cPKCγ membrane translocation is involved in herkinorin‑induced neuroprotection against cerebral ischemia/reperfusion injury in mice

Herkinorin negatively regulates NLRP3 inflammasome to alleviate neuronal ischemic injury through activating Mu opioid receptor and inhibiting the NF-κB pathway

Herkinorin is a novel opioid receptor agonist. Activation of opioid receptors, a member of G protein coupled receptors (GPCRs), may play an important role in Herkinorin neuroprotection. GPCRs may modulate NOD-like receptor protein 3 (NLRP3)-mediated inflammatory responses in the mechanisms of inflammation-associated disease and pathological processes. In this study, we investigated the effects of Herkinorin on NLRP3 and the underlying receptor and molecular mechanisms in oxygen-glucose deprivation/reperfusion (OGD/R)-treated rat cortex neurons. First, Western blot analysis showed that Herkinorin can inhibit the activation of NLRP3 and Caspase-1, decrease the expression of interleukin (IL)-1β, and decrease the secretion of IL-6 and tumour necrosis factor α detected by enzyme-linked immunosorbent assay in OGD/R-treated neurons. Then we found that Herkinorin downregulated NLRP3 levels by inhibiting the activation of nuclear factor kappa B (NF-κB) pathway, reducing the phosphorylation level of p65 and IκBα in OGD/R-treated neurons (p < .05 or .01, n = 3 per group). Instead, both the mu opioid receptor (MOR) inhibitor, β-funaltrexamine, and MOR knockdown reversed the effects of Herkinorin on NLRP3 (p < .05 or .01, n = 3 per group). Further, we found that the level of β-arrestin2 decreased in the cell membrane and increased in the cytoplasm after Herkinorin pretreatment in OGD/R-treated neurons. In co-immunoprecipitation experiments, Herkinorin increased the binding of IκBα with β-arrestin2, decreased the ubiquitination level of IκBα, and β-arrestin2 knockdown reversed the effects of Herkinorin on IκBα in OGD/R-treated neurons (p < .05 or .01, n = 3 per group). Our data demonstrated that Herkinorin negatively regulated NLRP3 inflammasome to alleviate neuronal ischemic injury through inhibiting NF-κB pathway mediated primarily by MOR activation. Inhibition of the NF-κB pathway by Herkinorin may be achieved by decreasing the ubiquitination level of IκBα, in which β-arrestin2 may play an important role.

Neurons derived from human-induced pluripotent stem cells express mu and kappa opioid receptors

Neuroprotection studies have shown that induced pluripotent stem (iPS) cells have the possibility to transform neuroprotection research. In the present study, iPS cells were generated from human renal epithelial cells and were then differentiated into neurons. Cells in the iPS-cell group were maintained in stem cell medium. In contrast, cells in the iPS-neuron group were first maintained in neural induction medium and expansion medium containing ROCK inhibitors, and then cultivated in neuronal differentiation medium and neuronal maturation medium to induce the neural stem cells to differentiate into neurons. The expression of relevant markers was compared at different stages of differentiation. Immunofluorescence staining revealed that cells in the iPS-neuron group expressed the neural stem cell markers SOX1 and nestin on day 11 of induction, and neuronal markers TUBB3 and NeuN on day 21 of induction. Polymerase chain reaction results demonstrated that, compared with the iPS-cell group, TUBB3 gene expression in the iPS-neuron group was increased 15.6-fold. Further research revealed that, compared with the iPS-cell group, the gene expression and immunoreactivity of mu opioid receptor in the iPS-neuron group were significantly increased (38.3-fold and 5.7-fold, respectively), but those of kappa opioid receptor had only a slight change (1.33-fold and 1.57-fold increases, respectively). Together, these data indicate that human iPS cells can be induced into mu opioid receptor- and kappa opioid receptor-expressing neurons, and that they may be useful to simulate human opioid receptor function in vitro and explore the underlying mechanisms of human conditions.