Oxytocin induced epithelium-mesenchimal transition through Rho-ROCK pathway in ARPE-19 cells, a human retinal pigmental cell line

Proteomic analysis of s-acylated proteins in human retinal pigment epithelial cells and the role of palmitoylation of Niemann-Pick type C1 protein in cholesterol transport

Palmitoylation is a dynamic process that regulates the activity of the modified proteins. Retinal pigment epithelial (RPE) cells play pivotal roles in the visual cycle and maintaining healthy photoreceptor cells. Dysfunctional RPE cells are often associated with degenerative retinal diseases. The aim of the study was to identify potentially palmitoylated proteins in human RPE cells. By using the detergent-resistant membrane, we found 312 potentially palmitoylated peptides which corresponded to 192 proteins in RPE cells, including 55 new candidate proteins which were not reported before. Gene enrichment analysis highlighted significant enrichment of palmitoylated proteins in cell-matrix adhesion, cell-cell recognition, protein cellular localization, and translation, among others. We further studied the effect of 3 potential palmitoylation sites (Cys 799, 900, and 816) of Niemann-Pick type C1 protein (NPC1) on cholesterol accumulation. We found that mutation of any single Cys alone had no significant effect on intracellular cholesterol accumulation while simultaneous mutation of Cys799 and 800 caused significant cholesterol accumulation in the late endosome. No further cholesterol accumulation was observed by adding another mutation at Cys 816. However, the mutation did not alter the cellular localization of the protein. Conclusion: PRE cells have an abundant number of palmitoylated proteins which are involved in cellular processes critical to visual function. The palmitoylation at Cys799 and 800 was needed for cholesterol export, but not the intracellular localization of NPC1.

Neural Functions of Hypothalamic Oxytocin and its Regulation

Oxytocin (OT), a nonapeptide, has a variety of functions. Despite extensive studies on OT over past decades, our understanding of its neural functions and their regulation remains incomplete. OT is mainly produced in OT neurons in the supraoptic nucleus (SON), paraventricular nucleus (PVN) and accessory nuclei between the SON and PVN. OT exerts neuromodulatory effects in the brain and spinal cord. While magnocellular OT neurons in the SON and PVN mainly innervate the pituitary and forebrain regions, and parvocellular OT neurons in the PVN innervate brainstem and spinal cord, the two sets of OT neurons have close interactions histologically and functionally. OT expression occurs at early life to promote mental and physical development, while its subsequent decrease in expression in later life stage accompanies aging and diseases. Adaptive changes in this OT system, however, take place under different conditions and upon the maturation of OT release machinery. OT can modulate social recognition and behaviors, learning and memory, emotion, reward, and other higher brain functions. OT also regulates eating and drinking, sleep and wakefulness, nociception and analgesia, sexual behavior, parturition, lactation and other instinctive behaviors. OT regulates the autonomic nervous system, and somatic and specialized senses. Notably, OT can have different modulatory effects on the same function under different conditions. Such divergence may derive from different neural connections, OT receptor gene dimorphism and methylation, and complex interactions with other hormones. In this review, brain functions of OT and their underlying neural mechanisms as well as the perspectives of their clinical usage are presented.

Co-Stimulation of Oxytocin and Arginine-Vasopressin Receptors Affect Hypothalamic Neurospheroid Size

Oxytocin (OXT) is a neuropeptide involved in a plethora of behavioral and physiological processes. However, there is a prominent lack of 3D cell culture models that investigate the effects of OXT on a cellular/molecular level. In this study, we established a hypothalamic neuronal spheroid model to investigate the cellular response in a more realistic 3D setting. Our data indicate that the formation of spheroids itself does not alter the basic characteristics of the cell line and that markers of cellular morphology and connectivity are stably expressed. We found that both OXT and arginine vasopressin (AVP) treatment increase spheroid size (surface area and volume), as well as individual nucleus size, which serves as an indicator for cellular proliferation. The cellular response to both OXT and AVP seems mainly to be mediated by the AVP receptor 1a (V1aR); however, the OXT receptor (OXTR) contributes significantly to the observed proliferative effect. When we blocked the OXTR pharmacologically or knocked down the OXTR by siRNA, the OXT- or AVP-induced cellular proliferation decreased. In summary, we established a 3D cell culture model of the neuronal response to OXT and AVP and found that spheroids react to the treatment via their respective receptors but also via cross-talk between the two receptor types.

