins were upregulated while 37 proteins were downregulated. PANTHER classification revealed eleven functional groups, and the phosphorylated proteins were identified as transferases (27.8 %), calcium-binding proteins (11.1 %), etc. DAVID functional classification showed that the phosphorylated proteins could be attributed to eight functions, including protein phosphorylation and regulation of GTPase activity. STRING protein-protein interaction network analysis showed that Akt1 was one of the most important hubs for the phosphorylated proteins. The phosphorylation changes of Akt1 and CaMK2β were consistent in both the Phospho Explorer antibody microarray and Western blot.

CONCLUSION

Acupuncture can significantly ameliorate RL, and the MT-2 mRNA and protein levels in lung tissue are increased during treatment. MT-2 significantly relaxes ASMCs and induces a series of protein phosphorylation. These phosphorylation changes, including Akt1 and CaMK2β, may play important roles in the therapeutic effects of acupuncture on asthma.

Dexamethasone reduces cisplatin-induced hair cell damage by inducing cisplatin resistance through metallothionein-2

PURPOSE

Hair cell damage is a common side effect caused by the anticancer drug cisplatin (CDDP), which reduces patient quality of life. One CDDP resistance mechanism that occurs in recurrent cancers is heavy metal detoxification by metallothionein-2 (mt2). Here, we show that in zebrafish larvae, dexamethasone (DEX) reduces CDDP-induced hair cell damage by enhancing mt2 expression.

METHODS

Transgenic zebrafish (cldn: gfp; atoh1: rfp) that express green and red fluorescent proteins in neuromasts and hair cells, respectively, were used. The zebrafish were pretreated with DEX at 52 h post-fertilization (hpf) for 8 h, followed by CDDP treatment for 12 h. The lateral line hair cells of CDDP-treated zebrafish at 72 hpf were observed by fluorescence microscopy.

RESULTS

Reporting odds ratio (ROR) analysis using an adverse event database indicated an association between a decrease in CDDP-induced ototoxicity and DEX as an antiemetic treatment for cancer chemotherapy. Pretreatment with DEX protected 72 hpf zebrafish hair cells from CDDP-induced damage. The expression of mt2 mRNA was significantly increased by the combination of 10 µM DEX with CDDP. Gene editing of mt2 reversed the protective effect of DEX against CDDP-induced damage in hair cells.

CONCLUSION

DEX protects hair cells from CDDP-induced damage through increased mt2 expression, which is a resistance mechanism for platinum-based anticancer drugs.

Interleukin-17 prevents oxidative stress from damaging osteoblast formation by inhibiting autophagic degradation of metallothionein-2

Interleukin 17A (IL-17A) is a key cytokine promoting osteoblast formation, which contributes to osteogenesis. IL-17A functions in autophagy inhibition within osteoblasts. Metallothionein-2 (MT-2), as an important reactive oxygen species (ROS)-scavenging molecule, prevents oxidative stress from damaging osteoblast formation. The relationship between IL-17A-regulated autophagy and MT-2 production under oxidative stress deserves further exploration. In this study, we first investigated the roles of IL-17A in osteoblastic differentiation and ROS production in osteoblast precursors in the presence of hydrogen peroxide (H2O2). Next, we explored the effects of IL-17A on autophagic activity and MT-2 protein expression in osteoblast precursors in the presence of H2O2. Ultimately, by using autophagic pharmacological agonist (rapamycin) and lentiviral transduction technology, the relationship between autophagy, IL-17A-regulated MT-2 protein expression and IL-17A-regulated ROS production was further elucidated. Our results showed that in the presence of H2O2, IL-17A promoted osteoblastic differentiation and inhibited ROS production. Moreover, in the presence of H2O2, IL-17A inhibited autophagic activity and promoted MT-2 protein expression in osteoblast precursors. Importantly, IL-17A-promoted MT-2 protein levels and -inhibited ROS production were reversed by autophagy activation with rapamycin. Furthermore, IL-17A-inhibited ROS production were blocked by MT-2 silencing. In conclusion, IL-17A promotes ROS clearance by inhibiting autophagic degradation of MT-2, thereby protecting osteoblast formation from oxidative stress.