Advanced glycation end product-induced astrocytic differentiation of cultured neurospheres through inhibition of Notch-Hes1 pathway-mediated neurogenesis

Progress in the Pathogenesis of Diabetic Encephalopathy: The Key Role of Neuroinflammation

Diabetic encephalopathy (DE) is a severe complication that occurs in the central nervous system (CNS) and leads to cognitive impairment. DE involves various pathophysiological processes, and its pathogenesis is still unclear. This review summarised current research on the pathogenesis of diabetic encephalopathy, which involves neuroinflammation, oxidative stress, iron homoeostasis, blood-brain barrier disruption, altered gut microbiota, insulin resistance, etc. Among these pathological mechanisms, neuroinflammation has been focused on. This paper summarises some of the molecular mechanisms involved in neuroinflammation, including the Mammalian Target of Rapamycin (mTOR), Lipocalin-2 (LCN-2), Pyroptosis, Advanced Glycosylation End Products (AGEs), and some common pro-inflammatory factors. In addition, we discuss recent advances in the study of potential therapeutic targets for the treatment of DE against neuroinflammation. The current research on the pathogenesis of DE is progressing slowly, and more research is needed in the future. Further study of neuroinflammation as a mechanism is conducive to the discovery of more effective treatments for DE in the future.

Effects of advanced glycation end products (AGEs) on the differentiation potential of primary stem cells: a systematic review

The formation and accumulation of advanced glycation end products (AGEs) have been associated with aging and the development, or worsening, of many degenerative diseases, such as atherosclerosis, chronic kidney disease, and diabetes. AGEs can accumulate in a variety of cells and tissues, and organs in the body, which in turn induces oxidative stress and inflammatory responses and adversely affects human health. In addition, under abnormal pathological conditions, AGEs create conditions that are not conducive to stem cell differentiation. Moreover, an accumulation of AGEs can affect the differentiation of stem cells. This, in turn, leads to impaired tissue repair and further aggravation of diabetic complications. Therefore, this systematic review clearly outlines the effects of AGEs on cell differentiation of various types of primary isolated stem cells and summarizes the possible regulatory mechanisms and interventions. Our study is expected to reveal the mechanism of tissue damage caused by the diabetic microenvironment from a cellular and molecular point of view and provide new ideas for treating complications caused by diabetes.

PHPB Attenuated Cognitive Impairment in Type 2 Diabetic KK-Ay Mice by Modulating SIRT1/Insulin Signaling Pathway and Inhibiting Generation of AGEs

Diabetes mellitus (DM) has been recognized as an increased risk factor for cognitive impairment, known as diabetic encephalopathy (DE). Hyperglycemia and insulin resistance are the main initiators of DE, which is related to the accumulation of advanced glycation end products (AGEs). Potassium 2-(1-hydroxypentyl)-benzoate (PHPB), a derivative of 3-n-butylphthalide (dl-NBP), has emerged various properties including improved mitochondrial function, antioxidant, anti-neuroinflammation, and neuroprotective effects. The present study aimed to investigate the neuroprotective effect of PHPB against AGEs accumulation in type 2 diabetic KK-Ay mice model with DE and further explore the underlying mechanisms. The results showed that PHPB markedly ameliorated the spatial learning ability of KK-Ay mice in the Morris water maze and decreased AD-like pathologic changes (Tau hyperphosphorylation) in the cortex. Furthermore, we found that PHPB treatment significantly reduced AGEs generation via up-regulation of glyoxalase-1 (GLO1) protein and enhancement of methylglyoxal (MG) trapping, while there was no obvious difference in levels of glucose in plasma or brain, contents of total cholesterol (TC), triglycerides (TG), and plasma insulin. Also, PHPB treatment improved the insulin signaling pathway by increasing sirtuin1 (SIRT1) deacetylase activity and attenuated oxidative stress evidenced by elevating glucose-6-phosphate dehydrogenase (G-6-PD) protein expression, promoting the production of reduced glutathione (GSH) and reduced nicotinamide adenine dinucleotide phosphate (NADPH), restoring mitochondrial membrane potential, increasing adenosine triphosphate (ATP) generation, and reducing malondialdehyde (MDA) levels in the brain. Taken together, PHPB exhibited a beneficial effect on DE, which involved modulating the SIRT1/insulin signaling pathway and reducing oxidative stress by inhibiting the generation of AGEs.

Genomics, transcriptomics, proteomics and big data analysis in the discovery of new diagnostic markers and targets for therapy development

Highly complex endophenotypes and underlying molecular mechanisms have prevented effective diagnosis and treatment of autism spectrum disorder. Despite extensive studies to identify relevant biosignatures, no biomarker and therapeutic targets are available in the current clinical practice. While our current knowledge is still largely incomplete, -omics technology and machine learning-based big data analysis have provided novel insights on the etiology of autism spectrum disorders, elucidating systemic impairments that can be translated into biomarker and therapy target candidates. However, more integrated and sophisticated approaches are vital to realize molecular stratification and individualized treatment strategy. Ultimately, systemic approaches based on -omics and big data analysis will significantly contribute to more effective biomarker and therapy development for autism spectrum disorder.

