Dopamine elevates intracellular zinc concentration in cultured rat embryonic cortical neurons through the cAMP-nitric oxide signaling cascade

Glutamate gradually elevates [Zn2+]i via the CaM-CaMKII-NOS cascade in primary cultured rat embryonic cortical neurons

Zn2+ is essential for neuronal signaling, but imbalance cause cell death and neurodegenerative disorders. While the buffering system maintains low cytosolic Zn2+ concentration ([Zn2+]i), the details on physiological stimuli elevating [Zn2+]i for neuronal processes remain limited. Our previous reports have demonstrated that dopamine elevates [Zn2+]i through the cAMP-NO pathway, activating autophagy and inflammation in neurons. In this study, we adopted the Zn2+ imaging technique to verify how glutamate elevated [Zn2+]i in cultured cortical neurons and examined the inflammatory response. Our results showed that glutamate elevates the [Zn2+]i, by activating ionotropic glutamate receptors. Inhibitors of calmodulin (CaM), CaM-dependent protein kinase II (CaMKII), and NO synthase (NOS) blocked the glutamate-induced Zn2+ response. High-K+ buffer induced-membrane depolarization significantly elevated the intracellular Ca2+ concentration ([Ca2+]i) but only slightly increased [Zn2+]i and NO production. Glutamate also transiently increased NOS phosphorylation at Ser1417 within 15 min. The Zn2+ chelator, TPEN suppressed glutamate-induced inflammasome formation. These results indicate that glutamate-induced local increment in [Ca2+]i via the ionotropic glutamate receptors activates the CaM-CaMKII-NOS complex to produce NO and elevate [Zn2+]i. which trigger inflammation in cultured neurons. Henceforth, this novel glutamate-Zn2+ signaling pathway after glutamate depolarization elevates [Ca2+]i indicates the involvement of Zn2+ in modulating long-term neuronal activities.

Dopamine Activates the D1R-Zn2+ Signaling Pathway to Trigger Inflammatory Response in Primary-Cultured Rat Embryonic Cortical Neurons

Neuroinflammation is an early event during the pathogenesis of neurodegenerative disorders. Most studies focus on how the factors derived from pathogens or tissue damage activate the inflammation-pyroptosis cell death pathway. It is unclear whether endogenous neurotransmitters could induce inflammatory responses in neurons. Our previous reports have shown that dopamine-induced elevation of intracellular Zn2+ concentration via the D1-like receptor (D1R) is a prerequisite for autophagy and cell death in primary cultured rat embryonic neurons. Here we further examined that this D1R-Zn2+ signaling initiates the transient inflammatory response leading to cell death in cultured cortical neurons. Pretreating the cultured neurons with Zn2+ chelator and inhibitors against inflammation could enhance the cell viability in neurons treated with dopamine and dihydrexidine, an agonist of D1R. Both dopamine and dihydrexidine greatly enhanced inflammasome formation; a Zn2+ chelator, N,N,N',N'-tetrakis(2-pyridinylmethyl)-1,2-ethanediamine, suppressed this increment. Dopamine and dihydrexidine increased the expression levels of NOD-like receptor pyrin domain-containing protein 3 and enhanced the maturation of caspase-1, gasdermin D, and IL-1β; these changes were all Zn2+-dependent. Dopamine treatment did not recruit the N-terminal of the gasdermin D to the plasma membrane but enhanced its localization to the autophagosomes. Pretreating the neurons with IL-1β could increase the viability of neurons challenged with dopamine. These results demonstrate a novel D1R-Zn2+ signaling cascade activating neuroinflammation and cell death. Therefore, maintaining a balance between dopamine homeostasis and inflammatory responses is an important therapeutic target for neurodegeneration. Dopamine elicits transient inflammatory responses in cultured cortical neurons via the D1R-Zn2+ signaling pathway. Dopamine elevates [Zn2+]i to induce the formation of inflammasomes, which activates caspase-1, resulting in the maturation of IL-1β and gasdermin D (GSDMD). Therefore, the homeostasis of dopamine and Zn2+ are critical therapeutic targets for inflammation-derived neurodegeneration.

