Hyperglycemic Neurovasculature-On-A-Chip to Study the Effect of SIRT1-Targeted Therapy for the Type 3 Diabetes "Alzheimer's Disease"

Metformin improves cognitive dysfunction through SIRT1/NLRP3 pathway-mediated neuroinflammation in db/db mice

Diabetes mellitus (DM), an important public health problem, aggravates the global economic burden. Diabetic encephalopathy (DE) is a serious complication of DM in the central nervous system. Metformin has been proven to improve DE. However, the mechanism is still unclear. In this study, the db/db mice, a common model used for DE, were employed to explore and study the neuroprotective effect of metformin and related mechanisms. Behavioral tests indicated that metformin (100 or 200 mg/kg/day) could significantly improve the learning and memory abilities of db/db mice. The outcomes from the oral glucose tolerance test (OGTT) and insulin tolerance test (ITT) demonstrate that metformin effectively modulates glucose and insulin signaling pathways in db/db mice. The results of body weight and blood lipid panel (total cholesterol, triglycerides, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol) show that metformin promotes the level of lipid metabolism in db/db mice. Furthermore, data from oxidative stress assays, which measured levels of malondialdehyde, superoxide dismutase, catalase, and glutathione peroxidase, suggest that metformin suppresses oxidative stress-induced brain damage in db/db mice. In addition, western blot, Nissl staining, and immunofluorescence results showed that metformin increased the expressions of nerve growth factor and postsynaptic density 95 and repaired neuronal structural damage. For the mechanism study, metformin activated SIRT1 and inhibited the expression of NLRP3 inflammasome (NLRP3, ASC, caspase-1, IL-1β, and IL-18) and inflammatory cytokines (TNFα and IL-6). In conclusion, metformin could ameliorate cognitive dysfunction through the SIRT1/NLRP3 pathway, which might be a promising mechanism for DE treatment.

Challenges and Future Perspectives in Modeling Neurodegenerative Diseases Using Organ-on-a-Chip Technology

Neurodegenerative diseases (NDDs) affect more than 50 million people worldwide, posing a significant global health challenge as well as a high socioeconomic burden. With aging constituting one of the main risk factors for some NDDs such as Alzheimer's disease (AD) and Parkinson's disease (PD), this societal toll is expected to rise considering the predicted increase in the aging population as well as the limited progress in the development of effective therapeutics. To address the high failure rates in clinical trials, legislative changes permitting the use of alternatives to traditional pre-clinical in vivo models are implemented. In this regard, microphysiological systems (MPS) such as organ-on-a-chip (OoC) platforms constitute a promising tool, due to their ability to mimic complex and human-specific tissue niches in vitro. This review summarizes the current progress in modeling NDDs using OoC technology and discusses five critical aspects still insufficiently addressed in OoC models to date. Taking these aspects into consideration in the future MPS will advance the modeling of NDDs in vitro and increase their translational value in the clinical setting.

Advances in gut-brain organ chips

The brain and gut are sensory organs responsible for sensing, transmitting, integrating, and responding to signals from the internal and external environment. In-depth analysis of brain-gut axis interactions is important for human health and disease prevention. Current research on the brain-gut axis primarily relies on animal models. However, animal models make it difficult to study disease mechanisms due to inherent species differences, and the reproducibility of experiments is poor because of individual animal variations, which leads to a significant limitation of real-time sensory responses. Organ-on-a-chip platforms provide an innovative approach for disease treatment and personalized research by replicating brain and gut ecosystems in vitro. This enables a precise understanding of their biological functions and physiological responses. In this article, we examine the history and most current developments in brain, gut, and gut-brain chips. The importance of these systems for understanding pathophysiology and developing new drugs is emphasized throughout the review. This article also addresses future directions and present issues with the advancement and application of gut-brain-on-a-chip technologies.

Alterations of the blood-brain barrier during aging

The blood-brain barrier (BBB) is a complex and dynamic interface that regulates the exchange of molecules and cells between the blood and the central nervous system. It undergoes structural and functional changes during aging, which may compromise its integrity and contribute to the pathogenesis of neurodegenerative diseases. In recent years, advances in microscopy and high-throughput bioinformatics have allowed a more in-depth investigation of the aging mechanisms of BBB. This review summarizes age-related alterations of the BBB structure and function from six perspectives: endothelial cells, astrocytes, pericytes, basement membrane, microglia and perivascular macrophages, and fibroblasts, ranging from the molecular level to the human multi-system level. These basic components are essential for the proper functioning of the BBB. Recent imaging methods of BBB were also reviewed. Elucidation of age-associated BBB changes may offer insights into BBB homeostasis and may provide effective therapeutic strategies to protect it during aging.