Advanced glycation end products inhibit neural stem cell differentiation via upregualtion of HDAC3 expression

Diabetes mellitus (DM) is a highly prevalent chronic systemic disease, which may cause cognitive decline and degenerative change of the brain. Neuronal differentiation defects of neural stem cells (NSCs) played an important role in the development and progression of diabetes-associated cognitive decline (DACD), but the intrinsic pathological mechanism remains largely unclear. In the present study, we demonstrated that expression level of HDAC3 was upregulated in diabetic mice with reduced learning and memory abilities and in cultured NSCs after advanced glycation end products (AGEs) induction. In addition, AGEs interfered with normal differentiation of the cultured NSCs, and knocking down the expression of HDAC3 could partially attenuate the inhibitory effect of AGEs on NSCs differentiation. Findings in this study demonstrate that HDAC3 may serve as an experimental clue for revealing the pathogenesis of DACD.

Interleukin-1β Disturbs the Proliferation and Differentiation of Neural Precursor Cells in the Hippocampus via Activation of Notch Signaling in Postnatal Rats Exposed to Lipopolysaccharide

Infectious exposure during the perinatal period may predispose to permanent neurological disorders in later life. Here we investigated whether changes in interleukin-1β (IL-1β) are associated with cognitive dysfunction in later life of septic neonatal rats through suppression of neurogenesis in the hippocampus. Sprague-Dawley rats (1-day old) administered lipopolysaccharide (LPS) showed upregulated expression of IL-1β and IL-1 receptors in the hippocampus. At 28 days of age, rats showed longer escape latencies and decreased numbers of crossings after LPS administration. This was coupled with increased numbers of glial fibrillary acidic protein positive (GFAP⁺) astrocytes and decreased numbers of neuronal nuclei positive (NeuN⁺) cells. The numbers of sex-determining region Y-box 2 positive (SOX2⁺) and doublecortin positive (DCX⁺) cells were decreased at 1 and 3 days but was increased at 7 and 14 days. The proliferation of SOX2⁺ cells was inhibited at 1 and 3 days but increased at 7 and 14 days. In vitro IL-1β administration suppressed the proliferation of neural progenitor cells (NPCs) in neurospheres derived from the hippocampus. GFAP expression was upregulated in differentiated NPCs treated with IL-1β for 4 days, but expression of DCX and microtubule associated protein-2 (MAP2) was decreased. Remarkably, the Notch signaling pathway involved in antineurogenic and progliogenic differentiation of NPCs was activated after IL-1β administration. The results show that following LPS injection in neonatal rats, microglia were activated and generated excess amounts of IL-1β in the hippocampus. It is suggested that this might have contributed to inhibiting neurogenesis but promoting gliogenesis of NPCs via activation of the Notch signaling pathway and maybe one of the causes for cognitive dysfunction in septic neonatal rats in later life.

F1F0 ATP Synthase-Cyclophilin D Interaction Contributes to Diabetes-Induced Synaptic Dysfunction and Cognitive Decline

Mitochondrial abnormalities are well known to cause cognitive decline. However, the underlying molecular basis of mitochondria-associated neuronal and synaptic dysfunction in the diabetic brain remains unclear. Here, using a mitochondrial single-channel patch clamp and cyclophilin D (CypD)-deficient mice (Ppif -/-) with streptozotocin-induced diabetes, we observed an increase in the probability of Ca2+-induced mitochondrial permeability transition pore (mPTP) opening in brain mitochondria of diabetic mice, which was further confirmed by mitochondrial swelling and cytochrome c release induced by Ca2+ overload. Diabetes-induced elevation of CypD triggers enhancement of F1F0 ATP synthase-CypD interaction, which in turn leads to mPTP opening. Indeed, in patients with diabetes, brain cypD protein levels were increased. Notably, blockade of the F1F0 ATP synthase-CypD interaction by CypD ablation protected against diabetes-induced mPTP opening, ATP synthesis deficits, oxidative stress, and mitochondria dysfunction. Furthermore, the absence of CypD alleviated deficits in synaptic plasticity, learning, and memory in diabetic mice. Thus, blockade of ATP synthase interaction with CypD provides a promising new target for therapeutic intervention in diabetic encephalopathy.