Injectable Hydrogel Guides Neurons Growth with Specific Directionality

Visual disabilities affect more than 250 million people, with 43 million suffering from irreversible blindness. The eyes are an extension of the central nervous system which cannot regenerate. Neural tissue engineering is a potential method to cure the disease. Injectability is a desirable property for tissue engineering scaffolds which can eliminate some surgical procedures and reduce possible complications and health risks. We report the development of the anisotropic structured hydrogel scaffold created by a co-injection of cellulose nanofiber (CNF) solution and co-polypeptide solution. The positively charged poly (L-lysine)-r-poly(L-glutamic acid) with 20 mol% of glutamic acid (PLLGA) is crosslinked with negatively charged CNF while promoting cellular activity from the acid nerve stimulate. We found that CNF easily aligns under shear forces from injection and is able to form hydrogel with an ordered structure. Hydrogel is mechanically strong and able to support, guide, and stimulate neurite growth. The anisotropy of our hydrogel was quantitatively determined in situ by 2D optical microscopy and 3D X-ray tomography. The effects of PLLGA:CNF blend ratios on cell viability, neurite growth, and neuronal signaling are systematically investigated in this study. We determined the optimal blend composition for stimulating directional neurite growth yielded a 16% increase in length compared with control, reaching anisotropy of 30.30% at 10°/57.58% at 30°. Using measurements of calcium signaling in vitro, we found a 2.45-fold increase vs. control. Based on our results, we conclude this novel material and unique injection method has a high potential for application in neural tissue engineering.

Nitric Oxide Mobilizes Intracellular Zn2+ via the GC/cGMP/PKG Signaling Pathway and Stimulates Adipocyte Differentiation

Plasma and tissue zinc ion levels are associated with the development of obesity. Previous studies have suggested that zinc ions may regulate adipocyte metabolism and that nitric oxide (NO) plays a pivotal role in the regulation of adipocyte physiology. Our previous study showed that chronic NO deficiency causes a significant decrease in adipose tissue mass in rats. Studies also suggested that zinc ions play an important modulatory role in regulating NO function. This study aims to explore the role of zinc ions in NO-regulated adipocyte differentiation. We hypothesized that NO could increase intracellular Zn2+ level and then stimulate adipocyte differentiation. ZnCl2 and the NO donor, NONOate, were used to explore the effects of Zn2+ and NO on adipocyte differentiation. Regulatory mechanisms of NO on intracellular Zn2+ mobilization were determined by detection. Then, Zn2+-selective chelator TPEN was used to clarify the role of intracellular Zn2+ on NO-regulated adipocyte differentiation. Furthermore, the relationship between adipocyte size, Zn2+ level, and NOS expression in human subcutaneous fat tissue was elucidated. Results showed that both ZnCl2 and NO stimulated adipocyte differentiation in a dose-dependent manner. NO stimulated intracellular Zn2+ mobilization in adipocytes through the guanylate cyclase (GC)/cyclic guanosine monophosphate (cGMP)/protein kinase G (PKG) pathway, and NO-stimulated adipocyte differentiation was Zn2+-dependent. In human subcutaneous adipose tissue, adipocyte size was negatively correlated with expression of eNOS. In conclusion, NO treatment stimulates intracellular Zn2+ mobilization through the GC/cGMP/PKG pathway, subsequently stimulating adipocyte differentiation.

Journey to the Center of the Fetal Brain: Environmental Exposures and Autophagy

Fetal brain development is known to be affected by adverse environmental exposures during pregnancy, including infection, inflammation, hypoxia, alcohol, starvation, and toxins. These exposures are thought to alter autophagy activity in the fetal brain, leading to adverse perinatal outcomes, such as cognitive and sensorimotor deficits. This review introduces the physiologic autophagy pathways in the fetal brain. Next, methods to detect and monitor fetal brain autophagy activity are outlined. An additional discussion explores possible mechanisms by which environmental exposures during pregnancy alter fetal brain autophagy activity. In the final section, a correlation of fetal autophagy activity with the observed postnatal phenotype is attempted. Our main purpose is to provide the current understanding or a lack thereof mechanisms on autophagy, underlying the fetal brain injury exposed to environmental insults.