Pericytes (PCs) are crucial in maintaining the quiescence of endothelial cells (ECs) and the integrity of EC tight junctions. Especially in diabetic retinopathy (DR), PC loss is one of the early pathologic changes in capillaries of diabetic retinas. Thus, preventing PC loss is beneficial for attenuating vision impairment in patients with DR. Although many studies have revealed the mechanism of PC loss in retinas, little is known about the mechanisms that increase PC survival. We focused on the effect of β-adrenergic receptor agonists (β-agonists) on PC loss in diabetic retinas. In this study, β-agonists increased the cell viability of PCs by increasing PC survival and proliferation. Mechanistically, β-agonist-induced protein kinase B activation in PCs reduced PC apoptosis in response to various stimuli. β2-agonists more potently increased PC survival than β1-agonists. β2-Agonist reduced vascular leakage and PC loss in retinas of mice with streptozotocin-induced diabetes. In cocultures of PCs and ECs, β2-agonists restored the altered permeability and ZO-1 expression in ECs induced by PC loss. We concluded that β-agonists, especially β2-agonists, increase PC survival, thereby preventing diabetes-induced PC loss in retinas. These results provide a potential therapeutic benefit of β-agonists for preventing PC loss in DR.-Yun, J.-H., Jeong, H.-S., Kim, K.-J., Han, M. H., Lee, E. H., Lee, K., Cho, C.-H. β-Adrenergic receptor agonists attenuate pericyte loss in diabetic retinas through Akt activation.

Diabetes mellitus (DM) characterized by hyperglycemia leads to a variety of complications, including cognitive impairment or memory loss. The hippocampus is a key brain area for learning and memory and is one of the regions that is most sensitive to diabetes. However, the pathogenesis of diabetic neuronal lesion is not yet completely understood. We focused on the association of microglia activation and brain lesions in diabetes. In this study, we investigated whether and how signal transducer and activator of transcription 3 (STAT3) activation in microglia affects neuronal lesions in diabetic brains. Using a streptozotocin‐induced type 1 DM model, we showed enhanced hippocampal neuronal apoptosis that was associated with increased STAT3 activation. We found that hyperglycemia increased the expression of inflammatory cytokines such as interferon‐γ (IFN‐γ) and interleukin‐6, in the diabetic hippocampus. In particular, IFN‐γ induced autocrine activation of microglia, and STAT3 activation is important for this process. We also demonstrated that STAT3 activation in microglia increased tumor necrosis factor‐α (TNF‐α) expression; subsequently, TNF‐α increased neuronal apoptosis by increasing reactive oxygen species (ROS) levels in the neuronal cells. We also took advantage of mice lacking STAT3 in microglia and demonstrated that depletion of microglial STAT3 reduced neuronal apoptosis in the diabetic hippocampus. Taken together, these results suggest that STAT3 activation in microglia plays an important role in hyperglycemia‐induced neuronal apoptosis in the diabetic hippocampus and provide a potential therapeutic benefit of STAT3 inhibition in microglia for preventing diabetic neuronal lesions.

Thymoquinone (TQ) is a component found in the seeds of Nigella sativa, an annual plant growing on the Mediterranean coast, and is known for its anticancer and anti-inflammatory effects. However, to date, at least to the best of our knowledge, limited studies are available examining the molecular mechanisms through which TQ inhibits melanogenesis. Accordingly, this study aimed to treat B16F10 mouse melanoma cells with TQ to investigate its apparent effects and its molecular regulatory mechanisms. Treatment of the B16F10 cells with 10, 15 and 20 µM of TQ for 48 h resulted in a dose-dependent decrease in the expression of microphthalmia-associated transcription factor (MITF), tyrosinase expression and tyrosinase activity, and these treatments simultaneously led to a decrease in the protein expression and transcription of β-catenin, a Wnt signaling pathway protein. Pre-treatment of the cells with the proteasome inhibitor, MG132, to confirm the inhibition of melanogenesis through the β-catenin pathway by TQ treatment resulted in an increase in the expression of β-catenin that was initially reduced by TQ, and the expression and activity of MITF and tyrosinase also increased. Pre-treatment with LiCl, which is known to inactivate glycogen synthase kinase 3β (GSK3β) by inducing the phosphorylation of the Ser-9 site, resulted in an increased phospho-GSK3β expression accompanied by β-catenin that was initially reduced by TQ, and the recovery of the expression and activity of tyrosinase was also confirmed. The transfection of S37A cDNA into B16F10 cells that overexpress β-catenin resulted in the recovery of β-catenin expression that was initially reduced by TQ, and this treatment also recovered the expression and activity of tyrosinase. When zebrafish eggs were treated with 1, 2.5 and 5 µM of TQ at 10 h following fertilization, their melanin content decreased in a dose-dependent manner. On the whole, these findings demonstrated that the inhibition of melanogenesis in B16F10 mouse melanoma cells by TQ treatment resulted from the inhibition of the β-catenin pathway and confirmed that TQ treatment inhibited melanogenesis in zebrafish.

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