Nicotinamide suppresses bevacizumab-induced epithelial-mesenchymal transition of ARPE-19 cells by attenuating oxidative stress

AIM

To investigate the effects of nicotinamide (NAM) on bevacizumab (BEV)-induced epithelial-mesenchymal transition (EMT) of human retinal pigment epithelial cells (ARPE-19) and the underling mechanisms.

METHODS

ARPE-19 cells were treated with BEV for 24, 48, and 72h, and the variation degrees of EMT-related markers (fibronectin, α-SMA, vimentin, and ZO-1) were assessed by Western blotting to select the optimal treatment time point which exhibited the most obvious changes of EMT-related markers for the subsequent experiments. Furthermore, NAM was added to the medium, the mRNA and protein levels of the EMT-related markers were then measured. The accumulation of reactive oxygen species (ROS) and H₂O₂ and the total antioxidant capacity (TAC) of the cells were also measured to evaluate the level of oxidative stress.

RESULTS

After being treated with BEV for 72h, the protein expression levels of EMT-related markers in ARPE-19 cells showed significant changes. Meanwhile the levels of ROS and H₂O₂ were obviously increased, and the TAC of ARPE-19 cells was decreased. Totally 72h was chosen to be the optimal treatment time point in subsequent experiments. Furthermore, NAM inhibited BEV-induced EMT by downregulating fibronectin, α-SMA, and vimentin and upregulating ZO-1, decreased the accumulation of ROS and H₂O₂, and enhanced TAC in BEV-treated ARPE-19 cells.

CONCLUSION

This study demonstrates that NAM suppressed BEV-induced EMT in ARPE-19 cells by attenuating oxidative stress. Hence, NAM may be a potential therapeutic agent for alleviating neovascular fibrosis of the ocular fundus after anti-vascular endothelial growth factor therapy.

LRG1 promotes epithelial-mesenchymal transition of retinal pigment epithelium cells by activating NOX4

AIM

To investigate the effect of leucine-rich-alpha-2-glycoprotein 1 (LRG1) on epithelial-mesenchymal transition (EMT) in retinal pigment epithelium (RPE) cells, and to explore the role of NADPH oxidase 4 (NOX4).

METHODS

RPE cells (ARPE-19 cell line) were treated with transforming growth factor-β1 (TGF-β1) to induce EMT. Changes of the mRNA and protein expression levels of LRG1 were tested in the TGF-β1 treated cells. The recombinant human LRG1 protein (rLRG1) and siRNA of LRG1 were used to establish accumulation of exogenous LRG1 model and the down-regulation of LRG1 model in ARPE-19 cells respectively, and to detect EMT-related markers including fibronectin, α-smooth muscle actin (α-SMA) and zonula occludens-1 (ZO-1). The mRNA and protein expression level of NOX4 were measured according to the above treatments. VAS2870 was used as a NOX4 inhibitor in rLRG1-treated cells. EMT-related markers were detected to verify the effect of NOX4 in the process of EMT.

RESULTS

TGF-β1 promoted the expression of LRG1 at both the mRNA and protein levels during the process of EMT which showed the up-regulation of fibronectin and α-SMA, as well as the down-regulation of ZO-1. Furthermore, the rLRG1 promoted EMT of ARPE-19 cells, which manifested high levels of fibronectin and α-SMA and low level of ZO-1, whereas knockdown of LRG1 prevented EMT by decreasing the expressions of fibronectin and α-SMA and increasing the expression of ZO-1 in ARPE-19 cells. Besides, the rLRG1 activated and LRG1 siRNA suppressed NOX4 expression. EMT was inhibited when VAS2870 was used in the rLRG1-treated cells.

CONCLUSION

These results for the first time demonstrate that LRG1 promotes EMT of RPE cells by activating NOX4, which may provide a novel direction to explore the mechanisms of subretinal fibrosis.