Breaking the circulus vitiosus of neuroinflammation: Resveratrol attenuates the human glial cell response to cytokines

Role of TGF-β1/SMADs signalling pathway in resveratrol-induced reduction of extracellular matrix deposition by dexamethasone-treated human trabecular meshwork cells

Deposition of extracellular matrix (ECM) in the trabecular meshwork (TM) increases aqueous humour outflow resistance leading to elevation of intraocular pressure (IOP) in primary open-angle glaucoma, which remains the only modifiable risk factor. Resveratrol has been shown to counteract the steroid-induced increase in IOP and increase the TM expression of ECM proteolytic enzymes; however, its effects on the deposition of ECM components by TM and its associated pathways, such as TGF-β-SMAD signalling remain uncertain. This study, therefore, explored the effects of trans-resveratrol on the expression of ECM components, SMAD signalling molecules, plasminogen activator inhibitor-1 and tissue plasminogen activator in dexamethasone-treated human TM cells (HTMCs). We also studied the nature of molecular interaction of trans -resveratrol with SMAD4 domains using ensemble docking. Treatment of HTMCs with 12.5 µM trans-resveratrol downregulated the dexamethasone-induced increase in collagen, fibronectin and α-smooth muscle actin at gene and protein levels through downregulation of TGF-β1, SMAD4, and upregulation of SMAD7. Downregulation of TGF-β1 signalling by trans-resveratrol could be attributed to its effect on the transcriptional activity due to high affinity for the MH2 domain of SMAD4. These effects may contribute to resveratrol's IOP-lowering properties by reducing ECM deposition and enhancing aqueous humour outflow in the TM.

Magnesium-lithium thin films for neurological applications-An in vitro investigation of glial cytocompatibility and neuroinflammatory response

Lithium (Li), a widely used drug for bipolar disorder management, is associated with many side effects due to systemic exposure. The localized delivery of lithium through implants could be an approach to overcome this challenge, for which biodegradable magnesium (Mg)-based materials are a promising choice. In this study, we focus on Mg-Li thin film alloys as potential Li-releasing implants. Therefore, we investigated the in vitro short-term corrosion behavior and cytocompatibility of two alloys, Mg-1.6wt%Li and Mg-9.5wt%Li. As glial cells are the key players of foreign body responses to implants, we used human glial cell lines for cytocompatibility studies, and a murine brain slice model for a more holistic view at the neuroinflammatory response. We found that Mg-1.6wt%Li corrodes approximately six times slower than Mg-9.5wt%Li. Microscopic analysis showed that the material surface (Mg-1.6wt%Li) is suitable for cell adhesion. The cytocompatibility test with Mg-1.6wt%Li and Mg-9.5wt%Li alloy extracts revealed that both cell types proliferated well up to 10 mM Mg concentration, irrespective of the Li concentration. In the murine brain slice model, Mg-1.6wt%Li and Mg-9.5wt%Li alloy extracts did not provoke a significant upregulation of glial inflammatory/ reactivity markers (IL-1β, IL-6, FN1, TNC) after 24 h of exposure. Furthermore, the gene expression of IL-1β (up to 3-fold) and IL-6 (up to 16-fold) were significantly downregulated after 96 h, and IL-6 downregulation showed a Li concentration dependency. Together, these results indicate the acute cytocompatibility of two Mg-Li thin film alloys and provide basis for future studies to explore promising applications of the material. STATEMENT OF SIGNIFICANCE: We propose the idea of lithium delivery to the brain via biodegradable implants to reduce systemic side effects of lithium for bipolar disorder therapy and other neurological applications. This is the first in vitro study investigating Mg-xLi thin film degradation under physiological conditions and its influence on cellular responses such as proliferation, viability, morphology and inflammation. Utilizing human brain-derived cell lines, we showed that the material surface of such a thin film alloy is suitable for normal cell attachment. Using murine brain slices, which comprise a multicellular network, we demonstrated that the material extracts did not elicit a pro-inflammatory response. These results substantiate that degradable Mg-Li materials are biocompatible and support the further investigation of their potential as neurological implants.

