Ghrelin exerts a wide range of physiological actions throughout the body and appears to be a promising target for disease therapy. Endogenous ghrelin receptors (GHSRs) are present in extrahypothalamic sites including the substantia nigra pars compacta (SNc), which is related to phenotypic dysregulation or frank degeneration in Parkinson’s disease (PD). Here we found a dramatic decrease in the expression of GHSR in PD-specific induced pluripotent stem cell (iPSC)-derived dopaminergic (DAnergic) neurons generated from patients carrying parkin gene (PARK2) mutations compared to those from healthy controls. Consistently, a significant decrease in the expression of GHSR was found in DAnergic neurons of isogenic PARK2-iPSC lines that mimicked loss of function of the PARK2 gene through CRISPR Cas9 technology. Furthermore, either intracerebroventricular injection or microinjection into the SNc of the selective GHSR1a antagonist [D-Lys3]-GHRP6 in normal mice produced cataleptic behaviors related to dysfunction of motor coordination. These findings suggest that the down-regulation of GHSRs in SNc-DA neurons induced the initial dysfunction of DA neurons, leading to extrapyramidal disorder under PD.Electronic supplementary materialThe online version of this article (10.1186/s13041-018-0349-8) contains supplementary material, which is available to authorized users.

BackgroundThe EGFR tyrosine kinase inhibitor gefitinib is used in therapy for non-small-cell lung cancer (NSCLC). However, its application is limited by resistance-accelerated disease progression, which is accompanied by the epithelial-to-mesenchymal transition (EMT). In the present study, we performed multiple expression analyses of microRNAs (miRNAs) and quantified the expression of several related EMT players in gefitinib-resistant NSCLC cells.Methods and resultsTo establish gefitinib-resistant NSCLC cells, gefitinib-sensitive HCC827 cells, which exhibit an in-frame deletion [E746-A750] in EGFR exon 19, were exposed to gefitinib for at least 1.5 months. Next, to profile “gefitinib-resistant HCC827 (HCC827GR)” cells, which have a secondary T790M mutation in EGFR exon 20, a miRNA array analysis was performed in HCC827 and HCC827GR cells. The greatest differences were seen in the levels of miR-155 and miR-200c, which essentially disappeared in HCC827GR cells. In addition to these reductions, the levels of smad2 and zeb1, which are both key players in EMT and targets for miR-155 and miR-200c, respectively, were dramatically increased in HCC827GR cells. In HCC827GR cells, the expression of epithelial-cadherin (E-cadherin) was greatly reduced with repressive histone modifications, whereas vimentin, which is expressed in mesenchymal cells, was dramatically increased with active histone modifications. In another gefitinib-resistant NSCLC cell line (H1975 cells), similar to the findings in HCC827GR cells, both miR-155 and miR-200c were absent, and the EMT was induced along with epigenetic modifications. Interestingly, the inhibition of both miR-155 and miR-200c in HCC827 cells without gefitinib induced significant increases in smad2 and zeb1 along with a dramatic decrease in E-cadherin and a slight increase in vimentin. Furthermore, although the inhibition of these miRNAs in HCC827 cells decreased gefitinib sensitivity, this dual-inhibition in HCC827 cells without gefitinib did not produce a secondary T790M mutation in EGFR exon 20.Conclusion and implicationsThese results suggest that chronic treatment of NSCLC cells with gefitinib changes the expression of miRNAs, including dramatic reductions in miR-155 and miR-200c along with an EGFR mutation. Furthermore, this depletion of miR-155 and miR-200c may be associated with the EMT along with histone modifications, and may contribute to the decrease in the sensitivity to gefitinib independent of a secondary EGFR mutation.

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Emerging evidence suggests that the mesolimbic dopaminergic network plays a role in the modulation of pain. As chronic pain conditions are associated with hypodopaminergic tone in the nucleus accumbens (NAc), we evaluated the effects of increasing signaling at dopamine D1/D2-expressing neurons in the NAc neurons in a model of neuropathic pain induced by partial ligation of sciatic nerve. Bilateral microinjection of either the selective D1-receptor (Gs-coupled) agonist Chloro-APB or the selective D2-receptor (Gi-coupled) agonist quinpirole into the NAc partially reversed nerve injury-induced thermal allodynia. Either optical stimulation of D1-receptor-expressing neurons or optical suppression of D2-receptor-expressing neurons in both the inner and outer substructures of the NAc also transiently, but significantly, restored nerve injury-induced allodynia. Under neuropathic pain-like condition, specific facilitation of terminals of D1-receptor-expressing NAc neurons projecting to the VTA revealed a feedforward-like antinociceptive circuit. Additionally, functional suppression of cholinergic interneurons that negatively and positively control the activity of D1- and D2-receptor-expressing neurons, respectively, also transiently elicited anti-allodynic effects in nerve injured animals. These findings suggest that comprehensive activation of D1-receptor-expressing neurons and integrated suppression of D2-receptor-expressing neurons in the NAc may lead to a significant relief of neuropathic pain.