Microbiota-gut-brain axis and its therapeutic applications in neurodegenerative diseases

The human gastrointestinal tract is populated with a diverse microbial community. The vast genetic and metabolic potential of the gut microbiome underpins its ubiquity in nearly every aspect of human biology, including health maintenance, development, aging, and disease. The advent of new sequencing technologies and culture-independent methods has allowed researchers to move beyond correlative studies toward mechanistic explorations to shed light on microbiome-host interactions. Evidence has unveiled the bidirectional communication between the gut microbiome and the central nervous system, referred to as the "microbiota-gut-brain axis". The microbiota-gut-brain axis represents an important regulator of glial functions, making it an actionable target to ameliorate the development and progression of neurodegenerative diseases. In this review, we discuss the mechanisms of the microbiota-gut-brain axis in neurodegenerative diseases. As the gut microbiome provides essential cues to microglia, astrocytes, and oligodendrocytes, we examine the communications between gut microbiota and these glial cells during healthy states and neurodegenerative diseases. Subsequently, we discuss the mechanisms of the microbiota-gut-brain axis in neurodegenerative diseases using a metabolite-centric approach, while also examining the role of gut microbiota-related neurotransmitters and gut hormones. Next, we examine the potential of targeting the intestinal barrier, blood-brain barrier, meninges, and peripheral immune system to counteract glial dysfunction in neurodegeneration. Finally, we conclude by assessing the pre-clinical and clinical evidence of probiotics, prebiotics, and fecal microbiota transplantation in neurodegenerative diseases. A thorough comprehension of the microbiota-gut-brain axis will foster the development of effective therapeutic interventions for the management of neurodegenerative diseases.

Mechanobiological Adaptation to Hyperosmolarity Enhances Barrier Function in Human Vascular Microphysiological System

In infectious disease such as sepsis and COVID-19, blood vessel leakage treatment is critical to prevent fatal progression into multi-organ failure and ultimately death, but the existing effective therapeutic modalities that improve vascular barrier function are limited. Here, this study reports that osmolarity modulation can significantly improve vascular barrier function, even in an inflammatory condition. 3D human vascular microphysiological systems and automated permeability quantification processes for high-throughput analysis of vascular barrier function are utilized. Vascular barrier function is enhanced by >7-folds with 24-48 h hyperosmotic exposure (time window of emergency care; >500 mOsm L-1 ) but is disrupted after hypo-osmotic exposure (<200 mOsm L-1 ). By integrating genetic and protein level analysis, it is shown that hyperosmolarity upregulates vascular endothelial-cadherin, cortical F-actin, and cell-cell junction tension, indicating that hyperosmotic adaptation mechanically stabilizes the vascular barrier. Importantly, improved vascular barrier function following hyperosmotic exposure is maintained even after chronic exposure to proinflammatory cytokines and iso-osmotic recovery via Yes-associated protein signaling pathways. This study suggests that osmolarity modulation may be a unique therapeutic strategy to proactively prevent infectious disease progression into severe stages via vascular barrier function protection.

Brain organoid-on-a-chip: A next-generation human brain avatar for recapitulating human brain physiology and pathology

Neurodegenerative diseases and neurodevelopmental disorders have become increasingly prevalent; however, the development of new pharmaceuticals to treat these diseases has lagged. Animal models have been extensively utilized to identify underlying mechanisms and to validate drug efficacies, but they possess inherent limitations including genetic heterogeneity with humans. To overcome these limitations, human cell-based in vitro brain models including brain-on-a-chip and brain organoids have been developed. Each technique has distinct advantages and disadvantages in terms of the mimicry of structure and microenvironment, but each technique could not fully mimic the structure and functional aspects of the brain tissue. Recently, a brain organoid-on-a-chip (BOoC) platform has emerged, which merges brain-on-a-chip and brain organoids. BOoC can potentially reflect the detailed structure of the brain tissue, vascular structure, and circulation of fluid. Hence, we summarize recent advances in BOoC as a human brain avatar and discuss future perspectives. BOoC platform can pave the way for mechanistic studies and the development of pharmaceuticals to treat brain diseases in future.