Resveratrol Alleviates the Early Challenges of Implant-Based Drug Delivery in a Human Glial Cell Model

Brain diseases are oftentimes life-threatening and difficult to treat. The local administration of drug substances using brain implants can increase on-site concentrations and decrease systemic side effects. However, the biocompatibility of potential brain implant materials needs to be evaluated carefully as implants can trigger foreign body reactions, particularly by increasing the microglia and astrocyte reactivity. To date, these tests have been frequently conducted in very simple in vitro models, in particular not respecting the key players in glial cell reactions and the challenges of surgical implantation characterized by the disruption of oxygen and nutrient supply. Thus, we established an in vitro model in which we treated human glial cell lines with reduced oxygen and glucose levels. The model displayed cytokine and reactive oxygen species release from reactive microglia and an increase in a marker of reactive astrocytes, galectin-3. Moreover, the treatment caused changes in the cell survival and triggered the production of hypoxia-inducible factor 1α. In this comprehensive platform, we demonstrated the protective effect of the natural polyphenol resveratrol as a model substance, which might be included in brain implants to ease the undesired glial cell response. Overall, a glial-cell-based in vitro model of the initial challenges of local brain disease treatment may prove useful for investigating new therapy options.

Roles of microglia in adult hippocampal neurogenesis in depression and their therapeutics

Adult hippocampal neurogenesis generates functional neurons from neural progenitor cells in the hippocampal dentate gyrus (DG) to complement and repair neurons and neural circuits, thus benefiting the treatment of depression. Increasing evidence has shown that aberrant microglial activity can disrupt the appropriate formation and development of functional properties of neurogenesis, which will play a crucial role in the occurrence and development of depression. However, the mechanisms of the crosstalk between microglia and adult hippocampal neurogenesis in depression are not yet fully understood. Therefore, in this review, we first introduce recent discoveries regarding the roles of microglia and adult hippocampal neurogenesis in the etiology of depression. Then, we systematically discuss the possible mechanisms of how microglia regulate adult hippocampal neurogenesis in depression according to recent studies, which involve toll-like receptors, microglial polarization, fractalkine-C-X3-C motif chemokine receptor 1, hypothalamic-pituitary-adrenal axis, cytokines, brain-derived neurotrophic factor, and the microbiota-gut-brain axis, etc. In addition, we summarize the promising drugs that could improve the adult hippocampal neurogenesis by regulating the microglia. These findings will help us understand the complicated pathological mechanisms of depression and shed light on the development of new treatment strategies for this disease.

Inducing Mechanical Stimuli to Tissues Grown on a Magnetic Gel Allows Deconvoluting the Forces Leading to Traumatic Brain Injury

Traumatic brain injury (TBI), which is characterized by damage to the brain resulting from a sudden traumatic event, is a major cause of death and disability worldwide. It has short- and long-term effects, including neuroinflammation, cognitive deficits, and depression. TBI consists of multiple steps that may sometimes have opposing effects or mechanisms, making it challenging to investigate and translate new knowledge into effective therapies. In order to better understand and address the underlying mechanisms of TBI, we have developed an in vitro platform that allows dynamic simulation of TBI conditions by applying external magnetic forces to induce acceleration and deceleration injury, which is often observed in human TBI. Endothelial and neuron-like cells were successfully grown on magnetic gels and applied to the platform. Both cell types showed an instant response to the TBI model, but the endothelial cells were able to recover quickly-in contrast to the neuron-like cells. In conclusion, the presented in vitro model mimics the mechanical processes of acceleration/deceleration injury involved in TBI and will be a valuable resource for further research on brain injury.

Resveratrol Mitigates Metabolism in Human Microglia Cells

The recognition of the role of microglia cells in neurodegenerative diseases has steadily increased over the past few years. There is growing evidence that the uncontrolled and persisting activation of microglial cells is involved in the progression of diseases such as Alzheimer's or Parkinson's disease. The inflammatory activation of microglia cells is often accompanied by a switch in metabolism to higher glucose consumption and aerobic glycolysis. In this study, we investigate the changes induced by the natural antioxidant resveratrol in a human microglia cell line. Resveratrol is renowned for its neuroprotective properties, but little is known about its direct effect on human microglia cells. By analyzing a variety of inflammatory, neuroprotective, and metabolic aspects, resveratrol was observed to reduce inflammasome activity, increase the release of insulin-like growth factor 1, decrease glucose uptake, lower mitochondrial activity, and attenuate cellular metabolism in a ¹H NMR-based analysis of whole-cell extracts. To this end, studies were mainly performed by analyzing the effect of exogenous stressors such as lipopolysaccharide or interferon gamma on the metabolic profile of microglial cells. Therefore, this study focuses on changes in metabolism without any exogenous stressors, demonstrating how resveratrol might provide protection from persisting neuroinflammation.