Inhibition of Notch rescues the angiogenic potential impaired by cardiovascular risk factors in epicardial adipose stem cells

The epicardial adipose tissue (EAT) is a reservoir of adipose-derived stem cells (ASCs), with as yet unknown effects on myocardial and coronary arteries homeostasis. The purpose of this study was to investigate the angiogenic function of epicardial ASCs and their regulation by the common cardiovascular risk factors (CVRFs) affecting heart disease. Epicardial fat was obtained from a rodent model with clustering of CVRFs [Zucker diabetic fatty (ZDF)-Lepr(fa)] rats and from their lean control (ZDF-Crl) littermates without CVRFs, ASCs were isolated, and their function was assessed by proliferation and differentiation assays, flow cytometry, gene expression, and in vivo Matrigel angiogenesis analysis. Epicardial ASCs from both groups showed adipogenic and osteogenic differentiation capacity; however, epicardial ASCs from CVRF animals had a lesser ability to form tubular structures in vitro after endothelial differentiation, as well as a reduced angiogenic potential in vivo compared to control animals. Epicardial ASCs from CVRF rats showed up-regulation of the downstream Notch signaling genes Hes7, Hey1, and Heyl compared with control animals. The inhibition of Notch signaling by conditioning epicardial ASCs from CVRF animals with a γ-secretase inhibitor induced a reduction in Hes/Hey gene expression and rescued their angiogenic function in vivo We report for the first time the impact of CVRF burden on the ASCs of EAT and that the defective function is in part caused by increased Notch signaling. Conditioning ASCs by blocking Notch signaling rescues their angiogenic potential.-Bejar, M. T., Ferrer-Lorente, R., Peña, E., Badimon, L. Inhibition of Notch rescues the angiogenic potential impaired by cardiovascular risk factors in epicardial adipose stem cells.

A CREB-Sirt1-Hes1 Circuitry Mediates Neural Stem Cell Response to Glucose Availability

Adult neurogenesis plays increasingly recognized roles in brain homeostasis and repair and is profoundly affected by energy balance and nutrients. We found that the expression of Hes-1 (hairy and enhancer of split 1) is modulated in neural stem and progenitor cells (NSCs) by extracellular glucose through the coordinated action of CREB (cyclic AMP responsive element binding protein) and Sirt-1 (Sirtuin 1), two cellular nutrient sensors. Excess glucose reduced CREB-activated Hes-1 expression and results in impaired cell proliferation. CREB-deficient NSCs expanded poorly in vitro and did not respond to glucose availability. Elevated glucose also promoted Sirt-1-dependent repression of the Hes-1 promoter. Conversely, in low glucose, CREB replaced Sirt-1 on the chromatin associated with the Hes-1 promoter enhancing Hes-1 expression and cell proliferation. Thus, the glucose-regulated antagonism between CREB and Sirt-1 for Hes-1 transcription participates in the metabolic regulation of neurogenesis.

FAT1 cadherin acts upstream of Hippo signalling through TAZ to regulate neuronal differentiation

The Hippo pathway is emerging as a critical nexus that balances self-renewal of progenitors against differentiation; however, upstream elements in vertebrate Hippo signalling are poorly understood. High expression of Fat1 cadherin within the developing neuroepithelium and the manifestation of severe neurological phenotypes in Fat1-knockout mice suggest roles in neurogenesis. Using the SH-SY5Y model of neuronal differentiation and employing gene silencing techniques, we show that FAT1 acts to control neurite outgrowth, also driving cells towards terminal differentiation via inhibitory effects on proliferation. FAT1 actions were shown to be mediated through Hippo signalling where it activated core Hippo kinase components and antagonised functions of the Hippo effector TAZ. Suppression of FAT1 promoted the nucleocytoplasmic shuttling of TAZ leading to enhanced transcription of the Hippo target gene CTGF together with accompanying increases in nuclear levels of Smad3. Silencing of TAZ reversed the effects of FAT1 depletion thus connecting inactivation of TAZ-TGFbeta signalling with Hippo signalling mediated through FAT1. These findings establish FAT1 as a new upstream Hippo element regulating early stages of differentiation in neuronal cells.

Inhibition of Notch signaling facilitates the differentiation of human-induced pluripotent stem cells into neural stem cells

Neural stem cells (NSCs) derived from induced pluripotent stem cells (iPSCs) are becoming an appealing source of cell-based therapies of brain diseases. As such, it is important to understand the molecular mechanisms that regulate the differentiation of iPSCs toward NSCs. It is well known that Notch signaling governs the retention of stem cell features and drives stem cells fate. However, further studies are required to investigate the role of Notch signaling in the NSCs differentiation of iPSCs. In this study, we successfully generated NSCs from human iPSCs using serum-free medium supplemented with retinoic acid (RA) in vitro. We then assessed changes in the expression of Notch signaling-related molecules and some miRNAs (9, 34a, 200b), which exert their regulation by targeting Notch signaling. Moreover, we used a γ-secretase inhibitor (DAPT) to disturb Notch signaling. Data revealed that the levels of the Notch signaling-related molecules decreased, whereas those miRNAs increased, during this differentiation process. Inhibition of Notch signaling accelerated the formation of the neural rosette structures and the expression of NSC and mature neurocyte marker genes. This suggests that Notch signaling negatively regulated the neuralization of human iPSCs, and that this process may be regulated by some miRNAs.